Infection of porcine small intestinal enteroids with human and pig rotavirus A strains reveals contrasting roles for histo-blood group antigens and terminal sialic acids

A Passion for Small Things and Staying Primed: My Career in Virology and Immunology

A love of science and animals, perseverance, and happenstance propelled my career in veterinary virology and immunology. I have focused on deadly enteric and respiratory viral infections in neonatal livestock and humans with an aim to understand their prevalence, pathogenesis, interspecies transmission, and immunity and develop vaccines. Research on animal coronaviruses (CoVs), including their broad interspecies transmission, provided a foundation to understand emerging zoonotic fatal human respiratory CoVs [severe acute respiratory syndrome, Middle East respiratory syndrome, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)] and reverse zoonosis of SARS-CoV-2 to animals. A highlight of my early research was the discovery of the gut-mammary gland-sIgA axis, documenting a common mucosal immune system. The latter remains pivotal to designing maternal vaccines for passive immunity in neonates. Our discovery and innovative cell propagation of fastidious human and animal rotaviruses and caliciviruses and their infectivity in germ-free animals has provided cell-adapted and animal disease models for ongoing virologic and immunologic investigations and vaccines. Nevertheless, besides the research discoveries, my lasting legacy remains the outstanding mentees who have enriched my science and my life.

1α,25-hydroxyvitamin D3 alleviated rotavirus infection induced ferroptosis in IPEC-J2 cells by regulating the ATF3-SLC7A11-GPX4 axis

Rotavirus (RV) mainly infects mature intestinal epithelial cells and impairs intestinal absorption function, which leads to the death of infected cells and eventually fatal diarrhea. Ferroptosis is a novel regulatory cell death pattern, which can be caused by virus infection. 1α,25-hydroxyvitamin D3 (1,25D3) has an anti-RV infection effect and can regulate ferroptosis. However, whether RV infection can induce ferroptosis, and whether 1,25D3 can inhibit RV infection by regulating ferroptosis has not yet been studied. Present study shows that RV infection or erastin treatment induces IPEC-J2 cell death, which results in mitochondrial shrinkage, decreased mitochondrial membrane potential (MMP) and glutathione (GSH) content, increased MMP, intracellular Fe2+, reactive oxygen species (ROS), and malondialdehyde (MDA) contents. Meanwhile, ferrostatin-1 (Fer-1), liproxstatin-1 (Lip-1), and deferoxamine (DFO) treatment can effectively reverse the increase of intracellular Fe2+, ROS and MDA levels induced by RV infection. Moreover, RV infection increases activating transcription factor 3 (ATF3) mRNA and protein expressions, and inhibited SLC7A11 and glutathione peroxidase 4 (GPX4) expressions, which was partially alleviated by siATF3. 1,25D3 treatment significantly eliminates RV induced ferroptosis via ATF3-SLC7A11-GPX4 axis. Therefore, these results reveals that RV infection induces ferroptosis in IPEC-J2 cell and 1,25D3 alleviates RV induced ferroptosis by regulating the ATF3-SLC7A11-GPX4 axis.

Wuzhishan miniature pig-derived intestinal 2D monolayer organoids to investigate the enteric coronavirus infection

Intestinal organoids are valuable tools for investigating intestinal physiology and pathology ex vivo. In previous studies, intestinal organoids of commercial pigs have been developed. Here, we established intestinal organoids derived from Wuzhishan miniature pigs (WZS pigs), a unique kind of pig in the Hainan province of China. Three-dimensional (3D) intestinal organoids and organoid monolayers were developed and assessed. Furthermore, the susceptibility of organoid monolayers of WZS pigs to transmissible gastroenteritis virus (TGEV) was demonstrated. An RNA-seq analysis revealed that the TGEV infection stimulated antiviral and inflammatory immune responses in organoid monolayer models. The study implied the transmission risk of swine enteric coronavirus on WZS pigs and provided useful tools for further research on WZS pigs as laboratory miniature pig models.

Bacterial-derived sialidases inhibit porcine rotavirus OSU replication by interfering with the early steps of infection

Rotavirus infections in suckling and weaning piglets cause severe dehydration and death, resulting in significant economic losses in the pig breeding industry. With the continuous emergence of porcine rotavirus (PoRV) variants and poor vaccine cross-protection among various genotypes, there is an urgent need to develop alternative strategies such as seeking effective antiviral products from nature, microbial metabolites and virus-host protein interaction. Sialidases play a crucial role in various physiopathological processes and offer a promising target for developing antivirus drugs. However, the effect of bacterial-derived sialidases on the infection of PoRVs remains largely unknown. Herein, we investigated the impact of bacterial-derived sialidases (sialidase Cp and Vc) on PoRV strain OSU(Group A) infection, using differentiated epithelial monkey kidney cells (MA104) as a model. Our results indicated that the pretreatment of MA104 with exogenous sialidases effectively suppressed PoRV OSU in a concentration-dependent manner. Notably, even at a concentration of 0.01 μU/mL, sialidases significantly inhibited the virus (MOI = 0.01). Meanwhile, we found that sialidase Vc pretreatment sharply reduced the binding rate of PoRV OSU. Last, we demonstrated that PoRV OSU might recognize α-2,3-linked sialic acid as the primary attachment factor in MA104. Our findings provide new insights into the underlying mechanism of PoRV OSU infections, shedding lights on the development of alternative antivirus approaches based on bacteria-virus interaction.

Histo-Blood Group Antigen-Producing Bacterial Cocktail Reduces Rotavirus A, B, and C Infection and Disease in Gnotobiotic Piglets

The suboptimal performance of rotavirus (RV) vaccines in developing countries and in animals necessitates further research on the development of novel therapeutics and control strategies. To initiate infection, RV interacts with cell-surface O-glycans, including histo-blood group antigens (HBGAs). We have previously demonstrated that certain non-pathogenic bacteria express HBGA- like substances (HBGA+) capable of binding RV particles in vitro. We hypothesized that HBGA+ bacteria can bind RV particles in the gut lumen protecting against RV species A (RVA), B (RVB), and C (RVC) infection in vivo. In this study, germ-free piglets were colonized with HBGA+ or HBGA- bacterial cocktail and infected with RVA/RVB/RVC of different genotypes. Diarrhea severity, virus shedding, immunoglobulin A (IgA) Ab titers, and cytokine levels were evaluated. Overall, colonization with HBGA+ bacteria resulted in reduced diarrhea severity and virus shedding compared to the HBGA- bacteria. Consistent with our hypothesis, the reduced severity of RV disease and infection was not associated with significant alterations in immune responses. Additionally, colonization with HBGA+ bacteria conferred beneficial effects irrespective of the piglet HBGA phenotype. These findings are the first experimental evidence that probiotic performance in vivo can be improved by including HBGA+ bacteria, providing decoy epitopes for broader/more consistent protection against diverse RVs.

Differential transcriptome response following infection of porcine ileal enteroids with species A and C rotaviruses

BACKGROUND

Rotavirus C (RVC) is the major causative agent of acute gastroenteritis in suckling piglets, while most RVAs mostly affect weaned animals. Besides, while most RVA strains can be propagated in MA-104 and other continuous cell lines, attempts to isolate and culture RVC strains remain largely unsuccessful. The host factors associated with these unique RVC characteristics remain unknown.

METHODS

In this study, we have comparatively evaluated transcriptome responses of porcine ileal enteroids infected with RVC G1P[1] and two RVA strains (G9P[13] and G5P[7]) with a focus on innate immunity and virus-host receptor interactions.

RESULTS

The analysis of differentially expressed genes regulating antiviral immune response indicated that in contrast to RVA, RVC infection resulted in robust upregulation of expression of the genes encoding pattern recognition receptors including RIG1-like receptors and melanoma differentiation-associated gene-5. RVC infection was associated with a prominent upregulation of the most of glycosyltransferase-encoding genes except for the sialyltransferase-encoding genes which were downregulated similar to the effects observed for G9P[13].

CONCLUSIONS

Our results provide novel data highlighting the unique aspects of the RVC-associated host cellular signalling and suggest that increased upregulation of the key antiviral factors maybe one of the mechanisms responsible for RVC age-specific characteristics and its inability to replicate in most cell cultures.

Host Cell Response to Rotavirus Infection with Emphasis on Virus-Glycan Interactions, Cholesterol Metabolism, and Innate Immunity

Although rotavirus A (RVA) is the primary cause of acute viral gastroenteritis in children and young animals, mechanisms of its replication and pathogenesis remain poorly understood. We previously demonstrated that the neuraminidase-mediated removal of terminal sialic acids (SAs) significantly enhanced RVA-G9P[13] replication, while inhibiting RVA-G5P[7] replication. In this study, we compared the transcriptome responses of porcine ileal enteroids (PIEs) to G5P[7] vs. G9P[13] infections, with emphasis on the genes associated with immune response, cholesterol metabolism, and host cell attachment. The analysis demonstrated that G9P[13] infection led to a robust modulation of gene expression (4093 significantly modulated genes vs. 488 genes modulated by G5P[7]) and a significant modulation of glycosyltransferase-encoding genes. The two strains differentially affected signaling pathways related to immune response, with G9P[13] mostly upregulating and G5P[7] inhibiting them. Both RVAs modulated the expression of genes encoding for cholesterol transporters. G9P[13], but not G5P[7], significantly affected the ceramide synthesis pathway known to affect both cholesterol and glycan metabolism. Thus, our results highlight the unique mechanisms regulating cellular response to infection caused by emerging/re-emerging and historical RVA strains relevant to RVA-receptor interactions, metabolic pathways, and immune signaling pathways that are critical in the design of effective control strategies.

Sodium butyrate protects against rotavirus-induced intestinal epithelial barrier damage by activating AMPK-Nrf2 signaling pathway in IPEC-J2 cells

Rotavirus (RV) mainly infects intestinal epithelial cells, which leads to diarrhea in newborn piglets with dysfunction in the intestinal mucosal mechanical barrier. Sodium butyrate (SB) is one of the metabolites excreted by gut microbes. However, the protective effect of SB on RV infection induced intestinal mucosal mechanical barrier injury and its potential mechanism has not been well elucidated. In the present study, IPEC-J2 cells with RV infection was a model of intestinal mucosal mechanical barrier injury. Our results demonstrated that the appropriate concentration of SB can effectively alleviate TJ structural damage and up-regulating the expression of TJ-related genes. Furthermore, the appropriate concentration of SB can effectively reverse the increase of intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) level induced by RV infection. Meanwhile, the levels of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-px) and antioxidant proteins NAD(P)H dehydrogenase quinone 1 (NQO1) and heme oxygenase-1 (HO-1) were increased through SB treatment. In addition, we found that SB increased cellular antioxidant capacity by activating the adenosine monophosphate-activated protein kinase (AMPK)-nuclear factor erythroid 2-related factor (Nrf2) signaling pathway and the cytoprotective effect of SB is limited by GPR109A siRNA. Thus, our findings revealed that SB reduces oxidative stress caused by RV infection and restores the intestinal mucosal mechanical barrier function by activating the AMPK-Nrf2 signal pathway mediated by the receptor GPR109A.

Isolation and Characterization of Distinct Rotavirus A in Bat and Rodent Hosts

Rotavirus A (RVA) causes diarrheal disease in humans and various animals. Recent studies have identified bat and rodent RVAs with evidence of zoonotic transmission and genome reassortment. However, the virological properties of bat and rodent RVAs with currently identified genotypes still need to be better clarified. Here, we performed virus isolation-based screening for RVA in animal specimens and isolated RVAs (representative strains: 16-06 and MpR12) from Egyptian fruit bat and Natal multimammate mouse collected in Zambia. Whole-genome sequencing and phylogenetic analysis revealed that the genotypes of bat RVA 16-06 were identical to that of RVA BATp39 strain from the Kenyan fruit bat, which has not yet been characterized. Moreover, all segments of rodent RVA MpR12 were highly divergent and assigned to novel genotypes, but RVA MpR12 was phylogenetically closer to bat RVAs than to other rodent RVAs, indicating a unique evolutionary history. We further investigated the virological properties of the isolated RVAs. In brief, we found that 16-06 entered cells by binding to sialic acids on the cell surface, while MpR12 entered in a sialic acid-independent manner. Experimental inoculation of suckling mice with 16-06 and MpR12 revealed that these RVAs are causative agents of diarrhea. Moreover, 16-06 and MpR12 demonstrated an ability to infect and replicate in a 3D-reconstructed primary human intestinal epithelium with comparable efficiency to the human RVA. Taken together, our results detail the unique genetic and virological features of bat and rodent RVAs and demonstrate the need for further investigation of their zoonotic potential. IMPORTANCE Recent advances in nucleotide sequence detection methods have enabled the detection of RVA genomes from various animals. These studies have discovered multiple divergent RVAs and have resulted in proposals for the genetic classification of novel genotypes. However, most of these RVAs have been identified via dsRNA viral genomes and not from infectious viruses, and their virological properties, such as cell/host tropisms, transmissibility, and pathogenicity, are unclear and remain to be clarified. Here, we successfully isolated RVAs with novel genome constellations from three bats and one rodent in Zambia. In addition to whole-genome sequencing, the isolated RVAs were characterized by glycan-binding affinity, pathogenicity in mice, and infectivity to the human gut using a 3D culture of primary intestinal epithelium. Our study reveals the first virological properties of bat and rodent RVAs with high genetic diversity and unique evolutional history and provides basic knowledge to begin estimating the potential of zoonotic transmission.

Intestinal mucin-type O-glycans: the major players in the host-bacteria-rotavirus interactions

Rotavirus (RV) causes severe diarrhea in young children and animals worldwide. Several glycans terminating in sialic acids (SAs) and histo-blood group antigens (HBGAs) on intestinal epithelial cell (IEC) surface have been recognized to act as attachment sites for RV. IECs are protected by the double layer of mucus of which O-glycans (including HBGAs and SAs) are a major organic component. Luminal mucins, as well as bacterial glycans, can act as decoy molecules removing RV particles from the gut. The composition of the intestinal mucus is regulated by complex O-glycan-specific interactions among the gut microbiota, RV and the host. In this review, we highlight O-glycan-mediated interactions within the intestinal lumen prior to RV attachment to IECs. A better understanding of the role of mucus is essential for the development of alternative therapeutic tools including the use of pre- and probiotics to control RV infection.

Glycan-mediated interactions between bacteria, rotavirus and the host cells provide an additional mechanism of antiviral defence

Limited efficacy of rotavirus (RV) vaccines in children in developing countries and in animals remains a significant problem necessitating further search for additional approaches to control RV-associated gastroenteritis. During cell attachment and entry events, RV interacts with cell surface O-glycans including histo-blood group antigens (HBGAs). Besides modulation of the protective immunity against RV, several commensal and probiotic bacteria were shown to express HBGA-like substances suggesting that they may affect RV attachment and entry into the host cells. Moreover, some beneficial bacteria have been shown to possess the ability to bind host HBGAs via sugar specific proteins called lectins. However, limited research has been done to evaluate the effects of HBGA-expressing and/or HBGA-binding bacteria on RV infection. The aim of this study was to investigate the ability of selected commensal and probiotic bacteria to bind different RV strains via HBGAs and to block RV infection of IPEC-J2 cells. Our data indicated that Gram-negative probiotic Escherichia coli Nissle 1917 (E. coli Nissle 1917) and commensal Gram-positive (Streptococcus bovis and Bifidobacterium adolescentis) and Gram-negative (Bacteroides thetaiotaomicron, Clostridium clostridioforme and Escherichia coli G58 (E. coli G58) bacteria of swine origin expressed HBGAs which correlated with their ability to bind group A and C RVs. Additionally, Gram-positive E. coli 1917 and E. coli G58 demonstrated the ability to block RV attachment onto IPEC-J2 cells. Taken together, our results support the hypothesis that physical interactions between RVs and HBGA-expressing beneficial bacteria may limit RV replication.

Auxotrophic Lactobacillus Expressing Porcine Rotavirus VP4 Constructed Using CRISPR-Cas9D10A System Induces Effective Immunity in Mice

Porcine rotavirus (PoRV) mainly causes acute diarrhea in piglets under eight weeks of age and has potentially high morbidity and mortality rates. As vaccine carriers for oral immunization, lactic acid bacteria (LAB) are an ideal strategy for blocking PoRV infections. However, the difficulty in knocking out specific genes, inserting foreign genes, and the residues of antibiotic selection markers are major challenges for the oral vaccination of LAB. In this study, the target gene, alanine racemase (alr), in the genome of Lactobacillus casei strain W56 (L. casei W56) was knocked out to construct an auxotrophic L. casei strain (L. casei Δalr W56) using the CRISPR-Cas9D10A gene editing system. A recombinant strain (pPG-alr-VP4/Δalr W56) was constructed using an electrotransformed complementary plasmid. Expression of the alr-VP4 fusion protein from pPG-alr-VP4/Δalr W56 was detected using Western blotting. Mice orally immunized with pPG-alr-VP4/Δalr W56 exhibited high levels of serum IgG and mucosal secretory immunoglobulin A (SIgA), which exhibited neutralizing effects against PoRV. Cytokines levels in serum detected using ELISA, indicated that the recombinant strain induced an immune response dominated by Th2 cells. Our data suggest that pPG-alr-VP4/Δalr W56, an antibiotic-resistance-free LAB, provides a safer vaccine strategy against PoRV infection.

Re-Examining Rotavirus Innate Immune Evasion: Potential Applications of the Reverse Genetics System

Rotaviruses represent one of the most successful pathogens in the world, with high infectivity and efficient transmission between the young of many animal species, including humans. To overcome host defenses, rotaviruses have evolved a plethora of strategies to effectively evade the innate immune response, establish initial infection in the small intestine, produce progeny, and shed into the environment. Previously, studying the roles and relative contributions of specific rotaviral factors in innate immune evasion had been challenging without a plasmid-only reverse genetics system. Although still in its infancy, current reverse genetics technology will help address important research questions regarding rotavirus innate immune evasion, host range restriction, and viral pathogenesis. In this review, we summarize the current knowledge about the antiviral host innate immune defense mechanisms, countermeasures of rotavirus-encoded factors, and strategies to better understand these interactions using the rotavirus reverse genetics system.

Rotavirus C Replication in Porcine Intestinal Enteroids Reveals Roles for Cellular Cholesterol and Sialic Acids

Rotaviruses (RVs) are a significant cause of severe diarrheal illness in infants and young animals, including pigs. Group C rotavirus (RVC) is an emerging pathogen increasingly reported in pigs and humans worldwide, and is currently recognized as the major cause of gastroenteritis in neonatal piglets that results in substantial economic losses to the pork industry. However, little is known about RVC pathogenesis due to the lack of a robust cell culture system, with the exception of the RVC Cowden strain. Here, we evaluated the permissiveness of porcine crypt-derived 3D and 2D intestinal enteroid (PIE) culture systems for RVC infection. Differentiated 3D and 2D PIEs were infected with porcine RVC (PRVC) Cowden G1P[1], PRVC104 G3P[18], and PRVC143 G6P[5] virulent strains, and the virus replication was measured by qRT-PCR. Our results demonstrated that all RVC strains replicated in 2D-PIEs poorly, while 3D-PIEs supported a higher level of replication, suggesting that RVC selectively infects terminally differentiated enterocytes, which were less abundant in the 2D vs. 3D PIE cultures. While cellular receptors for RVC are unknown, target cell surface carbohydrates, including histo-blood-group antigens (HBGAs) and sialic acids (SAs), are believed to play a role in cell attachment/entry. The evaluation of the selective binding of RVCs to different HBGAs revealed that PRVC Cowden G1P[1] replicated to the highest titers in the HBGA-A PIEs, while PRVC104 or PRVC143 achieved the highest titers in the HBGA-H PIEs. Further, contrasting outcomes were observed following sialidase treatment (resulting in terminal SA removal), which significantly enhanced Cowden and RVC143 replication, but inhibited the growth of PRVC104. These observations suggest that different RVC strains may recognize terminal (PRVC104) as well as internal (Cowden and RVC143) SAs on gangliosides. Finally, several cell culture additives, such as diethylaminoethyl (DEAE)-dextran, cholesterol, and bile extract, were tested to establish if they could enhance RVC replication. We observed that only DEAE-dextran significantly enhanced RVC attachment, but it had no effect on RVC replication. Additionally, the depletion of cellular cholesterol by MβCD inhibited Cowden replication, while the restoration of the cellular cholesterol partially reversed the MβCD effects. These results suggest that cellular cholesterol plays an important role in the replication of the PRVC strain tested. Overall, our study has established a novel robust and physiologically relevant system to investigate RVC pathogenesis. We also generated novel, experimentally derived evidence regarding the role of host glycans, DEAE, and cholesterol in RVC replication, which is critical for the development of control strategies.

Milk lactose protects against porcine group A rotavirus infection

Rotavirus A (RVA) is an important pathogen causing acute gastroenteritis in animals and humans. Attachment to the host receptor is a crucial step for virus replication. The VP8* domain is the distal terminal region of the RVA spike protein VP4 (expressed by the P gene) and is important for rotavirus binding and infectivity. Recent studies have indicated a role for non-sialylated glycans, including mucin core 2 and histo-blood group antigens (HBGAs), in the infectivity of human and animal group A rotaviruses. In the present study, we determined if porcine rotavirus-derived recombinant VP8* of the endemic strains 14R103 G5P[6], 13R054 G5P[7], 12R010 G4P[13], 12R046 G9P[23], and 12R022 G2P[27] interact with hitherto uncharacterized glycans. We successfully produced five recombinant GST-VP8* proteins of genotype P[6], P[7], P[13], P[23], and P[27]. The hemagglutination assay showed genotypes P[7] and P[23] hemagglutinate porcine and human red blood cells. In an array screen of > 300 glycans, recombinant VP8* of rotavirus genotype P[6], P[7], and P[13] showed specific binding to glycans with a Gal-β-1,4-Glc (β-lactose) motif, which forms the core structure of HBGAs. The specificity of glycan-binding was confirmed through an ELISA-based oligosaccharide binding assay. Further, 13R054 G5P[7] and 12R046 G9P[23] infectivity was significantly reduced by β-lactose in MA104 cells and primary porcine enterocytes. These data suggest that lactose, the main natural sugar in milk, plays an important role in protecting piglets from enteric viral replication and diarrhea.

Current Advances in Structure-Function Relationships and Dose-Dependent Effects of Human Milk Oligosaccharides

HMOs (human milk oligosaccharides) are the third most important nutrient in breast milk. As complex glycans, HMOs play an important role in regulating neonatal intestinal immunity, resisting viral and bacterial infections, displaying anti-inflammatory characteristics, and promoting brain development. Although there have been some previous reports of HMOs, a detailed literature review summarizing the structure-activity relationships and dose-dependent effects of HMOs is lacking. Hence, after introducing the structures and synthetic pathways of HMOs, this review summarizes and categorizes identified structure-function relationships of HMOs. Differential mechanisms of different structural HMOs utilization by microorganisms are summarized. This review also emphasizes the recent advances in the interactions between different health benefits and the variance of dosage effect based on in vitro cell tests, animal experiments, and human intervention studies. The potential relationships between the chemical structure, the dosage selection, and the physiological properties of HMOs as functional foods are vital for further understanding of HMOs and their future applications.

Frequent Occurrence of Simultaneous Infection with Multiple Rotaviruses in Swiss Pigs

Rotavirus (RV) infections are the most important viral cause of diarrhea in piglets in Switzerland and are thought to cause substantial economic losses to the pig industry. However, no data are available on the occurrence and dynamics of the main porcine RV species, namely RVA, RVB, and RVC, and the diversity of the circulating strains. We therefore tested fecal samples from a cross-sectional (n = 95) and a longitudinal (n = 48) study for RVA, RVB, and RVC by real-time RT-PCR and compared the results of the cross-sectional study to postmortem findings. In addition, eight samples were fully genotyped by using next-generation sequencing. In the cross-sectional study, triple RV infections significantly correlated with diarrhea and wasting and were most frequent in the weaned age group. In the longitudinal study, the shedding of RV peaked one week after weaning and decreased thereafter. Here, mainly double infections were seen, and only a few animals showed diarrhea. The full-genome sequencing revealed a genotype pattern similar to other European countries and, importantly, co-infection by up to four RVA strains. Our results imply that the weaning of piglets may trigger not only RV shedding but facilitate co-infection of multiple RV species and strains in the same host.

Rotavirus Interactions With Host Intestinal Epithelial Cells

Rotavirus (RV) is the foremost enteric pathogen associated with severe diarrheal illness in young children (<5years) and animals worldwide. RV primarily infects mature enterocytes in the intestinal epithelium causing villus atrophy, enhanced epithelial cell turnover and apoptosis. Intestinal epithelial cells (IECs) being the first physical barrier against RV infection employs a range of innate immune strategies to counteract RVs invasion, including mucus production, toll-like receptor signaling and cytokine/chemokine production. Conversely, RVs have evolved numerous mechanisms to escape/subvert host immunity, seizing translation machinery of the host for effective replication and transmission. RV cell entry process involve penetration through the outer mucus layer, interaction with cell surface molecules and intestinal microbiota before reaching the IECs. For successful cell attachment and entry, RVs use sialic acid, histo-blood group antigens, heat shock cognate protein 70 and cell-surface integrins as attachment factors and/or (co)-receptors. In this review, a comprehensive summary of the existing knowledge of mechanisms underlying RV-IECs interactions, including the role of gut microbiota, during RV infection is presented. Understanding these mechanisms is imperative for developing efficacious strategies to control RV infections, including development of antiviral therapies and vaccines that target specific immune system antagonists within IECs.

The Role of Host Glycobiology and Gut Microbiota in Rotavirus and Norovirus Infection, an Update

Rotavirus (RV) and norovirus (NoV) are the leading causes of acute gastroenteritis (AGE) worldwide. Several studies have demonstrated that histo-blood group antigens (HBGAs) have a role in NoV and RV infections since their presence on the gut epithelial surfaces is essential for the susceptibility to many NoV and RV genotypes. Polymorphisms in genes that code for enzymes required for HBGAs synthesis lead to secretor or non-secretor and Lewis positive or Lewis negative individuals. While secretor individuals appear to be more susceptible to RV infections, regarding NoVs infections, there are too many discrepancies that prevent the ability to draw conclusions. A second factor that influences enteric viral infections is the gut microbiota of the host. In vitro and animal studies have determined that the gut microbiota limits, but in some cases enhances enteric viral infection. The ways that microbiota can enhance NoV or RV infection include virion stabilization and promotion of virus attachment to host cells, whereas experiments with microbiota-depleted and germ-free animals point to immunoregulation as the mechanism by which the microbiota restrict infection. Human trials with live, attenuated RV vaccines and analysis of the microbiota in responder and non-responder individuals also allowed the identification of bacterial taxa linked to vaccine efficacy. As more information is gained on the complex relationships that are established between the host (glycobiology and immune system), the gut microbiota and intestinal viruses, new avenues will open for the development of novel anti-NoV and anti-RV therapies.

Zoonotic and reverse zoonotic transmission of viruses between humans and pigs

Humans and pigs share a close contact relationship, similar biological traits, and one of the highest estimated number of viruses compared to other mammalian species. The contribution and directionality of viral exchange between humans and pigs remain unclear for some of these viruses, but their transmission routes are important to characterize in order to prevent outbreaks of disease in both host species. This review collects and assesses the evidence to determine the likely transmission route of 27 viruses between humans and pigs.

Microbiota Depletion Promotes Human Rotavirus Replication in an Adult Mouse Model

Intestinal microbiota-virus-host interaction has emerged as a key factor in mediating enteric virus pathogenicity. With the aim of analyzing whether human gut bacteria improve the inefficient replication of human rotavirus in mice, we performed fecal microbiota transplant (FMT) with healthy infants as donors in antibiotic-treated mice. We showed that a simple antibiotic treatment, irrespective of FMT, resulted in viral shedding for 6 days after challenge with the human rotavirus G1P[8] genotype Wa strain (RVwa). Rotavirus titers in feces were also significantly higher in antibiotic-treated animals with or without FMT but they were decreased in animals subject to self-FMT, where a partial re-establishment of specific bacterial taxons was evidenced. Microbial composition analysis revealed profound changes in the intestinal microbiota of antibiotic-treated animals, whereas some bacterial groups, including members of Lactobacillus, Bilophila, Mucispirillum, and Oscillospira, recovered after self-FMT. In antibiotic-treated and FMT animals where the virus replicated more efficiently, differences were observed in gene expression of immune mediators, such as IL1β and CXCL15, as well as in the fucosyltransferase FUT2, responsible for H-type antigen synthesis in the small intestine. Collectively, our results suggest that antibiotic-induced microbiota depletion eradicates the microbial taxa that restrict human rotavirus infectivity in mice.

Protective effects of sodium butyrate on rotavirus inducing endoplasmic reticulum stress-mediated apoptosis via PERK-eIF2α signaling pathway in IPEC-J2 cells

BACKGROUND

Rotavirus (RV) is a major pathogen that causes severe gastroenteritis in infants and young animals. Endoplasmic reticulum (ER) stress and subsequent apoptosis play pivotal role in virus infection. However, the protective mechanisms of intestinal damage caused by RV are poorly defined, especially the molecular pathways related to enterocytes apoptosis. Thus, the aim of this study was to investigate the protective effect and mechanism of sodium butyrate (SB) on RV-induced apoptosis of IPEC-J2 cells.

RESULTS

The RV infection led to significant cell apoptosis, increased the expression levels of ER stress (ERS) markers, phosphorylated protein kinase-like ER kinase (PERK), eukaryotic initiation factor 2 alpha (eIF2α), caspase9, and caspase3. Blocking PERK pathway using specific inhibitor GSK subsequently reversed RV-induced cell apoptosis. The SB treatment significantly inhibited RV-induced ERS by decreasing the expression of glucose regulated protein 78 (GRP78), PERK, and eIF2α. In addition, SB treatment restrained the ERS-mediated apoptotic pathway, as indicated by downregulation of C/EBP homologous protein (CHOP) mRNA level, as well as decreased cleaved caspase9 and caspase3 protein levels. Furthermore, siRNA-induced GPR109a knockdown significantly suppressed the protective effect of SB on RV-induced cell apoptosis.

CONCLUSIONS

These results indicate that SB exerts protective effects against RV-induced cell apoptosis through inhibiting ERS mediated apoptosis by regulating PERK-eIF2α signaling pathway via GPR109a, which provide new ideas for the prevention and control of RV.

Viruses Like Sugars: How to Assess Glycan Involvement in Viral Attachment

The first step of viral infection requires interaction with the host cell. Before finding the specific receptor that triggers entry, the majority of viruses interact with the glycocalyx. Identifying the carbohydrates that are specifically recognized by different viruses is important both for assessing the cellular tropism and for identifying new antiviral targets. Advances in the tools available for studying glycan-protein interactions have made it possible to identify them more rapidly; however, it is important to recognize the limitations of these methods in order to draw relevant conclusions. Here, we review different techniques: genetic screening, glycan arrays, enzymatic and pharmacological approaches, and surface plasmon resonance. We then detail the glycan interactions of enterovirus D68 and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), highlighting the aspects that need further clarification.