miR29a and miR378b Influence CpG-Stimulated Dendritic Cells and Regulate cGAS/STING Pathway

The 4EHP-mediated translational repression of cGAS impedes the host immune response against DNA viruses

A critical host response against viral infections entails the activation of innate immune signaling that culminates in the production of antiviral proteins. DNA viruses are sensed by the cytosolic pattern recognition receptor cyclic GMP-AMP synthase (cGAS), which initiates a signaling pathway that results in production of proinflammatory cytokines such as Interferon-β (IFN-β) and activation of the antiviral response. Precise regulation of the antiviral innate immune response is required to avoid deleterious effects of its overactivation. We previously reported that the 4EHP/GIGYF2 translational repressor complex reduces the translation of Ifnb1 mRNA, which encodes IFN-β, upon RNA viral infections. Here, we report a distinct regulatory mechanism by which 4EHP controls replication of DNA viruses by translational repression of the Cgas mRNA, which encodes the DNA viral sensor cGAS. We show that 4EHP is required for effective translational repression of Cgas mRNA triggered by miR-23a. Upon infection, 4EHP deficiency bolsters the elicited innate immune response against the diverse DNA viruses Herpes simplex virus 1 (HSV-1) and Vaccinia Virus (VacV) and concomitantly reduces their rate of replication in vitro and in vivo. This study elucidates an intrinsic regulatory mechanism of the host response to DNA viruses which may provide unique opportunities for countering viral infections.

The dual actions of miRNA16a in restricting Bovine Coronavirus replication through downregulation of Furin and enhancing the host immune response

The roles of host cell miRNAs have not been well studied in the context of BCoV replication and immune regulation. This study aimed to identify miRNA candidates that regulate essential host genes involved in BCoV replication, tissue tropism, and immune regulation. To achieve these goals, we used two isolates of BCoV (enteric and respiratory) to infect bovine endothelial cells (BECs) and Madine Darby Bovine Kidney (MDBK) cells. We determined the miRNA expression profiles of these cells after BCoV infection. The expression of miRNA16a is differentially altered during BCoV infection. Our data show that miRNA16a is a significantly downregulated miRNA in both in vitro and ex vivo models. We confirmed the miRNA16aexpression profile by qRT-PCR. Overexpression of pre-miRNA16ain the BEC and the MDBK cell lines markedly inhibited BCoV infection, as determined by the viral genome copy numbers measured by qRT‒PCR, viral protein expression (S and N) measured by Western blot, and virus infectivity using a plaque assay. Our bioinformatic prediction showed that Furin is a potential target of miRNA16a. We compared the Furin protein expression level in pre-miRNA16a-transfected/BCoV-infected cells to that in pre-miRNA-scrambled-transfected cells. Our qRT-PCR and Western blot data revealed marked inhibition of Furin expression at the mRNA and protein levels, respectively. BCoV-S protein expression was markedly inhibited at both the mRNA and protein levels. To further confirm the impact of the downregulation of the Furin enzyme on the replication of BCoV, we transfected cells with specific Furin-siRNAs parallel to the scrambled siRNA. Marked inhibition of BCoV replication was observed in the Furin-siRNA-treated group. To further validate Furin as a novel target for miRNA16a, we cloned the 3'UTR of bovine Furin carrying the seed region of miRNA16a in the dual luciferase vector. Our data showed that luciferase activity in pre-miRNA16a-transfected cells decreased by more than 50% compared to cells transfected with the construct carrying the mutated Furin seed region. Our data confirmed that miRNA16ainhibits BCoV replication by targeting the host cell line Furin and the BCoV-S glycoprotein. It also enhances the host immune response, which contributes to the inhibition of viral replication. This is the first study to confirm that Furin is a valid target of miRNA16a. Our findings highlight the clinical applications of host miRNA16a as a potential miRNA-based vaccine/antiviral therapy.

Blood transcriptome analysis uncovered COVID-19-myocarditis crosstalk

BACKGROUND

The condition of COVID-19-related myocarditis has emerged as a prominent contributor to COVID-19 mortality. As the epidemic persists, its incidence continues to rise. Despite ongoing efforts, the elucidation of COVID-19-related myocarditis underlying molecular mechanisms still requires further investigation.

METHODS

Hub genes for COVID-19-related myocarditis were screened by integrating gene expression profile analysis via differential expression in COVID-19 (GSE196822) and myocarditis (GSE148153 and GSE147517). After verification with independent datasets (GSE211979, GSE167028, GSE178491 and GSE215865), the hub genes were studied using a range of systems-biology approaches, such as ceRNA, TF-mRNA networks and PPI networks, as well as gene ontology, pathway enrichment, immune infiltration analysis and drug target identification.

RESULTS

TBKBP1 and ERGIC1 were identified as COVID-19-related myocarditis hub genes via integrated bioinformatics analysis. In addition, receiver operating characteristic curves constructed based on the expression levels of TBKBP1 and ERGIC1 could effectively distinguish healthy control individuals from patients with COVID-19. Functional enrichment analysis suggested several enriched biological pathways related to inflammation and immune response. Immune cell changes correlated with TBKBP1 and ERGIC1 levels in patients with COVID-19 or patients with COVID-19 and myocarditis. Tamibarotene, methotrexate and theophylline were identified as a potential drug targeting TBKBP1 and ERGIC1.

CONCLUSION

TBKBP1 and ERGIC1 were identified as crucial genes in the development of COVID-19-related myocarditis and have demonstrated a strong association with innate antiviral immunity. The present work may be helpful for further investigation of the molecular mechanisms and new therapeutic drug targets correlated with myocarditis in COVID-19.

IRF7: role and regulation in immunity and autoimmunity

Interferon regulatory factor (IRF) 7 was originally identified as master transcriptional factor that produced IFN-I and regulated innate immune response, subsequent studies have revealed that IRF7 performs a multifaceted and versatile functions in multiple biological processes. In this review, we provide a comprehensive overview on the current knowledge of the role of IRF7 in immunity and autoimmunity. We focus on the latest regulatory mechanisms of IRF7 in IFN-I, including signaling pathways, transcription, translation, and post-translational levels, the dimerization and nuclear translocation, and the role of IRF7 in IFN-III and COVID-19. In addition to antiviral immunity, we also discuss the role and mechanism of IRF7 in autoimmunity, and the further research will expand our understanding of IRF7.

Epigenetic changes induced by pathogenic Chlamydia spp

Chlamydia trachomatis, C. pneumoniae, and C. psittaci, the three Chlamydia species known to cause human disease, have been collectively linked to several pathologies, including conjunctivitis, trachoma, respiratory disease, acute and chronic urogenital infections and their complications, and psittacosis. In vitro, animal, and human studies also established additional correlations, such as between C. pneumoniae and atherosclerosis and between C. trachomatis and ovarian cancer. As part of their survival and pathogenesis strategies as obligate intracellular bacteria, Chlamydia spp. modulate all three major types of epigenetic changes, which include deoxyribonucleic acid (DNA) methylation, histone post-translational modifications, and microRNA-mediated gene silencing. Some of these epigenetic changes may be implicated in key aspects of pathogenesis, such as the ability of the Chlamydia spp. to induce epithelial-to-mesenchymal transition, interfere with DNA damage repair, suppress cholesterol efflux from infected macrophages, act as a co-factor in human papillomavirus (HPV)-mediated cervical cancer, prevent apoptosis, and preserve the integrity of mitochondrial networks in infected host cells. A better understanding of the individual and collective contribution of epigenetic changes to pathogenesis will enhance our knowledge about the biology of Chlamydia spp. and facilitate the development of novel therapies and biomarkers. Pathogenic Chlamydia spp. contribute to epigenetically-mediated gene expression changes in host cells by multiple mechanisms.

Emerging role of STING signalling in CNS injury: inflammation, autophagy, necroptosis, ferroptosis and pyroptosis

Stimulator of interferons genes (STING), which is crucial for the secretion of type I interferons and proinflammatory cytokines in response to cytosolic nucleic acids, plays a key role in the innate immune system. Studies have revealed the participation of the STING pathway in unregulated inflammatory processes, traumatic brain injury (TBI), spinal cord injury (SCI), subarachnoid haemorrhage (SAH) and hypoxic–ischaemic encephalopathy (HIE). STING signalling is markedly increased in CNS injury, and STING agonists might facilitate the pathogenesis of CNS injury. However, the effects of STING-regulated signalling activation in CNS injury are not well understood. Aberrant activation of STING increases inflammatory events, type I interferon responses, and cell death. cGAS is the primary pathway that induces STING activation. Herein, we provide a comprehensive review of the latest findings related to STING signalling and the cGAS–STING pathway and highlight the control mechanisms and their functions in CNS injury. Furthermore, we summarize and explore the most recent advances toward obtaining an understanding of the involvement of STING signalling in programmed cell death (autophagy, necroptosis, ferroptosis and pyroptosis) during CNS injury. We also review potential therapeutic agents that are capable of regulating the cGAS–STING signalling pathway, which facilitates our understanding of cGAS–STING signalling functions in CNS injury and the potential value of this signalling pathway as a treatment target.

From nasal to basal: single-cell sequencing of the bursa of Fabricius highlights the IBDV infection mechanism in chickens

BACKGROUND

Chickens, important food animals and model organisms, are susceptible to many RNA viruses that invade via the nasal cavity. To determine the nasal entry site of the virus and clarify why avians are susceptible to RNA viruses, infectious bursal disease virus (IBDV) was selected because it is a typical avian RNA virus that infects chickens mainly via the nasal route.

RESULTS

First, we found that IBDV infected the posterior part of the nasal cavity in chickens, which is rich in lymphoid tissue and allows the virus to be easily transferred to the blood. Via the blood circulation, IBDV infected peripheral blood mononuclear cells (PBMCs) and was transferred to the bursa of Fabricius to damage the IgM + B lymphocyte population. Subsequently, the single-cell RNA sequencing (scRNA-seq) results suggested the more detailed response of different bursal cell populations (B cells, epithelial cells, dendritic cells, and fibroblasts) to IBDV. Regarding B cells, IBDV infection greatly decreased the IgM + B cell population but increased the IgA + B cell population in the bursal follicles. In contrast to B cells, bursal epithelial cells, especially basal cells, accumulated a large number of IBDV particles. Furthermore, we found that both innate RNA sensors and interferon-stimulated genes (ISGs) were highly expressed in the IBDV-infected groups, while dicer and ago2 expression was largely blocked by IBDV infection. This result suggests that dicer-related RNA interference (RNAi) might be an effective antiviral strategy for IBDV infection in avian.

CONCLUSION

Our study not only comprehensively elaborates on the transmission of airborne IBDV via the intranasal route and establishes the main target cell types for productive IBDV infection but also provides sufficient evidence to explain the cellular antiviral mechanism against IBDV infection.

Circular RNA circSamd4a Regulates Antiviral Immunity in Teleost Fish by Upregulating STING through Sponging miR-29a-3p

Circular RNAs (circRNAs) are a subgroup of endogenous noncoding RNA that is covalently closed rings and widely expressed. In recent years, there is accumulating evidence indicating that circRNAs are a class of important regulators, which play an important role in various biological processes. However, the biological functions and regulation mechanism of circRNAs in lower vertebrates are little known. In this study, we discovered a circRNA Samd4a (circSamd4a) that is related to the antiviral immune response of teleost fish. It can act as a key regulator of the host's antiviral response and play a key role in inhibiting Sininiperca chuatsi rhabdovirus replication. Further studies have shown that circSamd4a may act as a competing endogenous RNA, which can enhance the STING-mediated NF-κB/IRF3 signaling pathway by adsorbing miR-29a-3p, thereby enhancing the antiviral immune response. Therefore, circSamd4a plays an active regulatory role in the antiviral immune response of bony fish. Our research results provide a strong foundation for circular RNA to play a regulatory role in the antiviral immune response of teleost fish.

miR-23a/b suppress cGAS-mediated innate and autoimmunity

Cyclic GMP-AMP synthase (cGAS), a key sensor of intracellular DNA, is essential for eliciting innate immunity against infection, whereas aberrant activation of cGAS by endogenous DNA promotes severe autoimmune diseases. However, it is largely unknown how cGAS expression is regulated during pathogen infection and autoimmunity. Here, we report that during herpes simplex virus type 1 (HSV-1) infection, two microRNAs (miR-23a and miR-23b) whose levels significantly decrease due to their interaction with the lncRNA Oasl2-209 directly regulate the expression of cGAS. Overexpression of miR-23a/b markedly dampens cytosolic DNA-induced innate immune responses, whereas inhibition of miR-23a/b enhances these responses. Mice treated with miR-23a/b agomirs exhibit increased susceptibility to HSV-1 infection. Moreover, cGAS is significantly upregulated in the Trex1-/- mouse autoimmune disease model. Administration of miR-23a/b blunts self DNA-induced autoinflammatory responses in Trex1-/- mice. Collectively, our study not only reveals a novel regulatory mechanism of cGAS expression by miRNAs but also identifies a potential therapy for cGAS-related autoimmune diseases.

Cytosolic sensor STING in mucosal immunity: a master regulator of gut inflammation and carcinogenesis

The stimulator of interferon genes (STING) connects microbial cytosolic sensing with host cell effector functions. STING signaling plays a central role in cyclic dinucleotides (CDNs) and DNA sensing to induce secretion of interferons and pro-inflammatory mediators. Although activated STING signaling favors antimicrobial progress and facilitates mucosal would healing, its role in mucosal immunity and gut homeostasis is paradoxical, ranging from positive and negative effects within the gut. In our review, we summarize recent advance of STING signaling in gut homeostasis and inflammation, especially focusing on its molecular basis in mucosal immune response. Deep understanding of the regulatory mechanisms of intestinal STING pathway could promote clinical manipulation of this fundamental signaling as a promising immunomodulatory therapy.

cGAS-STING signaling in cancer immunity and immunotherapy

Recent studies have shown that the innate immune cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway may play an important role in antitumor immunity. Additionally, the cGAS-STING pathway promotes the senescence of cancer cells, induces apoptosis of cancer cells, and increases the protective effect of cytotoxic T cells and natural killer cell-mediated cytotoxicity. We believe that the combination of the cGAS-STING signaling pathway with other therapeutic methods provides a new perspective from which to overcome obstacles in the application of this review. Further, we highlight the antitumor mechanism of the cGAS-STING signaling pathway and the latest advances in monotherapy and combination therapy with related agonists.

March of Mycobacterium: miRNAs intercept host cell CD40 signalling

The disease tuberculosis is fatal if untreated. It is caused by the acid-fast bacilli Mycobacterium tuberculosis. Mycobacterium resides and replicates within the alveolar macrophages, causing inflammation and granuloma, wherein macrophage-T cell interactions enhance the inflammation-causing pulmonary caseous lesions. The first interactions between Mycobacterium and the receptors on macrophages decide the fate of Mycobacterium because of phagolysosomal impairments and the expression of several miRNAs, which may regulate CD40 expression on macrophages. While the altered phagolysosomal functions impede antigen presentation to the T cell-expressed antigen receptor, the interactions between the macrophage-expressed CD40 and the T cell-expressed CD40-ligand (CD40L or CD154) provide signals to T cells and Mycobacterium-infected macrophages. These two functions significantly influence the resolution or persistence of Mycobacterium infection. CD40 controls T-cell polarisation and host-protective immunity by eliciting interleukin-12p40, nitric oxide, reactive oxygen species and IFN-γ production. Indeed, CD40-deficient mice succumb to low-dose aerosol infection with Mycobacterium because of deficient interleukin (IL)-12 production leading to impaired IFN-γ-secreting T-cell response. In contrast, despite generating fewer granulomas, the CD40L-deficient mice developed anti-mycobacterial T-cell responses to the levels observed in the wild-type mice. These host-protective responses are significantly subdued by the Mycobacterium-infected macrophage produced TGF-β and IL-10, which promote pro-mycobacterial T-cell responses. The CD40-CD40L-induced counteractive immune responses against Mycobacterium thus present a conundrum that we explain here with a reconciliatory hypothesis. Experimental validation of the hypothesis will provide a rationale for designing anti-tubercular immunotherapy.

Correction: miR29a and miR378b Influence CpG-Stimulated Dendritic Cells and Regulate cGAS/STING Pathway

The authors wish to make the following corrections to this paper [...].