Thrombopoietin stimulates migration and activates multiple signaling pathways in hepatoblastoma cells.

Thrombopoietin (TPO), a cytokine that participates in the differentiation and maturation of megakaryocytes, is produced in the liver, but only limited information is available on the biological response of liver-derived cells to TPO. In this study, we investigated whether HepG2 cells express c-Mpl, the receptor for TPO, and whether TPO elicits biological responses and intracellular signaling in this cell type. Specific transcripts for c-Mpl were detected in HepG2 cells by RT-PCR, and expression of the protein was demonstrated by Western blot analysis and immunofluorescence. Exposure of HepG2 cells to TPO was associated with a dose-dependent increase in cell migration and chemoinvasion through Matrigel-coated filters. A checkerboard analysis showed that the effects of TPO on cell migration were dependent on both chemotaxis and chemokinesis. Exposure of HepG2 cells to TPO resulted in the activation of different members of the MAPK family, including ERK and JNK, as assessed using phosphorylation-specific antibodies and immune complex kinase assays. TPO also activated phosphatidylinositol 3-kinase (PI3K) and the downstream kinase Akt in a time-dependent manner. Finally, activation of c-Mpl was associated with increased activation of nuclear factor-kappaB. With the use of specific inhibitors, tyrosine phosphorylation and activation of PI3K were found to be required for the induction of migration in response to TPO. We conclude that TPO exerts biological actions on cultured hepatoblastoma cells via activation of c-Mpl and its downstream signaling.

Thiazolidinedione treatment inhibits bile duct proliferation and fibrosis in a rat model of chronic cholestasis.

AIM: To investigate the effects of troglitazone (TGZ), an anti-diabetic drug which activates peroxisome proliferator-activated receptor-gamma (PPAR-gamma), for liver tissue repair, and the development of ductular reaction, following common bile duct ligation (BDL) in rats. METHODS: Rats were supplemented with TGZ (0.2% w/w in the pelleted food) for 1 wk before BDL or sham operation. Animals were killed at 1, 2, or 4 wk after surgery. RESULTS: The development of liver fibrosis was reduced in rats receiving TGZ, as indicated by significant decreases of procollagen type I gene expression and liver hydroxy-proline levels. Accumulation of alpha-smooth-muscle actin (SMA)-expressing cells surrounding newly formed bile ducts following BDL, as well as total hepatic levels of SMA were partially inhibited by TGZ treatment, indicating the presence of a reduced number and/or activation of hepatic stellate cells (HSC) and myofibroblasts. Development of the ductular reaction was inhibited by TGZ, as indicated by histochemical evaluation and hepatic activity of gamma-glutamyl-transferase (GGT). CONCLUSION: Treatment with thiazolidinedione reduces ductular proliferation and fibrosis in a model of chronic cholestasis, and suggests that limiting cholangiocyte proliferation may contribute to the lower development of scarring in this system.

4-Hydroxynonenal as a selective pro-fibrogenic stimulus for activated human hepatic stellate cells.

BACKGROUND/AIMS: 4-Hydroxynonenal (HNE) is a putative pro-fibrogenic product of oxidative stress able to elicit apoptosis and cytotoxicity in several cell types. This study has been performed to evaluate its 'in vivo' levels in injured liver and whether HNE may induce apoptosis and/or affect selected phenotypic responses in activated human hepatic stellate cells (HSC/MF). METHODS/RESULTS: During the development of acute liver injury induced by CCl(4), liver tissue HNE levels were in the range 0.5-10 microM, as shown by high performance liquid chromatography analysis. Cultured human HSC/MF, developed cytotoxicity only if exposed to very high HNE concentrations (25-50 microM) without any sign of induction of classic, caspase-dependent apoptosis, as assessed by evaluating morphology and biochemical parameters of cell death. HNE, at non-cytotoxic doses, up-regulated procollagen type I and tissue inhibitor of metalloproteinases-1 gene expression and/or protein synthesis without significantly affecting chemotaxis (wound healing and haptotaxis assay), matrix metalloproteinases 1 and 2 mRNA expression and activity as well as basal DNA synthesis. CONCLUSIONS: HNE, at concentrations compatible with those detected in vivo, does not elicit HSC/MF classic apoptosis but, rather, may act as a potent pro-fibrogenic stimulus for the expression of genes involved in excess extracellular matrix deposition and proposed as survival signals for HSC/MF.

Dehydroepiandrosterone modulates nuclear factor-kappaB activation in hippocampus of diabetic rats.

Oxidative stress induced by chronic hyperglycemia contributes to cerebrovascular complications in diabetes. Reactive oxygen species activate the transcription factor nuclear factor-kappaB (NF-kappaB), which in turn activates a variety of target genes linked to the development of diabetic complications. Dehydroepiandrosterone, an adrenal steroid, which possesses a multitargeted antioxidant effects, is also synthesized de novo by the brain. Normoglycemic and streptozotocin-diabetic rats were either treated with dehydroepiandrosterone (DHEA) for 7, 14, or 21 d (4 mg/d per rat) or left untreated. Oxidative state, antioxidant balance and activation of nuclear transcriptional redox-sensitive factor NF-kappaB were evaluated in the hippocampus area. In streptozotocin-treated rats, besides the strong increase in oxygen reactive species, there is also a persistent activation of NF-kappaB. The derangement of the oxidative balance in the brain induced by diabetes improves with DHEA. Moreover, DHEA completely counteracts NF-kappaB activation, measured as DNA binding activity, and hinders the increase of IkappaB-alpha inhibitory subunit induced by oxidative stress. The time-lag of DHEA's effects on NF-kappaB activation parallels its effects on oxidative balance. Results indicate that DHEA might protect hippocampus from chronic activation of NF-kappaB-dependent genes by reducing NF-kappaB nuclear translocation. This could result in protection from diabetes-dependent brain damage.