Increased superoxide and endothelial NO synthase uncoupling in blood vessels of Bmal1-knockout mice.
BACKGROUND
Disruption of the circadian clock in mice produces vascular dysfunction as evidenced by impairments in endothelium-dependent signaling, vasomotion, and blood vessel remodeling. Although the altered function of endothelial NO synthase and the overproduction of reactive oxygen species are central to dysfunction of the endothelium, to date, the impact of the circadian clock on endothelial NO synthase coupling and vascular reactive oxygen species production is not known.


OBJECTIVE
The goals of the present study were to determine whether deletion of a critical component of the circadian clock, Bmal1, can influence endothelial NO synthase coupling and reactive oxygen species levels in arteries from Bmal1-knockout (KO) mice.


RESULTS
Endothelial function was reduced in aortae from Bmal1-KO mice and improved by scavenging reactive oxygen species with polyethylene glycol-superoxide dismutase and nonselectively inhibiting cyclooxygenase isoforms with indomethacin. Aortae from Bmal1-KO mice exhibited enhanced superoxide levels as determined by electron paramagnetic resonance spectroscopy and dihydroethidium fluorescence, an elevation that was abrogated by administration of nitro-l-arginine methyl ester. High-performance liquid chromatography analysis revealed a reduction in tetrahydrobiopterin and an increase in dihydrobiopterin levels in the lung and aorta of Bmal1-KO mice, whereas supplementation with tetrahydrobiopterin improved endothelial function in the circadian clock KO mice. Furthermore, levels of tetrahydrobiopterin, dihydrobiopterin, and the key enzymes that regulate biopterin bioavailability, GTP cyclohydrolase and dihydrofolate reductase 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 endothelial NO synthase, production of superoxide, and maintenance of endothelial function.
Department of Pharmacology and Toxicology, Georgia Health Sciences University, Augusta, GA 30912, USA.
Ciprian B
CB
Anea
Bo
B
Cheng
Shruti
S
Sharma
Sanjiv
S
Kumar
R William
RW
Caldwell
Lin
L
Yao
M Irfan
MI
Ali
Ana M
AM
Merloiu
David W
DW
Stepp
Stephen M
SM
Black
David J R
DJ
Fulton
R Daniel
RD
Rudic
D056930:ARNTL Transcription Factors / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001011:Aorta / Q000166:cytology / Q000378:metabolism*; D001158:Arteries / Q000166:cytology / Q000378:metabolism*; D001708:Biopterins / Q000031:analogs & derivatives / Q000378:metabolism; D002478:Cells, Cultured; D057906:Circadian Clocks / Q000502:physiology*; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism; D006136:GTP Cyclohydrolase / Q000378:metabolism; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D023421:Models, Animal; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism
D056930:ARNTL Transcription Factors; C538961:Bmal1 protein, mouse; D017382:Reactive Oxygen Species; D013481:Superoxides; D001708:Biopterins; C017226:7,8-dihydrobiopterin; D052250:Nitric Oxide Synthase Type III; D013762:Tetrahydrofolate Dehydrogenase; D006136:GTP Cyclohydrolase; C003402:sapropterin