MicroRNA (miR)-1 and -133 play a crucial role in skeletal and cardiac muscle biology and pathophysiology. However, their expression and regulation in vascular cell physiology and disease is currently unknown.

The aim of the present study was to evaluate the role, if any, of miR-1 and miR-133 in vascular smooth muscle cell (VSMC) phenotypic switch in vitro and in vivo.

We demonstrate here that miR-133 is robustly expressed in vascular smooth muscle cells (VSMCs) in vitro and in vivo, whereas miR-1 vascular levels are negligible. miR-133 has a potent inhibitory role on VSMC phenotypic switch in vitro and in vivo, whereas miR-1 does not have any relevant effect per se. miR-133 expression is regulated by extracellular signal–regulated kinase 1/2 activation and is inversely correlated with VSMC growth. Indeed, miR-133 decreases when VSMCs are primed to proliferate in vitro and following vascular injury in vivo, whereas it increases when VSMCs are coaxed back to quiescence in vitro and in vivo. miR-133 loss- and gain-of-function experiments show that miR-133 plays a mechanistic role in VSMC growth. Accordingly, adeno-miR-133 reduces but anti-miR-133 exacerbates VSMC proliferation and migration in vitro and in vivo. miR-133 specifically suppresses the transcription factor Sp-1 expression in vitro and in vivo and through Sp-1 repression regulates smooth muscle gene expression.

Our data show that miR-133 is a key regulator of vascular smooth muscle cell phenotypic switch in vitro and in vivo, suggesting its potential therapeutic application for vascular diseases.