The clock‐output gene DBP regulates muscle insulin sensitivity and its fluctuations

OBJECTIVE: Circadian rhythm disruption is associated with metabolic disorders, yet the role of clock genes in glucose metabolism remains unclear. D-box binding protein (DBP) is a clock output gene that activates the D-box, and we used systemic Dbp knockout (KO) mice to investigate DBP's role in glucose metabolism. METHODS: We generated two independent KO mouse lines. Intraperitoneal insulin tolerance tests (IPITTs) were performed in 13-week-old male mice at zeitgeber time (ZT) 1 and ZT 13. To assess hepatic and muscle insulin sensitivity, we examined 2-deoxy-D-glucose (2DG) content and AKT phosphorylation followed by transcriptome analysis using muscle. RESULTS: In the KO mice, enhanced insulin sensitivity was observed in ZT1 following IPITT compared to wild-type (WT) mice, but not in ZT13. These findings indicate that while systemic insulin sensitivity fluctuates throughout the day in WT mice, it does not fluctuate in KO mice. Increased glucose uptake and AKT phosphorylation in gastrocnemius muscle (GM), but not the liver, were observed in KO mice at ZT1. Plasma nonesterified fatty acid (NEFA) levels were reduced during the inactive phase in KO mice. Muscle transcriptome analysis identified chemokine and cytokine-related pathways as the most enriched, including C-C motif chemokine ligand 5 (CCL5) and its receptor C-C chemokine receptor type 5 (CCR5). CONCLUSION: Muscle insulin sensitivity oscillates, with a reduction during the inactive phase. This study demonstrates that DBP deficiency suppresses circadian fluctuations of muscle insulin sensitivity, likely via plasma NEFA and CCL5-CCR5 signaling. DBP plays a role in circadian regulation of muscle insulin sensitivity.