Cathepsin S regulates renal fibrosis in mouse models of mild and severe hydronephrosis.

As a member of the cysteine protease family, cathepsin S (CTSS) serves an important role in diseases such as cancer, arthritis and atherosclerosis. Nevertheless, its role in renal fibrosis is unknown. In the present study, the effects of CTSS on renal fibrosis in mild (group M) and severe (group S) hydronephrosis were studied by reverse transcription‑-quantitative PCR (RT‑qPCR), western blot analysis (WB), Masson's trichrome staining and immunohistochemical staining in mouse models. The effects of CTSS on extracellular matrix (ECM) deposition and epithelial‑mesenchymal transition (EMT) and the potential mechanisms were further studied by RT‑qPCR and WB in transforming growth factor (TGF‑β1)‑stimulated TCMK‑1 cells. Compared with group N (no hydronephrosis), the expression levels of CTSS in the M and S groups were significantly higher, and a significant increase in ECM deposition was observed in the S group. In addition, compared with group N, the expression levels of TGF‑β1, α‑smooth muscle actin (α‑SMA), SMAD2, SMAD3, phosphorylated (p)SMAD2 and pSMAD3 in groups M and S were significantly higher, whereas the expression of E‑cadherin was significantly lower. Inhibition of CTSS expression increased the expression levels of TGF‑β1, α‑SMA, fibronectin, collagen‑I, SMAD2, SMAD3, pSMAD2 and pSMAD3, whereas E‑cadherin expression decreased. A significant increase in CTSS was observed in the TGF‑β1‑stimulated TCMK‑1 cell line. ECM deposition and EMT were also intensified. The opposite outcomes occurred after intervention with small interfering RNA targeting CTSS. In conclusion, CTSS affected EMT and the deposition of ECM. CTSS may mediate the regulation of fibrosis by the TGF‑β/SMAD signaling pathway. CTSS may serve an important role in the treatment of renal fibrosis.