Characterization of Novel Aptamers Specifically Directed to Red-Spotted Grouper Nervous Necrosis Virus (RGNNV)-Infected Cells for Mediating Targeted siRNA Delivery

M1-type polarized macrophage contributes to brain damage through CXCR3.2/CXCL11 pathways after RGNNV infection in grouper

The vertebrate central nervous system (CNS) is the most complex system of the body. The CNS, especially the brain, is generally regarded as immune-privileged. However, the specialized immune strategies in the brain and how immune cells, specifically macrophages in the brain, respond to virus invasion remain poorly understood. Therefore, this study aimed to examine the potential immune response of macrophages in the brain of orange-spotted groupers (Epinephelus coioides) following red-spotted grouper nervous necrosis virus (RGNNV) infection. We observed that RGNNV induced macrophages to produce an inflammatory response in the brain of orange-spotted grouper, and the macrophages exhibited M1-type polarization after RGNNV infection. In addition, we found RGNNV-induced macrophage M1 polarization via the CXCR3.2- CXCL11 pathway. Furthermore, we observed that RGNNV triggered M1 polarization in macrophages, resulting in substantial proinflammatory cytokine production and subsequent damage to brain tissue. These findings reveal a unique mechanism for brain macrophage polarization, emphasizing their role in contributing to nervous tissue damage following viral infection in the CNS.

Slc43a2+ T cell metastasis from spleen to brain in RGNNV infected teleost

The origin of T cells in the teleost's brain is unclear. While viewing the central nervous system (CNS) as immune privileged has been widely accepted, previous studies suggest that T cells residing in the thymus but not in the spleen of the teleost play an essential role in communicating with the peripheral organs. Here, we identified nine T cell subpopulations in the thymus and spleen of orange-spotted grouper (Epinephelus coioices) through single-cell RNA-sequencing analysis. After viral CNS infection with red-spotted grouper nervous necrosis virus (RGNNV), the number of slc43a2+ T cells synchronously increased in the spleen and brain. During the infection tests in asplenic zebrafish (tlx1▲ zebrafish model), no increase in the number of slc43a2+ T cells was observed in the brain. Single-cell transcriptomic analysis indicated that slc43a2+ T cells mature and functionally differentiate within the spleen and then migrate into the brain to trigger an immune response. This study suggests a novel route for T cell migration from the spleen to the brain during viral infection in fish.

Aptamer-based diagnostic and therapeutic approaches for animal viruses: A review

Animal diseases often have significant consequences due to the unclear and time-consuming diagnosis process. Furthermore, the emergence of new viral infections and drug-resistant pathogens has further complicated the diagnosis and treatment of viral diseases. Aptamers, which are obtained through systematic evolution of ligands by exponential enrichment (SELEX) technology, provide a promising solution as they enable specific identification and binding to targets, facilitating pathogen detection and the development of novel therapeutics. This review presented an overview of aptasensors for animal virus detection, discussed the antiviral activity and mechanisms of aptamers, and highlighted advancements in aptamer-based antiviral research following the COVID-19 pandemic. Additionally, the challenges and prospects of aptamer-based virus diagnosis and treatment research were explored. Although this review was not exhaustive, it offered valuable insights into the progress of aptamer-based antiviral drug research, target mechanisms, as well as the development of novel antiviral drugs and biosensors.

Study on aptamer based high throughput approach identifies natural ingredients against RGNNV

Nervous necrosis virus (NNV) is one of the most destructive pathogens in marine fish aquaculture and is capable of infecting more than 50 fish species worldwide, which resulted in great economic losses. Effective drugs for managing NNV infection are urgently required. Medicinal plants have been known for thousands of years and benefit of medicinal plants against pathogens in aquaculture have emerged. Nowadays, the most commonly used method for detecting virus infection and assessing antiviral drugs efficacy is reverse transcription-quantitative real-time PCR. However, the application is limited on account of high reagent costs, complex time-consuming operations and long detection time. Aptamers have been widely applied in application of pathogens or diseases diagnosis and treatments because of high specificity, strong affinity, good stability, easy synthesized and low costs. This study aimed to establish an aptamer (GBN34)-based high-throughput screening (GBN34-AHTS) model for efficient selection and evaluation of natural ingredients against NNV infection. GBN34-AHTS is an expeditious rapid method for selecting natural ingredients against NNV, which is characterized with high-speed, dram, sensitive and accurate. AHTS strategy could reduce work intensity and experimental costs and shorten the whole screening cycle of effective ingredients. AHTS should be suitable for rapid selection of effective ingredients against other viruses, which is important for improving the prevention and controlling of aquatic diseases.

Advances in Aptamer-Based Biosensors and Cell-Internalizing SELEX Technology for Diagnostic and Therapeutic Application

Aptamers are a group of synthetic single-stranded nucleic acids. They are generated from a random library of single-stranded DNA or RNA by a technology named systematic evolution of ligands by exponential enrichment (SELEX). SELEX is a repetitive process to select and identify suitable aptamers that show high affinity and specificity towards target cells. Great strides have been achieved in the design, construction, and use of aptamers up to this point. However, only a small number of aptamer-based applications have achieved widespread commercial and clinical acceptance. Additionally, finding more effective ways to acquire aptamers with high affinity remains a challenge. Therefore, it is crucial to thoroughly examine the existing dearth and advancement in aptamer-related technologies. This review focuses on aptamers that are generated by SELEX to detect pathogenic microorganisms and mammalian cells, as well as in cell-internalizing SELEX for diagnostic and therapeutic purposes. The development of novel aptamer-based biosensors using optical and electrical methods for microbial detection is reported. The applications and limitations of aptamers are also discussed.

Selection and Characterization of ssDNA Aptamers Targeting Largemouth Bass Virus Infected Cells With Antiviral Activities

Largemouth bass virus (LMBV) is one of the most devastating viral pathogens in farmed Largemouth bass. Aptamers are novel molecule probes and have been widely applied in the field of efficient therapeutic and diagnostic agents development. LMBV-infected fathead minnow cells (LMBV-FHM) served as target cells in this study, and three DNA aptamers (LBVA1, LBVA2, and LBVA3) were generated against target cells by SELEX technology. The selected aptamers could specifically bind to LMBV-FHM cells, with rather high calculated dissociation constants (Kd) of 890.09, 517.22, and 249.31 nM for aptamers LBVA1, LBVA2, and LBVA3, respectively. Three aptamers displayed efficient antiviral activities in vitro. It indicates that the selected aptamers have great potentials in developing efficient anti-viruses treatments. The targets of aptamers LBVA1, LBVA2, and LBVA3 could be membrane proteins on host cells. The targets of aptamers (LBVA1, LBVA2, and LBVA3) come out on the cells surface at 8, 10, 8 h post-infection. As novel molecular probes for accurate recognition, aptamer LBVA3 could detect LMBV infection in vitro and in vivo, it indicates that the selected aptamers could be applied in the development of rapid detective technologies, which are characterized by high sensitivity, accuracy, and easy operation.

Oligonucleotide aptamers for pathogen detection and infectious disease control

During an epidemic or pandemic, the primary task is to rapidly develop precise diagnostic approaches and effective therapeutics. Oligonucleotide aptamer-based pathogen detection assays and control therapeutics are promising, as aptamers that specifically recognize and block pathogens can be quickly developed and produced through simple chemical synthesis. This work reviews common aptamer-based diagnostic techniques for communicable diseases and summarizes currently available aptamers that target various pathogens, including the SARS-CoV-2 virus. Moreover, this review discusses how oligonucleotide aptamers might be leveraged to control pathogen propagation and improve host immune system responses. This review offers a comprehensive data source to the further develop aptamer-based diagnostics and therapeutics specific for infectious diseases.

Polystyrene nanoplastics alter virus replication in orange-spotted grouper (Epinephelus coioides) spleen and brain tissues and spleen cells

Polystyrene nanoplastics (PS-NPs) are known to impair the function of the digestive system, intestinal flora, immune system, and nervous system of marine organisms. We tested whether PS-NPs influence viral infection of orange-spotted grouper (Epinephelus coioides). We found that grouper spleen (GS) cells took up PS-NPs at exposure concentrations of 5, 50, and 500 μg/mL and experienced cytotoxicity at 50 and 500 μg/mL concentrations. At 12 h after exposure to 50 μg/mL of PS-NPs, the replication of Singapore grouper iridovirus (SGIV) and red-spotted grouper nervous necrosis virus (RGNNV) increased in GS cells after their invasion. Juvenile fish exposed to 300 and 3000 μg/L of PS-NPs for 7 d showed PS-NPs uptake to the spleen and vacuole formation in brain tissue. Moreover, PS-NPs exposure accelerated SGIV replication in the spleen and RGNNV replication in the brain. PS-NP exposure also decreased the expression of toll-like receptor genes and interferon-related genes before and after virus invasion in vitro and in vivo, thus reducing the resistance of cells and tissues to viral replication. This is the first report that PS-NPs have toxic effects on GS cells and spleen and brain tissues, and it provides new insights into assessing the impact of PS-NPs on marine fish.

Efficient RNA virus targeting via CRISPR-CasRx in fish

The emergence of the CRISPR-Cas system as a technology has transformed our ability to modify nucleic acids, and the CRISPR-Cas13 system has been used to target RNA. CasRx is a small sized type VI-D effector (Cas13d) with RNA knockdown efficiency that may have an interference effect on RNA viruses. However, the RNA virus-targeting activity of CasRx still needs to be verified in vivo in vertebrates. In this study, we successfully engineered a highly effective CasRx system for fish virus interference. We designed synthetic mRNA coding for CasRx and used CRISPR RNAs to guide it to target the grouper nervous necrosis virus (RGNNV). This technique resulted in significant interference with virus infections both in vitro and in vivo. These results indicate that CRISPR/CasRx can be used to engineer interference against RNA viruses in fish, which provides a potential novel mechanism for RNA-guided immunity against other RNA viruses in vertebrates. Importance RNA viruses are most important viral pathogens infecting vertebrates and mammals. RNA virus populations are highly dynamic due to short generation times, large population sizes, and high mutation frequencies. Therefore, it is difficult to find a widely effective ways to inhibit RNA viruses. Therefore, we urgently need to develop effective antiviral methods. CasRx is a small sized type VI-D effector (Cas13d) with RNA knockdown efficiency that can have an interference effect on RNA viruses. Nervous necrosis virus (NNV), a non-enveloped positive-strand RNA virus, is one of the most serious viral pathogens infecting more than 40 cultured fish species resulting in huge economic losses worldwide. Here, we establish a novel efective CasRx system for RNA virus interference using NNV and grouper (Epinephelus coioices) as model. Our data show that CasRx have the most robust for RNA virus interference applications in fish and demonstrate its suitability for studying key questions relating to virus biology.

Generation and characterization of aptamers against grass carp reovirus infection for the development of rapid detection assay

Grass carp reovirus (GCRV) causes devastating viral haemorrhagic disease in farmed grass carp (Ctenopharyngon idellus). As novel molecular probes, aptamers have been widely applied in rapid diagnosis and efficient therapies against virus or diseases. In this study, three single-stranded DNA (ssDNA) aptamers were selected against GCRV-infected CIK cells via SELEX (systematic evolution of ligands by exponential enrichment technology). Secondary structures predicted by MFOLD indicated that aptamers formed stem-loop structures, and GVI-11 had the lowest ΔG value of -30.84 KJ/mol. Three aptamers could specifically recognize GCRV-infected CIK cells, with calculated dissociation constants (Kd) of 220.86, 176.63 and 278.66 nM for aptamers GVI-1, GVI-7 and GVI-11, respectively, which indicated that they could serve as specific delivery system for antiviral therapies. The targets of aptamers GVI-1, GVI-7 and GVI-11 on the surface of GCRV-infected cells could be membrane proteins, which were trypsin-sensitive. Furthermore, FAM-labelled aptamer GVI-7 could be applied to detect GCRV infection in vivo. It is the first time to generate and characterize aptamers against GCRV-infected cells. These aptamers have great potentials in development of rapid diagnosis technology and antiviral agents against GCRV infection in aquaculture.

Specific Aptamer-Based Probe for Analyzing Biomarker MCP Entry Into Singapore Grouper Iridovirus-Infected Host Cells via Clathrin-Mediated Endocytosis

Biomarkers have important roles in various physiological functions and disease pathogenesis. As a nucleocytoplasmic DNA virus, Singapore grouper iridovirus (SGIV) causes high economic losses in the mariculture industry. Aptamer-Q5-complexed major capsid protein (MCP) in the membrane of SGIV-infected cells can be used as a specific molecular probe to investigate the crucial events of MCP endocytosis into SGIV-infected host cells during viral infection. Chlorpromazine blocks clathrin-mediated endocytosis, and MCP endocytosis into SGIV-infected cells decreased significantly when the cells were pretreated with chlorpromazine. The disruption of cellular cholesterol by methyl-β-cyclodextrin also significantly reduced MCP endocytosis. In contrast, inhibitors of key regulators of caveolae/raft-dependent endocytosis and macropinocytosis, including genistein, Na⁺/H⁺ exchanger, p21-activated kinase 1 (PAK1), myosin II, Rac1 GTPase, and protein kinase C (PKC), had no effect on MCP endocytosis. The endocytosis of the biomarker MCP is dependent on low pH and cytoskeletal actin filaments, as shown with various inhibitors (chloroquine, ammonia chloride, cytochalasin D). Therefore, MCP enters SGIV-infected host cells via clathrin-mediated endocytosis, which is dependent on dynamin, cholesterol, low pH, and cytoskeletal actin filaments. This is the first report of a specific aptamer-based probe used to analyze MCP endocytosis into SGIV-infected host cells during viral infection. This method provides a convenient strategy for exploring viral pathogenesis and facilitates the development of diagnostic tools for and therapeutic approaches to viral infection.