BackgroundOvarian ageing causes endocrine disturbances and the degeneration of systemic tissue and organ functions to seriously affect women's physical and mental health, and effective treatment methods are urgently needed. Based on our previous studies using juvenile rhesus monkey bone marrow mesenchymal stem cells (BMMSCs) to treat ovarian ageing in rhesus monkey, we found that BMMSCs improved ovarian structure and function. This study continues to explore the mechanism by which BMMSCs reversed granulosa cell (GC) ageing.MethodsA GC ageing model and coculture system of BMMSCs were established, changes in the level of the N6-methyladenosine (m6A) methylation modification were detected, m6A-modified RNA immunoprecipitation sequencing (MeRIP-seq) were performed, correlations between m6A peaks and mRNA expression were determined, and the expression of hub genes was identified using Q-PCR, immunofluorescence staining, and western blot.ResultsOur results showed that H2O2successfully induced GC ageing and that BMMSCs reversed measures of GC ageing. BMMSCs increased the expression of the FTO protein and reduced the overall level of m6A. We identified 797 m6A peaks (348 hypomethylated and 449 hypermethylated peaks) and 817 differentially expressed genes (DEGs) (412 upregulated and 405 downregulated) after aged GCs were cocultured with BMMSCs, which significantly associated with ovarian function and epigenetic modification. The epigenetic repressive mark and important cell cycle regulator lysine demethylase 8 (KDM8) was downregulated at both the mRNA and protein levels, histone H3 was upregulated in aged GCs after BMMSC coculture, and KDM8 was upregulated after FTO was inhibited through FB23.ConclusionsOur study revealed an essential role for m6A in BMMSCs in reversing GC ageing, and FTO regulated KDM8 mediates histone H3 changes may as a novel regulatory mechanism in BMMSCs to reverse GC ageing.Graphical AbstractSupplementary InformationThe online version contains supplementary material available at 10.1007/s12015-022-10485-y.