Hepatic vascular endothelial growth factor regulates recruitment of rat liver sinusoidal endothelial cell progenitor cells

Angiocrine signaling in sinusoidal homeostasis and liver diseases

The hepatic sinusoids are composed of liver sinusoidal endothelial cells (LSECs), which are surrounded by hepatic stellate cells (HSCs) and contain liver-resident macrophages called Kupffer cells, and other patrolling immune cells. All these cells communicate with each other and with hepatocytes to maintain sinusoidal homeostasis and a spectrum of hepatic functions under healthy conditions. Sinusoidal homeostasis is disrupted by metabolites, toxins, viruses, and other pathological factors, leading to liver injury, chronic liver diseases, and cirrhosis. Alterations in hepatic sinusoids are linked to fibrosis progression and portal hypertension. LSECs are crucial regulators of cellular crosstalk within their microenvironment via angiocrine signaling. This review discusses the mechanisms by which angiocrine signaling orchestrates sinusoidal homeostasis, as well as the development of liver diseases. Here, we summarise the crosstalk between LSECs, HSCs, hepatocytes, cholangiocytes, and immune cells in health and disease and comment on potential novel therapeutic methods for treating liver diseases.

Vascular damage and excessive proliferation compromise liver function after extended hepatectomy in mice

BACKGROUND AND AIMS

Surgical resection remains the gold standard for liver tumor treatment, yet the emergence of postoperative liver failure, known as the small-for-size syndrome (SFSS), poses a significant challenge. The activation of hypoxia sensors in an SFSS liver remnant initiated early angiogenesis, improving the vascular architecture, safeguarding against liver failure, and reducing mortality. The study aimed to elucidate vascular remodeling mechanisms in SFSS and their impact on hepatocyte function and subsequent liver failure.

APPROACH AND RESULTS

Mice underwent extended partial hepatectomy to induce SFSS, with a subset exposed to hypoxia immediately after surgery. Hypoxia bolstered posthepatectomy survival rates. The early proliferation of liver sinusoidal cells, coupled with recruitment of putative endothelial progenitor cells, increased vascular density, improved lobular perfusion, and limited hemorrhagic events in the regenerating liver under hypoxia. Administration of granulocyte colony-stimulating factor in hepatectomized mice mimicked the effects of hypoxia on vascular remodeling and endothelial progenitor cell recruitment but failed to rescue survival. Compared to normoxia, hypoxia favored hepatocyte function over proliferation, promoting functional preservation in the regenerating remnant. Injection of Adeno-associated virus serotype 8-thyroxine-binding globulin-hepatocyte nuclear factor 4 alpha virus for hepatocyte-specific overexpression of hepatocyte nuclear factor 4 alpha, the master regulator of hepatocyte function, enforced functionality in proliferating hepatocytes but did not rescue survival. The combination of hepatocyte nuclear factor 4 alpha overexpression and granulocyte colony-stimulating factor treatment rescued survival after SFSS-setting hepatectomy.

CONCLUSIONS

In summary, SFSS arises from an imbalance and desynchronized interplay between functional regeneration and vascular restructuring. To improve survival following SFSS hepatectomy, it is essential to adopt a 2-pronged strategy aimed at preserving the function of proliferating parenchymal cells and simultaneously attenuating vascular damage.

Advances in experimental animal models of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a common malignant tumor with insidious early symptoms, easy metastasis, postoperative recurrence, poor drug efficacy, and a high drug resistance rate when surgery is missed, leading to a low 5-year survival rate. Research on the pathogenesis and drugs is particularly important for clinical treatment. Animal models are crucial for basic research, which is conducive to studying pathogenesis and drug screening more conveniently and effectively. An appropriate animal model can better reflect disease occurrence and development, and the process of anti-tumor immune response in the human body. This review summarizes the classification, characteristics, and advances in experimental animal models of HCC to provide a reference for researchers on model selection.

Mesenchymal stem cell-released oncolytic virus: an innovative strategy for cancer treatment

Oncolytic viruses (OVs) infect, multiply, and finally remove tumor cells selectively, causing no damage to normal cells in the process. Because of their specific features, such as, the ability to induce immunogenic cell death and to contain curative transgenes in their genomes, OVs have attracted attention as candidates to be utilized in cooperation with immunotherapies for cancer treatment. This treatment takes advantage of most tumor cells' inherent tendency to be infected by certain OVs and both innate and adaptive immune responses are elicited by OV infection and oncolysis. OVs can also modulate tumor microenvironment and boost anti-tumor immune responses. Mesenchymal stem cells (MSC) are gathering interest as promising anti-cancer treatments with the ability to address a wide range of cancers. MSCs exhibit tumor-trophic migration characteristics, allowing them to be used as delivery vehicles for successful, targeted treatment of isolated tumors and metastatic malignancies. Preclinical and clinical research were reviewed in this study to discuss using MSC-released OVs as a novel method for the treatment of cancer. Video Abstract.

In Vitro Evidence of Differential Immunoregulatory Response between MDA-MB-231 and BT-474 Breast Cancer Cells Induced by Bone Marrow-Derived Mesenchymal Stromal Cells Conditioned Medium

Inside tumors, cancer cells display several mechanisms to create an immunosuppressive environment. On the other hand, by migration processes, mesenchymal stromal cells (MSCs) can be recruited by different cancer tumor types from tissues as distant as bone marrow and contribute to tumor pathogenesis. However, the impact of the immunoregulatory role of MSCs associated with the aggressiveness of breast cancer cells by soluble molecules has not been fully elucidated. Therefore, this in vitro work aimed to study the effect of the conditioned medium of human bone marrow-derived-MSCs (hBM-MSC-cm) on the immunoregulatory capability of MDA-MB-231 and BT-474 breast cancer cells. The hBM-MSC-cm on MDA-MB-231 cells induced the overexpression of TGF-β, IDO, and IL-10 genes. Additionally, immunoregulation assays of mononuclear cells (MNCs) in co-culture with MDA-MB-231 and hBM-MSC-cm decreased lymphocyte proliferation, and increased proteins IL-10, TGF-β, and IDO while also reducing TNF levels, shooting the proportion of regulatory T cells. Conversely, the hBM-MSC-cm did not affect the immunomodulatory capacity of BT-474 cells. Thus, a differential immunoregulatory effect was observed between both representative breast cancer cell lines from different origins. Thus, understanding the immune response in a broader tumor context could help to design therapeutic strategies based on the aggressive behavior of tumor cells.

Living Donor Liver Transplantation for Hepatic Venoocclusive Disease/Sinusoidal Obstruction Syndrome Originating from Hematopoietic Stem Cell Transplantation

Background

Venoocclusive disease (VOD), also known as sinusoidal obstruction syndrome (SOS), is a life-threatening hematopoietic stem cell transplantation (HSCT) complication. Cases of mild and moderate VOD/SOS are self-limiting; however, the mortality for severe VOD/SOS has reached 80%. Recently, defibrotide became available and has been used for VOD/SOS; however, the outcome for patients with severe VOD/SOS is not satisfactory, and liver transplantation is attempted in these severe cases.

Method

We describe a case of living donor liver transplantation (LDLT) for acute liver failure secondary to VOD/SOS that originates from HSCT.

Result

Liver regeneration after LDLT was impaired, and several infections were developed before liver regeneration completion. Our patient suffered sepsis and finally died of multiorgan failure.

Conclusion

Severe VOD/SOS originating from HSCT is associated with a very poor prognosis. The liver transplantation outcome for VOD/SOS has not been satisfied, but it may provide long-term survival if successful. We considered liver transplantation as a therapeutic option, especially in cases where sufficient graft volume is secured, considering impaired liver regeneration under bone marrow suppression after HSCT.

Prednisolone and mesenchymal stem cell preloading protect liver cell migration and mitigate extracellular matrix modification in transplanted decellularized rat liver

INTRODUCTION

Regenerative medicine provides promising approaches for treating chronic liver diseases. Previous studies indicate that decellularized liver architecture is damaged by invading non-hepatic inflammatory cells. This study aimed to use anti-inflammatory and regenerative potency of bone marrow-derived mesenchymal stem cells (BM-MSC) and prednisolone for reducing fibrosis and balancing inflammatory cell migration into the decellularized liver scaffold.

MATERIAL AND METHOD

The liver was decellularized by perfusing Sodium Lauryl Ether Sulfate (SLES), and nuclei depletion and extracellular matrix (ECM) retention were confirmed by DNA quantification, histochemical, and immunohistochemical assessments. Scaffolds were loaded with BM-MSCs, prednisolone, or a combination of both, implanted at the anatomical place in the rat partial hepatectomized and followed up for 2 and 4 weeks.

RESULTS

Labeled-MSCs were traced in the transplanted scaffolds; however, they did not migrate into the intact liver. Immunohistochemistry showed that the hepatoblasts, cholangiocytes, stellate, and oval cells invaded into all the scaffolds. Bile ducts were more abundant in the border of the scaffolds and intact liver. Stereological assessments showed a significant reduction in the number of lymphocytes and neutrophils in prednisolone-loaded scaffolds. The regeneration process and angiogenesis were significantly higher in the group treated with cell/prednisolone-loaded bioscaffolds. Collagen fibers were significantly reduced in the scaffolds pre-treated with cell/prednisolone, prednisolone, or BM-MSCs, compared to the control group.

CONCLUSION

Loading prednisolone into the scaffolds can be a worthy approach to restrict inflammation after transplantation. Although pre-loading of the scaffolds with a combination of cells/prednisolone could not alleviate inflammation, it played an important role in regeneration and angiogenesis.

Liver regeneration biology: Implications for liver tumour therapies

The liver has remarkable regenerative potential, with the capacity to regenerate after 75% hepatectomy in humans and up to 90% hepatectomy in some rodent models, enabling it to meet the challenge of diverse injury types, including physical trauma, infection, inflammatory processes, direct toxicity, and immunological insults. Current understanding of liver regeneration is based largely on animal research, historically in large animals, and more recently in rodents and zebrafish, which provide powerful genetic manipulation experimental tools. Whilst immensely valuable, these models have limitations in extrapolation to the human situation. In vitro models have evolved from 2-dimensional culture to complex 3 dimensional organoids, but also have shortcomings in replicating the complex hepatic micro-anatomical and physiological milieu. The process of liver regeneration is only partially understood and characterized by layers of complexity. Liver regeneration is triggered and controlled by a multitude of mitogens acting in autocrine, paracrine, and endocrine ways, with much redundancy and cross-talk between biochemical pathways. The regenerative response is variable, involving both hypertrophy and true proliferative hyperplasia, which is itself variable, including both cellular phenotypic fidelity and cellular trans-differentiation, according to the type of injury. Complex interactions occur between parenchymal and non-parenchymal cells, and regeneration is affected by the status of the liver parenchyma, with differences between healthy and diseased liver. Finally, the process of termination of liver regeneration is even less well understood than its triggers. The complexity of liver regeneration biology combined with limited understanding has restricted specific clinical interventions to enhance liver regeneration. Moreover, manipulating the fundamental biochemical pathways involved would require cautious assessment, for fear of unintended consequences. Nevertheless, current knowledge provides guiding principles for strategies to optimise liver regeneration potential.

Insights into Macrophage/Monocyte-Endothelial Cell Crosstalk in the Liver: A Role for Trem-2

Liver disease accounts for millions of deaths worldwide annually being a major cause of global morbidity. Hepatotoxic insults elicit a multilayered response involving tissue damage, inflammation, scar formation, and tissue regeneration. Liver cell populations act coordinately to maintain tissue homeostasis and providing a barrier to external aggressors. However, upon hepatic damage, this tight regulation is disrupted, leading to liver pathology which spans from simple steatosis to cirrhosis. Inflammation is a hallmark of liver pathology, where macrophages and endothelial cells are pivotal players in promoting and sustaining disease progression. Understanding the drivers and mediators of these interactions will provide valuable information on what may contribute to liver resilience against disease. Here, we summarize the current knowledge on the role of macrophages and liver sinusoidal endothelial cells (LSEC) in homeostasis and liver pathology. Moreover, we discuss the expanding body of evidence on cell-to-cell communication between these two cell compartments and present triggering receptor expressed on myeloid cells-2 (Trem-2) as a plausible mediator of this cellular interlink. This review consolidates relevant knowledge that might be useful to guide the pursue of successful therapeutic targets and pharmacological strategies for controlling liver pathogenesis.

Stem cell therapy and tissue engineering strategies using cell aggregates and decellularized scaffolds for the rescue of liver failure

Liver failure is a lethal condition with hepatocellular dysfunction, and liver transplantation is presently the only effective treatment. However, due to the limited availability of donors and the potential immune rejection, novel therapeutic strategies are actively sought to restore the normal hepatic architectures and functions, especially for livers with inherited metabolic dysfunctions or chronic diseases. Although the conventional cell therapy has shown promising results, the direct infusion of hepatocytes is hampered by limited hepatocyte sources, poor cell viability, and engraftment. Hence, this review mainly highlights the role of stem cells and progenitors as the alternative cell source and summarizes the potential approaches based on tissue engineering to improve the delivery efficiency of cells. Particularly, the underlying mechanisms for cell therapy using stem cells and progenitors are discussed in two main aspects: paracrine effect and cell differentiation. Moreover, tissue-engineering approaches using cell aggregates and decellularized liver scaffolds for bioengineering of functional hepatic constructs are discussed and compared in terms of the potential to replicate liver physiological structures. In the end, a potentially effective strategy combining the premium advantages of stem cell aggregates and decellularized liver scaffolds is proposed as the future direction of liver tissue engineering and regeneration.

Mesenchymal stem cells as a double-edged sword in tumor growth: focusing on MSC-derived cytokines

Mesenchymal stem cells (MSCs) show homing capacity towards tumor sites. Numerous reports indicate that they are involved in multiple tumor-promoting processes through several mechanisms, including immunosuppression; stimulation of angiogenesis; transition to cancer-associated fibroblasts; inhibition of cancer cell apoptosis; induction of epithelial-mesenchymal transition (EMT); and increase metastasis and chemoresistance. However, other studies have shown that MSCs suppress tumor growth by suppressing angiogenesis, incrementing inflammatory infiltration, apoptosis and cell cycle arrest, and inhibiting the AKT and Wnt signaling pathways. In this review, we discuss the supportive and suppressive impacts of MSCs on tumor progression and metastasis. We also discuss MSC-based therapeutic strategies for cancer based on their potential for homing to tumor sites.

Prognostic factors for pyrrolizidine alkaloid-induced hepatic sinusoidal obstruction syndrome: a multicenter study in China

Background

In China, one of the major causes of hepatic sinusoidal obstruction syndrome (HSOS) is the intake of herbals containing pyrrolizidine alkaloid (PA). However, prognostic factors for PA-induced HSOS are poorly understood. The aim of this study was to identify the independent prognostic factors for PA-induced HSOS using a multi-center study.

Methods

A total of 117 PA-induced HSOS patients were enrolled for data collection in three university hospitals from November 2003 to September 2018. Univariate and multivariate Cox proportional hazards analysis were used to determine prognostic factors for PA-induced HSOS.

Results

The median age of the PA-induced HSOS patients was 61 years (range, 21–88 years), and 64% of them were male. The survival rates at 1, 3, and 36 months were 89.71%, 72.60%, and 69.19%, respectively. Significant differences in prothrombin time (PT), international normalized ratio, total bilirubin, severity grading [new criteria for severity grading of hematopoietic stem cell transplantation (HSCT)-related HSOS in adults] were found between patients who survived and those who died. Univariate and multivariate survival analysis using Cox’s regression model demonstrated low serum albumin (<35 g/L), elevated serum urea (>8.2 mmol/L) and severe or very severe HSOS (European Society for Blood and Marrow Transplantation 2016 criteria) were independent prognostic factors of survival.

Conclusions

Serum albumin, serum urea, and severity grading were independent prognostic factors for patients with PA-induced HSOS, and can contribute to identifying potentially high-risk patients for early effective intervention.

Trial registration

ChiCTR-DRD-17010709 (www.chictr.org.cn).

Sinusoidal Endothelial Cell Progenitor Cells Promote Tumour Progression in Patients with Hepatocellular Carcinoma

Objective

As sinusoidal endothelial cell progenitor cells (SEPCs) play a significant role in liver regeneration, it is necessary to elucidate whether SEPCs participate in tumour progression of hepatocellular carcinoma (HCC).

Methods

A total of 45 patients with primary HCC who underwent liver resection were included in this study. The liver tumours were removed from the patients, and partial tissues were prepared to identify SEPCs through double staining of CD133/CD45 and CD133/CD31 at the same location. Blood samples were collected to examine liver function parameters and tumour markers. The demographics and clinicopathological characteristics of the patients were collected for correlation analysis with SEPCs.

Results

SEPCs were observed in several blood vessels within the HCC nodules of all 45 patients, but no SEPCs were detected in the tumour-adjacent tissues. The number of SEPCs was correlated with the expression levels of HCC tumour markers α-fetoprotein (AFP) and CA199. There was a positive correlation between the expression of SEPC markers and diameter of HCC tumours in differently differentiated specimens (P < 0.01). The expression levels of SEPC markers were significantly higher in patients with poorly differentiated HCC than in patients with moderately and highly differentiated HCC (P < 0.05).

Conclusions

SEPCs are closely associated with HCC progression; therefore, SEPCs may be considered potential prognostic and metastatic biomarkers and therapeutic candidates for HCC.

Susceptibility of Rat Steatotic Liver to Ischemia-Reperfusion Is Treatable With Liver-Selective Matrix Metalloproteinase Inhibition

BACKGROUND AND AIMS

This study examined whether enhanced susceptibility of steatotic liver to ischemia-reperfusion (I/R) injury is due to impaired recruitment of bone marrow (BM) progenitors of liver sinusoidal endothelial cells (LSECs, also called sinusoidal endothelial cell progenitor cells [sprocs]) with diminished repair of injured LSECs and whether restoring signaling to recruit BM sprocs reduces I/R injury.

APPROACH AND RESULTS

Hepatic vessels were clamped for 1 hour in rats fed a high-fat, high-fructose (HFHF) diet for 5, 10, or 15 weeks. Matrix metalloproteinase 9 (MMP-9) antisense oligonucleotides (ASO) or an MMP inhibitor were used to induce liver-selective MMP-9 inhibition. HFHF rats had mild, moderate, and severe steatosis, respectively, at 5, 10, and 15 weeks. I/R injury was enhanced in HFHF rats; this was accompanied by complete absence of hepatic vascular endothelial growth factor (VEGF)-stromal cell-derived factor 1 (sdf1) signaling, leading to lack of BM sproc recruitment. Liver-selective MMP-9 inhibition to protect against proteolytic cleavage of hepatic VEGF using either MMP-9 ASO or intraportal MMP inhibitor in 5-week and 10-week HFHF rats enhanced hepatic VEGF-sdf1 signaling, increased BM sproc recruitment, and reduced alanine aminotransferase (ALT) by 92% and 77% at 5 weeks and by 80% and 64% at 10 weeks of the HFHF diet, respectively. After I/R injury in 15-week HFHF rats, the MMP inhibitor reduced active MMP-9 expression by 97%, ameliorated histologic evidence of injury, and reduced ALT by 58%, which is comparable to control rats sustaining I/R injury. Rescue therapy with intraportal MMP inhibitor, given after ischemia, in the 5-week HFHF rat reduced ALT by 71% and reduced necrosis.

CONCLUSIONS

Lack of signaling to recruit BM sprocs that repair injured LSECs renders steatotic liver more susceptible to I/R injury. Liver-selective MMP-9 inhibition enhances VEGF-sdf1 signaling and recruitment of BM sprocs, which markedly protects against I/R injury, even in severely steatotic rats.

Portal venous repopulation of decellularised rat liver scaffolds with syngeneic bone marrow stem cells

Liver transplantation is the only life-saving treatment for end-stage liver failure but is limited by the organ shortage and consequences of immunosuppression. Repopulation of decellularised scaffolds with recipient cells provides a theoretical solution, allowing reliable and timely organ sourcing without the need for immunosuppression. Recellularisation of the vasculature of decellularised liver scaffolds was investigated as an essential prerequisite to the survival of other parenchymal components. Liver decellularisation was carried out by portal vein perfusion using a detergent-based solution. Decellularised scaffolds were placed in a sterile perfusion apparatus consisting of a sealed organ chamber, functioning at 37°C in normal atmospheric conditions. The scaffold was perfused via portal vein with culture medium. A total of 10⁷ primary cultured bone marrow stem cells, selected by plastic adherence, were infused into the scaffold, after which repopulated scaffolds were perfused for up to 30 days. The cultured stem cells were assessed for key marker expression using fluorescence-activated cell sorting (FACS), and recellularised scaffolds were analysed by light, electron and immunofluorescence microscopy. Stem cells were engrafted in portal, sinusoidal and hepatic vein compartments, with cell alignment reminiscent of endothelium. Cell surface marker expression altered following engraftment, from haematopoietic to endothelial phenotype, and engrafted cells expressed sinusoidal endothelial endocytic receptors (mannose, Fc and stabilin receptors). These results represent one step towards complete recellularisation of the liver vasculature and progress towards the objective of generating transplantable neo-organs.

LSEC model of aging

Data obtained from genetically modified mouse models suggest a detrimental role for p16High senescent cells in physiological aging and age-related pathologies. Our recent analysis of aging mice revealed a continuous and noticeable accumulation of liver sinusoid endothelial cells (LSECs) expressing numerous senescence markers, including p16. At early stage, senescent LSECs show an enhanced ability to clear macromolecular waste and toxins including oxidized LDL (oxLDL). Later in life, however, the efficiency of this important detoxifying function rapidly declines potentially due to increased endothelial thickness and senescence-induced silencing of scavenger receptors and endocytosis genes. This inability to detoxify toxins and macromolecular waste, which can be further exacerbated by increased intestinal leakiness with age, might be an important contributing factor to animal death. Here, we propose how LSEC senescence could serve as an endogenous clock that ultimately controls longevity and outline some of the possible approaches to extend the lifespan.

The Endothelium as a Driver of Liver Fibrosis and Regeneration

Liver fibrosis is a common feature of sustained liver injury and represents a major public health problem worldwide. Fibrosis is an active research field and discoveries in the last years have contributed to the development of new antifibrotic drugs, although none of them have been approved yet. Liver sinusoidal endothelial cells (LSEC) are highly specialized endothelial cells localized at the interface between the blood and other liver cell types. They lack a basement membrane and display open channels (fenestrae), making them exceptionally permeable. LSEC are the first cells affected by any kind of liver injury orchestrating the liver response to damage. LSEC govern the regenerative process initiation, but aberrant LSEC activation in chronic liver injury induces fibrosis. LSEC are also main players in fibrosis resolution. They maintain liver homeostasis and keep hepatic stellate cell and Kupffer cell quiescence. After sustained hepatic injury, they lose their phenotype and protective properties, promoting angiogenesis and vasoconstriction and contributing to inflammation and fibrosis. Therefore, improving LSEC phenotype is a promising strategy to prevent liver injury progression and complications. This review focuses on changes occurring in LSEC after liver injury and their consequences on fibrosis progression, liver regeneration, and resolution. Finally, a synopsis of the available strategies for LSEC-specific targeting is provided.

Mesenchymal stem cells to treat liver diseases

Mesenchymal stem cells (MSCs) are being developed for stem cell therapy and can be efficiently used in regenerative medicine. To date, more than 1,000 clinical trials have used MSCs; of these, more than 80 clinical trials have targeted liver disease. MSCs migrate to damaged liver tissues, differentiate into hepatocytes, reduce liver inflammatory responses, reduce liver fibrosis, and act as antioxidants. According to the reported literature, MSCs are safe, have no side effects, and improve liver function; however, their regenerative therapeutic effects are unsatisfactory. Here, we explain, in detail, the basic therapeutic effects and recent clinical advances of MSCs. Furthermore, we discuss future research directions for improving the regenerative therapeutic effects of MSCs.

RNA-Seq transcriptome profiling in three liver regeneration models in rats: comparative analysis of partial hepatectomy, ALLPS, and PVL

The liver is a unique organ that has a phenomenal capacity to regenerate after injury. Different surgical procedures, including partial hepatectomy (PH), intraoperative portal vein ligation (PVL), and associated liver partition and portal vein ligation for staged hepatectomy (ALPPS) show clinically distinct recovery patterns and regeneration. The observable clinical differences likely mirror some underlying variations in the patterns of gene activation and regeneration pathways. In this study, we provided a comprehensive comparative transcriptomic analysis of gene regulation in regenerating rat livers temporally spaced at 24 h and 96 h after PH, PVL, and ALPPS. The time-dependent factors appear to be the most important determinant of post-injury alterations of gene expression in liver regeneration. Gene expression profile after ALPPS showed more similar expression pattern to the PH than the PVL at the early phase of the regeneration. Early transcriptomic changes and predicted upstream regulators that were found in all three procedures included cell cycle associated genes (E2F1, CCND1, FOXM1, TP53, and RB1), transcription factors (Myc, E2F1, TBX2, FOXM1), DNA replication regulators (CDKN1A, EZH2, RRM2), G1/S-transition regulators (CCNB1, CCND1, RABL6), cytokines and growth factors (CSF2, IL-6, TNF, HGF, VEGF, and EGF), ATM and p53 signaling pathways. The functional pathway, upstream, and network analyses revealed both unique and overlapping molecular mechanisms and pathways for each surgical procedure. Identification of molecular signatures and regenerative signaling pathways for each surgical procedure further our understanding of key regulators of liver regeneration as well as patient populations that are likely to benefit from each procedure.

Transplantation of mesenchymal stem cells and their derivatives effectively promotes liver regeneration to attenuate acetaminophen-induced liver injury

Acetaminophen (APAP)-induced injury is a common clinical phenomenon that not only occurs in a dose-dependent manner but also occurs in some idiosyncratic individuals in a dose-independent manner. APAP overdose generally results in acute liver injury via the initiation of oxidative stress, endoplasmic reticulum (ER) stress, autophagy, liver inflammation, and microcirculatory dysfunction. Liver transplantation is the only effective strategy for treating APAP-induced liver failure, but liver transplantation is inhibited by scarce availability of donor liver grafts, acute graft rejection, lifelong immunosuppression, and unbearable costs. Currently, N-acetylcysteine (NAC) effectively restores liver functions early after APAP intake, but it does not protect against APAP-induced injury at the late stage. An increasing number of animal studies have demonstrated that mesenchymal stem cells (MSCs) significantly attenuate acute liver injury through their migratory capacity, hepatogenic differentiation, immunoregulatory capacity, and paracrine effects in acute liver failure (ALF). In this review, we comprehensively discuss the mechanisms of APAP overdose-induced liver injury and current therapies for treating APAP-induced liver injury. We then comprehensively summarize recent studies about transplantation of MSC and MSC derivatives for treating APAP-induced liver injury. We firmly believe that MSCs and their derivatives will effectively promote liver regeneration and liver injury repair in APAP overdose-treated animals and patients. To this end, MSC-based therapies may serve as an effective strategy for patients who are waiting for liver transplantation during the early and late stages of APAP-induced ALF in the near future.

Fetal liver stem cell transplantation for liver diseases

Stem cell transplantation exhibited a promising lifesaving therapy for various end-stage liver diseases and could serve as a salvaging bridge until curative methods can be performed. In past decades, mature hepatocytes, liver progenitor cells, mesenchymal stem cells and induced pluripotent stem cells have been practiced in above settings. However, long-term survival rates and continuous proliferation ability of these cells in vivo are unsatisfactory, whereas, fetal liver stem cells (FLSCs), given their unique superiority, may be the best candidate for stem cell transplantation technique. Recent studies have revealed that FLSCs could be used as an attractive genetic therapy or regenerative treatments for inherited metabolic or other hepatic disorders. In this study, we reviewed current status and advancements of FLSCs-based treatment.

Pyrrolizidine alkaloids-induced hepatic sinusoidal obstruction syndrome: Pathogenesis, clinical manifestations, diagnosis, treatment, and outcomes

Hepatic sinusoidal obstruction syndrome (HSOS) can be caused by the intake of pyrrolizidine alkaloids (PAs). To date, PAs-induced HSOS has not been extensively studied. In view of the difference in etiology of HSOS between the West and China, clinical profiles, imaging findings, treatment, and outcomes of HSOS associated with hematopoietic stem cell transplantation or oxaliplatin might be hardly extrapolated to PAs-induced HSOS. Reactive metabolites derived from PAs form pyrrole-protein adducts that result in toxic destruction of hepatic sinusoidal endothelial cells. PAs-induced HSOS typically manifests as painful hepatomegaly, ascites, and jaundice. Laboratory tests revealed abnormal liver function tests were observed in most of the patients with PAs-induced HSOS. In addition, contrast computed tomography and magnetic resonance imaging scan show that patients with PAs-induced HSOS have distinct imaging features, which reveal that radiological imaging provides an effective noninvasive method for the diagnosis of PAs-induced HSOS. Liver biopsy and histological examination showed that PAs-induced HSOS displayed distinct features in acute and chronic stages. Therapeutic strategies for PAs-induced HSOS include rigorous fluid management, anticoagulant therapy, glucocorticoids, transjugular intrahepatic portosystemic shunt, liver transplantation, etc. The aim of this review is to describe the pathogenesis, clinical profiles, diagnostic criteria, treatment, and outcomes of PAs-induced HSOS.

Incomplete Differentiation of Engrafted Bone Marrow Endothelial Progenitor Cells Initiates Hepatic Fibrosis in the Rat

Normal liver sinusoidal endothelial cells (LSECs) promote quiescence of hepatic stellate cells (HSCs). Prior to fibrosis, LSECs undergo capillarization, which is permissive for HSC activation, the proximate event in hepatic fibrosis. The aims of this study were to elucidate the nature of and mechanisms leading to capillarization and to determine how LSECs promote HSC quiescence and why "capillarized LSECs" lose control of HSC activation. The contribution of bone marrow (BM) endothelial progenitor cells to capillarization was identified using rats transplanted with transgenic enhanced green fluorescent protein-positive BM. Shotgun proteomics and informatics were used to identify the LSEC mediator that maintains HSC quiescence. The study shows that capillarization is due to repair of injured LSECs by BM endothelial progenitors that engraft but fail to fully mature. Lack of maturation of BM-derived LSECs is due to cell autonomous pathways that inhibit the nitric oxide pathway. We identify heparin binding epidermal growth factor-like growth factor (HB-EGF) as the signal that maintains HSC quiescence and show that immature LSECs are unable to shed HB-EGF from the cytosolic membrane. Conclusion: Chronic liver injury can recruit BM progenitors of LSECs that engraft and fail to fully differentiate, which creates an environment that is permissive for hepatic fibrosis; elucidation of these early events in the fibrotic process will provide targets for treatment of hepatic fibrosis.

Liver-Selective MMP-9 Inhibition in the Rat Eliminates Ischemia-Reperfusion Injury and Accelerates Liver Regeneration

Recruitment of liver sinusoidal endothelial cell progenitor cells (sprocs) from the bone marrow by vascular endothelial growth factor-stromal cell-derived factor-1 (VEGF-sdf-1) signaling promotes recovery from injury and drives liver regeneration. Matrix metalloproteinases (MMPs) can proteolytically cleave VEGF, which might inhibit progenitor cell recruitment, but systemic matrix metalloproteinase inhibition might prevent efflux of progenitors from the bone marrow. The hypothesis for this study was that liver-selective MMP-9 inhibition would protect the hepatic VEGF-sdf-1 signaling pathway, enhance bone marrow sproc recruitment, and thereby ameliorate liver injury and accelerate liver regeneration, whereas systemic MMP inhibition would impair bone marrow sproc mobilization and therefore have less benefit or be detrimental. We found that liver-selective MMP-9 inhibition accelerated liver regeneration after partial hepatectomy by 40%, whereas systemic MMP inhibition impaired liver regeneration. Liver-selective MMP-9 inhibition largely abolished warm ischemia-reperfusion injury. In the extended hepatectomy model, liver-selective MMP-9 inhibition restored liver sinusoidal endothelial cell integrity, enhanced liver regeneration, and reduced ascites. Liver-selective MMP-9 inhibition markedly increased recruitment and engraftment of bone marrow sprocs, whereas systemic MMP inhibition impaired mobilization of bone marrow sprocs and their hepatic engraftment. Hepatic MMP-9 proteolytically cleaved VEGF after partial hepatectomy. Liver-selective MMP-9 inhibition prevented VEGF cleavage and doubled protein expression of VEGF and its downstream signaling partner sdf-1. In contrast, systemic MMP inhibition enhanced recruitment and engraftment of infused allogeneic progenitors. Conclusion: Liver-selective MMP inhibition prevents proteolytic cleavage of hepatic VEGF, which enhances recruitment and engraftment of bone marrow sprocs after liver injury. This ameliorates injury and accelerates liver regeneration. Liver-selective MMP-9 inhibition may be a therapeutic tool for liver injury that damages the vasculature, whereas systemic MMP inhibition can enhance the benefit of stem cell therapy with endothelial progenitor cells.

Patient-Specific iPSC-Derived Endothelial Cells Provide Long-Term Phenotypic Correction of Hemophilia A

We generated patient-specific disease-free induced pluripotent stem cells (iPSCs) from peripheral blood CD34+ cells and differentiated them into functional endothelial cells (ECs) secreting factor VIII (FVIII) for gene and cell therapy approaches to cure hemophilia A (HA), an X-linked bleeding disorder caused by F8 mutations. iPSCs were transduced with a lentiviral vector carrying FVIII transgene driven by an endothelial-specific promoter (VEC) and differentiated into bona fide ECs using an optimized protocol. FVIII-expressing ECs were intraportally transplanted in monocrotaline-conditioned non-obese diabetic (NOD) severe combined immune-deficient (scid)-IL2rγ null HA mice generating a chimeric liver with functional human ECs. Transplanted cells engrafted and proliferated in the liver along sinusoids, in the long term showed stable therapeutic FVIII activity (6%). These results demonstrate that the hemophilic phenotype can be rescued by transplantation of ECs derived from HA FVIII-corrected iPSCs, confirming the feasibility of cell-reprogramming strategy in patient-derived cells as an approach for HA gene and cell therapy.

Endothelial Notch activation reshapes the angiocrine of sinusoidal endothelia to aggravate liver fibrosis and blunt regeneration in mice

Liver sinusoidal endothelial cells (LSECs) critically regulate liver homeostasis and diseases through angiocrine factors. Notch is critical in endothelial cells (ECs). In the current study, Notch signaling was activated by inducible EC-specific expression of the Notch intracellular domain (NIC). We found that endothelial Notch activation damaged liver homeostasis. Notch activation resulted in decreased fenestration and increased basement membrane, and a gene expression profile with decreased LSEC-associated genes and increased continuous EC-associated genes, suggesting LSEC dedifferentiation. Consistently, endothelial Notch activation enhanced hepatic fibrosis (HF) induced by CCl₄ . Notch activation attenuated endothelial nitric oxide synthase (eNOS)/soluble guanylate cyclase (sGC) signaling, and activation of sGC by 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1) reversed the dedifferentiation phenotype. In addition, Notch activation subverted the hepatocyte-supporting angiocrine profile of LSECs by down-regulating critical hepatocyte mitogens, including Wnt2a, Wnt9b, and hepatocyte growth factor (HGF). This led to compromised hepatocyte proliferation under both quiescent and regenerating conditions. Whereas expression of Wnt2a and Wnt9b was dependent on eNOS-sGC signaling, HGF expression was not rescued by the sGC activator, suggesting heterogeneous mechanisms of LSECs to maintain hepatocyte homeostasis.

CONCLUSION

Endothelial Notch activation results in LSEC dedifferentiation and accelerated liver fibrogenesis through eNOS-sGC signaling, and alters the angiocrine profile of LSECs to compromise hepatocyte proliferation and liver regeneration (LR). (Hepatology 2018).

Taking advantage of the potential of mesenchymal stromal cells in liver regeneration: Cells and extracellular vesicles as therapeutic strategies

Cell-based therapies for acute and chronic liver diseases are under continuous progress. Mesenchymal stem/stromal cells (MSCs) are multipotent cells able to migrate selectively to damaged tissue and contribute to its healing and regeneration. The MSC pro-regenerative effect occurs due to their immunomodulatory capacity and their ability to produce factors that promote cell protection and survival. Likewise, it has been observed that part of their paracrine effect is mediated by MSC-derived extracellular vesicles (EVs). EVs contain proteins, lipids and nucleic acids (DNA, mRNA, miRNA, lncRNA) from the cell of origin, allowing for intercellular communication. Recently, different studies have demonstrated that MSC-derived EVs could reproduce, at least in part, the biological effects obtained by MSC-based therapies. Moreover, due to EVs' stability for long periods of time and easy isolation methods they have become a therapeutic option to MSCs treatments. This review summarizes the latest results achieved in clinical trials using MSCs as cell therapy for liver regeneration, the role of EVs in liver physiopathology and the potential of MSCderived EVs as intercellular mediators and therapeutic tools in liver diseases.

Adult hepatocytes direct liver organogenesis through non-parenchymal cell recruitment in the kidney

BACKGROUND & AIMS

Since the first account of the myth of Prometheus, the amazing regenerative capacity of the liver has fascinated researchers because of its enormous medical potential. Liver regeneration is promoted by multiple types of liver cells, including hepatocytes and liver non-parenchymal cells (NPCs), through complex intercellular signaling. However, the mechanism of liver organogenesis, especially the role of adult hepatocytes at ectopic sites, remains unknown. In this study, we demonstrate that hepatocytes alone spurred liver organogenesis to form an organ-sized complex 3D liver that exhibited native liver architecture and functions in the kidneys of mice.

METHODS

Isolated hepatocytes were transplanted under the kidney capsule of monocrotaline (MCT) and partial hepatectomy (PHx)-treated mice. To determine the origin of NPCs in neo-livers, hepatocytes were transplanted into MCT/PHx-treated green fluorescent protein transgenic mice or wild-type mice transplanted with bone marrow cells isolated from green fluorescent protein-mice.

RESULTS

Hepatocytes engrafted at the subrenal space of mice underwent continuous growth in response to a chronic hepatic injury in the native liver. More than 1.5 years later, whole organ-sized liver tissues with greater mass than those of the injured native liver had formed. Most remarkably, we revealed that at least three types of NPCs with similar phenotypic features to the liver NPCs were recruited from the host tissues including bone marrow. The neo-livers in the kidney exhibited liver-specific functions and architectures, including sinusoidal vascular systems, zonal heterogeneity, and emergence of bile duct cells. Furthermore, the neo-livers successfully rescued the mice with lethal liver injury.

CONCLUSION

Our data clearly show that adult hepatocytes play a leading role as organizer cells in liver organogenesis at ectopic sites via NPC recruitment.

LAY SUMMARY

The role of adult hepatocytes at ectopic locations has not been clarified. In this study, we demonstrated that engrafted hepatocytes in the kidney proliferated, recruited non-parenchymal cells from host tissues including bone marrow, and finally created an organ-sized, complex liver system that exhibited liver-specific architectures and functions. Our results revealed previously undescribed functions of hepatocytes to direct liver organogenesis through non-parenchymal cell recruitment and organize multiple cell types into a complex 3D liver at ectopic sites. Transcript profiling: Microarray data are deposited in GEO (GEO accession: GSE99141).

Heterogenic transplantation of bone marrow-derived rhesus macaque mesenchymal stem cells ameliorates liver fibrosis induced by carbon tetrachloride in mouse

Liver fibrosis is a disease that causes high morbidity and has become a major health problem. Liver fibrosis can lead to the end stage of liver diseases (livercirrhosisand hepatocellularcarcinoma). Currently, liver transplantation is the only effective treatment for end-stage liver disease. However, the shortage of organ donors, high cost of medical surgery, immunological rejection and transplantation complications severely hamper liver transplantation therapy. Mesenchymal stem cells (MSCs) have been regarded as promising cells for clinical applications in stem cell therapy in the treatment of liver diseases due to their unique multipotent differentiation capacity, immunoregulation and paracrine effects. Although liver fibrosis improvements by MSC transplantation in preclinical experiments as well as clinical trials have been reported, the in vivo fate of MSCs after transportation and their therapeutic mechanisms remain unclear. In this present study, we isolated MSCs from the bone marrow of rhesus macaques. The cells exhibited typical MSC markers and could differentiate into chondrocytes, osteocytes, and adipocytes, which were not affected by labeling with enhanced green fluorescent protein (EGFP). The harvested MSCs respond to interferon-γ stimulation and have the ability to inhibit lymphocyte proliferation in vitro. EGFP-labeled MSCs (1 × 10⁶ cells) were transplanted into mice with carbon tetrachloride-induced liver fibrosis via tail vein injection. The ability of the heterogenic MSC infusion to ameliorate liver fibrosis in mice was evaluated by a blood plasma chemistry index, pathological examination and liver fibrosis-associated gene expression. Additionally, a small number of MSCs that homed and engrafted in the mouse liver tissues were evaluated by immunofluorescence analysis. Our results showed that the transplantation of heterogenic MSCs derived from monkey bone marrow can be used to treat liver fibrosis in the mouse model and that the paracrine effects of MSCs may play an important role in the improvement of liver fibrosis.

Current Perspectives Regarding Stem Cell-Based Therapy for Liver Cirrhosis

Liver cirrhosis is a major cause of mortality and a common end of various progressive liver diseases. Since the effective treatment is currently limited to liver transplantation, stem cell-based therapy as an alternative has attracted interest due to promising results from preclinical and clinical studies. However, there is still much to be understood regarding the precise mechanisms of action. A number of stem cells from different origins have been employed for hepatic regeneration with different degrees of success. The present review presents a synopsis of stem cell research for the treatment of patients with liver cirrhosis according to the stem cell type. Clinical trials to date are summarized briefly. Finally, issues to be resolved and future perspectives are discussed with regard to clinical applications.

Liver Sinusoidal Endothelial Cell: An Update

This update focuses on two main topics. First, recent developments in our understanding of liver sinusoidal endothelial cell (LSEC) function will be reviewed, specifically elimination of blood-borne waste, immunological function of LSECs, interaction of LSECs with liver metastases, LSECs and liver regeneration, and LSECs and hepatic fibrosis. Second, given the current emphasis on rigor and transparency in biomedical research, the update discusses the need for standardization of methods to demonstrate identity and purity of isolated LSECs, pitfalls in methods that might lead to a selection bias in the types of LSECs isolated, and questions about long-term culture of LSECs. Various surface markers used for immunomagnetic selection are reviewed.

Tumor-educated mesenchymal stem cells promote pro-metastatic phenotype

Multipotent mesenchymal stem cells (MSCs) are recruited into tumor microenvironment in response to multiple signals produced by cancer cells. Molecules involved in their homing to tumors are the same inflammatory mediators produced by injured tissues: chemokines, cytokines and growth factors. When MSCs arrive into the tumor microenvironment these are “educated” to have pro-metastatic behaviour. Firstly, they promote cancer immunosuppression modulating both innate and adaptive immune systems. Moreover, tumor associated-MSCs trans-differentiating into cancer-associated fibroblasts can induce epithelial-mesenchymal-transition program in tumor cells. This process determinates a more aggressive phenotype of cancer cells by increasing their motility and invasiveness and favoring their dissemination to distant sites. In addition, MSCs are involved in the formation and modelling of pre-metastatic niches creating a supportive environment for colonization of circulating tumor cells.

The development of novel therapeutic approaches targeting the different functions of MSCs in promoting tumor progression as well as the mechanisms underlying their activities could enhance the efficacy of conventional and immune anti-cancer therapies.

Furthermore, many studies report the use of MSCs engineered to express different genes or as vehicle to specifically deliver novel drugs to tumors exploiting their strong tropism. Importantly, this approach can enhance local therapeutic efficacy and reduce the risk of systemic side effects.

Regeneration and Cell Recruitment in an Improved Heterotopic Auxiliary Partial Liver Transplantation Model in the Rat

BACKGROUND

Auxiliary partial liver transplantation (APLT) in humans is a therapeutic modality used especially to treat liver failure in children or congenital metabolic disease. Animal models of APLT have helped to explore therapeutic options. Though many groups have suggested improvements, standardizing the surgical procedure has been challenging. Additionally, the question of whether graft livers are reconstituted by recipient-derived cells after transplantation has been controversial. The aim of this study was to improve experimental APLT in rats and to assess cell recruitment in the liver grafts.

METHODS

To inhibit recipient liver regeneration and to promote graft regeneration, we treated recipients with retrorsine and added arterial anastomosis. Using green fluorescence protein transgenic rats as recipients, we examined liver resident cell recruitment within graft livers by immunofluorescence costaining.

RESULTS

In the improved APLT model, we achieved well-regenerated grafts that could maintain regeneration for at least 4 weeks. Regarding the cell recruitment, there was no evidence of recipient-derived hepatocyte, cholangiocyte, or hepatic stellate cell recruitment into the graft. Macrophages/monocytes, however, were consistently recruited into the graft and increased over time, which might be related to inflammatory responses. Very few endothelial cells showed colocalization of markers.

CONCLUSIONS

We have successfully established an improved rat APLT model with arterial anastomosis as a standard technique. Using this model, we have characterized cell recruitment into the regenerating grafts.

Effects of heme oxygenase-1-modified bone marrow mesenchymal stem cells on microcirculation and energy metabolism following liver transplantation

AIM

To investigate the effects of heme oxygenase-1 (HO-1)-modified bone marrow mesenchymal stem cells (BMMSCs) on the microcirculation and energy metabolism of hepatic sinusoids following reduced-size liver transplantation (RLT) in a rat model.

METHODS

BMMSCs were isolated and cultured in vitro using an adherent method, and then transduced with HO-1-bearing recombinant adenovirus to construct HO-1/BMMSCs. A rat acute rejection model following 50% RLT was established using a two-cuff technique. Recipients were divided into three groups based on the treatment received: normal saline (NS), BMMSCs and HO-1/BMMSCs. Liver function was examined at six time points. The levels of endothelin-1 (ET-1), endothelial nitric-oxide synthase (eNOS), inducible nitric-oxide synthase (iNOS), nitric oxide (NO), and hyaluronic acid (HA) were detected using an enzyme-linked immunosorbent assay. The portal vein pressure (PVP) was detected by Power Lab ML880. The expressions of ET-1, iNOS, eNOS, and von Willebrand factor (vWF) protein in the transplanted liver were detected using immunohistochemistry and Western blotting. ATPase in the transplanted liver was detected by chemical colorimetry, and the ultrastructural changes were observed under a transmission electron microscope.

RESULTS

HO-1/BMMSCs could alleviate the pathological changes and rejection activity index of the transplanted liver, and improve the liver function of rats following 50% RLT, with statistically significant differences compared with those of the NS group and BMMSCs group (P < 0.05). In term of the microcirculation of hepatic sinusoids: The PVP on POD7 decreased significantly in the HO-1/BMMSCs and BMMSCs groups compared with that of the NS group (P < 0.01); HO-1/BMMSCs could inhibit the expressions of ET-1 and iNOS, increase the expressions of eNOS and inhibit amounts of NO production, and maintain the equilibrium of ET-1/NO (P < 0.05); and HO-1/BMMSCs increased the expression of vWF in hepatic sinusoidal endothelial cells (SECs), and promoted the degradation of HA, compared with those of the NS group and BMMSCs group (P < 0.05). In term of the energy metabolism of the transplanted liver, HO-1/BMMSCs repaired the damaged mitochondria, and improved the activity of mitochondrial aspartate aminotransferase (ASTm) and ATPase, compared with the other two groups (P <0.05).

CONCLUSION

HO-1/BMMSCs can improve the microcirculation of hepatic sinusoids significantly, and recover the energy metabolism of damaged hepatocytes in rats following RLT, thus protecting the transplanted liver.

Ultrasound-guided percutaneous portal transplantation of peripheral blood monocytes in patients with liver cirrhosis

BACKGROUND/AIMS

Liver transplantation offers the only definite cure for cirrhosis but lacking donors is problem. Stem cell therapy is attractive in this setting. In this study, we aimed to explore the safety and efficacy of ultrasound-guided percutaneous portal transplantation of peripheral blood monocyte cell (PBMC) in cirrhotic patients.

METHODS

A total of nine decompensated cirrhotic patients were randomized into three groups: group 1 (n = 3) was control group, group 2 (n = 3) received granulocyte-colony stimulating factor (G-CSF) mobilization for 3 days, and group 3 (n = 3) received G-CSF mobilized PBMCs by leukapheresis and PBMC transplantation through ultrasound-guided percutaneous portal vein puncture. Liver function and clinical features were evaluated.

RESULTS

At baseline, the Child-Turcotte-Pugh and the model for end-stage liver disease scores were comparable in study groups. Compared with group 1, there was a tendency to improve liver function in group 3 at 6 months after treatment. Treatment was tolerable and no complications were encountered related to the G-CSF mobilization or percutaneous portal administration of PBMCs. Imaging studies showed patent portal veins at the end of the study period.

CONCLUSIONS

Autologous PBMC transplantation through ultrasound-guided percutaneous portal vein puncture could be considered as a safe alternative treatment for decompensated cirrhotic patients.

Regulators of Cholangiocyte Proliferation

Cholangiocytes, a small population of cells within the normal liver, have been the focus of a significant amount of research over the past two decades because of their involvement in cholangiopathies such as primary sclerosing cholangitis and primary biliary cholangitis. This article summarizes landmark studies in the field of cholangiocyte physiology and aims to provide an updated review of biliary pathogenesis. The historical approach of rodent extrahepatic bile duct ligation and the relatively recent utilization of transgenic mice have led to significant discoveries in cholangiocyte pathophysiology. Cholangiocyte physiology is a complex system based on heterogeneity within the biliary tree and a number of signaling pathways that serve to regulate bile composition. Studies have expanded the list of neuropeptides, neurotransmitters, and hormones that have been shown to be key regulators of proliferation and biliary damage. The peptide histamine and hormones, such as melatonin and angiotensin, angiotensin, as well as numerous sex hormones, have been implicated in cholangiocyte proliferation during cholestasis. Numerous pathways promote cholangiocyte proliferation during cholestasis, and there is growing evidence to suggest that cholangiocyte proliferation may promote hepatic fibrosis. These pathways may represent significant therapeutic potential for a subset of cholestatic liver diseases that currently lack effective therapies.

Intraportal mesenchymal stem cell transplantation prevents acute liver failure through promoting cell proliferation and inhibiting apoptosis

BACKGROUND

Transplantation of mesenchymal stem cells (MSCs) has been regarded as a potential treatment for acute liver failure (ALF), but the optimal route was unknown. The present study aimed to explore the most effective MSCs transplantation route in a swine ALF model.

METHODS

The swine ALF model induced by intravenous injection of D-Gal was treated by the transplantation of swine MSCs through four routes including intraportal injection (InP group), hepatic intra-arterial injection (AH group), peripheral intravenous injection (PV group) and intrahepatic injection (IH group). The living conditions and survival time were recorded. Blood samples before and after MSCs transplantation were collected for the analysis of hepatic function. The histology of liver injury was interpreted and scored in terminal samples. Hepatic apoptosis was detected by TUNEL assay. Apoptosis and proliferation related protein expressions including cleaved caspase-3, survivin, AKT, phospho-AKT (Ser473), ERK and phospho-ERK (Tyr204) were analyzed by Western blotting.

RESULTS

The average survival time of each group was 10.7+/-1.6 days (InP), 6.0+/-0.9 days (AH), 4.7+/-1.4 days (PV), 4.3+/-0.8 days (IH), respectively, when compared with the average survival time of 3.8+/-0.8 days in the D-Gal group. The survival rates between the InP group and D-Gal group revealed a statistically significant difference (P<0.01). Pathological and biochemical analysis showed that liver damage was the worst in the D-Gal group, while less injury in the InP group. Histopathological scores revealed a significant decrease in the InP group (3.17+/-1.04, P<0.01) and AH group (8.17+/-0.76, P<0.05) as compared with that in the D-Gal group (11.50+/-1.32). The apoptosis rate in the InP group (25.0%+/-3.4%, P<0.01) and AH group (40.5%+/-1.0%, P<0.05) was lower than that in the D-Gal group (70.6%+/-8.5%). The expression of active caspase-3 was inhibited, while the expression of survivin, AKT, phospho-AKT (Ser473), ERK and phospho-ERK (Tyr204) was elevated in the InP group.

CONCLUSIONS

Intraportal injection was superior to other pathways for MSC transplantation. Intraportal MSC transplantation could improve liver function, inhibit apoptosis and prolong the survival time of swine with ALF. The transplanted MSCs may participate in liver regeneration via promoting cell proliferation and suppressing apoptosis during the initial stage of ALF.

Sinusoidal communication in liver fibrosis and regeneration

Cellular crosstalk is a process through which a message is transmitted within an individual cell (intracellular crosstalk) or between different cells (intercellular crosstalk). Intercellular crosstalk within the liver microenvironment is critical for the maintenance of normal hepatic functions and for cells survival. Hepatic cells are closely connected to each other, work in synergy, and produce molecules that modulate their differentiation and activity. This review summarises the current knowledge regarding paracrine communication networks in parenchymal and non-parenchymal cells in liver fibrosis due to chronic injury, and regeneration after partial hepatectomy.

Hepatic stellate cells: fibrogenic, regenerative or both? Heterogeneity and context are key

Since their original identification, our understanding of the role of hepatic stellate cells in both health and disease continues to grow. Numerous studies have delineated the role of stellate cell activation in contributing to the pool of myofibroblasts responsible for liver fibrosis, and these have resulted in the development of a number of anti-fibrotic strategies targeting this cell. However, their potential role in liver regeneration, both initiation and termination, is also emerging and needs to be contemplated when considering targeted therapy. Perhaps what is most striking is the increasing recognition that this is not just one cell, but rather, a heterogenous population made up of a number of different subsets of cells, each with differentiated and specific functions. The tools are emerging for this dissection and are greatly needed to truly develop targeted therapies that will inhibit fibrosis while promoting liver regeneration and repair.

The Involving Roles of Intrahepatic and Extrahepatic Stem/Progenitor Cells (SPCs) to Liver Regeneration

Liver regeneration is usually attributed to mature hepatocytes, which possess a remarkable potential to proliferate under mild to moderate injury. However, when the liver is severely damaged or hepatocyte proliferation is greatly inhibited, liver stem/progenitor cells (LSPCs) will contribute to the liver regeneration process. LSPCs in the developing liver have been extensively characterized, however, their contributing role to liver regeneration has not been completely understood. In addition to the restoration of the liver parenchymal tissue by hepatocytes or/and LSPCs, or in some cases bone marrow (BM) derived cells, such as hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs), the wound healing after injury in terms of angiopoiesis by liver sinusoidal endothelial cells (LSECs) or/and sinusoidal endothelial progenitor cells (SEPCs) is another important aspect taking place during regeneration. To conclude, liver regeneration can be mainly divided into three distinct restoring levels according to the cause and severity of injury: hepatocyte dominant regeneration, LSPCs mediated regeneration, extrahepatic stem cells participative regeneration. In this review, we focus on the recent findings of liver regeneration, especially on those related to stem/progenitor cells (SPCs)-mediated regeneration and their potential clinical applications and challenges.

VEGF-sdf1 recruitment of CXCR7+ bone marrow progenitors of liver sinusoidal endothelial cells promotes rat liver regeneration

In liver injury, recruitment of bone marrow (BM) progenitors of liver sinusoidal endothelial cells (sprocs) is necessary for normal liver regeneration. Hepatic vascular endothelial growth factor (VEGF) is a central regulator of the recruitment process. We examine whether stromal cell-derived factor 1 [sdf1, or CXC ligand 12 (CXCL12)] acts downstream from VEGF to mediate recruitment of BM sprocs, what the sdf1 receptor type [CXC receptor (CXCR)-4 or CXCR7] is on sprocs, and whether sdf1 signaling is required for normal liver regeneration. Studies were performed in the rat partial hepatectomy model. Tracking studies of BM sprocs were performed in wild-type Lewis rats that had undergone BM transplantation from transgenic enhanced green fluorescent protein-positive Lewis rats. Knockdown studies were performed using antisense oligonucleotides (ASOs). Expression of sdf1 doubles in liver and liver sinusoidal endothelial cells (LSECs) after partial hepatectomy. Upregulation of sdf1 expression increases proliferation of sprocs in the BM, mobilization of CXCR7(+) BM sprocs to the circulation, and engraftment of CXCR7(+) BM sprocs in the liver and promotes liver regeneration. Knockdown of hepatic VEGF with ASOs decreases hepatic sdf1 expression and plasma sdf1 levels. When the effect of VEGF knockdown on sdf1 is offset by infusion of sdf1, VEGF knockdown-induced impairment of BM sproc recruitment after partial hepatectomy is completely attenuated and liver regeneration is normalized. These data demonstrate that the VEGF-sdf1 pathway regulates recruitment of CXCR7(+) BM sprocs to the hepatic sinusoid after partial hepatectomy and is required for normal liver regeneration.

Mesenchymal Stem Cell-Mediated Effects of Tumor Support or Suppression

Mesenchymal stem cells (MSCs) can exhibit a marked tropism towards site of tumors. Many studies have reported that tumor progression and metastasis increase by MSCs. In contrast, other studies have shown that MSCs suppress growth of tumors. MSCs contribute to tumor growth promotion by several mechanisms: (1) transition to tumor-associated fibroblasts; (2) suppression of immune response; (3) promotion of angiogenesis; (4) stimulation of epithelial-mesenchymal transition (EMT); (5) contribution to the tumor microenvironment; (6) inhibition of tumor cell apoptosis; and (7) promotion of tumor metastasis. In contrast to the tumor-promoting properties, MSCs inhibit tumor growth by increasing inflammatory infiltration, inhibiting angiogenesis, suppressing Wnt signaling and AKT signaling, and inducing cell cycle arrest and apoptosis. In this review, we will discuss potential mechanisms by which MSC mediates tumor support or suppression and then the possible tumor-specific therapeutic strategies using MSCs as delivery vehicles, based on their homing potential to tumors.

Reinfusion of highly purified CD133+ bone marrow-derived stem/progenitor cells in patients with end-stage liver disease: A phase I clinical trial

BACKGROUND

Bone marrow stem/progenitor cells seem to be effective in liver regeneration after tissue injury.

AIM

To evaluate the feasibility and safety of the mobilization and reinfusion of CD133+ stem/progenitor cells in patients with end-stage liver disease.

METHODS

Autologous CD133+ stem/progenitor cells, mobilized with granulocyte-colony stimulating factor, were collected by leukapheresis and reinfused at increasing doses through the hepatic artery starting from 5×10(4)/kg up to 1×10(6)/kg.

RESULTS

16 subjects with Model for End-stage Liver Disease (MELD) score between 17 and 25 were enrolled, 14 mobilized an adequate number of CD133+ stem/progenitor cells and 12 were reinfused. No severe adverse events related to the procedure were reported. MELD score significantly worsened during mobilization in Child Turcotte Pugh-C patients. A significant improvement of liver function was observed 2 months after reinfusion (MELD 19.5 vs. 16; P=0.045). Overall, 5 patients underwent liver transplantation within 12 months from reinfusion and 2 died because of progressive liver failure.

CONCLUSIONS

CD133+ stem/progenitor cells reinfusion in patients with end-stage liver disease is feasible and safe. A worsening of liver function was observed during mobilization in Child Turcotte Pugh-C patients. The temporary improvement of MELD score after reinfusion suggests that stem cells therapy may be a "bridge to transplant" approach for these patients.

Autologous bone marrow stem cell transplantation in patients with liver failure: a meta-analytic review

Autologous bone marrow stem cell (ABMSC) transplantation has been utilized in clinical practice to treat patients with liver failure, but the therapeutic effect remains to be defined. A meta-analysis is essential to assess clinical advantages of ABMSC transplantation in patients with liver failure. A systematic search of published works [eg, PubMed, Medline, Embase, Chin J Clinicians (Electronic edition), and Science Citation Index] was conducted to compare clinical outcomes of ABMSC transplantation in patients with liver failure. Meta-analytic results were tested by fixed-effects model or random-effects model, dependent on the characteristics of variables. A total of 534 patients from seven studies were included in final meta-analysis. Subsequent to ABMSC transplantation, there was no significant improvement in general symptom and signs such as loss of appetite, fatigue, and ascites. Activities of serum ALT were not significantly decreased with weighted mean difference (WMD) of -19.36 and 95% confidence interval (CI) -57.53 to 18.80 (P=0.32). Postoperative level of albumin (ALB) was expectedly enhanced by stem cell transplantation (WMD 2.97, 95% CI 0.52 to 5.43, P<0.05, I(2)=84%). Coagulation function was improved as demonstrated by a short prothrombin time (PT) (WMD -1.18, 95% CI -2.32 to -0.03, P<0.05, I(2)=6%), but was not reflected by prothrombin activity (PTA) (P=0.39). Total bilirubin (TBIL) was drastically diminished after ABMSC therapy (WMD -14.85, 95% CI -20.39 to -9.32, P<0.01, I(2)=73%). Model for end-stage liver disease (MELD) scores were dramatically reduced (WMD -2.27, 95% CI -3.53 to -1.02, P<0.01, I(2)=0%). The advantage of ABMSC transplantation could be maintained more than 24 weeks as displayed by time-courses of ALB, TBIL, and MELD score. ABMSC transplantation does provide beneficial effects for patients with liver failure. Therapeutic effects can last for 6 months. However, long-term effects need to be determined.

Mesenchymal stem cell therapy for liver fibrosis

Currently, the most effective treatment for end-stage liver fibrosis is liver transplantation; however, transplantation is limited by a shortage of donor organs, surgical complications, immunological rejection, and high medical costs. Recently, mesenchymal stem cell (MSC) therapy has been suggested as an effective alternate approach for the treatment of hepatic diseases. MSCs have the potential to differentiate into hepatocytes, and therapeutic value exists in their immune-modulatory properties and secretion of trophic factors, such as growth factors and cytokines. In addition, MSCs can suppress inflammatory responses, reduce hepatocyte apoptosis, increase hepatocyte regeneration, regress liver fibrosis and enhance liver functionality. Despite these advantages, issues remain; MSCs also have fibrogenic potential and the capacity to promote tumor cell growth and oncogenicity. This paper summarizes the properties of MSCs for regenerative medicine and their therapeutic mechanisms and clinical application in the treatment of liver fibrosis. We also present several outstanding risks, including their fibrogenic potential and their capacity to promote pre-existing tumor cell growth and oncogenicity.

Progress and challenges in the development of a cell-based therapy for hemophilia A

Hemophilia A results from an insufficiency of factor VIII (FVIII). Although replacement therapy with plasma-derived or recombinant FVIII is a life-saving therapy for hemophilia A patients, such therapy is a life-long treatment rather than a cure for the disease. In this review, we discuss the possibilities, progress, and challenges that remain in the development of a cell-based cure for hemophilia A. The success of cell therapy depends on the type and availability of donor cells, the age of the host and method of transplantation, and the levels of engraftment and production of FVIII by the graft. Early therapy, possibly even prenatal transplantation, may yield the highest levels of engraftment by avoiding immunological rejection of the graft. Potential cell sources of FVIII include a specialized subset of endothelial cells known as liver sinusoidal endothelial cells (LSECs) present in the adult and fetal liver, or patient-specific endothelial cells derived from induced pluripotent stem cells that have undergone gene editing to produce FVIII. Achieving sufficient engraftment of transplanted LSECs is one of the obstacles to successful cell therapy for hemophilia A. We discuss recent results from transplants performed in animals that show production of functional and clinically relevant levels of FVIII obtained from donor LSECs. Hence, the possibility of treating hemophilia A can be envisioned through persistent production of FVIII from transplanted donor cells derived from a number of potential cell sources or through creation of donor endothelial cells from patient-specific induced pluripotent stem cells.

Hepatic stellate cells and liver fibrosis

Hepatic stellate cells are resident perisinusoidal cells distributed throughout the liver, with a remarkable range of functions in normal and injured liver. Derived embryologically from septum transversum mesenchyme, their precursors include submesothelial cells that invade the liver parenchyma from the hepatic capsule. In normal adult liver, their most characteristic feature is the presence of cytoplasmic perinuclear droplets that are laden with retinyl (vitamin A) esters. Normal stellate cells display several patterns of intermediate filaments expression (e.g., desmin, vimentin, and/or glial fibrillary acidic protein) suggesting that there are subpopulations within this parental cell type. In the normal liver, stellate cells participate in retinoid storage, vasoregulation through endothelial cell interactions, extracellular matrix homeostasis, drug detoxification, immunotolerance, and possibly the preservation of hepatocyte mass through secretion of mitogens including hepatocyte growth factor. During liver injury, stellate cells activate into alpha smooth muscle actin-expressing contractile myofibroblasts, which contribute to vascular distortion and increased vascular resistance, thereby promoting portal hypertension. Other features of stellate cell activation include mitogen-mediated proliferation, increased fibrogenesis driven by connective tissue growth factor, and transforming growth factor beta 1, amplified inflammation and immunoregulation, and altered matrix degradation. Evolving areas of interest in stellate cell biology seek to understand mechanisms of their clearance during fibrosis resolution by either apoptosis, senescence, or reversion, and their contribution to hepatic stem cell amplification, regeneration, and hepatocellular cancer.