Peritoneal mesothelial cells give rise to myofibroblasts via mesothelial‐mesenchymal transition in peritoneal fibrosis (60.10)

Abstract

Mesothelial cells (MCs) cover the surface of the internal organs, and the peritoneal cavities as it have a phenotype intermediate between epithelial and mesenchymal cells, expressing markers indicative of both cell types. Peritoneal mesothelium is used as a semipermeable barrier for the exchange of toxic substance in peritoneal dialysis, a renal failure therapy. When peritoneal MCs are exposed to non‐physiological dialysis fluids in long term, tissue fibrosis and failure of treatment occurs. Myofibroblasts (MFs) synthesize excessive extracellular matrix proteins and participate in peritoneal fibrosis. However, the origin of MFs remains obscure. Epithelial‐mesenchymal transition (EMT), typically defined by the loss of E‐cadherin and up regulation of mesenchymal markers, been suggested to involved in this process. However, as MCs do not express E‐cadherin, this mechanism needs to be clarified as we propose mesothelial‐mesenchymal transition (MMT) instead of EMT. In the present study, we examined whether peritoneal MCs undergo MMT and give rise to MFs in mouse peritoneal fibrosis induced by injections of chlorhexidine gluconate (CG) solution. Peritoneal MCs expressed glycoprotein M6A (GPM6A), vimentin, cytokeratin 19, and Wilms tumor 1 (WT1). We isolated peritoneal MCs from mice using antibodies against GPM6A and magnetic beads. In culture, MCs formed epithelial colonies and changed shape to myofibroblastic cells in the presence of TGF‐β. To trace lineages of peritoneal MCs, we used Wt1‐CreERT2 and Rosa26mTmGflox mice. By tamoxifen injection, we specifically labeled peritoneal MCs as GFP+ cells. After injections of CG, most of the single MC layer was eliminated and GFP+ MFs accumulated in the fibrotic area of the peritoneum. Interestingly, when we stopped injections of CG, the mesothelial layer re‐formed and some of MCs expressed GFP in the regenerating mesothelium. These results demonstrate that mesothelial cells are the source of myofibroblasts in peritoneal fibrosis.Grant Funding Source: Supported by NICHD T32 Training Program