Molecular mechanisms regulating the antifibrogenic protein heme-oxygenase-1 in human hepatic myofibroblasts

Background/Aims Hepatic myofibroblasts are central in liver fibrogenesis associated with chronic liver diseases. We previously showed that heme-oxygenase-1 (HO-1) displays antifibrogenic properties in human hepatic myofibroblasts. Here, we further investigated the mechanisms regulating HO-1 expression. Methods Expression of HO-1 was assayed in cultured human hepatic myofibroblasts by Northern and Western blot. Functional studies were also performed in cultured human hepatic myofibroblasts. Results 15-Deoxy-Δ12,14-prostaglandin J2 (15-d-PGJ2) elicited inhibition of proliferation and of α1(I) collagen mRNA expression. These effects were reproduced by the glutathione depletor diethyl maleate and blunted by the glutathione precursor N-acetyl cysteine, indicating the involvement of oxidative stress. Two consecutive events mediated inhibition of proliferation and of α1(I) collagen mRNA expression by 15-d-PGJ2: (i) mild oxidative stress characterized by a transient GSH decrease and (ii) activation of p38 MAPK, resulting in increased HO-1 mRNA stability. Conclusions Our results provide new insights into the regulatory mechanisms governing HO-1 expression in human hepatic myofibroblasts and identify mild oxidative stress and p38 MAPK as two consecutive early signals promoting HO-1 induction that are crucial for its antifibrogenic properties, namely inhibition of growth and extracellular matrix gene expression.