Blockade of thrombospondin‐1 ameliorates high glucose‐induced peritoneal fibrosis through downregulation of TGF‐β1/Smad3 signaling pathway

BACKGROUND: Transforming growth factor-β1 (TGF-β1) is a profibrotic cytokine which induces mesothelial cell mesothelial-to-mesenchymal transition (MMT) and peritoneal fibrosis in patients receiving treatment of peritoneal dialysis. Because thrombospondin-1 (TSP-1) is able to activate latent TGF-β1 in vivo, we investigated whether blockade of TSP-1 could modulate mesothelial cell MMT and ameliorate peritoneal fibrosis. METHODS: Human pleural mesothelial cells (Met-5A cells) were treated with TSP-1 and addition of TGF-β1 neutralizing antibody to assess the effect of TSP-1 on MMT. Furthermore, TSP-1 blocking peptide Leu-Ser-Lys-Leu (LSKL) was applied to Met-5A cells treated with 4.25% d-glucose to determine its function in high glucose-induced MMT. Consequently, a uremic dialysate injection rat model was set up to confirm the results in vivo. RESULTS: Exposure of Met-5A cells to TSP-1 increased TGF-β1 secretion, expression and bioactivity, triggered Smad3 phosphorylation, upregulated the expression of mesenchymal molecules including fibronectin, collagen type III, α-smooth muscle actin, Snail, and decreased calretinin expression. The effect was partially attenuated by TGF-β1 neutralizing antibody. TSP-1 expression in Met-5A cells was increased by 4.25% d-glucose, followed by increased secretion and bioactivity of TGF-β1, the onset of Smad3 phosphorylation and induction of MMT. LSKL significantly attenuated high glucose-mediated mesothelial cell MMT and ameliorated peritoneal fibrosis in uremic rats receiving dextrose dialysate injection. CONCLUSIONS: Taken together, these data demonstrated that TSP-1 contributes to mesothelial cell MMT by activating TGF-β1/Smad3 signaling pathway and blockade of TSP-1 attenuates high glucose-mediated mesothelial cell MMT and peritoneal fibrosis.