The wHole Story About Fenestrations in LSEC

ADAMTS18-fibronectin interaction regulates the morphology of liver sinusoidal endothelial cells

Liver sinusoidal endothelial cells (LSECs) have a unique morphological structure known as "fenestra" that plays a crucial role in liver substance exchange and homeostasis maintenance. In this study, we demonstrate that ADAMTS18 protease is primarily secreted by fetal liver endothelial cells. ADAMTS18 deficiency leads to enlarged fenestrae and increased porosity of LSECs, microthrombus formation in liver vessels, and an imbalance of liver oxidative stress. These defects worsen carbon tetrachloride (CCl4)-induced liver fibrosis and diethylnitrosamine (DEN)/high-fat-induced hepatocellular carcinoma (HCC) in adult Adamts18-deficient mice. Mechanically, ADAMTS18 functions as a modifier of fibronectin (FN) to regulate the morphological acquisition of LSECs via the vascular endothelial growth factor A (VEGFA) signaling pathways. Collectively, a mechanism is proposed for LSEC morphogenesis and liver homeostasis maintenance via ADAMTS18-FN-VEGFA niches.

Advancing liposome technology for innovative strategies against malaria

This review discusses the potential of liposomes as drug delivery systems for antimalarial therapies. Malaria continues to be a significant cause of mortality and morbidity, particularly among children and pregnant women. Drug resistance due to patient non-compliance and troublesome side effects remains a significant challenge in antimalarial treatment. Liposomes, as targeted and efficient drug carriers, have garnered attention owing to their ability to address these issues. Liposomes encapsulate hydrophilic and/or hydrophobic drugs, thus providing comprehensive and suitable therapeutic drug delivery. Moreover, the potential of passive and active drug delivery enables drug concentration in specific target tissues while reducing adverse effects. However, successful liposome formulation is influenced by various factors, including drug physicochemical characteristics and physiological barriers encountered during drug delivery. To overcome these challenges, researchers have explored modifications in liposome nanocarriers to achieve efficient drug loading, controlled release, and system stability. Computational approaches have also been adopted to predict liposome system stability, membrane integrity, and drug-liposome interactions, improving formulation development efficiency. By leveraging computational methods, optimizing liposomal drug delivery systems holds promise for enhancing treatment efficacy and minimizing side effects in malaria therapy. This review consolidates the current understanding and highlights the potential of liposome strategies against malaria.

Protein disulfide isomerase A1 regulates fenestration dynamics in primary mouse liver sinusoidal endothelial cells (LSECs)

Protein disulfide isomerases (PDIs) are involved in many intracellular and extracellular processes, including cell adhesion and cytoskeletal reorganisation, but their contribution to the regulation of fenestrations in liver sinusoidal endothelial cells (LSECs) remains unknown. Given that fenestrations are supported on a cytoskeleton scaffold, this study aimed to investigate whether endothelial PDIs regulate fenestration dynamics in primary mouse LSECs. PDIA3 and PDIA1 were found to be the most abundant among PDI isoforms in LSECs. Taking advantage of atomic force microscopy, the effects of PDIA1 or PDIA3 inhibition on the fenestrations in LSECs were investigated using a classic PDIA1 inhibitor (bepristat) and novel aromatic N-sulfonamides of aziridine-2-carboxylic acid derivatives as PDIA1 (C-3389) or PDIA3 (C-3399) inhibitors. The effect of PDIA1 inhibition on liver perfusion was studied in vivo using dynamic contrast-enhanced magnetic resonance imaging. Additionally, PDIA1 inhibitors were examined in vitro in LSECs for effects on adhesion, cytoskeleton organisation, bioenergetics, and viability. Inhibition of PDIA1 with bepristat or C-3389 significantly reduced the number of fenestrations in LSECs, while inhibition of PDIA3 with C-3399 had no effect. Moreover, the blocking of free thiols by the cell-penetrating N-ethylmaleimide, but not by the non-cell-penetrating 4-chloromercuribenzenesulfonate, resulted in LSEC defenestration. Inhibition of PDIA1 did not affect LSEC adhesion, viability, and bioenergetics, nor did it induce a clear-cut rearrangement of the cytoskeleton. However, PDIA1-dependent defenestration was reversed by cytochalasin B, a known fenestration stimulator, pointing to the preserved ability of LSECs to form new pores. Importantly, systemic inhibition of PDIA1 in vivo affected intra-parenchymal uptake of contrast agent in mice consistent with LSEC defenestration. These results revealed the role of intracellular PDIA1 in the regulation of fenestration dynamics in LSECs, and in maintaining hepatic sinusoid homeostasis.

A nanochitosan-D-galactose formulation increases the accumulation of primaquine in the liver

Primaquine is the mainstream antimalarial drug to prevent Plasmodium vivax relapses. However, this drug can induce hemolysis in patients with glucose-6-phosphate dehydrogenase deficiency. Nanostructure formulations of primaquine loaded with D-galactose were used as a strategy to target the drug to the liver and decrease the hemolytic risks. Nanoemulsion (NE-Pq) and nanochitosan (NQ-Pq) formulations of primaquine diphosphate containing D-galactose were prepared and characterized by their physicochemistry properties. Pharmacokinetic and biodistribution studies were conducted using Swiss Webster mice. A single dose of 10 mg/kg of each nanoformulation or free primaquine solution was administered by gavage to the animals, which were killed at 0.5, 1, 2, 4, 8, and 24 hours. Blood samples and tissues were collected, processed, and analyzed by high-performance liquid chromatography. The nanoformulation showed sizes around 200 nm (NE-Pq) and 400 nm (NQ-Pq) and physicochemical stability for over 30 days. Free primaquine solution achieved higher primaquine Cmax in the liver than NE-Pq or NQ-Pq at 0.5 hours. However, the half-life and mean residence time (MRT) of primaquine in the liver were three times higher with the NQ-Pq formulation than with free primaquine, and the volume distribution was four times higher. Conversely, primaquine's half-life, MRT, and volume distribution in the plasma were lower for NQ-Pq than for free primaquine. NE-Pq, on the other hand, accumulated more in the lungs but not in the liver. Galactose-coated primaquine nanochitosan formulation showed increased drug targeting to the liver compared to free primaquine and may represent a promising strategy for a more efficient and safer radical cure for vivax malaria.

FAK-p38 signaling serves as a potential target for reverting matrix stiffness-modulated liver sinusoidal endothelial cell defenestration

Liver sinusoidal endothelial cells (LSECs) are highly specific endothelial cells which play an essential role in the maintenance of liver homeostasis. During the progression of liver fibrosis, matrix stiffening promotes LSEC defenestration, however, the underlying mechanotransduction mechanism remains poorly understood. Here, we applied stiffness-tunable hydrogels to assess the matrix stiffening-induced phenotypic changes in primary mouse LSECs. Results indicated that increased stiffness promoted LSEC defenestration through cytoskeletal reorganization. LSECs sensed the increased matrix stiffness via focal adhesion kinase (FAK), leading to the activation of p38-mitogen activated protein kinase activated protein kinase 2 (MK2) pathway, thereby inducing actin remodeling via LIM Kinase 1 (LIMK1) and Cofilin. Interestingly, inhibition of FAK or p38-MK2 pathway was able to effectively restore the fenestrae to a certain degree in LSECs isolated from early to late stages of liver fibrosis mice. Thus, this study highlights the impact of mechanotransduction in LSEC defenestration, and provides novel insights for potential therapeutic interventions for liver fibrosis.

The Role of microRNAs in Hepatocellular Cancer: A Narrative Review Focused on Tumor Microenvironment and Drug Resistance

Globally, hepatic cancer ranks fourth in terms of cancer-related mortality and is the sixth most frequent kind of cancer. Around 80% of liver cancers are hepatocellular carcinomas (HCC), which are the leading cause of cancer death. It is well known that HCC may develop resistance to the available chemotherapy treatments very fast. One of the biggest obstacles in providing cancer patients with appropriate care is drug resistance. According to reports, more than 90% of cancer-specific fatalities are caused by treatment resistance. By binding to the 3'-untranslated region of target messenger RNAs (mRNAs), microRNAs (miRNAs), a group of noncoding RNAs which are around 17 to 25 nucleotides long, regulate target gene expression. Moreover, they play role in the control of signaling pathways, cell proliferation, and cell death. As a result, miRNAs play an important role in the microenvironment of HCC by changing immune phenotypes, hypoxic conditions, and acidification, as well as angiogenesis and extracellular matrix components. Moreover, changes in miRNA levels in HCC can effectively resist cancer cells to chemotherapy by affecting various cellular processes such as autophagy, apoptosis, and membrane transporter activity. In the current work, we narratively reviewed the role of miRNAs in HCC, with a special focus on tumor microenvironment and drug resistance.

Infection of liver sinusoidal endothelial cells with Muromegalovirus muridbeta1 involves binding to neuropilin-1 and is dynamin-dependent

Liver sinusoidal endothelial cells (LSEC) are scavenger cells with a remarkably high capacity for clearance of several blood-borne macromolecules and nanoparticles, including some viruses. Endocytosis in LSEC is mainly via the clathrin-coated pit mediated route, which is dynamin-dependent. LSEC can also be a site of infection and latency of betaherpesvirus, but mode of virus entry into these cells has not yet been described. In this study we have investigated the role of dynamin in the early stage of muromegalovirus muridbeta1 (MuHV-1, murid betaherpesvirus 1, murine cytomegalovirus) infection in mouse LSECs. LSEC cultures were freshly prepared from C57Bl/6JRj mouse liver. We first examined dose- and time-dependent effects of two dynamin-inhibitors, dynasore and MitMAB, on cell viability, morphology, and endocytosis of model ligands via different LSEC scavenger receptors to establish a protocol for dynamin-inhibition studies in these primary cells. LSECs were challenged with MuHV-1 (MOI 0.2) ± dynamin inhibitors for 1h, then without inhibitors and virus for 11h, and nuclear expression of MuHV-1 immediate early antigen (IE1) measured by immune fluorescence. MuHV-1 efficiently infected LSECs in vitro. Infection was significantly and independently inhibited by dynasore and MitMAB, which block dynamin function via different mechanisms, suggesting that initial steps of MuHV-1 infection is dynamin-dependent in LSECs. Infection was also reduced in the presence of monensin which inhibits acidification of endosomes. Furthermore, competitive binding studies with a neuropilin-1 antibody blocked LSEC infection. This suggests that MuHV-1 infection in mouse LSECs involves virus binding to neuropilin-1 and occurs via endocytosis.

Pharmacological Inhibition and Genetic Deletion of Cystathionine Gamma-Lyase in Mice Protects against Organ Injury in Sepsis: A Key Role of Adhesion Molecules on Endothelial Cells

Hydrogen sulfide (H2S), synthesized by cystathionine gamma-lyase (Cth), contributes to the inflammatory response observed in sepsis. This study examines the effect of Cth-derived H2S in adhesion molecules on endothelial cells of vital organs in mice in a cecal ligation puncture (CLP)-induced model of sepsis, using two different and complementary approaches: Cth gene deletion and pharmacological inhibition. Our findings revealed a decreased level of H2S-synthesizing activity (via Cth) in both Cth-/- mice and PAG-treated wild-type (WT) mice following CLP-induced sepsis. Both treatment groups had reduced MPO activity and expression of chemokines (MCP-1 and MIP-2α), adhesion molecules (ICAM-1 and VCAM-1), ERK1/2 phosphorylation, and NF-κB in the liver and lung compared with in CLP-WT mice. Additionally, we found that PAG treatment in Cth-/- mice had no additional effect on the expression of ERK1/2 phosphorylation, NF-κB, or the production of chemokines and adhesion molecules in the liver and lung compared to Cth-/- mice following CLP-induced sepsis. The WT group with sepsis had an increased immunoreactivity of adhesion molecules on endothelial cells in the liver and lung than the WT sham-operated control. The Cth-/-, PAG-treated WT, and Cth-/- groups of mice showed decreased immunoreactivity of adhesion molecules on endothelial cells in the liver and lung following sepsis. Inhibition of H2S production via both approaches reduced adhesion molecule expression on endothelial cells and reduced liver and lung injury in mice with sepsis. In conclusion, this study demonstrates that H2S has an important role in the pathogenesis of sepsis and validates PAG use as a suited tool for investigating the Cth/H2S-signalling axis in sepsis.

Effect of caffeine and other xanthines on liver sinusoidal endothelial cell ultrastructure

Xanthines such as caffeine and theobromine are among the most consumed psychoactive stimulants in the world, either as natural components of coffee, tea and chocolate, or as added ingredients. The present study assessed if xanthines affect liver sinusoidal endothelial cells (LSEC). Cultured primary rat LSEC were challenged with xanthines at concentrations typically obtained from normal consumption of xanthine-containing beverages, food or medicines; and at higher concentrations below the in vitro toxic limit. The fenestrated morphology of LSEC were examined with scanning electron and structured illumination microscopy. All xanthine challenges had no toxic effects on LSEC ultrastructure as judged by LSEC fenestration morphology, or function as determined by endocytosis studies. All xanthines in high concentrations (150 μg/mL) increased fenestration frequency but at physiologically relevant concentrations, only theobromine (8 μg/mL) showed an effect. LSEC porosity was influenced only by high caffeine doses which also shifted the fenestration distribution towards smaller pores. Moreover, a dose-dependent increase in fenestration number was observed after caffeine treatment. If these compounds induce similar changes in vivo, age-related reduction of LSEC porosity can be reversed by oral treatment with theobromine or with other xanthines using targeted delivery.

Liver Cell Type-Specific Targeting by Nanoformulations for Therapeutic Applications

Hepatocytes exert pivotal roles in metabolism, protein synthesis and detoxification. Non-parenchymal liver cells (NPCs), largely comprising macrophages, dendritic cells, hepatic stellate cells and liver sinusoidal cells (LSECs), serve to induce immunological tolerance. Therefore, the liver is an important target for therapeutic approaches, in case of both (inflammatory) metabolic diseases and immunological disorders. This review aims to summarize current preclinical nanodrug-based approaches for the treatment of liver disorders. So far, nano-vaccines that aim to induce hepatitis virus-specific immune responses and nanoformulated adjuvants to overcome the default tolerogenic state of liver NPCs for the treatment of chronic hepatitis have been tested. Moreover, liver cancer may be treated using nanodrugs which specifically target and kill tumor cells. Alternatively, nanodrugs may target and reprogram or deplete immunosuppressive cells of the tumor microenvironment, such as tumor-associated macrophages. Here, combination therapies have been demonstrated to yield synergistic effects. In the case of autoimmune hepatitis and other inflammatory liver diseases, anti-inflammatory agents can be encapsulated into nanoparticles to dampen inflammatory processes specifically in the liver. Finally, the tolerance-promoting activity especially of LSECs has been exploited to induce antigen-specific tolerance for the treatment of allergic and autoimmune diseases.

Liver metastasis from colorectal cancer: pathogenetic development, immune landscape of the tumour microenvironment and therapeutic approaches

Colorectal cancer liver metastasis (CRLM) is one of the leading causes of death among patients with colorectal cancer (CRC). Although immunotherapy has demonstrated encouraging outcomes in CRC, its benefits are minimal in CRLM. The complex immune landscape of the hepatic tumour microenvironment is essential for the development of a premetastatic niche and for the colonisation and metastasis of CRC cells; thus, an in-depth understanding of these mechanisms can provide effective immunotherapeutic targets for CRLM. This review summarises recent studies on the immune landscape of the tumour microenvironment of CRLM and highlights therapeutic prospects for targeting the suppressive immune microenvironment of CRLM.

Customized liver organoids as an advanced in vitro modeling and drug discovery platform for non-alcoholic fatty liver diseases

Non-alcoholic fatty liver disease (NAFLD) and its progressive form non-alcoholic steatohepatitis (NASH) have presented a major and common health concern worldwide due to their increasing prevalence and progressive development of severe pathological conditions such as cirrhosis and liver cancer. Although a large number of drug candidates for the treatment of NASH have entered clinical trial testing, all have not been released to market due to their limited efficacy, and there remains no approved treatment for NASH available to this day. Recently, organoid technology that produces 3D multicellular aggregates with a liver tissue-like cytoarchitecture and improved functionality has been suggested as a novel platform for modeling the human-specific complex pathophysiology of NAFLD and NASH. In this review, we describe the cellular crosstalk between each cellular compartment in the liver during the pathogenesis of NAFLD and NASH. We also summarize the current state of liver organoid technology, describing the cellular diversity that could be recapitulated in liver organoids and proposing a future direction for liver organoid technology as an in vitro platform for disease modeling and drug discovery for NAFLD and NASH.

Advanced approaches to overcome biological barriers in respiratory and systemic routes of administration for enhanced nucleic acid delivery to the lung

INTRODUCTION

Numerous delivery strategies, primarily novel nucleic acid delivery carriers, have been developed and explored to enable therapeutically relevant lung gene therapy. However, its clinical translation is yet to be achieved despite over 30 years of efforts, which is attributed to the inability to overcome a series of biological barriers that hamper efficient nucleic acid transfer to target cells in the lung.

AREAS COVERED

This review is initiated with the fundamentals of nucleic acid therapy and a brief overview of previous and ongoing efforts on clinical translation of lung gene therapy. We then walk through the nature of biological barriers encountered by nucleic acid carriers administered via respiratory and/or systemic routes. Finally, we introduce advanced strategies developed to overcome those barriers to achieve therapeutically relevant nucleic acid delivery efficiency in the lung.

EXPERT OPINION

We are now stepping close to the clinical translation of lung gene therapy, thanks to the discovery of novel delivery strategies that overcome biological barriers via comprehensive preclinical studies. However, preclinical findings should be cautiously interpreted and validated to ultimately realize meaningful therapeutic outcomes with newly developed delivery strategies in humans. In particular, individual strategies should be selected, tailored, and implemented in a manner directly relevant to specific therapeutic applications and goals.

DLL4 promotes partial endothelial-to-mesenchymal transition at atherosclerosis-prone regions of arteries

Flowing blood regulates vascular development, homeostasis and disease by generating wall shear stress which has major effects on endothelial cell (EC) physiology. Low oscillatory shear stress (LOSS) induces a form of cell plasticity called endothelial-to-mesenchymal transition (EndMT). This process has divergent effects; in embryos LOSS-induced EndMT drives the development of atrioventricular valves, whereas in adult arteries it is associated with inflammation and atherosclerosis. The Notch ligand DLL4 is essential for LOSS-dependent valve development; here we investigated whether DLL4 is required for responses to LOSS in adult arteries. Analysis of cultured human coronary artery EC revealed that DLL4 regulates the transcriptome to induce markers of EndMT and inflammation under LOSS conditions. Consistently, genetic deletion of Dll4 from murine EC reduced SNAIL (EndMT marker) and VCAM-1 (inflammation marker) at a LOSS region of the murine aorta. We hypothesized that endothelial Dll4 is pro-atherogenic but this analysis was confounded because endothelial Dll4 negatively regulated plasma cholesterol levels in hyperlipidemic mice. We conclude that endothelial DLL4 is required for LOSS-induction of EndMT and inflammation regulators at atheroprone regions of arteries, and is also a regulator of plasma cholesterol.

The Association of Integrins β3, β4, and αVβ5 on Exosomes, CTCs and Tumor Cells with Localization of Distant Metastasis in Breast Cancer Patients

Integrins are cell adhesion receptors, which play a role in breast cancer invasion, angiogenesis, and metastasis. Moreover, it has been shown that exosomal integrins provide organotropic metastasis in a mouse model. In our study, we aimed to investigate the expression of integrins β3, β4, and αVβ5 on exosomes and tumor cells (circulating tumor cells and primary tumor) and their association with the localization of distant metastasis. We confirmed the association of exosomal integrin β4 with lung metastasis in breast cancer patients. However, we were unable to evaluate the role of integrin β3 in brain metastasis due to the rarity of this localization. We established no association of exosomal integrin αVβ5 with liver metastasis in our cohort of breast cancer patients. The further evaluation of β3, β4, and αVβ5 integrin expression on CTCs revealed an association of integrin β4 and αVβ5 with liver, but not the lung metastases. Integrin β4 in the primary tumor was associated with liver metastasis. Furthermore, an in-depth analysis of phenotypic characteristics of β4+ tumor cells revealed a significantly increased proportion of E-cadherin+ and CD44+CD24- cells in patients with liver metastases compared to patients with lung or no distant metastases.

Gene therapy for liver diseases - progress and challenges

Gene therapy is poised to revolutionize modern medicine, with seemingly unlimited potential for treating and curing genetic disorders. For otherwise incurable indications, including most inherited metabolic liver disorders, gene therapy provides a realistic therapeutic option. In this Review, we discuss gene supplementation and gene editing involving the use of recombinant adeno-associated virus (rAAV) vectors for the treatment of inherited liver diseases, including updates on several ongoing clinical trials that are producing promising results. Clinical testing has been essential in highlighting many key translational challenges associated with this transformative therapy. In particular, the interaction of a patient's immune system with the vector raises issues of safety and the duration of treatment efficacy. Furthermore, several serious adverse events after the administration of high doses of rAAVs suggest greater involvement of innate immune responses and pre-existing hepatic conditions than initially anticipated. Finally, permanent modification of the host genome associated with rAAV genome integration and gene editing raises concerns about the risk of oncogenicity that require careful evaluation. We summarize the main progress, challenges and pathways forward for gene therapy for liver diseases.

Lipid Nanoparticles for Nucleic Acid Delivery to Endothelial Cells

Endothelial cells play critical roles in circulatory homeostasis and are also the gateway to the major organs of the body. Dysfunction, injury, and gene expression profiles of these cells can cause, or are caused by, prevalent chronic diseases such as diabetes, cardiovascular disease, and cancer. Modulation of gene expression within endothelial cells could therefore be therapeutically strategic in treating longstanding disease challenges. Lipid nanoparticles (LNP) have emerged as potent, scalable, and tunable carrier systems for delivering nucleic acids, making them attractive vehicles for gene delivery to endothelial cells. Here, we discuss the functions of endothelial cells and highlight some receptors that are upregulated during health and disease. Examples and applications of DNA, mRNA, circRNA, saRNA, siRNA, shRNA, miRNA, and ASO delivery to endothelial cells and their targets are reviewed, as well as LNP composition and morphology, formulation strategies, target proteins, and biomechanical factors that modulate endothelial cell targeting. Finally, we discuss FDA-approved LNPs as well as LNPs that have been tested in clinical trials and their challenges, and provide some perspectives as to how to surmount those challenges.

microRNAs-based diagnostic and therapeutic applications in liver fibrosis

Liver fibrosis is a process of over-extracellular matrix (ECM) aggregation and angiogenesis, which develops into cirrhosis and hepatocellular carcinoma (HCC). With the increasing pressure of liver fibrosis, new therapeutics to cure this disease requires much attention. Exosome-cargoed microRNAs (miRNAs) are emerging approaches in the precision of the liver fibrotic paradigm. In this review, we outlined the different types of hepatic cells derived miRNAs that drive intra-/extra-cellular interactive communication in liver fibrosis with different physiological and pathological processes. Specifically, we highlighted the possible mechanism of liver fibrosis pathogenesis associated with immune response and angiogenesis. In addition, potential clinical biomarkers and different stem cell transplant-derived miRNAs-based therapeutic strategies in liver fibrosis were summarized in this review. miRNAs-based approaches might help researchers devise new candidates for the cell-free treatment of liver fibrosis. This article is categorized under: RNA in Disease and Development > RNA in Disease.

Numerical simulation of flow characteristics in a permeable liver sinusoid with leukocytes

Double-layered channels of sinusoid lumen and Disse space separated by fenestrated liver sinusoidal endothelial cells (LSECs) endow the unique mechanical environment of the liver sinusoid network, which further guarantees its biological function. It is also known that this mechanical environment changes dramatically under liver fibrosis and cirrhosis, including the reduced plasma penetration and metabolite exchange between the two flow channels and the reduced Disse space deformability. The squeezing of leukocytes through narrow sinusoid lumen also affects the mechanical environment of liver sinusoid. To date, the detailed flow-field profile of liver sinusoid is still far from clear due to experimental limitations. It also remains elusive whether and how the varied physical properties of the pathological liver sinusoid regulate the fluid flow characteristics. Here a numerical model based on the immersed boundary method was established, and the effects of Disse space and leukocyte elasticities, endothelium permeability, and sinusoidal stenosis degree on fluid flow as well as leukocyte trafficking were specified upon a mimic liver sinusoid structure. Results showed that endothelium permeability dominantly controlled the plasma penetration velocity across the endothelium, whereas leukocyte squeezing promoted local penetration and significantly regulated wall shear stress on hepatocytes, which was strongly related to the Disse space and leukocyte deformability. Permeability and elasticity cooperatively regulated the process of leukocytes trafficking through the liver sinusoid, especially for stiffer leukocytes. This study will offer new insights into deeper understanding of the elaborate mechanical features of liver sinusoid and corresponding biological function.

Oxidized low density lipoprotein in the liver causes decreased permeability of liver lymphatic- but not liver sinusoidal-endothelial cells via VEGFR-3 regulation of VE-Cadherin

The lymphatic vasculature of the liver is vital for liver function as it maintains fluid and protein homeostasis and is important for immune cell transport to the lymph node. Chronic liver disease is associated with increased expression of inflammatory mediators including oxidized low-density lipoprotein (oxLDL). Intrahepatic levels of oxLDL are elevated in nonalcoholic fatty liver disease (NAFLD), chronic hepatitis C infection (HCV), alcohol-associated liver disease (ALD), and cholestatic liver diseases. To determine if liver lymphatic function is impaired in chronic liver diseases, in which increased oxLDL has been documented, we measured liver lymphatic function in murine models of NAFLD, ALD and primary sclerosing cholangitis (PSC). We found that Mdr2-/- (PSC), Lieber-DeCarli ethanol fed (ALD) and high fat and high cholesterol diet fed (NAFLD) mice all had a significant impairment in the ability to traffic FITC labeled dextran from the liver parenchyma to the liver draining lymph nodes. Utilizing an in vitro permeability assay, we found that oxLDL decreased the permeability of lymphatic endothelial cells (LEC)s, but not liver sinusoidal endothelial cells (LSEC)s. Here we demonstrate that LECs and LSECs differentially regulate SRC-family kinases, MAPK kinase and VE-Cadherin in response to oxLDL. Furthermore, Vascular Endothelial Growth Factor (VEGF)C or D (VEGFR-3 ligands) appear to regulate VE-Cadherin expression as well as decrease cellular permeability of LECs in vitro and in vivo after oxLDL treatment. These findings suggest that oxLDL acts to impede protein transport through the lymphatics through tightening of the cell-cell junctions. Importantly, engagement of VEGFR-3 by its ligands prevents VE-Cadherin upregulation and improves lymphatic permeability. These studies provide a potential therapeutic target to restore liver lymphatic function and improve liver function.

Cancer cells produce liver metastasis via gap formation in sinusoidal endothelial cells through proinflammatory paracrine mechanisms

Intracellular gap (iGap) formation in liver sinusoidal endothelial cells (LSECs) is caused by the destruction of fenestrae and appears under pathological conditions; nevertheless, their role in metastasis of cancer cells to the liver remained unexplored. We elucidated that hepatotoxin-damaged and fibrotic livers gave rise to LSECs-iGap formation, which was positively correlated with increased numbers of metastatic liver foci after intrasplenic injection of Hepa1-6 cells. Hepa1-6 cells induced interleukin-23-dependent tumor necrosis factor-α (TNF-α) secretion by LSECs and triggered LSECs-iGap formation, toward which their processes protruded to transmigrate into the liver parenchyma. TNF-α triggered depolymerization of F-actin and induced matrix metalloproteinase 9 (MMP9), intracellular adhesion molecule 1, and CXCL expression in LSECs. Blocking MMP9 activity by doxycycline or an MMP2/9 inhibitor eliminated LSECs-iGap formation and attenuated liver metastasis of Hepa1-6 cells. Overall, this study revealed that cancer cells induced LSEC-iGap formation via proinflammatory paracrine mechanisms and proposed MMP9 as a favorable target for blocking cancer cell metastasis to the liver.

Changes in the proteome and secretome of rat liver sinusoidal endothelial cells during early primary culture and effects of dexamethasone

Introduction

Liver sinusoidal endothelial cells (LSECs) are specialized fenestrated scavenger endothelial cells involved in the elimination of modified plasma proteins and tissue turnover waste macromolecules from blood. LSECs also participate in liver immune responses. A challenge when studying LSEC biology is the rapid loss of the in vivo phenotype in culture. In this study, we have examined biological processes and pathways affected during early-stage primary culture of rat LSECs and checked for cell responses to the pro-inflammatory cytokine interleukin (IL)-1β and the anti-inflammatory drug dexamethasone.

Methods

LSECs from male Sprague Dawley rats were cultured on type I collagen in 5% oxygen atmosphere in DMEM with serum-free supplements for 2 and 24 h. Quantitative proteomics using tandem mass tag technology was used to examine proteins in cells and supernatants. Validation was done with qPCR, ELISA, multiplex immunoassay, and caspase 3/7 assay. Cell ultrastructure was examined by scanning electron microscopy, and scavenger function by quantitative endocytosis assays.

Results

LSECs cultured for 24 h showed a characteristic pro-inflammatory phenotype both in the presence and absence of IL-1β, with upregulation of cellular responses to cytokines and interferon-γ, cell-cell adhesion, and glycolysis, increased expression of fatty acid binding proteins (FABP4, FABP5), and downregulation of several membrane receptors (STAB1, STAB2, LYVE1, CLEC4G) and proteins in pyruvate metabolism, citric acid cycle, fatty acid elongation, amino acid metabolism, and oxidation-reduction processes. Dexamethasone inhibited apoptosis and improved LSEC viability in culture, repressed inflammatory and immune regulatory pathways and secretion of IL-1β and IL-6, and further upregulated FABP4 and FABP5 compared to time-matched controls. The LSEC porosity and endocytic activity were reduced at 24 h both with and without dexamethasone but the dexamethasone-treated cells showed a less stressed phenotype.

Conclusion

Rat LSECs become activated towards a pro-inflammatory phenotype during early culture. Dexamethasone represses LSEC activation, inhibits apoptosis, and improves cell viability.

Tuning of Liver Sieve: The Interplay between Actin and Myosin Regulatory Light Chain Regulates Fenestration Size and Number in Murine Liver Sinusoidal Endothelial Cells

Liver sinusoidal endothelial cells (LSECs) facilitate the efficient transport of macromolecules and solutes between the blood and hepatocytes. The efficiency of this transport is realized via transcellular nanopores, called fenestrations. The mean fenestration size is 140 ± 20 nm, with the range from 50 nm to 350 nm being mostly below the limits of diffraction of visible light. The cellular mechanisms controlling fenestrations are still poorly understood. In this study, we tested a hypothesis that both Rho kinase (ROCK) and myosin light chain (MLC) kinase (MLCK)-dependent phosphorylation of MLC regulates fenestrations. We verified the hypothesis using a combination of several molecular inhibitors and by applying two high-resolution microscopy modalities: structured illumination microscopy (SIM) and scanning electron microscopy (SEM). We demonstrated precise, dose-dependent, and reversible regulation of the mean fenestration diameter within a wide range from 120 nm to 220 nm and the fine-tuning of the porosity in a range from ~0% up to 12% using the ROCK pathway. Moreover, our findings indicate that MLCK is involved in the formation of new fenestrations—after inhibiting MLCK, closed fenestrations cannot be reopened with other agents. We, therefore, conclude that the Rho-ROCK pathway is responsible for the control of the fenestration diameter, while the inhibition of MLCK prevents the formation of new fenestrations.

Multiscale biomechanics and mechanotransduction from liver fibrosis to cancer

A growing body of multiscale biomechanical studies has been proposed to highlight the mechanical cues in the development of hepatic fibrosis and cancer. At the cellular level, changes in mechanical microenvironment induce phenotypic and functional alterations of hepatic cells, initiating a positive feedback loop that promotes liver fibrogenesis and hepatocarcinogenesis. Tumor mechanical microenvironment of hepatocellular carcinoma facilitates tumor cell growth and metastasis, and hinders the drug delivery and immunotherapy. At the molecular level, mechanical forces are sensed and transmitted into hepatic cells via allosteric activation of mechanoreceptors on the cell membrane, leading to the activation of various mechanotransduction pathways including integrin and YAP signaling and then regulating cell function. Thus, the application of mechanomedicine concept in the treatment of liver diseases is promising for rational design and cell-specific delivery of therapeutic drugs. This review mainly discusses the correlation between biomechanical cues and liver diseases from the viewpoint of mechanobiology.

Enrichment Methods for Murine Liver Non-Parenchymal Cells Differentially Affect Their Immunophenotype and Responsiveness towards Stimulation

Hepatocytes comprise the majority of the liver and largely exert metabolic functions, whereas non-parenchymal cells (NPCs)—comprising Kupffer cells, dendritic cells and liver sinusoidal endothelial cells—control the immunological state within this organ. Here, we compared the suitability of two isolation methods for murine liver NPCs. Liver perfusion (LP) with collagenase/DNase I applied via the portal vein leads to efficient liver digestion, whereas the modified liver dissociation (LD) method combines mechanical dissociation of the retrieved organ with enzymatic degradation of the extracellular matrix. In cases of both LP and LD, NPCs were enriched by subsequent gradient density centrifugation. Our results indicate that LP and LD are largely comparable with regards to the yield, purity, and composition of liver NPCs. However, LD-enriched liver NPCs displayed a higher degree of activation after overnight cultivation, and accordingly were less responsive towards stimulation with toll-like receptor ligands that are frequently used as adjuvants, e.g., in nano-vaccines. We conclude that LP is more suitable for obtaining liver NPCs for subsequent in vitro studies, whereas LD as the less laborious method, is more convenient for parallel isolation of larger numbers of samples for ex vivo analysis.