Activation of hepatic stellate cells by TGF alpha and collagen type I is mediated by oxidative stress through c-myb expression.
Excessive production of collagen type I is a major contributor to hepatic fibrosis. Activated (myofibroblastic), but not quiescent, hepatic stellate cells (lipocytes) have a high level of collagen type I and alpha-smooth muscle actin expression. Therefore, stellate cell activation is a critical step in hepatic fibrosis. Here we show that quiescent stellate cells were activated by the generation of free radicals with ascorbate/FeSO4 and by malondialdehyde, a product of lipid peroxidation. In addition, stellate cell activation by collagen type I matrix and TGF alpha was blocked by antioxidants, such as d-alpha-tocopherol and butylated hydroxytoluene. Moreover, oxidative stress, TGF alpha and collagen type I markedly stimulated stellate cell entry into S-phase, NFkB activity, and c-myb expression, which were prevented by antioxidants. c-myb antisense oligonucleotide blocked the activation and proliferation of stellate cells induced by TGF alpha. Nuclear extracts from activated, but not from quiescent, stellate cells formed a complex with the critical promoter E box of the alpha-smooth muscle actin gene, which was disrupted by c-myb and NFkB65 antibodies, and competed by c-myb and NFkB cognate DNA. c-Myb expression was also stimulated in activated stellate cells in carbon tetrachloride-induced hepatic injury and fibrogenesis. This study indicates that oxidative stress plays an essential role, through the induction of c-myb and NFkB, on stellate cell activation.
Lee
K S
KS
Department of Medicine, Veterans Affairs Medical Center, San Diego, California, USA.
Buck
M
M
Houglum
K
K
Chojkier
M
M
D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D002455:Cell Division; D002478:Cells, Cultured; D003094:Collagen / Q000494:pharmacology*; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000378:metabolism; D018384:Oxidative Stress; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis*; D020598:Proto-Oncogene Proteins c-myb; D051381:Rats; D017207:Rats, Sprague-Dawley; D016211:Transforming Growth Factor alpha / Q000494:pharmacology*
D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; D020598:Proto-Oncogene Proteins c-myb; D016211:Transforming Growth Factor alpha; D003094:Collagen