Suppression Of Innate Immune Responses Research Articles

The SARS-CoV-2 ORF6 protein inhibits nuclear export of mRNA and spliceosomal U snRNA.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of coronavirus disease 19 (COVID-19). SARS-CoV-2 infection suppresses host innate immunity and impairs cell viability. Among the viral proteins, ORF6 exhibits potent interferon (IFN) antagonistic activity and cellular toxicity. It also interacts with the RNA export factor RAE1, which bridges the nuclear pore complex and nuclear export receptors, suggesting an effect on RNA export. Using the Xenopus oocyte microinjection system, I found that ORF6 blocked the export of not only mRNA but also spliceosomal U snRNA. I further demonstrated that ORF6 affects the interaction between RAE1 and nuclear export receptors and inhibits the RNA binding of RAE1. These effects of ORF6 may cumulatively block the export of several classes of RNA. I also found that ORF6 binds RNA and forms oligomers. These findings provide insights into the suppression of innate immune responses and the reduction in cell viability caused by SARS-CoV-2 infection, contributing to the development of antiviral drugs targeting ORF6.

#3211 INHIBITION OF TRAINED INNATE IMMUNITY BY MYELOID CD40-TRAF6 BLOCKADE PROMOTES ALLOGRAFT TOLERANCE

Abstract Background and Aims Allograft rejection is largely mediated by adaptive immune cells. Although innate immune cells are also involved, their role is less clear. We hypothesize that suppression of innate immune responses, particularly trained innate immunity, can contribute to graft tolerance in transplantation. Trained immunity refers to the long-term epigenetic and metabolic reprogramming of innate immune cells, which potentiates responses to secondary stimuli. Here, we studied the effect of blocking CD40-TRAF6 signaling in myeloid cells on trained immunity induction using in vitro stimulations, ChIP-sequencing and metabolic analyses. We evaluated the effect of myeloid CD40-TRAF6 inhibition on T cell responses in mixed lymphocyte reactions (MLR) and the effect of CD40-TRAF6 inhibitor (TRAF6i) nanobiologic (NB) treatment on allograft rejection in a murine heterotopic heart transplantation model. Method Human peripheral blood mononuclear cells (PBMCs) were stimulated for 24 h with heat-killed Candida albicans (HKCA), a well-described inducer of trained immunity, in presence or absence of TRAF6i, or RPMI medium (control) followed by 5 days of rest. Interleukin-6 (IL-6) and tumor necrosis factor (TNF) production upon restimulation with lipopolysaccharide (LPS) was assessed using ELISA. We performed ChIP-sequencing and metabolic analyses with Seahorse assays at day 6. To investigate the effect of TRAF6i on T cell responses to allogeneic stimuli, we performed 7-day MLR with HKCA- or HKCA+TRAF6i trained monocytes and CellTrace Violet-labeled naïve T cells. Proliferation and FOXP3 expression of naïve T cells was measured by flow cytometry. The effect of TRAF6i-NB on graft survival was assessed by injection of myeloid-directed TRAF6i-NB 0, 2 and 5 days post-transplantation in C57BL/6J mice heterotopically transplanted with BALB/c hearts, that did or did not receive pre-operative CTLA4-Ig treatment. Results TRAF6i treatment inhibited IL-6 and TNF production upon LPS restimulation of HKCA-treated PBMCs in vitro (Fig. 1A). ChIP-sequencing analysis and Seahorse technology respectively revealed that the epigenetic changes (Fig. 1B) and metabolic alterations (Fig. 1C) underlying trained immunity were prevented by TRAF6i. Induction of trained immunity in monocytes reduced differentiation of naïve T cells to FOXP3+CD4+ T cells upon allogeneic stimulation, which was partially reversed by TRAF6i treatment of monocytes (Fig. 1D). Treatment with TRAF6i-NB, combined with CTLA4-Ig, induced >100 days graft survival in 5 out of 6 C57BL/6J mice heterotopically transplanted with BALB/c hearts, while one graft was rejected at 99 days post-transplantation (Fig. 1E). Conclusion Inhibition of TRAF6 prevents trained immunity in monocytes at the functional, epigenetic and metabolic level. We show in vitro that inhibiting trained immunity has the effect of modulating T cell responses to allogeneic stimuli towards FOXP3+CD4+ T cell differentiation. Using a mouse heart transplant model, we show that the combination of TRAF6i and CTLA4-Ig treatment prevents allograft rejection in vivo. This study identifies CD40-TRAF6 signaling as a novel target to inhibit trained immunity and to promote allograft tolerance.

Effector-mediated partial and nonhost disease resistance in wheat.

Effector-mediated partial and nonhost disease resistance in wheat.

Terminalia brownii Fresen: Stem Bark Dichloromethane Extract Alleviates Pyrogallol-Induced Suppression of Innate Immune Responses in Swiss Albino Mice.

Terminalia brownii is widely used in folklore medicine and has diverse biological activities. However, its effect on the immune system is yet to be studied. Therefore, our study evaluated the immunomodulatory effect of T. brownii on nonspecific immunity. Innate immunity is the initial defence phase against pathogens or injuries. Dichloromethane plant extracts were tested on female Swiss albino mice and Wister rats. The effect of the extract on innate immunity was assessed via total and differential leukocyte counts, tumor necrosis factor-alpha, and nitric oxide production by mouse macrophages. The 3-(4, 5-dimethyl thiazolyl-2)-2, 5-diphenyltetrazolium bromide assay was employed for viability testing. Phytochemical profiling was carried out using gas chromatography-mass spectrometry, while toxicity studies were carried out following the Organization for Economic Cooperation and Development guidelines. Our results demonstrated that administration of T. brownii stem bark dichloromethane extract to pyrogallol-immuno compromised mice significantly (p < 0.05) increased total and differential leukocyte counts compared with the control. The extract showed no adverse effect on the viability of Vero cells and macrophages and significantly (p < 0.05) augmented tumor necrosis factor-alpha and nitric oxide production. Hexadecanoic acid, linoleic acid, octadecanoic acid, squalene, campesterol, stigmasterol, and β-sitosterol, all of which stimulate, were identified in the extract. The extract did not cause any death or toxic signs in rats. In conclusion, T. brownii dichloromethane extract has an immunoenhancing effect on innate immune responses and is not toxic. The observed immunoenhancing impact of the extract was attributed to the presence of the identified compounds. The results of this study provide crucial ethnopharmacological leads towards the development of novel immunomodulators for managing immune-related disorders.

Electroacupuncture Alleviates Pain Responses and Inflammation in Collagen-Induced Arthritis Rats via Suppressing the TLR2/4-MyD88-NF-κB Signaling Pathway.

EA intervention and OxPAPC injection could relieve mechanical allodynia and thermal hyperalgesia caused by CIA. Paw edema and pathological damage of synovium were significantly ameliorated after EA intervention and OxPAPC injection. Furthermore, EA intervention and OxPAPC injection markedly reduced the contents of serum TNF-α, IL-1β, and IL-6, as well as the protein expression levels of synovial TLR2, TLR4, MyD88, and NF-κB p-p65. In particular, the expression of TLR2 and TLR4 on synovial fibroblasts and macrophages in synovium was significantly reduced by EA intervention. Repeated EA stimulation at ST36 and SP6 can effectively relieve joint pain and synovial inflammation caused by RA in CIA rats. The analgesic and anti-inflammatory effect of EA may be closely related to the inhibition of innate immune responses driven by the TLR2/4-MyD88-NF-κB signaling pathway in the synovium.

Strategies of Influenza A Virus to Ensure the Translation of Viral mRNAs.

Viruses are obligatorily intracellular pathogens. To generate progeny virus particles, influenza A viruses (IAVs) have to divert the cellular machinery to ensure sufficient translation of viral mRNAs. To this end, several strategies have been exploited by IAVs, such as host gene shutoff, suppression of host innate immune responses, and selective translation of viral mRNAs. Various IAV proteins are responsible for host gene shutoff, e.g., NS1, PA-X, and RdRp, through inhibition of cellular gene transcription, suppression of cellular RNA processing, degradation of cellular RNAs, and blockage of cellular mRNA export from the nucleus. Host shutoff should suppress the innate immune responses and also increase the translation of viral mRNAs indirectly due to the reduced competition from cellular mRNAs for cellular translational machinery. However, many other mechanisms are also responsible for the suppression of innate immune responses by IAV, such as prevention of the detection of the viral RNAs by the RLRs, inhibition of the activities of proteins involved in signaling events of interferon production, and inhibition of the activities of interferon-stimulated genes, mainly through viral NS1, PB1-F2, and PA-X proteins. IAV mRNAs may be selectively translated in favor of cellular mRNAs through interacting with viral and/or cellular proteins, such as NS1, PABPI, and/or IFIT2, in the 5'-UTR of viral mRNAs. This review briefly summarizes the strategies utilized by IAVs to ensure sufficient translation of viral mRNAs focusing on recent developments.

Deacetylation of Notch1 by SIRT1 contributes to HBsAg- and HBeAg-mediated M2 macrophage polarization.

Hepatic macrophages are involved in both pathogen clearance and immunopathogenesis. Emerging evidence demonstrates that macrophage polarization plays a critical role in hepatitis B virus (HBV)-induced immune impairment and liver pathology. However, it remains largely unknown as to how HBV infection facilitates M2 macrophage polarization. Here, a mouse HBV infection model was established by hydrodynamic injection with a vector containing 1.3-fold overlength HBV genome via the tail vein. Coculture experiments with HBV-producing HepG2.2.15 cells and macrophages were established in vitro. We found that HBV-inhibited M1 while enhancing M2 markers, which was accompanied by decreased proinflammatory tumor necrosis factor-α (TNF-α) and augmented anti-inflammatory IL-10 expression. Furthermore, both hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) secretion contributed to HBV-triggered macrophage polarization from M1 toward M2 phenotype. Mechanistically, HBsAg and HBeAg could upregulate the sirtuins 1 (SIRT1) deacetylase expression, which in turn promote deacetylation of the Notch1 intracellular domain (NICD), leading to increased Akt phosphorylation and decreased NF-κB nuclear translocation in macrophages. Our findings suggest that NICD deacetylation by SIRT1 contributes to HBsAg- and HBeAg-mediated M2 macrophage polarization, raising the possibility of targeting SIRT1/Notch1 pathway in macrophages to treat HBV immune evasion and chronic HBV infection.NEW & NOTEWORTHY This study identified a previously unrecognized molecular mechanism of HBV-mediated suppression of innate immune responses. We demonstrate that deacetylation of NICD by SIRT1 contributes to HBsAg- and HBeAg-mediated M2 macrophage polarization, which may aid in the development of new macrophage-based immunotherapy for chronic HBV infection and related diseases.

The Role of TLR2 in Infectious Diseases Caused by Mycobacteria: From Cell Biology to Therapeutic Target.

Simple SummaryDue to the broad functions of Toll-like receptor 2 (TLR2) in innate immunity, the drive for the development of TLR2-targeted therapeutic treatments has accelerated in recent decades. However, its dual role in both the activation and suppression of innate immune responses makes it very difficult to use the results from gathered basic research and apply them to the development of clinical trials. Therefore, this review aims to summarize the knowledge of the function of TLR2 in innate immunity and metabolism to provide some future research directions.Innate immunity is considered the first line of defense against microbial invasion, and its dysregulation can increase the susceptibility of hosts to infections by invading pathogens. Host cells rely on pattern recognition receptors (PRRs) to recognize invading pathogens and initiate protective innate immune responses. Toll-like receptor 2 (TLR2) is believed to be among the most important Toll-like receptors for defense against mycobacterial infection. TLR2 has been reported to have very broad functions in infectious diseases and also in other diseases, such as chronic and acute inflammatory diseases, cancers, and even metabolic disorders. However, TLR2 has an unclear dual role in both the activation and suppression of innate immune responses. Moreover, in some studies, the function of TLR2 was shown to be controversial, and therefore its role in several diseases is still inconclusive. Therefore, although TLR2 has been shown to have an important function in innate immunity, its usefulness as a therapeutic target in clinical application is still uncertain. In this literature review, we summarize the knowledge of the functions of TLR2 in host–mycobacterial interactions, discuss controversial results, and suggest possibilities for future research.

Negative Regulation of RNF90 on RNA Virus-Triggered Antiviral Immune Responses Targeting MAVS.

The antiviral innate immunity is the first line of host defense against viral infection. Mitochondrial antiviral signaling protein (MAVS, also named Cardif/IPS-1/VISA) is a critical protein in RNA virus-induced antiviral signaling pathways. Our previous research suggested that E3 ubiquitin-protein ligases RING-finger protein (RNF90) negatively regulate cellular antiviral responses by targeting STING for degradation, though its role in RNA virus infection remains unknown. This study demonstrated that RNF90 negatively regulated RNA virus-triggered antiviral innate immune responses in RNF90-silenced PMA-THP1 cells, RNF90-deficient cells (including HaCaTs, MEFs, and BMDMs), and RNF90-deficient mice. However, RNF90 regulated RNA virus-triggered antiviral innate immune responses independent of STING. RNF90 promoted K48-linked ubiquitination of MAVS and its proteasome-dependent degradation, leading to the inhibition of innate immune responses. Altogether, our findings suggested a novel function and mechanism of RNF90 in antiviral innate immunity.

Contribution of the NADase function of bacterial TIR domain proteins to the inhibition of innate immune responses

Abstract Pathogenic microbes have evolved various mechanisms to evade recognition by host immune responses, which can lead to the prevalence of disease and infection. Many strains of pathogenic bacteria contain genes encoding Toll/Interleukin-1 receptor (TIR) domain-containing proteins that function through the inhibition of TLR and myeloid differentiation factor 88 (MyD88) signaling. Previous research has also revealed that prokaryotic TIR domains may regulate bacterial and host metabolic pathways by acting as NAD+ glycohydrolases (NADases). We hypothesize that this NADase activity may contribute to the role of bacterial TIRs as virulence factors. In order to test this hypothesis, we observed the effects of TIR NADase activity on the binding interactions between bacterial TIRs and host MyD88, and on the ability of bacterial TIRs to block NF-kB signaling. For this, we have identified amino acids predicted to play a role in TIR NADase activity and have expressed and purified recombinant bacterial TIR proteins that have incorporated these mutations. We then tested the NADase activity of these mutants in comparison with that of wild-type TIR proteins and TIRs with mutations already known to inhibit NADase activity. We are now using mutant TIRs with deficiencies in NADase activity in pull-down assays to test their binding to MyD88 and utilizing reporter assays to analyze the effects of these mutant TIRs on NF-kB signaling. This information will allow us to gain a deeper understanding into the relationship between NADase activity in bacterial TIRs and their virulence activity, and can potentially uncover new mechanisms for pathogenic evasion of host immune defenses.

Inhibition of innate immune response ameliorates Zika virus-induced neurogenesis deficit in human neural stem cells.

Global Zika virus (ZIKV) outbreaks and their strong link to microcephaly have raised major public health concerns. ZIKV has been reported to affect the innate immune responses in neural stem/progenitor cells (NS/PCs). However, it is unclear how these immune factors affect neurogenesis. In this study, we used Asian-American lineage ZIKV strain PRVABC59 to infect primary human NS/PCs originally derived from fetal brains. We found that ZIKV overactivated key molecules in the innate immune pathways to impair neurogenesis in a cell stage-dependent manner. Inhibiting the overactivated innate immune responses ameliorated ZIKV-induced neurogenesis reduction. This study thus suggests that orchestrating the host innate immune responses in NS/PCs after ZIKV infection could be promising therapeutic approach to attenuate ZIKV-associated neuropathology.

Phase II trial of opaganib in patients with metastatic castration-resistant prostate cancer progressing on abiraterone or enzalutamide (NCT04207255).

TPS191 Background: Opaganib (Yeliva, ABC294640) is a first-in-class, sphingosine kinase-2 (SK2) selective inhibitor, with anticancer, anti-inflammatory and anti-viral activities. SK2, a lipid kinase catalyzes formation of the lipid signaling molecule sphingosine 1-phosphate (S1P). S1P promotes cancer growth, and proliferation and pathological inflammation, including inflammatory cytokine production. Specifically, by inhibiting the SK2 enzyme, opaganib blocks the synthesis of S1P which regulates fundamental biological processes such as cell proliferation, migration, immune cell trafficking and angiogenesis, and are also involved in immune-modulation and suppression of innate immune responses from T cells. Opaganib is a sphingosine-competitive inhibitor of SK2 and also inhibits dihydroceramide desaturase. Opaganib has antitumor activity against human and murine prostate cancer cell lines, and in xenograft (LNCaP) and syngeneic (MycCAP, TRAMP-C1) murine tumor models. In addition to its target effect of reducing sphingosine-1-phosphate, opaganib reduces both MYC and AR proteins through its kinase-blocking and desaturase-inhibiting properties, respectively. Methods: The study is open to patients with mCRPC who have been treated with at least one newer androgen antagonist (abiraterone or enzalutamide) and no prior chemotherapy for castration-resistant disease. Patients who are failing either abiraterone or enzalutamide may enroll, with the addition of opaganib. The trial design includes brief safety lead-in cohort 1a (abiraterone + opaganib 250 mg Q 12hr, 3/3 enrolled) and 1b (enzalutamide + opaganib 250 mg Q 12hr, 3/3 enrolled). These cohorts have been completed without any DLTs. We are now enrolling cohort 2 (abiraterone + opaganib 500 mg Q 12hr, 0/27 enrolled) and cohort 3 (enzalutamide + opaganib 500 mg Q 12hr, 8/27 enrolled). A total of 60 patients will be enrolled and response will be evaluated after 4 cycles (28 days/cycle) using a composite metric based on PSA, bone scan and RECIST measurements per PCWG3 criteria. Safety and tolerability will be monitored, and dose modifications will be allowed. Primary endpoint is disease control (stable disease or better) after 4 cycles. Secondary endpoints include overall survival, radiographic progression-free survival and PSA progression-free survival. Correlative studies include assessment of quality of life (QOL), circulating MDSCs, immune cells and clones with amplified AR or MYC. Supported by NIH grant P01 CA203628. Clinical trial information: NCT04207255.

Viral Evasion of RIG-I-Like Receptor-Mediated Immunity through Dysregulation of Ubiquitination and ISGylation.

Viral dysregulation or suppression of innate immune responses is a key determinant of virus-induced pathogenesis. Important sensors for the detection of virus infection are the RIG-I-like receptors (RLRs), which, in turn, are antagonized by many RNA viruses and DNA viruses. Among the different escape strategies are viral mechanisms to dysregulate the post-translational modifications (PTMs) that play pivotal roles in RLR regulation. In this review, we present the current knowledge of immune evasion by viral pathogens that manipulate ubiquitin- or ISG15-dependent mechanisms of RLR activation. Key viral strategies to evade RLR signaling include direct targeting of ubiquitin E3 ligases, active deubiquitination using viral deubiquitinating enzymes (DUBs), and the upregulation of cellular DUBs that regulate RLR signaling. Additionally, we summarize emerging new evidence that shows that enzymes of certain coronaviruses such as SARS-CoV-2, the causative agent of the current COVID-19 pandemic, actively deISGylate key molecules in the RLR pathway to escape type I interferon (IFN)-mediated antiviral responses. Finally, we discuss the possibility of targeting virally-encoded proteins that manipulate ubiquitin- or ISG15-mediated innate immune responses for the development of new antivirals and vaccines.

Assessment of nanopolystyrene toxicity under fungal infection condition in Caenorhabditis elegans.

Due to the potential of release and accumulation in the environment, nanoplastics have attracted an increasing attention. In this study, we investigated the effect of exposure to nanopolystyrene (30nm) in nematode Caenorhabditis elegans after the fungal infection. After Candida albicans infection, exposure to nanopolystyrene (10 and 100μg/L) for 24-h could cause the more severe toxicity on lifespan and locomotion behavior compared with fungal infection alone. The more severe activation of oxidative stress and suppression of SOD-3:GFP expression and mitochondrial unfolded protein response (mt UPR) were associated with this observed toxicity enhancement induced by nanopolystyrene exposure. Moreover, the more severe C. albicans colony formation and suppression of innate immune response as indicated by the alteration in expression of anti-microbial genes (abf-2, cnc-4, cnc-7, and fipr-22/23) further contributed to the formation of this toxicity enhancement induced by nanopolystyrene exposure. Our results demonstrated that short-term exposure to nanopolystyrene in the range of μg/L potentially enhances the adverse effects of fungal infection on organisms.

Differential effects of BCG vaccine on immune responses induced by vi polysaccharide typhoid fever vaccination: an explorative randomized trial

The Vi polysaccharide typhoid fever vaccine (TFV) provides incomplete protection against typhoid fever. BCG, the vaccine against tuberculosis, can potentiate immune responses to other vaccines through induction of trained innate immunity and heterologous adaptive immunity. We performed an explorative, randomized, noncontrolled open trial to investigate whether BCG vaccination increases humoral and cellular response to TFV and whether BCG and TFV modulate nonspecific immune responses. Thirty volunteers were randomized to receive either TFV alone or BCG followed by TFV after 2 weeks. Ex vivo leukocyte responses and anti-Vi IgG antibody titers were measured 2 weeks and 3 months after TFV. BCG administration prior to TFV vaccination did not increase specific humoral or cellular immune responses to Salmonella typhi. TFV vaccination decreased pro-inflammatory responses to non-related stimuli. This effect was counteracted by prior BCG administration, which also led to decreased IL-10 and increased IL-22 responses to non-related stimuli. In an in vitro model of trained immunity TFV led to immunotolerance, which was partially reversed by BCG-induced trained immunity. BCG does not modulate adaptive immune responses to TFV but partially prevents inhibition of innate immune responses induced by TFV. Nonspecific effects of vaccines to unrelated microbial stimuli must be considered in the evaluation of their biological effects (ClinicalTrials.gov NCT02175420).

The dNTPase activity of SAMHD1 is important for its suppression of innate immune responses in differentiated monocytic cells

Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) is a deoxynucleoside triphosphohydrolase (dNTPase) with a nuclear localization signal (NLS). SAMHD1 suppresses innate immune responses to viral infection and inflammatory stimuli by inhibiting the NF-κB and type I interferon (IFN-I) pathways. However, whether the dNTPase activity and nuclear localization of SAMHD1 are required for its suppression of innate immunity remains unknown. Here, we report that the dNTPase activity, but not nuclear localization of SAMHD1, is important for its suppression of innate immune responses in differentiated monocytic cells. We generated monocytic U937 cell lines stably expressing WT SAMHD1 or mutated variants defective in dNTPase activity (HD/RN) or nuclear localization (mNLS). WT SAMHD1 in differentiated U937 cells significantly inhibited lipopolysaccharide-induced expression of tumor necrosis factor α (TNF-α) and interleukin-6 (IL-6) mRNAs, as well as IFN-α, IFN-β, and TNF-α mRNA levels induced by Sendai virus infection. In contrast, the HD/RN mutant did not exhibit this inhibition in either U937 or THP-1 cells, indicating that the dNTPase activity of SAMHD1 is important for suppressing NF-κB activation. Of note, in lipopolysaccharide-treated or Sendai virus-infected U937 or THP-1 cells, the mNLS variant reduced TNF-α or IFN-β mRNA expression to a similar extent as did WT SAMHD1, suggesting that SAMHD1-mediated inhibition of innate immune responses is independent of SAMHD1's nuclear localization. Moreover, WT and mutant SAMHD1 similarly interacted with key proteins in NF-κB and IFN-I pathways in cells. This study further defines the role and mechanisms of SAMHD1 in suppressing innate immunity.

Type I interferon antagonistic properties of influenza B virus polymerase proteins.

The innate immune system, in particular the type I interferon (IFN) response, is a powerful defence against virus infections. In turn, many if not all viruses have evolved various means to circumvent, resist, or counteract this host response to ensure efficient replication and propagation. Influenza viruses are no exception to this rule, and several viral proteins have been described to possess IFN-antagonistic functions. Although the viral nonstructural protein 1 appears to be a major antagonist in influenza A and B viruses (IAV and IBV), we have previously shown that a specific motif in the IAV polymerase proteins exerts an IFN-suppressive function very early in infection. The question remained whether a similar function would also exist in IBV polymerases. Here, we show that indeed a specific amino acid position (A523) of the PB1 protein in the IBV polymerase complex confers IFN-antagonistic properties. Mutation of this position leads to enhanced activation of the IFN-mediated signalling pathway after infection and subsequent reduction of virus titres. This indicates that inhibition of innate immune responses is a conserved activity shared by polymerase proteins of IAV and IBV.

HIV-2/SIV Vpx targets a novel functional domain of STING to selectively inhibit cGAS-STING-mediated NF-κB signalling.

Innate immunity is the first line of host defence against pathogens. Suppression of innate immune responses is essential for the survival of all viruses. However, the interplay between innate immunity and HIV/SIV is only poorly characterized. We have discovered Vpx as a novel inhibitor of innate immune activation that associates with STING signalosomes and interferes with the nuclear translocation of NF-κB and the induction of innate immune genes. This new function of Vpx could be separated from its role in mediating degradation of the antiviral factor SAMHD1, and is conserved among diverse HIV-2/SIV Vpx. Vpx selectively suppressed cGAS-STING-mediated nuclear factor-κB signalling. Furthermore, Vpx and Vpr had complementary activities against cGAS-STING activity. Since SIVMAC lacking both Vpx and Vpr was less pathogenic than SIV deficient for Vpr or Vpx alone, suppression of innate immunity by HIV/SIV is probably a key pathogenic determinant, making it a promising target for intervention.

Influenza A Virus NS1 Protein Suppresses JNK1-Dependent Autophagosome Formation Mediated by Rab11a Recycling Endosomes.

Autophagy is an essential process for cellular metabolism and homeostasis, but also functions as one of innate immune responses against pathogen infection. However, in contrast to cellular metabolism and homeostasis pathways, less is known about how virus infection leads to autophagosome formation. Here, we showed that influenza A virus NS1 protein inhibits the formation of autophagosomes. The autophagosome formation was induced by infection with NS1 mutant virus lacking the dsRNA-binding activity for inhibition of innate immune responses (R38AK41A) or the activation of PI3K-Akt signaling pathway (Y89F). R38AK41A mutant infection induced phosphorylation of JNK1 and up-regulated the expression of autophagy-related genes which are downstream of JNK1 signaling pathway. We also found that the amount of phosphorylated TSC2, which activates mTOR, increased in wild type-infected cells but not in Y89F mutant-infected cells. These findings suggest that NS1 inhibits the autophagosome formation through both the inhibition of JNK1 and the activation of PI3K-Akt-mTOR pathway. Further, viral ribonucleoprotein (vRNP) complexes were selectively sequestered into autophagosomes, and knockdown of Rab11a, which is responsible for the apical transport of vRNP complexes, impaired not only engulfment of vRNP complexes by autophagosomes but also the formation of autophagosomes in R38AK41A mutant-infected cells. This indicates that Rab11a-positive recycling endosomes function as a donor membrane for the phagophore elongation and an autophagic receptor for the selective engulfment of viral RNP complexes. Based on these results, we propose that NS1 inhibits JNK1-mediated autophagy induction and the sequestration of vRNP complexes into autophagosomes.

Impact of combined ischemic preconditioning and remote ischemic perconditioning on ischemia-reperfusion injury after liver transplantation

Ischemic preconditioning (IPC) and remote ischemic perconditioning (RIPer) confer protective effects against liver ischemia-reperfusion injury (IRI), but data about RIPer applying in liver transplantation is lacking. The study aimed to evaluate whether the combination of IPC and RIPer provides reinforced protective effects. C57BL/6 mice (160 pairs) were allocated into four groups: control, subjected to liver transplantation only; IPC, donor hilar was clamped for 10 min followed by 15 min of reperfusion; RIPer, three cycles of occlusion (5 min) and opening (5 min) of femoral vascular bundle were performed before reperfusion; IPC + RIPer, donors and recipients were subjected to IPC and RIPer respectively. Liver tissues were obtained for histological evaluation, TUNEL staining, malondialdehyde assays, GSH-Px assays, and NF-κB p65 protein and Bcl-2/Bax mRNA analyses. Blood samples were used to evaluate ALT, AST, TNF-α, NOx levels and flow cytometry. We found that protective efficacy of RIPer is less than IPC in terms of ALT, TNF-α, GSH-Px and NOx at 2 h postoperation, but almost equivalent at 24 h and 72 h postoperation. Except for Suzuki scores, ALT, Bcl-2/Bax mRNA ratio, other indices showed that combined treatment brought enhanced attenuation in IRI, compared with single treatment, through additive effects on antioxidation, anti-apoptosis, modulation of microcirculation disturbance, and inhibition of innate immune response. This study suggested a combined strategy that could enhance protection against IRI in clinical liver transplantation, otherwise, provided a hint that RIPer’s mechanism might be partly or totally different from IPC in humoral pathway.