Herpes Simplex Virus Type 1 Infection Disturbs the Mitochondrial Network, Leading to Type I Interferon Production through the RNA Polymerase III/RIG-I Pathway

Understanding the interplay between oHSV and the host immune system: Implications for therapeutic oncolytic virus development

Oncolytic herpes simplex viruses (oHSV) preferentially replicate in cancer cells while inducing antitumor immunity, and thus, they are often referred to as in situ cancer vaccines. OHSV infection of tumors elicits diverse host immune responses comprising both innate and adaptive components. Although the innate and adaptive immune responses primarily target the tumor, they also contribute to antiviral immunity, limiting viral replication/oncolysis. OHSV-encoded proteins use various mechanisms to evade host antiviral pathways and immune recognition, favoring oHSV replication, oncolysis, and spread. In general, oHSV infection and replication within tumors results in a series of sequential events, such as oncolysis and release of tumor and viral antigens, dendritic cell-mediated antigen presentation, T cell priming and activation, T cell trafficking and infiltration to tumors, and T cell recognition of cancer cells, leading to tumor (and viral) clearance. These sequential events align with all steps of the cancer-immunity cycle. However, a comprehensive understanding of the interplay between oHSV and host immune responses is crucial to optimize oHSV-induced antitumor immunity and efficacy. Therefore, this review aims to elucidate oHSV's communication with innate and adaptive immune systems and use such interactions to improve oHSV's potential as a potent immunovirotherapeutic agent against cancer.

Intra-host genomic diversity and integration landscape of human tissue-resident DNA virome

The viral intra-host genetic diversities and interactions with the human genome during decades of persistence remain poorly characterized. In this study, we analyzed the variability and integration sites of persisting viruses in nine organs from thirteen individuals who died suddenly from non-viral causes. The viruses studied included parvovirus B19, six herpesviruses, Merkel cell (MCPyV) and JC polyomaviruses, totaling 127 genomes. The viral sequences across organs were remarkably conserved within each individual, suggesting that persistence stems from single dominant strains. This indicates that intra-host viral evolution, thus far inferred primarily from immunocompromised patients, is likely overestimated in healthy subjects. Indeed, we detected increased viral subpopulations in two individuals with putative reactivations, suggesting that replication status influences diversity. Furthermore, we identified asymmetrical mutation patterns reflecting selective pressures exerted by the host. Strikingly, our analysis revealed non-clonal viral integrations even in individuals without cancer. These included MCPyV integrations and truncations resembling clonally expanded variants in Merkel cell carcinomas, as well as novel junctions between herpesvirus 6B and mitochondrial sequences, the significance of which remains to be evaluated. Our work systematically characterizes the genomic landscape of the tissue-resident virome, highlighting potential deviations occurring during disease.

Pseudorabies virus infection triggers mitophagy to dampen the interferon response and promote viral replication

Pseudorabies virus (PRV) utilizes multiple strategies to inhibit type I interferon (IFN-I) production and signaling to achieve innate immune evasion. Among several other functions, mitochondria serve as a crucial immune hub in the initiation of innate antiviral responses. It is currently unknown whether PRV inhibits innate immune responses by manipulating mitochondria. In this study, we found that PRV infection damages mitochondrial structure and function, as shown by mitochondrial membrane potential depolarization, reduction in mitochondrial numbers, and an imbalance in mitochondrial dynamics. In addition, PRV infection triggered PINK1-Parkin-mediated mitophagy to eliminate the impaired mitochondria, which resulted in a suppression of IFN-I production, thereby promoting viral replication. Furthermore, we found that mitophagy resulted in the degradation of the mitochondrial antiviral signaling protein, which is located on the mitochondrial outer membrane. In conclusion, the data of the current study indicate that PRV-induced mitophagy represents a previously uncharacterized PRV evasion mechanism of the IFN-I response, thereby promoting virus replication.IMPORTANCEPseudorabies virus (PRV), a pathogen that induces different disease symptoms and is often fatal in domestic animals and wildlife, has caused great economic losses to the swine industry. Since 2011, different PRV variant strains have emerged in Asia, against which current commercial vaccines may not always provide optimal protection in pigs. In addition, there are indications that some of these PRV variant strains may sporadically infect people. In the current study, we found that PRV infection causes mitochondria injury. This is associated with the induction of mitophagy to eliminate the damaged mitochondria, which results in suppressed antiviral interferon production and signaling. Hence, our study reveals a novel mechanism that is used by PRV to antagonize the antiviral host immune response, providing a theoretical basis that may contribute to the research toward and development of new vaccines and antiviral drugs.

Inhibition of mitophagy via the EIF2S1-ATF4-PRKN pathway contributes to viral encephalitis

INTRODUCTION

Mitophagy, a selective form of autophagy responsible for maintaining mitochondrial homeostasis, regulates the antiviral immune response and acts as viral replication platforms to facilitate infection with various viruses. However, its precise role in herpes simplex virus 1 (HSV-1) infection and herpes simplex encephalitis (HSE) remains largely unknown.

OBJECTIVES

We aimed to investigate the regulation of mitophagy by HSV-1 neurotropic infection and its role in viral encephalitis, and to identify small compounds that regulate mitophagy to affect HSV-1 infection.

METHODS

The antiviral effects of compounds were investigated by Western blot, RT-PCR and plaque assay. The changes of Parkin (PRKN)-mediated mitophagy and Nuclear Factor kappa B (NFKB)-mediated neuroinflammation were examined by TEM, RT-qPCR, Western blot and ELISA. The therapeutic effect of taurine or PRKN-overexpression was confirmed in the HSE mouse model by evaluating survival rate, eye damage, neurodegenerative symptoms, immunohistochemistry analysis and histopathology.

RESULTS

HSV-1 infection caused the accumulation of damaged mitochondria in neuronal cells and in the brain tissue of HSE mice. Early HSV-1 infection led to mitophagy activation, followed by inhibition in the later viral infection. The HSV-1 proteins ICP34.5 or US11 deregulated the EIF2S1-ATF4 axis to suppress PRKN/Parkin mRNA expression, thereby impeding PRKN-dependent mitophagy. Consequently, inhibition of mitophagy by specific inhibitor midiv-1 promoted HSV-1 infection, whereas mitophagy activation by PRKN overexpression or agonists (CCCP and rotenone) attenuated HSV-1 infection and reduced the NF-κB-mediated neuroinflammation. Moreover, PRKN-overexpressing mice showed enhanced resistance to HSV-1 infection and ameliorated HSE pathogenesis. Furthermore, taurine, a differentially regulated gut microbial metabolite upon HSV-1 infection, acted as a mitophagy activator that transcriptionally promotes PRKN expression to stimulate mitophagy and to limit HSV-1 infection both in vitro and in vivo.

CONCLUSION

These results reveal the protective function of mitophagy in HSE pathogenesis and highlight mitophagy activation as a potential antiviral therapeutic strategy for HSV-1-related diseases.

Co-option of mitochondrial nucleic acid sensing pathways by HSV-1 UL12.5 for reactivation from latent Infection

Although viruses subvert innate immune pathways for their replication, there is evidence they can also co-opt anti-viral responses for their benefit. The ubiquitous human pathogen, Herpes Simplex Virus-1 (HSV-1), encodes a protein (UL12.5) that induces the release of mitochondrial nucleic acid into the cytosol, which activates immune sensing pathways and reduces productive replication in non-neuronal cells. HSV-1 establishes latency in neurons and can reactivate to cause disease. We found that UL12.5 is required for HSV-1 reactivation in neurons and acts to directly promote viral lytic gene expression during initial exit from latency. Further, the direct activation of innate immune sensing pathways triggered HSV reactivation and compensated for a lack of UL12.5. Finally, we found that the induction of HSV-1 lytic genes during reactivation required intact RNA and DNA sensing pathways, demonstrating that HSV-1 can both respond to and active antiviral nucleic acid sensing pathways to reactivate from a latent infection.

MITOCHONDRIAL ANTIVIRAL PATHWAYS CONTROL ANTI-HIV RESPONSES AND ISCHEMIC STROKE OUTCOMES VIA THE RIG-1 SIGNALING AND INNATE IMMUNITY MECHANISMS

Occludin (ocln) is one of the main regulatory cells of the blood-brain barrier (BBB). Ocln silencing resulted in alterations of the gene expression signatures of a variety of genes of the innate immunity system, including IFN-stimulated genes (ISGs) and the antiviral retinoic acid-inducible gene-1 (RIG-1) signaling pathway, which functions as a regulator of the cytoplasmic sensors upstream of the mitochondrial antiviral signaling protein (MAVS). Indeed, we observed dysfunctional mitochondrial bioenergetics, dynamics, and autophagy in our system. Alterations of mitochondrial bioenergetics and innate immune protection translated into worsened ischemic stroke outcomes in EcoHIV-infected ocln deficient mice. Overall, these results allow for a better understanding of the molecular mechanisms of viral infection in the brain and describe a previously unrecognized role of ocln as a key factor in the control of innate immune responses and mitochondrial dynamics, which affect cerebral vascular diseases such as ischemic stroke.

Polyphenols from Maackia amurensis Heartwood Protect Neuronal Cells from Oxidative Stress and Prevent Herpetic Infection

Here, we continued the investigation of anti-HSV-1 activity and neuroprotective potential of 14 polyphenolic compounds isolated from Maackia amurensis heartwood. We determined the absolute configurations of asymmetric centers in scirpusin A (13) and maackiazin (10) as 7R,8R and 1″S,2″S, respectively. We showed that dimeric stilbens maackin (9) and scirpusin A (13) possessed the highest anti-HSV-1 activity among polyphenols 1-14. We also studied the effect of polyphenols 9 and 13 on the early stages of HSV-1 infection. Direct interaction with the virus (virucidal activity) was the main mechanism of the antiviral activity of these compounds. The neuroprotective potential of polyphenolic compounds from M. amurensis was studied using models of 6-hydroxydopamine (6-OHDA)-and paraquat (PQ)-induced neurotoxicity. A dimeric stilbene scirpusin A (13) and a flavonoid liquiritigenin (6) were shown to be the most active compounds among the tested polyphenols. These compounds significantly increased the viability of 6-OHDA-and PQ-treated Neuro-2a cells, elevated mitochondrial membrane potential and reduced the intracellular ROS level. We also found that scirpusin A (13), liquiritigenin (6) and retusin (3) considerably increased the percentage of live Neuro-2a cells and decreased the number of early apoptotic cells. Scirpusin A (13) was the most promising compound possessing both anti-HSV-1 activity and neuroprotective potential.

Regulation of type I and type III interferon induction in response to pathogen sensing

Type I and III interferons (IFN-I and IFN-III) have a central role in the early antimicrobial response against invading pathogens. Induction of IFN-Is and IFN-IIIs arises due to the sensing by pattern recognition receptors of pathogen-associated molecular patterns (from micro-organisms) or of damage-associated molecular patterns (DAMPs; produced by host cells). Here, we review recent developments on how IFN-I and IFN-III expression is stimulated by different pathogens and how the signalling pathways leading to IFN induction are tightly regulated. We also summarise the growing knowledge of the sensing pathways that lead to IFN-I and IFN-III induction in response to severe acute respiratory syndrome coronavirus 2.

Progression of herpesvirus infection remodels mitochondrial organization and metabolism

Viruses target mitochondria to promote their replication, and infection-induced stress during the progression of infection leads to the regulation of antiviral defenses and mitochondrial metabolism which are opposed by counteracting viral factors. The precise structural and functional changes that underlie how mitochondria react to the infection remain largely unclear. Here we show extensive transcriptional remodeling of protein-encoding host genes involved in the respiratory chain, apoptosis, and structural organization of mitochondria as herpes simplex virus type 1 lytic infection proceeds from early to late stages of infection. High-resolution microscopy and interaction analyses unveiled infection-induced emergence of rough, thin, and elongated mitochondria relocalized to the perinuclear area, a significant increase in the number and clustering of endoplasmic reticulum-mitochondria contact sites, and thickening and shortening of mitochondrial cristae. Finally, metabolic analyses demonstrated that reactivation of ATP production is accompanied by increased mitochondrial Ca2+ content and proton leakage as the infection proceeds. Overall, the significant structural and functional changes in the mitochondria triggered by the viral invasion are tightly connected to the progression of the virus infection.

Critical contribution of mitochondria in the development of cardiomyopathy linked to desmin mutation

BACKGROUND

Beyond the observed alterations in cellular structure and mitochondria, the mechanisms linking rare genetic mutations to the development of heart failure in patients affected by desmin mutations remain unclear due in part, to the lack of relevant human cardiomyocyte models.

METHODS

To shed light on the role of mitochondria in these mechanisms, we investigated cardiomyocytes derived from human induced pluripotent stem cells carrying the heterozygous DESE439K mutation that were either isolated from a patient or generated by gene editing. To increase physiological relevance, cardiomyocytes were either cultured on an anisotropic micropatterned surface to obtain elongated and aligned cardiomyocytes, or as a cardiac spheroid to create a micro-tissue. Moreover, when applicable, results from cardiomyocytes were confirmed with heart biopsies of suddenly died patient of the same family harboring DESE439K mutation, and post-mortem heart samples from five control healthy donors.

RESULTS

The heterozygous DESE439K mutation leads to dramatic changes in the overall cytoarchitecture of cardiomyocytes, including cell size and morphology. Most importantly, mutant cardiomyocytes display altered mitochondrial architecture, mitochondrial respiratory capacity and metabolic activity reminiscent of defects observed in patient's heart tissue. Finally, to challenge the pathological mechanism, we transferred normal mitochondria inside the mutant cardiomyocytes and demonstrated that this treatment was able to restore mitochondrial and contractile functions of cardiomyocytes.

CONCLUSIONS

This work highlights the deleterious effects of DESE439K mutation, demonstrates the crucial role of mitochondrial abnormalities in the pathophysiology of desmin-related cardiomyopathy, and opens up new potential therapeutic perspectives for this disease.

Mitochondrial nucleic acids in innate immunity and beyond

Mitochondria participate in a wide range of cellular processes. One essential function of mitochondria is to be a platform for antiviral signaling proteins during the innate immune response to viral infection. Recently, studies have revealed that mitochondrion-derived DNAs and RNAs are recognized as non-self molecules and act as immunogenic ligands. More importantly, the cytosolic release of these mitochondrial nucleic acids (mt-NAs) is closely associated with the pathogenesis of human diseases accompanying aberrant immune activation. The release of mitochondrial DNAs (mtDNAs) via BAX/BAK activation and/or VDAC1 oligomerization activates the innate immune response and inflammasome assembly. In addition, mitochondrial double-stranded RNAs (mt-dsRNAs) are sensed by pattern recognition receptors in the cytosol to induce type I interferon expression and initiate apoptotic programs. Notably, these cytosolic mt-NAs also mediate adipocyte differentiation and contribute to mitogenesis and mitochondrial thermogenesis. In this review, we summarize recent studies of innate immune signaling pathways regulated by mt-NAs, human diseases associated with mt-NAs, and the emerging physiological roles of mt-NAs.

Elevated phospholipids and acylcarnitines C4 and C5 in cerebrospinal fluid distinguish viral CNS infections from autoimmune neuroinflammation

BACKGROUND

Viral and autoimmune encephalitis may present with similar symptoms, but require different treatments. Thus, there is a need for biomarkers to improve diagnosis and understanding of pathogenesis. We hypothesized that virus-host cell interactions lead to different changes in central nervous system (CNS) metabolism than autoimmune processes and searched for metabolite biomarkers in cerebrospinal fluid (CSF) to distinguish between the two conditions.

METHODS

We applied a targeted metabolomic/lipidomic analysis to CSF samples from patients with viral CNS infections (n = 34; due to herpes simplex virus [n = 9], varicella zoster virus [n = 15], enteroviruses [n = 10]), autoimmune neuroinflammation (n = 25; autoimmune anti-NMDA-receptor encephalitis [n = 8], multiple sclerosis [n = 17), and non-inflamed controls (n = 31; Gilles de la Tourette syndrome [n = 20], Bell's palsy with normal CSF cell count [n = 11]). 85 metabolites passed quality screening and were evaluated as biomarkers. Standard diagnostic CSF parameters were assessed for comparison.

RESULTS

Of the standard CSF parameters, the best biomarkers were: CSF cell count for viral infections vs. controls (area under the ROC curve, AUC = 0.93), Q-albumin for viral infections vs. autoimmune neuroinflammation (AUC = 0.86), and IgG index for autoimmune neuroinflammation vs. controls (AUC = 0.90). Concentrations of 2 metabolites differed significantly (p < 0.05) between autoimmune neuroinflammation and controls, with proline being the best biomarker (AUC = 0.77). In contrast, concentrations of 67 metabolites were significantly higher in viral infections than controls, with SM.C16.0 being the best biomarker (AUC = 0.94). Concentrations of 68 metabolites were significantly higher in viral infections than in autoimmune neuroinflammation, and the 10 most accurate metabolite biomarkers (AUC = 0.89-0.93) were substantially better than Q-albumin (AUC = 0.86). These biomarkers comprised six phosphatidylcholines (AUC = 0.89-0.92), two sphingomyelins (AUC = 0.89, 0.91), and acylcarnitines isobutyrylcarnitine (C4, AUC = 0.92) and isovalerylcarnitine (C5, AUC = 0.93). Elevated C4 and C5 concentrations suggested dysfunctional mitochondrial β-oxidation and correlated only moderately with CSF cell count (Spearman ρ = 0.41 and 0.44), indicating that their increase is not primarily driven by inflammation.

CONCLUSIONS

Changes in CNS metabolism differ substantially between viral CNS infections and autoimmune neuroinflammation and reveal CSF metabolites as pathophysiologically relevant diagnostic biomarkers for the differentiation between the two conditions. In viral CNS infections, the observed higher concentrations of free phospholipids are consistent with disruption of host cell membranes, whereas the elevated short-chain acylcarnitines likely reflect compromised mitochondrial homeostasis and energy generation.

The use of RNA-based treatments in the field of cancer immunotherapy

Over the past several decades, mRNA vaccines have evolved from a theoretical concept to a clinical reality. These vaccines offer several advantages over traditional vaccine techniques, including their high potency, rapid development, low-cost manufacturing, and safe administration. However, until recently, concerns over the instability and inefficient distribution of mRNA in vivo have limited their utility. Fortunately, recent technological advancements have mostly resolved these concerns, resulting in the development of numerous mRNA vaccination platforms for infectious diseases and various types of cancer. These platforms have shown promising outcomes in both animal models and humans. This study highlights the potential of mRNA vaccines as a promising alternative approach to conventional vaccine techniques and cancer treatment. This review article aims to provide a thorough and detailed examination of mRNA vaccines, including their mechanisms of action and potential applications in cancer immunotherapy. Additionally, the article will analyze the current state of mRNA vaccine technology and highlight future directions for the development and implementation of this promising vaccine platform as a mainstream therapeutic option. The review will also discuss potential challenges and limitations of mRNA vaccines, such as their stability and in vivo distribution, and suggest ways to overcome these issues. By providing a comprehensive overview and critical analysis of mRNA vaccines, this review aims to contribute to the advancement of this innovative approach to cancer treatment.

PRRSV infection activates NLRP3 inflammasome through inducing cytosolic mitochondrial DNA stress

Porcine reproductive and respiratory syndrome virus (PRRSV) infection causes severe interstitial pneumonia and inflammatory response in piglets and growing pigs. IL-1β is implicated in PRRSV-mediated inflammatory response and the pathogenesis of PRRSV infection. Mitochondria are critical intracellular organelles which is served as signaling platform for antiviral immunity response to participate in immune response of virus infection. The role of mitochondria in PRRSV-mediated inflammatory response and the pathogenesis of PRRSV infection has not been elucidated. Here, our data suggested that PRRSV infection facilitates mitochondrial dysfunction, which induces cytosolic mitochondrial DNA (mtDNA) stress and ROS accumulation, severally activates the NLRP3 inflammasome and NF-κB signaling pathway, and consequently stimulates IL-1β production in PAMs. Furthermore, mtDNA degradation by DNase I abrogates the activation of NLRP3 inflammasome and IL-1β secretion during PRRSV infection. Scavenging ROS significantly inhibits NF-κB signaling activation and the subsequently transcription and secretion of IL-1β. In conclusion, our results indicate that cytosolic mtDNA stress and ROS accumulation after PRRSV infection-induced mitochondrial dysfunction activate NLRP3 inflammasome and NF-κB signaling pathway to promote IL-1β production, revealing a new strategy for vaccine and drug development to PRRSV.

Mitofusin 1-Mediated Redistribution of Mitochondrial Antiviral Signaling Protein Promotes Type 1 Interferon Response in Human Cytomegalovirus Infection

One of the most potent anti-human cytomegalovirus (HCMV) immune mechanisms possessed by host cells is type I interferon (IFN1), which induces the expression of IFN-stimulated genes (ISGs). During this process, mitochondria play an important role in the IFN1 response, and mitofusin 1 (MFN1) is a key regulator of mitochondrial fusion located on the outer mitochondrial membrane. However, the underlying mechanism of MFN1's promotion of IFN1 during HCMV infection still remains unknown. In this study, HCMV infection promoted IFN1 production and enhanced ISG expression. Meanwhile, it promoted the increase of mitochondrial fusion in THP-1 cells and peripheral blood mononuclear cells (PBMCs), especially the expression of MFN1. Phosphorylation of tank binding kinase 1 (p-TBK1), interferon regulatory factor 3 (p-IRF3), and ISGs was significantly decreased in MFN1 or mitochondrial antiviral signaling protein (MAVS)-knockdown THP-1 cells, and MFN1 was constitutively associated with MAVS, positively regulated mitochondrial fusion, and IFN1 production. Knockdown of MFN1 inhibited the MAVS redistribution without affecting the MAVS expression, whereas the HCMV-induced IFN1 production decreased. Conversely, leflunomide could induce the expression of MFN1, thereby producing IFN1 and stimulating the expression of ISG in leflunomide-treated THP-1 cells. These observations reveal that HCMV infection leads to MFN1-mediated redistribution of MAVS and then induces an antiviral response of IFN1 and that the MFN-agonist leflunomide promotes IFN1 responses and may serve as a potential anti-HCMV therapy. IMPORTANCE Human cytomegalovirus (HCMV) infection is ubiquitous and is often asymptomatic in healthy individuals, but it can cause great damage to newborns, AIDS patients, and other immune deficiency patients. In this study, we found that HCMV infection caused mitochondrial fusion, and expression of mitofusin 1 (MFN1), which is a protein associated with mitochondrial antiviral signaling protein (MAVS), positively regulates mitochondrial fusion and HCMV-induced IFN1 response. Knockdown of MFN1 or MAVS can inhibit the HCMV-induced IFN1 production. What is more, confocal laser-scanning microscope showed that knockdown of MFN1 inhibits the HCMV-induced redistribution of MAVS. Conversely, MFN1 agonist leflunomide could induce IFN1 production. In conclusion, we provide new insight into the relationship between MFN1 and IFN1 during HCMV infection and show that MFN1 may serve as a potential strategy against HCMV infection.

Exploiting RIG-I-like receptor pathway for cancer immunotherapy

RIG-I-like receptors (RLRs) are intracellular pattern recognition receptors that detect viral or bacterial infection and induce host innate immune responses. The RLRs family comprises retinoic acid-inducible gene 1 (RIG-I), melanoma differentiation-associated gene 5 (MDA5) and laboratory of genetics and physiology 2 (LGP2) that have distinctive features. These receptors not only recognize RNA intermediates from viruses and bacteria, but also interact with endogenous RNA such as the mislocalized mitochondrial RNA, the aberrantly reactivated repetitive or transposable elements in the human genome. Evasion of RLRs-mediated immune response may lead to sustained infection, defective host immunity and carcinogenesis. Therapeutic targeting RLRs may not only provoke anti-infection effects, but also induce anticancer immunity or sensitize "immune-cold" tumors to immune checkpoint blockade. In this review, we summarize the current knowledge of RLRs signaling and discuss the rationale for therapeutic targeting RLRs in cancer. We describe how RLRs can be activated by synthetic RNA, oncolytic viruses, viral mimicry and radio-chemotherapy, and how the RNA agonists of RLRs can be systemically delivered in vivo. The integration of RLRs agonism with RNA interference or CAR-T cells provides new dimensions that complement cancer immunotherapy. Moreover, we update the progress of recent clinical trials for cancer therapy involving RLRs activation and immune modulation. Further studies of the mechanisms underlying RLRs signaling will shed new light on the development of cancer therapeutics. Manipulation of RLRs signaling represents an opportunity for clinically relevant cancer therapy. Addressing the challenges in this field will help develop future generations of cancer immunotherapy.

Antagonism of ALAS1 by the Measles Virus V protein contributes to degradation of the mitochondrial network and promotes interferon response

Viruses have evolved countless mechanisms to subvert and impair the host innate immune response. Measles virus (MeV), an enveloped, non-segmented, negative-strand RNA virus, alters the interferon response through different mechanisms, yet no viral protein has been described as directly targeting mitochondria. Among the crucial mitochondrial enzymes, 5'-aminolevulinate synthase (ALAS) is an enzyme that catalyzes the first step in heme biosynthesis, generating 5'-aminolevulinate from glycine and succinyl-CoA. In this work, we demonstrate that MeV impairs the mitochondrial network through the V protein, which antagonizes the mitochondrial enzyme ALAS1 and sequesters it to the cytosol. This re-localization of ALAS1 leads to a decrease in mitochondrial volume and impairment of its metabolic potential, a phenomenon not observed in MeV deficient for the V gene. This perturbation of the mitochondrial dynamics demonstrated both in culture and in infected IFNAR-/- hCD46 transgenic mice, causes the release of mitochondrial double-stranded DNA (mtDNA) in the cytosol. By performing subcellular fractionation post infection, we demonstrate that the most significant source of DNA in the cytosol is of mitochondrial origin. Released mtDNA is then recognized and transcribed by the DNA-dependent RNA polymerase III. The resulting double-stranded RNA intermediates will be captured by RIG-I, ultimately initiating type I interferon production. Deep sequencing analysis of cytosolic mtDNA editing divulged an APOBEC3A signature, primarily analyzed in the 5'TpCpG context. Finally, in a negative feedback loop, APOBEC3A an interferon inducible enzyme will orchestrate the catabolism of mitochondrial DNA, decrease cellular inflammation, and dampen the innate immune response.

HSV Replication: Triggering and Repressing STING Functionality

Herpes simplex virus (HSV) has persisted within human populations due to its ability to establish both lytic and latent infection. Given this, human hosts have evolved numerous immune responses to protect against HSV infection. Critical in this defense against HSV, the host protein stimulator of interferon genes (STING) functions as a mediator of the antiviral response by inducing interferon (IFN) as well as IFN-stimulated genes. Emerging evidence suggests that during HSV infection, dsDNA derived from either the virus or the host itself ultimately activates STING signaling. While a complex regulatory circuit is in operation, HSV has evolved several mechanisms to neutralize the STING-mediated antiviral response. Within this review, we highlight recent progress involving HSV interactions with the STING pathway, with a focus on how STING influences HSV replication and pathogenesis.

Herpes Simplex Type 1 UL43 Multiple Membrane-Spanning Protein Increases Energy Metabolism in Host Cells through Interacting with ARL2

Non-essential proteins for viral replication affect host cell metabolism, while the function of the UL43 protein of herpes simplex virus 1 (HSV-1) is not clear. Herein, we performed a comprehensive microarray analysis of HUVEC cells infected with HSV-1 and its UL43-deficient mutant and found significant variation in genes associated with cellular energy metabolic pathways. The localization of UL43 protein in host cells and how it affects cellular energy metabolism pathways were further investigated. Internalization analysis showed that the UL43 protein could be endocytosis-mediated by YPLF motif (aa144-147) and localized to mitochondria. At the same time, more ATP was produced by coupling with mitochondrial small G protein ARF-like 2 (ARL2) GTPase, which triggered the phosphorylation of ANT1 (SLC25A4) to affect the opening degree of mitochondrial permeability transition pore (mPTP), and significantly promoted the aerobic oxidation and oxidative phosphorylation of glucose. Our study shows that UL43 mediates the improvement of host cell metabolism after HSV-1 infection. Additionally, UL43 protein could be a valuable ATP-stimulating factor for mammalian cells.

The A137R Protein of African Swine Fever Virus Inhibits Type I Interferon Production via the Autophagy-Mediated Lysosomal Degradation of TBK1

African swine fever is a lethal hemorrhagic disease of pigs caused by African swine fever virus (ASFV), which greatly threatens the pig industry in many countries. Deletion of virulence-associated genes to develop live attenuated ASF vaccines is considered to be a promising strategy. A recent study has revealed that the A137R gene deletion results in ASFV attenuation, but the underlying mechanism remains unknown. To elucidate the mechanism of the A137R gene regulating ASFV virulence, an ASFV mutant with the A137R gene deleted (ASFV-ΔA137R) was generated based on the wild-type ASFV HLJ/2018 strain (ASFV-WT). Using transcriptome sequencing analysis, we found that ASFV-ΔA137R induced higher type I interferon (IFN) production in primary porcine alveolar macrophages (PAMs) than did ASFV-WT. Overexpression of the A137R protein (pA137R) inhibited the activation of IFN-β or IFN-stimulated response element. Mechanistically, pA137R interacts with TANK-binding kinase 1 (TBK1) and promotes the autophagy-mediated lysosomal degradation of TBK1, which blocks the nuclear translocation of interferon regulator factor 3, leading to decreased type I IFN production. Taken together, our findings clarify that pA137R negatively regulates the cGAS-STING-mediated IFN-β signaling pathway via the autophagy-mediated lysosomal degradation of TBK1, which highlights the involvement of pA137R regulating ASFV virulence.

IMPORTANCE African swine fever (ASF) is a lethal viral disease of pigs caused by African swine fever virus (ASFV). No commercial vaccines and antiviral treatments are available for the prevention and control of the disease. Several virulence-associated genes of ASFV have been identified, but the underlying attenuation mechanisms are not clear. Compared with the virulent parental ASFV, the A137R gene-deleted ASFV mutant promoted the expression of type I interferon (IFN) in primary porcine alveolar macrophages. Further analysis indicated that the A137R protein negatively regulated the cGAS-STING-mediated IFN-β signaling pathway through targeting TANK-binding kinase 1 (TBK1) for autophagy-mediated lysosomal degradation. This study not only facilitates the understanding of ASFV immunoevasion strategies, but also provides new clues to the development of live attenuated ASF vaccines.

Acute Cerebellar Inflammation and Related Ataxia: Mechanisms and Pathophysiology

The cerebellum governs motor coordination and motor learning. Infection with external microorganisms, such as viruses, bacteria, and fungi, induces the release and production of inflammatory mediators, which drive acute cerebellar inflammation. The clinical observation of acute cerebellitis is associated with the emergence of cerebellar ataxia. In our animal model of the acute inflammation of the cerebellar cortex, animals did not show any ataxia but hyperexcitability in the cerebellar cortex and depression-like behaviors. In contrast, animal models with neurodegeneration of the cerebellar Purkinje cells and hypoexcitability of the neurons show cerebellar ataxia. The suppression of the Ca2+-activated K+ channels in vivo is associated with a type of ataxia. Therefore, there is a gap in our interpretation between the very early phase of cerebellar inflammation and the emergence of cerebellar ataxia. In this review, we discuss the hypothesized scenario concerning the emergence of cerebellar ataxia. First, compared with genetically induced cerebellar ataxias, we introduce infection and inflammation in the cerebellum via aberrant immunity and glial responses. Especially, we focus on infections with cytomegalovirus, influenza virus, dengue virus, and SARS-CoV-2, potential relevance to mitochondrial DNA, and autoimmunity in infection. Second, we review neurophysiological modulation (intrinsic excitability, excitatory, and inhibitory synaptic transmission) by inflammatory mediators and aberrant immunity. Next, we discuss the cerebellar circuit dysfunction (presumably, via maintaining the homeostatic property). Lastly, we propose the mechanism of the cerebellar ataxia and possible treatments for the ataxia in the cerebellar inflammation.

Evolution of the RNA Cleavage Subunit C11/RPC10, and Recycling by RNA Polymerase III

Nuclear RNA polymerase (Pol) III synthesizes large amounts of tRNAs and other short non-coding (nc)RNAs by a unique process that involves a termination-associated reinitiation-recycling mechanism. In addition to its two largest of 17 subunits, which contribute to active center RNA-DNA binding and catalytic site, a smaller subunit of ~110 aa (yeast C11, human RPC10) monitors this site, can modify its activity, and is essential for reinitiation-recycling. Distinct, but relevant to human immunity is cytoplasmic (cyto-)Pol III that is a direct sensor of AT-rich viral DNA from which it synthesizes 5'-ppp-RNA signaling molecules that activate interferon (IFN) production. Mutations in genes encoding Pol III subunits cause severe anti-viral immunodeficiency although the mechanisms responsible for cyto-Pol III initiation on this AT-rich DNA are unknown. Cyto-Pol III has also been implicated in inducing IFN in response to cytosolic mitochondrial DNA in autoimmune dysfunction. A focus of this commentary is recent biochemical and genetics research that examined the roles of the individual domains of C11 in the Pol III termination-associated reinitiation-recycling process as well as more recent cryo-EM structural and accompanying analyses, that are considered in evolutionary and other biological contexts. The N-terminal domain (NTD) of C11/RPC10 anchors at the periphery of Pol III from which a highly conserved linker extends to the mobile C-terminal RNA cleavage domain that can reach into the active center and rescue arrested complexes. Biochemical data indicate separable activities for the NTD and CTD in the transcription cycle, whereas the NTD-Linker can confer the evolutionary unique Pol III termination-reinitiation-recycling activity. A model produced from single particle cryo-EM conformations indicates that the C11-Linker-CTD swings in and out of the active center coordinated with allosteric movements of the DNA-binding clamp by the largest subunit, coupling termination to reinitiation-recycling. These may be relevant to DNA loading by cyto-Pol III during immune signaling.