Downregulation of Sox9 Expression Associates with Hepatogenic Differentiation of Human Liver Mesenchymal Stem/Progenitor Cells

Engineered Platforms for Maturing Pluripotent Stem Cell-Derived Liver Cells for Disease Modeling

Several liver diseases (eg, hepatitis B/C viruses, alcoholic/nonalcoholic fatty liver, malaria, monogenic diseases, and drug-induced liver injury) significantly impact global mortality and morbidity. Species-specific differences in liver functions limit the use of animals to fully elucidate/predict human outcomes; therefore, in vitro human liver models are used for basic and translational research to complement animal studies. However, primary human liver cells are in short supply and display donor-to-donor variability in viability/quality. In contrast, human hepatocyte-like cells (HLCs) differentiated from induced pluripotent stem cells and embryonic stem cells are a near infinite cell resource that retains the patient/donor's genetic background; however, conventional protocols yield immature phenotypes. HLC maturation can be significantly improved using advanced techniques, such as protein micropatterning to precisely control cell-cell interactions, controlled sized spheroids, organoids with multiple cell types and layers, 3-dimensional bioprinting to spatially control cell populations, microfluidic devices for automated nutrient exchange and to induce liver zonation via soluble factor gradients, and synthetic biology to genetically modify the HLCs to accelerate and enhance maturation. Here, we present design features and characterization for representative advanced HLC maturation platforms and then discuss HLC use for modeling various liver diseases. Lastly, we discuss desirable advances to move this field forward. We anticipate that with continued advances in this space, pluripotent stem cell-derived liver models will provide human-relevant data much earlier in preclinical drug development and reduce animal usage, help elucidate liver disease mechanisms for the discovery of efficacious and safe therapeutics, and be useful as cell-based therapies for patients suffering from end-stage liver failure.

Therapeutic Efficiency of Nasal Mucosa-Derived Ectodermal Mesenchymal Stem Cells in Rats with Acute Hepatic Failure

Background

Liver transplantation is limited by the insufficiency of liver organ donors when treating end-stage liver disease or acute liver failure (ALF). Ectodermal mesenchymal stem cells (EMSCs) derived from nasal mucosa have emerged as an alternative cell-based therapy. However, the role of EMSCs in acute liver failure remains unclear.

Methods

EMSCs were obtained from the nasal mucosa tissue of rats. First, EMSCs were seeded on the gelatin-chitosan scaffolds, and the biocompatibility was evaluated. Next, the protective effects of EMSCs were investigated in carbon tetrachloride- (CCl₄-) induced ALF rats. Finally, we applied an indirect coculture system to analyze the paracrine effects of EMSCs on damaged hepatocytes. A three-step nontransgenic technique was performed to transform EMSCs into hepatocyte-like cells (HLCs) in vitro.

Results

EMSCs exhibited a similar phenotype to other mesenchymal stem cells along with self-renewal and multilineage differentiation capabilities. EMSC-seeded gelatin-chitosan scaffolds can increase survival rates and ameliorate liver function and pathology of ALF rat models. Moreover, transplanted EMSCs can secrete paracrine factors to promote hepatocyte regeneration, targeted migration, and transdifferentiate into HLCs in response to the liver's microenvironment, which will then repair or replace the damaged hepatocytes. Similar to mature hepatocytes, HLCs generated from EMSCs possess functions of expressing specific hepatic markers, storing glycogen, and producing urea.

Conclusions

These results confirmed the feasibility of EMSCs in acute hepatic failure treatment. To our knowledge, this is the first time that EMSCs are used in the therapy of liver diseases. EMSCs are expected to be a novel and promising cell source in liver tissue engineering.

Mechanisms of Action of Mesenchymal Stem Cells in Metabolic-Associated Fatty Liver Disease

Metabolic-associated fatty liver disease (MAFLD) is currently the most common chronic liver disease worldwide. However, its pathophysiological mechanism is complicated, and currently, it has no FDA-approved pharmacological therapies. In recent years, mesenchymal stem cell (MSC) therapy has attracted increasing attention in the treatment of hepatic diseases. MSCs are multipotent stromal cells that originated from mesoderm mesenchyme, which have self-renewal and multipotent differentiation capability. Recent experiments and studies have found that MSCs have the latent capacity to be used for MAFLD treatment. MSCs have the potential to differentiate into hepatocytes, which could be induced into hepatocyte-like cells (HLCs) with liver-specific morphology and function under appropriate conditions to promote liver tissue regeneration. They can also reduce liver tissue injury and reverse the development of MAFLD by regulating immune response, antifibrotic activities, and lipid metabolism. Moreover, several advantages are attributed to MSC-derived exosomes (MSC-exosomes), such as targeted delivery, reliable reparability, and poor immunogenicity. After entering the target cells, MSC-exosomes help regulate cell function and signal transduction; thus, it is expected to become an emerging treatment for MAFLD. In this review, we comprehensively discussed the roles of MSCs in MAFLD, main signaling pathways of MSCs that affect MAFLD, and mechanisms of MSC-exosomes on MAFLD.

Effects of 4-n-nonylphenol in liver of male and female viviparous fish (Poecilia vivipara)

4-n-Nonylphenol (NP) is one of the most toxic alkylphenols found in the environment. To evaluate the transcriptional effects of NP in the viviparous fish Poecilia vivipara, a hepatic transcriptome and qPCR analysis of genes were carried out. Guppies separated by sex were injected with two doses of NP (15 μg/g and 150 μg/g) or peanut oil (control). After 24 h, analysis of transcriptional level of Aryl Hydrocarbon Receptor (AhR), Estrogen Nuclear Receptor Alpha (ESR1), Pregnane X Receptor (PXR), Cytochromes P450 (CYP1A, CYP2K1 and CYP3A30), Glutathione S-transferase A3 and Mu 3 (GSTa3 and GSTMu3), SRY-Box Transcription Factor 9 (SOX9), Vitellogenin-1 (VIT), ATP Binding Cassette Subfamily C Member 1 (ABCC1), Multidrug Resistance-Associated Protein 2 (MRP2) and UDP Glucuronosyltransferase Family 1 Member A1 (UGT1A1) was evaluated. 205,046 transcripts were assembled and protein prediction resulted in 203,147 predicted peptides. In females, no significant changes were detected in the transcription of some phase I biotransformation and ABC transporter genes. AhR, PXR, GSTa3 and SOX9 genes where higher in the lower dose group (15 μg/g) compared to control. In male fish, no changes were observed in the transcript levels of the nuclear receptors, in endocrine disruption and phase I biotransformation genes. GSTa3 showed lower transcription in fish treated with both doses. ABCC1 was higher in guppies treated with the lower dose while MRP2 showed less transcripts. This short-term and low-dose exposure to NP caused changes that could serve as early indicators of deleterious processes. These results indicate P. vivipara as a good sentinel in biomonitoring programs.

Inflammation Differentially Modulates the Biological Features of Adult Derived Human Liver Stem/Progenitor Cells

The progression of mesenchymal stem cell-based therapy from concept to cure closely depends on the optimization of conditions that allow a better survival and favor the cells to achieve efficient liver regeneration. We have previously demonstrated that adult-derived human liver stem/progenitor cells (ADHLSC) display significant features that support their clinical development. The current work aims at studying the impact of a sustained pro-inflammatory environment on the principal biological features of ADHLSC in vitro. METHODS: ADHLSC from passages 4–7 were exposed to a cocktail of inflammatory cytokines for 24 h and 9 days and subsequently analyzed for their viability, expression, and secretion profiles by using flow cytometry, RT-qPCR, and antibody array assay. The impact of inflammation on the hepatocytic differentiation potential of ADHLSC was also evaluated. RESULTS: ADHLSC treated with a pro-inflammatory cocktail displayed significant decrease of cell yield at both times of treatment while cell mortality was observed at 9 days post-priming. After 24 h, no significant changes in the immuno-phenotype of ADHLSC expression profile could be noticed while after 9 days, the expression profile of relevant markers has changed both in the basal conditions and after inflammation treatment. Inflammation cocktail enhanced the release of IL-6, IL-8, CCL5, monocyte-chemo-attractant protein-2 and 3, CXCL1/GRO, and CXCL5/ENA78. Furthermore, while IP-10 secretion was increased after 24 h priming, granulocyte macrophage colony-stimulating factor enhanced secretion was noticed after 9 days treatment. Finally, priming of ADHLSC did not affect their potential to differentiate into hepatocyte-like cells. CONCLUSION: These results indicate that ADHLSCs are highly sensitive to inflammation and respond to such signals by adjusting their gene and protein expression. Accordingly, monitoring the inflammatory status of patients at the time of cell transplantation, will certainly help in enhancing ADHLSC safety and efficiency.

Increased Expression of Sox9 during Balance of BMSCs/Chondrocyte Bricks in Platelet-Rich Plasma Promotes Construction of a Stable 3-D Chondrogenesis Microenvironment for BMSCs

Sox9 is an intrinsic transcription factor related to the determination and maintenance of chondrogenic lineage of bone marrow mesenchymal stem cells (BMSCs). In recent research, we have proved that fragmented chondrocyte aggregates (cell bricks) could promote chondrogenesis of BMSCs in vivo. However, it is still unknown whether the ratio of BMSCs/chondrocyte bricks has a significant influence on 3-D cartilage regeneration and related molecular mechanism. To address this issue, the current study subcutaneously injected three groups of cell complex with different rabbit BMSCs/chondrocyte bricks' ratios (1 : 2, 1 : 1, and 2 : 1) into nude mice. Gross morphology observation, histological and immunohistochemical assays, biochemical analysis, gene expression analysis, and western blot were used to compare the influence of different BMSCs/chondrocyte bricks' ratios on the properties of tissue-engineered cartilage and explore the related molecular mechanism. The constructs of 1 : 1 BMSCs/chondrocyte bricks, (B1CB1) group resulted in persistent chondrogenesis with appropriate morphology and adequate central nutritional perfusion without ossification. The related mechanism is that increased expression of Sox9 in the B1C1 group promoted chondrogenesis and inhibited the osteogenesis of BMSCs through upregulating Col-II as well as downregulating RUNX2 and downstream of Col-X and Col-I by upregulating Nkx3.2. This study demonstrated that BMSCs/chondrocyte bricks 1:1 should be a suitable ratio and the Sox9-Nkx3.2-RUNX2 pathway was a related mechanism which played an important role in the niche for stable chondrogenesis of BMSCs constructed by chondrocyte bricks and PRP.

Inferring TF activation order in time series scRNA-Seq studies

Methods for the analysis of time series single cell expression data (scRNA-Seq) either do not utilize information about transcription factors (TFs) and their targets or only study these as a post-processing step. Using such information can both, improve the accuracy of the reconstructed model and cell assignments, while at the same time provide information on how and when the process is regulated. We developed the Continuous-State Hidden Markov Models TF (CSHMM-TF) method which integrates probabilistic modeling of scRNA-Seq data with the ability to assign TFs to specific activation points in the model. TFs are assumed to influence the emission probabilities for cells assigned to later time points allowing us to identify not just the TFs controlling each path but also their order of activation. We tested CSHMM-TF on several mouse and human datasets. As we show, the method was able to identify known and novel TFs for all processes, assigned time of activation agrees with both expression information and prior knowledge and combinatorial predictions are supported by known interactions. We also show that CSHMM-TF improves upon prior methods that do not utilize TF-gene interaction.

An important attribute of time series single cell RNA-Seq (scRNA-Seq) data, is the ability to infer continuous trajectories of genes based on orderings of the cells. While several methods have been developed for ordering cells and inferring such trajectories, to date it was not possible to use these to infer the temporal activity of several key TFs. These TFs are are only post-transcriptionally regulated and so their expression does not provide complete information on their activity. To address this we developed the Continuous-State Hidden Markov Models TF (CSHMM-TF) methods that assigns continuous activation time to TFs based on both, their expression and the expression of their targets. Applying our method to several time series scRNA-Seq datasets we show that it correctly identifies the key regulators for the processes being studied. We analyze the temporal assignments for these TFs and show that they provide new insights about combinatorial regulation and the ordering of TF activation. We used several complementary sources to validate some of these predictions and discuss a number of other novel suggestions based on the method. As we show, the method is able to scale to large and noisy datasets and so is appropriate for several studies utilizing time series scRNA-Seq data.

Different approaches for transformation of mesenchymal stem cells into hepatocyte-like cells

Due to the prominent role of the liver in the body and detoxification, its functionality can be affected in an irreversible manner by diseases. This phenomenon renders the liver to stop working, leading to morbidity and mortality. Therefore, liver transplantation is the only way to tackle this issue.In order to compensate for the lack of adequate healthy liver tissue for transplantation, therapeutic approaches such as hepatocyte transplantation have been proposed as an alternative. Recognizing the fact that mesenchymal stem cells are adult stem cells with the capacity to differentiate into several cell types, different methods have been invented to produce hepatocyte-like cells from mesenchymal stem cells. They can be divided into three main categories, such as addition of cytokines and growth factors, genetic modifications, and adjustment of microenvironment as well as physical parameters.In this review, we attempted to introduce diverse efficient methods for differentiating mesenchymal stem cells and their capability for transformation into hepatocyte-like cells.

Mesenchymal Stem Cells in the Adult Human Liver: Hype or Hope?

Chronic liver diseases constitute a significant economic, social, and biomedical burden. Among commonly adopted approaches, only organ transplantation can radically help patients with end-stage liver pathologies. Cell therapy with hepatocytes as a treatment for chronic liver disease has demonstrated promising results. However, quality human hepatocytes are in short supply. Stem/progenitor cells capable of differentiating into functionally active hepatocytes provide an attractive alternative approach to cell therapy for liver diseases, as well as to liver-tissue engineering, drug screening, and basic research. The application of methods generally used to isolate mesenchymal stem cells (MSCs) and maintain them in culture to human liver tissue provides cells, designated here as liver MSCs. They have much in common with MSCs from other tissues, but differ in two aspects-expression of a range of hepatocyte-specific genes and, possibly, inherent commitment to hepatogenic differentiation. The aim of this review is to analyze data regarding liver MSCs, probably another type of liver stem/progenitor cells different from hepatic stellate cells or so-called hepatic progenitor cells. The review presents an analysis of the phenotypic characteristics of liver MSCs, their differentiation and therapeutic potential, methods for isolating these cells from human liver, and discusses issues of their origin and heterogeneity. Human liver MSCs are a fascinating object of fundamental research with a potential for important practical applications.

Liver Progenitors and Adult Cell Plasticity in Hepatic Injury and Repair: Knowns and Unknowns

The liver is a complex organ performing numerous vital physiological functions. For that reason, it possesses immense regenerative potential. The capacity for repair is largely attributable to the ability of its differentiated epithelial cells, hepatocytes and biliary epithelial cells, to proliferate after injury. However, in cases of extreme acute injury or prolonged chronic insult, the liver may fail to regenerate or do so suboptimally. This often results in life-threatening end-stage liver disease for which liver transplantation is the only effective treatment. In many forms of liver injury, bipotent liver progenitor cells are theorized to be activated as an additional tier of liver repair. However, the existence, origin, fate, activation, and contribution to regeneration of liver progenitor cells is hotly debated, especially since hepatocytes and biliary epithelial cells themselves may serve as facultative stem cells for one another during severe liver injury. Here, we discuss the evidence both supporting and refuting the existence of liver progenitor cells in a variety of experimental models. We also debate the validity of developing therapies harnessing the capabilities of these cells as potential treatments for patients with severe and chronic liver diseases.

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.

Notch Inhibition Promotes Differentiation of Liver Progenitor Cells into Hepatocytes via sox9b Repression in Zebrafish

Liver regeneration after most forms of injury is mediated through the proliferation of hepatocytes. However, when hepatocyte proliferation is impaired, such as during chronic liver disease, liver progenitor cells (LPCs) arising from the biliary epithelial cell (BEC) compartment can give rise to hepatocytes to mediate hepatic repair. Promotion of LPC-to-hepatocyte differentiation in patients with chronic liver disease could serve as a potentially new therapeutic option, but first requires the identification of the molecular mechanisms driving this process. Notch signaling has been identified as an important signaling pathway promoting the BEC fate during development and has also been implicated in regulating LPC differentiation during regeneration. SRY-related HMG box transcription factor 9 (Sox9) is a direct target of Notch signaling in the liver, and Sox9 has also been shown to promote the BEC fate during development. We have recently shown in a zebrafish model of LPC-driven liver regeneration that inhibition of Hdac1 activity through MS-275 treatment enhances sox9b expression in LPCs and impairs LPC-to-hepatocyte differentiation. Therefore, we hypothesized that inhibition of Notch signaling would promote LPC-to-hepatocyte differentiation by repressing sox9b expression in zebrafish. We ablated the hepatocytes of Tg(fabp10a:CFP-NTR) larvae and blocked Notch activation during liver regeneration through treatment with γ-secretase inhibitor LY411575 and demonstrated enhanced induction of Hnf4a in LPCs. Alternatively, enhancing Notch signaling via Notch3 intracellular domain (N3ICD) overexpression impaired Hnf4a induction. Hepatocyte ablation in sox9b heterozygous mutant embryos enhanced Hnf4a induction, while BEC-specific Sox9b overexpression impaired LPC-to-hepatocyte differentiation. Our results establish the Notch-Sox9b signaling axis as inhibitory to LPC-to-hepatocyte differentiation in a well-established in vivo LPC-driven liver regeneration model.

Hdac1 Regulates Differentiation of Bipotent Liver Progenitor Cells During Regeneration via Sox9b and Cdk8

BACKGROUND & AIMS

Upon liver injury in which hepatocyte proliferation is compromised, liver progenitor cells (LPCs), derived from biliary epithelial cells (BECs), differentiate into hepatocytes. Little is known about the mechanisms of LPC differentiation. We used zebrafish and mouse models of liver injury to study the mechanisms.

METHODS

We used transgenic zebrafish, Tg(fabp10a:CFP-NTR), to study the effects of compounds that alter epigenetic factors on BEC-mediated liver regeneration. We analyzed zebrafish with disruptions of the histone deacetylase 1 gene (hdac1) or exposed to MS-275 (an inhibitor of Hdac1, Hdac2, and Hdac3). We also analyzed zebrafish with mutations in sox9b, fbxw7, kdm1a, and notch3. Zebrafish larvae were collected and analyzed by whole-mount immunostaining and in situ hybridization; their liver tissues were collected for quantitative reverse transcription polymerase chain reaction. We studied mice in which hepatocyte-specific deletion of β-catenin (Ctnnb1^flox/flox mice injected with Adeno-associated virus serotype 8 [AAV8]-TBG-Cre) induces differentiation of LPCs into hepatocytes after a choline-deficient, ethionine-supplemented (CDE) diet. Liver tissues were collected and analyzed by immunohistochemistry and immunoblots. We performed immunohistochemical analyses of liver tissues from patients with compensated or decompensated cirrhosis or acute on chronic liver failure (n = 15).

RESULTS

Loss of Hdac1 activity in zebrafish blocked differentiation of LPCs into hepatocytes by increasing levels of sox9b mRNA and reduced differentiation of LPCs into BECs by increasing levels of cdk8 mRNA, which encodes a negative regulator gene of Notch signaling. We identified Notch3 as the receptor that regulates differentiation of LPCs into BECs. Loss of activity of Kdm1a, a lysine demethylase that forms repressive complexes with Hdac1, produced the same defects in differentiation of LPCs into hepatocytes and BECs as observed in zebrafish with loss of Hdac1 activity. Administration of MS-275 to mice with hepatocyte-specific loss of β-catenin impaired differentiation of LPCs into hepatocytes after the CDE diet. HDAC1 was expressed in reactive ducts and hepatocyte buds of liver tissues from patients with cirrhosis.

CONCLUSIONS

Hdac1 regulates differentiation of LPCs into hepatocytes via Sox9b and differentiation of LPCs into BECs via Cdk8, Fbxw7, and Notch3 in zebrafish with severe hepatocyte loss. HDAC1 activity was also required for differentiation of LPCs into hepatocytes in mice with liver injury after the CDE diet. These pathways might be manipulated to induce LPC differentiation for treatment of patients with advanced liver diseases.

YAP Activation Drives Liver Regeneration after Cholestatic Damage Induced by Rbpj Deletion

Liver cholestasis is a chronic liver disease and a major health problem worldwide. Cholestasis is characterised by a decrease in bile flow due to impaired secretion by hepatocytes or by obstruction of bile flow through intra- or extrahepatic bile ducts. Thereby cholestasis can induce ductal proliferation, hepatocyte injury and liver fibrosis. Notch signalling promotes the formation and maturation of bile duct structures. Here we investigated the liver regeneration process in the context of cholestasis induced by disruption of the Notch signalling pathway. Liver-specific deletion of recombination signal binding protein for immunoglobulin kappa j region (Rbpj), which represents a key regulator of Notch signalling, induces severe cholestasis through impaired intra-hepatic bile duct (IHBD) maturation, severe necrosis and increased lethality. Deregulation of the biliary compartment and cholestasis are associated with the change of several signalling pathways including a Kyoto Encyclopedia of Genes and Genomes (KEGG) gene set representing the Hippo pathway, further yes-associated protein (YAP) activation and upregulation of SRY (sex determining region Y)-box 9 (SOX9), which is associated with transdifferentiation of hepatocytes. SOX9 upregulation in cholestatic liver injury in vitro is independent of Notch signalling. We could comprehensively address that in vivo Rbpj depletion is followed by YAP activation, which influences the transdifferentiation of hepatocytes and thereby contributing to liver regeneration.

Liver epithelioid progenitor cells derived from fetal Luxi bovine alleviate liver fibrosis

Liver epithelioid progenitor cells (LEPCs) have important roles in liver therapy because of their hepatic differentiation potency in vitro and in vivo. Despite many researches on humans, mice, and rats, equivalent progenitor cells derived from bovine are relatively rare. The purpose of our current study is to characterize bovine LEPCs, and research on the cure potency of this heteroplastic progenitor cells on mice liver fibrosis. We have used collagenase IV digesting and differential adhesion method to isolate slabstone shape, EpCAM, LGR5, NCAM1 and SOX9 positive progenitor cells from fetal Luxi bovine liver. When cultured in hepatic differentiation media containing 20 ng/ml Oncostatin M, LEPCs can differentiate into hepatocytes in vitro. After 4 weeks of intravenous tail vein injection into CCl₄-injured mouse liver, LEPCs engrafted into liver parenchyma, differentiated into ALB positive hepatocytes, and could alleviate liver fibrosis through down regulating fibrosis genes-Tgfb1 and α-SMA as well as decreasing expression of collagen gene Col1a1, Col3a1, and Col4a1, and regain liver function by recovering ALT and AST. Our findings provided a useful tool for studying liver development in vitro, new cell resource for heterograft on mouse liver diseases, and a new platform for researches on immune rejection of heterogeneous cell transplantation.

SOX9 is targeted for proteasomal degradation by the E3 ligase FBW7 in response to DNA damage

SOX9 encodes a transcription factor that governs cell fate specification throughout development and tissue homeostasis. Elevated SOX9 is implicated in the genesis and progression of human tumors by increasing cell proliferation and epithelial-mesenchymal transition. We found that in response to UV irradiation or genotoxic chemotherapeutics, SOX9 is actively degraded in various cancer types and in normal epithelial cells, through a pathway independent of p53, ATM, ATR and DNA-PK. SOX9 is phosphorylated by GSK3β, facilitating the binding of SOX9 to the F-box protein FBW7α, an E3 ligase that functions in the DNA damage response pathway. The binding of FBW7α to the SOX9 K2 domain at T236-T240 targets SOX9 for subsequent ubiquitination and proteasomal destruction. Exogenous overexpression of SOX9 after genotoxic stress increases cell survival. Our findings reveal a novel regulatory mechanism for SOX9 stability and uncover a unique function of SOX9 in the cellular response to DNA damage. This new mechanism underlying a FBW7-SOX9 axis in cancer could have implications in therapy resistance.

Liver-derived human mesenchymal stem cells: a novel therapeutic source for liver diseases

Mesenchymal stem cells (MSCs) represent an attractive cell type for research and therapy due to their ability to proliferate, differentiate, modulate immune reactions, and secrete trophic factors. MSCs exist in a multitude of tissues, including bone marrow, umbilical cord, and adipose tissues. Moreover, MSCs have recently been isolated from the liver. Compared with other MSC types, liver-derived human MSCs (LHMSCs) possess general morphologies, immune functions, and differentiation capacities. Interestingly, LHMCSs produce higher levels of pro-angiogenic, anti-inflammatory, and anti-apoptotic cytokines than those of bone marrow-derived MSCs. Thus, these cells may be a promising therapeutic source for liver diseases. This paper summarizes the biological characteristics of LHMSCs and their potential benefits and risks for the treatment of liver diseases.

Rat liver regeneration following ablation with irreversible electroporation

During the past decade, irreversible electroporation (IRE) ablation has emerged as a promising tool for the treatment of multiple diseases including hepatic cancer. However, the mechanisms behind the tissue regeneration following IRE ablation have not been investigated. Our results indicate that IRE treatment immediately kills the cells at the treatment site preserving the extracellular architecture, in effect causing in vivo decellularization. Over the course of 4 weeks, progenitor cell differentiation, through YAP and notch pathways, together with hepatocyte expansion led to almost complete regeneration of the ablated liver leading to the formation of hepatocyte like cells at the ablated zone. We did not observe significant scarring or tumor formation at the regenerated areas 6 months post IRE. Our study suggests a new model to study the regeneration of liver when the naïve extracellular matrix is decellularized in vivo with completely preserved extracellular architecture.

The multiple functional roles of mesenchymal stem cells in participating in treating liver diseases

Mesenchymal stem cells (MSCs) are a group of stem cells derived from the mesodermal mesenchyme. MSCs can be obtained from a variety of tissues, including bone marrow, umbilical cord tissue, umbilical cord blood, peripheral blood and adipose tissue. Under certain conditions, MSCs can differentiate into many cell types both in vitro and in vivo, including hepatocytes. To date, four main strategies have been developed to induce the transdifferentiation of MSCs into hepatocytes: addition of chemical compounds and cytokines, genetic modification, adjustment of the micro-environment and alteration of the physical parameters used for culturing MSCs. Although the phenomenon of transdifferentiation of MSCs into hepatocytes has been described, the detailed mechanism is far from clear. Generally, the mechanism is a cascade reaction whereby stimulating factors activate cellular signalling pathways, which in turn promote the production of transcription factors, leading to hepatic gene expression. Because MSCs can give rise to hepatocytes, they are promising to be used as a new treatment for liver dysfunction or as a bridge to liver transplantation. Numerous studies have confirmed the therapeutic effects of MSCs on hepatic fibrosis, cirrhosis and other liver diseases, which may be related to the differentiation of MSCs into functional hepatocytes. In addition to transdifferentiation into hepatocytes, when MSCs are used to treat liver disease, they may also inhibit hepatocellular apoptosis and secrete various bioactive molecules to promote liver regeneration. In this review, the capacity and molecular mechanism of MSC transdifferentiation, and the therapeutic effects of MSCs on liver diseases are thoroughly discussed.

The versatile functions of Sox9 in development, stem cells, and human diseases

The transcription factor Sox9 was first discovered in patients with campomelic dysplasia, a haploinsufficiency disorder with skeletal deformities caused by dysregulation of Sox9 expression during chondrogenesis. Since then, its role as a cell fate determiner during embryonic development has been well characterized; Sox9 expression differentiates cells derived from all three germ layers into a large variety of specialized tissues and organs. However, recent data has shown that ectoderm- and endoderm-derived tissues continue to express Sox9 in mature organs and stem cell pools, suggesting its role in cell maintenance and specification during adult life. The versatility of Sox9 may be explained by a combination of post-transcriptional modifications, binding partners, and the tissue type in which it is expressed. Considering its importance during both development and adult life, it follows that dysregulation of Sox9 has been implicated in various congenital and acquired diseases, including fibrosis and cancer. This review provides a summary of the various roles of Sox9 in cell fate specification, stem cell biology, and related human diseases. Ultimately, understanding the mechanisms that regulate Sox9 will be crucial for developing effective therapies to treat disease caused by stem cell dysregulation or even reverse organ damage.