Reconstituted high-density lipoproteins rescue diabetes-impaired endothelial cell metabolic reprograming and angiogenic responses to hypoxia

Objective: Impaired angiogenic responses to ischemia underlie diabetic vascular complications. Reconstituted high-density lipoproteins (rHDL) have proangiogenic effects in diabetes. The pyruvate dehydrogenase kinase 4 (PDK4)/pyruvate dehydrogenase complex (PDC) axis is an oxygen-conserving mechanism that preserves EC functions in hypoxia. We aimed to determine the role of the PDK4/PDC axis in angiogenesis, the effect of diabetes on its regulation in response to ischemia, and in the proangiogenic properties of rHDL. Approach and Results: In a murine wound healing model, PDK4 and pPDC were elevated early (24h) post induction of wound ischemia in non-diabetic wounds, which did not occur in diabetic mice. Topical rHDL rescued this impairment, enhancing PDK4 (68%, P<0.05) and pPDC (165%, P<0.01) in diabetic wounds. In parallel, wound neovascularization (62%, P<0.05) and closure (154%, P<0.0001) were increased in diabetic rHDL-treated wounds. In vitro, PDK4 and pPDC levels were increased in ECs exposed to hypoxia (65%, 70% respectively, P<0.05). High glucose did not elicit a further step-wise induction in PDK4/pPDC, with aberrant increases in mitochondrial respiration (19%, P<0.05), coupled with impaired EC angiogenic functions. Importantly, rHDL increased PDK4 and pPDC two-fold, returning mitochondrial respiration and EC angiogenic functions to normal glucose levels. In vitro, PDK4 siRNA knockdown attenuated the proangiogenic effects of rHDL. In vivo PDK4 inhibition ameliorated topical rHDL-mediated increases in wound angiogenesis and closure. Using chromatin immunoprecipitation, rHDL increased forkhead box O1 (FOXO1) binding to the PDK4 promoter and suppressed FOXO1 phosphorylation, presenting FOXO1 as a mechanism for the induction of PDK4 by rHDL. Conclusion: The PDK4/PDC axis response to ischemia is impaired in diabetes and important for the proangiogenic effects of rHDL.