Intrinsic circadian oscillation of myosin light chain phosphorylation in vascular smooth muscle cells

Abstract

The onset of coronary artery disease, such as myocardial infarction, shows an apparent circadian variation. However, its molecular mechanism still remains to be elucidated. This study investigated the role of intrinsic vascular clock in the circadian regulation of vascular contractility. The porcine coronary artery smooth muscle cells in culture were exposed to 100 nM dexamethosone for 2 hr (Dex shock) to induce a circadian rhythm. The response of the myosin light chain (MLC) phosphorylation to the contractile stimuli was evaluated as an index of vascular contractility. A real‐time PCR analysis revealed a circadian oscillation of the expression of clock genes, such as bmal1 and per1. The resting level of MLC phosphorylation did not significantly change after DEX shock. In contrast, the level of MLC phosphorylation induced by thrombin exhibited a circadian oscillation with a 25.3‐hr cycle, reaching peaks at 36 hr and 60 hr. MLC phosphorylation changed from 0.85 at a nadir to 1.05 PO4 mol/MLC mol at a peak. However, there was no change in the level of thrombin receptor. The thrombin‐induced contraction of smooth muscle cells also exhibited a circadian oscillation after DEX shock. The results demonstrated the existence of an intrinsic circadian oscillation of the response of MLC phosphorylation. The present study thus suggests the vascular clock to contribute to the circadian regulation of vascular contractility.