MON-264 Molecular Mechanisms of Progesterone Receptor in Inguinal Hernia Formation via Skeletal Muscle Fibrosis and Atrophy

Abstract Disclosure: T. You: None. N.C. Piehl: None. M. Zandigohar: None. T. Potluri: None. R. Lieber: None. J. Stulberg: None. H. Zhao: None. S.E. Bulun: None. Introduction: Inguinal hernias are incredibly common, affecting up to 27% of men in their lifetime. Despite this high prevalence, non-surgical approaches are unavailable to treat this disease, as the molecular mechanisms underlying hernia formation are poorly understood. We previously showed that concurrent exogenous administration of estradiol (E2) and progesterone (P4) in male mice led to the development of large scrotal hernias. These hernias were caused by fibrosis and atrophy of the lower abdominal muscle (LAM) tissue. This process was related to LAM fibroblasts that expressed high levels of estrogen receptor alpha (ESR1) and ESR1-induced progesterone receptor (PGR). We also found that co-administration of RU486 (P4/PGR antagonist) in these E2/P4-treated mice prevented hernia development. However, the downstream mechanisms through which P4/PGR signaling causes LAM fibrosis remain unknown. Methods: Histologic analysis and single-nuclei (sn) multiomic (snRNA+snATAC) sequencing were performed on LAM tissue of WT mice treated with Vehicle (Veh), E2+P4 (EP), and E2+P4+RU486 (EPR) for 8-10 weeks. Findings were validated utilizing Xenium spatial transcriptomics in mouse LAM and multiplex RNA in situ hybridization in LAM from human hernia patients. Results: All WT mice treated with EP developed large hernias (>225mm2) within 2-4 weeks of treatment while mice treated with Veh or EPR did not develop hernias. LAM of EP-treated mice had significantly increased fibrosis and decreased myofiber area. snRNA-sequencing revealed a unique population of Esr1+/Pgr+ fibroblasts only present in EP LAM that had upregulated expression of profibrotic/proinflammatory genes. Cell-type proportion analysis also showed that EP LAM had significantly decreased myofibers and increased mesothelial-like cells compared to Veh and EPR LAM. Utilizing cell-cell communication inference and spatial transcriptomics, we provide evidence that these Pgr+ fibroblasts utilize Tgfb2 signaling to communicate with Pgr- fibroblasts/mesothelial-like cells to induce profibrotic gene expression (Tgfbr2, Plod2, and Adamts19) and with myofibers to induce myofiber atrophy-associated gene expression (Fbxo32, Trim63). Pgr+/Pgr- fibroblasts, mesothelial-like cells, and atrophying myofibers were also found in herniated LAM from human patients. These cell types had increased expression of Tgfb2, Tgfbr2, or myofiber atrophy genes in herniated LAM compared to adjacent healthy muscle. Conclusion: Our results suggest that P4/PGR signaling in highly P4-sensitive LAM tissues is critical for LAM fibrosis and hernia development partially via TGFB2 signaling. Our findings are one of the first to show the importance of PGR signaling in men and provide evidence that PGR antagonists may be useful as a therapeutic alternative to hernia repair surgery. Presentation: Monday, July 14, 2025