Alteration of gut microbiota contributes to peritoneal fibrosis through increased production of trimethylamine N-oxide.

Peritoneal fibrosis is a common complication in peritoneal dialysis (PD) patients, which results in ultrafiltration failure (UFF) and PD withdrawal. PD patients demonstrate altered structural and functional profiles of the gut microbiota. Herein, we investigated the role of the gut microbiota and trimethylamine N-oxide (TMAO), a bacterial metabolite, in the pathogenesis of PD-associated peritoneal fibrosis. PD mice displayed mesenchymal transition features and fibrosis in the peritoneum, which were accompanied by an altered gut microbiota profile and elevated serum TMAO levels, and these peritoneal histologic abnormalities were ameliorated by gut microbiota depletion. Fecal microbiota transplantation (FMT) from PD patients induced mesenchymal and fibrotic alterations within the peritoneum of wild-type mice, and the effect was more pronounced in mice receiving FMT from PD patients with UFF. Intraperitoneal supplementation with TMAO enhanced PD-induced peritoneal fibrosis in wild-type mice. On the contrary, PD- or FMT-induced mesenchymal features and fibrosis within the peritoneal membrane were lessened in flavin-containing monooxygenase 3 gene knockout mice, which were incapable of synthesizing TMAO. TMAO treatment enhanced high glucose-mediated phenotypic transition and fibrogenesis in cultured peritoneal mesothelial cells and fibroblasts, partly by increasing TGF-β1 synthesis and secretion and subsequent phosphorylation of Smad2/3 and activation of the Wnt/β-catenin pathway. Collectively, we found that altered gut microbiota plays an important role in the development of PD-associated peritoneal fibrosis through dysregulated production of the bacterial metabolite TMAO.