Increased Superoxide and eNOS Uncoupling in Blood Vessels of Bmal1-KO mice
Rationale: Disruption of the circadian clock in mice produces vascular dysfunction as evidenced by impairments in endothelium-dependent signalling, vasomotion, and blood vessel remodeling. While altered function of endothelial nitric oxide synthase (eNOS) and the overproduction of reactive oxygen species (ROS) are central to dysfunction of the endothelium, to date, the impact of the circadian clock on eNOS coupling and vascular ROS production is not known.
Objective: The goals of the current study were to determine if deletion of a critical component of the circadian clock, Bmal1, can influence eNOS coupling and ROS levels in arteries from Bmal1-KO mice.
Methods and Results: Endothelial function was reduced in aortae from Bmal1-KO mice and improved by scavenging ROS with PEG-SOD and non-selectively inhibiting cyclooxygenase isoforms with indomethacin. Aortae from Bmal1-KO mice exhibited enhanced superoxide levels as determined by EPR spectroscopy and DHE fluorescence, an elevation that was abrogated by administration of L-NAME. HPLC analysis revealed a reduction in tetrahydrobiopterin and an increase in dihydrobiopterin levels in the lung and aorta of Bmal1-KO mice while supplementation with BH4 improved endothelial function in the circadian clock knockout mice. Furthermore, levels of BH4, BH2, and the key enzymes that regulate biopterin bioavailability, GTP-cyclohydrolase (GTPCH-1) and dihydrofolate reductase (DHFR), exhibited a circadian expression pattern.
Conclusions: Having an established influence in the metabolic control of glucose and lipids, herein, we describe a novel role for the circadian clock in metabolism of biopterins, with a significant impact in the vasculature, to regulate coupling of eNOS, production of superoxide, and maintenance of endothelial function.
- Endothelial nitric oxide synthase
- Uncoupling protein
- Vascular endothelium
- Received November 30, 2011.
- Accepted August 17, 2012.
- Copyright © 2012, American Heart Association