A well balanced body energy budget controlled by limitation of calorie uptake and͞or increment of energy expenditure, which is typically achieved by proper physical exercise, is most effective against obesity and diabetes mellitus. Recently, peroxisome proliferator-activated receptor (PPAR) ␥, a member of the nuclear receptor, and its cofactors have been shown to be involved in lipid metabolism and in the control of energy expenditure. Here we show that PPAR␥ coactivator 1 (PGC-1) ␤ functions as ERRL1 (for ERR ligand 1), which can bind and activate orphan ERRs (estrogen receptor-related receptors) in vitro. Consistently, PGC-1␤͞ERRL1 transgenic mice exhibit increased expression of the medium-chain acyl CoA dehydrogenase, a known ERR target and a pivotal enzyme of mitochondrial ␤-oxidation in skeletal muscle. As a result, the PGC-1␤͞ERRL1 mice show a state similar to an athlete; namely, the mice are hyperphagic and of elevated energy expenditure and are resistant to obesity induced by a high-fat diet or by a genetic abnormality. These results demonstrate that PGC-1␤͞ERRL1 can function as a protein ligand of ERR, and that its level contributes to the control of energy balance in vivo, and provide a strategy for developing novel antiobesity drugs.

Hepatic stellate cells (HSC) are the main producers of type I collagen in fibrotic liver, and transforming growth factor-beta (TGF-beta) plays critical roles in stimulating collagen gene expression in the cells mainly at the level of transcription. We have previously identified an upstream sequence of alpha2(I) collagen gene (COL1A2) that is essential for its basal and TGF-beta-stimulated transcription in skin fibroblasts and HSC. We designated this region the TGF-beta-responsive element (TbRE). Recently Smad3, an intracellular mediator of TGF-beta signal transduction, has been shown to bind to the TbRE and stimulate COL1A2 transcription when overexpressed in skin fibroblasts. In the present study, we demonstrate increased transcription of COL1A2 and plasminogen activator inhibitor-1 (PAI-1) genes and low response to TGF-beta in an activated HSC clone derived from a cirrhotic liver. Western blot analyses indicated constitutive phosphorylation of Smad3 in the cells. Immunofluorescence studies revealed that, in contrast to Smad2 that translocated from the cytoplasm to the nucleus upon TGF-beta treatment, Smad3 and Smad4 were present in the nucleus irrespective of ligand stimulation. Increased COL1A2 and PAI-1 gene transcription in the cells was not affected by overexpression of inhibitory Smad7. Altogether, the results correlate abnormality in TGF-beta/Smad signaling with pathologically accelerated collagen gene transcription in activated HSC.

The equilibrium between the production and degradation of collagen is rigorously controlled by a number of growth factors and cytokines. Interferon alfa (IFN-a) is now widely used for the treatment of chronic hepatitis C, which can improve serum levels of fibrotic markers and the degree of hepatic fibrosis, not only in patients who responded to therapy but also in those in whom it is ineffective. These findings may suggest that IFN-a possesses direct antifibrotic effects in addition to its antiviral activity. However, in contrast to IFN-y, which has been shown to suppress collagen gene transcription, little is known about the mechanisms responsible for the antifibrotic effects of IFN-a. Here, we report that IFN-a, when administered into transgenic mice harboring the a2(I) collagen gene (COLlA2) promoter sequence, significantly repressed promoter activation and prevented the progression of hepatic fibrosis induced by carbon tetrachloride injection. Transient transfection assays indicated that IFN-a decreased the steady-state levels of COLlA2 messenger RNA (mRNA) and inhibited basal and TGF-PISmad3-stimulated COLlA2 transcription in activated hepatic stellate cells (HSC). These inhibitory effects of IFN-a on COLlA2 transcription were exerted through the interaction between phosphorylated Stat1 and p300. Blocking of the IFN-a signal by overexpressing the intracellular domain-deleted IFN receptor increased basal COLlA2 transcription and abolished the inhibitory effects of IFN-a. In conclusion, our results indicate that IFN-a antagonizes the TGF-/3ISmad3-stimulated COLlA2 transcription in vitro and suppresses COLlA2 promoter activation in vim, providing a molecular basis for antifibrotic effects of IFN-a. (HEPATOLOGY 2003;38:890-899.)

The equilibrium between the production and degradation of collagen is rigorously controlled by a number of growth factors and cytokines. Interferon alfa (IFN-alpha) is now widely used for the treatment of chronic hepatitis C, which can improve serum levels of fibrotic markers and the degree of hepatic fibrosis, not only in patients who responded to therapy but also in those in whom it is ineffective. These findings may suggest that IFN-alpha possesses direct antifibrotic effects in addition to its antiviral activity. However, in contrast to IFN-gamma, which has been shown to suppress collagen gene transcription, little is known about the mechanisms responsible for the antifibrotic effects of IFN-alpha. Here, we report that IFN-alpha, when administered into transgenic mice harboring the alpha2(I) collagen gene (COL1A2) promoter sequence, significantly repressed promoter activation and prevented the progression of hepatic fibrosis induced by carbon tetrachloride injection. Transient transfection assays indicated that IFN-alpha decreased the steady-state levels of COL1A2 messenger RNA (mRNA) and inhibited basal and TGF-beta/Smad3-stimulated COL1A2 transcription in activated hepatic stellate cells (HSC). These inhibitory effects of IFN-alpha on COL1A2 transcription were exerted through the interaction between phosphorylated Stat1 and p300. Blocking of the IFN-alpha signal by overexpressing the intracellular domain-deleted IFN receptor increased basal COL1A2 transcription and abolished the inhibitory effects of IFN-alpha. In conclusion, our results indicate that IFN-alpha antagonizes the TGF-beta/Smad3-stimulated COL1A2 transcription in vitro and suppresses COL1A2 promoter activation in vivo, providing a molecular basis for antifibrotic effects of IFN-alpha.