Project description:Background & Aims: Rapid induction of beta-PDGF receptor (beta-PDGFR) is a core feature of hepatic stellate cell activation, the hallmark of liver fibrogenesis. However, biological consequences of the induction are not well characterized. We aimed to determine the involvement of beta-PDGFR-mediated molecular pathway activation on hepatic stellate cells in liver injury, fibrogenesis, and carcinogenesis in vivo. Methods: Loss and constitutive activation of beta-PDGFR were assessed in mouse models with either a stellate cell-specific beta-PDGFR knockout or the expression of an autoactivating mutation respectively. Liver injury and fibrosis were induced in two mechanistically distinct models: carbontetrachloride (CCl4) treatment and ligation of the common bile duct. Hepatocarcinogenesis with underlying liver injury/fibrosis was assessed by a single dose of diethylnitrosamine (DEN) followed by repeated injections of CCl4. Genome-wide expression profiling was performed isolated stellate cells from these models to determine deregulated pathways. Results: Depletion of beta-PDGFR in hepatic stellate cells led to decreased histological liver injury, serum transaminases, collagen alpha 1(I) and alpha smooth muscle actin expression, and collagen deposition. Stellate cell proliferation was significantly reduced after acute hepatic injury in vivo. In contrast, autoactivation of beta-PDGFR in stellate cells accelerated liver fibrosis, most prominently after 6 weeks of CCl4 induced injury. There was no difference in development of DEN-induced pre-neoplastic loci according to the status of beta-PDGFR. Conclusions: Depletion of beta-PDGFR in hepatic stellate cells attenuated the development of liver injury, fibrosis, and stellate cell proliferation in multiple animal models, whereas the constitutive activation of beta-PDGFR enhanced fibrosis. However, manipulation of beta-PDGFR alone did not reduce development of dysplastic nodules. These findings indicate that titration of receptor beta-PDGFR expression on stellate cells parallels fibrosis and injury, but may not impact the development of hepatic neoplasia alone. Hepatic stellate cells were isolated from liver of beta-PDGFR-wild-type or knockout mice, and treated with beta-PDGF ligand or vehicle control.

Project description:Activated hepatic stellate cells (HSC) that transdifferentiate to myofibroblasts in the injured liver are responsible for scar formation that leads to fibrosis and eventually cirrhosis. To investigate the gene expression profile during different stages of this process, we performed serial analysis of gene expression (SAGE), representing a quantitative and qualitative description of all expressed genes. Stellate cells were isolated from human livers and cultured. SAGE was performed on RNA isolated from quiescent, activated and transdifferentiated HSC. Comparison of the three resulting transcriptomes showed that less than 5% of all genes changed significantly in expression. Established markers of liver fibrosis showed enhanced expression in accordance with the transdifferentiation process. In addition, induction was seen for several genes not yet recognized to be involved in liver fibrosis, such as insulin-like growth factor binding proteins (IGFBP) and antagonists of bone morphogenic proteins: follistatin and gremlin. The induction of these genes was validated in vivo in mice developing liver fibrosis. The expression of IGFBPs and gremlin was measurable in the livers of these mice while it was low or undetectable in control mice without liver fibrosis. Since gremlin modulates the activity of bone morphogenic growth factors, it may represent a novel pathway and a target for therapeutic intervention and together with IGFBPs as a specific marker of liver fibrosis. In conclusion, the comparison of the three transcriptomes of (activated) stellate cells reveals novel genes involved in fibrogenesis and provides an appreciation of the sequence and timing of the fibrotic process in liver. Keywords: cell type comparison Human hepatic stellate cells (HSC) were isolated from wedge sections of normal human liver unsuitable for transplantation or from tumor-free human liver after partial hepatectomy as previously reported. Briefly, after a combined digestion with collagenase/pronase, HSC were separated from other liver nonparenchymal cells by ultracentrifugation over gradients of Larcoll (Sigma). The percentage of HSC in these isolates was > 90% as assessed by transmission microscopy, autofluorescence of vitamin A and immunofluorescence of vimentin. Immediately after isolation RNA was extracted for the construction of the SAGE library of quiescent HSC. To obtain activated stellate cells, these cells were cultured for 15 days on plastic culture dishes in modified Dulbecco's medium supplemented with 0.6 U/ml insulin, 2.0 mmol/L glutamine, 0.1 mmol/L nonessential amino acids, 1.0 mmol/L sodium pyruvate, antibiotic antifungal solution (Gibco) and 20% fetal bovine serum. To obtain fully transdifferentiated hepatic stellate cells, or myofibroblasts, the cells were cultured until they had reached passage 6 to 7. Myofibroblast phenotype was confirmed by detection of vimentin and ?-smooth muscle actin using immunofluorescence with monoclonal antibodies from Dako and Sigma, respectively. Medium was refreshed twice a week and at the indicated period RNA was extracted using Trizol (Quiagen)

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