Contribution of p62/SQSTM1 to PDGF-BB-induced myofibroblast-like phenotypic transition in vascular smooth muscle cells lacking Smpd1 gene

Accumulating evidence indicates a critical role of autophagy in regulating vascular smooth muscle cell (SMC) homeostasis in atherogenesis. However, little is known about the modulatory role of autophagy in PDGF-BB-induced SMC transition towards the synthetic phenotype and extracellular matrix remodeling. We recently demonstrated that acid sphingomyelinase (ASM, encoded by Smpd1 gene) controls autophagy maturation in coronary arterial SMCs. Here, we demonstrate that PDGF-BB stimulation causes a myofibroblast-like non-canonical synthetic phenotype transition in Smpd1−/− SMCs. These non-canonical phenotypic changes induced by PDGF-BB in Smpd1−/− SMCs were characterized by increased expression of fibroblast-specific protein (FSP-1), massive deposition of collagen type I, decreased cell size, elevated inflammatory status with enhanced cytokine release and adhesion molecule expression. Mechanistically, PDGF-BB induces prolonged Akt activation that causes decreased autophagosome biogenesis and thereby exaggerates p62/SQSTM1 accumulation in Smpd1−/− SMCs. More importantly, Akt inhibition or p62/SQSTM1 gene silencing attenuates PDGF-BB-induced phenotypic changes in Smpd1−/− SMCs. This first demonstration of a p62/SQSTM1-dependent myofibroblast-like phenotypic transition in Smpd1−/− SMCs suggests that ASM-mediated autophagy pathway contributes to maintaining the arterial smooth muscle homeostasis in situation of vascular remodeling during atherosclerosis.