Simvastatin potenciates PGI 2 release induced by HDL in human VSMC: effect on Cox-2 up-regulation and MAPK signalling pathways activated by HDL

Abstract

High density lipoproteins (HDL) induce prostacyclin (PGI 2) release in vascular smooth muscle cells (VSMC) by up-regulation of cyclooxygenase-2 (Cox-2). Our goal was to analyse the mechanisms underlying this effect, and its potential modulation by HMG-CoA reductase inhibition in human VSMC. The contribution of mitogen-activated protein kinase (MAPK) signalling pathways was assessed by Western blot analysis and using specific inhibitors [PD098059 for p42/44 MAPK kinase (MEK); SB203580 for p38 MAPK or L-JNKI1 for c-Jun N-terminal kinase-1 (JNK-1)]. HDL-induced PGI 2 release was inhibited by rofecoxib (a specific Cox-2 inhibitor, 5 μM). HDL induced the early activation of p42 MAPK, p38 MAPK and JNK-1. p42/44 MAPK was the major pathway involved in both Cox-2 up-regulation and PGI 2 synthesis; p38 MAPK was also involved in both processes while JNK inhibition only affected PGI 2 synthesis. Pertussis toxin (an inhibitor of Gαi/Gαo proteins) prevented MAPK activation and inhibited both Cox-2 up-regulation and PGI 2 release. Genistein (a tyrosine kinase inhibitor) inhibited PGI 2 release without affecting MAPK activation or Cox-2 up-regulation. Simvastatin (0.1–1 μM) increased HDL-induced PGI 2 release (≈45% at 1 μM) but did not significantly modify early MAPK activation or Cox-2 expression. Simvastatin alone did not significantly affect PGI 2 release. Our results suggest that mechanisms associated with G protein-coupled receptor activation, trigger Cox-2 up-regulation and PGI 2 release via multiple MAPK signalling pathways in VSMC. The mechanism is independent of tyrosine kinase receptors, although cytosolic tyrosine kinases could activate Cox-2 post-translationally. The potential contribution of HDL to vascular homeostasis, via increases in PGI 2 synthesis, could be enhanced by HMG-CoA reductase inhibitors.