A Ca(2+)-dependent signalling circuit regulates influenza A virus internalization and infection

Respiratory tract barrier dysfunction in viral-bacterial co-infection cases

A preceding viral infection of the respiratory tract predisposes the host to secondary bacterial pneumonia, known as a major cause of morbidity and mortality. However, the underlying mechanism of the viral-bacterial synergy that leads to disease progression has remained elusive, thus hampering the production of effective prophylactic and therapeutic intervention options. In addition to viral-induced airway epithelial damage, which allows dissemination of bacteria to the lower respiratory tract and increases their invasiveness, dysfunction of immune defense following a viral infection has been implicated as a factor for enhanced susceptibility to secondary bacterial infections. Given the proximity of the oral cavity to the respiratory tract, where viruses enter and replicate, it is also well-established that oral health status can significantly influence the initiation, progression, and pathology of respiratory viral infections. This review was conducted to focus on the dysfunction of the respiratory barrier, which plays a crucial role in providing physical and secretory barriers as well as immune defense in the context of viral-bacterial synergy. Greater understanding of barrier response to viral-bacterial co-infections, will ultimately lead to development of effective, broad-spectrum therapeutic approaches for prevention of enhanced susceptibility to these pathogens.

Conserved sequence features in intracellular domains of viral spike proteins

Viral spike proteins mutate frequently, but conserved features within these proteins often have functional importance and can inform development of anti-viral therapies which circumvent the effects of viral sequence mutations. Through analysis of large numbers of viral spike protein sequences from several viral families, we found highly (>99%) conserved patterns within their intracellular domains. The patterns generally consist of one or more basic amino acids (arginine or lysine) adjacent to a cysteine, many of which are known to undergo acylation. These patterns were not enriched in cellular proteins in general. Molecular dynamics simulations show direct electrostatic and hydrophobic interactions between these conserved residues in hemagglutinin (HA) from influenza A and B and the phosphoinositide PIP2. Super-resolution microscopy shows nanoscale colocalization of PIP2 and several of the same viral proteins. We propose the hypothesis that these conserved viral spike protein features can interact with phosphoinositides such as PIP2.

Effect of calcium channel blockers on influenza incidence: a population-based retrospective cohort study using administrative claims data in Japan

OBJECTIVES

Laboratory experiments have indicated that calcium channel blockers (CCBs) inhibit the entry and replication of influenza A virus in cells. However, no clinical studies have assessed the incidence of influenza among patients receiving CCBs. This study aimed to investigate the association between CCB use and the incidence of influenza among patients with hypertension using administrative claims data in Japan.

DESIGN

Retrospective cohort study.

SETTING

Administrative health insurance claims database of Kumamoto Prefecture, Japan.

PARTICIPANTS

360 515 patients with hypertension (10th edition of the International Classification of Diseases code I10) who were prescribed CCBs and 171 142 patients who were prescribed angiotensin-converting enzyme inhibitors (ACEIs)/angiotensin receptor blockers (ARBs) between 2012 and 2016.

PRIMARY OUTCOME

We compared the incidence of influenza between the CCB and ACEI/ARB groups using high-dimensional propensity-score (HD-PS) matching.

RESULTS

A total of 166 814 HD-PS matched pairs were obtained. Before HD-PS matching, the CCB group had a significantly lower influenza incidence than the ACEI/ARB group in the overall analysis (2.4% vs 2.5%, p=0.007; risk ratio 0.95, 95% CI 0.92 to 0.99). However, no significant difference was observed between the two groups after HD-PS matching (2.4% vs 2.5%, p=0.067; risk ratio 0.96, 95% CI 0.92 to 1.00); only in 2012 did the CCB group have a significantly lower likelihood of influenza than the ACEI/ARB group.

CONCLUSIONS

No significant difference was observed in the influenza incidence between the CCB and ACEI/ARB groups. A direct comparative study between background-matched patients with and without CCBs is warranted to confirm the effect of CCBs on reducing the incidence of influenza.

Vagal-α7 nicotinic acetylcholine receptor signaling exacerbates influenza severity by promoting lung epithelial cell infection

The vagus nerve circuit, operating through the alpha-7 nicotinic acetylcholine receptor (α7 nAChR), regulates the inflammatory response by influencing immune cells. However, the role of vagal-α7 nAChR signaling in influenza virus infection is unclear. In particular, does vagal-α7 nAChR signaling impact the infection of alveolar epithelial cells (AECs), the primary target cells of influenza virus? Here, we demonstrated a distinct role of α7 nAChR in type II AECs compared to its role in immune cells during influenza infection. We found that deletion of Chrna7 (encoding gene of α7 nAChR) in type II AECs or disruption of vagal circuits reduced lung influenza infection and protected mice from influenza-induced lung injury. We further unveiled that activation of α7 nAChR enhanced influenza infection through PTP1B-NEDD4L-ASK1-p38MAPK pathway. Mechanistically, activation of α7 nAChR signaling decreased p38MAPK phosphorylation during infection, facilitating the nuclear export of influenza viral ribonucleoproteins and thereby promoting infection. Taken together, our findings reveal a mechanism mediated by vagal-α7 nAChR signaling that promotes influenza viral infection and exacerbates disease severity. Targeting vagal-α7 nAChR signaling may offer novel strategies for combating influenza virus infections.

Diltiazem HCl suppresses porcine reproductive and respiratory syndrome virus infection in susceptible cells and in swine

Porcine reproductive and respiratory syndrome virus (PRRSV) is a pathogen for swine, resulting in substantial economic losses to the swine industry. However, there has been little success in developing effective vaccines or drugs for PRRSV control. In the present study, we discovered that Diltiazem HCl, an inhibitor of L-type Ca2+ channel, effectively suppresses PRRSV replication in MARC-145, PK-15CD163 and PAM cells in dose-dependent manner. Furthermore, it demonstrates a broad-spectrum activity against both PRRSV-1 and PRRSV-2 strains. Additionally, we explored the underlying mechanisms and found that Diltiazem HCl -induced inhibition of PRRSV associated with regulation of calcium ion homeostasis in susceptible cells. Moreover, we evaluated the antiviral effects of Diltiazem HCl in PRRSV-challenged piglets, assessing rectal temperature, viremia, and gross and microscopic lung lesions. Our results indicate that Diltiazem HCl treatment alleviates PRRSV-induced rectal temperature spikes, pulmonary pathological changes, and serum viral load. In conclusion, our data suggest that Diltiazem HCl could serve as a novel therapeutic drug against PRRSV infection.

The pathogenesis of influenza in intact alveoli: virion endocytosis and its effects on the lung's air-blood barrier

Lung infection by influenza A virus (IAV) is a major cause of global mortality from lung injury, a disease defined by widespread dysfunction of the lung's air-blood barrier. Endocytosis of IAV virions by the alveolar epithelium - the cells that determine barrier function - is central to barrier loss mechanisms. Here, we address the current understanding of the mechanistic steps that lead to endocytosis in the alveolar epithelium, with an eye to how the unique structure of lung alveoli shapes endocytic mechanisms. We highlight where future studies of alveolar interactions with IAV virions may lead to new therapeutic approaches for IAV-induced lung injury.

Identification of a small chemical as a lysosomal calcium mobilizer and characterization of its ability to inhibit autophagy and viral infection

We previously identified glyceraldehyde 3-phosphate dehydrogenase (GAPDH) as one of the cyclic adenosine diphosphoribose (cADPR)'s binding proteins and found that GAPDH participates in cADPR-mediated Ca2+ release from endoplasmic reticulum via ryanodine receptors (RyRs). Here, we aimed to chemically synthesise and pharmacologically characterise novel cADPR analogues. Based on the simulated cADPR-GAPDH complex structure, we performed the structure-based drug screening, identified several small chemicals with high docking scores to cADPR's binding pocket in GAPDH and showed that two of these compounds, C244 and C346, are potential cADPR antagonists. We further synthesised several analogues of C346 and found that its analogue, G42, also mobilised Ca2+ release from lysosomes. G42 alkalised lysosomal pH and inhibited autophagosome-lysosome fusion. Moreover, G42 markedly inhibited Zika virus (ZIKV, a flavivirus) or murine hepatitis virus (MHV, a β-coronavirus) infections of host cells. These results suggest that G42 inhibits virus infection, likely by triggering lysosomal Ca2+ mobilisation and inhibiting autophagy.

Transcriptomic Profiling of Influenza A Virus-Infected Mouse Lung at Recovery Stage Using RNA Sequencing

Influenza A virus (IAV) is known to cause mild to severe respiratory illness. Under some conditions, the infection can lead to pneumonia (viral or bacterial), acute respiratory distress syndrome, and other complications that can be fatal, especially in vulnerable populations such as the elderly, young children, and individuals with underlying health conditions. Despite previous studies, little is known about the host immune response and neuroimmune interactions in IAV infection. Using RNA sequencing, we performed transcriptomic analysis of murine lung tissue 21 days post infection (dpi) with IAV (H1N1) in order to find the differentially expression genes (DEGs) related to the host immune response and neuroimmune interactions inside the lung during recovery. Among 792 DEGs, 434 genes were up-regulated, whereas 358 genes were down-regulated. The most prominent molecular functions of the up-regulated genes were related to the immune response and tissue repair, whereas a large proportion of the down-regulated genes were associated with neural functions. Although further molecular/functional studies need to be performed for these DEGs, our results facilitate the understanding of the host response (from innate immunity to adaptive immunity) and neuroimmune interactions in infected lungs at the recovery stage of IAV infection. These genes might have potential uses as mechanistic/diagnostic biomarkers and represent possible targets for anti-IAV therapies.

Targeting host calcium channels and viroporins: a promising strategy for SARS-CoV-2 therapy

Despite passing the pandemic phase of the COVID-19, researchers are still investigating various drugs. Previous evidence suggests that blocking the calcium channels may be a suitable treatment option. Ca2+ is required to enhance the fusion process of Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Also, some important inflammatory factors during SARS-CoV-2 infection are dependent on Ca2+ level. On the other hand, viroporins have emerged as attractive targets for antiviral therapy due to their essential role in viral replication and pathogenesis. By inhibiting the host calcium channels and viroporins, it is possible to limit the spread of infection. Therefore, calcium channel blockers (CCBs) and drugs targeting Viroporins can be considered an effective option in the fight against SARS-CoV-2.

Rhinovirus C causes heterogeneous infection and gene expression in airway epithelial cell subsets

Rhinoviruses infect ciliated airway epithelial cells, and rhinoviruses' nonstructural proteins quickly inhibit and divert cellular processes for viral replication. However, the epithelium can mount a robust innate antiviral immune response. Therefore, we hypothesized that uninfected cells contribute significantly to the antiviral immune response in the airway epithelium. Using single-cell RNA sequencing, we demonstrate that both infected and uninfected cells upregulate antiviral genes (e.g. MX1, IFIT2, IFIH1, and OAS3) with nearly identical kinetics, whereas uninfected non-ciliated cells are the primary source of proinflammatory chemokines. Furthermore, we identified a subset of highly infectable ciliated epithelial cells with minimal interferon responses and determined that interferon responses originate from distinct subsets of ciliated cells with moderate viral replication. These findings suggest that the composition of ciliated airway epithelial cells and coordinated responses of infected and uninfected cells could determine the risk of more severe viral respiratory illnesses in children with asthma, chronic obstructive pulmonary disease, and genetically susceptible individuals.

Advanced fluorescence microscopy in respiratory virus cell biology

Respiratory viruses are a major public health burden across all age groups around the globe, and are associated with high morbidity and mortality rates. They can be transmitted by multiple routes, including physical contact or droplets and aerosols, resulting in efficient spreading within the human population. Investigations of the cell biology of virus replication are thus of utmost importance to gain a better understanding of virus-induced pathogenicity and the development of antiviral countermeasures. Light and fluorescence microscopy techniques have revolutionized investigations of the cell biology of virus infection by allowing the study of the localization and dynamics of viral or cellular components directly in infected cells. Advanced microscopy including high- and super-resolution microscopy techniques available today can visualize biological processes at the single-virus and even single-molecule level, thus opening a unique view on virus infection. We will highlight how fluorescence microscopy has supported investigations on virus cell biology by focusing on three major respiratory viruses: respiratory syncytial virus (RSV), Influenza A virus (IAV) and SARS-CoV-2. We will review our current knowledge of virus replication and highlight how fluorescence microscopy has helped to improve our state of understanding. We will start by introducing major imaging and labeling modalities and conclude the chapter with a perspective discussion on remaining challenges and potential opportunities.

Interaction of Teleost Fish TRPV4 with DEAD Box RNA Helicase 1 Regulates Iridovirus Replication

Viral diseases are a significant risk to the aquaculture industry. Transient receptor potential vanilloid 4 (TRPV4) has been reported to be involved in regulating viral activity in mammals, but its regulatory effect on viruses in teleost fish remains unknown. Here, the role of the TRPV4-DEAD box RNA helicase 1 (DDX1) axis in viral infection was investigated in mandarin fish (Siniperca chuatsi). Our results showed that TRPV4 activation mediates Ca2+ influx and facilitates infectious spleen and kidney necrosis virus (ISKNV) replication, whereas this promotion was nearly eliminated by an M709D mutation in TRPV4, a channel Ca2+ permeability mutant. The concentration of cellular Ca2+ increased during ISKNV infection, and Ca2+ was critical for viral replication. TRPV4 interacted with DDX1, and the interaction was mediated primarily by the N-terminal domain (NTD) of TRPV4 and the C-terminal domain (CTD) of DDX1. This interaction was attenuated by TRPV4 activation, thereby enhancing ISKNV replication. DDX1 could bind to viral mRNAs and facilitate ISKNV replication, which required the ATPase/helicase activity of DDX1. Furthermore, the TRPV4-DDX1 axis was verified to regulate herpes simplex virus 1 replication in mammalian cells. These results suggested that the TRPV4-DDX1 axis plays an important role in viral replication. Our work provides a novel molecular mechanism for host involvement in viral regulation, which would be of benefit for new insights into the prevention and control of aquaculture diseases. IMPORTANCE In 2020, global aquaculture production reached a record of 122.6 million tons, with a total value of $281.5 billion. Meanwhile, frequent outbreaks of viral diseases have occurred in aquaculture, and about 10% of farmed aquatic animal production has been lost to infectious diseases, resulting in more than $10 billion in economic losses every year. Therefore, an understanding of the potential molecular mechanism of how aquatic organisms respond to and regulate viral replication is of great significance. Our study suggested that TRPV4 enables Ca2+ influx and interactions with DDX1 to collectively promote ISKNV replication, providing novel insights into the roles of the TRPV4-DDX1 axis in regulating the proviral effect of DDX1. This advances our understanding of viral disease outbreaks and would be of benefit for studies on preventing aquatic viral diseases.

Coronavirus Porcine Epidemic Diarrhea Virus Utilizes Chemokine Interleukin-8 to Facilitate Viral Replication by Regulating Ca2+ Flux

Chemokine production by epithelial cells is crucial for neutrophil recruitment to sites of inflammation during viral infection. However, the effect of chemokine on epithelia and how chemokine is involved in coronavirus infection remains to be fully understood. Here, we identified an inducible chemokine interleukin-8 (CXCL8/IL-8), which could promote coronavirus porcine epidemic diarrhea virus (PEDV) infection in African green monkey kidney epithelial cells (Vero) and Lilly Laboratories cell-porcine kidney 1 epithelial cells (LLC-PK1). IL-8 deletion restrained cytosolic calcium (Ca2+), whereas IL-8 stimulation improved cytosolic Ca2+. The consumption of Ca2+ restricted PEDV infection. PEDV internalization and budding were obvious reductions when cytosolic Ca2+ was abolished in the presence of Ca2+ chelators. Further study revealed that the upregulated cytosolic Ca2+ redistributes intracellular Ca2+. Finally, we identified that G protein-coupled receptor (GPCR)-phospholipase C (PLC)-inositol trisphosphate receptor (IP3R)-store-operated Ca2+ (SOC) signaling was crucial for enhancive cytosolic Ca2+ and PEDV infection. To our knowledge, this study is the first to uncover the function of chemokine IL-8 during coronavirus PEDV infection in epithelia. PEDV induces IL-8 expression to elevate cytosolic Ca2+, promoting its infection. Our findings reveal a novel role of IL-8 in PEDV infection and suggest that targeting IL-8 could be a new approach to controlling PEDV infection. IMPORTANCE Coronavirus porcine epidemic diarrhea virus (PEDV) is a highly contagious enteric coronavirus that caused severe economic losses worldwide, and more effort is needed to develop economical and efficient vaccines to control or eliminate this disease. The chemokine interleukin-8 (CXCL8/IL-8) is indispensable for the activation and trafficking of inflammatory mediators and tumor progression and metastasis. This study evaluated the effect of IL-8 on PEDV infection in epithelia. We found that IL-8 expression improved cytosolic Ca2+ in epithelia, facilitating PEDV rapid internalization and egress. G protein-coupled receptor (GPCR)-phospholipase C (PLC)-inositol trisphosphate receptor (IP3R)-SOC signaling was activated by IL-8, releasing the intracellular Ca2+ stores from endoplasmic reticulum (ER). These findings provide a better understanding of the role of IL-8 in PEDV-induced immune responses, which will help develop small-molecule drugs for coronavirus cure.

Broad-Spectrum Antivirals Derived from Natural Products

Scientific advances have led to the development and production of numerous vaccines and antiviral drugs, but viruses, including re-emerging and emerging viruses, such as SARS-CoV-2, remain a major threat to human health. Many antiviral agents are rarely used in clinical treatment, however, because of their inefficacy and resistance. The toxicity of natural products may be lower, and some natural products have multiple targets, which means less resistance. Therefore, natural products may be an effective means to solve virus infection in the future. New techniques and ideas are currently being developed for the design and screening of antiviral drugs thanks to recent revelations about virus replication mechanisms and the advancement of molecular docking technology. This review will summarize recently discovered antiviral drugs, mechanisms of action, and screening and design strategies for novel antiviral agents.

Modulation of CaV1.2 Channel Function by Interacting Proteins and Post-Translational Modifications: Implications in Cardiovascular Diseases and COVID-19

Ca_V1.2 calcium channel is the primary conduit for Ca²⁺ influx into cardiac and smooth muscles that underscores its importance in the pathogenesis of hypertension, atherosclerosis, myocardial infarction, and heart failure. But, a few controversies still remain. Therefore, exploring new ways to modulate Ca_V1.2 channel activity will augment the arsenal of Ca_V1.2 channel-based therapeutics for treatment of cardiovascular diseases. Here, we will mainly introduce a couple of emerging Ca_V1.2 channel interacting proteins, such as Galectin-1 and Cereblon, and discuss their roles in hypertension and heart failure through fine-tuning Ca_V1.2 channel activity. Of current interest, we will also evaluate the implication of the role of Ca_V1.2 channel in SARS-CoV-2 infection and the potential treatments of COVID-19-related cardiovascular symptoms.

Understanding the role of Ca2+ via transient receptor potential (TRP) channel in viral infection: Implications in developing future antiviral strategies

Transient receptor potential (TRP) channels are a superfamily of cation-specific permeable channels primarily conducting Ca2+ions across various membranes of the cell. The perturbation of the Ca2+ homeostasis is the hallmark of viral infection. Viruses hijack the host cell Ca2+ signaling, employing tailored Ca2+ requirements via TRP channels to meet their own cellular demands. This review summarizes the importance of Ca2+ across diverse viruses based on the Baltimore classification and focuses on the associated role of Ca2+-conducting TRP channels in viral pathophysiology. More emphasis has been given to the role of the TRP channel in viral life-cycle events such as viral fusion, viral entry, viral replication, virion maturation, and egress. Additionally, this review highlights the TRP channel as a store-operated channel which has been discussed vividly. The TRP channels form an essential aspect of host-virus interaction by virtue of its Ca2+ permeability. These channels are directly involved in regulating the viral calcium dynamics in host cells and thereby affect the viral infection. Considering its immense potential in regulating viral infection, the TRP channels may act as a target for antiviral therapeutics.

Nisoldipine Inhibits Influenza A Virus Infection by Interfering with Virus Internalization Process

Influenza virus infections and the continuing spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are global public health concerns. As there are limited therapeutic options available in clinical practice, the rapid development of safe, effective and globally available antiviral drugs is crucial. Drug repurposing is a therapeutic strategy used in treatments for newly emerging and re-emerging infectious diseases. It has recently been shown that the voltage-dependent Ca²⁺ channel Cav1.2 is critical for influenza A virus entry, providing a potential target for antiviral strategies. Nisoldipine, a selective Ca²⁺ channel inhibitor, is commonly used in the treatment of hypertension. Here, we assessed the antiviral potential of nisoldipine against the influenza A virus and explored the mechanism of action of this compound. We found that nisoldipine treatment could potently inhibit infection with multiple influenza A virus strains. Mechanistic studies further revealed that nisoldipine impaired the internalization of the influenza virus into host cells. Overall, our findings demonstrate that nisoldipine exerts antiviral effects against influenza A virus infection and could serve as a lead compound in the design and development of new antivirals.

The Transient Receptor Potential Vanilloid 2 (TRPV2) Channel Facilitates Virus Infection Through the Ca2+ -LRMDA Axis in Myeloid Cells

The transient receptor potential vanilloid 2 (TRPV2) channel is a nonselective cation channel that has been implicated in multiple sensory processes in the nervous system. Here, it is shown that TRPV2 in myeloid cells facilitates virus penetration by promoting the tension and mobility of cell membrane through the Ca²⁺ -LRMDA axis. Knockout of TRPV2 in myeloid cells or inhibition of TRPV2 channel activity suppresses viral infection and protects mice from herpes simplex virus 1 (HSV-1) and vesicular stomatitis virus (VSV) infection. Reconstitution of TRPV2 but not the Ca²⁺ -impermeable mutant TRPV2^E572Q into LyZ2-Cre;Trpv2^fl/fl bone marrow-derived dendritic cells (BMDCs) restores viral infection. Mechanistically, knockout of TRPV2 in myeloid cells inhibits the tension and mobility of cell membrane and the penetration of viruses, which is restored by reconstitution of TRPV2 but not TRPV2^E572Q . In addition, knockout of TRPV2 leads to downregulation of Lrmda in BMDCs and BMDMs, and knockdown of Lrmda significantly downregulates the mobility and tension of cell membrane and inhibits viral infections in Trpv2^fl/fl but not LyZ2-Cre;Trpv2^fl/fl BMDCs. Consistently, complement of LRMDA into LyZ2-Cre;Trpv2^fl/fl BMDCs partially restores the tension and mobility of cell membrane and promotes viral penetration and infection. These findings characterize a previously unknown function of myeloid TRPV2 in facilitating viral infection though the Ca2⁺ -LRMDA axis.

Phosphatidylinositol 4,5-Bisphosphate Mediates the Co-Distribution of Influenza A Hemagglutinin and Matrix Protein M1 at the Plasma Membrane

The fully assembled influenza A virus (IAV) has on its surface the highest density of a single membrane protein found in nature-the glycoprotein hemagglutinin (HA) that mediates viral binding, entry, and assembly. HA clusters at the plasma membrane of infected cells, and the HA density (number of molecules per unit area) of these clusters correlates with the infectivity of the virus. Dense HA clusters are considered to mark the assembly site and ultimately lead to the budding of infectious IAV. The mechanism of spontaneous HA clustering, which occurs with or without other viral components, has not been elucidated. Using super-resolution fluorescence photoactivation localization microscopy (FPALM), we have previously shown that these HA clusters are interdependent on phosphatidylinositol 4,5-biphosphate (PIP2). Here, we show that the IAV matrix protein M1 co-clusters with PIP2, visualized using the pleckstrin homology domain. We find that cetylpyridinium chloride (CPC), which is a positively charged quaternary ammonium compound known for its antibacterial and antiviral properties at millimolar concentrations, disrupts M1 clustering and M1-PIP2 co-clustering at micromolar concentrations well below the critical micelle concentration (CMC). CPC also disrupts the co-clustering of M1 with HA at the plasma membrane, suggesting the role of host cell PIP2 clusters as scaffolds for gathering and concentrating M1 and HA to achieve their unusually high cluster densities in the IAV envelope.

Calcium Ions Signaling: Targets for Attack and Utilization by Viruses

Calcium, as a second intracellular messenger, participate in various physiological and biochemical processes, including cell growth and proliferation, energy metabolism, information transfer, cell death, and immune response. Ca2+ channels or pumps in plasma and organelle membranes and Ca2+-related proteins maintain Ca2+ homeostasis by regulating Ca2+ inflow, outflow and buffering to avoid any adverse effects caused by Ca2+ overload or depletion. Thus, Ca2+ signaling also provides a target for virus invasion, replication, proliferation and release. After hijacking the host cell, viruses exploit Ca2+ signaling to regulate apoptosis and resist host immunity to establish persistent infection. In this review, we discuss cellular Ca2+ signaling and channels, interaction of calcium-associated proteins with viruses, and host cell fate, as well as the role of Ca2+ in cell death and antiviral response during viral infection.

Comparison of Cell Fusions Induced by Influenza Virus and SARS-CoV-2

Virus–cell fusion is the key step for viral infection in host cells. Studies on virus binding and fusion with host cells are important for understanding the virus–host interaction and viral pathogenesis for the discovery of antiviral drugs. In this review, we focus on the virus–cell fusions induced by the two major pandemic viruses, including the influenza virus and SARS-CoV-2. We further compare the cell fusions induced by the influenza virus and SARS-CoV-2, especially the pH-dependent fusion of the influenza virus and the fusion of SARS-CoV-2 in the type-II transmembrane serine protease 2 negative (TMPRSS2^-) cells with syncytia formation. Finally, we present the development of drugs used against SARA-CoV-2 and the influenza virus through the discovery of anti-fusion drugs and the prevention of pandemic respiratory viruses.

Essential role of Rnd1 in innate immunity during viral and bacterial infections

Intracellular and cell surface pattern-recognition receptors (PRRs) are an essential part of innate immune recognition and host defense. Here, we have compared the innate immune responses between humans and bats to identify a novel membrane-associated protein, Rnd1, which defends against viral and bacterial infection in an interferon-independent manner. Rnd1 belongs to the Rho GTPase family, but unlike other small GTPase members, it is constitutively active. We show that Rnd1 is induced by pro-inflammatory cytokines during viral and bacterial infections and provides protection against these pathogens through two distinct mechanisms. Rnd1 counteracts intracellular calcium fluctuations by inhibiting RhoA activation, thereby inhibiting virus internalisation. On the other hand, Rnd1 also facilitates pro-inflammatory cytokines IL-6 and TNF-α through Plxnb1, which are highly effective against intracellular bacterial infections. These data provide a novel Rnd1-mediated innate defense against viral and bacterial infections.

Endolysosomal cation channels point the way towards precision medicine of cancer and infectious diseases

Infectious diseases and cancer are among the key medical challenges that humankind is facing today. A growing amount of evidence suggests that ion channels in the endolysosomal system play a crucial role in the pathology of both groups of diseases. The development of advanced patch-clamp technologies has allowed us to directly characterize ion fluxes through endolysosomal ion channels in their native environments. Endolysosomes are essential organelles for intracellular transport, digestion and metabolism, and maintenance of homeostasis. The endolysosomal ion channels regulate the function of the endolysosomal system through four basic mechanisms: calcium release, control of membrane potential, pH change, and osmolarity regulation. In this review, we put particular emphasis on the endolysosomal cation channels, including TPC2 and TRPML2, which are particularly important in monocyte function. We discuss existing endogenous and synthetic ligands of these channels and summarize current knowledge of their impact on channel activity and function in different cell types. Moreover, we summarize recent findings on the importance of TPC2 and TRPML2 channels as potential drug targets for the prevention and treatment of the emerging infectious diseases and cancer.

The ins and outs of virus trafficking through acidic Ca2+ stores

Many viruses exploit host-cell Ca2+ signaling processes throughout their life cycle. This is especially relevant for viruses that translocate through the endolysosomal system, where cellular infection is keyed to the microenvironment of these acidic Ca2+ stores and Ca2+-dependent trafficking pathways. As regulators of the endolysosomal ionic milieu and trafficking dynamics, two families of endolysosomal Ca2+-permeable cation channels - two pore channels (TPCs) and transient receptor potential mucolipins (TRPMLs) - have emerged as important host-cell factors in viral entry. Here, we review: (i) current evidence implicating Ca2+ signaling in viral translocation through the endolysosomal system, (ii) the roles of these ion channels in supporting cellular infection by different viruses, and (iii) areas for future research that will help define the potential of TPC and TRPML ligands as progressible antiviral agents.

Network Meta-Analysis of Chicken Microarray Data Following Avian Influenza Challenge—A Comparison of Highly and Lowly Pathogenic Strains

The current bioinformatics study was undertaken to analyze the transcriptome of chicken (Gallus gallus) after influenza A virus challenge. A meta-analysis was carried out to explore the host expression response after challenge with lowly pathogenic avian influenza (LPAI) (H1N1, H2N3, H5N2, H5N3 and H9N2) and with highly pathogenic avian influenza (HPAI) H5N1 strains. To do so, ten microarray datasets obtained from the Gene Expression Omnibus (GEO) database were normalized and meta-analyzed for the LPAI and HPAI host response individually. Different undirected networks were constructed and their metrics determined e.g., degree centrality, closeness centrality, harmonic centrality, subgraph centrality and eigenvector centrality. The results showed that, based on criteria of centrality, the CMTR1, EPSTI1, RNF213, HERC4L, IFIT5 and LY96 genes were the most significant during HPAI challenge, with PARD6G, HMG20A, PEX14, RNF151 and TLK1L having the lowest values. However, for LPAI challenge, ZDHHC9, IMMP2L, COX7C, RBM18, DCTN3, and NDUFB1 genes had the largest values for aforementioned criteria, with GTF3C5, DROSHA, ATRX, RFWD2, MED23 and SEC23B genes having the lowest values. The results of this study can be used as a basis for future development of treatments/preventions of the effects of avian influenza in chicken.

Could Lower Testosterone in Older Men Explain Higher COVID-19 Morbidity and Mortalities?

The health scourge imposed on humanity by the COVID-19 pandemic seems not to recede. This fact warrants refined and novel ideas analyzing different aspects of the illness. One such aspect is related to the observation that most COVID-19 casualties were older males, a tendency also noticed in the epidemics of SARS-CoV in 2003 and the Middle East respiratory syndrome in 2012. This gender-related difference in the COVID-19 death toll might be directly involved with testosterone (TEST) and its plasmatic concentration in men. TEST has been demonstrated to provide men with anti-inflammatory and immunological advantages. As the plasmatic concentration of this androgen decreases with age, the health benefit it confers also diminishes. Low plasmatic levels of TEST can be determinant in the infection’s outcome and might be related to a dysfunctional cell Ca²⁺ homeostasis. Not only does TEST modulate the activity of diverse proteins that regulate cellular calcium concentrations, but these proteins have also been proven to be necessary for the replication of many viruses. Therefore, we discuss herein how TEST regulates different Ca²⁺-handling proteins in healthy tissues and propose how low TEST concentrations might facilitate the replication of the SARS-CoV-2 virus through the lack of modulation of the mechanisms that regulate intracellular Ca²⁺ concentrations.

Roles of Glycans and Non-glycans on the Epithelium and in the Immune System in H1-H18 Influenza A Virus Infections

The large variation of influenza A viruses (IAVs) in various susceptible hosts and their rapid evolution, which allows host/tissue switching, host immune escape, vaccine escape, and drug resistance, are difficult challenges for influenza control in all countries worldwide. Access and binding of the IAV to actual receptors at endocytic sites is critical for the establishment of influenza infection. In this chapter, the progress in identification of and roles of glycans and non-glycans on the epithelium and in the immune system in H1-H18 IAV infections are reviewed. The first part of the review is on current knowledge of H1-H16 IAV receptors on the epithelium including sialyl glycans, other negatively charged glycans, and annexins. The second part of the review focuses on H1-H16 IAV receptors in the immune system including acidic surfactant phospholipids, Sia on surfactant proteins, the carbohydrate recognition domain (CRD) of surfactant proteins, Sia on mucins, Sia and C-type lectins on macrophages and dendritic cells, and Sia on NK cells. The third part of the review is about a possible H17-H18 IAV receptor. Binding of these receptors to IAVs may result in inhibition or enhancement of IAV infection depending on their location, host cell type, and IAV strain. Among these receptors, host sialyl glycans are key determinants of viral hemagglutinin (HA) lectins for H1-H16 infections. HA must acquire mutations to bind to sialyl glycans that are dominant on a new target tissue when switching to a new host for efficient transmission and to bind to long sialyl glycans found in the case of seasonal HAs with multiple glycosylation sites as a consequence of immune evasion. Although sialyl receptors/C-type lectins on immune cells are decoy receptors/pathogen recognition receptors for capturing viral HA lectin/glycans protecting HA antigenic sites, some IAV strains do not escape, such as by release with neuraminidase, but hijack these molecules to gain entry and replication in immune cells. An understanding of the virus-host battle tactics at the receptor level might lead to the establishment of novel strategies for effective control of influenza.

Localization-Based Super-Resolution Microscopy Reveals Relationship between SARS-CoV2 Spike and Phosphatidylinositol (4,5)-bisphosphate

Localization microscopy circumvents the diffraction limit by identifying and measuring the positions of numerous subsets of individual fluorescent molecules, ultimately producing an image whose resolution depends on the uncertainty and density of localization, and whose capabilities are compatible with imaging living specimens. Spectral resolution can be improved by incorporating a dichroic or dispersive element in the detection path of a localization microscope, which can be useful for separation of multiple probes imaged simultaneously and for detection of changes in emission spectra of fluorophores resulting from changes in their environment. These methodological advances enable new biological applications, which in turn motivate new questions and technical innovations. As examples, we present fixed-cell imaging of the spike protein SARS-CoV2 (S) and its interactions with host cell components. Results show a relationship between S and the lipid phosphatidylinositol (4,5)-bisphosphate (PIP2). These findings have ramifications for several existing models of plasma membrane organization.

An Integrated Analysis Reveals Geniposide Extracted From Gardenia jasminoides J.Ellis Regulates Calcium Signaling Pathway Essential for Influenza A Virus Replication

Geniposide, an iridoid glycoside purified from the fruit of Gardenia jasminoides J.Ellis, has been reported to possess pleiotropic activity against different diseases. In particular, geniposide possesses a variety of biological activities and exerts good therapeutic effects in the treatment of several strains of the influenza virus. However, the molecular mechanism for the therapeutic effect has not been well defined. This study aimed to investigate the mechanism of geniposide on influenza A virus (IAV). The potential targets and signaling pathways of geniposide in the IAV infection were predicted using network pharmacology analysis. According to the result of network pharmacology analysis, we validated the calcium signaling pathway induced by IAV and investigated the effect of geniposide extracted from Gardenia jasminoides J.Ellis on this pathway. The primary Gene Ontology (GO) biological processes and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways KEGG enrichment analysis indicated that geniposide has a multi-target and multi-pathway inhibitory effect against influenza, and one of the mechanisms involves calcium signaling pathway. In the current study, geniposide treatment greatly decreased the levels of RNA polymerase in HEK-293T cells infected with IAV. Knocking down CAMKII in IAV-infected HEK-293T cells enhanced virus RNA (vRNA) production. Geniposide treatment increased CAMKII expression after IAV infection. Meanwhile, the CREB and c-Fos expressions were inhibited by geniposide after IAV infection. The experimental validation data showed that the geniposide was able to alleviate extracellular Ca2+ influx, dramatically decreased neuraminidase activity, and suppressed IAV replication in vitro via regulating the calcium signaling pathway. These anti-IAV effects might be related to the disrupted interplay between IAV RNA polymerase and CAMKII and the regulation of the downstream calcium signaling pathway essential for IAV replication. Taken together, the findings reveal a new facet of the mechanism by which geniposide fights IAV in a way that depends on CAMKII replication.

Inhibitors of L-Type Calcium Channels Show Therapeutic Potential for Treating SARS-CoV-2 Infections by Preventing Virus Entry and Spread

COVID-19 is caused by a novel coronavirus, the severe acute respiratory syndrome coronavirus (CoV)-2 (SARS-CoV-2). The virus is responsible for an ongoing pandemic and concomitant public health crisis around the world. While vaccine development is proving to be highly successful, parallel drug development approaches are also critical in the response to SARS-CoV-2 and other emerging viruses. Coronaviruses require Ca2+ ions for host cell entry, and we have previously shown that Ca2+ modulates the interaction of the viral fusion peptide with host cell membranes. In an attempt to accelerate drug repurposing, we tested a panel of L-type calcium channel blocker (CCB) drugs currently developed for other conditions to determine whether they would inhibit SARS-CoV-2 infection in cell culture. All the CCBs tested showed varying degrees of inhibition, with felodipine and nifedipine strongly limiting SARS-CoV-2 entry and infection in epithelial lung cells at concentrations where cell toxicity was minimal. Further studies with pseudotyped particles displaying the SARS-CoV-2 spike protein suggested that inhibition occurs at the level of virus entry. Overall, our data suggest that certain CCBs have the potential to treat SARS-CoV-2 infections and are worthy of further examination for possible treatment of COVID-19.

Dysregulation of host cell calcium signaling during viral infections: Emerging paradigm with high clinical relevance

Viral infections are one of the leading causes of human illness. Viruses take over host cell signaling cascades for their replication and infection. Calcium (Ca2+) is a versatile and ubiquitous second messenger that modulates plethora of cellular functions. In last two decades, a critical role of host cell Ca2+ signaling in modulating viral infections has emerged. Furthermore, recent literature clearly implicates a vital role for the organellar Ca2+ dynamics (influx and efflux across organelles) in regulating virus entry, replication and severity of the infection. Therefore, it is not surprising that a number of viral infections including current SARS-CoV-2 driven COVID-19 pandemic are associated with dysregulated Ca2+ homeostasis. The focus of this review is to first discuss the role of host cell Ca2+ signaling in viral entry, replication and egress. We further deliberate on emerging literature demonstrating hijacking of the host cell Ca2+ dynamics by viruses. In particular, a variety of viruses including SARS-CoV-2 modulate lysosomal and cytosolic Ca2+ signaling for host cell entry and replication. Moreover, we delve into the recent studies, which have demonstrated the potential of several FDA-approved drugs targeting Ca2+ handling machinery in inhibiting viral infections. Importantly, we discuss the prospective of targeting intracellular Ca2+ signaling for better management and treatment of viral pathogenesis including COVID-19. Finally, we highlight the key outstanding questions in the field that demand critical and timely attention.

Targeting lysophospholipid acid receptor 1 and ROCK kinases promotes antiviral innate immunity

Growing evidence indicates the vital role of lipid metabolites in innate immunity. The lipid lysophosphatidic acid (LPA) concentrations are enhanced in patients upon HCV or SARS-CoV-2 infection, but the function of LPA and its receptors in innate immunity is largely unknown. Here, we found that viral infection promoted the G protein–coupled receptor LPA1 expression, and LPA restrained type I/III interferon production through LPA1. Mechanistically, LPA1 signaling activated ROCK1/2, which phosphorylated IRF3 Ser⁹⁷ to suppress IRF3 activation. Targeting LPA1 or ROCK in macrophages, fibroblasts, epithelial cells, and LPA1 conditional KO mice promoted interferon-induced clearance of multiple viruses. LPA1 was colocalized with the receptor ACE2 in lung and intestine. Together with previous findings that LPA1 and ROCK1/2 promoted vascular leaking or lung fibrosis, we propose that the current available preclinical drugs targeting the LPA1-ROCK module might protect from SARS-CoV-2 or various virus infections in the intestine or lung.

Drug repurposing of dextromethorphan as a cellular target for the management of influenza

BACKGROUND

Influenza viruses are responsible for seasonal epidemics and sporadic pandemics of varying severity in humans, and additional treatment options are needed. High-throughput siRNA screens and a pre-clinical research model demonstrated that dextromethorphan (DM) has anti-viral activity as a cellular target for treatment of influenza. This study examined DM usage and hospitalization rates among patients with laboratory-confirmed influenza in a national cohort of United States veterans. We aimed to evaluate the potential drug repurposing of DM as a cellular target for the management of influenza utilizing a large, national claims and electronic health record database.

METHODS

This retrospective drug-disease association cohort study was conducted using data from the Veterans Affairs Informatics and Computing Infrastructure (VINCI). We used a cohort with laboratory-confirmed diagnosis of influenza and international classification of disease (ICD)-9/10 diagnosis codes of fever, cough, influenza, or acute upper respiratory infection in an outpatient setting. The study outcome is inpatient hospitalization (all-cause and respiratory) within 30 days of influenza diagnosis. We estimated the relative risk for all-cause and respiratory hospitalizations using Poisson generalized linear model (GLM) and a greedy nearest neighbor propensity score 1:1 matched sub-analysis for both hospitalization models.

FINDINGS

A total of 18,677 patients met the inclusion and exclusion criteria and were evaluated in our study. The cohorts consisted of 2801 patients dispensed DM and 15,876 untreated patients (no DM). The Poisson GLM adjusted for covariates demonstrated a relative risk reduction of 34% for all-cause hospitalizations (Relative Risk (RR) 0.66, 95% Confidence Interval (CI) 0.525-0.832) and 40% for respiratory hospitalizations (RR 0.597, 95% CI 0.423-0.843) in patients with influenza treated with DM.

CONCLUSION

Influenza viruses continue to emerge and cause infection (including pandemics) in humans, so there remains a critical need to advance the understanding of influenza treatment. Our results demonstrated reduced hospitalization rates for influenza patients treated with DM. Further research on cellular targets and/or DM is warranted for the treatment of influenza.

GP96 Drives Exacerbation of Secondary Bacterial Pneumonia following Influenza A Virus Infection

Influenza A virus (IAV) infection predisposes the host to secondary bacterial pneumonia, known as a major cause of morbidity and mortality during influenza virus epidemics. Analysis of interactions between IAV-infected human epithelial cells and Streptococcus pneumoniae revealed that infected cells ectopically exhibited the endoplasmic reticulum chaperone glycoprotein 96 (GP96) on the surface. Importantly, efficient pneumococcal adherence to epithelial cells was imparted by interactions with extracellular GP96 and integrin α_V, with the surface expression mediated by GP96 chaperone activity. Furthermore, abrogation of adherence was gained by chemical inhibition or genetic knockout of GP96 as well as addition of RGD peptide, an inhibitor of integrin-ligand interactions. Direct binding of extracellular GP96 and pneumococci was shown to be mediated by pneumococcal oligopeptide permease components. Additionally, IAV infection induced activation of calpains and Snail1, which are responsible for degradation and transcriptional repression of junctional proteins in the host, respectively, indicating increased bacterial translocation across the epithelial barrier. Notably, treatment of IAV-infected mice with the GP96 inhibitor enhanced pneumococcal clearance from lung tissues and ameliorated lung pathology. Taken together, the present findings indicate a viral-bacterial synergy in relation to disease progression and suggest a paradigm for developing novel therapeutic strategies tailored to inhibit pneumococcal colonization in an IAV-infected respiratory tract.

G-Protein-Coupled Receptor and Ion Channel Genes Used by Influenza Virus for Replication

Influenza virus causes epidemics and sporadic pandemics resulting in morbidity, mortality, and economic losses. Influenza viruses require host genes to replicate. RNA interference (RNAi) screens can identify host genes coopted by influenza virus for replication. Targeting these proinfluenza genes can provide therapeutic strategies to reduce virus replication. Nineteen proinfluenza G-protein-coupled receptor (GPCR) and 13 proinfluenza ion channel genes were identified in human lung (A549) cells by use of small interfering RNAs (siRNAs). These proinfluenza genes were authenticated by testing influenza virus A/WSN/33-, A/CA/04/09-, and B/Yamagata/16/1988-infected A549 cells, resulting in the validation of 16 proinfluenza GPCR and 5 proinfluenza ion channel genes. These findings showed that several GPCR and ion channel genes are needed for the production of infectious influenza virus. These data provide potential targets for the development of host-directed therapeutic strategies to impede the influenza virus productive cycle so as to limit infection.IMPORTANCE Influenza epidemics result in morbidity and mortality each year. Vaccines are the most effective preventive measure but require annual reformulation, since a mismatch of vaccine strains can result in vaccine failure. Antiviral measures are desirable particularly when vaccines fail. In this study, we used RNAi screening to identify several GPCR and ion channel genes needed for influenza virus replication. Understanding the host genes usurped by influenza virus during viral replication can help identify host genes that can be targeted for drug repurposing or for the development of antiviral drugs. The targeting of host genes is refractory to drug resistance generated by viral mutations, as well as providing a platform for the development of broad-spectrum antiviral drugs.

A Dynamic, Supramolecular View on the Multivalent Interaction between Influenza Virus and Host Cell

Understanding how influenza viruses traverse the mucus and recognize host cells is critical for evaluating their zoonotic potential, and for prevention and treatment of the disease. The surface of the influenza A virus is covered with the receptor-binding protein hemagglutinin and the receptor-cleaving enzyme neuraminidase, which jointly control the interactions between the virus and the host cell. These proteins are organized in closely spaced trimers and tetramers to facilitate multivalent interactions with sialic acid-terminated glycans. This review shows that the individually weak multivalent interactions of influenza viruses allow superselective binding, virus-induced recruitment of receptors, and the formation of dynamic complexes that facilitate molecular walking. Techniques to measure the avidity and receptor specificity of influenza viruses are reviewed, and the pivotal role of multivalent interactions with their emergent properties in crossing the mucus and entering host cells is discussed. A model is proposed for the initiation of cell entry through virus-induced receptor clustering. The multivalent interactions of influenza viruses are maintained in a dynamic regime by a functional balance between binding and cleaving.

Megalocytivirus Induces Complicated Fish Immune Response at Multiple RNA Levels Involving mRNA, miRNA, and circRNA

Megalocytivirus is an important viral pathogen to many farmed fishes, including Japanese flounder (Paralichthys olivaceus). In this study, we examined megalocytivirus-induced RNA responses in the spleen of flounder by high-throughput sequencing and integrative analysis of various RNA-seq data. A total of 1327 microRNAs (miRNAs), including 368 novel miRNAs, were identified, among which, 171 (named DEmiRs) exhibited significantly differential expressions during viral infection in a time-dependent manner. For these DEmiRs, 805 differentially expressed target mRNAs (DETmRs) were predicted, whose expressions not only significantly changed after megalocytivirus infection but were also negatively correlated with their paired DEmiRs. Integrative analysis of immune-related DETmRs and their target DEmiRs identified 12 hub DEmiRs, which, together with their corresponding DETmRs, formed an interaction network containing 84 pairs of DEmiR and DETmR. In addition to DETmRs, 19 DEmiRs were also found to regulate six key immune genes (mRNAs) differentially expressed during megalocytivirus infection, and together they formed a network consisting of 21 interactive miRNA-messenger RNA (mRNA) pairs. Further analysis identified 9434 circular RNAs (circRNAs), 169 of which (named DEcircRs) showed time-specific and significantly altered expressions during megalocytivirus infection. Integrated analysis of the DETmR-DEmiR and DEcircR-DEmiR interactions led to the identification of a group of competing endogenous RNAs (ceRNAs) constituted by interacting triplets of circRNA, miRNA, and mRNA involved in antiviral immunity. Together these results indicate that complicated regulatory networks of different types of non-coding RNAs and coding RNAs are involved in megalocytivirus infection.

8-O-(E-p-methoxycinnamoyl)harpagide Inhibits Influenza A Virus Infection by Suppressing Intracellular Calcium

Calcium (Ca²⁺) dependent signaling circuit plays a critical role in influenza A virus (IAV) infection. The 8-O-(E-p-methoxycinnamoyl)harpagide (MCH) exhibits pharmacological activities that exert neuroprotective, hepatoprotective, anti-inflammatory and other biological effects. However, not have reports of antiviral effects. To investigate the antiviral activity of MCH on IAV-infected human lung cells mediated by calcium regulation. We examined the inhibitory effect of MCH on IAV infections and measured the level of viral proteins upon MCH treatment using Western blotting. We also performed molecular docking simulation with MCH and IAV M2 protein. Finally, we analyzed MCH’s suppression of intracellular calcium and ROS (reactive oxygen species) in IAV-infected human lung cells using a flow cytometer. The results shown that MCH inhibited the infection of IAV and increased the survival of the infected human lung cells. The levels of IAV protein M1, M2, NS1 and PA were inhibited in MCH-treated human lung cells compared to that in infected and untreated cells. Also, docking simulation suggest that MCH interacted with M2 on its hydrophobic wall (L40 and I42) and polar amino acids (D44 and R45), which formed intermolecular contacts and were a crucial part of the channel gate along with W41. Lastly, MCH inhibited IAV infection by reducing intracellular calcium and mitochondrial Ca²⁺/ROS levels in infected human lung cells. Taken together, these data suggest that MCH inhibits IAV infection and increases the survival of infected human lung cells by suppressing calcium levels. These results indicate that MCH is useful for developing IAV treatments.

Conflicts over calcium and the treatment of COVID-19

Several recent studies have provided evidence that use of calcium channel blockers (CCBs), especially amlodipine and nifedipine, can reduce mortality from coronavirus disease 2019 (COVID-19). Moreover, hypocalcemia (a reduced level of serum ionized calcium) has been shown to be strongly positively associated with COVID-19 severity. Both effectiveness of CCBs as antiviral therapy, and positive associations of hypocalcemia with mortality, have been demonstrated for many other viruses as well. We evaluate these findings in the contexts of virus–host evolutionary conflicts over calcium metabolism, and hypocalcemia as either pathology, viral manipulation or host defence against pathogens. Considerable evidence supports the hypothesis that hypocalcemia represents a host defence. Indeed, hypocalcemia may exert antiviral effects in a similar manner as do CCBs, through interference with calcium metabolism in virus-infected cells. Prospective clinical studies that address the efficacy of CCBs and hypocalcemia should provide novel insights into the pathogenicity and treatment of COVID-19 and other viruses.

Low serum calcium and phosphorus and their clinical performance in detecting COVID-19 patients

BACKGROUND

This study aimed to evaluate the clinical performance of low serum calcium and phosphorus in discriminative diagnosis of the severity of patients with coronavirus disease 2019 (COVID-19). We conducted a single-center hospital-based study and consecutively recruited 122 suspected and 104 confirmed patients with COVID-19 during January 24 to April 25, 2020. Clinical risk factors of COVID-19 were identified. The discriminative power of low calcium and phosphorus regarding the disease severity was evaluated. Low calcium and low phosphorus are more prevalent in severe or critical COVID-19 patients than moderate COVID-19 patients (odds ratio [OR], 15.07; 95% confidence interval [CI], 1.59-143.18 for calcium; OR, 6.90; 95% CI, 2.43-19.64 for phosphorus). The specificity in detecting the severe or critical patients among COVID-19 patients reached 98.5% (95% CI, 92.0%-99.7%) and 84.8% (95% CI, 74.3%-91.6%) by low calcium and low phosphorus, respectively, albeit with suboptimal sensitivity. Calcium and phosphorus combined with lymphocyte count could obtain the best discriminative performance for the severe COVID-19 patients (area under the curve [AUC] = 0.80), and combined with oxygenation index was promising (AUC = 0.71). Similar discriminative performances of low calcium and low phosphorus were found between suspected and confirmed COVID-19 patient. Low calcium and low phosphorus could indicate the severity of COVID-19 patients, and may be utilized as promising clinical biomarkers for discriminative diagnosis.

Equine Alphaherpesviruses Require Activation of the Small GTPases Rac1 and Cdc42 for Intracellular Transport

Viruses utilize host cell signaling to facilitate productive infection. Equine herpesvirus type 1 (EHV-1) has been shown to activate Ca2+ release and phospholipase C upon contact with α4β1 integrins on the cell surface. Signaling molecules, including small GTPases, have been shown to be activated downstream of Ca2+ release, and modulate virus entry, membrane remodeling and intracellular transport. In this study, we show that EHV-1 activates the small GTPases Rac1 and Cdc42 during infection. The activation of Rac1 and Cdc42 is necessary for virus-induced acetylation of tubulin, effective viral transport to the nucleus, and cell-to-cell spread. We also show that inhibitors of Rac1 and Cdc42 did not block virus entry, but inhibited overall virus infection. The Rac1 and Cdc42 signaling is presumably orthogonal to Ca2+ release, since Rac1 and Cdc42 inhibitors affected the infection of both EHV-1 and EHV-4, which do not bind to integrins.

Environmental complex exposure and the risk of influenza-like illness among housewives: A case study in Shanxi Province, China

The association between environmental pollution and risk of influenza-like illness (ILI) among general population has been reported. However, the relationships between the individual pollutants and ILI risk are still under discussion. Our study aimed to explore the associations of the typical environmental polycyclic aromatic hydrocarbons (PAHs) and metal(loid)s with ILI risk among women population. We carried out a cross-sectional study and included a total of 396 housewives in Shanxi Province, China. The information on their general characteristics and ILI frequency was collected by questionnaire. We collected their hair samples and analyzed the concentrations of PAHs and various metal(loid)s. The results indicated that only acenaphthylene concentration of the nine detected PAH congeners in the hair was significantly associated with ILI risk with adjusted odds ratio (AOR) and 95% confidence interval (95% CI) of 0.58 (0.38 - 0.91). Among the concerned 4 toxic metal(loid)s and 15 rare earth elements, only the hair concentration of arsenic had a positive dose-response relationship with ILI risk. In addition, we found that there were negative dose-response associations of the three essential trace elements (i.e. chromium, cobalt, and nickel), and four essential alkaline earth elements (i.e. magnesium, calcium, strontium, barium) with ILI risk. It was concluded that the environmental exposure to certain compounds of housewives may contribute to their ILI development.

Clinical Features of Patients Infected with the 2019 Novel Coronavirus (COVID-19) in Shanghai, China

BACKGROUND

Since mid-December 2019, a cluster of pneumonia-like diseases caused by a novel coronavirus, now designated COVID-19 by the WHO, emerged in Wuhan city and rapidly spread throughout China. Here we identify the clinical characteristics of COVID-19 in a cohort of patients in Shanghai.

METHODS

Cases were confirmed by real-time RT-PCR and were analysed for demographic, clinical, laboratory and radiological features.

RESULTS

Of 198 patients, the median duration from disease onset to hospital admission was 4 days. The mean age of the patients was 50.1 years, and 51.0% patients were male. The most common symptom was fever. Less than half of the patients presented with respiratory systems including cough, sputum production, itchy or sore throat, shortness of breath, and chest congestion. 5.6% patients had diarrhoea. On admission, T lymphocytes were decreased in 45.8% patients. Ground glass opacity was the most common radiological finding on chest computed tomography. 9.6% were admitted to the ICU because of the development of organ dysfunction. Compared with patients not treated in ICU, patients treated in the ICU were older, had longer waiting time to admission, fever over 38.5o C, dyspnoea, reduced T lymphocytes, elevated neutrophils and organ failure.

CONCLUSIONS

In this single centre cohort of COVID-19 patients, the most common symptom was fever, and the most common laboratory abnormality was decreased blood T cell counts. Older age, male, fever over 38.5oC, symptoms of dyspnoea, and underlying comorbidity, were the risk factors most associated with severity of disease.

KEY WORDS

2019 novel coronavirus; acute respiratory infection; risk factors for disease severity.

Influenza A virus uncoating

Influenza A virus (IAV) is an enveloped virus of the Orthomyxoviridae with a negative-sense single-stranded RNA genome. During virus cell entry, viral and cellular cues are delivered in a stepwise manner within two distinct cellular compartments-the endosomes and the cytosol. Endosome maturation primes the viral core for uncoating by cytosolic host proteins and host-mediated virus disaggregation is essential for genome import and replication in the nucleus. Recent evidence shows that two well-known cellular proteins-histone deacetylase 6 (HDAC6) and karyopherin-β2 (kapβ2)-uncoat influenza virus. HDAC6 is 1 of 11 HDACs and an X-linked, cytosolic lysine deacetylase. Under normal cellular conditions HDAC6 is the tubulin deacetylase. Under proteasomal stress HDAC6 binds unanchored ubiquitin, dynein and myosin II to sequester misfolded protein aggregates for autophagy. Kapβ2 is a member of the importin β family that transports RNA-binding proteins into the nucleus by binding to disordered nuclear localization signals (NLSs) known as PY-NLS. Kapβ2 is emerging as a universal uncoating factor for IAV and human immunodeficiency virus type 1 (HIV-1). Kapβ2 can also reverse liquid-liquid phase separation (LLPS) of RNA-binding proteins by promoting their disaggregation. Thus, it is becoming evident that key players in the management of cellular condensates and membraneless organelles are potent virus uncoating factors. This emerging concept reveals implications in viral pathogenesis, as well as, the promise for cell-targeted therapeutic strategies to block universal virus uncoating pathways hijacked by enveloped RNA viruses.

Breaking the Convention: Sialoglycan Variants, Coreceptors, and Alternative Receptors for Influenza A Virus Entry

The influenza A virus (IAV) envelope protein hemagglutinin binds α2,6- or α2,3-linked sialic acid as a host cell receptor. Bat IAV subtypes H17N10 and H18N11 form an exception to this rule and do not bind sialic acid but enter cells via major histocompatibility complex (MHC) class II. Here, we review current knowledge on IAV receptors with a focus on sialoglycan variants, protein coreceptors, and alternative receptors that impact IAV attachment and internalization beyond the well-described sialic acid binding.

Host Calcium Channels and Pumps in Viral Infections

Ca²⁺ is essential for virus entry, viral gene replication, virion maturation, and release. The alteration of host cells Ca²⁺ homeostasis is one of the strategies that viruses use to modulate host cells signal transduction mechanisms in their favor. Host calcium-permeable channels and pumps (including voltage-gated calcium channels, store-operated channels, receptor-operated channels, transient receptor potential ion channels, and Ca²⁺-ATPase) mediate Ca²⁺ across the plasma membrane or subcellular organelles, modulating intracellular free Ca²⁺. Therefore, these Ca²⁺ channels or pumps present important aspects of viral pathogenesis and virus–host interaction. It has been reported that viruses hijack host calcium channels or pumps, disturbing the cellular homeostatic balance of Ca²⁺. Such a disturbance benefits virus lifecycles while inducing host cells’ morbidity. Evidence has emerged that pharmacologically targeting the calcium channel or calcium release from the endoplasmic reticulum (ER) can obstruct virus lifecycles. Impeding virus-induced abnormal intracellular Ca²⁺ homeostasis is becoming a useful strategy in the development of potent antiviral drugs. In this present review, the recent identified cellular calcium channels and pumps as targets for virus attack are emphasized.

Influenza Virus Mounts a Two-Pronged Attack on Host RNA Polymerase II Transcription

Influenza virus intimately associates with host RNA polymerase II (Pol II) and mRNA processing machinery. Here, we use mammalian native elongating transcript sequencing (mNET-seq) to examine Pol II behavior during viral infection. We show that influenza virus executes a two-pronged attack on host transcription. First, viral infection causes decreased Pol II gene occupancy downstream of transcription start sites. Second, virus-induced cellular stress leads to a catastrophic failure of Pol II termination at poly(A) sites, with transcription often continuing for tens of kilobases. Defective Pol II termination occurs independently of the ability of the viral NS1 protein to interfere with host mRNA processing. Instead, this termination defect is a common effect of diverse cellular stresses and underlies the production of previously reported downstream-of-gene transcripts (DoGs). Our work has implications for understanding not only host-virus interactions but also fundamental aspects of mammalian transcription.

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Influenza virus infection dysregulates host transcription

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Viral infection depletes Pol II from gene bodies downstream of the TSS

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Virus-induced stress leads to a catastrophic failure of Pol II termination

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Defective termination does not require viral NS1: host CPSF30 interaction

The Interferon-Inducible Proteoglycan Testican-2/SPOCK2 Functions as a Protective Barrier against Virus Infection of Lung Epithelial Cells

Proteoglycans function not only as structural components of the extracellular compartment but also as regulators of various cellular events, including cell migration, inflammation, and infection. Many microbial pathogens utilize proteoglycans to facilitate adhesion and invasion into host cells. Here we report a secreted form of a novel heparan sulfate proteoglycan that functions against virus infection. The expression of SPOCK2/testican-2 was significantly induced in virus-infected lungs or in interferon (IFN)-treated alveolar lung epithelial cells. Overexpression from a SPOCK2 expression plasmid alone or the treatment of cells with recombinant SPOCK2 protein efficiently blocked influenza virus infection at the step of viral attachment to the host cell and entry. Moreover, mice treated with purified SPOCK2 were protected against virus infection. Sialylated glycans and heparan sulfate chains covalently attached to the SPOCK2 core protein were critical for its antiviral activity. Neuraminidase (NA) of influenza virus cleaves the sialylated moiety of SPOCK2, thereby blocking its binding to the virus. Our data suggest that IFN-induced SPOCK2 functions as a decoy receptor to bind and block influenza virus infection, thereby restricting entry of the infecting virus into neighboring cells.IMPORTANCE Here we report a novel proteoglycan protein, testican-2/SPOCK2, that prevents influenza virus infection. Testican-2/SPOCK2 is a complex type of secreted proteoglycan with heparan sulfate GAG chains attached to the core protein. SPOCK2 expression is induced upon virus infection or by interferons, and the protein is secreted to an extracellular compartment, where it acts directly to block virus-cell attachment and entry. Treatment with purified testican-2/SPOCK2 protein can efficiently block influenza virus infection in vitro and in vivo We also identified the heparan sulfate moiety as a key regulatory module for this inhibitory effect. Based on its mode of action (cell attachment/entry blocker) and site of action (extracellular compartment), we propose testican-2/SPOCK2 as a potential antiviral agent that can efficiently control influenza virus infection.