[Influence of celastrol on toll-like receptor 4-mediated signaling pathway in the free fatty acids-induced HepG2 cells].

To investigate the effect and mechanism of celastrol on free fatty acids (FFAs)-induced HepG2 cells. Cultured human HepG2 cells were transfected with toll-like receptor 4 (TLR4) siRNA, and the interference efficiencies were examined by real-time PCR. HepG2 cells were treated with FFAs and celastrol, and the untreated cells were used as a normal control (NC). Deposition of lipids in the HepG2 cells were visualized by Oil Red O staining. The protein expression of TLR4 and downstream inflammatory mediators [myeloid differentiation factor 88 (MyD88), nuclear factor (NF)-κBp65, interleukin (IL)-1β and tumor necrosis factor α (TNF-α)] in the HepG2 cells were determined by Western blotting. The significance of the data obtained was evaluated using analysis of variance (ANOVA). Red lipid droplets were extensively deposited in HepG2 cells after 0.5 mmol/L FFAs induction and significantly decreased in the celastrol-treated group. The protein expression of TLR4 and downstream inflammatory mediators (MyD88, NF-κBp65, IL-1β and TNF-α) in the FFAs-induced HepG2 cells increased significantly compared with those of the NC group (all <0.05), and were suppressed in TLR4 siRNA-treated and celastrol-treated group (TLR4: 0.69±0.14, 1.63±0.12 vs 2.46±0.23; MyD88: 1.21±0.12, 1.35±0.18 vs 1.62±0.19; NF-κBp65: 1.69±0.14, 1.54±0.36 vs 2.19±0.47; IL-1β: 1.51±0.16, 1.45±0.38 vs 1.82±0.27; TNF-α: 1.60±0.14, 1.41±0.29 vs 1.88±0.19) (all <0.01). Co-treatment with TLR4 siRNA and celastrol further reduced the expression of inflammation mediators compared with those of the TLR4 siRNA-treated group (MyD88: 1.09±0.23 vs 1.21±0.12; NF-κBp65: 1.24±0.20 vs 1.69±0.14; IL-1β: 1.28±0.31 vs 1.51±0.16; TNF-α: 1.10±0.29 vs 1.60±0.14) (all <0.01). Celastrol exerts its protective effect partly via inhibiting the TLR4-mediated signaling pathways in the steatotic HepG2 cells.