Early response of alpha2(I) collagen to acetaldehyde in human hepatic stellate cells is TGF-beta independent.
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 alpha2(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 beta (TGF-beta)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-beta1. These include significant time-course differences in the expression of COL1A2 and TGF-beta1 mRNAs and inability of neutralizing antibodies to TGF-beta1 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-beta1 was PI3K independent. In conclusion, acetaldehyde-dependent mechanisms involved in COL1A2 upregulation are similar, but not identical, to those of TGF-beta1. We suggest that early acetaldehyde-dependent events induce the late expression of TGF-beta1 and create an H(2)O(2)-dependent autocrine loop that may sustain and amplify the fibrogenic response of this alcohol metabolite.
Svegliati-Baroni
Gianluca
G
Clinica di Gastroenterologia, Universita Politecnica delle Marche, Ancona, Italy.
Inagaki
Yutaka
Y
Rincon-Sanchez
Ana-Rosa
AR
Else
Cindy
C
Saccomanno
Stefania
S
Benedetti
Antonio
A
Ramirez
Francesco
F
Rojkind
Marcos
M
D000079:Acetaldehyde / Q000633:toxicity*; D002478:Cells, Cultured; D003094:Collagen / Q000235:genetics*; D024042:Collagen Type I; D004268:DNA-Binding Proteins / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008103:Liver Cirrhosis / Q000139:chemically induced*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D051900:Smad3 Protein; D016329:Sp1 Transcription Factor / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000502:physiology*
D024042:Collagen Type I; D004268:DNA-Binding Proteins; D012333:RNA, Messenger; C497790:SMAD3 protein, human; D051900:Smad3 Protein; D016329:Sp1 Transcription Factor; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D003094:Collagen; D006861:Hydrogen Peroxide; D000079:Acetaldehyde