Context: Activation of hepatic stellate cells (HSCs) is a hallmark of liver fibrosis. Quercetin has benefits for liver fibrosis, but the mechanisms are unknown.
Objective: We investigated the quercetin effect on HSC survival and the role of endoplasmic reticulum stress (ERS).
Materials and methods: Rat HSCs and LO2 hepatocytes were treated with quercetin (0.5-120 μM) for 24 h. Quercetin (10-40 μM) effects on apoptosis for 24 h were analyzed by flow cytometry and TUNEL staining. Quercetin (10-40 μM) effects on the expression of Bcl-2, caspase-9, caspase-3, PARP-1, PERK, IRE1, ATF6, calnexin and CHOP for 24 h were analyzed by Western blot. Quercetin (10-40 μM) effects on mRNA expression of calnexin and CHOP for 24 h were analyzed by Real-time PCR.
Results: Quercetin at concentrations greater than 20 μM significantly inhibited HSC proliferation (IC50 27.2 μM), but did not affect hepatocyte growth until 80 μM (IC50 68.5 μM). Quercetin stimulated HSC apoptosis and the apoptotic rate reached 40% at a concentration of 40 μM (EC50 51.6 μM). Quercetin induced downregulation of Bcl-2 and upregulation of Bax, and increased cytochrome C in the cytoplasm in HSCs. The cleaved forms of caspase-9, caspase-3 and PARP-1 were also increased by quercetin. Furthermore, quercetin elevated mRNA and protein expression of calnexin and CHOP in HSCs but not in hepatocytes. Quercetin also increased phosphorylation of PERK and IRE1 and ATF6 cleavage. However, ERS inhibitor salubrinal significantly abrogated quercetin induction of HSC apoptosis.
Conclusion: Quercetin activated ERS pathway in HSCs leading to apoptosis. We characterized an ERS-mediated mechanism for quercetin as a promising antifibrotic agent.
Keywords: Bcl-2; Hepatic fibrosis; hepatocyte; salubrinal.