Oncostatin-M: a novel leukocyte-derived factor facilitating the ovulatory process in the human ovary

STUDY QUESTION: Does leukocyte-derived Oncostatin-M (OSM) regulate the ovulatory process in human dominant follicles? SUMMARY ANSWER: Leukocyte-derived OSM activates key signaling pathways in human preovulatory granulosa cells and modulates steroidogenesis, prostaglandin synthesis, and tissue remodeling in human ovulatory follicles. WHAT IS KNOWN ALREADY: Leukocytes are essential regulators of ovulation. Our recent single-cell RNA sequencing (scRNA-seq) has identified diverse leukocyte subpopulations in follicular aspirates obtained from IVF patients and revealed the expression of OSM in leukocytes and its receptors (OSMR, LIFR, IL6ST) in follicular cells. However, the function of leukocyte-derived OSM in human ovulatory follicle remains unclear. STUDY DESIGN, SIZE, DURATION: This study analyzed dominant follicles from naturally cycling women (n ¼ 19) across the periovulatory period and follicular aspirates from IVF patients (n ¼ 12). Primary human granulosa/lutein cells (hGLCs) treated with hCG and/ or recombinant human OSM (rhOSM) were used to assess its functional effects. PARTICIPANTS/MATERIALS, SETTING, METHODS: Our recent scRNA-seq dataset was used to identify cell types expressing OSM and its receptors in human follicular aspirates. The expression of OSM and its receptors was assessed in dominant follicles by quantitative PCR (qPCR) and immunohistochemistry. hGLCs were treated with hCG and/or rhOSM, and functional analyses included qPCR, western blotting, RNA sequencing, and hormone assays for progesterone (P4), estradiol (E2), and prostaglandin E2 (PGE2) production. MAIN RESULTS AND THE ROLE OF CHANCE: Bioinformatics analysis of scRNA-seq revealed that OSM is exclusively expressed in leukocytes, whereas its receptors are predominantly expressed in granulosa cells. Immunohistochemistry and qPCR analyses exhibited increased OSM expression in leukocytes and receptor expression in granulosa cells, respectively, after ovulatory hCG administration (P < 0.05). Western blotting demonstrated that rhOSM treatment activated STAT3, ERK1/2, AKT, and p38MAPK pathways in hGLCs. RNA sequencing and following qPCR revealed rhOSM-induced significant transcriptional changes in genes involved in steroidogenesis, prostaglandin synthesis/transport, inflammation, and tissue remodeling (FDR < 0.05). Functionally, rhOSM increased P4 and PGE2 secretion (P < 0.05) while decreasing E2 production (P < 0.05), suggesting a role in ovulation and luteinization. LARGE SCALE DATA: RNA sequencing datasets are available in the Gene Expression Omnibus under accession number GSE277343. LIMITATIONS, REASONS FOR CAUTION: This study was conducted using in vitro hGLC cultures, which may not fully recapitulate in vivo ovulatory dynamics. Additionally, the findings are specific to human samples and require validation in other mammalian species. WIDER IMPLICATIONS OF THE FINDINGS: These results suggest that leukocyte-derived OSM is a key cytokine regulating ovulatory events, providing novel insights into the immunoendocrine crosstalk within the human follicle. This study enhances our understanding of cytokine-mediated follicular maturation and may have implications for improving ovulation-related fertility treatments. STUDY FUNDING/COMPETING INTERESTS: This study was supported by grants P01HD71875 (to M.J. and T.E.C.), R01HD096077 (to M. J.), R03HD095098 (to Y.C.), and R01HD115554 (to Y.C.). The authors declare no competing interests.