Melatonin attenuates Drp1-mediated excessive mitochondrial fission through upregulation of SIRT1 in granulosa cells in polycystic ovary syndrome

In brief It remains unclear whether mitochondrial fission in granulosa cells contributes to polycystic ovary syndrome pathogenesis and mitochondrial dysfunction, and what role melatonin plays. This study elucidates the mechanism by which melatonin ameliorates mitochondrial function in polycystic ovary syndrome by suppressing excessive mitochondrial fission. Abstract Mitochondrial dysfunction in granulosa cells (GCs) has been implicated in polycystic ovary syndrome (PCOS) pathogenesis. Dynamin-related protein 1 (Drp1)-mediated mitochondrial fission is critical for maintaining intact mitochondrial function. This study aims to investigate whether mitochondrial fission contributes to mitochondrial dysfunction in the GCs of individuals with PCOS and the molecular effects of melatonin on mitochondrial fission. Transmission electron microscopy of human GCs showed that the mitochondria exhibited a condensed and small spherical morphology with a tendency toward fragmentation in PCOS patients. At the molecular level, GCs from patients with PCOS presented significant increases in both the p-Drp1(Ser616)/(Ser637) ratio and mitochondrial fission factor (MFF). In a dihydrotestosterone (DHT)-induced PCOS-like mouse model, excessive mitochondrial fission in GCs was similarly observed, characterized by fragmented mitochondrial morphology via transmission electron microscopy and increased expression of the mitochondrion-localized Drp1 (mito-Drp1) protein. Similarly, in vitro experiments demonstrated that DHT treatment increased the expression of mito-Drp1, the p-Drp1(Ser616)/(Ser637) ratio, and MFF in KGN cells. Melatonin treatment effectively reversed these abnormalities, restoring mitochondrial morphology, reducing fission markers (mito-Drp1, the p-Drp1 ratio, and MFF), decreasing mitochondrial reactive oxygen species, and enhancing mitochondrial membrane potential. Mechanistically, melatonin upregulated sirtuin-1, which restored the imbalance of Drp1 phosphorylation and blocked its MFF-dependent mitochondrial recruitment, thereby attenuating Drp1-mediated excessive mitochondrial fission. Our findings reveal a novel protective mechanism of melatonin in PCOS via the sirtuin-1-Drp1 signaling axis, offering a potential therapeutic target for PCOS management.