Influenza Virus Infection Induces ZBP1 Expression and Necroptosis in Mouse Lungs

Cytosolic nucleic acid sensing as driver of critical illness: mechanisms and advances in therapy

Nucleic acids from both self- and non-self-sources act as vital danger signals that trigger immune responses. Critical illnesses such as acute respiratory distress syndrome, sepsis, trauma and ischemia lead to the aberrant cytosolic accumulation and massive release of nucleic acids that are detected by antiviral innate immune receptors in the endosome or cytosol. Activation of receptors for deoxyribonucleic acids and ribonucleic acids triggers inflammation, a major contributor to morbidity and mortality in critically ill patients. In the past decade, there has been growing recognition of the therapeutic potential of targeting nucleic acid sensing in critical care. This review summarizes current knowledge of nucleic acid sensing in acute respiratory distress syndrome, sepsis, trauma and ischemia. Given the extensive research on nucleic acid sensing in common pathological conditions like cancer, autoimmune disorders, metabolic disorders and aging, we provide a comprehensive summary of nucleic acid sensing beyond critical illness to offer insights that may inform its role in critical conditions. Additionally, we discuss potential therapeutic strategies that specifically target nucleic acid sensing. By examining nucleic acid sources, sensor activation and function, as well as the impact of regulating these pathways across various acute diseases, we highlight the driving role of nucleic acid sensing in critical illness.

A narrative review on lung injury: mechanisms, biomarkers, and monitoring

Lung injury is closely associated with the heterogeneity, severity, mortality, and prognosis of various respiratory diseases. Effective monitoring of lung injury is crucial for the optimal management and improved outcomes of patients with lung diseases. This review describes acute and chronic respiratory diseases characterized by significant lung injury and current clinical tools for assessing lung health. Furthermore, we summarized the mechanisms of lung cell death observed in these diseases and highlighted recently identified biomarkers in the plasma indicative of injury to specific cell types and scaffold structure in the lung. Last, we propose an artificial intelligence-driven lung injury monitoring model to assess disease severity, and predict mortality and prognosis, aiming to achieve precision and personalized medicine.

Inflammatory response to SARS-CoV 2 and other respiratory viruses

INTRODUCTION

Lower respiratory tract infections (LRTI) remain a significant global cause of mortality and disability. Viruses constitute a substantial proportion of LRTI cases, with their pandemic potential posing a latent threat. After the SARS-CoV-2 pandemic, the resurgence of other respiratory viruses, including Influenza and Respiratory Syncytial Virus responsible for LRTI has been observed especially in susceptible populations.

AREAS COVERED

This review details the inflammatory mechanisms associated with three primary respiratory viruses: SARS-CoV-2, Influenza, and Respiratory Syncytial Virus (RSV). The focus will be on elucidating the activation of inflammatory pathways, understanding cellular contributions to inflammation, exploring the role of interferon and induced cell death in the response to these pathogens and detailing viral evasion mechanisms. Furthermore, the distinctive characteristics of each virus will be explained.

EXPERT OPINION

The study of viral pneumonia, notably concerning SARS-CoV-2, Influenza, and RSV, offers critical insights into infectious and inflammatory mechanisms with wide-ranging implications. Addressing current limitations, such as diagnostic accuracy and understanding host-virus interactions, requires collaborative efforts and investment in technology. Future research holds promise for uncovering novel therapeutic targets, exploring host microbiome roles, and addressing long-term sequelae. Integrating advances in molecular biology and technology will shape the evolving landscape of viral pneumonia research, potentially enhancing global public health outcomes.

Targeting necroptosis: a promising avenue for respiratory disease treatment

Respiratory diseases are a growing concern in public health because of their potential to endanger the global community. Cell death contributes critically to the pathophysiology of respiratory diseases. Recent evidence indicates that necroptosis, a unique form of programmed cell death (PCD), plays a vital role in the molecular mechanisms underlying respiratory diseases, distinguishing it from apoptosis and conventional necrosis. Necroptosis is a type of inflammatory cell death governed by receptor-interacting serine/threonine protein kinase 1 (RIPK1), RIPK3, and mixed-lineage kinase domain-like protein (MLKL), resulting in the release of intracellular contents and inflammatory factors capable of initiating an inflammatory response in adjacent tissues. These necroinflammatory conditions can result in significant organ dysfunction and long-lasting tissue damage within the lungs. Despite evidence linking necroptosis to various respiratory diseases, there are currently no specific alternative treatments that target this mechanism. This review provides a comprehensive overview of the most recent advancements in understanding the significance and mechanisms of necroptosis. Specifically, this review emphasizes the intricate association between necroptosis and respiratory diseases, highlighting the potential use of necroptosis as an innovative therapeutic approach for treating these conditions.

ZBP1-mediated PANoptosis: A possible novel mechanism underlying the therapeutic effects of penehyclidine hydrochloride on myocardial ischemia-reperfusion injury

Although penehyclidine hydrochloride (PHC) has been identified to alleviate myocardial injury induced by ischemia/reperfusion (I/R), the regulatory molecules and related mechanisms are unknown. In this study, bioinformatics, molecular biology, and biochemistry methods were used to explore the molecular mechanisms and targets of PHC. In the myocardial ischemia-reperfusion injury (MIRI)-induced rat model, PHC pretreatment significantly improved cardiac function (p < 0.01). Multiple differentially expressed genes, including Z-DNA binding protein 1 (ZBP1), were identified through mRNA sequencing analysis of myocardial ischemic penumbra tissue in MIRI rats. The transduction of the ZBP1 adenovirus vector (Ad-Zbp1) in PHC-pretreated rats exhibited a reversible augmentation in myocardial infarct size (p < 0.01), pronounced pathological damage to the myocardial tissue, as well as a significant elevation of serum myocardial enzymes (p < 0.05). The interaction among ZBP1, fas-associating via death domain (FADD), and receptor-interacting serine/threonine-protein kinase 3 (RIPK3) leads to a remarkable up-regulation of cleaved-Caspase-1 (Cl-Casp-1), N-terminal gasdermin D (N-GSDMD), phospho-mixed lineage kinase domain-like Ser358 (p-MLKLS358), and other regulatory proteins, thereby triggering pyroptosis, apoptosis, and necroptosis (PANoptosis) in cardiomyocytes of MIRI rats. Moreover, the transduction of Ad-Zbp1 in the oxygen-glucose deprivation/re-oxygenation (OGD/R)-induced H9c2 cell model also dramatically augmented the number of cell deaths. However, the intervention of PHC considerably enhanced cell viability (p < 0.01), effectively mitigated the release of myocardial enzymes (p < 0.05), and markedly attenuated the expression levels of PANoptosis regulatory proteins through restraint of ZBP1 expression. Therefore, the therapeutic efficacy of PHC in improving MIRI might be attributed to targeting ZBP1-mediated PANoptosis.

Host Innate Antiviral Response to Influenza A Virus Infection: From Viral Sensing to Antagonism and Escape

Influenza virus possesses an RNA genome of single-stranded, negative-sensed, and segmented configuration. Influenza virus causes an acute respiratory disease, commonly known as the "flu" in humans. In some individuals, flu can lead to pneumonia and acute respiratory distress syndrome. Influenza A virus (IAV) is the most significant because it causes recurring seasonal epidemics, occasional pandemics, and zoonotic outbreaks in human populations, globally. The host innate immune response to IAV infection plays a critical role in sensing, preventing, and clearing the infection as well as in flu disease pathology. Host cells sense IAV infection through multiple receptors and mechanisms, which culminate in the induction of a concerted innate antiviral response and the creation of an antiviral state, which inhibits and clears the infection from host cells. However, IAV antagonizes and escapes many steps of the innate antiviral response by different mechanisms. Herein, we review those host and viral mechanisms. This review covers most aspects of the host innate immune response, i.e., (1) the sensing of incoming virus particles, (2) the activation of downstream innate antiviral signaling pathways, (3) the expression of interferon-stimulated genes, (4) and viral antagonism and escape.

Nucleic Acid Sensor-Mediated PANoptosis in Viral Infection

Innate immunity, the first line of host defense against viral infections, recognizes viral components through different pattern-recognition receptors. Nucleic acids derived from viruses are mainly recognized by Toll-like receptors, nucleotide-binding domain leucine-rich repeat-containing receptors, absent in melanoma 2-like receptors, and cytosolic DNA sensors (e.g., Z-DNA-binding protein 1 and cyclic GMP-AMP synthase). Different types of nucleic acid sensors can recognize specific viruses due to their unique structures. PANoptosis is a unique form of inflammatory cell death pathway that is triggered by innate immune sensors and driven by caspases and receptor-interacting serine/threonine kinases through PANoptosome complexes. Nucleic acid sensors (e.g., Z-DNA-binding protein 1 and absent in melanoma 2) not only detect viruses, but also mediate PANoptosis through providing scaffold for the assembly of PANoptosomes. This review summarizes the structures of different nucleic acid sensors, discusses their roles in viral infections by driving PANoptosis, and highlights the crosstalk between different nucleic acid sensors. It also underscores the promising prospect of manipulating nucleic acid sensors as a therapeutic approach for viral infections.

Z-DNA binding protein 1 orchestrates innate immunity and inflammatory cell death

Innate immunity is not only the first line of host defense against microbial infections but is also crucial for the host responses against a variety of noxious stimuli. Z-DNA binding protein 1 (ZBP1) is a cytosolic nucleic acid sensor that can induce inflammatory cell death in both immune and nonimmune cells upon sensing of incursive virus-derived Z-form nucleic acids and self-nucleic acids via its Zα domain. Mechanistically, aberrantly expressed or activated ZBP1 induced by pathogens or noxious stimuli enables recruitment of TANK binding kinase 1 (TBK1), interferon regulatory factor 3 (IRF3), receptor-interacting serine/threonine-protein kinase 1 (RIPK1) and RIPK3 to drive type I interferon (IFN-I) responses and activation of nuclear factor kappa B (NF-κB) signaling. Meanwhile, ZBP1 promotes the assembly of ZBP1- and absent in melanoma 2 (AIM2)-PANoptosome, which ultimately triggers PANoptosis through caspase 3-mediated apoptosis, mixed lineage kinase domain like pseudokinase (MLKL)-mediated necroptosis, and gasdermin D (GSDMD)-mediated pyroptosis. In response to damaged mitochondrial DNA, ZBP1 can interact with cyclic GMP-AMP synthase to augment IFN-I responses but inhibits toll like receptor 9-mediated inflammatory responses. This review summarizes the structure and expression pattern of ZBP1, discusses its roles in human diseases through immune-dependent (e.g., the production of IFN-I and pro-inflammatory cytokines) and -independent (e.g., the activation of cell death) functions, and highlights the attractive prospect of manipulating ZBP1 as a promising therapeutic target in diseases.

The emerging role of PANoptosis in cancer treatment

Programmed cell death (PCD) is a key mechanism for the study of anticancer drugs and has a significant impact on the development and management of cancer. A growing amount of data indicates that different kinds of PCD, particularly pyroptosis, apoptosis, and necroptosis, interact closely. Recent research has revealed the existence of the distinct inflammatory PCD modality known as PANoptosis, which is controlled by complex PANoptosome complexes built by combining elements from different PCD pathways. No single PCD route is sufficient to explain all of the physiologic effects seen in PANoptosis. Numerous studies have demonstrated that PANoptosis can successfully stop cancer cells from growing, proliferating, and developing drug resistance. As a result, it has changed the focus of targeted anticancer therapy. In this review, we outlined the molecular processes of PANoptosis activation and modulation as well as the mechanisms of innate immune cell death. In order to provide a theoretical foundation for the development of drugs targeting PANoptosis as an anti-cancer target, we also highlight the PANoptosomes discovered to date and give an overview of the implications of PANoptosis in cancer treatment.

A Concise Review: Nutritional Interventions for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)

Wuhan, China reported a novel coronavirus-related sickness in late 2019, which quickly spread into a global epidemic. One crucial factor in combating the coronavirus infection appears to be the presence of a robust, long-lasting, and active immune system. The immune response is affected by several factors, including food. Nutritional insufficiency can cause immune deficits, making infections more likely to cause fatality. Thus, understanding numerous behaviors, particularly dietary habits, is essential to determining their capacity to reduce severe acute respiratory syndrome coronavirus 2 risks and improve prognosis. In this paper, the authors summarize the complex interaction between nutritional status and severe acute respiratory syndrome corona virus 2 infections, as well as the consequences of poor nutrients with regard of the extent to which disease is affected. The literature was compiled by searching a number of reputable scientific databases including Scopus, Science Direct, Springer, Nature, PubMed, Web of Science resources. The accumulating evidence demonstrates that malnutrition impairs the immune system's ability to function, weakening the body's infection resistance. This review emphasizes the significance of nutritional status in the care of coronavirus disease patients as well as demonstrates that functional foods may contribute to better outcomes. Ageing, Obesity, Malnutrition, Undernutrition, Lack of exercise are having a devastating effect on people's health in general and during this coronavirus disease. The severity and prognosis of coronavirus illness seem to be significantly influenced by lifestyle choices, nutritional imbalances, and impaired immune response.

Deciphering the molecular mechanisms of Maxing Huoqiao Decoction in treating pulmonary fibrosis via transcriptional profiling and circRNA-miRNA-mRNA network analysis

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, fibrotic interstitial lung condition with unknown etiology and high mortality. Chinese herbal medicine has been used for more than a thousand years to treat various lung diseases.

PURPOSE

The current study aimed to examine whether Chinese herbal Maxing Huoqiao Decoction (MXHQD) exerts therapeutic effects on IPF and to further uncover its underlying molecular mechanisms.

METHODS

Mouse model of acute lung injury (ALI) or IPF was induced by intratracheal instillation of LPS or bleomycin, respectively. ALI mice were treated with MXHQD for 7 days, and lung tissues were taken for test after modeling 24 h. IPF mice were gavaged for 21 days after modeling. Lung tissues were subjected to whole transcriptome detection, and the differential RNAs were experimentally verified.

RESULTS

The results showed that MXHQD alleviated the computed tomography (CT) and the pathological degree changes in mice with IPF, improved changes in the expression of fibrosis related genes and reduced the hydroxyproline expression in IPF mice. MXHQD also decreased the cell numbers in bronchoalveolar lavage fluids, and the expression levels of the inflammatory factors in the ALI mice lung tissues were significantly inhibited. By applying whole transcriptome analysis, results showed that MXHQD acted on 40 mRNAs, 15 miRNAs, 25 novel lncRNAs and 17 circRNAs to resist pulmonary fibrosis. The competing endogenous RNA (ceRNA) network diagram showed that the multiple components of MXHQD against fibrosis through a network of multiple targets. The differential mRNAs were mainly related to the innate immune response and the defense response to virus. Then the expression of mRNAs in the differential mRNA-miRNA-differential circRNA network in the lung tissue of IPF was verified. The expression of ZBP1 and ISG15 related to immune system and anti virus was verified at both gene and protein expressions. MXHQD could significantly inhibit the elevation of ZBP1 and ISG15 factors induced by the fibrosis model.

CONCLUSION

Overall, our findings provide compelling evidence that MXHQD can alleviate IPF by modulating innate immunity. This is the first study to reveal the molecular mechanism underlying the multi-components, multi-channels and multi-targets anti-IPF immune injury of MXHQD, and supports its potential clinical application for IPF.

Inflammatory cell death: how macrophages sense neighbouring cell infection and damage

Programmed cell death is a critical host defence strategy during viral infection. Neighbouring cells deal with this death in distinct ways depending on how the infected cell dies. While apoptosis is considered immunologically silent, the lytic pathways of necroptosis and pyroptosis trigger inflammatory responses by releasing inflammatory host molecules. All these pathways have been implicated in influenza A virus infection. Here, we review how cells sense neighbouring infection and death and how sensing shapes ensuing inflammatory responses.

ZBP1/DAI-Dependent Cell Death Pathways in Influenza A Virus Immunity and Pathogenesis

Influenza A viruses (IAV) are members of the Orthomyxoviridae family of negative-sense RNA viruses. The greatest diversity of IAV strains is found in aquatic birds, but a subset of strains infects other avian as well as mammalian species, including humans. In aquatic birds, infection is largely restricted to the gastrointestinal tract and spread is through feces, while in humans and other mammals, respiratory epithelial cells are the primary sites supporting productive replication and transmission. IAV triggers the death of most cell types in which it replicates, both in culture and in vivo. When well controlled, such cell death is considered an effective host defense mechanism that eliminates infected cells and limits virus spread. Unchecked or inopportune cell death also results in immunopathology. In this chapter, we discuss the impact of cell death in restricting virus spread, supporting the adaptive immune response and driving pathogenesis in the mammalian respiratory tract. Recent studies have begun to shed light on the signaling pathways underlying IAV-activated cell death. These pathways, initiated by the pathogen sensor protein ZBP1 (also called DAI and DLM1), cause infected cells to undergo apoptosis, necroptosis, and pyroptosis. We outline mechanisms of ZBP1-mediated cell death signaling following IAV infection.

DNA sensor-associated type I interferon signaling is increased in ulcerative colitis and induces JAK-dependent inflammatory cell death in colonic organoids

DNA sensor pathways can initiate inflammasome, cell death, and type I interferon (IFN) signaling in immune-mediated inflammatory diseases (IMIDs), including type I interferonopathies. We investigated the involvement of these pathways in the pathogenesis of ulcerative colitis (UC) by analyzing the expression of DNA sensor, inflammasome, and type I IFN biomarker genes in colonic mucosal biopsy tissue from control (n = 31), inactive UC (n = 31), active UC (n = 33), and a UC single-cell RNA-Seq dataset. The effects of type I IFN (IFN-β), IFN-γ, and TNF-α on gene expression, cytokine production, and cell death were investigated in human colonic organoids. In organoids treated with cytokines alone, or in combination with NLR family pyrin domain-containing 3 (NLRP3), caspase, or JAK inhibitors, cell death was measured, and supernatants were assayed for IL-1β/IL-18/CXCL10. The expression of DNA sensor pathway genes-PYHIN family members [absent in melanoma 2 (AIM2), IFI16, myeloid cell nuclear differentiation antigen (MNDA), and pyrin and HIN domain family member 1 (PYHIN1)- as well as Z-DNA-binding protein 1 (ZBP1), cyclic GMP-AMP synthase (cGAS), and DDX41 was increased in active UC and expressed in a cell type-restricted pattern. Inflammasome genes (CASP1, IL1B, and IL18), type I IFN inducers [stimulator of interferon response cGAMP interactor 1 (STING), TBK1, and IRF3), IFNB1, and type I IFN biomarker genes (OAS2, IFIT2, and MX2) were also increased in active UC. Cotreatment of organoids with IFN-β or IFN-γ in combination with TNFα increased expression of IFI16, ZBP1, CASP1, cGAS, and STING induced cell death and IL-1β/IL-18 secretion. This inflammatory cell death was blocked by the JAK inhibitor tofacitinib but not by inflammasome or caspase inhibitors. Increased type I IFN activity may drive elevated expression of DNA sensor genes and JAK-dependent but inflammasome-independent inflammatory cell death of colonic epithelial cells in UC.NEW & NOTEWORTHY This study found that patients with active UC have significantly increased colonic gene expression of cytosolic DNA sensor, inflammasome, STING, and type I IFN signaling pathways. The type I IFN, IFN-β, in combination with TNF-α induced JAK-dependent but NLRP3 and inflammasome-independent inflammatory cell death of colonic organoids. This novel inflammatory cell death phenotype is relevant to UC immunopathology and may partially explain the efficacy of the JAKinibs tofacitinib and upadacitinib in patients with UC.

Inducible general knockout of Runx3 profoundly reduces pulmonary cytotoxic CD8+ T cells with minimal effect on outcomes in mice following influenza infection

Respiratory viruses pose a continuing and substantive threat to human health globally. Host innate and adaptive immune responses are the critical antiviral defense mechanisms to control viral replication and spread. The present study is designed to determine the role of transcription factor Runx3 in the host immune response to influenza A virus (IAV) infection. As Runx3 is required for embryonic development, we generated an inducible Runx3 global knockout (KO) mouse model and found that Runx3 KO in adult C57BL/6 mice minimally affected thymic function under normal conditions and survival was at least 250 days post Runx3 deletion. We applied the mouse model to IAV infection and found that Runx3 KO resulted in a huge reduction (>85%) in numbers of total and antigen-specific pulmonary CD8+ cytotoxic T cells during IAV infection, while it had a minor effect on pulmonary generation of CD4+ T cells. To our surprise, this general KO of Runx3 did not significantly alter viral clearance and animal survival following IAV infection. Interestingly, we found that Runx3 KO significantly increased the numbers of pulmonary innate immune cells such as macrophages and neutrophils and the production of pro-inflammatory cytokines during IAV infection. We further found that Runx3 was strongly detected in CCR2+ immune cells in IAV-infected mouse lungs and was induced in activated macrophages and dendritic cells (DCs). As pulmonary CD8+ cytotoxic T cells play a central role in the clearance of IAV, our findings suggest that Runx3 KO may enhance host innate immunity to compensate for the loss of pulmonary CD8+ cytotoxic T cells during IAV infection.

ZBP1: A Powerful Innate Immune Sensor and Double-Edged Sword in Host Immunity

Z-conformation nucleic acid binding protein 1 (ZBP1), a powerful innate immune sensor, has been identified as the important signaling initiation factor in innate immune response and the multiple inflammatory cell death known as PANoptosis. The initiation of ZBP1 signaling requires recognition of left-handed double-helix Z-nucleic acid (includes Z-DNA and Z-RNA) and subsequent signaling transduction depends on the interaction between ZBP1 and its adapter proteins, such as TANK-binding kinase 1 (TBK1), interferon regulatory factor 3 (IRF3), receptor-interacting serine/threonine-protein kinase 1 (RIPK1), and RIPK3. ZBP1 activated innate immunity, including type-I interferon (IFN-I) response and NF-κB signaling, constitutes an important line of defense against pathogenic infection. In addition, ZBP1-mediated PANoptosis is a double-edged sword in anti-infection, auto-inflammatory diseases, and tumor immunity. ZBP1-mediated PANoptosis is beneficial for eliminating infected cells and tumor cells, but abnormal or excessive PANoptosis can lead to a strong inflammatory response that is harmful to the host. Thus, pathogens and host have each developed multiplex tactics targeting ZBP1 signaling to maintain strong virulence or immune homeostasis. In this paper, we reviewed the mechanisms of ZBP1 signaling, the effects of ZBP1 signaling on host immunity and pathogen infection, and various antagonistic strategies of host and pathogen against ZBP1. We also discuss existent gaps regarding ZBP1 signaling and forecast potential directions for future research.

Association between expression of ZBP1, AIM2, and MDA5 genes and severity of COVID-19

Antiviral and inflammatory responses following the detection of the virus genome by nucleic acid sensors play a vital role in the pathogenesis and outcome of diseases. In this study, we investigated the ZBP1, AIM2, and MDA5 expression levels in COVID-19 patients with different intensities of the disease. 75 quantitative Real-Time PCR (qRT-PCR)-confirmed COVID-19 patients were included consecutively and divided into 3 groups of mild, severe, and critical based on the severity of the disease. Also, 25 healthy volunteer subjects were included. PBMCs were collected from the whole blood, and RNA was extracted using commercial kit. The expression of ZBP1, AIM2, and MDA5 genes was investigated using qRT-PCR technique. The mean age of the patients and healthy volunteers was 52.73±13.78 and 49.120±12.490, respectively. In each group, 13 out of 25 participants were male. The expression levels of ZBP1 (P=0.001), AIM2 (P=0.001), and MDA5 (P= 0.003) transcript were significantly higher in COVID-19 patients than the control group. The results also revealed that the expression levels of ZBP1, AIM2, and MDA5 were significantly higher in the critical and severe COVID-19 patients compared to those with mild disease (P<0.05). Moreover, regarding the gender, the expression levels of AIM2 and MDA5 were significantly elevated in male severe (P=0.04 and P=0.003, respectively) and critical (P=0.005 and P=0.0004, respectively) patients than the female ones. The results indicated that ZBP1, AIM2, and MDA5 genes might have an important role in the severity of COVID-19 disease. Moreover, the severity of COVID-19 disease in male and female patients might be related to AIM2, and MDA5 expression levels. More studies are recommended to be conducted to clarify this issue.

Molecular Events Involved in Influenza A Virus-Induced Cell Death

Viral infection usually leads to cell death. Moderate cell death is a protective innate immune response. By contrast, excessive, uncontrolled cell death causes tissue destruction, cytokine storm, or even host death. Thus, the struggle between the host and virus determines whether the host survives. Influenza A virus (IAV) infection in humans can lead to unbridled hyper-inflammatory reactions and cause serious illnesses and even death. A full understanding of the molecular mechanisms and regulatory networks through which IAVs induce cell death could facilitate the development of more effective antiviral treatments. In this review, we discuss current progress in research on cell death induced by IAV infection and evaluate the role of cell death in IAV replication and disease prognosis.

Coagulation System Activation for Targeting of COVID-19: Insights into Anticoagulants, Vaccine-Loaded Nanoparticles, and Hypercoagulability in COVID-19 Vaccines

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), also known as COVID-19, is currently developing into a rapidly disseminating and an overwhelming worldwide pandemic. In severe COVID-19 cases, hypercoagulability and inflammation are two crucial complications responsible for poor prognosis and mortality. In addition, coagulation system activation and inflammation overlap and produce life-threatening complications, including coagulopathy and cytokine storm, which are associated with overproduction of cytokines and activation of the immune system; they might be a lead cause of organ damage. However, patients with severe COVID-19 who received anticoagulant therapy had lower mortality, especially with elevated D-dimer or fibrin degradation products (FDP). In this regard, the discovery of natural products with anticoagulant potential may help mitigate the numerous side effects of the available synthetic drugs. This review sheds light on blood coagulation and its impact on the complication associated with COVID-19. Furthermore, the sources of natural anticoagulants, the role of nanoparticle formulation in this outbreak, and the prevalence of thrombosis with thrombocytopenia syndrome (TTS) after COVID-19 vaccines are also reviewed. These combined data provide many research ideas related to the possibility of using these anticoagulant agents as a treatment to relieve acute symptoms of COVID-19 infection.

Necroptosis in Pulmonary Diseases: A New Therapeutic Target

In the past decades, apoptosis has been the most well-studied regulated cell death (RCD) that has essential functions in tissue homeostasis throughout life. However, a novel form of RCD called necroptosis, which requires receptor-interacting protein kinase-3 (RIPK3) and mixed-lineage kinase domain-like pseudokinase (MLKL), has recently been receiving increasing scientific attention. The phosphorylation of RIPK3 enables the recruitment and phosphorylation of MLKL, which oligomerizes and translocates to the plasma membranes, ultimately leading to plasma membrane rupture and cell death. Although apoptosis elicits no inflammatory responses, necroptosis triggers inflammation or causes an innate immune response to protect the body through the release of damage-associated molecular patterns (DAMPs). Increasing evidence now suggests that necroptosis is implicated in the pathogenesis of several human diseases such as systemic inflammation, respiratory diseases, cardiovascular diseases, neurodegenerative diseases, neurological diseases, and cancer. This review summarizes the emerging insights of necroptosis and its contribution toward the pathogenesis of lung diseases.

The Crucial Role of NLRP3 Inflammasome in Viral Infection-Associated Fibrosing Interstitial Lung Diseases

Idiopathic pulmonary fibrosis (IPF), one of the most common fibrosing interstitial lung diseases (ILD), is a chronic-age-related respiratory disease that rises from repeated micro-injury of the alveolar epithelium. Environmental influences, intrinsic factors, genetic and epigenetic risk factors that lead to chronic inflammation might be implicated in the development of IPF. The exact triggers that initiate the fibrotic response in IPF remain enigmatic, but there is now increasing evidence supporting the role of chronic exposure of viral infection. During viral infection, activation of the NLRP3 inflammasome by integrating multiple cellular and molecular signaling implicates robust inflammation, fibroblast proliferation, activation of myofibroblast, matrix deposition, and aberrant epithelial-mesenchymal function. Overall, the crosstalk of the NLRP3 inflammasome and viruses can activate immune responses and inflammasome-associated molecules in the development, progression, and exacerbation of IPF.

Novel insights into the pathogenesis of virus-induced ARDS: review on the central role of the epithelial-endothelial barrier

Introduction: Respiratory viruses can directly or indirectly damage the pulmonary defense barrier, potentially contributing to acute respiratory distress syndrome (ARDS). Despite developments in the understanding of the pathogenesis of ARDS, the underlying pathophysiology still needs to be elucidated.Areas covered: The PubMed database was reviewed for relevant papers published up to 2021. This review summarizes the currently immunological and clinical studies to provide a systemic overview of the epithelial-endothelial barrier, given the recently published immunological profiles upon viral pneumonia, and the potentially detrimental contribution to respiratory function caused by damage to this barrier.Expert opinion: The biophysical structure of host pulmonary defense is intrinsically linked with the ability of alveolar epithelial and capillary endothelial cells, known as the epithelial-endothelial barrier, to respond to, and instruct the delicate immune system to protect the lungs from infections and injuries. Recently published immunological profiles upon viral infection, and its contributions to the damage of respiratory function, suggest a central role for the pulmonary epithelial and endothelial barrier in the pathogenesis of ARDS. We suggest a central role and common pathways by which the epithelial-endothelial barrier contributes to the pathogenesis of ARDS.

Nutritional Impact and Its Potential Consequences on COVID-19 Severity

Background: During late 2019 a viral disease due to a novel coronavirus was reported in Wuhan, China, which rapidly developed into an exploding pandemic and poses a severe threat to human health all over the world. Until now (May 2021), there are insufficient treatment options for the management of this global disease and shortage of vaccines. Important aspects that help to defeat coronavirus infection seems to be having a healthy, strong, and resilient immune system. Nutrition and metabolic disorders, such as obesity and diabetes play a crucial role on the community health situation in general and especially during this new pandemic. There seems to be an enormous impact of lifestyle, metabolic disorders, and immune status on coronavirus disease 2019 (COVID-19) severity and recovery. For this reason, it is important to consider the impact of lifestyle and the consumption of well-defined healthy diets during the pandemic. Aims: In this review, we summarise recent findings on the effect of nutrition on COVID-19 susceptibility and disease severity and treatment. Understanding how specific dietary features might help to improve the public health strategies to reduce the rate and severity of COVID-19.

Influenza-Induced Oxidative Stress Sensitizes Lung Cells to Bacterial-Toxin-Mediated Necroptosis

Pneumonias caused by influenza A virus (IAV) co- and secondary bacterial infections are characterized by their severity and high mortality rate. Previously, we have shown that bacterial pore-forming toxin (PFT)-mediated necroptosis is a key driver of acute lung injury during bacterial pneumonia. Here, we evaluate the impact of IAV on PFT-induced acute lung injury during co- and secondary Streptococcus pneumoniae (Spn) infection. We observe that IAV synergistically sensitizes lung epithelial cells for PFT-mediated necroptosis in vitro and in murine models of Spn co-infection and secondary infection. Pharmacoelogical induction of oxidative stress without virus sensitizes cells for PFT-mediated necroptosis. Antioxidant treatment or inhibition of necroptosis reduces disease severity during secondary bacterial infection. Our results advance our understanding on the molecular basis of co- and secondary bacterial infection to influenza and identify necroptosis inhibition and antioxidant therapy as potential intervention strategies.

Viral dosing of influenza A infection reveals involvement of RIPK3 and FADD, but not MLKL

RIPK3 was reported to play an important role in the protection against influenza A virus (IAV) in vivo. Here we show that the requirement of RIPK3 for protection against IAV infection in vivo is only apparent within a limited dose range of IAV challenge. We found that this protective outcome is independent from RIPK3 kinase activity and from MLKL. This shows that platform function of RIPK3 rather than its kinase activity is required for protection, suggesting that a RIPK3 function independent of necroptosis is implicated. In line with this finding, we show that FADD-dependent apoptosis has a crucial additional effect in protection against IAV infection. Altogether, we show that RIPK3 contributes to protection against IAV in a narrow challenge dose range by a mechanism that is independent of its kinase activity and its capacity to induce necroptosis.

Enhanced RIPK3 kinase activity-dependent lytic cell death in M1 but not M2 macrophages

Macrophages play a crucial role in host innate immune defense against infection and tissue injury. Macrophages are highly plastic cells and their subtypes have been characterized as M1 (also termed classically activated) and M2 (alternatively activated). Although the M1/M2 paradigm has been well documented, less is known regarding the role of macrophage activation/polarization in inflammation-associated necrotic cell death. To address this gap in current knowledge, we prepared bone marrow-derived macrophages, induced them to M1 or M2 subtypes, and then investigated the expression of necroptosis signaling molecules and macrophage subtype-dependent responses to different necroptosis inducers. We found that necroptosis effector mixed lineage kinase domain-like protein (MLKL) and the key necroptosis regulator Z-DNA/RNA binding protein 1 were predominantly induced in M1 but not M2 macrophages. Interestingly, the protein but not mRNA levels of receptor-interacting protein kinase-3 (RIPK3) were also upregulated in M1 macrophages. We further found that macrophage necrotic cell death, the releases of lactate dehydrogenase and dead cell proteases as well as MLKL phosphorylation at Ser345 in response to various necroptosis inducers were greatly augmented in M1 but not M2 macrophages, and the accelerated effects were blocked by two structurally distinct specific RIPK3 inhibitors GSK872 or GSK843. Thus, our findings demonstrate that M1 but not M2 subtypes of macrophages are more susceptible to inflammation-related lytic cell death in an RIPK3 kinase activity-dependent manner.

Innate Immune Responses to Acute Viral Infection During Pregnancy

Immunological adaptations in pregnancy allow maternal tolerance of the semi-allogeneic fetus but also increase maternal susceptibility to infection. At implantation, the endometrial stroma, glands, arteries and immune cells undergo anatomical and functional transformation to create the decidua, the specialized secretory endometrium of pregnancy. The maternal decidua and the invading fetal trophoblast constitute a dynamic junction that facilitates a complex immunological dialogue between the two. The decidual and peripheral immune systems together assume a pivotal role in regulating the critical balance between tolerance and defense against infection. Throughout pregnancy, this equilibrium is repeatedly subjected to microbial challenge. Acute viral infection in pregnancy is associated with a wide spectrum of adverse consequences for both mother and fetus. Vertical transmission from mother to fetus can cause developmental anomalies, growth restriction, preterm birth and stillbirth, while the mother is predisposed to heightened morbidity and maternal death. A rapid, effective response to invasive pathogens is therefore essential in order to avoid overwhelming maternal infection and consequent fetal compromise. This sentinel response is mediated by the innate immune system: a heritable, highly evolutionarily conserved system comprising physical barriers, antimicrobial peptides (AMP) and a variety of immune cells—principally neutrophils, macrophages, dendritic cells, and natural killer cells—which express pattern-receptors that detect invariant molecular signatures unique to pathogenic micro-organisms. Recognition of these signatures during acute infection triggers signaling cascades that enhance antimicrobial properties such as phagocytosis, secretion of pro-inflammatory cytokines and activation of the complement system. As well as coordinating the initial immune response, macrophages and dendritic cells present microbial antigens to lymphocytes, initiating and influencing the development of specific, long-lasting adaptive immunity. Despite extensive progress in unraveling the immunological adaptations of pregnancy, pregnant women remain particularly susceptible to certain acute viral infections and continue to experience mortality rates equivalent to those observed in pandemics several decades ago. Here, we focus specifically on the pregnancy-induced vulnerabilities in innate immunity that contribute to the disproportionately high maternal mortality observed in the following acute viral infections: Lassa fever, Ebola virus disease (EVD), dengue fever, hepatitis E, influenza, and novel coronavirus infections.

Lytic Cell Death Mechanisms in Human Respiratory Syncytial Virus-Infected Macrophages: Roles of Pyroptosis and Necroptosis

Human respiratory syncytial virus (RSV) is the most common cause of viral bronchiolitis and pneumonia in infants and children worldwide. Inflammation induced by RSV infection is responsible for its hallmark manifestation of bronchiolitis and pneumonia. The cellular debris created through lytic cell death of infected cells is a potent initiator of this inflammation. Macrophages are known to play a pivotal role in the early innate immune and inflammatory response to viral pathogens. However, the lytic cell death mechanisms associated with RSV infection in macrophages remains unknown. Two distinct mechanisms involved in lytic cell death are pyroptosis and necroptosis. Our studies revealed that RSV induces lytic cell death in macrophages via both of these mechanisms, specifically through the ASC (Apoptosis-associated speck like protein containing a caspase recruitment domain)-NLRP3 (nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3) inflammasome activation of both caspase-1 dependent pyroptosis and receptor-interacting serine/threonine-protein kinase 3 (RIPK3), as well as a mixed lineage kinase domain like pseudokinase (MLKL)-dependent necroptosis. In addition, we demonstrated an important role of reactive oxygen species (ROS) during lytic cell death of RSV-infected macrophages.

Necroptosis in Hepatosteatotic Ischaemia-Reperfusion Injury

While liver transplantation remains the sole treatment option for patients with end-stage liver disease, there are numerous limitations to liver transplantation including the scarcity of donor livers and a rise in livers that are unsuitable to transplant such as those with excess steatosis. Fatty livers are susceptible to ischaemia-reperfusion (IR) injury during transplantation and IR injury results in primary graft non-function, graft failure and mortality. Recent studies have described new cell death pathways which differ from the traditional apoptotic pathway. Necroptosis, a regulated form of cell death, has been associated with hepatic IR injury. Receptor-interacting protein kinase 3 (RIPK3) and mixed-lineage kinase domain-like pseudokinase (MLKL) are thought to be instrumental in the execution of necroptosis. The study of hepatic necroptosis and potential therapeutic approaches to attenuate IR injury will be a key factor in improving our knowledge regarding liver transplantation with fatty donor livers. In this review, we focus on the effect of hepatic steatosis during liver transplantation as well as molecular mechanisms of necroptosis and its involvement during liver IR injury. We also discuss the immune responses triggered during necroptosis and examine the utility of necroptosis inhibitors as potential therapeutic approaches to alleviate IR injury.

Die Another Way: Interplay between Influenza A Virus, Inflammation and Cell Death

Influenza A virus (IAV) is a major concern to human health due to the ongoing global threat of a pandemic. Inflammatory and cell death signalling pathways play important roles in host defence against IAV infection. However, severe IAV infections in humans are characterised by excessive inflammation and tissue damage, often leading to fatal disease. While the molecular mechanisms involved in the induction of inflammation during IAV infection have been well studied, the pathways involved in IAV-induced cell death and their impact on immunopathology have not been fully elucidated. There is increasing evidence of significant crosstalk between cell death and inflammatory pathways and a greater understanding of their role in host defence and disease may facilitate the design of new treatments for IAV infection.

The involvement of regulated cell death forms in modulating the bacterial and viral pathogenesis

Apoptosis, necroptosis and pyroptosis represent three distinct types of regulated cell death forms, which play significant roles in response to viral and bacterial infections. Whereas apoptosis is characterized by cell shrinkage, nuclear condensation, bleb formation and retained membrane integrity, necroptosis and pyroptosis exhibit osmotic imbalance driven cytoplasmic swelling and early membrane damage. These three cell death forms exert distinct immune stimulatory potential. The caspase driven apoptotic cell demise is considered in many circumstances as anti-inflammatory, whereas the two lytic cell death modalities can efficiently trigger immune response by releasing damage associated molecular patterns to the extracellular space. The relevance of these cell death modalities in infections can be best demonstrated by the presence of viral proteins that directly interfere with cell death pathways. Conversely, some pathogens hijack the cell death signaling routes to initiate a targeted attack against the immune cells of the host, and extracellular bacteria can benefit from the destruction of intact extracellular barriers upon cell death induction. The complexity and the crosstalk between these cell death modalities reflect a continuous evolutionary race between pathogens and host. This chapter discusses the current advances in the research of cell death signaling with regard to viral and bacterial infections and describes the network of the cell death initiating molecular mechanisms that selectively recognize pathogen associated molecular patterns.