The Release of Cyclophilin A from Rapamycin-Stimulated Vascular Smooth Muscle Cells Mediated by Myosin II Activation: Involvement of Apoptosis but Not Autophagy

Introduction: The exocytosis of cyclophilin A (CyPA) by a vesicular pathway in response to reactive oxygen species has been determined. However, other sources of extracellular CyPA remain obscure. Objective: The aim of this study was to determine the role of autophagy in the secretion of CyPA. Methods and Results: Rapamycin induced the activation of autophagy and release of CyPA from primary cultured rat aortic smooth muscle cells (RASMCs). However, inhibition of autophagy by knockdown of Atg7 or chloroquine did not affect the rapamycin-induced release of CyPA. With the exception of myosin II activity, rho-associated coiled-coil kinase (ROCK), actin remodelling, and synaptic vesicles were not implicated in the release of rapamycin-induced CyPA. Finally, we confirmed that rapamycin-induced extracellular CyPA originated from apoptotic RASMCs. Furthermore, the decreased activation of myosin II by blebbistatin blocked the release of CyPA from apoptotic RASMCs induced by rapamycin. Conclusions: Rapamycin induced the release of CyPA from apoptotic RASMCs but did not affect exocytosis through autophagosomes. ROCK, actin remodelling, and synaptic vesicles were not involved in the apoptosis-related release of CyPA. Myosin II activation modulated the apoptosis of vascular smooth muscle cells and the release of CyPA from rapamycin-induced apoptotic cell death.