DDAH2 suppresses RLR-MAVS-mediated innate antiviral immunity by stimulating nitric oxide-activated, Drp1-induced mitochondrial fission

Redefining the biological and pathophysiological role of dimethylarginine dimethylaminohydrolase 2

The enzyme dimethylarginine dimethylaminohydrolase (DDAH) 1 metabolizes asymmetric dimethylarginine (ADMA), a critical endogenous cardiovascular risk factor. In the past two decades, there has been significant controversy about whether DDAH2, the other DDAH isoform, is also able to directly metabolize ADMA. There has been evidence that DDAH2 regulates several critical processes involved in cardiovascular and immune homeostasis. However, the molecular mechanisms underpinning these effects are unclear. In this opinion, we discuss the previous and current knowledge of ADMA metabolism by DDAH in light of a recent consortium study, which convincingly demonstrated that DDAH2 is not capable of metabolizing ADMA, unlike DDAH1. Thus, further research in this field is needed to uncover the molecular mechanisms of DDAH2 and its role in various disorders.

Japanese encephalitis virus NS1 and NS1' proteins induce vimentin rearrangement via the CDK1-PLK1 axis to promote viral replication

The host cytoskeleton plays crucial roles in various stages of virus infection, including viral entry, transport, replication, and release. However, the specific mechanisms by which intermediate filaments are involved in orthoflavivirus infection have not been well understood. In this study, we demonstrate that the Japanese encephalitis virus (JEV) remodels the vimentin network, resulting in the formation of cage-like structures that support viral replication. Mechanistically, JEV NS1 and NS1' proteins induce the translocation of CDK1 from the nucleus to the cytoplasm and interact with it, leading to the phosphorylation of vimentin at Ser56. This phosphorylation event recruits PLK1, which further phosphorylates vimentin at Ser83. Consequently, these phosphorylation modifications convert the typically filamentous vimentin into non-filamentous "particles" or "squiggles." These vimentin "particles" or "squiggles" are then transported retrogradely along microtubules to the endoplasmic reticulum, where they form cage-like structures. Notably, NS1' is more effective than NS1 in triggering the CDK1-PLK1 cascade response. Overall, our study provides new insights into how JEV NS1 and NS1' proteins manipulate the vimentin network to facilitate efficient viral replication.

IMPORTANCE

Japanese encephalitis virus (JEV) is a mosquito-borne orthoflavivirus that causes severe encephalitis in humans, particularly in Asia. Despite the availability of a safe and effective vaccine, JEV infection remains a significant public health threat due to limited vaccination coverage. Understanding the interactions between JEV and host proteins is essential for developing more effective antiviral strategies. In this study, we investigated the role of vimentin, an intermediate filament protein, in JEV replication. Our findings reveal that JEV NS1 and NS1' proteins induce vimentin rearrangement, resulting in the formation of cage-like structures that envelop the viral replication factories (RFs), thus facilitating efficient viral replication. Our research highlights the importance of the interplay between the cytoskeleton and orthoflavivirus, suggesting that targeting vimentin could be a promising approach for the development of antiviral strategies to inhibit JEV propagation.

Physiological functions of RIG-I-like receptors

RIG-I-like receptors (RLRs) are crucial for pathogen detection and triggering immune responses and have immense physiological importance. In this review, we first summarize the interferon system and innate immunity, which constitute primary and secondary responses. Next, the molecular structure of RLRs and the mechanism of sensing non-self RNA are described. Usually, self RNA is refractory to the RLR; however, there are underlying host mechanisms that prevent immune reactions. Studies have revealed that the regulatory mechanisms of RLRs involve covalent molecular modifications, association with regulatory factors, and subcellular localization. Viruses have evolved to acquire antagonistic RLR functions to escape the host immune reactions. Finally, the pathologies caused by the malfunction of RLR signaling are described.

Bioinformatics-based analysis of the relationship between disulfidptosis and prognosis and treatment response in pancreatic cancer

Tumor formation is closely associated with disulfidptosis, a new form of cell death induced by disulfide stress-induced. The exact mechanism of action of disulfidptosis in pancreatic cancer (PCa) is not clear. This study analyzed the impact of disulfidptosis-related genes (DRGs) on the prognosis of PCa and identified clusters of DRGs, and based on this, a risk score (RS) signature was developed to assess the impact of RS on the prognosis, immune and chemotherapeutic response of PCa patients. Based on transcriptomic data and clinical information from PCa tissue and normal pancreatic tissue samples obtained from the TCGA and GTEx databases, differentially expressed and differentially surviving DRGs in PCa were identified from among 15 DRGs. Two DRGs clusters were identified by consensus clustering by merging the PCa samples in the GSE183795 dataset. Analysis of DRGs clusters about the PCa tumor microenvironment and differential analysis to obtain differential genes between the two DRG clusters. Patients were then randomized into the training and testing sets, and a prognostic prediction signature associated with disulfidptosis was constructed in the training set. Then all samples were divided into high-disulfidptosis-risk (HDR) and low-disulfidptosis-risk (LDR) subgroups based on the RS calculated from the signature. The predictive efficacy of the signature was assessed by survival analysis, nomograms, correlation analysis of clinicopathological characteristics, and the receiver operating characteristic (ROC) curves. To assess differences between different risk subgroups in immune cell infiltration, expression of immune checkpoint molecules, somatic gene mutations, and effectiveness of immunotherapy and chemotherapy. The GSE57495 dataset was used as external validation, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used to detect the expression levels of DRGs. A total of 12 DRGs with differential expression and prognosis in PCa were identified, based on which a risk-prognosis signature containing five differentially expressed genes (DEGs) was developed. The signature was a good predictor and an independent risk factor. The nomogram and calibration curve shows the signature's excellent clinical applicability. Functional enrichment analysis showed that RS was associated with tumor and immune-related pathways. RS was strongly associated with the tumor microenvironment, and analysis of response to immunotherapy and chemotherapy suggests that the signature can be used to assess the sensitivity of treatments. External validation further demonstrated the model's efficacy in predicting the prognosis of PCa patients, with RT-qPCR and immunohistochemical maps visualizing the expression of each gene in PCa cell lines and the tissue. Our study is the first to apply the subtyping model of disulfidptosis to PCa and construct a signature based on the disulfidptosis subtype, which can provide an accurate assessment of prognosis, immunotherapy, and chemotherapy response in PCa patients, providing new targets and directions for the prognosis and treatment of PCa.

Virus-Host Protein Interaction Network of the Hepatitis E Virus ORF2-4 by Mammalian Two-Hybrid Assays

Throughout their life cycle, viruses interact with cellular host factors, thereby influencing propagation, host range, cell tropism and pathogenesis. The hepatitis E virus (HEV) is an underestimated RNA virus in which knowledge of the virus-host interaction network to date is limited. Here, two related high-throughput mammalian two-hybrid approaches (MAPPIT and KISS) were used to screen for HEV-interacting host proteins. Promising hits were examined on protein function, involved pathway(s), and their relation to other viruses. We identified 37 ORF2 hits, 187 for ORF3 and 91 for ORF4. Several hits had functions in the life cycle of distinct viruses. We focused on SHARPIN and RNF5 as candidate hits for ORF3, as they are involved in the RLR-MAVS pathway and interferon (IFN) induction during viral infections. Knocking out (KO) SHARPIN and RNF5 resulted in a different IFN response upon ORF3 transfection, compared to wild-type cells. Moreover, infection was increased in SHARPIN KO cells and decreased in RNF5 KO cells. In conclusion, MAPPIT and KISS are valuable tools to study virus-host interactions, providing insights into the poorly understood HEV life cycle. We further provide evidence for two identified hits as new host factors in the HEV life cycle.

Targeting mitochondrial shape: at the heart of cardioprotection

There remains an unmet need to identify novel therapeutic strategies capable of protecting the myocardium against the detrimental effects of acute ischemia-reperfusion injury (IRI), to reduce myocardial infarct (MI) size and prevent the onset of heart failure (HF) following acute myocardial infarction (AMI). In this regard, perturbations in mitochondrial morphology with an imbalance in mitochondrial fusion and fission can disrupt mitochondrial metabolism, calcium homeostasis, and reactive oxygen species production, factors which are all known to be critical determinants of cardiomyocyte death following acute myocardial IRI. As such, therapeutic approaches directed at preserving the morphology and functionality of mitochondria may provide an important strategy for cardioprotection. In this article, we provide an overview of the alterations in mitochondrial morphology which occur in response to acute myocardial IRI, and highlight the emerging therapeutic strategies for targeting mitochondrial shape to preserve mitochondrial function which have the future therapeutic potential to improve health outcomes in patients presenting with AMI.

A multicentric consortium study demonstrates that dimethylarginine dimethylaminohydrolase 2 is not a dimethylarginine dimethylaminohydrolase

Dimethylarginine dimethylaminohydrolase 1 (DDAH1) protects against cardiovascular disease by metabolising the risk factor asymmetric dimethylarginine (ADMA). However, the question whether the second DDAH isoform, DDAH2, directly metabolises ADMA has remained unanswered. Consequently, it is still unclear if DDAH2 may be a potential target for ADMA-lowering therapies or if drug development efforts should focus on DDAH2's known physiological functions in mitochondrial fission, angiogenesis, vascular remodelling, insulin secretion, and immune responses. Here, an international consortium of research groups set out to address this question using in silico, in vitro, cell culture, and murine models. The findings uniformly demonstrate that DDAH2 is incapable of metabolising ADMA, thus resolving a 20-year controversy and providing a starting point for the investigation of alternative, ADMA-independent functions of DDAH2.

Association of DNA Promoter Methylation and BRAF Mutation in Thyroid Cancer

The BRAF V600E mutation and DNA promoter methylation play important roles in the pathogenesis of thyroid cancer (TC). However, the association of these genetic and epigenetic alterations is not clear. In this study, using paired tumor and surrounding normal tissue from the same patients, on a genome-wide scale we tried to identify (a) any association between BRAF mutation and DNA promoter methylation, and (b) if the molecular findings may provide a basis for therapeutic intervention. We included 40 patients with TC (female = 28, male = 12) without distant metastasis. BRAF mutation was present in 18 cases. We identified groups of differentially methylated loci (DML) that are found in (a) both BRAF mutant and wild type, (b) only in BRAF mutant tumors, and (c) only in BRAF wild type. BRAF mutation-specific promoter loci were more frequently hypomethylated, whereas BRAF wild-type-specific loci were more frequently hypermethylated. Common DML were enriched in cancer-related pathways, including the mismatch repair pathway and Wnt-signaling pathway. Wild-type-specific DML were enriched in RAS signaling. Methylation status of checkpoint signaling genes, as well as the T-cell inflamed genes, indicated an opportunity for the potential use of PDL1 inhibitors in BRAF mutant TC. Our study shows an association between BRAF mutation and methylation in TC that may have biological significance.

Innate sensing and cellular metabolism: role in fine tuning antiviral immune responses

Several studies over the last decade have identified intimate links between cellular metabolism and macrophage function. Metabolism has been shown to both drive and regulate macrophage function by producing bioenergetic and biosynthetic precursors as well as metabolites (and other bioactive molecules) that regulate gene expression and signal transduction. Many studies have focused on lipopolysaccharide-induced reprogramming, assuming that it is representative of most inflammatory responses. However, emerging evidence suggests that diverse pathogen-associated molecular patterns (PAMPs) are associated with unique metabolic profiles, which may drive pathogen specific immune responses. Further, these metabolic pathways and processes may act as a rheostat to regulate the magnitude of an inflammatory response based on the biochemical features of the local microenvironment. In this review, we will discuss recent work examining the relationship between cellular metabolism and macrophage responses to viral PAMPs and describe how these processes differ from lipopolysaccharide-associated responses. We will also discuss how an improved understanding of the specificity of these processes may offer new insights to fine-tune macrophage function during viral infections or when using viral PAMPs as therapeutics.

Crosstalk between mitophagy and innate immunity in viral infection

Mitochondria are important organelles involved in cell metabolism and programmed cell death in eukaryotic cells and are closely related to the innate immunity of host cells against viruses. Mitophagy is a process in which phagosomes selectively phagocytize damaged or dysfunctional mitochondria to form autophagosomes and is degraded by lysosomes, which control mitochondrial mass and maintain mitochondrial dynamics and cellular homeostasis. Innate immunity is an important part of the immune system and plays a vital role in eliminating viruses. Viral infection causes many physiological and pathological alterations in host cells, including mitophagy and innate immune pathways. Accumulating evidence suggests that some virus promote self-replication through regulating mitophagy-mediated innate immunity. Clarifying the regulatory relationships among mitochondria, mitophagy, innate immunity, and viral infection will shed new insight for pathogenic mechanisms and antiviral strategies. This review systemically summarizes the activation pathways of mitophagy and the relationship between mitochondria and innate immune signaling pathways, and then discusses the mechanisms of viruses on mitophagy and innate immunity and how viruses promote self-replication by regulating mitophagy-mediated innate immunity.

Long-term exposure to azoxystrobin induces immunodeficiency in fish that are vulnerable to subsequent rhabdovirus infection

Azoxystrobin (AZ) is one of the most widely used strobilurin fungicides in the world, and its residue has seriously endangered aquatic ecological security. Our previous data showed that AZ exposure may reduce the resistance of fish to rhabdovirus infection in aquatic environment. Here, we further reported a potential long-term adverse effect of AZ exposure on the antiviral and immunosuppressive recovery in fish, and observed that mitochondrial dynamic balance was disturbed by AZ in which excessive mitochondrial fission occurred in response to decreased ATP levels. When a recovery operation was performed in AZ-exposed cells and fish, infectivity of our model virus, spring viraemia of carp virus (SVCV), was significantly decreased in vitro (using the epithelioma papulosum cyprini [EPC] fish cell line) and in vivo (using zebrafish) in a time-dependent manner. Also, the expression of eight innate antiviral immune genes (IFNs, ISG15, MX1, RIG-I, IRF3, Nrf2 and HO-1) showed a similar change to SVCV replication between the longer exposure period and the expression recovery. Additionally, AZ facilitated horizontal transmission of SVCV in a static cohabitation challenge model, predicting the increase of the potential for the viral outbreak. Therefore, our data suggest that long-term effect of AZ on irreparable impairment in fish made AZ residue potentially greater for ecological risks.

Empagliflozin activates Wnt/β-catenin to stimulate FUNDC1-dependent mitochondrial quality surveillance against type-3 cardiorenal syndrome

Objectives

Cardiorenal syndrome type-3 (CRS-3) is an abrupt worsening of cardiac function secondary to acute kidney injury. Mitochondrial dysfunction is a key pathological mechanism of CRS-3, and empagliflozin can improve mitochondrial biology by promoting mitophagy. Here, we assessed the effects of empagliflozin on mitochondrial quality surveillance in a mouse model of CRS-3.

Methods

Cardiomyocyte-specific FUNDC1-knockout (FUNDC1^CKO) mice were subjected to CRS-3 prior to assessment of mitochondrial homeostasis in the presence or absence of empagliflozin.

Results

CRS-3 model mice exhibited lower heart function, increased inflammatory responses and exacerbated myocardial oxidative stress than sham-operated controls; however, empagliflozin attenuated these alterations. Empagliflozin stabilized the mitochondrial membrane potential, suppressed mitochondrial reactive oxygen species production, increased mitochondrial respiratory complex activity and restored the oxygen consumption rate in cardiomyocytes from CRS-3 model mice. Empagliflozin also normalized the mitochondrial morphology, mitochondrial dynamics and mitochondrial permeability transition pore opening rate in cardiomyocytes. Cardiomyocyte-specific ablation of FUN14 domain-containing protein 1 (FUNDC1) in mice abolished the protective effects of empagliflozin on mitochondrial homeostasis and myocardial performance. Empagliflozin activated β-catenin and promoted its nuclear retention, thus increasing FUNDC1-induced mitophagy in heart tissues; however, a β-catenin inhibitor reversed these effects.

Conclusions

In summary, empagliflozin activated Wnt/β-catenin to stimulate FUNDC1-dependent mitochondrial quality surveillance, ultimately improving mitochondrial function and cardiac performance during CRS-3. Thus, empagliflozin could be considered for the clinical management of heart function following acute kidney injury.

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Empagliflozin reduces myocardial damage and improves myocardial function after CRS-3.

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Empagliflozin normalizes the mitochondrial structure in cardiomyocytes during CRS-3.

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Empagliflozin attenuates cardiomyocyte mitochondrial dysfunction during CRS-3.

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Empagliflozin activates FUNDC1-dependent mitophagy and preserves mitochondrial integrity in the heart during CRS-3.

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Loss of FUNDC1 abolishes the cardioprotective effects of empagliflozin during CRS-3.

Japanese Encephalitis Virus (JEV) NS1' Enhances the Viral Infection of Dendritic Cells (DCs) and Macrophages in Pig Tonsils

Pigs are the amplifying hosts of Japanese encephalitis virus (JEV). Currently, the safe and effective live attenuated vaccine made of JEV strain SA14-14-2, which does not express NS1', is widely used in humans and domestic animals to prevent JEV infection. In this study, we constructed the NS1' expression recombinant virus (rA66G) through a single nucleotide mutation in NS2A of JEV strain SA14-14-2. Animal experiments showed that NS1' significantly enhanced JEV infection in pig central nervous system (CNS) and tonsil tissues. Pigs shed virus in oronasal secretions in the JEV rA66G virus inoculation group, indicating that NS1' may facilitate the horizontal transmission of JEV. Additionally, dendritic cells (DCs) and macrophages are the main target cells of JEV infection in pig tonsils, which are an important site of persistent JEV infection. The reduction of major histocompatibility complex class II (MHC II) and activation of inducible nitric oxide synthase (iNOS) in pig tonsils caused by viral infection may create a beneficial environment for persistent JEV infection. These results are of significance for JEV infection in pigs and lay the foundation for future studies of JEV persistent infection in pig tonsils. IMPORTANCE Pigs are amplification hosts for Japanese encephalitis virus (JEV). JEV can persist in the tonsils for months despite the presence of neutralizing antibodies. The present study shows that NS1' increases JEV infection in pig tonsils. In addition, DCs and macrophages in the tonsils are the target cells for JEV infection, and JEV NS1' promotes virus infection in DCs and macrophages. This study reveals a novel function of JEV NS1' protein and lays the foundation for future studies of JEV persistent infection in pig tonsils.

Mitochondrial Dysfunction and Oxidative Stress in Rheumatoid Arthritis

Control of excessive mitochondrial oxidative stress could provide new targets for both preventive and therapeutic interventions in the treatment of chronic inflammation or any pathology that develops under an inflammatory scenario, such as rheumatoid arthritis (RA). Increasing evidence has demonstrated the role of mitochondrial alterations in autoimmune diseases mainly due to the interplay between metabolism and innate immunity, but also in the modulation of inflammatory response of resident cells, such as synoviocytes. Thus, mitochondrial dysfunction derived from several danger signals could activate tricarboxylic acid (TCA) disruption, thereby favoring a vicious cycle of oxidative/mitochondrial stress. Mitochondrial dysfunction can act through modulating innate immunity via redox-sensitive inflammatory pathways or direct activation of the inflammasome. Besides, mitochondria also have a central role in regulating cell death, which is deeply altered in RA. Additionally, multiple evidence suggests that pathological processes in RA can be shaped by epigenetic mechanisms and that in turn, mitochondria are involved in epigenetic regulation. Finally, we will discuss about the involvement of some dietary components in the onset and progression of RA.

Empagliflozin attenuates cardiac microvascular ischemia/reperfusion through activating the AMPKα1/ULK1/FUNDC1/mitophagy pathway

Mitophagy preserves microvascular structure and function during myocardial ischemia/reperfusion (I/R) injury. Empagliflozin, an anti-diabetes drug, may also protect mitochondria. We explored whether empagliflozin could reduce cardiac microvascular I/R injury by enhancing mitophagy. In mice, I/R injury induced luminal stenosis, microvessel wall damage, erythrocyte accumulation and perfusion defects in the myocardial microcirculation. Additionally, I/R triggered endothelial hyperpermeability and myocardial neutrophil infiltration, which upregulated adhesive factors and endothelin-1 but downregulated vascular endothelial cadherin and endothelial nitric oxide synthase in heart tissue. In vitro, I/R impaired the endothelial barrier function and integrity of cardiac microvascular endothelial cells (CMECs), while empagliflozin preserved CMEC homeostasis and thus maintained cardiac microvascular structure and function. I/R activated mitochondrial fission, oxidative stress and apoptotic signaling in CMECs, whereas empagliflozin normalized mitochondrial fission and fusion, neutralized supraphysiologic reactive oxygen species concentrations and suppressed mitochondrial apoptosis. Empagliflozin exerted these protective effects by activating FUNDC1-dependent mitophagy through the AMPKα1/ULK1 pathway. Both in vitro and in vivo, genetic ablation of AMPKα1 or FUNDC1 abolished the beneficial effects of empagliflozin on the myocardial microvasculature and CMECs. Taken together, the preservation of mitochondrial function through an activation of the AMPKα1/ULK1/FUNDC1/mitophagy pathway is the working mechanism of empagliflozin in attenuating cardiac microvascular I/R injury.

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Empagliflozin reduces I/R-induced microvascular damage.

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Empagliflozin suppresses I/R-induced endothelial cell damage.

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Empagliflozin activates FUNDC1-dependent mitophagy through the AMPKα1/ULK1 pathway.

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Ablation of FUNDC1 or AMPKα1 abolishes the protective effects of empagliflozin against I/R-induced microvascular damage.

Metabolism and Innate Immunity Meet at the Mitochondria

Mitochondria are master regulators of metabolism and have emerged as key signalling organelles of the innate immune system. Each mitochondrion harbours potent agonists of inflammation, including mitochondrial DNA (mtDNA), which are normally shielded from the rest of the cell and extracellular environment and therefore do not elicit detrimental inflammatory cascades. Mitochondrial damage and dysfunction can lead to the cytosolic and extracellular exposure of mtDNA, which triggers inflammation in a number of diseases including autoimmune neurodegenerative disorders. However, recent research has revealed that the extra-mitochondrial exposure of mtDNA is not solely a negative consequence of mitochondrial damage and pointed to an active role of mitochondria in innate immunity. Metabolic cues including nucleotide imbalance can stimulate the release of mtDNA from mitochondria in order to drive a type I interferon response. Moreover, important effectors of the innate immune response to pathogen infection, such as the mitochondrial antiviral signalling protein (MAVS), are located at the mitochondrial surface and modulated by the cellular metabolic status and mitochondrial dynamics. In this review, we explore how and why metabolism and innate immunity converge at the mitochondria and describe how mitochondria orchestrate innate immune signalling pathways in different metabolic scenarios. Understanding how cellular metabolism and metabolic programming of mitochondria are translated into innate immune responses bears relevance to a broad range of human diseases including cancer.