Interference of soluble mediators into liver matrix triggered dedifferentiation of human hepatocytes

Integrin α2 and β1 Cross-Communication with mTOR/AKT and the CDK-Cyclin Axis in Hepatocellular Carcinoma Cells

Simple Summary

Hepatocellular carcinoma (HCC) progression depends on two major processes, tumor growth and invasion. The present study investigated how these events are linked. A panel of HCC cell lines were stimulated with insulin-like growth factor-1 (IGF1) and the biological behavior was evaluated. IGF1 activated the proliferation and invasion cascade by altering the expression level of integrin α subtypes, which were associated with the AKT-mTOR pathway and the CDK-Cyclin axis. We assume that HCC progression is controlled by a fine-tuned network between IGF1 driven integrin signaling, the Akt-mTOR pathway, and the CDK-Cyclin axis. Concerted targeting of these pathways may, therefore, become an innovative option to prevent cancer dissemination.

Abstract

Integrin receptors contribute to hepatocellular carcinoma (HCC) invasion, while AKT-mTOR signaling controls mitosis. The present study was designed to explore the links between integrins and the AKT-mTOR pathway and the CDK-Cyclin axis. HCC cell lines (HepG2, Huh7, Hep3B) were stimulated with soluble collagen or Matrigel to activate integrins, or with insulin-like growth factor 1 (IGF1) to activate AKT-mTOR. HCC growth, proliferation, adhesion, and chemotaxis were evaluated. AKT/mTOR-related proteins, proteins of the CDK-Cyclin axis, focal adhesion kinase (FAK), and integrin-linked kinase (ILK) were determined following IGF1-stimulation or integrin knockdown. Stimulation with collagen or Matrigel increased tumor cell growth and proliferation. This was associated with significant alteration of the integrins α2, αV, and β1. Blockade of these integrins led to cell cycle arrest in G2/M and diminished the number of tumor cell clones. Knocking down the integrins α2 or β1 suppressed ILK, reduced FAK-phosphorylation and diminished AKT/mTOR, as well as the proteins of the CDK-Cyclin axis. Activating the cells with IGF1 enhanced the expression of the integrins α2, αV, β1, activated FAK, and increased tumor cell adhesion and chemotaxis. Blocking the AKT pathway canceled the enhancing effect of IGF on the integrins α2 and β1. These findings reveal that HCC growth, proliferation, and invasion are controlled by a fine-tuned network between α2/β1-FAK signaling, the AKT-mTOR pathway, and the CDK–Cyclin axis. Concerted blockade of the integrin α2/β1 complex along with AKT-mTOR signaling could, therefore, provide an option to prevent progressive dissemination of HCC.

Effects of membrane molecular weight cutoff on performance of a novel bioartificial liver

Immunoisolation using semipermeable membranes has been incorporated into bioartificial liver (BAL) devices to separate cellular components of the recipient's immune system from the cells within the BAL device. This study was designed to explore the influence of membrane molecular weight cutoff on performance of the multilayer radial-flow BAL using porcine hepatocytes cocultured with mesenchymal stem cells. In this study, healthy beagles underwent 6-h treatment with a BAL containing membrane with 200 kDa retention rating or 1200 kDa retention rating. Functional markers of BAL performance were monitored before and after treatment, as well as cytotoxic immune response to BAL therapy. The results showed that hepatocyte performance levels such as albumin secretion, urea synthesis, and viability were all significantly higher in 200 kDa retention rating group compared with the 1200 kDa retention rating group after treatment (P <  0.05). Significant levels of canine proteins were detected in BAL medium from the 1200 kDa retention rating group. Fluorescence microscopy further verified that heavy deposition of canine IgG, IgM, and complement (C3) on coculture cells was obtained after BAL treatment in the 1200 kDa retention rating group. However, only trace deposits of canine immunoproteins were observed on coculture cells obtained from BAL in the 200 kDa retention rating group. Small membrane molecular weight cutoff of the BAL could reduce the transfer of xenoreactive antibodies into the BAL medium and improve the performance of the BAL.

Primary human hepatocytes on biodegradable poly(l-lactic acid) matrices: a promising model for improving transplantation efficiency with tissue engineering

Liver transplantation is an established treatment for acute and chronic liver disease. However, because of the shortage of donor organs, it does not fulfill the needs of all patients. Hepatocyte transplantation is promising as an alternative method for the treatment of end-stage liver disease and as bridging therapy until liver transplantation. Our group has been working on the optimization of matrix-based hepatocyte transplantation. In order to increase cell survival after transplantation, freshly isolated human hepatocytes were seeded onto biodegradable poly(l-lactic acid) (PLLA) polymer scaffolds and were cultured in a flow bioreactor. PLLA discs were seeded with human hepatocytes and exposed to a recirculated medium flow for 6 days. Human hepatocytes formed spheroidal aggregates with a liver-like morphology and active metabolic function. Phase contrast microscopy showed increasing numbers of spheroids of increasing diameter during the culture period. Hematoxylin and eosin histology showed viable and intact hepatocytes inside the spheroids. Immunohistochemistry confirmed sustained hepatocyte function and a preserved hepatocyte-specific cytoskeleton. Albumin, alpha-1-antitrypsin, and urea assays showed continued production during the culture period. Northern blot analysis demonstrated increasing albumin signals. Scanning electron micrographs showed hepatocyte spheroids with relatively smooth undulating surfaces and numerous microvilli. Transmission electron micrographs revealed intact hepatocytes and junctional complexes with coated pits and vesicles inside the spheroids. Therefore, we conclude that primary human hepatocytes, precultured in a flow bioreactor on a PLLA scaffold, reorganize to form morphologically intact liver neotissue, and this might offer an optimized method for hepatocyte transplantation because of the expected reduction of the initial cell loss, the high regenerative potential in vivo, and the preformed functional integrity.

Contribution of bone marrow mesenchymal stem cells to porcine hepatocyte culture in vitro

One of the greatest challenges in the attempt to create functional bioartificial liver designs is the maintenance of porcine hepatocyte differentiated functions in vitro. Co-cultivation of hepatocytes with nonparenchymal cells may be beneficial for optimizing cell functions via mimicry of physiological microenvironment. However, the underlying mechanisms remain to be elucidated. An equal number of freshly isolated porcine hepatocytes and purified bone marrow mesenchymal stem cells (MSCS) was randomly co-cultured and the morphological and functional changes of heterotypic interactions were characterized. Furthermore, contributions of soluble factors involved in the separated co-culture system were evaluated. The purity of the third-passage MSCS and primary hepatocytes was more than 90% and 99%, respectively. Hepatocyte viability was greater than 95%. A rapid attachment and self-organization of three-dimensional hepatocyte spheroids were encouraged, which was due to the supporting MSCS of high motility. The elevated induction of both albumin production and urea synthesis was achieved in co-culture (P < 0.05). Data from semipermeable membrane cultures suggested that interleukin-6 is one of the key stimulators in hepatic functional enhancement. These results demonstrate for the first time that soluble factors have beneficial effects on the preservation of hepatic morphology and functionality in the co-culture of hepatocytes with MSCS in vitro, which could represent a promising tool for tissue engineering, cell biology, and bioartificial liver devices.

De-differentiation of primary human hepatocytes depends on the composition of specialized liver basement membrane

Basement membrane (BM) is a highly specialized extracellular matrix (ECM), which is associated with epithelia and endothelia. BM provide epithelia with structural support and also regulate cell behavior. The liver contains a unique ECM within the space of Disse, which consists of basement membrane constituents as well as fibrillar ECM molecules. Changes in composition of this ECM are considered detrimental for viability of hepatocytes during progression of liver disease. Mouse tumor-derived BM preparations, such as Matrigel, which are commonly used as a model for BM in vitro, differ significantly in their composition from liver BM present in vivo. In order to gain further insights into the role of BM in the regulation of hepatocyte behavior in health and disease, we generated a liver-derived basement membrane matrix (LBLM). LBLM allowed investigation of BM-hepatocyte interactions in vitro. Here we report a novel approach of generating a liver-derived basement membrane matrix by separate isolation of type IV collagen, laminin, nidogen, and heparan sulfate proteoglycans, and subsequent reconstitution into a matrix-like gel. Adhesion of primary human hepatocytes to LBLM was increased and the rate of de-differentiation was decreased compared to hepatocyte cultivation on Matrigel or type I collagen matrix. Primary human hepatocytes maintained their differentiated epithelial phenotype on LBLM isolated from normal human livers for more than 21 days, whereas they de-differentiated rapidly on LBLM isolated from cirrhotic human livers. Normal human LBLM contains a unique isoform composition of type IV collagen, namely alpha1 (IV), alpha2(IV), alpha4(IV), and alpha6(IV) chains, whereas cirrhotic LBLM contains only alpha1(IV) and alpha2(IV) isoforms, albeit present in increased amounts. These findings suggest that the composition of liver basement membrane is important for the maintenance of hepatocyte viability and provide anti-de-differentiation clues.