TNF-α inhibits liver collagen-α1(I) gene expression through a tissue-specific regulatory region.

Although tumor necrosis factor-α (TNF-α) inhibits collagen-α1(I) gene expression in cultured hepatic stellate cells, assessment of its effects on hepatic collagen expression is complicated by the confounding variables of tissue necrosis and inflammation. Therefore, we analyzed whether chronically elevated serum TNF-α affects constitutive hepatic collagen metabolism in vivo by inoculating nude mice with Chinese hamster ovary (CHO) cells secreting TNF-α (TNF-α mice) or with control CHO cells (control mice). Before the onset of weight loss, collagen synthesis and collagen gene expression were inhibited in the liver of TNF-α mice. In transgenic mice, after 8 h, TNF-α (500 ng at 0 and 5 h) inhibited the liver expression of the collagen-α1(I)-human growth hormone (hGH) transgene containing the first intron and -440 bp of the 5' region. Similarly, in cultured hepatic stellate cells isolated from these transgenic animals, the -440 bp collagen-α1(I)-hGH transgene was responsive to TNF-α treatment independent of the activation of these cells. Transfection studies in stellate cells allowed further characterization of this TNF-α-responsive segment to -220 bp of the 5' region. Because in the skin the inhibitory effect of TNF-α involves a regulatory region of the collagen-α1(I) gene beyond -440 bp, we herein identify a novel tissue-specific regulation of collagen-α1(I) gene by TNF-α.