Metformin alleviates auditory cell senescence by mitophagy induction

Age-related hearing loss is the most common type of hearing loss in older adults. However, its underlying cellular mechanism is still unclear. Impaired mitochondrial function is a hallmark of various age-related pathologies. To maintain mitochondrial function in senescent cells, mitophagy is a crucial process for dysfunctional mitochondria turnover. Metformin has been reported to induce mitophagy. This study aimed to investigate the effect of metformin on preventing senescence in auditory cells. Low-dose H₂O₂ represented senescence-associated secretory phenotype (SASP) and reduced mitophagy-related molecules in House Ear Institute-Organ of Corti 1 (HEI-OC1) cells and cochlear explants. Metformin significantly decreased the expression of SASP in H₂O₂-induced senescent cells. Metformin also decreased the expression of senescence-associated p53 and p21, and increased the expression of mitophagy-related PINK1, Parkin, and BNIP3 in H₂O₂-induced senescent cells and cochlear explants. The co-localization of mitophagy dye and lyso dye decreased in H₂O₂-induced senescent cells, but metformin pre-treatment significantly increased their colocalization. Metformin significantly decreased the percentage of β-galactosidase-stained senescent cells and increased the expression of OXPHOS complexes in H₂O₂-induced senescent cells and cochlear explants. Metformin also significantly increased mitochondrial function in senescent cells. These results indicate that metformin prevented premature senescence in auditory cells by counteracting reduced mitophagy. Therefore, maintaining mitochondrial function using metformin might be a potential strategy for the prevention of age-related hearing loss.