1138-OR: Mitochondrial Calcium Signaling Promotes Thermogenic Adipocyte Differentiation

Introduction and Objective: Thermogenic adipocytes enhance energy expenditure and improve glucose metabolism. Mitochondrial calcium signaling has emerged as a regulator of thermogenic programming, but whether it governs the differentiation and recruitment of thermogenic adipocytes remains unknown. The mitochondrial calcium uniporter complex, composed of the pore-forming subunit MCU and its regulatory partner MICU1, is a key gatekeeper of mitochondrial calcium uptake. We hypothesized that MCU and MICU1 control thermogenic adipocyte differentiation and systemic metabolic function. Methods: Gain- and loss-of-function of MCU and MICU1 were performed in human white and brown preadipocytes during adipogenesis. Mitochondrial structure, calcium-dependent respiration, UCP1 expression, and thermogenic capacity were assessed in vitro. Diet-induced obese mice with preadipocyte-specific MCU/MICU1 deficiency underwent metabolic phenotyping. RNA sequencing and motif analyses identified downstream regulators, which were subsequently validated using gene-knockout approaches. Results: Combined deletion of MCU and MICU1 in brown preadipocytes impaired mitochondrial integrity, reduced calcium-stimulated thermogenesis, and suppressed UCP1 induction. Conversely, co-overexpression of MCU and MICU1 in human white preadipocytes enhanced mitochondrial biogenesis, oxidative capacity, and thermogenic gene expression. Mice lacking MCU/MICU1 in brown preadipocytes exhibited exacerbated diet-induced metabolic dysfunction. Transcriptomic analyses identified enrichment of MAF-binding motifs among differentially expressed genes. Consistently, MAF knockout abolished MCU/MICU1-driven increases in UCP1 expression, mitochondrial activity, and thermogenesis. Conclusion: MCU and MICU1 are critical regulators of thermogenic adipocyte differentiation and function via an MAF-dependent pathway. These findings establish mitochondrial calcium handling as a key determinant of thermogenic adipocyte recruitment and metabolic homeostasis. Disclosure T. Tsuji: None. C. Wang: None. L. Wu: None. C. Yang: None. T. Huang: None. Y. Tseng: Consultant; Ended; Paratus Sciences. Consultant; Current; Sofinova Partners. Funding MGH NORCH P Joslin DRC P&F Program (5P30 DK036836-39).