300-OR: The Transcriptional Coregulator CITED2 Suppresses Expression of IRS-2 in Endothelial Cells and Impairs Vascular Insulin Signaling In Vivo

Endothelial insulin signaling regulates perfusion, leukocyte adhesion, and angiogenesis, and its impairment may contribute to the development of vascular complications in diabetes. Hypoxia-inducible factors (HIF) are known modulators of insulin signaling and we have recently shown that a negative regulator of HIF activity, CBP/p300 interacting transactivator-2 (CITED2), is increased in the vasculature of people with type 2 diabetes. Therefore, we examined the role of CITED2 in endothelial insulin signaling by generating a mouse model with endothelial-specific loss of Cited2. We found that in the aorta and isolated endothelial cells, loss of Cited2 markedly enhanced insulin-stimulated Akt phosphorylation at Ser473 without altering ERK1/2 phosphorylation. Consistent with this observation, Cited2 deletion in endothelial cells increased insulin-stimulated Vegfa expression, endothelial nitric oxide synthase phosphorylation, and cell proliferation. Endothelial cells lacking CITED2 exhibited a 3.6-fold increase in insulin receptor substrate (IRS)-2 protein, a key mediator of the insulin signaling cascade, and 66% increase in Irs2 mRNA expression while IRS-1 was unchanged. Similarly, overexpression of CITED2 in endothelial cells decreased IRS-2 levels by 55% without altering IRS-1. Expression of HIF-2α significantly increased transcription of the Irs2 promoter and co-expression of CITED2 abolished this increase. Moreover, ChIP showed that loss of CITED2 increases occupancy of p300, a key component of the HIF transcriptional complex, on the Irs2 promoter. Together, these results suggest that loss of CITED2 enhances endothelial insulin signaling through de-repression of HIF-dependent Irs2 expression. The CITED2-p300 interaction can likely be interrupted by a small-molecule drug, and is thus a potential target to improve insulin action on endothelial cells in order to prevent vascular complications of diabetes. Disclosure B. Kunkemoeller: None. K. Chen: None. X. Wang: None. C. Rask-Madsen: None. Funding National Institutes of Health (5T32DK007260)