HCV core and NS3 proteins mediate toll like receptor induced innate immune response in corneal epithelium

Dry eye disease caused by viral infection: Past, present and future

Following viral infection, the innate immune system senses viral products, such as viral nucleic acids, to activate innate defence pathways, leading to inflammation and apoptosis, control of cell proliferation, and consequently, threat to the whole body. The ocular surface is exposed to the external environment and extremely vulnerable to viral infection. Several studies have revealed that viral infection can induce inflammation of the ocular surface and reduce tear secretion of the lacrimal gland (LG), consequently triggering ocular morphological and functional changes and resulting in dry eye disease (DED). Understanding the mechanisms of DED caused by viral infection and its potential therapeutic strategies are crucial for clinical interventional advances in DED. This review summarizes the roles of viral infection in the pathogenesis of DED, applicable diagnostic and therapeutic strategies, and potential regions of future studies.

Flaviviridae Nonstructural Proteins: The Role in Molecular Mechanisms of Triggering Inflammation

Members of the Flaviviridae family are posing a significant threat to human health worldwide. Many flaviviruses are capable of inducing severe inflammation in humans. Flaviviridae nonstructural proteins, apart from their canonical roles in viral replication, have noncanonical functions strongly affecting antiviral innate immunity. Among these functions, antagonism of type I IFN is the most investigated; meanwhile, more data are accumulated on their role in the other pathways of innate response. This review systematizes the last known data on the role of Flaviviridae nonstructural proteins in molecular mechanisms of triggering inflammation, with an emphasis on their interactions with TLRs and RLRs, interference with NF-κB and cGAS-STING signaling, and activation of inflammasomes.

Toll-like Receptor Response to Hepatitis C Virus Infection: A Recent Overview

Hepatitis C virus (HCV) infection remains a major global health burden, causing chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Toll-like receptors (TLRs) are evolutionarily conserved pattern recognition receptors that detect pathogen-associated molecular patterns and activate downstream signaling to induce proinflammatory cytokine and chemokine production. An increasing number of studies have suggested the importance of TLR responses in the outcome of HCV infection. However, the exact role of innate immune responses, including TLR response, in controlling chronic HCV infection remains to be established. A proper understanding of the TLR response in HCV infection is essential for devising new therapeutic approaches against HCV infection. In this review, we discuss the progress made in our understanding of the host innate immune response to HCV infection, with a particular focus on the TLR response. In addition, we discuss the mechanisms adopted by HCV to avoid immune surveillance mediated by TLRs.

AIP1 suppresses neovascularization by inhibiting the NOX4-induced NLRP3/NLRP6 imbalance in a murine corneal alkali burn model

Background

Apoptosis signal-regulating kinase 1-interacting protein 1 (AIP1) participates in inflammatory neovascularization induction. NADPH oxidase 4 (NOX4) produces reactive oxygen species (ROS), leading to an imbalance in nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3) and NLR family pyrin domain containing 6 (NLRP6) expression. The mechanisms of AIP1, NOX4, ROS and inflammasomes in corneal neovascularization were studied herein.

Methods

C57BL/6 and AIP1-knockout mice were used in this study. The alkali burn procedure was performed on the right eye. Adenovirus encoding AIP1 plus green fluorescence protein (GFP) (Ad-AIP1-GFP) or GFP alone was injected into the right anterior chamber, GLX351322 was applied as a NOX4 inhibitor, and then corneal neovascularization was scored. The expression of related genes was measured by quantitative real-time polymerase chain reaction, western blotting and immunofluorescence staining. 2′,7′-Dichlorofluorescin diacetate staining was used to determine the ROS levels.

Results

The expression of AIP1 was decreased, while that of cleaved interleukin-1β (clv-IL-1β) and vascular endothelial growth factor A (VEGFa) was increased after alkali burn injury. NOX4 expression was increased, the imbalance in NLRP3/NLRP6 was exacerbated, and corneal neovascularization was increased significantly in AIP1-knockout mice compared with those in C57BL/6 mice after alkali burns. These effects were reversed by AIP1 overexpression. NLRP3/NLRP6 expression was imbalanced after alkali burns. GLX351322 reversed the imbalance in NLRP3/NLRP6 by reducing the ROS levels. This treatment also reduced the expression of clv-IL-1β and VEGFa, suppressing neovascularization.

Conclusions

AIP1 and NOX4 can regulate corneal inflammation and neovascularization after alkali burn injury. Based on the pathogenesis of corneal neovascularization, these findings are expected to provide new therapeutic strategies for patients.

Plain English summary

Corneal alkali burn injury is a common type of ocular injury that is difficult to treat in the clinic. The cornea is a clear and avascular tissue. Corneal neovascularization after alkali burn injury is a serious complication; it not only seriously affects the patient’s vision but also is the main reason for failed corneal transplantation. Corneal neovascularization affects approximately 1.4 million patients a year. We show for the first time that AIP1 and NOX4 can regulate corneal inflammation and neovascularization after alkali burns. The expression of AIP1 was decreased, while that of clv-IL-1β and VEGFa was increased after alkali burns. We tried to elucidate the specific molecular mechanisms by which AIP1 regulates corneal neovascularization. NOX4 activation was due to decreased AIP1 expression in murine corneas with alkali burns. NOX4 expression was increased, the imbalance in NLRP3/NLRP6 was exacerbated, and corneal neovascularization was increased significantly in AIP1-knockout mice compared with those in C57BL/6 mice after alkali burns. These effects were reversed by AIP1 overexpression. Additionally, NLRP3/NLRP6 expression was unbalanced, with NLRP3 activation and NLRP6 suppression in the corneal alkali burn murine model. Eye drops containing GLX351322, a NOX4 inhibitor, reversed the imbalance in NLRP3/NLRP6 by reducing ROS expression. This treatment also reduced the expression of clv-IL-1β and VEGFa, reducing neovascularization. Therefore, we provide new gene therapeutic strategies for patients. With the development of neovascularization therapy, we believe that in addition to corneal transplantation, new drug or gene therapies can achieve better results.

Cytokines and serum amyloid A in the pathogenesis of hepatitis C virus infection

Expression of the acute phase protein serum amyloid A (SAA) is dependent on the release of the pro-inflammatory cytokines IL-1, IL-6 and TNF-α during infection and inflammation. Hepatitis C virus (HCV) upregulates SAA-inducing cytokines. In line with this, a segment of chronically infected individuals display increased circulating levels of SAA. SAA has even been proposed to be a potential biomarker to evaluate treatment efficiency and the course of disease. SAA possesses antiviral activity against HCV via direct interaction with the viral particle, but might also divert infectivity through its function as an apolipoprotein. On the other hand, SAA shares inflammatory and angiogenic activity with chemotactic cytokines by activating the G protein-coupled receptor, formyl peptide receptor 2. These latter properties might promote chronic inflammation and hepatic injury. Indeed, up to 80 % of infected individuals develop chronic disease because they cannot completely clear the infection, due to diversion of the immune response. In this review, we summarize the interconnection between SAA and cytokines in the context of HCV infection and highlight the dual role SAA could play in this disease. Nevertheless, more research is needed to establish whether the balance between those opposing activities can be tilted in favor of the host defense.

Uncommon immune-mediated extrahepatic manifestations of HCV infection

INTRODUCTION

Chronic hepatitis C virus (HCV) infection has been associated with myriad extrahepatic manifestations, often resulting from aberrant immune responses. Among the most common immune-mediated manifestations of HCV infection, mixed cryoglobulinemia is the best known extra-hepatic complication. Areas covered: Here we review less common extrahepatic manifestations of HCV infection, with ascertained or presumed immune pathogenesis and the role of the new all oral direct-acting antiviral agents. Rheumatologic, dermatologic, ophthalmologic, renal, pulmonary, hematologic, cardiovascular, and neuropsychiatric manifestations of HCV infection have been considered. Expert commentary: Pathogenesis of HCV-induced aberrant immune responses resulting in peculiar clinical manifestations is not restricted to a single mechanism. A sound approach would therefore consider implementation of an etiologic treatment, through use of antiviral medications, to stop upstream in the pathogenic process all the immune mechanisms leading to hepatic and extrahepatic abnormalities. With the recent introduction of interferon-free, direct antiviral agents, capable of warranting cure for nearly all HCV-infected patients subjected to therapy, both common and uncommon extrahepatic manifestations of chronic hepatitis C are expected to no longer constitute a matter of comorbidity in the course of HCV infection.

TLR4-MyD88 pathway promotes the imbalanced activation of NLRP3/NLRP6 via caspase-8 stimulation after alkali burn injury

Alkali burn (AB) is one of the most serious ocular traumas in the world, characterized by extreme ocular surface disorders, critical secondary dry eye and irreversible vision loss. The exact mechanisms involved are unknown. Innate immunity, including the involvement of Toll-like receptors (TLRs) and NOD-like receptors (NLRs), is believed to participate in the pathogenesis of the epithelia, but the exact mechanisms by which TLRs transduce signals to NLRs and downstream molecules to initiate innate immunity remain poorly defined. In this present study, we used murine models of AB and AB concomitant desiccating stress (DS) to investigate the potential functions and mechanisms of TLR4 in regulating NLRP3 and NLRP6 during AB injury and secondary dry eye. We demonstrated that AB injury induced activation of the TLR4-MyD88 pathway, leading to imbalanced NLRP3 and NLRP6 via the activation of caspase-8 signaling. DS worsened ocular surface disorders post-AB injury by magnifying this phenomenon. Caspase-8 signaling promoted NLRP3 upregulation via the nuclear factor (NF)-κB pathway, while NLRP6 suppressed NF-κB activation. Our findings also revealed that TLR4-MyD88 knockout can alleviate AB-induced or DS-worsened ocular surface disorders, shedding light on the potential therapeutic strategies in the future for AB injury. Taken together, our findings demonstrate that AB promotes the TLR4-MyD88-caspase-8 axis to cause imbalanced NLRP3/NLRP6, and DS exacerbates ocular surface damage via magnifying this imbalance.

Anti-angiogenic effect of a humanized antibody blocking the Wnt/β-catenin signaling pathway

PURPOSE

Our previous study demonstrated that Mab2F1, a murine monoclonal antibody blocking the Wnt/β-catenin signaling pathway, has beneficial effects on experimental diabetic retinopathy and choroidal neovascularization (NV). The aforementioned antibody has been humanized. This study evaluated effects of the humanized antibody, H1L1, on NV.

METHODS

H1L1 was evaluated in the alkali burn-induced corneal NV rat model. Rats with corneal NV were injected subconjunctivally with Mab2F1 or H1L1 using non-specific mouse or human IgG as controls. Corneal NV and opacity were evaluated using corneal NV area and inflammatory index. Expression of angiogenic and inflammatory factors and components of the Wnt/β-catenin pathway in both the corneas of the animal model and human corneal epithelial (HCE) cells exposed to Wnt3a conditioned medium (WCM) were determined by Western blotting and a luciferase-based promoter assay. Cytotoxicities of these antibodies were evaluated by MTT assay.

RESULTS

H1L1 reduced the area of corneal NV and opacity, similar to Mab2F1. Both Mab2F1 and H1L1 down-regulated the overexpression of angiogenic and inflammatory factors including VEGF, TNF-α and ICAM-1, and blocked the aberrant activation of the Wnt/β-catenin pathway as shown by down-regulation of phosphorylated LRP6, total LRP6 and non-phosphorylated β-catenin in the cornea of the NV model and cultured HCE cells exposed to WCM. Both antibodies also inhibited the transcriptional activity of β-catenin induced by WCM in HCE cells. No toxic effects of the antibodies were observed in cultured HCE cells.

CONCLUSIONS

H1L1 exhibits anti-angiogenic activities through blocking the Wnt/β-catenin pathway.

Modulation of Cell Death Pathways by Hepatitis C Virus Proteins in Huh7.5 Hepatoma Cells

The hepatitis C virus (HCV) causes chronic liver disease leading to fibrosis, cirrhosis, and hepatocellular carcinoma. HCV infection triggers various types of cell death which contribute to hepatitis C pathogenesis. However, much is still unknown about the impact of viral proteins on them. Here we present the results of simultaneous immunocytochemical analysis of markers of apoptosis, autophagy, and necrosis in Huh7.5 cells expressing individual HCV proteins or their combinations, or harboring the virus replicon. Stable replication of the full-length HCV genome or transient expression of its core, Е1/Е2, NS3 and NS5B led to the death of 20-47% cells, 72 h posttransfection, whereas the expression of the NS4A/B, NS5A or NS3-NS5B polyprotein did not affect cell viability. HCV proteins caused different impacts on the activation of caspases-3, -8 and -9 and on DNA fragmentation. The structural core and E1/E2 proteins promoted apoptosis, whereas non-structural NS4A/B, NS5A, NS5B suppressed apoptosis by blocking various members of the caspase cascade. The majority of HCV proteins also enhanced autophagy, while NS5A also induced necrosis. As a result, the death of Huh7.5 cells expressing the HCV core was induced via apoptosis, the cells expressing NS3 and NS5B via autophagy-associated death, and the cells expressing E1/E2 glycoproteins or harboring HCV the replicon via both apoptosis and autophagy.

Inhibition of NLRP3 Inflammasome Pathway by Butyrate Improves Corneal Wound Healing in Corneal Alkali Burn

Epithelial cells are involved in the regulation of innate and adaptive immunity in response to different stresses. The purpose of this study was to investigate if alkali-injured corneal epithelia activate innate immunity through the nucleotide-binding oligomerization domain-containing protein (NOD)-like receptor family pyrin domain containing 3 (NLRP3) inflammasome pathway. A unilateral alkali burn (AB) was created in the central cornea of C57BL/6 mice. Mice received either no topical treatment or topical treatment with sodium butyrate (NaB), β-hydroxybutyric acid (HBA), dexamethasone (Dex), or vehicle (balanced salt solution, BSS) quater in die (QID) for two or five days (d). We evaluated the expression of inflammasome components including NLRP3, apoptosis-associated speck-like protein (ASC), and caspase-1, as well as the downstream cytokine interleukin (IL)-1β. We found elevation of NLRP3 and IL-1β messenger RNA (mRNA) transcripts, as well as levels of inflammasome component proteins in the alkali-injured corneas compared to naïve corneas. Treatment with NLRP3 inhibitors using NaB and HBA preserved corneal clarity and decreased NLRP3, caspase-1, and IL-1β mRNA transcripts, as well as NLRP3 protein expression on post-injury compared to BSS-treated corneas. These findings identified a novel innate immune signaling pathway activated by AB. Blocking the NLRP3 pathway in AB mouse model decreases inflammation, resulting in greater corneal clarity. These results provide a mechanistic basis for optimizing therapeutic intervention in alkali injured eyes.

Internalisation of hepatitis C virus core protein by human conjunctival fibroblasts

Recent studies indicate that hepatitis C virus (HCV) proteins can mediate innate immune response and inflammation in conjunctival fibroblasts which contributes to the pathology of dry eye condition associated with chronic HCV infection. The present study investigates the phagocytic potential of human conjunctival fibroblasts (HCFj) for HCV core protein. HCFj cells were incubated with HCV core antigen for different periods of time, and fluorescent micrographs were taken to observe protein internalisation. HCFj cells were capable of internalising HCV core antigen within 1 h; this gives an insight into another molecular mechanism which may contribute towards HCV-associated conjunctival inflammation.

Relative Expression of Toll-Like Receptors 2 and 7 mRNA in Peripheral Blood of Patients With Hepatitis C

BACKGROUND

Hepatitis C virus (HCV) is an important human pathogen affecting an estimated 120 - 170 million individuals in the world. Toll-Like receptors (TLRs) are pattern-recognition receptors that recognize pathogen-associated molecular patterns, and stimulate immune responses.

OBJECTIVES

The aim of this study was to determine the mRNA expression level of TLR2 and TLR7 in HCV-infected patients in comparison with normal controls.

PATIENTS AND METHODS

Nineteen consecutive patients with HCV infection and nineteen sex and age-matched healthy controls were studied in a case-controlled research.

RESULTS

Our results showed that the expressions of TLR7 in HCV infected samples were significantly increased in comparison those of the controls (P = 0.02), while the expression of TLR2 was similar between the case and the control group (P = 0.8). There were no associations between the expression levels of TLR2 and TLR7 with HCV viral load and HCV genotypes. Also, there was no association between viral load and genotypes of the virus.

CONCLUSIONS

Our findings showed that HCV infection could lead to increased expression level of TLR7 mRNA in peripheral blood cells of HCV infected samples. The viral load and genotypes of HCV did not affect the mRNA expression levels of TLR2 and TLR7.