A key feature in the pathogenesis of liver fibrosis is fibrillar Collagen-I deposition; yet, mediators that could be key therapeutic targets remain elusive. We hypothesized that osteopontin (OPN), an extracellular matrix (ECM) cytokine expressed in hepatic stellate cells (HSCs), could drive fibrogenesis by modulating the HSC pro-fibrogenic phenotype and Collagen-I expression. Recombinant OPN (rOPN) up-regulated Collagen-I protein in primary HSCs in a transforming growth factor beta (TGFβ)–independent fashion, whereas it down-regulated matrix metalloprotease-13 (MMP13), thus favoring scarring. rOPN activated primary HSCs, confirmed by increased α-smooth muscle actin (αSMA) expression and enhanced their invasive and wound-healing potential. HSCs isolated from wild-type (WT) mice were more profibrogenic than those from OPN knockout ( Opn −/−) mice and infection of primary HSCs with an Ad-OPN increased Collagen-I, indicating correlation between both proteins. OPN induction of Collagen-I occurred via integrin αvβ3 engagement and activation of the phosphoinositide 3-kinase/phosphorylated Akt/nuclear factor kappa B (PI3K/pAkt/NFκB)–signaling pathway, whereas cluster of differentiation 44 (CD44) binding and mammalian target of rapamycin/70-kDa ribosomal protein S6 kinase (mTOR/p70S6K) were not involved. Neutralization of integrin αvβ3 prevented the OPN-mediated activation of the PI3K/pAkt/NFκB–signaling cascade and Collagen-I up-regulation. Likewise, inhibition of PI3K and NFκB blocked the OPN-mediated Collagen-I increase. Hepatitis C Virus (HCV) cirrhotic patients showed coinduction of Collagen-I and cleaved OPN compared to healthy individuals. Acute and chronic liver injury by CCl4 injection or thioacetamide (TAA) treatment elevated OPN expression. Reactive oxygen species up-regulated OPN in vitro and in vivo and antioxidants prevented this effect. Transgenic mice overexpressing OPN in hepatocytes ( Opn HEP Tg) mice developed spontaneous liver fibrosis compared to WT mice. Last, chronic CCl4 injection and TAA treatment caused more liver fibrosis to WT than to Opn −/− mice and the reverse occurred in Opn HEP Tg mice. Conclusion : OPN emerges as a key cytokine within the ECM protein network driving the increase in Collagen-I protein contributing to scarring and liver fibrosis. (Hepatology 2012)

Objective: Fibroblast growth factor 15/19 (FGF15/19), an enterokine that regulates synthesis of hepatic bile acids (BA), has been proposed to influence fat metabolism. Without FGF15/19, mouse liver regeneration after partial hepatectomy (PH) is severely impaired. We studied the role of FGF15/19 in response to a high fat diet (HFD) and its regulation by saturated fatty acids. We developed a fusion molecule encompassing FGF19 and apolipoprotein A-I, termed Fibapo, and evaluated its pharmacological properties in fatty liver regeneration. Design: Fgf15^−/− mice were fed a HFD. Liver fat and the expression of fat metabolism and endoplasmic reticulum (ER) stress-related genes were measured. Influence of palmitic acid (PA) on FGF15/19 expression was determined in mice and in human liver cell lines. In vivo half-life and biological activity of Fibapo and FGF19 were compared. Hepatoprotective and proregenerative activities of Fibapo were evaluated in obese db/db mice undergoing PH. Results: Hepatosteatosis and ER stress were exacerbated in HFD-fed Fgf15^−/− mice. Hepatic expression of Pparγ2 was elevated in Fgf15^−/− mice, being reversed by FGF19 treatment. PA induced FGF15/19 expression in mouse ileum and human liver cells, and FGF19 protected from PA-mediated ER stress and cytotoxicity. Fibapo reduced liver BA and lipid accumulation, inhibited ER stress and showed enhanced half-life. Fibapo provided increased db/db mice survival and improved regeneration upon PH. Conclusions: FGF15/19 is essential for hepatic metabolic adaptation to dietary fat being a physiological regulator of Pparγ2 expression. Perioperative administration of Fibapo improves fatty liver regeneration.

Objective: Liver fibrosis is associated with significant collagen-I deposition largely produced by activated hepatic stellate cells (HSCs); yet, the link between hepatocyte damage and the HSC profibrogenic response remains unclear. Here we show significant induction of osteopontin (OPN) and high-mobility group box-1 (HMGB1) in liver fibrosis. Since OPN was identified as upstream of HMGB1, we hypothesised that OPN could participate in the pathogenesis of liver fibrosis by increasing HMGB1 to upregulate collagen-I expression. Design and results: Patients with long-term hepatitis C virus (HCV) progressing in disease stage displayed enhanced hepatic OPN and HMGB1 immunostaining, which correlated with fibrosis stage, whereas it remained similar in non-progressors. Hepatocyte cytoplasmic OPN and HMGB1 expression was significant while loss of nuclear HMGB1 occurred in patients with HCV-induced fibrosis compared with healthy explants. Well-established liver fibrosis along with marked induction of HMGB1 occurred in CCl₄-injected Opn ^Hep transgenic yet it was less in wild type and almost absent in Opn^−/− mice. Hmgb1 ablation in hepatocytes (Hmgb1 ^ΔHep) protected mice from CCl₄-induced liver fibrosis. Coculture with hepatocytes that secrete OPN plus HMGB1 and challenge with recombinant OPN (rOPN) or HMGB1 (rHMGB1) enhanced collagen-I expression in HSCs, which was blunted by neutralising antibodies (Abs) and by Opn or Hmgb1 ablation. rOPN induced acetylation of HMGB1 in HSCs due to increased NADPH oxidase activity and the associated decrease in histone deacetylases 1/2 leading to upregulation of collagen-I. Last, rHMGB1 signalled via receptor for advanced glycation end-products and activated the PI3K–pAkt1/2/3 pathway to upregulate collagen-I. Conclusions: During liver fibrosis, the increase in OPN induces HMGB1, which acts as a downstream alarmin driving collagen-I synthesis in HSCs.

Objective: In human chronic liver disease, there is association between ductular reaction (DR) and fibrosis; yet, the mechanism triggering its onset and its role in scar formation remains unknown. Since we previously showed that osteopontin (OPN) is highly induced during drug-induced liver fibrosis, we hypothesised that OPN could drive oval cells (OC) expansion and DR and signal to hepatic stellate cells (HSC) to promote scarring.Results: In vivo studies demonstrated increased OPN expression in biliary epithelial cells (BEC) and in OC in thioacetamide (TAA)-treated mice. OPN ablation protected mice from TAA and bile duct ligation-induced liver injury, DR and scarring. This was associated with greater hepatocyte proliferation, lower OC expansion and DR along with less fibrosis, suggesting that OPN could activate the OC compartment to differentiate into BEC, which could then signal to HSC to enhance scarring. Since TAA-treated wild-type mice and cirrhotic patients showed TGF-β⁺BEC, which were lacking in TAA-treatedOpn^−/−mice and in healthy human explants, this suggested that OPN could regulate TGF-β, a profibrogenic factor. In vitro experiments confirmed that recombinant OPN (rOPN) decreases hepatocyte proliferation and increases OC and BEC proliferation. To evaluate how BEC regulate collagen-I production in HSC, co-cultures were established. Co-cultured BEC upregulated OPN and TGF-β expression and enhanced collagen-I synthesis by HSC. Lastly, recombinant TGF-β (rTGFβ) and rOPN promoted BEC proliferation and neutralisation of OPN and TGF-β reduced collagen-I expression in co-cultured HSC.Conclusions: OPN emerges as a key matricellular protein driving DR and contributing to scarring and liver fibrosis via TGF-β.

The identification of molecular mechanisms involved in the maintenance of the transformed phenotype of hepatocellular carcinoma (HCC) cells is essential for the elucidation of therapeutic strategies. Here, we show that human HCC cells display an autocrine loop mediated by connective tissue growth factor (CTGF) that promotes DNA synthesis and cell survival. Expression of CTGF was stimulated by epidermal growth factor receptor (EGFR) ligands and was dependent on the expression of the transcriptional coactivator, Yes-associated protein (YAP). We identified elements in the CTGF gene proximal promoter that bound YAP-enclosing complexes and were responsible for basal and EGFR-stimulated CTGF expression. We also demonstrate that YAP expression can be up-regulated through EGFR activation not only in HCC cells, but also in primary human hepatocytes. CTGF contributed to HCC cell dedifferentiation, expression of inflammation-related genes involved in carcinogenesis, resistance toward doxorubicin, and in vivo HCC cell growth. Importantly, CTGF down-regulated tumor necrosis factor–related apoptosis-inducing ligand (TRAIL) receptor 2 expression and was involved in the reduced sensitivity of these cells toward TRAIL-mediated apoptosis. Conclusion: We have identified autocrine CTGF as a novel determinant of HCC cells' neoplastic behavior. Expression of CTGF can be stimulated through the EGFR-signaling system in HCC cells in a novel cross-talk with the oncoprotein YAP. Moreover, to our knowledge, this is the first study that identifies a signaling mechanism triggering YAP gene expression in healthy and transformed liver parenchymal cells. (Hepatology 2011)