Liver synthetic and metabolic function can only be optimised by the growth of cells within a supportive liver matrix. This can be achieved by the utilisation of decellularised human liver tissue. Here we demonstrate complete decellularization of whole human liver and lobes to form an extracellular matrix scaffold with a preserved architecture. Decellularized human liver cubic scaffolds were repopulated for up to 21 days using human cell lines hepatic stellate cells (LX2), hepatocellular carcinoma (Sk-Hep-1) and hepatoblastoma (HepG2), with excellent viability, motility and proliferation and remodelling of the extracellular matrix. Biocompatibility was demonstrated by either omental or subcutaneous xenotransplantation of liver scaffold cubes (5 × 5 × 5 mm) into immune competent mice resulting in absent foreign body responses. We demonstrate decellularization of human liver and repopulation with derived human liver cells. This is a key advance in bioartificial liver development.

Leptin upregulates collagen expression in hepatic stellate cells (HSCs), but the possible modulation of other actions has not been elucidated. The aim of this study was to investigate the expression and function of leptin receptors (ObR) in human HSCs and the biological actions regulated by leptin. Exposure of HSCs to leptin resulted in upregulation of monocyte chemoattractant protein 1 (MCP‐1) expression. Leptin also increased gene expression of the proangiogenic cytokines vascular endothelial growth factor (VEGF) and angiopoietin‐1, and VEGF was also upregulated at the protein level. Activated HSCs express ObRb and possibly other ObR isoforms. Exposure to leptin increased the tyrosine kinase activity of ObR immunoprecipitates and resulted in activation of signal transducer and activator of transcription 3. Several signaling pathways were activated by leptin in HSCs, including extracellular‐signal–regulated kinase, Akt, and nuclear factor κB, the latter being relevant for chemokine expression. Leptin also increased the abundance of hypoxia‐inducible factor 1α, which regulates angiogenic gene expression, in an extracellular‐signal–regulated kinase– and phoshatidylinositol 3‐kinase–dependent fashion. In vivo, leptin administration induced higher MCP‐1 expression and more severe inflammation in mice after acute liver injury. Conversely, in leptin‐deficient mice, the increase in MCP‐1 messenger RNA and mononuclear infiltration was less marked than in wild‐type littermates. Finally, ObR expression colocalized with VEGF and α‐smooth muscle actin after induction of fibrosis in rats. In conclusion, ObR activation in HSCs leads to increased expression of proinflammatory and proangiogenic cytokines, indicating a complex role for leptin in the regulation of the liver wound‐healing response.(HEPATOLOGY 2005;42:1339–1348.)

Hepatic stellate cells are the major cellular sources of extracellular matrix in chronic liver diseases leading to fibrosis. We explored the antifibrogenic effect of two histone deacetylase inhibitors, sodium butyrate and trichostatin A (TSA), on this cell typein vitro.Primary hepatic stellate cells as well as culture activated cells were exposed to butyrate (0.01–1 mmol/L) or TSA (1–100 nmol7sol;L); their effect on collagen types I and III and smooth muscle α–actin was examined by quantitative immunoprecipitation and by Northern analysis. Their antiproliferative effect was examined by³H–thymidine incorporation and cell counting. Hyperacetylation of histones was demonstrated by acid urea/Triton–X–100 (AUT) polyacrylamide gel electrophoresis. Possible cytotoxic effects were judged on stellate cells by evaluatingde novototal protein synthesis, and on hepatocytes by measuring lactate dehydrogenase (LDH) leakage, albumin secretion, and epoxide hydrolase and ethoxycoumarinO–deethylase activity. TSA at 100 nmol/L and butyrate at 1 mmol/L retarded the morphological changes characteristic for activation of primary stellate cells. TSA at 100 nmol/ inhibited synthesis of collagen types I and III and smooth muscle α–actin by 62%, 70%, and 88%. Butyrate at 1 mmol/L showed a modest inhibitory effect on collagen type III and smooth muscle α–actin, but had no effect on collagen type I. Northern analysis suggested that these inhibitory effects on collagen type III and smooth muscle α–actin were transcriptional, while the effect on collagen type I was largely posttranscriptional. At 100 nmol/L, TSA strongly suppressed proliferation of primary hepatic stellate cells. Inhibition of activation of stellate cells was preceded by hyperacetylation of histone H4. When tested on cells at day 14 in culture, butyrate had no inhibitory effects on the synthesis of collagens or smooth muscle α–actin. One hundred or 10 nmol/L TSA modestly inhibited the synthesis of collagens type I (-24%,-22%) and III (-34%,-22%), and smooth muscle α–actin (-27%,-12%). We conclude that TSA inhibits transdifferentiation of stellate cells into myofibroblasts by interfering with the level of acetylation of histone H4.

Focal adhesion kinase (FAK) is a key molecule in focal adhesions and regulates fundamental processes in cells such as growth, survival, and migration. FAK is one of the first molecules recruited to focal adhesions in response to external mechanical stimuli and therefore is a pivotal mediator of cell mechanosignaling, and relays these stimuli to other mechanotransducers within the cytoplasm. Yes‐associated protein (YAP) has been identified recently as one of these core mechanotransducers. YAP translocates to the nucleus following changes in cell mechanics to promote the expression of genes implicated in motility, apoptosis, proliferation, and organ growth. Here, we show that FAK controls the nuclear translocation and activation of YAP in response to mechanical activation and submit that the YAP‐dependent process of durotaxis requires a cell with an asymmetric distribution of active and inactive FAK molecules.—Lachowski, D., Cortes, E., Robinson, B., Rice, A., Rombouts, K., Del Río Hernández, A. E. FAK controls the mechanical activation of YAP, a transcriptional regulator required for durotaxis. FASEB J. 32, 1099–1107 (2018). www.fasebj.org