Abstract 656: Lipid Phosphate Phosphatase-3 Mediated Inflammation and Angiogenesis

Abstract

A recent meta-analysis of genome-wide association studies (GWAS) of coronary artery disease (CAD) involving over 86,000 individuals identified PPAP2B (gene that encodes lipid phosphate phosphatase-3; LPP3) as 1 of 13 new loci that associate with CAD. The PPAP2B loci independently predicted CAD (P = 3.81 X 10-19) and lacked association with traditional risk factors. The lipid phosphate phosphatase 3 is a cell surface integral membrane protein that regulates the bio availability of major bioactive lysophospholipids, like lysophosphatidic acid (LPA). Our group also made the surprising discovery that tissue-specific deficiency of LPP3 exaggerates vascular inflammation and promotes the development of neointima after vascular injury. Here we present evidence that enothelial cell LPP3 serves as an intrinsic negative regulator of vascular inflammation, promotes endothelial barrier function. Our results suggest that loss of LPP3 by siRNA mediated knockdown enhanced proliferation with elevated pErk signaling whereas migration was inhibited in human microvascular endothelial cells (HMEC). The endothelial cells that were silenced for LPP3 were further subjected LPA receptor knockdown and we found that although LPA-induced Erk phosphorylation was similar between LPA 1 and LPA 4 silencing, LPA 4 silencing resulted in enhancement of Akt phosphorylation at Thr-308 in response to LPA. Dual inhibition of LPA 1 and LPA 4 abolished LPA mediated migration in LPP3 silenced HMEC suggesting that the signaling response is mediated through the LPA 1 receptor. Rac activation in response to LPA was barely detectable in LPP3 silenced HMEC, which correlated with its weak migratory response. In contrast, a prominent increase in Rac-GTP levels was observed upon LPA 4 silencing under these conditions. Activation of HMEC with LPA increased phosphorylation of MSK downstream of p38, and CREB phosphorylation was inhibited upon LPA 4 receptor blockade in LPP3 silenced endothelial cells.