HCV replication suppresses cellular glucose uptake through down-regulation of cell surface expression of glucose transporters

HCV affects KATP channels through GnT-IVa-mediated N-glycosylation of GLUT2 on the surface of pancreatic β-cells leading to impaired insulin secretion

PURPOSE

To explore the mechanism of insulin secretion dysfunction in pancreatic beta cells induced by N-glycosylation mediated by an infection from the hepatitis C virus (HCV).

METHODS

Min6 cell models infected with HCV and stimulated with glucose were constructed. Meanwhile, an HCV-infected animal model and a type 2 diabetes mellitus (T2DM) rat model were constructed. Glucose uptake in the Min6 cells was detected, and insulin secretion was detected by ELISA. Flow cytometry, immunofluorescence staining, Western blotting, RT-qPCR, and lectin blotting were used to detect the expression levels of related proteins and mRNA, as well as the level of N-glycosylation. HE staining was used to observe the pathological changes in the pancreatic tissue, and an oral glucose tolerance test (OGTT) was used to evaluate the glucose tolerance of the rats.

RESULTS

Compared with the NC group, the expression levels of GnT-IVa, GLUT2, galectin-9, and voltage-dependent calcium channel 1.2 (Cav1.2) were significantly downregulated in the HCV-infected group. The ATP-sensitive potassium channel (KATP) component proteins SUR1 and Kir6.2 were significantly upregulated, while intracellular glucose intake and insulin secretion decreased, N-glycosylation levels and ATP levels significantly decreased, and the overexpression of GnT-IVa reversed the effect of the HCV infection. However, treatment with the glycosylation inhibitor kifunensine (KIF) or the KATP channel activator diazine (Dia) reversed the effects of the overexpression of GnT-IVa. In the animal experiments, HE staining revealed serious pathological injuries in the pancreatic tissue of the HCV-infected rats, with decreased glucose tolerance and glycosylation levels, decreased insulin secretion, downregulated expression of GnT-IVa, GLUT2, and Cav1.2, and upregulated expression of SUR1 and Kir6.2. The overexpression treatment of GnT-IVa or the KATP channel antagonist miglinide reversed the effects of HCV.

CONCLUSION

HCV infection inhibits GLUT2 N-glycosylation on the pancreatic β cell surface by downregulating the expression of GnT-IVa and then activates the KATP pathway, which ultimately leads to disturbances in insulin secretion.

Mechanisms and clinical relevance of the bidirectional relationship of viral infections with metabolic diseases

Viruses have been present during all evolutionary steps on earth and have had a major effect on human history. Viral infections are still among the leading causes of death. Another public health concern is the increase of non-communicable metabolic diseases in the last four decades. In this Review, we revisit the scientific evidence supporting the presence of a strong bidirectional feedback loop between several viral infections and metabolic diseases. We discuss how viruses might lead to the development or progression of metabolic diseases and conversely, how metabolic diseases might increase the severity of a viral infection. Furthermore, we discuss the clinical relevance of the current evidence on the relationship between viral infections and metabolic disease and the present and future challenges that should be addressed by the scientific community and health authorities.

The role of GLUT2 in glucose metabolism in multiple organs and tissues

The glucose transporter family has an important role in the initial stage of glucose metabolism; Glucose transporters 2 (GLUTs, encoded by the solute carrier family 2, SLC2A genes) is the major glucose transporter in β-cells of pancreatic islets and hepatocytes but is also expressed in the small intestine, kidneys, and central nervous system; GLUT2 has a relatively low affinity to glucose. Under physiological conditions, GLUT2 transports glucose into cells and allows the glucose concentration to reach balance on the bilateral sides of the cellular membrane; Variation of GLUT2 is associated with various endocrine and metabolic disorders; In this study, we discussed the role of GLUT2 in participating in glucose metabolism and regulation in multiple organs and tissues and its effects on maintaining glucose homeostasis.

mTOR-inhibitors and post-transplant diabetes mellitus: a link still debated in kidney transplantation

The mammalian target of rapamycin inhibitors (mTOR-Is, Sirolimus, and Everolimus) are immunosuppressive drugs widely employed in kidney transplantation. Their main mechanism of action includes the inhibition of a serine/threonine kinase with a pivotal role in cellular metabolism and in various eukaryotic biological functions (including proteins and lipids synthesis, autophagy, cell survival, cytoskeleton organization, lipogenesis, and gluconeogenesis). Moreover, as well described, the inhibition of the mTOR pathway may also contribute to the development of the post-transplant diabetes mellitus (PTDM), a major clinical complication that may dramatically impact allograft survival (by accelerating the development of the chronic allograft damage) and increase the risk of severe systemic comorbidities. Several factors may contribute to this condition, but the reduction of the beta-cell mass, the impairment of the insulin secretion and resistance, and the induction of glucose intolerance may play a pivotal role. However, although the results of several in vitro and in animal models, the real impact of mTOR-Is on PTDM is still debated and the entire biological machinery is poorly recognized. Therefore, to better elucidate the impact of the mTOR-Is on the risk of PTDM in kidney transplant recipients and to potentially uncover future research topics (particularly for the clinical translational research), we decided to review the available literature evidence regarding this important clinical association. In our opinion, based on the published reports, we cannot draw any conclusion and PTDM remains a challenge. However, also in this case, the administration of the lowest possible dose of mTOR-I should also be recommended.

Interdependence of glycemic and lipid modulation in cured chronic hepatitis C patients by direct-acting antiviral agents

BACKGROUND

Chronic hepatitis C virus (HCV) infection causes various liver diseases and metabolic disorders. With direct-acting antiviral agents (DAAs), which effectively eradicate pan-genotypic HCV, hepatic and concomitant metabolic restorations are achieved. The study aims to evaluate the posttherapeutic benefits of lipid and glycemic homeostasis.

METHODS

Nighty-five chronic hepatitis C patients who achieved sustained virological response (SVR) by using DAAs were enrolled to collect plasma samples and fractionated lipoproteins at baseline, SVR, and during the post-SVR follow-ups for 6 months (pS6m) and 1 year (pS1yr). The lipid and glycemic parameters were analyzed to establish muturally modulatory relationships.

RESULTS

Plasma cholesterol (Chol) and glucose were elevated at SVR from baseline, whereas plasma Chol remained increased until pS1yr; however, glucose returned to the basal level. The post-SVR responses included a peak elevation of glycated hemoglobin at pS6m, a sustained elevation of triglyceride (Tg), and sustained declines in insulin, homeostasis model assessment (HOMA)-insulin resistance, and HOMA-beta levels until pS1yr. The changes in plasma Chol and high-density-lipoprotein Chol showed positive correlations, as did the plasma Tg with low-density-lipoprotein Tg and very-low-density-lipoprotein Tg per particle load. Very-low-density-lipoprotein was found to be loaded with increased Tg and Chol and underwent efficient Tg catabolism in the form of conversion into low-density-lipoprotein. Additionally, the posttherapeutic dynamics exhibited correlations of high-density-lipoprotein Chol with plasma glucose and HOMA-beta.

CONCLUSION

Irrespective of the baseline metabolic status, the posttherapeutic interdependent modulation of blood glycemic and lipid metabolic parameters were revealed in chronic hepatitis C patients following clearance of HCV viremia by DAA treatment.

Viruses and Endocrine Diseases

Viral infections have been frequently associated with physiological and pathological changes in the endocrine system for many years. The numerous early and late endocrine complications reported during the current pandemic of coronavirus disease 2019 (COVID-19) reinforce the relevance of improving our understanding of the impact of viral infections on the endocrine system. Several viruses have been shown to infect endocrine cells and induce endocrine system disturbances through the direct damage of these cells or through indirect mechanisms, especially the activation of the host antiviral immune response, which may lead to the development of local or systemic inflammation or organ-specific autoimmunity. In addition, endocrine disorders may also affect susceptibility to viral infections since endocrine hormones have immunoregulatory functions. This review provides a brief overview of the impact of viral infections on the human endocrine system in order to provide new avenues for the control of endocrine diseases.

The Effects of Viruses on Insulin Sensitivity and Blood-Brain Barrier Function

In this review manuscript, we discuss the effects of select common viruses on insulin sensitivity and blood-brain barrier (BBB) function and the potential overlapping and distinct mechanisms involved in these effects. More specifically, we discuss the effects of human immunodeficiency virus (HIV), herpes, hepatitis, influenza, respiratory syncytial virus (RSV), and SARS-CoV-2 viruses on insulin sensitivity and BBB function and the proposed underlying mechanisms. These viruses differ in their ability to be transported across the BBB, disrupt the BBB, and/or alter the function of the BBB. For RSV and SARS-CoV-2, diabetes increases the risk of infection with the virus, in addition to viral infection increasing the risk for development of diabetes. For HIV and hepatitis C and E, enhanced TNF-a levels play a role in the detrimental effects. The winter of 2022-2023 has been labeled as a tridemic as influenza, RSV, and COVID-19 are all of concern during this flu season. There is an ongoing discussion about whether combined viral exposures of influenza, RSV, and COVID-19 have additive, synergistic, or interference effects. Therefore, increased efforts are warranted to determine how combined viral exposures affect insulin sensitivity and BBB function.

An Update on the Metabolic Landscape of Oncogenic Viruses

Viruses play an important role in cancer development as about 12% of cancer types are linked to viral infections. Viruses that induce cellular transformation are known as oncoviruses. Although the mechanisms of viral oncogenesis differ between viruses, all oncogenic viruses share the ability to establish persistent chronic infections with no obvious symptoms for years. During these prolonged infections, oncogenic viruses manipulate cell signaling pathways that control cell cycle progression, apoptosis, inflammation, and metabolism. Importantly, it seems that most oncoviruses depend on these changes for their persistence and amplification. Metabolic changes induced by oncoviruses share many common features with cancer metabolism. Indeed, viruses, like proliferating cancer cells, require increased biosynthetic precursors for virion production, need to balance cellular redox homeostasis, and need to ensure host cell survival in a given tissue microenvironment. Thus, like for cancer cells, viral replication and persistence of infected cells frequently depend on metabolic changes. Here, we draw parallels between metabolic changes observed in cancers or induced by oncoviruses, with a focus on pathways involved in the regulation of glucose, lipid, and amino acids. We describe whether and how oncoviruses depend on metabolic changes, with the perspective of targeting them for antiviral and onco-therapeutic approaches in the context of viral infections.

What role for cellular metabolism in the control of hepatitis viruses?

Hepatitis B, C and D viruses (HBV, HCV, HDV, respectively) specifically infect human hepatocytes and often establish chronic viral infections of the liver, thus escaping antiviral immunity for years. Like other viruses, hepatitis viruses rely on the cellular machinery to meet their energy and metabolite requirements for replication. Although this was initially considered passive parasitism, studies have shown that hepatitis viruses actively rewire cellular metabolism through molecular interactions with specific enzymes such as glucokinase, the first rate-limiting enzyme of glycolysis. As part of research efforts in the field of immunometabolism, it has also been shown that metabolic changes induced by viruses could have a direct impact on the innate antiviral response. Conversely, detection of viral components by innate immunity receptors not only triggers the activation of the antiviral defense but also induces in-depth metabolic reprogramming that is essential to support immunological functions. Altogether, these complex triangular interactions between viral components, innate immunity and hepatocyte metabolism may explain why chronic hepatitis infections progressively lead to liver inflammation and progression to cirrhosis, fibrosis and hepatocellular carcinoma (HCC). In this manuscript, we first present a global overview of known connections between the innate antiviral response and cellular metabolism. We then report known molecular mechanisms by which hepatitis viruses interfere with cellular metabolism in hepatocytes and discuss potential consequences on the innate immune response. Finally, we present evidence that drugs targeting hepatocyte metabolism could be used as an innovative strategy not only to deprive viruses of key metabolites, but also to restore the innate antiviral response that is necessary to clear infection.

Hepatitis C Virus, Insulin Resistance, and Diabetes: A Review

Hepatitis C virus (HCV) infection and diabetes mellitus (DM) are two chronic diseases that are a cause of significant health and economic burdens worldwide. HCV is associated with the development of insulin resistance (IR) and diabetes mellitus (DM). The mechanisms through which HCV induces IR and DM include direct viral effects, pro-inflammatory cytokines and other immune-mediated processes. Type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) are both chronic diseases that involve impaired glucose homeostasis, albeit through different mechanisms. T1DM is an autoimmune disease that leads to the destruction of pancreatic beta cells resulting in insulin deficiency. In T2DM, a combination of peripheral insulin resistance and irregular production of insulin eventually lead to beta cell destruction and insulin insufficiency. Both type 1 and type 2 DM etiologies involve a combination of genetic and environmental factors. The data on HCV and T1DM association is limited, unlike T2DM, where a large body of evidence linking HCV to T2DM is available. Here, we intend to outline the current state of knowledge on HCV, IR, and DM. This article is protected by copyright. All rights reserved.

GLUT1 and ASCT2 Protein Expression in Papillary Thyroid Carcinoma Patients and Relation to Hepatitis C Virus: A Propensity-Score Matched Analysis

Purpose

Recently, glucose and amino acid transporters have gradually become a hot topic in thyroid gland biology and cancer research. We aimed to investigate the expressions of glucose transporter 1 (GLUT1) and glutamine transporter 2 (ASCT2) in papillary thyroid carcinoma (PTC) and their clinical significance and relation to HCV-related hepatitis.

Patients and Methods

Screening 202 TC tissue samples against the selection criteria using a propensity-score matched analysis to adjust for age, sex, side of tumor, histopathological variants, TNM staging system, and the positivity for HCV yielded 51 matched (17 HCV positive and 34 HCV negative) PTC samples. The expressions of GLUT1 and ASCT2 expressions were detected by immunohistochemical staining. Kaplan–Meier survival curves were generated for disease-free and overall survival, and multivariate Cox regression analysis was applied to identify predictors for mortality.

Results

Of 51 thyroid cancer tissues, 85% showed positive GLUT1 cytoplasmic staining, and 26% had a high expression score. All thyroid cancer specimens demonstrated ASCT2 cytoplasmic staining with membranous accentuation. Of these, 78% showed a high expression score, and 22% showed weak staining. On stratifying the study cohort based on the HCV status, HCV negative cohort showed a significantly higher immunoreactivity score for GLUT1 (p = 0.004) but not ASCT2 (p = 0.94) than HCV positive group. The expressions of the studied transporters showed no significant associations with the prognostic features of PTC nor the disease-free/overall survival.

Conclusion

GLUT1 and ASCT2 immunohistochemical staining showed positive expression with variable intensity in nearly 85% and 100% of PTC tissue samples compared to normal ones, respectively. Furthermore, GLUT1 protein expression, not ASCT2, showed a higher immunoreactivity score in PTC patients who are negative for HCV than cancer patients with positive HCV. Meanwhile, the expression of both protein markers was not associated with the clinicopathological characteristics of the studied PTC patients. Further large-scale multicenter studies are recommended to validate the present findings.

Long-term surveillance of liver histological changes in chronic hepatitis C patients completing pegylated interferon-α plus ribavirin therapy: an observational cohort study

BACKGROUND

For chronic hepatitis C (CHC) patients completing pegylated interferon (PegIFN)-α/ribavirin therapy, long-term liver histological changes remain largely unexplored.

METHODS

This observational cohort study included 85 CHC patients completing PegIFN-α/ribavirin therapy with liver biopsies performed at baseline and the end of surveillance (EOS). Median years between paired biopsies were 6.75 (interquartile range: 5.63-7.54).

RESULTS

In patients with baseline METAVIR fibrosis stages (F) <4 (able to undergo fibrosis progression; n = 77), cases achieving sustained virological response (SVR) (n = 52) had a significantly lower rate of fibrosis progression than non-SVR cases (n = 25) (3.8% versus 24.0%, p = 0.012). Among the entire cohort (n = 85), the rate of activity response [METAVIR activity grades (A) decreasing or maintaining at A0] in SVR cases (n = 59) was significantly higher than that in non-SVR cases (n = 26) (94.9% versus 65.4%, p = 0.001). For SVR cases among the entire cohort, independent predictors of fibrosis clearance included baseline F <2 [odds ratio (OR) = 7.877, p = 0.042] and aspartate transaminase (AST) levels declining by >70% at EOS compared with baseline (OR = 9.013, p = 0.038). For non-SVR cases among the entire cohort, baseline AST levels >80 U/l and glucose levels ⩽ 105 mg/dl independently predicted significant fibrosis (F2/F3/F4) at EOS (OR = 12.558, p = 0.049) and activity response (OR = 17.741, p = 0.047), respectively.

CONCLUSIONS

Among CHC patients completing PegIFN-α/ribavirin therapy, SVR lowers the risk of liver histological progression but does not guarantee fibrosis clearance. For SVR cases, those with baseline F ⩾ 2 or without significantly declined follow-up AST levels should be specifically monitored. As for non-SVR cases, those with a higher baseline AST or glucose level should preferentially receive retreatment.

Effect of different direct-acting antiviral regimens for treatment of nondiabetic hepatitis C virus–infected Egyptian patients on insulin resistance and sensitivity

Background

The association between hepatitis C virus (HCV), insulin resistance (IR), and metabolic syndrome has been extensively investigated. Direct-acting antivirals (DAAs) have a high sustained virologic response (SVR) rate, reaching > 90%. The effect of SVR after DAA treatment on metabolic parameters and IR in nondiabetic patients could be an important factor in the patient’s long-term outcome. The aim of the study is to evaluate the impact of different DAA regimens on IR and sensitivity in naïve chronic HCV-infected nondiabetic patients (before and after 12 weeks of treatment).

Methods

This prospective cohort study was conducted on 100 HCV-infected Child A nondiabetic patients eligible for DAA treatment in the Department of Gastroenterology and Hepatology, Ain Shams University, and Kobry El-Kobba Military Hospital among patients attending the outpatient clinic.

Patients were categorized into four groups according to the HCV regimens they received for 12 weeks.

All patient were subjected to the following tests before and 12 weeks after treatment: HCV quantitative PCR, Fibroscan, fasting insulin level (using insulin quantitative test kit), fasting and postprandial blood glucose (PPG), lipid profile, liver enzymes, BMI, and waist circumference.

Results

All patients achieved SVR at 12 weeks. In all treatment groups, lab was assessed before and after treatment, the 2-h PPG, high-density lipoprotein, and low-density lipoprotein levels showed statistically significant increases, whereas triglyceride, fasting glucose, hemoglobin A1C, and fasting plasma insulin levels showed statistically significant decreases. The homeostasis model assessment of insulin resistance (HOMA-IR) exhibited statistically significant decreases, whereas the quantitative insulin sensitivity check index (QUICKI) and Matsuda index showed statistically significant increases, across the four groups.

Conclusions

DAA treatment in naïve nondiabetic HCV-infected patients affects metabolic profile and insulin resistance/sensitivity, with similar effect among different DAA regimens.

A proposed lectin-mediated mechanism to explain the in Vivo antihyperglycemic activity of γ-conglutin from Lupinus albus seeds

Experiments conducted in vitro and in vivo, as well as clinical trials for hypoglycemic therapeutics, support the hypoglycemic properties of the lectin γ-conglutin, a Lupinus seed storage protein, by a mechanism not yet been clarified. Structural studies established that binding of γ-conglutin, in native and denatured form, to insulin occurs by a strong binding that resists rupture when 0.4 M NaCl and 0.4 M galactose are present, suggesting that strong electrostatic interactions are involved. Studies on binding of γ-conglutin in native and denatured form to HepG2 membrane glycosylated receptors were conducted, which reveal that only the native form of γ-conglutin with lectin activity is capable of binding to these receptors. Glycosylated insulin receptors were detected on purified HepG2 cell membranes and characterized by 1D and 2D analyses. Preclinical assays with male mice (CD-1) indicated that native and denatured γ-conglutins display antihyperglycemic effect, decreasing glucose in blood comparable after 120 min to that exhibited by the animal group treated with metformin, used to treat T2D and used as a positive control. Measurement of organ injury/functional biomarkers (hepatic, pancreatic, renal, and lipid profile) was comparable to that of metformin treatment or even better in terms of safety endpoints (pancreatic and hepatic biomarkers).

Hepatitis C: clinical management and debated issues

Hepatitis C virus represents an important global health issue with 71 million of infected people in the word. Direct-acting antivirals are quite new molecules that hit specific Hepatitis C virus proteins useful for viral replication and assembly. Notably, Direct-acting antivirals bring to high sustained virological response rates showing also a great safety profile. This treatment revolution had an impact on transplantation world, in fact the number of liver transplants due to Hepatitis C virus-related cirrhosis and hepatocellular carcinoma is quickly decreasing. Even if this therapy has achieved excellent results in terms of morbility and mortality rates' reduction, there are some debated issues to consider. In the present review the main clinical challenges in every-day management of Hepatitis C virus patients treated with Direct-acting antivirals and the debated effects of viral clearance (metabolic, cardiovascular, immunologic and neoplastic) are discussed. The detection of barriers that can preclude the delivery of Hepatitis C virus care, is the most complex challenge for the scientific community. To obtain the Hepatitis C virus global eradication by 2030, as the World Health Organization has set, will be complex and laborious and will need a further multilevel effort.

Hepatitis C virus associated hepatocellular carcinoma

Liver cancer is a global problem and hepatocellular carcinoma (HCC) accounts for about 85% of this cancer. In the USA, etiologies and risk factors for HCC include chronic hepatitis C virus (HCV) infection, diabetes, non-alcoholic steatohepatitis (NASH), obesity, excessive alcohol drinking, exposure to tobacco smoke, and genetic factors. Chronic HCV infection appears to be associated with about 30% of HCC. Chronic HCV infection induces multistep changes in liver, involving metabolic disorders, steatosis, cirrhosis and HCC. Liver carcinogenesis requires initiation of neoplastic clones, and progression to clinically diagnose malignancy. Tumor progression associates with profound exhaustion of tumor-antigen-specific CD8⁺T cells, and accumulation of PD-1^hi CD8⁺T cells and Tregs. In this chapter, we provide a brief description of HCV and environmental/genetic factors, immune regulation, and highlight mechanisms of HCV associated HCC. We also underscore HCV treatment and recent paradigm of HCC progression, highlighted the current treatment and potential future therapeutic opportunities.

FIB-4 Regression With Direct-Acting Antiviral Therapy in Patients With Hepatitis C Infection: A Safety-Net Hospital Experience

Background: Liver fibrosis stage determines the risk of morbidity and mortality from chronic hepatitis C virus (HCV) infection. The majority of HCV-infected patients are underserved and have other comorbid conditions that lead to more progressive liver disease such as cirrhosis and hepatocellular carcinoma. Safety net hospitals are the prime location to treat these patients. Direct acting antiviral (DAA) agents are highly effective in virus eradication.

Aim: We aimed to evaluate the effect of treatment with DAAs on FIB-4 index.

Methods: We identified 343 patients who initiated HCV treatment with DAAs from 2016 to 2018 and achieved a sustained virologic response (SVR) in Metrohealth Medical Center, a safety net hospital system. We compared the severity of hepatic fibrosis before and 1 year after SVR was attained. We evaluated whether the presence of other comorbid conditions influenced liver fibrosis regression. All analyses were performed using SAS software.

Results: There was a statistically significant drop in mean FIB-4 score from baseline to post-SVR (3.47 ± 2.84 vs. 2.28 ± 1.60, P < 0.001). One hundred seventeen patients had baseline FIB-4 scores ≥3.25, 56% had FIB-4 scores <3.25 after SVR. Alcohol use disorder was associated with a higher baseline FIB-4 score compared to low level drinking (3.85 ± 0.20 vs. 3.15 ± 0.16). These patients showed greater improvement in FIB-4 scores after treatment when compared to those without alcohol use disorder (1.44 ± 0.15 vs. 0.97 ± 0.13, P = 0.02).

Conclusion: FIB-4 index is a useful non-invasive tool for monitoring fibrosis regression after antiviral therapy. Patients with a history of alcohol abuse had the greatest reduction in FIB-4 score post-SVR.

Glucose transporters in adipose tissue, liver, and skeletal muscle in metabolic health and disease

A family of facilitative glucose transporters (GLUTs) is involved in regulating tissue-specific glucose uptake and metabolism in the liver, skeletal muscle, and adipose tissue to ensure homeostatic control of blood glucose levels. Reduced glucose transport activity results in aberrant use of energy substrates and is associated with insulin resistance and type 2 diabetes. It is well established that GLUT2, the main regulator of hepatic hexose flux, and GLUT4, the workhorse in insulin- and contraction-stimulated glucose uptake in skeletal muscle, are critical contributors in the control of whole-body glycemia. However, the molecular mechanism how insulin controls glucose transport across membranes and its relation to impaired glycemic control in type 2 diabetes remains not sufficiently understood. An array of circulating metabolites and hormone-like molecules and potential supplementary glucose transporters play roles in fine-tuning glucose flux between the different organs in response to an altered energy demand.

Direct-acting Antiviral in the Treatment of Chronic Hepatitis C: Bonuses and Challenges

Owing to the rapid development and wide clinical application of direct acting antiviral (DAA) drugs in the treatment of hepatitis C virus (HCV) infection, the era of interferon-based therapy has almost come to an end. Cumulative studies show that DAA therapy renders high cure efficiency (>90%) and good safety profile, and may even bring some unexpected benefits to the patients. However, some issues of concern arise, one of which is the resistance mutation of HCV genome leading to failure of treatment. With the aim of providing some meaningful references for the treatment of chronic hepatitis C (CHC), this article summarizes the research progress on benefits of DAA accompanied by viral clearance in the treatment of chronic hepatitis and the drug resistance.

Hepatitis C, systemic inflammation and oxidative stress: correlations with metabolic diseases

Introduction: Hepatitis C chronic infection has long been correlated with numerous systemic diseases, such as diabetes mellitus and hepatic steatosis. Recent studies have also revealed an association with atherosclerosis.Areas covered: An analysis is presented on the mechanisms through which the hepatitis C viral infection can lead to a systemic increase in pro-inflammatory markers, especially tumor necrosis factor-a and interleukin-6. The immunological imbalance created may, through different mechanisms, act on the metabolic pathways that contribute to the development of insulin resistance, the accumulation of lipids in the liver, and even the formation of atherosclerotic plaques. Moreover, an additional contributing factor to the above-mentioned metabolic derangements is the unopposed oxidative stress observed in chronic hepatitis C viral infection. The virus itself contributes to the formation of oxidative stress, through alterations in the trace metal homeostasis and its effect on pro-inflammatory cytokines, such as tumor necrosis factor-a.Expert opinion: The scope of this review is to emphasize the importance of the metabolic manifestations of hepatitis C viral infection and to elucidate the pathophysiological mechanisms behind their emergence.

Systematic review: chronic viral hepatitis and metabolic derangement

BACKGROUND

The liver has a critical role in the metabolism of glucose and lipids. Chronic hepatitis B virus (HBV) or hepatitis C virus (HCV) infection leads to a spectrum of liver disease including chronic hepatitis, cirrhosis and hepatocellular carcinoma. Metabolic syndrome (MetS) has a rising incidence owing to an epidemic of type 2 diabetes mellitus (T2DM) and obesity. Non-alcoholic fatty liver disease is a liver manifestation of MetS and has become the most common cause of chronic liver disease worldwide.

AIM

To summarise the interplay among hepatitis viruses, MetS and its components.

METHODS

We searched the literature about HBV, HCV infection, MetS, fatty liver and its components from PubMed.

RESULTS

With respect to the viral replication cycle, lipids are important mediators between viral entry and hepatocyte in HCV infection, but not in HBV infection. Thus, HCV infection is inversely associated with hyperlipidaemia and lipid rebound occurs following sustained viral response induced by interferon-based therapy or direct antiviral agents. In addition, HCV infection is positively associated with insulin resistance, hepatic steatosis, MetS and the risk of T2DM and atherosclerosis. In contrast, HBV infection may protect infected subjects from the development of MetS and hepatic steatosis. Accumulating evidence suggests that HBV infection is inversely associated with lipid metabolism, and exhibits no conclusive association with insulin resistance or the risk of T2DM and arteriosclerosis.

CONCLUSIONS

In patients with viral hepatitis and concurrent metabolic diseases, a multidisciplinary approach should be given rather than simply antiviral treatment.

Endocrine disorders associated with hepatitis C virus chronic infection

The term "HCV syndrome" encompasses several organ- and systemic pathophysiological states, which often recognize autoimmunity or neoplastic evolution in their pathophysiology, as well as chronic HCV infection as trigger. The clinical features of HCV patients are heterogenous, and may include endocrine or metabolic disorders, namely autoimmune thyroiditis, type 2 diabetes mellitus, and erectile/sexual dysfunctions. In this review, we summarize current knowledge on the endocrine/metabolic diseases associated with chronic HCV infection, focusing on the main concepts emerged in the recent literature in this field. The application of this knowledge in everyday clinical practice may be relevant, in order to reinforce a holistic vision of the patient with chronic HCV infection, stimulating in turn a multi-disciplinary approach, thus increasing the probability of early diagnosis, more effective treatments, and a better prognostic outcome.

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.

Hepatitis C Virus NS5A Protein Promotes the Lysosomal Degradation of Hepatocyte Nuclear Factor 1α via Chaperone-Mediated Autophagy

Hepatitis C virus (HCV) infection is closely associated with type 2 diabetes. We reported that HCV infection induces the lysosomal degradation of hepatocyte nuclear factor 1 alpha (HNF-1α) via interaction with HCV nonstructural protein 5A (NS5A) protein, thereby suppressing GLUT2 gene expression. The molecular mechanisms of selective degradation of HNF-1α caused by NS5A are largely unknown. Chaperone-mediated autophagy (CMA) is a selective lysosomal degradation pathway. Here, we investigated whether CMA is involved in the selective degradation of HNF-1α in HCV-infected cells and observed that the pentapeptide spanning from amino acid (aa) 130 to aa 134 of HNF-1α matches the rule for the CMA-targeting motif, also known as KFERQ motif. A cytosolic chaperone protein, heat shock cognate protein of 70 kDa (HSC70), and a lysosomal membrane protein, lysosome-associated membrane protein type 2A (LAMP-2A), are key components of CMA. Immunoprecipitation analysis revealed that HNF-1α was coimmunoprecipitated with HSC70, whereas the Q130A mutation (mutation of Q to A at position 130) of HNF-1α disrupted the interaction with HSC70, indicating that the CMA-targeting motif of HNF-1α is important for the association with HSC70. Immunoprecipitation analysis revealed that increasing amounts of NS5A enhanced the association of HNF-1α with HSC70. To determine whether LAMP-2A plays a role in the degradation of HNF-1α protein, we knocked down LAMP-2A mRNA by RNA interference; this knockdown by small interfering RNA (siRNA) recovered the level of HNF-1α protein in HCV J6/JFH1-infected cells. This result suggests that LAMP-2A is required for the degradation of HNF-1α. Immunofluorescence study revealed colocalization of NS5A and HNF-1α in the lysosome. Based on our findings, we propose that HCV NS5A interacts with HSC70 and recruits HSC70 to HNF-1α, thereby promoting the lysosomal degradation of HNF-1α via CMA.IMPORTANCE Many viruses use a protein degradation system, such as the ubiquitin-proteasome pathway or the autophagy pathway, for facilitating viral propagation and viral pathogenesis. We investigated the mechanistic details of the selective lysosomal degradation of hepatocyte nuclear factor 1 alpha (HNF-1α) induced by hepatitis C virus (HCV) NS5A protein. Using site-directed mutagenesis, we demonstrated that HNF-1α contains a pentapeptide chaperone-mediated autophagy (CMA)-targeting motif within the POU-specific domain of HNF-1α. The CMA-targeting motif is important for the association with HSC70. LAMP-2A is required for degradation of HNF-1α caused by NS5A. We propose that HCV NS5A interacts with HSC70, a key component of the CMA machinery, and recruits HSC70 to HNF-1α to target HNF-1α for CMA-mediated lysosomal degradation, thereby facilitating HCV pathogenesis. We discovered a role of HCV NS5A in CMA-dependent degradation of HNF-1α. Our results may lead to a better understanding of the role of CMA in the pathogenesis of HCV.

Correlation of CD81 and SCARB1 polymorphisms on virological responses in Iranian patients with chronic hepatitis C virus genotype 1

The cluster of differentiation 81 (CD81) and scavenger receptor class B member 1 (SCARB1) plays an important role in the entry of hepatitis C virus (HCV). We assessed the correlation of five single nucleotide polymorphisms (SNPs) of CD81 (rs800136, rs2651842, rs2522012, rs800146, and rs708564) and SCARB1 rs10846744 polymorphisms with treatment responses in 395 treatment-naïve patients with chronic HCV (CHC) genotype 1 treated with pegylated interferon-α and ribavirin (pegIFN-α/RBV). The frequency of rapid virologic response (RVR), complete early virologic response (cEVR) and sustained virologic response (SVR) were 57.2%, 55.2%, and 58.2%, respectively. RVR, cEVR, and SVR were significantly associated with CD81 rs800136 (CC), CD81 rs2651842 (AA), CD81 rs708564 (TT), and SCARB1 rs10846744 (CC). High rates of RVR, cEVR, and SVR were reported for the CD81 rs800136 (CC), CD81 rs2651842 (AA), and CD81 rs708564 (TT) genotypes when correlated with higher levels of low-density lipoprotein (LDL) and lower levels of high-density lipoprotein (HDL) as well as lower levels of HDL and LDL in the SCARB1 rs10846744 (CC) genotype. In addition, patients with GG genotype had higher fasting blood glucose (FBS) level than those with CC genotype. In conclusion, CD81 and SCARB1 SNPs may serve as powerful predictor factors for treatment responses in CHC patients, and this effect is correlated with serum lipoprotein and FBS levels.

Regulation of insulin resistance and type II diabetes by hepatitis C virus infection: A driver function of circulating miRNAs

Hepatitis C virus (HCV) infection is a serious worldwide healthcare issue. Its association with various liver diseases including hepatocellular carcinoma (HCC) is well studied. However, the study on the relationship between HCV infection and the development of insulin resistance and diabetes is very limited. Current research has already elucidated some underlying mechanisms, especially on the regulation of metabolism and insulin signalling by viral proteins. More studies have emerged recently on the correlation between HCV infection‐derived miRNAs and diabetes and insulin resistance. However, no studies have been carried out to directly address if these miRNAs, especially circulating miRNAs, have causal effects on the development of insulin resistance and diabetes. Here, we proposed a new perspective that circulating miRNAs can perform regulatory functions to modulate gene expression in peripheral tissues leading to insulin resistance and diabetes, rather than just a passive factor associated with these pathological processes. The detailed rationales were elaborated through comprehensive literature review and bioinformatic analyses. miR‐122 was identified to be one of the most potential circulating miRNAs to cause insulin resistance. This result along with the idea about the driver function of circulating miRNAs will promote further investigations that eventually lead to the development of novel strategies to treat HCV infection‐associated extrahepatic comorbidities.

Robust Regression Analysis of GCMS Data Reveals Differential Rewiring of Metabolic Networks in Hepatitis B and C Patients

About one in 15 of the world’s population is chronically infected with either hepatitis virus B (HBV) or C (HCV), with enormous public health consequences. The metabolic alterations caused by these infections have never been directly compared and contrasted. We investigated groups of HBV-positive, HCV-positive, and uninfected healthy controls using gas chromatography-mass spectrometry analyses of their plasma and urine. A robust regression analysis of the metabolite data was conducted to reveal correlations between metabolite pairs. Ten metabolite correlations appeared for HBV plasma and urine, with 18 for HCV plasma and urine, none of which were present in the controls. Metabolic perturbation networks were constructed, which permitted a differential view of the HBV- and HCV-infected liver. HBV hepatitis was consistent with enhanced glucose uptake, glycolysis, and pentose phosphate pathway metabolism, the latter using xylitol and producing threonic acid, which may also be imported by glucose transporters. HCV hepatitis was consistent with impaired glucose uptake, glycolysis, and pentose phosphate pathway metabolism, with the tricarboxylic acid pathway fueled by branched-chain amino acids feeding gluconeogenesis and the hepatocellular loss of glucose, which most probably contributed to hyperglycemia. It is concluded that robust regression analyses can uncover metabolic rewiring in disease states.

SLC2A2 (GLUT2) as a novel prognostic factor for hepatocellular carcinoma

High rates of glucose transport via solute carrier (SLC2A, GLUT) family members are required to satisfy the high metabolic demands of cancer cells, and because of this characteristic of cancer cells 2-¹⁸fluoro-deoxy-D-glucose (¹⁸FDG)-PET has become a powerful diagnostic tool. However, its sensitivity for hepatocellular carcinoma (HCC) is lower than for other malignancies, which suggests SLC2A family members are differentially expressed in HCC. In the present study, the expression patterns of SLC2A family members in tumor tissues and their associations with HCC progression were analyzed using data obtained from The Cancer Genome Atlas (TCGA). It was found that the expression of SLC2A2 (GLUT2) was higher in HCC than those of other members of the SLC2A family. The associations of the expression levels of SLC2A family members and previously known prognostic factors with clinical stages were examined using the T-test or the Mann-Whitney U test, and interestingly, SLC2A2 expression was found to be associated with an advanced clinical stage (p = 0.0015). Furthermore, Kaplan-Meier analysis using the log-rank or the Gehan-Breslow-Wilcoxon test showed SLC2A2 expression was positively associated with overall survival (p < 0.001, Gehan-Breslow-Wilcoxon test and p = 0.0145 by multivariate Cox regression). The prognostic significance of SLC2A2 was similar in both early and late stages. However, it was more significant in HCC patients without alcohol consumption history and hepatitis C infection. Taken together, SLC2A2 was associated with clinical stages and independently associated with overall survival in patients with HCC. We suggest that SLC2A2 be considered a new prognostic factor for HCC.

Hepatitis C virus induces a prediabetic state by directly impairing hepatic glucose metabolism in mice

Virus-related type 2 diabetes is commonly observed in individuals infected with the hepatitis C virus (HCV); however, the underlying molecular mechanisms remain unknown. Our aim was to unravel these mechanisms using FL-N/35 transgenic mice expressing the full HCV ORF. We observed that these mice displayed glucose intolerance and insulin resistance. We also found that Glut-2 membrane expression was reduced in FL-N/35 mice and that hepatocyte glucose uptake was perturbed, partly accounting for the HCV-induced glucose intolerance in these mice. Early steps of the hepatic insulin signaling pathway, from IRS2 to PDK1 phosphorylation, were constitutively impaired in FL-N/35 primary hepatocytes via deregulation of TNFα/SOCS3. Higher hepatic glucose production was observed in the HCV mice, despite higher fasting insulinemia, concomitant with decreased expression of hepatic gluconeogenic genes. Akt kinase activity was higher in HCV mice than in WT mice, but Akt-dependent phosphorylation of the forkhead transcription factor FoxO1 at serine 256, which triggers its nuclear exclusion, was lower in HCV mouse livers. These findings indicate an uncoupling of the canonical Akt/FoxO1 pathway in HCV protein-expressing hepatocytes. Thus, the expression of HCV proteins in the liver is sufficient to induce insulin resistance by impairing insulin signaling and glucose uptake. In conclusion, we observed a complete set of events leading to a prediabetic state in HCV-transgenic mice, providing a valuable mechanistic explanation for HCV-induced diabetes in humans.

Hepatitis C virus-induced glucose metabolic disorder

Hepatitis C virus (HCV) infection often causes intrahepatic diseases, such as chronic hepatitis, liver chirrohsis, and hepatocellular carcinoma (HCC). Moreover, HCV infection exhibits various extrahepatic manifestations, such as thyroiditis, glucose and lipid metabolic disorder, and iron metabolic disorder. HCV infection is often associated with type 2 diabetes, involving hepatic fibrosis and poor prognosis. Type 2 diabetes increases the risk of HCC. We have been investigating molecular mechanisms of HCV-induced glucose metabolic disorder and we reported that HCV infection promotes hepatic gluconeogenesis through forkhead box O1 (FoxO1)-dependent pathway and that HCV infection suppresses the cell surface expression of glucose transporter 2 (GLUT2), resulting in suppression of glucose uptake. We have found that HCV NS5A protein plays important roles in these two independent pathways. Here we discuss the roles of HCV NS5A in HCV-induced glucose metabolic disorder.

Diabetes mellitus, insulin resistance and hepatitis C virus infection: A contemporary review

AIM

To summarise the literature data on hepatitis C virus (HCV)-infected patients concerning the prevalence of glucose abnormalities and associated risk.

METHODS

We conducted a PubMed search and selected all studies found with the key words "HCV" or "hepatitis C virus" and "diabetes" or "insulin resistance". We included only comparative studies written in English or in French, published from January 2000 to April 2015. We collected the literature data on HCV-infected patients concerning the prevalence of glucose abnormalities [diabetes mellitus (DM) and insulin resistance (IR)] and associated risk [i.e., severe liver fibrosis, response to antivirals, and the occurrence of hepatocellular carcinoma (HCC)].

RESULTS

HCV infection is significantly associated with DM/IR compared with healthy volunteers and patients with hepatitis B virus infection. Glucose abnormalities were associated with advanced liver fibrosis, lack of sustained virologic response to interferon alfa-based treatment and with a higher risk of HCC development. As new antiviral therapies may offer a cure for HCV infection, such data should be taken into account, from a therapeutic and preventive point of view, for liver and non-liver consequences of HCV disease. The efficacy of antidiabetic treatment in improving the response to antiviral treatment and in decreasing the risk of HCC has been reported by some studies but not by others. Thus, the effects of glucose abnormalities correction in reducing liver events need further studies.

CONCLUSION

Glucose abnormalities are strongly associated with HCV infection and show a negative impact on the main liver related outcomes.

Hepatitis C virus infection triggers a tumor-like glutamine metabolism

Chronic infection with hepatitis C virus (HCV) is one of the main causes of hepatocellular carcinoma. However, the molecular mechanisms linking the infection to cancer development remain poorly understood. Here we used HCV-infected cells and liver biopsies to study how HCV modulates the glutaminolysis pathway, which is known to play an important role in cellular energetics, stress defense, and neoplastic transformation. Transcript levels of glutaminolytic factors were quantified in Huh7.5 cells or primary human hepatocytes infected with the Japanese fulminant hepatitis 1 HCV strain as well as in biopsies of chronic HCV patients. Nutrient deprivation, biochemical analysis, and metabolite quantification were performed with HCV-infected Huh7.5 cells. Furthermore, short hairpin RNA vectors and small molecule inhibitors were used to investigate the dependence of HCV replication on metabolic changes. We show that HCV modulates the transcript levels of key enzymes of glutamine metabolism in vitro and in liver biopsies of chronic HCV patients. Consistently, HCV infection increases glutamine use and dependence. We finally show that inhibiting glutamine metabolism attenuates HCV infection and the oxidative stress associated with HCV infection.

CONCLUSION

Our data suggest that HCV establishes glutamine dependence, which is required for viral replication, and, importantly, that glutamine addiction is a hallmark of tumor cells. While HCV induces glutaminolysis to create an environment favorable for viral replication, it predisposes the cell to transformation. Glutaminolytic enzymes may be interesting therapeutic targets for prevention of hepatocarcinogenesis in chronic hepatitis C. (Hepatology 2017;65:789-803).

Transmissible Gastroenteritis Virus Infection Enhances SGLT1 and GLUT2 Expression to Increase Glucose Uptake

Transmissible gastroenteritis virus (TGEV) is a coronavirus that causes villus atrophy, followed by crypt hyperplasia, reduces the activities of intestinal digestive enzymes, and disrupts the absorption of intestinal nutrients. In vivo, TGEV primarily targets and infects intestinal epithelial cells, which play an important role in glucose absorption via the apical and basolateral transporters Na⁺-dependent glucose transporter 1 (SGLT1) and facilitative glucose transporter 2 (GLUT2), respectively. In this study, we therefore sought to evaluate the effects of TGEV infection on glucose uptake and SGLT1 and GLUT2 expression. Our data demonstrate that infection with TGEV resulted in increased glucose uptake and augmented expression of EGFR, SGLT1 and GLUT2. Moreover, inhibition studies showed that EGFR modulated glucose uptake in control and TGEV infected cells. Finally, high glucose absorption was subsequently found to promote TGEV replication.

Interaction of the hepatitis B virus X protein with the lysine methyltransferase SET and MYND domain-containing 3 induces activator protein 1 activation

Hepatitis B virus (HBV) is a widespread human pathogen that often causes chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. The detailed mechanisms underlying HBV pathogenesis remain poorly understood. The HBV X protein (HBx) is a multifunctional regulator that modulates viral replication and host cell functions, such as cell cycle progression, apoptosis and protein degradation through interaction with a variety of host factors. Recently, the nonstructural protein 5A (NS5A) of hepatitis C virus has been reported to interact with methyltransferase SET and MYND domain-containing 3 (SMYD3), which is implicated in chromatin modification and development of cancer. Because HBx shares fundamental regulatory functions concerning viral replication and pathogenesis with NS5A, it was decided to examine whether HBx interacts with SMYD3. In the present study, it was demonstrated by co-immunoprecipitation analysis that HBx interacts with both ectopically and endogenously expressed SMYD3 in Huh-7.5 cells. Deletion mutation analysis revealed that the C-terminal region of HBx (amino acids [aa] 131-154) and an internal region of SMYD3 (aa 269-288) are responsible for their interaction. Immunofluorescence and proximity ligation assays showed that HBx and SMYD3 co-localize predominantly in the cytoplasm. Luciferase reporter assay demonstrated that the interaction between HBx and SMYD3 activates activator protein 1 (AP-1) signaling, but not that of nuclear factor-kappa B (NF-κB). On the other hand, neither overexpression nor knockdown of SMYD3 altered production of HBV transcripts and HBV surface antigen (HBsAg). In conclusion, a novel HBx-interacting protein, SMYD3, was identified, leading to proposal of a novel mechanism of AP-1 activation in HBV-infected cells.

Association of SCARB1 Gene Polymorphisms with Virological Response in Chronic Hepatitis C Patients Receiving Pegylated Interferon plus Ribavirin Therapy

The scavenger receptor type B class I(SR-BI) is a receptor for high-density lipoproteins(HDL) and one of entry factors for hepatitis C virus(HCV). We examined the association of single nucleotide polymorphisms(SNPs) of the SCARB1 gene, which encodes SR-BI, with virologic responses to pegylated interferon-based treatment in Asian chronic hepatitis C(CHC) patients. Human genomic and clinical data were collected from 156 consecutive Taiwanese HCV genotype 1 or 2 patients who received pegylated interferon plus ribavirin therapy and 153 non-HCV healthy subjects. Three SNPs(rs10846744, rs5888, and rs3782287) of the SCARB1 gene that have been linked to humans diseases were investigated. rs10846744 rather than rs5888 or rs3782287 was associated with serum HCV RNA level and sustained virologic response(SVR) to pegylated interferon plus ribavirin therapy in CHC patients(GG vs. non-GG genotype, Adjusted Odds Ratio, 95% CI: 0.32, 0.11–0.95, P = 0.039). Among patients with IL28B rs8099917 non-TT genotypes, those with rs10846744 non-GG genotype had a higher SVR rate than those with GG genotypes. In addition, patients with GG genotype had a higher fasting blood glucose level than those with CC genotype. In conclusion, SCARB1 gene polymorphisms may serve as a potential predictor of treatment responses in CHC patients receiving interferon-based therapy. (ClinicalTrials.gov number, NCT02714712).

GLUT1-mediated glucose uptake plays a crucial role during Plasmodium hepatic infection

Intracellular pathogens have evolved mechanisms to ensure their survival and development inside their host cells. Here, we show that glucose is a pivotal modulator of hepatic infection by the rodent malaria parasite Plasmodium berghei and that glucose uptake via the GLUT1 transporter is specifically enhanced in P. berghei‐infected cells. We further show that ATP levels of cells containing developing parasites are decreased, which is known to enhance membrane GLUT1 activity. In addition, GLUT1 molecules are translocated to the membrane of the hepatic cell, increasing glucose uptake at later stages of infection. Chemical inhibition of GLUT1 activity leads to a decrease in glucose uptake and the consequent impairment of hepatic infection, both in vitro and in vivo. Our results reveal that changes in GLUT1 conformation and cellular localization seem to be part of an adaptive host response to maintain adequate cellular nutrition and energy levels, ensuring host cell survival and supporting P. berghei hepatic development.

Physical and functional interaction between hepatitis C virus NS5A protein and ovarian tumor protein deubiquitinase 7B

Hepatitis C virus (HCV) NS5A protein plays crucial roles in viral RNA replication, virus assembly, and viral pathogenesis. Although NS5A has no known enzymatic activity, it modulates various cellular pathways through interaction with cellular proteins. HCV NS5A (and other HCV proteins) are reportedly degraded through the ubiquitin-proteasome pathway; however, the physiological roles of ubiquitylation and deubiquitylation in HCV infection are largely unknown. To elucidate the role of deubiquitylation in HCV infection, an attempt was made to identify a deubiquitinase (DUB) that can interact with NS5A protein. An ovarian tumor protein (OTU), deubiquitinase 7B (OTUD7B), was identified as a novel NS5A-binding protein. Co-immunoprecipitation analyses showed that NS5A interacts with OTUD7B in both Huh-7 and HCV RNA replicon cells. Immunofluorescence staining revealed that HCV NS5A protein colocalizes with OTUD7B in the cytoplasm. Moreover, HCV infection was found to enhance the nuclear localization of OTUD7B. The OTUD7B-binding domain on NS5A was mapped using a series of NS5A deletion mutants. The present findings suggest that the domain I of NS5A is important and the region from amino acid 121 to 126 of NS5A essential for the interaction. Either V121A or V124A mutation in NS5A disrupts the NS5A-OTUD7B interaction. The results of this in vivo ubiquitylation assay suggest that HCV NS5A enhances OTUD7B DUB activity. Taken together, these results suggest that HCV NS5A protein interacts with OTUD7B, thereby modulating its DUB activity.

Oxidative Stress Attenuates Lipid Synthesis and Increases Mitochondrial Fatty Acid Oxidation in Hepatoma Cells Infected with Hepatitis C Virus

Cytopathic effects are currently believed to contribute to hepatitis C virus (HCV)-induced liver injury and are readily observed in Huh7.5 cells infected with the JFH-1 HCV strain, manifesting as apoptosis highly correlated with growth arrest. Reactive oxygen species, which are induced by HCV infection, have recently emerged as activators of AMP-activated protein kinase. The net effect is ATP conservation via on/off switching of metabolic pathways that produce/consume ATP. Depending on the scenario, this can have either pro-survival or pro-apoptotic effects. We demonstrate reactive oxygen species-mediated activation of AMP-activated kinase in Huh7.5 cells during HCV (JFH-1)-induced growth arrest. Metabolic labeling experiments provided direct evidence that lipid synthesis is attenuated, and β-oxidation is enhanced in these cells. A striking increase in nuclear peroxisome proliferator-activated receptor α, which plays a dominant role in the expression of β-oxidation genes after ligand-induced activation, was also observed, and we provide evidence that peroxisome proliferator-activated receptor α is constitutively activated in these cells. The combination of attenuated lipid synthesis and enhanced β-oxidation is not conducive to lipid accumulation, yet cellular lipids still accumulated during this stage of infection. Notably, the serum in the culture media was the only available source for polyunsaturated fatty acids, which were elevated (2-fold) in the infected cells, implicating altered lipid import/export pathways in these cells. This study also provided the first in vivo evidence for enhanced β-oxidation during HCV infection because HCV-infected SCID/Alb-uPA mice accumulated higher plasma ketones while fasting than did control mice. Overall, this study highlights the reprogramming of hepatocellular lipid metabolism and bioenergetics during HCV infection, which are predicted to impact both the HCV life cycle and pathogenesis.

HCV upregulates Bim through the ROS/JNK signalling pathway, leading to Bax-mediated apoptosis

We previously reported that hepatitis C virus (HCV) infection induces Bax-triggered, mitochondrion-mediated apoptosis by using the HCV J6/JFH1 strain and Huh-7.5 cells. However, it was still unclear how HCV-induced Bax activation. In this study, we showed that the HCV-induced activation and mitochondrial accumulation of Bax were significantly attenuated by treatment with a general antioxidant, N-acetyl cysteine (NAC), or a specific c-Jun N-terminal kinase (JNK) inhibitor, SP600125, with the result suggesting that the reactive oxygen species (ROS)/JNK signalling pathway is upstream of Bax activation in HCV-induced apoptosis. We also demonstrated that HCV infection transcriptionally activated the gene for the pro-apoptotic protein Bim and the protein expression of three major splice variants of Bim (BimEL, BimL and BimS). The HCV-induced increase in the Bim mRNA and protein levels was significantly counteracted by treatment with NAC or SP600125, suggesting that the ROS/JNK signalling pathway is involved in Bim upregulation. Moreover, HCV infection led to a marked accumulation of Bim on the mitochondria to facilitate its interaction with Bax. On the other hand, downregulation of Bim by siRNA (small interfering RNA) significantly prevented HCV-mediated activation of Bax and caspase 3. Taken together, these observations suggest that HCV-induced ROS/JNK signalling transcriptionally activates Bim expression, which leads to Bax activation and apoptosis induction.

A single-amino-acid mutation in hepatitis C virus NS5A disrupts physical and functional interaction with the transcription factor HNF-1α

Hepatitis C virus (HCV) infection often causes extrahepatic manifestations, such as type 2 diabetes. We previously reported that HCV infection induces the lysosomal degradation of the transcription factor HNF-1α via an interaction with viral NS5A, thereby suppressing GLUT2 gene expression. However, the molecular mechanism of NS5A-induced degradation of HNF-1α is largely unknown. We aimed to identify the determinants necessary for the degradation of HNF-1α induced by NS5A. Coimmunoprecipitation analysis revealed that the POU specific (POUs) domain spanning from aa 91 to 181 of HNF-1α is responsible for the interaction of NS5A. We also found that the region from aa 121 to 126 of NS5A, which is known as the binding motif of the HCV replication factor FKBP8, is important for the degradation of HNF-1α. A NS5A V121A mutation disrupted the NS5A-HNF-1α interaction as well as the degradation of HNF-1α. Our findings suggest that NS5A Val121 is crucial for viral pathogenesis.

Double stranded viral RNA induces inflammation and insulin resistance in skeletal muscle from pregnant women in vitro

OBJECTIVE

Maternal peripheral insulin resistance and increased inflammation are two features of pregnancies complicated by pre-existing maternal obesity and gestational diabetes mellitus (GDM). There is now increasing evidence that activation of Toll-like receptor (TLR) signalling pathways by viral products may play a role in the pathophysiology of diabetes. Thus, the aim of this study was to assess the effect of the TLR3 ligand and viral dsRNA analogue polyinosinic polycytidilic acid (poly(I:C)) on inflammation and the insulin signalling pathway in skeletal muscle from pregnant women.

MATERIALS/METHODS

Human skeletal muscle tissue explants were performed to determine the effect of poly(I:C) on the expression and secretion of markers of inflammation, and the insulin signalling pathway and glucose uptake.

RESULTS

Poly(I:C) significantly increased the expression of a number of inflammatory markers in skeletal muscle from pregnant women. Specifically, there was an increase in the expression and/or secretion of the pro-inflammatory cytokines TNF-α, and IL-6 and the pro-inflammatory chemokines IL-8 and MCP-1. These effect of poly(I:C) appear to mediated via a number of signalling molecules including the pro-inflammatory transcription factor NF-κB, and the serine threonine kinases GSK3 and AMPKα. Additionally, poly(I:C) decreased insulin stimulated GLUT-4 expression and glucose uptake in skeletal muscle from pregnant women.

CONCLUSIONS

The in vitro data presented in this study suggests that viral infection may contribute to the pathophysiology of pregnancies complicated by pre-existing maternal obesity and/or GDM. It should be noted that the in vitro studies cannot be directly used to infer the same outcomes in the intact subject.

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.

Inhibition of IRS-1 by hepatitis C virus infection leads to insulin resistance in a PTEN-dependent manner

Background

Hepatitis C virus (HCV) infection was recently recognized as an independent risk factor for insulin resistance (IR), the onset phase of type 2 diabetes mellitus (T2DM). Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) negatively regulates PI3K/Akt signaling pathway, which is critical for IR development and progression of cirrhosis to hepatocellular carcinoma (HCC). Here, we investigate the role of PTEN in HCV-associated IR and explored the mechanisms by which HCV regulates PTEN.

Methods

Western blotting was used to detect the levels of insulin signaling pathway components, including insulin receptor substrate-1 (IRS-1), phosphorylated IRS-1 (pIRS-1) at serine 307 (Ser307), both phosphorylated Akt (pAkt) and total Akt. A time-course experiment measuring activation of the insulin signaling pathway was performed to assess the effect of HCV infection on insulin sensitivity by examining the phosphorylation levels of Akt and GSK3β, a downstream target of Akt. Huh7.5.1 cells were transduced with a lentiviral vector expressing PTEN or PTEN shRNA, and IRS-1 and pIRS-1 (Ser307) levels were determined in both HCV-infected and uninfected cells. The pc-JFH1-core plasmid was constructed to explore the underlying mechanisms by which HCV regulated PTEN and therefore IRS-1 levels.

Results

HCV infection inhibited the insulin signaling pathway by reducing the levels of IRS-1 and pAkt/Akt while increasing phosphorylation of IRS-1 Ser307. In addition, HCV infection decreased the sensitivity to insulin-induced stimulation by inhibiting Akt and GSK3β phosphorylation. Furthermore, PTEN mRNA and protein levels were reduced upon HCV infection as well as transfection with the pc-JFH1-core plasmid. The reduction in IRS-1 level observed in HCV-infected cells was rescued to a limited extent by overexpression of PTEN, which in turn slightly reduced pIRS-1 (Ser307) level. In contrast, IRS-1 level were significantly decreased and phosphorylation of IRS-1 at Ser-307 was strongly enhanced by PTEN knockdown, suggesting that both reduction in IRS-1 level and increase in IRS-1 phosphorylation at Ser307 upon HCV infection occurred in a PTEN-dependent manner.

Conclusions

HCV infection suppresses the insulin signaling pathway and promotes IR by repressing PTEN, subsequently leading to decreased levels of IRS-1 and increased levels of pIRS-1 at Ser307. The findings provide new insight on the mechanism of HCV-associated IR.

Dysregulated hepatic expression of glucose transporters in chronic disease: contribution of semicarbazide-sensitive amine oxidase to hepatic glucose uptake

Insulin resistance is common in patients with chronic liver disease (CLD). Serum levels of soluble vascular adhesion protein-1 (VAP-1) are also increased in these patients. The amine oxidase activity of VAP-1 stimulates glucose uptake via translocation of transporters to the cell membrane in adipocytes and smooth muscle cells. We aimed to document human hepatocellular expression of glucose transporters (GLUTs) and to determine if VAP-1 activity influences receptor expression and hepatic glucose uptake. Quantitative PCR and immunocytochemistry were used to study human liver tissue and cultured cells. We also used tissue slices from humans and VAP-1-deficient mice to assay glucose uptake and measure hepatocellular responses to stimulation. We report upregulation of GLUT1, -3, -5, -6, -7, -8, -9, -10, -11, -12, and -13 in CLD. VAP-1 expression and enzyme activity increased in disease, and provision of substrate to hepatic VAP-1 drives hepatic glucose uptake. This effect was sensitive to inhibition of VAP-1 and could be recapitulated by H2O2. VAP-1 activity also altered expression and subcellular localization of GLUT2, -4, -9, -10, and -13. Therefore, we show, for the first time, alterations in hepatocellular expression of glucose and fructose transporters in CLD and provide evidence that the semicarbazide-sensitive amine oxidase activity of VAP-1 modifies hepatic glucose homeostasis and may contribute to patterns of GLUT expression in chronic disease.

Functional analyse of GLUT1 and GLUT12 in glucose uptake in goat mammary gland epithelial cells

Glucose transport, mediated by glucose transporters, is necessary for mammary gland development and lactation. GLUT1 and GLUT12 could both be expressed in the pregnant and lactating mammary gland to participate in the glucose uptake process. In this study, the goat GLUT1 and GLUT12 genes were cloned from Saanen dairy goats and transfected into goat mammary gland epithelial cells to assess their biological functions and distributions. The results showed that both goat GLUT1 and GLUT12 had 12 predicted membrane-spanning helices. Goat GLUT1 and GLUT12 each influenced the mRNA expression of the other transporter and increased the glucose consumption and lactose yield in GLUT1- and GLUT12-transfected goat mammary gland epithelial cells, respectively. The overexpression of GLUT1 or GLUT12 also increased the expression of amino acid transporters SLC1A5, SLC3A2 and SLC7A5 and affected genes expressions in GMGE cells. Using immunofluorescence staining, GLUT1 was detected throughout the cytoplasm and localized to the Golgi apparatus around the nuclear membrane, whereas GLUT12 was mainly distributed in the perinuclear region and cytoplasm. This study contributes to the understanding of how GLUT1 and GLUT12 cooperate in the incorporation of nutrient uptake into mammary gland epithelial cells and the promotion of milk synthesis in the goat mammary gland during lactation.

Hepatic expression and cellular distribution of the glucose transporter family

Glucose and other carbohydrates are transported into cells using members of a family of integral membrane glucose transporter (GLUT) molecules. To date 14 members of this family, also called the solute carrier 2A proteins have been identified which are divided on the basis of transport characteristics and sequence similarities into several families (Classes 1 to 3). The expression of these different receptor subtypes varies between different species, tissues and cellular subtypes and each has differential sensitivities to stimuli such as insulin. The liver is a contributor to metabolic carbohydrate homeostasis and is a major site for synthesis, storage and redistribution of carbohydrates. Situations in which the balance of glucose homeostasis is upset such as diabetes or the metabolic syndrome can lead metabolic disturbances that drive chronic organ damage and failure, confirming the importance of understanding the molecular regulation of hepatic glucose homeostasis. There is a considerable literature describing the expression and function of receptors that regulate glucose uptake and release by hepatocytes, the most import cells in glucose regulation and glycogen storage. However there is less appreciation of the roles of GLUTs expressed by non parenchymal cell types within the liver, all of which require carbohydrate to function. A better understanding of the detailed cellular distribution of GLUTs in human liver tissue may shed light on mechanisms underlying disease pathogenesis. This review summarises the available literature on hepatocellular expression of GLUTs in health and disease and highlights areas where further investigation is required.

Hepatitis C virus infection suppresses GLUT2 gene expression via downregulation of hepatocyte nuclear factor 1α

Hepatitis C virus (HCV) infection causes not only intrahepatic diseases but also extrahepatic manifestations, including type 2 diabetes. We previously reported that HCV replication suppresses cellular glucose uptake by downregulation of cell surface expression of glucose transporter 2 (GLUT2) (D. Kasai et al., J. Hepatol. 50:883-894, 2009). GLUT2 mRNA levels were decreased in both HCV RNA replicon cells and HCV J6/JFH1-infected cells. To elucidate molecular mechanisms of HCV-induced suppression of GLUT2 gene expression, we analyzed transcriptional regulation of the GLUT2 promoter using a series of GLUT2 promoter-luciferase reporter plasmids. HCV-induced suppression of GLUT2 promoter activity was abrogated when the hepatocyte nuclear factor 1α (HNF-1α)-binding motif was deleted from the GLUT2 promoter. HNF-1α mRNA levels were significantly reduced in HCV J6/JFH1-infected cells. Furthermore, HCV infection remarkably decreased HNF-1α protein levels. We assessed the effects of proteasome inhibitor or lysosomal protease inhibitors on the HCV-induced reduction of HNF-1α protein levels. Treatment of HCV-infected cells with a lysosomal protease inhibitor, but not with a proteasome inhibitor, restored HNF-1α protein levels, suggesting that HCV infection promotes lysosomal degradation of HNF-1α protein. Overexpression of NS5A protein enhanced lysosomal degradation of HNF-1α protein and suppressed GLUT2 promoter activity. Immunoprecipitation analyses revealed that the region from amino acids 1 to 126 of the NS5A domain I physically interacts with HNF-1α protein. Taken together, our results suggest that HCV infection suppresses GLUT2 gene expression via downregulation of HNF-1α expression at transcriptional and posttranslational levels. HCV-induced downregulation of HNF-1α expression may play a crucial role in glucose metabolic disorders caused by HCV.

JC virus T-antigen regulates glucose metabolic pathways in brain tumor cells

Recent studies have reported the detection of the human neurotropic virus, JCV, in a significant population of brain tumors, including medulloblastomas. Accordingly, expression of the JCV early protein, T-antigen, which has transforming activity in cell culture and in transgenic mice, results in the development of a broad range of tumors of neural crest and glial origin. Evidently, the association of T-antigen with a range of tumor-suppressor proteins, including p53 and pRb, and signaling molecules, such as β-catenin and IRS-1, plays a role in the oncogenic function of JCV T-antigen. We demonstrate that T-antigen expression is suppressed by glucose deprivation in medulloblastoma cells and in glioblastoma xenografts that both endogenously express T-antigen. Mechanistic studies indicate that glucose deprivation-mediated suppression of T-antigen is partly influenced by 5′-activated AMP kinase (AMPK), an important sensor of the AMP/ATP ratio in cells. In addition, glucose deprivation-induced cell cycle arrest in the G1 phase is blocked with AMPK inhibition, which also prevents T-antigen downregulation. Furthermore, T-antigen prevents G1 arrest and sustains cells in the G2 phase during glucose deprivation. On a functional level, T-antigen downregulation is partially dependent on reactive oxygen species (ROS) production during glucose deprivation, and T-antigen prevents ROS induction, loss of ATP production, and cytotoxicity induced by glucose deprivation. Additionally, we have found that T-antigen is downregulated by the glycolytic inhibitor, 2-deoxy-D-glucose (2-DG), and the pentose phosphate inhibitors, 6-aminonicotinamide and oxythiamine, and that T-antigen modulates expression of the glycolytic enzyme, hexokinase 2 (HK2), and the pentose phosphate enzyme, transaldolase-1 (TALDO1), indicating a potential link between T-antigen and metabolic regulation. These studies point to the possible involvement of JCV T-antigen in medulloblastoma proliferation and the metabolic phenotype and may enhance our understanding of the role of viral proteins in glycolytic tumor metabolism, thus providing useful targets for the treatment of virus-induced tumors.

Hepatitis C virus activates the mTOR/S6K1 signaling pathway in inhibiting IRS-1 function for insulin resistance

Hepatitis C virus (HCV) infection significantly increases the prevalence of type 2 diabetes mellitus (T2DM). Insulin receptor substrate 1 (IRS-1) plays a key role in insulin signaling, thus enabling metabolic regulation in mammalian cells. We have previously shown that HCV infection modulates phosphorylation of Akt, a downstream target of IRS-1. In this study, we further examined the status of total IRS-1 and the downstream regulation of the Akt pathway in understanding mTOR/S6K1 signaling using HCV genotype 2a (clone JFH1)-infected hepatocytes. Inhibition of IRS-1 expression was observed in HCV-infected hepatocytes compared to that in a mock-infected control. The status of the tuberous sclerosis complex (TSC-1/TSC-2) was significantly decreased after HCV infection of human hepatocytes, showing a modulation of the downstream Akt pathway. Subsequent study indicated an increased level of Rheb and mTOR expression in HCV-infected hepatocytes. Interestingly, the phosphoS6K1 level was higher in HCV-infected hepatocytes, suggesting a novel mechanism for IRS-1 inhibition. Ectopic expression of TSC-1/TSC-2 significantly recovered the IRS-1 protein expression level in HCV-infected hepatocytes. Further analyses indicated that HCV core protein plays a significant role in modulating the mTOR/S6K1 signaling pathway. Proteasome inhibitor MG 132 recovered IRS-1 and TSC1/2 expression, suggesting that degradation occurred via the ubiquitin proteasome pathway. A functional consequence of IRS-1 inhibition was reflected in a decrease in GLUT4 protein expression and upregulation of the gluconeogenic enzyme PCK2 in HCV-infected hepatocytes. Together, these observations suggested that HCV infection activates the mTOR/S6K1 pathway in inhibiting IRS-1 function and perturbs glucose metabolism via downregulation of GLUT4 and upregulation of PCK2 for insulin resistance.