Mitochondrial complex I subunit deficiency promotes pancreatic α-cell proliferation

OBJECTIVE: There is strong evidence that mitochondrial DNA mutations and mitochondrial dysfunction play a role in diabetes pathogenesis. The homozygous knock-in mtDNA mutator mouse is a model of premature aging due to the accumulation of mitochondrial DNA mutations. We used this mouse model to investigate the relationship between mitochondrial subunit expression and pancreatic islet cell composition. METHODS: Quadruple immunofluorescence was used to quantify mitochondrial subunit expression (complex I and IV) and cell composition in pancreatic islets from mitochondrial DNA mutator mice (PolgA(mut/mut)) and control C57BL/6 mice at 12 and 44 weeks of age. RESULTS: Mitochondrial complex I subunit expression was decreased in islets from 12 week PolgA(mut/mut) mice. This complex I deficiency persisted with age and was associated with decreased insulin staining intensity at 44 weeks. Complex I deficiency was greater in α-cells compared with β-cells in islets from 44 week PolgA(mut/mut) mice. Islet cell composition was normal in 12 week PolgA(mut/mut) mice, but the β: α cell ratio was decreased in islets from 44 week PolgA(mut/mut) mice. This was due to an increase in α-cell number linked to an increase in α-cell proliferation. CONCLUSION: Complex I deficiency promotes α-cell proliferation and alters islet cell composition.