Hepatic inflammation mediated by hepatitis C virus core protein is ameliorated by blocking complement activation

From complement to complosome in non-alcoholic fatty liver disease: When location matters

Non-alcoholic fatty liver disease (NAFLD) is a growing public health threat and becoming the leading cause of liver transplantation. Nevertheless, no approved specific treatment is currently available for NAFLD. The pathogenesis of NAFLD is multifaceted and not yet fully understood. Accumulating evidence suggests a significant role of the complement system in the development and progression of NAFLD. Here, we provide an overview of the complement system, incorporating the novel concept of complosome, and summarise the up-to-date evidence elucidating the association between complement dysregulation and the pathogenesis of NAFLD. In this process, the extracellular complement system is activated through various pathways, thereby directly contributing to, or working together with other immune cells in the disease development and progression. We also introduce the complosome and assess the evidence that implicates its potential influence in NAFLD through its direct impact on hepatocytes or non-parenchymal liver cells. Additionally, we expound upon how complement system and the complosome may exert their effects in relation with hepatic zonation in NAFLD. Furthermore, we discuss the potential therapeutic implications of targeting the complement system, extracellularly and intracellularly, for NAFLD treatment. Finally, we present future perspectives towards a better understanding of the complement system's contribution to NAFLD.

A Dual Role of Complement Activation in the Development of Fulminant Hepatic Failure Induced by Murine-Beta-Coronavirus Infection

With the epidemic of betacoronavirus increasing frequently, it poses a great threat to human public health. Therefore, the research on the pathogenic mechanism of betacoronavirus is becoming greatly important. Murine hepatitis virus strain-3 (MHV-3) is a strain of betacoronavirus which cause tissue damage especially fulminant hepatic failure (FHF) in mice, and is commonly used to establish models of acute liver injury. Recently, MHV-3-infected mice have also been introduced to a mouse model of COVID-19 that does not require a Biosafety Level 3 (BSL-3) facility. FHF induced by MHV-3 is a type of severe liver damage imbalanced by regenerative hepatocellular activity, which is related to numerous factors. The complement system plays an important role in host defense and inflammation and is involved in first-line immunity and/or pathogenesis of severe organ disorders. In this study, we investigated the role of aberrant complement activation in MHV-3 infection-induced FHF by strategies that use C3-deficient mice and intervene in the complement system. Our results showed that mice deficient in C3 had more severe liver damage, a higher viral load in the liver and higher serum concentrations of inflammatory cytokines than wild-type controls. Treatment of C57BL/6 mice with C3aR antagonist or anti-C5aR antibody reduced liver damage, viral load, and serum IFN-γ concentration compared with the control group. These findings indicated that complement system acts as a double-edged sword during acute MHV-3 infection. However, its dysregulated activation leads to sustained inflammatory responses and induces extensive liver damage. Collectively, by investigating the role of complement activation in MHV-3 infection, we can further understand the pathogenic mechanism of betacoronavirus, and appropriate regulation of immune responses by fine-tuning complement activation may be an intervention for the treatment of diseases induced by betacoronavirus infection.

Altering retinol binding protein 4 levels in hepatitis C: Inflammation and steatosis matter

Both hepatitis C virus (HCV) infection and retinol-binding protein 4 (RBP4) might contribute to insulin resistance (IR), how RBP4 links to IR in HCV infection remain elusive. A joint study of a prospective cohort of 842 chronically HCV-infected (CHC) patients (with 842 controls) and a line of HCV core transgenic mice was conducted. Of 842 patients, 771 had completed anti-HCV therapy and 667 had sustained virological responses (SVRs). Compared with controls, CHC patients had lower RBP4 levels. At baseline, age (95% CI β: -0.87~-0.317), BMI (0.516~2.036), triglycerides (0.03~0.127), neutrophil-to-lymphocyte ratio (NLR) (1.561~7.327), and estimated glomerular filtration rate (eGFR) (-0.342~-0.149) levels were associated with RBP4 levels in CHC patients. At 24-week post-therapy, male sex (0.652~8.129), BMI (0.199~1.254), triglycerides (0.039~0.088), uric acid (0.599~3.067), eGFR (-0.247 ~-0.14) levels, and fibrosis-4 (-3.602~-0.039) scores were associated with RBP4 levels in SVR patients; compared with baseline, except genotype 3 HCV-infected patients, SVR patients had increased RBP4 levels, which were comparable with controls, while no HOMA-IR index alteration was noted after SVR. The HCV core transgenic mice exhibited nonobese hepatic steatosis, had higher hepatic RBP4 expression, higher serum levels of RBP4 and triglycerides, but comparable HOMA-IR levels than non-transgenic littermates. In conclusion, steatosis, sex, age, uric acid, NLR, and FIB-4 levels were associated with HCV-related RBP4 levels; BMI, triglycerides, and eGFR levels were associated with non-HCV-related RBP4 levels. Reversal of low RBP4 levels after SVR was evident in non-genotype 3 HCV-infected patients. Steatosis and inflammation linked with metabolic alteration other than IR, determined RBP4 levels in HCV-infected patients.

Association between Leptin and Complement in Hepatitis C Patients with Viral Clearance: Homeostasis of Metabolism and Immunity

BACKGROUND

The association between leptin and complement in hepatitis C virus (HCV) infection remains unknown.

METHODS

A prospective study was conducted including 474 (250 genotype 1, 224 genotype 2) consecutive chronic hepatitis C (CHC) patients who had completed an anti-HCV therapy course and undergone pre-therapy and 24-week post-therapy assessments of interferon λ3-rs12979860 and HCV RNA/genotypes, anthropometric measurements, metabolic and liver profiles, and complement component 3 (C3), C4, and leptin levels.

RESULTS

Of the 474 patients, 395 had a sustained virological response (SVR). Pre-therapy leptin levels did not differ between patients with and without an SVR. Univariate and multivariate analyses showed that sex (pre- and post-therapy, p<0.001), body mass index (BMI) (pre- and post-therapy, p<0.001), and C3 levels (pre-therapy, p = 0.027; post-therapy, p = 0.02) were independently associated with leptin levels with or without HCV infection. Pre-therapy BMI, total cholesterol (TC), C4 levels, and the rs12979860 genotype were independently associated with pre-therapy C3 levels in all patients. Post-therapy BMI, alanine aminotransferase, TC, C4 levels, white blood cell counts, and hepatic steatosis were independently associated with the post-therapy C3 levels of SVR patients. Compared with pre-therapy levels, SVR patients showed higher 24-week post-therapy C4 (20.32+/-7.30 vs. 21.55+/-7.07 mg/dL, p<0.001) and TC (171.68+/-32.67 vs. 186.97+/-36.09 mg/dL, p<0.001) levels; however, leptin and C3 levels remained unchanged after therapy in patients with and without an SVR.

CONCLUSIONS

Leptin and C3 may maintain immune and metabolic homeostasis through association with C4 and TC. Positive alterations in C4 and TC levels reflect viral clearance after therapy in CHC patients.

Plasma protein biomarkers of hepatocellular carcinoma in HCV-infected alcoholic patients with cirrhosis

Hepatocellular carcinoma (HCC) is one of the most common and lethal cancers in the world, with limited options for treatment unless timely diagnosed. Chronic hepatitis C virus (HCV) infection and persistent heavy alcohol consumption are independent risk factors for HCC development, which may induce a specific protein expression pattern different from those caused separately. The aim of the study was to identify protein biomarkers for the detection of HCC in HCV-infected alcoholic patients with cirrhosis in order to improve survival. We compared protein expression profiles of plasma samples from 52 HCV-infected alcoholic patients with and without HCC, using 2-D DIGE coupled with MALDI-TOF/TOF mass spectrometry. The 2-D DIGE results were analyzed statistically using Decyder software, and verified by western-blot and ELISA. In plasma samples from HCV-infected alcoholic patients, we found significantly differential expression profiles of carboxypeptidase-N, ceruloplasmin (CP), complement component 4a (C4a), fibrinogen-alpha (FGA), immunoglobulin mu chain C region, serum albumin, and serum paraoxonase/arylesterase 1 (PON1). Deregulation of plasma/serum levels of the identified proteins was associated to HCV, ethanol consumption, and/or HCC progression. In the validation through ELISA, C4a serum concentration was increased in HCC patients (2.4±1 ng/mg vs 1.8±0.6 ng/mg; p = 0.029), being the only independent predictor of HCC in the multivariate analysis (OR = 2.15; p = 0.015), with an AUROC = 0.70. The combination of C4a, FGA, CP and PON1 improved slightly the predictive ability of C4a alone (AUROC 0.81). In conclusion, we identified proteins related to acute-phase response, oxidative stress, or immune response, whose differential expression in plasma may be attributed to the presence of HCC. Among them, C4a, and its combination with CP, FGA and PON1, could be considered as potentially reliable biomarkers for the detection of HCC in HCV-infected alcoholic patients.

Production and pathogenicity of hepatitis C virus core gene products

Hepatitis C virus (HCV) is a major cause of chronic liver diseases, including steatosis, cirrhosis and hepatocellular carcinoma, and its infection is also associated with insulin resistance and type 2 diabetes mellitus. HCV, belonging to the Flaviviridae family, is a small enveloped virus whose positive-stranded RNA genome encoding a polyprotein. The HCV core protein is cleaved first at residue 191 by the host signal peptidase and further cleaved by the host signal peptide peptidase at about residue 177 to generate the mature core protein (a.a. 1-177) and the cleaved peptide (a.a. 178-191). Core protein could induce insulin resistance, steatosis and even hepatocellular carcinoma through various mechanisms. The peptide (a.a. 178-191) may play a role in the immune response. The polymorphism of this peptide is associated with the cellular lipid drop accumulation, contributing to steatosis development. In addition to the conventional open reading frame (ORF), in the +1 frame, an ORF overlaps with the core protein-coding sequence and encodes the alternative reading frame proteins (ARFP or core+1). ARFP/core+1/F protein could enhance hepatocyte growth and may regulate iron metabolism. In this review, we briefly summarized the current knowledge regarding the production of different core gene products and their roles in viral pathogenesis.

Serum complements C3 and C4 in chronic HCV infection and their correlation with response to pegylated interferon and ribavirin treatment

BACKGROUND AND STUDY AIMS

To search for an immunological parameter that may correlate with the response to interferon (IFN) treatment is very crucial. The objective of this study was to correlate the levels of C3 and C4 complement components with the response to IFN treatment in patients with chronic hepatitis C virus (HCV) infection.

PATIENTS AND METHODS

This study was conducted on 100 patients and control subjects classified into three groups. Group (I) consisted of 50 patients with chronic hepatitis C who were receiving IFN treatment and showed various responses; group (II) included 25 patients with chronic hepatitis C naive to IFN treatment; and group (III) included 25 healthy subjects matched for age and sex who served as controls. Measurement of the level of complement C3 and C4 was done by a quantitative turbidimetric test. Measurement of complement levels in group (I) was done at the end of treatment at the 48th week.

RESULTS

Serum levels of C3 and C4 were found to be significantly reduced in all patients with chronic HCV infection in both groups (I and II) compared to the healthy control group (III) (p<0.05). Moreover, chronic HCV patients treated with IFN and ribavirin had significantly lower levels of C3 and C4 compared with patients naive to IFN and ribavirin treatment. At the end of treatment, both C3 and C4 had significantly increased in responders to IFN when compared to non-responders (p=0.025 and 0.05, respectively). There was a significant negative correlation between C3 and C4 levels and the concentration of serum alanine aminotransferase (ALT) measured simultaneously.

CONCLUSION

Higher C3 and C4 serum concentrations were found to be positively correlated to the end-of-treatment response in patients with chronic HCV infection treated with IFN and ribavirin.

Chronic HCV infection and inflammation: Clinical impact on hepatic and extra-hepatic manifestations

The liver has a central role in regulating inflammation by its capacity to secrete a number of proteins that control both local and systemic inflammatory responses. Chronic inflammation or an exaggerated inflammatory response can produce detrimental effects on target organs. Chronic hepatitis C virus (HCV) infection causes liver inflammation by complex and not yet well-understood molecular pathways, including direct viral effects and indirect mechanisms involving cytokine pathways, oxidative stress and steatosis induction. An increasing body of evidence recognizes the inflammatory response in chronic hepatitis C as pathogenically linked to the development of both liver-limited injury (fibrosis, cirrhosis and hepatocellular carcinoma) and extrahepatic HCV-related diseases (lymphoproliferative disease, atherosclerosis, cardiovascular and brain disease). Defining the complex mechanisms of HCV-induced inflammation could be crucial to determine the global impact of infection, to estimate progression of the disease, and to explore novel therapeutic approaches to avert HCV-related diseases. This review focuses on HCV-related clinical conditions as a result of chronic liver and systemic inflammatory states.

Identification and comparative analysis of hepatitis C virus-host cell protein interactions

Hepatitis C virus (HCV) alters the global behavior of the host cell to create an environment conducive to its own replication, but much remains unknown about how HCV proteins elicit these changes. Thus, a better understanding of the interface between the virus and host cell is required. Here we report the results of a large-scale yeast two-hybrid screen to identify protein-protein interactions between HCV genotype 2a (strain JFH1) and cellular factors. Our study identified 112 unique interactions between 7 HCV and 94 human proteins, over 40% of which have been linked to HCV infection by other studies. These interactions develop a more complete picture of HCV infection, providing insight into HCV manipulation of pathways, such as lipid and cholesterol metabolism, that were previously linked to HCV infection and implicating novel targets within microtubule-organizing centers, the complement system and cell cycle regulatory machinery. In an effort to understand the relationship between HCV and related viruses, we compared the HCV 2a interactome to those of other HCV genotypes and to the related dengue virus. Greater overlap was observed between HCV and dengue virus targets than between HCV genotypes, demonstrating the value of parallel screening approaches when comparing virus-host cell interactomes. Using siRNAs to inhibit expression of cellular proteins, we found that five of the ten shared targets tested (CUL7, PCM1, RILPL2, RNASET2, and TCF7L2) were required for replication of both HCV and dengue virus. These shared interactions provide insight into common features of the viral life cycles of the family Flaviviridae.

Specific acquisition of functional CD59 but not CD46 or CD55 by hepatitis C virus

Viruses of different families encode for regulators of the complement system (RCAs) or acquire such RCAs from the host to get protection against complement-mediated lysis (CML). As hepatitis C virus (HCV) shares no genetic similarity to any known RCA and is detectable at high titers in sera of infected individuals, we investigated whether HCV has adapted host-derived RCAs to resist CML. Here we report that HCV selectively incorporates CD59 while neither CD55, nor CD46 are associated with the virus. The presence of CD59 was shown by capture assays using patient- and cell culture-derived HCV isolates. Association of CD59 with HCV was further confirmed by Western blot analysis using purified viral supernatants from infected Huh 7.5 cells. HCV captured by antibodies specific for CD59 remained infectious for Huh 7.5 cells. In addition, blocking of CD59 in the presence of active complement reduced the titer of HCV most likely due to CML. HCV produced in CD59 knock-down cells were more significantly susceptible to CML compared to wild type virus, but neither replication, assembly nor infectivity of the virus seemed to be impaired in the absence of CD59. In summary our data indicate that HCV incorporates selectively CD59 in its envelope to gain resistance to CML in serum of infected individuals.

Molecular characterization of transcriptome-wide interactions between highly pathogenic porcine reproductive and respiratory syndrome virus and porcine alveolar macrophages in vivo

Porcine reproductive and respiratory syndrome virus (PRRSV) infects mainly the porcine alveolar macrophages (PAMs) and causes porcine reproductive and respiratory syndrome (PRRS). Previous studies have analyzed the global gene expression profiles of lung tissue in vivo and PAMs in vitro following infection with PRRSV, however, transcriptome-wide understanding of the interaction between highly pathogenic PRRSV (HP-PRRSV) and PAMs in vivo has not yet been established. In this study, we employed Affymetrix microarrays to investigate the gene expression patterns of PAMs isolated from Tongcheng piglets (a Chinese indigenous breed) after infection with HP-PRRSV. During the infection, Tongcheng piglets exhibited typical clinical signs, e.g. fever, asthma, coughing, anorexia, lethargy and convulsion, but displayed mild regional lung damage at 5 and 7 dpi. Microarray analysis revealed that HP-PRRSV infection has affected PAMs in expression of the important genes involved in cytoskeleton and exocytosis organization, protein degradation and folding, intracellular calcium and zinc homeostasis. Several potential antiviral strategies might be employed in PAMs, including upregulating IFN-induced genes and increasing intracellular zinc ion concentration. And inhibition of the complement system likely attenuated the lung damage during HP-PRRSV infection. Transcriptomic analysis of PAMs in vivo could lead to a better understanding of the HP-PRRSV-host interaction, and to the identification of novel antiviral therapies and genetic components of swine tolerance/susceptibility to HP-PRRS.

Tissue-specific subnetworks and characteristics of publicly available human protein interaction databases

MOTIVATION

Protein-protein interaction (PPI) databases are widely used tools to study cellular pathways and networks; however, there are several databases available that still do not account for cell type-specific differences. Here, we evaluated the characteristics of six interaction databases, incorporated tissue-specific gene expression information and finally, investigated if the most popular proteins of scientific literature are involved in good quality interactions.

RESULTS

We found that the evaluated databases are comparable in terms of node connectivity (i.e. proteins with few interaction partners also have few interaction partners in other databases), but may differ in the identity of interaction partners. We also observed that the incorporation of tissue-specific expression information significantly altered the interaction landscape and finally, we demonstrated that many of the most intensively studied proteins are engaged in interactions associated with low confidence scores. In summary, interaction databases are valuable research tools but may lead to different predictions on interactions or pathways. The accuracy of predictions can be improved by incorporating datasets on organ- and cell type-specific gene expression, and by obtaining additional interaction evidence for the most 'popular' proteins.

CONTACT

kitano@sbi.jp

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Complement and viral pathogenesis

The complement system functions as an immune surveillance system that rapidly responds to infection. Activation of the complement system by specific recognition pathways triggers a protease cascade, generating cleavage products that function to eliminate pathogens, regulate inflammatory responses, and shape adaptive immune responses. However, when dysregulated, these powerful functions can become destructive and the complement system has been implicated as a pathogenic effector in numerous diseases, including infectious diseases. This review highlights recent discoveries that have identified critical roles for the complement system in the pathogenesis of viral infection.

New insights of an old defense system: structure, function, and clinical relevance of the complement system

The complement system was discovered a century ago as a potent defense cascade of innate immunity. After its first description, continuous experimental and clinical research was performed, and three canonical pathways of activation were established. Upon activation by traumatic or surgical tissue damage, complement reveals beneficial functions of pathogen and danger defense by sensing and clearing injured cells. However, the latest research efforts have provided a more distinct insight into the complement system and its clinical subsequences. Complement has been shown to play a significant role in the pathogenesis of various inflammatory processes such as sepsis, multiorgan dysfunction, ischemia/reperfusion, cardiovascular diseases and many others. The three well-known activation pathways of the complement system have been challenged by newer findings that demonstrate direct production of central complement effectors (for example, C5a) by serine proteases of the coagulation cascade. In particular, thrombin is capable of producing C5a, which not only plays a decisive role on pathogens and infected/damaged tissues, but also acts systemically. In the case of uncontrolled complement activation, “friendly fire” is generated, resulting in the destruction of healthy host tissue. Therefore, the traditional research that focuses on a mainly positive-acting cascade has now shifted to the negative effects and how tissue damage originated by the activation of the complement can be contained. In a translational approach including structure-function relations of this ancient defense system, this review provides new insights of complement-mediated clinical relevant diseases and the development of complement modulation strategies and current research aspects.