Inhibition of inhibitor of κB kinases stimulates hepatic stellate cell apoptosis and accelerated recovery from rat liver fibrosis

Background & Aims: Resolution of liver fibrosis is associated with clearance of hepatic myofibroblasts by apoptosis; development of strategies that promote this process in a selective way is therefore important. The aim of this study was to determine whether the inhibitor of κB kinase suppresser sulfasalazine stimulates hepatic myofibroblast apoptosis and recovery from fibrosis. Methods: Hepatic myofibroblasts were generated by culture activation of rat and human hepatic stellate cells. Fibrosis was established in rat livers by chronic injury with carbon tetrachloride followed by recovery with or without sulfasalazine (150 mg/kg) treatment. Results: Treatment of hepatic stellate cells with sulfasalazine (0.5–2.0 mmol/L) induced apoptosis of activated rat and human hepatic stellate cells. A single in vivo administration of sulfasalazine promoted accelerated recovery from fibrosis as assessed by improved fibrosis score, selective clearance of smooth muscle α-actin-positive myofibroblasts, reduced hepatic procollagen I and tissue inhibitor of metalloproteinase 1 messenger RNA expression, and increased matrix metalloproteinase 2 activity. Mechanistic studies showed that sulfasalazine selectively blocks nuclear factor-κB-dependent gene transcription, inhibits hepatic stellate cell expression of Gadd45β, stimulates phosphorylation of Jun N-terminal kinase 2, and promotes apoptosis by a mechanism that is prevented by the Jun N-terminal kinase inhibitor SP600125. As further evidence for a survival role for the inhibitor of κB kinase/nuclear factor-κB pathway in activated hepatic stellate cells, a highly selective cell-permeable peptide inhibitor of κB kinase activation also stimulated hepatic stellate cell apoptosis via a Jun N-terminal kinase-dependent mechanism. Conclusions: Inhibition of the inhibitor of κB kinase/nuclear factor-κB pathway is sufficient to increase the rate at which activated hepatic stellate cells undergo apoptosis both in vitro and in vivo, and drugs that selectively target inhibitor of κB kinase have potential as antifibrotics.

Abbreviations used in this paper:  HSC, hepatic stellate cells , IκB, inhibitor of κB , IKK, inhibitor of κB kinase , IL, interleukin , JNK, Jun N-terminal kinase , MMP, matrix metalloproteinase , MPT, mitochondrial permeability transition , NBD, NEMO-binding domain , NF-κB, nuclear factor-κB , α-SMA, α-smooth muscle actin , TIMP1, tissue inhibitor of metalloproteinase 1 , TMRM, tetramethylrhodamine methylester , TNF, tumor necrosis factor , TUNEL, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling