Objective: Calcium is a key regulator of insulin secretion; yet, regulation of mitochondrial calcium handling is understudied in pancreatic β-cells. The mitochondrial calcium uniporter (MCU) and the mitochondrial sodium-calcium exchanger (NCLX) were identified as the major routes for calcium influx and efflux across the inner mitochondrial membrane, respectively. Previous studies have shown that reduced mitochondrial calcium in β-cells by MCU ablation during development does not cause glucose intolerance, but there are few studies that focus on mitochondrial calcium overload. Here, we assessed whether calcium overload by NCLX deletion in β-cells is sufficient to perturb glucose homeostasis in vivo. Hypothesis: Given that mitochondrial metabolic activity is calcium-dependent, we hypothesized that NCLX ablation would lead to excess mitochondrial calcium, impairing mitochondrial function, and thus, perturbing glucose homeostasis by reducing β-cell function or mass. Methods: NCLX fl/fl mice were bred with constitutively active Ins1-cre or the tamoxifen-inducible, Mip-creERTM transgenic models to allow for β-cell-specific deletion of the NCLX in the starting fetal stage 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 in adult animals. Data were analyzed by a Student’s t-test for single-variable comparisons or 2-way ANOVA for multiple dependent variable outcomes. Data: Control and βNCLXKO mice exhibited similar fasted and non-fasted glucose levels, and βNCLXKO mice presented comparable glucose and insulin tolerance to their control counterparts. 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, inducible deletion of the NCLX in mature β-cells (i-βNCLXKO) caused significant glucose intolerance in male mice (p< 0.05). Summary of results: 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 mitochondrial calcium regulation when the NCLX is deleted during development, whereas terminally differentiated β-cells fail to adapt to the acute deletion of the protein. Disclosure of funding sources: This work was funded by National Institutes of Health Grant (R01DK115720, R01DK136237, R56DK136293 to EUA; F31DK131860 to SJ; R25DK140753 to YY). This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Youn et al. (Fri,) studied this question.