Smooth Muscle Cells-Expressed Bmal1 Regulates Vascular Calcification Independent of the Canonical Circadian Pathway

Vascular calcification is a major cardiovascular issue that increases morbidity and mortality in diabetes patients. While dysregulation of the circadian master regulator Basic Helix-Loop-Helix ARNT-Like Protein 1 (Bmal1) in vascular smooth muscle cells (VSMC) under diabetic conditions has been suggested, its role in vascular calcification is unclear. In VSMC, Bmal1 was upregulated under high glucose treatment and in aortic tissues from a diabetic mouse model. RNA sequencing from isolated VSMC between Bmal1 deletion and wildtype mice indicated Bmal1's pro-calcification role. Indeed, reduced levels of the osteogenic master regulator, Runt-Related Transcription Factor 2 (Runx2), were found in Bmal1 deletion VSMC under diabetic conditions. Alizarin red staining showed reduced calcification in Bmal1 deletion VSMC in vitro and vascular rings ex vivo . Furthermore, in a diabetic mouse model, SMC-Bmal1 deletion showed reduced calcium deposition in aortas. Collectively, diabetes-upregulated circadian regulator Bmal1 in VSMC contributes to vascular calcification. Maintaining normal circadian regulation may improve vascular health in diabetes.