Increasing 3D Matrix Rigidity Strengthens Proliferation and Spheroid Development of Human Liver Cells in a Constant Growth Factor Environment

Hepatotoxicity of cyanotoxin microcystin-LR in human: Insights into mechanisms of action in the 3D culture model Hepoid-HepaRG

Microcystin-LR (MC-LR) is a potent hepatotoxin produced by harmful cyanobacterial blooms (CyanoHABs). MC-LR targets highly differentiated hepatocytes expressing organic anion transporting polypeptides OATP1B1 and OATP1B3 that are responsible for hepatocellular uptake of the toxin. The present study utilized an advanced 3D in vitro human liver model Hepoid-HepaRG based on the cultivation of collagen-matrix embedded multicellular spheroids composed of highly differentiated and polarized hepatocyte-like cells. 14-d-old Hepoid-HepaRG cultures showed increased expression of OATP1B1/1B3 and sensitivity to MC-LR cytotoxicity at concentrations >10 nM (48 h exposure, EC20 = 26 nM). MC-LR induced neither caspase 3/7 activity nor expression of the endoplasmic reticulum stress marker gene BiP/GRP78, but increased release of pro-inflammatory cytokine IL-8, indicating a necrotic type of cell death. Subcytotoxic (10 nM) and cytotoxic (≥100 nM) MC-LR concentrations disrupted hepatocyte functions, such as xenobiotic metabolism phase-I enzyme activities (cytochrome P450 1A/1B) and albumin secretion, along with reduced expression of CYP1A2 and ALB genes. MC-LR also decreased expression of HNF4A gene, a critical regulator of hepatocyte differentiation and function. Genes encoding hepatobiliary membrane transporters (OATP1B1, BSEP, NTCP), hepatocyte gap junctional gene connexin 32 and the epithelial cell marker E-cadherin were also downregulated. Simultaneous upregulation of connexin 43 gene, primarily expressed by liver progenitor and non-parenchymal cells, indicated a disruption of tissue homeostasis. This was associated with a shift in the expression ratio of E-cadherin to N-cadherin towards the mesenchymal cell marker, a process linked to epithelial-mesenchymal transition (EMT) and hepatocarcinogenesis. The effects observed in the human liver cell in vitro model revealed mechanisms that can potentially contribute to the MC-LR-induced promotion and progression of hepatocellular carcinoma (HCC). Hepoid-HepaRG cultures provide a robust, accessible and versatile in vitro model, capable of sensitively detecting hepatotoxic effects at toxicologically relevant concentrations, allowing for assessing hepatotoxicity mechanisms, human health hazards and impacts of environmental hepatotoxins, such as MC-LR.

[Biomechanics of diabetic vitreopapillary traction syndrome]

Diabetic vitreopapillary traction syndrome (VPT) is a variant of diabetic retinopathy (DR) that can lead to vision loss in advanced stages. This review reports on the biomechanics of the vitreous in the pathogenesis of proliferative DR, in particular diabetic VPT. The article analyzes and summarizes literature data, presents the views of different authors on this problem, and provides the results of Russian and foreign scientific research on this pathology. It is concluded that further research in this area can lead to a significant improvement in the results of therapy, timely diagnosis, and preservation of vision in patients with DR.

Suppression of the Epithelial-Mesenchymal Transition and Maintenance of the Liver Functions in Primary Hepatocytes through Dispersion Culture within a Dome-Shaped Collagen Matrix

Primary hepatocytes are valuable for studying liver diseases, drug-induced liver injury, and drug metabolism. However, when cultured in a two-dimensional (2D) environment, primary hepatocytes undergo rapid dedifferentiation via an epithelial-mesenchymal transition (EMT) and lose their liver-specific functions. On the other hand, a three-dimensional (3D) culture of primary hepatocyte organoids presents challenges for analyzing cellular functions and molecular behaviors due to strong cell-cell adhesion among heterogeneous cells. In this study, we developed a novel dispersion culture method of hepatocytes within a dome-shaped collagen matrix, overcoming conventional limitations. The expression levels of EMT-related genes were lower in rat primary hepatocytes cultured using this method for 4 d than in cells cultured using the 2D method. Furthermore, albumin production, a marker of liver function, declined sharply in rat primary hepatocytes cultured in two dimensions from 6.40 µg/mL/48 h on day 4 to 1.35 µg/mL/48 h on day 8, and declined gradually from 4.92 µg/mL/48 h on day 8 to 3.89 µg/mL/48 h on day 14 in rat primary hepatocytes cultured using our new method. These findings indicate that the newly developed culture method can suppress EMT and maintain liver functions for 14 d in rat primary hepatocytes, potentially expanding the utility of primary hepatocyte cultured by using conventional 3D methods.

The Material World of 3D-Bioprinted and Microfluidic-Chip Models of Human Liver Fibrosis

Biomaterials are extensively used to mimic cell-matrix interactions, which are essential for cell growth, function, and differentiation. This is particularly relevant when developing in vitro disease models of organs rich in extracellular matrix, like the liver. Liver disease involves a chronic wound-healing response with formation of scar tissue known as fibrosis. At early stages, liver disease can be reverted, but as disease progresses, reversion is no longer possible, and there is no cure. Research for new therapies is hampered by the lack of adequate models that replicate the mechanical properties and biochemical stimuli present in the fibrotic liver. Fibrosis is associated with changes in the composition of the extracellular matrix that directly influence cell behavior. Biomaterials could play an essential role in better emulating the disease microenvironment. In this paper, the recent and cutting-edge biomaterials used for creating in vitro models of human liver fibrosis are revised, in combination with cells, bioprinting, and/or microfluidics. These technologies have been instrumental to replicate the intricate structure of the unhealthy tissue and promote medium perfusion that improves cell growth and function, respectively. A comprehensive analysis of the impact of material hints and cell-material interactions in a tridimensional context is provided.

Gelatin scaffold ameliorates proliferation & stem cell differentiation into the hepatic like cell and support liver regeneration in partial-hepatectomized mice model

Stem cell-based tissue engineering is an emerging tool for developing functional tissues of choice. To understand pluripotency and hepatic differentiation of mouse embryonic stem cells (mESCs) on a three-dimensional (3D) scaffold, we established an efficient approach for generating hepatocyte-like cells (HLCs) from hepatoblast cells. We developed porous and biodegradable scaffold, which was stimulated with exogenous growth factors and investigated stemness and differentiation capacity of mESCs into HLCs on the scaffoldin-vitro. In animal studies, we had cultured mESCs-derived hepatoblast-like cells on the scaffold and then, transplanted them into the partially hepatectomized C57BL/6 male mice model to evaluate the effect of gelatin scaffold on hepatic regeneration. The 3D culture system allowed maintenance of stemness properties in mESCs. The step-wise induction of mESCs with differentiation factors leads to the formation of HLCs and expressed liver-specific genes, including albumin, hepatocyte nucleic factor 4 alpha, and cytokeratin 18. In addition, cells also expressed Ki67, indicating cells are proliferating. The secretome showed expression of albumin, urea, creatinine, alanine transaminase, and aspartate aminotransferase. However, the volume of the excised liver which aids regeneration has not been studied. Our results indicate that hepatoblast cells on the scaffold implanted in PH mouse indicates that these cells efficiently differentiate into HLCs and cholangiocytes, forming hepatic lobules with central and portal veins, and bile duct-like structures with neovascularization. The gelatin scaffold provides an efficient microenvironment for liver differentiation and regeneration bothin-vitroandin-vivo. These hepatoblasts cells would be a valuable source for 3D liver tissue engineering/transplantation in liver diseases.

Whole Liver Derived Acellular Extracellular Matrix for Bioengineering of Liver Constructs: An Updated Review

Biomaterial templates play a critical role in establishing and bioinstructing three-dimensional cellular growth, proliferation and spatial morphogenetic processes that culminate in the development of physiologically relevant in vitro liver models. Various natural and synthetic polymeric biomaterials are currently available to construct biomimetic cell culture environments to investigate hepatic cell-matrix interactions, drug response assessment, toxicity, and disease mechanisms. One specific class of natural biomaterials consists of the decellularized liver extracellular matrix (dECM) derived from xenogeneic or allogeneic sources, which is rich in bioconstituents essential for the ultrastructural stability, function, repair, and regeneration of tissues/organs. Considering the significance of the key design blueprints of organ-specific acellular substrates for physiologically active graft reconstruction, herein we showcased the latest updates in the field of liver decellularization-recellularization technologies. Overall, this review highlights the potential of acellular matrix as a promising biomaterial in light of recent advances in the preparation of liver-specific whole organ scaffolds. The review concludes with a discussion of the challenges and future prospects of liver-specific decellularized materials in the direction of translational research.

Multiscale biomechanics and mechanotransduction from liver fibrosis to cancer

A growing body of multiscale biomechanical studies has been proposed to highlight the mechanical cues in the development of hepatic fibrosis and cancer. At the cellular level, changes in mechanical microenvironment induce phenotypic and functional alterations of hepatic cells, initiating a positive feedback loop that promotes liver fibrogenesis and hepatocarcinogenesis. Tumor mechanical microenvironment of hepatocellular carcinoma facilitates tumor cell growth and metastasis, and hinders the drug delivery and immunotherapy. At the molecular level, mechanical forces are sensed and transmitted into hepatic cells via allosteric activation of mechanoreceptors on the cell membrane, leading to the activation of various mechanotransduction pathways including integrin and YAP signaling and then regulating cell function. Thus, the application of mechanomedicine concept in the treatment of liver diseases is promising for rational design and cell-specific delivery of therapeutic drugs. This review mainly discusses the correlation between biomechanical cues and liver diseases from the viewpoint of mechanobiology.

In vitro long term differentiation and functionality of three-dimensional bioprinted primary human hepatocytes: application for in vivo engraftment

In recent decades, 3D in vitro cultures of primary human hepatocytes (PHH) have been increasingly developed to establish models capable of faithfully mimicking main liver functions. The use of 3D bioprinting, capable of recreating structures composed of cells embedded in matrix with controlled microarchitectures, is an emergent key feature for tissue engineering. In this work, we used an extrusion-based system to print PHH in a methacrylated gelatin matrix (GelMa). PHH bioprinted in GelMa rapidly organized into polarized hollow spheroids and were viable for at least 28 days of culture. These PHH were highly differentiated with maintenance of liver differentiation genes over time, as demonstrated by transcriptomic analysis and functional approaches. The cells were polarized with localization of apico/canalicular regions, and displayed activities of phase I and II biotransformation enzymes that could be regulated by inducers. Furthermore, the implantation of the bioprinted structures in mice demonstrated their capability to vascularize, and their ability to maintain human hepatic specific functions for at least 28 days was illustrated by albumin secretion and debrisoquine metabolism. This model could hold great promise for human liver tissue generation and its use in future biotechnological developments.

Design by Nature: Emerging Applications of Native Liver Extracellular Matrix for Cholangiocyte Organoid-Based Regenerative Medicine

Organoid technology holds great promise for regenerative medicine. Recent studies show feasibility for bile duct tissue repair in humans by successfully transplanting cholangiocyte organoids in liver grafts during perfusion. Large-scale expansion of cholangiocytes is essential for extending these regenerative medicine applications. Human cholangiocyte organoids have a high and stable proliferation capacity, making them an attractive source of cholangiocytes. Commercially available basement membrane extract (BME) is used to expand the organoids. BME allows the cells to self-organize into 3D structures and stimulates cell proliferation. However, the use of BME is limiting the clinical applications of the organoids. There is a need for alternative tissue-specific and clinically relevant culture substrates capable of supporting organoid proliferation. Hydrogels prepared from decellularized and solubilized native livers are an attractive alternative for BME. These hydrogels can be used for the culture and expansion of cholangiocyte organoids in a clinically relevant manner. Moreover, the liver-derived hydrogels retain tissue-specific aspects of the extracellular microenvironment. They are composed of a complex mixture of bioactive and biodegradable extracellular matrix (ECM) components and can support the growth of various hepatobiliary cells. In this review, we provide an overview of the clinical potential of native liver ECM-based hydrogels for applications with human cholangiocyte organoids. We discuss the current limitations of BME for the clinical applications of organoids and how native ECM hydrogels can potentially overcome these problems in an effort to unlock the full regenerative clinical potential of the organoids.

Immune Score Indicator for the Survival of Melanoma Patients Based on Tumor Microenvironment

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DMSO-free highly differentiated HepaRG spheroids for chronic toxicity, liver functions and genotoxicity studies

The liver is essential in the elimination of environmental and food contaminants. Given the interspecies differences between rodents and humans, the development of relevant in vitro human models is crucial to investigate liver functions and toxicity in cells that better reflect pathophysiological processes. Classically, the differentiation of the hepatic HepaRG cell line requires high concentration of dimethyl sulfoxide (DMSO), which restricts its usefulness for drug-metabolism studies. Herein, we describe undifferentiated HepaRG cells embedded in a collagen matrix in DMSO-free conditions that rapidly organize into polarized hollow spheroids of differentiated hepatocyte-like cells (Hepoid-HepaRG). Our conditions allow concomitant proliferation with high levels of liver-specific functions and xenobiotic metabolism enzymes expression and activities after a few days of culture and for at least 4 weeks. By studying the toxicity of well-known injury-inducing drugs by treating cells with 1- to 100-fold of their plasmatic concentrations, we showed appropriate responses and demonstrate the sensitivity to drugs known to induce various degrees of liver injury. Our results also demonstrated that the model is well suited to estimate cholestasis and steatosis effects of drugs following chronic treatment. Additionally, DNA alterations caused by four genotoxic compounds (Aflatoxin B₁ (AFB₁), Benzo[a]Pyrene (B[a]P), Cyclophosphamide (CPA) and Methyl methanesulfonate (MMS)) were quantified in a dose-dependent manner by the comet and micronucleus assays. Their genotoxic effects were significantly increased after either an acute 24 h treatment (AFB₁: 1.5-6 μM, CPA: 2.5-10 μM, B[a]P: 12.5-50 μM, MMS: 90-450 μM) or after a 14-day treatment at much lower concentrations (AFB₁: 0.05-0.2 μM, CPA: 0.125-0.5 μM, B[a]P: 0.125-0.5 μM) representative to human exposure. Altogether, the DMSO-free 3D culture of Hepoid-HepaRG provides highly differentiated and proliferating cells relevant for various toxicological in vitro assays, especially for drug-preclinical studies and environmental chemicals risk assessment.

Generation of proliferating human adult hepatocytes using optimized 3D culture conditions

Generating the proliferation of differentiated normal adult human hepatocytes is a major challenge and an expected central step in understanding the microenvironmental conditions that regulate the phenotype of human hepatocytes in vitro. In this work, we described optimized 3D culture conditions of primary human hepatocytes (PHH) to trigger two waves of proliferation and we identified matrix stiffness and cell-cell interactions as the main actors necessary for this proliferation. We demonstrated that DNA replication and overexpression of cell cycle markers are modulate by the matrix stiffness while PHH cultured in 3D without prior cellular interactions did not proliferate. Besides, we showed that PHH carry out an additional cell cycle after transient inhibition of MAPK MER1/2-ERK1/2 signaling pathway. Collagen cultured hepatocytes are organized as characteristic hollow spheroids able to maintain survival, cell polarity and hepatic differentiation for long-term culture periods of at least 28 days. Remarkably, we demonstrated by transcriptomic analysis and functional experiments that proliferating cells are mature hepatocytes with high detoxication capacities. In conclusion, the advanced 3D model described here, named Hepoid, is particularly relevant for obtaining normal human proliferating hepatocytes. By allowing concomitant proliferation and differentiation, it constitutes a promising tool for many pharmacological and biotechnological applications.

Synergistic effect of three-dimensional coculture and photobiomodulation therapy on vascularized liver spheroid formation by stem cells

Despite studies reporting functional differentiation of liver cells, a three-dimensional, vascularized liver organ has yet to be developed from mesenchymal stem cells. We investigated whether treatment with photobiomodulation (PBM) before three-dimensional liver spheroid transplantation improved the recovery of liver function via stimulation of angiogenesis and hepatocyte differentiation. Liver spheroids composed of hepatic, endothelial, and mesenchymal cells were subjected to PBM therapy. To evaluate the in vivo therapeutic effect of the liver spheroids treated with PBM, phosphate-buffered saline, liver spheroid, and PBM-treated liver spheroid were transplanted into a damaged host liver using conventional chimeric mouse models. To further characterize the maturation of transplanted PBM-liver spheroid compared with the newly generated non-PBM-liver spheroid or human liver tissues, the expression profiles of mature liver signature genes were analyzed. Liver spheroids expressed hepatocyte growth factors, including vascular endothelial growth factor and angiogenic factors. The cells in liver spheroid compensated for the low viability and improved the function of hepatocytes. Here, we demonstrate the formation of vascularized and functional human liver spheroid from human adipose-derived stem cells by transplantation of liver tissue created in vitro. Albumin secretion by PBM-treated liver spheroid was higher on Day 28 compared with liver spheroid-seeded transplant group. PBM-liver spheroids serve as individual vascularization units, promoting the simultaneous development of new microvascular networks at different locations inside the implanted tissue constructs. The vasculature in the liver spheroid transplants became functional by connecting to the host vessels within 48 h. These PBM-liver spheroids may be useful in designing artificial three-dimensional hepatic tissue constructs and in cell therapy with limited numbers of human hepatocytes.

3D culture of HepaRG cells in GelMa and its application to bioprinting of a multicellular hepatic model

Bioprinting is an emergent technology that has already demonstrated the capacity to create complex and/or vascularized multicellular structures with defined and organized architectures, in a reproducible and high throughput way. Here, we present the implementation of a complex liver model by the development of a three-dimensional extrusion bioprinting process, including parameters for matrix polymerization of methacrylated gelatin, using two hepatic cell lines, Huh7 and HepaRG. The printed structures exhibited long-term viability (28 days), proliferative ability, a relevant hepatocyte phenotype and functions equivalent to or better than those of their 2D counterparts using standard DMSO treatment. This work served as a basis for the bioprinting of complex multicellular models associating the hepatic parenchymal cells, HepaRG, with stellate cells (LX-2) and endothelial cells (HUVECs), able of colonizing the surface of the structure and thus recreating a pseudo endothelial barrier. When bioprinted in 3D monocultures, LX-2 expression was modulated by TGFβ-1 toward the induction of myofibroblastic genes such as ACTA2 and COL1A1. In 3D multicellular bioprinted structures comprising HepaRG, LX-2 and endothelial cells, we evidenced fibrillar collagen deposition, which is never observed in monocultures of either HepaRG or LX-2 alone. These observations indicate that a precise control of cellular communication is required to recapitulate key steps of fibrogenesis. Bioprinted 3D co-cultures therefore open up new perspectives in studying the molecular and cellular basis of fibrosis development and provide better access to potential inducers and inhibitors of collagen expression and deposition.

Matrix Mechanics as Regulatory Factors and Therapeutic Targets in Hepatic Fibrosis

The hallmark of liver fibrosis is excessive extracellular matrix (ECM) synthesis and deposition that improve liver matrix remodeling and stiffening. Increased matrix stiffness is not only a pathological consequence of liver fibrosis in traditional view, but also recognized as a key driver in pathological progression of hepatic fibrosis. Cells can perceive changes in the mechanical characteristics of hepatic matrix and respond by means of mechanical signal transduction pathways to regulate cell behavior. In this review, the authors first classify causes of liver matrix stiffening during fibrotic progression, such as higher degree of collagen cross-linking. The latest advances of the research on the matrix mechanics in regulating activation of HSCs or fibroblasts under two-dimensional (2D) and three-dimensional (3D) microenvironment is also classified and summarized. The mechanical signaling pathways involved in the process of hepatic matrix stiffening, such as YAP-TAZ signaling pathway, are further summarized. Finally, some potential therapeutic concepts and strategies based on matrix mechanics will be detailed. Collectively, these findings reinforce the importance of matrix mechanics in hepatic fibrosis, and underscore the value of clarifying its modulation in hopes of advancing the development of novel therapeutic targets and strategies for hepatic fibrosis.

Hydrogels for Liver Tissue Engineering

Bioengineered livers are promising in vitro models for drug testing, toxicological studies, and as disease models, and might in the future be an alternative for donor organs to treat end-stage liver diseases. Liver tissue engineering (LTE) aims to construct liver models that are physiologically relevant. To make bioengineered livers, the two most important ingredients are hepatic cells and supportive materials such as hydrogels. In the past decades, dozens of hydrogels have been developed to act as supportive materials, and some have been used for in vitro models and formed functional liver constructs. However, currently none of the used hydrogels are suitable for in vivo transplantation. Here, the histology of the human liver and its relationship with LTE is introduced. After that, significant characteristics of hydrogels are described focusing on LTE. Then, both natural and synthetic materials utilized in hydrogels for LTE are reviewed individually. Finally, a conclusion is drawn on a comparison of the different hydrogels and their characteristics and ideal hydrogels are proposed to promote LTE.

High density Huh7.5 cell hollow fiber bioreactor culture for high-yield production of hepatitis C virus and studies of antivirals

Chronic hepatitis C virus (HCV) infection poses a serious global public health burden. Despite the recent development of effective treatments there is a large unmet need for a prophylactic vaccine. Further, antiviral resistance might compromise treatment efficiency in the future. HCV cell culture systems are typically based on Huh7 and derived hepatoma cell lines cultured in monolayers. However, efficient high cell density culture systems for high-yield HCV production and studies of antivirals are lacking. We established a system based on Huh7.5 cells cultured in a hollow fiber bioreactor in the presence or absence of bovine serum. Using an adapted chimeric genotype 5a virus, we achieved peak HCV infectivity and RNA titers of 7.6 log₁₀ FFU/mL and 10.4 log₁₀ IU/mL, respectively. Bioreactor derived HCV showed high genetic stability, as well as buoyant density, sensitivity to neutralizing antibodies AR3A and AR4A, and dependency on HCV co-receptors CD81 and SR-BI comparable to that of HCV produced in monolayer cell cultures. Using the bioreactor platform, treatment with the NS5A inhibitor daclatasvir resulted in HCV escape mediated by the NS5A resistance substitution Y93H. In conclusion, we established an efficient high cell density HCV culture system with implications for studies of antivirals and vaccine development.

Cell-derived matrices for studying cell proliferation and directional migration in a complex 3D microenvironment

2D surfaces offer simple analysis of cells in culture, yet these often yield different cell morphologies and responses from those observed in vivo. Considerable effort has therefore been expended on the generation of more tissue-like environments for the study of cell behavior in vitro. Purified matrix proteins provide a 3D scaffold that better mimics the in vivo situation; however, these are far removed from the complex tissue composition seen in vivo. Cell-derived matrices (CDMs) offer a more physiologically relevant alternative for studying in vivo-like cell behavior in vitro. In the protocol described here, fibroblasts cultured on gelatin-coated surfaces are maintained in the presence of ascorbic acid to strengthen matrix deposition over 1-3 weeks. The resulting fibrillar CDMs are denuded of cells, and other cells are subsequently cultured on them, after which their behavior is monitored. We also demonstrate how to use CDMs as an in vivo-relevant reductionist model for studying tumor-stroma-induced changes in carcinoma cell proliferation and migration.