Although endothelial dysfunction, defined as abnormal vasoreactivity, is a common early finding in individuals with type 2 diabetes, the endothelium has not been known to regulate metabolism. As PPARγ, a transcriptional regulator of energy balance, is expressed in endothelial cells, we set out to investigate the role of endothelial cell PPARγ in metabolism using mice that lack PPARγ in the endothelium and BM (γEC/BM-KO). When γEC/BM-KO mice were fed a high-fat diet, they had decreased adiposity and increased insulin sensitivity compared with control mice, despite increased serum FFA and triglyceride (TG) levels. After fasting or olive oil gavage, γEC/BM-KO mice exhibited significant dyslipidemia and failed to respond to the FFA and TG lowering effects of the PPARγ agonist rosiglitazone. BM transplantation studies, which reconstituted hematopoietic PPARγ, established that these metabolic phenotypes were due to endothelial PPARγ deficiency. We further found that the impairment in TG-rich lipoprotein metabolism in γEC/BM-KO mice was associated with fatty acid-mediated lipoprotein lipase inhibition and changes in a PPARγ-regulated endothelial cell transcriptional program. Despite their metabolic improvements, high-fat diet-fed γEC/BM-KO mice had impaired vasoreactivity. Taken together, these data suggest that PPARγ in the endothelium integrates metabolic and vascular responses and may contribute to the effects of PPARγ agonists, thus expanding what endothelial function and dysfunction may entail.

Summary Endothelial dysfunction is a central hallmark of diabetes. The transcriptional coactivator PGC-1α is a powerful regulator of metabolism, but its role in endothelial cells remains poorly understood. We show here that endothelial PGC-1α expression is high in diabetic rodents and humans and that PGC-1α powerfully blocks endothelial migration in cell culture and vasculogenesis in vivo. Mechanistically, PGC-1α induces Notch signaling, blunts activation of Rac/Akt/eNOS signaling, and renders endothelial cells unresponsive to established angiogenic factors. Transgenic overexpression of PGC-1α in the endothelium mimics multiple diabetic phenotypes, including aberrant re-endothelialization after carotid injury, blunted wound healing, and reduced blood flow recovery after hindlimb ischemia. Conversely, deletion of endothelial PGC-1α rescues the blunted wound healing and recovery from hindlimb ischemia seen in type 1 and type 2 diabetes. Endothelial PGC-1α thus potently inhibits endothelial function and angiogenesis, and induction of endothelial PGC-1α contributes to multiple aspects of vascular dysfunction in diabetes.

Nitric oxide (NO) and hydrogen peroxide (H 2 O 2 ) are synthesized within cardiac myocytes and play key roles in modulating cardiovascular signaling. Cardiac myocytes contain both the endothelial (eNOS) and neuronal (nNOS) NO synthases, but the differential roles of these NOS isoforms and the interplay of reactive oxygen species and reactive nitrogen species in cardiac signaling pathways are poorly understood. Using a recently developed NO chemical sensor [Cu 2 ðFL2EÞ] to study adult cardiac myocytes from wild-type, eNOS null , and nNOS null mice, we discovered that physiological concentrations of H 2 O 2 activate eNOS but not nNOS. H 2 O 2 -stimulated eNOS activation depends on phosphorylation of both the AMPactivated protein kinase and kinase Akt, and leads to the robust phosphorylation of eNOS. Cardiac myocytes isolated from mice infected with lentivirus expressing the recently developed H 2 O 2 biosensor HyPer2 show marked H 2 O 2 synthesis when stimulated by angiotensin II, but not following β-adrenergic receptor activation. We discovered that the angiotensin-II-promoted increase in cardiac myocyte contractility is dependent on H 2 O 2 , whereas β-adrenergic contractile responses occur independently of H 2 O 2 signaling. These studies establish differential roles for H 2 O 2 in control of cardiac contractility and receptor-dependent NOS activation in the heart, and they identify new points for modulation of NO signaling responses by oxidant stress.

Caveolin-1 is a scaffolding/regulatory protein that interacts with diverse signaling molecules. Caveolin-1null mice have marked metabolic abnormalities, yet the underlying molecular mechanisms are incompletely understood. We found the redox stress plasma biomarker plasma 8-isoprostane was elevated in caveolin-1null mice, and discovered that siRNA-mediated caveolin-1 knockdown in endothelial cells promoted significant increases in intracellular H2O2. Mitochondrial ROS production was increased in endothelial cells after caveolin-1 knockdown; 2-deoxy-D-glucose attenuated this increase, implicating caveolin-1 in control of glycolytic pathways. We performed unbiased metabolomic characterizations of endothelial cell lysates following caveolin-1 knockdown, and discovered strikingly increased levels (up to 30-fold) of cellular dipeptides, consistent with autophagy activation. Metabolomic analyses revealed that caveolin-1 knockdown led to a decrease in glycolytic intermediates, accompanied by an increase in fatty acids, suggesting a metabolic switch. Taken together, these results establish that caveolin-1 plays a central role in regulation of oxidative stress, metabolic switching, and autophagy in the endothelium, and may represent a critical target in cardiovascular diseases.