DDX3X coordinates host defense against influenza virus by activating the NLRP3 inflammasome and type I interferon response

Angiogenin-mediated tsRNAs control inflammation and metabolic disorder by regulating NLRP3 inflammasome

The cellular stress response system in immune cells plays a crucial role in regulating the development of inflammatory diseases. In response to cellular damage or microbial infection, the assembly of the NLRP3 inflammasome induces pyroptosis and the release of inflammatory cytokines. Meanwhile, Angiogenin (Ang)-mediated transfer RNA-derived small RNAs (tsRNAs) promote cell survival under stressful conditions. While both tsRNAs and inflammasomes are induced under stress conditions, the interplay between these two systems and their implications in regulating inflammatory diseases remains poorly understood. In this study, it was demonstrated that Ang deficiency exacerbated sodium arsenite-induced activation of NLRP3 inflammasome and pyroptosis. Moreover, Ang-induced 5'-tsRNAs inhibited NLRP3 inflammasome activation and pyroptosis. Mechanistically, 5'-tsRNAs recruit DDX3X protein into stress granules (SGs), consequently inhibiting the interaction between DDX3X and NLRP3, thus leading to the suppression of NLRP3 inflammasome activation. Furthermore, in vivo results showed that Ang deficiency led to the downregulation of tsRNAs, ultimately leading to an exacerbation of NLRP3 inflammasome-dependent inflammation, including lipopolysaccharide-induced systemic inflammation and type-2 diabetes-related inflammation. Altogether, our study sheds a new light on the role of Ang-induced 5'-tsRNAs in regulating NLRP3 inflammasome activation via SGs, and highlights tsRNAs as a promising target for the treatment of NLRP3 inflammasome-related diseases.

TRIM21 reduces H1N1-induced inflammation and apoptosis by regulating the TBK1-IRF3 signaling pathway in A549 cells

Triple motif protein 21 (TRIM21) has an antiviral function that inhibits various viral infections. However, its role in the progress of influenza A virus (IAV) infection is unclear. In this study, we investigated the role and molecular mechanism of TRIM21 in IAV infection. RT-qPCR was used to determine the level of TRIM21 mRNA, and ELISA was used to measure the levels of IFN-α, IFN-β, IL-6, and TNF-α. The levels of the TRIM21, NP, TBK1, IRF3, p-TBK1, and p-IRF3 proteins were estimated by Western blot. The results showed that, after IAV infection, TRIM21 was upregulated in clinical patient serum and A549 cells, and this was correlated with the IFN response. Overexpression of TRIM21 reduced IAV replication and transcription in in vitro cell experiments. TRIM21 also increased IFN-α and IFN-β levels and decreased IL-6 and TNF-α levels in A549 cells. In addition, overexpression of TRIM21 inhibited IAV-induced apoptosis. Further experiments demonstrated that TBK1-IRF3 signaling was activated by TRIM21 and was involved in the inhibitory effect of TRIM21 on virus replication. In summary, our study suggests that TRIM21 inhibits viral replication by activating the TBK1-IRF3 signaling pathway, further inhibiting the infection process of IAV.

A comprehensive review on DDX3X liquid phase condensation in health and neurodevelopmental disorders

DEAD-box helicases are global regulators of liquid-liquid phase separation (LLPS), a process that assembles membraneless organelles inside cells. An outstanding member of the DEAD-box family is DDX3X, a multi-functional protein that plays critical roles in RNA metabolism, including RNA transcription, splicing, nucleocytoplasmic export, and translation. The diverse functions of DDX3X result from its ability to bind and remodel RNA in an ATP-dependent manner. This capacity enables the protein to act as an RNA chaperone and an RNA helicase, regulating ribonucleoprotein complex assembly. DDX3X and its orthologs from mouse, yeast (Ded1), and C. elegans (LAF-1) can undergo LLPS, driving the formation of neuronal granules, stress granules, processing bodies or P-granules. DDX3X has been related to several human conditions, including neurodevelopmental disorders, such as intellectual disability and autism spectrum disorder. Although the research into the pathogenesis of aberrant biomolecular condensation in neurodegenerative diseases is increasing rapidly, the role of LLPS in neurodevelopmental disorders is underexplored. This review summarizes current findings relevant for DDX3X phase separation in neurodevelopment and examines how disturbances in the LLPS process can be related to neurodevelopmental disorders.

Influenza Virus Host Restriction Factors: The ISGs and Non-ISGs

Influenza virus has been one of the most prevalent and researched viruses globally. Consequently, there is ample information available about influenza virus lifecycle and pathogenesis. However, there is plenty yet to be known about the determinants of influenza virus pathogenesis and disease severity. Influenza virus exploits host factors to promote each step of its lifecycle. In turn, the host deploys antiviral or restriction factors that inhibit or restrict the influenza virus lifecycle at each of those steps. Two broad categories of host restriction factors can exist in virus-infected cells: (1) encoded by the interferon-stimulated genes (ISGs) and (2) encoded by the constitutively expressed genes that are not stimulated by interferons (non-ISGs). There are hundreds of ISGs known, and many, e.g., Mx, IFITMs, and TRIMs, have been characterized to restrict influenza virus infection at different stages of its lifecycle by (1) blocking viral entry or progeny release, (2) sequestering or degrading viral components and interfering with viral synthesis and assembly, or (3) bolstering host innate defenses. Also, many non-ISGs, e.g., cyclophilins, ncRNAs, and HDACs, have been identified and characterized to restrict influenza virus infection at different lifecycle stages by similar mechanisms. This review provides an overview of those ISGs and non-ISGs and how the influenza virus escapes the restriction imposed by them and aims to improve our understanding of the host restriction mechanisms of the influenza virus.

Gadd45β is critical for regulation of type I interferon signaling by facilitating G3BP-mediated stress granule formation

Stress granules (SGs) constitute a signaling hub that plays a critical role in type I interferon responses. Here, we report that growth arrest and DNA damage-inducible beta (Gadd45β) act as a positive regulator of SG-mediated interferon signaling by targeting G3BP upon RNA virus infection. Gadd45β deficiency markedly impairs SG formation and SG-mediated activation of interferon signaling in vitro. Gadd45β knockout mice are highly susceptible to RNA virus infection, and their ability to produce interferon and cytokines is severely impaired. Specifically, Gadd45β interacts with the RNA-binding domain of G3BP, leading to conformational expansion of G3BP1 via dissolution of its autoinhibitory electrostatic intramolecular interaction. The acidic loop 1- and RNA-binding properties of Gadd45β markedly increase the conformational expansion and RNA-binding affinity of the G3BP1-Gadd45β complex, thereby promoting assembly of SGs. These findings suggest a role for Gadd45β as a component and critical regulator of G3BP1-mediated SG formation, which facilitates RLR-mediated interferon signaling.

Altered splicing factor and alternative splicing events in a mouse model of diet- and polychlorinated biphenyl-induced liver disease

Non-alcoholic fatty liver disease (NAFLD) is associated with human environmental exposure to polychlorinated biphenyls (PCBs). Alternative splicing (AS) is dysregulated in steatotic liver disease and is regulated by splicing factors (SFs) and N-6 methyladenosine (m6A) modification. Here integrated analysis of hepatic mRNA-sequencing data was used to identify differentially expressed SFs and differential AS events (ASEs) in the livers of high fat diet-fed C57BL/6 J male mice exposed to Aroclor1260, PCB126, Aroclor1260 + PCB126, or vehicle control. Aroclor1260 + PCB126 co-exposure altered 100 SFs and replicate multivariate analysis of transcript splicing (rMATS) identified 449 ASEs in 366 genes associated with NAFLD pathways. These ASEs were similar to those resulting from experimental perturbations in m6A writers, readers, and erasers. These results demonstrate specific hepatic SF and AS regulatory mechanisms are disrupted by HFD and PCB exposures, contributing to the expression of altered isoforms that may play a role in NAFLD progression to NASH.

The Viral Protein K7 Inhibits Biochemical Activities and Condensate Formation by the DEAD-box Helicase DDX3X

The DEAD-box RNA helicase DDX3X promotes translation initiation and associates with stress granules. A range of diverse viruses produce proteins that target DDX3X, including hepatitis C, dengue, vaccinia, and influenza A. The interaction of some of these viral proteins with DDX3X has been shown to affect antiviral intracellular signaling, but it is unknown whether and how viral proteins impact the biochemical activities of DDX3X and its physical roles in cells. Here we show that the protein K7 from vaccinia virus, which binds to an intrinsically disordered region in the N-terminus of DDX3X, inhibits RNA helicase and RNA-stimulated ATPase activities, as well as liquid-liquid phase separation of DDX3X in vitro. We demonstrate in HCT 116 cells that K7 inhibits association of DDX3X with stress granules, as well as the formation of aberrant granules induced by expression of DDX3X with a point mutation linked to medulloblastoma and DDX3X syndrome. The results show that targeting of the intrinsically disordered N-terminus is an effective viral strategy to modulate the biochemical functions and subcellular localization of DDX3X. Our findings also have potential therapeutic implications for diseases linked to aberrant DDX3X granule formation.

Aluminum exposure induces central nervous system impairment via activating NLRP3-medicated pyroptosis pathway

PURPOSE

Aluminum is an environmental toxicant whose long-term exposure is closely associated with nervous system impairment. This study mainly investigated neurological impairment induced by subchronic aluminum exposure via activating NLRP3-medicated pyroptosis pathway.

METHODS

In vivo, Kunming mice were exposed to AlCl3 (30.3 mg/kg, 101 mg/kg and 303 mg/kg) via drinking water for 3 months, and administered with Rsv (100 mg/kg) by gavage for 1 month. Cognitive impairment was assessed by Morris water maze test, and pathological injury was detected via H&E staining. BBB integrity, pyroptosis and neuroinflammation were evaluated through western blotting and immunofluorescence methods. In vitro, BV2 microglia was treated with AlCl3 (0.5 mM, 1 mM and 2 mM) to sensitize pyroptosis pathway. The protein interaction was verified by co-immunoprecipitation, and neuronal damage was estimated via a conditioned medium co-culture system with BV2 and TH22 cells.

RESULTS

Our results showed that AlCl3 induced mice memory disorder, BBB destruction, and pathological injury. Besides, aluminum caused glial activation, sensitized DDX3X-NLRP3 pyroptosis pathway, released cytokines IL-1β and IL-18, initiating neuroinflammation. BV2 microglia treated with AlCl3 emerged hyperactivation and pyroptotic death, and Ddx3x knockdown inhibited pyroptosis signaling pathway. DDX3X acted as a live-or-die checkpoint in stressed cells by regulating NLRP3 inflammasome and G3BP1 stress granules. Furthermore, aluminum-activated microglia had an adverse effect on co-cultured neurons and destroyed nervous system homeostasis.

CONCLUSION

Aluminum exposure could induce pyroptosis and neurotoxicity. DDX3X determined live or die via selectively regulating pro-survival stress granules or pro-death NLRP3 inflammasome. Excessive activation of microglia might damage neurons and aggravate nerve injury.

Interaction among inflammasome, PANoptosise, and innate immune cells in infection of influenza virus: Updated review

BACKGROUND

Influenza virus (IV) is a leading cause of respiratory tract infections, eliciting responses from key innate immune cells such as Macrophages (MQs), Neutrophils, and Dendritic Cells (DCs). These cells employ diverse mechanisms to combat IV, with Inflammasomes playing a pivotal role in viral infection control. Cellular death mechanisms, including Pyroptosis, Apoptosis, and Necroptosis (collectively called PANoptosis), significantly contribute to the innate immune response.

METHODS

In this updated review, we delve into the intricate relationship between PANoptosis and Inflammasomes within innate immune cells (MQs, Neutrophils, and DCs) during IV infections. We explore the strategies employed by IV to evade these immune defenses and the consequences of unchecked PANoptosis and inflammasome activation, including the potential development of severe complications such as cytokine storms and tissue damage.

RESULTS

Our analysis underscores the interplay between PANoptosis and Inflammasomes as a critical aspect of the innate immune response against IV. We provide insights into IV's various mechanisms to subvert these immune pathways and highlight the importance of understanding these interactions to develop effective antiviral medications.

CONCLUSION

A comprehensive understanding of the dynamic interactions between PANoptosis, Inflammasomes, and IV is essential for advancing our knowledge of innate immune responses to viral infections. This knowledge will be invaluable in developing targeted antiviral therapies to combat IV and mitigate potential complications, including cytokine storms and tissue damage.

Membraneless Organelles and Condensates Orchestrate Innate Immunity Against Viruses

The cellular defense against viruses involves the assembly of oligomers, granules and membraneless organelles (MLOs) that govern the activation of several arms of the innate immune response. Upon interaction with specific pathogen-derived ligands, a number of pattern recognition receptors (PRRs) undergo phase-separation thus triggering downstream signaling pathways. Among other relevant condensates, inflammasomes, apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC) specks, cyclic GMP-AMP synthase (cGAS) foci, protein kinase R (PKR) clusters, ribonuclease L-induced bodies (RLBs), stress granules (SGs), processing bodies (PBs) and promyelocytic leukemia protein nuclear bodies (PML NBs) play different roles in the immune response. In turn, viruses have evolved diverse strategies to evade the host defense. Viral DNA or RNA, as well as viral proteases or proteins carrying intrinsically disordered regions may interfere with condensate formation and function in multiple ways. In this review we discuss current and hypothetical mechanisms of viral escape that involve the disassembly, repurposing, or inactivation of membraneless condensates that govern innate immunity. We summarize emerging interconnections between these diverse condensates that ultimately determine the cellular outcome.

Targeting Inflammasome Activation in Viral Infection: A Therapeutic Solution?

Inflammasome activation is exclusively involved in sensing activation of innate immunity and inflammatory response during viral infection. Accumulating evidence suggests that the manipulation of inflammasome assembly or its interaction with viral proteins are critical factors in viral pathogenesis. Results from pilot clinical trials show encouraging results of NLRP3 inflammasome suppression in reducing mortality and morbidity in SARS-CoV-2-infected patients. In this article, we summarize the up-to-date understanding of inflammasomes, including NLRP3, AIM2, NLRP1, NLRP6, and NLRC4 in various viral infections, with particular focus on RNA viruses such as SARS-CoV-2, HIV, IAV, and Zika virus and DNA viruses such as herpes simplex virus 1. We also discuss the current achievement of the mechanisms involved in viral infection-induced inflammatory response, host defense, and possible therapeutic solutions.

Roles and Mechanisms of NLRP3 in Influenza Viral Infection

Pathogenic viral infection represents a major challenge to human health. Due to the vast mucosal surface of respiratory tract exposed to the environment, host defense against influenza viruses has perpetually been a considerable challenge. Inflammasomes serve as vital components of the host innate immune system and play a crucial role in responding to viral infections. To cope with influenza viral infection, the host employs inflammasomes and symbiotic microbiota to confer effective protection at the mucosal surface in the lungs. This review article aims to summarize the current findings on the function of NACHT, LRR and PYD domains-containing protein 3 (NLRP3) in host response to influenza viral infection involving various mechanisms including the gut-lung crosstalk.

Porcine Circovirus Modulates Swine Influenza Virus Replication in Pig Tracheal Epithelial Cells and Porcine Alveolar Macrophages

The pathogenesis of porcine circovirus type 2b (PCV2b) and swine influenza A virus (SwIV) during co-infection in swine respiratory cells is poorly understood. To elucidate the impact of PCV2b/SwIV co-infection, newborn porcine tracheal epithelial cells (NPTr) and immortalized porcine alveolar macrophages (iPAM 3D4/21) were co-infected with PCV2b and SwIV (H1N1 or H3N2 genotype). Viral replication, cell viability and cytokine mRNA expression were determined and compared between single-infected and co-infected cells. Finally, 3'mRNA sequencing was performed to identify the modulation of gene expression and cellular pathways in co-infected cells. It was found that PCV2b significantly decreased or improved SwIV replication in co-infected NPTr and iPAM 3D4/21 cells, respectively, compared to single-infected cells. Interestingly, PCV2b/SwIV co-infection synergistically up-regulated IFN expression in NPTr cells, whereas in iPAM 3D4/21 cells, PCV2b impaired the SwIV IFN induced response, both correlating with SwIV replication modulation. RNA-sequencing analyses revealed that the modulation of gene expression and enriched cellular pathways during PCV2b/SwIV H1N1 co-infection is regulated in a cell-type-dependent manner. This study revealed different outcomes of PCV2b/SwIV co-infection in porcine epithelial cells and macrophages and provides new insights on porcine viral co-infections pathogenesis.

Pseudorabies virus hijacks DDX3X, initiating an addictive "mad itch" and immune suppression, to facilitate viral spread

Infections with defined Herpesviruses, such as Pseudorabies virus (PRV) and Varicella zoster virus (VZV) can cause neuropathic itch, referred to as "mad itch" in multiple species. The underlying mechanisms involved in neuropathic "mad itch" are poorly understood. Here, we show that PRV infections hijack the RNA helicase DDX3X in sensory neurons to facilitate anterograde transport of the virus along axons. PRV induces re-localization of DDX3X from the cell body to the axons which ultimately leads to death of the infected sensory neurons. Inducible genetic ablation of Ddx3x in sensory neurons results in neuronal death and "mad itch" in mice. This neuropathic "mad itch" is propagated through activation of the opioid system making the animals "addicted to itch". Moreover, we show that PRV co-opts and diverts T cell development in the thymus via a sensory neuron-IL-6-hypothalamus-corticosterone stress pathway. Our data reveal how PRV, through regulation of DDX3X in sensory neurons, travels along axons and triggers neuropathic itch and immune deviations to initiate pathophysiological programs which facilitate its spread to enhance infectivity.

Interaction of SARS-CoV-2 Nucleocapsid Protein and Human RNA Helicases DDX1 and DDX3X Modulates Their Activities on Double-Stranded RNA

The nucleocapsid protein Np of SARS-CoV-2 is involved in the replication, transcription, and packaging of the viral genome, but it also plays a role in the modulation of the host cell innate immunity and inflammation response. Ectopic expression of Np alone was able to induce significant changes in the proteome of human cells. The cellular RNA helicase DDX1 was among the proteins whose levels were increased by Np expression. DDX1 and its related helicase DDX3X were found to physically interact with Np and to increase 2- to 4-fold its affinity for double-stranded RNA in a helicase-independent manner. Conversely, Np inhibited the RNA helicase activity of both proteins. These functional interactions among Np and DDX1 and DDX3X highlight novel possible roles played by these host RNA helicases in the viral life cycle.

The involvement of DDX3X in compression-induced nucleus pulposus pyroptosis

OBJECTIVE

A study has been conducted to investigate the relationship between DDX3X and nucleus pulposus (NP) pyroptosis.

METHODS

DDX3X and pyroptosis-related proteins (Caspase-1, Full-length GSDMD, Cleaved GSDMD) were measured in compression-induced human NP cells and tissue. DDX3X was overexpressed or knocked down by gene transfection. The expressions of NLRP3, ASC, and pyroptosis-related proteins were detected by Western blot assay. IL-1β and IL-18 were detected by ELISA. HE staining and immunohistochemistry were used to observe the expression of DDX3X, NLRP3, and Caspase-1 in the rat model of compression-induced disc degeneration.

RESULTS

DDX3X, NLRP3, and Caspase-1 were highly expressed in degenerated NP tissue. Overexpression of DDX3X induced pyroptosis in NP cells and increased levels of NLRP3, IL-1β, IL-18, and pyroptosis-related proteins. Knockdown of DDX3X showed an opposite trend to overexpression of DDX3X. The NLRP3 inhibitor CY-09 effectively prevented the up-regulation of the expression of IL-1β, IL-18, ASC, Pro-caspase-1, Full-length GSDMD, and Cleaved GSDMD. Increased expression of DDX3X, NLRP3, and Caspase-1 was observed in the rat model of compression-induced disc degeneration.

CONCLUSION

Our study showed that DDX3X mediates pyroptosis of NP cells by upregulating NLRP3 expression, which ultimately leads to intervertebral disc degeneration (IDD). This discovery deepens the understanding of IDD pathogenesis and provides a promising and novel therapeutic target for IDD.

Multiple functions of stress granules in viral infection at a glance

Stress granules (SGs) are distinct RNA granules induced by various stresses, which are evolutionarily conserved across species. In general, SGs act as a conservative and essential self-protection mechanism during stress responses. Viruses have a long evolutionary history and viral infections can trigger a series of cellular stress responses, which may interact with SG formation. Targeting SGs is believed as one of the critical and conservative measures for viruses to tackle the inhibition of host cells. In this systematic review, we have summarized the role of SGs in viral infection and categorized their relationships into three tables, with a particular focus on Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection. Moreover, we have outlined several kinds of drugs targeting SGs according to different pathways, most of which are potentially effective against SARS-CoV-2. We believe this review would offer a new view for the researchers and clinicians to attempt to develop more efficacious treatments for virus infection, particularly for the treatment of SARS-CoV-2 infection.

Phase separation in innate immune response and inflammation-related diseases

Inflammation induced by nonspecific pathogenic or endogenous danger signals is an essential mechanism of innate immune response. The innate immune responses are rapidly triggered by conserved germline-encoded receptors that recognize broad patterns indicative of danger, with subsequent signal amplification by modular effectors, which have been the subject of intense investigation for many years. Until recently, however, the critical role of intrinsic disorder-driven phase separation in facilitating innate immune responses went largely unappreciated. In this review, we discuss emerging evidences that many innate immune receptors, effectors, and/or interactors function as "all-or-nothing" switch-like hubs to stimulate acute and chronic inflammation. By concentrating or relegating modular signaling components to phase-separated compartments, cells construct flexible and spatiotemporal distributions of key signaling events to ensure rapid and effective immune responses to a myriad of potentially harmful stimuli.

A New Long Noncoding RNA, MAHAT, Inhibits Replication of Porcine Reproductive and Respiratory Syndrome Virus by Recruiting DDX6 To Bind to ZNF34 and Promote an Innate Immune Response

Long noncoding RNAs (lncRNAs) have increasingly been recognized as being integral to cellular processes, including the antiviral immune response. Porcine reproductive and respiratory syndrome virus (PRRSV) is costly to the global swine industry. To identify PRRSV-related lncRNAs, we performed RNA deep sequencing and compared the profiles of lncRNAs in PRRSV-infected and uninfected Marc-145 cells. We identified a novel lncRNA called MAHAT (maintaining cell morphology-associated and highly conserved antiviral transcript; LTCON_00080558) that inhibits PRRSV replication. MAHAT binds and negatively regulates ZNF34 expression by recruiting and binding DDX6, an RNA helicase forming a complex with ZNF34. Inhibition of ZNF34 expression results in increased type I interferon expression and decreased PRRSV replication. This finding reveals a novel mechanism by which PRRSV evades the host antiviral innate immune response by downregulating the MAHAT-DDX6-ZNF34 pathway. MAHAT could be a host factor target for antiviral therapies against PRRSV infection. IMPORTANCE Long noncoding RNAs (lncRNAs) play important roles in viral infection by regulating the transcription and expression of host genes, and interferon signaling pathways. Porcine reproductive and respiratory syndrome virus (PRRSV) causes huge economic losses in the swine industry worldwide, but the mechanisms of its pathogenesis and immunology are not fully understood. Here, a new lncRNA, designated MAHAT, was identified as a regulator of host innate immune responses. MAHAT negatively regulates the expression of its target gene, ZNF34, by recruiting and binding DDX6, an RNA helicase, forming a complex with ZNF34. Inhibition of ZNF34 expression increases type I interferon expression and decreases PRRSV replication. This finding suggests that MAHAT has potential as a new target for developing antiviral drugs against PRRSV infection.

The multifaceted roles of NLRP3-modulating proteins in virus infection

The innate immune response to viruses is critical for the correct establishment of protective adaptive immunity. Amongst the many pathways involved, the NLRP3 [nucleotide-binding oligomerisation domain (NOD)-like receptor protein 3 (NLRP3)] inflammasome has received considerable attention, particularly in the context of immunity and pathogenesis during infection with influenza A (IAV) and SARS-CoV-2, the causative agent of COVID-19. Activation of the NLRP3 inflammasome results in the secretion of the proinflammatory cytokines IL-1β and IL-18, commonly coupled with pyroptotic cell death. While this mechanism is protective and key to host defense, aberrant NLRP3 inflammasome activation causes a hyperinflammatory response and excessive release of cytokines, both locally and systemically. Here, we discuss key molecules in the NLRP3 pathway that have also been shown to have significant roles in innate and adaptive immunity to viruses, including DEAD box helicase X-linked (DDX3X), vimentin and macrophage migration inhibitory factor (MIF). We also discuss the clinical opportunities to suppress NLRP3-mediated inflammation and reduce disease severity.

Role of pyroptosis in inflammation and cancer

Pyroptosis is a form of programmed cell death mediated by gasdermin and is a product of continuous cell expansion until the cytomembrane ruptures, resulting in the release of cellular contents that can activate strong inflammatory and immune responses. Pyroptosis, an innate immune response, can be triggered by the activation of inflammasomes by various influencing factors. Activation of these inflammasomes can induce the maturation of caspase-1 or caspase-4/5/11, both of which cleave gasdermin D to release its N-terminal domain, which can bind membrane lipids and perforate the cell membrane. Here, we review the latest advancements in research on the mechanisms of pyroptosis, newly discovered influencing factors, antitumoral properties, and applications in various diseases. Moreover, this review also provides updates on potential targeted therapies for inflammation and cancers, methods for clinical prevention, and finally challenges and future directions in the field.

The DEAD-box helicase DDX3x ameliorates non-alcoholic fatty liver disease via mTORC1 signalling pathway

BACKGROUND & AIMS

The DEAD (Asp-Glu-Ala-Asp)-box helicase family member DDX3x has been proven to involve in hepatic lipid disruption during HCV infection. However, the role of DDX3x in non-alcoholic fatty liver disease (NAFLD), in which lipid homeostasis is severely disrupted, remains unclear. Here, we aimed to illustrate the potential role of DDX3x in NAFLD.

METHODS

DDX3x protein levels were evaluated in NAFLD patients and NAFLD models via immunohistochemistry or western blotting. In vivo ubiquitin assay was performed to identify the ubiquitination levels of DDX3x in the progression of steatosis. DDX3x protein levels in mice livers were manipulated by adeno-associated virus-containing DDX3x short hairpin RNA or DDX3x overexpression plasmid. Hepatic or serum triglyceride and total cholesterol were evaluated and hepatic steatosis was confirmed by haematoxylin and eosin staining and oil red o staining. Western blotting was performed to identify the underlying mechanisms of DDX3x involving in the progression of NAFLD.

RESULTS

DDX3x protein levels were significantly decreased in NAFLD patients and NAFLD models. DDX3x protein might be degraded via ubiquitin-proteasome system in the progression of steatosis. Knockdown of hepatic DDX3x exacerbated HFD-induced hepatic steatosis in mice, while overexpression of hepatic DDX3x alleviated HFD-induced hepatic steatosis in mice. Further explorative experiments revealed that knockdown of DDX3x could lead to the overactivation of mTORC1 signalling pathway which exacerbates NAFLD.

CONCLUSIONS

DDX3x involved in the progression of NAFLD via affecting the mTORC1 signalling pathway. DDX3x might be a potential target for NAFLD treatment.

DEAD-Box Helicase DDX3X as a Host Target against Emerging Viruses: New Insights for Medicinal Chemical Approaches

In recent years, globalization, global warming, and population aging have contributed to the spread of emerging viruses, such as coronaviruses (COVs), West Nile (WNV), Dengue (DENV), and Zika (ZIKV). The number of reported infections is increasing, and considering the high viral mutation rate, it is conceivable that it will increase significantly in the coming years. The risk caused by viruses is now more evident due to the COVID-19 pandemic, which highlighted the need to find new broad-spectrum antiviral agents able to tackle the present pandemic and future epidemics. DDX3X helicase is a host factor required for viral replication. Selective inhibitors have been identified and developed into broad-spectrum antivirals active against emerging pathogens, including SARS-CoV-2 and most importantly against drug-resistant strains. This perspective describes the inhibitors identified in the last years, highlighting their therapeutic potential as innovative broad-spectrum antivirals.

Roles of RNA Sensors in Host Innate Response to Influenza Virus and Coronavirus Infections

Influenza virus and coronavirus are two important respiratory viruses, which often cause serious respiratory diseases in humans and animals after infection. In recent years, highly pathogenic avian influenza virus (HPAIV) and SARS-CoV-2 have become major pathogens causing respiratory diseases in humans. Thus, an in-depth understanding of the relationship between viral infection and host innate immunity is particularly important to the stipulation of effective control strategies. As the first line of defense against pathogens infection, innate immunity not only acts as a natural physiological barrier, but also eliminates pathogens through the production of interferon (IFN), the formation of inflammasomes, and the production of pro-inflammatory cytokines. In this process, the recognition of viral pathogen-associated molecular patterns (PAMPs) by host pattern recognition receptors (PRRs) is the initiation and the most important part of the innate immune response. In this review, we summarize the roles of RNA sensors in the host innate immune response to influenza virus and coronavirus infections in different species, with a particular focus on innate immune recognition of viral nucleic acids in host cells, which will help to develop an effective strategy for the control of respiratory infectious diseases.

A Dual Role of DDX3X in dsRNA-Derived Innate Immune Signaling

DEAD-Box Helicase 3 X-Linked (DDX3X) is essential for RNA metabolism and participates in various cellular processes involving RNA. DDX3X has been implicated in cancer growth and metastasis. DDX3X is involved in antiviral responses for viral RNAs and contributes to pro- or anti-microbial responses. A better understanding of how human cells regulate innate immune response against the viral “non-self” double-stranded RNAs (dsRNAs) and endogenous viral-like “self” dsRNAs is critical to understanding innate immune sensing, anti-microbial immunity, inflammation, immune cell homeostasis, and developing novel therapeutics for infectious, immune-mediated diseases, and cancer. DDX3X has known for activating the viral dsRNA-sensing pathway and innate immunity. However, accumulating research reveals a more complex role of DDX3X in regulating dsRNA-mediated signaling in cells. Here, we discuss the role of DDX3X in viral dsRNA- or endogenous dsRNA-mediated immune signaling pathways.

TLR4 aggravates microglial pyroptosis by promoting DDX3X-mediated NLRP3 inflammasome activation via JAK2/STAT1 pathway after spinal cord injury

Background

Toll‐like receptor 4 (TLR4) participates in the initiation of neuroinflammation in various neurological diseases, including central nervous system injuries. NLR family pyrin domain containing 3 (NLRP3) inflammasome‐mediated microglial pyroptosis is crucial for the inflammatory response during secondary spinal cord injury (SCI). However, the underlying mechanism by which TLR4 regulates NLRP3 inflammasome activation and microglial pyroptosis after SCI remains uncertain.

Methods

We established an in vivo mouse model of SCI using TLR4‐knockout (TLR4‐KO) and wild‐type (WT) mice. The levels of pyroptosis, tissue damage and neurological function recovery were evaluated in the three groups (Sham, SCI, SCI‐TLR4‐KO). To identify differentially expressed proteins, tandem mass tag (TMT)‐based proteomics was conducted using spinal cord tissue between TLR4‐KO and WT mice after SCI. For our in vitro model, mouse microglial BV2 cells were exposed to lipopolysaccharides (1 µg/ml, 8 h) and adenosine triphosphate (ATP) (5 mM, 2 h) to induce pyroptosis. A series of molecular biological experiments, including Western blot (WB), real‐time quantitative polymerase chain reaction (RT‐qPCR), enzyme‐linked immunosorbent assay (ELISA), immunofluorescence (IF), immunohistochemical (IHC), chromatin immunoprecipitation (ChIP), Dual‐Luciferase Reporter assay (DLA) and co‐immunoprecipitation (Co‐IP), were performed to explore the specific mechanism of microglial pyroptosis in vivo and in vitro.

Results

Our results indicated that TLR4 promoted the expression of dead‐box helicase 3 X‐linked (DDX3X), which mediated NLRP3 inflammasome activation and microglial pyroptosis after SCI. Further analysis revealed that TLR4 upregulated the DDX3X/NLRP3 axis by activating the JAK2/STAT1 signalling pathway, and importantly, STAT1 was identified as a transcription factor promoting DDX3X expression. In addition, we found that biglycan was increased after SCI and interacted with TLR4 to jointly regulate microglial pyroptosis through the JAK2/STAT1/DDX3X/NLRP3 axis after SCI.

Conclusion

Our study preliminarily identified a novel mechanism by which TLR4 regulates NLRP3 inflammasome‐mediated microglial pyroptosis in response to SCI—providing a novel and promising therapeutic target for SCI.

DEAD/H-Box Helicases in Immunity, Inflammation, Cell Differentiation, and Cell Death and Disease

DEAD/H-box proteins are the largest family of RNA helicases in mammalian genomes, and they are present in all kingdoms of life. Since their discovery in the late 1980s, DEAD/H-box family proteins have been a major focus of study. They have been found to play central roles in RNA metabolism, gene expression, signal transduction, programmed cell death, and the immune response to bacterial and viral infections. Aberrant functions of DEAD/H-box proteins have been implicated in a wide range of human diseases that include cancer, neurodegeneration, and inherited genetic disorders. In this review, we provide a historical context and discuss the molecular functions of DEAD/H-box proteins, highlighting the recent discoveries linking their dysregulation to human diseases. We will also discuss the state of knowledge regarding two specific DEAD/H-box proteins that have critical roles in immune responses and programmed cell death, DDX3X and DDX58, also known as RIG-I. Given their importance in homeostasis and disease, an improved understanding of DEAD/H-box protein biology and protein-protein interactions will be critical for informing strategies to counteract the pathogenesis associated with several human diseases.

DExD/H-box helicases: multifunctional regulators in antiviral innate immunity

DExD/H-box helicases play critical roles in multiple cellular processes, including transcription, cellular RNA metabolism, translation, and infections. Several seminal studies over the past decades have delineated the distinct functions of DExD/H-box helicases in regulating antiviral innate immune signaling pathways, including Toll-like receptors, retinoic acid-inducible gene I-like receptors, cyclic GMP-AMP synthase-the stimulator of interferon gene, and NOD-like receptors signaling pathways. Besides the prominent regulatory roles, there is increasing attention on their functions as nucleic acid sensors involved in antiviral innate immunity. Here we summarize the complex regulatory roles of DExD/H-box helicases in antiviral innate immunity. A better understanding of the underlying molecular mechanisms of DExD/H-box helicases' regulatory roles is vital for developing new therapeutics targeting DExD/H-box helicases and their mediated signaling transduction in viral infectious diseases.

Erianin: A Direct NLRP3 Inhibitor With Remarkable Anti-Inflammatory Activity

Erianin (Eri) is the extract of Dendrobium chrysotoxum Lindl. The NLRP3 inflammasome is a multiprotein complex that plays key roles in a wide variety of chronic inflammation-driven human diseases. Nevertheless, little is known about the protection of Eri against NLRP3 inflammasome-related diseases. In this study, we demonstrated that Eri inhibited NLRP3 inflammasome activation in vitro and in vivo. Mechanistically, Eri directly interacted with NLRP3, leading to inhibition of NLRP3 inflammasome assembly. Eri associated with the Walker A motif in the NACHT domain and suppressed NLRP3 ATPase activity. In mouse models, Eri had therapeutic effects on peritonitis, gouty arthritis and type 2 diabetes, via NLRP3. More importantly, Eri was active ex vivo for synovial fluid cells and monocytes from patients with IAV infection and gout. Eri may serve as a potential novel therapeutic compound against NLRP3-driven diseases.

TLR and IKK Complex-Mediated Innate Immune Signaling Inhibits Stress Granule Assembly

Cellular stress can induce cytoplasmic ribonucleoprotein complexes called stress granules that allow the cells to survive. Stress granules are also central to cellular responses to infections, in which they can act as platforms for viral sending or modulate innate immune signaling through pattern recognition receptors. However, the effect of innate immune signaling on stress granules is poorly understood. In this study, we report that prior induction of innate immune signaling through TLRs inhibited stress granule assembly in a TLR ligand dose-dependent manner in murine bone marrow-derived macrophages. Time course analysis suggests that TLR stimulation can reverse stress granule assembly even after it has begun. Additionally, both MYD88- and TRIF-mediated TLR signaling inhibited stress granule assembly in response to endoplasmic reticulum stress in bone marrow-derived macrophages and the chemotherapeutic drug oxaliplatin in murine B16 melanoma cells. This inhibition was not due to a decrease in expression of the critical stress granule proteins G3BP1 and DDX3X and was independent of IRAK1/4, JNK, ERK and P38 kinase activity but dependent on IKK complex kinase activity. Overall, we have identified the TLR-IKK complex signaling axis as a regulator of stress granule assembly-disassembly dynamics, highlighting cross-talk between processes that are critical in health and disease.