2215-LB: MCU Overexpression and NCLX Ablation in β-Cells—How Increasing Mitochondrial Ca 2+ Affects Glucose Homeostasis

Introduction and Objective: Calcium (Ca²⁺) is a key regulator of aerobic metabolism; yet, regulation of mitochondrial Ca²⁺ handling is understudied in pancreatic β-cells. The mitochondrial calcium uniporter (MCU) and mitochondrial sodium-calcium exchanger (NCLX) were identified as the major routes for Ca²⁺ influx and efflux across the inner mitochondrial membrane. Prior studies have shown that reduced mitochondrial Ca²⁺ in β-cells by MCU ablation does not cause glucose intolerance, but few studies focus on mitochondrial Ca²⁺ overload. Here, we assessed whether Ca²⁺ overload by MCU overexpression or NCLX deletion in β-cells is sufficient to perturb glucose homeostasis in vivo. Given that mitochondrial metabolic activity is Ca²⁺-dependent, we hypothesized that MCU overexpression or NCLX ablation would lead to excess mitochondrial Ca²⁺, thus causing perturbations in glucose homeostasis by β-cell failure.Methods: Glucose was administered i.p. to examine glucose homeostasis in vivo, and primary pancreatic islets were isolated for in vitro measurements of insulin secretion and oxygen consumption rates (OCR). Data were analyzed by a Student’s t-test for single variable comparisons or 2-way ANOVA for multiple dependent variable outcomes.Results: MCU overexpression led to significant glucose intolerance that progressively worsened with age in both male and female mice in vivo (p<0.05), but the mechanisms by which intolerance developed were sexually dimorphic; intolerance was driven by reduced β-cell mass in males and reduced β-cell function in females. In contrast, βNCLXKO mice presented comparable glucose tolerance to their control counterparts but exhibited significantly reduced glucose-stimulated insulin secretion (p<0.05) and OCR (p<0.05) at the islet level in vitro.Conclusion: Collectively, these data suggest that NCLX ablation is insufficient to induce glucose intolerance in vivo, whereas regulation of mitochondrial Ca²⁺ entry via the MCU is critical in glucose homeostasis in a sexually dimorphic manner.

Y. Youn: None. S. Jo: None. E. Alejandro: None.

Minnesota Postbaccalaureate Research Education Program in Diabetes, Endocrinology and Metabolic Diseases (1R25DK140753)



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