Abstract 5447: Thromboxane A2 Receptor Activation Attenuates Insulin Signaling and Angiogenesis by Upregulating Phosphatase PTEN in Cultured Endothelial Cells
Increasing evidence indicates that elevated levels of endogenous thromboxane receptor (TPr) agonists including thromboxane (Tx) A2, prostaglandin H2, and 8-iso-prostaglandin F2a contribute to insulin resistance, endothelial dysfunction, and accelerated atherosclerosis in diabetes. However, the mechanisms by which TPr triggers insulin resistance in endothelial cells remaine poorly defined. Here we show how TPr activation impairs insulin signaling and angiogenesis in endothelial cells. Exposure of cultured human umbilical vein endothelial cells (HUVEC) to a structurally related TxA2 mimetic (IBOP, U46619, or carboxy-TxA2) for 3 or 16h significantly inhibited both basal- and insulin-stimulated Akt-Ser473 phosphorylation, Akt activity, the serine 1177 phosphorylation of endothelial nitric oxide synthase (eNOS-Ser1177), and angiogenesis. Concomitantly, IBOP significantly increased the levels of Phosphatase and TENsin homolog deleted on chromosome 10 (PTEN) and PTEN phosphorylation at Ser380/Thr382/383. Further, Y27632, a Rho kinase (ROCK) inhibitor, abolished the effects of IBOP on the phosphorylation of PTEN, Akt and eNOS, and the PTEN level. Similarly, inhibition of PTEN by small interference RNA (siRNA), like the selective TPr antagonist, SQ29548, or knockdown of TPr by siRNA, abolished IBOP-induced inhibition on both the phosphorylation of the Akt-eNOS axis and angiogenesis. Furthermore, IBOP significantly increased the Ser428 phosphorylation of LKB1, a known upstream kinase for PTEN. Finally, suppression of LKB1 abolished IBOP-induced PTEN phosphorylation and PTEN accumulation in HUVEC. We conclude that TPr suppresses insulin signaling and angiogenesis by upregulating RhoA mediated but LKB1-dependent PTEN phosphorylation in endothelial cells.
This research has received full or partial funding support from the American Heart Association, AHA South Central Affiliate (Arkansas, New Mexico, Oklahoma & Texas).