Thymopentin promotes ovarian angiogenesis in mice by activating N6-methyladenosine (m6A) RNA modification of key factors in the Notch/Tie1 pathway

Abstract: BACKGROUND: Premature ovarian failure (POF) is a typical condition of pathological ovarian ageing. Injuries and atrophies of blood vessels in the ovaries can lead to ovarian insufficiency, but the underlying mechanism remains unclear. AIMS: This study investigated the epigenetic mechanism by which thymopentin (TP-5) activated ovarian angiogenesis to achieve its effects on POF. MATERIALS AND METHODS: The qPCR, western blot and immunofluorescence staining were used to detecte the expression levels of gene. The hematoxylin and eosin stainingwas used to histopathological examination. The RNA-Seq sequencing was used to transcriptome detection. RESULTS: First, pathological examination revealed that TP-5 significantly increased ovary weight in the cyclophosphamide-induced POF mouse model. The proportion of atretic follicles was reduced, and the level of E2 in the peripheral blood was elevated. Meanwhile, immunofluorescence staining showed that TP-5 increased protein expression of CD31 and Tie1 in the ovarian tissues of mice with POF, suggesting that TP-5 could induce ovarian angiogenesis. RNA-Seq sequencing results suggested that TP-5 could induce the high level of Notch/Tie2 pathway expression that is associated with angiogenesis in ovarian tissues. qPCR and western blotting showed significantly increased expression of METTL3, a methyltransferase that catalyses the formation of N6-methyladenosine (m6A) in RNA. Meanwhile, the results of the dot blot suggested that the overall RNA methylation level was significantly higher in the ovarian tissues of mice in the TP-5 group than in the control group. Finally, RIP-PCR analysis showed that specific sites in the 3'-untranslated region (3'UTR) of the mRNA of key factors in the Notch/Tie2 pathway were hypermethylated in the ovaries of mice in the TP-5 treatment group. CONCLUSION: Therefore, this study demonstrated that TP-5 exerted its therapeutic effect on POF by stimulating angiogenesis. The mechanism of action is the promotion of the expression of RNA m6A methyltransferases by TP5, which increases the overall RNA m6A methylation level in mouse ovarian tissue. Specifically, the methylation ofspecific m6A sites in the 3'UTR of the RNA of key factors in the Notch/Tie2 pathway increased, which enhanced their stability and expression levels, leading to the induction of angiogenesis.