Extracellular Succinate Derived From Ectopic Milieu Drives Adhesion and Implantation Growth of Endometrial stromal cells via the SUCNR1 signal in endometriosis

Abstract

Abstract Background As a dual-function metabolite, succinate has emerged in cell function and plays a key signaling role in linking mitochondrial function to other cellular functions. Succinate accumulation in the cytoplasm is commonly associated with hypoxia in the microenvironment and immune cell activation. Meanwhile, extracellular succinate released into the microenvironment is considered an inflammatory alarm that can be sensed by its membrane receptor SUCNR1, boosts proinflammatory responses and acts akin to classical hormones and cytokines. Succinate has been reported to play an important role in inflammatory disease. It is worth exploring whether succinate can facilitate the progress of endometriosis (EMs), which is characterized by chronic inflammation and peritoneal adhesion. Objective To evaluate the main source and potential role of succinate in endometriosis, we mimics the ectopic milieu in vitro and in vivo. The molecular and functional effects of succinate on macrophages and peritoneal mesothelial cells in peritoneal cavity were assessed. The succinate/SUCNR1 signal acting on ectopic endometrial stromal cells (ESCs) was further explored in this study. Methods In this study, we used targeted organic acid metabolomics analysis and in vitro assay to assess whether there was an obvious accumulation of succinate in the peritoneal fluid of EMs patients and its correlated with disease severity, Visual Analogue Scale (VAS), and the Endometriosis Fertility Index (EFI). Flow cytometry, Enzyme linked immunosorbent assay (ELISA), western-blot assay, and quantitative real-time PCR, and other molecular biology techniques were used for exploring the potential mechanisms. Results By mimicking the ectopic milieu, we constructed an in vitro co-culture system and found that M1 polarized macrophages and the peritoneal mesothelial cell line (HMrSV5) mainly released succinate into their microenvironment and activated the succinate receptor (SUCNR1) signal, which further polarizes macrophages and significantly enhances the invasive survival of ESCs, and the adhesion with peritoneum. We further investigated the pathological effect of extracellular succinate in vivo using xenograft mouse models of endometriosis. Conclusions Collectively, the succinate-SUCNR1 signal facilitates in creating the inflammatory nice and plays a vital role in EMs progression and peritoneal adhesion. Our work on the molecular mechanism of succinate accumulation and function will be helpful to elucidate the phenotypic mystery of pain and infertility in EMs.