Longitudinal transcriptomic characterization of viral genes in HSV-1 infected tree shrew trigeminal ganglia

Identification and characterization of the tumor necrosis factor receptor superfamily in the Chinese tree shrew (Tupaia belangeri chinensis)

The tumor necrosis factor receptor superfamily (TNFRSF) plays a vital role in eliciting immune responses against infections. The tree shrew, closely related to primates, is often utilized in human disease models. Here, we analyzed TNFRSF members from 11 different animal species, including the Chinese tree shrew, and identified 24 tree shrew TNFRSF (tTNFRSF) genes, which were grouped into seven subcategories with similar motifs, sequences, and gene structures. As expected, the multi-species collinearity analysis revealed that tTNFRSF genome bears a greater resemblance to humans than to mice. Transcriptome data from 28 samples across ten organ types showed high TNFRSF expression predominantly in immune organs. It was seen that TNFRSF13C co-expresses consistently with the B cell surface marker CD79A, which is consistent with its characteristics in humans. The tissue distribution and co-expression were confirmed via RT-qPCR and immunofluorescence. Evaluation of transcriptome data from 70 samples infected with six types of viruses showed that most TNFRSF genes were upregulated in tree shrew post-viral infection. TNFRSF exerts antiviral function most probably through the activation of the NF-κB pathway, subsequently causing apoptosis of infected cells. Our findings provide evolutionary and functional insights into tTNFRSF, indicating its potential utility in human viral infection models.

Mechanisms of HSV gene regulation during latency and reactivation

Herpes simplex virus 1 and 2 (HSV-1 and HSV-2) are prevalent human pathogens associated with many diseases. After productive (lytic) infection in peripheral tissues, HSV establishes lifelong latent infection in neurons of the peripheral nervous system. Periodic reactivation from latency, triggered by certain stimuli, can resume the lytic cycle. Lytic infection, latent infection and reactivation follow distinct viral gene expression patterns. The switch between the different infection programs is controlled by complicated regulatory mechanisms involving numerous viral and host molecules. Recent studies integrating cutting-edge technologies including neuronal culture techniques have greatly improved our understanding of the molecular details of latency and reactivation but many questions remain. This review summarizes the current knowledge about how HSV gene expression is regulated during latency and reactivation and discusses the important questions remaining to be addressed in future.

Study of tree shrew biology and models: A booming and prosperous field for biomedical research

The tree shrew ( Tupaia belangeri) has long been proposed as a suitable alternative to non-human primates (NHPs) in biomedical and laboratory research due to its close evolutionary relationship with primates. In recent years, significant advances have facilitated tree shrew studies, including the determination of the tree shrew genome, genetic manipulation using spermatogonial stem cells, viral vector-mediated gene delivery, and mapping of the tree shrew brain atlas. However, the limited availability of tree shrews globally remains a substantial challenge in the field. Additionally, determining the key questions best answered using tree shrews constitutes another difficulty. Tree shrew models have historically been used to study hepatitis B virus (HBV) and hepatitis C virus (HCV) infection, myopia, and psychosocial stress-induced depression, with more recent studies focusing on developing animal models for infectious and neurodegenerative diseases. Despite these efforts, the impact of tree shrew models has not yet matched that of rodent or NHP models in biomedical research. This review summarizes the prominent advancements in tree shrew research and reflects on the key biological questions addressed using this model. We emphasize that intensive dedication and robust international collaboration are essential for achieving breakthroughs in tree shrew studies. The use of tree shrews as a unique resource is expected to gain considerable attention with the application of advanced techniques and the development of viable animal models, meeting the increasing demands of life science and biomedical research.

Small Animal Models to Study Herpes Simplex Virus Infections

Herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2) are two of the most prevalent human viruses worldwide. They are known to cause a variety of diseases including genital herpes, meningitis, encephalitis, cold sores and herpes stromal keratitis. The seropositive rate for HSV-1 is around 90%, whereas for HSV-2 it remains around 20-25% for the general adult population. The infections caused by these viruses remain difficult to study because a large proportion of infected individuals are asymptomatic. Furthermore, given the neurotropic characteristics of the virus, studies aimed at understanding the complex pathogenesis in humans is difficult. As a result, animal models have been developed to understand several characteristics of HSV biology, pathogenesis, disease and host responses to infection. These models are also commonly used as the first evaluation of new drugs and vaccines. There are several well-established animal models to study infection with HSV, including mice, guinea pigs and rabbits. Variables within the animal models depend on the species of animal, route of infection, viral strain, dosage, etc. This review aims at summarizing the most commonly used animal models to study HSV pathogenesis and therapies.

Persistent inflammation and neuronal loss in the mouse brain induced by a modified form of attenuated herpes simplex virus type I

Herpes simplex virus-1 (HSV-1) is a widespread neurotropic virus that can reach the brain and cause a rare but acute herpes simplex encephalitis (HSE) with a high mortality rate. Most patients present with changes in neurological and behavioral status, and survivors suffer long-term neurological sequelae. To date, the pathogenesis leading to brain damage is still not well understood. HSV-1 induced encephalitis in the central nervous system (CNS) in animals are usually very diffuse and progressing rapidly, and mostly fatal, making the analysis difficult. Here, we established a mouse model of HSE via intracerebral inoculation of modified version of neural-attenuated strains of HSV-1 (deletion of ICP34.5 and inserting a strong promoter into the latency-associated transcript region), in which the LMR-αΔpA strain initiated moderate productive infection, leading to strong host immune and inflammatory response characterized by persistent microglia activation. This viral replication activity and prolonged inflammatory response activated signaling pathways in neuronal damage, amyloidosis, Alzheimer's disease, and neurodegeneration, eventually leading to neuronal loss and behavioral changes characterized by hypokinesia. Our study reveals detailed pathogenic processes and persistent inflammatory responses in the CNS and provides a controlled, mild and non-lethal HSE model for studying long-term neuronal injury and increased risk of neurodegenerative diseases due to HSV-1 infection.

Tree Shrew as an Emerging Small Animal Model for Human Viral Infection: A Recent Overview

Viral infection is a global public health threat causing millions of deaths. A suitable small animal model is essential for viral pathogenesis and host response studies that could be used in antiviral and vaccine development. The tree shrew (Tupaia belangeri or Tupaia belangeri chinenesis), a squirrel-like non-primate small mammal in the Tupaiidae family, has been reported to be susceptible to important human viral pathogens, including hepatitis viruses (e.g., HBV, HCV), respiratory viruses (influenza viruses, SARS-CoV-2, human adenovirus B), arboviruses (Zika virus and dengue virus), and other viruses (e.g., herpes simplex virus, etc.). The pathogenesis of these viruses is not fully understood due to the lack of an economically feasible suitable small animal model mimicking natural infection of human diseases. The tree shrew model significantly contributes towards a better understanding of the infection and pathogenesis of these important human pathogens, highlighting its potential to be used as a viable viral infection model of human viruses. Therefore, in this review, we summarize updates regarding human viral infection in the tree shrew model, which highlights the potential of the tree shrew to be utilized for human viral infection and pathogenesis studies.

The Tree Shrew as a Model for Cancer Research

Animal disease models are necessary in medical research, and an appropriate animal model is of great importance for studies about the prevention or treatment of cancer. The most important thing in the selection of animal models is to consider the similarity between animals and humans. The tree shrew (Tupaia belangeri) is a squirrel-like mammal which placed in the order Scandentia. Whole-genome sequencing has revealed that tree shrews are extremely similar to primate and humans than to rodents, with many highly conserved genes, which makes the data from studies that use tree shrews as models more convincing and the research outcomes more easily translatable. In tumor research, tree shrews are often used as animal models for hepatic and mammary cancers. As research has progressed, other types of tree shrew tumor models have been developed and exhibit clinical manifestations similar to those of humans. Combining the advantages of both rodents and primates, the tree shrew is expected to be the most powerful animal model for studying tumors.