Background: We aimed to evaluate whether insulin influences vascular endothelial growth factor (VEGF) synthesis and secretion in cultured vascular smooth muscle cells (VSMCs) via nitric oxide (NO) and whether these putative effects are lost in insulin-resistant states.
Materials and methods: In VSMC derived from human arterioles and from aortas of insulin-sensitive Zucker fa/+rats and insulin-resistant Zucker fa/fa rats incubated with different concentrations of human regular insulin with or without inhibitors of phosphatidylinositol 4,5-bisphosphate 3-kinase (PI3-K), mitogen-activated protein kinase (MAPK), nitric oxide synthase (NOS) and guanosine 3',5'cyclic monophosphate(cGMP)-dependent protein kinase (PKG), we measured protein expression (Western blot) and secretion (ELISA) of VEGF.
Results: We found that in VSMCs from humans and from insulin-sensitive Zucker fa/+rats, insulin increases VEGF protein expression and secretion, with mechanisms blunted by wortmannin and LY294002 (PI3-K inhibitors), PD98059 (MAPK inhibitor), L-NMMA (NOS inhibitor) and Rp-8pCT-cGMPs (PKG inhibitor). Also the NO donor sodium nitroprusside (SNP) and the cGMP analogue 8-Bromo-cGMP increase VEGF protein expression and secretion, with mechanisms inhibited by wortmannin and PD98059. The insulin effects on VEGF are impaired in VSMCs from Zucker fa/fa rats, which also present a reduced insulin ability to increase NO.
Conclusions: In VSMCs from humans and insulin-sensitive Zucker fa/+rats: (i) insulin increases VEGF protein expression and secretion via both PI3-K and MAPK; (ii) the insulin effects on VEGF are mediated by nitric oxide. The insulin action on both nitric oxide and VEGF is impaired in VSMCs from Zucker fa/fa rats, an animal model of metabolic and vascular insulin-resistance.