NR1D1 (REV-ERBα) is a heme-binding nuclear receptor that functions as a transcriptional repressor coordinating circadian rhythms and metabolic homeostasis 1. As a core component of the circadian clock, NR1D1 directly represses clock genes including BMAL1, CLOCK, and CRY1, while also suppressing inflammatory cytokines and interleukin-6 expression 2. The receptor recognizes specific DNA response elements and recruits the NCOR1/HDAC3 corepressor complex in a heme-dependent manner to enhance transcriptional repression 1. Beyond circadian function, NR1D1 regulates diverse metabolic pathways including lipid and bile acid metabolism, gluconeogenesis, and adipogenesis 1. In vascular smooth muscle cells, NR1D1 represses aconitase-2 (ACO2), a mitochondrial tricarboxylic acid cycle enzyme, and its dysregulation contributes to abdominal aortic aneurysm development 3. NR1D1 also modulates hepatic stellate cell lipophagy through Rab7 ubiquitination, controlling lipid droplet metabolism in liver fibrosis 4. Clinically, NR1D1 represents a promising therapeutic target. Synthetic NR1D1 agonists improve circadian behavior, reduce obesity, and ameliorate dyslipidemia and hyperglycemia in diet-induced obese mice 5. In rheumatoid arthritis, NR1D1 activation suppresses NLRP3 inflammasome signaling, reducing inflammatory cytokines 6. These findings establish NR1D1 as a critical nexus integrating circadian regulation with metabolic and immune homeostasis.