Curcumin induces apoptosis in hepatic stellate cells via inhibition of the MyD88 pathway

Abstract

Turmeric (Curcuma longa L.) and its constituent curcumin exert positive effects on hepatic fibrosis in rat-models, inducing apoptosis and inhibiting proliferation of hepatic stellate cells (HSCs) [1]. Although some studies implicated a role for MyD88 in the development of fibrosis [2], the interaction of curcumin with this pathway is still unknown. HSCs were divided into four groups, namely control group (A), MyD88 siRNA group (B), curcumin group (C), and curcumin + MyD88 siRNA group (D). Groups B and D were subjected to transient transfection with siRNA for 48h. Groups C and D were incubated with curcumin (25 µmol/L) for 24h. MyD88 protein expression was observed by Western Blot, apoptosis was detected by flow cytometry, mRNA expression was detected by RT-PCR. Treatment with curcumin or MyD88 siRNA significantly reduced the expression of MyD88 in HSCs (both P < 0.05 vs. control), even more so if cells were treated with both agents simultaneously (P < 0.01 vs. control). Both curcumin and MyD88 siRNA inhibited the expression the cytokines TLR2, TLR4, NF-κB, TNF-1α, and IL-1B on the mRNA level. For curcumin these effects were significant for all five (all P < 0.05 vs. control). For MyD88 siRNA only the effects on NF-κB, TNF-1α, and IL-1B were significant (all P < 0.05 vs. control). For cells receiving both treatments, a significant inhibition of the expression of all five cytokines was observed (all P < 0.01 vs. control). Correspondingly, a significant induction of apoptosis was observed for both agents with apoptosis rate of 20% for the controls, 40% (P < 0.05 vs. control) for cell incubated with curcumin, 41% (P < 0.05 vs. control) for cells treated with MyD88 siRNA, and 47% (P < 0.01 vs. control) for cells receiving both treatments. This study shows that curcumin promotes apoptosis of HSCs by inhibiting the expression of Myd88 pathway related cytokines on the mRNA level.