Unveiling the mechanism of miR‑122‑5p in the mediation of forkhead box O3 (FOXO3) in regards to cochlear hair cell damage provides an effective solution for the treatment of ear hearing disorders. An oxidative stress model using a mouse cochlear hair cell line (HEI‑OC1) was established via hydrogen peroxide (H₂O₂). Then HEI‑OC1 cells were transfected with miR‑122‑5p mimic, miR‑122‑5p inhibitor, and lentiviral vector FOXO3‑WT/MUT. Cell viability and apoptosis rate were determined by MTT assay and flow cytometry. Reactive oxygen species (ROS) were observed by confocal laser scanning microscopy. Bcl‑2, Bax, capase‑3 and c‑caspase‑9 levels were quantified by western blot analysis and quantitative reverse transcription polymerase chain reaction (RT‑qPCR). Enzyme‑linked immunosorbent assay (ELISA) was used to detect superoxide dismutase (SOD) and malondialdehyde (MDA) levels, and flow cytometry was performed to measure the mitochondrial membrane potential levels. In the HEI‑OC1 oxidative stress model after transfection, the miR‑122‑5p level was decreased, whereas the FOXO3 level was increased, Moreover, the increased FOXO3 level diminished the cell viability, but promoted cell apoptosis. Apart from this, the Bcl‑2 level was downregulated, while levels of Bax, c‑caspase‑3, c‑caspase‑9, ROS and MDA were upregulated. Meanwhile, the mitochondrial membrane potential level was also elevated. Overexpression of miR‑122‑5p was able to partially offset the effects of FOXO3 in the H₂O₂‑treated HEI‑OC1 cells. Collectively, miR‑122‑5p restrained the decrease in HEI‑OC1 cell viability and apoptosis induced by treatment with H₂O₂.

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