Surgical Adhesions derived from MSLN-Positive Mesothelium Cells. Mus musculus strain:B6(Cg)-Tyrc-2J/J

Peritoneal adhesions are fibrous tissues that tether organs to one another or to the peritoneal wall and are a significant cause of post-surgical and infectious morbidity. Previous studies suggest that hematopoietic/lymphoid cells, cytokines, and fibrindeposition from various mesenchymal sources play a role in promoting adhesion formation. However, the primary chain of events leading to the initiation of adhesions has been elusive, chiefly due to the lack of identifiable cells of origin. Here we identify cells of the injured surface mesothelium that express transmembrane proteins podoplanin (PDPN) and mesothelin (MSLN), as the primary cells of origin for peritoneal adhesions. We have previously shown that mesothelial cells are stem cells for abdominal and thoracic organ smooth muscle cells and fibroblasts. Here we show by clonal analysis andlineage tracing methods that adhesions are formed from expansions of MSLN+PDPN+ mesothelial cells. Using RNA sequencing and bioinformatics analyses on purified injured mesothelial cells, we reveal the pathological mechanism of adhesion development and some of its candidate regulators. We show that hypoxia inducible factor 1 alpha (HIF1α) is an early and necessary regulator of adhesion development. Inhibition of the HIF1α signaling pathway largely ameliorates the injury program in damaged mesothelial cells, and diminishes adhesion severity. A combined anti-MSLN and anti-CD47 antibody mediated immunotherapy diminishes preformed adhesions, clearing mesothelial surfaces of all adhesion inducing cell subsets. Analyses of human adhesion tissue suggest that similar pathways and surface markers contribute to human disease. These results highlight the critical role mesothelial cells play in adhesion formation and demonstrate multiple new and promising therapeutic approaches for treatments of adhesions, with broad clinical implications that may extend to various fibrotic diseases.