Cell surface α2,3-linked sialic acid facilitates Zika virus internalization

A single mutation in the PrM gene of Zika virus determines AXL dependency for infection of human neural cells

Zika virus (ZIKV) is spread by mosquito bites and is unique among known flaviviruses for being able to cause microcephaly. Entry factors for ZIKV are incompletely understood, but phosphatidylserine (PS) receptors, including the TAM (Tyro3, AXL, and Mer) and TIM (T-cell Ig mucin) families, can serve as cofactors for flavivirus entry in a cell type-specific manner. We identify AXL as the top hit in a CRISPR/Cas9 genome-wide screen in human glioblastoma cells and establish a definitive role of AXL, but not TYRO3 or MerTK, for ZIKV infection. Additionally, Spondweni virus also shows AXL dependency, while dengue virus infection is not affected by AXL knockout. Passage of ZIKV in AXL knockout (KO) cells generated a mutant virus capable of infection via AXL-independent mechanisms, and multiple independent selections identified a common mutation, H83R, in the prM coding region of the ZIKV genome. The mutant virus exhibits an increased infectivity rate in AXL KO cells as compared to wild-type ZIKV and is dependent upon the single H83R mutation. The mutant virus' ability to infect cells in an AXL-independent manner is unrelated to interferon signaling antagonism but likely pertains to a change in virus maturation that leads to a structural disturbance of the ZIKV virion. Our study provides evidence for a potential mechanism linking the viral structural proteins and host PS receptor usage during flavivirus infection.IMPORTANCEA major challenge in elucidating the mechanism of Zika virus (ZIKV) pathogenesis is the multitude of cell types it infects with distinct requirements. The role of phosphatidylserine (PS) receptors in ZIKV infection is cell type-specific, and the controversy surrounds their function in flavivirus entry. Here, we establish a definitive requirement of AXL for infection of human glioblastoma cells by both Zika and Spondweni virus. We then identified a single amino acid mutation (H83R) in the prM protein of ZIKV that allowed AXL-independent infection of these cells. The H83R-mediated escape of AXL requirement is independent of interferon (IFN) signaling suppression by AXL; instead, the mutation has the potential to disrupt the virus assembly and virion structure. This study reveals a previously unknown connection between the PS receptor usage and the flavivirus prM gene, which can guide detailed molecular mechanism studies of the interplay between virion assembly and virus entry.

Cellular sialoglycans are differentially required for endosomal and cell-surface entry of SARS-CoV-2 in lung cell lines

Cell entry of severe acute respiratory coronavirus-2 (SARS-CoV-2) and other CoVs can occur via two distinct routes. Following receptor binding by the spike glycoprotein, membrane fusion can be triggered by spike cleavage either at the cell surface in a transmembrane serine protease 2 (TMPRSS2)-dependent manner or within endosomes in a cathepsin-dependent manner. Cellular sialoglycans have been proposed to aid in CoV attachment and entry, although their functional contributions to each entry pathway are unknown. In this study, we used genetic and enzymatic approaches to deplete sialic acid from cell surfaces and compared the requirement for sialoglycans during endosomal and cell-surface CoV entry using lentiviral particles pseudotyped with the spike proteins of different sarbecoviruses. We show that entry of SARS-CoV-1, WIV1-CoV and WIV16-CoV, like the SARS-CoV-2 omicron variant, depends on endosomal cathepsins and requires cellular sialoglycans for entry. Ancestral SARS-CoV-2 and the delta variant can use either pathway for entry, but only require sialic acid for endosomal entry in cells lacking TMPRSS2. Binding of SARS-CoV-2 spike protein to cells did not require sialic acid, nor was sialic acid required for SARS-CoV-2 entry in TMRPSS2-expressing cells. These findings suggest that cellular sialoglycans are not strictly required for SARS-CoV-2 attachment, receptor binding or fusion, but rather promote endocytic entry of SARS-CoV-2 and related sarbecoviruses. In contrast, the requirement for sialic acid during entry of MERS-CoV pseudoparticles and authentic HCoV-OC43 was not affected by TMPRSS2 expression, consistent with a described role for sialic acid in merbecovirus and embecovirus cell attachment. Overall, these findings clarify the role of sialoglycans in SARS-CoV-2 entry and suggest that cellular sialoglycans mediate endosomal, but not cell-surface, SARS-CoV-2 entry.

Testicular immunity

The testis is a unique environment where immune responses are suppressed to allow the development of sperm that possess autoimmunogenic antigens. There are several contributors responsible for testicular immune privilege, including the blood-testis barrier, testicular immune cells, immunomodulation by Sertoli cells, and high levels of steroid hormones. Despite multiple mechanisms in place to regulate the testicular immune environment, pathogens that disrupt testicular immunity can lead to long-term effects such as infertility. If testicular immunity is disturbed, autoimmune reactions can also occur, leading to aberrant immune cell infiltration and subsequent attack of autoimmunogenic germ cells. Here we discuss cellular and molecular factors underlying testicular immunity and how testicular infection or autoimmunity compromise immune privilege. We also describe infections and autoimmune diseases that impact the testis. Further research into testicular immunity will reveal how male fertility is maintained and will help update therapeutic strategies for infertility and other testicular disorders.

Preventing human influenza and coronaviral mono or coinfection by blocking virus-induced sialylation

Influenza A viruses (IAVs) and endemic coronaviruses (eCoVs) are common etiologic agents for seasonal respiratory infections. The human H1N1 of IAV and coronavirus OC43 (HCoV-OC43) can result in hospitalization, acute respiratory distress syndrome (ARDS), and even death, particularly in immunocompromised individuals. They infect the epithelium of the respiratory tract by interacting with host cell sialic acid (Sia)- linked receptors whose synthesis is catalyzed by sialyltransferases (STs). Viral coinfection is challenging to treat because of the need to target specific components of two or more distinct pathogens. Emerging drug and vaccine resistance due to the high mutation rate of viral genomes further complicates the treatment and prevention of viral infection. Sialylation mediated by STs may be a potential drug target for treating viral diseases. ST is an attractive target because it could be effective before identifying the pathogen that has occurred, providing a novel direction for overcoming drug resistance and achieving a broad-spectrum antiviral effect. We developed an H1N1 and OC43 mono or coinfection model using 14 days post-plating (14 PP) human primary small airway epithelial cells (HSAEC) grown on transwell inserts at an air-fluid interface (ALI), mimicking in vivo cellular dynamics. Using this model, we have observed that mono or coinfection with OC43 and H1N1 results in increased sialic acid levels and synergistic viral infection. We showed for the first time that H1N1 and OC43 mono- and coinfection in HSAEC caused increased expression and activity of STs, which can be blocked by pan-STs inhibitor (3Fax-Peracetyl Neu5Ac) with no host cell toxicity.

Sialic acids as attachment factors in mosquitoes mediating Japanese encephalitis virus infection

The role of Culex mosquitoes in the transmission of Japanese encephalitis virus (JEV) is crucial, yet the mechanisms of JEV infection in these vectors remain unclear. Previous research has indicated that various host factors participate in JEV infection. Herein, we present evidence that mosquito sialic acids enhance JEV infection both in vivo and in vitro. By treating mosquitoes and C6/36 cells with neuraminidase or lectin, the function of sialic acids is effectively blocked, resulting in significant inhibition of JEV infection. Furthermore, knockdown of the sialic acid biosynthesis genes in Culex mosquitoes also leads to a reduction in JEV infection. Moreover, our research revealed that sialic acids play a role in the attachment of JEV to mosquito cells, but not in its internalization. To further explore the mechanisms underlying the promotion of JEV attachment by sialic acids, we conducted immunoprecipitation experiments to confirm the direct binding of sialic acids to the last α-helix in JEV envelope protein domain III. Overall, our study contributes to a molecular comprehension of the interaction between mosquitoes and JEV and offers potential strategies for preventing the dissemination of flavivirus in natural environments.IMPORTANCEIn this study, we aimed to investigate the impact of glycoconjugate sialic acids on mosquito infection with Japanese encephalitis virus (JEV). Our findings demonstrate that sialic acids play a crucial role in enhancing JEV infection by facilitating the attachment of the virus to the cell membrane. Furthermore, our investigation revealed that sialic acids directly bind to the final α-helix in the JEV envelope protein domain III, thereby accelerating virus adsorption. Collectively, our results highlight the significance of mosquito sialic acids in JEV infection within vectors, contributing to a better understanding of the interaction between mosquitoes and JEV.

Human cytokeratin 1 plays a role in the interaction of Pteropine orthoreovirus with Hek293 cells but not HeLa cells

Pteropine orthoreovirus (PRV) causes respiratory tract infections in humans. Despite its emergence as a zoonotic and respiratory virus, little is known about its cell tropism, which hampers progress in fully understanding its pathogenesis in humans. Hek293 cells are most susceptible to PRV infection, while HeLa cells are the least. Human cytokeratin 1 (CK1) was identified as the protein that interacts with PRV. The immunofluorescence assay and qPCR results revealed prior treatment with anti-CK1 may provide Hek293 cells protection against PRV. The KRT1-knockout Hek293 cells were less susceptible to PRV infection. Further study into the pathogenesis of PRV in humans is needed.

Vector-Transmitted Flaviviruses: An Antiviral Molecules Overview

Flaviviruses cause numerous pathologies in humans across a broad clinical spectrum with potentially severe clinical manifestations, including hemorrhagic and neurological disorders. Among human flaviviruses, some viral proteins show high conservation and are good candidates as targets for drug design. From an epidemiological point of view, flaviviruses cause more than 400 million cases of infection worldwide each year. In particular, the Yellow Fever, dengue, West Nile, and Zika viruses have high morbidity and mortality-about an estimated 20,000 deaths per year. As they depend on human vectors, they have expanded their geographical range in recent years due to altered climatic and social conditions. Despite these epidemiological and clinical premises, there are limited antiviral treatments for these infections. In this review, we describe the major compounds that are currently under evaluation for the treatment of flavivirus infections and the challenges faced during clinical trials, outlining their mechanisms of action in order to present an overview of ongoing studies. According to our review, the absence of approved antivirals for flaviviruses led to in vitro and in vivo experiments aimed at identifying compounds that can interfere with one or more viral cycle steps. Still, the currently unavailability of approved antivirals poses a significant public health issue.

Multivalent sialic acid materials for biomedical applications

Sialic acid is a kind of monosaccharide expressed on the non-reducing end of glycoproteins or glycolipids. It acts as a signal molecule combining with its natural receptors such as selectins and siglecs (sialic acid-binding immunoglobulin-like lectins) in intercellular interactions like immunological surveillance and leukocyte infiltration. The last few decades have witnessed the exploration of the roles that sialic acid plays in different physiological and pathological processes and the use of sialic acid-modified materials as therapeutics for related diseases like immune dysregulation and virus infection. In this review, we will briefly introduce the biomedical function of sialic acids in organisms and the utilization of multivalent sialic acid materials for targeted drug delivery as well as therapeutic applications including anti-inflammation and anti-virus.

Viral tropism for the testis and sexual transmission

The mammalian testis adopts an immune privileged environment to protect male germ cells from adverse autoimmune reaction. The testicular immune privileged status can be also hijacked by various microbial pathogens as a sanctuary to escape systemic immune surveillance. In particular, several viruses have a tropism for the testis. To overcome the immune privileged status and mount an effective local defense against invading viruses, testicular cells are well equipped with innate antiviral machinery. However, several viruses may persist an elongated duration in the testis and disrupt the local immune homeostasis, thereby impairing testicular functions and male fertility. Moreover, the viruses in the testis, as well as other organs of the male reproductive system, can shed to the semen, thus allowing sexual transmission to partners. Viral infection in the testis, which can impair male fertility and lead to sexual transmission, is a serious concern in research on known and on new emerging viruses. To provide references for our scientific peers, this article reviews research achievements and suggests future research focuses in the field.

Advancement in the Development of Therapeutics Against Zika Virus Infection

Zika virus (ZIKV), a re-emerging arbovirus, causes teratogenic effects on the fetus and normal nerve functions, resulting in harmful autoimmune responses, which call for the development of therapeutics against ZIKV infection. In this review, we introduce the pathogenesis of ZIKV infection and summarize the advancement in the development of therapeutics against ZIKV infection. It provides guidance for the development of effective therapeutics against ZIKV infection.

SARS-CoV-2 Attacks in the Brain: Focus on the Sialome

The epidemiological observations suggest that respiratory and gastrointestinal symptoms caused by severe acute respiratory coronavirus 2 (SARS-CoV-2) are accompanied by short- and long-term neurological manifestations. There is increasing evidence that the neuroinvasive potential of SARS-CoV-2 is closely related to its capacity to interact with cell membrane sialome. Given the wide expression of sialylated compounds of cell membranes in the brain, the interplay between cell membrane sialoglycans and the virus is crucial for its attachment and cell entry, transport, neuronal damage and brain immunity. Here, we focus on the significance of the brain sialome in the progress of coronavirus disease 2019 (COVID-19) and SARS-CoV-2-induced neuropathology.

Zika Virus Neuropathogenesis: The Different Brain Cells, Host Factors and Mechanisms Involved

Zika virus (ZIKV), despite being discovered six decades earlier, became a major health concern only after an epidemic in French Polynesia and an increase in the number of microcephaly cases in Brazil. Substantial evidence has been found to support the link between ZIKV and neurological complications in infants. The virus targets various cells in the brain, including radial glial cells, neural progenitor cells (NPCs), astrocytes, microglial and glioblastoma stem cells. It affects the brain cells by exploiting different mechanisms, mainly through apoptosis and cell cycle dysregulation. The modulation of host immune response and the inflammatory process has also been demonstrated to play a critical role in ZIKV induced neurological complications. In addition to that, different ZIKV strains have exhibited specific neurotropism and unique molecular mechanisms. This review provides a comprehensive and up-to-date overview of ZIKV-induced neuroimmunopathogenesis by dissecting its main target cells in the brain, and the underlying cellular and molecular mechanisms. We highlighted the roles of the different ZIKV host factors and how they exploit specific host factors through various mechanisms. Overall, it covers key components for understanding the crosstalk between ZIKV and the brain.

Host Molecules Regulating Neural Invasion of Zika Virus and Drug Repurposing Strategy

Zika virus (ZIKV) is a mosquito-borne, single-stranded RNA virus belonging to the genus Flavivirus. Although ZIKV infection is usually known to exhibit mild clinical symptoms, intrauterine ZIKV infections have been associated with severe neurological manifestations, including microcephaly and Guillain Barre syndrome (GBS). Therefore, it is imperative to understand the mechanisms of ZIKV entry into the central nervous system (CNS) and its effect on brain cells. Several routes of neuro-invasion have been identified, among which blood–brain barrier (BBB) disruption is the commonest mode of access. The molecular receptors involved in viral entry remain unknown; with various proposed molecular ZIKV-host interactions including potential non-receptor mediated cellular entry. As ZIKV invade neuronal cells, they trigger neurotoxic mechanisms via cell-autonomous and non-cell autonomous pathways, resulting in neurogenesis dysfunction, viral replication, and cell death, all of which eventually lead to microcephaly. Together, our understanding of the biological mechanisms of ZIKV exposure would aid in the development of anti-ZIKV therapies targeting host cellular and/or viral components to combat ZIKV infection and its neurological manifestations. In this present work, we review the current understanding of ZIKV entry mechanisms into the CNS and its implications on the brain. We also highlight the status of the drug repurposing approach for the development of potential antiviral drugs against ZIKV.

AXL receptor is required for Zika virus strain MR-766 infection in human glioblastoma cell lines

Recent reports have shown that Zika virus (ZIKV) has oncolytic potential against human glioblastoma (GBM); however, the mechanisms underlying its tropism and cell entry are not completely understood. The receptor tyrosine kinase AXL has been identified as an entry receptor for ZIKV in a cell-type-specific manner. Interestingly, AXL is frequently overexpressed in GBM patients. Using commercially available GBM cell lines, we first show that cells expressing AXL are permissive for ZIKV infection, while cells that do not express AXL are not. Furthermore, inhibition of AXL kinase using R428 and antibody blockade of AXL receptor strongly attenuated virus entry in GBM cell lines. Additionally, CRISPR knockout of the AXL gene in GBM cell lines completely abolished ZIKV infection, significantly inhibited viral replication, and significantly reduced apoptosis compared with parental lines. Lastly, introduction of AXL receptor into non-expressing cell lines renders the cells susceptible to ZIKV infection. Together, these findings demonstrate that ZIKV entry into GBM cells in vitro is mediated by the AXL receptor and that following cell entry, productive infection is cytotoxic. Thus, ZIKV is a potential oncolytic virus for GBM.

Zika Virus Requires the Expression of Claudin-7 for Optimal Replication in Human Endothelial Cells

Zika virus (ZIKV) infection has been associated with a series of neurological pathologies. In patients with ZIKV-induced neurological disorders, the virus is detectable in the central nervous system. Thus, ZIKV is capable of neuroinvasion, presumably through infection of the endothelial cells that constitute the blood-brain barrier (BBB). We demonstrate that susceptibility of BBB endothelial cells to ZIKV infection is modulated by the expression of tight-junction protein claudin-7 (CLDN7). Downregulation of CLDN7 reduced viral RNA yield, viral protein production, and release of infectious viral particles in several endothelial cell types, but not in epithelial cells, indicating that CLDN7 implication in viral infection is cell-type specific. The proviral activity of CLDN7 in endothelial cells is ZIKV-specific since related flaviviruses were not affected by CLDN7 downregulation. Together, our data suggest that CLDN7 facilitates ZIKV infection in endothelial cells at a post-internalization stage and prior to RNA production. Our work contributes to a better understanding of the mechanisms exploited by ZIKV to efficiently infect and replicate in endothelial cells and thus of its ability to cross the BBB.

The epidermal growth factor receptor is a relevant host factor in the early stages of Zika virus life cycle in vitro

Zika virus (ZIKV) is a flavivirus well-known for the epidemic in the Americas in 2015-2016, where microcephaly in newborns and other neurological complications were connected to ZIKV infection. Many aspects of the viral life cycle, including binding and entry into the host cell, are still enigmatic. Based on the observation that CHO cells lack the expression of EGFR and are not permissive for various ZIKV strains, the relevance of EGFR for the viral life cycle was analyzed. Infection of A549 cells by ZIKV leads to a rapid internalization of EGFR that colocalizes with the endosomal marker EEA1. Moreover, the infection by different ZIKV strains is associated with an activation of EGFR and subsequent activation of the MAPK/ERK signaling cascade. However, treatment of the cells with MβCD, which on the one hand leads to an activation of EGFR but on the other hand prevents EGFR internalization, impairs ZIKV infection. Specific inhibition of EGFR or of the RAS-RAF-MEK-ERK signal transduction cascade hinders ZIKV infection by inhibition of ZIKV entry. In accordance to this, knockout of EGFR expression impedes ZIKV entry. In case of an already established infection, inhibition of EGFR or of downstream signaling does not affect viral replication. Taken together, these data demonstrate the relevance of EGFR in the early stages of ZIKV infection and identify EGFR as a target for antiviral strategies. Importance These data deepen the knowledge about the ZIKV infection process and demonstrate the relevance of EGFR for ZIKV entry. In light of the fact that a variety of specific and efficient inhibitors of EGFR and of EGFR-dependent signaling were developed and licensed, repurposing of these substances could be a helpful tool to prevent the spreading of ZIKV infection in an epidemic outbreak.

The key amino acids of E protein involved in early flavivirus infection: viral entry

Flaviviruses are enveloped viruses that infect multiple hosts. Envelope proteins are the outermost proteins in the structure of flaviviruses and mediate viral infection. Studies indicate that flaviviruses mainly use envelope proteins to bind to cell attachment receptors and endocytic receptors for the entry step. Here, we present current findings regarding key envelope protein amino acids that participate in the flavivirus early infection process. Among these sites, most are located in special positions of the protein structure, such as the α-helix in the stem region and the hinge region between domains I and II, motifs that potentially affect the interaction between different domains. Some of these sites are located in positions involved in conformational changes in envelope proteins. In summary, we summarize and discuss the key envelope protein residues that affect the entry process of flaviviruses, including the process of their discovery and the mechanisms that affect early infection.

Binding of the SARS-CoV-2 spike protein to glycans

The pandemic of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a high number of deaths in the world. To combat it, it is necessary to develop a better understanding of how the virus infects host cells. Infection normally starts with the attachment of the virus to cell-surface glycans like heparan sulfate (HS) and sialic acid-containing glycolipids/glycoproteins. In this study, we examined and compared the binding of the subunits and spike (S) proteins of SARS-CoV-2, SARS-CoV, and Middle East respiratory disease (MERS)-CoV to these glycans. Our results revealed that the S proteins and subunits can bind to HS in a sulfation-dependent manner and no binding with sialic acid residues was detected. Overall, this work suggests that HS binding may be a general mechanism for the attachment of these coronaviruses to host cells, and supports the potential importance of HS in infection and in the development of antiviral agents against these viruses.

Racemases and epimerases operating through a 1,1-proton transfer mechanism: reactivity, mechanism and inhibition

Racemases and epimerases catalyse changes in the stereochemical configurations of chiral centres and are of interest as model enzymes and as biotechnological tools. They also occupy pivotal positions within metabolic pathways and, hence, many of them are important drug targets. This review summarises the catalytic mechanisms of PLP-dependent, enolase family and cofactor-independent racemases and epimerases operating by a deprotonation/reprotonation (1,1-proton transfer) mechanism and methods for measuring their catalytic activity. Strategies for inhibiting these enzymes are reviewed, as are specific examples of inhibitors. Rational design of inhibitors based on substrates has been extensively explored but there is considerable scope for development of transition-state mimics and covalent inhibitors and for the identification of inhibitors by high-throughput, fragment and virtual screening approaches. The increasing availability of enzyme structures obtained using X-ray crystallography will facilitate development of inhibitors by rational design and fragment screening, whilst protein models will facilitate development of transition-state mimics.

Gist of Zika Virus pathogenesis

Zika virus (ZIKV) is a mosquito-borne neurotropic flavivirus. ZIKV infection may lead to microcephaly in developing fetus and Guillain-Barré Syndrome (GBS) like symptoms in adults. ZIKV was first reported in humans in 1952 from Uganda and the United Republic of Tanzania. Later, ZIKV outbreak was reported in 2007 from the Yap Island. ZIKV re-emerged as major outbreak in the year 2013 from French Polynesia followed by second outbreak in the year 2015 from Brazil. ZIKV crosses the blood-tissue barriers to enter immune-privileged organs. Clinical manifestations in ZIKV disease includes rash, fever, conjunctivitis, muscle and joint pain, headache, transverse myelitis, meningoencephalitis, Acute Disseminated Encephalomyelitis (ADEM). The understanding of the molecular mechanism of ZIKV pathogenesis is very important to develop potential diagnostic and therapeutic interventions for ZIKV infected patients.

Effects of oral sialic acid on gut development, liver function and gut microbiota in mice

Sialic acid (N-acetylneuraminic acid), a 9-carbon monosaccharide, has been widely studied in immunology, oncology and neurology. However, the effects of sialic acid on organ and intestinal development, liver function and gut microbiota were rarely studied. In this study, we found that oral sialic acid tended to increase the relative weight of liver and decreased the serum aspartate aminotransferase (GPT) activity. In addition, sialic acid treatment markedly reduced gut villus length, depth, the ratio of villus length/depth (L/D), areas, width and the number of goblet cells. Furthermore, gut microbes were changed in response to oral sialic acid, such as Staphylococcus lentus, Corynebacterium stationis, Corynebacterium urealyticum, Jeotgalibaca sp_PTS2502, Ignatzschineria indica, Sporosarcina pasteurii, Sporosarcina sp_HW10C2, Facklamia tabacinasalis, Oblitimonas alkaliphila, Erysipelatoclostridium ramosum, Blautia sp_YL58, Bacteroids thetaiotaomicron, Morganella morganii, Clostridioides difficile, Helicobacter tryphlonius, Clostridium sp_Clone47, Alistipes finegoldii, [pseudomonas]_geniculata and Pseudomonas parafulva at the species level. In conclusion, oral sialic acid altered the intestinal pathological state and microbial compositions, and the effect of sialic acid on host health should be further studied.

Mumps Orchitis: Clinical Aspects and Mechanisms

The causative agent of mumps is a single-stranded, non-segmented, negative sense RNA virus belonging to the Paramyxoviridae family. Besides the classic symptom of painfully swollen parotid salivary glands (parotitis) in mumps virus (MuV)-infected men, orchitis is the most common form of extra-salivary gland inflammation. Mumps orchitis frequently occurs in young adult men, and leads to pain and swelling of the testis. The administration of MuV vaccines in children has been proven highly effective in reducing the incidence of mumps. However, a recent global outbreak of mumps and the high rate of orchitis have recently been considered as threats to male fertility. The pathogenesis of mumps orchitis remains largely unclear due to lack of systematic clinical data analysis and animal models studies. The alarming increase in the incidence of mumps orchitis and the high risk of the male fertility have thus become a major health concern. Recent studies have revealed the mechanisms by which MuV-host cells interact and MuV infection induces inflammatory responses in testicular cells. In this mini-review, we highlight advances in our knowledge of the clinical aspects and possible mechanisms of mumps orchitis.

Sialic Acid Receptors: The Key to Solving the Enigma of Zoonotic Virus Spillover

Emerging viral diseases are a major threat to global health, and nearly two-thirds of emerging human infectious diseases are zoonotic. Most of the human epidemics and pandemics were caused by the spillover of viruses from wild mammals. Viruses that infect humans and a wide range of animals have historically caused devastating epidemics and pandemics. An in-depth understanding of the mechanisms of viral emergence and zoonotic spillover is still lacking. Receptors are major determinants of host susceptibility to viruses. Animal species sharing host cell receptors that support the binding of multiple viruses can play a key role in virus spillover and the emergence of novel viruses and their variants. Sialic acids (SAs), which are linked to glycoproteins and ganglioside serve as receptors for several human and animal viruses. In particular, influenza and coronaviruses, which represent two of the most important zoonotic threats, use SAs as cellular entry receptors. This is a comprehensive review of our current knowledge of SA receptor distribution among animal species and the range of viruses that use SAs as receptors. SA receptor tropism and the predicted natural susceptibility to viruses can inform targeted surveillance of domestic and wild animals to prevent the future emergence of zoonotic viruses.

Usefulness of salivary sialic acid as a tumor marker in tobacco chewers with oral cancer

Aim

This study aims to assess the usefulness of salivary sialic acid (SA) as a tumor marker in the detection of oral squamous cell carcinoma (OSCC) among tobacco chewers.

Materials and Methods

After the approval of study protocol by the Institutional Ethics Committee and informed voluntary consent, salivary samples were collected from 96 participants in each group of tobacco chewers with OSCC, tobacco chewers without precancerous or cancerous lesion, and healthy controls. Salivary protein-bound SA (PBSA) and salivary-free SA (FSA) were measured by Yao et al.'s method of acid ninhydrin reaction, and the data were subjected to appropriate statistical analysis.

Results

The salivary PBSA and FSA levels in the Groups 1, 2, and 3 participants were 31.17 ± 7.6 mg/dL and 63.45 ± 9.8 mg/dL, 25.45 ± 16.61 mg/dL and 33.18 ± 11.38 mg/dL, and 22.73 ± 3.01 mg/dL and 21.62 ± 8.86 mg/dL, respectively. Salivary FSA levels were significantly increased among the tobacco chewers with OSCC patients (Group 1) and tobacco chewers with no premalignant lesions of the oral cavity (Group 2) compared to the healthy controls (Group 3) with P < 0.05 being statistically significant. Salivary FSA levels were significantly increased in Group 1 as compared with Group 2. The salivary PBSA was high among Group 1 as compared to the control Group 3; there was however no significant difference in the levels of salivary PBSA between Group 1 and Group 2. There was no significant difference in the PBSA levels between OSCC patients of Group 1 and the tobacco chewers without precancerous or cancerous lesion in the oral cavity of Group 2.

Conclusion

Salivary PBSA and FSA are significantly raised in both tobacco chewers with OSCC and in tobacco chewers with no precancerous or cancerous lesions in the oral cavity. SA should therefore be used cautiously while considering it as a marker for the early detection of oral cancer. Tobacco can be a crucial confounding factor when SA is used as a biomarker in OSCC since their levels are elevated to some extent even in tobacco chewers without any clinically obvious precancerous or cancerous lesions in the oral cavity.

Advances in the development of entry inhibitors for sialic-acid-targeting viruses

Over the past decades, several antiviral drugs have been developed to treat a range of infections. Yet the number of treatable viral infections is still limited, and resistance to current drug regimens is an ever-growing problem. Therefore, additional strategies are needed to provide a rapid cure for infected individuals. An interesting target for antiviral drugs is the process of viral attachment and entry into the cell. Although most viruses use distinct host receptors for attachment to the target cell, some viruses share receptors, of which sialic acids are a common example. This review aims to give an update on entry inhibitors for a range of sialic-acid-targeting viruses and provides insight into the prospects for those with broad-spectrum potential.

ANKS4B Restricts Replication of Zika Virus by Downregulating the Autophagy

Infection of Zika virus (ZIKV) has become a severe threaten to global health while no specific drug is available. In this study, we explored the relationship between ZIKV and a cellular protein, ankyrin repeat and sterile motif domain containing 4b (ANKS4B). Our data revealed that the expression of ANKS4B in cultured cells and in neonatal mice was downregulated by ZIKV infection. The reduction of ANKS4B upon ZIKV infection was caused by decrease of two hepatocyte nuclear factors HNF1α and HNF4α. Through CRISPR/Cas9 gene editing system, we generated two ANKS4B knockout (KO) cell clones in A549 and Huh7 cells respectively. In the ANKS4B-KO cells, the viral replication levels including viral RNA, protein, and titer were significantly enhanced, which was reversed by trans-complementation of ANKS4B. ANKS4B did not affect the viral entry step, but impaired the autophagy induced by ZIKV infection. Furthermore, our data showed that inhibition of autophagy led to similar replication levels of ZIKV in ANKS4B-sufficient and ANKS4B-deficient cells, suggesting the antiviral effect of ANKS4B relied on its modulation on the autophagy. Therefore, our work identified ANKS4B as a new restriction factor of ZIKV.

Roles of Sialic Acid, AXL, and MER Receptor Tyrosine Kinases in Mumps Virus Infection of Mouse Sertoli and Leydig Cells

The mumps virus (MuV) causes epidemic parotitis. MuV also frequently infects the testis and induces orchitis, an important etiological factor contributing to male infertility. However, mechanisms underlying MuV infection of the testis remain unknown. Here, we describe that sialic acid, AXL, and MER receptor tyrosine kinases regulate MuV entry and replication in mouse major testicular cells, including Sertoli and Leydig cells. Sialic acid, AXL, and MER were present in Sertoli and Leydig cells. Sialic acid specifically mediated MuV entry into Sertoli and Leydig cells, whereas both AXL and MER facilitated MuV replication within cells through the inhibition of cellular innate antiviral responses. Mechanistically, the inhibition of type 1 interferon signaling by AXL and MER is essential for MuV replication in Sertoli and Leydig cells. Our findings provide novel insights into the mechanisms behind MuV infection and replication in the testis.

Zika virus infection studies with CD34+ hematopoietic and megakaryocyte-erythroid progenitors, red blood cells and platelets

BACKGROUND

To date, several cases of transfusion-transmitted ZIKV infections have been confirmed. Multiple studies detected prolonged occurrence of ZIKV viral RNA in whole blood as compared to plasma samples indicating potential ZIKV interaction with hematopoietic cells. Also, infection of cells from the granulocyte/macrophage lineage has been demonstrated. Patients may develop severe thrombocytopenia, microcytic anemia, and a fatal course of disease occurred in a patient with sickle cell anemia suggesting additional interference of ZIKV with erythroid and megakaryocytic cells. Therefore, we analyzed whether ZIKV propagates in or compartmentalizes with hematopoietic progenitor, erythroid, and megakaryocytic cells.

METHODS

ZIKV RNA replication, protein translation and infectious particle formation in hematopoietic cell lines as well as primary CD34⁺ HSPCs and ex vivo differentiated erythroid and megakaryocytic cells was monitored using qRT-PCR, FACS, immunofluorescence analysis and infectivity assays. Distribution of ZIKV RNA and infectious particles in spiked red blood cell (RBC) units or platelet concentrates (PCs) was evaluated.

RESULTS

While subsets of K562 and KU812Ep6^EPO cells supported ZIKV propagation, primary CD34⁺ HSPCs, MEP cells, RBCs, and platelets were non-permissive for ZIKV infection. In spiking studies, ZIKV RNA was detectable for 7 days in all fractions of RBC units and PCs, however, ZIKV infectious particles were not associated with erythrocytes or platelets.

CONCLUSION

Viral particles from plasma or contaminating leukocytes, rather than purified CD34⁺ HSPCs or the cellular component of RBC units or PCs, present the greatest risk for transfusion-transmitted ZIKV infections.