Polycystin-1 Is a Cardiomyocyte Mechanosensor That Governs L-Type Ca 2+ Channel Protein Stability

Abstract

Background— L-type calcium channel activity is critical to afterload-induced hypertrophic growth of the heart. However, the mechanisms governing mechanical stress–induced activation of L-type calcium channel activity are obscure. Polycystin-1 (PC-1) is a G protein–coupled receptor–like protein that functions as a mechanosensor in a variety of cell types and is present in cardiomyocytes. Methods and Results— We subjected neonatal rat ventricular myocytes to mechanical stretch by exposing them to hypo-osmotic medium or cyclic mechanical stretch, triggering cell growth in a manner dependent on L-type calcium channel activity. RNAi-dependent knockdown of PC-1 blocked this hypertrophy. Overexpression of a C-terminal fragment of PC-1 was sufficient to trigger neonatal rat ventricular myocyte hypertrophy. Exposing neonatal rat ventricular myocytes to hypo-osmotic medium resulted in an increase in α1C protein levels, a response that was prevented by PC-1 knockdown. MG132, a proteasomal inhibitor, rescued PC-1 knockdown–dependent declines in α1C protein. To test this in vivo, we engineered mice harboring conditional silencing of PC-1 selectively in cardiomyocytes (PC-1 knockout) and subjected them to mechanical stress in vivo (transverse aortic constriction). At baseline, PC-1 knockout mice manifested decreased cardiac function relative to littermate controls, and α1C L-type calcium channel protein levels were significantly lower in PC-1 knockout hearts. Whereas control mice manifested robust transverse aortic constriction–induced increases in cardiac mass, PC-1 knockout mice showed no significant growth. Likewise, transverse aortic constriction–elicited increases in hypertrophic markers and interstitial fibrosis were blunted in the knockout animals Conclusion— PC-1 is a cardiomyocyte mechanosensor that is required for cardiac hypertrophy through a mechanism that involves stabilization of α1C protein.