SARS-CoV-2 N protein promotes NLRP3 inflammasome activation to induce hyperinflammation

Exploring the role of mitochondrial dysfunction and aging in COVID-19-Related neurological complications

The COVID-19 pandemic, caused by SARS-CoV-2, posed a tremendous challenge to healthcare systems globally. Severe COVID-19 infection was reported to be associated with altered immunometabolism and cytokine storms, contributing to poor clinical outcomes and in many cases resulting in mortality. Despite promising preclinical results, many drugs have failed to show efficacy in clinical trials, highlighting the need for novel approaches to combat the virus and its severe manifestations. Mitochondria, crucial for aerobic respiration, play a pivotal role in modulating immunometabolism and neuronal function, making their compromised capability as central pathological mechanism contributing to the development of neurological complications in COVID-19. Dysregulated mitochondrial dynamics can lead to uncontrolled immune responses, underscoring the importance of mitochondrial regulation in shaping clinical outcomes. Aging further accelerates mitochondrial dysfunction, compounding immune dysregulation and neurodegeneration, making older adults particularly vulnerable to severe COVID-19 and its neurological sequelae. COVID-19 infection impairs mitochondrial oxidative phosphorylation, contributing to the long-term neurological complications associated with the disease. Additionally, recent reports also suggest that up to 30% of COVID-19 patients experience lingering neurological issues, thereby highlighting the critical need for further research into mitochondrial pathways to mitigate long-tern neurological consequences of Covid-19. This review examines the role of mitochondrial dysfunction in COVID-19-induced neurological complications, its connection to aging, and potential biomarkers for clinical diagnostics. It also discusses therapeutic strategies aimed at maintaining mitochondrial integrity to improve COVID-19 outcomes.

Targeting USP22 to promote K63-linked ubiquitination and degradation of SARS-CoV-2 nucleocapsid protein

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) generally hijacks the cellular machinery of host cells for survival. However, how SARS-CoV-2 employs the host's deubiquitinase to facilitate virus replication remains largely unknown. In this study, we identified the host deubiquitinase USP22 as a crucial regulator of the expression of SARS-CoV-2 nucleocapsid protein (SARS-CoV-2 NP), which is essential for SARS-CoV-2 replication. We demonstrated that SARS-CoV-2 NP proteins undergo ubiquitination-dependent degradation in host cells, while USP22 interacts with SARS-CoV-2 NP and downregulates K63-linked polyubiquitination of SARS-CoV-2 NP, thereby protecting SARS-CoV-2 NP from degradation. Importantly, we further revealed that sulbactam, an antibiotic, can reduce USP22 protein levels, eventually promoting the degradation of SARS-CoV-2 NP in vitro and in vivo. This study reveals the mechanism by which SARS-CoV-2-encoded NP protein employs host deubiquitinase for virus survival and provides a potential strategy to fight against SARS-CoV-2 infection.IMPORTANCESevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid protein (SARS-CoV-2 NP) plays a pivotal role in viral infection by binding to viral RNA, stabilizing the viral genome, and promoting replication. However, the interactions between SARS-CoV-2 NP and host intracellular proteins had not been elucidated. In this study, we provide evidence that SARS-CoV-2 NP interacts with the deubiquitinase USP22 in host cells, which downregulates SARS-CoV-2 NP ubiquitination. This reduction in ubiquitination effectively prevents intracellular degradation of SARS-CoV-2 NP, thereby enhancing its stability, marking USP22 as a potential target for antiviral strategies. Additionally, our findings indicate that sulbactam significantly decreases the protein levels of USP22, thereby reducing SARS-CoV-2 NP levels. This discovery suggests a novel therapeutic pathway in which sulbactam could be repurposed as an antiviral agent, demonstrating how certain antibiotics might contribute to antiviral treatment. This work thus opens avenues for drug repurposing and highlights the therapeutic potential of targeting host pathways to inhibit viral replication.

Structure of the human TWIK-2 potassium channel and its inhibition by pimozide

The potassium channel TWIK-2 is crucial for ATP-induced activation of the NLRP3 inflammasome in macrophages. The channel is a member of the two-pore domain potassium (K2P) channel superfamily and an emerging therapeutic target to mitigate severe inflammatory injury involving NLRP3 activation. We report the cryo-EM structure of human TWIK-2. In comparison to other K2P channels, the structure reveals an unusual "up" conformation of Tyr111 in the selectivity filter and a resulting SF1-P1 pocket behind the filter. Density for acyl chains is present in fenestrations within the transmembrane region that connects the central cavity of the pore to the lipid membrane. Despite its importance as a drug target, limited pharmacological tools are available for TWIK-2. A previous study suggested that the FDA-approved small molecule pimozide might inhibit TWIK-2. Using a reconstituted system, we show that pimozide directly inhibits the channel and we determine a cryo-EM structure of a complex with the drug. Pimozide displaces the acyl chains within the fenestrations and binds below the selectivity filter where it would impede ion permeation. The drug may access its binding site by lateral diffusion in the membrane, suggesting that other hydrophobic small molecules could have utility for inhibiting TWIK-2. The work defines the structure of TWIK-2 and provides a structural foundation for development of more specific inhibitors with potential utility as anti-inflammatory drugs.

Inhibition of RACK1-Mediated NLRP3 Oligomerization (Active Conformation) Ameliorates Acute Respiratory Distress Syndrome

Aberrant activation of the NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) inflammasome contributes to the pathogenesis of fatal and perplexing pulmonary diseases. Although pharmacological inhibition of the NLRP3 inflammasome brings potent therapeutic effects in clinical trials and preclinical models, the molecular chaperones and transition governing its transformation from an auto-suppressed state to an active oligomer remain controversial. Here, this work shows that sesquiterpene bigelovin inhibited NLRP3 inflammasome activation and downstream pro-inflammatory cytokines release via canonical, noncanonical, and alternative pathways at nanomolar ranges. Chemoproteomic target identification discloses that bigelovin covalently bound to Cys168 of RACK1, disrupting the interaction between RACK1 and NLRP3 monomer and thereby suppressing NLRP3 inflammasome oligomerization in vitro and in vivo. Bigelovin treatment significantly alleviates the severity of NLRP3-related pulmonary disorders in murine models, such as LPS-induced ARDS and silicosis. These results consolidated the intricate role of RACK1 in transiting the NLRP3 state and provided a new anti-inflammatory lead and therapy for NLRP3-driven diseases.

NLRP3 inflammasome: From drug target to drug discovery

The immune system employs innate and adaptive immunity to combat pathogens and stress stimuli. Innate immunity rapidly detects pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) via pattern recognition receptors (PRRs), whereas adaptive immunity mediates antigen-specific T/B cell responses. The NLRP3 inflammasome, a key cytoplasmic PRR, consists of leucine-rich repeat, nucleotide-binding, and pyrin domains. Its activation requires priming (signal 1: Toll-like receptors/NOD-like receptors/cytokine receptors) and activation (signal 2: PAMPs/DAMPs/particulates). NLRP3 triggers cytokine storms and neuroinflammation, contributing to inflammatory diseases. Emerging therapies target NLRP3 via nuclear receptors (transcriptional regulation), adeno-associated virus (AAV) vectors (gene delivery), and microRNAs (post-transcriptional modulation). This review highlights NLRP3's signaling cascade, pathological roles, and combinatorial treatments leveraging nuclear receptors, AAVs, and microRNAs for immunomodulation.

Updated insights into the molecular networks for NLRP3 inflammasome activation

Over the past decade, significant advances have been made in our understanding of how NACHT-, leucine-rich-repeat-, and pyrin domain-containing protein 3 (NLRP3) inflammasomes are activated. These findings provide detailed insights into the transcriptional and posttranslational regulatory processes, the structural-functional relationship of the activation processes, and the spatiotemporal dynamics of NLRP3 activation. Notably, the multifaceted mechanisms underlying the licensing of NLRP3 inflammasome activation constitute a focal point of intense research. Extensive research has revealed the interactions of NLRP3 and its inflammasome components with partner molecules in terms of positive and negative regulation. In this Review, we provide the current understanding of the complex molecular networks that play pivotal roles in regulating NLRP3 inflammasome priming, licensing and assembly. In addition, we highlight the intricate and interconnected mechanisms involved in the activation of the NLRP3 inflammasome and the associated regulatory pathways. Furthermore, we discuss recent advances in the development of therapeutic strategies targeting the NLRP3 inflammasome to identify potential therapeutics for NLRP3-associated inflammatory diseases. As research continues to uncover the intricacies of the molecular networks governing NLRP3 activation, novel approaches for therapeutic interventions against NLRP3-related pathologies are emerging.

Pyroptosis in Pulpitis

Pulpitis is an inflammatory disease occurs in the pulp tissues. Continuous development of pulpitis can lead to apical periodontitis and seriously damage the function of teeth, affecting the oral health and daily life of patients. Pyroptosis, alternatively termed inflammatory necrosis, is a type of programmed cell death that is characterized by the swelling of cells until the cell membrane is broken. The GSDM family of proteins can be activated by a variety of pathways, which can lead to the puncture of cell membrane, inducing the release of cellular contents and inflammatory cytokines like IL-1β and IL-18 to activate a strong inflammatory response. Pyroptosis in dental pulp may be an important direction to find new targets for pulpal inflammation prevention and treatment, which deserves further study. In this article, we reviewed the activation mechanism and potential role of pyroptosis in the progression of pulpitis, along with the interaction between pyroptosis and other regulated cell death (RCD) pathways. This review aims to enrich the mechanism under the development of dental pulp inflammation, and to uncover potential therapeutic targets for early alleviation and treatment of pulp inflammation.

VCL/ICAM-1 pathway is associated with lung inflammatory damage in SARS-CoV-2 Omicron infection

SARS-CoV-2 variants present diverse clinical manifestations, necessitating deeper insights into their pathogenic effects. This study employs multi-omics approaches to investigate the molecular mechanisms underlying SARS-CoV-2 infection, focusing on vascular damage. Plasma proteomic analysis of unvaccinated participants infected with Omicron BA.2.76 or ancestral variants identifies key signaling pathways associated with endothelial dysfunction, with the vinculin (VCL) pathway emerging as a hallmark of Omicron infections, contributing to lung exudation. Metabolomic analysis of plasma samples from the same cohort reveals disruptions in immune function, cell membrane integrity, and metabolic processes, including altered tricarboxylic acid cycle and glycolysis pathways. An integrated analysis of proteomic and metabolomic data underscores the role of VCL in inflammation and extravasation, highlighting its interactions with adhesion molecules and inflammatory metabolites. A validation cohort of plasma samples from Omicron-infected participants confirms this association by replicating proteomic analysis, showing elevated VCL levels correlated with inflammatory markers. Functional studies in a male rat model of lung injury demonstrate that anti-VCL intervention reduces plasma VCL levels, mitigates alveolar edema, and restores alveolar-capillary barrier integrity, as assessed by histological staining and electron microscopy, thereby illustrating VCL modulation's impact on vascular leakage and extravasation. These findings establish VCL as a potential therapeutic target for mitigating vascular complications in SARS-CoV-2 infections.

The effect of asparagine-13 in porcine epidemic diarrhea virus envelope protein on pathogenicity

The pathogenesis of porcine epidemic diarrhea virus (PEDV) has not been fully clarified, which seriously hinders the prevention of the disease. The envelope (E) protein of PEDV induces the expression of pro-inflammatory cytokines, but the role of these inflammatory reactions in PEDV pathogenicity is still unknown. In this study, the asparagine at position 13 was found to be crucial to PEDV E protein induced inflammatory response. Exogenously expressing the parent E protein, rather than the E mutant carrying N13A, induces the activation of NF-κB and expression of inflammatory factors, including IL-6, IL-8, and TNF-α. Compared with the parental rPEDV strain, the recombinant strain rPEDV-EN13A exhibited a significantly lower infectious titer and formed smaller plaques. In addition, rPEDV-EN13A induced lower expression of inflammatory factors in vitro and in vivo. The pathogenicity assay shows that the rPEDV-EN13A strain caused diminished fecal PEDV RNA shedding, delayed death time, and milder histopathological lesions to intestinal villi. Our data provide a unique perspective for exploring the pathogenic mechanism of PEDV and a new target for the development of attenuated PEDV live vaccines.

Chasing Virus Replication and Infection: PAMP-PRR Interaction Drives Type I Interferon Production, Which in Turn Activates ISG Expression and ISGylation

The innate immune response, particularly the interferon-mediated pathway, serves as the first line of defense against viral infections. During virus infection, viral pathogen-associated molecular patterns (PAMPs) are recognized by host pattern recognition receptors (PRRs), triggering downstream signaling pathways. This leads to the activation of transcription factors like IRF3, IRF7, and NF-κB, which translocate to the nucleus and induce the production of type I interferons (IFN-α and IFN-β). Once secreted, type I interferons bind to their receptors (IFNARs) on the surfaces of infected and neighboring cells, activating the JAK-STAT pathway. This results in the formation of the ISGF3 complex (composed of STAT1, STAT2, and IRF9), which translocates to the nucleus and drives the expression of interferon-stimulated genes (ISGs). Some ISGs exert antiviral effects by directly or indirectly blocking infection and replication. Among these ISGs, ISG15 plays a crucial role in the ISGylation process, a ubiquitin-like modification that tags viral and host proteins, regulating immune responses and inhibiting viral replication. However, viruses have evolved counteractive strategies to evade ISG15-mediated immunity and ISGylation. This review first outlines the PAMP-PRR-induced pathways leading to the production of cytokines and ISGs, followed by a summary of ISGylation's role in antiviral defense and viral evasion mechanisms targeting ISG15 and ISGYlation.

Maternal Immune Activation: Implications for Congenital Heart Defects

Congenital heart defects (CHD) are the most common major birth defects and one of the leading causes of death from congenital defects after birth. CHD can arise in pregnancy from the combination of genetic and non-genetic factors. The maternal immune activation (MIA) hypothesis is widely implicated in embryonic neurodevelopmental abnormalities. MIA has been found to be associated with the development of asthma, diabetes mellitus, and other diseases in the offspring. Given the important role of cardiac immune cells and cytokines in embryonic heart development, it is hypothesized that MIA may play a significant role in embryonic heart development. This review aims to stimulate further investigation into the relationship between MIA and CHD and to highlight the gaps in the knowledge. It evaluates the impact of MIA on CHD in the context of pregnancy complications, immune-related diseases, infections, and environmental and lifestyle factors. The review outlines the mechanisms by which immune cells and their secretome indirectly regulate the immuno-microenvironment of the embryonic heart by influencing placental development. Furthermore, the inflammatory cytokines cross the placenta to induce related reactions including oxidative stress in the embryonic heart directly. This review delineates the role of MIA in CHD and underscores the impact of maternal factors, especially immune factors, as well as the embryonic cardiac immuno-microenvironment, on embryonic heart development. This review extends our understanding of the importance of MIA in the pathogenesis of CHD and provides important insights into prenatal prevention and treatment strategies for this congenital condition.

The Yin and Yang of TLR4 in COVID-19

Various pattern recognition receptors (PRRs), including toll-like receptors (TLRs), play a crucial role in recognizing invading pathogens as well as damage-associated molecular patterns (DAMPs) released in response to infection. The resulting signaling cascades initiate appropriate immune responses to eliminate these pathogens. Current evidence suggests that SARS-CoV-2-driven activation of TLR4, whether through direct recognition of the spike glycoprotein (alone or in combination with endotoxin) or by sensing various TLR4-activating DAMPs or alarmins released during viral infection, acts as a critical mediator of antiviral immunity. However, TLR4 exerts a dual role in COVID-19, demonstrating both beneficial and deleterious effects. Dysregulated TLR4 signaling is implicated in the proinflammatory consequences linked to the immunopathogenesis of COVID-19. Additionally, TLR4 polymorphisms contribute to severity of the disease. Given its significant immunoregulatory impact on COVID-19 immunopathology and host immunity, TLR4 has emerged as a key target for developing inhibitors and immunotherapeutic strategies to mitigate the adverse effects associated with SARS-CoV-2 and related infections. Furthermore, TLR4 agonists are also being explored as adjuvants to enhance immune responses to SARS-CoV-2 vaccines.

Nintedanib improves bleomycin-induced pulmonary fibrosis by inhibiting the Clec7a/SPP1 pathway in interstitial macrophages

Idiopathic pulmonary fibrosis (IPF) is a terminal lung disease with high mortality rate. Although Nintedanib (Nin) is an effective treatment for IPF, its precise mechanism of action remains unclear. In this study, we performed an integrated analysis of single-cell sequencing and RNA-seq data from lung tissues of both fibrotic and Nin-treated fibrotic mice to uncover new therapeutic mechanisms of Nin in IPF. Our results revealed an increase in interstitial macrophages following bleomycin (BLM) treatment. We used Monocle2, Cellchat, and in vivo experiments to demonstrate that Nin can inhibit Clec7a in interstitial macrophages, thereby suppressing the SPP1-mediated profibrotic pathway. Additionally, we utilized Scenic to predict transcription factors and identified NFκB as a major transcription factor in interstitial macrophages. In the in vitro experiments, we found that inhibiting Clec7a improved the secretion of SPP1 by M2 macrophages through the NFκB pathway. In subsequent in vivo experiments, we found that inhibiting of Clec7a improves pulmonary fibrosis through the NFκB/SPP1 pathway, and Nin alleviated BLM-induced pulmonary fibrosis by inhibiting Clec7a in interstitial macrophages. In summary, our study indicates that interstitial macrophages are upregulated in pulmonary fibrosis, and Nin reduces fibrosis by inhibiting Clec7a in interstitial macrophages, which in turn diminishes the NFκB /SPP1 pathway. These findings provided a new perspective on the mechanism of action of Nin in treating pulmonary fibrosis.

Deficiency in platelet 12-lipoxygenase exacerbates inflammation and disease severity during SARS-CoV-2 infection

Platelets, known for maintaining blood balance, also participate in antimicrobial defense. Upon severeacute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, platelets become hyperactivated, releasing molecules such as cytokines, granule contents, and bioactive lipids. The key effector biolipids produced by platelets include 12-hydroxyeicosatetraenoic acid (12-HETE) and 12-hydroxyeicosatrienoic acid (12-HETrE), produced by 12-lipoxygenase (12-LOX), and prostaglandins and thromboxane, produced by cyclooxygenase-1. While prostaglandin E2 and thromboxane B2 were previously associated with lung inflammation in severe COVID-19, the role of platelet 12-LOX in SARS-CoV-2 infection remains unclear. Using mice deficient for platelets' 12-LOX, we report that SARS-CoV-2 infection resulted in higher lung inflammation characterized by histopathological tissue analysis, increased leukocyte infiltrates, and cytokine production relative to wild-type mice. In addition, distinct platelet and lung transcriptomic changes, including alterations in NOD-like receptor (NLR) family pyrin domain-containing 1 (NLRP1) inflammasome-related gene expression, were observed. Mass spectrometry lipidomic analysis in 12-LOX-deficient-infected mice revealed significant changes in bioactive lipid content, including reduced levels of 12-HETrE that inversely correlated with disease severity. Finally, platelet 12-LOX deficiency was associated with increased morbidity and lower survival rates relative to wild type (WT) mice. Overall, this study highlights the complex interplay between 12-LOX-related lipid metabolism and inflammatory responses during SARS-CoV-2 infection. The findings provide valuable insights into potential therapeutic targets aimed at mitigating severe outcomes, emphasizing the pivotal role of platelet enzymes in the host response to viral infections.

Cell death in acute lung injury: caspase-regulated apoptosis, pyroptosis, necroptosis, and PANoptosis

There has been abundant research on the variety of programmed cell death pathways. Apoptosis, pyroptosis, and necroptosis under the action of the caspase family are essential for the innate immune response. Caspases are classified into inflammatory caspase-1/4/5/11, apoptotic caspase-3/6/7, and caspase-2/8/9/10. Although necroptosis is not caspase-dependent to transmit cell death signals, it can cross-link with pyroptosis and apoptosis signals under the regulation of caspase-8. An increasing number of studies have reiterated the involvement of the caspase family in acute lung injuries caused by bacterial and viral infections, blood transfusion, and ventilation, which is influenced by noxious stimuli that activate or inhibit caspase engagement pathways, leading to subsequent lung injury. This article reviews the role of caspases implicated in diverse programmed cell death mechanisms in acute lung injury and the status of research on relevant inhibitors against essential target proteins of the described cell death mechanisms. The findings of this review may help in delineating novel therapeutic targets for acute lung injury.

Predicting coronavirus disease 2019 severity using explainable artificial intelligence techniques

Predictive models for determining coronavirus disease 2019 (COVID-19) severity have been established; however, the complexity of the interactions among factors limits the use of conventional statistical methods. This study aimed to establish a simple and accurate predictive model for COVID-19 severity using an explainable machine learning approach. A total of 3,301 patients ≥ 18 years diagnosed with COVID-19 between February 2020 and October 2022 were included. The discovery cohort comprised patients whose disease onset fell before October 1, 2020 (N = 1,023), and the validation cohort comprised the remaining patients (N = 2,278). Pointwise linear and logistic regression models were used to extract 41 features. Reinforcement learning was used to generate a simple model with high predictive accuracy. The primary evaluation was the area under the receiver operating characteristic curve (AUC). The predictive model achieved an AUC of ≥ 0.905 using four features: serum albumin levels, lactate dehydrogenase levels, age, and neutrophil count. The highest AUC value was 0.906 (sensitivity, 0.842; specificity, 0.811) in the discovery cohort and 0.861 (sensitivity, 0.804; specificity, 0.675) in the validation cohort. Simple and well-structured predictive models were established, which may aid in patient management and the selection of therapeutic interventions.

Interaction, diagnosis, and treatment of lung microbiota-NLRP3 inflammasome-target organ axis in sepsis

Sepsis is defined as a life-threatening condition caused by a dysregulated host response to infection, leading to multi-organ dysfunction, and representing a significant global health burden. The progression of sepsis is closely linked to disruptions in lung microbiota, including bacterial translocation, impaired barrier function, and local microenvironmental disturbances. Conversely, the worsening of sepsis exacerbates lung microbiota imbalances, contributing to multi-organ dysfunction. Recent culture-independent microbiological techniques have unveiled the complexity of the respiratory tract microbiome, necessitating a reassessment of the interactions between the host, microbes, and pathogenesis in sepsis. This review synthesizes current insights into the causes of microbiota dysbiosis and the regulatory mechanisms of the NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome, as well as their interactions during sepsis and sepsis-induced organ dysfunction. In addition, we summarize novel diagnostic and therapeutic approaches from the current study that may offer promising prospects for the management of sepsis.

Inflammasome Activation by RNA Respiratory Viruses: Mechanisms, Viral Manipulation, and Therapeutic Insights

Respiratory viruses, including SARS-CoV-2, influenza, parainfluenza, rhinovirus, and respiratory syncytial virus (RSV), are pathogens responsible for lower respiratory tract infections, particularly in vulnerable populations such as children and the elderly. Upon infection, these viruses are recognized by pattern recognition receptors, leading to the activation of inflammasomes, which are essential for mediating inflammatory responses. This review discusses the mechanisms by which these RNA respiratory viruses activate inflammasomes, emphasizing the roles of various signaling pathways and components involved in this process. Additionally, we highlight the specific interactions between viral proteins and inflammasome sensors, elucidating how these viruses manipulate the host immune response to facilitate infection. Understanding the dynamics of inflammasome activation in response to respiratory viruses provides critical insights for developing immunomodulatory therapeutic strategies aimed at mitigating inflammation and improving outcomes in respiratory tract infections.

Diverse strategies utilized by coronaviruses to evade antiviral responses and suppress pyroptosis

Viral infections trigger inflammasome-mediated caspase-1 activation. Nevertheless, limited understanding exists regarding how viruses use the active caspase-1 to evade host immune response. Here, we use porcine epidemic diarrhea virus (PEDV) as a model of coronaviruses (CoVs) to illustrate the intricate regulation of CoVs to combat IFN-I signaling and pyroptosis. Our findings demonstrate that PEDV infection stabilizes caspase-1 expression via papain-like protease PLP2's deubiquitinase activity. This stabilization of caspase-1 disrupts IFN-I signaling by cleaving RIG-I at the D189 residue. Furthermore, we demonstrate that 6-thioguanine (6TG), a PLP2 inhibitor, reverses the inhibitory effect on IFN-I signaling mediated by PLP2 and significantly reduces PEDV replication. Additionally, PLP2 degrades GSDMD-p30 by removing its K27-linked ubiquitin chain at K275 to restrain pyroptosis. Papain-like proteases from other genera of CoVs (PDCoV and SARS-CoV-2) have the similar activity to degrade GSDMD-p30. We further demonstrate that SARS-CoV-2 N protein induced NLRP3 inflammasome activation also uses the active caspase-1 to counter IFN-I signaling by cleaving RIG-I. Therefore, our work unravels a novel antagonistic mechanism employed by CoVs to evade host antiviral response.

Dissecting the COVID-19 Immune Response: Unraveling the Pathways of Innate Sensing and Response to SARS-CoV-2 Structural Proteins

Severe acute respiratory syndrome coronavirus (SARS-CoV), the virus responsible for COVID-19, interacts with the host immune system through complex mechanisms that significantly influence disease outcomes, affecting both innate and adaptive immunity. These interactions are crucial in determining the disease's severity and the host's ability to clear the virus. Given the virus's substantial socioeconomic impact, high morbidity and mortality rates, and public health importance, understanding these mechanisms is essential. This article examines the diverse innate immune responses triggered by SARS-CoV-2's structural proteins, including the spike (S), membrane (M), envelope (E), and nucleocapsid (N) proteins, along with nonstructural proteins (NSPs) and open reading frames. These proteins play pivotal roles in immune modulation, facilitating viral replication, evading immune detection, and contributing to severe inflammatory responses such as cytokine storms and acute respiratory distress syndrome (ARDS). The virus employs strategies like suppressing type I interferon production and disrupting key antiviral pathways, including MAVS, OAS-RNase-L, and PKR. This study also explores the immune pathways that govern the activation and suppression of immune responses throughout COVID-19. By analyzing immune sensing receptors and the responses initiated upon recognizing SARS-CoV-2 structural proteins, this review elucidates the complex pathways associated with the innate immune response in COVID-19. Understanding these mechanisms offers valuable insights for therapeutic interventions and informs public health strategies, contributing to a deeper understanding of COVID-19 immunopathogenesis.

Regorafenib as a potential drug for severe COVID-19: inhibition of inflammasome activation in mice

SARS-CoV-2 infection can lead to severe COVID-19, particularly in elderly individuals and those with compromised immunity. Cellular senescence has been implicated as a key pathogenic mechanism. This study investigated the therapeutic potential of regorafenib, a previously characterized senomorphic drug, for severe COVID-19. SARS-CoV-2 virus-infected K18-hACE2 mice, overexpressing the human ACE2 receptor, exhibited 100% mortality by 10 days post infection. Regorafenib treatment significantly improved survival rates, approximately 43% remaining alive. Mechanistically, regorafenib effectively suppressed type I and II interferon and cytokine signaling. Notably, regorafenib inhibited NLR family pyrin domain containing 3 (NLRP3) inflammasome activation, a key driver of the cytokine storm associated with severe COVID-19. Our findings elucidate the molecular mechanisms underlying therapeutic effects of regorafenib and suggest its potential use as a promising treatment option for severe COVID-19.

Suppression of NLRP3 inflammasome by a small molecule targeting CK1α-β-catenin-NF-κB and CK1α-NRF2-mitochondrial OXPHOS pathways during mycobacterial infection

Introduction

Pyroptosis is an important inflammatory form of cell death and Mycobacterium tuberculosis (M.tb) chronic infection triggers excessive inflammatory pyroptosis of macrophages. Our previous research has confirmed that a small compound pyrvinium pamoate (PP) could inhibit inflammatory pathological changes and mycobacterial burden in M.tb-infected mice, but the potential mechanism of PP for inhibiting M.tb-induced inflammation remains unexplored.

Methods

The effects of PP on the NLRP3-ASC-Casp1 inflammasome assembly and activation, gasdermin D (GSDMD) mediated pyroptosis and inflammatory cytokines expression were assessed in human THP-1-derived macrophages after M.tb H37Rv/H37Ra/ Salmonella typhimurium (S. typhimurium) infection or LPS treatment by Transcriptome sequencing, RT-qPCR, Co-immunoprecipitation and Western Blot (WB) analysis. The lactate dehydrogenase (LDH) release assay was used to evaluate the CC50 of PP in M.tb-infected THP-1 cells.

Results

We found that M.tb/S. typhimurium infection and LPS treatment significantly activate NLRP3-ASC-Casp1 inflammasome activation, GSDMD-mediated pyroptosis and inflammatory cytokines (IL-1β and IL-18) expression in macrophages, whereas PP could suppress these inflammatory effects in a dose dependent manner. Regarding the PP-inhibition mechanism, we further found that this inhibitory activity is mediated through the PP-targeting casein kinase 1A1 (CK1α)-β-catenin-NF-κB pathway and CK1α-NRF2-mitochondrial oxidative phosphorylation (OXPHOS) pathway. In addition, a CK1α specific inhibitor D4476 or CK1α siRNA could reverse these inhibitory effects of PP on bacteria-induced inflammatory responses in macrophages.

Conclusions

This study reveals a previously unreported mechanism that pyrvinium can inhibit NLRP3 inflammasome and GSDMD-IL-1β inflammatory pyroptosis via targeting suppressing CK1α-β-catenin-NF-κB and CK1α-NRF2-mitochondrial OXPHOS pathways, suggesting that pyrvinium pamoate holds great promise as a host directed therapy (HDT) drug for mycobacterial-induced excessive inflammatory response.

Promotion of NLRP3 autophagosome degradation by PV-K nanodevice for protection against macrophage pyroptosis-mediated lung injury

Acute respiratory distress syndrome (ARDS) has emerged as a significant global health challenge, with no definitive curative treatment available. Recent evidence suggests that pyroptosis of immune cells plays a pivotal role in the pathogenesis of ARDS. Targeting and modulating immune cell pyroptosis in lung tissue may offer a promising strategy to mitigate the harmful inflammation associated with this condition. In this study, we designed and synthesized a novel class of peptide-functionalized nanoparticles, PV-K, which possess an intrinsic capacity for phagocytosis by macrophages. Concurrently, the incorporation of two FFD functional groups into a single polypeptide enhances the biological activity of PV-K. Amazingly, PV-K demonstrated potent inhibitory effects on nucleotide-binding domain, leucine-rich repeat, and pyrin domain-containing protein 3 (NLRP3)-mediated pyroptosis in both mouse bone marrow-derived macrophages and the human THP-1 cell-derived macrophages. In both lipopolysaccharide and cecal ligation and puncture induced acute lung injury mouse models, treatment with PV-K significantly reduced disease severity by alleviating pulmonary inflammation and inhibiting macrophage pyroptosis. Transcriptomic analysis revealed that PV-K enhanced SQSM1/p62-mediated autophagy through upregulation of the NRF2 signaling pathway. Mechanistically, PV-K facilitated the interaction between SQSTM1/p62 and NLRP3, promoting the autolysosomal degradation of NLRP3. Notably, the inhibitory effect of PV-K on macrophage pyroptosis during acute lung injury was abrogated in Nrf2-/- mice. This study introduces a novel nanotherapeutic approach aiming at regulating macrophage pyroptosis by facilitating NLRP3 degradation, thereby controlling inflammation in ARDS/ALI. This strategy may complement existing clinical treatments for ARDS/ALI.

Structure of the human TWIK-2 potassium channel and its inhibition by pimozide

The potassium channel TWIK-2 is crucial for ATP-induced activation of the NLRP3 inflammasome in macrophages. The channel is a member of the two-pore domain potassium (K2P) channel superfamily and an emerging therapeutic target to mitigate severe inflammatory injury involving NLRP3 activation. We report the cryo-EM structure of human TWIK-2. In comparison to other K2P channels, the structure reveals a unique 'up' conformation of Tyr111 in the selectivity filter and a SF1-P1 pocket behind the filter that could serve as a binding site for channel modulators. Density for acyl chains is present in fenestrations within the transmembrane region that connect the central cavity of the pore to the lipid membrane. Limited pharmacological tools are available for TWIK-2 despite its importance as a drug target. We show that the small molecule pimozide inhibits TWIK-2 and determine a structure of the channel with pimozide. Pimozide displaces the acyl chains and binds below the selectivity filter to block ion conduction. The drug may access its binding site via the membrane, suggesting that other hydrophobic small molecules could have utility for inhibiting TWIK-2. The work defines the structure of TWIK-2 and provides a structural foundation for development of specific inhibitors with potential utility as anti-inflammatory drugs.

Significance Statement

The TWIK-2 potassium channel is a member of the two-pore domain potassium (K2P) channel superfamily and a potential therapeutic target to control severe inflammatory injury involving the NLRP3 inflammasome. We report the cryo-EM structure of the human TWIK-2 channel at 2.85 Å resolution, revealing differences in comparison to other K2P channels. We identify that pimozide, an FDA-approved drug for Tourette syndrome, inhibits TWIK-2. A cryo-EM structure of TWIK-2 in complex with pimozide identifies its binding location and mechanism of inhibition. The work provides a structural foundation for development of specific TWIK-2 inhibitors that have potential therapeutic utility for inflammatory diseases involving NLRP3 activation.

Identification of anti-inflammatory and anti-cancer compounds targeting the NF-κB-NLRP3 inflammasome pathway from a phytochemical library of the Sideritis genus

ETHNOBOTANICAL RELEVANCE

For centuries, the aerial parts of Sideritis species have been known for their medicinal properties as herbal teas. Although the antioxidant and anti-inflammatory properties of the genus have been widely documented, the underlying mechanisms are yet to be sufficiently clarified.

AIM OF THE STUDY

We investigated the anti-inflammatory and anticancer activities of phytochemicals of the Sideritis genus.

MATERIAL AND METHODS

Through literature mining, a chemical library containing 657 components of the Sideritis genus was formed. We studied these compounds for binding to NLRP3 and NF-κB proteins in silico by virtual drug screening and molecular docking, and in vitro by microscale thermophoresis (MST). Liquid chromatography-high-resolution mass spectrometry analysis (LC-HRMS) was performed in the Sideritis extracts. One of the identified compounds, verbascoside, was investigated for its cytotoxic activity by mining a panel of 49 tumor cell lines in the data repository of the National Cancer Institute (NCI, USA).

RESULTS

Virtual screening and molecular docking results highlighted two compounds targeting both proteins of interest, i.e., verbascoside (acteoside) and apigenin 7,4'-bis(trans-p-coumarate), as both had lowest binding energies of less than -10 kcal/mol. Using MST, we then verified that both compounds bound to the target proteins. Verbascoside bound to NLRP3 and NF-κB with Kd values of 0.67 ± 0.18 μM and 0.01 ± 0.08 μM, while apigenin 7,4'-bis(trans-p-coumarate) had Kd values of 4.60 ± 1.66 μM and 0.27 ± 0.75 μM, respectively. Verbascoside was abundant in the Sideritis extracts, according to LC-HRMS analysis. Since inflammation is strongly related to carcinogenesis, we investigated the anticancer activity of verbascoside in the second part of this study. We investigated the activity of verbascoside in 49 tumor cell lines of the NCI. Comparing its activity with 81 standard anticancer drugs revealed numerous interactions with DNA-damaging agents (alkylators, topoisomerase I/II inhibitors, antimetabolites), indicating that verbascoside may also affect the DNA of tumor cells. We further investigated the involvement of verbascoside in several main drug resistance mechanisms, i.e., ABC transporters, oncogenes, tumor suppressors, cellular proliferation rates, and other parameters. Except for the correlation to the mutational status of NRAS, no other significant relationships were found, indicating that verbascoside is not involved in most of the common drug resistance mechanisms. Two-dimensional cluster analysis-based heatmap generation of a proteomic profile from 40 out of 3171 proteins revealed a significant correlation between the expression of these proteins in 49 tumor cell lines, and the cellular response to verbascoside. This indicates that the presence of these proteins is a determinant for sensitivity or resistance to this natural product.

CONCLUSION

The database established here represents a valuable resource for the screening of bioactivites of the Sideritis genus. The experimental validation of the anti-inflammatory and cytotoxic activities of selected compounds proved that virtual drug screening and molecular docking are suitable tools for the identification of putative drug candidates. Verbascoside was among the top 10 compounds binding to two key anti-inflammatory proteins, NLRP3 and NF-kB. Additionally, data from the NCI indicate that verbascoside is not linked to main drug resistance mechanisms.

Antibody-dependent enhancement of coronaviruses

The COVID-19 pandemic presents a significant challenge to the global health and the world economy, with humanity engaged in an extended struggle against the virus. Notable advancements have been achieved in the development of vaccines and therapeutic interventions, including the application of neutralizing antibodies (NAbs) and convalescent plasma (CP). While antibody-dependent enhancement (ADE) has not been observed in human clinical studies related to SARS-CoV-2, the potential for ADE remains a critical concern and challenge in addressing SARS-CoV-2 infections. Moreover, the causal relationship between ADE and viral characteristics remains to be clearly elucidated. Viruses that present with severe clinical manifestations of ADE have demonstrated the capacity to replicate in macrophages or other immune cells, or to alter the immunological status of these cells, which induces abortive infections characterized by systemic inflammation. In this review, we summarize experimental observations and clinical evidence concerning the ADE effect associated with coronaviruses. We critically examine the potential mechanisms through which coronaviruses mediate ADE, and propose strategies to mitigate this phenomenon in the context of viral infection treatment. Our aim is to offer informed recommendations for the containment of the COVID-19 pandemic and to strengthen the response to SARS-CoV-2, as well as to prepare for potential future coronavirus threats.

A Heparan Sulfate Mimetic RAFT Copolymer Inhibits SARS-CoV-2 Infection and Ameliorates Viral-Induced Inflammation

The high transmissibility and mutation ability of coronaviruses enable them to easily escape existing immune protection and also pose a challenge to existing antiviral drugs. Moreover, drugs only targeting viruses cannot always attenuate the "cytokine storm". Herein, a synthetic heparan sulfate (HS) mimetic, HMSA-06 is reported, that exhibited antiviral activities against both the SARS-CoV-2 prototype and Omicron strains by targeting viral entry and replication. Of particular note, HMSA-06 demonstrated more potent anti-SARS-CoV-2 effects than PG545 and Roneparstat. SARS-CoV-2 is reported to hijack autophagy to facilitate its replication, therefore boosting autophagy can attenuate SARS-CoV-2 infection. It is revealed that HMSA-06, but not a similar HS mimetic that failed to inhibit SARS-CoV-2, can upregulate cellular autophagy flux. In addition, HMSA-06 was found to robustly block the NLRP3-mediated inflammatory reaction in SARS-CoV-2 infected THP-1 derived macrophages as evidenced by a reduction in inflammasome formation and the subsequent decreased secretion of mature caspase-1 and IL-1β. The HMSA-06's inflammation inhibitory function is further confirmed using a LPS/ATP-stimulated THP-1 macrophage model. Altogether, this study has identified a promising HS mimetic to combat SARS-CoV-2-associated diseases by inhibiting viral infection and attenuating viral-induced inflammatory reaction, providing insights into the development of novel anti-coronavirus drugs in the future.

ABHD8 antagonizes inflammation by facilitating chaperone-mediated autophagy-mediated degradation of NLRP3

The NLRP3 inflammasome is a multiprotein complex that plays a vital role in the innate immune system in response to microbial infections and endogenous danger signals. Aberrant activation of the NLRP3 inflammasome is implicated in a spectrum of inflammatory and autoimmune diseases, emphasizing the necessity for precise regulation of the NLRP3 inflammasome to maintain immune homeostasis. The protein level of NLRP3 is a limiting step for inflammasome activation, which must be tightly controlled to avoid detrimental consequences. Here, we demonstrate that ABHD8, a member of the α/β-hydrolase domain-containing (ABHD) family, interacts with NLRP3 and promotes its degradation through the chaperone-mediated autophagy (CMA) pathway. ABHD8 acts as a scaffold to recruit palmitoyltransferase ZDHHC12 to NLRP3 for its palmitoylation as well as subsequent CMA-mediated degradation. Notably, ABHD8 deficiency results in the stabilization of NLRP3 protein and promotes NLRP3 inflammasome activation. We further confirm that ABHD8 overexpression ameliorates LPS- or alum-triggered NLRP3 inflammasome activation in vivo. Interestingly, the nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) impairs the ABHD8-NLRP3 association, resulting in an elevation in NLRP3 protein level and excessive inflammasome activation. These findings demonstrate that ABHD8 May represent a potential therapeutic target in conditions associated with NLRP3 inflammasome dysregulation.Abbreviations: 3-MA: 3-methyladenine; ABHD: α/β-hydrolase domain-containing; BMDMs: Bone marrow-derived macrophages; CFZ: carfilzomib; CHX: cycloheximide; CMA: chaperone-mediated autophagy; CQ: chloroquine; DAMPs: danger/damage-associated molecular patterns; HSPA8/HSC70: heat shock protein family A (Hsp70) member 8; LAMP2A: lysosomal associated membrane protein 2A; NH4Cl: ammonium chloride; NLRP3: NLR family pyrin domain containing 3; PAMPs: pathogen-associated molecular patterns; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2.

Monoclonal antibody development and antigenic epitope identification of chicken pro-IL-1β

Pro-IL-1β is an important inflammatory factor and is also a biomarker for detecting early pro-inflammatory immune responses. However, commercially available antibodies against chicken inflammatory factors are lacking, which prohibits an in-depth exploration of the mechanism of chicken inflammation. This study cloned and expressed chicken pro-IL-1β, and developed a hybridoma cell line 1E12 capable of stably secreting chicken pro-IL-1β monoclonal antibody (mAb). The secreted mAb 1E12 can recognize exogenous or endogenous chicken pro-IL-1β by Western blot and IFA techniques, and for the first time, a novel antigen epitope 13SSLSEETFY21 of chicken pro-IL-1β recognized by this mAb was identified. This study not only provides an important tool for the detection and research of chicken pro-IL-1β, but also has significant implications for understanding the antigenic structure and biochemical characteristics of chicken pro-IL-1β.

Induction of the Inflammasome by the SARS-CoV-2 Accessory Protein ORF9b, Abrogated by Small-Molecule ORF9b Homodimerization Inhibitors

Viral accessory proteins play critical roles in viral escape from host innate immune responses and in viral inflammatory pathogenesis. Here we show that the SARS-CoV-2 accessory protein, ORF9b, but not other SARS-CoV-2 accessory proteins (ORF3a, ORF3b, ORF6, ORF7, ORF8, ORF9c, and ORF10), strongly activates inflammasome-dependent caspase-1 in A549 lung carcinoma cells and THP-1 monocyte-macrophage cells. Exposure to lipopolysaccharide (LPS) and ATP additively enhanced the activation of caspase-1 by ORF9b, suggesting that ORF9b and LPS follow parallel pathways in the activation of the inflammasome and caspase-1. Following rational in silico approaches, we have designed small molecules capable of inhibiting the homodimerization of ORF9b, which experimentally inhibited ORF9b-ORF9b homotypic interactions, caused mitochondrial eviction of ORF9b, inhibited ORF9b-induced activation of caspase-1 in A549 and THP-1 cells, cytokine release in THP-1 cells, and restored type I interferon (IFN-I) signaling suppressed by ORF9b in both cell models. These small molecules are first-in-class compounds targeting a viral accessory protein critical for viral-induced exacerbated inflammation and escape from innate immune responses, with the potential of mitigating the severe immunopathogenic damage induced by highly pathogenic coronaviruses and restoring antiviral innate immune responses curtailed by viral infection.

Caspase family in autoimmune diseases

Programmed cell death (PCD) plays a crucial role in maintaining tissue homeostasis, with its primary forms including apoptosis, pyroptosis, and necroptosis. The caspase family is central to these processes, and its complex functions across different cell death pathways and other non-cell death roles have been closely linked to the pathogenesis of autoimmune diseases. This article provides a comprehensive review of the role of the caspase family in autoimmune diseases such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), type 1 diabetes (T1D), and multiple sclerosis (MS). It particularly emphasizes the intricate functions of caspases within various cell death pathways and their potential as therapeutic targets, thereby offering innovative insights and a thorough discussion in this field. In terms of therapy, strategies targeting caspases hold significant promise. We emphasize the importance of a holistic understanding of caspases in the overall concept of cell death, exploring their unique functions and interrelationships across multiple cell death pathways, including apoptosis, pyroptosis, necroptosis, and PANoptosis. This approach transcends the limitations of previous studies that focused on singular cell death pathways. Additionally, caspases play a key role in non-cell death functions, such as immune cell activation, cytokine processing, inflammation regulation, and tissue repair, thereby opening new avenues for the treatment of autoimmune diseases. Regulating caspase activity holds the potential to restore immune balance in autoimmune diseases. Potential therapeutic approaches include small molecule inhibitors (both reversible and irreversible), biological agents (such as monoclonal antibodies), and gene therapies. However, achieving specific modulation of caspases to avoid interference with normal physiological functions remains a major challenge. Future research must delve deeper into the regulatory mechanisms of caspases and their associated complexes linked to PANoptosis to facilitate precision medicine. In summary, this article offers a comprehensive and in-depth analysis, providing a novel perspective on the complex roles of caspases in autoimmune diseases, with the potential to catalyze breakthroughs in understanding disease mechanisms and developing therapeutic strategies.

The Tan-Re-Qing Capsule mitigates acute lung injury by suppressing the NLRP3 inflammasome and MAPK/NF-κB signaling pathways

OBJECTIVE

The Tan-Re-Qing Capsule (TRQC), a traditional Chinese medicine (TCM) preparation, has been historically utilized in treating acute lung injury (ALI) and COVID-19-induced pulmonary diseases. This study aimed to explore the effect and underlying mechanisms of TRQC in lipopolysaccharide (LPS)-induced ALI models.

METHODS

The changes of acute lung injury and inflammatory response were observed after TRQC treatment of the LPS-induced ALI mouse model. Based on active compounds in TRQC and network pharmacology analysis, potential targeting signals were identified. The effects of TRQC on signaling in LPS-stimulated BMDMs were investigated. Additionally, the defecatory status of mice and the mechanism of Cl- secretion in HBE cells and T84 colonic epithelial cells were examined.

RESULTS

TRQC exhibited a notable amelioration of inflammatory injuries in ALI mice. Utilizing a systems-pharmacology approach based on active chemical compounds, TRQC was found to regulate inflammation-related pathways, including NF-κB, NOD-like signaling, and MAPK signaling. In vitro experiments demonstrated that TRQC effectively suppressed LPS-induced activation of macrophages and the assembly of the NLRP3 inflammasome induced by LPS and Nigericin. These effects were attributed to the suppression of NF-κB and NOD-like signaling pathways. Furthermore, TRQC blocked MAPK signaling, thereby mitigating the inhibitory effects of LPS and Nigericin on Ca2+-dependent Cl- efflux across colonic epithelial cells. This mechanism generated a cathartic effect, potentially aiding in the removal of harmful substances and pathogenic bacteria.

CONCLUSION

Our study demonstrates that TRQC significantly mitigates ALI by effectively suppressing the NLRP3 inflammasome and MAPK/NF-κB signaling pathways. These findings suggest that TRQC could serve as a promising therapeutic candidate for inflammatory lung diseases, offering a novel approach to managing conditions like ALI and potentially extending to other inflammatory diseases.

Caspase-1 activation, IL-1/IL-6 signature and IFNγ-induced chemokines in lungs of COVID-19 patients

Rationale

COVID-19-associated acute-respiratory distress syndrome (C-ARDS) results from a direct viral injury associated with host excessive innate immune response mainly affecting the lungs. However, cytokine profile in the lung compartment of C-ARDS patients has not been widely studied, nor compared to non-COVID related ARDS (NC-ARDS).

Objectives

To evaluate caspase-1 activation, IL-1 signature, and other inflammatory cytokine pathways associated with tissue damage using post-mortem lung tissues, bronchoalveolar lavage fluids (BALF), and serum across the spectrum of COVID-19 severity.

Methods

Histological features were described and activated-caspase-1 labeling was performed in 40 post-mortem biopsies. Inflammatory cytokines were quantified in BALF and serum from 19 steroid-treated-C-ARDSand compared to 19 NC-ARDS. Cytokine concentrations were also measured in serum from 128 COVID-19 patients at different severity stages.

Measurements and main results

Typical "diffuse alveolar damage" in lung biopsies were associated with activated caspase-1 expression and vascular lesions. Soluble Caspase-1p20, IL-1β, IL-1Ra, IL-6 and at lower level IFNγ and CXCL-10, were highly elevated in BALF from steroid-treated-C-ARDS as well as in NC-ARDS. IL-1β appeared concentrated in BALF, whereas circulating IL-6 and IL-1Ra concentrations were comparable to those in BALF and correlated with severity. TNFα, TNFR1 and CXCL8 however, were significantly higher in NC-ARDS compared to C-ARDS, treated by steroid.

Conclusions

In the lungs of C-ARDS, both caspase-1 activation with a predominant IL-1β/IL-6 signature and IFNγ -associated chemokines are elevated despite steroid treatment. These pathways may be specifically targeted in ARDS to improve response to treatment and to limit alveolar and vascular lung damage.

Progesterone suppresses rhinovirus-induced airway inflammation by inhibiting neutrophil infiltration and extracellular traps formation

BACKGROUND

The process of NETosis is observed in a range of inflammatory conditions. Progesterone (P4) has been shown to alleviate inflammation caused by viral infections such as influenza and SARS-CoV-2. However, the precise molecular mechanisms responsible for this effect are not yet fully understood. Therefore, the present investigation aims to explore whether P4 can exert its anti-inflammatory properties by inhibiting NETosis and the related molecular pathways.

METHODS

Airway inflammation caused by rhinovirus serotype-1b (RV-1b) was induced in male BALB/c mice. The inflammation was assessed through histological examination and calculation of inflammatory cells present in the bronchoalveolar lavage fluid. Flow cytometry was used to analyze the inflammatory cells and NETotic neutrophils. Western blotting analysis was conducted to detect proteins associated with NETosis, inflammasome activation, and signaling. Furthermore, confocal microscopy was utilized to observe neutrophil extracellular trap (NET) structures in vivo tissues and in vitro neutrophils, neutrophil infiltration, and inflammasome formation.

RESULTS

The administration of P4 proved to be an effective treatment for reducing airway inflammation and the production of NETs caused by RV-1b infection. The infection triggered the activation of NLRP3 inflammasomes in neutrophils, which led to the maturation of IL-1β and subsequent activation of both the NF-κB and p38 signaling pathways. The activation of NF-κB signaling resulted in the secretion of downstream chemokines CCL3 and IL-6, which led to an increase in neutrophil infiltration into the lung airways. Moreover, the activation of p38 signaling led to the generation of reactive oxygen species, resulting in NETosis. However, the administration of P4 inhibited the activation of the NLRP3 inflammasome, which subsequently led to the deactivation of both the IL-1β-NF-κB and IL-1β-p38 axes. As a result, there was a reduction in neutrophil infiltration and NETosis. Furthermore, TGF-β-activated kinase 1 (TAK1) was identified as an intermediary enzyme. P4 inhibits both the NF-κB and IL-1β-p38 pathways by suppressing the activity of TAK1.

CONCLUSION

The capacity of P4 to mitigate rhinovirus-induced airway inflammation is attributed to its ability to impede the infiltration of neutrophils and NETosis. As inflammation mediated by NETosis is widespread in diverse disorders, our findings propose that P4 could potentially function as a universal therapeutic agent in the management of such ailments.

SARS-CoV-2 specific adaptations in N protein inhibit NF-κB activation and alter pathogenesis

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and severe acute respiratory syndrome coronavirus (SARS-CoV) exhibit differences in their inflammatory responses and pulmonary damage, yet the specific mechanisms remain unclear. Here, we discovered that the SARS-CoV-2 nucleocapsid (N) protein inhibits the activation of the nuclear factor-κB (NF-κB) pathway and downstream signal transduction by impeding the assembly of the transforming growth factor β-activated kinase1 (TAK1)-TAK1 binding protein 2/3 (TAB2/3) complex. In contrast, the SARS-CoV N protein does not impact the NF-κB pathway. By comparing the amino acid sequences of the SARS-CoV-2 and SARS-CoV N proteins, we identified Glu-290 and Gln-349 as critical residues in the C-terminal domain (CTD) of the SARS-CoV-2 N protein, essential for its antagonistic function. These findings were further validated in a SARS-CoV-2 trans-complementation system using cellular and animal models. Our results reveal the distinctions in inflammatory responses triggered by SARS-CoV-2 and SARS-CoV, highlighting the significance of specific amino acid alterations in influencing viral pathogenicity.

The R203M and D377Y mutations of the nucleocapsid protein promote SARS-CoV-2 infectivity by impairing RIG-I-mediated antiviral signaling

The viral protein mutations can modify virus-host interactions during virus evolution, and thus alter the extent of infection or pathogenicity. Studies indicate that nucleocapsid (N) protein of SARS-CoV-2 participates in viral genome assembly, intracellular signal regulation and immune interference. However, its biological function in viral evolution is not well understood. SARS-CoV-2 N protein mutations were analyzed in Delta, Omicron, and original strains. Two mutations with a methionine (M) residue at site 203 and a tyrosine (Y) residue at site 377 of the N protein were found in Delta strain but not in Omicron and original strains, and promoted SARS-CoV-2 infection therein. Those mutations, R203M and D377Y, enhanced the inhibitory impact of N protein on the impairment of RIG-I-mediated antiviral signaling, such as IRF3 phosphorylation and IFN-β activation. The viral RNA-binding activity of N protein was promoted by these mutations, effectively attenuating the recognition and interaction of RIG-I with viral RNA compared to the original or other variants. The R203M/D377Y mutations thus enhanced the suppressive activity of the N protein on RIG-I-mediated interferon induction both in vitro and in vivo, which in turn promoted viral replication. This study helps to understand the variability of SARS-CoV-2 in regulating host immunity.

A20 as a Potential Therapeutic Target for COVID-19

BACKGROUND

Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a major concern due to its astonishing prevalence and high fatality rate, especially among elderly people. Patients suffering from COVID-19 may exhibit immunosuppression in the initial stage of infection, while a cytokine storm can occur when the disease progresses to a severe stage. This inopportune immune rhythm not only makes patients more susceptible to the virus but also leads to numerous complications resulting from the excessive production of inflammatory factors. A20, which is widely accepted as a pivotal regulator of inflammation, has been shown to be implicated in the processes of antiviral responses and immunosuppression. Thus, A20 may participate in regulating the pathological processes of COVID-19.

METHODS

This narrative literature review summarizes recent evidence on the mechanisms of A20 in regulating the pathological processes of COVID-19. We also downloaded single-cell RNA-seq data sets from healthy individuals and patients with varying severities of COVID-19 from the NCBI GEO database to further dissect A20's regulatory mechanisms of these intricate cytokine pathways that are closely associated with SARS-CoV-2 infection.

RESULTS

A20 might be one of the most critical anti-infectious and anti-inflammatory factors involved in the pathogenesis of COVID-19. It effectively suppresses the immune damage and inflammatory storm caused by viral infection.

CONCLUSIONS

Understanding the relationship between A20-regulated signaling pathways and pathological processes of COVID-19 can provide insight into potential targets for intervention. Precise regulation of A20 to induce antiviral activity and an anti-inflammatory response could mediate the pathogenesis of COVID-19 and could become an effective treatment.

Overexpression of Parkin promotes the protective effect of mitochondrial autophagy on the lung of rats with exertional heatstroke

Background

The roles of the Pink1/Parkin pathway and mitophagy in lung injury during heat stroke remain unclear. In this study, we investigated the role of Pink1/Parkin-mediated mitophagy in acute lung injury (ALI) in rats with exertional heat stroke (EHS).

Methods

Sixty Sprague Dawley rats were randomly divided into control (CON), control + Parkin overexpression (CON + Parkin), EHS, and EHS + Parkin overexpression (EHS + Parkin) groups. Parkin was overexpressed by injecting an adeno-associated virus carrying the Parkin gene into the tail vein, and a rat model of EHS was established. Pathological changes in the lung tissue were analyzed using microcomputed tomography (micro-CT), and the lung coefficient and pulmonary capillary permeability were measured. Enzyme-linked immunosorbent assay were used to determine the levels of interleukin-6 (IL-6), IL-1β, and tumor necrosis factor-α, and reactive oxygen species. The morphology of mitochondria in type Ⅱ epithelial cells of lung tissue was observed using transmission electron microscopy; and the apoptosis of lung tissue, the level of mitophagy, and the co-localization of Pink1 and Parkin were determined using immunofluorescence. The expression of Pink1, Parkin, mitofusin-2 (MFN2), phosphatase and tensin homolog (PTEN), PTEN-L, p62, and the autophagy marker microtubule-associated protein 1 light chain 3 (LC3) in rat lung tissue was measured by Western blotting, and the ratio of LC3II/LC3I was calculated.

Results

Compared with the EHS group, the survival rate of rats in the EHS + Parkin group was significantly higher. Their lung coefficient and pulmonary vascular permeability decreased and the pathological changes were significantly alleviated (P <0.05). Their levels of inflammatory factors and reactive oxygen species were significantly decreased (P <0.05), and the degree of mitochondrial swelling in pulmonary type II epithelial cells was alleviated. The apoptosis of lung tissue was alleviated, the colocalization of Pink1 and Parkin, LC3 and Tom20 was enhanced, and the ratio of LC3-II/LC3-I increased. The expression of Pink1, MFN2, PTEN-L, and p62 decreased, whereas the expression of PTEN was not significantly different from that in the EHS group (P >0.05).

Conclusion

Pink1/Parkin-mediated mitophagy dysfunction is one of the mechanisms underlying ALI in rats with EHS, and activation of Parkin overexpression-mediated mitophagy can alleviate ALI caused by EHS.

PRRSV-2 nsp2 Ignites NLRP3 inflammasome through IKKβ-dependent dispersed trans-Golgi network translocation

The NLRP3 inflammasome is a fundamental component of the innate immune system, yet its excessive activation is intricately associated with viral pathogenesis. Porcine reproductive and respiratory syndrome virus type 2 (PRRSV-2), belonging to the family Arteriviridae, triggers dysregulated cytokine release and interstitial pneumonia, which can quickly escalate to acute respiratory distress and death. However, a mechanistic understanding of PRRSV-2 progression remains unclear. Here, we screen that PRRSV-2 nsp2 activates the NLRP3 inflammasome, thereby instigating a state of hyperinflammation. Mechanistically, PRRSV-2 nsp2 interacts with the nucleotide-binding and oligomerization (NACHT) domain of NLRP3, augmenting IKKβ recruitment to driving NLRP3 translocation to the dispersed trans-Golgi network (dTGN) for oligomerization. This process facilitates ASC polymerization, culminating in the activation of the NLRP3 inflammasome. In addition, the IKKβ-dependent NLRP3 translocation to the dTGN is pivotal for pseudorabies virus (PRV) and encephalomyocarditis virus (EMCV)-induced inflammatory responses. Collectively, these results elucidate a novel mechanism of NLRP3 inflammasome activation during PRRSV-2 infection, providing valuable insights into PRRSV-2 pathogenesis.

SARS-CoV-2 3CLpro (main protease) regulates caspase activation of gasdermin-D/E pores leading to secretion and extracellular activity of 3CLpro

SARS-CoV-2 3C-like protease (3CLpro or Mpro) cleaves the SARS-CoV-2 polyprotein and >300 intracellular host proteins to enhance viral replication. By lytic cell death following gasdermin (GSDM) pore formation in cell membranes, antiviral pyroptosis decreases 3CLpro expression and viral replication. Unexpectedly, 3CLpro and nucleocapsid proteins undergo unconventional secretion from infected cells via caspase-activated GSDMD/E pores in the absence of cell lysis. Bronchoalveolar lavage fluid of wild-type SARS-CoV-2-infected mice contains 3CLpro, which decreases in Gsdmd-/-Gsdme-/- mice. We identify new 3CLpro cut-sites in GSDMD at LQ29↓30SS, which blocks pore formation by 3CLpro cleavage at LH270↓N lying adjacent to the caspase activation site (NFLTD275↓G). Cleavage inactivation of GSDMD prevents excessive pore formation, thus countering antiviral pyroptosis and increasing 3CLpro secretion. Extracellular 3CLpro retains activity in serum, dampens platelet activation and aggregation, and inactivates antiviral interferon-λ1. Thus, in countering gasdermin pore formation and pyroptosis in SARS-CoV-2 infection, 3CLpro is secreted with extracellular pathological sequelae.

The role of inflammatory gene polymorphisms in severe COVID-19: a review

The COVID-19 pandemic, caused by the novel coronavirus SARS-CoV-2, has profoundly impacted global healthcare systems and spurred extensive research efforts over the past three years. One critical aspect of the disease is the intricate interplay between the virus and the host immune response, particularly the role of inflammatory gene expression in severe COVID-19. While numerous previous studies have explored the role of genetic polymorphisms in COVID-19, research specifically focusing on inflammatory genes and their associations with disease severity remains limited. This review explores the relationship between severe COVID-19 outcomes and genetic polymorphisms within key inflammatory genes. By investigating the impact of genetic variations on immune responses, which include cytokine production and downstream signalling pathways, we aim to provide a comprehensive overview of how genetic polymorphisms contribute to the variability in disease presentation. Through an in-depth analysis of existing literature, we shed light on potential therapeutic targets and personalized approaches that may enhance our understanding of disease pathogenesis and treatment strategies.

Viral sepsis: diagnosis, clinical features, pathogenesis, and clinical considerations

Sepsis, characterized as life-threatening organ dysfunction resulting from dysregulated host responses to infection, remains a significant challenge in clinical practice. Despite advancements in understanding host-bacterial interactions, molecular responses, and therapeutic approaches, the mortality rate associated with sepsis has consistently ranged between 10 and 16%. This elevated mortality highlights critical gaps in our comprehension of sepsis etiology. Traditionally linked to bacterial and fungal pathogens, recent outbreaks of acute viral infections, including Middle East respiratory syndrome coronavirus (MERS-CoV), influenza virus, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), among other regional epidemics, have underscored the role of viral pathogenesis in sepsis, particularly when critically ill patients exhibit classic symptoms indicative of sepsis. However, many cases of viral-induced sepsis are frequently underdiagnosed because standard evaluations typically exclude viral panels. Moreover, these viruses not only activate conventional pattern recognition receptors (PRRs) and retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) but also initiate primary antiviral pathways such as cyclic guanosine monophosphate adenosine monophosphate (GMP-AMP) synthase (cGAS)-stimulator of interferon genes (STING) signaling and interferon response mechanisms. Such activations lead to cellular stress, metabolic disturbances, and extensive cell damage that exacerbate tissue injury while leading to a spectrum of clinical manifestations. This complexity poses substantial challenges for the clinical management of affected cases. In this review, we elucidate the definition and diagnosis criteria for viral sepsis while synthesizing current knowledge regarding its etiology, epidemiology, and pathophysiology, molecular mechanisms involved therein as well as their impact on immune-mediated organ damage. Additionally, we discuss clinical considerations related to both existing therapies and advanced treatment interventions, aiming to enhance the comprehensive understanding surrounding viral sepsis.

Role of AhR-Hsp90-MDM2-mediated VDR ubiquitination in PM2.5-induced renal toxicity

BACKGROUND AND OBJECTIVES

The kidney is a primary target for the accumulation of particulate matter (PM2.5). This study aimed to investigate PM2.5-induced renal toxicity mechanisms, focusing on the aryl hydrocarbon receptor (AhR)-Hsp90-MDM2 axis and its impact on vitamin D receptor (VDR) ubiquitination.

METHODS

PM2.5's role in activating the AhR and its downstream pathways was investigated using in vitro and in vivo models. Renal damage and therapeutic effects in PM2.5-exposed and paricalcitol-treated mice were evaluated using weight measurements, histopathology, and scanning electron microscopy. AhR, Hsp90, and VDR localization and expression in renal cells were assessed using FISH and Western blot. Protein interactions were examined using co-immunoprecipitation. Differentially expressed gene (DEG) analysis of GEO datasets was used to identify related proteins and genes.

RESULTS

PM2.5 exposure caused significant renal damage in mice, including increased serum creatinine, albuminuria, and histopathological deterioration, which were alleviated by paricalcitol. PM2.5 induced the nuclear translocation of AhR and Hsp90 and reduced nuclear VDR expression; paricalcitol reversed these effects. Immunohistochemistry confirmed these findings. PM2.5 upregulated the NLRP3/caspase-1/IL-1β/IL-18 axis, which was reversed by paricalcitol treatment. Inhibition of Hsp90 increased nuclear VDR expression through MDM2 mediation. DEG analysis identified VDR-regulated genes; PM2.5 increased the mRNA levels of IL-6, IL-2, and CXCL8, which were downregulated by Hsp90 and MDM2 inhibitors, with VDR agonists further decreasing these levels.

CONCLUSION

This study reveals a novel mechanism of PM2.5-induced renal toxicity through the AhR-Hsp90-MDM2 axis, promoting VDR ubiquitination and degradation and increasing inflammation. These findings provide a foundation for future studies and lay the groundwork for developing targeted interventions to mitigate the public health impact of PM2.5 exposure.

Detrimental Effects of Anti-Nucleocapsid Antibodies in SARS-CoV-2 Infection, Reinfection, and the Post-Acute Sequelae of COVID-19

Antibody-dependent enhancement (ADE) is a phenomenon in which antibodies enhance subsequent viral infections rather than preventing them. Sub-optimal levels of neutralizing antibodies in individuals infected with dengue virus are known to be associated with severe disease upon reinfection with a different dengue virus serotype. For Severe Acute Respiratory Syndrome Coronavirus type-2 infection, three types of ADE have been proposed: (1) Fc receptor-dependent ADE of infection in cells expressing Fc receptors, such as macrophages by anti-spike antibodies, (2) Fc receptor-independent ADE of infection in epithelial cells by anti-spike antibodies, and (3) Fc receptor-dependent ADE of cytokine production in cells expressing Fc receptors, such as macrophages by anti-nucleocapsid antibodies. This review focuses on the Fc receptor-dependent ADE of cytokine production induced by anti-nucleocapsid antibodies, examining its potential role in severe COVID-19 during reinfection and its contribution to the post-acute sequelae of COVID-19, i.e., prolonged symptoms lasting at least three months after the acute phase of the disease. We also discuss the protective effects of recently identified anti-spike antibodies that neutralize Omicron variants.

Identification of apigenin as a multi-target inhibitor against SARS-CoV-2 by computational exploration

Multi-target strategy can serve as a valid treatment for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but existing drugs most focus on a single target. Thus, multi-target drugs that bind multiple sites simultaneously need to be urgently studied. Apigenin has antiviral and anti-inflammatory properties. Here, we comprehensively explored the potential effect and mechanism of apigenin in SARS-CoV-2 treatment by a network algorithm, deep learning, molecular docking, molecular dynamics (MD) simulation, and normal mode analysis (NMA). KATZ-based VDA prediction method (VDA-KATZ) indicated that apigenin may provide a latent drug therapy for SARS-CoV-2. Prediction of DTA using convolution model with self-attention (CSatDTA) showed potential binding affinity of apigenin with multiple targets of virus entry, assembly, and cytokine storms including cathepsin L (CTSL), membrane (M), envelope (E), Toll-like receptor 4 (TLR4), nuclear factor-kappa B (NF-κB), NOD-like receptor pyrin domain-containing protein 3 (NLRP3), apoptosis-associated speck-like protein (ASC), and cysteinyl aspartate-specific proteinase-1 (Caspase-1). Molecular docking indicated that apigenin could effectively bind these targets, and its stability was confirmed using MD simulation and NMA. Overall, apigenin is a multi-target inhibitor for the entry, assembly, and cytokine storms of SARS-CoV-2.

Porcine Epidemic Diarrhea Virus Infection of Porcine Intestinal Epithelial Cells Causes Mitochondrial DNA Release and the Activation of the NLRP3 Inflammasome to Mediate Interleukin-1β Secretion

Porcine epidemic diarrhea virus (PEDV) induces enteritis and diarrhea in piglets. Mitochondrial DNA (mtDNA) contributes to virus-induced inflammatory responses; however, the involvement of inflammasomes in PEDV infection responses remains unclear. We investigated the mechanism underlying inflammasome-mediated interleukin (IL)-1β secretion during the PEDV infection of porcine intestinal epithelial (IPEC-J2) cells. IL-1β production and caspase-1 activity were assessed by quantitative PCR and enzyme-linked immunosorbent assay. NLRP3 inflammasome activation was assessed using immunoprecipitation experiments. Mitochondrial damage was evaluated by analyzing the mitochondrial membrane potential and ATP levels and by the flow cytometry examination of mitochondrial reactive oxygen species (mtROS). Mitochondria and mtDNA localization were observed using immunofluorescence. The inhibition of mtROS and mtDNA production allowed NLRP3 inflammasome and IL-1β expression detection and the evaluation of the pathway underlying NLRP3 inflammasome activation in PEDV-infected IPEC-J2 cells. IPEC-J2 cells upregulated IL-1β upon PEDV infection, where mature IL-1β secretion depended on caspase-1 activity, triggered NLRP3 inflammasome expression and assembly, and caused mitochondrial dysfunction, leading to mtDNA release and NLRP3 inflammasome activation, while mtROS contributed to NF-κB pathway activation, enhancing IL-1β secretion. This is the first demonstration of the mechanism underlying mtDNA release and NLRP3 inflammasome activation facilitating IL-1β secretion from PEDV-infected IPEC-J2 cells. These data enhance our understanding of the inflammatory mechanisms triggered by PEDV.

The impact of COVID-19 on accelerating of immunosenescence and brain aging

The COVID-19 pandemic, caused by the novel coronavirus SARS-CoV-2, has profoundly impacted global health, affecting not only the immediate morbidity and mortality rates but also long-term health outcomes across various populations. Although the acute effects of COVID-19 on the respiratory system have initially been the primary focus, it is increasingly evident that the virus can have significant impacts on multiple physiological systems, including the nervous and immune systems. The pandemic has highlighted the complex interplay between viral infection, immune aging, and brain health, that can potentially accelerate neuroimmune aging and contribute to the persistence of long COVID conditions. By inducing chronic inflammation, immunosenescence, and neuroinflammation, COVID-19 may exacerbate the processes of neuroimmune aging, leading to increased risks of cognitive decline, neurodegenerative diseases, and impaired immune function. Key factors include chronic immune dysregulation, oxidative stress, neuroinflammation, and the disruption of cellular processes. These overlapping mechanisms between aging and COVID-19 illustrate how the virus can induce and accelerate aging-related processes, leading to an increased risk of neurodegenerative diseases and other age-related conditions. This mini-review examines key features and possible mechanisms of COVID-19-induced neuroimmune aging that may contribute to the persistence and severity of long COVID. Understanding these interactions is crucial for developing effective interventions. Anti-inflammatory therapies, neuroprotective agents, immunomodulatory treatments, and lifestyle interventions all hold potential for mitigating the long-term effects of the virus. By addressing these challenges, we can improve health outcomes and quality of life for millions affected by the pandemic.

The comprehensive SARS-CoV-2 'hijackome' knowledge base

The continuous evolution of SARS-CoV-2 has led to the emergence of several variants of concern (VOCs) that significantly affect global health. This study aims to investigate how these VOCs affect host cells at proteome level to better understand the mechanisms of disease. To achieve this, we first analyzed the (phospho)proteome changes of host cells infected with Alpha, Beta, Delta, and Omicron BA.1 and BA.5 variants over time frames extending from 1 to 36 h post infection. Our results revealed distinct temporal patterns of protein expression across the VOCs, with notable differences in the (phospho)proteome dynamics that suggest variant-specific adaptations. Specifically, we observed enhanced expression and activation of key components within crucial cellular pathways such as the RHO GTPase cycle, RNA splicing, and endoplasmic reticulum-associated degradation (ERAD)-related processes. We further utilized proximity biotinylation mass spectrometry (BioID-MS) to investigate how specific mutation of these VOCs influence viral-host protein interactions. Our comprehensive interactomics dataset uncovers distinct interaction profiles for each variant, illustrating how specific mutations can change viral protein functionality. Overall, our extensive analysis provides a detailed proteomic profile of host cells for each variant, offering valuable insights into how specific mutations may influence viral protein functionality and impact therapeutic target identification. These insights are crucial for the potential use and design of new antiviral substances, aiming to enhance the efficacy of treatments against evolving SARS-CoV-2 variants.

Generation of a SARS-CoV-2-susceptible mouse model using adenovirus vector expressing human angiotensin-converting enzyme 2 driven by an elongation factor 1α promoter with leftward orientation

Introduction

To analyze the molecular pathogenesis of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), a small animal model such as mice is needed: human angiotensin converting enzyme 2 (hACE2), the receptor of SARS-CoV-2, needs to be expressed in the respiratory tract of mice.

Methods

We conferred SARS-CoV-2 susceptibility in mice by using an adenoviral vector expressing hACE2 driven by an elongation factor 1α (EF1α) promoter with a leftward orientation.

Results

In this model, severe pneumonia like human COVID-19 was observed in SARS-CoV-2-infected mice, which was confirmed by dramatic infiltration of inflammatory cells in the lung with efficient viral replication. An early circulating strain of SARS-CoV-2 caused the most severe weight loss when compared to SARS-CoV-2 variants such as Alpha, Beta and Gamma, although histopathological findings, viral replication, and cytokine expression characteristics were comparable.

Discussion

We found that a distinct proteome of an early circulating strain infected lung characterized by elevated complement activation and blood coagulation, which were mild in other variants, can contribute to disease severity. Unraveling the specificity of early circulating SARS-CoV-2 strains is important in elucidating the origin of the pandemic.

Structural proteins of human coronaviruses: what makes them different?

Following COVID-19 outbreak with its unprecedented effect on the entire world, the interest to the coronaviruses increased. The causative agent of the COVID-19, severe acute respiratory syndrome coronavirus - 2 (SARS-CoV-2) is one of seven coronaviruses that is pathogenic to humans. Others include SARS-CoV, MERS-CoV, HCoV-HKU1, HCoV-OC43, HCoV-NL63 and HCoV-229E. The viruses differ in their pathogenicity. SARS-CoV, MERS-CoV, and SARS-CoV-2 are capable to spread rapidly and cause epidemic, while HCoV-HKU1, HCoV-OC43, HCoV-NL63 and HCoV-229E cause mild respiratory disease. The difference in the viral behavior is due to structural and functional differences. All seven human coronaviruses possess four structural proteins: spike, envelope, membrane, and nucleocapsid. Spike protein with its receptor binding domain is crucial for the entry to the host cell, where different receptors on the host cell are recruited by different viruses. Envelope protein plays important role in viral assembly, and following cellular entry, contributes to immune response. Membrane protein is an abundant viral protein, contributing to the assembly and pathogenicity of the virus. Nucleocapsid protein encompasses the viral RNA into ribonucleocapsid, playing important role in viral replication. The present review provides detailed summary of structural and functional characteristics of structural proteins from seven human coronaviruses, and could serve as a practical reference when pathogenic human coronaviruses are compared, and novel treatments are proposed.