ORF14-04 - Pancreatic Β-Cell Mitochondrial Ca² ⁺ Dysregulation Impairs Glucose Homeostasis through Sex-Dependent Mechanisms

Defective insulin secretion from pancreatic β-cells is a central driver of type 2 diabetes. Maintenance of intracellular Ca²⁺ homeostasis is critical for β-cell viability and function, with Ca²⁺ dynamically distributed among organelles such as the endoplasmic reticulum and mitochondria to support insulin biosynthesis and secretion. Mitochondrial Ca²⁺ is a key regulator of oxidative metabolism, redox balance and cell death in β-cells. The mitochondrial Ca²⁺ uniporter (MCU) mediates Ca²⁺ entry into the mitochondrial matrix and is upregulated in diabetic mouse models and lipid-exposed islets; however, whether this increase is adaptive or pathogenic remains unknown.
To directly test the consequences of enhanced mitochondrial Ca²⁺ uptake, we generated a β-cell–specific MCU overexpression mouse model (Ins1-Cre; CAG-CAT-MCU, βMCUOE). We hypothesized that chronic elevation of MCU expression induces mitochondrial Ca²⁺ overload, leading to β-cell dysfunction and impaired glucose homeostasis.
βMCUOE mice developed progressive, sex-dependent impairments in glucose homeostasis. Male βMCUOE mice exhibited age-dependent glucose intolerance, emerging by 28 weeks of age, whereas female βMCUOE mice displayed persistent, mild glucose intolerance from 8 to 28 weeks. In both sexes, glucose intolerance was associated with reduced in vivo glucose-stimulated insulin secretion (GSIS), implicating impaired β-cell function as a primary defect.
Mechanistic analyses revealed divergent pathways underlying β-cell dysfunction. Male βMCUOE mice exhibited reduced β-cell mass, with preserved islet insulin secretory capacity, while female βMCUOE mice maintained normal β-cell mass but displayed intrinsic defects in islet insulin secretion ex vivo. Bulk RNA sequencing demonstrated only 26.1% overlap in differentially expressed genes between sexes, indicating fundamentally distinct transcriptional responses to mitochondrial Ca²⁺ overload. Male βMCUOE islets showed enrichment of cell survival and stress-response pathways, whereas female islets exhibited induction of acinar/exocrine gene programs. Immunohistochemical analyses confirmed an increased population of insulin/amylase co-positive cells in female βMCUOE islets, suggesting altered β-cell identity.
Together, these findings identify excessive mitochondrial Ca²⁺ uptake as a pathogenic driver of β-cell failure and demonstrate that mitochondrial Ca²⁺ overload disrupts glucose homeostasis through distinct, sex-specific mechanisms. These data position mitochondrial Ca²⁺ regulation as a critical determinant of β-cell fate and a potential therapeutic target in diabetes.