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Traumatic brain injury (TBI) is of significant concern in the realm of high impact contact sports, including mixed martial arts (MMA). Extracellular vesicles (EVs) travel between the brain and oral cavity and may be isolated from salivary samples as a noninvasive biomarker of TBI. Salivary EVs may highlight acute neurocognitive or neuropathological changes, which may be particularly useful as a biomarker in high impact sports. Pre and post-fight samples of saliva were isolated from 8 MMA fighters and 7 from controls. Real-time PCR of salivary EVs was done using the TaqMan Human Inflammatory array. Gene expression profiles were compared pre-fight to post-fight as well as pre-fight to controls. Largest signals were noted for fighters sustaining a loss by technical knockout (higher impact mechanism of injury) or a full match culminating in referee decision (longer length of fight), while smaller signals were noted for fighters winning by joint or choke submission (lower impact mechanism as well as less time). A correlation was observed between absolute gene information signals and fight related markers of head injury severity. Gene expression was also significantly different in MMA fighters pre-fight compared to controls. Our findings suggest that salivary EVs as a potential biomarker in the acute period following head injury to identify injury severity and can help elucidate pathophysiological processes involved in TBI.

Hematopoietic stem cells express differentiation markers B220 and Gr1 and are proliferative. We have shown that the expression of these entities changes with cell cycle passage. Overall, we conclude that primitive hematopoietic stem cells alter their differentiation potential with cell cycle progression. Graphical Abstract Murine derived long-term hematopoietic stem cells (LT-HSC) are cycling and thus always changing phenotype. Here we show that over one half of marrow LT-HSC are in the population expressing differentiation epitopes and that B220 and Gr-1 positive populations are replete with LT-HSC after a single FACS separation but if subjected to a second separation these cells no longer contain LT-HSC. However, with second separated cells there is a population appearing that is B220 negative and replete with cycling c-Kit, Sca-1 CD150 positive LT-HSC. There is a 3–4 h interval between the first and second B220 or GR-1 FACS separation during which the stem cells continue to cycle. Thus, the LT-HSC have lost B220 or GR-1 expression as the cells progress through cell cycle, although they have maintained the c-kit, Sca-1 and CD150 stem cells markers over this time interval. These data indicate that cycling stem cells express differentiation epitopes and alter their differentiation potential with cell cycle passage.

Mesenchymal stem cell extracellular vesicles attenuate pulmonary hypertension, but their ability to reverse established disease in larger animal models and the duration and mechanism(s) of their effect are unknown. We sought to determine the efficacy and mechanism of mesenchymal stem cells’ extracellular vesicles in attenuating pulmonary hypertension in rats with Sugen/hypoxia-induced pulmonary hypertension. Male rats were treated with mesenchymal stem cell extracellular vesicles or an equal volume of saline vehicle by tail vein injection before or after subcutaneous injection of Sugen 5416 and exposure to 3 weeks of hypoxia. Pulmonary hypertension was assessed by right ventricular systolic pressure, right ventricular weight to left ventricle + septum weight, and muscularization of peripheral pulmonary vessels. Immunohistochemistry was used to measure macrophage activation state and recruitment to lung. Mesenchymal stem cell extracellular vesicles injected before or after induction of pulmonary hypertension normalized right ventricular pressure and reduced right ventricular hypertrophy and muscularization of peripheral pulmonary vessels. The effect was consistent over a range of doses and dosing intervals and was associated with lower numbers of lung macrophages, a higher ratio of alternatively to classically activated macrophages (M2/M1 = 2.00 ± 0.14 vs. 1.09 ± 0.11; P

Chitinase 3 like 1 (CHI3L1) is the prototypic chitinase-like protein mediating inflammation, cell proliferation, and tissue remodeling. Limited data suggest CHI3L1 is elevated in human pulmonary arterial hypertension (PAH) and is associated with disease severity. Despite its importance as a regulator of injury/repair responses, the relationship between CHI3L1 and pulmonary vascular remodeling is not well understood. We hypothesize that CHI3L1 and its signaling pathways contribute to the vascular remodeling responses that occur in pulmonary hypertension (PH). We examined the relationship of plasma CHI3L1 levels and severity of PH in patients with various forms of PH, including group 1 PAH and group 3 PH, and found that circulating levels of serum CHI3L1 were associated with worse hemodynamics and correlated directly with mean pulmonary artery pressure and pulmonary vascular resistance. We also used transgenic mice with constitutive knockout and inducible overexpression of CHI3L1 to examine its role in hypoxia-, monocrotaline-, and bleomycin-induced models of pulmonary vascular disease. In all 3 mouse models of pulmonary vascular disease, pulmonary hypertensive responses were mitigated in CHI3L1-null mice and accentuated in transgenic mice that overexpress CHI3L1. Finally, CHI3L1 alone was sufficient to induce pulmonary arterial smooth muscle cell proliferation, inhibit pulmonary vascular endothelial cell apoptosis, induce the loss of endothelial barrier function, and induce endothelial-mesenchymal transition. These findings demonstrate that CHI3L1 and its receptors play an integral role in pulmonary vascular disease pathobiology and may offer a target for the treatment of PAH and PH associated with fibrotic lung disease.

Rationale Mesenchymal stem cell extracellular vesicles (MSC EVs) reverse pulmonary hypertension, but little information is available regarding what dose is effective and how often it needs to be given. This study examined the effects of dose reduction and use of longer dosing intervals and the effect of hypoxic stress of MSC prior to EV collection. Methods Adult male rats with pulmonary hypertension induced by Sugen 5416 and three weeks of hypoxia (SuHx-pulmonary hypertension) were injected with MSC EV or phosphate buffered saline the day of removal from hypoxia using one of the following protocols: (1) Once daily for three days at doses of 0.2, 1, 5, 20, and 100 µg/kg, (2) Once weekly (100 µg/kg) for five weeks, (3) Once every other week (100 µg/kg) for 10 weeks, (4) Once daily (20 µg/kg) for three days using EV obtained from MSC exposed to 48 h of hypoxia (HxEV) or MSC kept in normoxic conditions (NxEV). Main results MSC EV reversed increases in right ventricular systolic pressure (RVSP), right ventricular to left ventricle + septum weight (RV/LV+S), and muscularization index of pulmonary vessels ≤50 µm when given at doses of 20 or 100 μg/kg. RVSP, RV/LV+S, and muscularization index were significantly higher in SuHx-pulmonary hypertension rats treated once weekly with phosphate buffered saline for five weeks or every other week for 10 weeks than in normoxic controls, but not significantly increased in SuHx-pulmonary hypertension rats given MSC EV. Both NxEV and HxEV significantly reduced RVSP, RV/LV+S, and muscularization index, but no differences were seen between treatment groups. Conclusions MSC EV are effective at reversing SuHx-pulmonary hypertension when given at lower doses and longer dosing intervals than previously reported. Hypoxic stress does not enhance the efficacy of MSC EV at reversing pulmonary hypertension. These findings support the feasibility of MSC EV as a long-term treatment for pulmonary hypertension.

Traumatic brain injury (TBI) is a common cause of death and acquired disability in adults and children. Identifying biomarkers for mild TBI (mTBI) that can predict functional impairments on neuropsychiatric and neurocognitive testing after head trauma is yet to be firmly established. Extracellular vesicles (EVs) are known to traffic from the brain to the oral cavity and can be detected in saliva. We hypothesize the genetic profile of salivary EVs in patients who have suffered head trauma will differ from normal healthy controls, thus constituting a unique expression signature for mTBI. We enrolled a total of 54 subjects including for saliva sampling, 23 controls with no history of head traumas, 16 patients enrolled from an outpatient concussion clinic, and 15 patients from the emergency department who had sustained a head trauma within 24 hr. We performed real‐time PCR of the salivary EVs of the 54 subjects profiling 96 genes from the TaqMan Human Alzheimer's disease array. Real‐time PCR analysis revealed 57 (15 genes, p

Rationale: Sex hormones play a role in pulmonary arterial hypertension (PAH), but the menstrual cycle has never been studied. Objectives: We conducted a prospective observational study of eight women with stable PAH and 20 healthy controls over one cycle. Methods: Participants completed four study visits 1 week apart starting on the first day of menstruation. Relationships between sex hormones, hormone metabolites, and extracellular vesicle microRNA (miRNA) expression and clinical markers were compared with generalized linear mixed modeling. Results: Women with PAH had higher but less variable estradiol (E2) levels (P

Aims Pulmonary arterial hypertension (PAH) is a fatal disease without a cure. Previously, we found that transcription factor RUNX1-dependent haematopoietic transformation of endothelial progenitor cells may contribute to the pathogenesis of PAH. However, the therapeutic potential of RUNX1 inhibition to reverse established PAH remains unknown. In the current study, we aimed to determine whether RUNX1 inhibition was sufficient to reverse Sugen/hypoxia (SuHx)-induced pulmonary hypertension (PH) in rats. We also aimed to demonstrate possible mechanisms involved. Methods and results We administered a small molecule specific RUNX1 inhibitor Ro5-3335 before, during, and after the development of SuHx-PH in rats to investigate its therapeutic potential. We quantified lung macrophage recruitment and activation in vivo and in vitro in the presence or absence of the RUNX1 inhibitor. We generated conditional VE-cadherin-CreERT2; ZsGreen mice for labelling adult endothelium and lineage tracing in the SuHx-PH model. We also generated conditional Cdh5-CreERT2; Runx1(flox/flox) mice to delete Runx1 gene in adult endothelium and LysM-Cre; Runx1(flox/flox) mice to delete Runx1 gene in cells of myeloid lineage, and then subjected these mice to SuHx-PH induction. RUNX1 inhibition in vivo effectively prevented the development, blocked the progression, and reversed established SuHx-induced PH in rats. RUNX1 inhibition significantly dampened lung macrophage recruitment and activation. Furthermore, lineage tracing with the inducible VE-cadherin-CreERT2; ZsGreen mice demonstrated that a RUNX1-dependent endothelial to haematopoietic transformation occurred during the development of SuHx-PH. Finally, tissue-specific deletion of Runx1 gene either in adult endothelium or in cells of myeloid lineage prevented the mice from developing SuHx-PH, suggesting that RUNX1 is required for the development of PH. Conclusion By blocking RUNX1-dependent endothelial to haematopoietic transformation and pulmonary macrophage recruitment and activation, targeting RUNX1 may be as a novel treatment modality for pulmonary arterial hypertension.

The role of bone marrow (BM) cells in modulating pulmonary hypertensive responses is not well understood. Determine if BM-derived endothelial progenitor cells (EPCs) induce pulmonary hypertension (PH) and if this is attenuated by mesenchymal stem cell (MSC)-derived extracellular vesicles (EVs). Three BM populations were studied: (a) BM from vehicle and monocrotaline (MCT)-treated mice (PH induction), (b) BM from vehicle-, MCT-treated mice that received MSC-EV infusion after vehicle, MCT treatment (PH reversal, in vivo), (c) BM from vehicle-, MCT-treated mice cultured with MSC-EVs (PH reversal, in vitro). BM was separated into EPCs (sca-1+/c-kit+/VEGFR2+) and non-EPCs (sca-1-/c-kit-/VEGFR2-) and transplanted into healthy mice. Right ventricular (RV) hypertrophy was assessed by RV-to-left ventricle+septum (RV/LV+S) ratio and pulmonary vascular remodeling by blood vessel wall thickness-to-diameter (WT/D) ratio. EPCs but not non-EPCs from mice with MCT-induced PH (MCT-PH) increased RV/LV+S, WT/D ratios in healthy mice (PH induction). EPCs from MCT-PH mice treated with MSC-EVs did not increase RV/LV+S, WT/D ratios in healthy mice (PH reversal, in vivo). Similarly, EPCs from MCT-PH mice treated with MSC-EVs pre-transplantation did not increase RV/LV+S, WT/D ratios in healthy mice (PH reversal, in vitro). MSC-EV infusion reversed increases in BM-EPCs and increased lung tissue expression of EPC genes and their receptors/ligands in MCT-PH mice. These findings suggest that the pulmonary hypertensive effects of BM are mediated by EPCs and those MSC-EVs attenuate these effects. These findings provide new insights into the pathogenesis of PH and offer a potential target for development of novel PH therapies.

Studies in hematopoietic aging have shown that classically defined, highly purified hematopoietic stem cells (HSCs) increase in number but have impaired function and exhibit myeloid skewing. However, we identified a cycling population of HSCs in young mice that appear to be preferentially lost during standard HSC isolations and therefore poorly represented within the purified HSC population. Here, we sought to determine how aging may alter this total HSC population in unseparated murine whole bone marrow (WBM). In limit dilution competitive bone marrow transplantation, we found that, at 6 months post-transplant, old (24-26-mo-old) WBM had a 4-fold increase in functional HSCs compared to young (6-8-wk-old) WBM. Unlike purified old HSCs, old WBM showed only minimal myeloid skewing (myeloid: 26%±11% of old donor peripheral blood vs.19%±16% of young donor peripheral blood; average percent donor peripheral blood ± SD; n=26 mice). Interestingly, in two experiments, old WBM retained full engraftment capacity in secondary transplant with no myeloid skewing, while in a third experiment, old WBM engraftment was significantly decreased when compared to young WBM (15%±9% vs. 57%±3%, respectively; average% donor chimerism ± SD), and exhibited clear myeloid skewing (myeloid: 65%±7% of old donor peripheral blood vs. 20%±10% of young donor peripheral blood; 4-5mice/grp/exp). These data suggest that only those old HSCs in unseparated WBM with high engraftment capacity may retain youthful myeloid/lymphoid ratio patterns. Preliminary data in female mice were similar, showing that HSCs were 7.8-fold increased in old vs. young WBM, retained repopulation capacity in secondary transplantation, and displayed no significant myeloid skewing. These patterns of robust reconstitution without myeloid skewing by old WBM are quite distinct from those of the classically-defined, purified old HSCs, suggesting the presence of a unique HSC population in WBM with differential susceptibility to aging. Further study of this population may yield novel insights into the effects of aging on HSC function and lineage fate decisions and facilitate innovative rejuvenation strategies.

At present, there is no reliable biomarker for the diagnosis of traumatic brain injury (TBI). Studies have shown that extracellular vesicles released by damaged cells into biological fluids can be used as potential biomarkers for diagnosis of TBI and evaluation of TBI severity. We hypothesize that the genetic profile of salivary extracellular vesicles in patients with head trauma differs from that in uninjured subjects. Findings from this hypothesis would help investigate the severity of TBI. This study included 19 subjects, consisting of seven healthy controls who denied history of head trauma, six patients diagnosed with concussion injury from an outpatient concussion clinic, and six patients with TBI who received treatment in the emergency department within 24 hours after injury. Real-time PCR analysis of salivary extracellular vesicles in participants was performed using TaqMan Human Inflammation array. Gene expression analysis revealed nine upregulated genes in emergency department patients (LOX5, ANXA3, CASP1, IL2RG, ITGAM, ITGB2, LTA4H, MAPK14, and TNFRSF1A) and 13 upregulated genes in concussion clinic patients compared with healthy participants (ADRB1, ADRB2, BDKRB1, HRH1, HRH2, LTB4R2, LTB4R, PTAFR, CYSLTR1, CES1, KLK1, MC2R, and PTGER3). Each patient group had a unique profile. Comparison between groups showed that 15 inflammation-related genes had significant expression change. Our results indicate that inflammation biomarkers can be used for diagnosis of TBI and evaluation of disease severity. This study was approved by the Institutional Review Board on December 18, 2015 (approval No. 0078-12) and on June 9, 2016 (approval No. 4093-16).

Endothelial dysfunction is a hallmark of pulmonary arterial hypertension (PAH) but there are no established methods to study pulmonary artery endothelial cells (PAECs) from living patients. We sought to culture PAECs from pulmonary artery catheter (PAC) balloons used during right-heart catheterisation (RHC) to characterise successful culture attempts and to describe PAEC behaviour.PAECs were grown in primary culture to confluence and endothelial cell phenotype was confirmed. Standard assays for apoptosis, migration and tube formation were performed between passages three to eight. We collected 49 PAC tips from 45 subjects with successful PAEC culture from 19 balloons (39%).There were no differences in subject demographic details or RHC procedural details in successful versus unsuccessful attempts. However, for subjects who met haemodynamic criteria for PAH, there was a higher but nonsignificant (p=0.10) proportion amongst successful attempts (10 out of 19, 53%) versus unsuccessful attempts (nine out of 30, 30%). A successful culture was more likely in subjects with a lower cardiac index (p=0.03) and higher pulmonary vascular resistance (p=0.04). PAECs from a subject with idiopathic PAH were apoptosis resistant compared to commercial PAECs (p=0.04) and had reduced migration compared to PAECs from a subject with portopulmonary hypertension with high cardiac output (p=0.01). PAECs from a subject with HIV-associated PAH formed fewer (p=0.01) and shorter (p=0.02) vessel networks compared to commercial PAECs.Sustained culture and characterisation of PAECs from RHC balloons is feasible, especially in PAH with high haemodynamic burden. This technique may provide insight into endothelial dysfunction during PAH pathogenesis.

Mesenchymal stromal cells (MSCs) have been shown to reverse radiation damage to marrow stem cells. We have evaluated the capacity of MSC-derived extracellular vesicles (MSC-EVs) to mitigate radiation injury to marrow stem cells at 4 h to 7 days after irradiation. Significant restoration of marrow stem cell engraftment at 4, 24 and 168 h post irradiation by exposure to MSC-EVs was observed at 3 weeks to 9 months after transplant and further confirmed by secondary engraftment. Intravenous injection of MSC-EVs to 500cGy exposed mice led to partial recovery of peripheral blood counts and restoration of the engraftment of marrow. The murine hematopoietic cell line, FDC-P1 exposed to 500cGy, showed reversal of growth inhibition, DNA damage and apoptosis on exposure to murine or human MSC-EVs. Both murine and human MSC-EVs reverse radiation damage to murine marrow cells and stimulate normal murine marrow stem cell/progenitors to proliferate. A preparation with both exosomes and microvesicles was found to be superior to either microvesicles or exosomes alone. Biologic activity was seen in freshly isolated vesicles and in vesicles stored for up to 6 months in 10% dimethyl sulfoxide at -80 °C. These studies indicate that MSC-EVs can reverse radiation damage to bone marrow stem cells.

Aims Extracellular vesicles (EVs) from mice with monocrotaline (MCT)-induced pulmonary hypertension (PH) induce PH in healthy mice, and the exosomes (EXO) fraction of EVs from mesenchymal stem cells (MSCs) can blunt the development of hypoxic PH. We sought to determine whether the EXO fraction of EVs is responsible for modulating pulmonary vascular responses and whether differences in EXO-miR content explains the differential effects of EXOs from MSCs and mice with MCT-PH. Methods and results Plasma, lung EVs from MCT-PH, and control mice were divided into EXO (exosome), microvesicle (MV) fractions and injected into healthy mice. EVs from MSCs were divided into EXO, MV fractions and injected into MCT-treated mice. PH was assessed by right ventricle-to-left ventricle + septum (RV/LV + S) ratio and pulmonary arterial wall thickness-to-diameter (WT/D) ratio. miR microarray analyses were also performed on all EXO populations. EXOs but not MVs from MCT-injured mice increased RV/LV + S, WT/D ratios in healthy mice. MSC-EXOs prevented any increase in RV/LV + S, WT/D ratios when given at the time of MCT injection and reversed the increase in these ratios when given after MCT administration. EXOs from MCT-injured mice and patients with idiopathic pulmonary arterial hypertension (IPAH) contained increased levels of miRs-19b,-20a,-20b, and -145, whereas miRs isolated from MSC-EXOs had increased levels of anti-inflammatory, anti-proliferative miRs including miRs-34a,-122,-124, and -127. Conclusion These findings suggest that circulating or MSC-EXOs may modulate pulmonary hypertensive effects based on their miR cargo. The ability of MSC-EXOs to reverse MCT-PH offers a promising potential target for new PAH therapies.

Extracellular vesicles (EVs) are critical mediators of intercellular communication within the bone marrow niche and have been implicated in numerous features of aging. However, their role in natural hematopoietic stem cell (HSC) aging has not been fully elucidated. The goal of this work was to test the hypothesis that EVs from whole bone marrow (BM-EVs) can modulate the HSC aging phenotype in vivo. With respect to HSC aging, our prior work showed that, in contrast to the well-known reduced functional capacity and prominent myeloid skewing displayed by old immunophenotypically-defined HSCs, old unseparated whole bone marrow (WBM) (24-26-mo-old) had a 4-fold increase in functional HSCs compared to young (6-8-wk-old) WBM in limit dilution competitive bone marrow transplantation, and showed minimal to no myeloid skewing. In order to test the ability of BM-EVs derived from this total WBM population to alter HSC aging phenotype, we first isolated EVs from WBM flushed from old (24-26-month old) and young (6-8-week old) C57/BL6 (CD45.2) mice by differential centrifugation (2000 × g for 30 min, supernatant centrifuged 100,000 × g for 1 hour, BM-EV pellet collected). Utilizing nanoparticle tracking analysis, we found no difference in mean particle size between old and young BM-EVs, but there was an approximately 2-fold increase in the number of EVs from old WBM compared to young WBM. To test the ability of these BM-EVs to alter HSC function in vivo, we injected old CD45.2 mice with 2 x 109 young BM-EVs and young CD45.2 mice with 2 x 109 old BM-EVs mice via tail vein, daily x 3 days. Control mice were injected with age-matched BM-EVs or vehicle alone. At one-month post injection, we isolated total WBM and Lineage negative/c-Kit+/Sca-1+/CD150+ cells (LSK-SLAM) from the EV-exposed or vehicle control mice. We injected either 3 x 105 WBM cells or 400 LSK-SLAM mixed with 3 x 105 healthy WBM competitor cells from young B6.SJL (CD45.1) mice into lethally irradiated young CD45.1 hosts and measured peripheral blood chimerism and lineage contribution by flow cytometry up to 6 months post-transplant. For the young marrow, exposure to old BM-EVs had no appreciable effects on engraftment capacity or lineage distribution. However, old WBM exposed to young BM-EVs exhibited a significant decrease in engraftment (15% ± 5%) when compared to old WBM exposed to age-matched old BM-EVs (61% ± 14%) or vehicle control (47% ± 7%) (% average donor chimerism ± SEM, n=4-5 mice/group, p Disclosures No relevant conflicts of interest to declare.

Pulmonary hypertension (PH) is an incurable disease characterized by pulmonary vascular remodeling and ultimately death. Two rodent models of PH include treatment with monocrotaline or exposure to a vascular endothelial growth factor receptor inhibitor and hypoxia. Studies in these models indicated that damaged lung cells evolve extracellular vesicles which induce production of progenitors that travel back to the lung and induce PH. A study in patients with pulmonary myelofibrosis and PH indicated that 100 cGy lung irradiation could remit both diseases. Previous studies indicated that murine progenitors were radiosensitive at very low doses, suggesting that 100 cGy treatment of mice with induced PH might be an effective PH therapy. Our hypothesis is that the elimination of the PH‐inducing marrow cells by low dose irradiation would remove the cellular influences creating PH. Here we show that low dose whole‐body irradiation can both prevent and reverse established PH in both rodent models of PH.

Extracellular vesicles (EVs) are important mediators of intercellular communication and have been implicated in myriad physiologic and pathologic processes within the hematopoietic system. Numerous factors influence the ability of EVs to communicate with target marrow cells, but little is known about how circadian oscillations alter EV function. In order to explore the effects of daily rhythms on EV-mediated intercellular communication, we used a well-established model of lung-derived EV modulation of the marrow cell transcriptome. In this model, co-culture of whole bone marrow cells (WBM) with lung-derived EVs induces expression of pulmonary specific mRNAs in the target WBM. To determine if daily rhythms play a role in this phenotype modulation, C57BL/6 mice were entrained in 12-hour light/12-hour dark boxes. Lungs harvested at discrete time-points throughout the 24-hour cycle were co-cultured across a cell-impermeable membrane with murine WBM. Alternatively, WBM harvested at discrete time-points was co-cultured with lung-derived EVs. Target WBM was collected 24hrs after co-culture and analyzed for the presence of pulmonary specific mRNA levels by RT-PCR. In both cases, there were clear time-dependent variations in the patterns of pulmonary specific mRNA levels when either the daily time-point of the lung donor or the daily time-point of the recipient marrow cells was altered. In general, WBM had peak pulmonary-specific mRNA levels when exposed to lung harvested at Zeitgeber time (ZT) 4 and ZT 16 (ZT 0 defined as the time of lights on, ZT 12 defined as the time of lights off), and was most susceptible to lung-derived EV modulation when target marrow itself was harvested at ZT 8- ZT 12. We found increased uptake of EVs when the time-point of the receptor WBM was between ZT 20 -ZT 24, suggesting that the time of day-dependent changes in transcriptome modulation by the EVs were not due simply to differential EV uptake. Based on these data, we conclude that circadian rhythms can modulate EV-mediated intercellular communication.

Early work on platelet and erythrocyte vesicles interpreted the phenomena as a discard of material from cells. Subsequently, vesicles were studied as possible vaccines and, most recently, there has been a focus on the effects of vesicles on cell fate. Recent studies have indicated that extracellular vesicles, previously referred to as microvesicles or exosomes, have the capacity to change the phenotype of neighboring cells. Extensive work has shown that vesicles derived from either the lung or liver can enter bone marrow cells (this is a prerequisite) and alter their fate toward that of the originating liver and lung tissue. Lung vesicles interacted with bone marrow cells result in the bone marrow cells expressing surfactants A–D, Clara cell protein, and aquaporin-5 mRNA. In a similar vein, liver-derived vesicles induce albumin mRNA in target marrow cells. The vesicles contain protein, mRNA, microRNA, and noncoding RNA and variably some DNA. This genetic package is delivered to cells and alters the phenotype. Further studies have shown that initially the altered phenotype is due to the transfer of mRNA and a transcriptional modulator, but long-term epigenetic changes are induced through transfer of a transcriptional factor, and the mRNA is rapidly degraded in the cell. Studies on the capacity of vesicles to restore injured tissue have been quite informative. Mesenchymal stem cell-derived vesicles are able to reverse the injury to the damaged liver and kidney. Other studies have shown that mesenchymal stem cell-derived vesicles can reverse radiation toxicity of bone marrow stem cells. Extracellular vesicles offer an intriguing strategy for treating a number of diseases characterized by tissue injury.

Aging is accompanied by loss of tissue homeostasis, deterioration in organ function and an increased incidence of disease. Age-related changes in the adult stem/progenitor compartment likely drive much of this aging phenotype. For the hematopoietic system, it has been shown that the number of hematopoietic stem cells (HSCs) increases with age, but their renewal potential decreases and they exhibit aberrant lineage production with myeloid skewing. These age-related findings have been based primarily on studies of highly purified, immunophenotypically defined HSCs. However, our data indicate that young murine WBM contains a large population of cycling HSCs not represented within the purified HSC population. The goal of this work was to determine the effects of aging on this total population of stem cells in un-separated WBM. We first performed limiting dilution competitive bone marrow transplantation assays to determine the relative frequency of HSCs in old and young murine WBM. We injected serial dilutions of WBM from either old (24 month old) or young (6-8week old) donor C57BL/6 (CD45.2) mice into lethally irradiated young B6.SJL (CD45.1) hosts. Each mouse received 3x105 competitor WBM cells derived from young B6.SJL mice. At 6 months post transplant, we measured peripheral blood chimerism and lineage composition. According to the Poisson distribution, the estimated frequency of stem cells (with positive engraftment defined as ≥1% donor chimerism) was 1 in 9.8 x 103 for old marrow and 1 in 40 x 103 for young marrow, an approximately 4-fold increase in functional stem cells in old marrow, similar to reports in the literature. Interestingly, in contrast to what has been observed with old purified HSCs, the lineage analysis of donor-derived peripheral blood from aged WBM showed minimal to no myeloid skewing (Table, Row A). To test stem cell function in secondary transplantation, lethally irradiated young recipient mice were initially transplanted with old or young donor WBM mixed with equal numbers of young competitor WBM. At 6 months post-transplant, WBM was harvested and serially transplanted into lethally irradiated secondary recipient young mice. Peripheral blood chimerism was analyzed at 6 months. Similar to young WBM, the stem cells within old WBM retained robust stem cell capacity in serial transplantation, and aged WBM continued to show little to no myeloid skewing (Table, Row B, C). Finally, using tritiated thymidine (3H-thymidine) suicide and Hoechst 33342 staining, we determined the cell cycle status of the aged HSCs in WBM. WBM harvested from old or young donor mice was exposed to 3H-thymidine in vitro for 30 minutes, during which time any cell traversing S-phase would be selectively killed. Cells were then mixed with equal numbers of un-manipulated young competitor WBM and transplanted into lethally irradiated young host mice. Controls included donor WBM un-manipulated or incubated with unlabeled thymidine. We found a significant reduction in engraftment capacity in old WBM post 3H- thymidine incubation (Table, Row D), suggesting the presence of cycling HSCs. Utilizing Hoechst 33342, we isolated G0/G1 and S/G2/M cell cycle-specific fractions of old WBM by FACS and injected each population with equal numbers of young competitor WBM into lethally irradiated young recipient mice. At 6 months post transplant, aged WBM cells in S/G2/M contributed to peripheral blood chimerism, albeit to a lesser extent than cells in G0/G1 (Table, Row E). We previously published that, although purified HSCs in young marrow are quiescent, cells in S/G2/M and in G0/G1 from young un-separated WBM had equal engraftment capacity. Thus, it appears that this cycling stem cell population is still present in old marrow but declines with age. In conclusion, in contrast to purified HSCs, functional engraftment capacity in un-separated WBM does not seem to diminish with age, shows minimal to no myeloid skewing, and is due, in part, to cycling stem cells. These data support the existence of a population of HSCs in WBM distinct from conventionally defined purified HSCs, with seemingly differential susceptibility to aging with respect to self-renewal and lineage fate decisions. Thus, we propose that approaches to reverse aging and define mechanisms underlying age-related hematologic diseases may need to be broadened to incorporate a more heterogeneous HSC compartment not fully represented by the purified HSCs. Table Disclosures No relevant conflicts of interest to declare.

We have previously shown that injury induced by irradiation to murine marrow can be partially or completely reversed by exposure to human or murine mesenchymal stem cell (MSC)-derived extracellular vesicles (EVs). Investigation of the biodistribution of EVs in vivo is essential for understanding EV biology. In this study, we evaluated the DiD lipid dye labeled MSC-EV biodistribution in mice under different conditions, including different MSC-EV doses and injection schedules, time post MSC-EV injection, and doses of radiation. DiD-labeled MSC-EVs appeared highest in the liver and spleen, lower in bone marrow of the tibia, femur, and spine, and were undetectable in the heart, kidney and lung, while a predominant EV accumulation was detected in the lung of mice infused with human lung fibroblast cell derived EVs. There was significantly increased MSC-EV accumulation in the spleen and bone marrow (tibia and femur) post radiation appearing with an increase of MSC-EV uptake by CD11b+ and F4/80+ cells, but not by B220 cells, compared to those organs from non-irradiated mice. We further demonstrated that increasing levels of irradiation caused a selective increase in vesicle homing to marrow. This accumulation of MSC-EVs at the site of injured bone marrow could be detected as early as 1 h after MSC- EV injection and was not significantly different between 2 and 24 h post MSC-EV injection. Our study indicates that irradiation damage to hematopoietic tissue in the spleen and marrow targets MSC-EVs to these tissues.

We have shown that hematopoietic stem/progenitor cell phenotype and differentiative potential change throughout cell cycle. Lung-derived microvesicles (LDMVs) also change marrow cell phenotype by inducing them to express pulmonary epithelial cell-specific mRNA and protein. These changes are accentuated when microvesicles isolated from injured lung. We wish to determine if microvesicle-treated stem/progenitor cell phenotype is linked to cell cycle and to the injury status of the lung providing microvesicles. Lineage depleted, Sca-1+ (Lin-/Sca-1+) marrow isolated from mice were cultured with interleukin 3 (IL-3), IL-6, IL-11, and stem cell factor (cytokine-cultured cells), removed at hours zero (cell cycle phase G0/G1), 24 (late G1/early S), and 48 (late S/early G2/M), and cocultured with lung tissue, lung conditioned media (LCM), or LDMV from irradiated or nonirradiated mice. Alternatively, Lin-/Sca-1+ cells not exposed to exogenous cytokines were separated into G0/G1 and S/G2/M cell cycle phase populations by fluorescence-activated cell sorting (FACS) and used in coculture. Separately, LDMV from irradiated and nonirradiated mice were analyzed for the presence of adhesion proteins. Peak pulmonary epithelial cell-specific mRNA expression was seen in G0/G1 cytokine-cultured cells cocultured with irradiated lung and in late G1/early S cells cocultured with nonirradiated lung. The same pattern was seen in cytokine-cultured Lin-/Sca-1 cells cocultured with LCM and LDMV and when FACS-separated Lin-/Sca-1 cells unexposed to exogenous cytokines were used in coculture. Cells and LDMV expressed adhesion proteins whose levels differed based on cycle status (cells) or radiation injury (LDMV), suggesting a mechanism for microvesicle entry. These data demonstrate that microvesicle modification of progenitor/stem cells is influenced by cell cycle and the treatment of the originator lung tissue.

Extracellular vesicles (EVs) including exosomes and microvesicles, have been found to deliver both mRNA and transcriptional modulators to target cells and affect their phenotype. Vesicles derived from mesenchymal stem cells (MSC) have been shown to affect the phenotype and induce healing of many different cell types. Our recent published work has shown that pretreated irradiated murine bone marrow stem cells with human or murine MSC-EV in vitro, could significantly improve the engraftment capacity of radiation-damaged stem cells up to 9 months post-transplantation. Interestingly, the restoration of engraftment was not significantly observed within the first month of post-transplant, the predominant reversal effect occurred on later period of post-transplant from 3 months up to 9 months. This is indicating a long-term effect of MSC-EVs on reversal of radiation damage of stem cell engraftment capacity. To confirm this hypothesis, in our current study, the effect of human MSC-EVs on reversal of engraftment capacity of bone marrow stem cells post-radiation was investigated by an in vivo study. C57BL/6 mice were exposed to 500 cGy total body irradiation. MSC-EVs or vehicle were then injected intravenously 24, 48 and 72 hours after irradiation. The whole bone marrow were harvested at 6, 12, 26 and 53 weeks post EV-injection and then transplanted into 950 cGy exposed B6.SJL mice and engraftment evaluated at 1 and 3 months post-transplantation. In those transplanted mice at 6 weeks post-EV injection, there was slight increase in the restoration of engraftment rate (the percent of irradiated mice with EV/Vehicle treatment engraftment rate compared to healthy non-irradiated mice engraftment rate) in EV treated mice (17.58±2.32% compared to untreated mice (13.80±1.41%) after 1 month post-transplantation. However, for those mice transplanted at 12, 26, and 53 weeks post-EV injection, there were the significant higher restorations of engraftment rate in EV treated mice (40.48±6.03%, 33.93±3.76%, and 56.62±3.635) compared to untreated mice (12.39±1.30%, 15.14±2.21%, 36.21±3.63%) after 1 month transplantation respectively. The similar restorations of engraftment were also seen in 3 months post-transplantation. Our study also showed that there was a significant inhibition of stem cell engraftment at 53 weeks post 500cGy whole body radiation mice which was 36.21±3.63% of engraftment rate from healthy mice. Thus our data suggest that there is a long-term effect of MSC-EVs on the restoration of engraftment of stem cells in radiation-exposed mice. Disclosures No relevant conflicts of interest to declare.

The SUV3 gene is present in all eukaryotes and encodes an RNA/DNA helicase which operates both in mitochondria and cell nuclei. To assess its function in mammals we generated a mouse mutant strain in which the 3′ part of the SUV3 gene is disrupted. The mutated allele is a hypomorph transmitted from one generation to another at a frequency about 35% lower than expected while mice homozygous for the mutation die in utero before midgestation. Using ELISA binding assays we show that human SUV3 protein interacts with human WRN and BLM helicases. The binding to BLM protein was 10-fold stronger (with a Kd of 0.5 nM) than to WRN protein (Kd of 5 nM). Silencing of the SUV3 gene in the human cell line HeLa resulted in elevation of homologous recombination as measured by the frequency of sister chromatid exchange during mitotic cell division. These results indicate that the SUV3 protein is required in mammalian development and in somatic cells participates in genome maintenance through interaction with other genome fidelity housekeepers.

Raf kinase inhibitory protein (RKIP-1) is involved in the regulation of the MAP kinase, NF-kappaB, and GPCR signaling pathways. It is expressed in numerous tissues and cell types and orthologues have been documented throughout the animal and plant kingdoms. RKIP-1 has also been reported as an inhibitor of serine proteases, and a precursor of a neurostimulatory peptide. RKIP-1 has been implicated as a suppressor of metastases in several human cancers. We generated a knockout strain of mice to further assess RKIP-1's function in mammals. RKIP-1 is expressed in many tissues with the highest protein levels detectable in testes and brain. In the brain, expression was ubiquitous in limbic formations, and homozygous mice developed olfaction deficits in the first year of life. We postulate that RKIP-1 may be a modulator of behavioral responses.

Background : Our group has previously demonstrated that murine whole bone marrow cells (WBM) that internalize lung-derived extracellular vesicles (LDEVs) in culture express pulmonary epithelial cell–specific genes for up to 12 weeks. In addition, the lungs of lethally irradiated mice transplanted with lung vesicle–modulated marrow have 5 times more WBM-derived type II pneumocytes compared to mice transplanted with unmanipulated WBM. These findings indicate that extracellular vesicle modification may be an important consideration in the development of marrow cell–based cellular therapies. Current studies were performed to determine the specific marrow cell types that LDEV stably modify. Methods : Murine WBM-derived stem/progenitor cells (Lin-/Sca-1+) and differentiated erythroid cells (Ter119+), granulocytes (Gr-1+) and B cells (CD19+) were cultured with carboxyfluorescein N -succinimidyl ester (CFSE)-labelled LDEV. LDEV+ cells (CFSE+) and LDEV− cells (CFSE−) were separated by flow cytometry and visualized by fluorescence microscopy, analyzed by RT-PCR or placed into long-term secondary culture. In addition, murine Lin-/Sca-1+ cells were cultured with CFSE-labelled LDEV isolated from rats, and RT-PCR analysis was performed on LDEV+ and–cells using species-specific primers for surfactant (rat/mouse hybrid co-cultures). Results : Stem/progenitor cells and all of the differentiated cell types studied internalized LDEV in culture, but heterogeneously. Expression of a panel of pulmonary epithelial cell genes was higher in LDEV+cells compared to LDEV− cells and elevated expression of these genes persisted in long-term culture. Rat/mouse hybrid co-cultures revealed only mouse-specific surfactant B and C expression in LDEV+ Lin-/Sca-1+cells after 4 weeks of culture, indicating stable de novo gene expression. Conclusions : LDEV can be internalized by differentiated and more primitive cells residing in the bone marrow in culture and can induce stable de novo pulmonary epithelial cell gene expression in these cells for several weeks after internalization. The gene expression represents a transcriptional activation of the target marrow cells. These studies serve as the basis for determining marrow cell types that can be used for cell-based therapies for processes that injure the pulmonary epithelial surfaces. Keywords: bone marrow cells; pulmonary epithelial cells; extracellular vesicles (Published: 16 September 2015) Citation: Journal of Extracellular Vesicles 2015, 4: 26166 - http://dx.doi.org/10.3402/jev.v4.26166

Marrow cells are a rich source of vesicles (released from their surface or endosomal compartment that may deliver proteins, ribonucleic acid (RNA), and microRNA (miRNA) into damaged organs. Based on this, paracrine effects probably make major contributions in most of the currently reported positive results in clinical trials employing adult hematopoietic stem cells. In this chapter, we will discuss our data showing that extracellular vesicles might have significant therapeutic potential in various tissue injuries as well as in treatment of cancer.

Prevailing wisdom holds that hematopoietic stem cells (HSCs) are predominantly quiescent. Although HSC cycle status has long been the subject of scrutiny, virtually all marrow stem cell research has been based on studies of highly purified HSCs. Here we explored the cell cycle status of marrow stem cells in un-separated whole bone marrow (WBM). We show that a large number of long-term multi-lineage engraftable stem cells within WBM are in S/G2/M phase. Using bromodeoxyuridine, we show rapid transit through the cell cycle of a previously defined relatively dormant purified stem cell, the long-term HSC (LT-HSC; Lineage(-)/c-kit(+)/Sca-1(+)/Flk-2(-)). Actively cycling marrow stem cells have continually changing phenotype with cell cycle transit, likely rendering them difficult to purify to homogeneity. Indeed, as WBM contains actively cycling stem cells, and highly purified stem cells engraft predominantly while quiescent, it follows that the population of cycling marrow stem cells within WBM are lost during purification. Our studies indicate that both the discarded lineage-positive and lineage-negative marrow cells in a stem cell separation contain cycling stem cells. We propose that future work should encompass this larger population of cycling stem cells that is poorly represented in current studies solely focused on purified stem cell populations.

Aims Circulating endothelium-derived extracellular vesicles (EV) levels are altered in pulmonary arterial hypertension (PAH) but whether they are biomarkers of cellular injury or participants in disease pathogenesis is unknown. Previously, we found that lung-derived EVs (LEVs) induce bone marrow-derived progenitor cells to express lung-specific mRNA and protein. In this study, we sought to determine whether LEV or plasma-derived EV (PEV) alter pulmonary vascular endothelial or marrow progenitor cell phenotype to induce pulmonary vascular remodelling. Methods and results LEV, PEV isolated from monocrotaline (MCT-EV)- or vehicle-treated mice (vehicle-EV) were injected into healthy mice. Right ventricular (RV) hypertrophy and pulmonary vascular remodelling were assessed by RV-to-body weight (RV/BW) and blood vessel wall thickness-to-diameter (WT/D) ratios. RV/BW, WT/D ratios were elevated in MCT- vs. vehicle-injected mice (1.99 ± 0.09 vs. 1.04 ± 0.09 mg/g; 0.159 ± 0.002 vs. 0.062 ± 0.009%). RV/BW, WT/D ratios were higher in mice injected with MCT-EV vs. mice injected with vehicle-EV (1.63 ± 0.09 vs. 1.08 ± 0.09 mg/g; 0.113 ± 0.02 vs. 0.056 ± 0.01%). Lineage-depleted bone marrow cells incubated with MCT-EV and marrow cells isolated from mice infused with MCT-EV had greater expression of endothelial progenitor cell mRNAs and mRNAs abnormally expressed in PAH than cells incubated with vehicle-EV or isolated from vehicle-EV infused mice. MCT-EV induced an apoptosis-resistant phenotype in murine pulmonary endothelial cells and lineage-depleted bone marrow cells incubated with MCT-EV induced pulmonary hypertension when injected into healthy mice. Conclusions EV from MCT-injured mice contribute to the development of MCT-induced pulmonary hypertension. This effect may be mediated directly by EV on the pulmonary vasculature or by differentiation of bone marrow cells to endothelial progenitor cells that induce pulmonary vascular remodelling.

The hierarchical models of stem cell biology have been based on work first demonstrating pluripotental spleen-colony-forming units, then showing progenitors with many differentiation fates assayed in in vitro culture; there followed the definition and separation of "stem cells" using monoclonal antibodies to surface epitopes and fluorescent-activated cell characterization and sorting (FACS). These studies led to an elegant model of stem cell biology in which primitive dormant G0 stem cells with tremendous proliferative and differentiative potential gave rise to progressively more restricted and differentiated classes of stem/progenitor cells, and finally differentiated marrow hematopoietic cells. The holy grail of hematopoietic stem cell biology became the purification of the stem cell and the clonal definition of this cell. Most recently, the long-term repopulating hematopoietic stem cell (LT-HSC) has been believed to be a lineage negative sca-1+C-kit+ Flk3- and CD150+ cell. However, a series of studies over the past 10 years has indicated that murine marrow stem cells continuously change phenotype with cell cycle passage. We present here studies using tritiated thymidine suicide and pyronin-Hoechst FACS separations indicating that the murine hematopoietic stem cell is a cycling cell. This would indicate that the hematopoietic stem cell must be continuously changing in phenotype and, thus, could not be purified. The extant data indicate that murine marrow stem cells are continually transiting cell cycle and that the purification has discarded these cycling cells. Further in vivo BrdU studies indicate that the "quiescent" LT-HSC in G0 rapidly transits cycle. Further complexity of the marrow stem cell system is indicated by studies on cell-derived microvesicles showing that they enter marrow cells and transcriptionally alter their cell fate and phenotype. Thus, the stem cell model is a model of continuing changing potential tied to cell cycle and microvesicle exposure. The challenge of the future is to define the stem cell population, not purify the stem cell. We are at the beginning of elucidation of quantum stemomics.

Background: Interest has been generated in the capacity of cellular-derived microvesicles to alter the fate of different target cells. Lung, liver, heart and brain-derived vesicles can alter the genetic phenotype of murine marrow cells; however, the stability of such changes and the mechanism of these changes remain unclear. In the present work, we show that lung-derived microvesicles (LDMV) alter the transcriptome and proteome of target marrow cells initially by mRNA and regulator(s) of transcription transfer, but that long term phenotype change is due solely to transfer of a transcriptional regulator with target cell. Methods/results: In vivo studies: Whole bone marrow cells (WBM) were co-cultured with LDMV (both isolated from male C57BL/6 mice) or cultured alone (control). One week later, cultured WBM was transplanted into lethally-irradiated female C57BL/6 mice. Recipient mice were sacrificed 6 weeks later and WBM, spleens and livers were examined for the presence of lung-specific gene expression, including surfactants A, B, C and D, aquaporin-5, and clara cell specific protein, via real-time RT-PCR. Immunohistochemistry was also performed on lungs to determine the number of transplanted marrowderived (Y chromosome+) type II pneumocytes (prosurfactant C+). Mice transplanted with LDMV cocultured WBM expressed pulmonary epithelial cell genes in the cells of their bone marrow, livers and spleens and over fivefold more transplanted marrow-derived Y+/prosurfactant C+cells could be found in their lungs (vs. control mice). In vitro studies: WBM (from mice or rats) was cultured with or without LDMV (from mice or rats) for 1 week then washed and cultured alone. WBM was harvested at 2-week intervals for real-time RT-PCR analysis, using species-specific surfactant primers, and for Western Blot analysis. Proteomic and microRNA microarray analyses were also performed on cells. LDMV co-cultured WBM maintained expression of pulmonary epithelial cell genes and proteins for up to 12 weeks in culture. Surfactant produced at later time points was specific only to the species of the marrow cell in culture indicating de novo mRNA transcription. These findings, in addition to the altered protein and microRNA profiles of LDMV co-cultured WBM, support a stable transcriptional mechanism for these changes. Conclusions: These data indicate that microvesicle alteration of cell fate is robust and long-term and represents an important new aspect of cellular biology. Keywords: bone marrow cells; lung; microvesicles; bone marrow transplant; transcription factor (Published: 16 April 2012) Citation: Journal of Extracellular Vesicles 2012, 1 : 18163 - http://dx.doi.org/10.3402/jev.v1i0.18163

Objective. Microvesicles have been shown to mediate intercellular communication. Previously, we have correlated entry of murine lung-derived microvesicles into murine bone marrow cells with expression of pulmonary epithelial cell-specific messenger RNA (mRNA) in these marrow cells. The present studies establish that entry of lung-derived microvesicles into marrow cells is a prerequisite for marrow expression of pulmonary epithelial cell-derived mRNA. Materials and Methods. Murine bone marrow cells cocultured with rat lung, but separated from them using a cell-impermeable membrane (0.4-mu m pore sire), were analyzed using species-specific printers (for rat or mouse). Results. These studies revealed that surfactant 13 and C mRNA produced by murine marrow cells were of both rat and mouse origin. Similar results were obtained using murine lung cocultured with rat bone marrow cells or when bone marrow cells were analyzed for the presence of Species-Specific albumin mRNA after coculture with rat or murine liver. These studies show that microvesicles both deliver mRNA to marrow cells and mediate marrow cell transcription of tissue-specific mRNA. The latter likely Underlies the longer-term stable change in genetic phenotype that has been observed. We have also observed microRNA in lung-derived microvesicles, and studies with RNase-treated microvesicles indicate that microRNA negatively modulates pulmonary epithelial cell-specific mRNA levels in cocultured marrow cells. In addition, we have also observed tissue-specific expression of brain, heart, and liver mRNA in cocultured marrow cells. suggesting that microvesicle-mediated cellular phenotype change is a universal phenomena. Conclusion. These studies suggest that cellular systems :are more phenotypically labile than previously considered. (C) 2010 ISEH - Society for Hematology and Stem Cells. Published by Elsevier Inc.

Rationale: We have demonstrated that whole, undifferentiated bone marrow (WBM) cells isolated from mice with monocrotaline (MCT)-induced pulmonary hypertension (PH) cause pulmonary hypertensive changes when transplanted into lethally-irradiated mice (Aliotta et al., 2014 ATS abstract). In addition, mesenchymal stem cell (MSC)-derived extracellular vesicles (EVs), sub-cellular particles shed by activated cells, can reverse features of MCT-induced PH (Aliotta et al., 2015 ATS abstract). Endothelial progenitor cells (EPCs) have been implicated in the pathogenesis of human PH as more have been noted to be present in the circulation and remodeled pulmonary vasculature of these patients compared with healthy humans. We wished to determine if bone marrow-derived EPCs isolated from mice with MCT PH were the cells responsible for inducing PH in healthy mice and if so, whether exposure of these EPCs to MSC EVs prevented the development of PH. Methods: Sca-1+/ckit+/flk1+ cells (EPCs) and sca-1-/ckit-/flk1- cells (non-EPCs) were isolated from the bone marrow of MCT-injured and vehicle-injected mice. Cohorts of lethally-irradiated mice were transplanted with EPCs (2,000 EPCs + 300,000 helper WBM cells/recipient) or non-EPCs (200,000 non-EPCs + 200,000 helper WBM cells/recipient) from the bone marrow of MCT-injured and vehicle-injected mice. 28 days after transplantation, recipient mouse right ventricular (RV) hypertrophy was assessed by RV-to-left ventricle+septum (RV/LV+S) ratio (mg/g) and pulmonary vascular remodeling by blood vessel wall thickness-to-diameter (WT/D) ratio. In addition, WBM from MCT-injured and vehicle-injected mice was cultured with or without MSC EVs for 48 hours. EPCs (80-100 EPCs + 300,000 helper WBM cells/recipient) and non-EPCs (500,000-700,000 non- EPCs + 300,000 helper WBM cells/recipient) were separated by flow cytometry and infused into lethally-irradiated mice which were analyzed 28 days post-transplant. Results: RV/LV+S ratios of mice transplanted with EPCs from MCT-injured mice (0.256+/-0.142 mg/g) were similar to those of MCT-injured mice (0.274+/-0.211 mg/g, p=NS, n=5/cohort) but elevated compared to mice transplanted with EPCs and non-EPCs from vehicle-injected mice (0.126+/-0.111 and 0.121+/-0.134 mg/g, p Conclusions: These findings suggest that EPCs are among the pathogenic bone marrow cells in MCT-injured mice that are responsible for inducing RV hypertrophy and pulmonary vascular remodeling, key features of PH, upon transplantation into healthy mice. MSC EVs appear to be capable of reversing this disease via interactions with EPCs. Disclosures No relevant conflicts of interest to declare.

We have shown that Human or mouse mesenchymal stem cell (MSC) derived vesicles separated by differential centrifugation (300g, 10kg &100kg) can reverse radiation whole bone marrow (WBM) damage in vitro on the hematopoietic cell line FDC-P1 and in vivo on recovery of stem cells and differentiated blood cells after whole body irradiation. The vesicle separation is a classic method for preparations of exosomes. However, this separation isolates the smaller vesicles, discarding larger vesicles. Biologic healing effects of larger vesicles with or without smaller vesicles have not been investigated. Here, we investigated the healing effects of 3 different preparations of vesicles: 10k pellet (microvesicles), 100-10k pellet (exosomes) & 100k pellet (no 10k spin). Three different fractions (10k pellet, 100-10k pellet &100k pellet) of murine/human MSC or murine WBM derived vesicles were isolated by differential centrifugation. FDC-P1 cells were exposed at 500cGy irradiation and cultured with or without the addition of 3 different preparations of murine WBM or human MSC-derived vesicles for 7 days. A significant increase in cell proliferation was observed after 3 different vesicle fractions treatments. However, exosomes were clearly inferior, microvesicles and the combined exosomes and microvesicles population were superior. The capacity of human MSC-derived vesicles of different fractions on reversal of murine bone marrow damage was also evaluated in vivo. Again, the combined fractions shown a significant increase donor chimerism in bone marrow at 6 month post-transplant with 5x's the level of engraftment compared to irradiation control. The 10k and 100-10k fractions showed intermediate healing. Exposure to vesicles in irradiated FDC-P1 cells downregulated phosphorylated H2AX, the DNA damage marker and decreased apoptosis marker, PARP cleavage part. We further investigated the effect of murine marrow MSC-derived vesicles on the gene expression in peripheral blood cells from radiation damaged mice. 28 genes were altered by irradiation, 22 showed partial or complete reversal of these alterations. The characterization of three different fractions of vesicles derived from murine bone marrow cells and human MSC were evaluated by miRNA realtime PCR array (total 750 miRNA). Several MSC-EV associated miRNA responsible for the reversal of radiation damage were evaluated. Our preliminary data shown that miR-221, miR654-3p and miR210-5p could partially reverse radiation damage in FDC-P1 cells There are different biological effects in different extracellular vesicles populations. For reversal of radiation toxicity the most effective vesicle population would include both smaller (exosomes) and larger vesicles (microvesicles). Acknowedgements: This work was support by the NIH grant 5UH2TR00080 Disclosures No relevant conflicts of interest to declare.

Background: Hematopoietic stem cells (HSCs) have tremendous self-renewal and differentiation capacity. The majority of murine hematopoietic stem cell studies have focused on rare purified populations of HSCs, conventionally described as negative for lineage-specific markers and positive for particular cell surface epitope profiles, including c-Kit, Sca-1, and CD150. However, our data indicate that such purifications lead to the loss of a significant population of actively cycling marrow cells with long-term multi-lineage stem cell potential. In the studies presented here, we tested the hypothesis that this discarded stem cell population lies, in part, within the lineage positive (Lin+) fraction of marrow. Methods: We flushed whole bone marrow (WBM) from B6.SJL mice and incubated it with allophycocyanin-tagged antibodies against erythroid (TER119), myeloid (CD11b, GR1), B-lymphoid (B220), or T-lymphoid (CD3, CD4, CD8) markers. Different doses of each specific Lin+ subset isolated by fluorescence activated cell sorting were competitively engrafted into lethally irradiated C57BL/6 host mice. At 1,3, and 6 months post-transplant, peripheral blood was analyzed for donor contribution to chimerism and lineage specificity. Results: Although typically considered to be without stem cell activity, we found that all Lin+ sub-fractions upon single sorting were able to contribute to marrow repopulation in competitive bone marrow transplants. For example, when lethally irradiated recipient mice received 3x105 C57BL/6J competitive whole bone marrow cells in combination with single-sorted GR1+ ± CD11b+ cells (2x106 cells/mouse), peripheral blood showed 15% donor chimerism at 6 months. Similarly, if single sorted CD3+ ±CD4+ ±CD8+ cells (70,000 cells/mouse), B220+ cells (1x106 cells/mouse), or Ter119+ cells (1x106 cells/mouse) were competitively engrafted with 3x105 C57BL/6 WBM cells, the donor Lin+ sub-fractions contributed to 2%, 15%, and 35% peripheral blood chimerism at 6 months post-transplant, respectively. This contribution was multi-lineage in all cases. When we performed double sorting of the Lin+ subsets, there was a dramatically reduced engraftment capacity between 1-6% donor chimerism for all subgroups. However, we do not think the loss of stem cell capacity with double sorting seen in these studies is due merely to the loss of classical hematopoietic stem cells (Lineage-/stem cell marker+). In our earlier studies, we showed that the total Lin+ population contains long-term multi-lineage engraftment capacity due almost entirely to actively cycling cells. Therefore, if the engraftment capacity within the single sorted Lin+ sub-fractions was due solely to the presence of classical HSCs lost with double sorting, the engraftment capacity found within the Lin+ compartment should be due only to quiescent cells in keeping with the cell cycle status of engrafting highly purified stem cells. Conclusions: Based on these data, we predict that a cycling population of stem cells exists within this single sorted, Lin+ enriched fraction discarded with conventional HSC purification. Future studies are ongoing to further characterize the subsets of Lin+ cells that both remain Lin+ and are found to be Lin- upon double sorting. We will analyze these populations for engraftment capacity, concomitant stem cell marker expression and cell cycle status, in order to fully characterize the total stem cell potential within whole bone marrow that is not included in the purified HSC populations. Disclosures No relevant conflicts of interest to declare.

Introduction: Extracellular vesicles (EVs) are membrane-bound, subcellular fragments that contain DNA, RNA, protein and lipids, and play an important role in intercellular communication. They have been implicated in myriad physiologic and pathologic processes within the hematopoietic system including thrombosis and leukemia, and as such, have tremendous therapeutic potential if manipulated appropriately. In order to fully harness their clinical potential, it will be important to more fully characterize the factors that modulate their biogenesis and function. Numerous factors are thought to influence EVs and their ability to communicate with target marrow cells, but little is known about how circadian oscillations alter EV function. Using a well-established model of lung-derived EV modulation of marrow phenotype, we report here our studies exploring the effects of circadian rhythm on the ability of lung-derived EVs to alter the transcriptome of bone marrow target cells. Methods: C57BL/6 mice were housed on a 12-hour light/dark schedule. For the first set of experiments, lungs, blood and bone marrow were harvested (6-16 mice/time) at three different circadian time-points (8,12 and 24 hours after light onset (HALOs). EVs were isolated from each tissue at each time-point and quantified by nanoparticle tracking analysis. Second, to determine if circadian rhythm influences the ability of lung-derived EVs to modulate the transcriptome of target whole bone marrow cells (WBM), lungs were harvested (3 mice/time-point x 2 experiments) at 4,12,16, and 24 hours after light onset and co-cultured, across a cell-impermeable membrane, with murine WBM. The WBM was harvested after 24hrs in co-culture and analyzed for the induction of pulmonary specific mRNA expression by RT-PCR. Finally, to determine if altering the circadian timepoint of the target whole bone marrow influenced the ability of EVs to modulate marrow phenotype, lungs harvested from mice sacrificed at HALO 2 were cultured for 48hrs. EVs were isolated from the lung-conditioned media by ultracentrifugation. WBM was then harvested at different circadian time-points (HALO 4, 8, 12, 16, 20, and 24; 3 mice/time-point x 2 experiments), cultured with or without the lung-derived EVs for 24hrs, and then analyzed for pulmonary-specific mRNAs by RT-PCR. Results: There were changes in EV quantity related to circadian timepoint. There were significantly increased numbers of EVs generated from lungs harvested at HALO 24 and HALO 8 when compared to HALO 16. Similarly, marrow harvested at HALO 8 had significantly increased number of EVs as compared to WBM harvested at HALO 16 and 24. In addition to circadian-related differences in EV quantity, there were clear oscillations in the expression patterns of pulmonary specific mRNAs when both the circadian timepoint of the lung donor and the circadian timepoint of the recipient marrow cells were altered. If lung was harvested at HALO 12 or HALO 16, the co-cultured WBM showed significantly increased expression of pulmonary-specific mRNAs when compared to WBM co-cultured with lung harvested at HALO 4 or HALO 24. Likewise, when WBM harvested at different circadian time-points was incubated with lung-derived EVs, there was significantly increased expression of surfactant A, surfactant B, and aquaporin 5 when WBM was harvested at HALO 16 when compared to HALO 12 or HALO 24. Conclusions: Based on these data, we conclude that circadian rhythm is likely an important modulator of EV-mediated intercellular communication with whole bone marrow cells and warrants more detailed study. Disclosures No relevant conflicts of interest to declare.

The study of highly purified hematopoietic stem cells (HSCs) has dominated the field of hematopoietic stem cell biology. It is widely believed that the true stem cell population lies within the Lineage negative (Lin-) population, further sub-fractionated using positive and negative selection for surface markers such as c-Kit, Sca-1, CD150, CD41, CD48, and CD34. It is research on these highly purified subsets of HSCs that forms the foundation for almost all our knowledge of HSCs, and has led to the dogma that marrow stem cells are quiescent with a stable phenotype and therefore can be purified to near homogeneity. In contrast, we have shown that a large percentage of long-term multi-lineage marrow repopulating cells in whole bone marrow (WBM) are actively cycling, that these cycling stem cells are lost during conventional HSC isolation, and that they can be found, in part, within the discarded Lineage positive (Lin+) population. Here we present data further characterizing the stem cell potential in the Lin+ fraction. We incubated WBM from B6.SJL mice with fluorescently tagged antibodies directed against TER119, B220, or T-cell markers (CD3, CD4, CD8), isolated the distinct Lin+ subsets by FACS, and then competitively engrafted each Lin+ subset into lethally irradiated C57BL/6 host mice. Donor chimerism and lineage specificity of donor cells in peripheral blood were analyzed by flow cytometry at 3 months. Although classically considered devoid of stem cell activity, we found that, when competed against equal numbers of C57BL/6 WBM, the TER119+ and B220+ B6.SJL donor cells contributed to 33% and 13% of the peripheral blood chimerism, respectively. In both cases, the engraftment was multi-lineage. When 70,000 T cell marker+ donor cells were competed with 300,000 C57BL/6 WBM, the donor cells contributed up to 1.6% of the peripheral blood multi-lineage chimerism. Given the size of the Lin+ fraction in WBM, such chimerism indicates a significant stem cell potential within this typically discarded population. Further time-points, secondary transplants and limited dilution studies are in progress to further define the prevalence and potency of this stem cell population. We have been testing mechanisms governing the loss of this stem cell population during HSC purification. First, we have previously shown that bulk Lin+ engraftment potential is due to cycling stem cells. We hypothesize that fluctuations in surface epitope expression with cell cycle transit render this population difficult to isolate with antibody-mediated strategies that rely on stable epitope expression. To begin testing this, we tracked the fluctuation of stem cell markers on Lin- cells in vitro. We isolated Lin- cells that were also negative for the stem cell markers c-Kit and Sca-1, placed them in liquid culture and, 18 hours later, re-assessed for stem cell marker expression by flow cytometry. We found that, although initially stem cell marker negative, up to 6%, 14%, and 2% of the Lin-/stem cell marker negative cells became positive for c-Kit alone, Sca-1 alone, or both c-Kit and Sca-1 expression, respectively. We are currently testing this population for a correlation between gain of c-Kit- and Sca-1 expression and stem cell function. Second, it is possible that there is a distinct subset of HSCs that are positive for both Lin+ markers and stem cell markers with stable stem cell capacity and that these distinct stem cells are thrown out in the process of lineage depletion. To begin testing this hypothesis, we have simultaneously stained WBM with antibodies directed against the Lin+ markers and conventional stem cell markers. Our preliminary data indicate that each Lin+ fraction tested to date has a subpopulation that is also positive for c-Kit and Sca-1. For example, 21% of CD3+ cells, 6.2% of CD4+ cells, 2.26% of CD8+ cells, 0.5% of B220+, and 0.45% of TER119+ cells express both c-Kit and Sca-1. We suspect these two populations have distinct functional phenotypes and experiments characterizing the molecular phenotype and engraftment capacity of these subpopulations are ongoing. In sum, our data indicate that stem cell purification skews isolation towards a small population of quiescent stem cells, underrepresenting a potentially large pool of actively cycling HSCs that are found within the Lin+ fraction. These data underscore the need to re-evaluate the total hematopoietic stem cell potential in marrow on a population level. Disclosures No relevant conflicts of interest to declare.

Adult marrow hematopoiesis has been felt to represent a classical hierarchical system with a primitive stem cell progressively differentiating into hematopoietic cells. Colony-forming unit spleen was the initial stem cell and there followed definition of a wide variety of progenitors with different lineage potentials. Purification studies indicated that the critical stem cells were lineage negative and Sca-1+c-kit+CD150+.1 Our studies over the past decade indicate that the phenotype of the stem cell changes reversibly with cell cycle transit. Characteristics showing such changes include long-term multilineage engraftment into irradiated mice, differentiation, homing to marrow, expression of adherence proteins and global gene expression, progenitor phenotype and uptake of extracellular vesicles. It was demonstrated that most stem cells are discarded during the separation. The final purified stem cell is in fact dormant, but the vast majority of stem cells that are discarded (over 90%) are in active cell cycle.2 In these studies it was shown that cells in S/G2/M accounted for over 50% of long-term engraftment of whole unseparated marrow and that the classical purified lineage-negative Sca-1-c-kit+CD150+ stem cell rapidly progressed through the cell cycle so that after 48 h exposure to in vivo bromodeoxyuridine up to 80% of the ‘dormant' cells incorporated bromodeoxyuridine. These data indicated that most mature marrow stem cells were discarded with the purification and that these cells were virtually all proliferating. Studies on the different fractions of a purification indicated that the vast majority of adult marrow stem cells were present in the lineage-positive and lineage-negative populations and that these cells were cycling. Thus, the true marrow stem cells rapidly transited the cell cycle and were continually changing phenotype; they could not be ‘purified' by assessing a set number of epitopic markers. The bulk of studies on murine marrow stem cells has been carried out on ‘purified stem cells' and thus have been addressing an irrelevant population of cells. These studies need to be readdressed. Further heterogeneity of adult marrow stem cells is introduced by considerations of interactions of these cells with extracellular vesicles.3 Studies on lineage-negative Sca-1+ progenitor/stem cells traversing the cell cycle under cytokine stimulation in liquid culture indicated that vesicle uptake varied with both the cell cycle state of the target cell and the nature of treatment of the originator lung cells (irradiation or no irradiation). Thus the adult marrow stem cell continually alters phenotype with cell cycle transit and this is further impacted upon by interactions with vesicles from a variety of cell types. The cell phenotype induced by vesicle exposure appears to be a stable epigenetic change induced by an RNase-sensitive agent that is not messenger RNA, presumably a non-coding RNA species. These observations suggest unique strategies for determination of cell fate and restoration of damaged cells. These data also suggest that while cell populations may be stable at the tissue or population level they are not stable at the individual cell level.

Abstract 4480 Objective Pulmonary complications are common in bone marrow transplant (BMT) recipients and often of an infectious etiology or attributed to intensive conditioning regimens. Cases of pulmonary arterial hypertension have been described in the setting of autologous BMT but are believed to be the result of acquired infections or previously-administered chemotherapy. Whether transplanted marrow cells themselves are toxic to the recipient's lungs is unknown. Methods To address this, non-irradiated female BALB/C mice were transplanted with 5-6×107 whole bone marrow (WBM) cells from male BALB/C mice daily for four days on week zero, then again on week eight (4.5×108 cells total/mouse), or an equal volume of diluent (control). On week 24, transplanted mice received 1000 cGy of chest-only radiation or no radiation. On week 32, histochemical and immunohistochemical analyses were performed on recipient's lungs. Results Bone marrow chimerism was not significantly different in the irradiated and non-irradiated cohorts at the time of sacrifice (average 45.11+6.25% Y chromosome+, all mice). Recipient lungs contained few non-hematopoietic donor marrow-derived cells. These cells were exclusively epithelial (Y+/cytokeratin+), primarily type II pneumocytes (Y+/prosurfactant C+), while no endothelial (Y+/von Willebrand+) or vascular smooth muscle (Y+/alpha-actin+) cells were identified. Irradiated and non-irradiated cohorts had similar quantities of these cells (0.80+0.22% vs. 0.51+0.08% Y+/cytokeratin+; 0.37+0.08% vs. 0.32+0.12% Y+/prosurfactant C+, p>0.2). Pulmonary vessel wall thickness-to-blood vessel diameter ratios (PVWT/D) were significantly increased in the non-irradiated cohort compared with controls and these ratios were further increased in the irradiated cohort (141+5.75%, 161+5.34% of control, p Conclusions These data indicated that marrow cell infusion alone results in pulmonary vascular remodeling and this effect is augmented by radiation injury. These changes are independent of transplanted marrow cell conversion to pulmonary vascular endothelial, smooth muscle cells. These studies suggest that transplanted cells may be lung toxic entities in the setting clinical BMT. Disclosures: No relevant conflicts of interest to declare.

Abstract 5190 Rationale: Circulating endothelial cell-derived microparticles (MP) are altered in pulmonary arterial hypertension (PAH) but whether they are biomarkers of cellular injury or participants in disease pathogenesis is unknown. We have shown that lung-derived MP induce marrow cells to express lung-specific mRNA, protein. Objectives: Determine if lung, plasma-derived MP (LMP, PMP) alter pulmonary vascular endothelial or marrow progenitor cell phenotype to induce pulmonary vascular remodeling in PAH. Methods and Main Results: LMP, PMP isolated from monocrotaline (MCT)- or vehicle-treated mice were injected into healthy mice. Right ventricular (RV) hypertrophy and pulmonary vascular remodeling were assessed by RV-to-body weight (RV/BW), blood vessel wall thickness-to-diameter (WT/D) ratios. RV/BW, WT/D ratios were elevated in MCT vs. vehicle-injected mice (1. 99+0. 09vs. 1. 04+0. 09mg/g; 0. 159+0. 002vs. 0. 062+0. 009%). MP from MCT and vehicle-treated mice were quantitatively similar; however, MCT-LMP had higher endothelial cell mRNA expression and higher expression of mRNAs of proteins known to be abnormally expressed in PAH vs. vehicle-LMP. RV/BW, WT/D ratios were higher in mice injected with MCT-MP vs. mice injected with vehicle-MP (1. 63+0. 09vs. 1. 08+0. 09mg/g; 0. 113+0. 02vs. 0. 056+0. 01%). Lineage-depleted bone marrow cells co-cultured with MCT-MP and bone marrow cells isolated from MCT-MP infused mice had higher endothelial progenitor cell gene expression vs. cells co-cultured with vehicle-MP or cells isolated from vehicle MP infused mice. Conclusions: MP from MCT-injured mice have increased expression of growth factors implicated in PAH pathogenesis and induce RV hypertrophy, pulmonary vascular remodeling in healthy mice. Circulating MP may contribute to the development of MCT-induced pulmonary hypertension by inducing a pathologic phenotype in pulmonary vascular endothelial and endothelial progenitor cells. Disclosures: No relevant conflicts of interest to declare.

Abstract 2308 Hematopoietic stem cell biologists have amassed a tremendous depth of knowledge about the biology of the marrow stem cell over the past few decades, facilitating invaluable basic scientific and translational advances in the field. Most of the studies to date have focused on highly purified populations of marrow cells, with emphasis placed on the need to isolate increasingly restricted subsets of marrow cells within the larger population of resident bone marrow cells in order to get an accurate picture of the true stem cell phenotype. Such studies have led to the dogma that marrow stem cells are quiescent with a stable phenotype and therefore can be purified to homogeneity. However, work from our laboratory, focusing on the stem cell potential in un-separated whole bone marrow (WBM), supports an alternate view of marrow stem cell biology in which a large population of marrow stem cells are actively cycling, continually changing phenotype with cell cycle transit, and therefore, cannot be purified to homogeneity. Our studies separating WBM into cell cycle-specific fractions using Hoechst 33342/Pyronin Y or exposing WBM to tritiated thymidine suicide followed by competitive engraftment into lethally irradiated mice revealed that over 50% of the long-term multi-lineage engraftment potential in un-separated marrow was due to cells in S/G2/M. This is in stark contrast to studies showing that highly purified stem cell populations such as LT-HSC (Lineage–c-kit+sca-1+flk2−) engraft predominantly when in G0. Additionally, by performing standard isolation of a highly purified population of stem cells, SLAM cells (Lineage–c-kit+sca-1+flk2−CD150+CD41−CD48−), and testing the engraftment potential of different cellular fractions created and routinely discarded during this purification process, we found that 90% of the potential engraftment capacity in WBM was lost during conventional SLAM cell purification. Incubation of the Lineage-positive and Lineage-negative fractions with tritiated thymidine, a DNA analogue which selectively kills cells traversing S-phase, led to dramatic reductions in long-term multi-lineage engraftment potential found within both cellular fractions (over 95% and 85% reduction, respectively). This indicates that the discarded population of stem cells during antibody-based stem cell purification is composed largely of cycling cells. In sum, these data strongly support that 1) whole bone marrow contains actively cycling stem cells capable of long-term multi-lineage engraftment, 2) these actively cycling marrow stem cells are lost during the standard stem cell purification strategies, and 3) the protean phenotype of actively cycling cells as they transit through cell cycle will render cycling marrow stem cells difficult to purify to homogeneity. Given the loss of a large pool of actively cycling HSC during standard stem cell isolation techniques, these data underscore the need to re-evaluate the total hematopoietic stem cell pool on a population level in addition to a clonal level in order to provide a more comprehensive study of HSC biology. Disclosures: No relevant conflicts of interest to declare.

e21086 Background: Microvesicles are subcellular entities that are derived from a variety of cells and contain DNA, RNA and protein. We have previously shown that microvesicles isolated from murine...

e21092 Background: We have previously shown that lung-derived microvesicles (MVs) can enter target marrow cells, resulting in increased levels of lung-specific mRNAs. Marrow which has been exposed ...

Abstract 4803 We have previously shown that murine bone marrow cells co-cultured opposite murine lung cells, but separated from them by a cell-impermeable membrane, express pulmonary epithelial cell-specific mRNAs, including Surfactants A-D, Aquaporin-5 and Clara Cell Specific Protein. This effect appears to be enhanced when the lungs used in co-culture are harvested from previously-irradiated mice. We have also shown that lung cells release membrane-bound particles called microvesicles which contain lung cell-specific proteins and mRNA. Microvesicles are capable of entering marrow cells in culture and inducing lung-specific mRNA and protein expression in marrow cells that have internalized them (Aliotta JM, et al, Stem Cells, 2007). Currently, it is not known how microvesicles gain entry into marrow cells and if this process involves the binding of specific adhesion proteins present on the marrow cells and/or the surface of microvesicles. Microvesicles derived from sources other than the lung have been described as expressing various adhesion proteins which facilitate their entry into target cells. In order to determine the presence of adhesion proteins on lung-derived microvesicles, we ultracentrifuged (100,000 g) cell-free conditioned media made from the lungs of C57BL/6 mice. Pelleted material was labeled with one of several directly-conjugated antibodies to an adhesion protein. Microvesicles which were positive for the adhesion protein of interest were identified by flow cytometry and quantified relative to its isotype control. Adhesion proteins that were found to be present on lung-derived microvesicles included CD29 (β1 integrin), CD41 (α2b integrin), CD49e (α5 integrin), CD49f (α6 integrin), CD51 (αv integrin), CD54 (ICAM-1), CD61 (β3 integrin), CD62L (L-selectin), CD81 (TAPA-1), CD107a (LAMP-1), CD154 (CD40 ligand), CD184 (CXCR4) and CD309 (VEGFR2). Those not present included CD9 (p24), CD11b (Mac-1), CD18 (β2 integrin), CD31 (PECAM-1), CD49d (α4 integrin), CD62P (P-selectin) and CD162 (PSGL-1). Lung-derived microvesicles isolated from mice that had been exposed to 500 centigrey total body irradiation five days prior to sacrifice were enriched with certain populations of adhesion protein positive microvesicles compared to those isolated from non-irradiated mice. These populations included ICAM-1 (78% increase), TAPA-1 (45% increase), CD40 ligand (108% increase) and VEGFR2 (136% increase) positive microvesicles. We are attempting to determine if lung-derived microvesicle entry into marrow cells is mediated by interactions with these adhesion proteins. These data indicate that adhesion proteins are present on lung-derived microvesicles. It is possible that differences in mRNA expression seen in marrow cells exposed to microvesicles derived from irradiated and non-irradiated lung in be related to qualitative and quantitative differences in those microvesicles. Disclosures: No relevant conflicts of interest to declare.

Abstract 4799 We have previously shown that microvesicles derived from irradiated murine lung cells enter murine bone marrow cells and induce expression of the pulmonary epithelial cell-specific mRNAs Surfactants A-D (Sp-A-D), Aquaporin-5 (Aq-5) and Clara Cell Specific Protein (CCSP). The early mRNA increases are due to direct delivery of mRNA and due to the transfer of a transcription factor to marrow cells (Aliotta JM, et al, Exp Hematol, 2010). The modulated marrow cells produce pulmonary epithelial cell-specific protein and have an enhanced ability to convert into pulmonary epithelial cells after transplantation into lethally-irradiated mice. In the present studies, we evaluated the stability of pulmonary epithelial cell-specific mRNA expression in cytokine-stimulated liquid culture and after in vivo transplantation into lethally-irradiated mice. Whole bone marrow cells isolated from C57BL/6 mice were cultured for seven days opposite C57BL/6 lung fragments, but separated from them by a 0.4 micron cell-impermeable membrane. Marrow cells were then either infused into lethally-irradiated C57BL/6 mice or established in culture with DMEM supplemented with IL-3, IL-6, IL-11 and steel factor. Engrafted mice were sacrificed six weeks after transplantation and real-time RT-PCR was carried out on marrow, liver, spleen and thymus tissue. Expression of Sp-A, B and D, CCSP and Aq-5 were variably seen in all tissues and increases over control ranged from 12-fold to 58-fold. Liquid culture was analyzed every two weeks out to 12 weeks and high levels of expression of different pulmonary epithelial cell-specific mRNAs and proteins (by western blot and Immunohistochemical staining) were observed. In order to determine the mechanism for the increased expression in culture, we established co-cultures of Fischer-344 rat lung opposite C57BL/6 mouse bone marrow cells and, using species-specific primers, determined whether the increased pulmonary epithelial cell-specific mRNA expression at each time point of secondary cytokine-supported culture was rat or mouse-specific. In every instance, the pulmonary epithelial cell-specific mRNA which was detected was mouse-specific, not rat-specific, and thus the long-term expression of lung-specific mRNA in mouse marrow was due to induced transcription by the mouse marrow cells. These data indicate that lung-derived microvesicles induce long-term stable epigenetic changes in marrow cells and suggests that the genetic changes induced by tissue microvesicles in neighboring cells may be biologically important. Disclosures: No relevant conflicts of interest to declare.