Abstract 509: Essential Role of Vascular Smooth Muscle Bmal1 in Diurnal Variations of Contraction and Blood Pressure

Bmal1 is an obligatory core clock gene that is ubiquitously expressed but has been demonstrated to have tissue specific functions. However, the vascular smooth muscle specific function of bmal1 is unknown. We generated a smooth muscle specific bmal1 knockout mouse model (SM-bmal1-ko) and investigated the role of bmal1 in vascular smooth muscle contraction and blood pressure regulation. Isometric contractions were measured in isolated right renal artery and 2 nd order branch of mesenteric artery helical strips. Blood pressure was monitored in conscious free-moving mice using radiotelemetry. We demonstrated that bmal1 was selectively deleted in smooth muscle enriched tissues like mesenteric arteries. Moreover, the diurnal variations of bmal1 target genes per1/2 were abolished in mesenteric arteries. The isometric contractions in response to alpha1 agonist phenylephrine and to 5-HT were significantly diminished in vascular helical strips isolated from SM-bmal1-ko mice compared to that from control flox mice. The contractile diurnal variations detected in the renal arteries isolated from control flox mice were significantly diminished in samples isolated from SM-bmal1-ko mice. Moreover, in vivo , the diurnal variations in the instantaneous pressor responses to intravenous phenylephrine injection were significantly diminished in SM-bmal1-ko mice compared to control flox mice. Twenty four hour mean arterial blood pressure was significantly decreased under 12:12 light:dark, constant light or constant dark conditions. Importantly, the amplitude of blood pressure diurnal variations was significantly diminished in SM-bmal1-ko mice. Importantly, neither the level nor the diurnal variations of locomotor activity was affected by bmal1 deletion. This indicates that the central SCN clock function is not affected in the SM-bmal1-ko mice and the blood pressure alterations in SM-bmal1-ko mice is not a consequence of changed locomotor activity. Taken together, our results demonstrate an essential role of bmal1 in the diurnal variations of vascular smooth muscle contraction and blood pressure.