Pivotal Role of Rho-Associated Kinase 2 in Generating the Intrinsic Circadian Rhythm of Vascular Contractility
Background—The circadian variation in the incidence of cardiovascular events may be attributable to the circadian changes in vascular contractility. The circadian rhythm of vascular contractility is determined by the interplay between the central and peripheral clocks. However, the molecular mechanism of vascular intrinsic clock that generates the circadian rhythm of vascular contractility still remains largely unknown.
Methods and Results—The agonist-induced phosphorylation of myosin light chain (MLC) in cultured smooth muscle cells synchronized by dexamethasone pulse treatment, exhibited an apparent circadian oscillation, with a 25.4-hr cycle length. The pharmacological inhibition and knockdown of Rho-associated kinase 2 (ROCK2) abolished the circadian rhythm of MLC phosphorylation. The expression and activity of ROCK2 exhibited a circadian rhythm in phase with that of MLC phosphorylation. A clock gene, RORα, activated the promoter of the ROCK2 gene, while its knockdown abolished the rhythmic expression of ROCK2. In the mouse aorta, ROCK2 expression exhibited the circadian oscillation, with a peak at Zeitgeber time (ZT) 0/24 and a nadir at ZT12. The myofilament Ca2+ sensitization induced by GTPγS and U46619, a thromboxane A2 analog, at ZT0/24 was greater than that seen at ZT12. The circadian rhythm of ROCK2 expression and myofilament Ca2+ sensitivity was abolished in staggerer mutant mice, which lack a functional RORα.
Conclusions—ROCK2 plays a pivotal role in generating the intrinsic circadian rhythm of vascular contractility by receiving a cue from RORα. The ROCK2-mediated intrinsic rhythm of vascular contractility may underlie the diurnal variation of the incidence of cardiovascular diseases.
- Received August 6, 2012.
- Accepted October 22, 2012.
- Copyright © 2012, American Heart Association, Inc. All rights reserved. Unauthorized use prohibited