title: Pivotal role of Rho-associated kinase 2 in generating the intrinsic circadian rhythm of vascular contractility.
abstract: 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 the vascular intrinsic clock that generates the circadian rhythm of vascular contractility still remains largely unknown.
  
  
  RESULTS
  The agonist-induced phosphorylation of myosin light chain in cultured smooth muscle cells synchronized by dexamethasone pulse treatment exhibited an apparent circadian oscillation, with a 25.4-hour cycle length. The pharmacological inhibition and knockdown of Rho-associated kinase 2 (ROCK2) abolished the circadian rhythm of myosin light chain phosphorylation. The expression and activity of ROCK2 exhibited a circadian rhythm in phase with that of myosin light chain phosphorylation. A clock gene, RORα, activated the promoter of the ROCK2 gene, whereas its knockdown abolished the rhythmic expression of ROCK2. In the mouse aorta, ROCK2 expression exhibited the circadian oscillation, with a peak at Zeitgeber time 0/24 and a nadir at Zeitgeber time 12. The myofilament Ca(2+) sensitization induced by GTPγS and U46619, a thromboxane A2 analog, at Zeitgeber time 0/24 was greater than that seen at Zeitgeber time 12. The circadian rhythm of ROCK2 expression and myofilament Ca(2+) 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.
authors.affiliation: Division of Molecular Cardiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Toshiro
authors.initials: T
authors.lastname: Saito
authors.forename: Mayumi
authors.initials: M
authors.lastname: Hirano
authors.forename: Tomomi
authors.initials: T
authors.lastname: Ide
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Ichiki
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Koibuchi
authors.forename: Kenji
authors.initials: K
authors.lastname: Sunagawa
authors.forename: Katsuya
authors.initials: K
authors.lastname: Hirano
mesh_terms: D000818:Animals; D001011:Aorta / Q000166:cytology; D002478:Cells, Cultured; D002940:Circadian Rhythm / Q000502:physiology*; D003331:Coronary Vessels / Q000166:cytology / Q000502:physiology; D005260:Female; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008818:Mice, Neurologic Mutants; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000502:physiology; D009200:Myocardial Contraction / Q000502:physiology*; D018994:Myosin Light Chains / Q000378:metabolism; D057094:Nuclear Receptor Subfamily 1, Group F, Member 1 / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000502:physiology; D034741:RNA, Small Interfering / Q000235:genetics; D013552:Swine; D014661:Vasoconstriction / Q000502:physiology*; D054460:rho-Associated Kinases / Q000235:genetics* / Q000378:metabolism*
chemical_list: D018994:Myosin Light Chains; D057094:Nuclear Receptor Subfamily 1, Group F, Member 1; D034741:RNA, Small Interfering; C539739:Rora protein, mouse; C515855:Rock2 protein, mouse; D054460:rho-Associated Kinases