Ablation of myd88 alters the immune gene expression and immune cell recruitment during VHSV infection in zebrafish

Myeloid differentiation primary response protein-88 (MYD88) is an essential adaptor molecule in pathogen-related pattern recognition signaling pathways. Toll-like and interleukin receptors recognize numerous signals and are funneled through MyD88 to express genes responsible for the innate and adaptive immune systems. In the present study, the relevance of MyD88 in viral hemorrhagic septicemia virus (VHSV) was investigated by generating myd88-/- zebrafish. The model was challenged with VHSV, and viral propagation was quantified by evaluating clinical symptoms, mortality, and VHSV copy number. The infected fish showed abnormal morphologies, such as subcutaneous hemorrhages, abdominal swelling, and bulging eyes, which were comparatively more intense in myd88-/- fish than in the wild-type. An injury infection experiment conducted in zebrafish larvae indicated a substantial spread of VHSV in the wound site. The number of neutrophils and macrophages recruited to the wounded area were markedly reduced in myd88-/- fish. According to gene expression analysis, VHSV NP gene expression was considerably upregulated in myd88-/- fish. Substantial gene expression and immune cell marker modulation were observed in the mutant model compared to that in the wild-type. These results suggest that the lack of a significant adaptor protein for immune signal transduction results in enhanced VHSV replication.

Purification of an antiviral protein from the seeds of quinoa (Chenopodium quinoa Willd.) and characterization of its antiviral properties

Plant viral pathogens cause damaging diseases in many agriculture systems, and emerging viral infections are a serious threat for providing adequate food to a continuously growing population. Recent studies of biogenic substances have provided new opportunities for producing novel antiviral agents. The present work has been conducted to evaluate the antiviral activity of quinoa (Chenopodium quinoa Willd.) seeds crude extract. The antiviral activity was retained in different buffer solutions of various pH ranges (5.2-8.5) and remained after the diafiltration process. The putative virus inhibitor was sensitive to treatment with sodium dodecyl sulfate and trichloroacetic acid. An antiviral protein with ~ 25 kDa molecular weight was isolated from the seed quinoa extract using ammonium sulfate precipitation, anion and cation exchange chromatography. The purified protein (Quinoin-I) significantly inhibited TMV on tobacco leaves with an IC₅₀ value at a 6.81 μg/ml concentration. Enzyme activity assay revealed the RNase activity of Quinoin-I, and this feature was retained in the presence of β-mercaptoethanol and ethylene diamine tetraacetic acid. This antiviral protein has been shown as a promising leading molecule for further development as a novel antiviral agent.

The influence of IFITM3 polymorphisms on susceptibility to SARS-CoV-2 infection and severity of COVID-19

Background and aims

The interferon-induced transmembrane protein 3 (IFITM3) plays an important role in the adaptive and innate immune response by inhibiting viral membrane hemifusion between the host and viral cell cytoplasm. Single nucleotide polymorphisms (SNPs) in the gene IFITM3 have been associated with susceptibility and severity of influenza or other viral infections. We aimed to analyze the role of SNPs in the gene IFITM3 in SARS-CoV-2 infection.

Methods

We performed genotyping of the SNPs rs12252 and rs34481144 in the gene IFITM3 in 239 SARS-CoV-2-positive and 253 SARS-CoV-2-negative patients. We analyzed the association of the SNPs with susceptibility to SARS-CoV-2 infection and severity of COVID-19.

Results

SARS-CoV-2-positive and SARS-CoV-2-negative patients did not differ regarding demographics. Neither IFITM3 rs12252 nor rs34481144 polymorphisms were related to SARS-CoV-2 infection risk or severity of COVID-19. Interestingly, we observed the putative deleterious rs12252 CC genotype only in SARS-CoV-2-positive patients (N = 2). Also, we found a non-significant higher frequency of rs34481144 A-allele carriers in the patients with 'serious' COVID-19.

Conclusions

In summary, we could not confirm the recently reported influence of polymorphisms in the gene IFITM3 on SARS-CoV-2 infection risk or severity of COVID-19 in a German cohort. Additional studies are needed to clarify the influence of the rs12252 CC genotype on SARS-CoV-2 infection risk and the rs34481144 A-allele on course of COVID-19.

Transcription profile, NF-ĸB promoter activation, and antiviral activity of Amphiprion clarkii Akirin-2

Animal defense system constitutes a series of distinct mechanisms that specifically defend against microbial invasion. Understanding these complex biological mechanisms is of paramount importance for implementing disease prevention strategies. In this study, the transcription factor, Akirin-2 was identified from ornamental fish Amphiprion clarkii and its involvement in immune response was characterized. A. clarkii Akirin-2 (AcAkirin-2) was identified as a highly conserved protein with two nuclear localization signals. In-vitro localization analysis in fathead minnow cells revealed that AcAkirin-2 is strictly localized to the nucleus. With regard to tissue-specific expression without immune challenge, AcAkirin-2 expression was highest in the brain and lowest in the liver. Immune challenge experiments revealed that AcAkirin-2 expression was the strongest in response to poly I:C. Overexpression of AcAkirin-2 alone did not enhanced NF-ĸB activity significantly in HEK293T cells; however, it significantly enhanced NF-ĸB activity in the presence of poly I:C. AcAkirin-2-mediated expression of antiviral genes was analyzed using qPCR in mullet kidney cells and plaque assay was performed to decipher the involvement of AcAkirin-2 in antiviral immunity. AcAkirin-2 overexpression significantly enhanced the expression of Viperin but not of Mx. Plaque assays revealed the ability of AcAkirin-2 to enervate VHSV titers. Taken together, this study unveiled the involvement of AcAkirin-2 in NF-ĸB-mediated transcription of antiviral genes.

The role of enzymatic activities of antiviral proteins from plants for action against plant pathogens

Antiviral proteins (AVPs) from plants possess multiple activities, such as N-glycosidase, RNase, DNase enzymatic activity, and induce pathogenesis-related proteins, salicylic acid, superoxide dismutase, peroxidase, and catalase. The N-glycosidase activity releases the adenine residues from sarcin/ricin (S/R) loop of large subunit of ribosomes and interfere the host protein synthesis process and this activity has been attributed for antiviral activity in plant. It has been shown that AVP binds directly to viral genome-linked protein of plant viruses and interfere with protein synthesis of virus. AVPs also possess the RNase and DNase like activity and may be targeting nucleic acid of viruses directly. Recently, the antifungal, antibacterial, and antiinsect properties of AVPs have also been demonstrated. Gene encoding for AVPs has been used for the development of transgenic resistant crops to a broad range of plant pathogens and insect pests. However, the cytotoxicity has been observed in transgenic crops using AVP gene in some cases which can be a limiting factor for its application in agriculture. In this review, we have reviewed various aspects of AVPs particularly their characteristics, possible mode of action and application.

The Interferon-induced transmembrane protein 3 gene (IFITM3) rs12252 C variant is associated with COVID-19

BACKGROUND AND AIMS

The interferon-induced transmembrane proteins play an important antiviral role by preventing viruses from traversing the cellular lipid bilayer. IFITM3 gene variants have been associated with the clinical response to influenza and other viruses. Our aim was to determine whether the IFITM3 rs12252 polymorphism was associated with the risk of developing severe symptoms of COVID-19 in our population.

METHODS

A total of 288 COVID-19 patients who required hospitalization (81 in the intensive care unit) and 440 age matched controls were genotyped with a Taqman assay. Linear regression models were used to compare allele and genotype frequencies between the groups, correcting for age and sex.

RESULTS

Carriers of the minor allele frequency (rs12252 C) were significantly more frequent in the patients compared to controls after correcting by age and sex (p = 0.01, OR = 2.02, 95%CI = 1.19-3.42). This genotype was non-significantly more common among patients who required ICU.

CONCLUSIONS

The IFITM3 rs12252 C allele was a risk factor for COVID-19 hospitalization in our Caucasian population. The extent of the association was lower than the reported among Chinese, a population with a much higher frequency of the risk allele.

Cardiomyocyte-specific deletion of Senp2 contributes to CVB3 viral replication and inflammation

Viral myocarditis (VMC) is characterized by cardiac inflammation and excessive inflammatory responses after viral infection. SENP2, a deSUMO-specific protease, has been reported to regulate antiviral innate immunity. This study aimed to investigate whether SENP2 affects CVB3-induced VMC. We generated a CVB3-induced VMC mouse model in 6-week-old cardiomyocyte-specific Senp2 knockout mice. The mice were sacrificed at days 0, 2, 4 and 6 after CVB3 infection. The survival rate, body weight, myocardial histopathological changes, viral load, cytokine levels and antiviral gene expression in cardiac tissues of both groups were investigated. Our study indicated that the expression of Senp2 in primary cardiomyocytes was upregulated by CVB3 infection. Moreover, deletion of Senp2 in the heart exacerbated CVB3 infection-induced myocarditis, facilitated CVB3 viral replication and downregulated the expression of antiviral proteins. In conclusion, our findings suggest a protective role for SENP2 in CVB3-induced VMC.

S-palmitoylation of swine interferon-inducible transmembrane protein is essential for its anti-JEV activity

Japanese encephalitis virus (JEV) is an infectious pathogen spreading in a wide range of vertebrate species. Pigs are amplifying hosts of JEV and thought to be maintained in nature predominantly by avian-mosquito cycles. In the innate immune system, interferon-inducible transmembrane protein (IFITM) is a small transmembrane protein family and has been identified as the first line of defense against a broad range of RNA virus invasion. In this paper, we found that swine IFITM (sIFITM) could restrict the replication of both JEV vaccine strain and wild strain NJ-2008. The cysteine S-palmitoylation modification of sIFITM plays important roles in their anti-JEV effects and intracellular distributions. Our findings show the anti-JEV activities of swine interferon-inducible transmembrane proteins and broaden the antiviral spectrum of IFITM protein family. The preliminary exploration of S-palmitoylation modification of sIFITM may contribute to understanding of the antiviral molecular mechanism of sIFITM.

MicroRNA 876-5p modulates EV-A71 replication through downregulation of host antiviral factors

BACKGROUND

Human enterovirus 71 (EV-A71) is a non-enveloped virus that has a single stranded positive sense RNA genome. In a previous study, we showed that miR-876-5p upregulation was observed in the serum of patients with severe EV-A71 infection. Micro-876-5p (miR-876-5p) is a circulating miRNA that can be identified to modulate EV-A71 infections through both in vitro and in vivo studies. However, the regulatory mechanisms that involve miR-876-5p in the EV-A71 infection cycle remain unclear.

METHODS

We demonstrated that miR-876-5p facilitated EV-A71 replication and expression by overexpression and knocking-down of miR-876-5p through the transfection of miR-876-5p plasmid and miR-876-5p inhibitor. Although miR-876-5p suppressed CREB5 expression, luciferase reporter assay confirmed this. We also evaluated the role of miR-876-5p in the EV-A71 infection cycle by CREB5 mediated by transfection with an anti-miR-876-5P inhibitor or in combination with an si-CREB5 plasmid.

RESULTS

MicroR-876-5p was upregulated in EV-A71-infected neuroblastoma cells. Overexpression of miR-876-5p or knockdown of cyclic-AMP responsive element binding protein 5 (CREB5) promoted EV-A71 replication. The downregulation of miR-876-5p inhibited the accumulation of viral RNA and the production of viral proteins. Interestingly, CREB5 overexpression also suppressed EV-A71 replication. Our in vitro studies reveal that miR-876-5p directly targets CREB5. Finally, downregulation of CREB5 protein abated the inhibitory effect of anti-miR-876-5p and induced inhibitory effect of EV-A71 replication.

CONCLUSIONS

Our results suggest that intracellular miR-876-5p promotes EV-A71 replication indirectly by targeting the host CREB5 protein.

Molecular characterization and expression analysis of rockfish (Sebastes schlegelii) viperin, and its ability to enervate RNA virus transcription and replication in vitro

Viperin, also known as RSAD2 (Radical S-adenosyl methionine domain containing 2), is an interferon-induced endoplasmic reticulum-associated antiviral protein. Previous studies have shown that viperin levels are elevated in the presence of viral RNA, but it has rarely been characterized in marine organisms. This study was designed to functionally characterize rockfish viperin (SsVip), to examine the effects of different immune stimulants on its expression, and to determine its subcellular localization. SsVip is a 349 amino acid protein with a predicted molecular mass of 40.24 kDa. It contains an S-adenosyl l-methionine binding conserved domain with a CNYKCGFC sequence. Unchallenged tissue expression analysis using quantitative real time PCR (qPCR) revealed SsVip expression to be the highest in the blood, followed by the spleen. When challenged with poly I:C, SsVip was upregulated by approximately 60-fold in the blood after 24 h, and approximately 50-fold in the spleen after 12 h. Notable upregulation was detected throughout the poly I:C challenge experiment in both tissues. Significant expression of SsVip was detected in the blood following Streptococcus iniae and lipopolysaccharide challenge, and viral hemorrhagic septicemia virus (VHSV) gene transcription was significantly downregulated during SsVip overexpression. Furthermore, cell viability assay and virus titer quantification with the presence of SsVip revealed a significant reduction in virus replication. As with previously identified viperin counterparts, SsVip was localized in the endoplasmic reticulum. Our findings show that SsVip is an antiviral protein crucial to innate immune defense.

Different antiviral activities of natural APOBEC3C, APOBEC3G, and APOBEC3H variants against hepatitis B virus

Some APOBEC3 family members have antiviral activity against retroviruses and DNA viruses. Hepatitis B virus (HBV) is a DNA virus that is the major causative factor of severe liver diseases such as cirrhosis and hepatocellular carcinoma. To determine whether APOBEC3 variants in humans have different anti-HBV activities, we evaluated natural variants of APOBEC3C, APOBEC3G, and APOBEC3H using an HBV-replicating cell culture model. Our data demonstrate that the APOBEC3C variant S188I had increased restriction activity and hypermutation frequency against HBV DNA. In contrast, the APOBEC3G variant H186R did not alter the anti-HBV and hypermutation activities. Among APOBEC3H polymorphisms (hap I-VII) and splicing variants (SV-200, SV-183, SV-182, and SV-154), hap II SV-183 showed the strongest restriction activity. These data suggest that the genetic variations in APOBEC3 genes may affect the efficiency of HBV elimination in humans.

Molecular and transcriptional insights into viperin protein from Big-belly seahorse (Hippocampus abdominalis), and its potential antiviral role

Viperin is recognized as an antiviral protein that is stimulated by interferon, viral exposures, and other pathogenic molecules in vertebrate. In this study, a viperin homolog in the Big-belly seahorse (Hippocampus abdominalis; HaVip) was functionally characterized to determine its subcellular localization, expression pattern, and antiviral activity in vitro. The HaVip coding sequence encodes a 348 amino acid polypeptide with predicted molecular weight of 38.48 kDa. Sequence analysis revealed that HaVip comprises three main domains: the N-terminal amphipathic α-helix, a radical S-adenosyl-l-methionine (SAM) domain, and a conserved C-terminal domain. Transfected GFP-tagged HaVip protein was found to localize to the endoplasmic reticulum (ER). Overexpressed-HaVip in FHM cells was found to significantly reduce viral capsid gene expression in VHSV infection in vitro. Under normal physiological conditions, HaVip expression was ubiquitously detected in all 14 examined tissues of the seahorse, with the highest expression observed in the heart, followed by skin and blood. In vivo studies showed that HaVip was rapidly and predominantly upregulated in blood, kidney, and intestinal tissue upon poly (I:C) stimulus. LPS and Streptococus iniae challenges caused a significant increase in expression of HaVip in all the analyzed tissues. The obtained results suggest that HaVip is involved in the immune system of the seahorse, triggering antiviral and antibacterial responses, upon viral and bacterial pathogenic infections.

Molecular characterization of AID-mediated reduction of hepatitis B virus transcripts

Hepatitis B virus (HBV) is the major cause of liver cirrhosis and hepatocellular carcinoma. After entering a hepatocyte, HBV forms a nuclear viral episome and produces pregenomic (pg) RNA with a stem-loop structure called an epsilon, which acts to signal encapsidation. We previously demonstrated that TGF-β upregulates activation-induced cytidine deaminase (AID) expression in hepatocytes, which in turn downregulates HBV transcripts by recruiting the RNA exosome complex. The molecular mechanism underlying AID-mediated HBV RNA reduction remains largely unclear. Here we used a pgRNA reporter system having a reporter gene within pgRNA to identify sis- and trans-acting elements in AID-mediated HBV RNA reduction. We found that the epsilon RNA and C-terminus of AID are required for AID-mediated HBV RNA reduction. Importantly, this reduction was reproduced in a hydrodynamic HBV transfection mouse model. The molecular mechanism of AID-mediated HBV RNA reduction is discussed.

Molecular cloning, characterization, and expression of duck 2'-5'-oligoadenylate synthetase-like gene

2'-5'-Oligoadenylate synthetase-like protein (OASL) is an interferon-inducible antiviral protein that exerts antiviral effects through the RNase L- or retinoic acid-inducible gene I (RIG-I)-dependent signalling pathway. In this study, we identified and cloned the OASL gene (named duOASL) from healthy adult Cherry Valley ducks. Full-length duOASL cDNA (1630bp) encoded a 504-amino acid polypeptide containing three conserved domains, namely, nucleotidyltransferase domain, 2'-5'-oligoadenylate synthetase domain, and two ubiquitin-like repeats. DuOASL mRNA expression was quantified by performing quantitative reverse transcription-PCR (qRT-PCR). Results of qRT-PCR showed that duOASL was broadly expressed in all examined tissues, with the highest mRNA expression in the large intestine. Antiviral activity of duOASL was measured by determining its effect on Duck Tembusu virus (DTMUV) replication in vitro. We found that duOASL overexpression slightly inhibited DTMUV replication, whereas duOASL knockdown by using a specific small interfering RNA increased DTMUV replication in DF-1 cells. Thus, we successfully cloned and characterized the antiviral protein duOASL from Cherry Valley ducks and found that it exerted antiviral effects against DTMUV. These results provide a solid foundation for performing further studies to determine the mechanism underlying the antiviral effect of duOASL at the cellular level.

CsIFIT1, an interferon-induced protein with tetratricopeptide repeat, inhibits viral infection in tongue sole (Cynoglossus semilaevis)

Interferon-induced protein with tetratricopeptide repeats (IFIT) is involved in antiviral immunity in mammalian cells. In fish, the function of this group of proteins is unknown. In this study, we report the identification of an IFIT homologue (named CsIFIT1) from tongue sole (Cynoglossus semilaevis) and examined its antiviral potential. CsIFIT1 is composed of 436 residues and shares 30.9%-58.7% overall sequence identities with the known IFITs of a number of teleost species. In silico analysis identified two tetratricopeptide repeats in CsIFIT1. Quantitative real time RT-PCR analysis showed that CsIFIT1 expression was most abundant in immune relevant organs and upregulated, in a time-dependent manner, by experimental infection with the fish viral pathogen megalocytivirus. When CsIFIT1 was overexpressed in tongue sole before megalocytivirus infection, viral replication in fish tissues was blocked to significant extents. Consistently, when CsIFIT1 expression in tongue sole was knocked down by siRNA, viral replication in fish tissues was significantly enhanced. Taken together, these results indicate that CsIFIT1 is likely a key factor of antiviral immunity and is required for optimal defense against viral infection.

Functional analysis of an orange-spotted grouper (Epinephelus coioides) interferon gene and characterisation of its expression in response to nodavirus infection

We cloned and sequenced 2C I-IFN, a two-cysteine containing type I interferon (I-IFN) gene, in orange-spotted grouper (Epinephelus coioides). The cDNA has 769 base pairs, the protein has 172 amino acids, and the predicted signal peptide has 18 amino acids with two cysteines. This gene is similar to I-FNs from sea bass and other teleosts. 2C I-IFN has 5 exons and 4 introns, also similar to other teleost I-IFNs. Immunohistochemical (IHC) analysis indicated that expression is predominantly membrane-localized in healthy grouper, but has a zonal distribution in nodavirus-infected grouper. Grouper infected with nodavirus had elevated levels of 2C I-IFN at 72 h and Mx at days 6-7. Recombinant 2C I-IFN activated grouper Mx, leading to upregulated antiviral activity. The grouper Mx promoter was highly induced after treatment with recombinant 2C I-IFN. The present results suggest that expression of grouper 2C I-IFN may participate in the immunologic barrier function against nodavirus.