SARS-CoV-2 spike protein S1 subunit induces pro-inflammatory responses via toll-like receptor 4 signaling in murine and human macrophages

Diminazene aceturate inhibits the SARS-CoV-2 spike protein-induced inflammation involving leukocyte migration and DNA extracellular traps formation

AIMS

To investigate the SARS-CoV-2 Spike protein (Spk)-induced inflammatory response and its downmodulation by diminazene aceturate (DIZE).

MATERIALS AND METHODS

Through inducing Spk inflammation in murine models, leukocyte migration to the peritoneum, levels of myeloperoxidase (MPO), malondialdehyde (MDA), rolling and adhesion of mesenteric leukocytes, and vascular permeability were investigated. Extracellular DNA traps (DETs) induced by Spk and the production of IL-6 and TNF-α were analyzed using human neutrophils, monocytes, and macrophages. In silico assays assessed the molecular interaction between DIZE and molecules related to leukocyte migration and DETs induction.

KEY FINDINGS

Spk triggered acute inflammation, demonstrated by increasing leukocyte migration. Oxidative stress was evidenced by elevated levels of MPO and MDA in the peritoneal liquid. DIZE attenuated cell migration, rolling, and leukocyte adhesion, improved vascular barrier function, mitigated DETs, and reduced the production of Spk-induced pro-inflammatory cytokines. Computational studies supported our findings, showing the molecular interaction of DIZE with targets such as β2 integrin, PI3K, and PAD2 due to its intermolecular coupling.

SIGNIFICANCE

Our results outline a novel role of DIZE as a potential therapeutic agent for mitigating Spk-induced inflammation.

Interplay of TLR4 and SARS-CoV-2: Unveiling the Complex Mechanisms of Inflammation and Severity in COVID-19 Infections

The late 2019 emergence of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19, caused profound and unprecedented disruption to the global socio-economic structure, negatively affecting millions of lives worldwide. A typical hallmark of severe COVID-19 is hyper inflammation due to aberrant cytokine release (cytokine storm) by innate immune cells. Recent studies have revealed that SARS-CoV-2, through its spike (S) protein, can activate the body's innate immune cells via Toll-Like Receptors (TLRs), particularly TLR4. In silico studies have demonstrated that the S protein binds with high affinity to TLR4, triggering downstream signaling processes that result in pro-inflammatory cytokine release. Compared to other TLRs, such as TLR2, TLR4 plays a more significant role in initiating and sustaining the inflammatory response associated with severe COVID-19. Furthermore, interactions between the virus and target cells can enhance the cellular expression of TLR4, making cells more susceptible to viral interactions and subsequent inflammation. This increased expression of TLR4 upon viral entry creates a feedback loop, where heightened TLR4 levels lead to amplified inflammatory responses, contributing to the severity of the disease. Additionally, TLR4's potent activation of inflammatory pathways sets it apart from other TLRs, underscoring its pivotal role in the pathogenesis of COVID-19. In this review, we thoroughly explore the multitude of regulatory signaling pathways that SARS-CoV-2 employs to incite inflammation. We specifically focus on the critical impact of TLR4 activation compared to other TLRs, highlighting how TLR4's interactions with the viral S protein can exacerbate the severity of COVID-19. By delving into the mechanisms of TLR4-mediated inflammation, we aim to shed light on potential therapeutic targets that could mitigate the inflammatory damage caused by severe COVID-19. Understanding the unique role of TLR4 in the context of SARS-CoV-2 infection could pave the way for novel treatment strategies that specifically inhibit this receptor's activity, thereby reducing the overall disease burden and improving patient outcomes.

Basic implications on three pathways associated with SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) interacts between the host and virus and govern induction, resulting in multiorgan impacts. Its pathophysiology involves the followings: 1) the angiotensin-converting enzyme (ACE2) and Toll-like receptor (TLR) pathways: 2) the neuropilin (NRP) pathway: 3) the spike protein pathway. Therefore, it is necessary to block the pathological course with modulating innate lymphoid cells against diverse corona variants in the future.

Network-based integrative multi-omics approach reveals biosignatures specific to COVID-19 disease phases

Background

COVID-19 disease is characterized by a spectrum of disease phases (mild, moderate, and severe). Each disease phase is marked by changes in omics profiles with corresponding changes in the expression of features (biosignatures). However, integrative analysis of multiple omics data from different experiments across studies to investigate biosignatures at various disease phases is limited. Exploring an integrative multi-omics profile analysis through a network approach could be used to determine biosignatures associated with specific disease phases and enable the examination of the relationships between the biosignatures.

Aim

To identify and characterize biosignatures underlying various COVID-19 disease phases in an integrative multi-omics data analysis.

Method

We leveraged a multi-omics network-based approach to integrate transcriptomics, metabolomics, proteomics, and lipidomics data. The World Health Organization Ordinal Scale WHO Ordinal Scale was used as a disease severity reference to harmonize COVID-19 patient metadata across two studies with independent data. A unified COVID-19 knowledge graph was constructed by assembling a disease-specific interactome from the literature and databases. Disease-state specific omics-graphs were constructed by integrating multi-omics data with the unified COVID-19 knowledge graph. We expanded on the network layers of multiXrank, a random walk with restart on multilayer network algorithm, to explore disease state omics-specific graphs and perform enrichment analysis.

Results

Network analysis revealed the biosignatures involved in inducing chemokines and inflammatory responses as hubs in the severe and moderate disease phases. We observed distinct biosignatures between severe and moderate disease phases as compared to mild-moderate and mild-severe disease phases. Mild COVID-19 cases were characterized by a unique biosignature comprising C-C Motif Chemokine Ligand 4 (CCL4), and Interferon Regulatory Factor 1 (IRF1). Hepatocyte Growth Factor (HGF), Matrix Metallopeptidase 12 (MMP12), Interleukin 10 (IL10), Nuclear Factor Kappa B Subunit 1 (NFKB1), and suberoylcarnitine form hubs in the omics network that characterizes the moderate disease state. The severe cases were marked by biosignatures such as Signal Transducer and Activator of Transcription 1 (STAT1), Superoxide Dismutase 2 (SOD2), HGF, taurine, lysophosphatidylcholine, diacylglycerol, triglycerides, and sphingomyelin that characterize the disease state.

Conclusion

This study identified both biosignatures of different omics types enriched in disease-related pathways and their associated interactions (such as protein-protein, protein-transcript, protein-metabolite, transcript-metabolite, and lipid-lipid interactions) that are unique to mild, moderate, and severe COVID-19 disease states. These biosignatures include molecular features that underlie the observed clinical heterogeneity of COVID-19 and emphasize the need for disease-phase-specific treatment strategies. The approach implemented here can be used to find associations between transcripts, proteins, lipids, and metabolites in other diseases.

Anti-Melanogenic and Anti-Inflammatory Effects of 2'-Hydroxy-4',6'-dimethoxychalcone in B16F10 and RAW264.7 Cells

Chalcone is a type of flavonoid compound that is widely biosynthesized in plants. Studies have shown that consuming flavonoids from fruits and vegetables or applying individual ingredients reduces the risk of skin disease. However, the effects of chalcone on melanogenesis and inflammation have not been fully investigated. The aim of this study was to evaluate the anti-melanogenic and anti-inflammatory effects of 2'-hydroxy-3,4'-dimethoxychalcone (3,4'-DMC), 2'-hydroxy-4,4'-dimethoxychalcone (4,4'-DMC), 2'-hydroxy-3',4'-dimethoxychalcone (3',4'-DMC), and 2'-hydroxy-4',6'-dimethoxychalcone (4',6'-DMC). Among the derivatives of 2'-hydroxy-4'-methoxychalcone, 4',6'-DMC demonstrated the most potent melanogenesis-inhibitory and anti-inflammatory effects. As evidenced by various biological assays, 4',6'-DMC showed no cytotoxicity and notably decreased the expression of tyrosinase, tyrosinase-related protein (TRP)-1, and TRP-2 enzymes. Furthermore, it reduced cellular melanin content and intracellular tyrosinase activity in B16F10 melanoma cells by downregulating microphthalmia-associated transcription factor (MITF), cAMP-dependent protein kinase (PKA), cAMP response element-binding protein (CREB), p38, c-Jun N-terminal kinase (JNK), β-catenin, glycogen synthase kinase-3β (GSK3β), and protein kinase B (AKT) proteins, while upregulating extracellular signal-regulated kinase (ERK) and p-β-catenin. Additionally, treatment with 4',6'-DMC significantly mitigated the lipopolysaccharide (LPS)-induced expression of NO, PGE2, inflammatory cytokines, COX-2, and iNOS proteins. Overall, 4',6'-DMC treatment notably alleviated LPS-induced damage by reducing nuclear factor kappa B (NF-κB), p38, JNK protein levels, and NF-kB/p65 nuclear translocation. Finally, the topical applicability of 4',6'-DMC was evaluated in a preliminary human skin irritation test and no adverse effects were found. These findings suggest that 4',6'-DMC may offer new possibilities for use as functional ingredients in cosmeceuticals and ointments.

Synergistic effect of Toll-like receptor 2 ligands and alendronate on proinflammatory cytokine production in mouse macrophage-like RAW-ASC cells is accompanied by upregulation of MyD88 expression

OBJECTIVES

Toll-like receptors (TLRs) recognize whole cells or components of microorganisms. Alendronate (ALN) is an anti-bone-resorptive drug that has inflammatory side effects. The aim in this study was to examine whether ALN augments TLR2 ligand-induced proinflammatory cytokine production using mouse macrophage-like RAW264.7 cells transfected with murine apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) gene (hereafter, referred to as "RAW-ASC cells").

METHODS

RAW-ASC cells were pretreated with or without ALN and then incubated with or without TLR2 ligands. The levels of secreted mouse IL-1α, IL-1β, IL-6, and tumor necrosis factor-α (TNF-α) in culture supernatants and the activation of activator protein-1 (AP-1) or nuclear factor-κB (NF-κB) were measured using enzyme-linked immunosorbent assay (ELISA). The expressions of myeloid differentiation factor 88 (MyD88), caspase-11, nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3), ASC, NF-κB p65, and actin were analyzed via Western blotting. TLR2 expression was analyzed using flow cytometry.

RESULTS

ALN substantially upregulated the Pam3CSK4-induced release of IL-1α, IL-1β, IL-6, and TNF-α and MyD88 expression in RAW-ASC cells. ST-2825, a MyD88 inhibitor, inhibited the ALN-augmented release of these cytokines. Pretreatment with ALN augmented Pam3CSK4-induced NF-κB activation in RAW-ASC cells and upregulated AP-1 activation. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) S protein and ALN synergically upregulated the release of IL-1α, IL-1β, IL-6 and TNF-α in RAW-ASC cells.

CONCLUSIONS

Our findings suggest that ALN augments TLR2 ligand-induced proinflammatory cytokine production via the upregulation of MyD88 expression, and this augmentation is accompanied by the activation of NF-κB and AP-1 in RAW-ASC cells.

Toll like receptor 4 mediates the inhibitory effect of SARS-CoV-2 spike protein on proximal tubule albumin endocytosis

Tubular proteinuria is a common feature in COVID-19 patients, even in the absence of established acute kidney injury. SARS-CoV-2 spike protein (S protein) was shown to inhibit megalin-mediated albumin endocytosis in proximal tubule epithelial cells (PTECs). Angiotensin-converting enzyme type 2 (ACE2) was not directly involved. Since Toll-like receptor 4 (TLR4) mediates S protein effects in various cell types, we hypothesized that TLR4 could be participating in the inhibition of PTECs albumin endocytosis elicited by S protein. Two different models of PTECs were used: porcine proximal tubule cells (LLC-PK1) and human embryonic kidney cells (HEK-293). S protein reduced Akt activity by specifically inhibiting of threonine 308 (Thr308) phosphorylation, a process mediated by phosphoinositide-dependent kinase 1 (PDK1). GSK2334470, a PDK1 inhibitor, decreased albumin endocytosis and megalin expression mimicking S protein effect. S protein did not change total TLR4 expression but decreased its surface expression. LPS-RS, a TLR4 antagonist, also counteracted the effects of the S protein on Akt phosphorylation at Thr308, albumin endocytosis, and megalin expression. Conversely, these effects of the S protein were replicated by LPS, an agonist of TLR4. Incubation of PTECs with a pseudovirus containing S protein inhibited albumin endocytosis. Null or VSV-G pseudovirus, used as control, had no effect. LPS-RS prevented the inhibitory impact of pseudovirus containing the S protein on albumin endocytosis but had no influence on virus internalization. Our findings demonstrate that the inhibitory effect of the S protein on albumin endocytosis in PTECs is mediated through TLR4, resulting from a reduction in megalin expression.

Diverse pro-inflammatory ability of mutated spike protein derived from variant strains of SARS-CoV-2

The severity of COVID-19 has been reported to differ among SARS-CoV-2 mutant variants. The overactivation of macrophages is involved in severe COVID-19, yet the effects of SARS-CoV-2 mutations on macrophages remain poorly understood. To clarify the effects, we examined whether mutations of spike proteins (S-proteins) affect macrophage activation. CD14+ monocyte-derived macrophages were stimulated with the recombinant S-protein of the wild-type, Delta, and Omicron strains or live viral particles of individual strains. Regarding IL-6 and TNF-α, Delta or Omicron S-protein had stronger or weaker pro‑inflammatory ability, respectively, than the wild-type. Similar trends were observed between S-proteins and viral particles. S-protein mutations could be related to the diversity in macrophage activation and severity rates in COVID-19 caused by various SARS-CoV-2 strains.

In Silico Analyses Indicate a Lower Potency for Dimerization of TLR4/MD-2 as the Reason for the Lower Pathogenicity of Omicron Compared to Wild-Type Virus and Earlier SARS-CoV-2 Variants

The SARS-CoV-2 Omicron variants have replaced all earlier variants, due to increased infectivity and effective evasion from infection- and vaccination-induced neutralizing antibodies. Compared to earlier variants of concern (VoCs), the Omicron variants show high TMPRSS2-independent replication in the upper airway organs, but lower replication in the lungs and lower mortality rates. The shift in cellular tropism and towards lower pathogenicity of Omicron was hypothesized to correlate with a lower toll-like receptor (TLR) activation, although the underlying molecular mechanisms remained undefined. In silico analyses presented here indicate that the Omicron spike protein has a lower potency to induce dimerization of TLR4/MD-2 compared to wild type virus despite a comparable binding activity to TLR4. A model illustrating the molecular consequences of the different potencies of the Omicron spike protein vs. wild-type spike protein for TLR4 activation is presented. Further analyses indicate a clear tendency for decreasing TLR4 dimerization potential during SARS-CoV-2 evolution via Alpha to Gamma to Delta to Omicron variants.

Comparison of the pathogenicity and neutrophil and monocyte response between SARS-CoV-2 prototype and Omicron BA.1 in a lethal mouse model

BACKGROUND

SARS-CoV-2, first identified in late 2019, has given rise to numerous variants of concern (VOCs), posing a significant threat to human health. The emergence of Omicron BA.1.1 towards the end of 2021 led to a pandemic in early 2022. At present, the lethal mouse model for the study of SARS-CoV-2 needs supplementation, and the alterations in neutrophils and monocytes caused by different strains remain to be elucidated.

METHODS

Human ACE2 transgenic mice were inoculated with the SARS-CoV-2 prototype and Omicron BA.1, respectively. The pathogenicity of the two strains was evaluated by observing clinical symptoms, viral load and pathology. Complete blood count, immunohistochemistry and flow cytometry were performed to detect the alterations of neutrophils and monocytes caused by the two strains.

RESULTS

Our findings revealed that Omicron BA.1 exhibited significantly lower virulence compared to the SARS-CoV-2 prototype in the mouse model. Additionally, we observed a significant increase in the proportion of neutrophils late in infection with the SARS-CoV-2 prototype and Omicron BA.1. We found that the proportion of monocytes increased at first and then decreased. The trends in the changes in the proportions of neutrophils and monocytes induced by the two strains were similar.

CONCLUSION

Our study provides valuable insights into the utility of mouse models for simulating the severe disease of SARS-CoV-2 prototype infection and the milder manifestation associated with Omicron BA.1. SARS-CoV-2 prototype and Omicron BA.1 resulted in similar trends in the changes in neutrophils and monocytes.

ACE2 expression and spike S1 protein-mediated immune responses in oral mucosal cells

OBJECTIVES

ACE2, known as a host receptor involved with SARS-CoV-2 infection, binds to viral spike proteins for host cell entry. However, details regarding its induction and function in oral mucosal cells remain unknown.

MATERIALS AND METHODS

We examined ACE2 expression and its induction by transfected mimic nucleotides and pro-inflammatory cytokines in oral keratinocytes (RT7) and fibroblasts (GT1). Subsequently, the effects of viral spike S1 protein via ACE2 on CXCL10 expression induced by pro-inflammatory cytokines in both cells were examined.

RESULTS

ACE2 was constitutively expressed in RT7 and GT1. Transfected Poly(I:C) and Poly(dA:dT) increased ACE2 expression in those cells, while knockdown of RIG-I decreased ACE2 expression induced by those transfected ds nucleotides. IFN-γ and TNF-α enhanced transfected ds nucleotides-induced ACE2 expression in RT7 but not GT1. S1 protein alone did not affect CXCL10 expression in either cell type, whereas it enhanced IFN-β-induced CXCL10 in both, while immune responses of IFN-γ- and TNF-α-induced CXCL10 enhanced by S1 protein were different between RT7 and GT1. Finally, knockdown of ACE2 decreased cytokines and S1 protein mediated-CXCL10 levels in both cells.

CONCLUSIONS

ACE2 in oral mucosal cells may contribute to development of infection and inflammation in cooperation with pro-inflammatory cytokines following SARS-CoV-2 invasion.

SARS-CoV-2 Omicron Spike shows strong binding affinity and favourable interaction landscape with the TLR4/MD2 compared to other variants

Emergences of SARS-CoV-2 variants have made the pandemic more critical. Toll-like receptor 4 (TLR4) recognizes the molecular patterns of pathogens and activates the production of proinflammatory cytokines to restrain the infection. We have identified a molecular basis of interaction between the Spike and TLR4 of SARS-CoV-2 and its present and past VOCs (variant- of concern) through in silico analysis. The interaction of wild type Spike with TLR4 showed 15 number hydrogen bonds formation. Similarly, the Alpha variants' Spike with the TLR4 has illustrated that 14 hydrogen bonds participated in the interaction. However, the Delta Spike and TLR4 interaction interface showed that 17 hydrogen bonds were formed during the interaction. Furthermore, Omicron S-glycoprotein and TLR4 interaction interface was depicted (interaction score: -170.3), and 16 hydrogen bonds were found to have been formed in the interaction. Omicron S-glycoprotein shows stronger binding affinity with the TLR4 than wild type, Alpha, and Delta variants. Similarly, the Alpha Spike shows higher binding affinity with TLR4 than the wild type and Delta variant. Now, it is an open question of the molecular basis of the interaction of Spike and TLR4 and the activated downstream signaling events of TLR4 for SARS-CoV-2 and its variants.

The Role of Furin in the Pathogenesis of COVID-19-Associated Neurological Disorders

Neurological disorders have been reported in a large number of coronavirus disease 2019 (COVID-19) patients, suggesting that this disease may have long-term adverse neurological consequences. COVID-19 occurs from infection by a positive-sense single-stranded RNA virus called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The membrane fusion protein of SARS-CoV-2, the spike protein, binds to its human host receptor, angiotensin-converting enzyme 2 (ACE2), to initiate membrane fusion between the virus and host cell. The spike protein of SARS-CoV-2 contains the furin protease recognition site and its cleavage enhances the infectivity of this virus. The binding of SARS-CoV-2 to the ACE2 receptor has been shown to downregulate ACE2, thereby increasing the levels of pathogenic angiotensin II (Ang II). The furin protease cleaves between the S1 subunit of the spike protein with the binding domain toward ACE2 and the S2 subunit with the transmembrane domain that anchors to the viral membrane, and this activity releases the S1 subunit into the blood circulation. The released S1 subunit of the spike protein also binds to and downregulates ACE2, in turn increasing the level of Ang II. Considering that a viral particle contains many spike protein molecules, furin-dependent cleavage would release many free S1 protein molecules, each of which can downregulate ACE2, while infection with a viral particle only affects one ACE2 molecule. Therefore, the furin-dependent release of S1 protein would dramatically amplify the ability to downregulate ACE2 and produce Ang II. We hypothesize that this amplification mechanism that the virus possesses, but not the infection per se, is the major driving force behind COVID-19-associated neurological disorders.

A single-dose MCMV-based vaccine elicits long-lasting immune protection in mice against distinct SARS-CoV-2 variants

Current vaccines against COVID-19 elicit immune responses that are overall strong but wane rapidly. As a consequence, the necessary booster shots have led to vaccine fatigue. Hence, vaccines that would provide lasting protection against COVID-19 are needed, but are still unavailable. Cytomegaloviruses (CMV) elicit lasting and uniquely strong immune responses. Used as vaccine vectors, they may be attractive tools that obviate the need for boosters. Therefore, we tested the murine CMV (MCMV) as a vaccine vector against COVID-19 in relevant preclinical models of immunization and challenge. We have previously developed a recombinant murine CMV (MCMV) vaccine vector expressing the spike protein of the ancestral SARS-CoV-2 (MCMVS). In this study, we show that the MCMVS elicits a robust and lasting protection in young and aged mice. Notably, S-specific humoral and cellular immunity was not only maintained but even increased over a period of at least 6 months. During that time, antibody avidity continuously increased and expanded in breadth, resulting in neutralization of genetically distant variants, like Omicron BA.1. A single dose of MCMVS conferred rapid virus clearance upon challenge. Moreover, MCMVS vaccination controlled two immune-evading variants of concern (VoCs), the Beta (B.1.135) and the Omicron (BA.1) variants. Thus, CMV vectors provide unique advantages over other vaccine technologies, eliciting broadly reactive and long-lasting immune responses against COVID-19.

Acellular Human Amniotic Fluid-Derived Extracellular Vesicles as Novel Anti-Inflammatory Therapeutics against SARS-CoV-2 Infection

The ongoing COVID-19 pandemic caused by SARS-CoV-2 is associated with acute respiratory distress syndrome (ARDS) and fatal pneumonia. Excessive inflammation caused by SARS-CoV-2 is the key driver of ARDS and lethal disease. Several FDA-approved drugs that suppress virus replication are in clinical use. However, despite strong evidence for the role of virus-induced inflammation in severe COVID-19, no effective anti-inflammatory drug is available to control fatal inflammation as well as efficiently clear the virus. Therefore, there is an urgent need to identify biologically derived immunomodulators that suppress inflammation and promote antiviral immunity. In this study, we evaluated acellular human amniotic fluid (acAF) containing extracellular vesicles (hAF-EVs) as a potential non-toxic and safe biologic for immunomodulation during COVID-19. Our in vitro results showed that acAF significantly reduced inflammatory cytokine production in TLR2/4/7 and SARS-CoV-2 structural protein-stimulated mouse macrophages. Importantly, an intraperitoneal administration of acAF reduced morbidity and mortality in SARS-CoV-2-infected mice. A detailed examination of SARS-CoV-2-infected lungs revealed that the increased protection in acAF-treated mice was associated with reduced viral titers and levels of inflammatory myeloid cell infiltration. Collectively, our results identify a novel biologic that has potential to suppress excessive inflammation and enhance survival following SARS-CoV-2 infection, highlighting the translational potential of acAF against COVID-19.

SARS-CoV-2: A Glance at the Innate Immune Response Elicited by Infection and Vaccination

The COVID-19 pandemic caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has led to almost seven million deaths worldwide. SARS-CoV-2 causes infection through respiratory transmission and can occur either without any symptoms or with clinical manifestations which can be mild, severe or, in some cases, even fatal. Innate immunity provides the initial defense against the virus by sensing pathogen-associated molecular patterns and triggering signaling pathways that activate the antiviral and inflammatory responses, which limit viral replication and help the identification and removal of infected cells. However, temporally dysregulated and excessive activation of the innate immune response is deleterious for the host and associates with severe COVID-19. In addition to its defensive role, innate immunity is pivotal in priming the adaptive immune response and polarizing its effector function. This capacity is relevant in the context of both SARS-CoV-2 natural infection and COVID-19 vaccination. Here, we provide an overview of the current knowledge of the innate immune responses to SARS-CoV-2 infection and vaccination.

Targeting MAPK signaling: A promising approach for treating inflammatory lung disease

The extracellular signals that initiate intracellular reactions are dispatched by the mitogen-activated protein kinases (MAPKs), which oversee a multitude of cellular activities. p38, Extracellular signal-regulated kinase (ERK), and c-Jun NH2-terminal kinase (JNK) are members of the vertebrate family of MAPKs, and each MAPK signaling pathway consists of a MAPK kinase (MAP3K), a MAPK kinase (MAP2K), and a MAPK. These signaling pathways orchestrate numerous cellular processes, including cell growth, survival, differentiation, and apoptosis. The emergence of various inflammatory respiratory diseases in humans has been linked to the dysregulation of MAPK signaling pathways. Conditions such as asthma, lung cancer, pulmonary fibrosis, and COPD are among the prevalent respiratory ailments where MAPK plays a pivotal role. Additionally, MAPK is implicated in infectious diseases, including COVID-19, pneumonia, and tuberculosis. COPD, asthma, emphysema, chronic bronchitis, and other inflammatory lung disorders highlight the significance of MAPK as a potential target for therapeutic development. Further studies are needed to delve into the molecular mechanisms by which the MAPK signaling pathway contributes to inflammatory lung disorders, representing an area that demands continued research.

SARS-CoV-2 ORF8 as a Modulator of Cytokine Induction: Evidence and Search for Molecular Mechanisms

Severe cases of SARS-CoV-2 infection are characterized by an immune response that leads to the overproduction of pro-inflammatory cytokines, resulting in lung damage, cardiovascular symptoms, hematologic symptoms, acute kidney injury and multiple organ failure that can lead to death. This remarkable increase in cytokines and other inflammatory molecules is primarily caused by viral proteins, and particular interest has been given to ORF8, a unique accessory protein specific to SARS-CoV-2. Despite plenty of research, the precise mechanisms by which ORF8 induces proinflammatory cytokines are not clear. Our investigations demonstrated that ORF8 augments production of IL-6 induced by Poly(I:C) in human embryonic kidney (HEK)-293 and monocyte-derived dendritic cells (mono-DCs). We discuss our findings and the multifaceted roles of ORF8 as a modulator of cytokine response, focusing on type I interferon and IL-6, a key component of the immune response to SARS-CoV-2. In addition, we explore the hypothesis that ORF8 may act through pattern recognition receptors of dsRNA such as TLRs.

The dangerous liaisons in innate immunity involving recombinant proteins and endotoxins: Examples from the literature and the Leptospira field

Endotoxins, also known as lipopolysaccharides (LPS), are essential components of cell walls of diderm bacteria such as Escherichia coli. LPS are microbe-associated molecular patterns that can activate pattern recognition receptors. While trying to investigate the interactions between proteins and host innate immunity, some studies using recombinant proteins expressed in E. coli reported interaction and activation of immune cells. Here, we set out to provide information on endotoxins that are highly toxic to humans and bind to numerous molecules, including recombinant proteins. We begin by outlining the history of the discovery of endotoxins, their receptors and the associated signaling pathways that confer extreme sensitivity to immune cells, acting alone or in synergy with other microbe-associated molecular patterns. We list the various places where endotoxins have been found. Additionally, we warn against the risk of data misinterpretation due to endotoxin contamination in recombinant proteins, which is difficult to estimate with the Limulus amebocyte lysate assay, and cannot be completely neutralized (e.g., treatment with polymyxin B or heating). We further illustrate our point with examples of recombinant heat-shock proteins and viral proteins from severe acute respiratory syndrome coronavirus 2, dengue and HIV, for which endotoxin contamination has eventually been shown to be responsible for the inflammatory roles previously ascribed. We also critically appraised studies on recombinant Leptospira proteins regarding their putative inflammatory roles. Finally, to avoid these issues, we propose alternatives to express recombinant proteins in nonmicrobial systems. Microbiologists wishing to undertake innate immunity studies with their favorite pathogens should be aware of these difficulties.

Integrin α5β1 contributes to cell fusion and inflammation mediated by SARS-CoV-2 spike via RGD-independent interaction

The Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus infects host cells by engaging its spike (S) protein with human ACE2 receptor. Recent studies suggest the involvement of integrins in SARS-CoV-2 infection through interaction with the S protein, but the underlying mechanism is not well understood. This study investigated the role of integrin α5β1, which recognizes the Arg-Gly-Asp (RGD) motif in its physiological ligands, in S-mediated virus entry and cell-cell fusion. Our results showed that α5β1 does not directly contribute to S-mediated cell entry, but it enhances S-mediated cell-cell fusion in collaboration with ACE2. This effect cannot be inhibited by the putative α5β1 inhibitor ATN-161 or the high-affinity RGD-mimetic inhibitor MK-0429 but requires the participation of α5 cytoplasmic tail (CT). We detected a direct interaction between α5β1 and the S protein, but this interaction does not rely on the RGD-containing receptor binding domain of the S1 subunit of the S protein. Instead, it involves the S2 subunit of the S protein and α5β1 homo-oligomerization. Furthermore, we found that the S protein induces inflammatory responses in human endothelial cells, characterized by NF-κB activation, gasdermin D cleavage, and increased secretion of proinflammatory cytokines IL-6 and IL-1β. These effects can be attenuated by the loss of α5 expression or inhibition of the α5 CT binding protein phosphodiesterase-4D (PDE4D), suggesting the involvement of α5 CT and PDE4D pathway. These findings provide molecular insights into the pathogenesis of SARS-CoV-2 mediated by a nonclassical RGD-independent ligand-binding and signaling function of integrin α5β1 and suggest potential targets for antiviral treatment.

Alendronate augments lipid A‑induced IL‑1β release by ASC‑deficient RAW264 cells via AP‑1 activation

Alendronate (ALN) is an anti-bone-resorptive drug with inflammatory side effects. ALN upregulates lipid A-induced interleukin (IL)-1α and IL-1β release by J774.1 cells via apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) activation. The present study examined whether ALN augmented lipid A-induced proinflammatory cytokine production using ASC-deficient mouse macrophage-like RAW264 cells. Pretreatment of RAW264 cells with ALN significantly augmented lipid A-induced IL-1β release, although ALN did not upregulate the expression of Toll-like receptor 4, myeloid differentiation factor 88 (MyD88) and caspase-11. Moreover, pretreatment of caspase-11-deficient RAW264.7 cells with ALN significantly augmented lipid A-induced IL-1β release. Notably, ALN upregulated the activation of FosB, c-Jun or JunD, but not c-Fos or NF-κB in RAW264 cells. Furthermore, pretreatment with the activator protein 1 (AP-1) inhibitor SR11302, but not the c-Fos inhibitor T-5224, before addition of ALN inhibited ALN-augmented IL-1β release by lipid A-treated RAW264 cells. SR11302 also reduced ALN-augmented lactate dehydrogenase release by the cells. These findings collectively suggested that ALN augmented lipid A-induced IL-1β release and cell membrane damage in ASC-deficient RAW264 cells via activation of AP-1, but not NF-κB.

Calreticulin Regulates SARS-CoV-2 Spike Protein Turnover and Modulates SARS-CoV-2 Infectivity

Cardiovascular complications are major clinical hallmarks of acute and post-acute coronavirus disease 2019 (COVID-19). However, the mechanistic details of SARS-CoV-2 infectivity of endothelial cells remain largely unknown. Here, we demonstrate that the receptor binding domain (RBD) of the SARS-CoV-2 spike (S) protein shares a similarity with the proline-rich binding ena/VASP homology (EVH1) domain and identified the endoplasmic reticulum (ER) resident calreticulin (CALR) as an S-RBD interacting protein. Our biochemical analysis showed that CALR, via its proline-rich (P) domain, interacts with S-RBD and modulates proteostasis of the S protein. Treatment of cells with the proteasomal inhibitor bortezomib increased the expression of the S protein independent of CALR, whereas the lysosomal/autophagy inhibitor bafilomycin 1A, which interferes with the acidification of lysosome, selectively augmented the S protein levels in a CALR-dependent manner. More importantly, the shRNA-mediated knockdown of CALR increased SARS-CoV-2 infection and impaired calcium homeostasis of human endothelial cells. This study provides new insight into the infectivity of SARS-CoV-2, calcium hemostasis, and the role of CALR in the ER-lysosome-dependent proteolysis of the spike protein, which could be associated with cardiovascular complications in COVID-19 patients.

The spike protein of SARS-CoV-2 induces inflammation and EMT of lung epithelial cells and fibroblasts through the upregulation of GADD45A

Lung epithelial cells and fibroblasts poorly express angiotensin-converting enzyme 2, and the study aimed to investigate the role of the spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on inflammation and epithelial-mesenchymal transition (EMT) in two lung cell lines and to understand the potential mechanism. Lung epithelial cells (BEAS-2B) and fibroblasts (MRC-5) were treated with the spike protein, then inflammatory and EMT phenotypes were detected by enzyme-linked immunosorbent assay, Transwell, and western blot assays. RNA-sequence and bioinformatic analyses were performed to identify dysregulated genes. The roles of the candidate genes were further investigated. The results showed that treatment with 1,000 ng/mL of spike protein in two lung cell lines caused increased levels of IL-6, TNF-α, CXCL1, and CXCL3, and the occurrence of EMT. RNA-sequence identified 4,238 dysregulated genes in the spike group, and 18 candidate genes were involved in both inflammation- and EMT-related processes. GADD45A had the highest verified fold change (abs), and overexpression of GADD45A promoted the secretion of cytokines and EMT in the two lung cell lines. In conclusion, the spike protein induces inflammation and EMT in lung epithelial cells and fibroblasts by upregulating GADD45A, providing a new target to inhibit inflammation and EMT.

Excess iron aggravates the severity of COVID-19 infection

Coronavirus disease-19 (COVID-19) can induce severe inflammation of the lungs and respiratory system. Severe COVID-19 is frequently associated with hyper inflammation and hyper-ferritinemia. High iron levels are known to trigger pro-inflammatory effects. Cumulative iron loading negatively impacts on a patients innate immune effector functions and increases the risk for infection related complications. Prognosis of severe acute respiratory SARS-CoV-2 patients may be impacted by iron excess. Iron is an essential co-factor for numerous essential cellular enzymes and vital cellular operations. Viruses hijack cells in order to replicate, and efficient replication requires an iron-replete host. Utilizing iron loaded cells in culture we evaluated their susceptibility to infection by pseudovirus expressing the SARS-CoV-2 spike protein and resultant cellular inflammatory response. We observed that, high levels of iron enhanced host cell ACE2 receptor expression contributing to higher infectivity of pseudovirus. In vitro Cellular iron overload also synergistically enhanced the levels of; reactive oxygen species, reactive nitrogen species, pro-inflammatory cytokines (IL-1β, IL-6, IL-8 & TNF-α) and chemokine (CXCL-1&CCL-4) production in response to inflammatory stimulation of cells with spike protein. These results were confirmed using an in vivo mouse model. In future, limiting iron levels may be a promising adjuvant strategy in treating viral infection.

SARS-CoV-2 activates the TLR4/MyD88 pathway in human macrophages: A possible correlation with strong pro-inflammatory responses in severe COVID-19

Background

Toll-like receptors (TLRs) play a pivotal role in the immunologic response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Exaggerated inflammatory response of innate immune cells, however, may drive morbidity and death in Coronavirus disease 19 (COVID-19).

Objective

We investigated the engagement of SARS-CoV-2 with TLR4 in order to better understand how to tackle hyperinflammation in COVID-19.

Methods

We combined RNA-sequencing data of human lung tissue and of bronchoalveolar lavage fluid cells derived from COVID-19 patients with functional studies in human macrophages using SARS-CoV-2 spike proteins and viable SARS-CoV-2. Pharmacological inhibitors as well as gene editing with CRISPR/Cas9 were used to delineate the signalling pathways involved.

Results

We found TLR4 to be the most abundantly upregulated TLR in human lung tissue irrespective of the underlying pathology. Accordingly, bronchoalveolar lavage fluid cells from patients with severe COVID-19 showed an NF-κB-pathway dominated immune response, whereas they were mostly defined by type I interferon signalling in moderate COVID-19. Mechanistically, we found the Spike ectodomain, but not receptor binding domain monomer to induce TLR4-dependent inflammation in human macrophages. By using pharmacological inhibitors as well as CRISPR/Cas9 deleted macrophages, we identify SARS-CoV-2 to engage canonical TLR4-MyD88 signalling. Importantly, we demonstrate that TLR4 blockage prevents exaggerated inflammatory responses in human macrophages infected with different SARS-CoV-2 variants, including immune escape variants B.1.1.7.-E484K and B.1.1.529 (omicron).

Conclusion

Our study critically extends the current knowledge on TLR-mediated hyperinflammatory responses to SARS-CoV-2 in human macrophages, paving the way for novel approaches to tackle severe COVID-19.

Take-home message

Our study combining human lung transcriptomics with functional studies in human macrophages clearly supports the design and development of TLR4 - directed therapeutics to mitigate hyperinflammation in severe COVID-19.

Cryo-electron microscopy in the fight against COVID-19-mechanism of virus entry

Cryogenic electron microscopy (cryo-EM) and electron tomography (cryo-ET) have become a critical tool for studying viral particles. Cryo-EM has enhanced our understanding of viral assembly and replication processes at a molecular resolution. Meanwhile, in situ cryo-ET has been used to investigate how viruses attach to and invade host cells. These advances have significantly contributed to our knowledge of viral biology. Particularly, prompt elucidations of structures of the SARS-CoV-2 spike protein and its variants have directly impacted the development of vaccines and therapeutic measures. This review discusses the progress made by cryo-EM based technologies in comprehending the severe acute respiratory syndrome coronavirus-2 (SARS-Cov-2), the virus responsible for the devastating global COVID-19 pandemic in 2020 with focus on the SARS-CoV-2 spike protein and the mechanisms of the virus entry and replication.

The SARS-CoV-2 spike glycoprotein interacts with MAO-B and impairs mitochondrial energetics

SARS-CoV-2 infection is associated with both acute and post-acute neurological symptoms. Emerging evidence suggests that SARS-CoV-2 can alter mitochondrial metabolism, suggesting that changes in brain metabolism may contribute to the development of acute and post-acute neurological complications. Monoamine oxidase B (MAO-B) is a flavoenzyme located on the outer mitochondrial membrane that catalyzes the oxidative deamination of monoamine neurotransmitters. Computational analyses have revealed high similarity between the SARS-CoV-2 spike glycoprotein receptor binding domain on the ACE2 receptor and MAO-B, leading to the hypothesis that SARS-CoV-2 spike glycoprotein may alter neurotransmitter metabolism by interacting with MAO-B. Our results empirically establish that the SARS-CoV-2 spike glycoprotein interacts with MAO-B, leading to increased MAO-B activity in SH-SY5Y neuron-like cells. Common to neurodegenerative disease pathophysiological mechanisms, we also demonstrate that the spike glycoprotein impairs mitochondrial bioenergetics, induces oxidative stress, and perturbs the degradation of depolarized aberrant mitochondria through mitophagy. Our findings also demonstrate that SH-SY5Y neuron-like cells expressing the SARS-CoV-2 spike protein were more susceptible to MPTP-induced necrosis, likely necroptosis. Together, these results reveal novel mechanisms that may contribute to SARS-CoV-2-induced neurodegeneration.

Near-Infrared Light Exposure Triggers ROS to Downregulate Inflammatory Cytokines Induced by SARS-CoV-2 Spike Protein in Human Cell Culture

The leading cause of mortality from SARS-CoV-2 is an exaggerated host immune response, triggering cytokine storms, multiple organ failure and death. Current drug- and vaccine-based therapies are of limited efficacy against novel viral variants. Infrared therapy is a non-invasive and safe method that has proven effective against inflammatory conditions for over 100 years. However, its mechanism of action is poorly understood and has not received widespread acceptance. We herein investigate whether near-infrared (NIR) light exposure in human primary alveolar and macrophage cells could downregulate inflammatory cytokines triggered by the SARS-CoV-2 spike (S) protein or lipopolysaccharide (LPS), and via what underlying mechanism. Our results showed a dramatic reduction in pro-inflammatory cytokines within days of NIR light treatment, while anti-inflammatory cytokines were upregulated. Mechanistically, NIR light stimulated mitochondrial metabolism, induced transient bursts in reactive oxygen species (ROS) and activated antioxidant gene transcription. These, in turn, downregulated ROS and inflammatory cytokines. A causal relationship was shown between the induction of cellular ROS by NIR light exposure and the downregulation of inflammatory cytokines triggered by SARS-CoV-2 S. If confirmed by clinical trials, this method would provide an immediate defense against novel SARS-CoV-2 variants and other inflammatory infectious diseases.

SARS-CoV-2 suppresses TLR4-induced immunity by dendritic cells via C-type lectin receptor DC-SIGN

SARS-CoV-2 causes COVID-19, an infectious disease with symptoms ranging from a mild cold to severe pneumonia, inflammation, and even death. Although strong inflammatory responses are a major factor in causing morbidity and mortality, superinfections with bacteria during severe COVID-19 often cause pneumonia, bacteremia and sepsis. Aberrant immune responses might underlie increased sensitivity to bacteria during COVID-19 but the mechanisms remain unclear. Here we investigated whether SARS-CoV-2 directly suppresses immune responses to bacteria. We studied the functionality of human dendritic cells (DCs) towards a variety of bacterial triggers after exposure to SARS-CoV-2 Spike (S) protein and SARS-CoV-2 primary isolate (hCoV-19/Italy). Notably, pre-exposure of DCs to either SARS-CoV-2 S protein or a SARS-CoV-2 isolate led to reduced type I interferon (IFN) and cytokine responses in response to Toll-like receptor (TLR)4 agonist lipopolysaccharide (LPS), whereas other TLR agonists were not affected. SARS-CoV-2 S protein interacted with the C-type lectin receptor DC-SIGN and, notably, blocking DC-SIGN with antibodies restored type I IFN and cytokine responses to LPS. Moreover, blocking the kinase Raf-1 by a small molecule inhibitor restored immune responses to LPS. These results suggest that SARS-CoV-2 modulates DC function upon TLR4 triggering via DC-SIGN-induced Raf-1 pathway. These data imply that SARS-CoV-2 actively suppresses DC function via DC-SIGN, which might account for the higher mortality rates observed in patients with COVID-19 and bacterial superinfections.

Modulation of IRAK enzymes as a therapeutic strategy against SARS-CoV-2 induced cytokine storm

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of the current pandemic coronavirus disease 2019 (COVID-19). Dysregulated and excessive production of cytokines and chemokines, known as cytokine storm, is frequently seen in patients with severe COVID-19 disease and it can provoke a severe systematic inflammation in the patients. The IL-1R/TLRs/IRAKs signaling network is a key pathway in immune cells that plays a central role in regulating innate immunity and inflammatory responses via stimulating the expression and production of various proinflammatory molecules including cytokines. Modulation of IRAKs activity has been proposed to be a promising strategy in the treatment of inflammatory disorders. In this review, we highlight the biochemical properties of IRAKs and their role in regulating inflammatory molecular signaling pathways and discuss the potential targeting of IRAKs to suppress the SARS-CoV-2-induced cytokine storm in COVID-19 patients.

Selective Impact of Selenium Compounds on Two Cytokine Storm Players

COVID-19 patients suffer from the detrimental effects of cytokine storm and not much success has been achieved to overcome this issue. We sought to test the ability of selenium to reduce the impact of two important cytokine storm players: IL-6 and TNF-α. The effects of four selenium compounds on the secretion of these cytokines from THP-1 macrophages were evaluated in vitro following an LPS challenge. Also, the potential impact of methylseleninic acid (MSeA) on Nrf2 and IκBα was determined after a short treatment of THP-1 macrophages. MSeA was found to be the most potent selenium form among the four selenium compounds tested that reduced the levels of IL-6 and TNF-α secreted by THP-1 macrophages. In addition, an increase in Nrf2 and decrease in pIκBα in human macrophages was observed following MSeA treatment. Our data indicate that COVID-19 patients might benefit from the addition of MSeA to the standard therapy due to its ability to suppress the key players in the cytokine storm.

In Situ Noninvasive Observation of Nitric Oxide Fluctuation in SARS-CoV-2 Infection In Vivo by Organic Near-Infrared-II Fluorescent Molecular Nanoprobes

The pathogenesis understanding of SARS-CoV-2 infection is crucial to prevent the rampant spread of COVID-19 and its contribution to deterioration in health, even death. Nitric oxide (NO), a crucial molecule involved in signal transduction and cytotoxicity, is a possible key regulator in the occurrence and development of COVID-19. However, understanding the pathogenesis of NO in SARS-CoV-2 infection is still in its infancy due to the lack of suitable in situ monitoring probes of NO fluctuation in the complex SARS-CoV-2 infection environment in deep lung tissues. Herein, we developed an activatable near-infrared-II fluorescent molecular nanoprobe (OSNP) that uncages high-resolution and deep-tissue-penetrating near-infrared-II fluorescence signal in specific response to NO for in situ and noninvasive visualization of NO fluctuation in a SARS-CoV-2 infection mouse model in lung tissues. In vivo visualization revealed that the NO level is a positive relationship with SARS-CoV-2 infection progress. With the assistance of immuno-histochemical analyses, we uncovered the NO-involved pathological mechanism, that being the improved NO level is associated with an increase in inducible NO synthase rather than endothelial NO synthase. Our study not only provides the example of a near-infrared-II fluorescent imaging of NO in SARS-CoV-2 infection but also provides opportunities to uncover tunderlying pathomechanism of NO for SARS-Cov-2 infections.

Anti-inflammatory effects of dexamethasone in COVID-19 patients: Translational population PK/PD modeling and simulation

Dexamethasone (DEX) given at a dose of 6 mg once-daily for 10 days is a recommended dosing regimen in patients with coronavirus disease 2019 (COVID-19) requiring oxygen therapy. We developed a population pharmacokinetic and pharmacodynamic (PopPK/PD) model of DEX anti-inflammatory effects in COVID-19 and provide simulations comparing the expected efficacy of four dosing regimens of DEX. Nonlinear mixed-effects modeling and simulations were performed using Monolix Suite version 2021R1 (Lixoft, France). Published data for DEX PK in patients with COVID-19 exhibited moderate variability with a clearance of about half that in healthy adults. No accumulation of the drug was expected even with daily oral doses of 12 mg. Indirect effect models of DEX inhibition of TNFα, IL-6, and CRP plasma concentrations were enacted and simulations performed for DEX given at 1.5, 3, 6, and 12 mg daily for 10 days. The numbers of individuals that achieved specified reductions in inflammatory biomarkers were compared among the treatment groups. The simulations indicate the need for 6 or 12 mg daily doses of DEX for 10 days for simultaneous reductions in TNFα, IL-6, and CRP. Possibly beneficial is DEX given at a dose of 12 mg compared to 6 mg. The PopPK/PD model may be useful in the assessment of other anti-inflammatory compounds as well as drug combinations in the treatment of cytokine storms.

The Role of Toll-like Receptor-4 in Macrophage Imbalance in Lethal COVID-19 Lung Disease, and Its Correlation with Galectin-3

To the current data, there have been 6,955,141 COVID-19-related deaths worldwide, reported to WHO. Toll-like receptors (TLRs) implicated in bacterial and virus sensing could be a crosstalk between activation of persistent innate-immune inflammation, and macrophage's sub-population alterations, implicated in cytokine storm, macrophage over-activation syndrome, unresolved Acute Respiratory Disease Syndrome (ARDS), and death. The aim of this study is to demonstrate the association between Toll-like-receptor-4 (TLR-4)-induced inflammation and macrophage imbalance in the lung inflammatory infiltrate of lethal COVID-19 disease. Twenty-five cases of autopsy lung tissues were studied by digital pathology-based immunohistochemistry to evaluate expression levels of TLR-4 (CD 284), pan-macrophage marker CD68 (clone KP1), sub-population marker related to alveolar macrophage Galectin-3 (GAL-3) (clone 9C4), and myeloid derived CD163 (clone MRQ-26), respectively. SARS-CoV-2 viral persistence has been evaluated by in situ hybridation (ISH) method. This study showed TLR-4 up-regulation in a subgroup of patients, increased macrophage infiltration in both Spike-1(+) and Spike-1(-) lungs (p < 0.0001), and a macrophage shift with important down-regulation of GAL-3(+) alveolar macrophages associated with Spike-1 persistence (p < 0.05), in favor of CD163(+) myeloid derived monocyte-macrophages. Data show that TLR-4 expression induces a persistent activation of the inflammation, with inefficient resolution, and pathological macrophage shift, thus explaining one of the mechanisms of lethal COVID-19.

Unlocking therapeutic potential: integration of drug repurposing and immunotherapy for various disease targeting

Drug repurposing, also known as drug repositioning, entails the application of pre-approved or formerly assessed drugs having potentially functional therapeutic amalgams for curing various disorders or disease conditions distinctive from their original remedial indication. It has surfaced as a substitute for the development of drugs for treating cancer, cardiovascular diseases, neurodegenerative disorders, and various infectious diseases like Covid-19. Although the earlier lines of findings in this area were serendipitous, recent advancements are based on patient centered approaches following systematic, translational, drug targeting practices that explore pathophysiological ailment mechanisms. The presence of definite information and numerous records with respect to beneficial properties, harmfulness, and pharmacologic characteristics of repurposed drugs increase the chances of approval in the clinical trial stages. The last few years have showcased the successful emergence of repurposed drug immunotherapy in treating various diseases. In this light, the present review emphasises on incorporation of drug repositioning with Immunotherapy targeted for several disorders.

SARS-CoV-2 Spike Proteins and Cell-Cell Communication Induce P-Selectin and Markers of Endothelial Injury, NETosis, and Inflammation in Human Lung Microvascular Endothelial Cells and Neutrophils: Implications for the Pathogenesis of COVID-19 Coagulopathy

COVID-19 progression often involves severe lung injury, inflammation, coagulopathy, and leukocyte infiltration into pulmonary tissues. The pathogenesis of these complications is unknown. Because vascular endothelium and neutrophils express angiotensin-converting enzyme-2 and spike (S)-proteins, which are present in bodily fluids and tissues of SARS-CoV-2-infected patients, we investigated the effect of S-proteins and cell-cell communication on human lung microvascular endothelial cells and neutrophils expression of P-selectin, markers of coagulopathy, NETosis, and inflammation. Exposure of endothelial cells or neutrophils to S-proteins and endothelial-neutrophils co-culture induced P-selectin transcription and expression, significantly increased expression/secretion of IL-6, von Willebrand factor (vWF, pro-coagulant), and citrullinated histone H3 (cit-H3, NETosis marker). Compared to the SARS-CoV-2 Wuhan variant, Delta variant S-proteins induced 1.4-15-fold higher P-selectin and higher IL-6 and vWF. Recombinant tissue factor pathway inhibitor (rTFPI), 5,5'-dithio-bis-(2-nitrobenzoic acid) (thiol blocker), and thrombomodulin (anticoagulant) blocked S-protein-induced vWF, IL-6, and cit-H3. This suggests that following SARS-CoV-2 contact with the pulmonary endothelium or neutrophils and endothelial-neutrophil interactions, S-proteins increase adhesion molecules, induce endothelial injury, inflammation, NETosis and coagulopathy via the tissue factor pathway, mechanisms involving functional thiol groups, and/or the fibrinolysis system. Using rTFPI, effectors of the fibrinolysis system and/or thiol-based drugs could be viable therapeutic strategies against SARS-CoV-2-induced endothelial injury, inflammation, NETosis, and coagulopathy.

Role of toll-like receptors in the pathogenesis of COVID-19: Current and future perspectives

The coronavirus disease 2019 (COVID-19) pandemic underlines a persistent threat of respiratory tract infectious diseases and warrants preparedness for a rapid response. At present, COVID-19 has had a serious social impact and imposed a heavy global burden on public health. The exact pathogenesis of COVID-19 has not been fully elucidated. Since the outbreak of COVID-19, a renewed attention has been brought to Toll-like receptors (TLRs). Available data and new findings have demonstrated that the interaction of human TLRs and SARS-CoV-2 is a vital mediator of COVID-19 immunopathogenesis. TLRs such as TLR2, 4, 7 and 8 are potentially important in viral combat and activation of immunity in patients with COVID-19. Therapeutics targeting TLRs are currently considered promising options against the pandemic. A number of TLR-targeting immunotherapeutics are now being investigated in preclinical studies and different phases of clinical trials. In addition, innovative vaccines based on TLRs under development could be a promising approach for building a new generation of vaccines to solve the current challenges. In this review, we summarize recent progress in the role of TLRs in COVID-19, focusing the new candidate drugs targeting TLRs, the current technology and potential paths forward for employing TLR agonists as vaccine adjuvants.

Exploring the immunogenic properties of SARS-CoV-2 structural proteins: PAMP:TLR signaling in the mediation of the neuroinflammatory and neurologic sequelae of COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) produces an array of neurologic and neuropsychiatric symptoms in the acute and post-acute phase of infection (PASC; post-acute sequelae of SARS-CoV-2 infection). Neuroinflammatory processes are considered key factors in the etiology of these symptoms. Several mechanisms underpinning the development of inflammatory events in the brain have been proposed including SARS-CoV-2 neurotropism and peripheral inflammatory responses (i.e., cytokine storm) to infection, which might produce neuroinflammation via immune-to-brain signaling pathways. In this review, we explore evidence in support of an alternate mechanism whereby structural proteins (e.g., spike and spike S1 subunit) derived from SARS-CoV-2 virions function as pathogen-associated molecular patterns (PAMPs) to elicit proinflammatory immune responses in the periphery and/or brain via classical Toll-Like Receptor (TLR) inflammatory pathways. We propose that SARS-CoV-2 structural proteins might directly produce inflammatory processes in brain independent of and/or in addition to peripheral proinflammatory effects, which might converge to play a causal role in the development of neurologic/neuropsychiatric symptoms in COVID-19.

In vivo inhibition of nuclear ACE2 translocation protects against SARS-CoV-2 replication and lung damage through epigenetic imprinting

In vitro, ACE2 translocates to the nucleus to induce SARS-CoV-2 replication. Here, using digital spatial profiling of lung tissues from SARS-CoV-2-infected golden Syrian hamsters, we show that a specific and selective peptide inhibitor of nuclear ACE2 (NACE2i) inhibits viral replication two days after SARS-CoV-2 infection. Moreover, the peptide also prevents inflammation and macrophage infiltration, and increases NK cell infiltration in bronchioles. NACE2i treatment increases the levels of the active histone mark, H3K27ac, restores host translation in infected hamster bronchiolar cells, and leads to an enrichment in methylated ACE2 in hamster bronchioles and lung macrophages, a signature associated with virus protection. In addition, ACE2 methylation is increased in myeloid cells from vaccinated patients and associated with reduced SARS-CoV-2 spike protein expression in monocytes from individuals who have recovered from infection. This protective epigenetic scarring of ACE2 is associated with a reduced latent viral reservoir in monocytes/macrophages and enhanced immune protection against SARS-CoV-2. Nuclear ACE2 may represent a therapeutic target independent of the variant and strain of viruses that use the ACE2 receptor for host cell entry.

Corilagin ameliorates macrophages inflammation in atherosclerosis through TLR4-NFκB/MAPK pathway

Corilagin, a polyphenolic tannic acid compound, showed significant anti-inflammatory activity in atherosclerotic mice. The present study aimed to evaluate the effect and mechanism of corilagin in atherosclerosis by in vivo, in vitro and in molecular docking strategies analysis. An atherosclerotic model was established by feeding ApoE-/- mice a high-fat diet. Murine RAW264.7 macrophages were cultured and induced with lipopolysaccharide (LPS). Treatment with corilagin had a marked inhibitory effect on the plaque area and lipid accumulation in atherosclerotic mice. Corilagin decreased the expression of iNOS and promoted the expression of CD206 in aortic plaque, as well as inhibited the production of proinflammatory factors in HFD-fed ApoE-/- mice and LPS-induced RAW264.6 cell. Corilagin also obviously inhibited the expression of TLR4, reduced the phosphorylation of the JNK, the protein expressions of p38 and NF-κB pathway. In addition, corilagin markedly diminished the nuclear translocation of NF-κBp65. Similarly, molecular docking study suggested that hydrogen bonds were detected between the corilagin and the five proteins (TLR4, Myd88, p65, P38, and JNK) with a significant "CDOCKER energy". These results showed that the antiatherosclerotic effect of corilagin against M1 macrophage polarization and inflammation via suppression the activation of TLR4-NFκB/MAPK signaling pathway. Therefore, corilagin could be a promising lead compound to develop drugs for the treatment of atherosclerosis.

Recombinant SARS-CoV-2 Spike Protein Stimulates Secretion of Chymase, Tryptase, and IL-1β from Human Mast Cells, Augmented by IL-33

SARS-CoV-2 infects cells via its spike (S) protein binding to its surface receptor angiotensin-converting enzyme 2 (ACE2) and results in the production of multiple proinflammatory cytokines, especially in the lungs, leading to what is known as COVID-19. However, the cell source and the mechanism of secretion of such cytokines have not been adequately characterized. In this study, we used human cultured mast cells that are plentiful in the lungs and showed that recombinant SARS-CoV-2 full-length S protein (1-10 ng/mL), but not its receptor-binding domain (RBD), stimulates the secretion of the proinflammatory cytokine interleukin-1β (IL-1β) as well as the proteolytic enzymes chymase and tryptase. The secretion of IL-1β, chymase, and tryptase is augmented by the co-administration of interleukin-33 (IL-33) (30 ng/mL). This effect is mediated via toll-like receptor 4 (TLR4) for IL-1β and via ACE2 for chymase and tryptase. These results provide evidence that the SARS-CoV-2 S protein contributes to inflammation by stimulating mast cells through different receptors and could lead to new targeted treatment approaches.

Expression profile of HERVs and inflammatory mediators detected in nasal mucosa as a predictive biomarker of COVID-19 severity

Introduction

Our research group and others demonstrated the implication of the human endogenous retroviruses (HERVs) in SARS-CoV-2 infection and their association with disease progression, suggesting HERVs as contributing factors in COVID-19 immunopathology. To identify early predictive biomarkers of the COVID-19 severity, we analyzed the expression of HERVs and inflammatory mediators in SARS-CoV-2-positive and -negative nasopharyngeal/oropharyngeal swabs with respect to biochemical parameters and clinical outcome.

Methods

Residuals of swab samples (20 SARS-CoV-2-negative and 43 SARS-CoV-2-positive) were collected during the first wave of the pandemic and expression levels of HERVs and inflammatory mediators were analyzed by qRT-Real time PCR.

Results

The results obtained show that infection with SARS-CoV-2 resulted in a general increase in the expression of HERVs and mediators of the immune response. In particular, SARS-CoV-2 infection is associated with increased expression of HERV-K and HERV-W, IL-1β, IL-6, IL-17, TNF-α, MCP-1, INF-γ, TLR-3, and TLR-7, while lower levels of IL-10, IFN-α, IFN-β, and TLR-4 were found in individuals who underwent hospitalization. Moreover, higher expression of HERV-W, IL-1β, IL-6, IFN-α, and IFN-β reflected the respiratory outcome of patients during hospitalization. Interestingly, a machine learning model was able to classify hospitalized vs not hospitalized patients with good accuracy based on the expression levels of HERV-K, HERV-W, IL-6, TNF-a, TLR-3, TLR-7, and the N gene of SARS-CoV-2. These latest biomarkers also correlated with parameters of coagulation and inflammation.

Discussion

Overall, the present results suggest HERVs as contributing elements in COVID-19 and early genomic biomarkers to predict COVID-19 severity and disease outcome.

Toll-like receptor 7 (TLR7)-mediated antiviral response protects mice from lethal SARS-CoV-2 infection

SARS-CoV-2-induced impaired antiviral and excessive inflammatory responses cause fatal pneumonia. However, the key pattern recognition receptors that elicit effective antiviral and lethal inflammatory responses in-vivo are not well defined. CoVs possess single-stranded RNA (ssRNA) genome that is abundantly produced during infection and stimulates both antiviral interferon (IFN) and inflammatory cytokine/ chemokine responses. Therefore, in this study, using wild-type control and TLR7 deficient BALB/c mice infected with a mouse-adapted SARS-COV-2 (MA-CoV-2), we evaluated the role of TLR7 signaling in MA-CoV-2-induced antiviral and inflammatory responses and disease outcome. We show that TLR7-deficient mice are more susceptible to MA-CoV-2 infection as compared to infected control mice. Further evaluation of MA-CoV-2 infected lungs showed significantly reduced mRNA levels of antiviral type I (IFNα/β) and type III (IFNλ) IFNs, IFN stimulated genes (ISGs, ISG15 and CXCL10), and several pro-inflammatory cytokines/chemokines in TLR7 deficient compared to control mice. Reduced lung IFN/ISG levels and increased morbidity/mortality in TLR7 deficient mice correlated with high lung viral titer. Detailed examination of total cells from MA-CoV-2 infected lungs showed high neutrophil count in TLR7 deficient mice compared to control mice. Additionally, blocking TLR7 activity post-MA-CoV-2 infection using a specific inhibitor also enhanced disease severity. In summary, our results conclusively establish that TLR7 signaling is protective during SARS-CoV-2 infection, and despite robust inflammatory response, TLR7-mediated IFN/ISG responses likely protect the host from lethal disease. Given similar outcomes in control and TLR7 deficient humans and mice, these results show that MA-CoV-2 infected mice serve as excellent model to study COVID-19.

Innate and adaptive immunity to SARS-CoV-2 and predisposing factors

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus (SARS-CoV-2), has affected all countries worldwide. Although some symptoms are relatively mild, others are still associated with severe and even fatal clinical outcomes. Innate and adaptive immunity are important for the control of SARS-CoV-2 infections, whereas a comprehensive characterization of the innate and adaptive immune response to COVID-19 is still lacking and the mechanisms underlying immune pathogenesis and host predisposing factors are still a matter of scientific debate. Here, the specific functions and kinetics of innate and adaptive immunity involved in SARS-CoV-2 recognition and resultant pathogenesis are discussed, as well as their immune memory for vaccinations, viral-mediated immune evasion, and the current and future immunotherapeutic agents. We also highlight host factors that contribute to infection, which may deepen the understanding of viral pathogenesis and help identify targeted therapies that attenuate severe disease and infection.

Orthohantavirus Replication in the Context of Innate Immunity

Orthohantaviruses are rodent-borne, negative-sense RNA viruses that are capable of causing severe vascular disease in humans. Over the course of viral evolution, these viruses have tailored their replication cycles in such a way as to avoid and/or antagonize host innate immune responses. In the rodent reservoir, this results in life long asymptomatic infections. However, in hosts other than its co-evolved reservoir, the mechanisms for subduing the innate immune response may be less efficient or absent, potentially leading to disease and/or viral clearance. In the case of human orthohantavirus infection, the interaction of the innate immune response with viral replication is thought to give rise to severe vascular disease. The orthohantavirus field has made significant advancements in understanding how these viruses replicate and interact with host innate immune responses since their identification by Dr. Ho Wang Lee and colleagues in 1976. Therefore, the purpose of this review, as part of this special issue dedicated to Dr. Lee, was to summarize the current knowledge of orthohantavirus replication, how viral replication activates innate immunity, and how the host antiviral response, in turn, impacts viral replication.

Novel Therapeutic Target Critical for SARS-CoV-2 Infectivity and Induction of the Cytokine Release Syndrome

We discovered a novel therapeutic target critical for SARS-CoV-2, cellular infectivity and the induction of the cytokine release syndrome. Here, we show that the mammalian enzyme neuraminidase-1 (Neu-1) is part of a highly conserved signaling platform that regulates the dimerization and activation of the ACE2 receptors and the Toll-like receptors (TLRs) implicated in the cytokine release syndrome (CRS). Activated Neu-1 cleaves glycosylated residues that provide a steric hindrance to both ACE2 and TLR dimerization, a process critical to both viral attachment to the receptor and entry into the cell and TLR activation. Blocking Neu-1 inhibited ACE2 receptor dimerization and internalization, TLR dimerization and activation, and the expression of several key inflammatory molecules implicated in the CRS and death from ARDS. Treatments that target Neu-1 are predicted to be highly effective against infection with SARS-CoV-2, given the central role played by this enzyme in viral cellular entry and the induction of the CRS.

The shed P2X7 receptor is an index of adverse clinical outcome in COVID-19 patients

Introduction

The pathophysiology of the Corona Virus Disease 2019 (COVID-19) is incompletely known. A robust inflammatory response caused by viral replication is a main cause of the acute lung and multiorgan injury observed in critical patients. Inflammasomes are likely players in COVID-19 pathogenesis. The P2X7 receptor (P2X7R), a plasma membrane ATP-gated ion channel, is a main activator of the NLRP3 inflammasome, of the ensuing release of inflammatory cytokines and of cell death by pyroptosis. The P2X7R has been implicated in COVID-19-dependent hyperinflammation and in the associated multiorgan damage. Shed P2X7R (sP2X7R) and shed NLRP3 (sNLRP3) have been detected in plasma and other body fluids, especially during infection and inflammation.

Methods

Blood samples from 96 patients with confirmed SARS-CoV-2 infection with various degrees of disease severity were tested at the time of diagnosis at hospital admission. Standard haematological parameters and IL-6, IL-10, IL-1β, sP2X7R and sNLRP3 levels were measured, compared to reference values, statistically validated, and correlated to clinical outcome.

Results

Most COVID-19 patients included in this study had lymphopenia, eosinopenia, neutrophilia, increased inflammatory and coagulation indexes, and augmented sNLRP3, IL-6 and IL-10 levels. Blood concentration of sP2X7R was also increased, and significantly positively correlated with lymphopenia, procalcitonin (PCT), IL-10, and alanine transaminase (ALT). Patients with increased sP2X7R levels at diagnosis also showed fever and respiratory symptoms, were more often transferred to Pneumology division, required mechanical ventilation, and had a higher likelihood to die during hospitalization.

Conclusion

Blood sP2X7R was elevated in the early phases of COVID-19 and predicted an adverse clinical outcome. It is suggested that sP2X7R might be a useful marker of disease progression.

TLRs: Innate Immune Sentries against SARS-CoV-2 Infection

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been responsible for a devastating pandemic since March 2020. Toll-like receptors (TLRs), crucial components in the initiation of innate immune responses to different pathogens, trigger the downstream production of pro-inflammatory cytokines, interferons, and other mediators. It has been demonstrated that they contribute to the dysregulated immune response observed in patients with severe COVID-19. TLR2, TLR3, TLR4 and TLR7 have been associated with COVID-19 severity. Here, we review the role of TLRs in the etiology and pathogenesis of COVID-19, including TLR7 and TLR3 rare variants, the L412F polymorphism in TLR3 that negatively regulates anti-SARS-CoV-2 immune responses, the TLR3-related cellular senescence, the interaction of TLR2 and TLR4 with SARS-CoV-2 proteins and implication of TLR2 in NET formation by SARS-CoV-2. The activation of TLRs contributes to viral clearance and disease resolution. However, TLRs may represent a double-edged sword which may elicit dysregulated immune signaling, leading to the production of proinflammatory mediators, resulting in severe disease. TLR-dependent excessive inflammation and TLR-dependent antiviral response may tip the balance towards the former or the latter, altering the equilibrium that drives the severity of disease.

Improved understanding of biorisk for research involving microbial modification using annotated sequences of concern

Regulation of research on microbes that cause disease in humans has historically been focused on taxonomic lists of 'bad bugs'. However, given our increased knowledge of these pathogens through inexpensive genome sequencing, 5 decades of research in microbial pathogenesis, and the burgeoning capacity of synthetic biologists, the limitations of this approach are apparent. With heightened scientific and public attention focused on biosafety and biosecurity, and an ongoing review by US authorities of dual-use research oversight, this article proposes the incorporation of sequences of concern (SoCs) into the biorisk management regime governing genetic engineering of pathogens. SoCs enable pathogenesis in all microbes infecting hosts that are 'of concern' to human civilization. Here we review the functions of SoCs (FunSoCs) and discuss how they might bring clarity to potentially problematic research outcomes involving infectious agents. We believe that annotation of SoCs with FunSoCs has the potential to improve the likelihood that dual use research of concern is recognized by both scientists and regulators before it occurs.

COVID-19, Blood Lipid Changes, and Thrombosis

Although there is increasing evidence that oxidative stress and inflammation induced by COVID-19 may contribute to increased risk and severity of thromboses, the underlying mechanism(s) remain to be understood. The purpose of this review is to highlight the role of blood lipids in association with thrombosis events observed in COVID-19 patients. Among different types of phospholipases A₂ that target cell membrane phospholipids, there is increasing focus on the inflammatory secretory phospholipase A₂ IIA (sPLA₂-IIA), which is associated with the severity of COVID-19. Analysis indicates increased sPLA₂-IIA levels together with eicosanoids in the sera of COVID patients. sPLA₂ could metabolise phospholipids in platelets, erythrocytes, and endothelial cells to produce arachidonic acid (ARA) and lysophospholipids. Arachidonic acid in platelets is metabolised to prostaglandin H2 and thromboxane A₂, known for their pro-coagulation and vasoconstrictive properties. Lysophospholipids, such as lysophosphatidylcholine, could be metabolised by autotaxin (ATX) and further converted to lysophosphatidic acid (LPA). Increased ATX has been found in the serum of patients with COVID-19, and LPA has recently been found to induce NETosis, a clotting mechanism triggered by the release of extracellular fibres from neutrophils and a key feature of the COVID-19 hypercoagulable state. PLA2 could also catalyse the formation of platelet activating factor (PAF) from membrane ether phospholipids. Many of the above lipid mediators are increased in the blood of patients with COVID-19. Together, findings from analyses of blood lipids in COVID-19 patients suggest an important role for metabolites of sPLA₂-IIA in COVID-19-associated coagulopathy (CAC).