286 : Circus Recurrent Pregnancy Loss by Modulating SETD1B/H3K4me2/me3 LoopK40 Regulates Cell Survival and Participates in

Background and Aims: The epigenetic mechanisms involved in the etiology of unexplained recurrent pregnancy loss (uRPL) is largely unknown. This study aims to investigate the molecular mechanisms of circRNAs modulating decidua function by regulating methylation modification of histones and whereby participating in uRPL. Method: RNA sequencings on decidua of uRPL couples and endometrial stromal cells (ESCs) after overexpressed with circSTK40 were performed to confirm the regulatory relationship between circSTK40 and SETD1B. Functional experiments including TUNEL, autophagy double-label system, the tests of glucose intake, lactic acid production were performed to determine the effects of circSTK40 and SETD1B on ESCs. Mechanism studies were conducted using RNA pulldown, RNA binding protein immunoprecipitation, chromatin immunoprecipitation et al. Results: The expression levels of circSTK40 and SETD1B were significantly downregulated in the decidua of uRPL patients, and a positive regulatory relationship was observed between them. Both circSTK40 and SETD1B promoted cell survival and participated in the maintenance of pregnancy by regulating apoptosis, autophagy and glycolysis of decidualized ESCs. After the knockdown of SETD1B, the protective effect of circSTK40 could be eliminated, resulting in elevated apoptosis, reduced autophagy level and increased cellular glycolysis, leading to pregnancy loss. Regarding mechanism studies, circSTK40 is directly bound to SETD1B and histone H3 to promote their interaction and increase the methylation level of H3K4. H3K4me2 and H3K4me3 reversely bound to the promoter region of SETD1B and enhanced its transcription, resulting in upregulation of SETD1B, and consequently formed a SETD1B/H3K4me2/3 regulatory loop. Conclusion: CircSTK40 influences cell survival by modulating the SETD1B/H3K4me2/me3 regulatory loop. Downregulation of circSTK40 and SETD1B in decidua may contribute to uRPL via promoting cell apoptosis. Our findings indicate a novel epigenetic mechanism for uRPL pathogenesis involving circSTK40 activity and histone methylation modification.