Reduced DNMT1 expression associated with TP53 promoter hypomethylation mediate enhanced granulosa cell senescence during ovarian aging

BACKGROUND: The effects of granulose cell (GC) senescence on premature ovarian insufficiency/premature ovarian failure have been extensively examined, the association between GC senescence and ovarian aging remains to be clarified. METHODS: Human and mouse GCs from young/control and old/advanced maternal age (AMA) groups were collected, and GC senescence was determined. The role of the DNMT1-p53 axis in GC senescence during ovarian aging was examined and validated in a KGN cell senescence model. RESULTS: SA-beta-gal-positive GCs were significantly increased in the AMA group, accompanied by activation of the p53-p21 pathway, which was also found in GCs from aged mice and H₂O₂-induced senescent KGN cells. Pyrosequencing methylation analysis revealed that increased expression of p53 was associated with decreased average methylation levels of CpG sites (-1031, -1019, -1012 and -1008) within the P53 promoter CpG island in senescenct GCs and KGN cells. We further found that decreased DNA-methyltransferase 1 (DNMT1) expression was responsible for the reduced methylation levels of the CpG sites. CONCLUSION: Decreased DNMT1 with hypomethylation of the CpG sites within the P53 promoter CpG island in GCs is involved in ovarian aging.