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We discovered that innate immunity plays an important role in the reprogramming of fibroblasts into cardiomyocytes. In this report, we define the role of a novel retinoic acid-inducible gene 1 Yin Yang 1 (Rig1:YY1) pathway. We found that fibroblast to cardiomyocyte reprogramming efficacy was enhanced by specific Rig1 activators. To understand the mechanism of action, we performed various transcriptomic, nucleosome occupancy, and epigenomic approaches. Analysis of the datasets indicated that Rig1 agonists had no effect on reprogramming-induced changes in nucleosome occupancy or loss of inhibitory epigenetic motifs. Instead, Rig1 agonists were found to modulate cardiac reprogramming by promoting the binding of YY1 specifically to cardiac genes. To conclude, these results show that the Rig1:YY1 pathway plays a critical role in fibroblast to cardiomyocyte reprogramming.

Stem cell injections are an attractive therapeutic tool. It has been demonstrated that injected stem cells promote tissue repair and regeneration via paracrine mechanisms. However, the effects of injected stem cells continue for far longer than they are present. We hypothesized that the effects of injected stem cells are prolonged because of a sequential paracrine relay mechanism. Conditioned media was collected from mesenchymal stem cells (MSCs) after 24 h. This media was then added to RAW264.7. Media was collected from the macrophages after 24 h and was then added to endothelial cells (ECs). This conditioned macrophage media, but not control media, promoted wound healing and induced EC differentiation. Similar results were observed with primary macrophages. To identify the active paracrine factors released by macrophages in response to stimulation by MSC conditioned media we used an antibody array, identifying increased expression of the angiogenesis-related proteins stromal cell-derived factor 1 (SDF1) and plasminogen activator inhibitor-1 (PAI-1). Knockdown of either protein inhibited the ability of conditioned media derived from MSC paracrine factor-stimulated macrophages to induce EC differentiation both in vitro and in vivo. Conditioned media derived from postnatal day 7 (P7) mouse macrophages induced EC differentiation. Moreover, SDF1 and PAI-1 levels were >120 higher in P7 macrophages compared with adult macrophages, suggesting that MSC paracrine factors promote adult macrophages to adopt a juvenile phenotype. These results indicate that MSC paracrine factors induce macrophages to secrete SDF1 and PAI-1, in-turn inducing endothelial cells to differentiate. Identification of a sequential paracrine mechanism opens new therapeutic avenues for stem cell therapy.

Juxtaglomerular (JG) cells, major sources of renin, differentiate from metanephric mesenchymal cells that give rise to JG cells or a subset of smooth muscle cells of the renal afferent arteriole. During periods of dehydration and salt deprivation, renal mesenchymal stromal cells (MSCs) differentiate from JG cells. JG cells undergo expansion and smooth muscle cells redifferentiate to express renin along the afferent arteriole. Gene expression profiling comparing resident renal MSCs with JG cells indicates that the transcription factor Sox6 is highly expressed in JG cells in the adult kidney. In vitro, loss of Sox6 expression reduces differentiation of renal MSCs to renin-producing cells. In vivo, Sox6 expression is upregulated after a low-Na+ diet and furosemide. Importantly, knockout of Sox6 in Ren1d+ cells halts the increase in renin-expressing cells normally seen during a low-Na+ diet and furosemide as well as the typical increase in renin. Furthermore, Sox6 ablation in renin-expressing cells halts the recruitment of smooth muscle cells along the afferent arteriole, which normally express renin under these conditions. These results support a previously undefined role for Sox6 in renin expression.

miRNA-based cellular fate reprogramming offers an opportunity to investigate the mechanisms of long-term gene silencing. To further understand how genes are silenced in a tissue-specific manner, we leveraged our miRNA-based method of reprogramming fibroblasts into cardiomyocytes. Through screening approaches, we identified three proteins that were downregulated during reprogramming of fibroblasts into cardiomyocytes: heterochromatin protein Cbx1, transcriptional activator protein PurB, and transcription factor Sp3. We show that knockdown of Cbx1, PurB, and Sp3 was sufficient to induce cardiomyocyte gene expression in fibroblasts. Similarly, gene editing to ablate Cbx1, PurB, and Sp3 expression induced fibroblasts to convert into cardiomyocytes in vivo. Furthermore, high-throughput DNA sequencing and coimmunoprecipitation experiments indicated that Cbx1, PurB, and Sp3 also bound together as a complex and were necessary to localize nucleosomes to cardiomyocyte genes on the chromosome. Finally, we found that the expression of these genes led to nucleosome modification via H3K27me3 (trimethylated histone-H3 lysine-27) deposition through an interaction with the polycomb repressive PRC2 complex. In summary, we conclude that Cbx1, PurB, and Sp3 control cell fate by actively repressing lineage-specific genes.

Cardiomyogenesis, the process by which the body generates cardiomyocytes, is poorly understood. We have recently shown that Sfrp2 promotes cardiomyogenesis in vitro. The objective of this study was to determine if Sfrp2 would similarly promote cardiomyogenesis in vivo. To test this hypothesis, we tracked multipotent cKit(+) cells in response to Sfrp2 treatment. In control adult mice, multipotent cKit(+) cells typically differentiated into endothelial cells but not cardiomyocytes. In contrast, Sfrp2 switched the fate of these cells. Following Sfrp2 injection, multipotent cKit(+) cells differentiated solely into cardiomyocytes. Sfrp2-derived cardiomyocytes integrated into the myocardium and exhibited identical physiological properties to preexisting native cardiomyocytes. The ability of Sfrp2 to promote cardiomyogenesis was further supported by tracking EdU-labeled cells. In addition, Sfrp2 did not promote the formation of new cardiomyocytes when the cKit(+) cell population was selectively ablated in vivo using a diphtheria toxin receptor-diphtheria toxin model. Notably, Sfrp2-induced cardiomyogenesis was associated with significant functional improvements in a cardiac injury model. In summary, our study further demonstrates the importance of Sfrp2 in cardiomyogenesis.

Hypertension is a major contributor to the global burden of disease. Unfortunately, hypertension is controlled in less than one-fifth of patients worldwide due to either failure to treat or lack of compliance to medication. An ideal therapy would be administered one time only and yield lifelong blood pressure control. We investigated our hypothesis that CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeat–associated 9)-mediated disruption of a key gene in the renin-angiotensin system, AGT (angiotensinogen), specifically in the liver, would result in sustained and possibly lifelong reduction in blood pressure. We demonstrated in vitro that the CRISPR/Cas9 system led to a significant reduction in AGT expression in hepatocytes. Delivery of the CRISPR/Cas9 system into the liver via the hepatocyte-targeting adeno-associated virus 8 reduced both AGT expression (40% decrease) and circulating AGT levels (30% decrease). In the SHR (spontaneously hypertensive rat) model of hypertension, CRISPR/Cas9-mediated loss of AGT expression reduced blood pressure in adult animals with established hypertension and prevented the spontaneous development of hypertension in young SHR. Moreover, reductions in blood pressure were prolonged and sustained up to 1 year of follow-up. In addition, the partial disruption of the hepatic AGT gene was sufficient to control hypertension but did not affect the homeostatic response to cardiovascular stress such as sodium depletion and furosemide. In summary, we have demonstrated that targeting the CRISPR/Cas9 system to hepatic AGT results in sustained reduction of blood pressure and is a potential therapy to achieve sustained and possibly lifelong control of human hypertension.

There are currently no effective treatments to regenerate the heart after cardiac injury. Following cardiac injury, heart muscle cells, also known as cardiomyocytes, die in large numbers. The adult mammalian heart does not have the ability to replace these dead cardiomyocytes. In their place, fibroblasts invade the injury zone and generate a scar. The scar impairs cardiac function. An important approach to cardiac regeneration is direct cardiac reprogramming, whereby cardiac fibroblasts within the scar are directly converted into functional cardiomyocytes. Several laboratories have achieved direct cardiac reprogramming via overexpression of the cardiac transcription factors. In contrast, we utilize a combination of four miRNAs (miR-1, miR-133, miR-208, miR-499) that we call miR Combo. One common issue regarding direct cardiac reprogramming strategies is low efficiency. Recently, we have demonstrated that the efficiency of direct cardiac reprogramming is enhanced in the chemically defined reprogramming media.

There are currently no effective treatments to regenerate the heart after cardiac injury. Following cardiac injury, heart muscle cells, also known as cardiomyocytes, die in large numbers. The adult mammalian heart does not have the ability to replace these dead cardiomyocytes. In their place, fibroblasts invade the injury zone and generate a scar. The scar impairs cardiac function. An important approach to cardiac regeneration is direct cardiac reprogramming, whereby cardiac fibroblasts within the scar are directly converted into functional cardiomyocytes. Several laboratories have achieved direct cardiac reprogramming via overexpression of the cardiac transcription factors. In contrast, we utilize a combination of four miRNAs (miR-1, miR-133, miR-208, miR-499) that we call miR Combo. One common issue regarding direct cardiac reprogramming strategies is low efficiency. Recently, we have demonstrated that the efficiency of direct cardiac reprogramming is enhanced in the chemically defined reprogramming media.

Hypertension is recognized as one of the largest contributors to the global burden of disease. Unfortunately, for the majority of patients, hypertension is poorly controlled due, in part, to poor medical compliance resulting from the need to take one or more drugs, often several times daily. An ideal therapy would be administered a single time but yield long-term blood pressure control. Under the appropriate condition, we hypothesize that this modality could potentially lead to a cure for hypertension. In this study, we investigated whether that sustained, and possibly life-long, reductions in blood pressure could be achieved via Crispr-Cas9 mediated disruption of a key gene in the RAAS, Angiotensinogen (AGT). In vitro, we demonstrated that expression of Crispr-Cas9 system in the BRL 3A rat liver cell line led to a significant reduction in AGT protein levels (75% reduction, N=3, P

We have shown that miR combo directly reprograms fibroblasts into cardiomyocytes. However, both in vitro and in vivo, the generated cardiomyocytes are immature. Recently, we discovered that cardiomyocyte maturation is enhanced by NFkB activation. While miR combo initiates reprogramming, the effect on NFkB activity is modest. Therefore, miR combo only has a modest effect on maturation. We have now made an important discovery that 5’triphosphorylation (5’ppp) of RNA molecules markedly enhance NFkB activation; leading to increased and accelerated maturation of reprogramed cardiomyocytes. The addition of 5’ppp-RNA increased the number of mature cardiomyocytes by 4-fold (N=5, P initiate reprogramming and accelerate maturation of cardiomyocytes. Indeed, 5’ppp modification of the miR combo miR-1 increased the expression of the mature cardiomyocyte markers Actn2 (4-fold, N=3, P

Induced pluripotent stem (iPS) cells provide a novel avenue to investigate how precursors differentiate into cardiomyocytes. In this study we examined our hypothesis that iPS differentiation is regulated by a balance between cardiogenic and inhibitory Wnt proteins. Recently, we have discovered that iPS cells differentiate into cardiomyocytes in response to Sfrp2 (control: 0% cardiomyocytes; Sfrp2 treated: 25% cardiomyocytes. N=3. P

In this review, we summarize the role of Wnt proteins in cardiomyogenesis. More specifically, we focus on how the development of cardiomyocytes from precursor cells involves a complex interplay between Wnt canonical β‐catenin signaling pathways and Wnt noncanonical signaling pathways involving PCP and JNK. We also describe recent literature which suggests that endogenous Wnt inhibitors such as the Sfrp and DKK proteins play important roles in regulating the cardiomyocyte differentiation., Srfp2 mediates cardiomyocyte differentiation by inhibiting Wnt3a. Wnt3a is a canonical Wnt that activates b‐catenin and inhibits cardiac specification. In contrast, Wnt11 is a noncanonical Wnt, inhibits b‐catenin and promotes differentiation into cardiomyocytes. The addition of Sfrp2 upsets this balance as it binds, and sequesters, Wnt3a but not Wnt11; thereby leaving Wnt11 free to bind to Fzd5 and activate the noncanonical pathway resulting in cardiac differentiation.

Following heart injury, cardiomyocytes, are lost and are not regenerated. In their place, fibroblasts invade the dead tissue where they generate a scar, which reduces cardiac function. We and others have demonstrated that combinations of specific miRNAs (miR combo) or transcription factors (GMT), delivered by individual lenti-/retro-viruses in vivo, can convert fibroblasts into cardiomyocytes and improve cardiac function. However, the effects are relatively modest due to the low efficiency of delivery of miR combo or GMT. We hypothesized that efficiency would be improved by optimizing delivery. In the first instance, we developed a multicistronic system to express all four miRNAs of miR combo from a single construct. The order of each miRNA in the multicistronic construct gave rise to different levels of miRNA expression. A combination that resulted in equivalent expression levels of each of the four miRNAs of miR combo showed the highest reprogramming efficiency. Further efficiency can be achieved by directly targeting fibroblasts. Screening of several AAV serotypes indicated that AAV1 displayed tropism towards cardiac fibroblasts. Combining multicistronic expression with AAV1 delivery robustly reprogrammed cardiac fibroblasts into cardiomyocytes in vivo.

Reprogramming scar fibroblasts into new heart muscle cells has the potential to restore function to the injured heart. However, the effectiveness of reprogramming is notably low. We have recently demonstrated that the effectiveness of reprogramming fibroblasts into heart muscle cells (cardiomyocytes) is increased by the addition of RNA-sensing receptor ligands. Clinical use of these ligands is problematic due to their ability to induce adverse inflammatory events. To overcome this issue, we sought to determine whether synthetic analogs of natural RNA-sensing receptor ligands, which avoid generating inflammatory insults and are nuclease resistant, would similarly enhance fibroblast reprogramming into cardiomyocytes. Indeed, one such stabilized RNA, ICR2, increased the expression of cardiomyocyte-specific mRNAs in reprogrammed fibroblasts. Moreover, ICR2 enhanced the ability of reprogramming factors to produce cardiomyocytes with mature sarcomeres. Knockdown assays indicated that the effects of ICR2 were mediated by the RNA-sensing receptors Rig-I and TLR3. In addition, ICR2 reduced the effective dose and number of reprogramming factors needed for efficient reprogramming. In summary, the synthetic RNA oligonucleotide ICR2 is a potential therapeutic agent to enhance cardiac reprogramming efficiency., Graphical Abstract, Fibroblast reprogramming to cardiomyocytes has the potential to restore function in the injured heart. Dzau and colleagues have discovered that the efficiency of fibroblast reprogramming to cardiomyocytes is enhanced by the synthetic RNA, ICR2. ICR2 was found to exert its effects via the receptors TLR3 and Rig-1 acting through NF-κB.

The development of biased agonist drugs is widely recognized to be important for the treatment of many diseases, including cardiovascular disease. While GPCR biased agonism has been heavily characterized there is a distinct lack of information with respect to RTK biased agonism both in the identification of biased agonists as well as their attendant mechanisms. One such RTK, the Insulin-like Growth Factor 1 Receptor (IGF1R) plays an important role in a range of biological and disease processes. The micropeptide LL37 has been described as a biased agonist of the IGF1R. We were interested to further understand the mechanism by which LL37 promotes biased signaling through the IGF1R. We found that LL37 biased agonism is dependent on β-arrestin 2. Moreover, BRET assays indicated that LL37 biased agonism is explained by the inability of LL37 to promote the recruitment of IRS1 to the IGF1R compared to IGF1. LL37 promotes an altered association of IGF1R with GRK6, which could also serve as an explanation for bias. We also demonstrated a functional consequence of this bias by showing that while LL37 can promote cell proliferation, it does not induce protein synthesis, unlike IGF1, which does both. We have recently identified HASF, a natural protein released by mesenchymal stem cells, as a novel ligand of the IGF1R. HASF is a paracrine factor with potent cardioprotective and cardio-regenerative properties which also acts via IGF1R biased signaling, preferentially activated ERK over Akt.

We have recently shown that hypoxia and Akt-induced stem cell factor (HASF) protects the heart from ischemia-induced damage and promotes cardiomyocyte proliferation. While we have identified certain signaling pathways responsible for these protective effects, the receptor mediating these effects was unknown. Here, we undertook studies to identify the HASF receptor. A yeast two-hybrid screen identified a partial fragment of insulin-like growth factor 1 receptor (IGF1R) as a binding partner of HASF. Subsequent co-immunoprecipitation experiments showed that HASF bound to full-length IGF1R. Binding assays revealed a high affinity of HASF for IGF1R. The treatment of neonatal ventricular cardiomyocytes with HASF resulted in the phosphorylation of IGF1R and other proteins known to be involved in IGF1R-mediated signaling pathways. HASF-mediated ERK activation was abrogated by IGF1R pharmacological inhibitors and siRNAs that targeted IGF1R. However, siRNA-mediated knockdown of either IGF2R or the insulin receptor had no effect on HASF-induced cell signaling. Additionally, pharmacologic inhibition of IGF1R impeded HASF's ability to induce cardiomyocyte proliferation. Finally, we documented that in vivo deletion of the IGF1R completely abolished the ability of HASF to promote cardiomyocyte proliferation in an overexpression mouse model providing further evidence in vivo that the IGF1R is the functional receptor for HASF.

Juxtaglomerular (JG) cells, major sources of renin, differentiate from metanephric mesenchymal cells which give rise to JG cells or a subset of smooth muscle cells of the renal afferent arteriole. During periods of dehydration and salt deprivation JG cells undergo expansion. Gene expression profiling comparing resident renal Mesenchymal Stromal Cells (MSCs) with JG cells indicate that the transcription factor Sox6 is highly expressed in JG cells in the adult kidney. In vitro, loss of Sox6 expression reduces differentiation of renal MSCs to renin producing cells. In vivo, Sox6 expression is up-regulated during JG cell expansion. Importantly, knockout of Sox6 in Ren1d+ cells halts the increase in renin expressing cells normally seen during JG cell expansion as well as the typical increase in renin. These results support a previously undefined role for Sox6 in renin expression during normal and pathophysiological conditions.

The process by which fibroblasts are directly reprogrammed into cardiomyocytes involves two stages; initiation and maturation. Initiation represents the initial expression of factors that induce fibroblasts to transdifferentiate into cardiomyocytes. Following initiation, the cell undergoes a period of maturation before becoming a mature cardiomyocyte. We wanted to understand the role of cardiac development transcription factors in the maturation process. We directly reprogram fibroblasts into cardiomyocytes by a combination of miRNAs (miR combo). The ability of miR combo to induce cardiomyocyte-specific genes in fibroblasts was lost following the knockdown of the cardiac transcription factors Gata4, Mef2C, Tbx5 and Hand2 (GMTH). To further clarify the role of GMTH in miR combo reprogramming we utilized a modified CRISPR-Cas9 approach to activate endogenous GMTH genes. Importantly, both miR combo and the modified CRISPR-Cas9 approach induced comparable levels of GMTH expression. While miR combo was able to reprogram fibroblasts into cardiomyocyte-like cells, the modified CRISPR-Cas9 approach could not. Indeed, we found that cardiomyocyte maturation only occurred with very high levels of GMT expression. Taken together, our data indicates that while endogenous cardiac transcription factors are insufficient to reprogram fibroblasts into mature cardiomyocytes, endogenous cardiac transcription factors are necessary for expression of maturation genes.

In the past decade, substantial evidence supports the paradigm that stem cells exert their reparative and regenerative effects, in large part, through the release of biologically active molecules acting in a paracrine fashion on resident cells. The data suggest the existence of a tissue microenvironment where stem cell factors influence cell survival, inflammation, angiogenesis, repair, and regeneration in a temporal and spatial manner.

The insulin-like growth factor 1 receptor (IGF1R) is a receptor tyrosine kinase with critical roles in various biological processes. Recent results from clinical trials targeting IGF1R indicate that IGF1R signaling pathways are more complex than previously thought. Moreover, it has become increasingly clear that the function of many proteins can be understood only in the context of a network of interactions. To that end, we sought to profile IGF1R–protein interactions with the proximity-labeling technique BioID. We applied BioID by generating a HEK293A cell line that stably expressed the BirA* biotin ligase fused to the IGF1R. Following stimulation by IGF1, biotinylated proteins were analyzed by MS. This screen identified both known and previously unknown interactors of IGF1R. One of the novel interactors was sorting nexin 6 (SNX6), a protein that forms part of the retromer complex, which is involved in intracellular protein sorting. Using co-immunoprecipitation, we confirmed that IGF1R and SNX6 physically interact. SNX6 knockdown resulted in a dramatic diminution of IGF1-mediated ERK1/2 phosphorylation, but did not affect IGF1R internalization. Bioluminescence resonance energy transfer experiments indicated that the SNX6 knockdown perturbed the association between IGF1R and the key adaptor proteins insulin receptor substrate 1 (IRS1) and SHC adaptor protein 1 (SHC1). Intriguingly, even in the absence of stimuli, SNX6 overexpression significantly increased Akt phosphorylation. Our study confirms the utility of proximity-labeling methods, such as BioID, to screen for interactors of cell-surface receptors and has uncovered a role of one of these interactors, SNX6, in the IGF1R signaling cascade.

Rationale : A major goal for the treatment of heart tissue damaged by cardiac injury is to develop strategies for restoring healthy heart muscle through the regeneration and repair of damaged myocardium. We recently demonstrated that administration of a specific combination of microRNAs (miR combo) into the infarcted myocardium leads to direct in vivo reprogramming of noncardiac myocytes to cardiac myocytes. However, the biological and functional consequences of such reprogramming are not yet known. Objective : The aim of this study was to determine whether noncardiac myocytes directly reprogrammed using miRNAs in vivo develop into mature functional cardiac myocytes in situ, and whether reprogramming leads to improvement of cardiac function. Methods and Results : We subjected fibroblast-specific protein 1-Cre mice/tandem dimer Tomato (tdTomato) mice to cardiac injury by permanent ligation of the left anterior descending coronary artery and injected lentiviruses encoding miR combo or a control nontargeting miRNA. miR combo significantly increased the number of reprogramming events in vivo. Five to 6 weeks after injury, morphological and physiological properties of tdTomato − and tdTomato + cardiac myocyte–like cells were analyzed ex vivo. tdTomato + cells expressed cardiac myocyte markers, sarcomeric organization, excitation–contraction coupling, and action potentials characteristic of mature ventricular cardiac myocytes (tdTomato − cells). Reprogramming was associated with improvement of cardiac function, as analyzed by serial echocardiography. There was a time delayed and progressive improvement in fractional shortening and other measures of ventricular function, indicating that miR combo promotes functional recovery of damaged myocardium. Conclusions : The findings from this study further validate the potential use of miRNA-mediated reprogramming as a therapeutic approach to promote cardiac regeneration after myocardial injury.

The process by which committed precursors mature into cardiomyocytes is poorly understood. We found that TLR3 inhibition blocked cardiomyocyte maturation; precursor cells committed to the cardiomyocyte lineage failed to express maturation genes and sarcomeres did not develop. Using various approaches, we found that the effects of TLR3 upon cardiomyocyte maturation were dependent upon the RelA subunit of nuclear factor kappa B (NFκB). Importantly, under conditions that promote the development of mature cardiomyocytes NFκB became significantly enriched at the promoters of cardiomyocyte maturation genes. Furthermore, activation of the TLR3-NFκB pathway enhanced cardiomyocyte maturation. This study, therefore, demonstrates that the TLR3-NFκB pathway is necessary for the maturation of committed precursors into mature cardiomyocytes.

Introduction: Hypertension, a common condition that affects 33% of the US population, is a major risk factor for heart disease and stroke. Treatments for hypertension are limited and there is a critical need to develop new therapies. The Renin Angiotensin Aldosterone System (RAAS) plays a key role in regulating blood pressure, and renin controls its rate-limiting step. In adults, renin is produced and stored by renal Juxtaglomerular (JG) cells. During sodium restriction and other pathophysiological stresses that require an increase in renin expression and release, the adult kidney increases the number of cells expressing renin, in a process known as JG cell expansion. JG cells formation mechanisms remain unclear. Our aim is to determine new regulators of renin and blood pressure control. Methods: In vivo: JG cell expansion was induced by 10 days of low sodium diet (0.01% Na) and furosemide (0.1 mg/g body weight). In vitro: primary renal Mesenchymal Stromal Cells (MSC) were isolated from wild type mice and used until passage 5. MSC were differentiated into renin expressing cells by 7 days I&F (IBMX-100 uM and Forskolin-10 uM) treatment. Sox6 was down regulated in MSCs with lentivirus carrying vectors for Sox6 shRNA or controls scramble shRNA. Results: In vitro, I&F induced renin expression in MSCs (Renin relative expression to gapdh 0.0153±0.005, n=3, P= 0.05, no renin expression in MSCs). Gene arrays comparing renal MSCs and JG cells identified Sox6 as a potential gene that controlled MSC differentiation. In vitro silencing of Sox6 by shRNA inhibited the differentiation of renal MSCs into renin producing cells (3.5 fold decrease compared to control shRNA, n= 4, P= 0.01). In a new transgenic mouse model, in which Sox6 is deleted specifically in renin expressing cells (Ren1d Cre /Sox6 fl/fl ), plasma renin concentration was not affected at baseline (0.3 vs W.T. 0.5 ug Ang I/ml/h, n=3, P>0.05). However, under conditions that promote JG cell expansion, Sox6 ablation halted the increase in the number of JG cells (8.75 fold decrease, n= 6 to 9, P= 0.001). Conclusion: Our data indicates that Sox6 plays a novel role in renal physiology; modulating renin expression during pathological conditions. These findings suggest that Sox6 may become a new target for blood pressure control.

Rationale: Direct reprogramming of cardiac fibroblasts to cardiomyocytes has recently emerged as a novel and promising approach to regenerate the injured myocardium. We have previously demonstrated the feasibility of this approach in vitro and in vivo using a combination of 4 microRNAs (miR-1, miR-133, miR-208, and miR-499) that we named miR combo. However, the mechanism of miR combo mediated direct cardiac reprogramming is currently unknown. Objective: Here, we investigated the possibility that miR combo initiated direct cardiac reprogramming through an epigenetic mechanism. Methods and Results: Using a quantitative polymerase chain reaction array, we found that histone methyltransferases and demethylases that regulate the trimethylation of H3K27 (H3K27me3), an epigenetic modification that marks transcriptional repression, were changed in miR combo–treated fibroblasts. Accordingly, global H3K27me3 levels were downregulated by miR combo treatment. In particular, the promoter region of cardiac transcription factors showed decreased H3K27me3 as revealed by chromatin immunoprecipitation coupled with quantitative polymerase chain reaction. Inhibition of H3K27 methyltransferases or of the PRC2 (Polycomb Repressive Complex 2) by pharmaceutical inhibition or siRNA reduced the levels of H3K27me3 and induced cardiogenic markers at the RNA and protein level, similarly to miR combo treatment. In contrast, knockdown of the H3K27 demethylases Kdm6A and Kdm6B restored the levels of H3K27me3 and blocked the induction of cardiac gene expression in miR combo–treated fibroblasts. Conclusions: In summary, we demonstrated that removal of the repressive mark H3K27me3 is essential for the induction of cardiac reprogramming by miR combo. Our data not only highlight the importance of regulating the epigenetic landscape during cell fate conversion but also provide a framework to improve this technique.

Rationale : Cardiac progenitor cells (CPCs) are thought to differentiate into the major cell types of the heart: cardiomyocytes, smooth muscle cells, and endothelial cells. We have recently identified ABI family, member 3 (NESH) binding protein (Abi3bp) as a protein important for mesenchymal stem cell biology. Because CPCs share several characteristics with mesenchymal stem cells, we hypothesized that Abi3bp would similarly affect CPC differentiation and proliferation. Objective : To determine whether Abi3bp regulates CPC proliferation and differentiation. Methods and Results : In vivo, genetic ablation of the Abi3bp gene inhibited CPC differentiation, whereas CPC number and proliferative capacity were increased. This correlated with adverse recovery after myocardial infarction. In vitro, CPCs, either isolated from Abi3bp knockout mice or expressing an Abi3bp shRNA construct, displayed a higher proliferative capacity and, under differentiating conditions, reduced expression of both early and late cardiomyocyte markers. Abi3bp controlled CPC differentiation via integrin-β1, protein kinase C-ζ, and v-akt murine thymoma viral oncogene homolog. Conclusions : We have identified Abi3bp as a protein important for CPC differentiation and proliferation.

The capacity of the adult mammalian heart to repair itself after injury is limited. In contrast, lower vertebrates such as Zebrafish can completely regenerate the organ after damage. A recent article from Aguirre et al1 in Cell Stem Cell shows that this difference is because of a microRNA program that is active in Zebrafish but silent in mammals. Crucially, reactivation of this dormant microRNA program in the murine heart induces regeneration of the myocardium. The adult mammalian heart possesses a limited capacity to regenerate lost or damaged cardiomyocytes after cardiac insult.2 This is, in part, because of the low proliferative capacity of adult cardiomyocytes. Myocardial injury increases cardiomyocyte proliferation3; however, it is clearly insufficient to completely regenerate the myocardium, and many strategies to enhance the weak regenerative response of the mammalian heart to injury are currently under investigation. The neonatal mammalian heart potentially possesses a higher regenerative capacity compared with the adult organ. In one study, cardiac regeneration was observed in 1-day-old neonatal mice after partial surgical resection.4 Using genetic fate mapping techniques, the researchers showed that the regenerated myocardium originated from preexisting cardiomyocytes proliferating in response to injury.4 This regenerative capacity was lost by day 7.4 Other studies have also pointed to an enhanced natural regenerative capacity in neonatal mice.5,6 In contrast to mammals, lower vertebrates such as Zebrafish retain the ability to regenerate their hearts throughout life. In the case of the Zebrafish, this natural ability is particularly robust as complete cardiac regeneration has been observed even when ≈20% of the ventricular myocardium was removed.7 The proliferation of partially dedifferentiated cardiomyocytes underlies this process.8 Specifically, cardiomyocytes that are adjacent to the site of injury break down their sarcomeres, express the embryonic cardiogenesis gene Gata4, and enter …

We have recently shown that a combination of microRNAs, miR combo, can directly reprogram cardiac fibroblasts into functional cardiomyocytes in vitro and in vivo. Reprogramming of cardiac fibroblasts by miR combo in vivo is associated with improved cardiac function following myocardial infarction. However, the efficiency of direct reprogramming in vitro is relatively modest and new strategies beyond the traditional two-dimensional (2D) culture should be identified to improve reprogramming process. Here, we report that a tissue-engineered three-dimensional (3D) hydrogel environment enhanced miR combo reprogramming of neonatal cardiac and tail-tip fibroblasts. This was associated with significantly increased MMPs expression in 3D vs. 2D cultured cells, while pharmacological inhibition of MMPs blocked the effect of the 3D culture on enhanced miR combo mediated reprogramming. We conclude that 3D tissue-engineered environment can enhance the direct reprogramming of fibroblasts to cardiomyocytes via a MMP-dependent mechanism.

Hypertension afflicts 33% of the U.S. adult population. Despite current treatments, approximately 50% of people are unresponsive to treatment. There is a critical need to develop new therapies to treat this disease and its complications. The Renin Angiotensin Aldosterone System plays a key role in regulating blood pressure in humans. Renin controls the rate-limiting step in the conversion of angiotensinogen to angiotensin I. In adults, renin is produced and stored by Juxtaglomerular (JG) cells in the kidney. However, the transcriptional mechanisms that govern formation of renin expressing cells under normal or pathophysiological conditions remain poorly understood. During blood pressure changes the number of adult renal cells expressing renin increase through a process known as JG cell expansion. We found that this process involves differentiation of mesenchymal stromal-like cells (MSC) to renin expressing cells among others. We aim to determine new regulators of renin expression and blood pressure control. Renin expression in vitro was induced by treatment of MSCs with 3-isobutyl-1-methylxanthine (IBMX) and Forskolin. MSCs were transduced with lentivirus carrying vectors Sox6 shRNA or control shRNA. A new transgenic mouse, in which Sox6 is deleted specifically in renin expressing cells (Ren1dCre/Sox6 fl/fl ), was used to study the impact of Sox6 in renin expression in vivo . Gene array comparing renal MSC and JG cells identified potential genes that control MSC differentiation, including Sox6. In vitro silencing of Sox6 by shRNA decreased differentiation of renal MSCs into renin producing cells (3.5 fold, n=4, P= 0.01). Preliminary IHC data showed that the transcription factor Sox6 is expressed by renin producing cells in the adult kidney during JG cell expansion. Plasma renin concentration (PRC) increased during JG cell expansion (induced with low sodium diet and furosemide) in wild type mice (27-fold), whereas in mice lacking Sox6 in JG cells PRC was as low as non-treated mice. We conclude that Sox6 has a novel role in modulating renin expression and thereby can contribute to renal physiology, opening new possibilities of addressing questions regarding physiological regulation of renin and hypertension.

We have recently shown that a combination of microRNAs, miR combo, can directly reprogram cardiac fibroblasts into functional cardiomyocytes in vitro and in vivo. However, direct reprogramming strategies are inefficient and slow. Moving towards the eventual goal of clinical application it is necessary to develop new methodologies to overcome these limitations. Here, we report the identification of a specific media composition, reprogramming media (RM), which augmented the effect of miR combo by 5–15-fold depending upon the cardiac marker tested. RM alone was sufficient to strongly induce cardiac gene and protein expression in neonatal tail-tip as well as cardiac fibroblasts. Expression of pluripotency markers Nanog, Oct4, Sox2 and Klf4 was significantly enhanced by RM, with miR combo augmenting the effect further. Knockdown of Nanog by siRNA inhibited the effect of RM on cardiac gene expression. Removal of insulin-transferrin-selenium completely inhibited the effect of reprogramming media upon cardiac gene expression and the addition of selenium to standard culture media recapitulated the effects of RM. Moreover, selenium enhanced the reprogramming efficiency of miR combo.

Many studies have demonstrated that the exogenous delivery of stem cells into injured myocardium results in functional improvements. It was originally thought that the regenerative properties of these stem cells arose from engraftment into the myocardium and subsequent differentiation into cardiac cells. However, this process was found to occur very rarely; far too low to account for the functional benefits observed. In the past decade, a new paradigm has emerged, namely that stem cells exert their reparative and regenerative effects predominantly through the release of biologically active molecules acting in a paracrine fashion on resident cells.

Toll-like receptors (TLRs), a large group of proteins which recognize various pathogen-associated molecular patterns, are critical for the normal function of the innate immune system. Following their discovery many single nucleotide polymorphisms within TLRs and components of their signaling machinery have been discovered and subsequently implicated in a wide range of human diseases including atherosclerosis, sepsis, asthma, and immunodeficiency. This review discusses the effect of genetic variation on TLR function and how they may precipitate disease.

Objective— Diabetes is a major risk factor for coronary heart disease. Accumulation of advanced glycation end-products (AGEs) attributable to hyperglycemia in diabetics promotes the development of atherosclerosis. However, the underlying mechanisms remain unclear. Methods and Results— The advanced glycation end-product of low-density-lipoprotein (AGE-LDL) induced proinflammatory cytokine production in human coronary artery endothelial cells and human- and mouse-macrophages. AGE-LDL stimulated cytokine synthesis was markedly reduced in mouse macrophages with a TLR4 loss-of-function mutation. Coimmunoprecipitation experiments indicated AGE-LDL interacts with TLR4, RAGE, and CD36. Incubation of cultured macrophages with TLR4, RAGE, or CD36 antibodies inhibited AGE-LDL stimulation of tumor necrosis factor (TNF)α production. A competitive binding inhibitor of TLR4 blocked AGE-LDL binding to the receptor. After transfection of a HEK293 cell system with wild-type TLR4, AGE-LDL activated a signaling pathway including p38α, JNK, and ERK1 kinases and AP1, Elk1, and NF–κB transcription factors; the net result being increased cytokine production. These effects were absent when cells were transfected with empty plasmid. Two common polymorphisms in TLR4, D299G and T399I, reduced the response of TLR4 to lipopolysaccharide (LPS) but had no effect on AGE-LDL signaling. Conclusions— These results indicate that AGE-LDL activates a TLR4-mediated signaling pathway, thus inducing proinflammatory cytokine production. This mechanism may partly explain the increased risk of atherosclerosis observed in diabetics.

SummaryFibrinogen has been implicated in atherosclerosis; in part by activating the lipopolysaccharide (LPS) receptor Toll-like receptor 4 (TLR4). The fibrinogen-TLR4 signalling pathway remains un-characterised. In human macrophages fibrinogen stimulated interleukin (IL)6 expression and ERK (extracellular signal-related kinase) phosphorylation. In HEK293-CD14-MD2 cells expressing TLR4, fibrinogen induced robust phosphorylation of ERK1, p38α and JNK and activated transcription factors NFκB, Elk-1 and AP-1 (activator protein-1).The net effect of this signaling pathway was a pro-inflammatory response characterised by IL6 and TNFα synthesis and increased IL8,matrix metalloproteinase (MMP)1, MMP9, and MCP-1 promoter activity. Two common TLR4 mutations, D299G and T399I, render the receptor LPS hyporesponsive. The effect of fibrinogen on polymorphic variant TLR4s was markedly different; enhancing activation of kinases, transcription factors, cytokine synthesis and promoter activity. This study indicates that fibrinogen activates TLR4, explaining how fibrinogen promotes inflammatory protein expression.

ATP-binding-cassette-transporter-A1 (ABCA1) plays a pivotal role in intracellular cholesterol removal, exerting a protective effect against atherosclerosis. ABCA1 gene severe mutations underlie Tangier disease, a rare Mendelian disorder that can lead to premature coronary artery disease (CAD), with age of CAD onset being two decades earlier in mutant homozygotes and one decade earlier in heterozygotes than in mutation non-carriers. It is unknown whether common polymorphisms in ABCA1 could influence age of symptom onset of CAD in the general population. We examined common promoter and non-synonymous coding polymorphisms in relation to age of symptom onset in a group of CAD patients (n = 1164), and also carried out in vitro assays to test effects of the promoter variations on ABCA1 promoter transcriptional activity and effects of the coding variations on ABCA1 function in mediating cellular cholesterol efflux. Age of symptom onset was found to be associated with the promoter - 407G > C polymorphism, being 2.82 years higher in C allele homozygotes than in G allele homozygotes and intermediate in heterozygotes (61.54, 59.79 and 58.72 years, respectively; P = 0.002). In agreement, patients carrying ABCA1 haplotypes containing the -407C allele had higher age of symptom onset. Patients of the G/G or G/C genotype of the -407G > C polymorphism had significant coronary artery stenosis (>75%) at a younger age than those of the C/C genotype (P = 0.003). Reporter gene assays showed that ABCA1 haplotypes bearing the -407C allele had higher promoter activity than haplotypes with the -407G allele. Functional analyses of the coding polymorphisms showed an effect of the V825I substitution on ABCA1 function, with the 825I variant having higher activity in mediating cholesterol efflux than the wild-type (825V). A trend towards higher symptom onset age in 825I allele carriers was observed. The data indicate an influence of common ABCA1 functional polymorphisms on age of symptom onset in CAD patients.

The human heart has a limited capacity to regenerate lost or damaged cardiomyocytes after cardiac insult. Instead, myocardial injury is characterized by extensive cardiac remodeling by fibroblasts, resulting in the eventual deterioration of cardiac structure and function. Cardiac function would be improved if these fibroblasts could be converted into cardiomyocytes. MicroRNAs (miRNAs), small noncoding RNAs that promote mRNA degradation and inhibit mRNA translation, have been shown to be important in cardiac development. Using this information, various researchers have used miRNAs to promote the formation of cardiomyocytes through several approaches. Several miRNAs acting in combination promote the direct conversion of cardiac fibroblasts into cardiomyocytes. Moreover, several miRNAs have been identified that aid the formation of inducible pluripotent stem cells and miRNAs also induce these cells to adopt a cardiac fate. MiRNAs have also been implicated in resident cardiac progenitor cell differentiation. In this review, we discuss the current literature as it pertains to these processes, as well as discussing the therapeutic implications of these findings.

Protein kinase B appears to play a key role in insulin signaling and in the control of apoptosis, although the precise targets of PKB are incompletely understood. PKB exists as three isoforms (alpha, beta, and gamma) that may have unique as well as common functions within the cell. To facilitate understanding the precise roles of PKB and its isoforms, novel tools of widespread applicability are described. These tools are antisense oligonucleotide probes that enable the specific and potent knock down of endogenous PKB alpha, beta, or gamma isoforms, individually or in various combinations, including concurrent removal of all three isoforms. The probes were applied to dissect the role of PKB in phosphorylating glycogen synthase kinase-3 (GSK-3), a critical mediator in multiple responses, and other potentially key targets. Triple antisense knock down of PKB alpha, beta, and gamma so that total PKB was

Insulin-stimulated glucose transport requires a signalling cascade through kinases protein kinase (PK) Czeta/lambda and PKB that leads to movement of GLUT4 vesicles to the plasma membrane. The aim of this study was to identify missing links between the upstream insulin-regulated kinases and the GLUT4 vesicle trafficking system.A yeast two-hybrid screen was conducted, using as bait full-length mouse munc18c, a protein known to be part of the GLUT4 vesicle trafficking machinery.The yeast two-hybrid screen identified PKCzeta as a novel interactor with munc18c. Glutathione S transferase (GST) pull-downs with GST-tagged munc18c constructs confirmed the interaction, mapped a key region of munc18c that binds PKCzeta to residues 295-338 and showed that the N-terminal region of PKCzeta was required for the interaction. Endogenous munc18c was shown to associate with endogenous PKCzeta in vivo in various cell types. Importantly, insulin stimulation increased the association by approximately three-fold. Moreover, disruption of PKCzeta binding to munc18c by deletion of residues 295-338 of munc18c or deletion of the N-terminal region of PKCzeta markedly inhibited the ability of insulin to stimulate glucose uptake or GLUT4 translocation.We have identified a physiological interaction between munc18c and PKCzeta that is insulin-regulated. This establishes a link between a kinase (PKCzeta) involved in the insulin signalling cascade and a known component of the GLUT4 vesicle trafficking pathway (munc18c). The results indicate that PKCzeta regulates munc18c and suggest a model whereby insulin triggers the docking of PKCzeta to munc18c, resulting in enhanced GLUT4 translocation to the plasma membrane.

PKCzeta (protein kinase Czeta) is a serine/threonine protein kinase controlled by insulin, various growth factors and phosphoinositide 3-kinase. It has been implicated in controlling glucose transport in response to insulin by the translocation of GLUT4-(glucose transporter 4) containing vesicles to the plasma membrane in stimulated cells. How PKCzeta modulates GLUT4 vesicle trafficking remains unknown. A yeast two-hybrid screen using full-length human PKCzeta identified 80K-H protein as an interactor with PKCzeta. GST (glutathione S-transferase) pull-down assays with GST-tagged 80K-H constructs confirmed the interaction and showed that the N-terminal portion of 80K-H was not required for the interaction. Immunoprecipitates of endogenous PKCzeta from Cho cells, 3T3-L1 adipocytes or L6 myotubes contained endogenous 80K-H, demonstrating a physiological interaction. Insulin stimulation enhanced the association 3-5-fold. Immunoprecipitates of endogenous 80K-H contained endogenous munc18c and immunoprecipitates of endogenous munc18c contained endogenous PKCzeta, with insulin markedly increasing the amount of co-immunoprecipitated protein in each case. These results show that insulin triggers interactions in vivo between PKCzeta, 80K-H and munc18c. Overexpression of 80K-H constructs mimicked the action of insulin in stimulating both glucose uptake and translocation of Myc-tagged GLUT4 in Cho cells, with the level of effect proportional to the ability of the constructs to associate with munc18c. These results identify 80K-H as a new player involved in GLUT4 vesicle transport and identify a link between a kinase involved in the insulin signalling cascade, PKCzeta, and a known component of the GLUT4 vesicle trafficking pathway, munc18c. The results suggest a model whereby insulin triggers the formation of a PKCzeta-80K-H-munc18c complex that enhances GLUT4 translocation to the plasma membrane.