Abstract 5543: The P2Y2 Nucleotide Receptor Contributes To Intimal Lesion Growth And Regulates Lymphotoxin-α Secretion
Inflammatory processes play a crucial role in atherosclerotic lesion growth. A number of pro-inflammatory molecules have been implicated in the pathogenesis of atherosclerosis, including lymphotoxin-α (LTA). Our research has shown that activation of a G protein-coupled P2Y2 nucleotide receptor (P2Y2R) expressed in vascular cells mediates inflammatory responses. To examine the role of the P2Y2R in lesion growth, we developed P2Y2R over-expressing transgenic rats. Collar-induced injury to the carotid artery of P2Y2R transgenic rats caused a dramatic increase in intimal lesion growth and significant macrophage accumulation, which nearly blocked the arterial lumen. Immunohistochemical staining showed that LTA and galectin-2 (gal-2) were abundantly expressed in smooth muscle cells (SMC) and macrophages in carotid lesions of P2Y2R transgenic rats. We also identified galectin-2 as a P2Y2R binding partner using the yeast two-hybrid system and a co-immunoprecipitation assay. P2Y2R agonist, UTP, stimulated gal-2 mRNA expression in rat carotid SMC. Transient transfection of SMC with a genomic fragment including the rat galectin (LGALS2) promoter incorporated into a luciferase (pGL-3) reporter vector showed that UTP markedly increased LGALS2 promoter activity in a dose-dependent manner. Moreover, UTP induced LTA secretion in cultured aortic SMC from wild type, but not P2Y2R−/− mice. Adenoviral expression of the full length P2Y2R in SMC from P2Y2R−/− mice fully restored UTP-induced LTA secretion. However, expression of a mutant P2Y2R that does not bind filamin A, an actin-binding protein that interacts with the P2Y2R, only partially restored UTP-induced LTA secretion in P2Y2R−/− SMC. Gal-2 siRNA partially inhibited LTA release into medium of cultured SMC expressing the P2Y2R. In contrast, gal-2 siRNA abolished UTP-induced LTA secretion in SMC isolated from P2Y2R−/− mice expressing the filamin A binding mutant P2Y2R. These results indicate that P2Y2Rs regulate gal-2-dependent LTA secretion in SMC via a filamin A-dependent mechanism that likely contributes to vascular inflammation.