HCV infection induces mitochondrial bioenergetic unbalance: causes and effects

Involvement of mitochondrial fatty acid β-oxidation in the antiviral innate immune response in head kidney macrophages of large yellow croaker (Larimichthys crocea)

As a vital pathway for cellular energy production, mitochondrial fatty acid β-oxidation (FAO) is essential in regulating immune responses to bacterial pathogens and maintaining intracellular homeostasis in vertebrates. However, the specific role of FAO in antiviral innate immune response in macrophages remains insufficiently understood. In this study, virus infection simulated by poly(I:C) inhibited FAO, as indicated by the reduced expression of FAO-related genes and proteins in the head kidney of large yellow croaker, with similar results observed in poly(I:C)-stimulated macrophages. Then, inhibition of FAO by supplementary mildronate in vivo and etomoxir treatment in vitro revealed varying increases in the mRNA expression of antiviral innate immune response genes after stimulated by poly(I:C) in the head kidney and macrophages. Notably, etomoxir significantly facilitated the transcriptional up-regulation of the IFNh promoter by IRF3. Moreover, inhibiting FAO by knockdown of cpt1b promoted antiviral innate immune response triggered by poly(I:C) in macrophages. Conversely, activating FAO through overexpression of cpt1b or cpt2 significantly reduced the mRNA levels of antiviral response genes in macrophages stimulated by poly(I:C). Unlike etomoxir, cpt1b overexpression inhibited the transcriptional up-regulation of the IFNh promoter by IRF3. Furthermore, in vivo dietary palm oil feeding and in vitro exposure to palmitic acid inhibited the antiviral innate immune response triggered by poly(I:C) in the head kidney and macrophages, respectively. These effects were partly associated with FAO activation, as evidenced by etomoxir. In summary, this study elucidates FAO's critical role in regulating antiviral innate immune response in head kidney macrophages. These findings not only deepen insights into the interaction between metabolic remodeling and host immune responses, but also offer valuable guidance for developing nutritional strategies to improve antiviral immunity in aquaculture.

Positive-strand RNA virus replication organelles at a glance

Membrane-bound replication organelles (ROs) are a unifying feature among diverse positive-strand RNA viruses. These compartments, formed as alterations of various host organelles, provide a protective niche for viral genome replication. Some ROs are characterised by a membrane-spanning pore formed by viral proteins. The RO membrane separates the interior from immune sensors in the cytoplasm. Recent advances in imaging techniques have revealed striking diversity in RO morphology and origin across virus families. Nevertheless, ROs share core features such as interactions with host proteins for their biogenesis and for lipid and energy transfer. The restructuring of host membranes for RO biogenesis and maintenance requires coordinated action of viral and host factors, including membrane-bending proteins, lipid-modifying enzymes and tethers for interorganellar contacts. In this Cell Science at a Glance article and the accompanying poster, we highlight ROs as a universal feature of positive-strand RNA viruses reliant on virus-host interplay, and we discuss ROs in the context of extensive research focusing on their potential as promising targets for antiviral therapies and their role as models for understanding fundamental principles of cell biology.

Does oncolytic viruses-mediated metabolic reprogramming benefit or harm the immune microenvironment?

Oncolytic virus immunotherapy as a new tumor therapy has made remarkable achievements in clinical practice. And metabolic reprogramming mediated by oncolytic virus has a significant impact on the immune microenvironment. This review summarized the reprogramming of host cell glucose metabolism, lipid metabolism, oxidative phosphorylation, and glutamine metabolism by oncolytic virus and illustrated the effects of metabolic reprogramming on the immune microenvironment. It was found that oncolytic virus-induced reprogramming of glucose metabolism in tumor cells has both beneficial and detrimental effects on the immune microenvironment. In addition, oncolytic virus can promote fatty acid synthesis in tumor cells, inhibit oxidative phosphorylation, and promote glutamine catabolism, which facilitates the anti-tumor immune function of immune cells. Therefore, targeted metabolic reprogramming is a new direction to improve the efficacy of oncolytic virus immunotherapy.

Leveraging metformin to combat hepatocellular carcinoma: its therapeutic promise against hepatitis viral infections

Hepatocellular carcinoma (HCC) is categorized among the most common primary malignant liver cancer and a primary global cause of death from cancer. HCC tends to affect males 2-4 times more than females in many nations. The main factors that raise the incidence of HCC are chronic liver diseases, hepatotropic viruses like hepatitis B (HBV) and C (HCV), non-alcoholic fatty liver disease, exposure to toxins like aflatoxin, and non-alcoholic steatohepatitis (NASH). Among these, hepatitis B and C are the most prevalent causes of chronic hepatitis globally. Metformin, which is made from a naturally occurring compound called galegine, derived from the plant Galega officinalis (G. officinalis ), has been found to exhibit antitumor effects in a wide range of malignancies, including HCC. In fact, compared to patients on sulphonylureas or insulin, studies have demonstrated that metformin treatment significantly lowers the risk of HCC in patients with chronic liver disease. This article will first describe the molecular mechanism of hepatitis B and C viruses in the development of HCC. Then, we will provide detailed explanations about metformin, followed by a discussion of the association between metformin and hepatocellular carcinoma caused by the viruses mentioned above.

HCV and HCC Tango-Deciphering the Intricate Dance of Disease: A Review Article

Hepatitis C virus (HCV) is a major cause of hepatocellular carcinoma (HCC) accounting for around one-third of all HCC cases. Prolonged inflammation in chronic hepatitis C (CHC), maintained through a variety of pro- and anti-inflammatory mediators, is one of the aspects of carcinogenesis, followed by mitochondrial dysfunction and oxidative stress. Immune response dysfunction including the innate and adaptive immunity also plays a role in the development, as well as in the recurrence of HCC after treatment. Some of the tumor suppressor genes inhibited by the HCV proteins are p53, p73, and retinoblastoma 1. Mutations in the telomerase reverse transcriptase promoter and the oncogene catenin beta 1 are two more important carcinogenic signaling pathways in HCC associated with HCV. Furthermore, in HCV-related HCC, numerous tumor suppressor and seven oncogenic genes are dysregulated by epigenetic changes. Epigenetic regulation of gene expression is considered as a lasting "epigenetic memory", suggesting that HCV-induced changes persist and are associated with liver carcinogenesis even after cure. Epigenetic changes and immune response dysfunction are recognized targets for potential therapy of HCC.

Comparison of serum acylcarnitine levels in patients with myalgic encephalomyelitis/chronic fatigue syndrome and healthy controls: a systematic review and meta-analysis

BACKGROUND

Myalgic encephalomyelitis/chronic fatigue syndrome/systemic exertion intolerance disease (ME/CFS/SEID) is a condition diagnosed primarily based on clinical symptoms, including prolonged fatigue and post-exertional malaise; however, there is no specific test for the disease. Additionally, diagnosis can be challenging since healthcare professionals may lack sufficient knowledge about the disease. Prior studies have shown that patients with ME/CFS/SEID have low serum acylcarnitine levels, which may serve as a surrogate test for patients suspected of having this disease. This systematic review and meta-analysis aimed to investigate the differences in serum acylcarnitine levels between patients with ME/CFS/SEID and healthy controls.

METHODS

This systematic review was conducted using PubMed and Ichushi-Web databases. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement, we included all studies from the databases' inception until February 17, 2023, that evaluated blood tests in both patients with ME/CFS/SEID and healthy control groups. The primary endpoint was the difference in serum acylcarnitine levels between the two groups.

RESULTS

The electronic search identified 276 studies. Among them, seven met the eligibility criteria. The serum acylcarnitine levels were analyzed in 403 patients with ME/CFS/SEID. The patient group had significantly lower serum acylcarnitine levels when compared with the control group, and the statistical heterogeneity was high.

CONCLUSION

The patient group had significantly lower serum acylcarnitine levels when compared with the control group. In the future, the measurement of serum acylcarnitine levels, in addition to clinical symptoms, may prove to be a valuable diagnostic tool for this condition.

A case of post-COVID-19 myalgic encephalomyelitis/chronic fatigue syndrome characterized by post-exertional malaise and low serum acylcarnitine level

COVID-19 afflicts patients with acute symptoms and longer term sequelae. One of the sequelae is myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), which is often difficult to diagnose, having no established tests. In this article, we synthesize information from literature reviews on patients with ME/CSF that developed after recovery from COVID-19.

Redox Control of the Immune Response in the Hepatic Progenitor Cell Niche

The liver commonly self-regenerates by a proliferation of mature cell types. Nevertheless, in case of severe or protracted damage, the organ renewal is mediated by the hepatic progenitor cells (HPCs), adult progenitors capable of differentiating toward the biliary and the hepatocyte lineages. This regeneration process is determined by the formation of a stereotypical niche surrounding the emerging progenitors. The organization of the HPC niche microenvironment is crucial to drive biliary or hepatocyte regeneration. Furthermore, this is the site of a complex immunological activity mediated by several immune and non-immune cells. Indeed, several cytokines produced by monocytes, macrophages and T-lymphocytes may promote the activation of HPCs in the niche. On the other side, HPCs may produce pro-inflammatory cytokines induced by liver inflammation. The inflamed liver is characterized by high generation of reactive oxygen and nitrogen species, which in turn lead to the oxidation of macromolecules and the alteration of signaling pathways. Reactive species and redox signaling are involved in both the immunological and the adult stem cell regeneration processes. It is then conceivable that redox balance may finely regulate the immune response in the HPC niche, modulating the regeneration process and the immune activity of HPCs. In this perspective article, we summarize the current knowledge on the role of reactive species in the regulation of hepatic immunity, suggesting future research directions for the study of redox signaling on the immunomodulatory properties of HPCs.

Targeted Metabolic Reprogramming to Improve the Efficacy of Oncolytic Virus Therapy

Oncolytic viruses (OVs) represent a promising new class of cancer therapeutics and cause antitumor effects by two major mechanisms: (1) directly killing cancer cells in a process known as oncolysis, or (2) initiating a powerful antitumor immune response. Interestingly, energy metabolism, within either cancer cells or immune cells, plays a pivotal role in defining the outcome of OV-mediated antitumor effects. Following therapeutic administration, OVs must hijack host cell metabolic pathways to acquire building blocks such as nucleotides, lipids, and amino acids for the process of replication that is necessary for oncolysis. Additionally, OV-stimulated antitumor immune responses are highly dependent on the metabolic state within the tumor microenvironment. Thus, metabolic reprogramming strategies bear the potential to enhance the efficacy of both OV-mediated oncolysis and antitumor immune responses.

Hepatitis C Virus Downregulates Core Subunits of Oxidative Phosphorylation, Reminiscent of the Warburg Effect in Cancer Cells

Hepatitis C Virus (HCV) mainly infects liver hepatocytes and replicates its single-stranded plus strand RNA genome exclusively in the cytoplasm. Viral proteins and RNA interfere with the host cell immune response, allowing the virus to continue replication. Therefore, in about 70% of cases, the viral infection cannot be cleared by the immune system, but a chronic infection is established, often resulting in liver fibrosis, cirrhosis and hepatocellular carcinoma (HCC). Induction of cancer in the host cells can be regarded to provide further advantages for ongoing virus replication. One adaptation in cancer cells is the enhancement of cellular carbohydrate flux in glycolysis with a reduction of the activity of the citric acid cycle and aerobic oxidative phosphorylation. To this end, HCV downregulates the expression of mitochondrial oxidative phosphorylation complex core subunits quite early after infection. This so-called aerobic glycolysis is known as the “Warburg Effect” and serves to provide more anabolic metabolites upstream of the citric acid cycle, such as amino acids, pentoses and NADPH for cancer cell growth. In addition, HCV deregulates signaling pathways like those of TNF-β and MAPK by direct and indirect mechanisms, which can lead to fibrosis and HCC.

Oxidative stress response in the pathogenesis of dengue virus virulence, disease prognosis and therapeutics: an update

Dengue virus (DENV) is a mosquito-borne arbovirus that causes febrile illness and can lead to a potentially lethal disease. The mechanism of disease pathogenesis is not completely understood, and there are currently no vaccines or therapeutic drugs available to protect against all four serotypes of DENV. Although many reasons have been suggested for the development of the disease, dengue studies have shown that, during DENV infection, there is an imbalance between oxidants and antioxidants that disrupts homeostasis. An increase in reactive oxygen species (ROS) levels triggers the sudden release of cytokines, which can lead to plasma leakage and other severe symptoms. In the present review, we give an overview of the oxidative stress response and its effect on the progression of dengue disease. We also discuss the role of oxidative-stress-associated molecules in disease prognostic and therapeutics.

Transforming Growth Factor β Acts as a Regulatory Molecule for Lipogenic Pathways among Hepatitis C Virus Genotype-Specific Infections

Hepatitis C virus (HCV) infection promotes metabolic disorders, and the severity of lipogenic disease depends upon the infecting virus genotype. Here, we have examined HCV genotype 1-, 2-, or 3-specific regulation of lipid metabolism, involving transforming growth factor β (TGF-β)-regulated phospho-Akt (p-Akt) and peroxisome proliferator-activated receptor alpha (PPARα) axes. Since HCV core protein is one of the key players in metabolic regulation, we also examined its contribution in lipid metabolic pathways. The expression of regulatory molecules, TGF-β1/2, phospho-Akt (Ser473), PPARα, sterol regulatory element-binding protein 1 (SREBP-1), fatty acid synthase (FASN), hormone-sensitive lipase (HSL), and acyl dehydrogenases was analyzed in virus-infected hepatocytes. Interestingly, HCV genotype 3a exhibited much higher activation of TGF-β and p-Akt, with a concurrent decrease in PPARα expression and fatty acid oxidation. A significant and similar decrease in HSL, unlike in HCV genotype 1a, was observed with both genotypes 2a and 3a. Similar observations were made from ectopic expression of the core genomic region from each genotype. The key role of TGF-β was further verified using specific small interfering RNA (siRNA). Together, our results highlight a significant difference in TGF-β-induced activity for the HCV genotype 2a- or 3a-induced lipogenic pathway, exhibiting higher triglyceride synthesis and a decreased lipolytic mechanism. These results may help in therapeutic modalities for early treatment of HCV genotype-associated lipid metabolic disorders.IMPORTANCE Hepatic steatosis is a frequent complication associated with chronic hepatitis C virus (HCV) infection and is a key prognostic indicator for progression to fibrosis and cirrhosis. Several mechanisms are proposed for the development of steatosis, especially with HCV genotype 3a. Our observations suggest that transforming growth factor β (TGF-β) and peroxisome proliferator-activated receptor alpha (PPARα)-associated mechanistic pathways in hepatocytes infected with HCV genotype 2a and 3a differ from those in cells infected with genotype 1a. The results suggest that a targeted therapeutic approach for enhanced PPARα and lipolysis may reduce HCV genotype-associated lipid metabolic disorder in liver disease.

Competition for nutrients and its role in controlling immune responses

Changes in cellular metabolism are associated with the activation of diverse immune subsets. These changes are fuelled by nutrients including glucose, amino acids and fatty acids, and are closely linked to immune cell fate and function. An emerging concept is that nutrients are not equally available to all immune cells, suggesting that the regulation of nutrient utility through competitive uptake and use is important for controlling immune responses. This review considers immune microenvironments where nutrients become limiting, the signalling alterations caused by insufficient nutrients, and the importance of nutrient availability in the regulation of immune responses.

Immune cells adapt distinct metabolic strategies to accommodate specific functions associated with cell types or differentiation stages. Here in this review the authors discuss the nutrients, sensors, and mediators of such a metabolic adaption in nutrient-limiting immune microenvironments such as tumors or infections.

Cellular Gene Expression during Hepatitis C Virus Replication as Revealed by Ribosome Profiling

Background: Hepatitis C virus (HCV) infects human liver hepatocytes, often leading to liver cirrhosis and hepatocellular carcinoma (HCC). It is believed that chronic infection alters host gene expression and favors HCC development. In particular, HCV replication in Endoplasmic Reticulum (ER) derived membranes induces chronic ER stress. How HCV replication affects host mRNA translation and transcription at a genome wide level is not yet known. Methods: We used Riboseq (Ribosome Profiling) to analyze transcriptome and translatome changes in the Huh-7.5 hepatocarcinoma cell line replicating HCV for 6 days. Results: Established viral replication does not cause global changes in host gene expression—only around 30 genes are significantly differentially expressed. Upregulated genes are related to ER stress and HCV replication, and several regulated genes are known to be involved in HCC development. Some mRNAs (PPP1R15A/GADD34, DDIT3/CHOP, and TRIB3) may be subject to upstream open reading frame (uORF) mediated translation control. Transcriptional downregulation mainly affects mitochondrial respiratory chain complex core subunit genes. Conclusion: After establishing HCV replication, the lack of global changes in cellular gene expression indicates an adaptation to chronic infection, while the downregulation of mitochondrial respiratory chain genes indicates how a virus may further contribute to cancer cell-like metabolic reprogramming (“Warburg effect”) even in the hepatocellular carcinoma cells used here.

Redox cell signaling and hepatic progenitor cells

Hepatic diseases are widespread in the world and organ transplantation is currently the only treatment for liver failure. New cell-based approaches have been considered, since stem cells may represent a possible source to treat liver diseases. Acute and chronic liver diseases are characterized by high production of reactive oxygen and nitrogen species, with consequent oxidative modifications of cellular macromolecules and alteration of signaling pathways, metabolism and cell cycle. Although considered harmful molecules, reactive species are involved in cell growth and differentiation processes, modulating the activity of transcription factors, which take part in stemness/proliferation. It is conceivable that redox balance may regulate the development of hepatic progenitor cells, function and survival in synchrony with metabolism during chronic liver diseases. This review aims to summarize diverse redox-sensitive signaling pathways involved in stem cell fate, highlighting the important role of hepatic progenitor cells as a possible source to treat end-stage liver disease for organ regeneration.

Tissue-resident NK cells differ in their expression profile of the nutrient transporters Glut1, CD98 and CD71

Metabolism is a critical basis for immune cell functionality. It was recently shown that NK cell subsets from peripheral blood modulate their expression of nutrient receptors following cytokine stimulation, demonstrating that NK cells can adjust to changes in metabolic requirements. As nutrient availability in blood and tissues can significantly differ, we examined NK cells isolated from paired blood-liver and blood-spleen samples and compared expression of the nutrient transporters Glut1, CD98 and CD71. CD56^bright tissue-resident (CXCR6⁺) NK cells derived from livers and spleens expressed lower levels of Glut1 but higher levels of the amino acid transporter CD98 following stimulation than CD56^bright NK cells from peripheral blood. In line with that, CD56^dim NK cells, which constitute the main NK cell population in the peripheral blood, expressed higher levels of Glut1 and lower levels of CD98 and CD71 compared to liver CD56^bright NK cells. Our results show that NK cells from peripheral blood differ from liver- and spleen-resident NK cells in the expression profile of nutrient transporters, consistent with a cell-adaptation to the different nutritional environment in these compartments.

Targeting Endoplasmic Reticulum and/or Mitochondrial Ca2+ Fluxes as Therapeutic Strategy for HCV Infection

Chronic hepatitis C is characterized by metabolic disorders and by a microenvironment in the liver dominated by oxidative stress, inflammation and regeneration processes that can in the long term lead to liver cirrhosis and hepatocellular carcinoma. Several lines of evidence suggest that mitochondrial dysfunctions play a central role in these processes. However, how these dysfunctions are induced by the virus and whether they play a role in disease progression and neoplastic transformation remains to be determined. Most in vitro studies performed so far have shown that several of the hepatitis C virus (HCV) proteins also localize to mitochondria, but the consequences of these interactions on mitochondrial functions remain contradictory and need to be confirmed in the context of productively replicating virus and physiologically relevant in vitro and in vivo model systems. In the past decade we have been proposing a temporal sequence of events in the HCV-infected cell whereby the primary alteration is localized at the mitochondria-associated ER membranes and causes release of Ca²⁺ from the ER, followed by uptake into mitochondria. This ensues successive mitochondrial dysfunction leading to the generation of reactive oxygen and nitrogen species and a progressive metabolic adaptive response consisting in decreased oxidative phosphorylation and enhanced aerobic glycolysis and lipogenesis. Here we resume the major results provided by our group in the context of HCV-mediated alterations of the cellular inter-compartmental calcium flux homeostasis and present new evidence suggesting targeting of ER and/or mitochondrial calcium transporters as a novel therapeutic strategy.

Mitochondrial Proteins Coded by Human Tumor Viruses

Viruses must exploit the cellular biosynthetic machinery and evade cellular defense systems to complete their life cycles. Due to their crucial roles in cellular bioenergetics, apoptosis, innate immunity and redox balance, mitochondria are important functional targets of many viruses, including tumor viruses. The present review describes the interactions between mitochondria and proteins coded by the human tumor viruses human T-cell leukemia virus type 1, Epstein-Barr virus, Kaposi's sarcoma-associated herpesvirus, human hepatitis viruses B and C, and human papillomavirus, and highlights how these interactions contribute to viral replication, persistence and transformation.

Molecular basis of hepatocellular carcinoma induced by hepatitis C virus infection

Present study outlines a comprehensive view of published information about the underlying mechanisms operational for progression of chronic hepatitis C virus (HCV) infection to development of hepatocellular carcinoma (HCC). These reports are based on the results of animal experiments and human based studies. Although, the exact delineated mechanism is not yet established, there are evidences available to emphasize the involvement of HCV induced chronic inflammation, oxidative stress, insulin resistance, endoplasmic reticulum stress, hepato steatosis and liver fibrosis in the progression of HCV chronic disease to HCC. Persistent infection with replicating HCV not only initiates several liver alterations but also creates an environment for development of liver cancer. Various studies have reported that HCV acts both directly as well as indirectly in promoting this process. Whereas HCV related proteins, like HCV core, E1, E2, NS3 and NS5A, modulate signal pathways dysregulating cell cycle and cell metabolism, the chronic infection produces similar changes in an indirect way. HCV is an RNA virus and does not integrate with host genome and therefore, HCV induced hepatocarcinogenesis pursues a totally different mechanism causing imbalance between suppressors and proto-oncogenes and genomic integrity. However, the exact mechanism of HCC inducement still needs a full understanding of various steps involved in this process.

Implications of oxidative stress on viral pathogenesis

Reactive species are frequently formed after viral infections. Antioxidant defences, including enzymatic and non-enzymatic components, protect against reactive species, but sometimes these defences are not completely adequate. An imbalance in the production of reactive species and the body's inability to detoxify these reactive species is referred to as oxidative stress. The aim of this review is to analyse the role of oxidative stress in the pathogenesis of viral infections and highlight some major therapeutic approaches that have gained importance, with regards to controlling virus-induced oxidative injury. Attention will be focused on DNA viruses (papillomaviruses, hepadnaviruses), RNA viruses (flaviviruses, orthomyxoviruses, paramyxoviruses, togaviruses) and retroviruses (human immunodeficiency virus). In general, viruses cause an imbalance in the cellular redox environment, which depending on the virus and the cell can result in different responses, e.g. cell signaling, antioxidant defences, reactive species, and other processes. Therefore, the modulation of reactive species production and oxidative stress potentially represents a novel pharmacological approach for reducing the consequences of viral pathogenesis.

Magnetomitotransfer: An efficient way for direct mitochondria transfer into cultured human cells

In the course of mitochondrial diseases standard care mostly focuses on treatment of symptoms, while therapeutic approaches aimed at restoring mitochondrial function are currently still in development. The transfer of healthy or modified mitochondria into host cells would open up the possibilities of new cell therapies. Therefore, in this study, a novel method of mitochondrial transfer is proposed by anti-TOM22 magnetic bead-labeled mitochondria with the assistance of a magnetic plate. In comparison to the passive transfer method, the magnetomitotransfer method was more efficient at transferring mitochondria into cells (78–92% vs 0–17% over 3 days). This transfer was also more rapid, with a high ratio of magnetomitotransferred cells and high density of transferred mitochondria within the first day of culture. Importantly, transferred mitochondria appeared to be functional as they strongly enhanced respiration in magnetomitotransferred cells. The novel method of magnetomitotransfer may offer potential for therapeutic approaches for treatment of a variety of mitochondria-associated pathologies, e.g. various neurodegenerative diseases.

Molecular mechanisms of hepatitis C virus-induced hepatocellular carcinoma

Hepatitis C virus (HCV) is a major leading cause of hepatocellular carcinoma (HCC). HCV-induced hepatocarcinogenesis is a multistep process resulting from a combination of pathway alterations that are either caused directly by viral factors or immune mediated as a consequence of a chronic state of inflammation. Host genetic variation is now emerging as an additional element that contribute to increase the risk of developing HCC. The advent of direct-acting antiviral agents foresees a rapid decline of HCC rate in HCV patients. However, a full understanding of the HCV-mediated tumourigenic process is required to elucidate if pro-oncogenic signatures may persist after virus clearance, and to identify novel tools for HCC prevention and therapy. In this review, we summarize the current knowledge of the molecular mechanisms responsible for HCV-induced hepatocarcinogenesis.

Structural Changes In Cells Imaged by Soft X-ray Cryo-Tomography During Hepatitis C Virus Infection

Chronic hepatitis C virus (HCV) infection causes severe liver disease in millions of humans worldwide. Pathogenesis of HCV infection is strongly driven by a deficient immune response of the host, although intersection of different aspects of the virus life cycle with cellular homeostasis is emerging as an important player in the pathogenesis and progression of the disease. Cryo soft X-ray tomography (cryo-SXT) was performed to investigate the ultrastructural alterations induced by the interference of HCV replication with cellular homeostasis. Native, whole cell, three-dimensional (3D) maps were obtained in HCV replicon-harboring cells and in a surrogate model of HCV infection. Tomograms from HCV-replicating cells show blind-ended endoplasmic reticulum tubules with pseudospherical extrusions and marked alterations of mitochondrial morphology that correlated spatially with the presence of endoplasmic reticulum alterations, suggesting a short-range influence of the viral machinery on mitochondrial homeostasis. Both mitochondrial and endoplasmic reticulum alterations could be reverted by a combination of sofosbuvir/daclatasvir, which are clinically approved direct-acting antivirals for the treatment of chronic HCV infection. In addition to providing structural insight into cellular aspects of HCV pathogenesis, our study illustrates how cryo-SXT is a powerful 3D wide-field imaging tool for the assessment and understanding of complex cellular processes in a setting of near-native whole hydrated cells. Our results also constitute a proof of concept for the use of cryo-SXT as a platform that enables determining the potential impact of candidate compounds on the ultrastructure of the cell that may assist drug development at a preclinical level.

Metabolic regulation of natural killer cells

Natural killer (NK) cells have key roles in anti-viral and anti-tumour immune responses. Recent research demonstrates that cellular metabolism is an important determinant for the function of pro-inflammatory immune cells, including activated NK cells. The mammalian target of rapamcyin (mTOR) complex 1 (mTORC1) has been identified as a key metabolic regulator that promotes glycolytic metabolism in multiple immune cell subsets. Glycolysis is integrally linked to pro-inflammatory immune responses such that activated NK cells and effector T-cell subsets are reliant on sufficient glucose availability for maximal effector function. This article will discuss the regulation of cellular metabolism in NK cells as compared with that of T lymphocytes and discuss the implications for NK cell responses to viral infection and cancer.

Quantitative Proteomics Identifies Serum Response Factor Binding Protein 1 as a Host Factor for Hepatitis C Virus Entry

Hepatitis C virus (HCV) enters human hepatocytes through a multistep mechanism involving, among other host proteins, the virus receptor CD81. How CD81 governs HCV entry is poorly characterized, and CD81 protein interactions after virus binding remain elusive. We have developed a quantitative proteomics protocol to identify HCV-triggered CD81 interactions and found 26 dynamic binding partners. At least six of these proteins promote HCV infection, as indicated by RNAi. We further characterized serum response factor binding protein 1 (SRFBP1), which is recruited to CD81 during HCV uptake and supports HCV infection in hepatoma cells and primary human hepatocytes. SRFBP1 facilitates host cell penetration by all seven HCV genotypes, but not of vesicular stomatitis virus and human coronavirus. Thus, SRFBP1 is an HCV-specific, pan-genotypic host entry factor. These results demonstrate the use of quantitative proteomics to elucidate pathogen entry and underscore the importance of host protein-protein interactions during HCV invasion.

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Hepatitis C virus binding alters host protein interactions with the receptor CD81

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Six out of 26 virus-dependent CD81-interacting proteins promote virus entry

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SRFBP1 binds CD81 and aids infection of all HCV, but not VSV, genotypes

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SRFBP1 is membrane-associated and required for HCV entry

Cellular stress responses in hepatitis C virus infection: Mastering a two-edged sword

Hepatitis C virus (HCV) infection affects chronically more than 150 million humans worldwide. Chronic HCV infection causes severe liver disease and hepatocellular carcinoma. While immune response-mediated events are major players in HCV pathogenesis, the impact that viral replication has on cellular homeostasis is increasingly recognized as a necessary contributor to pathological manifestations of HCV infection such as steatosis, insulin-resistance or liver cancer. In this review, we will briefly overview the different cellular stress pathways that are induced by hepatitis C virus infection, the response that the cell promotes to attempt regaining homeostasis or to induce dysfunctional cell death, and how the virus co-opts these response mechanisms to promote both viral replication and survival of the infected cell. We will review the role of unfolded protein and oxidative stress responses as well as the role of auto- and mitophagy in HCV infection. Finally, we will discuss the recent discovery of a cellular chaperone involved in stress responses, the sigma-1 receptor, as a cellular factor required at the onset of HCV infection and the potential molecular events underlying the proviral role of this cellular factor in HCV infection.

Hepatitis C virus attenuates mitochondrial lipid β-oxidation by downregulating mitochondrial trifunctional-protein expression

The course of hepatitis C virus (HCV) infection and disease progression involves alterations in lipid metabolism, leading to symptoms such as hypocholesterolemia and steatosis. Steatosis can be induced by multiple mechanisms, including increases in lipid biosynthesis and uptake, impaired lipoprotein secretion, and/or attenuation of lipid β-oxidation. However, little is known about the effects of HCV on lipid β-oxidation. A previous proteomics study revealed that HCV interacted with both the α- and β-subunits of the mitochondrial trifunctional protein (MTP), an enzyme complex which catalyzes the last 3 steps of mitochondrial lipid β-oxidation for cellular energy production. Here we show that in HCV-infected Huh7.5 cells, lipid β-oxidation was significantly attenuated. Consistently with this, MTP protein and mRNA levels were suppressed by HCV infection. A loss-of-function study showed that MTP depletion rendered cells less responsive to alpha interferon (IFN-α) treatment by impairing IFN-stimulated gene expression. These aspects of host-virus interaction explain how HCV alters host energy homeostasis and how it may also contribute to the establishment of persistent infection in the liver.

IMPORTANCE

HCV infection triggers metabolic alterations, which lead to significant disease outcomes, such as fatty liver (steatosis). This study revealed that HCV impairs mitochondrial lipid β-oxidation, which results in low lipid combustion. On the other hand, the HCV-induced defects in metabolic status played an important role in the control of the type I interferon system. Under the conditions of impaired lipid β-oxidation, host cells were less responsive to the ability of exogenously added IFN-α to suppress HCV replication. This suggests that interference with lipid β-oxidation may assist the virus in the establishment of a long-term, persistent infection. Further understanding of this aspect of virus-host interaction may lead to improvements in the current standard therapy.

Enterovirus 71 induces mitochondrial reactive oxygen species generation that is required for efficient replication

Redox homeostasis is an important host factor determining the outcome of infectious disease. Enterovirus 71 (EV71) infection has become an important endemic disease in Southeast Asia and China. We have previously shown that oxidative stress promotes viral replication, and progeny virus induces oxidative stress in host cells. The detailed mechanism for reactive oxygen species (ROS) generation in infected cells remains elusive. In the current study, we demonstrate that mitochondria were a major ROS source in EV71-infected cells. Mitochondria in productively infected cells underwent morphologic changes and exhibited functional anomalies, such as a decrease in mitochondrial electrochemical potential ΔΨ_m and an increase in oligomycin-insensitive oxygen consumption. Respiratory control ratio of mitochondria from infected cells was significantly lower than that of normal cells. The total adenine nucleotide pool and ATP content of EV71-infected cells significantly diminished. However, there appeared to be a compensatory increase in mitochondrial mass. Treatment with mito-TEMPO reduced eIF2α phosphorylation and viral replication, suggesting that mitochondrial ROS act to promote viral replication. It is plausible that EV71 infection induces mitochondrial ROS generation, which is essential to viral replication, at the sacrifice of efficient energy production, and that infected cells up-regulate biogenesis of mitochondria to compensate for their functional defect.

mTORC1-dependent metabolic reprogramming is a prerequisite for NK cell effector function

The mammalian target of rapamycin complex 1 (mTORC1) is a key regulator of cellular metabolism and also has fundamental roles in controlling immune responses. Emerging evidence suggests that these two functions of mTORC1 are integrally linked. However, little is known regarding mTORC1 function in controlling the metabolism and function of NK cells, lymphocytes that play key roles in antiviral and antitumor immunity. This study investigated the hypothesis that mTORC1-controlled metabolism underpins normal NK cell proinflammatory function. We demonstrate that mTORC1 is robustly stimulated in NK cells activated in vivo and in vitro. This mTORC1 activity is required for the production of the key NK cell effector molecules IFN-γ, which is important in delivering antimicrobial and immunoregulatory functions, and granzyme B, a critical component of NK cell cytotoxic granules. The data reveal that NK cells undergo dramatic metabolic reprogramming upon activation, upregulating rates of glucose uptake and glycolysis, and that mTORC1 activity is essential for attaining this elevated glycolytic state. Directly limiting the rate of glycolysis is sufficient to inhibit IFN-γ production and granzyme B expression. This study provides the highly novel insight that mTORC1-mediated metabolic reprogramming of NK cells is a prerequisite for the acquisition of normal effector functions.

Oxidative stress as a crucial factor in liver diseases

Redox state constitutes an important background of numerous liver disorders. The redox state participates in the course of inflammatory, metabolic and proliferative liver diseases. Reactive oxygen species (ROS) are primarily produced in the mitochondria and in the endoplasmic reticulum of hepatocytes via the cytochrome P450 enzymes. Under the proper conditions, cells are equipped with special molecular strategies that control the level of oxidative stress and maintain a balance between oxidant and antioxidant particles. Oxidative stress represents an imbalance between oxidant and antioxidant agents. Hepatocytic proteins, lipids and DNA are among the cellular structures that are primarily affected by ROS and reactive nitrogen species. The process results in structural and functional abnormalities in the liver. Thus, the phenomenon of oxidative stress should be investigated for several reasons. First, it may explain the pathogenesis of various liver disorders. Moreover, monitoring oxidative markers among hepatocytes offers the potential to diagnose the degree of liver damage and ultimately to observe the response to pharmacological therapies. The present report focuses on the role of oxidative stress in selected liver diseases.

RNA Viruses: ROS-Mediated Cell Death

Reactive oxygen species (ROS) are well known for being both beneficial and deleterious. The main thrust of this review is to investigate the role of ROS in ribonucleic acid (RNA) virus pathogenesis. Much evidences has accumulated over the past decade, suggesting that patients infected with RNA viruses are under chronic oxidative stress. Changes to the body's antioxidant defense system, in relation to SOD, ascorbic acid, selenium, carotenoids, and glutathione, have been reported in various tissues of RNA-virus infected patients. This review focuses on RNA viruses and retroviruses, giving particular attention to the human influenza virus, Hepatitis c virus (HCV), human immunodeficiency virus (HIV), and the aquatic Betanodavirus. Oxidative stress via RNA virus infections can contribute to several aspects of viral disease pathogenesis including apoptosis, loss of immune function, viral replication, inflammatory response, and loss of body weight. We focus on how ROS production is correlated with host cell death. Moreover, ROS may play an important role as a signal molecule in the regulation of viral replication and organelle function, potentially providing new insights in the prevention and treatment of RNA viruses and retrovirus infections.

Protective role of amantadine in mitochondrial dysfunction and oxidative stress mediated by hepatitis C virus protein expression

Amantadine is an antiviral and antiparkinsonian drug that has been evaluated in combination therapies against hepatitis C virus (HCV) infection. Controversial results have been reported concerning its efficacy, and its mechanism of action remains unclear. Data obtained in vitro suggested a role of amantadine in inhibiting HCV p7-mediated cation conductance. In keeping with the fact that mitochondria are responsible to ionic fluxes and that HCV infection impairs mitochondrial function, we investigated a potential role of amantadine in modulating mitochondrial function. Using a well-characterized inducible cell line expressing the full-length HCV polyprotein, we found that amantadine not only prevented but also rescued HCV protein-mediated mitochondrial dysfunction. Specifically, amantadine corrected (i) overload of mitochondrial Ca²⁺; (ii) inhibition of respiratory chain activity and oxidative phosphorylation; (iii) reduction of membrane potential; and (iv) overproduction of reactive oxygen species. The effects of amantadine were observed within 15 min following drug administration and confirmed in Huh-7.5 cells transfected with an infectious HCV genome. These effects were also observed in cells expressing subgenomic HCV constructs, indicating that they are not mediated or only in part mediated by p7. Single organelle analyzes carried out on isolated mouse liver mitochondria demonstrated that amantadine induces hyperpolarization of the membrane potential. Moreover, amantadine treatment increased the calcium threshold required to trigger mitochondrial permeability transition opening. In conclusion, these results support a role of amantadine in preserving cellular bioenergetics and redox homeostasis in HCV-infected cells and unveil an effect of the drug which might be exploited for a broader therapeutic utilization.

Oxidative stress and hepatitis C virus

The disproportionate imbalance between the systemic manifestation of reactive oxygen species and body's ability to detoxify the reactive intermediates is referred to as oxidative stress. Several biological processes as well as infectious agents, physiological or environmental stress, and perturbed antioxidant response can promote oxidative stress. Oxidative stress usually happens when cells are exposed to more electrically charged reactive oxygen species (ROS) such as H2O2 or O2-. The cells' ability to handle such pro-oxidant species is impeded by viral infections particularly within liver that plays an important role in metabolism and detoxification of harmful substances. During liver diseases (such as hepatocellular or cholestatic problems), the produced ROS are involved in transcriptional activation of a large number of cytokines and growth factors, and continued production of ROS and Reactive Nitrogen Species (RNS) feed into the vicious cycle. Many human viruses like HCV are evolved to manipulate this delicate pro- and antioxidant balance; thus generating the sustainable oxidative stress that not only causes hepatic damage but also stimulates the processes to reduce treatment of damage. In this review article, the oxidant and antioxidant pathways that are perturbed by HCV genes are discussed. In the first line of risk, the pathways of lipid metabolism present a clear danger in accumulation of viral induced ROS. Viral infection leads to decrease in cellular concentrations of glutathione (GSH) resulting in oxidation of important components of cells such as proteins, DNA and lipids as well as double strand breakage of DNA. These disorders have the tendency to lead the cells toward cirrhosis and hepatocellular carcinoma in adults due to constant insult. We have highlighted the importance of such pathways and revealed differences in the extent of oxidative stress caused by HCV infection.

Interactions Between Hepatitis C Virus and Mitochondria: Impact on Pathogenesis and Innate Immunity

Hepatitis C virus (HCV) causes a persistent chronic infection of hepatocytes resulting in progressive fibrosis and carcinogenesis. Abnormalities in mitochondria are prominent features of clinical disease where ultrastructural changes, alterations in electron transport, and excess reactive oxygen species (ROS) production occur. These mitochondrial abnormalities correlate with disease severity and resolve with viral eradication. Multiple viral proteins, particularly core and NS3/4a bind to mitochondria. The core and NS5a proteins primarily cause ER stress, ER Ca²⁺ release and enhance direct transfer of Ca²⁺ from ER to mitochondria. This results in electron transport changes, increased ROS production and sensitivity to mitochondrial permeability transition and cell death. The viral protease, NS3/4a, binds to mitochondria as well where it cleaves an important signaling adapter, MAVS, thus preventing viral clearance by endogenous interferon production. This review discusses the mechanisms by which HCV causes mitochondrial changes and consequences of these for disease.

Fluorescence lifetime imaging of alterations to cellular metabolism by domain 2 of the hepatitis C virus core protein

Hepatitis C virus (HCV) co-opts hepatic lipid pathways to facilitate its pathogenesis. The virus alters cellular lipid biosynthesis and trafficking, and causes an accumulation of lipid droplets (LDs) that gives rise to hepatic steatosis. Little is known about how these changes are controlled at the molecular level, and how they are related to the underlying metabolic states of the infected cell. The HCV core protein has previously been shown to independently induce alterations in hepatic lipid homeostasis. Herein, we demonstrate, using coherent anti-Stokes Raman scattering (CARS) microscopy, that expression of domain 2 of the HCV core protein (D2) fused to GFP is sufficient to induce an accumulation of larger lipid droplets (LDs) in the perinuclear region. Additionally, we performed fluorescence lifetime imaging of endogenous reduced nicotinamide adenine dinucleotides [NAD(P)H], a key coenzyme in cellular metabolic processes, to monitor changes in the cofactor’s abundance and conformational state in D2-GFP transfected cells. When expressed in Huh-7 human hepatoma cells, we observed that the D2-GFP induced accumulation of LDs correlated with an increase in total NAD(P)H fluorescence and an increase in the ratio of free to bound NAD(P)H. This is consistent with an approximate 10 fold increase in cellular NAD(P)H levels. Furthermore, the lifetimes of bound and free NAD(P)H were both significantly reduced – indicating viral protein-induced alterations in the cofactors’ binding and microenvironment. Interestingly, the D2-expressing cells showed a more diffuse localization of NAD(P)H fluorescence signal, consistent with an accumulation of the co-factor outside the mitochondria. These observations suggest that HCV causes a shift of metabolic control away from the use of the coenzyme in mitochondrial electron transport and towards glycolysis, lipid biosynthesis, and building of new biomass. Overall, our findings demonstrate that HCV induced alterations in hepatic metabolism is tightly linked to alterations in NAD(P)H functional states.

Sigma-1 receptor regulates early steps of viral RNA replication at the onset of hepatitis C virus infection

Hepatitis C virus (HCV) genome replication is thought to occur in a membranous cellular compartment derived from the endoplasmic reticulum (ER). The molecular mechanisms by which these membrane-associated replication complexes are formed during HCV infection are only starting to be unraveled, and both viral and cellular factors contribute to their formation. In this study, we describe the discovery of nonopioid sigma-1 receptor (S1R) as a cellular factor that mediates the early steps of viral RNA replication. S1R is a cholesterol-binding protein that resides in lipid-rich areas of the ER and in mitochondrion-associated ER membranes (MAMs). Several functions have been ascribed to this ER-resident chaperone, many of which are related to Ca(2+) signaling at the MAMs and lipid storage and trafficking. Downregulation of S1R expression by RNA interference (RNAi) in Huh-7 cells leads to a proportional decrease in susceptibility to HCV infection, as shown by reduced HCV RNA accumulation and intra- and extracellular infectivity in single-cycle infection experiments. Similar RNAi studies in persistently infected cells indicate that S1R expression is not rate limiting for persistent HCV RNA replication, as marked reduction in S1R in these cells does not lead to any decrease in HCV RNA or viral protein expression. However, subgenomic replicon transfection experiments indicate that S1R expression is rate limiting for HCV RNA replication without impairing primary translation. Overall, our data indicate that the initial steps of HCV infection are regulated by S1R, a key component of MAMs, suggesting that these structures could serve as platforms for initial RNA replication during HCV infection.

Alcohol's effect on other chronic liver diseases

In addition to directly causing liver disease, alcohol consumption is a common comorbid condition with other chronic liver diseases and may exacerbate liver injury, particularly in nonalcoholic fatty liver disease, chronic viral hepatitis, hereditary hemochromatosis, and autoimmune liver diseases. This synergism can result in increased hepatic inflammation and accelerated rates of fibrosis, with more rapid and earlier development of cirrhosis, and also increase the risk for liver cancer and death from liver disease.

Virus-induced changes in mitochondrial bioenergetics as potential targets for therapy

Infectious diseases such as those caused by virus, account for a vast proportion of deaths worldwide. Re-emerging aspects of host-virus interactions in recent literature include the vital role played by host metabolism on viral replication and the pro-active participation of mitochondria in this process. Different viruses use distinctive strategies to modulate mitochondrial bioenergetics and enhance viral replication. As a result, energy yielding metabolic pathways are programmed to provide both energy and biosynthetic resources to drive viral protein synthesis and produce infectious particles. Therefore, metabolic antagonists may prove important not only to outline efficient therapy strategies but also to shed light on the pathogenesis of viral infections. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

Decreased mitochondrial deoxyribonucleic acid and increased oxidative damage in chronic hepatitis C

AIM: To determine whether alteration of the mitochondria DNA (mtDNA) copy number and its oxidative damage index (mtDNA^∆CT) can be detected by analysis of peripheral blood cells in hepatitis C virus (HCV)-infected patients.

METHODS: This study enrolled two groups of patients aged 40-60 years: a control group and an HCV-infected group in Department of Gastroenterology and Hepatology in Changhua Christian Hospital. Patients with co-infection with hepatitis B virus or human immunodeficiency virus, autoimmune disease, malignant neoplasia, pregnancy, thyroid disease, or alcohol consumption > 40 g/d were excluded. HCV-infected patients who met the following criteria were included: (1) positive HCV antibodies for > 6 mo; (2) alanine aminotransferase (ALT) levels more than twice the upper limit of normal on at least two occasions during the past 6 mo; and (3) histological fibrosis stage higher than F1. The mtDNA copy number and oxidative damage index of HCV mtDNA (mtDNA^∆CT) were measured in peripheral blood leukocytes. The association between mtDNA copy number and mtDNA^∆CT was further analyzed using clinical data.

RESULTS: Forty-seven normal controls (male/female: 26/21, mean age 50.51 ± 6.15 years) and 132 HCV-infected patients (male/female: 76/61, mean age 51.65 ± 5.50 years) were included in the study. The genotypes of HCV-infected patients include type 1a (n = 3), type 1b (n = 83), type 2a (n = 32), and type 2b (n = 14). Liver fibrosis stages were distributed as follows: F1/F2/F3/F4 = 1/61/45/25 and activity scores were A0/A1/A2/A3 = 7/45/55/25. There were no age or gender differences between the two groups. HCV-infected patients had higher hepatitis activity (aspartate transaminase levels 108.77 ± 60.73 vs 23.19 ± 5.47, P < 0.01; ALT levels 168.69 ± 93.12 vs 23.15 ± 9.45, P < 0.01) and lower platelet count (170.40 ± 58.00 vs 251.24 ± 63.42, P < 0.01) than controls. The mtDNA copy number was lower in HCV-infected patients than in controls (173.49 vs 247.93, P < 0.05). The mtDNA^∆CT was higher in HCV-infected patients than in controls (2.92 vs 0.64, P < 0.05). To clarify the clinical significance of these results in HCV-infected patients, their association with different clinical parameters among HCV-infected patients was analyzed. A negative association was found between mtDNA copy number and elevated aspartate transaminase levels (r = -0.17, P < 0.05). Changes in mtDNA copy number were not associated with HCV RNA levels, HCV genotypes, liver fibrosis severity, or inflammatory activity in the liver biopsy specimen. However, a correlation was observed between mtDNA^∆CT and platelet count (r = -0.22, P < 0.01), HCV RNA level (r = 0.36, P < 0.01), and hepatitis activity (r = 0.20, P = 0.02). However, no difference in the change in mtDNA^∆CT was observed between different fibrosis stages or HCV genotypes.

CONCLUSION: Oxidative stress and mtDNA damage are detectable in patient’s peripheral leukocytes. Increased leukocyte mtDNA^∆CT correlates with higher HCV viremia, increased hepatitis activity, and lower platelet count.

PPARs and HCV-Related Hepatocarcinoma: A Mitochondrial Point of View

Hepatitis-C-virus-related infective diseases are worldwide spread pathologies affecting primarily liver. The infection is often asymptomatic, but when chronically persisting can lead to liver scarring and ultimately to cirrhosis, which is generally apparent after decades. In some cases, cirrhosis will progress to develop liver failure, liver cancer, or life-threatening esophageal and gastric varices. HCV-infected cells undergo profound metabolic dysregulation whose mechanisms are yet not well understood. An emerging feature in the pathogenesis of the HCV-related disease is the setting of a pro-oxidative condition caused by dysfunctions of mitochondria which proved to be targets of viral proteins. This causes deregulation of mitochondria-dependent catabolic pathway including fatty acid oxidation. Nuclear receptors and their ligands are fundamental regulators of the liver metabolic homeostasis, which are disrupted following HCV infection. In this contest, specific attention has been focused on the peroxisome proliferator activated receptors given their role in controlling liver lipid metabolism and the availability of specific pharmacological drugs of potential therapeutic utilization. However, the reported role of PPARs in HCV infection provides conflicting results likely due to different species-specific contests. In this paper we summarize the current knowledge on this issue and offer a reconciling model based on mitochondria-related features.

Targeting mitochondria in the infection strategy of the hepatitis C virus

Hepatitis C virus (HCV) infection induces a state of oxidative stress more pronounced than that observed in many other inflammatory diseases. Here, we propose a temporal sequence of events in the HCV-infected cell whereby the primary alteration consists of a release of Ca(2+) from the endoplasmic reticulum, followed by uptake into mitochondria. This ensues successive mitochondrial dysfunction leading to the generation of reactive oxygen species and a progressive metabolic adaptive response. Evidence is provided for a positive feed-back mechanism between alterations of calcium and redox homeostasis. This likely involves deregulation of the mitochondrial permeability transition and induces progressive dysfunction of cellular bioenergetics. Pathogenetic implications of the model and new opportunities for therapeutic intervention are discussed. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

The cyclophilin inhibitor alisporivir prevents hepatitis C virus-mediated mitochondrial dysfunction

Alisporivir (Debio-025) is an analogue of cyclosporine A and represents the prototype of a new class of non-immunosuppressive cyclophilin inhibitors. In vitro and in vivo studies have shown that alisporivir inhibits hepatitis C virus (HCV) replication, and ongoing clinical trials are exploring its therapeutic potential in patients with chronic hepatitis C. Recent data suggest that the antiviral effect is mediated by inhibition of cyclophilin A, which is an essential host factor in the HCV life cycle. However, alisporivir also inhibits mitochondrial permeability transition by binding to cyclophilin D. Because HCV is known to affect mitochondrial function, we explored the effect of alisporivir on HCV protein-mediated mitochondrial dysfunction. Through the use of inducible cell lines, which allow to investigate the effects of HCV polyprotein expression independent from viral RNA replication and which recapitulate the major alterations of mitochondrial bioenergetics observed in infectious cell systems, we show that alisporivir prevents HCV protein-mediated decrease of cell respiration, collapse of mitochondrial membrane potential, overproduction of reactive oxygen species and mitochondrial calcium overload. Strikingly, some of the HCV-mediated mitochondrial dysfunctions could even be rescued by alisporivir.

CONCLUSION

These observations provide new insights into the pathogenesis of HCV-related liver disease and reveal an additional mechanism of action of alisporivir that is likely beneficial in the treatment of chronic hepatitis C.

Topological analysis of protein co-abundance networks identifies novel host targets important for HCV infection and pathogenesis

Background

High-throughput methods for obtaining global measurements of transcript and protein levels in biological samples has provided a large amount of data for identification of 'target' genes and proteins of interest. These targets may be mediators of functional processes involved in disease and therefore represent key points of control for viruses and bacterial pathogens. Genes and proteins that are the most highly differentially regulated are generally considered to be the most important. We present topological analysis of co-abundance networks as an alternative to differential regulation for confident identification of target proteins from two related global proteomics studies of hepatitis C virus (HCV) infection.

Results

We analyzed global proteomics data sets from a cell culture study of HCV infection and from a clinical study of liver biopsies from HCV-positive patients. Using lists of proteins known to be interaction partners with pathogen proteins we show that the most differentially regulated proteins in both data sets are indeed enriched in pathogen interactors. We then use these data sets to generate co-abundance networks that link proteins based on similar abundance patterns in time or across patients. Analysis of these co-abundance networks using a variety of network topology measures revealed that both degree and betweenness could be used to identify pathogen interactors with better accuracy than differential regulation alone, though betweenness provides the best discrimination. We found that though overall differential regulation was not correlated between the cell culture and liver biopsy data, network topology was conserved to an extent. Finally, we identified a set of proteins that has high betweenness topology in both networks including a protein that we have recently shown to be essential for HCV replication in cell culture.

Conclusions

The results presented show that the network topology of protein co-abundance networks can be used to identify proteins important for viral replication. These proteins represent targets for further experimental investigation that will provide biological insight and potentially could be exploited for novel therapeutic approaches to combat HCV infection.

Herpes simplex type 1 activates glycolysis through engagement of the enzyme 6-phosphofructo-1-kinase (PFK-1)

Viruses such as HIV, HCV, Mayaro and HCMV affect cellular metabolic pathways, including glycolysis. Although some studies have suggested that the inhibition of glycolysis affects HSV-1 replication and that HSV-1-infected eyes have increased lactate production, the mechanisms by which HSV-1 induces glycolysis have never been investigated in detail. In this study, we observed an increase in glucose uptake, lactate efflux and ATP content in HSV-1-infected cells. HSV-1 triggered a MOI-dependent increase in the activity of phosphofructokinase-1 (PFK-1), a key rate-limiting enzyme of the glycolytic pathway. After HSV-1 infection, we observed increased PFK-1 expression, which increased PFK-1 total activity, and the phosphorylation of this enzyme at serine residues. HSV-1-induced glycolysis was associated with increased ATP content, and these events were critical for viral replication. In summary, our results suggest that HSV-1 triggers glycolysis through a different mechanism than other herpesviruses, such as HCMV. Thus, this study contributes to a better understanding of HSV-1 pathogenesis and provides insights into novel targets for antiviral therapy.

HIGHLIGHTS

►HSV-1 activates glycolysis by PFK-1 activation. ►In HSV-1-infected cells PFK-1 synthesis is up-regulated and phosphorylated at serine residues. ►PFK-1 knockdown impairs HSV-1 replication. ►HSV-1-mediated glycolysis activation increases ATP content.

Occult hepatitis C virus elicits mitochondrial oxidative stress in lymphocytes and triggers PI3-kinase-mediated DNA damage response

Occult hepatitis C viral infection (OHCI) is a newly reported pathological entity associated with increased risk of developing hepatocellular carcinoma and lymphoproliferative disorders. Although hepatocytes are the primary sites of viral replication, hepatitis C virus is potentially lymphotropic, invading and propagating in cells of the immune system. Lymphocytes, the extrahepatic viral reservoirs, are differentially implicated in the occult and the active forms of the disease. This study aimed to elucidate the implications of mitochondrial oxidative stress on the immune pathophysiological mechanisms of OHCI. We herein report that OHCI induces mitochondrial oxidative stress, leading to DNA double-strand breaks and elicitation of a phosphoinositol 3-kinase-mediated cellular response in peripheral blood lymphocytes. Compared to controls, OHCI subjects showed higher accumulation of pATM, pATR, γH2AX, and p-p53, along with active recruitment of repair proteins (Mre11, Rad50, and Nbs1) and altered mitochondrial DNA content. Increased mitochondrial membrane depolarization and circulating nucleosome levels along with chromatid-type aberrations and decreased T-cell proliferative index observed in the OHCI group further indicated that this damage might lead to Bax-triggered mitochondria-mediated cellular apoptosis. Together our results provide the mechanistic underpinnings of mitochondrial dysfunction in OHCI, a previously unknown paradigm, for explaining the immune pathogenesis in a redox-dependent manner.

Neuroinflammation and endoplasmic reticulum stress are coregulated by crocin to prevent demyelination and neurodegeneration

Endoplasmic reticulum (ER) stress is a homeostatic mechanism, which is used by cells to adapt to intercellular and intracellular changes. Moreover, ER stress is closely linked to inflammatory pathways. We hypothesized that ER stress is an integral component of neuroinflammation and contributes to the development of neurological diseases. In autopsied brain specimens from multiple sclerosis (MS) and non-MS patients, XBP-1 spliced variant (XBP-1/s) was increased in MS brains (p < 0.05) and was correlated with the expression of the human endogenous retrovirus-W envelope transcript, which encodes the glycoprotein, Syncytin-1 (p < 0.05). In primary human fetal astrocytes transfected with a Syncytin-1-expressing plasmid, XBP-1/s, BiP, and NOS2 were induced, which was suppressed by crocin treatment (p < 0.05). Crocin also protected oligodendrocytes exposed to cytotoxic supernatants derived from Syncytin-1-expressing astrocytes (p < 0.05) and NO-mediated oligodendrocytotoxicity (p < 0.05). During experimental autoimmune encephalomyelitis (EAE), the transcript levels of the ER stress genes XBP-1/s, BiP, PERK, and CHOP were increased in diseased spinal cords compared with healthy littermates (p < 0.05), although CHOP expression was not involved in the EAE disease phenotype. Daily treatment with crocin starting on day 7 post-EAE induction suppressed ER stress and inflammatory gene expression in spinal cords (p < 0.05), which was accompanied by preserved myelination and axonal density, together with reduced T cell infiltration and macrophage activation. EAE-associated neurobehavioral deficits were also ameliorated by crocin treatment (p < 0.05). These findings underscored the convergent roles of pathogenic ER stress and immune pathways in neuroinflammatory disease and point to potential therapeutic applications for crocin.