Hepatic stellate cell-targeted delivery of hepatocyte growth factor transgene via bile duct infusion enhances its expression at fibrotic foci to regress dimethylnitrosamine-induced liver fibrosis

Nano-encapsulation of drugs to target hepatic stellate cells: Toward precision treatments of liver fibrosis

Liver fibrosis is characterized by excessive extracellular matrix (ECM) deposition triggered by hepatic stellate cells (HSCs). As central players in fibrosis progression, HSCs are the most important therapeutic targets for antifibrotic therapy. However, owing to the limitations of systemic drug administration, there is still no suitable and effective clinical treatment. In recent years, nanosystems have demonstrated expansive therapeutic potential and evolved into a clinical modality. In liver fibrosis, nanosystems have undergone a paradigm shift from targeting the whole liver to locally targeted modifying processes. Nanomedicine delivered to HSCs has significant potential in managing liver fibrosis, where optimal management would benefit from targeted delivery, personalized therapy based on the specific site of interest, and minor side effects. In this review, we present a brief overview of the role of HSCs in the pathogenesis of liver fibrosis, summarize the different types of nanocarriers and their specific delivery applications in liver fibrosis, and highlight the biological barriers associated with the use of nanosystems to target HSCs and approaches available to solve this issue. We further discuss in-depth all the molecular target receptors overexpressed during HSC activation in liver fibrosis and their corresponding ligands that have been used for drug or gene delivery targeting HSCs.

Maladaptive regeneration and metabolic dysfunction associated steatotic liver disease: Common mechanisms and potential therapeutic targets

The normal liver has an extraordinary capacity of regeneration. However, this capacity is significantly impaired in steatotic livers. Emerging evidence indicates that metabolic dysfunction associated steatotic liver disease (MASLD) and liver regeneration share several key mechanisms. Some classical liver regeneration pathways, such as HGF/c-Met, EGFR, Wnt/β-catenin and Hippo/YAP-TAZ are affected in MASLD. Some recently established therapeutic targets for MASH such as the Thyroid Hormone (TH) receptors, Glucagon-like protein 1 (GLP1), Farnesoid X receptor (FXR), Peroxisome Proliferator-Activated Receptors (PPARs) as well as Fibroblast Growth Factor 21 (FGF21) are also reported to affect hepatocyte proliferation. With this review we aim to provide insight into common molecular pathways, that may ultimately enable therapeutic strategies that synergistically ameliorate steatohepatitis and improve the regenerating capacity of steatotic livers. With the recent rise of prolonged ex-vivo normothermic liver perfusion prior to organ transplantation such treatment is no longer restricted to patients undergoing major liver resection or transplantation, but may eventually include perfused (steatotic) donor livers or even liver segments, opening hitherto unexplored therapeutic avenues.

Vascular endothelial growth factor protein and gene delivery by novel nanomaterials for promoting liver regeneration after partial hepatectomy

Partial hepatectomy (PH) can lead to severe complications, including liver failure, due to the low regenerative capacity of the remaining liver, especially after extensive hepatectomy. Liver sinusoidal endothelial cells (LSECs), whose proliferation occurs more slowly and later than hepatocytes after PH, compose the lining of the hepatic sinusoids, which are the smallest blood vessels in the liver. Vascular endothelial growth factor (VEGF), secreted by hepatocytes, promotes LSEC proliferation. Supplementation of exogenous VEGF after hepatectomy also increases the number of LSECs in the remaining liver, thus promoting the reestablishment of the hepatic sinusoids and accelerating liver regeneration. At present, some shortcomings exist in the methods of supplementing exogenous VEGF, such as a low drug concentration in the liver and the reaching of other organs. More-over, VEGF should be administered multiple times and in large doses because of its short half-life. This review summarized the most recent findings on liver regeneration and new strategies for the localized delivery VEGF in the liver.

Effect of Hepatocyte Growth Factor-Transfected Human Umbilical Cord Mesenchymal Stem Cells on Hepatic Stellate Cells by Regulating Transforming Growth Factor-β1/Smads Signaling Pathway

Studies have shown that human umbilical cord mesenchymal stem cells (hUCMSCs) could ameliorate liver fibrosis (LF) through inhibiting the activation of hepatic stellate cells (HSCs). However, the specific mechanisms have not been studied clearly. The purpose of this study was to explore the possible mechanism of hepatocyte growth factor (HGF)-transfected hUCMSCs in inhibiting the proliferation and activation of HSCs-T6. The upper and lower double-cell coculture system was established among HGF-hUCMSCs, LV5-NC-hUCMSCs, hUCMSCs, and HSCs-T6 in experimental groups; HSCs-T6 were cultured alone as control group. After coculturing for 1, 2, and 3 days, results showed that HGF-transfected hUCMSCs could decrease cell viability of HSCs-T6 and promote apoptosis; inhibit their activation and reduce the expression of Collagen I, Collagen III, TGF-β1, Smad2 and Smad3, which may be related to inhibiting the activation of TGF-β1/Smads signaling pathway. These findings suggested that HGF-transfected hUCMSCs may be used as an alternative and novel therapeutic approach for the treatment of LF.

Hepatic stellate cells specific liposomes with the Toll-like receptor 4 shRNA attenuates liver fibrosis

The hepatic stellate cells (HSCs) play a significant role in the onset of liver fibrosis, which can be treated by the inhibition and reversal of HSC activation. The RNA interference-mediated TLR4 gene silencing might be a potential therapeutic approach for liver fibrosis. The crucial challenge in this method is the absence of an efficient delivery system for the RNAi introduction in the target cells. HSCs have an enhanced capacity of vitamin A intake as they contain retinoic acid receptors (RARs). In the current study, we developed cationic liposomes modified with vitamin A to improve the specificity of delivery vehicles for HSCs. The outcome of this study revealed that the VitA-coupled cationic liposomes delivered the TLR4 shRNA to aHSCs more efficiently, as compared to the uncoupled cationic liposomes, both in the in vitro and in vivo conditions. Besides, as evident from the outcome of this study, the TLR4 gene silencing inhibited the HSCs activation and attenuated the liver fibrosis via the NF-κB transcriptional inactivation, pro-inflammatory cytokines secretion and reactive oxygen species (ROS) synthesis. Thus, the VitA-coupled liposomes encapsulated with the TLR4-shRNA might prove as an efficient therapeutic agent for liver fibrosis.

Lipid Nanoparticles for Cell-Specific in Vivo Targeted Delivery of Nucleic Acids

The last few years have witnessed a great advance in the development of nonviral systems for in vivo targeted delivery of nucleic acids. Lipid nanoparticles (LNPs) are the most promising carriers for producing clinically approved products in the future. Compared with other systems used for nonviral gene delivery, LNPs provide several advantages including higher stability, low toxicity, and greater efficiency. Additionally, systems based on LNPs can be modified with ligands and devices for controlled biodistribution and internalization into specific cells. Efforts are ongoing to improve the efficiency of lipid-based gene vectors. These efforts depend on the appropriate design of nanocarriers as well as the development of new lipids with improved gene delivery ability. Several ionizable lipids have recently been developed and have shown dramatically improved efficiency. However, enhancing the ability of nanocarriers to target specific cells in the body remains the most difficult challenge. Systemically administered LNPs can access organs in which the capillaries are characterized by the presence of fenestrations, such as the liver and spleen. The liver has received the most attention to date, although targeted delivery to the spleen has recently emerged as a promising tool for modulating the immune system. In this review, we discuss recent advances in the use of LNPs for cell-specific targeted delivery of nucleic acids. We focus mainly on targeting liver hepatocytes and spleen immune cells as excellent targets for gene therapy. We also discuss the potential of endothelial cells as an alternate approach for targeting organs with a continuous endothelium.

Liver gene transfection by retrograde intrabiliary infusion facilitated by temporary biliary obstruction

BACKGROUND

The hepatobiliary tract may be a valuable administration site for gene delivery. We demonstrated the role of temporary biliary obstruction for gene transfection by retrograde intrabiliary infusion.

METHODS

Male Sprague-Dawley rats received intrabiliary infusion of luciferase plasmid via an artificial common bile duct, with temporary biliary obstruction for 0 minutes (NO group), 30 minutes (30 min group) and 24 hours (24 h group), respectively (n = 4 for each group). Gene expression levels were evaluated by luciferase bioluminescence on postoperative days (POD) 1, 2 and 7. Serum and livers were collected on POD 1 and 14 for liver biochemistry, hematoxylin and eosin staining, and immunohistochemistry.

RESULTS

On POD 1, luciferase chemoluminescence was significantly higher in the 24 h group than in the NO group (p = 0.002) and the 30 min group (p = 0.002). However, it decreased rapidly after reversal of the obstruction in the 24 h group (POD 1 versus POD 2, p = 0.002; POD 1 versus POD 7, p = 0.002). Liver biochemistry was changed on POD 1, but no significant differences were detected after 14 days of recovery (p > 0.05). Similar histological changes were found in the three groups, with no unwanted proliferation of biliary epithelial cells. The obstruction did not cause serious liver damage.

CONCLUSIONS

Temporary biliary obstruction for 24 hours facilitated the safe, feasible and effective transfection of plasmid DNA into the liver via the hepatobiliary tract. In the future, endoscopic retrograde cholangiopancreatography and its dilation balloon could be used to create biliary obstruction and allow the direct gene delivery into the liver. More research is necessary for achieving stable gene expression, as well as in terms of weighing its benefits against potential complications.

Therapeutic Effect of HGF on NASH Mice Through HGF/c-Met and JAK2-STAT3 Signalling Pathway

INTRODUCTION AND AIM

Hepatocyte growth factor (HGF) has been shown to ameliorate liver inflammation and fibrosis; however, the mechanism underlying its effects in non-alcoholic steatohepatitis (NASH) is unclear. This study aimed to analyse the relationship between the JAK2-STAT3 signalling pathway and the ameliorating effect of HGF on NASH.

MATERIAL AND METHODS

Mice were fed a high-fat diet (HFD) for 16 weeks, and then plasma and hepatic tissues were collected. Histological and clinical chemistry assays were performed to assess liver disease. The mRNA and protein levels of JAK2, STAT3, and c-Met were assessed by real-time PCR and western blotting, respectively.

RESULTS

Serum ALT, AST, and TG levels were increased in NASH mice. Histological analysis showed different degrees of steatosis, inflammatory infiltrates, and fibrosis in HFD animals. Exogenous administration of recombinant human (rh) HGF via the tail vein for 14 days markedly decreased ALT and AST to levels lower than those in the control group. Compared with the levels in HFD mice, c-Met, p-c-Met, JAK2, p-JAK2, and p-STAT3 levels were increased in mice that were administered HGF (P < 0.05). Furthermore, silencing of HGF or blocking of its receptor c-Met affected JAK2 and STAT3 protein phosphorylation.

CONCLUSIONS

Excess HGF highly probable improved NASH liver function. Combined with its ligand, c-Met, HGF may promote the phosphorylation of JAK2-STAT3 and inhibit inflammation in NASH. Therefore, it may be potentially useful treatment for NASH.

Therapeutic effect of hepatocyte growth factor-overexpressing bone marrow-derived mesenchymal stem cells on CCl4-induced hepatocirrhosis

Hepatocirrhosis is one of the most severe complications of chronic hepatic disease in terms of medical intervention, and the available therapies are limited and not very successful. In this study, bone marrow-derived mesenchymal stem cells (BM-MSCs) from host rats were transduced with an adenoviral vector labelled with green fluorescent protein (EGFP) to overexpress hepatocyte growth factor (HGF). The therapeutic effect of these modified stem cells (HGF-BM-MSC group) transplanted intravenously into hepatocirrhosis model rats treated with CCl₄ was evaluated using serological, biochemical and histological approaches. We compared the rats in the HGF-BM-MSC group with those in the other groups (rats treated with BM-MSCs, rats treated with HGF and untreated rats (Controls)) in detail. The localisation of EGFP-tagged BM-MSCs in the injured liver was evaluated using a microscope, and the cells co-expressed hepatocyte nuclear factor 4α, albumin and cytokeratin 18. After treatment for 4 weeks, the HGF-BM-MSC, BM-MSC and HGF groups exhibited increased protein and mRNA levels of hepatocyte nuclear factor 4α, albumin and cytokeratin 18, but decreased levels of aspartate aminotransferase, alanine aminotransferase and total bilirubin. These findings indicate that BM-MSC transplantation and HGF application have great potential for the treatment of hepatocirrhosis.

Vitamin A-coupled liposomes carrying TLR4-silencing shRNA induce apoptosis of pancreatic stellate cells and resolution of pancreatic fibrosis

Chronic pancreatitis leads to irreversible damage in pancreatic endocrine and exocrine functions. However, there is no clinically available antifibrotic drug. Pancreatic stellate cells (PSCs) can be activated by Toll-like receptor 4 (TLR4) responses to its ligands and they contribute to the formation of pancreatic fibrosis. Silencing the expression of TLR4 in PSCs by RNAi may be a novel therapeutic strategy for the treatment of pancreatic fibrosis. In addition, PSCs have a remarkable capacity for vitamin A uptake most likely through cellular retinol binding protein (CRBP). In our study, to ensure the efficient delivery of RNAi therapeutic agents to PSCs, VitA-coupled liposomes (VA-lips) were used as drug carriers to deliver plasmids expressing TLR4-specific short hairpin RNA (shRNA) to treat pancreatic fibrosis. Our study demonstrated that silencing the expression of TLR4 could induce mitochondrial apoptosis in aPSCs and might be an effective therapeutic strategy for the treatment of pancreatic fibrosis.

KEY MESSAGES

VA-lip-shRNA-TLR4 recovers pancreatic tissue damage. VA-lip-shRNA-TLR4 resolution of pancreatic fibrosis. VA-lip-shRNA-TLR4 accelerates ECM degradation and inhibits ECM synthesis. Silencing TLR4 induces aPSCs mitochondrial apoptosis. Silencing TLR4 inhibits the activation of NF-κB.

Vitamin A-coupled liposome system targeting free cholesterol accumulation in hepatic stellate cells offers a beneficial therapeutic strategy for liver fibrosis

AIM

Liver fibrosis is a life-threatening disorder for which no approved therapy is available. Recently, we reported that mouse hepatic stellate cell (HSC) activation increased free cholesterol (FC) accumulation, partly by enhancing signaling through sterol regulatory element-binding protein 2 (SREBP2) and microRNA-33a (miR-33a), which resulted in HSC sensitization to transforming growth factor-β (TGFβ)-induced activation in a "vicious cycle" of liver fibrosis.

METHODS

Human HSCs were isolated from surgical liver specimens from control patients and patients with liver fibrosis. C57BL/6 mice were treated with carbon tetrachloride for 4 weeks and concurrently given SREBP2-siRNA- or anti-miR-33a-bearing vitamin A-coupled liposomes.

RESULTS

In human activated HSCs obtained from patients with liver fibrosis, FC accumulation was enhanced independently of serum cholesterol levels through increased signaling by both SREBP2 and miR-33a. This increased FC accumulation enhanced Toll-like receptor 4 (TLR4) protein levels and lowered the TGFβ-pseudoreceptor Bambi (bone morphogenetic protein and activin membrane-bound inhibitor) mRNA levels in HSCs. Notably, in a mouse liver fibrosis model, reduction of FC accumulation, specifically in activated HSCs by suppression of SREBP2 or miR-33a expression using SREBP2-siRNA- or anti-miR-33a-bearing vitamin A-coupled liposomes, downregulated TLR4 signaling, increased Bambi expression, and consequently ameliorated liver fibrosis.

CONCLUSIONS

Our results suggest that FC accumulation in HSCs, as an intracellular mediator promoting HSC activation, contributes to a vicious cycle of HSC activation in human and mouse liver fibrosis independent of serum cholesterol levels. Targeting FC accumulation-related molecules in HSCs through a vitamin A-coupled liposomal system represents a favorable therapeutic strategy for liver fibrosis.

Hepatic stellate cell-targeted therapy for hepatic fibrosis

Hepatic fibrosis is the ultimate pathological feature of all forms of chronic hepatic damage. There is currently no clinical cure for advanced liver fibrosis. Activation and proliferation of hepatic stellate cells (HSCs) is a key step in the development of liver fibrosis, and therefore, HSCs are target cells for hepatic fibrosis treatment. Targeted delivery of drugs to activated HSCs would increase the drug concentration in the liver at the sites of active fibrogenesis and avoid undesirable systemic effects. Mannose 6-phosphate modified human serum albumin, vitamin A, and hyaluronic acid are three kinds of the most investigated carriers that deliver drugs to the activated HSCs specifically. Conjugation of these carriers with molecules with anti-fibrosis activity such as angiotensin receptor blockers, activin-like kinase 5 inhibitors, Rho-kinase inhibitors, small interfering RNAs, hepatocyte growth factor gene, or nitrogen monoxide can lead to specific distribution and effects in HSCs. This review will focus on these preclinical developments of HSCs-targeted drug conjugates for the treatment of liver fibrosis.

Hepatic Stellate Cells in Liver Fibrosis and siRNA-Based Therapy

Hepatic fibrosis is a reversible wound-healing response to either acute or chronic liver injury caused by hepatitis B or C, alcohol, and toxic agents. Hepatic fibrosis is characterized by excessive accumulation and reduced degradation of extracellular matrix (ECM). Excessive accumulation of ECM alters the hepatic architecture leading to liver fibrosis and cirrhosis. Cirrhosis results in failure of common functions of the liver. Hepatic stellate cells (HSC) play a major role in the development of liver fibrosis as HSC are the main source of the excessive production of ECM in an injured liver. RNA interference (RNAi) is a recently discovered therapeutic tool that may provide a solution to manage multiple diseases including liver fibrosis through silencing of specific gene expression in diseased cells. However, gene silencing using small interfering RNA (siRNA) is encountering many challenges in the body after systemic administration. Efficient and stable siRNA delivery to the target cells is a key issue for the development of siRNA therapeutic. For that reason, various viral and non-viral carriers for liver-targeted siRNA delivery have been developed. This review will cover the current strategies for the treatment of liver fibrosis as well as discussing non-viral approaches such as cationic polymers and lipid-based nanoparticles for targeted delivery of siRNA to the liver.

Exposure to human immunodeficiency virus/hepatitis C virus in hepatic and stellate cell lines reveals cooperative profibrotic transcriptional activation between viruses and cell types

Human immunodeficiency virus (HIV)/hepatitis C virus (HCV) coinfection accelerates progressive liver fibrosis; however, the mechanisms remain poorly understood. HCV and HIV independently induce profibrogenic markers transforming growth factor beta-1 (TGFβ1) (mediated by reactive oxygen species [ROS]) and nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) in hepatocytes and hepatic stellate cells in monoculture; however, they do not account for cellular crosstalk that naturally occurs. We created an in vitro coculture model and investigated the contributions of HIV and HCV to hepatic fibrogenesis. Green fluorescent protein reporter cell lines driven by functional ROS (antioxidant response elements), NFκB, and mothers against decapentaplegic homolog 3 (SMAD3) promoters were created in Huh7.5.1 and LX2 cells, using a transwell to generate cocultures. Reporter cell lines were exposed to HIV, HCV, or HIV/HCV. Activation of the 3 pathways was measured and compared according to infection status. Extracellular matrix products (collagen type 1 alpha 1 (CoL1A1) and tissue inhibitor of metalloproteinase 1 (TIMP1)) were also measured. Both HCV and HIV independently activated TGFβ1 signaling through ROS (antioxidant response elements), NFκB, and SMAD3 in both cell lines in coculture. Activation of these profibrotic pathways was additive following HIV/HCV coexposure. This was confirmed when examining CoL1A1 and TIMP1, where messenger RNA and protein levels were significantly higher in LX2 cells in coculture following HIV/HCV coexposure compared with either virus alone. In addition, expression of these profibrotic genes was significantly higher in the coculture model compared to either cell type in monoculture, suggesting an interaction and feedback mechanism between Huh7.5.1 and LX2 cells.

CONCLUSION

HIV accentuates an HCV-driven profibrogenic program in hepatocyte and hepatic stellate cell lines through ROS, NFκB, and TGFβ1 up-regulation; coculture of hepatocyte and hepatic stellate cell lines significantly increased expression of CoL1A1 and TIMP1; and our novel coculture reporter cell model represents an efficient and more authentic system for studying transcriptional fibrosis responses and may provide important insights into hepatic fibrosis. (Hepatology 2016;64:1951-1968).

Pharmacological Intervention in Hepatic Stellate Cell Activation and Hepatic Fibrosis

The activation and transdifferentiation of hepatic stellate cells (HSCs) into contractile, matrix-producing myofibroblasts (MFBs) are central events in hepatic fibrogenesis. These processes are driven by autocrine- and paracrine-acting soluble factors (i.e., cytokines and chemokines). Proof-of-concept studies of the last decades have shown that both the deactivation and removal of hepatic MFBs as well as antagonizing profibrogenic factors are in principle suitable to attenuate ongoing hepatic fibrosis. Although several drugs show potent antifibrotic activities in experimental models of hepatic fibrosis, there is presently no effective pharmaceutical intervention specifically approved for the treatment of liver fibrosis. Pharmaceutical interventions are generally hampered by insufficient supply of drugs to the diseased liver tissue and/or by adverse effects as a result of affecting non-target cells. Therefore, targeted delivery systems that bind specifically to receptors solely expressed on activated HSCs or transdifferentiated MFBs and delivery systems that can improve drug distribution to the liver in general are urgently needed. In this review, we summarize current strategies for targeted delivery of drugs to the liver and in particular to pro-fibrogenic liver cells. The applicability and efficacy of sequestering molecules, selective protein carriers, lipid-based drug vehicles, viral vectors, transcriptional targeting approaches, therapeutic liver- and HSC-specific nanoparticles, and miRNA-based strategies are discussed. Some of these delivery systems that had already been successfully tested in experimental animal models of ongoing hepatic fibrogenesis are expected to translate into clinically useful therapeutics specifically targeting HSCs.

HGF gene modified bone marrow mesenchymal stem cells for treatment of hepatic fibrosis

Hepatic fibrosis is a reversible pathological change caused by liver cell inflammation, necrosis, or abnormal hyperplasia of connective tissue. It has been proved that hepatocyte growth factor (HGF) gene modified bone marrow mesenchymal stem cells can reduce or inhibit liver fibrosis, with better effects than those of unmodified bone marrow mesenchymal stem cells. Thus, HGF gene modified bone marrow mesenchymal stem cells represent a promising method for anti-hepatic fibrosis.

New gene therapy strategies for hepatic fibrosis

The liver is the largest internal organ of the body, which may suffer acute or chronic injury induced by many factors, leading to cirrhosis and hepatocarcinoma. Cirrhosis is the irreversible end result of fibrous scarring and hepatocellular regeneration, characterized by diffuse disorganization of the normal hepatic structure, regenerative nodules and fibrotic tissue. Cirrhosis is associated with a high co-morbidity and mortality without effective treatment, and much research has been aimed at developing new therapeutic strategies to guarantee recovery. Liver-based gene therapy has been used to downregulate specific genes, to block the expression of deleterious genes, to delivery therapeutic genes, to prevent allograft rejection and to augment liver regeneration. Viral and non-viral vectors have been used, with viral vectors proving to be more efficient. This review provides an overview of the main strategies used in liver-gene therapy represented by non-viral vectors, viral vectors, novel administration methods like hydrodynamic injection, hybrids of two viral vectors and blocking molecules, with the hope of translating findings from the laboratory to the patient´s bed-side.

Animal Models for Fibrotic Liver Diseases: What We Have, What We Need, and What Is under Development

Liver fibrosis is part of the wound-healing response to liver damage of various origins and represents a major health problem. Although our understanding of the pathogenesis of liver fibrosis has grown considerably over the last 20 years, effective antifibrotic therapies are still lacking. The use of animal models is crucial for determining mechanisms underlying initiation, progression, and resolution of fibrosis and for developing novel therapies. To date, no animal model can recapitulate all the hepatic and extra-hepatic features of liver disease. In this review, we will discuss the current rodent models of liver injuries. We will then focus on the available ways to target specifically particular compounds of fibrogenesis and on the new models of liver diseases like the humanized liver mouse model.

The CD47-binding peptide of thrombospondin-1 induces defenestration of liver sinusoidal endothelial cells

BACKGROUND & AIMS

A fenestrated phenotype is characteristic of liver sinusoidal endothelial cells (LSECs), but liver sinusoids become defenestrated during fibrosis and other liver diseases. Thrombospondin-1 (TSP1) is a matrix glycoprotein with pro-fibrotic effects, and the CD47-binding fragment of TSP1 also has anti-angiogenic effects in endothelial cells. We hypothesized that the CD47-binding fragment of TSP1 could induce defenestration in LSECs through the Rho-Rho kinase (ROCK)-myosin pathway.

METHODS

Freshly isolated rat LSECs were treated with TSP1 or CD47-binding peptides of TSP1. LSEC fenestration was assessed with scanning electron microscopy, and myosin phosphorylation was assessed with immuno-fluorescence.

RESULTS

Treating LSECs with TSP1 caused a dose-dependent loss of fenestrae, and this effect could not be blocked by SB-431542, the TGF-β1 receptor inhibitor. A CD47-binding fragment of TSP1, p4N1, was able to induce defenestration, and a CD47-blocking antibody, B6H12, was able to suppress p4N1-induced defenestration. The p4N1 fragment also caused contraction of fenestra size, correlated with an increase in myosin activation. Pretreatment with Y-237642 (a ROCK inhibitor) prevented p4N1-induced myosin activation and fenestrae decrease. Simvastatin has also been shown to antagonize Rho-ROCK signalling, and we found that simvastatin pretreatment protected LSECs from p4N1-induced myosin activation and defenestration.

CONCLUSIONS

We conclude that CD47 signals through the Rho-ROCK-myosin pathway to induce defenestration in LSECs. In addition, our results show that simvastatin and Y-237642 have a beneficial impact on fenestration in vitro, providing an additional explanation for the efficacy of these compounds for regression of liver fibrosis.

Nuclear erythroid 2-related factor 2: a novel potential therapeutic target for liver fibrosis

Hepatic stellate cells (HSC) are the key fibrogenic cells of the liver. HSC activation is a process of cellular transdifferentiation that occurs upon liver injury, but the mechanisms underlying liver fibrosis are unknown. Nuclear erythroid 2-related factor 2 (Nrf2) is an oxidative stress-mediated transcription factor with a variety of downstream targets aimed at cytoprotection. However, Nrf2 has recently been implicated as a new therapeutic target for the treatment of liver fibrosis. This review focuses on the transcriptional repressors that either control liver injury or regulate specific fibrogenic functions of liver fibrosis. We also show that Nrf2 may reveal significant gene expression changes, suggesting that Nrf2 activation may ameliorate liver fibrosis.