425-P: Mechanisms Regulating VEGF Receptors in Diabetic Angiogenesis

Diabetes-related vascular complications underlie a number of life-threatening conditions including cardiovascular disease, stroke, and peripheral limb ulcerations, the latter of which can lead to severe infections and a multitude of serious medical issues. Our goal is to understand how chronic hyperglycemia impairs endothelial cell function to identify molecular targets that would form the basis for new therapies to treat the peripheral vascular complications associated with diabetes. Since VEGFRs are critical regulators of both angiogenesis and lymphangiogenesis, we and others have shown that VEGFRs 2 and 3 were significantly reduced in the endothelium of diabetic patients and animals. We demonstrated that loss of the endocytic adaptor proteins epsin 1 and 2 in lymphatic endothelial cells (LECs) prevents VEGFR3 endocytosis and degradation, leading to enhanced lymphangiogenesis in vivo and cell proliferation, migration, and tube formation in vitro. Mechanistically, reactive oxygen species produced in diabetes induced c-Src–dependent VEGFR3 phosphorylation and degradation, and upregulated epsins through the AP-1 transcription factor. Epsins bind to and promote the degradation of newly-synthesized VEGFR3 in the Golgi, resulting in reduced availability of VEGFR3 at the cell surface. Here, we show that diabetic conditions induce expression of the autophagosome-specific gene Ulk1, which promotes VEGFR2/3 degradation. Hence, Ulk1 deficiency inhibits autophagosome formation and enhances angiogenic responses under diabetic conditions through upregulation of multiple endothelial-specific pathways that support neovascularization. Loss of endothelial Ulk1 elevated VEGFR2/3 levels and enhanced in vitro angiogenesis as measured by endothelial proliferation, migration, and tube formation and augmented wound healing in diabetes. Collectively, our results show that inhibition of epsins and Ulk1 in diabetes can restore angiogenic and lymphangiogenic responses and provide therapeutic targets.