Cultured hepatocytes adopt progenitor characteristics and display bipotent capacity to repopulate the liver

Effect of lithium carbonate on autophagy and proliferative activity of isolated hepatocytes

The hepatocytes were cultivated in the presence of lithium carbonate (LC) for drugs testing or possible source for transplantation in the treatment of hereditary or terminal liver diseases. The LC, as an inducer of autophagy, is a promising drug for maintaining cell homeostasis and has a significant effect on the ultrastructural organization of hepatocyte cells. Within current investigation, new mechanisms of the biological effects of lithium and the ultrastructural analysis of the primary culture of hepatocytes were studied via flow cytofluorometry, light, and electron microscopy methods. Obtained results demonstrate the absence of the toxic effect of 5 mM of LC on the primary hepatocyte culture. In addition, LC does not block the cell cycle at the G₀/G₁ stage after 24 h of hepatocyte cultivation and promotes the preservation of their viability by 48 h of the experiment. Moreover, LC does not stimulate hepatocyte apoptosis, induces autophagy and the preserves the proliferative activity of hepatocytes.

Expansion of human primary hepatocytes in vitro through their amplification as liver progenitors in a 3D organoid system

Despite decades of investigation on the proliferation of adult human primary hepatocytes, their expansion in vitro still remains challenging. To later be able to consider hepatocytes as a cell therapy alternative or bridge to liver transplantation, dramatically impeded by a shortage in liver donors, the first step is having an almost unlimited source of these cells. The banking of transplantable hepatocytes also implies a protocol for their expansion that can be compatible with large-scale production. We show that adult human primary hepatocytes when grown in 3D organoids are easily amplified, providing a substantial source of functional hepatocytes ready for transplantation. Following their plating, differentiated human hepatocytes are amplified during a transient and reversible step as liver progenitors, and can subsequently be converted back to mature differentiated hepatocytes. The protocol we propose is not only compatible with automated and high-throughput cell culture systems, thanks to the expansion of hepatocytes in suspension, but also guarantees the generation of a high number of functional cells from the same patient sample, with a relatively easy set up.

Efficient and Controlled Generation of 2D and 3D Bile Duct Tissue from Human Pluripotent Stem Cell-Derived Spheroids

While in vitro liver tissue engineering has been increasingly studied during the last several years, presently engineered liver tissues lack the bile duct system. The lack of bile drainage not only hinders essential digestive functions of the liver, but also leads to accumulation of bile that is toxic to hepatocytes and known to cause liver cirrhosis. Clearly, generation of bile duct tissue is essential for engineering functional and healthy liver. Differentiation of human induced pluripotent stem cells (iPSCs) to bile duct tissue requires long and/or complex culture conditions, and has been inefficient so far. Towards generating a fully functional liver containing biliary system, we have developed defined and controlled conditions for efficient 2D and 3D bile duct epithelial tissue generation. A marker for multipotent liver progenitor in both adult human liver and ductal plate in human fetal liver, EpCAM, is highly expressed in hepatic spheroids generated from human iPSCs. The EpCAM high hepatic spheroids can, not only efficiently generate a monolayer of biliary epithelial cells (cholangiocytes), in a 2D differentiation condition, but also form functional ductal structures in a 3D condition. Importantly, this EpCAM high spheroid based biliary tissue generation is significantly faster than other existing methods and does not require cell sorting. In addition, we show that a knock-in CK7 reporter human iPSC line generated by CRISPR/Cas9 genome editing technology greatly facilitates the analysis of biliary differentiation. This new ductal differentiation method will provide a more efficient method of obtaining bile duct cells and tissues, which may facilitate engineering of complete and functional liver tissue in the future.

Immunohistochemical Analysis of the Stem Cell Marker LGR5 in Pediatric Liver Disease

Aims In regenerating liver, hepatic progenitor cells (HPCs) are recruited in response to injury; however, few highly specific human HPC markers exist for the hepatocyte lineage. Leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5), a Wnt-associated stem cell marker, has been extensively studied in intestinal stem cells, but little is known about its expression in human liver. We hypothesized that LGR5+ HPCs are induced in the regenerative response to pediatric liver injury. Methods and results Immunohistochemistry was used to characterize LGR5 expression in pediatric liver explants (n = 36). We found cytoplasmic LGR5 expression in all cases; although, much less was observed in acute hepatic necrosis compared to chronic liver diseases. In the latter cases, >50% of hepatocytes were LGR5+, signifying a robust regenerative response mainly in the periphery of regenerative nodules. Only weak LGR5 staining was noted in bile ducts, suggesting hepatocyte-specific expression at the interface. Conclusions Although we observed some degree of regenerative response in all cases, LGR5 was highly expressed in chronic liver disease, possibly due to alternate regeneration and reprogramming pathways. LGR5 is predominant in peri-septal hepatocytes rather than epithelial cell adhesion molecule (EpCAM) positive ductular reactions in chronic pediatric liver diseases and may represent a transitional HPC phenotype for the hepatocyte lineage. These studies are the first to support a unique role for LGR5 in human hepatocyte regeneration and as a potential predictive biomarker for recovery of liver function in children. Future work will also investigate the molecular mechanisms behind LGR5 expression.

Conversion of Terminally Committed Hepatocytes to Culturable Bipotent Progenitor Cells with Regenerative Capacity

A challenge for advancing approaches to liver regeneration is loss of functional differentiation capacity when hepatocyte progenitors are maintained in culture. Recent lineage-tracing studies have shown that mature hepatocytes (MHs) convert to an immature state during chronic liver injury, and we investigated whether this conversion could be recapitulated in vitro and whether such converted cells could represent a source of expandable hepatocytes. We report that a cocktail of small molecules, Y-27632, A-83-01, and CHIR99021, can convert rat and mouse MHs in vitro into proliferative bipotent cells, which we term chemically induced liver progenitors (CLiPs). CLiPs can differentiate into both MHs and biliary epithelial cells that can form functional ductal structures. CLiPs in long-term culture did not lose their proliferative capacity or their hepatic differentiation ability, and rat CLiPs were shown to extensively repopulate chronically injured liver tissue. Thus, our study advances the goals of liver regenerative medicine.

Explanted diseased livers - a possible source of metabolic competent primary human hepatocytes

Being an integral part of basic, translational and clinical research, the demand for primary human hepatocytes (PHH) is continuously growing while the availability of tissue resection material for the isolation of metabolically competent PHH remains limited. To overcome current shortcomings, this study evaluated the use of explanted diseased organs from liver transplantation patients as a potential source of PHH. Therefore, PHH were isolated from resected surgical specimens (Rx-group; n = 60) and explanted diseased livers obtained from graft recipients with low labMELD-score (Ex-group; n = 5). Using established protocols PHH were subsequently cultured for a period of 7 days. The viability and metabolic competence of cultured PHH was assessed by the following parameters: morphology and cell count (CyQuant assay), albumin synthesis, urea production, AST-leakage, and phase I and II metabolism. Both groups were compared in terms of cell yield and metabolic function, and results were correlated with clinical parameters of tissue donors. Notably, cellular yields and viabilities were comparable between the Rx- and Ex-group and were 5.3±0.5 and 2.9±0.7×10⁶ cells/g liver tissue with 84.3±1.3 and 76.0±8.6% viability, respectively. Moreover, PHH isolated from the Rx- or Ex-group did not differ in regards to loss of cell number in culture, albumin synthesis, urea production, AST-leakage, and phase I and II metabolism (measured by the 7-ethoxycoumarin-O-deethylase and uracil-5′-diphosphate-glucuronyltransferase activity). Likewise, basal transcript expressions of the CYP monooxygenases 1A1, 2C8 and 3A4 were comparable as was their induction when treated with a cocktail that consisted of 3-methylcholantren, rifampicin and phenobarbital, with increased expression of CYP 1A1 and 3A4 mRNA while transcript expression of CYP 2C8 was only marginally changed. In conclusion, the use of explanted diseased livers obtained from recipients with low labMELD-score might represent a valuable source of metabolically competent PHH which are comparable in viability and function to cells obtained from specimens following partial liver resection.