Regulation of Angiogenesis by the Transcriptional Coregulator CITED2 in Obesity and Type 2 Diabetes

Patients with diabetes have an impaired angiogenic response to hypoxia resulting in worse perfusion of tissue with chronic hypoxia and poor recovery after ischemic stroke and myocardial infarction. We have screened for insulin-regulated genes in vascular endothelial cells among 22 genes previously shown to be both regulated by the transcription factor FoxO and differentially regulated in pro-angiogenic endothelial cells. Among these genes, insulin robustly downregulated the transcriptional corepressor CITED2 (CBP/p300 interacting transactivator 2) in endothelial cells. We also showed that CITED2 is upregulated in arterial tissue from patients with type 2 diabetes, presumably because of insulin resistance in vascular tissue, where insulin fails to suppress CITED2 despite hyperinsulinemia. These are particularly interesting findings because CITED2 inhibits transactivation of hypoxia-inducible factor-α (HIF-1α), a key regulator of proangiogenic genes. Our preliminary data show that CITED2 overexpression or knockdown in endothelial cell culture inhibits or promotes, respectively, tube formation on Matrigel. We therefore propose that upregulation of CITED2 in type 2 diabetes and other insulin resistant states can in part explain impaired angiogenesis. In Aim 1, we will demonstrate, using endothelial cell culture, how CITED2 activates HIF responsive promoters through HIF-1α or HIF-2α, regulates HIF target genes, including VEGF and matrix metalloproteases, and influence invasion in extracellular matrix, tube formation and proliferation. In Aim 2, we will determine whether inducible and tissue-specific knockout of CITED2 in endothelial cells can improve hindlimb angiogenesis in mice with insulin resistance due to diet-induced obesity. Although development of antiangiogenic drugs has shown great progress, there are few targets like CITED2 which, when inhibited, promote angiogenesis. The expected outcome of this research is to provide evidence for whether downregulation of CITED2 in endothelial cells can improve angiogenesis in insulin resistance as well as mechanistic insight into this phenomenon.