Bmal1 Downregulation Worsens Critical Limb Ischemia by Promoting Inflammation and Impairing Angiogenesis

Critical limb ischemia (CLI) is the most advanced clinical stage of peripheral vascular disease with high mobility and mortality. CLI patients suffer from lower extremity rest pain, ulceration, and gangrene caused by insufficient blood and oxygen supply. Seeking for effective biomarkers and therapeutic targets is of great significance for improving the life quality of CLI patients. The circadian clock has been reported to be involved in the progression of kinds of cardiovascular diseases. Whether and how circadian genes play a role in CLI remains unknown. In this study, by collecting femoral artery and muscle specimens of CLI patients who underwent amputation, we confirmed that the circadian gene Bmal1 is downregulated in the CLI femoral artery and ischemic distal lower limb muscle. Furthermore, we verified that Bmal1 affects CLI by regulating lipid metabolism, inflammation, and angiogenesis. A hindlimb ischemia model performed in wild-type and Bmal1^-/- mice confirmed that Bmal1 disruption would lead to impaired angiogenesis. In vitro experiments indicated that the decreased expression of Bmal1 would increase ox-LDL uptake and impair endothelial cell functions, including proliferation, migration, and tube formation. As for mechanisms, Bmal1 represses inflammation by inhibiting lipid uptake and by activating IL-10 transcription and promotes angiogenesis by transcriptionally regulating VEGF expression. In conclusion, we provide evidence that the circadian gene Bmal1 plays an important role in CLI by inhibiting inflammation and promoting angiogenesis. Thus, Bmal1 may be an effective biomarker and a potential therapeutic target in CLI.