Differences in neuroinvasion and protective innate immune pathways between encephalitic California Serogroup orthobunyaviruses

A mix-and-match reverse genetics system for evaluating genetic determinants of orthobunyavirus neurological disease

The encephalitic orthobunyaviruses have tri-segmented, negative sense RNA genomes and can cause severe neurological disease in humans, including La Crosse virus (LACV), which is the leading cause of pediatric arboviral encephalitis in the United States. However, little is known about the genetic factors that drive neuropathogenesis. Reverse genetics systems (RGS) are valuable tools for studying viral genetics and pathogenesis. Plasmid-based cDNA reverse genetics systems are available for LACV, however the plasmid backbones are medium-copy number and have a propensity for recombination. We therefore generated a plasmid-based cDNA reverse genetics system for LACV utilizing a more stable and high-copy number plasmid backbone. Additionally, we created the first full reverse genetics systems for two closely related orthobunyaviruses, Jamestown Canyon virus (JCV), and Inkoo virus (INKV), which have differing reported disease incidences in humans and differing neuropathogenic phenotypes in mice compared to LACV. We compared wild type (wt) viruses with RGS-derived wt viruses in human neuronal cells and in mice, and found that RGS-derived wt viruses maintained the replication and neuropathogenic phenotypes of their wt counterpart. Additionally, we demonstrated that reverse genetics plasmids from different parental viruses can be readily mixed-and-matched to generate reassortant viruses. This system provides a valuable genetic tool utilizing viruses with differing neuropathogenic phenotypes to investigate the genetic determinants of orthobunyavirus neuropathogenesis.

Development of an RT-RPA assay for La Crosse virus detection provides insights into age-dependent neuroinvasion in mice

BACKGROUND

La Crosse virus (LACV) is a mosquito-borne arbovirus responsible for pediatric encephalitis in North America, predominantly affecting children under 16 years. Early and accurate diagnosis is critical to reducing morbidity in this vulnerable population. However, existing molecular and serological methods are limited in sensitivity, specificity, and accessibility.

METHODS

To address these limitations, we developed a reverse transcription recombinase polymerase amplification (RT-RPA) assay for LACV detection. Primers targeting the divergent M segment of the LACV genome were designed and screened for optimal performance. The assay's analytical sensitivity was evaluated through serial dilutions of LACV RNA prior to reverse transcription, while specificity was assessed using reverse transcribed RNA from related or geographically relevant arboviruses. We further adapted the RT-RPA test into a lateral flow assay (LFA) format for potential point-of-care use. Additionally, we employed a murine model to explore the age-dependent dynamics of LACV neuroinvasion and clearance, with the virus detected using RT-RPA and reverse transcription quantitative polymerase change reaction (RT-qPCR).

RESULTS

Primer screening identified an optimal primer pair that amplified LACV cDNA within 20 min at 39 °C, with a limit of detection (LOD) of 100 copies. The assay demonstrated high specificity, with no amplification of related or other geographically relevant arboviruses. Integration of the RT-RPA test into an LFA format preserved the LOD and specificity, enabling visual detection via test strips. In the murine model, weanling mice exhibited LACV neuroinvasion as early as 4 days post-infection (dpi), with sustained detection between 5 and 7 dpi. In adult mice, neuroinvasion was first detected at 5 dpi, plateauing between 6 and 10 dpi, and cleared entirely by 20 dpi in surviving animals.

CONCLUSIONS

This study establishes the RT-RPA assay as an efficient, specific, and sensitive diagnostic platform for LACV, with potential for adaptation into field-deployable LFA tests. Moreover, our findings provide valuable insights into the age-dependent dynamics of LACV neuroinvasion and clearance, informing future diagnostic and therapeutic strategies.

Retinoic acid-induced differentiation and oxidative stress inhibitors increase resistance of human neuroblastoma cells to La Crosse virus-induced cell death

La Crosse Virus (LACV) encephalitis patients are at risk for long-term deficits in cognitive function due to neuronal apoptosis following virus infection. However, the specific etiology underlying neuronal damage remains elusive. In this study, we examined how differentiation and mitotic inhibition of neuroblastoma cells influence their susceptibility to LACV infection and cell death. Treatment of SH-SY5Y cells with retinoic acid induced a neuronal cell phenotype which was similarly susceptible to LACV infection as untreated cells but had significantly delayed virus-induced cell death. Protein and RNA transcript analysis showed that retinoic acid-treated cells had decreased oxidative stress responses to LACV infection compared to untreated cells. Modulation of oxidative stress in untreated cells with specific compounds also delayed cell death, without substantially impacting virus production. Thus, the oxidative stress response of neurons to virus infection may be a key component of neuronal susceptibility to virus-induced cell death.

IMPORTANCE

Encephalitic viruses like La Crosse Virus (LACV) infect and kill neurons. Disease onset and progression is rapid meaning the time frame to treat patients before significant and long-lasting damage occurs is limited. Examining how neurons, the primary cells infected by LACV in the brain, resist virus-induced cell death can provide avenues for determining which pathways to target for effective treatments. In the current study, we studied how changing neuroblastoma growth and metabolism with retinoic acid treatment impacted their susceptibility to LACV-induced cell death. We utilized this information to test compounds for preventing death in these cells.

Lrp1 facilitates infection of neurons by Jamestown Canyon virus

Jamestown Canyon virus (JCV) is a bunyavirus and arbovirus responsible for neuroinvasive disease in the United States. Little is known about JCV pathogenesis, and no host factors required for cellular infection have been identified. Recently, we identified low-density lipoprotein receptor related protein 1 (Lrp1) as a host entry factor for two other bunyaviruses Rift Valley fever virus (RVFV) and Oropouche virus (OROV). Here, we assessed the role of Lrp1 in mediating JCV cellular infection of neurons. Both neuronal and non-neuronal immortalized cell lines deficient for Lrp1 displayed reduction in infection with JCV, and early stages of infection such as binding and internalization were impacted by lack of Lrp1. In primary rat neurons, Lrp1 was highly expressed, and the neurons were highly permissive for JCV infection. Treatment of primary neurons with recombinant receptor-associated protein (RAP), a high affinity ligand for Lrp1, resulted in reduced infectivity with JCV. In addition, pretreatment of cells with RVFV Gn inhibited JCV infection, suggesting that the two viruses may share overlapping binding sites. These results provide compelling evidence that Lrp1 is an important cellular factor for efficient infection by JCV, and thus multiple bunyaviruses with varying clinical manifestations and tissue tropism are facilitated by the host cell Lrp1. Reliance of multiple bunyaviruses on Lrp1 makes it a promising target for pan-bunyaviral antivirals and therapeutics.

Preliminary evidence that Bunyamwera virus causes severe disease characterized by systemic vascular and multiorgan necrosis in an immunocompromised mouse model

Bunyamwera virus (BUNV) is the prototypical member of the Bunyamwera serogroup within the Orthobunyvirus genus. BUNV is transmitted by mosquito vectors of the genera Culex, Aedes and Anopheles and has historically circulated in East Africa, though the transmission has been observed in Argentina. BUNV has been identified as an agent of human and animal disease and has also been misdiagnosed as other agents. BUNV is often thought to be an agent of mild febrile illness in humans, though it can cause abortions in ruminants and neurological disease in horses. Joint pain and gastritis have also been attributed to BUNV. There are limited data concerning the possible spectrum of disease and extent of pathogenesis of BUNV infection, and there are currently no therapeutics or vaccines available. Furthermore, options for animal models for Orthobunyaviruses in general - of which BUNV is the prototypical member - are limited. Eight mice deficient in the type I interferon response were infected with BUNV, and all developed overt disease. All mice developed detectable viraemia and clinical signs, including weight loss, hunched posture and lethargy. Three of the eight mice developed severe diseases, including vascular necrosis and necrosis in the liver, lungs, reproductive organs, bone marrow and spleen, as well as haemorrhages (n=1) and severe diffuse facial oedema (n=3), reminiscent of the pathology of Schmallenberg and the Arenaviruses Lassa and Lujo viruses. Thus, BUNV infection of IRF3/7 DKO mice could serve as a BSL-2 model for severe diseases of higher-risk group viruses, which often must be studied at BSL-4. Additionally, our results suggest that BUNV may have the ability to cause severe disease in immunocompromised hosts. Thus, further investigation into the potential spectrum of pathogenesis due to BUNV is important to prioritize for outbreak response, diagnostics and the development of countermeasures.

C-C motif chemokine receptor 2 and 7 synergistically control inflammatory monocyte recruitment but the infecting virus dictates monocyte function in the brain

Inflammatory monocytes (iMO) are recruited from the bone marrow to the brain during viral encephalitis. C-C motif chemokine receptor (CCR) 2 deficiency substantially reduces iMO recruitment for most, but not all encephalitic viruses. Here we show CCR7 acts synergistically with CCR2 to control this process. Following Herpes simplex virus type-1 (HSV-1), or La Crosse virus (LACV) infection, we find iMO proportions are reduced by approximately half in either Ccr2 or Ccr7 knockout mice compared to control mice. However, Ccr2/Ccr7 double knockouts eliminate iMO recruitment following infection with either virus, indicating these receptors together control iMO recruitment. We also find that LACV induces a more robust iMO recruitment than HSV-1. However, unlike iMOs in HSV-1 infection, LACV-recruited iMOs do not influence neurological disease development. LACV-induced iMOs have higher expression of proinflammatory and proapoptotic but reduced mitotic, phagocytic and phagolysosomal transcripts compared to HSV-1-induced iMOs. Thus, virus-specific activation of iMOs affects their recruitment, activation, and function.

La Crosse virus reassortants highlight genomic determinants of infection and pathogenesis

The genomic determinants that contribute to orthobunyavirus infection and pathogenesis are not well-defined. In this study, we harnessed the process of reassortment to understand which viral factors drive change in the replication and pathogenesis of La Crosse virus (LACV). We systematically reassorted the genomic segments of two genetically similar Lineage I LACV isolates into six unique reassortants. Despite the parental isolates having high levels of RNA and protein consensus, the reassortants demonstrate how minimal changes in RNA and protein structure can have significant changes in viral growth and reproduction in vitro in mammalian and insect models. We observed that swapping the S segment between isolates led to differences in replication and assembly resulting in one non-rescuable reassortant and one viable reassortant that exhibited an increase in viral growth dynamics. Switching the M segment led to changes in viral plaque phenotype and growth kinetics. L segment reassortants similarly differed in changes in viral growth dynamics. We further explored the M segment reassortants in a neonate mouse model and observed a role for the M segment in neuroinflammation and virulence. Through reassortment of the La Crosse virus genomic segments, we are able to further understand how genomic determinants of infection and pathogenesis operate in orthobunyaviruses. Future investigations will focus on identifying the specific molecular elements that govern the observed phenotypes in vitro and in vivo .

Importance

La Crosse virus is the leading cause of pediatric arboviral encephalitis in the United States, yet it is largely unknown how each of the three genomic segments contribute to pathogenesis and disease. Our study utilizes genomic reassortment between two similar Lineage I LACV isolates to understand genomic determinants for differences in infection and pathogenesis phenotypes in vitro and in vivo. By identifying roles for each segment in observed outcomes, we are able to plan further studies for molecular characterization of these phenotypes. Additionally, it is imperative to continue to characterize orthobunyavirus function since climate change will expand the range and prevalence of arthropod-borne diseases such as LACV in the United States.

Immunoinformatics-based potential multi-peptide vaccine designing against Jamestown Canyon Virus (JCV) capable of eliciting cellular and humoral immune responses

Jamestown Canyon virus (JCV) is a deadly viral infection transmitted by various mosquito species. This mosquito-borne virus belongs to Bunyaviridae family, posing a high public health threat in the in tropical regions of the United States causing encephalitis in humans. Common symptoms of JCV include fever, headache, stiff neck, photophobia, nausea, vomiting, and seizures. Despite the availability of resources, there is currently no vaccine or drug available to combat JCV. The purpose of this study was to develop an epitope-based vaccine using immunoinformatics approaches. The vaccine aimed to be secure, efficient, bio-compatible, and capable of stimulating both innate and adaptive immune responses. In this study, the protein sequence of JCV was obtained from the NCBI database. Various bioinformatics methods, including toxicity evaluation, antigenicity testing, conservancy analysis, and allergenicity assessment were utilized to identify the most promising epitopes. Suitable linkers and adjuvant sequences were used in the design of vaccine construct. 50s ribosomal protein sequence was used as an adjuvant at the N-terminus of the construct. A total of 5 CTL, 5 HTL, and 5 linear B cell epitopes were selected based on non-allergenicity, immunological potential, and antigenicity scores to design a highly immunogenic multi-peptide vaccine construct. Strong interactions between the proposed vaccine and human immune receptors, i.e., TLR-2 and TLR-4, were revealed in a docking study using ClusPro software, suggesting their possible relevance in the immunological response to the vaccine. Immunological and physicochemical properties assessment ensured that the proposed vaccine demonstrated high immunogenicity, solubility and thermostability. Molecular dynamics simulations confirmed the strong binding affinities, as well as dynamic and structural stability of the proposed vaccine. Immune simulation suggest that the vaccine has the potential to effectively stimulate cellular and humoral immune responses to combat JCV infection. Experimental and clinical assays are required to validate the results of this study.