Identification and characterization of mesenchymal-epithelial progenitor-like cells in normal and injured rat liver

CK19 and OV6 Expressions in the Liver of 2-AAF/CCl4 Rat Model

BACKGROUND: Liver regeneration on a chronic liver injury with rat model research is urgent to study the pathology of human chronic diseases. 2-Acetylaminofluorene (2-AAF) and Carbon Tetrachloride (CCl4) can be applied to study about liver regeneration by liver stem cells, known as oval cells. The use of 2-AAF and CCl4 (2-AAF/CCl4) to induce chronic liver injury can lead severe hepatocyte damages and extensive fibrosis. AIM: to observed the OV6 and CK19 expression in the liver of 2AAF/CCl4 rat model. METHODS: In this research, a high dose of 2-AAF (10mg/kg) was applied and combined repeatedly with CCl4 (2ml/kg) for 12 weeks. An immunohistochemistry (IHC) procedure by using OV6 and CK19 antibodies was also applied to examine the regeneration of oval cells. Both antibodies expressions were then examined semi-quantitatively according to the expressions percentage of each sample based on the liver zone. We have observed the OV6 and CK19 expressions in every zone, including in portae hepatis area.   RESULTS: The results showed that OV6 and CK19 with the highest expression in the zone I. A significant difference between OV6 and CK19 expressions was revealed in healthy (control group) and 2-AAF/CCl4 groups (both indicating p=0.045). Moreover, a ductular reaction was also found in Zone I and II of the 2-AAF/CCl4. CONCLUSIONS: We conclude that 2-AAF/CCl4 induced chronic rat liver injury model, could be utilized to investigate the oval cells with OV6 and CK19 expression.

The wHole Story About Fenestrations in LSEC

The porosity of liver sinusoidal endothelial cells (LSEC) ensures bidirectional passive transport of lipoproteins, drugs and solutes between the liver capillaries and the liver parenchyma. This porosity is realized via fenestrations - transcellular pores with diameters in the range of 50-300 nm - typically grouped together in sieve plates. Aging and several liver disorders severely reduce LSEC porosity, decreasing their filtration properties. Over the years, a variety of drugs, stimulants, and toxins have been investigated in the context of altered diameter or frequency of fenestrations. In fact, any change in the porosity, connected with the change in number and/or size of fenestrations is reflected in the overall liver-vascular system crosstalk. Recently, several commonly used medicines have been proposed to have a beneficial effect on LSEC re-fenestration in aging. These findings may be important for the aging populations of the world. In this review we collate the literature on medicines, recreational drugs, hormones and laboratory tools (including toxins) where the effect LSEC morphology was quantitatively analyzed. Moreover, different experimental models of liver pathology are discussed in the context of fenestrations. The second part of this review covers the cellular mechanisms of action to enable physicians and researchers to predict the effect of newly developed drugs on LSEC porosity. To achieve this, we discuss four existing hypotheses of regulation of fenestrations. Finally, we provide a summary of the cellular mechanisms which are demonstrated to tune the porosity of LSEC.

Matrine promotes hepatic oval cells differentiation into hepatocytes and alleviates liver injury by suppression of Notch signalling pathway

AIMS

Recent studies have shown that the hyperactive Notch pathway is involved in cirrhosis and hepatocellular carcinoma (HCC) development by regulating differentiation of hepatic oval cells (HOCs) into cancer cells. The aim of this study was to investigate whether matrine can alleviate liver injury and promote HOC differentiation into hepatocytes by suppression of Notch pathway.

MAIN METHODS

We evaluated the expression of Notch-1, Jagged-1, and Hes-1 in HCC tissue by immunohistochemistry. Stem cell characteristics of HOCs were evaluated by CCK-8, cell cycle, and apoptosis. The expression of Notch pathway, HOC markers and albumin (ALB) was detected by immunohistochemistry, QRT-PCR and western blotting. The effects of matrine in protecting liver in vivo were investigated in a rat Solt-Farber precancerous model.

KEY FINDINGS

We found an abnormal activated Notch pathway in HCC tissue, and the hyperactive Notch pathway was strongly associated with poor liver function in patients with cirrhosis with HCC. Using siNotch-1 to inhibit Notch pathway confirmed that Notch pathway could maintain stem cell characteristics of HOCs. Matrine inhibited stem cell characteristics of HOCs, the expression of Notch pathway and HOC markers but upregulated ALB. Matrine in combined with siNotch-1 RNA decreased the more potently inhibited HOC markers and Notch pathway. In rat Solt-Farber precancerous model, prophylactic application of matrine alleviated liver injury, downregulated Notch pathway and HOC markers, and upregulated ALB in a dose-dependent manner.

SIGNIFICANCE

Matrine could promote the differentiation of HOCs into hepatocytes by inhibiting the Notch signalling pathway and alleviate liver injury.

Blocking development of liver fibrosis augments hepatic progenitor cell-derived liver regeneration in a mouse chronic liver injury model

AIM

The roles of hepatic progenitor cells (HPCs) in regeneration of a diseased liver are unclear. Hepatic stellate cells (HSCs) contribute to liver fibrosis but are also a component of the HPC niche. Hepatic progenitor cells expand along with HSC activation and liver fibrosis. However, little is known about the interplay of liver fibrosis and HPC-mediated liver regeneration. This study aimed to investigate HSCs and HPCs in liver regeneration.

METHODS

Liver injury in mice was induced with 3,5-diethoxycarbonyl-1,4-dihydrocollidine, and HPC expansion and fibrosis were assessed. An angiotensin II type 1 receptor blocker (ARB) was administered to assess its effect on fibrosis and regeneration.

RESULTS

Treatment with ARB attenuated fibrosis and expansion of α-smooth muscle actin-positive activated HSCs as indicated by increased liver weight and Ki-67-positive hepatocytes. Immunohistochemical staining suggested that HPC differentiation was shifted toward hepatocytes (HCs) when ARB treatment decreased HPC encapsulation by HSCs and extracellular matrix. Conditioned medium produced by culturing the human HSC LX-2 line strongly augmented differentiation to biliary epithelial cells (BECs) but inhibited that to HCs. Activated HSCs expressed Jagged1, a NOTCH ligand, which plays a central role in differentiation of HPCs toward BECs.

CONCLUSIONS

Hepatic stellate cells, the HPC niche cells, control differentiation of HPCs, directing them toward BECs rather than HCs in a diseased liver model. Antifibrosis treatment with an ARB preferentially redirects HPC differentiation toward HCs by blocking the NOTCH pathway in the HPC niche, resulting in more efficient HPC-mediated liver regeneration.

Hepatic progenitor cell activation is induced by the depletion of the gut microbiome in mice

The homeostasis of the gut microbiome is crucial for human health and for liver function. However, it has not been established whether the gut microbiome influence hepatic progenitor cells (HPCs). HPCs are capable of self‐renewal and differentiate into hepatocytes and cholangiocytes; however, HPCs are normally quiescent and are rare in adults. After sustained liver damage, a ductular reaction occurs, and the number of HPCs is substantially increased. Here, we administered five broad‐spectrum antibiotics for 14 days to deplete the gut microbiomes of male C57BL/6 mice, and we measured the plasma aminotransferases and other biochemical indices. The expression levels of two HPC markers, SRY‐related high mobility group‐box gene 9 (Sox9) and cytokeratin (CK), were also measured. The plasma aminotransferase activities were not affected, but the triglyceride, lactate dehydrogenase, low‐density lipoprotein, and high‐density lipoprotein concentrations were significantly altered; this suggests that liver function is affected by the composition of the gut microbiome. The mRNA expression of Sox9 was significantly higher in the treated mice than it was in the control mice (p < 0.0001), and a substantial expression of Sox9 and CK was observed around the bile ducts. The mRNA expression levels of proinflammatory factors (interleukin [IL]‐1β, IL‐6, tumor necrosis factor [TNF]‐α, and TNF‐like weak inducer of apoptosis [Tweak]) were also significantly higher in the antibiotic‐treated mice than the levels in the control mice. These data imply that the depletion of the gut microbiome leads to liver damage, negatively impacts the hepatic metabolism and function, and activates HPCs. However, the underlying mechanisms remain to be determined.

Combination of cord blood-derived human hepatic progenitors and hepatogenic factors strongly improves recovery after acute liver injury in mice through modulation of the Wnt/β-catenin signaling

Cell therapy represents a promising alternative strategy for end-stage liver disease, and hepatic progenitors are the best candidates. The possibility to maximize the paracrine effects of transplanted cells represents a great potential benefit for cell therapy success. We studied how cell type and microenvironment modulate the Wnt/β-catenin signaling in vitro and in vivo. In vitro, the onset of hepatocyte commitment was characterized by the presence of nuclear truncated β-catenin. In vivo, we analyzed the effect of human hepatic progenitors on damage recovery and functional regeneration in a mouse model of acute liver injury, either in combination or in absence of a selected mix of hepatogenic factors. Animals injected with human hepatic progenitors and hepatogenic factors showed improved engraftment triggering the Wnt/β-catenin signaling cascade. Human hepatic progenitors expressing the human oval cell marker OV6 displayed a consistent colocalization with β-catenin and colocalized with Wnt1 main ligand of the canonical pathway. Wnt5a, on the contrary, was expressed in distinct liver cell populations. Epithelial mesenchymal transition-related markers showed enhanced expression and wider distribution, and the hepato-mesenchymal population Thy1 + CK19- was also present. Control animals injected with hepatogenic factors alone exhibited higher β-catenin, decreased Wnt5a levels, and persistent proliferation of the hepato-mesenchymal population. In conclusion, the combination of human hepatic progenitors with selected hepatogenic factors creates a positive synergy with local microenvironment, ameliorates cell engraftment, stimulates and accelerates regenerative process, and improves the rescue of hepatic function by modulating the Wnt/βcatenin signaling and activating hepato-mesenchymal population.

Bone marrow-derived mesenchymal stem cells ameliorate liver injury in a rat model of sepsis by activating Nrf2 signaling

Sepsis is a fatal condition that leads to serious systemic inflammation and multiple organ dysfunction syndromes. This study was designed to investigate the possible therapeutic effect of bone marrow-derived mesenchymal stem cells (BMSCs) on sepsis-induced liver injury. We also aimed to examine the role of Nrf2 activation in modulating the response to sepsis following BMSCs treatment. Twenty-four adult male albino rats were assigned to: control, lipopolysaccharide (LPS) and LPS-stem cell groups. Liver samples were processed for light and electron microscope examinations. Immunohistochemical localization of BAX, proliferating cell nuclear antigen and nuclear factor-erythroid 2-related factor 2 (Nrf2) was carried out. Liver homogenates were prepared for assessment of reduced glutathione, glutathione peroxidase, tumor necrosis factor-alpha and interleukin-6 and also real-time PCR analysis of Nrf2 expression. BMSCs treatment improved the histopathological changes of the liver, enhanced tissue regeneration and decreased apoptosis following sepsis. We reported highly significant enhancement in Nrf2 expressions at mRNA and protein levels in the LPS-stem cell group compared with the LPS group. The up regulation of Nrf2 was probably implicated in decreasing inflammatory cytokine levels and counteracting oxidative stress induced by sepsis. Thus, BMSCs therapies could be a viable approach to treat sepsis-induced liver damage by activating Nrf2 signaling.

Portal fibroblasts marked by the surface antigen Thy1 contribute to fibrosis in mouse models of cholestatic liver injury

Liver fibrosis, a condition that is characterized by excessive production and accumulation of extracellular matrix, including collagen, is the most common outcome of chronic liver injuries of different etiologies. Vitamin A‐storing hepatic stellate cells (HSCs) are considered to be the main source of this collagen production, with activation in response to liver injury. In contrast, the contribution of other cell types to this fibrogenic response remains largely elusive due to the lack of specific surface markers to identify and isolate these cells for detailed analysis. Here, we identify a mesenchymal population of thymus cell antigen 1 (Thy1)⁺ CD45⁻ cells (Thy1 MCs) in the mouse liver; these cells reside near the portal vein in vivo and indicate profibrogenic characteristics in vitro, shown by their expression of collagen and α‐smooth muscle actin. Flow cytometric analysis of mouse liver nonparenchymal cells revealed that vitamin A storage and Thy1 expression were mutually exclusive, indicating that Thy1 MCs are distinct from HSCs. Importantly, Thy1 MCs reacted and contributed to the development of liver fibrosis specifically in mouse models of cholestatic liver injury. With the occurrence of cholestatic liver injury, collagen‐producing Thy1 MCs expanded in cell number and inhibited collagen degradation through up‐regulation of matrix metalloproteinase inhibitor Timp1 expression, thereby promoting the accumulation of extracellular matrix in the periportal area. Conclusion: This study establishes Thy1 as a useful cell surface marker to prospectively identify and isolate periportal fibroblasts and further highlights a significant contribution of these cells to the pathogenesis of liver fibrosis caused by cholestatic liver injuries. We suggest that Thy1 MCs may be an interesting therapeutic target for treating liver fibrosis in addition to the well‐characterized HSCs. (Hepatology Communications 2017;1:198‐214)

Mesothelin/mucin 16 signaling in activated portal fibroblasts regulates cholestatic liver fibrosis

Cholestatic liver fibrosis is caused by obstruction of the biliary tract and is associated with early activation of portal fibroblasts (PFs) that express Thy-1, fibulin 2, and the recently identified marker mesothelin (MSLN). Here, we have demonstrated that activated PFs (aPFs) and myofibroblasts play a critical role in the pathogenesis of liver fibrosis induced by bile duct ligation (BDL). Conditional ablation of MSLN+ aPFs in BDL-injured mice attenuated liver fibrosis by approximately 50%. Similar results were observed in MSLN-deficient mice (Msln-/- mice) or mice deficient in the MSLN ligand mucin 16 (Muc16-/- mice). In vitro analysis revealed that MSLN regulates TGF-β1-inducible activation of WT PFs by disrupting the formation of an inhibitory Thy-1-TGFβRI complex. MSLN also facilitated the FGF-mediated proliferation of WT aPFs. Therapeutic administration of anti-MSLN-blocking Abs attenuated BDL-induced fibrosis in WT mice. Liver specimens from patients with cholestatic liver fibrosis had increased numbers of MSLN+ aPFs/myofibroblasts, suggesting that MSLN may be a potential target for antifibrotic therapy.

Relationship between hepatic progenitor cell-mediated liver regeneration and non-parenchymal cells

Hepatic progenitor cells (HPCs) are thought to reside in the canals of Hering and can be activated and contribute to liver regeneration in response to liver injury by proliferating and differentiating towards both hepatocytes and biliary epithelial cells. In this setting, several cytokines, chemokines, and growth factors related to liver inflammation and other liver cells comprising the HPC niche, namely hepatic stellate cells (HSCs), play crucial roles in HPC activation and differentiation. In response to several types of liver injury, tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is secreted by several inflammatory cells, including monocytes, T lymphocytes, and macrophages, and acts as an initiator of the HPC niche and HSC activation. Following TWEAK-induced activation of the HPC niche, fibroblast growth factor 7 and hepatocyte growth factor released from activated HSC play central roles in maintaining HPC proliferation. In contrast, HGF-MET and Wnt3a-β-catenin signals are the predominant mediators of the hepatocyte differentiation of HPC, whereas epidermal growth factor receptor-NOTCH signaling controls HPC differentiation towards biliary epithelial cells. These signals are maintained exclusively by activated HSC and inflammatory cells surrounding HPC. Together, HSC and inflammatory cells surrounding HPC are responsible for the precise control of HPC proliferation and differentiation fate. In this review, we discuss recent progress in understanding of interactions between HPC and other liver cells in HPC-mediated liver regeneration in the setting of liver inflammation.

Hepatic oval cells and liver diseases

In recent years, hepatic oval cells (HOC) have gradually become a research hotspot, and their participation in the reconstruction of liver structure and function has been preliminarily confirmed. This provides a new direction for the study of the pathogenesis and treatment of liver injury, hepatitis, liver fibrosis, cirrhosis, liver neoplasms and other liver diseases. This paper will discuss the relationship between hepatic oval cells and liver diseases.