Hyperglycemia decreases endothelial cells (EC) proliferation by inhibiting the insulin signaling pathway

Abstract

Hyperglycemia-induced EC proliferation deficiency may contribute to decreased angiogenesis in diabetes. We tested this hypothesis in cultured human iliac artery endothelial cells (HIAEC). We measured proliferation in HIAEC grown in 5, 20 and 40mM D-glucose for 10 days. We grew HIAEC in equimolar mannitol as control for hyperosmolar changes. Glucose at 20 and 40mM decreased proliferation while mannitol had no effect. Insulin at 26mU/ml restored proliferation only to HIAEC grown in 20mM glucose. Inhibition of the insulin signaling pathway at PI3k/Akt (1μM LY294002) significantly decreased proliferation in HIAEC grown in 5mM glucose. Glucose at 40 mM reduced threonine phosphorylation of Akt at P308 (p-308-Akt) even in the presence of insulin. Expression of total Akt remained unchanged. We next investigated IRS1 (insulin receptor substrate-1) upstream in the insulin signaling pathway as a possible target of hyperglycemia. Glucose at 40 mM reduced tyrosine phosphorylation of Y612 on IRS1 (p-Y612-IRS1) even in the presence of insulin. Glucose at 20 mM also reduced p-Y612-IRS1, but insulin restored it to normal. Expression of total IRS1 and p-S616 remained unchanged. We conclude that 20 and 40 mM glucose decrease proliferation of EC derived from human iliac arteries. High glucose reduces phosphorylation of Akt and IRS1, important elements in the insulin signaling pathway. Cells at 20 mM glucose were partially rescued by insulin while cells at 40 mM glucose were not rescued at all. (supported by grants from ACS and NIH 5RO1HL70634).