ROS-driven mitochondrial and mtDNA release as a novel pathway of metabolic injury in diabetes

Mitochondrial dysfunction driven by chronic hyperglycemia is a hallmark of diabetes, yet how this metabolic stress communicates pathological signals beyond individual cells remains poorly understood. In this study, we identified a novel mechanism linking chronic hyperglycemia to systemic metabolic impairment through ROS-mediated extracellular release of structurally intact mitochondria and mitochondrial DNA (mtDNA). In HepG2 cells exposed to high glucose (HG), extracellular release of structurally intact mitochondria was visualized by co-staining of mitochondria and the plasma membrane, together with electron microscopy. Mitochondria-enriched fractions isolated from culture supernatants were further quantified using flow cytometry and qPCR. Cell-free mtDNA (cf-mtDNA) was visualized with co-staining of mitochondria and double-stranded DNA, isolated through differential centrifugation and ultrafiltration, and quantified by qPCR. We demonstrate that HG stimulates the release of exosome-enclosed mtDNA and fragmented cf-mtDNA. Concurrently, HG induces mitochondrial dysfunction and markedly increases mitochondrial ROS (mtROS). Treatment with MitoTEMPO, a mitochondria-targeted ROS scavenger, significantly reduced HG-induced extracellular release of mitochondria and mtDNA, supporting the ROS dependence of this process. In diabetic mice, we detected elevated circulating mtDNA copy number and pronounced mitochondrial dysfunction in liver and muscle, including reduced ATP production, mitochondrial swelling, cristae disruption, and elevated MDA levels. Resting metabolic rate was markedly decreased, indicating impaired systemic respiratory metabolism. Serum analyses revealed increased 8-OHdG, pyruvic acid, GDF-15, and FGF-21, along with reduced FT3, reflecting severe oxidative stress and mtDNA damage. These findings uncover a novel mechanism in which hyperglycemia-induced ROS drive mitochondrial extrusion, potentially linking metabolic stress to systemic metabolic deterioration.