The evolving role of liver sinusoidal endothelial cells in liver health and disease

Molecular Mechanisms of Fibrosis in Cholestatic Liver Diseases and Regenerative Medicine-Based Therapies

The aim of this review is to explore the potential of new regenerative medicine approaches in the treatment of cholestatic liver fibrosis. Cholestatic liver diseases, such as primary biliary cholangitis (PBC), primary sclerosing cholangitis (PSC), and biliary atresia (BA), due to the accumulation of bile, often progress to liver fibrosis, cirrhosis, and liver failure. When the disease becomes severe enough to require liver transplantation. Deeply understanding the disease's progression and fibrosis formation is crucial for better diagnosis and treatment. Current liver fibrosis treatments mainly target the root causes and no direct treatment method in fibrosis itself. Recent advances in regenerative medicine offer a potential approach that may help find the ways to target fibrosis directly, offering hope for improved outcomes. We also summarize, analyze, and discuss the current state and benefits of regenerative medicine therapies such as mesenchymal stem cell (MSC) therapy, induced pluripotent stem cells (iPSCs), and organoid technology, which may help the treatment of cholestatic liver diseases. Focusing on the latest research may reveal new targets and enhance therapeutic efficacy, potentially leading to more effective management and even curative strategies for cholestatic liver diseases.

Single-cell transcriptome unveils unique transcriptomic signatures of human organ-specific endothelial cells

The heterogeneity of endothelial cells (ECs) across human tissues remains incompletely inventoried. We constructed an atlas of > 210,000 ECs derived from 38 regions across 24 human tissues. Our analysis reveals significant differences in transcriptome, phenotype, metabolism and transcriptional regulation among ECs from various tissues. Notably, arterial, venous, and lymphatic ECs shared more common markers in multiple tissues than capillary ECs, which exhibited higher heterogeneity. This diversity in capillary ECs suggests their greater potential as targets for drug development. ECs from different tissues and vascular beds were found to be associated with specific diseases. Importantly, tissue specificity of EC senescence is more determined by somatic site than by tissue type (e.g. subcutaneus adipose tissue and visceral adipose tissue). Additionally, sex-specific differences in brain EC senescence were observed. Our EC atlas offers valuble resoursce for identifying EC subclusters in single-cell datasets from body tissues or organoids, facilitating the screen of tissue-specific targeted therapies, and serving as a powerful tool for future discoveries.

Advances in the understanding of the role and mechanism of action of PFKFB3‑mediated glycolysis in liver fibrosis (Review)

Liver fibrosis is a pathophysiologic manifestation of chronic liver disease and a precursor to cirrhosis and hepatocellular carcinoma. Glycolysis provides intermediate metabolites as well as energy support for cell proliferation and phenotypic transformation in liver fibers. 6‑Phosphofructo‑2‑kinase/fructose‑2,6‑bisphosphatase 3 (PFKFB3) is a key activator of glycolysis and plays an important role in the process of glycolysis. The role of PFKFB3‑mediated glycolysis in myocardial fibrosis, renal fibrosis and pulmonary fibrosis has been demonstrated, and the role of PFKFB3 in the activation of hepatic stellate cells by aerobic glycolysis has been proven by relevant experiments. The present study reviews the research progress on the role and mechanism of action of PFKFB3‑mediated glycolysis in the progression of hepatic fibrosis to discuss the role of PFKFB3‑mediated glycolysis in hepatic fibrosis and to provide new ideas for research on PFKFB3 as a target for the treatment of hepatic fibrosis.

Bilirubin, a hepatoprotective agent that activates SIRT1, PGC-1α, and PPAR-α, while inhibiting NF-κB in rats with metabolic-associated fatty liver disease

Metabolic-associated fatty liver disease (MAFLD) is a chronic liver disorder characterized by fatty liver disease alongside overweight or obesity and/or type 2 diabetes mellitus (T2DM). Timely intervention is crucial for a potential cure. This study aimed to investigate the effects of bilirubin, an endogenous antioxidant, on lipid metabolism and inflammation in MAFLD. Specifically, it examined bilirubin's impact on SIRT1, PPAR-α, and NF-κB in the livers of rats with MAFLD induced by a high-fat diet (HFD) and streptozotocin (STZ) administration. Forty eight-week adult male Sprague Dawley rats were divided into five groups (n = 8): Control, HFD-STZ, HFD-S-BR6, HFD-S-BR14, and C-BR14. In the last three groups, bilirubin administration was performed intraperitoneally for 6 and 14 weeks (10 mg/kg/day). We selected the key genes associated with MAFLD and subsequently performed GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) analyses to explore the enriched biological processes and signaling pathways. Hence, the gene expression of SIRT1, PGC-1α, PPAR-α, and inflammatory genes (NF-κB, TNF-α, IL-6, and IL-1β) was measured using Real-time quantitative PCR. Stereological and histopathological alterations of liver structure as well as lipid profile, biochemical indices, and liver indices, were also assessed among different groups. The enrichment analysis identified that several signaling pathways and biological processes might be related to MAFLD. Bilirubin-treated rats contained higher PPAR-α, PGC-1α, and SIRT1 expression levels by approximately 5.7-, 2.1-, and 2.2-fold, respectively, compared to the HFD-receiving rats (p < 0.0001, p < 0.05, and p < 0.05). Whereas, the genes involved in the inflammatory cascades, including NF-κB, TNF-α, and IL-6, were downregulated by 0.6-fold (p < 0.05) following 14-week treatment of bilirubin, while only significantly decreased expression of NF-κB and IL-6 (approximately 0.6-fold, p < 0.05) were observed after 6-week treatment of bilirubin. Remarkably, bilirubin administration favorably reversed the effects of HFD on the liver's volume and cell numbers and ameliorated the related structural changes. It also improved lipid profile, biochemical parameters, and liver indices of HFD-STZ rats. This study indicated that bilirubin acts as a protective/ameliorative compound against MAFLD, particularly through regulating the key genes involved in lipid metabolism and inflammation in HFD-STZ rats.

Quercetin alleviates liver fibrosis via regulating glycolysis of liver sinusoidal endothelial cells and neutrophil infiltration

Liver fibrosis, a common characteristic in various chronic liver diseases, is largely influenced by glycolysis. Quercetin (QE), a natural flavonoid known to regulate glycolysis, was studied for its effects on liver fibrosis and its underlying mechanism. In a model of liver fibrosis induced by carbon tetrachloride (CCl4), we aimed to assess pathological features, serum marker levels, and analyze the expression of glycolysis-related enzymes at both mRNA and protein levels, with a focus on changes in liver sinusoidal endothelial cells (LSECs). Our results showed that QE effectively improved liver injury and fibrosis evident by improved pathological features and lowered levels of serum markers, such as alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), γ-glutamyl transferase (GGT), total bile acid (TBA), total bilirubin (TBIL), direct bilirubin (DBIL), hyaluronic acid (HA), laminin (LN), and procollagen type III (PCIII). QE also decreased lactate production and downregulated the expression of glycolysis-related enzymes-pyruvate kinase M2 (PKM2), phosphofructokinase platelet (PFKP), and hexokinase II (HK2)-at both the mRNA and protein levels. QE reduced the expression and activity of these enzymes, resulting in reduced glucose consumption, adenosine triphosphate (ATP) production, and lactate generation. Further analysis revealed that QE inhibited the production of chemokine (C-X-C motif) ligand 1 (CXCL1) and suppressed neutrophil recruitment. Overall, QE showed promising therapeutic potential for liver fibrosis by targeting LSEC glycolysis and reducing neutrophil infiltration.

Innate immune regulation in inflammation resolution and liver regeneration in drug-induced liver injury

Drug-induced liver injury (DILI) is an acute liver injury that poses a significant threat to human health. In severe cases, it can progress into chronic DILI or even lead to liver failure. DILI is typically caused by either intrinsic hepatotoxicity or idiosyncratic metabolic or immune responses. In addition to the direct damage drugs inflict on hepatocytes, the immune responses and liver inflammation triggered by hepatocyte death can further exacerbate DILI. Initially, we briefly discussed the differences in immune cell activation based on the type of liver cell death (hepatocytes, cholangiocytes, and LSECs). We then focused on the role of various immune cells (including macrophages, monocytes, neutrophils, dendritic cells, liver sinusoidal endothelial cells, eosinophils, natural killer cells, and natural killer T cells) in both the liver injury and liver regeneration stages of DILI. This article primarily reviews the role of innate immune regulation mediated by these immune cells in resolving inflammation and promoting liver regeneration during DILI, as well as therapeutic approaches targeting these immune cells for the treatment of DILI. Finally, we discussed the activation and function of liver progenitor cells (LPCs) during APAP-induced massive hepatic necrosis and the involvement of chronic inflammation in DILI.

CXCL12+ Tumor-associated Endothelial Cells Promote Immune Resistance in Hepatocellular Carcinoma

BACKGROUND

The tumor microenvironment (TME) plays a crucial role in the limited efficacy of existing treatments for hepatocellular carcinoma (HCC), with tumor-associated endothelial cells (TECs) serving as fundamental TME components that substantially influence tumor progression and treatment efficacy. However, the precise roles and mechanisms of TECs in HCC remain inadequately understood.

METHODS

We employed a multi-omics profiling strategy to investigate the single-cell and spatiotemporal evolution of TECs within the microenvironment of HCC tumors showcasing varied responses to immunotherapy. Through an analysis of a clinical cohort of HCC patients, we explored the correlation between TEC subpopulations and immunotherapy outcomes. The influence of TEC subsets on the immune microenvironment was confirmed through comprehensive in vitro and in vivo studies. To further explore the mechanisms of distinct TEC subpopulations in microenvironmental modulation and their impact on immunotherapy, we utilized TEC subset-specific knockout mouse models as well as humanized mouse models.

RESULTS

In this research, we identified a new subset of CXCL12+ TECs that exert a crucial role in immune suppression within the HCC TME. Functionally, CXCL12+ TECs impede the differentiation of CD8+ naïve T cells into CD8+ cytotoxic T cells by secreting CXCL12. Furthermore, they attract myeloid-derived suppressor cells (MDSCs). A bispecific antibody was developed to target both CXCL12 and PD1 specifically, showing significant promise in bolstering anti-tumor immune responses and advancing HCC therapy.

CONCLUSIONS

CXCL12+ TECs are pivotal in mediating immunosuppression within HCC microenvironment and targeting CXCL12+ TECs presents a promising approach to augment the efficacy of immunotherapies in HCC patients.

IMPACT AND IMPLICATION

This investigation reveals a pivotal mechanism in the HCC TME, where CXCL12+ TECs emerge as crucial modulators of immune suppression. The discovery of CXCL12+ TECs as inhibitors of CD8+ naïve T cell activation and recruiters of MDSCs significantly advances our grasp of the dynamic between HCC and immune regulation. Moreover, the development and application of a bispecific antibody precisely targeting CXCL12 and PD1 has proven to enhance immune responses in a humanized mouse HCC model. This finding underscores a promising therapeutic direction for HCC, offering the potential to amplify the impact of current immunotherapies.

LiverMap pipeline for 3D imaging of human liver reveals volumetric spatial dysregulation of cirrhotic vasculobiliary architecture

The liver contains an intricate microstructure that is critical for liver function. Architectural disruption of this spatial structure is pathologic. Unfortunately, 2D histopathology - the gold standard for pathological understanding of many liver diseases - can misrepresent or leave gaps in our understanding of complex 3D structural features. Here, we utilized immunostaining, tissue clearing, microscopy, and computational software to create 3D multilobular reconstructions of both non-fibrotic and cirrhotic human liver tissue. We found that spatial architecture in human cirrhotic liver samples with varying etiologies had sinusoid zonation dysregulation, reduction in glutamine synthetase-expressing pericentral hepatocytes, regression of central vein networks, disruption of hepatic arterial networks, and fragmentation of biliary networks, which together suggest a pro-portalization/decentralization phenotype in cirrhotic tissue. Further implementation of 3D pathological analyses may provide a deeper understanding of cirrhotic pathobiology and inspire novel treatments for liver disease.

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.

Metabolic dysfunction-associated liver disease and diabetes: Matrix remodeling, fibrosis, and therapeutic implications

Metabolic dysfunction-associated liver disease (MASLD) and steatohepatitis (MASH) are becoming the most common causes of chronic liver disease in the United States and worldwide due to the obesity and diabetes epidemics. It is estimated that by 2030 close to 100 million people might be affected and patients with type 2 diabetes are especially at high risk. Twenty to 30% of patients with MASLD can progress to MASH, which is characterized by steatosis, necroinflammation, hepatocyte ballooning, and in advanced cases, fibrosis progressing to cirrhosis. Clinically, it is recognized that disease progression in diabetic patients is accelerated and the role of various genetic and epigenetic factors, as well as cell-matrix interactions in fibrosis and stromal remodeling, have recently been recognized. While there has been great progress in drug development and clinical trials for MASLD/MASH, the complexity of these pathways highlights the need to improve diagnosis/early detection and develop more successful antifibrotic therapies that not only prevent but reverse fibrosis.

Bilirubin, once a toxin but now an antioxidant alleviating non-alcoholic fatty liver disease in an autophagy-dependent manner in high-fat diet-induced rats: a molecular and histopathological analysis

Background and purpose

As an endogenous antioxidant, bilirubin has surprisingly been inversely correlated with the risk of non-alcoholic fatty liver disease (NAFLD). Thereupon, the current evaluation was designed to assess the positive effects of bilirubin on the autophagy flux, as well as the other pathogenic processes and parameters involved in the expansion of NAFLD.

Experimental approach

Thirty adult male rats weighing 150-200 g with free access to sucrose solution (18%) were randomly subdivided into 5 groups (n = 6). Subsequently, the animals were euthanized, and their blood specimens and liver tissue samples were collected to measure serum biochemical indices, liver histopathological changes, intrahepatic triglycerides content, and tissue stereological alterations. Furthermore, the expression levels of autophagy-related genes (Atgs) were measured to assess the state of the autophagy flux.

Findings/Results

Fasting blood glucose, body weight, as well as liver weight, liver-specific enzyme activity, and serum lipid profile indices markedly decreased in rats that underwent a six-week bilirubin treatment compared to the control group. In addition, histopathological studies showed that hepatic steatosis, fibrosis, inflammation, and necrosis significantly decreased in the groups that received bilirubin compared to the control animals. Bilirubin also caused significant alterations in the expression levels of the Atgs, as well as the Beclin- 1 protein.

Conclusion and implication

Bilirubin may have potential ameliorative effects on NAFLD-associated liver damage. Moreover, the beneficial effects of bilirubin on intrahepatic lipid accumulation and steatosis were comparable with the group that did not ever receive bilirubin.

Transcriptome Analyses of Liver Sinusoidal Endothelial Cells Reveal a Consistent List of Candidate Genes Associated with Endothelial Dysfunction and the Fibrosis Progression

Liver fibrosis is an important step in the transformation of chronic liver disease into cirrhosis and liver cancer, and structural changes and functional disorders of liver sinusoidal endothelial cells (LSECs) are early events in the occurrence of liver fibrosis. Therefore, it is necessary to identify the key regulatory genes of endothelial dysfunction in the process of liver fibrosis to provide a reference for the diagnosis and treatment of liver fibrosis. In this study, we identified 230 common differentially expressed genes (Co-DEGs) by analyzing transcriptomic data of primary LSECs from three different liver fibrosis mouse models (carbon tetrachloride; choline-deficient, l-amino acid-defined diet; and nonalcoholic steatohepatitis). Enrichment analysis revealed that the Co-DEGs were mainly involved in regulating the inflammatory response, immune response, angiogenesis, formation and degradation of the extracellular matrix, and mediating chemokine-related pathways. A Venn diagram analysis was used to identify 17 key genes related to the progression of liver cirrhosis. Regression analysis using the Lasso-Cox method identified genes related to prognosis among these key genes: SOX4, LGALS3, SERPINE2, CD52, and LPXN. In mouse models of liver fibrosis (bile duct ligation and carbon tetrachloride), all five key genes were upregulated in fibrotic livers. This study identified key regulatory genes for endothelial dysfunction in liver fibrosis, namely SOX4, LGALS3, SERPINE2, CD52, and LPXN, which will provide new targets for the development of therapeutic strategies targeting endothelial dysfunction in LSECs and liver fibrosis.

Liver cirrhosis: current status and treatment options using western or traditional Chinese medicine

Liver cirrhosis arises from liver fibrosis and necroinflammation caused by various mechanisms of hepatic injury. It is a prevalent condition in clinical practice characterized by hepatocellular dysfunction, portal hypertension, and associated complications. Despite its common occurrence, the etiology and pathogenesis of liver cirrhosis remain incompletely understood, posing a significant health threat. Effective prevention of its onset and progression is paramount in medical research. Symptoms often include discomfort in the liver area, while complications such as sarcopenia, hepatic encephalopathy, ascites, upper gastrointestinal bleeding, and infection can arise. While the efficacy of Western medicine in treating liver cirrhosis is uncertain, Chinese medicine offers distinct advantages. This review explores advancements in liver cirrhosis treatment encompassing non-pharmacological and pharmacological modalities. Chinese medicine interventions, including Chinese medicine decoctions, Chinese patent medicines, and acupuncture, exhibit notable efficacy in cirrhosis reversal and offer improved prognoses. Nowadays, the combination of Chinese and Western medicine in the treatment of liver cirrhosis also has considerable advantages, which is worthy of further research and clinical promotion. Standardized treatment protocols based on these findings hold significant clinical implications.

Endothelial POFUT1 controls injury-induced liver fibrosis by repressing fibrinogen synthesis

BACKGROUND & AIMS

NOTCH signaling in liver sinusoidal endothelial cells (LSECs) regulates liver fibrosis, a pathological feature of chronic liver diseases. POFUT1 is an essential regulator of NOTCH signaling. Here, we investigated the role of LSEC-expressed POFUT1 in liver fibrosis.

METHODS

Endothelial-specific Pofut1 knockout mice were generated and experimental liver fibrosis was induced by chronic carbon tetrachloride exposure or common bile duct ligation. Liver samples were assessed by ELISA, histology, electron microscopy, immunostaining and RNA in situ hybridization. LSECs and hepatic stellate cells (HSCs) were isolated for gene expression analysis by RNA sequencing, qPCR, and western blotting. Signaling crosstalk between LSECs and HSCs was investigated by treating HSCs with supernatant from LSEC cultures. Liver single-cell RNA sequencing datasets from patients with cirrhosis and healthy individuals were analyzed to evaluate the clinical relevance of gene expression changes observed in mouse studies.

RESULTS

POFUT1 loss promoted injury-induced LSEC capillarization and HSC activation, leading to aggravated liver fibrosis. RNA sequencing analysis revealed that POFUT1 deficiency upregulated fibrinogen expression in LSECs. Consistently, fibrinogen was elevated in LSECs of patients with cirrhosis. HSCs treated with supernatant from LSECs of Pofut1 null mice showed exacerbated activation compared to those treated with supernatant from control LSECs, and this effect was attenuated by knockdown of fibrinogen or by pharmacological inhibition of fibrinogen receptor signaling, altogether suggesting that LSEC-derived fibrinogen induced the activation of HSCs. Mechanistically, POFUT1 loss augmented fibrinogen expression by enhancing NOTCH/HES1/STAT3 signaling.

CONCLUSIONS

Endothelial POFUT1 prevents injury-induced liver fibrosis by repressing the expression of fibrinogen, which functions as a profibrotic paracrine signal to activate HSCs. Therapies targeting the POFUT1/fibrinogen axis offer a promising strategy for the prevention and treatment of fibrotic liver diseases.

IMPACT AND IMPLICATIONS

Paracrine signals produced by liver vasculature play a major role in the development of liver fibrosis, which is a pathological hallmark of most liver diseases. Identifying those paracrine signals is clinically relevant in that they may serve as therapeutic targets. In this study, we discovered that genetic deletion of Pofut1 aggravated experimental liver fibrosis in mouse models. Moreover, fibrinogen was identified as a downstream target repressed by Pofut1 in liver endothelial cells and functioned as a novel paracrine signal that drove liver fibrosis. In addition, fibrinogen was found to be relevant to cirrhosis and may serve as a potential therapeutic target for this devastating human disease.

Advances in Noninvasive Molecular Imaging Probes for Liver Fibrosis Diagnosis

Liver fibrosis is a wound-healing response to chronic liver injury, which may lead to cirrhosis and cancer. Early-stage fibrosis is reversible, and it is difficult to precisely diagnose with conventional imaging modalities such as magnetic resonance imaging, positron emission tomography, single-photon emission computed tomography, and ultrasound imaging. In contrast, probe-assisted molecular imaging offers a promising noninvasive approach to visualize early fibrosis changes in vivo, thus facilitating early diagnosis and staging liver fibrosis, and even monitoring of the treatment response. Here, the most recent progress in molecular imaging technologies for liver fibrosis is updated. We start by illustrating pathogenesis for liver fibrosis, which includes capillarization of liver sinusoidal endothelial cells, cellular and molecular processes involved in inflammation and fibrogenesis, as well as processes of collagen synthesis, oxidation, and cross-linking. Furthermore, the biological targets used in molecular imaging of liver fibrosis are summarized, which are composed of receptors on hepatic stellate cells, macrophages, and even liver collagen. Notably, the focus is on insights into the advances in imaging modalities developed for liver fibrosis diagnosis and the update in the corresponding contrast agents. In addition, challenges and opportunities for future research and clinical translation of the molecular imaging modalities and the contrast agents are pointed out. We hope that this review would serve as a guide for scientists and students who are interested in liver fibrosis imaging and treatment, and as well expedite the translation of molecular imaging technologies from bench to bedside.

Single-Cell RNA Sequencing Reveals the Spatial Heterogeneity and Functional Alteration of Endothelial Cells in Chronic Hepatitis B Infection

Chronic Hepatitis B virus (CHB) infection is a global health challenge, causing damage ranging from hepatitis to cirrhosis and hepatocellular carcinoma. In our study, single-cell RNA sequencing (scRNA-seq) analysis was performed in livers from mice models with chronic inflammation induced by CHB infection and we found that endothelial cells (ECs) exhibited the largest number of differentially expressed genes (DEGs) among all ten cell types. NF-κB signaling was activated in ECs to induce cell dysfunction and subsequent hepatic inflammation, which might be mediated by the interaction of macrophage-derived and cholangiocyte-derived VISFATIN/Nampt signaling. Moreover, we divided ECs into three subclusters, including periportal ECs (EC_Z1), midzonal ECs (EC_Z2), and pericentral ECs (EC_Z3) according to hepatic zonation. Functional analysis suggested that pericentral ECs and midzonal ECs, instead of periportal ECs, were more vulnerable to HBV infection, as the VISFATIN/Nampt- NF-κB axis was mainly altered in these two subpopulations. Interestingly, pericentral ECs showed increasing communication with macrophages and cholangiocytes via the Nampt-Insr and Nampt-Itga5/Itgb1 axis upon CHB infection, which contribute to angiogenesis and vascular capillarization. Additionally, ECs, especially pericentral ECs, showed a close connection with nature killer (NK) cells and T cells via the Cxcl6-Cxcr6 axis, which is involved in shaping the microenvironment in CHB mice livers. Thus, our study described the heterogeneity and functional alterations of three subclusters in ECs. We revealed the potential role of VISFATIN/Nampt signaling in modulating ECs characteristics and related hepatic inflammation, and EC-derived chemokine Cxcl16 in shaping NK and T cell recruitment, providing key insights into the multifunctionality of ECs in CHB-associated pathologies.

Glycogen synthase kinase 3 activity enhances liver inflammation in MASH

Background & Aims

Metabolic dysfunction-associated steatohepatitis (MASH) is characterized by excessive circulating toxic lipids, hepatic steatosis, and liver inflammation. Monocyte adhesion to liver sinusoidal endothelial cells (LSECs) and transendothelial migration (TEM) are crucial in the inflammatory process. Under lipotoxic stress, LSECs develop a proinflammatory phenotype known as endotheliopathy. However, mediators of endotheliopathy remain unclear.

Methods

Primary mouse LSECs isolated from C57BL/6J mice fed chow or MASH-inducing diets rich in fat, fructose, and cholesterol (FFC) were subjected to multi-omics profiling. Mice with established MASH resulting from a choline-deficient high-fat diet (CDHFD) or FFC diet were also treated with two structurally distinct GSK3 inhibitors (LY2090314 and elraglusib [9-ING-41]).

Results

Integrated pathway analysis of the mouse LSEC proteome and transcriptome indicated that leukocyte TEM and focal adhesion were the major pathways altered in MASH. Kinome profiling of the LSEC phosphoproteome identified glycogen synthase kinase (GSK)-3β as the major kinase hub in MASH. GSK3β-activating phosphorylation was increased in primary human LSECs treated with the toxic lipid palmitate and in human MASH. Palmitate upregulated the expression of C-X-C motif chemokine ligand 2, intracellular adhesion molecule 1, and phosphorylated focal adhesion kinase, via a GSK3-dependent mechanism. Congruently, the adhesive and transendothelial migratory capacities of primary human neutrophils and THP-1 monocytes through the LSEC monolayer under lipotoxic stress were reduced by GSK3 inhibition. Treatment with the GSK3 inhibitors LY2090314 and elraglusib ameliorated liver inflammation, injury, and fibrosis in FFC- and CDHFD-fed mice, respectively. Immunophenotyping using cytometry by mass cytometry by time of flight of intrahepatic leukocytes from CDHFD-fed mice treated with elraglusib showed reduced infiltration of proinflammatory monocyte-derived macrophages and monocyte-derived dendritic cells.

Conclusion

GSK3 inhibition attenuates lipotoxicity-induced LSEC endotheliopathy and could serve as a potential therapeutic strategy for treating human MASH.

Impact and Implications

LSECs under lipotoxic stress in MASH develop a proinflammatory phenotype known as endotheliopathy, with obscure mediators and functional outcomes. The current study identified GSK3 as the major driver of LSEC endotheliopathy, examined its pathogenic role in myeloid cell-associated liver inflammation, and defined the therapeutic efficacy of pharmacological GSK3 inhibitors in murine MASH. This study provides preclinical data for the future investigation of GSK3 pharmacological inhibitors in human MASH. The results of this study are important to hepatologists, vascular biologists, and investigators studying the mechanisms of inflammatory liver disease and MASH, as well as those interested in drug development.

Biomimetic hepatic lobules from three-dimensional imprinted cell sheets

Liver-tissue engineering has proven valuable in treating liver diseases, but the construction of liver tissues with high fidelity remains challenging. Here, we present a novel three-dimensional (3D)-imprinted cell-sheet strategy for the synchronous construction of biomimetic hepatic microtissues with high accuracy in terms of cell type, density, and distribution. To achieve this, the specific composition of hepatic cells in a normal human liver was determined using a spatial proteogenomics dataset. The data and biomimetic hepatic micro-tissues with hexagonal hollow cross-sections indicate that cell information was successfully generated using a homemade 3D-imprinted device for layer-by-layer imprinting and assembling the hepatic cell sheets. By infiltrating vascular endothelial cells into the hollow section of the assembly, biomimetic hepatic microtissues with vascularized channels for nutrient diffusion and drug perfusion can be obtained. We demonstrate that the resultant vascularized biomimetic hepatic micro-tissues can not only be integrated into a microfluidic drug-screening liver-on-a-chip but also assembled into an enlarged physiological structure to promote liver regeneration. We believe that our 3D-imprinted cell sheets strategy will open new avenues for biomimetic microtissue construction.

Gut-liver axis: Recent concepts in pathophysiology in alcohol-associated liver disease

The growing recognition of the role of the gut microbiome's impact on alcohol-associated diseases, especially in alcohol-associated liver disease, emphasizes the need to understand molecular mechanisms involved in governing organ-organ communication to identify novel avenues to combat alcohol-associated diseases. The gut-liver axis refers to the bidirectional communication and interaction between the gut and the liver. Intestinal microbiota plays a pivotal role in maintaining homeostasis within the gut-liver axis, and this axis plays a significant role in alcohol-associated liver disease. The intricate communication between intestine and liver involves communication between multiple cellular components in each organ that enable them to carry out their physiological functions. In this review, we focus on novel approaches to understanding how chronic alcohol exposure impacts the microbiome and individual cells within the liver and intestine, as well as the impact of ethanol on the molecular machinery required for intraorgan and interorgan communication.

Vicious Cycle-Breaking Lipid Nanoparticles Remodeling Multicellular Crosstalk to Reverse Liver Fibrosis

During liver fibrogenesis, the reciprocal crosstalk among capillarized liver sinusoidal endothelial cells (LSECs), activated hepatic stellate cells (HSCs), and dysfunctional hepatocytes constructs a self-amplifying vicious cycle, greatly exacerbating the disease condition and weakening therapeutic effect. Limited by the malignant cellular interactions, the previous single-cell centric treatment approaches show unsatisfactory efficacy and fail to meet clinical demand. Herein, a vicious cycle-breaking strategy is proposed to target and repair pathological cells separately to terminate the malignant progression of liver fibrosis. Chondroitin sulfate-modified and vismodegib-loaded nanoparticles (CS-NPs/VDG) are designed to efficiently normalize the fenestrae phenotype of LSECs and restore HSCs to quiescent state by inhibiting Hedgehog signaling pathway. In addition, glycyrrhetinic acid-modified and silybin-loaded nanoparticles (GA-NPs/SIB) are prepared to restore hepatocytes function by relieving oxidative stress. The results show successful interruption of vicious cycle as well as distinct fibrosis resolution in two animal models through multiregulation of the pathological cells. This work not only highlights the significance of modulating cellular crosstalk but also provides a promising avenue for developing antifibrotic regimens.

Alcohol-Associated Liver Disease Outcomes: Critical Mechanisms of Liver Injury Progression

Alcohol-associated liver disease (ALD) is a substantial cause of morbidity and mortality worldwide and represents a spectrum of liver injury beginning with hepatic steatosis (fatty liver) progressing to inflammation and culminating in cirrhosis. Multiple factors contribute to ALD progression and disease severity. Here, we overview several crucial mechanisms related to ALD end-stage outcome development, such as epigenetic changes, cell death, hemolysis, hepatic stellate cells activation, and hepatic fatty acid binding protein 4. Additionally, in this review, we also present two clinically relevant models using human precision-cut liver slices and hepatic organoids to examine ALD pathogenesis and progression.

Single-cell transcriptome reveals a novel mechanism of C-Kit+-liver sinusoidal endothelial cells in NASH

AIM

To understand how liver sinusoidal endothelial cells (LSECs) respond to nonalcoholic steatohepatitis (NASH).

METHODS

We profiled single-LSEC from livers of control and MCD-fed mice. The functions of C-Kit+-LSECs were determined using coculture and bone marrow transplantation (BMT) methods.

RESULTS

Three special clusters of single-LSEC were differentiated. C-Kit+-LSECs of cluster 0, Msr1+-LSECs of cluster 1 and Bmp4+Selp+-VECs of cluster 2 were revealed, and these cells with diverse ectopic expressions of genes participated in regulation of endothelial, fibrosis and lipid metabolism in NASH. The number of C-Kit+-primary LSECs isolated from MCD mice was lower than control mice. Immunofluorescence co-staining of CD31 and C-KIT showed C-Kit+-LSECs located in hepatic sinusoid were also reduced in NASH patients and MCD mice, compared to AIH patients and control mice respectively. Interestingly, lipotoxic hepatocytes/HSCs cocultured with C-Kit+-LSECs or the livers of MCD mice receipting of C-Kit+-BMCs (bone marrow cells) showed less steatosis, inflammation and fibrosis, higher expression of prolipolytic FXR and PPAR-α, lower expression of TNF-α and α-SMA. Furthermore, coculturing or BMT of C-Kit+-endothelial derived cells could increase the levels of hepatic mitochondrial LC3B, decrease the degree of mitochondrial damage and ROS production through activating Pink1-mediated mitophagy pathway in NASH.

CONCLUSIONS

Hence, a novel transcriptomic view of LSECs was revealed to have heterogeneity and complexity in NASH. Importantly, a cluster of C-Kit+-LSECs was confirmed to recovery Pink1-related mitophagy and NASH progression.

The role of sinusoidal endothelial cells and TIMP1 in the regulation of fibrosis in a novel human liver 3D NASH model

BACKGROUND

The prevalence of NAFLD is rapidly increasing. NAFLD can progress to NASH, fibrosis, cirrhosis, and HCC, which will soon become the main causes of liver transplantation. To date, no effective drug for NASH has been approved by the Food and Drug Administration. This is partly due to the lack of reliable human in vitro models. Here, we present a novel human liver spheroid model that can be used to study the mechanisms underlying liver fibrosis formation and degradation.

METHODS AND RESULTS

Such spheroids, which contain hepatocytes, stellate cells, KC, and LSECs, spontaneously develop fibrosis that is exacerbated by treatment with free fatty acids. Conditioned medium from activated LSECs caused similar activation of fibrosis in spheroids containing primary human hepatocyte and NPCs, indicating the action of soluble mediators from the LSECs. Spheroids containing LSECs treated with free fatty acids produced tissue inhibitor of metalloproteinases inhibitor 1, a matrix metalloproteinases inhibitor important for fibrosis progression. Tissue inhibitor of metalloproteinases inhibitor 1 knockdown using siRNA led to a reduction in collagen and procollagen accumulation, which could be partially rescued using a potent matrix metalloproteinases inhibitor. Interestingly, tissue inhibitor of metalloproteinases inhibitor 1 was found to be expressed at higher levels, specifically in a subtype of endothelial cells in the pericentral region of human fibrotic livers, than in control livers.

CONCLUSION

Potential anti-NASH drugs and compounds were evaluated for their efficacy in reducing collagen accumulation, and we found differences in specificity between spheroids with and without LSECs. This new human NASH model may reveal novel mechanisms for the regulation of liver fibrosis and provide a more appropriate model for screening drugs against NASH.

Coffee, adenosine, and the liver

A variety of observational studies have demonstrated that coffee, likely acting through caffeine, improves health outcomes in patients with chronic liver disease. The primary pharmacologic role of caffeine is to act as an inhibitor of adenosine receptors. Because key liver cells express adenosine receptors linked to liver injury, regeneration, and fibrosis, it is plausible that the biological effects of coffee are explained by effects of caffeine on adenosinergic signaling in the liver. This review is designed to help the reader make sense of that hypothesis, highlighting key observations in the literature that support or dispute it.

The roles of liver sinusoidal endothelial cells in liver ischemia/reperfusion injury

Liver ischemia/reperfusion injury (IRI) is a major complication after partial hepatectomy and liver transplantation and during hypovolemic shock and hypoxia-related diseases. Liver IRI is a current research hotspot. The early stage of liver IRI is characterized by injury and dysfunction of liver sinusoidal endothelial cells (LSECs), which, along with hepatocytes, are the major cells involved in liver injury. In this review, we elaborate on the roles played by LSECs in liver IRI, including the pathological features of LSECs, LSECs exacerbation of the sterile inflammatory response, LSECs interactions with platelets and the promotion of liver regeneration, and the activation of LSECs autophagy. In addition, we discuss the study of LSECs as therapeutic targets for the treatment of liver IRI and the existing problems when applying LSECs in liver IRI research.

Aging aggravates liver fibrosis through downregulated hepatocyte SIRT1-induced liver sinusoidal endothelial cell dysfunction

BACKGROUND

Aging increases the susceptibility to chronic liver diseases and hastens liver fibrosis deterioration, but the underlying mechanisms remain partially understood. The aim of this study was to investigate the effect of aging and chronic liver diseases on hepatocyte Sirtuin 1 (SIRT1) and LSECs and their contribution to liver fibrosis pathogeneses.

METHODS

Young (8-12 wk) and aged (18-20 mo) mice were subjected to carbon tetrachloride-induced liver fibrosis. Primary HSCs and LSECs were isolated and cocultured for in vitro experiments. Liver tissues and blood samples from healthy controls and patients with liver fibrosis were analyzed.

RESULTS

Downregulated hepatocytes SIRT1 in aged mice increased high mobility group box 1 acetylation, cytoplasmic translocation, and extracellular secretion, causing LSECs dysfunction by means of the toll-like receptor 4/AK strain transforming (AKT)/endothelial nitric oxide synthase pathway, ultimately activating HSCs and increasing susceptibility to liver injury and fibrosis. Adeno-associated virus-mediated overexpression of SIRT1 in hepatocytes suppressed the abovementioned alterations and attenuated carbon tetrachloride-induced liver injury and fibrosis in liver fibrosis mice, and there were no significant differences in liver injury and fibrosis indicators between young and aged mice after SIRT1 overexpression treatment. In vitro experiments demonstrated that SIRT1 overexpression and endothelial nitric oxide synthase agonist YC-1 improved LSECs function and inhibited HSCs activation, mediated by nitric oxide. Similarly, downregulated hepatocytes SIRT1 and LSECs dysfunction were observed in the livers of aged individuals compared to young individuals and were more pronounced in aged patients with liver fibrosis.

CONCLUSIONS

Aging aggravates liver fibrosis through downregulated hepatocytes SIRT1-induced LSECs dysfunction, providing a prospective curative approach for preventing and treating liver fibrosis.

Autophagy and Senescence: The Molecular Mechanisms and Implications in Liver Diseases

The liver is the primary organ accountable for complex physiological functions, including lipid metabolism, toxic chemical degradation, bile acid synthesis, and glucose metabolism. Liver function homeostasis is essential for the stability of bodily functions and is involved in the complex regulation of the balance between cell proliferation and cell death. Cell proliferation-halting mechanisms, including autophagy and senescence, are implicated in the development of several liver diseases, such as cholestasis, viral hepatitis, nonalcoholic fatty liver disease, liver fibrosis, and hepatocellular carcinoma. Among various cell death mechanisms, autophagy is a highly conserved and self-degradative cellular process that recycles damaged organelles, cellular debris, and proteins. This process also provides the substrate for further metabolism. A defect in the autophagy machinery can lead to premature diseases, accelerated aging, inflammatory state, tumorigenesis, and cellular senescence. Senescence, another cell death type, is an active player in eliminating premalignant cells. At the same time, senescent cells can affect the function of neighboring cells by secreting the senescence-associated secretory phenotype and induce paracrine senescence. Autophagy can promote and delay cellular senescence under different contexts. This review decodes the roles of autophagy and senescence in multiple liver diseases to achieve a better understanding of the regulatory mechanisms and implications of autophagy and senescence in various liver diseases.

Oit3, a promising hallmark gene for targeting liver sinusoidal endothelial cells

Liver sinusoidal endothelial cells (LSECs) play a pivotal role in maintaining liver homeostasis and influencing the pathological processes of various liver diseases. However, neither LSEC-specific hallmark genes nor a LSEC promoter-driven Cre mouse line has been introduced before, which largely restricts the study of liver diseases with vascular disorders. To explore LSEC-specific hallmark genes, we compared the top 50 marker genes between liver endothelial cells (ECs) and liver capillary ECs and identified 18 overlapping genes. After excluding globally expressed genes and those with low expression percentages, we narrowed our focus to two final candidates: Oit3 and Dnase1l3. Through single-cell RNA sequencing (scRNA-seq) and analysis of the NCBI database, we confirmed the extrahepatic expression of Dnase1l3. The paired-cell sequencing data further demonstrated that Oit3 was predominantly expressed in the midlobular liver ECs. Subsequently, we constructed inducible Oit3-CreERT2 transgenic mice, which were further crossed with ROSA26-tdTomato mice. Microscopy validated that the established Oit3-CreERT2-tdTomato mice exhibited significant fluorescence in the liver rather than in other organs. The staining analysis confirmed the colocalization of tdTomato and EC markers. Ex-vivo experiments further confirmed that isolated tdTomato+ cells exhibited well-differentiated fenestrae and highly expressed EC markers, confirming their identity as LSECs. Overall, Oit3 is a promising hallmark gene for tracing LSECs. The establishment of Oit3-CreERT2-tdTomato mice provides a valuable model for studying the complexities of LSECs in liver diseases.

Angiocrine Signaling in Sinusoidal Health and Disease

Liver sinusoidal endothelial cells (LSECs) are key players in maintaining hepatic homeostasis. They also play crucial roles during liver injury by communicating with liver cell types as well as immune cells and promoting portal hypertension, fibrosis, and inflammation. Cutting-edge technology, such as single cell and spatial transcriptomics, have revealed the existence of distinct LSEC subpopulations with a clear zonation in the liver. The signals released by LSECs are commonly called "angiocrine signaling." In this review, we summarize the role of angiocrine signaling in health and disease, including zonation in healthy liver, regeneration, fibrosis, portal hypertension, nonalcoholic fatty liver disease, alcohol-associated liver disease, aging, drug-induced liver injury, and ischemia/reperfusion, as well as potential therapeutic advances. In conclusion, sinusoidal endotheliopathy is recognized in liver disease and promising preclinical studies are paving the path toward LSEC-specific pharmacotherapies.

New therapeutic concepts against ischemia-reperfusion injury in organ transplantation

INTRODUCTION

Ischemia-reperfusion injury (IRI) involves a positive amplification feedback loop that stimulates innate immune-driven tissue damage associated with organ procurement from deceased donors and during transplantation surgery. As our appreciation of its basic immune mechanisms has improved in recent years, translating putative biomarkers into therapeutic interventions in clinical transplantation remains challenging.

AREAS COVERED

This review presents advances in translational/clinical studies targeting immune responses to reactive oxygen species in IRI-stressed solid organ transplants, especially livers. Here we focus on novel concepts to rejuvenate suboptimal donor organs and improve transplant function using pharmacologic and machine perfusion (MP) strategies. Cellular damage induced by cold ischemia/warm reperfusion and the latest mechanistic insights into the microenvironment's role that leads to reperfusion-induced sterile inflammation is critically discussed.

EXPERT OPINION

Efforts to improve clinical outcomes and increase the donor organ pool will depend on improving donor management and our better appreciation of the complex mechanisms encompassing organ IRI that govern the innate-adaptive immune interface triggered in the peritransplant period and subsequent allo-Ag challenge. Computational techniques and deep machine learning incorporating the vast cellular and molecular mechanisms will predict which peri-transplant signals and immune interactions are essential for improving access to the long-term function of life-saving transplants.

Endotheliopathy in the metabolic syndrome: Mechanisms and clinical implications

The increasing prevalence of the metabolic syndrome (MetS) is a threat to global public health due to its lethal complications. Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the MetS characterized by hepatic steatosis, which is potentially progressive to the inflammatory and fibrotic nonalcoholic steatohepatitis (NASH). The adipose tissue (AT) is also a major metabolic organ responsible for the regulation of whole-body energy homeostasis, and thereby highly involved in the pathogenesis of the MetS. Recent studies suggest that endothelial cells (ECs) in the liver and AT are not just inert conduits but also crucial mediators in various biological processes via the interaction with other cell types in the microenvironment both under physiological and pathological conditions. Herein, we highlight the current knowledge of the role of the specialized liver sinusoidal endothelial cells (LSECs) in NAFLD pathophysiology. Next, we discuss the processes through which AT EC dysfunction leads to MetS progression, with a focus on inflammation and angiogenesis in the AT as well as on endothelial-to-mesenchymal transition of AT-ECs. In addition, we touch upon the function of ECs residing in other metabolic organs including the pancreatic islet and the gut, the dysregulation of which may also contribute to the MetS. Finally, we highlight potential EC-based therapeutic targets for human MetS, and NASH based on recent achievements in basic and clinical research and discuss how to approach unsolved problems in the field.