Stem and progenitor cell systems in liver development and regeneration

Past, present, and future of chemically induced hepatocarcinogenesis rodent models: Perspectives concerning classic and new cancer hallmarks

Hepatocellular carcinoma (HCC), the main primary liver cancer, accounts for 5 % of all incident cases and 8.4 % of all cancer-related deaths worldwide. HCC displays a spectrum of environmental risk factors (viral chronic infections, aflatoxin exposure, alcoholic- and nonalcoholic fatty liver diseases) that result in molecular complexity and heterogeneity, contributing to a rising epidemiological burden, poor prognosis, and non-satisfactory treatment options. The emergence of HCC (i.e., hepatocarcinogenesis) is a multistep and complex process that addresses many (epi)genetic alterations and phenotypic traits, the so-called cancer hallmarks. "Polymorphic microbiomes", "epigenetic reprogramming", "senescent cells" and "unlocking phenotypic plasticity" are trending hallmarks/enabling features in cancer biology. As the main molecular drivers of HCC are still undruggable, chemically induced in vivo models of hepatocarcinogenesis are useful tools in preclinical research. Thus, this narrative review aimed at recapitulating the basic features of chemically induced rodent models of hepatocarcinogenesis, eliciting their permanent translational value regarding the "classic" and the "new" cancer hallmarks/enabling features. We gathered state-of-art preclinical evidence on non-cirrhotic, inflammation-, alcoholic liver disease- and nonalcoholic fatty liver-associated HCC models, demonstrating that these bioassays indeed express the recently added hallmarks, as well as reflect the interplay between classical and new cancer traits. Our review demonstrated that these protocols remain valuable for translational preclinical application, as they recapitulate trending features of cancer science. Further "omics-based" approaches are warranted while multimodel investigations are encouraged in order to avoid "model-biased" responses.

Human Hepatic Cancer Stem Cells (HCSCs) Markers Correlated With Immune Infiltrates Reveal Prognostic Significance of Hepatocellular Carcinoma

Background

Several markers have been reported to be specific for hepatic cancer stem cells (HCSCs), which is usually thought to be highly associated with poor clinical outcomes. Tumor-infiltrating immune cells act as an important factor for oncogenesis. Little is known about the correlation of HCSC markers to prognosis and immune infiltrates.

Methods

Expression of HCSC markers was analyzed through Oncomine database, Gene Expression Profiling Interactive Analysis (GEPIA) and Integrative Molecular Database of Hepatocellular Carcinoma (HCCDB), respectively. The prognostic effect of HCSC markers was evaluated using Kaplan-Meier plotter in association with different tumor stages, risk factors, and gender. The correlation of HCSC markers to tumor-infiltrating immune cells was tested by Tumor Immune Estimation Resource (TIMER). HCSC markers related gene sets were investigated by GEPIA, with their biological functions being analyzed by Cytoscape software.

Results

The expression level of 10 HCSC markers in HCC was higher than that in normal tissues in at least one database. Among them, high expression of CD24, SOX9, and SOX12 was positively correlated with poor prognosis (CD24: OS P = 0.0012, PFS P = 7.9E–05. SOX9: OS P = 0.012. SOX12: OS P = 0.0004, PFS P = 0.0013, respectively). However, the expression of CD13, CD34 and ALDH1A1 was associated with prolonged OS and PFS. SOX12 was significantly upregulated in poor prognosis of HCC patients with different conditions. Besides, total nine HCSC markers were identified to be positively associated with immune infiltration, including SOX12. Furthermore, Toll-like receptor signaling pathway was found to be one major pathway of these HCSC markers related gene networks.

Conclusion

Our results suggest that seven upregulated HCSC markers (CD90, EpCAM, CD133, CD24, SOX9, CK19, and SOX12) are related with poor prognosis and immune infiltration in HCC. In addition, we find that high SOX12 expression remarkably affect prognosis in male HCC patients but not in female. HCC patients under viral infection or alcohol intake with increased SOX12 expression had poorer prognosis. Therefore, HCSCs markers likely play an important role in tumor related immune infiltration and SOX12 might be a potential therapeutic target in patients with HCC.

Myofibroblasts control the proliferation of fetal hepatoblasts and their differentiated cholangiocytes during the hepatoblast-to-cholangiocyte transition

Mesenchymal cells in the liver provide the microenvironment for hepatoblasts expansion and differentiation. We have previously demonstrated that myofibroblasts (MFs) promoted hepatoblasts differentiation into cholangiocytes, whereas its role in controlling the proliferation of hepatoblasts and their differentiated cholangiocytes remains elusive. Here, we investigated the role of MFs in regulating the proliferation of hepatoblasts and their differentiated cholangiocytes using an indirect coculture system. When cocultured with hepatoblasts, MFs promoted hepatoblasts differentiation into cholangiocytes and inhibited the proliferation and stemness of hepatoblasts. However, when hepatoblasts already differentiated into cholangiocytes, MFs promoted the differentiated cholangiocytes proliferation. In addition, hepatoblast proliferation genes such as hepatocyte growth factor (HGF), insulin-like growth factor-1 and 2 (IGF-1 and 2), midkine 1 (Mdk1), and pleiotrophin (Ptn) expression in MFs were down-regulated compared with their levels in fibroblasts. Our findings uncover the role of MFs in controlling the proliferation of hepatoblasts and their differentiated cholangiocytes, potentially providing a novel therapeutic strategy for cholangiocyte regeneration.

The Roles Of Angiogenesis And Cancer Stem Cells In Sorafenib Drug Resistance In Hepatocellular Carcinoma

Background

An increasing number of studies support cancer stem cells as the reason for chemoresistance to sorafenib therapy in hepatocellular carcinoma (HCC), but the mechanism is still unclear. In this study, the mechanism of sorafenib resistance in cancer stem cells was examined by in vitro experiments and xenograft mouse model.

Methods

The expression of cancer stem cell markers in the Chang liver cell line and PLC/PRF/5 and HepG2 hepatoma cell lines were compared by immunoblot assay before and after sorafenib treatment in vitro. As a xenograft mouse model, subcutaneous injection of hepatoma cells followed by sorafenib therapy was performed in NU/NU mice. The effects of sorafenib therapy on tumor growth and cancer stem cell markers were studied. Angiogenesis associated with cancer stem cells was studied by immunoblot and immunohistochemistry assay.

Results

The expression of cancer stem cell markers was higher in PLC/PRF/5 and HepG2 cells than Chang liver cells, indicating that these hepatoma cells had more stemness-related characteristics. The cancer stem cell markers were upregulated in the hepatoma cell lines following sorafenib treatment in vitro. In the xenograft model, tumors from PLC/PRF/5 and HepG2 cells with high E-cadherin expression were more resistance to sorafenib therapy. However, the expression of cancer stem cell markers was not significantly different after sorafenib therapy in these tumors. Furthermore, we found that sorafenib therapy induced angiogenesis within tumors from high E-cadherin expressing hepatoma cells.

Conclusion

The mechanism of chemoresistance in sorafenib therapy in HCC may be the tumor angiogenesis associated with high E-cadherin expression in cancer stem cells.

Mesenchymal stem cell transplantation in polytrauma: Evaluation of bone and liver healing response in an experimental rat model

PURPOSE

Trauma is the most common cause of death of young people in the world. As known, mesenchymal stem cells (MSCs) accelerate tissue regeneration mechanisms. In our study, we aimed to investigate the effects of MSCs transplantation on the healing of liver and bone tissue by considering trauma secondary inflammatory responses.

METHODS

56 adult Wistar-albino rats were divided into two groups: the polytrauma (liver and bone) (n = 28), and the liver trauma group (n = 28). At 36 h and 5th day after surgery, both rats with polytrauma and with isolated liver injury received either intravenous (IV) or intraperitoneal (IP) injections of MSCs (one million cells per kg body weight). Untreated groups received IV and IP saline injections. At day 21 after surgery, liver, tibia and fibula of the subjects were excised and evaluated for histopathologic and histomorphometric examination. Additionally, whole blood count (white blood cells, hemoglobin and platelets), C-reactive protein (CRP), glucose, alanine aminotransferase (ALT), aspartate aminotransferase (AST), albumin, blood gas, and trauma markers interleukin-1B (IL-1B), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF alpha) levels were investigated.

RESULTS

In general, MSC transplantations were well tolerated by the subjects. It was found that ALT, CRP, albumin were significantly lower in rats which received MSCs (p < 0.001). Inflammation of the liver and bone tissue in the MSC-injected rats were significantly lower than that of the untreated groups.

CONCLUSIONS

Herewith we have shown that MSC infusion in posttraumatic rats leads to less aggressive and more effective consequences on liver and bone tissue healing. Human MSC treatment for trauma is still in early stages of development; thus standard protocols, and patient inclusion criteria should be established beforehand clinical trials.

Direct and indirect coculture of mouse hepatic progenitor cells with mouse embryonic fibroblasts for the generation of hepatocytes and cholangiocytes

The widespread use of hepatocytes and cholangiocytes for regenerative medicine and tissue engineering is restricted by the limited number of hepatocytes and cholangiocytes; a simple and effective method for the expansion and differentiation of the hepatic progenitor cells (HPCs) is required. Recent studies demonstrated that mouse embryonic fibroblasts (MEFs) play an important role in supporting the proliferation of the mouse hepatic progenitor cells (mHPCs). However, the effect of direct and indirect coculture of MEFs with mHPCs on the differentiation of mHPCs is poorly studied. Herein, we show that mHPCs rapidly proliferate and form colonies in direct or indirect contact coculture with MEFs in the serum-free medium. Importantly, after direct contact coculture of the mHPCs with MEFs for 6 days, mHPCs expressed the hepatic marker albumin (ALB) and did not express the cholangiocyte marker CK19, indicating their differentiation into hepatocytes. In contrast, after indirect contact coculture of the mHPCs with MEFs for 6 days, mHPCs expressed the cholangiocyte marker CK19 and did not express the hepatic marker ALB, indicating their differentiation into cholangiocytes. These results indicate that direct and indirect contact cocultures of the mHPCs with MEFs are useful for rapidly producing hepatocytes and cholangiocytes.

An in vitro model of polycystic liver disease using genome-edited human inducible pluripotent stem cells

In the developing liver, bile duct structure is formed through differentiation of hepatic progenitor cells (HPC) into cholangiocytes. A subtype of polycystic liver diseases characterized by uncontrolled expansion of bile ductal cells is caused by genetic abnormalities such as in that of protein kinase C substrate 80 K-H (PRKCSH). In this study, we aimed to mimic the disease process in vitro by genome editing of the PRKCSH locus in human inducible pluripotent stem (iPS) cells. A proportion of cultured human iPS cell-derived CD13+CD133+ HPC differentiated into CD13- cells. During the subsequent gel embedding culture, CD13- cells formed bile ductal marker-positive cystic structures with the polarity of epithelial cells. A deletion of PRKCSH gene increased expression of cholangiocytic transcription factors in CD13- cells and the number of cholangiocytic cyst structure. These results suggest that PRKCSH deficiency promotes the differentiation of HPC-derived cholangiocytes, providing a good in vitro model to analyze the molecular mechanisms underlying polycystic diseases.

Current status of research on liver regeneration

The liver has a strong regenerative potential, and liver regeneration shows different ways according to the degree of liver injury. The current research on liver regeneration has achieved some promising results, and the cellular and molecular mechanism of liver regeneration has been deeply studied. Recently, the role of biomechanical factors in liver regeneration is gradually attracting attention. In addition to the proliferation of liver cells, liver regeneration also involves the proliferation and differentiation of hepatic stem cells. However, the exact mechanism of liver regeneration is not fully clear. This review will summarize the relevant studies on liver regeneration to discuss the current research status of liver regeneration, with regard to the liver regeneration model, cellular and molecular mechanism of liver regeneration, the effects of mechanical factors on regeneration, and the role of stem cells in liver regeneration. A better understanding of liver regeneration will provide a new avenue for the clinical diagnosis and treatment of liver related diseases.

Foetal hepatic progenitor cells assume a cholangiocytic cell phenotype during two-dimensional pre-culture

Liver consists of parenchymal hepatocytes and other cells. Liver progenitor cell (LPC) is the origin of both hepatocytes and cholangiocytic cells. The analyses of mechanism regulating differentiation of LPCs into these functional cells are important for liver regenerative therapy using progenitor cells. LPCs in adult livers were found to form cysts with cholangiocytic characteristics in 3D culture. In contrast, foetal LPCs cannot form these cholangiocytic cysts in the same culture. Thus, the transition of foetal LPCs into cholangiocytic progenitor cells might occur during liver development. Primary CD45(-)Ter119(-)Dlk1(+) LPCs derived from murine foetal livers formed ALBUMIN (ALB)(+)CYTOKERATIN (CK)19(-) non-cholangiocytic cysts within 3D culture. In contrast, when foetal LPCs were pre-cultured on gelatine-coated dishes, they formed ALB(-)CK19(+) cholangiocytic cysts. When hepatocyte growth factor or oncostatin M, which are inducers of hepatocytic differentiation, was added to pre-culture, LPCs did not form cholangiocytic cysts. These results suggest that the pre-culture on gelatine-coated dishes changed the characteristics of foetal LPCs into cholangiocytic cells. Furthermore, neonatal liver progenitor cells were able to form cholangiocytic cysts in 3D culture without pre-culture. It is therefore possible that the pre-culture of mid-foetal LPCs in vitro functioned as a substitute for the late-foetal maturation step in vivo.

R-spondin 1 and noggin facilitate expansion of resident stem cells from non-damaged gallbladders

Pioneering studies within the last few years have allowed the in vitro expansion of tissue‐specific adult stem cells from a variety of endoderm‐derived organs, including the stomach, small intestine, and colon. Expansion of these cells requires activation of the receptor Lgr5 by its ligand R‐spondin 1 and is likely facilitated by the fact that in healthy adults the stem cells in these organs are highly proliferative. In many other adult organs, such as the liver, proliferating cells are normally not abundant in adulthood. However, upon injury, the liver has a strong regenerative potential that is accompanied by the emergence of Lgr5‐positive stem cells; these cells can be isolated and expanded in vitro as organoids. In an effort to isolate stem cells from non‐regenerating mouse livers, we discovered that healthy gallbladders are a rich source of stem/progenitor cells that can be propagated in culture as organoids for more than a year. Growth of these organoids was stimulated by R‐spondin 1 and noggin, whereas in the absence of these growth factors, the organoids differentiated partially toward the hepatocyte fate. When transplanted under the liver capsule, gallbladder‐derived organoids maintained their architecture for 2 weeks. Furthermore, single cells prepared from dissociated organoids and injected into the mesenteric vein populated the liver parenchyma of carbon tetrachloride‐treated mice. Human gallbladders were also a source of organoid‐forming stem cells. Thus, under specific growth conditions, stem cells can be isolated from healthy gallbladders, expanded almost indefinitely in vitro, and induced to differentiate toward the hepatocyte lineage.

Disease Modeling and Gene Therapy of Copper Storage Disease in Canine Hepatic Organoids

The recent development of 3D-liver stem cell cultures (hepatic organoids) opens up new avenues for gene and/or stem cell therapy to treat liver disease. To test safety and efficacy, a relevant large animal model is essential but not yet established. Because of its shared pathologies and disease pathways, the dog is considered the best model for human liver disease. Here we report the establishment of a long-term canine hepatic organoid culture allowing undifferentiated expansion of progenitor cells that can be differentiated toward functional hepatocytes. We show that cultures can be initiated from fresh and frozen liver tissues using Tru-Cut or fine-needle biopsies. The use of Wnt agonists proved important for canine organoid proliferation and inhibition of differentiation. Finally, we demonstrate that successful gene supplementation in hepatic organoids of COMMD1-deficient dogs restores function and can be an effective means to cure copper storage disease.

Bone marrow-derived mesenchymal stem cell therapy for decompensated liver cirrhosis: A meta-analysis

AIM: To assess the efficacy and safety of bone marrow-derived mesenchymal stem cell (BM-MSC) in the treatment of decompensated liver cirrhosis.

METHODS: The search terms “bone marrow stem cell”“chronic liver disease”“transfusion” and “injection” were used in the Cochrane Library, Med-Line (Pub-Med) and Embase without any limitations with respect to publication date or language. Journals were also hand-searched and experts in the field were contacted. The studies which used BM-MSC in the treatment of any chronic liver disease were included. Comprehensive Review Manager and Meta-Analyst software were used for statistical analysis. Publication bias was evaluated using Begg’s test.

RESULTS: Out of 78 studies identified, five studies were included in the final analysis. The studies were conducted in China, Iran, Egypt and Brazil. Analysis of pooled data of two controlled studies by Review Manager showed that the mean decline in scores for the model for end-stage liver disease (MELD) was -1.23 [95%CI: -2.45-(-0.01)], -1.87 [95%CI: -3.16-(-0.58)], -2.01 [95%CI: -3.35-(-0.68)] at 2, 4 and 24 wk, respectively after transfusion. Meta-analysis of the 5 studies showed that the mean improvement in albumin levels was -0.28, 2.60, 5.28, 4.39 g/L at the end of 8, 16, 24, and 48 wk, respectively, after transfusion. MELD scores, alanine aminotransferase, total bilirubin levels and prothrombin times improved to some extent. BM-MSC injections resulted in no serious adverse events or complications.

CONCLUSION: BM-MSC infusion in the treatment of decompensated liver cirrhosis improved liver function. At the end of year 1, there were no serious side effects or complications.