Regulation of the Circadian Clock in Human Blood Vessels

Abstract

Approximately 5–10% of the mammalian genome oscillates with a circadian rhythm. Changes in gene expression are orchestrated by core circadian clock genes including Bmal1 and clock/NPAS2 which increase expression by target genes by binding to promoter E‐boxes. In contrast, Per and Cry genes reciprocally inhibit the activity of Bmal1:Clock/NPAS2. Recent studies revealed that expression of circadian clock genes, Bmal1, Clock, Per and Cry oscillate in murine arteries. We hypothesized that gene expression in human blood vessels is subject to circadian regulation. To investigate whether circadian genes oscillate in human blood vessels over time, we extracted RNA from saphenous veins and analyzed the ex‐vivo mRNA expression of clock genes for 24 hours at 3 hour interval. Surprisingly we found that the expression of core circadian genes failed to oscillate in saphenous veins. Studies in mice have shown that oscillation in gene expression in arteries is more robust than veins. Future studies are planned with human mammary arteries to confirm this in humans. To investigate the molecular regulation of circadian rhythms in vitro, we have generated circadian reporter cells using a bmal1‐luc lentivirus. In U20S cells we have recorded robust changes in luminescence over a 24 hour cycle. We plan to employ this lentivirus to explore the differences in circadian rhythmicity in human endothelial cells from different vascular beds.