Maintaining hepatic stem cell gene expression on biological and synthetic substrata

Blended electrospinning with human liver extracellular matrix for engineering new hepatic microenvironments

Tissue engineering of a transplantable liver could provide an alternative to donor livers for transplant, solving the problem of escalating donor shortages. One of the challenges for tissue engineers is the extracellular matrix (ECM); a finely controlled in vivo niche which supports hepatocytes. Polymers and decellularized tissue scaffolds each provide some of the necessary biological cues for hepatocytes, however, neither alone has proved sufficient. Enhancing microenvironments using bioactive molecules allows researchers to create more appropriate niches for hepatocytes. We combined decellularized human liver tissue with electrospun polymers to produce a niche for hepatocytes and compared the human liver ECM to its individual components; Collagen I, Laminin-521 and Fibronectin. The resulting scaffolds were validated using THLE-3 hepatocytes. Immunohistochemistry confirmed retention of proteins in the scaffolds. Mechanical testing demonstrated significant increases in the Young's Modulus of the decellularized ECM scaffold; providing significantly stiffer environments for hepatocytes. Each scaffold maintained hepatocyte growth, albumin production and influenced expression of key hepatic genes, with the decellularized ECM scaffolds exerting an influence which is not recapitulated by individual ECM components. Blended protein:polymer scaffolds provide a viable, translatable niche for hepatocytes and offers a solution to current obstacles in disease modelling and liver tissue engineering.

Downregulation of Glt25d1 aggravates carbon tetrachloride‑induced acute hepatic injury through activation of the TGF‑β1/Smad2 signaling pathway

Collagen β (1-O) galactosyltransferase 1 (GLT25D1) has been reported to transfer galactose to hydroxylysine residues via β (1-O) linkages in collagen. The present study investigated the function of the collagen galactosyltransferase activity of GLT25D1 against carbon tetrachloride (CCl₄)-induced acute liver injury in vitro. Glt25d1^+/− mice and wild-type (WT) mice were injected intraperitoneally with the same dose of CCl₄. The grade of hepatic injury and the extent of hepatocyte necrosis in the acute phase were assessed 48 h following CCl₄ injection. Hepatocyte necrosis was evaluated by histological examination and by serum alanine aminotransferase and aspartate aminotransferase levels, which were higher in the Glt25d1^+/− mice compared with those in the WT mice. Reverse transcription-quantitative polymerase chain reaction was performed, and the results demonstrated that the mRNA expression levels of inflammatory cytokines, including tumor necrosis factor-α and interleukin-6 were significantly increased in the Glt25d1^+/− mice. Furthermore, western blot analyses were performed, and the results demonstrated that the protein levels of cleaved caspase-3 and −9 were also markedly increased in the Glt25d1^+/− liver, indicating that hepatocyte apoptosis was induced. Additionally, the expression levels of transforming growth factor (TGF)-β1 and phosphorylated small mothers against decapentaplegic (Smad)2 were markedly upregulated, indicating activation of the TGF-β1/Smad2 signaling pathway during CCl₄-induced acute liver injury in Glt25d1^+/− mice. CCl₄ administration also resulted in severe damage to Glt25d1^+/− primary hepatocytes in vitro. Taken together, the downregulation of Glt25d1 deteriorated CCl₄-induced liver injury in mice, which may involve triggering inflammatory responses, apoptosis and TGF-β1/Smad2 signaling pathway activation.

New substrates for stem cell control

The capacity to culture stem cells in a controllable, robust and scalable manner is necessary in order to develop successful strategies for the generation of cellular and tissue platforms for drug screening, toxicity testing, tissue engineering and regenerative medicine. Creating substrates that support the expansion, maintenance or directional differentiation of stem cells would greatly aid these efforts. Optimally, the substrates used should be chemically defined and synthetically scalable, allowing growth under defined, serum-free culture conditions. To achieve this, the chemical and physical attributes of the substrates should mimic the natural tissue environment and allow control of their biological properties. Herein, recent advances in the development of materials to study/manipulate stem cells, both in vitro and in vivo, are described with a focus on the novelty of the substrates' properties, and on application of substrates to direct stem cells.This article is part of the theme issue 'Designer human tissue: coming to a lab near you'.

Shear stress upregulates regeneration-related immediate early genes in liver progenitors in 3D ECM-like microenvironments

The role of fluid stresses in activating the hepatic stem/progenitor cell regenerative response is not well understood. This study hypothesized that immediate early genes (IEGs) with known links to liver regeneration will be upregulated in liver progenitor cells (LPCs) exposed to in vitro shear stresses on the order of those produced from elevated interstitial flow after partial hepatectomy. The objectives were: (1) to develop a shear flow chamber for application of fluid stress to LPCs in 3D culture; and (2) to determine the effects of fluid stress on IEG expression in LPCs. Two hours of shear stress exposure at ∼4 dyn/cm² was applied to LPCs embedded individually or as 3D spheroids within a hyaluronic acid/collagen I hydrogel. Results were compared against static controls. Quantitative reverse transcriptase polymerase chain reaction was used to evaluate the effect of experimental treatments on gene expression. Twenty-nine genes were analyzed, including IEGs and other genes linked to liver regeneration. Four IEGs (CFOS, IP10, MKP1, ALB) and three other regeneration-related genes (WNT, VEGF, EpCAM) were significantly upregulated in LPCs in response to fluid mechanical stress. LPCs maintained an early to intermediate stage of differentiation in spheroid culture in the absence of the hydrogel, and addition of the gel initiated cholangiocyte differentiation programs which were abrogated by the onset of flow. Collectively the flow-upregulated genes fit the pattern of an LPC-mediated proliferative/regenerative response. These results suggest that fluid stresses are potentially important regulators of the LPC-mediated regeneration response in liver.

Stabilizing hepatocellular phenotype using optimized synthetic surfaces

Currently, one of the major limitations in cell biology is maintaining differentiated cell phenotype. Biological matrices are commonly used for culturing and maintaining primary and pluripotent stem cell derived hepatocytes. While biological matrices are useful, they permit short term culture of hepatocytes, limiting their widespread application. We have attempted to overcome the limitations using a synthetic polymer coating. Polymers represent one of the broadest classes of biomaterials and possess a wide range of mechanical, physical and chemical properties, which can be fine-tuned for purpose. Importantly, such materials can be scaled to quality assured standards and display batch-to-batch consistency. This is essential if cells are to be expanded for high through-put screening in the pharmaceutical testing industry or for cellular based therapy. Polyurethanes (PUs) are one group of materials that have shown promise in cell culture. Our recent progress in optimizing a polyurethane coated surface, for long-term culture of human hepatocytes displaying stable phenotype, is presented and discussed.

Modulating innate immunity improves hepatitis C virus infection and replication in stem cell-derived hepatocytes

In this study, human embryonic stem cell-derived hepatocytes (hESC-Heps) were investigated for their ability to support hepatitis C virus (HCV) infection and replication. hESC-Heps were capable of supporting the full viral life cycle, including the release of infectious virions. Although supportive, hESC-Hep viral infection levels were not as great as those observed in Huh7 cells. We reasoned that innate immune responses in hESC-Heps may lead to the low level of infection and replication. Upon further investigation, we identified a strong type III interferon response in hESC-Heps that was triggered by HCV. Interestingly, specific inhibition of the JAK/STAT signaling pathway led to an increase in HCV infection and replication in hESC-Heps. Of note, the interferon response was not evident in Huh7 cells. In summary, we have established a robust cell-based system that allows the in-depth study of virus-host interactions in vitro.