Extra Domain A-Spliced Fibronectin Variant Contributes to Peritoneal Inflammation and Fibrosis in a Murine Model of Peritoneal Fibrosis

Background: Peritoneal dialysis (PD) is an important mode of renal replacement therapy but preservation of the structural and functional integrity of the peritoneal membrane is a major challenge limiting the feasibility of long-term treatment. Onset of tissue fibrosis is characterized by the presence of fibronectin (FN) isoforms including extra domain A-spliced FN variant (EDA-FN). We investigated the role of EDA-FN in a murine model of PD. Methods: Male wild-type (WT) and EDA-FN knockout (KO) mice were randomized to receive saline (Control Group) or glucose-based PD fluid containing 40 mM methylglyoxal (PDF Group) by intra-peritoneal injection twice daily for 4, 8 and 12 weeks, after which time the parietal peritoneum was harvested to investigate peritoneal membrane histology and expression of mediators of inflammation and fibrosis using a combination of qPCR, Western blot analysis and cytochemical staining. Human peritoneal mesothelial cells were isolated from omentum to investigate the mechanism of EDA-FN induction. Results: PDF-treated WT mice developed submesothelial thickening after 12 weeks compared to saline-treated mice, accompanied by a marked influx of immune cells and mesothelial cell denudation. EDA-FN gene expression was increased in the peritoneal membrane of PDF-treated mice (1.00 ± 0.13 vs 15.46 ± 9.83 arbitrary units, saline vs PDF, p = 0.0095), accompanied by increased gene and/or protein expression of TGF-β1, IL-1β, IL-6, native FN, collagen I and III, α-smooth muscle actin and Adgre1 (F4/80). PDF-induced peritoneal membrane pathology and thickening were markedly reduced in EDA-FN KO mice compared to WT mice, with reduced immune cell infiltration and mediators of inflammation and fibrosis. In cultured mesothelial cells, PDF induced native FN and EDA-FN expression through the synergistic effect of TGF-β1 and IL-1β. Conclusion: Our data suggest that increased peritoneal EDA-FN expression in PDF-treated mice contributes to peritoneal inflammation and fibrosis in PD. Funding: Government Support – Non-U.S.