Reovirus-associated meningoencephalomyelitis in baboons

NgR1 binding to reovirus reveals an unusual bivalent interaction and a new viral attachment protein

Nogo-66 receptor 1 (NgR1) binds a variety of structurally dissimilar ligands in the adult central nervous system to inhibit axon extension. Disruption of ligand binding to NgR1 and subsequent signaling can improve neuron outgrowth, making NgR1 an important therapeutic target for diverse neurological conditions such as spinal crush injuries and Alzheimer's disease. Human NgR1 serves as a receptor for mammalian orthoreovirus (reovirus), but the mechanism of virus-receptor engagement is unknown. To elucidate how NgR1 mediates cell binding and entry of reovirus, we defined the affinity of interaction between virus and receptor, determined the structure of the virus-receptor complex, and identified residues in the receptor required for virus binding and infection. These studies revealed that central NgR1 surfaces form a bridge between two copies of viral capsid protein σ3, establishing that σ3 serves as a receptor ligand for reovirus. This unusual binding interface produces high-avidity interactions between virus and receptor to prime early entry steps. These studies refine models of reovirus cell-attachment and highlight the evolution of viruses to engage multiple receptors using distinct capsid components.

SARS-CoV-2 infection and viral fusogens cause neuronal and glial fusion that compromises neuronal activity

Numerous viruses use specialized surface molecules called fusogens to enter host cells. Many of these viruses, including the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can infect the brain and are associated with severe neurological symptoms through poorly understood mechanisms. We show that SARS-CoV-2 infection induces fusion between neurons and between neurons and glia in mouse and human brain organoids. We reveal that this is caused by the viral fusogen, as it is fully mimicked by the expression of the SARS-CoV-2 spike (S) protein or the unrelated fusogen p15 from the baboon orthoreovirus. We demonstrate that neuronal fusion is a progressive event, leads to the formation of multicellular syncytia, and causes the spread of large molecules and organelles. Last, using Ca2+ imaging, we show that fusion severely compromises neuronal activity. These results provide mechanistic insights into how SARS-CoV-2 and other viruses affect the nervous system, alter its function, and cause neuropathology.

Detection and Characterization of a Reassortant Mammalian Orthoreovirus Isolated from Bats in Xinjiang, China

Mammalian orthoreoviruses (MRVs) are increasingly reported to cause various diseases in humans and other animals, with many possibly originating from bats, highlighting the urgent need to investigate the diversity of bat-borne MRVs (BtMRVs). Here, we report the detection and characterization of a reassortant MRV that was isolated from a bat colony in Xinjiang, China. The BtMRV showed a wide host and organ tropism and can efficiently propagate the cell lines of different animals. It caused mild damage in the lungs of the experimentally inoculated suckling mice and was able to replicate in multiple organs for up to three weeks post-inoculation. Complete genome analyses showed that the virus was closely related to MRVs in a wide range of animals. An intricate reassortment network was revealed between the BtMRV and MRVs of human, deer, cattle, civet and other bat species. Specifically, we found a bat-specific clade of segment M1 that provides a gene source for the reassortment of human MRVs. These data provide important insights to understand the diversity of MRVs and their natural circulation between bats, humans, and other animals. Further investigation and surveillance of MRV in bats and other animals are needed to control and prevent potential MRV-related diseases.

Polycistronic Genome Segment Evolution and Gain and Loss of FAST Protein Function during Fusogenic Orthoreovirus Speciation

The Reoviridae family is the only non-enveloped virus family with members that use syncytium formation to promote cell–cell virus transmission. Syncytiogenesis is mediated by a fusion-associated small transmembrane (FAST) protein, a novel family of viral membrane fusion proteins. Previous evidence suggested the fusogenic reoviruses arose from an ancestral non-fusogenic virus, with the preponderance of fusogenic species suggesting positive evolutionary pressure to acquire and maintain the fusion phenotype. New phylogenetic analyses that included the atypical waterfowl subgroup of avian reoviruses and recently identified new orthoreovirus species indicate a more complex relationship between reovirus speciation and fusogenic capacity, with numerous predicted internal indels and 5’-terminal extensions driving the evolution of the orthoreovirus’ polycistronic genome segments and their encoded FAST and fiber proteins. These inferred recombination events generated bi- and tricistronic genome segments with diverse gene constellations, they occurred pre- and post-orthoreovirus speciation, and they directly contributed to the evolution of the four extant orthoreovirus FAST proteins by driving both the gain and loss of fusion capability. We further show that two distinct post-speciation genetic events led to the loss of fusion in the waterfowl isolates of avian reovirus, a recombination event that replaced the p10 FAST protein with a heterologous, non-fusogenic protein and point substitutions in a conserved motif that destroyed the p10 assembly into multimeric fusion platforms.

Fusogenic Reoviruses and Their Fusion-Associated Small Transmembrane (FAST) Proteins

With no limiting membrane surrounding virions, nonenveloped viruses have no need for membrane fusion to gain access to intracellular replication compartments. Consequently, nonenveloped viruses do not encode membrane fusion proteins. The only exception to this dogma is the fusogenic reoviruses that encode fusion-associated small transmembrane (FAST) proteins that induce syncytium formation. FAST proteins are the smallest viral membrane fusion proteins and, unlike their enveloped virus counterparts, are nonstructural proteins that evolved specifically to induce cell-to-cell, not virus-cell, membrane fusion. This distinct evolutionary imperative is reflected in structural and functional features that distinguish this singular family of viral fusogens from all other protein fusogens. These rudimentary fusogens comprise specific combinations of different membrane effector motifs assembled into small, modular membrane fusogens. FAST proteins offer a minimalist model to better understand the ubiquitous process of protein-mediated membrane fusion and to reveal novel mechanisms of nonenveloped virus dissemination that contribute to virulence.

Is Minocycline an Antiviral Agent? A Review of Current Literature

Minocycline is a second-generation semi-synthetic derivative of tetracycline and has well-known anti-bacterial effects. The drug possesses anti-inflammatory, anti-oxidant, anti-apoptotic and immunomodulatory effects. The drug is widely used in bacterial infections and non-infectious conditions such as acne, dermatitis, periodontitis and neurodegenerative conditions. Minocycline was shown to have antiviral activity in vitro and also against different viruses in some animal models. Some studies have been done on human patients infected with Human Immunodeficiency Virus. We have review the available data regarding minocycline activity as an antiviral agent.

The Nogo receptor NgR1 mediates infection by mammalian reovirus

Neurotropic viruses, including mammalian reovirus, must disseminate from an initial site of replication to the central nervous system (CNS), often binding multiple receptors to facilitate systemic spread. Reovirus engages junctional adhesion molecule A (JAM-A) to disseminate hematogenously. However, JAM-A is dispensable for reovirus replication in the CNS. We demonstrate that reovirus binds Nogo receptor NgR1, a leucine-rich repeat protein expressed in the CNS, to infect neurons. Expression of NgR1 confers reovirus binding and infection of nonsusceptible cells. Incubating reovirus virions with soluble NgR1 neutralizes infectivity. Blocking NgR1 on transfected cells or primary cortical neurons abrogates reovirus infection. Concordantly, reovirus infection is ablated in primary cortical neurons derived from NgR1 null mice. Reovirus virions bind to soluble JAM-A and NgR1, while infectious disassembly intermediates (ISVPs) bind only to JAM-A. These results suggest that reovirus uses different capsid components to bind distinct cell-surface molecules, engaging independent receptors to facilitate spread and tropism.

Correlation between presence of Trypanosoma cruzi DNA in heart tissue of baboons and cynomolgus monkeys, and lymphocytic myocarditis

Trypanosoma cruzi, the causative agent of Chagas' disease, preferentially infects cardiac and digestive tissues. Baboons living in Texas (Papio hamadryas) and cynomolgus monkeys (Macaca fascicularis) have been reported to be infected naturally with T. cruzi. In this study, we retrospectively reviewed cases of animals that were diagnosed with lymphocytic myocarditis and used a polymerase chain reaction (PCR)-based method (S36/S35 primer set) to amplify T. cruzi DNA from archived frozen and formalin-fixed paraffin-embedded (FFPE) cardiac tissues. We show that the PCR method is applicable in archived frozen and FFPE tissues and the sensitivity is in the femtogram range. A positive correlation between PCR positivity and lymphocytic myocarditis in both baboons and cynomolgus monkeys is shown. We also show epicarditis as a common finding in animals infected with T. cruzi.

Mortality in captive baboons (Papio spp.): a-23-year study

BACKGROUND

We report the causes of mortality for 4350 captive baboons that died or were euthanized due to natural causes during a 23 year period at the Southwest National Primate Research Center.

METHODS

Necropsy records were retrieved and reviewed to determine a primary cause of death or indication for euthanasia. Data was evaluated for morphological diagnosis, organ system, and etiology.

RESULTS

The 20 most common morphologic diagnoses accounted for 76% of the cases, including stillborn (10.8%); colitis (8.6%); hemorrhage (8.4%); ulcer (5.2%); seizures (4.7%); pneumonia (4.2%); inanition (4.1%); dermatitis (3.8%); spondylosis (3.3%); and amyloidosis (3.0%). The digestive system was most frequently involved (21.3%), followed by the urogenital (20.3%), cardiovascular (12.2%), and multisystem disease (10.3%). An etiology was not identified in approximately one-third of cases. The most common etiologies were trauma (14.8%), degenerative (9.5%), viral (8.7%), and neoplastic/proliferative (7.0%).

CONCLUSION

This information should be useful for individuals working with baboons.