Transforming growth factor β₁induces the expression of α1(i) procollagen mRNA by a hydrogen peroxide-C/EBPβ-dependent mechanism in rat hepatic stellate cells

Abstract

Oxidative stress plays a key role in liver fibrosis. Both inflammatory cells and activated Kupffer cells produce H2O2, an oxidant involved in the activation of hepatic stellate cells (HSC). Increased production of reactive oxygen intermediates (ROIs) in fibrotic livers is associated in part with the up-regulation of transforming growth factor beta (TGF-beta), and this cytokine enhances collagen production by cultured HSC. However, the possible link between oxidative stress and the molecular mechanisms by which TGF-beta induces collagen gene expression in HSC remains to be elucidated. To address this question, we investigated whether H2O2 is a mediator of TGF-beta-elicited alpha1(I) collagen gene (col1a1) up-regulation. We demonstrated that TGF-beta induces the accumulation of H2O2, and that this oxidant is, in turn, directly involved in up-regulating the expression of the col1a1 gene. While the addition of H2O2 to HSC induced the expression of alpha1(I) procollagen mRNA, catalase, an H2O2 enzyme scavenger, abrogated TGF-beta-mediated col1a1 gene up-regulation. We transfected HSC with chimeric plasmids driven by different segments of the mouse col1a1 promoter and mapped a cis-acting element (-370 to -344) essential for TGF-beta responsiveness. We further showed that TGF-beta induced the activation and binding of a C/EBPbeta-containing transcriptional complex to this sequence, an effect that was also mimicked by the addition of H2O2. Taken together, these data demonstrate a direct connection between TGF-beta-mediated accumulation of H2O2 and the up-regulation of col1a1 gene in HSC.

Zinc supplementation attenuates ethanol- and acetaldehyde-induced liver stellate cell activation by inhibiting reactive oxygen species (ROS) production and by influencing intracellular signaling

“…Of particular interest is the interaction between TGF- and ROS formation. In cultured HSCs, TGF- increases the production of hydrogen peroxide [32], which in turn induces the expression of 1(I) procolagen mRNA [33,34]. The direct profibrogenic effect of hydrogen peroxide has also been observed in co-cultures of HSCs with HepG2 cells overexpressing CYP2E1 [35].…”

Tumor necrosis factorα down-regulates expression of theα1(I) collagen gene in rat hepatic stellate cells through a p20C/EBPβ- and C/EBPδ-dependent mechanism

“…Reporter plasmids used in this study, driven by the sequences Ϫ412 to ϩ110 (Ϫ412col1a1CAT), Ϫ378 to ϩ110 (Ϫ378col1a1CAT), Ϫ345 to ϩ110 (Ϫ345col1a1CAT), and Ϫ220 to ϩ110 (Ϫ220col1a1CAT) of the mouse col1a1 gene have been described previously. 15,19 Integrity and orientation of these constructs were verified by DNA sequencing. HSC were cotransfected with 15 µg of each construct plus 3 µg of a luciferase control plasmid, pGL3-Basic (Promega, Madison, WI), using the calcium phosphate method.…”

“…15 We showed that TGF-␤ 1 induces the activation and binding to the TbRE of a protein complex that contains C/EBP␤, and demonstrated that H 2 O 2 acts as a second messenger of TGF-␤ 1 -mediated col1a1 gene up-regulation. 15 Because TNF-␣ is known to antagonize TGF-␤ 1 -mediated actions, 16 we considered it important to investigate whether the col1a1 TbRE plays any role in TNF-␣-mediated col1a1 down-regulation. In this article, we report that the TNF-␣-responsive element (TaRE) of the col1a1 gene colocalizes with the TbRE.…”

Role of free radicals in liver diseases

“…These cells, when activated, produce and secrete cytokines; cytokines may be proinflammatory, such as TNF-a and IL-1, or profibrotic, such as TGF-b. These proteins can further increase ROS and play important roles in the mediation of hepatic injury [23,[85][86][87], such as fatty liver, by inhibiting lipase of lipoprotein and adiponectin and fibrosis as a result of HSC activation [88][89][90].…”