Hepatitis C virus infection induces autocrine interferon signaling by human liver endothelial cells and release of exosomes, which inhibits viral replication

Macrophage-Derived Extracellular Vesicles Induce Long-Lasting Immunity Against Hepatitis C Virus Which Is Blunted by Polyunsaturated Fatty Acids

Extracellular vesicles (EVs) are increasingly recognized as important mediators of intercellular communication. In this study, we aimed to further characterize the role of macrophage-derived EVs in immune responses against hepatitis C virus (HCV) and the potential of polyunsaturated fatty acids (PUFAs) to modulate this modality of innate immunity. To this end, EVs were isolated from interferon-stimulated macrophage cultures or from serum of patients with acute or chronic hepatitis C. EVs were characterized by electron microscopy, flow cytometry, RNA-sequencing, and Western blot analysis. The effect of EVs on replication of HCV was assessed in coculture models. Functional analyses were performed to assess the impact of PUFAs on EV-mediated antiviral immunity. We found that macrophages secreted various cytokines shortly after stimulation with type I and II IFN, which orchestrated a fast but short-lasting antiviral state. This rapid innate immune answer was followed by the production of macrophage-derived EVs, which induced a late, but long-lasting inhibitory effect on HCV replication. Of note, exposure of macrophages to PUFAs, which are important regulators of immune responses, dampened EV-mediated antiviral immune responses. Finally, EVs from patients with hepatitis C exhibited long-lasting antiviral activities during IFN therapy as well. The antiviral effect of EVs from Caucasian and Japanese patients differed, which may be explained by different nutritional uptake of PUFAs. In conclusion, our data indicate that macrophage-derived EVs mediate long-lasting inhibitory effects on HCV replication, which may bridge the time until efficient adaptive immune responses are established, and which can be blunted by PUFAs.

A Cell Culture Platform to Maintain Long-term Phenotype of Primary Human Hepatocytes and Endothelial Cells

BACKGROUND AND AIMS

Modeling interactions between primary human hepatocytes (PHHs) and primary human liver sinusoidal endothelial cells (LSECs) in vitro can help elucidate human-specific mechanisms underlying liver physiology/disease and drug responses; however, existing hepatocyte/endothelial coculture models are suboptimal because of their use of rodent cells, cancerous cell lines, and/or nonliver endothelial cells. Hence, we sought to develop a platform that could maintain the long-term phenotype of PHHs and primary human LSECs.

METHODS

Primary human LSECs or human umbilical vein endothelial cells as the nonliver control were cocultivated with micropatterned PHH colonies (to control homotypic interactions) followed by an assessment of PHH morphology and functions (albumin and urea secretion, and cytochrome P-450 2A6 and 3A4 enzyme activities) over 3 weeks. Endothelial phenotype was assessed via gene expression patterns and scanning electron microscopy to visualize fenestrations. Hepatic responses in PHH/endothelial cocultures were benchmarked against responses in previously developed PHH/3T3-J2 fibroblast cocultures. Finally, PHH/fibroblast/endothelial cell tricultures were created and characterized as described previously.

RESULTS

LSECs, but not human umbilical vein endothelial cells, induced PHH albumin secretion for ∼11 days; however, neither endothelial cell type could maintain PHH morphology and functions to the same magnitude/longevity as the fibroblasts. In contrast, both PHHs and endothelial cells displayed stable phenotype for 3 weeks in PHH/fibroblast/endothelial cell tricultures; furthermore, layered tricultures in which PHHs and endothelial cells were separated by a protein gel to mimic the space of Disse displayed similar functional levels as the coplanar tricultures.

CONCLUSIONS

PHH/fibroblast/endothelial tricultures constitute a robust platform to elucidate reciprocal interactions between PHHs and endothelial cells in physiology, disease, and after drug exposure.

Exosomes in Pathogen Infections: A Bridge to Deliver Molecules and Link Functions

Exosomes are extracellular vesicles derived from cell endocytosis which act as transmitters between cells. They are composed of proteins, lipids, and RNAs through which they participate in cellular crosstalk. Consequently, they play an important role in health and disease. Our view is that exosomes exert a bidirectional regulatory effect on pathogen infections by delivering their content. First, exosomes containing proteins and RNAs derived from pathogens can promote infections in three ways: (1) mediating further infection by transmitting pathogen-related molecules; (2) participating in the immune escape of pathogens; and (3) inhibiting immune responses by favoring immune cell apoptosis. Second, exosomes play anti-infection roles through: (1) inhibiting pathogen proliferation and infection directly; (2) inducing immune responses such as those related to the function of monocyte-macrophages, NK cells, T cells, and B cells. We believe that exosomes act as “bridges” during pathogen infections through the mechanisms mentioned above. The purpose of this review is to describe present findings regarding exosomes and pathogen infections, and highlight their enormous potential in clinical diagnosis and treatment. We discuss two opposite aspects: infection and anti-infection, and we hypothesize a balance between them. At the same time, we elaborate on the role of exosomes in immune regulation.

Liver sinusoidal endothelial cells - gatekeepers of hepatic immunity

Liver sinusoidal endothelial cells (LSECs) line the low shear, sinusoidal capillary channels of the liver and are the most abundant non-parenchymal hepatic cell population. LSECs do not simply form a barrier within the hepatic sinusoids but have vital physiological and immunological functions, including filtration, endocytosis, antigen presentation and leukocyte recruitment. Reflecting these multifunctional properties, LSECs display unique structural and phenotypic features that differentiate them from the capillary endothelium present within other organs. It is now clear that LSECs have a critical role in maintaining immune homeostasis within the liver and in mediating the immune response during acute and chronic liver injury. In this Review, we outline how LSECs influence the immune microenvironment within the liver and discuss their contribution to immune-mediated liver diseases and the complications of fibrosis and carcinogenesis.

Hepatocyte-derived exosomes promote T follicular regulatory cell expansion during hepatitis C virus infection

Hepatitis C virus (HCV) is a global health concern that can cause severe liver disease, such as cirrhosis and hepatocellular carcinoma. Control of HCV requires vigorous T-cell responses, yet CD4⁺ T cells in chronic HCV patients are dysfunctional. T follicular regulatory (Tfr) cells are a subset of regulatory T cells that suppress T follicular helper (Tfh) cells and the generation of high affinity antibody-producing B cells. In this study, we examined the accumulation of Tfr cells in the liver compartment during chronic HCV infection and defined the cellular and molecular mechanisms underlying their expansion. Our analysis revealed a substantial population of Tfr cells in livers of chronic HCV patients that is absent in liver tissues from nonviral hepatitis or healthy subjects. Coculture of PBMCs from healthy subjects with HCV-infected hepatoma cells resulted in preferential expansion of circulating Tfr cells, leading to suppression of Tfh cells. Additionally, coculture of tonsillar cells with infected hepatoma cells lead to an expansion of germinal center Tfr. Notably, expansion was mediated by transforming growth factor beta (TGF-β)-containing exosomes released from HCV-infected hepatocytes given that blockade of exosome-associated TGF-β or inhibition of exosome release abrogated Tfr expansion.

CONCLUSION

These results show that liver-derived exosomes play a pivotal role in the accumulation of Tfr cells, likely leading to suppression of Tfh responses in HCV-infected patients. Our study identifies a novel pathway in which HCV infection in hepatocytes exacerbates Tfr cell responses to subvert antiviral immunity. (Hepatology 2018;67:71-85).

Extracellular vesicles: Novel mediator for cell to cell communications in liver pathogenesis

Extracellular vesicles (EVs) are membrane derived nanometer-sized vesicles. EVs are released by normal, diseased, and transformed cells in vitro and in vivo, and carry lipids, proteins, mRNAs, non-coding RNAs, and even DNA out of cells. Transferring biological information via EVs to neighboring cells and inter-cellular communication not only maintain physiological functions, but also involve in the pathogenesis of several diseases, including cancer. The aim of this review is to discuss the emerging role of EVs in viral hepatitis, non-alcoholic or alcoholic liver disease and liver cancers. We summarize what is known about exosome biogenesis, and role in liver disease progression, and discuss the potential clinical applications of EVs as predictive biomarkers and therapeutic modalities.

The HBx gene of hepatitis B virus can influence hepatic microenvironment via exosomes by transferring its mRNA and protein

The cellular secretory vesicles known as 'exosomes' have emerged as key player in intercellular transport and communication between different eukaryotic in order to maintain body homeostasis. Many pathogenic viruses utilize exosome pathway to efficiently transfer bioactive components from infected cells to naïve cells. Here, we show that HBx can tweak the exosome biogenesis machinery both by enhancing neutral sphingomyelinase2 activity as well as by interacting with exosomal biomarkers such as neutral sphingomyelinase2, CD9 and CD81. The nano particle tracking analysis revealed enhanced secretion of exosomes by the HBx-expressing cells while confocal studies confirmed the co-localization of HBx with CD9 and CD63. Importantly, we observed the encapsulation of HBx mRNA and protein in these exosomes besides some other qualitative changes. The exosomal cargo secreted by HBx-expressing cells had a profound effect on the recipient hepatic cells including creation of a milieu conducive for cellular-transformation. Thus, the present study unfolds a novel role of HBx in intercellular communication by facilitating horizontal transfer of viral gene products and other host factors via exosomes in order to support viral spread and pathogenesis.

Immunogenetic studies of the hepatitis C virus infection in an era of pan-genotype antiviral therapies - Effective treatment is coming

What are the factors that influence human hepatitis C virus (HCV) infection, hepatitis status establishment, and disease progression? Firstly, one has to consider the genetic background of the host and HCV genotypes. The immunogenetic host profile will reflect how each infected individual deals with infection. Secondly, there are environmental factors that drive susceptibility or resistance to certain viral strains. These will dictate (I) the susceptibility to infection; (II) whether or not an infected person will promote viral clearance; (III) the immune response and the response profile to therapy; and (IV) whether and how long it would take to the development of HCV-associated diseases, as well as their severity. Looking at this scenario, this review addresses clinical aspects of HCV infection, following by an update of molecular and cellular features of the immune response against the virus. The evasion mechanisms used by HCV are presented, considering the potential role of exosomes in infection. Genetic factors influencing HCV infection and pathogenesis are the main topics of the article. Shortly, HLAs, MBLs, TLRs, ILs, and IFNLs genes have relevant roles in the susceptibility to HCV infection. In addition, ILs, IFNLs, as well as TLRs genes are important modulators of HCV-associated diseases. The viral aspects that influence HCV infection are presented, followed by a discussion about evolutionary aspects of host and HCV interaction. HCV and HIV infections are close related. Thus, we also present a discussion about HIV/HCV co-infection, focusing on cellular and molecular aspects of this interaction. Pharmacogenetics and treatment of HCV infection are the last topics of this review. The understanding of how the host genetics interacts with viral and environmental factors is crucial for the development of new strategies to prevent HCV infection, even in an era of potential development of pan-genotypic antivirals.

The Telomeric Response to Viral Infection

The ends of linear genomes, whether viral or cellular, can elicit potent DNA damage and innate immune signals. DNA viruses entering the nucleus share many features with telomeres in their ability to either suppress or co-opt these pathways. Here, we review some of the common mechanisms that viruses and telomeres use to manage the DNA damage and innate immune response pathways. We highlight recent studies on the role of the telomere repeat-containing RNA (TERRA) in response to viral infection. We discuss how TERRA can be activated through a p53-response element embedded in a retrotransposon-like repeat found in human subtelomeres. We consider how TERRA can function as a danger signal when secreted in extracellular vesicles to induce inflammatory cytokines in neighboring cells. These findings suggest that TERRA may be part of the innate immune response to viral infection, and support the hypothesis that telomeres and viruses utilize common mechanisms to maintain genome integrity and regulate innate immunity.

Time-course microarrays reveal early activation of the immune transcriptome in a choline-deficient mouse model of liver injury

AIMS

Choline-deficient diet is extensively used as a model of nonalcoholic fatty liver disease (NAFLD). In this study, we explored genes in the liver for which the expression changed in response to the choline-deficient (CD) diet.

MAIN METHODS

Male CD-1 mice were divided into two groups and fed a CD diet with or without 0.2% choline bitartrate for one or three weeks. Hepatic levels of choline metabolites were analyzed by using liquid chromatography mass spectrometry and hepatic gene expression profiles were examined by DNA microarray analysis.

KEY FINDINGS

The CD diet lowered liver choline metabolites after one week and exacerbated fatty liver between one and three weeks. We identified >300 genes whose expression was significantly altered in the livers of mice after consumption of this CD diet for one week and showed that liver gene expression profiles could be classified into six distinct groups. This study showed that STAT1 and interferon-regulated genes was up-regulated after the CD diet consumption and that the Stat1 mRNA level was negatively correlated with liver phosphatidylcholine level. Stat1 mRNA expression was actually up-regulated in isolated hepatocytes from the mouse liver with the CD diet.

SIGNIFICANCE

This study provides insight into the genomic effects of the CD diet through the Stat1 expression, which might be involved in NAFLD development.

Inhibition of PRMT5 suppresses osteoclast differentiation and partially protects against ovariectomy-induced bone loss through downregulation of CXCL10 and RSAD2

Protein arginine methyltransferase 5 (PRMT5) is an arginine methylation methyltransferase that regulates various physiological processes. Abnormal PRMT5 activity has been reported in inflammation and various types of cancers. Because osteoclast differentiation is characterized by the activation of inflammation-related pathways, we speculated that PRMT5 may play a role in this process. In the present study, we found that PRMT5 was upregulated during osteoclast differentiation. Knockdown of PRMT5 with siRNA in bone marrow mononuclear cells (BMMs) resulted in inhibition of receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation. Consistent with the PRMT5 knockdown results, the PRMT5 inhibitor EPZ015666 (EPZ) suppressed osteoclast differentiation and bone resorption. Intraperitoneal administration of EPZ prevented ovariectomy-induced bone loss. Moreover, RANKL-induced NF-κB and MAPK activation was inhibited by EPZ. Expression microarrays showed that the expression of several osteoclast formation-related genes was altered by EPZ treatment, including chemokine C-X-C motif ligand 10 (CXCL10). Administration of recombinant CXCL10 partially reversed the osteoclastogenesis inhibition effect of the PRMT5 inhibitor. Intriguingly, RSAD2, which is a reported antiviral protein, was apparently suppressed when PRMT5 was inhibited. Knockdown of RSAD2 with siRNA in BMMs led to inhibition of osteoclast differentiation. Subsequent ChIP-qPCR identified that both PRMT5 inhibition and knockdown resulted in decreased H3R8 or/and H4R3 methylation at CXCL10 and RSAD2 promotors. In conclusion, our study found that PRMT5 is an activator of osteoclast differentiation and inhibition of PRMT5 partially suppressed osteoclastogenesis through downregulation of CXCL10 and RSAD2.

Immunofluorescence identifies distinct subsets of endothelial cells in the human liver

As well as systemic vascular endothelial cells, the liver has specialised sinusoidal endothelial cells (LSEC). LSEC dysfunction has been documented in many diseased states yet their phenotype in normal human liver has not been comprehensively assessed. Our aim was to improve characterisation of subsets of endothelial cells and associated pericytes in the human liver. Immunofluorescence microscopy was performed on normal human liver tissue samples to assess endothelial and structural proteins in a minimum of three donors. LSEC are distributed in an acinar pattern and universally express CD36, but two distinctive subsets of LSEC can be identified in different acinar zones. Type 1 LSEC are CD36^hiCD32⁻CD14⁻LYVE-1⁻ and are located in acinar zone 1 of the lobule, while Type 2 LSEC are LYVE-1⁺CD32^hiCD14⁺CD54⁺CD36^mid-lo and are located in acinar zones 2 and 3 of the lobule. Portal tracts and central veins can be identified using markers for systemic vascular endothelia and pericytes, none of which are expressed by LSEC. In areas of low hydrostatic pressure LSEC are lined by stellate cells that express the pericyte marker CD146. Our findings identify distinctive populations of LSEC and distinguish these cells from adjacent stellate cells, systemic vasculature and pericytes in different zones of the liver acinus.

Extracellular vesicles in liver diseases

Extracellular vesicles (EVs) are membrane-bound vesicles that are released by cells into their extracellular environment, have selective enrichment of specific proteins and RNA, and can mediate intercellular communication. In this review we highlight recent observations of the role of EVs in liver injury, viral hepatitis, alcoholic or nonalcoholic liver disease, biliary tract disease, and liver cancers. Potential applications as markers of diseases or for therapeutic applications are outlined to emphasize the new opportunities that are arising from the study of EVs.

Exosome-Mediated Intercellular Communication between Hepatitis C Virus-Infected Hepatocytes and Hepatic Stellate Cells

Fibrogenic pathways in the liver are principally regulated by activation of hepatic stellate cells (HSC). Fibrosis is associated with chronic hepatitis C virus (HCV) infection, although the mechanism is poorly understood. HSC comprise the major population of nonparenchymal cells in the liver. Since HCV does not replicate in HSC, we hypothesized that exosomes secreted from HCV-infected hepatocytes activate HSC. Primary or immortalized human hepatic stellate (LX2) cells were exposed to exosomes derived from HCV-infected hepatocytes (HCV-exo), and the expression of fibrosis-related genes was examined. Our results demonstrated that HCV-exo internalized to HSC and increased the expression of profibrotic markers. Further analysis suggested that HCV-exo carry miR-19a and target SOCS3 in HSC, which in turn activates the STAT3-mediated transforming growth factor β (TGF-β) signaling pathway and enhances fibrosis marker genes. The higher expression of miR-19a in exosomes was also observed from HCV-infected hepatocytes and in sera of chronic HCV patients with fibrosis compared to healthy volunteers and non-HCV-related liver disease patients with fibrosis. Together, our results demonstrated that miR-19a carried through the exosomes from HCV-infected hepatocytes activates HSC by modulating the SOCS-STAT3 axis. Our results implicated a novel mechanism of exosome-mediated intercellular communication in the activation of HSC for liver fibrosis in HCV infection.IMPORTANCE HCV-associated liver fibrosis is a critical step for end-stage liver disease progression. However, the molecular mechanisms for hepatic stellate-cell activation by HCV-infected hepatocytes are underexplored. Here, we provide a role for miR-19a carried through the exosomes in intercellular communication between HCV-infected hepatocytes and HSC in fibrogenic activation. Furthermore, we demonstrate the role of exosomal miR-19a in activation of the STAT3-TGF-β pathway in HSC. This study contributes to the understanding of intercellular communication in the pathogenesis of liver disease during HCV infection.

Emerging role of exosomes in liver physiology and pathology

Exosomes can mediate intercellular communication by conveying various bioactive molecules. Plentiful evidence suggests that exosomes are involved in many liver diseases including hepatitis C virus infection, hepatitis B virus infection, hepatocellular carcinoma, liver fibrosis, cirrhosis, non-alcoholic fatty liver disease, and alcoholic liver disease. Moreover, exosomes are present in nearly all human body fluids. Therefore, exosomal miRNA or proteins have the potential to be novel biomarkers of liver diseases. In the treatment of liver diseases, exosomes could participate in adaptive immune response and mesenchymal stem cell-based therapy. Exosomes can also be used as vehicles for genetic materials and drug delivery.

Mouse Liver Sinusoidal Endothelium Eliminates HIV-Like Particles from Blood at a Rate of 100 Million per Minute by a Second-Order Kinetic Process

We crafted human immunodeficiency virus (HIV)-like particles of diameter about 140 nm, which expressed two major HIV-1 proteins, namely, env and gag gene products, and used this reagent to simulate the rate of decay of HIV from the blood stream of BALB/c male mice. We found that most (~90%) of the particles were eliminated (cleared) from the blood by the liver sinusoidal endothelial cells (LSECs), the remainder from Kupffer cells; suggesting that LSECs are the major liver scavengers for HIV clearance from blood. Decay was rapid with kinetics suggesting second order with respect to particles, which infers dimerization of a putative receptor on LSEC. The number of HIV-like particles required for saturating the clearance mechanism was approximated. The capacity for elimination of blood-borne HIV-like particles by the sinusoid was 112 million particles per minute. Assuming that the sinusoid endothelial cells were about the size of glass-adherent macrophages, then elimination capacity was more than 540 particles per hour per endothelial cell.

"Hep C, where art thou": What are the remaining (fundable) questions in hepatitis C virus research?

Hepatitis C virus (HCV) has dominated the field of hepatology for the past 25 years, and its cure in the majority of treated patients is one of the greatest achievements in all of medicine. However, the latter has led to the belief by some that HCV research should be shelved for other, more pressing areas. The mission for HCV eradication is far from accomplished. As a historical reference, we should consider that disease elimination has required vaccination with all previously controlled infections including smallpox and polio and that simple, effective treatment is not sufficient in most infections to lead to substantial control. Syphilis is the best example, for which a single dose of penicillin (which literally costs pennies and that we have had since 1945) is curative in early stages. Not only have we not eradicated syphilis, rates of infection have increased in many places within the United States in recent years. Most HCV-infected subjects are unaware of their infection, remaining at risk for transmission to others and disease progression, including cirrhosis and hepatocellular carcinoma. In the era of highly effective direct-acting antivirals (DAAs), many questions pertaining to HCV remain, but they are more complex and difficult to answer. Here, I provide my perspective on some of these salient issues: the residual risk for disease progression after sustained virologic response, the optimal approach to current DAA failures, the impact of targeting people who inject drugs with DAAs, vaccine prospects, and application of neutralizing HCV glycoprotein antibodies. (Hepatology 2017;65:341-349).

Extracellular vesicles in liver pathobiology: Small particles with big impact

Extracellular vesicles (EVs) are nanometer-sized, membrane-bound vesicles released by cells into the extracellular milieu. EVs are now recognized to play a critical role in cell-to-cell communication. EVs contain important cargo in the form of proteins, lipids, and nucleic acids and serve as vectors for delivering this cargo from donor to acceptor or target cell. EVs are released under both physiologic and pathologic conditions, including liver diseases, and exert a wide range of effects on target cells. This review provides an overview on EV biogenesis, secretion, cargo, and target cell interactions in the context of select liver diseases. Specifically, the diverse roles of EVs in nonalcoholic steatohepatitis, alcoholic liver disease, viral hepatitis, cholangiopathies, and hepatobiliary malignancies are emphasized. Liver diseases often result in an increased release of EVs and/or in different cargo sorting into these EVs. Either of these alterations can drive disease pathogenesis. Given this fact, EVs represent a potential target for therapeutic intervention in liver disorders. Because altered EV composition may reflect the underlying disease condition, circulating EVs can be exploited for diagnostic and prognostic purposes as a liquid biopsy. Furthermore, ex vivo modified or synthesized EVs can be engineered as therapeutic nano-shuttles. Finally, we highlight areas that merit further investigation relevant to understanding how EVs regulate liver disease pathogenesis. (Hepatology 2016;64:2219-2233).

Exosomes contribute to the transmission of anti-HIV activity from TLR3-activated brain microvascular endothelial cells to macrophages

Human brain microvascular endothelial cells (HBMECs), the major cell type in the blood-brain barrier (BBB), play a key role in maintaining brain homeostasis. However, their role in the BBB innate immunity against HIV invasion of the central nervous system (CNS) remains to be determined. Our early work showed that TLR3 signaling of HBMECs could produce the antiviral factors that inhibit HIV replication in macrophages. The present study examined whether exosomes from TLR3-activated HBMECs mediate the intercellular transfer of antiviral factors to macrophages. Primary human macrophages could take up exosomes from TLR3-activated HBMECs. HBMECs-derived exosomes contained multiple antiviral factors, including several key IFN-stimulated genes (ISGs; ISG15, ISG56, and Mx2) at mRNA and protein levels. The depletion of exosomes from TLR3-activated HBMECs culture supernatant diminished HBMECs-mediated anti-HIV activity in macrophages. In conclusion, we demonstrate that exosomes shed by HBMECs are able to transport the antiviral molecules to macrophages. This finding suggests the possibility that HIV nonpermissive BBB cells (HBMECs) can help to restore the antiviral state in HIV-infected macrophages, which may be a defense mechanism against HIV neuroinvasion.

Exosomes in liver pathology

Exosomes are small (∼100nm) membrane-bound extracellular vesicles released by various types of cells into biological fluids. They contain proteins, mRNAs and miRNAs as cargo. Different cell types can take up exosomes by endocytosis and the cargo contained within them can be transferred horizontally to these recipient cells. Exosomal proteins and miRNAs can be functional and regulate physiological cell events modifying the microenvironment in target cells, a key event of liver pathology. Exosome-mediated cell-cell communication can alter tumor growth, cell migration, antiviral infection and hepatocyte regeneration, indicating that exosomes have great potential for development as diagnostic or therapeutic tools. Analyses of circulating total or exosomal miRNAs have identified a large number of candidate miRNAs that are regulated in liver diseases, and the diagnostic testing using single or multiple miRNAs shows good sensitivity and specificity. Some candidate miRNAs have been identified to play an important role in various liver disorders. This review summarizes recent findings on the role of extracellular vesicles in liver diseases and their diagnostic and therapeutic potential, mainly focusing on exosomes but also includes microvesicles in liver pathology.

Host parasite communications-Messages from helminths for the immune system: Parasite communication and cell-cell interactions

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Helminth parasites release a spectrum of mediators to dampen host immunity.

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Secreted proteins can act on host receptors and intracellular signalling.

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Parasites also produce exosome-like extracellular vesicles containing microRNAs.

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Exosomes can enter host cells and modulate host gene expression.

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Extracellular vesicles may be a more general mode of host-parasite interaction.

Helminths are metazoan organisms many of which have evolved parasitic life styles dependent on sophisticated manipulation of the host environment. Most notably, they down-regulate host immune responses to ensure their own survival, by exporting a range of immuno-modulatory mediators that interact with host cells and tissues. While a number of secreted immunoregulatory parasite proteins have been defined, new work also points to the release of extracellular vesicles, or exosomes, that interact with and manipulate host gene expression. These recent results are discussed in the overall context of how helminths communicate effectively with the host organism.

Organ system view of the hepatic innate immunity in HCV infection

An orchestration of innate and adaptive immunity determines the infection outcome and whether the host achieves clearance or allows the pathogen to establish persistent infection. The robust activation of the innate immune response plays the most critical role in both limiting viral replication and halting the spread of the pathogen immediately after infection. The magnitude of innate immune activation is coupled with the efficient mounting of the adaptive immunity. Although immunity against HCV infection is known to be inadequate as most cases transitions to chronicity, approximately 25% of acute infection cases result in spontaneous clearance. The exact immune mechanisms that govern the infection outcome remain largely unknown; recent discoveries suggest that the innate immune system facilitates this event. Both infected hepatocytes and local innate immune cells trigger the front line defense program of the liver as well as the recruitment of diverse adaptive immune cells to the site of infection. Although hepatocyte is the target of HCV infection, nearly all cell types that exist in the liver are involved in the innate defense and contribute to the pathophysiology of hepatic inflammation. The main focus of this comprehensive review is to discuss the current knowledge on how each hepatic cell type contributes to the organ system level innate immunity against HCV infection as well as interplays with the viral evasion program. Furthermore, this review article also aims to synchronize the observations from both molecular biological studies and clinical studies with the ultimate goal of improving our understanding of HCV mediated hepatitis. J. Med. Virol. 88:2025-2037, 2016. © 2016 Wiley Periodicals, Inc.

Subtoxic Alterations in Hepatocyte-Derived Exosomes: An Early Step in Drug-Induced Liver Injury?

Drug-induced liver injury (DILI) is a significant clinical and economic problem in the United States, yet the mechanisms that underlie DILI remain poorly understood. Recent evidence suggests that signaling molecules released by stressed hepatocytes can trigger immune responses that may be common across DILI mechanisms. Extracellular vesicles released by hepatocytes, principally hepatocyte-derived exosomes (HDEs), may constitute one such signal. To examine HDE alterations as a function of drug-induced stress, this work utilized prototypical hepatotoxicant acetaminophen (APAP) in male Sprague-Dawley (SD) rats, SD rat hepatocytes, and primary human hepatocytes. HDE were isolated using ExoQuick precipitation reagent and analyzed by quantification of the liver-specific RNAs albumin and microRNA-122 (miR-122). In vivo, significant elevations in circulating exosomal albumin mRNA were observed at subtoxic APAP exposures. Significant increases in exosomal albumin mRNA were also observed in primary rat hepatocytes at subtoxic APAP concentrations. In primary human hepatocytes, APAP elicited increases in both exosomal albumin mRNA and exosomal miR-122 without overt cytotoxicity. However, the number of HDE produced in vitro in response to APAP did not increase with exosomal RNA quantity. We conclude that significant drug-induced alterations in the liver-specific RNA content of HDE occur at subtoxic APAP exposures in vivo and in vitro, and that these changes appear to reflect selective packaging rather than changes in exosome number. The current findings demonstrate that translationally relevant HDE alterations occur in the absence of overt hepatocellular toxicity, and support the hypothesis that HDE released by stressed hepatocytes may mediate early immune responses in DILI.

Presentation of hepatocellular antigens

The liver is an organ in which antigen-specific T-cell responses manifest a bias toward immune tolerance. This is clearly seen in the rejection of allogeneic liver transplants, and multiple other phenomena suggest that this effect is more general. These include tolerance toward antigens introduced via the portal vein, immune failure to several hepatotropic viruses, the lack of natural liver-stage immunity to malaria parasites, and the frequent metastasis of cancers to the liver. Here we review the mechanisms by which T cells engage with hepatocellular antigens, the context in which such encounters occur, and the mechanisms that act to suppress a full T-cell response. While many mechanisms play a role, we will argue that two important processes are the constraints on the cross-presentation of hepatocellular antigens, and the induction of negative feedback inhibition driven by interferons. The constant exposure of the liver to microbial products from the intestine may drive innate immunity, rendering the local environment unfavorable for specific T-cell responses through this mechanism. Nevertheless, tolerance toward hepatocellular antigens is not monolithic and under specific circumstances allows both effective immunity and immunopathology.

The Dual Role of Exosomes in Hepatitis A and C Virus Transmission and Viral Immune Activation

Exosomes are small nanovesicles of about 100 nm in diameter that act as intercellular messengers because they can shuttle RNA, proteins and lipids between different cells. Many studies have found that exosomes also play various roles in viral pathogenesis. Hepatitis A virus (HAV; a picornavirus) and Hepatitis C virus (HCV; a flavivirus) two single strand plus-sense RNA viruses, in particular, have been found to use exosomes for viral transmission thus evading antibody-mediated immune responses. Paradoxically, both viral exosomes can also be detected by plasmacytoid dendritic cells (pDCs) leading to innate immune activation and type I interferon production. This article will review recent findings regarding these two viruses and outline how exosomes are involved in their transmission and immune sensing.

Immunopathogenesis of Hepatitis C Virus Infection

Despite advances in therapy, hepatitis C virus infection remains a major global health issue with 3 to 4 million incident cases and 170 million prevalent chronic infections. Complex, partially understood, host-virus interactions determine whether an acute infection with hepatitis C resolves, as occurs in approximately 30% of cases, or generates a persistent hepatic infection, as occurs in the remainder. Once chronic infection is established, the velocity of hepatocyte injury and resultant fibrosis is significantly modulated by immunologic as well as environmental factors. Immunomodulation has been the backbone of antiviral therapy despite poor understanding of its mechanism of action.

Natural Products as Tools for Defining How Cellular Metabolism Influences Cellular Immune and Inflammatory Function during Chronic Infection

Chronic viral infections like those caused by hepatitis C virus (HCV) and human immunodeficiency virus (HIV) cause disease that establishes an ongoing state of chronic inflammation. While there have been tremendous improvements towards curing HCV with directly acting antiviral agents (DAA) and keeping HIV viral loads below detection with antiretroviral therapy (ART), there is still a need to control inflammation in these diseases. Recent studies indicate that many natural products like curcumin, resveratrol and silymarin alter cellular metabolism and signal transduction pathways via enzymes such as adenosine monophosphate kinase (AMPK) and mechanistic target of rapamycin (mTOR), and these pathways directly influence cellular inflammatory status (such as NF-κB) and immune function. Natural products represent a vast toolkit to dissect and define how cellular metabolism controls cellular immune and inflammatory function.

Exosome Adherence and Internalization by Hepatic Stellate Cells Triggers Sphingosine 1-Phosphate-dependent Migration

Exosomes are cell-derived extracellular vesicles thought to promote intercellular communication by delivering specific content to target cells. The aim of this study was to determine whether endothelial cell (EC)-derived exosomes could regulate the phenotype of hepatic stellate cells (HSCs). Initial microarray studies showed that fibroblast growth factor 2 induced a 2.4-fold increase in mRNA levels of sphingosine kinase 1 (SK1). Exosomes derived from an SK1-overexpressing EC line increased HSC migration 3.2-fold. Migration was not conferred by the dominant negative SK1 exosome. Incubation of HSCs with exosomes was also associated with an 8.3-fold increase in phosphorylation of AKT and 2.5-fold increase in migration. Exosomes were found to express the matrix protein and integrin ligand fibronectin (FN) by Western blot analysis and transmission electron microscopy. Blockade of the FN-integrin interaction with a CD29 neutralizing antibody or the RGD peptide attenuated exosome-induced HSC AKT phosphorylation and migration. Inhibition of endocytosis with transfection of dynamin siRNA, the dominant negative dynamin GTPase construct Dyn2K44A, or the pharmacological inhibitor Dynasore significantly attenuated exosome-induced AKT phosphorylation. SK1 levels were increased in serum exosomes derived from mice with experimental liver fibrosis, and SK1 mRNA levels were up-regulated 2.5-fold in human liver cirrhosis patient samples. Finally, S1PR2 inhibition protected mice from CCl4-induced liver fibrosis. Therefore, EC-derived SK1-containing exosomes regulate HSC signaling and migration through FN-integrin-dependent exosome adherence and dynamin-dependent exosome internalization. These findings advance our understanding of EC/HSC cross-talk and identify exosomes as a potential target to attenuate pathobiology signals.

Pathogen-Associated Molecular Pattern Recognition of Hepatitis C Virus Transmitted/Founder Variants by RIG-I Is Dependent on U-Core Length

Despite the introduction of direct-acting antiviral (DAA) drugs against hepatitis C virus (HCV), infection remains a major public health concern because DAA therapeutics do not prevent reinfection and patients can still progress to chronic liver disease. Chronic HCV infection is supported by a variety of viral immune evasion strategies, but, remarkably, 20% to 30% of acute infections spontaneously clear prior to development of adaptive immune responses, thus implicating innate immunity in resolving acute HCV infection. However, the virus-host interactions regulating acute infection are unknown. Transmission of HCV involves one or a few transmitted/founder (T/F) variants. In infected hepatocytes, the retinoic acid-inducible gene I (RIG-I) protein recognizes 5' triphosphate (5'ppp) of the HCV RNA and a pathogen-associated molecular pattern (PAMP) motif located within the 3' untranslated region consisting of poly-U/UC. PAMP binding activates RIG-I to induce innate immune signaling and type 1 interferon antiviral defenses. HCV poly-U/UC sequences can differ in length and complexity, suggesting that PAMP diversity in T/F genomes could regulate innate immune control of acute HCV infection. Using 14 unique poly-U/UC sequences from HCV T/F genomes recovered from acute-infection patients, we tested whether RIG-I recognition and innate immune activation correlate with PAMP sequence characteristics. We show that T/F variants are recognized by RIG-I in a manner dependent on length of the U-core motif of the poly-U/UC PAMP and are recognized by RIG-I to induce innate immune responses that restrict acute infection. PAMP recognition of T/F HCV variants by RIG-I may therefore impart innate immune signaling and HCV restriction to impact acute-phase-to-chronic-phase transition.

IMPORTANCE

Recognition of nonself molecular patterns such as those seen with viral nucleic acids is an essential step in triggering the immune response to virus infection. Innate immunity is induced by hepatitis C virus infection through the recognition of viral RNA by the cellular RIG-I protein, where RIG-I recognizes a poly-uridine/cytosine motif in the viral genome. Variation within this motif may provide an immune evasion strategy for transmitted/founder viruses during acute infection. Using 14 unique poly-U/UC sequences from HCV T/F genomes recovered from acutely infected HCV patients, we demonstrate that RIG-I binding and activation of innate immunity depend primarily on the length of the uridine core within this motif. T/F variants found in acute infection contained longer U cores within the motif and could activate RIG-I and induce innate immune signaling sufficient to restrict viral infection. Thus, recognition of T/F variants by RIG-I could significantly impact the transition from acute to chronic infection.

HCV-infected cells and differentiation increase monocyte immunoregulatory galectin-9 production

The lectin galectin-9 may help establish and maintain chronic hepatitis C virus infection. Galectin-9 is elevated in the liver and sera of hepatitis C virus patients, induces apoptosis of hepatitis C virus-specific T cells, and increases inhibitory regulatory T cells. Kupffer cells stain strongly for galectin-9 protein in hepatitis C virus patients. In the current study, we determined stimuli that induce galectin-9 production by monocytes and macrophages in hepatitis C virus infection. With the use of real-time PCR and flow cytometry, we analyzed galectin-9 mRNA and protein from human monocytes cocultured with hepatitis C virus-infected cells or noninfectious hepatitis C virus subgenomic replicon cells. We focused on finding the stimuli for galectin-9 production. Additionally, we measured galectin-9 during monocyte-to-macrophage maturation. Finally, we examined galectin-9 in peripheral monocytes from hepatitis C virus patients using flow cytometry. Galectin-9 mRNA increased 8-fold when primary monocytes were exposed to hepatitis C virus--infected cells. Maximum induction required proximity or contact and did not require IFN-γ or hepatitis C virus virions. Coculture of monocytes with subgenomic replicon cells increased galectin-9 5-fold, and purified exosomes from infected cells stimulated galectin-9 production. Stimulation of monocyte TLR3, -7, and -8 increased galectin-9 production. Differentiation of monocytes to macrophages increased galectin-9, and nonclassic monocytes from hepatitis C virus patients had the highest levels of galectin-9. Hepatitis C virus-infected cells stimulated monocytes to produce galectin-9 in close proximity, possibly, in part, as a result of exosomes and endosomal TLRs. Differentiation of monocytes to macrophages increased galectin-9. Nonclassic monocytes from hepatitis C virus patients express the highest galectin-9 levels, suggesting they may contribute to elevated galectin-9 and adaptive immune inhibition in hepatitis C virus infection.

Natural Killer Cells in Viral Hepatitis

Natural killer (NK) cells are traditionally regarded as first-line effectors of the innate immune response, but they also have a distinct role in chronic infection. Here, we review the role of NK cells against hepatitis C virus (HCV) and hepatitis B virus (HBV), two agents that cause acute and chronic hepatitis in humans. Interest in NK cells was initially sparked by genetic studies that demonstrated an association between NK cell-related genes and the outcome of HCV infection. Viral hepatitis also provides a model to study the NK cell response to both endogenous and exogenous type I interferon (IFN). Levels of IFN-stimulated genes increase in both acute and chronic HCV infection and pegylated IFNα has been the mainstay of HCV and HBV treatment for decades. In chronic viral hepatitis, NK cells display decreased production of antiviral cytokines. This phenotype is found in both HCV and HBV infection but is induced by different mechanisms. Potent antivirals now provide the opportunity to study the reversibility of the suppressed cytokine production of NK cells in comparison with the antigen-induced defect in IFNγ and tumor necrosis factor-α production of virus-specific T cells. This has implications for immune reconstitution in other conditions of chronic inflammation and immune exhaustion, such as human immunodeficiency virus infection and cancer.

Hepatitis C Virus Sensing by Human Trophoblasts Induces Innate Immune Responses and Recruitment of Maternal NK Cells: Potential Implications for Limiting Vertical Transmission

Hepatitis C virus (HCV) is the world's most common blood-borne viral infection for which there is no vaccine. The rates of vertical transmission range between 3 and 6% with odds 90% higher in the presence of HIV coinfection. Prevention of vertical transmission is not possible because of lack of an approved therapy for use in pregnancy or an effective vaccine. Recently, HCV has been identified as an independent risk factor for preterm delivery, perinatal mortality, and other complications. In this study, we characterized the immune responses that contribute to the control of viral infection at the maternal-fetal interface (MFI) in the early gestational stages. In this study, we show that primary human trophoblast cells and an extravillous trophoblast cell line (HTR8), from first and second trimester of pregnancy, express receptors relevant for HCV binding/entry and are permissive for HCV uptake. We found that HCV-RNA sensing by human trophoblast cells induces robust upregulation of type I/III IFNs and secretion of multiple chemokines that elicit recruitment and activation of decidual NK cells. Furthermore, we observed that HCV-RNA transfection induces a proapoptotic response within HTR8 that could affect the morphology of the placenta. To our knowledge, for the first time, we demonstrate that HCV-RNA sensing by human trophoblast cells elicits a strong antiviral response that alters the recruitment and activation of innate immune cells at the MFI. This work provides a paradigm shift in our understanding of HCV-specific immunity at the MFI as well as novel insights into mechanisms that limit vertical transmission but may paradoxically lead to virus-related pregnancy complications.

Innate detection of hepatitis B and C virus and viral inhibition of the response

Viral hepatitis caused by hepatitis B virus (HBV) and hepatitis C virus (HCV) infections poses a significant burden to the public health system. Although HBV and HCV differ in structure and life cycles, they share unique characteristics, such as tropism to infect hepatocytes and association with hepatic and extrahepatic disorders that are of innate immunity nature. In response to HBV and HCV infection, the liver innate immune cells eradicate pathogens by recognizing specific molecules expressed by pathogens via distinct cellular pattern recognition receptors whose triggering activates intracellular signalling pathways inducing cytokines, interferons and anti-viral response genes that collectively function to clear infections. However, HBV and HCV evolve strategies to inactivate innate signalling factors and as such establish persistent infections without being recognized by the innate immunity. We review recent insights into how HBV and HCV are sensed and how they evade innate immunity to establish chronicity. Understanding the mechanisms of viral hepatitis is mandatory to develop effective and safe therapies for eradication of viral hepatitis.

The application of engineered liver tissues for novel drug discovery

INTRODUCTION

Drug-induced liver injury remains a major cause of drug attrition. Furthermore, novel drugs are being developed for treating liver diseases. However, differences between animals and humans in liver pathways necessitate the use of human-relevant liver models to complement live animal testing during preclinical drug development. Microfabrication tools and synthetic biomaterials now allow for the creation of tissue subunits that display more physiologically relevant and long-term liver functions than possible with declining monolayers.

AREAS COVERED

The authors discuss acellular enzyme platforms, two-dimensional micropatterned co-cultures, three-dimensional spheroidal cultures, microfluidic perfusion, liver slices and humanized rodent models. They also present the use of cell lines, primary liver cells and induced pluripotent stem cell-derived human hepatocyte-like cells in the creation of cell-based models and discuss in silico approaches that allow integration and modeling of the datasets from these models. Finally, the authors describe the application of liver models for the discovery of novel therapeutics for liver diseases.

EXPERT OPINION

Engineered liver models with varying levels of in vivo-like complexities provide investigators with the opportunity to develop assays with sufficient complexity and required throughput. Control over cell-cell interactions and co-culture with stromal cells in both two dimension and three dimension are critical for enabling stable liver models. The validation of liver models with diverse sets of compounds for different applications, coupled with an analysis of cost:benefit ratio, is important for model adoption for routine screening. Ultimately, engineered liver models could significantly reduce drug development costs and enable the development of more efficacious and safer therapeutics for liver diseases.

Identification, molecular cloning, and analysis of full-length hepatitis C virus transmitted/founder genotypes 1, 3, and 4

Hepatitis C virus (HCV) infection is characterized by persistent replication of a complex mixture of viruses termed a “quasispecies.” Transmission is generally associated with a stringent population bottleneck characterized by infection by limited numbers of “transmitted/founder” (T/F) viruses. Characterization of T/F genomes of human immunodeficiency virus type 1 (HIV-1) has been integral to studies of transmission, immunopathogenesis, and vaccine development. Here, we describe the identification of complete T/F genomes of HCV by single-genome sequencing of plasma viral RNA from acutely infected subjects. A total of 2,739 single-genome-derived amplicons comprising 10,966,507 bp from 18 acute-phase and 11 chronically infected subjects were analyzed. Acute-phase sequences diversified essentially randomly, except for the poly(U/UC) tract, which was subject to polymerase slippage. Fourteen acute-phase subjects were productively infected by more than one genetically distinct virus, permitting assessment of recombination between replicating genomes. No evidence of recombination was found among 1,589 sequences analyzed. Envelope sequences of T/F genomes lacked transmission signatures that could distinguish them from chronic infection viruses. Among chronically infected subjects, higher nucleotide substitution rates were observed in the poly(U/UC) tract than in envelope hypervariable region 1. Fourteen full-length molecular clones with variable poly(U/UC) sequences corresponding to seven genotype 1a, 1b, 3a, and 4a T/F viruses were generated. Like most unadapted HCV clones, T/F genomes did not replicate efficiently in Huh 7.5 cells, indicating that additional cellular factors or viral adaptations are necessary for in vitro replication. Full-length T/F HCV genomes and their progeny provide unique insights into virus transmission, virus evolution, and virus-host interactions associated with immunopathogenesis.

Hepatitis C virus (HCV) infects 2% to 3% of the world’s population and exhibits extraordinary genetic diversity. This diversity is mirrored by HIV-1, where characterization of transmitted/founder (T/F) genomes has been instrumental in studies of virus transmission, immunopathogenesis, and vaccine development. Here, we show that despite major differences in genome organization, replication strategy, and natural history, HCV (like HIV-1) diversifies essentially randomly early in infection, and as a consequence, sequences of actual T/F viruses can be identified. This allowed us to capture by molecular cloning the full-length HCV genomes that are responsible for infecting the first hepatocytes and eliciting the initial immune responses, weeks before these events could be directly analyzed in human subjects. These findings represent an enabling experimental strategy, not only for HCV and HIV-1 research, but also for other RNA viruses of medical importance, including West Nile, chikungunya, dengue, Venezuelan encephalitis, and Ebola viruses.

Transmitted/founder hepatitis C viruses induce cell-type- and genotype-specific differences in innate signaling within the liver

Hepatitis C virus (HCV) infection leads to persistence in the majority of cases despite triggering complex innate immune responses within the liver. Although hepatocytes are the preferred site for HCV replication, nonparenchymal cells (NPCs) can also contribute to antiviral immunity. Recent innovations involving single-genome amplification (SGA), direct amplicon sequencing, and phylogenetic inference have identified full-length transmitted/founder (T/F) viruses. Here, we tested the effect of HCV T/F viral RNA (vRNA) on innate immune signaling within hepatocytes and NPCs, including the HepG2 and Huh 7.5.1 cell lines, a human liver endothelial cell line (TMNK-1), a plasmacytoid dendritic cell line (GEN2.2), and a monocytic cell line (THP-1). Transfection with hepatitis C T/F vRNA induced robust transcriptional upregulation of type I and III interferons (IFNs) within HepG2 and TMNK-1 cells. Both the THP-1 and GEN2.2 lines demonstrated higher type I and III IFN transcription with genotype 3a compared to genotype 1a or 1b. Supernatants from HCV T/F vRNA-transfected TMNK-1 cells demonstrated superior viral control. Primary human hepatocytes (PHH) transfected with genotype 3a induced canonical pathways that included chemokine and IFN genes, as well as overrepresentation of RIG-I (DDX58), STAT1, and a Toll-like receptor 3 (TLR3) network. Full-length molecular clones of HCV induce broad IFN responses within hepatocytes and NPCs, highlighting that signals imparted by the various cell types within the liver may lead to divergent outcomes of infection. In particular, the finding that HCV genotypes differentially induce antiviral responses in NPCs and PHH might account for relevant clinical-epidemiological observations (higher clearance but greater necroinflammation in persistence with genotype 3).

IMPORTANCE

Hepatitis C virus (HCV) has become a major worldwide problem, and it is now the most common viral infection for which there is no vaccine. HCV infection often leads to persistence of the virus and is a leading cause of chronic hepatitis, liver cancer, and cirrhosis. There are multiple genotypes of the virus, and patients infected with different viral genotypes respond to traditional therapy differently. However, the immune response to the virus within the liver has not been fully elucidated. Here, we determined the responses to different genotypes of HCV in cell types of the liver. We found that the immune response varied according to both cell type and HCV genotype, leading to a more pronounced induction of inflammatory pathways after exposure to certain genotypes. Therefore, inflammatory pathways that are being robustly activated by certain HCV genotypes could lead to more severe damage to the liver, inducing diverse outcomes and responses to therapy.