Introduction and Objective: Calcium is a key regulator of insulin secretion; yet, regulation of mitochondrial calcium handling is understudied in pancreatic β-cells. Here, we assessed whether mitochondrial calcium (mtCa2+) overload by deletion of the mitochondrial sodium-calcium exchanger (NCLX) in β-cells is sufficient to perturb glucose homeostasis in vivo. Given that mitochondrial metabolic activity is calcium-dependent, we hypothesized that NCLX ablation would lead to excess mtCa2+, impairing mitochondrial function and perturbing glucose homeostasis by reducing β-cell function or mass.Methods: NCLX fl/fl mice were bred with constitutively active, Ins1-cre (βNCLXKO) or the tamoxifen-inducible, Ins1-creERTM (i-βNCLXKO) transgenic models to allow for β-cell-specific deletion of the NCLX in developing or mature β-cells. Glucose and insulin were 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. Data were analyzed by a Student’s t-test or 2-way ANOVA.Results: Control and βNCLXKO mice exhibited similar fasted and non-fasted glucose levels, as well as comparable glucose and insulin tolerance. Moreover, β-cell mass was comparable between genotypes. However, our findings show significantly reduced glucose-stimulated insulin secretion (p<0.001) and oxygen consumption rates (p<0.05) in βNCLXKO compared to littermate controls at the islet level in vitro. In contrast, male i-βNCLXKO mice presented transient glucose intolerance at four weeks post-induction (p<0.05).Conclusion: These data suggest that deletion of the NCLX in β-cells reduces the level of insulin release, likely due to impaired mitochondrial function, but this reduction only leads to significant perturbations in glucose homeostasis upon deletion in mature β-cells. These results suggest that there may be a physiological adaptation in mtCa2+ regulation, whether the NCLX is deleted during development or in terminally differentiated β-cells.
Y. Youn: None. S. Jo: None. E. Alejandro: None.
National Institutes of Health (R01DK115720, R01DK136237, R56DK136293, F31DK131860, R25DK140753)
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