Long-term exposure of indoxyl sulfate induces mesothelial-to-mesenchymal transition of peritoneal mesothelial cells via β-catenin-involved signaling pathway.

Background: Long-term peritoneal dialysis (PD) leads to peritoneal injury, with mesothelial-to-mesenchymal transition (MMT) potentially serving as an initial and reversible stage of this process. Indoxyl sulfate (IS), a protein-bound uremic toxin that accumulates in patients with declining renal function, is known to be associated with epithelial-mesenchymal transition (EMT) in proximal renal tubular cells. However, its effects on peritoneal mesothelial cells, which serve as the first-line barrier during PD, have not yet been investigated.

Objectives: This study aimed to evaluate whether IS induces MMT in human peritoneal mesothelial cells during PD through the β-catenin signaling pathway.

Material And Methods: A human peritoneal mesothelial cell line (HMrSV5) was used for this in vitro study. Cells were treated with IS or combined with β-catenin inhibitor ICG-001, and high glucose PD fluid (PDF) served as a positive control. Morphology, proliferation and adhesion were assessed, while the expression of β-catenin and α-smooth muscle actin (α-SMA) as mesenchymal markers, along with E-cadherin as a mesothelial marker, were analyzed at both RNA and protein levels using real-time polymerase chain reaction (PCR) and western blot, respectively.

Results: The number of viable and adherent cells was significantly increased in the IS and PDF groups compared to the control (p < 0.05). Treatment with ICG-001 significantly reduced both viable and adherent cell numbers compared to cells treated with IS or PDF alone (p < 0.05). At the RNA level, IS treatment significantly decreased E-cadherin expression (p = 0.002) while significantly increasing β-catenin (p = 0.001) and α-SMA (p = 0.002) expression compared to the control group. These changes were reversed by ICG-001 treatment. Protein expression showed similar trends.

Conclusions: Indoxyl sulfate induces MMT in human peritoneal mesothelial cells, and these changes can be reversed by the specific β-catenin inhibitor ICG-001. This suggests that IS may be considered as another inducer of MMT during PD through the β-catenin signaling pathway.