Knockdown of Autophagy Inhibits Infectious Hepatitis C Virus Release by the Exosomal Pathway. J Virol. 2016;90:1387-1396. [PMID: 26581990 DOI: 10.1128/jvi.02383-15]

Mechanisms Underlying Hepatitis C Virus-Associated Hepatic Fibrosis

Hepatitis C virus (HCV) infection often causes liver diseases, including fibrosis, cirrhosis and hepatocellular carcinoma (HCC). Liver fibrosis is the outcome of the wound healing response to tissue damage caused by chronic HCV infection. This process is characterized by the excessive accumulation of extracellular matrix (ECM) proteins, such as collagen fibers secreted by activated hepatic stellate cells (HSCs). Activation of HSCs from the quiescent stage is mediated by different mechanisms, including pro-inflammatory cytokines and chemokines released from HCV-infected hepatocytes and liver macrophages. HCV infection modulates the expression of different microRNAs that can be transported and delivered to the HSCs via exosomes released from infected cells, also leading to the development of advanced disease pathogenesis. Although recent advancements in direct-acting antiviral (DAA) treatment can efficiently control viremia, there are very few treatment strategies available that can be effective at preventing pathogenesis in advanced liver fibrosis or cirrhosis in patients. Assessment of fibrosis is considered to be the major part of proper patient care and decision making in clinical practice. In this review, we highlighted the current knowledge of molecular mechanisms responsible for the progression of liver fibrosis in chronically HCV-infected patients, and currently available methods for evaluation of fibrosis in patients. A detailed understanding of these aspects at the molecular level may contribute to the development of new therapies targeting HCV-related liver fibrosis.

Rewiring cellular networks by members of the Flaviviridae family

Members of the Flaviviridae virus family comprise a large group of enveloped viruses with a single-strand RNA genome of positive polarity. Several genera belong to this family, including the Hepacivirus genus, of which hepatitis C virus (HCV) is the prototype member, and the Flavivirus genus, which contains both dengue virus and Zika virus. Viruses of these genera differ in many respects, such as the mode of transmission or the course of infection, which is either predominantly persistent in the case of HCV or acutely self-limiting in the case of flaviviruses. Although the fundamental replication strategy of Flaviviridae members is similar, during the past few years, important differences have been discovered, including the way in which these viruses exploit cellular resources to facilitate viral propagation. These differences might be responsible, at least in part, for the various biological properties of these viruses, thus offering the possibility to learn from comparisons. In this Review, we discuss the current understanding of how Flaviviridae viruses manipulate and usurp cellular pathways in infected cells. Specifically, we focus on comparing strategies employed by flaviviruses with those employed by hepaciviruses, and we discuss the importance of these interactions in the context of viral replication and antiviral therapies.

Autophagy during viral infection - a double-edged sword

Autophagy is a powerful tool that host cells use to defend against viral infection. Double-membrane vesicles, termed autophagosomes, deliver trapped viral cargo to the lysosome for degradation. Specifically, autophagy initiates an innate immune response by cooperating with pattern recognition receptor signalling to induce interferon production. It also selectively degrades immune components associated with viral particles. Following degradation, autophagy coordinates adaptive immunity by delivering virus-derived antigens for presentation to T lymphocytes. However, in an ongoing evolutionary arms race, viruses have acquired the potent ability to hijack and subvert autophagy for their benefit. In this Review, we focus on the key regulatory steps during viral infection in which autophagy is involved and discuss the specific molecular mechanisms that diverse viruses use to repurpose autophagy for their life cycle and pathogenesis.

Autophagy is crucial for innate and adaptive antiviral immunity; in turn, viruses evade and subvert autophagy to support their replication and pathogenesis. In this Review, Choi, Bowman and Jung discuss the molecular mechanisms that govern autophagy during host–virus interactions.

Flaviviridae Viruses and Oxidative Stress: Implications for Viral Pathogenesis

Oxidative stress is induced once the balance of generation and neutralization of reactive oxygen species (ROS) is broken in the cell, and it plays crucial roles in a variety of natural and diseased processes. Infections of Flaviviridae viruses trigger oxidative stress, which affects both the cellular metabolism and the life cycle of the viruses. Oxidative stress associated with specific viral proteins, experimental culture systems, and patient infections, as well as its correlations with the viral pathogenesis attracts much research attention. In this review, we primarily focus on hepatitis C virus (HCV), dengue virus (DENV), Zika virus (ZIKV), Japanese encephalitis virus (JEV), West Nile virus (WNV), and tick-borne encephalitis virus (TBEV) as representatives of Flaviviridae viruses and we summarize the mechanisms involved in the relevance of oxidative stress for virus-associated pathogenesis. We discuss the current understanding of the pathogenic mechanisms of oxidative stress induced by Flaviviridae viruses and highlight the relevance of autophagy and DNA damage in the life cycle of viruses. Understanding the crosstalk between viral infection and oxidative stress-induced molecular events may offer new avenues for antiviral therapeutics.

Hepatitis C virus infection increases autophagosome stability by suppressing lysosomal fusion through an Arl8b-dependent mechanism

Autophagy is a conserved cellular process involving intracellular membrane trafficking and degradation. Pathogens, including hepatitis C virus (HCV), often exploit this process to promote their own survival. The aim of this study was to determine the mechanism by which HCV increases steady-state autophagosome numbers while simultaneously inhibiting flux through the autophagic pathway. Using the lysosomal inhibitor bafilomycin A1, we showed that HCV-induced alterations in autophagy result from a blockage of autophagosome degradation rather than an increase in autophagosome generation. In HCV-infected cells, lysosome function was normal, but a tandem RFP-GFP-LC3 failed to reach the lysosome even under conditions that activate autophagy. Autophagosomes and lysosomes isolated from HCV-infected cells were able to fuse with each other normally in vitro, suggesting that the cellular fusion defect resulted from trafficking rather than an inability of vesicles to fuse. Arl8b is an Arf-like GTPase that specifically localizes to lysosomes and plays a role in autophagic flux through its effect on lysosomal positioning. At basal levels, Arl8b was primarily found in a perinuclear localization and co-localized with LC3-positive autophagosomes. HCV infection increased the level of Arl8b 3-fold and redistributed Arl8b to a more diffuse, peripheral pattern that failed to co-localize with LC3. Knockdown of Arl8b in HCV-infected cells restored autophagosome-lysosome fusion and autophagic flux to levels seen in control cells. Thus, HCV suppresses autophagic flux and increases the steady-state levels of autophagosomes by increasing the expression of Arl8b, which repositions lysosomes and prevents their fusion with autophagosomes.

A Comprehensive Review of Autophagy and Its Various Roles in Infectious, Non-Infectious, and Lifestyle Diseases: Current Knowledge and Prospects for Disease Prevention, Novel Drug Design, and Therapy

Autophagy (self-eating) is a conserved cellular degradation process that plays important roles in maintaining homeostasis and preventing nutritional, metabolic, and infection-mediated stresses. Autophagy dysfunction can have various pathological consequences, including tumor progression, pathogen hyper-virulence, and neurodegeneration. This review describes the mechanisms of autophagy and its associations with other cell death mechanisms, including apoptosis, necrosis, necroptosis, and autosis. Autophagy has both positive and negative roles in infection, cancer, neural development, metabolism, cardiovascular health, immunity, and iron homeostasis. Genetic defects in autophagy can have pathological consequences, such as static childhood encephalopathy with neurodegeneration in adulthood, Crohn's disease, hereditary spastic paraparesis, Danon disease, X-linked myopathy with excessive autophagy, and sporadic inclusion body myositis. Further studies on the process of autophagy in different microbial infections could help to design and develop novel therapeutic strategies against important pathogenic microbes. This review on the progress and prospects of autophagy research describes various activators and suppressors, which could be used to design novel intervention strategies against numerous diseases and develop therapeutic drugs to protect human and animal health.

Exosomes and autophagy: rekindling the vesicular waste hypothesis

Exosomes were first described as waste carriers implicated in reticulocyte maturation but has during the past decade been associated with many other cellular functions. The biogenesis of exosomes has been extensively studied and several protein machineries have been identified to dictate their production and release. The newly discovered branches of the autophagy system implicate secretion of waste in endosomal-derived vesicles as is thought for exosome release. Many of the proteins that have been identified as responsible for the formation and release of these vesicles are the same as those identified in exosome biogenesis. In this Perspective, we discuss the possibility of exosomes being a part of the autophagy machinery and the consequences this could have on interpretation of exosome functions.

Microrna-130a Downregulates HCV Replication through an atg5-Dependent Autophagy Pathway

We previously identified that miR-130a downregulates HCV replication through two independent pathways: restoration of host immune responses and regulation of pyruvate metabolism. In this study, we further sought to explore host antiviral target genes regulated by miR-130a. We performed a RT² Profiler™ PCR array to identify the host antiviral genes regulated by miR-130a. The putative binding sites between miR-130a and its downregulated genes were predicted by miRanda. miR-130a and predicted target genes were over-expressed or knocked down by siRNA or CRISPR/Cas9 gRNA. Selected gene mRNAs and their proteins, together with HCV replication in JFH1 HCV-infected Huh7.5.1 cells were monitored by qRT-PCR and Western blot. We identified 32 genes that were significantly differentially expressed more than 1.5-fold following miR-130a overexpression, 28 of which were upregulated and 4 downregulated. We found that ATG5, a target gene for miR-130a, significantly upregulated HCV replication and downregulated interferon stimulated gene expression. miR-130a downregulated ATG5 expression and its conjugation complex with ATG12. ATG5 and ATG5-ATG12 complex affected interferon stimulated gene (ISG) such as MX1 and OAS3 expression and subsequently HCV replication. We concluded that miR-130a regulates host antiviral response and HCV replication through targeting ATG5 via the ATG5-dependent autophagy pathway.

Rapid hepatitis C virus clearance by antivirals correlates with immune status of infected patients

Altered immune parameters associated with hepatitis C virus (HCV) genotype 1b infection and their correlation with virus eradication in direct-acting antivirals (DAA)-treated patients were examined. Thirty-one HCV-infected patients were treated with DAAs for 12 weeks. Pre-DAA-treatment and post-DAA-treatment sera were analyzed for cytokines/chemokines using MILLIPLEX MAP. Serum complement level and antibody neutralization activity were measured separately. Sera from 11 spontaneously cleared HCV subjects were included for comparison. Rapid virological responders (RVR) or end-of-treatment responders (EOTR) were defined as patients with HCV RNA negative at week 4 or positive at week 4 and negative at week 12, respectively. HCV RNA eradication and a decrease in liver fibrosis-related cytokines after treatment were observed when compared with pretreatment sera from RVR and EOTR. In pretreatment sera, interferons and T-helper 1 or 2 cell-associated cytokines/chemokines were significantly higher among RVR as compared with EOTR. Furthermore, serum complement and virus neutralizing antibody levels were higher in pretreatment RVR sera. Eradication of HCV RNA by DAA decreased liver fibrosis-related cytokines. Pretreatment sera from RVR displayed an enhanced cytokine/chemokine, complement and virus neutralizing antibody response as compared with EOTR sera. Our results suggested that enhanced host immune status may play an additive role on HCV RNA clearance by DAA.

Differential dynamics of hepatic protein expressions with long-term cultivated hepatitis C virus infection

BACKGROUND

The liver maintains blood chemical homeostasis by active uptake and secretion through endocytosis, exocytosis, and intracellular trafficking between the plasma and intracellular membranes. Hepatitis C virus (HCV) infection affects the host membrane architecture and might thus impair the regulation of the cellular transportation machinery. Additionally, the hepatic expressions of differential protein dynamics with long-term HCV infection remain fully recover.

METHODS

In this study, comparative proteomic analysis was performed in HCV-infected and mock-control Huh7 cells according to the viral dynamics of exponential, plateau, declined, and silencing phases at the acute stage, and the chronic stage. The proteins with <0.8-fold and ≥1.25-fold changes in expression were analyzed using functional pathway clustering prediction.

RESULTS

The combined experimental repetitions identified full-spectrum cellular proteins in each of 5 sample sets from acute exponential, plateau, declined, and silencing phases, and the chronic stage. The clustering results revealed that HCV infection might differentiate regulatory pathways involving extracellular exosome, cadherin, melanosome, and RNA binding. Overall host proteins in HCV-infected cells exhibited kinetic pattern 1, in which cellular expression was downregulated from the acute exponential to plateau phases, reached a nadir, and was then elevated at the chronic stage. The proteins involved in the membrane-budding pathway exhibited kinetic pattern 2, in which their expressions were distinctly downregulated at the chronic stage.

CONCLUSION

The current comparative proteomics revealed the differential regulatory effects of HCV infection on host intracellular transport functional pathways, which might contribute to the pathogenic mechanisms of HCV in hepatocytes that sustain long-term infection.

Hepatitis C Virus Manipulates Humans as its Favorite Host for a Long-Term Relationship

Chronic hepatitis C virus (HCV) infection-associated liver disease is a global health problem. HCV often causes silent disease, and eventually progresses to end-stage liver disease. HCV infects hepatocytes; however, initial manifestation of liver disease is mostly displayed in hepatic stellate cells (HSCs), causing fibrosis/cirrhosis, and is believed to occur from inflammation in the liver. It remains unclear why HCV is not spontaneously cleared from infected liver in the majority of individuals and develops chronic infection with progressive liver disease. Direct-acting antivirals (DAAs) show excellent results in controlling viremia, although beneficial consequence in advanced liver disease remains to be understood. In this review, we highlight the current knowledge that has contributed to our understanding of the role of HCV in inflammation, immune evasion, metabolic disorders, liver pathogeneses, and efforts in vaccine development.

Diverse Functions of Autophagy in Liver Physiology and Liver Diseases

Autophagy is a catabolic process by which eukaryotic cells eliminate cytosolic materials through vacuole-mediated sequestration and subsequent delivery to lysosomes for degradation, thus maintaining cellular homeostasis and the integrity of organelles. Autophagy has emerged as playing a critical role in the regulation of liver physiology and the balancing of liver metabolism. Conversely, numerous recent studies have indicated that autophagy may disease-dependently participate in the pathogenesis of liver diseases, such as liver hepatitis, steatosis, fibrosis, cirrhosis, and hepatocellular carcinoma. This review summarizes the current knowledge on the functions of autophagy in hepatic metabolism and the contribution of autophagy to the pathophysiology of liver-related diseases. Moreover, the impacts of autophagy modulation on the amelioration of the development and progression of liver diseases are also discussed.

Label-free characterization of exosome via surface enhanced Raman spectroscopy for the early detection of pancreatic cancer

Pancreatic cancer is a highly lethal malignancy. Lack of early diagnostic markers makes timely detection of pancreatic cancer a highly challenging endeavor. Exosomes have emerged as information-rich cancer specific biomarkers. However, characterization of tumor-specific exosomes has been challenging. This study investigated the proof of principle that exosomes could be used for the detection of pancreatic cancer. Label-free analysis of exosomes purified from normal and pancreatic cancer cell lines was performed using surface enhanced Raman Spectroscopy (SERS) and principal component differential function analysis (PC-DFA), to identify tumor-specific spectral signatures. This method differentiated exosomes originating from pancreatic cancer or normal pancreatic epithelial cell lines with 90% accuracy. The cell line trained PC-DFA algorithm was next applied to SERS spectra of serum-purified exosomes. This method exhibited up to 87% and 90% predictive accuracy for HC and EPC individual samples, respectively. Overall, our study identified utility of SERS spectral signature for deciphering exosomal surface signature.

The Multifaceted Roles of Autophagy in Flavivirus-Host Interactions

Autophagy is an evolutionarily conserved cellular process in which intracellular components are eliminated via lysosomal degradation to supply nutrients for organelle biogenesis and metabolic homeostasis. Flavivirus infections underlie multiple human diseases and thus exert an immense burden on public health worldwide. Mounting evidence indicates that host autophagy is subverted to modulate the life cycles of flaviviruses, such as hepatitis C virus, dengue virus, Japanese encephalitis virus, West Nile virus and Zika virus. The diverse interplay between autophagy and flavivirus infection not only regulates viral growth in host cells but also counteracts host stress responses induced by viral infection. In this review, we summarize the current knowledge on the role of autophagy in the flavivirus life cycle. We also discuss the impacts of virus-induced autophagy on the pathogeneses of flavivirus-associated diseases and the potential use of autophagy as a therapeutic target for curing flavivirus infections and related human diseases.

Relevance of Rab Proteins for the Life Cycle of Hepatitis C Virus

Although potent direct-acting antiviral drugs for the treatment of chronic hepatitis C virus (HCV) infection are licensed, there are more than 70 million individuals suffering from chronic HCV infection. In light of the limited access to these drugs, high costs, and a lot of undiagnosed cases, it is expected that the number of HCV cases will not decrease worldwide in the next years. Therefore, and due to the paradigmatic character of HCV for deciphering the crosstalk between viral pathogens and the host cell, characterization of HCV life cycle remains a challenge. HCV belongs to the family of Flaviviridae. As an enveloped virus HCV life cycle depends in many steps on intracellular trafficking. Rab GTPases, a large family of small GTPases, play a central role in intracellular trafficking processes controlling fusion, uncoating, vesicle budding, motility by recruiting specific effector proteins. This review describes the relevance of various Rab proteins for the different steps of the HCV life cycle.

HCV Defective Genomes Promote Persistent Infection by Modulating the Viral Life Cycle

Defective interfering (DI) RNAs have been detected in several human viruses. HCV in-frame deletions mutants (IFDMs), missing mainly the envelope proteins, have been found in patient sera and liver tissues. IFDMs replicate independently and can be trans-packaged into infectious virions in the presence of full length viral genome. So far, their biological role is unclear. In this study, we have isolated and cloned IFDMs from sera samples and liver tissues of patients infected with HCV genotypes 1b, 2a, and 3a. IFDMs were present in up to 26% of samples tested. Using the in vitro HCV cell culture system, co-expression of the wild type (wt) HCV replicon with HCV IFDMs RNA resulted in increased HCV replication. Additionally, co-transfection of the HCV full length genome RNA and a defective mutant missing the envelope region led to increased viral release, collectively suggesting an important biological role for IFDMs in the virus life cycle. Recently, exosomes, masters of intercellular communication, have been implicated in the transport of HCV viral genomes. We report for the first time that exosomal RNA isolated from HCV sera samples contains HCV defective genomes. We also demonstrate that inhibition of exosomal biogenesis and release influences HCV viral replication. Overall, we provide evidence that the presence of HCV IFDMs affects both viral replication and release. IFDMs exploit exosomes as means of transport, a way to evade the immune system, to spread more efficiently and possibly maintain persistent infection.

Host Cell Rab GTPases in Hepatitis B Virus Infection

Hepatitis B virus (HBV) is a leading cause of liver disease and is presently estimated to infect more than 250 million humans. The extremely successful spread of this virus among the human population is explained by its effective transmission strategies and its manifold particle types, including virions, empty envelopes and naked capsids. Due to its tiny genome, HBV depends on cellular machineries to thrive in infected hepatocytes. To enter, traverse and exit the cell, HBV exploits host membrane trafficking pathways, including intracellular highways directed by Rab GTPases. Here, we review recent discoveries focused on how HBV co-opts and perturbs host Rab GTPase functions with an emphasis on Rab7A- and Rab33B-mediated trafficking pathways. Rab7A plays bidirectional roles in the viral life cycle, as it promotes the endocytic uptake of HBV in early stages, but restricts exocytic virion release in late stages. In intermediate stages of HBV propagation, Rab33B is needed to guide the assembly of replicative progeny nucleocapsids. Rab33B acts together with its Atg5-12/16L1 effector, a protein complex required for autophagosome formation, suggesting the concept that HBV exploits this Rab/effector complex as an assembly scaffold and machine. We also discuss whether Rab-directed trafficking pathways engaged by HBV may be applicable to other virus families. Identification of overlapping Rab functions may offer new chances to develop broad-spectrum host-targeted antiviral strategies.

Role of autophagy in IL-1β export and release from cells

The autophagy pathway known also as macroautophagy (herein referred to as autophagy) is characterized by the formation of double-membrane organelles that capture cytosolic material. Based on pathway termination alternatives, autophagy has been divided into degradative and secretory. During degradative autophagy, autophagosomes typically fuse with lysosomes upon which the sequestered material is degraded. During secretory autophagy, instead of degradation the sequestered cargo is subjected to active secretion or passive release. In this review, we focus on the mechanisms of secretion/passive release of the potent pro-inflammatory cytokine IL-1β, as a prototypical leaderless cytosolic protein cargo studied in the context of secretory autophagy.

Viral journeys on the intracellular highways

Viruses are obligate intracellular pathogens that are dependent on cellular machineries for their replication. Recent technological breakthroughs have facilitated reliable identification of host factors required for viral infections and better characterization of the virus-host interplay. While these studies have revealed cellular machineries that are uniquely required by individual viruses, accumulating data also indicate the presence of broadly required mechanisms. Among these overlapping cellular functions are components of intracellular membrane trafficking pathways. Here, we review recent discoveries focused on how viruses exploit intracellular membrane trafficking pathways to promote various stages of their life cycle, with an emphasis on cellular factors that are usurped by a broad range of viruses. We describe broadly required components of the endocytic and secretory pathways, the Endosomal Sorting Complexes Required for Transport pathway, and the autophagy pathway. Identification of such overlapping host functions offers new opportunities to develop broad-spectrum host-targeted antiviral strategies.

The interplay between exosomes and autophagy - partners in crime

The eukaryotic endomembrane system is a complex series of interconnected membranous organelles that play important roles in responding to stress and maintaining cell homeostasis during health and disease. Two components of this system, exosome biogenesis and autophagy, are linked by the endolysosomal pathway. Exosomes are cargo-laden extracellular vesicles that arise from endosome-derived multivesicular bodies, and autophagy is a lysosomal-dependent degradation and recycling pathway. Recent studies have revealed shared molecular machinery between exosome biogenesis and autophagy, as well as substantial crosstalk between these two processes. In this Review, we first describe the classic view of exosome biogenesis and autophagy, including their links to the endolysosomal pathway. We then present the evidence for autophagy-related proteins in exosome biogenesis, the emerging roles of amphisomes and the evolving models of exosome-autophagy pathway interactions. Finally, we discuss the implications of exosome and autophagy interplay in the context of neurodegeneration and cancer.

The functional role of exosome in hepatocellular carcinoma

PURPOSE

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide with limited therapeutic options. Exosome is a member of extracellular vesicles that can be released by different cells in liver to communicate with other cells. HCC development has been characterized by a dysfunction of exosome regulation through many molecular mechanisms. The aim of the present review is to summarize the literature on exosomes in HCC, their roles in hepatocarcinogenesis from liver disease, molecules exchange between tumor cells and neighboring cells, metastasis, chemoresistant, immunosuppression, early diagnose and therapy application.

METHODS

Literatures about HCC and exosomes from PubMed databases were reviewed in this article.

RESULTS

As our review described, exosomes can induce malignant transformation of liver disease via promoting viral diffusion and inflammation, exchange oncogenic factors between tumor cells, sustain tumor growth by neighboring stromal cells, play a important role in metastasis, trigger chemoresistance through transmitting long noncoding RNAs, stimulate immune activation as well as immune evasion, be utilized in biomarkers discovery and therapeutic options.

CONCLUSIONS

Available data suggested that exosomes may play an important role in HCC development. More studies on the way that exosomes mediated the HCC progression are needed to promote the clinical utilization of exosomes.

RAB26-dependent autophagy protects adherens junctional integrity in acute lung injury

Microvascular barrier dysfunction is the central pathophysiological feature of acute lung injury (ALI). RAB26 is a newly identified small GTPase involved in the regulation of endothelial cell (EC) permeability. However, the mechanism behind this protection has not been clearly elucidated. Here we found that RAB26 promoted the integrity of adherens junctions (AJs) in a macroautophagy/autophagy-dependent manner in ALI. RAB26 is frequently downregulated in mouse lungs after LPS treatment. Mice lacking Rab26 exhibited phosphorylated SRC expression and increased CDH5/VE-cadherin phosphorylation, leading to AJ destruction. rab26-null mice showed further aggravation of the effects of endotoxin insult on lung vascular permeability and water content. Depletion of RAB26 resulted in upregulation of phosphorylated SRC, enhancement of CDH5 phosphorylation, and aggravation of CDH5 internalization, thereby weakening AJ integrity and endothelial barrier function in human pulmonary microvascular endothelial cells (HPMECs). RAB26 overexpression caused active interaction between SRC and the autophagy marker LC3-II and promoted degradation of phosphorylated SRC. Furthermore, RAB26 was involved in a direct and activation-dependent manner in autophagy induction through interaction with ATG16L1 in its GTP-bound form. These findings demonstrate that RAB26 exerts a protective effect on endothelial cell (EC) permeability, which is in part dependent on autophagic targeting of active SRC, and the resultant CDH5 dephosphorylation maintains AJ stabilization. Thus, RAB26-mediated autophagic targeting of phosphorylated SRC can maintain barrier integrity when flux through the RAB26-SRC pathway is protected. These findings suggest that activation of RAB26-SRC signaling provides a new therapeutic opportunity to prevent vascular leakage in ALI.

ABBREVIATIONS

AJs: adherens junctions; ALI: acute lung injury; ARDS: acute respiratory distress syndrome; ATG5: autophagy related 5; ATG12: autophagy related 12; ATG 16L1: autophagy related 16 like; 1 BALF: bronchoalveolar lavage fluidCQ: chloroquine; Ctrl: control; EC: endothelial cell; GFP: green fluorescent protein; HA-tagged; RAB26^WT: HA-tagged wild-type; RAB26  HA-tagged; RAB26^QL: HA-tagged; RAB26^Q123LHA-tagged; RAB26^NI: HA-tagged; RAB26^N177IHPMECs: human pulmonary microvascular endothelial cells; H&E: hematoxylin & eosin; IgG: immunoglobulin; GIF: immunofluorescence; IP: immunoprecipitationi;. p.: intraperitoneal; LPS: lipopolysaccharide; PBS: phosphate-buffered salinesi; RNA: small interfering;RNASQSTM1/p62, sequestosome; 1TBS: Tris-buffered saline; VEGF: vascular endothelial growth factor; WB: western blot; WT: wild-type.

Regulation of Apolipoprotein E Trafficking by Hepatitis C Virus-Induced Autophagy

Apolipoprotein E (ApoE) plays an important role in the maturation and infectivity of hepatitis C virus (HCV). By analyzing the subcellular localization of ApoE in Huh7 hepatoma cells that harbored an HCV subgenomic RNA replicon, we found that ApoE colocalized with autophagosomes. This colocalization was marginally detected in HCV-infected cells, apparently due to the depletion of ApoE by HCV, as treatment with bafilomycin A1 (BafA1), a vacuolar ATPase inhibitor that inhibits autophagic protein degradation, partially restored the ApoE level and enhanced its colocalization with autophagosomes in HCV-infected cells. The role of HCV-induced autophagy in the degradation of ApoE was further supported by the observations that nutrient starvation, which induces autophagic protein degradation, led to the loss of ApoE in HCV subgenomic RNA replicon cells and that the knockdown of ATG7, a protein essential for the formation of autophagic vacuoles, increased the ApoE level in cells with productive HCV replication. Interestingly, the inhibition of autophagy by ATG7 knockdown reduced the colocalization of ApoE with the HCV E2 envelope protein and the HCV titers released from cells. In contrast, the treatment of cells with BafA1 enhanced the colocalization of ApoE and HCV E2 and increased both intracellular and extracellular HCV titers. These results indicated that autophagy played an important role in the trafficking of ApoE in HCV-infected cells. While it led to autophagic degradation of ApoE, it also promoted the interaction between ApoE and HCV E2 to enhance the production of infectious progeny viral particles.IMPORTANCE Hepatitis C virus (HCV) is one of the most important human pathogens. Its virion is associated with apolipoprotein E (ApoE), which enhances its infectivity. HCV induces autophagy to enhance its replication. In this report, we demonstrate that autophagy plays an important role in the trafficking of ApoE in HCV-infected cells. This leads to the degradation of ApoE by autophagy. However, if the autophagic protein degradation is inhibited, ApoE is stabilized and colocalized with autophagosomes. This leads to its enhanced colocalization with the HCV E2 envelope protein and increased production of infectious progeny viral particles. If autophagy is inhibited by suppressing the expression of ATG7, a gene essential for the formation of autophagosomes, the colocalization of ApoE with E2 is reduced, resulting in the reduction of progeny viral titers. These results indicate an important role of autophagy in the transport of ApoE to promote the production of infectious HCV particles.

Human Papilloma Virus and Autophagy

Human papilloma viruses (HPVs) are a group of double-stranded DNA viruses known to be the primary cause of cervical cancer. In addition, evidence has now established their role in non-melanoma skin cancers, head and neck cancer (HNC), and the development of other anogenital malignancies. The prevalence of HPV-related HNC, in particular oropharyngeal cancers, is rapidly increasing, foreseeing that HPV-positive oropharyngeal cancers will outnumber uterine cervical cancers in the next 15–20 years. Therefore, despite the successful advent of vaccines originally licensed for cervical cancer prevention, HPV burden is still very high, and a better understanding of HPV biology is urgently needed. Autophagy is the physiological cellular route that accounts for removal, degradation, and recycling of damaged organelles, proteins, and lipids in lysosomal vacuoles. In addition to this scavenger function, autophagy plays a fundamental role during viral infections and cancers and is, therefore, frequently exploited by viruses to their own benefit. Recently, a link between HPV and autophagy has clearly emerged, leading to the conceivable development of novel anti-viral strategies aimed at restraining HPV infectivity. Here, recent findings on how oncogenic HPV16 usurp autophagy are described, highlighting similarities and differences with mechanisms adopted by other oncoviruses.

Secretion of Hepatitis C Virus Replication Intermediates Reduces Activation of Toll-Like Receptor 3 in Hepatocytes

BACKGROUND & AIMS

Hepatitis C virus (HCV) infections most often result in chronic outcomes, although the virus constantly produces replication intermediates, in particular double-stranded RNA (dsRNA), representing potent inducers of innate immunity. We aimed to characterize the fate of HCV dsRNA in hepatocyte cultures to identify mechanisms contributing to viral persistence in presence of an active innate immune response.

METHODS

We analyzed hepatocyte-based culture models for HCV for induction of innate immunity, secretion of virus positive- or negative-strand RNA, and viral replication using different quantification methods and microscopy techniques. Expression of pattern recognition receptors was reconstituted in hepatoma cells by lentiviral transduction.

RESULTS

HCV-infected cells secrete substantial amounts of virus positive- and negative-strand RNAs in extracellular vesicles (EVs), toward the apical and basolateral domain of hepatocytes. Secretion of negative-strand RNA was independent from virus production, and viral RNA secreted in EVs contained higher relative amounts of negative-strands, indicating that mostly virus dsRNA is released. A substantial part of viral replication complexes and dsRNA was found in the endosomal compartment and multivesicular bodies, indicating that secretion of HCV replication intermediates is mediated by the exosomal pathway. Block of vesicle release in HCV-positive cells increased intracellular dsRNA levels and increased activation of toll-like receptor 3, inhibiting HCV replication.

CONCLUSIONS

Using hepatocyte-based culture models for HCV, we found a portion of HCV dsRNA intermediates to be released from infected cells in EVs, which reduces activation of toll-like receptor 3. This represents a novel mechanism how HCV evades host immune responses, potentially contributing to viral persistence.

Autophagy regulates exosomal release of prions in neuronal cells

Prions are protein-based infectious agents that autocatalytically convert the cellular prion protein PrP^C to its pathological isoform PrP^Sc. Subsequent aggregation and accumulation of PrP^Sc in nervous tissues causes several invariably fatal neurodegenerative diseases in humans and animals. Prions can infect recipient cells when packaged into endosome-derived nanoparticles called exosomes, which are present in biological fluids such as blood, urine, and saliva. Autophagy is a basic cellular degradation and recycling machinery that also affects exosomal processing, but whether autophagy controls release of prions in exosomes is unclear. Our work investigated the effect of autophagy modulation on exosomal release of prions and how this interplay affects cellular prion infection. Exosomes isolated from cultured murine central neuronal cells (CAD5) and peripheral neuronal cells (N2a) contained prions as shown by immunoblotting for PrP^Sc, prion-conversion activity, and cell culture infection. We observed that autophagy stimulation with the mTOR inhibitor rapamycin strongly inhibited exosomal prion release. In contrast, inhibition of autophagy by wortmannin or CRISPR/Cas9-mediated knockout of the autophagy protein Atg5 (autophagy-related 5) greatly increased the release of exosomes and exosome-associated prions. We also show that a difference in exosomal prion release between CAD5 and N2a cells is related to differences at the level of basal autophagy. Taken together, our results indicate that autophagy modulation can control lateral transfer of prions by interfering with their exosomal release. We describe a novel role of autophagy in the prion life cycle, an understanding that may provide useful targets for containing prion diseases.

Extracellular Vesicles as Carriers of Non-coding RNAs in Liver Diseases

Extracellular vesicles (EVs) are small membranous vesicles secreted from normal, diseased, and transformed cells in vitro and in vivo. EVs have been found to play a critical role in cell-to-cell communication by transferring non-coding RNAs (ncRNAs) including microRNAs (miRNAs), long ncRNAs (lncRNAs) and so on. Emerging evidence shows that transferring biological information through EVs to neighboring cells in intercellular communication not only keep physiological functions, but also participate in the pathogenesis of liver diseases. Liver diseases often promote release of EVs and/or in different cargo sorting into these EVs. Either of these modifications can promote disease pathogenesis. Given this fact, EV-associated ncRNAs, such as miR-192, miR-122 and lncRNA-ROR and so on, can serve as new diagnostic biomarkers and new therapeutic targets for liver disease, because altered EV-associated ncRNAs may reflect the underlying liver disease condition. In this review, we focus on understanding the emerging role of EV-associated ncRNAs in viral hepatitis, liver fibrosis, alcoholic hepatitis (AH), non-alcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC) and discuss their utility in biomarker discovery and therapeutics. A better understanding of this multifaceted pattern of communication between different type cells in liver may contribute to developing novel approaches for personalized diagnostics and therapeutics.

Human Cytomegalovirus Replication Is Inhibited by the Autophagy-Inducing Compounds Trehalose and SMER28 through Distinctively Different Mechanisms

Human cytomegalovirus (HCMV) is the top viral cause of birth defects worldwide, and current therapies have high toxicity. We previously reported that the mTOR-independent autophagy-inducing disaccharide trehalose inhibits HCMV replication in multiple cell types. Here, we examine the mechanism of inhibition and introduce the autophagy inducer SMER28 as an additional inhibitor of HCMV acting through a different mechanism. We find that trehalose induces vacuolation and acidification of vacuoles and that debris, including debris with an appearance consistent with that of abnormal virions, is present in multivesicular bodies. Trehalose treatment increased the levels of Rab7, a protein required for lysosomal biogenesis and fusion, and slightly decreased the levels of Rab11, which is associated with recycling endosomes. We also present evidence that trehalose can promote autophagy without altering cellular glucose uptake. We show that SMER28 inhibits HCMV at the level of early protein production and interferes with viral genome replication in a cell type-dependent fashion. Finally, we show that SMER28 treatment does not cause the vacuolation, acidification, or redistribution of Rab7 associated with trehalose treatment and shows only a modest and cell type-dependent effect on autophagy. We propose a model in which the reciprocal effects on Rab7 and Rab11 induced by trehalose contribute to the redirection of enveloped virions from the plasma membrane to acidified compartments and subsequent degradation, and SMER28 treatment results in decreased expression levels of early and late proteins, reducing the number of virions produced without the widespread vacuolation characteristic of trehalose treatment.IMPORTANCE There is a need for less toxic HCMV antiviral drugs, and modulation of autophagy to control viral infection is a new strategy that takes advantage of virus dependence on autophagy inhibition. The present study extends our previous work on trehalose by showing a possible mechanism of action and introduces another autophagy-inducing compound, SMER28, that is effective against HCMV in several cell types. The mechanism by which trehalose induces autophagy is currently unknown, although our data show that trehalose does not inhibit cellular glucose uptake in cells relevant for HCMV replication but instead alters virion degradation by promoting acidic vacuolization. The comparison of our cell types and those used by others highlights the cell type-dependent nature of studying autophagy.

Tetraspanin CD63 Bridges Autophagic and Endosomal Processes To Regulate Exosomal Secretion and Intracellular Signaling of Epstein-Barr Virus LMP1

The tetraspanin protein CD63 has been recently described as a key factor in extracellular vesicle (EV) production and endosomal cargo sorting. In the context of Epstein-Barr virus (EBV) infection, CD63 is required for the efficient packaging of the major viral oncoprotein latent membrane protein 1 (LMP1) into exosomes and other EV populations and acts as a negative regulator of LMP1 intracellular signaling. Accumulating evidence has also pointed to intersections of the endosomal and autophagy pathways in maintaining cellular secretory processes and as sites for viral assembly and replication. Indeed, LMP1 can activate the mammalian target of rapamycin (mTOR) pathway to suppress host cell autophagy and facilitate cell growth and proliferation. Despite the growing recognition of cross talk between endosomes and autophagosomes and its relevance to viral infection, little is understood about the molecular mechanisms governing endosomal and autophagy convergence. Here, we demonstrate that CD63-dependent vesicle protein secretion directly opposes intracellular signaling activation downstream of LMP1, including mTOR-associated proteins. Conversely, disruption of normal autolysosomal processes increases LMP1 secretion and dampens signal transduction by the viral protein. Increases in mTOR activation following CD63 knockout are coincident with the development of serum-dependent autophagic vacuoles that are acidified in the presence of high LMP1 levels. Altogether, these findings suggest a key role of CD63 in regulating the interactions between endosomal and autophagy processes and limiting cellular signaling activity in both noninfected and virally infected cells.IMPORTANCE The close connection between extracellular vesicles and viruses is becoming rapidly and more widely appreciated. EBV, a human gamma herpesvirus that contributes to the progression of a multitude of lymphomas and carcinomas in immunocompromised or genetically susceptible populations, packages its major oncoprotein, LMP1, into vesicles for secretion. We have recently described a role of the host cell protein CD63 in regulating intracellular signaling of the viral oncoprotein by shuttling LMP1 into exosomes. Here, we provide strong evidence of the utility of CD63-dependent EVs in regulating global intracellular signaling, including mTOR activation by LMP1. We also demonstrate a key role of CD63 in coordinating endosomal and autophagic processes to regulate LMP1 levels within the cell. Overall, this study offers new insights into the complex intersection of cellular secretory and degradative mechanisms and the implications of these processes in viral replication.

Exosomes: small vesicles with big roles in hepatocellular carcinoma

Despite improvements in the diagnosis and treatment of hepatocellular carcinoma (HCC), the prognosis is still poor. Pioneering work has demonstrated a potential role for tumour cell-derived exosomes (TEXs) in HCC. TEXs can mediate immune responses, antigen presentation and intracellular communication by serving as vehicles for the transfer of proteins, viruses, lipids and RNA between cells. An improved understanding of the roles played by exosomes could lead to a powerful new strategy for preventing and treating HCC. In this review, we summarise current understanding on the topic. The literature points to two faces of TEXs in HCC: 1) They can promote invasion, metastasis, immune evasion and modulation and 2) they can act as diagnostic and prognostic biomarkers, and can be used in anti-cancer drug resistance and immunotherapy in the future.

Atg5 Disassociates the V1V0-ATPase to Promote Exosome Production and Tumor Metastasis Independent of Canonical Macroautophagy

Autophagy and autophagy-related genes (Atg) have been attributed prominent roles in tumorigenesis, tumor growth, and metastasis. Extracellular vesicles called exosomes are also implicated in cancer metastasis. Here, we demonstrate that exosome production is strongly reduced in cells lacking Atg5 and Atg16L1, but this is independent of Atg7 and canonical autophagy. Atg5 specifically decreases acidification of late endosomes where exosomes are produced, disrupting the acidifying V₁V₀-ATPase by removing a regulatory component, ATP6V1E1, into exosomes. The effect of Atg5 on exosome production promotes the migration and in vivo metastasis of orthotopic breast cancer cells. These findings uncover mechanisms controlling exosome release and identify means by which autophagy-related genes can contribute to metastasis in autophagy-independent pathways.

Role of exosomes and exosomal microRNAs in hepatocellular carcinoma: Potential in diagnosis and antitumour treatments (Review)

Communication between hepatocellular carcinoma (HCC) cells and their environment is essential for the development and progression of HCC. Exosomes, which are microvesicles secreted by a number of cell types, are carriers of intercellular information and regulate the tumour microenvironment. Studies have demonstrated that exosomes are involved in the communication between HCC cells, endothelial cells and stem cells, and that they serve important roles in the metastasis and invasion, immune evasion and immunotherapy of HCC. In addition, the mechanism of HCC-derived exosome-mediated microRNA (miRNA) transfer is important in the environmental modulation of HCC growth and progression. As exosomes can be used for detecting and monitoring HCC, they can potentially serve as specific biomarkers for early-stage tumours and the tumour metastasis of HCC. Moreover, mesenchymal stem cell-derived exosomes can be transfected with miRNAs to inhibit HCC development. Therefore, as nucleic acid delivery vehicles, exosomes show a tremendous potential for effective treatment against HCC. In the present review, recent advances in our understanding of the source, composition and function of exosomes in HCC, and their potential value in the early diagnosis and treatment of HCC, are summarized.

Autophagy’s secret life: secretion instead of degradation

Autophagy is conventionally described as a degradative, catabolic pathway and a tributary to the lysosomal system where the cytoplasmic material sequestered by autophagosomes gets degraded. However, autophagosomes or autophagosome-related organelles do not always follow this route. It has recently come to light that autophagy can terminate in cytosolic protein secretion or release of sequestered material from the cells, rather than in their degradation. In this review, we address this relatively new but growing aspect of autophagy as a complex pathway, which is far more versatile than originally anticipated.

Isolation, BODIPY Labeling and Uptake of Exosomes in Hepatic Stellate Cells

Exosomes have emerged as an important mediator of intercellular communication. They are present in extracellular milieu and therefore, easily accessible by neighboring or distant cells. They carry mRNA, microRNAs and proteins within their vesicles and once internalized by recipient cells; they can modulate multiple signaling pathways with pleiotropic effects from inducing antiviral state to disease progression. We have previously shown that hepatitis C virus (HCV) infected hepatocytes or hepatoma cells harboring genome-length replicon secrete exosomes in culture supernatants. These exosomes are taken up by hepatic stellate cells (HSC) and activate them to induce fibrosis during HCV infection. Here, we describe detailed protocols for exosomes isolation and uptake of BODIPY labeled exosomes by hepatic stellate cells.

Autophagy and Inflammation

The cellular degradative pathway of autophagy has a fundamental role in immunity. Here, we review the function of autophagy and autophagy proteins in inflammation. We discuss how the autophagy machinery controls the burden of infectious agents while simultaneously limiting inflammatory pathologies, which often involves processes that are distinct from conventional autophagy. Among the newly emerging processes we describe are LC3-associated phagocytosis and targeting by autophagy proteins, both of which require many of the same proteins that mediate conventional autophagy. We also discuss how autophagy contributes to differentiation of myeloid and lymphoid cell types, coordinates multicellular immunity, and facilitates memory responses. Together, these functions establish an intimate link between autophagy, mucosal immunity, and chronic inflammatory diseases. Finally, we offer our perspective on current challenges and barriers to translation.

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.

Autophagy pathway induced by a plant virus facilitates viral spread and transmission by its insect vector

Many viral pathogens are persistently transmitted by insect vectors and cause agricultural or health problems. Generally, an insect vector can use autophagy as an intrinsic antiviral defense mechanism against viral infection. Whether viruses can evolve to exploit autophagy to promote their transmission by insect vectors is still unknown. Here, we show that the autophagic process is triggered by the persistent replication of a plant reovirus, rice gall dwarf virus (RGDV) in cultured leafhopper vector cells and in intact insects, as demonstrated by the appearance of obvious virus-containing double-membrane autophagosomes, conversion of ATG8-I to ATG8-II and increased level of autophagic flux. Such virus-containing autophagosomes seem able to mediate nonlytic viral release from cultured cells or facilitate viral spread in the leafhopper intestine. Applying the autophagy inhibitor 3-methyladenine or silencing the expression of Atg5 significantly decrease viral spread in vitro and in vivo, whereas applying the autophagy inducer rapamycin or silencing the expression of Torc1 facilitate such viral spread. Furthermore, we find that activation of autophagy facilitates efficient viral transmission, whereas inhibiting autophagy blocks viral transmission by its insect vector. Together, these results indicate a plant virus can induce the formation of autophagosomes for carrying virions, thus facilitating viral spread and transmission by its insect vector. We believe that such a role for virus-induced autophagy is common for vector-borne persistent viruses during their transmission by insect vectors.

Zika virus infection dysregulates human neural stem cell growth and inhibits differentiation into neuroprogenitor cells

The current outbreak of Zika virus-associated diseases in South America and its threat to spread to other parts of the world has emerged as a global health emergency. A strong link between Zika virus and microcephaly exists, and the potential mechanisms associated with microcephaly are under intense investigation. In this study, we evaluated the effect of Zika virus infection of Asian and African lineages (PRVABC59 and MR766) in human neural stem cells (hNSCs). These two Zika virus strains displayed distinct infection pattern and growth rates in hNSCs. Zika virus MR766 strain increased serine 139 phosphorylation of histone H2AX (γH2AX), a known early cellular response proteins to DNA damage. On the other hand, PRVABC59 strain upregulated serine 15 phosphorylation of p53, p21 and PUMA expression. MR766-infected cells displayed poly (ADP-ribose) polymerase (PARP) and caspase-3 cleavage. Interestingly, infection of hNSCs by both strains of Zika virus for 24 h, followed by incubation in astrocyte differentiation medium, induced rounding and cell death. However, astrocytes generated from hNSCs by incubation in differentiation medium when infected with Zika virus displayed minimal cytopathic effect at an early time point. Infected hNSCs incubated in astrocyte differentiating medium displayed PARP cleavage within 24–36 h. Together, these results showed that two distinct strains of Zika virus potentiate hNSC growth inhibition by different mechanisms, but both viruses strongly induce death in early differentiating neuroprogenitor cells even at a very low multiplicity of infection. Our observations demonstrate further mechanistic insights for impaired neuronal homeostasis during active Zika virus infection.

HCV-induced oxidative stress by inhibition of Nrf2 triggers autophagy and favors release of viral particles

Viruses are known to exploit the autophagic machinery for their own benefit. In case of the hepatitis C virus autophagy is induced. As autophagy serves as a degradation pathway to maintain cellular homeostasis, it is activated in response to cellular stress such as elevated levels of reactive oxygen species (ROS). Elevated levels of ROS trigger phosphorylation of the autophagic adaptor protein p62 on Ser349 (pS[349] p62) that is involved in the induction of autophagy. Consequently, pS[349] p62 binds with a higher affinity to Keap1 thereby releasing Nrf2 from the complex with Keap1. Although the released Nrf2 should induce as a heterodimer with the sMaf proteins the expression of Nrf2/ARE-dependent genes, in HCV-positive cells no activation of cytoprotective genes occurs even though elevated amounts of pS[349] p62 are present. In HCV-positive cells, free Nrf2 is trapped via delocalized sMaf proteins at the replicon complexes on the cytoplasmic face of the ER and is therefore prevented from its entry into the nucleus. Scavenging of ROS leads to decreased levels of pS[349] p62 and impaired induction of autophagy. Both, inhibition of autophagy and scavenging of ROS result in decreased amounts of released viral particles. Taken together, these data identify an intricate mechanism of HCV-dependent inhibition of Nrf2/ARE-mediated gene expression which counteracts pS[349] p62-induced activation of Nrf2. Thereby elevated ROS-levels are preserved that in turn activate autophagy to favor HCV particle release.

Hepatitis C Virus-Induced Autophagy and Host Innate Immune Response

Autophagy is a catabolic process that is important for maintaining cellular homeostasis. This pathway in hepatocytes is stimulated and controlled by the hepatitis C virus (HCV)—upon infection—to promote its own replication. HCV induces autophagy indirectly and directly through different mechanisms and temporally controls the autophagic flux. This enables the virus to maximize its replication and attenuate the innate immune responses that it activates. In this review, we discuss the relationship between HCV and autophagy, and the crosstalk between HCV-induced autophagy and host innate immune responses.

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.

Autophagy proteins in antigen processing for presentation on MHC molecules

Autophagy describes catabolic pathways that deliver cytoplasmic constituents for lysosomal degradation. Since major histocompatibility complex (MHC) molecules sample protein degradation products and present them to T cells for adaptive immunity, it is maybe not too surprising that autophagy contributes to this protein antigen processing for MHC presentation. However, the recently recognized breath of pathways, by which autophagy contributes to MHC antigen processing, is exciting. Macroautophagy does not only seem to deliver intracellular but facilitates also extracellular antigen processing by lysosomal hydrolysis for MHC class II presentation. Moreover, even MHC class I molecules that usually display proteasomal products are regulated by macroautophagy, probably using a pool of these molecules outside the endoplasmic reticulum, where MHC class I molecules are loaded with peptide during canonical MHC class I antigen processing. This review aims to summarize these recent developments and point out gaps of knowledge, which should be filled by further investigation, in order to harness the different antigen-processing pathways via autophagy for vaccine improvement.

TFEB-mediated activation of the lysosome-autophagy system affects the transduction efficiency of adeno-associated virus 2

Adeno-associated virus (AAV)-mediated gene transfer is an appealing therapeutic option due to AAV's safety profile. Effective delivery of AAV's genetic cargo to the nucleus, however, requires evasion of host cell barriers, including cellular clearance mechanisms mediated by the lysosome-autophagy system. We used AAV serotype 2 to monitor the autophagic response to cellular internalization of AAV and to characterize the effect of AAV-induced activation of autophagy on transgene expression. We found AAV2 internalization to induce activation of transcription factor EB, a master regulator of autophagy and lysosomal biogenesis, and upregulation of the lysosome-autophagy system. We showed that AAV2-induced activation of autophagy parallels a reduction in transgene expression, but also an increase in autophagic clearance of protein aggregates. These results can inform the design of AAV vectors with autophagy-modulating properties for applications ranging from the design of efficient gene delivery vectors to the treatment of diseases characterized by accumulation of autophagic cargo.

Identification of syntaxin 4 as an essential factor for the hepatitis C virus life cycle

Although there is evidence that multivesicular bodies (MVBs) are involved in the release of hepatitis C virus (HCV), many aspects of HCV release are still not fully understood. The amount of α-taxilin that prevents SNARE (soluble N-ethylmaleimidesensitive factor attachment protein receptor) complex formation by binding to free syntaxin 4 is reduced in HCV-positive cells. Therefore, it was analyzed whether the t-SNARE protein syntaxin 4 which mediates vesicles fusion is involved in the HCV life cycle. HCV-positive cells possess an increased amount of syntaxin 4 protein, although the amount of syntaxin 4-specific transcripts is decreased in HCV-positive Huh7.5 cells and in HCV-infected primary human hepatocytes. In HCV-positive cells a significant longer half-life of syntaxin 4 was found that overcompensates for the decreased expression and leads to the elevated level of syntaxin 4. Overexpression of syntaxin 4 reduces the intracellular amount of infectious viral particles by facilitating viral release, while silencing of syntaxin 4 expression using specific siRNAs inhibits the release of HCV particles and so leads to an increase in the intracellular amount of infectious viral particles. This indicates that HCV uses a SNARE-dependent pathway for viral release. Confocal immunofluorescence microscopy revealed a colocalization of syntaxin 4 with a MVB-specific marker, exosomes and HCV core, which suggests a fraction of syntaxin 4 is associated with exosomes loaded with HCV. Altogether, it is assumed that syntaxin 4 is a novel essential cellular factor for the release of HCV.

Attachment and Postattachment Receptors Important for Hepatitis C Virus Infection and Cell-to-Cell Transmission

Hepatitis C virus (HCV) requires multiple receptors for its attachment to and entry into cells. Our previous studies found that human syndecan-1 (SDC-1), SDC-2, and T cell immunoglobulin and mucin domain-containing protein 1 (TIM-1) are HCV attachment receptors. Other cell surface molecules, such as CD81, Claudin-1 (CLDN1), Occludin (OCLN), SR-BI, and low-density lipoprotein receptor (LDLR), function mainly at postattachment steps and are considered postattachment receptors. The underlying molecular mechanisms of different receptors in HCV cell-free and cell-to-cell transmission remain elusive. In the present study, we used a clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 technology, gene-specific small interfering RNAs, and a newly developed luciferase-based reporter system to quantitatively determine the importance of individual receptors in HCV cell-free and cell-to-cell transmission. Knockouts of SDC-1 and SDC-2 resulted in remarkable reductions of HCV infection and cell attachment, whereas SDC-3 and SDC-4 knockouts did not affect HCV infection. Defective HCV attachment to SDC-1 and/or SDC-2 knockout cells was completely restored by SDC-1 and SDC-2 but not SDC-4 expression. Knockout of the attachment receptors SDC-1, SDC-2, and TIM-1 also modestly decreased HCV cell-to-cell transmission. In contrast, silencing and knockout of the postattachment receptors CD81, CLDN1, OCLN, SR-BI, and LDLR greatly impaired both HCV cell-free and cell-to-cell transmission. Additionally, apolipoprotein E was found to be important for HCV cell-to-cell spread, but very-low-density lipoprotein (VLDL)-containing mouse serum did not affect HCV cell-to-cell transmission, although it inhibited cell-free infection. These findings demonstrate that attachment receptors are essential for initial HCV binding and that postattachment receptors are important for both HCV cell-free and cell-to-cell transmission.IMPORTANCE The importance and underlying molecular mechanisms of cell surface receptors in HCV cell-free and cell-to-cell transmission are poorly understood. The role of some of the HCV attachment and postattachment receptors in HCV infection and cell-to-cell spread remains controversial. Using CRISPR-Cas9-mediated knockouts of specific cellular genes, we demonstrate that both SDC-1 and SDC-2, but not SDC-3 or SDC-4, are bona fide HCV attachment receptors. We also used a newly developed luciferase-based reporter system to quantitatively determine the importance of attachment and postattachment receptors in HCV cell-to-cell transmission. SDC-1, SDC-2, TIM-1, and SR-BI were found to modestly promote HCV cell-to-cell spread. CD81, CLDN1, OCLN, and LDLR play more important roles in HCV cell-to-cell transmission. Likewise, apolipoprotein E (apoE) is critically important for HCV cell-to-cell spread, unlike VLDL-containing mouse serum, which did not affect HCV cell-to-cell spread. These findings suggest that the mechanism(s) of HCV cell-to-cell spread differs from that of cell-free infection.

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.