MDA5

Abstract: Respiratory mucosa especially nasal epithelium is well known as the first-line barrier of air-borne pathogens. High levels of reactive oxygen species (ROS) are detected in in vitro cultured human epithelial cells and in vivo lung. With identification of NADPH oxidase (Nox) system of respiratory epithelium, the antimicrobial role of ROS has been studied. Duox2 is the most abundant Nox isoform and produces the regulated amount of ROS in respiratory epithelium. Duox2-derived ROS are involved in antiviral innate immune responses but more studies are needed to verify the mechanism. In respiratory epithelium, Duox2-derived ROS is critical for recognition of virus through families retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated protein 5 (MDA5) at the early stage of antiviral innate immune responses. Various secreted interferons (IFNs) play essential roles for antiviral host defense by downstream cell signaling, and transcription of IFN-stimulated genes is started to suppress viral replication. Type I and type III IFNs are verified more responsible for influenza A virus (IAV) infection in respiratory epithelium and Duox2 is required to regulate IFN-related immune responses. Transient overexpression of Duox2 using cationic polymer polyethylenimine (PEI) induces secretion of type I and type III IFNs and significantly attenuated IAV replication in respiratory epithelium. Here, we discuss Duox2-mediated antiviral innate immune responses and the role of Duox2 as a mucosal vaccine to resist respiratory viral infection.

Abstract: Duck hepatitis A virus type 1 (DHAV-1) is a highly lethal virus that severely affects the duck industry worldwide. Long noncoding RNAs (lncRNAs) exert crucial roles in pathogen attacks. Here, we conducted deep transcriptome analysis to investigate the dynamic changes of host lncRNAs profiles in DHAV-1-infected duck embryo fibroblasts. We identified 16,589 lncRNAs in total and characterized their genomic features. Moreover, 772 and 616 differentially expressed lncRNAs (DELs) were screened at 12 and 24 h post-infection. Additionally, we predicted the DELs’ cis- and trans-target genes and constructed lncRNA-target genes regulatory networks. Functional annotation analyses indicated that the putative target genes of DELs participated in diverse vital biological processed, including immune responses, cellular metabolism, and autophagy. For example, we confirmed the dysregulation of pattern recognition receptors (TLR3, RIG-I, MDA5, LGP2, cGAS), signal transducers (STAT1), transcription factors (IRF7), immune response mediators (IL6, IL10, TRIM25, TRIM35, TRIM60, IFITM1, IFITM3, IFITM5), and autophagy-related genes (ULK1, ULK2, EIF4EBP2) using RT-qPCR. Finally, we confirmed that one DHAV-1 induced lncRNA-XR_003496198 is likely to inhibit DHAV-1 replication in DEFs. Our study comprehensively analyzed the lncRNA profiles upon DHAV-1 infection and screened the target genes involved in the innate immune response and autophagy signaling pathway, thereby revealing the essential roles of duck lncRNAs and broadening our understanding of host-virus interactions.

Abstract: The escape of mitochondrial double-stranded dsRNA (mt-dsRNA) into the cytosol has been recently linked to a number of inflammatory diseases. Here, we report that the release of mt-dsRNA into the cytosol is a general feature of senescent cells and a critical driver of their inflammatory secretome, known as senescence-associated secretory phenotype (SASP). Inhibition of the mitochondrial RNA polymerase, the dsRNA sensors RIGI and MDA5, or the master inflammatory signaling protein MAVS, all result in reduced expression of the SASP, while broadly preserving other hallmarks of senescence. Moreover, senescent cells are hypersensitized to mt-dsRNA-driven inflammation due to their reduced levels of PNPT1 and ADAR1, two proteins critical for mitigating the accumulation of mt-dsRNA and the inflammatory potency of dsRNA, respectively. We find that mitofusin MFN1, but not MFN2, is important for the activation of the mt-dsRNA/MAVS/SASP axis and, accordingly, genetic or pharmacologic MFN1 inhibition attenuates the SASP. Finally, we report that senescent cells within fibrotic and aged tissues present dsRNA foci, and inhibition of mitochondrial RNA polymerase reduces systemic inflammation associated to senescence. In conclusion, we uncover the mt-dsRNA/MAVS/MFN1 axis as a key driver of the SASP and we identify novel therapeutic strategies for senescence-associated diseases. The escape of mitochondrial double-stranded dsRNA (mt-dsRNA) into the cytosol has been recently linked to a number of inflammatory diseases. Here, the authors show that the release of mt-dsRNA to the cytosol is a general feature of senescent cells and a critical driver of their inflammatory secretome, known as senescence-associated secretory phenotype (SASP).

Abstract: Objective Hepatitis A virus (HAV) infections are considered not to trigger an innate immune response in vivo, in contrast to hepatitis C virus (HCV). This lack of immune induction has been imputed to strong immune counteraction by HAV proteases 3CD and 3ABC. We aimed at elucidating the mechanisms of innate immune induction and counteraction by HAV and HCV in vivo and in vitro. Design uPA-SCID mice with humanized liver were infected with HAV and HCV. Hepatic cell culture models were used to assess HAV and HCV sensing by TLR3 and RIG-I/MDA5, respectively. Cleavage of the adaptor proteins TRIF and MAVS was analyzed by transient and stable expression of HAV and HCV proteases and virus infection. Results We detected similar levels of Interferon stimulated genes (ISGs) induction in hepatocytes of HAV and HCV infected human liver chimeric mice. In cell culture, HAV induced ISGs exclusively upon sensing by MDA5 and dependent on LGP2. TRIF and MAVS were only partially cleaved by HAV 3ABC and 3CD, not sufficiently to abrogate signalling. In contrast, HCV NS3-4A efficiently degraded MAVS, as previously reported, whereas TRIF was not cleaved. Conclusions HAV induces an innate immune response in hepatocytes via MDA5/LGP2, with limited control of both pathways by proteolytic cleavage. HCV activates TLR3 and lacks TRIF cleavage, suggesting that this pathway mainly contributes to HCV induced antiviral response in hepatocytes. Our results shed new light on induction and counteraction of innate immunity by HAV and HCV and their potential contribution to clearance and persistence. SIGNIFICANCE OF THIS STUDY What is already known on this topic? — Despite sharing biological and molecular similarities, HAV infections are always cleared while HCV infections persist in most cases. — In infected chimpanzees HAV does not trigger a strong innate immune response, as opposed to HCV. This has been imputed to the action of HAV proteases abrogating the signalling pathways. — Physiological in vitro and in vivo models, based on human hepatocytes, to assess HAV and HCV mechanisms of induction and interference of innate immunity are still missing. What this study adds — HAV induces an innate immune response in vitro and in vivo, in systems with intact signalling pathways and devoid of adaptive immunity. — HAV 3ABC and 3CD proteases do not abolish the host innate immune response. — HCV NS3-4A protease disrupts the RLRs pathways, but cannot cleave TRIF and has no impact on TLR3 response. How this study might affect research, practice or policy — This study offers a comprehensive, side-by-side investigation on HAV and HCV infections in physiological models which recapitulate a cytokine response in the human liver, and allows a precise assessment of the viral interference related to the function of the respective signalling pathways. — Our results elucidate mechanisms, so far controversial or poorly investigated, thus contributing to our understanding of HAV clearance and HCV persistence.