Curcumin Interferes with TGF- β 1-Induced Fibrosis in NRK-49F Cells by Reversing ADAMTS18 Gene Methylation.

Objective: To explore the molecular mechanism by which curcumin affects renal interstitial fibrosis (RIF) progression by regulating ADAM metallopeptidase with thrombospondin type 1 motif 18 (ADAMTS18) methylation.

Methods: NRK-49F cells RIF model were induced with transforming growth factor β 1 (TGF- β 1). Effects of different concentrations of curcumin (0, 10, 20, and 30 μmol/L) on cell proliferation, cell cycle, cell apoptosis as well as cyclin D1 expression were analyzed by cell counting kit-8, flow cytometry and Western blot, respectively. ADAMTS18 methylation levels were determined by methylation-specific polymerase chain reaction. ADAMTS18, fibronectin (FN), type I collagen (Col- I) and alpha-smooth muscle actin (α -SMA) mRNA and protein expressions were analyzed by real-time PCR (RT-PCR) and Western blot, respectively. Meanwhile, cells were treated with 50 mmol/L 5-aza-2'-deoxycytidine (5-aza-dC, demethylation agent) for 72 h. Effect of curcumin on extracellular matrix (ECM) deposition was evaluated by immunochemical staining and Western blot. NRK-49F cells were transfected with ADAMTS18 small interfering RNA and grouped into a normal control, ADAMTS18-knock-out (KO), and ADAMTS18-KO+ 30 μmol/L curcumin groups, and whether curcumin can reverse the effect of ADAMTS18 knockdown on RIF was evaluated.

Results: Compared with the control group, TGF-β 1 significantly inhibited the proliferation of NRK-49F cells, blocked the G₁/G₀ phase, promoted cell apoptosis and inhibited cyclin D1 expression (P<0.01). Among the different concentrations of curcumin, 30 μmol/L curcumin significantly reversed these processes (P<0.01). Immunochemical staining and Western blot results showed that curcumin significantly inhibited the deposition of FN, Col- I and α-SMA (P<0.01). Curcumin and 5-zaz-dC had synergistic effects, promoting ADAMTS18 expression, removing ADAMTS18 methylation, and reducing ECM deposition. ADAMTS18 knockdown promoted ECM accumulation, and curcumin reversed this process (P<0.01).

Conclusion: TGF-β 1-induced fibrosis in NRK-49F cells. Curcumin promoted ADAMTS18 expression, reduced ECM accumulation, and alleviated RIF progression by inhibiting ADAMTS18 methylation.