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Objective:Neovascularization can maintain and even improve tissue perfusion in the setting of limb ischemia during peripheral artery disease. The molecular and cellular mechanisms mediating this process are incompletely understood. We investigate the potential role(s) for Id3 (inhibitor of differentiation 3) in regulating blood flow in a murine model of hindlimb ischemia (HLI).Approach and Results:HLI was modeled through femoral artery ligation and resection and blood flow recovery was quantified by laser Doppler perfusion imaging. Mice with global Id3 deletion had significantly impaired perfusion recovery at 14 and 21 days of HLI. Endothelial- or myeloid cell-specific deletion of Id3 revealed no effect on perfusion recovery while B-cell–specific knockout of Id3 (Id3BKO) revealed a significant attenuation of perfusion recovery. Flow cytometry revealed no differences in ischemia-induced T cells or myeloid cell numbers at 7 days of HLI, yet there was a significant increase in B-1b cells in Id3BKO. Consistent with these findings, ELISA (enzyme-linked immunoassay) demonstrated increases in skeletal muscle and plasma IgM. In vitro experiments demonstrated reduced proliferation and increased cell death when endothelial cells were treated with conditioned media from IgM-producing B-1b cells and tibialis anterior muscles in Id3BKOmice showed reduced density of total CD31+and αSMA+CD31+vessels.Conclusions:This study is the first to demonstrate a role for B-cell–specific Id3 in maintaining blood flow recovery during HLI. Results suggest a role for Id3 in promoting blood flow during HLI and limiting IgM-expressing B-1b cell expansion. These findings present new mechanisms to investigate in peripheral artery disease pathogenesis.

Rheumatic heart disease (RHD) is a major cause of valvular heart disease in developing nations. Endothelial cells (ECs) are considered crucial contributors to RHD, but greater insight into contributing mechanisms is needed. Cdh5-driven EC lineage tracing in the K/B.g7 mouse model of autoimmune valvular carditis revealed new capillary lymphatic vessels that develop from valve surface endothelial cells during the progression of disease. Human rheumatic valves contained similar lymphatics. Unsupervised clustering of mitral valve single-cell RNA sequencing data revealed lymphatic valve ECs (VECs) that express a transcriptional profile distinct from other VEC populations and upregulate genes controlling extracellular matrix composition and fibrosis during disease progression. Finally, inhibiting VEGFR3 prevented expansion of this mitral valve lymphatic network and decreased valve thickening and collagen density. These studies reveal a novel form of postnatal pathogenic lymphangiogenesis that promotes autoimmune valvular carditis.

Macrophages are important regulators of obesity-associated inflammation and PPARα and -γ agonism in macrophages has anti-inflammatory effects. In this study, we tested the efficacy with which liposomal delivery could target the PPARα/γ dual agonist tesaglitazar to macrophages while reducing drug action in common sites of drug toxicity: the liver and kidney, and whether tesaglitazar had anti-inflammatory effects in an in vivo model of obesity-associated dysmetabolism. Methods: Male leptin-deficient (ob/ob) mice were administered tesaglitazar or vehicle for one week in a standard oral formulation or encapsulated in liposomes. Following the end of treatment, circulating metabolic parameters were measured and pro-inflammatory adipose tissue macrophage populations were quantified by flow cytometry. Cellular uptake of liposomes in tissues was assessed using immunofluorescence and a broad panel of cell subset markers by flow cytometry. Finally, PPARα/γ gene target expression levels in the liver, kidney, and sorted macrophages were quantified to determine levels of drug targeting to and drug action in these tissues and cells. Results: Administration of a standard oral formulation of tesaglitazar effectively treated symptoms of obesity-associated dysmetabolism and reduced the number of pro-inflammatory adipose tissue macrophages. Macrophages are the major cell type that took up liposomes with many other immune and stromal cell types taking up liposomes to a lesser extent. Liposome delivery of tesaglitazar did not have effects on inflammatory macrophages nor did it improve metabolic parameters to the extent of a standard oral formulation. Liposomal delivery did, however, attenuate effects on liver weight and liver and kidney expression of PPARα and -γ gene targets compared to oral delivery. Conclusions: These findings reveal for the first time that tesaglitazar has anti-inflammatory effects on adipose tissue macrophage populations in vivo. These data also suggest that while nanoparticle delivery reduced off-target effects, yet the lack of tesaglitazar actions in non-targeted cells such (as hepatocytes and adipocytes) and the uptake of drug-loaded liposomes in many other cell types, albeit to a lesser extent, may have impacted overall therapeutic efficacy. This fulsome analysis of cellular uptake of tesaglitazar-loaded liposomes provides important lessons for future studies of liposome drug delivery.

Objective: The aim of this study was to unravel mechanisms whereby deficiency of the transcription factor Id3 (inhibitor of differentiation 3) leads to metabolic dysfunction in visceral obesity. We investigated the impact of loss of Id3 on hyaluronic acid (HA) production by the 3 HAS isoenzymes (HA synthases; -1, -2, and -3) and on obesity-induced adipose tissue (AT) accumulation of proinflammatory B cells. Approach and Results: Male Id3 −/− mice and respective wild-type littermate controls were fed a 60% high-fat diet for 4 weeks. An increase in inflammatory B2 cells was detected in Id3 −/− epididymal AT. HA accumulated in epididymal AT of high-fat diet–fed Id3 −/− mice and circulating levels of HA were elevated. Has2 mRNA expression was increased in epididymal AT of Id3 −/− mice. Luciferase promoter assays showed that Id3 suppressed Has2 promoter activity, while loss of Id3 stimulated Has2 promoter activity. Functionally, HA strongly promoted B2 cell adhesion in the AT and on cultured vascular smooth muscle cells of Id3 −/− mice, an effect sensitive to hyaluronidase. Conclusions: Our data demonstrate that loss of Id3 increases Has2 expression in the epididymal AT, thereby promoting HA accumulation. In turn, elevated HA content promotes HA-dependent binding of B2 cells and an increase in the B2 cells in the AT, which contributes to AT inflammation.

There is a growing interest in using liposomes to deliver compounds in vivo particularly for targeted treatment approaches. Depending on the liposome formulation, liposomes may be preferentially taken up by different cell types in the body. This may influence the efficacy of the therapeutic particle as progression of different diseases is tissue- and cell-type-specific. In this protocol, we present one method for synthesizing and fluorescently labeling liposomes using DSPC, cholesterol, and PEG-2000 DSPE and the lipid dye DiD as a fluorescent label. This protocol also presents an approach for delivering liposomes in vivo and assessing cell-specific uptake of liposomes using flow cytometry. This approach can be used to determine the types of cells that take up liposomes and quantify the distribution and proportion of liposome-uptake across cell types and tissues. While not mentioned in this protocol, additional assays such as immunofluorescence and single-cell fluorescence imaging on a cytometer will strengthen any findings or conclusions made as they permit assessment of intracellular staining. Protocols may also need to be adapted depending on the tissue(s) of interest.

Objective Peroxisome proliferator-activated receptors (PPARs) are key transcription factors that regulate adipose development and function, and the conversion of white into brown-like adipocytes. Here we investigated whether PPARα and PPARγ activation synergize to induce the browning of white fat. Methods A selection of PPAR activators was tested for their ability to induce the browning of both mouse and human white adipocytes in vitro, and in vivo in lean and obese mice. Results All dual PPARα/γ activators tested robustly increased uncoupling protein 1 (Ucp1) expression in both mouse and human adipocytes in vitro, with tesaglitazar leading to the largest Ucp1 induction. Importantly, dual PPARα/γ activator tesaglitazar strongly induced browning of white fat in vivo in both lean and obese male mice at thermoneutrality, greatly exceeding the increase in Ucp1 observed with the selective PPARγ activator rosiglitazone. While selective PPARγ activation was sufficient for the conversion of white into brown-like adipocytes in vitro, dual PPARα/γ activation was superior to selective PPARγ activation at inducing white fat browning in vivo. Mechanistically, the superiority of dual PPARα/γ activators is mediated at least in part via a PPARα-driven increase in fibroblast growth factor 21 (FGF21). Combined treatment with rosiglitazone and FGF21 resulted in a synergistic increase in Ucp1 mRNA levels both in vitro and in vivo. Tesaglitazar-induced browning was associated with increased energy expenditure, enhanced insulin sensitivity, reduced liver steatosis, and an overall improved metabolic profile compared to rosiglitazone and vehicle control groups. Conclusions PPARγ and PPARα synergize to induce robust browning of white fat in vivo, via PPARγ activation in adipose, and PPARα-mediated increase in FGF21., Graphical abstract Dual PPARα/γ activation is superior to selective PPARγ activation at inducing browning of white fat in vivo: via PPARγ action in the adipose and a PPARα-mediated action in the liver resulting in increased circulating fibroblast growth factor 21 (FGF21).Image 1, Highlights • Dual PPARα/γ activators robustly induce browning of white fat in vitro and in vivo. • PPARγ action alone is sufficient to convert white into brown-like adipocytes in vitro. • Dual PPARα/γ activators are superior to PPARγ activators for browning of white fat in vivo. • PPARγ action in adipose and PPARα-mediated increase in FGF21 synergize to induce browning of white fat in vivo.

ObjectiveExamine if adding aerobic exercise to standard medical care (EX+SC) prior to bariatric surgery improves metabolic health in relation to surgical outcomes.MethodsFourteen bariatric patients (age: 42.3±2.5y, BMI: 45.1±2.5 kg/m2) met inclusion criteria and were match-paired to pre-operative SC (n = 7) or EX+SC (n = 7; walking 30min/d, 5d/wk, 65-85% HRpeak) for 30d. A 120min mixed meal tolerance test was performed pre- and post-intervention (~2d prior to surgery) to assess insulin sensitivity (Matsuda Index) and metabolic flexibility (indirect calorimetry). Aerobic fitness (VO2peak), body composition (BodPod), and adipokines (adiponectin, leptin) were also measured. Omental adipose tissue was collected during surgery to quantify gene expression of adiponectin and leptin, and operating time and length of hospital stay were recorded. ANOVA and Cohen's d effect size (ES) was used to test group differences.ResultsSC tended to increase percent body fat (P = 0.06) after the intervention compared to EX+SC. Although SC and EX+SC tended to raise insulin sensitivity (P = 0.11), EX+SC enhanced metabolic flexibility (P = 0.01, ES = 1.55), reduced total adiponectin (P = 0.01, ES = 1.54) with no change in HMW adiponectin and decreased the length of hospital stay (P = 0.05) compared to SC. Albeit not statistically significant, EX+SC increased VO2peak 2.9% compared to a 5.9% decrease with SC (P = 0.24, ES = 0.91). This increased fitness correlated to shorter operating time (r = -0.57, P = 0.03) and length of stay (r = -0.58, P = 0.03). Less omental total adiponectin (r = 0.52, P = 0.09) and leptin (r = 0.58, P = 0.05) expression correlated with shorter operating time, and low leptin expression was linked to shorter length of stay (r = 0.70, P = 0.01), and low leptin expression was linked to shorter length of stay (r = 0.70, P = 0.01).ConclusionAdding pre-operative aerobic exercise to standard care may improve surgical outcomes through a fitness and adipose tissue derived mechanism.

Increasing brown adipose tissue abundance or activity or converting white into brown adipocytes holds promise for the treatment of type 2 diabetes and obesity. Several PPARγ agonists, including rosiglitazone, have been shown to robustly induce browning of white adipose tissue (WAT) in vitro but their effects in vivo are less pronounced, while PPARα agonists show modest browning effects both in vitro or in vivo. In the present study, we investigated whether PPARα and PPARγ dual agonism would have synergistic effects in inducing browning of WAT. We found that all tested dual PPARα/γ agonists robustly increased uncoupling protein 1 (Ucp1) expression in both mouse and human preadipocytes, with tesaglitazar giving the largest Ucp1 induction. Notably, tesaglitazar also strongly induced browning of WAT in vivo in both lean and obese mice at thermoneutrality, largely exceeding the increase in Ucp1 observed with rosiglitazone. Mechanistically, we found that selective PPARγ agonism was sufficient for the conversion of white into brown-like adipocytes in vitro, but dual PPARα/γ agonism was superior to selective PPARγ agonism at inducing white fat browning in vivo, at least in part via a PPARα-mediated increase in fibroblast growth factor 21 (FGF-21). In human preadipocytes in vitro, combined treatment with rosiglitazone and FGF-21 resulted in a robust and synergistic increase in UCP1 mRNA levels, superior to rosiglitazone- or FGF-21-monotreatments. Tesaglitazar-induced browning in obese mice was associated with increased energy expenditure, enhanced insulin sensitivity, reduced liver steatosis, and an overall improved metabolic profile compared to rosiglitazone and vehicle control groups. In conclusion, we found that dual PPARα/γ agonism robustly promotes browning of white fat in vivo, via synergistic action of FGF-21 and PPARγ agonism. Our findings identify a novel opportunity to develop compounds with robust browning of WAT, via dual modulation of PPARα and PPARγ. Disclosure T. Kroon: Employee; Self; AstraZeneca. M.J. Harms: Employee; Self; AstraZeneca. D. Nilsson: None. A. Lindblom: Employee; Self; AstraZeneca. P. Gennemark: Employee; Self; AstraZeneca. G. O'Mahony: Employee; Self; AstraZeneca. V. Osinski: None. C.A. McNamara: None. J. Boucher: Employee; Self; AstraZeneca.

Targeted nanoparticle delivery is a promising strategy for increasing efficacy and limiting side effects of therapeutics. When designing a targeted liposomal formulation, the in vivo biodistribution of the particles must be characterized to determine the value of the targeting approach. Peroxisome proliferator-activated receptor (PPAR) agonists effectively treat metabolic syndrome by decreasing dyslipidemia and insulin resistance but side effects have limited their use, making them a class of compounds that could benefit from targeted liposomal delivery. The adipose targeting sequence peptide (ATS) could fit this role, as it has been shown to bind to adipose tissue endothelium and induce weight loss when delivered conjugated to a pro-apoptotic peptide. To date, however, a full assessment of ATS in vivo biodistribution has not been reported, leaving important unanswered questions regarding the exact mechanisms whereby ATS targeting enhances therapeutic efficacy. We designed this study to evaluate the biodistribution of ATS-conjugated liposomes loaded with the PPARα/γ dual agonist tesaglitazar in leptin-deficient ob/ob mice. The ATS-liposome biodistribution in adipose tissue and other organs was examined at the cellular and tissue level using microscopy, flow cytometry, and fluorescent molecular tomography. Changes in metabolic parameters and gene expression were measured by target and off-target tissue responses to the treatment. Unexpectedly, ATS targeting did not increase liposomal uptake in adipose relative to other tissues, but did increase uptake in the kidneys. Targeting also did not significantly alter metabolic parameters. Analysis of the liposome cellular distribution in the stromal vascular fraction with flow cytometry revealed high uptake by multiple cell types. Our findings highlight the need for thorough study of in vivo biodistribution when evaluating a targeted therapy.

The development of new blood vessels is important during the progression of many diseases including cancer, obesity, and ischemia. While inhibiting blood vessel growth can prevent excess adiposity and tumor growth, it can also exacerbate symptoms of ischemia. Using flow cytometry to quantify total endothelial cells (ECs) in the gastrocnemius of mice who have undergone femoral artery resection (FAR), the number of ECs per gram of muscle increases approximately four-fold relative to uninjured gastrocnemius from the same mouse (442% increase, ± 208%) in a model of hindlimb ischemia. The helix-loop-helix (HLH) transcription factor Inhibitor of differentiation (ID3) promotes angiogenesis and whole tissue blood perfusion in models of cancer and obesity, but the potential role for ID3 in promoting ischemia-induced angiogenesis remains uninvestigated. Id3 mRNA levels in injured gastrocnemius are increased three days post-FAR relative to uninjured gastrocnemius (p < 0.05, n = 6). Furthermore, ID3 global knockout (KO) mice have attenuated perfusion recovery compared to wild type littermate controls at 14 days post-FAR (p < 0.05). Gastrocnemius muscles isolated from ID3 global KO mice 7 days post-FAR express higher levels of the cell cycle inhibitor p21 Cip1 mRNA than WT mice (p = 0.10, n = 3). Finally, flow cytometry analysis of cell subsets in a novel Id3 promoter-GFP reporter mouse line revealed that Id3 promoter activation is greater in CD31 + ECs than many other cell types (n = 10), suggesting ECs may be an important cell type in which ID3 is promoting pro-angiogenic effects. Together, these data support the hypothesis that ID3 promotes ischemia-induced angiogenesis by promoting EC proliferation and inhibiting cell cycle inhibitor p21 Cip1 . To investigate the role of ID3 in ECs during angiogenesis, an EC-specific, tamoxifen-inducible Id3 KO mouse (Id3 fl/fl Cdh5-Cre/ERT2) has been generated.

In adipose tissues of obese mice, macrophages accumulate in crown-like structures (CLS) formed around dying adipocytes. The CLS macrophages are thought to clear the dead adipocytes by exophagy, which involves exocytosis of lysosomes and digestion of apoptotic adipocytes. After digesting the plasma membrane and other cytosolic contents of the adipocyte, CLS macrophages come in contact with the large lipid droplet, however, it is unknown how macrophages response to such acellular adipocytes. We hypothesized that the acelular adipocytes in CLSs promote inflammation and metabolically activate the macrophages to promote clearance of the lipid. To mimic the in vivo scenario, we exposed cultured murine bone marrow-derived macrophages to lipid droplets isolated from the adipocytes of high-fat diet-induced obese C57BL/6 mice. In response to adipocyte lipid, macrophages accumulated lipid droplets, which were similar in size and number to lipid droplets of CLS macrophages in vivo . Acellular lipid exposure significantly increased TNF-α gene expression, which was suppressed by the CD36 inhibitor sulfo-N-succinimidyl oleate, supporting CD36-mediated inflammatory response. Moreover, lipid exposure significantly lowered metabolic activity of macrophages and impaired clearance of apoptotic bodies from 3T3-L1 adipocytes. Using specific inhibitors, unexpectedly we found that lipid droplet accumulation in macrophages was independent of CD36 activity or processes involved in exophagy such as exocytosis of lysosomes, extracellular lipase activity, lipolysis and phagocytosis. Interestingly, lipid droplet accumulation was dependent on acetyl-CoA carboxylase (ACC) as determined by use of ACC inhibitors soraphen A and TOFA, and siRNA knock-down of ACC in macrophages. Furthermore, confocal microscopy of whole mount adipose tissue revealed expression of ACC in CLS macrophages. Altogether, using a novel in vitro model we demonstrate that acelular adipocytes suppress metabolic activity, but induce inflammation and de novo lipogenesis-mediated lipid droplet formation in macrophages.

Rationale: Over half of the U.S. is overweight or obese and excessive weight gain greatly increases one’s risk of cardiovascular disease. Adipose tissue requires new blood vessel formation to support transport of nutrients during expansion. Our lab has previously published that global loss of the helix-loop-helix transcription factor Inhibitor of differentiation 3 (Id3) results in attenuated increases in adipose depot size and microvascular blood volume in mice fed a high fat diet (HFD). Id3 has also been implicated in regulating tumor angiogenesis. Together, our results suggest that Id3 is regulating HFD-induced angiogenesis in adipose tissue. Methods and Results: To determine if Id3 is regulating angiogenesis, we performed genetic, cellular, and arterial experiments and analyses. Using bromodeoxyuridine (BrdU) treatments and flow cytometry, we found that endothelial cells within adipose tissue of mice with a global genetic knockout of Id3 (Id3 KO) had fewer proliferating (BrdU-positive) endothelial cells (0.0679% BrdU+CD31+ cells) than wild type (WT) mice (0.754% BrdU+CD31+). Using mouse adipose tissue gene expression data from the Gene Ontology Consortium database, we found that genes correlating most significantly with Id3 were functionally classified under categories of vascular development (p = 4.45E-8, correlation significance) and angiogenesis (p = 1.66E-6). Sox18, a known transcriptional regulator of blood vessel formation, shows higher relative gene expression in Id3 WT (1.42 ± 0.417) than Id3 KO (0.332 ± 0.126) adipose tissue. Finally, preliminary findings using pressure myography demonstrate that Id3 KO mice have a higher baseline arterial diameter than Id3 WT. Conclusion: Dysregulation of vascular development during adipose tissue expansion is altering arterial function in an Id3-dependent manner.