Early response of α2(I) collagen to acetaldehyde in human hepatic stellate cells is TGF-β independent

✍ Scribed by Gianluca Svegliati-Baroni; Yutaka Inagaki; Ana-Rosa Rincon-Sanchez; Cindy Else; Stefania Saccomanno; Antonio Benedetti; Francesco Ramirez; Marcos Rojkind

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 355 KB
• Volume: 42
• Category: Article
• ISSN: 0270-9139
• DOI: 10.1002/hep.20798

✦ Synopsis

Acetaldehyde is fibrogenic and induces the expression of type I collagen genes in hepatic stellate cells. Some of these acetaldehyde-dependent events are mediated by H 2 O 2 and thus establish a direct connection between oxidative stress and collagen upregulation. We localized to the ؊378 to ؊183 region of the ␣2(I) collagen (COL1A2) promoter an acetaldehyde-responsive element (AcRE) functional in human hepatic stellate cells (HHSCs) and investigated molecular mechanisms whereby acetaldehyde stimulates and modulates its transcriptional activity. Because the AcRE co-localized with a previously described transforming growth factor ␤ (TGF-␤)1-responsive element, and both acetaldehyde and this cytokine induce their effects through H 2 O 2 , we investigated whether all fibrogenic actions of acetaldehyde were mediated by this cytokine. Here we show that acetaldehyde-induced COL1A2 upregulation in HHSCs recognizes two distinct but overlapping early and late stages that last from 1 to 6 hours and from 6 to 24 hours, respectively. We present several lines of evidence to show that early acetaldehyde-mediated events are independent of TGF-␤1. These include significant timecourse differences in the expression of COL1A2 and TGF-␤1 mRNAs and inability of neutralizing antibodies to TGF-␤1 to inhibit acetaldehyde-dependent collagen gene transcription and Smad 3 phosphorylation. We also show that although acetaldehyde-dependent upregulation of collagen was PI3K dependent, that of TGF-␤1 was PI3K independent. In conclusion, acetaldehyde-dependent mechanisms involved in COL1A2 upregulation are similar, but not identical, to those of TGF-␤1. We suggest that early acetaldehyde-dependent events induce the late expression of TGF-␤1 and create an H 2 O 2 -dependent autocrine loop that may sustain and amplify the fibrogenic response of this alcohol metabolite. (HEPATOLOGY 2005;42:343-352.) A lcohol-induced liver fibrosis is multifactorial and involves local and systemic events. At the systemic level, multiple cytokines, including those involved in the acute phase response, play a role in the pathophysiology of the disease and contribute to the fibrogenic process inducing apoptosis and upregulating the expression of type I collagen and tissue inhibitor of metalloproteinase-1 mRNAs. [1][2][3][4][5][6] At the local level, fibrogenic mechanisms are quite complex and involve various cell types, including hepatocytes, Kupffer cells, and hepatic stellate cells (HSCs). [7][8][9][10][11][12][13][14] Whereas hepatocytes are the main cells involved in ethanol metabolism, Kupffer cells contribute with the production of cytokines, chemokines, and growth factors that play key roles in attracting inflammatory cells to injured sites and in activating and transdifferentiating HSCs to myofibroblasts, the main type I collagen-producing cells in the liver. 11,12 Some of the molecular mechanisms whereby the various hepatic cell types contribute to liver fibrogenesis have been unraveled. [11][12][13][14] However, important key events by which ethanol metabolized to acetaldehyde by hepatocytes activates production of type I collagen in HSCs remain to be fully elucidated. We have already shown that, in a functional co-culture system containing hepatocytes and HSCs, the former cells metabolize ethanol and the latter produce type I collagen. 15 We and others have shown that acetaldehyde is fibrogenic per se and induces the expression of the ␣1(I) collagen (Col1a1) gene [16][17][18] by a mechanism dependent on the accumulation of H 2 O 2 . 18 We further established that H 2 O 2 induces the activation, nuclear translocation, and DNA binding of members of the