Comparative Pathogenicity and Transmissibility of Pandemic H1N1, Avian H5N1, and Human H7N9 Influenza Viruses in Tree Shrews

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.

Integrated analysis of miRNA-mRNA expression of newly emerging swine H3N2 influenza virus cross-species infection with tree shrews

BACKGROUND

Cross-species transmission of zoonotic IAVs to humans is potentially widespread and lethal, posing a great threat to human health, and their cross-species transmission mechanism has attracted much attention. miRNAs have been shown to be involved in the regulation of IAVs infection and immunity, however, few studies have focused on the molecular mechanisms underlying miRNAs and mRNAs expression after IAVs cross-species infection.

METHODS

We used tree shrews, a close relative of primates, as a model and used RNA-Seq and bioinformatics tools to analyze the expression profiles of DEMs and DEGs in the nasal turbinate tissue at different time points after the newly emerged swine influenza A virus SW2783 cross-species infection with tree shrews, and miRNA-mRNA interaction maps were constructed and verified by RT-qPCR, miRNA transfection and luciferase reporter assay.

RESULTS

14 DEMs were screened based on functional analysis and interaction map, miR-760-3p, miR-449b-2, miR-30e-3p, and miR-429 were involved in the signal transduction process of replication and proliferation after infection, miR-324-3p, miR-1301-1, miR-103-1, miR-134-5p, miR-29a, miR-31, miR-16b, miR-34a, and miR-125b participate in negative feedback regulation of genes related to the immune function of the body to activate the antiviral immune response, and miR-106b-3p may be related to the cross-species infection potential of SW2783, and the expression level of these miRNAs varies in different days after infection.

CONCLUSIONS

The miRNA regulatory networks were constructed and 14 DEMs were identified, some of them can affect the replication and proliferation of viruses by regulating signal transduction, while others can play an antiviral role by regulating the immune response. It indicates that abnormal expression of miRNAs plays a crucial role in the regulation of cross-species IAVs infection, which lays a solid foundation for further exploration of the molecular regulatory mechanism of miRNAs in IAVs cross-species infection and anti-influenza virus targets.

Pathogenicity and anti-infection immunity of animal H3N2 and H6N6 subtype influenza virus cross-species infection with tree shrews

Animal influenza viruses can spread across species and pose a fatal threat to human health due to the high pathogenicity and mortality. Animal models are crucial for studying cross-species infection and the pathogenesis of influenza viruses. Tupaia belangeri (tree shrew) has been emerging as an animal model for multiple human virus infections recently because of the close genetic relationship and phylogeny with humans. So far, tree shrew has been reported to be susceptible to human influenza virus subtype H1N1, avian influenza viruses subtype H9N2, subtype H5N1, and subtype H7N9. However, the pathogenicity, infection, and immunity of swine and land avian influenza viruses with low pathogenicity and the potential to jump to humans remain largely unexplored in the tree shrew model. Previously, our team has successfully isolated the newly emerging swine influenza virus subtype H3N2 (A/Swine/GX/NS2783/2010, SW2783) and avian influenza virus subtype H6N6 (A/CK/ZZ/346/2014, ZZ346). In this study, we observed the pathogenicity, immune characteristics, and cross-species infection potential ability of SW2783 and ZZ346 strains in tree shrew model with 50% tissue culture infective dose (TCID₅₀), hematoxylin and eosin (HE) staining, immunohistochemistry (IHC), real-time quantitative PCR (qRT-PCR) and other experimental methods. Both animal-borne influenza viruses had a strong ability on tissue infection in the turbinate and the trachea of tree shrews in vitro, in which SW2783 showed stronger replication ability than in ZZ346. SW2783 and ZZ346 both showed pathogenic ability with infected tree shrews model in vivo without prior adaptive culture, which mainly happened in the upper respiratory tract. However, the infection ability was weak, the clinical symptoms were mild, and the histopathological changes in the respiratory tract were relatively light. Furthermore, innate immune responses and adaptive immunity were observed in the tree shrew model after the infection of SW2783 and ZZ346 strains. We observed that the unadapted SW2783 and ZZ346 virus could transmit among tree shrews by direct contact. We also observed that SW2783 virus could transmit from tree shrews to guinea pigs. These results indicated that both animal-borne influenza viruses could induce similar pathogenicity and immune response to those caused by human-common influenza viruses. Tree shrews may be an excellent animal model for studying the interaction between the influenza virus and the host and the cross-species infection mechanism of the animal influenza virus.

Discovery and molecular elucidation of the anti-influenza material basis of Banlangen granules based on biological activities and ultra-high performance liquid chromatography coupled with quadrupole-orbitrap mass spectrometry

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicine (TCM) has a wide range of applications, including human healthcare-associated treatments and bioactive compound discovery. However, complex chemical systems present a significant challenge for chemical-material-based research and quality control. For instance, Banlangen (BLG) granules is a well-acknowledged TCM preparation widely used in clinical treatment of virus infection. However, its chemical basis of anti-influenza efficacy remains unclear.

AIM OF THE STUDY

In the present study, a systematic discovery strategy for identifying anti-influenza molecules based on biological activities and chemical analysis was established to contribute to the molecular elucidation of the anti-influenza material basis of Banlangen granules.

MATERIALS AND METHODS

Hemagglutinase inhibition (HAI) and neuraminidase inhibition (NAI) assays were used to compare the anti-influenza activities of different fractions of BLG granules against H1N1, H5N1 and H7N9 viruses. A comparative qualitative analysis of the chemical constituents in BLG granules and their fractions was performed using ultra-high-performance liquid chromatography coupled with quadrupole orbitrap mass spectrometry (UHPLC-Q-Exactive Orbitrap MS), in which a multiple mass spectrometry database platform and three compound identification strategies were used. The association between anti-influenza activities and chemical constituent characteristics was analyzed using multiple stoichiometries and data comparison strategies.

RESULTS

The results showed that the chromatography fractions F3 and F4 of the BLG granules had the highest anti-influenza activity. A total of 88 compounds were identified in the BLG granules, including 31 alkaloids, 16 organic acids, 10 nucleosides, 8 phenylpropanoids, 6 sulfur-containing compounds, 5 amino acids, 4 aromatic compounds, 3 aldehydes and ketones, 2 flavonoids, 1 alcohol, 1 carbohydrate, and 1 aliphatic compound. Out of these, 31 characteristic compounds were identified in fractions F3-F4 as candidate compounds with anti-influenza activity. Additionally, 6-methoxyquinoline and 4-guanidinobutanal were identified in BLG granules and its raw material (Isatidis Radix) for the first time.

CONCLUSION

In this study, we proposed a systematic discovery strategy to thoroughly investigate the anti-influenza activity, chemical identification, and constituents-activity relationship of BLG granules. These data not only provided a deeper understanding of the molecular mechanism of the activity of BLG granules, but also presented a basis for the discovery of potential novel drug candidates and quality evaluation and control of BLG granules.

Optimization of Milk Substitutes for the Artificial Rearing of Chinese Tree Shrews (Tupaia belangeri chinensis)

Simple Summary

The Chinese tree shrew, a squirrel-like mammal, has been widely used as a laboratory animal in biological research. However, the low survival rate of the pups has seriously hindered the establishment of inbred lines of this species and further limited its wider use. We found a milk substitute appropriate for artificial rearing of Chinese tree shrew pups independent of any obvious adverse effects on their survival, health, and reproductive performance compared to those of the maternally reared pups. The successful optimization of a milk substitute for the artificial rearing of Chinese tree shrew pups may increase the availability of this experimental animal.

Abstract

The Chinese tree shrew (Tupaia belangeri chinensis) has the potential to replace the use of non-human primates in biomedical research. To increase the availability of this species, we have undertaken the ambitious task of establishing inbred lines of the Chinese tree shrew; however, we have been hindered by a low survival rate of inbred pups. Here, we report our artificial rearing (AR) of Chinese tree shrew pups using four different milk substitutes: the formula described by Tsang and Collins (milk TC) and three commercially available milk substitutes intended for possums (milk A and milk C) and for guinea pigs (milk B). We compared the effects of these milk substitutes and maternal milk on the daily milk consumption, growth performance, and survival of the pups. We also assessed the life span and reproductive performance of the F₁ individuals given the best milk substitute as compared to the maternally reared (MR) pups. Milk B was found to be appropriate for AR. Pups fed with milk B had a high survival rate at the weaning age compared to those fed with the other milk substitutes. The AR pups fed with milk B had a life span similar to that of MR pups. AR females fed with milk B had an earlier age of the first reproduction, a larger number of litters, and a higher rate of survival of the offspring at the weaning age compared with the MR females. The successful optimization of a milk substitute for AR of Chinese tree shrew pups will undoubtedly facilitate the wide usage of this experimental animal.

Characterizing the role of Tupaia DNA damage inducible transcript 3 (DDIT3) gene in viral infections

DNA damage inducible transcript 3 (DDIT3, also known as CHOP) belongs to the CCAAT/enhancer-binding protein (C/EBP) family and plays an essential role in endoplasmic reticulum stress. Here, we characterized the potential role of the Chinese tree shrew (Tupaia belangeri chinensis) DDIT3 (tDDIT3) in viral infections. The tDDIT3 protein is highly conserved and has a species-specific insertion of the SQSS repeat upstream of the C-terminal basic-leucine zipper (bZIP) domain. Phylogenetic analysis of DDIT3 protein sequences of tree shrew and related mammals indicated a closer genetic affinity between tree shrew and primates than between tree shrew and rodents. Three positively selected sites (PSSs: Glu83, Pro93, and Ser172) were identified in tDDIT3 based on the branch-site model. Expression analysis of tDDIT3 showed a constitutively expressed level in different tissues and a significantly increased level in tree shrew cells upon herpes simplex virus type 1 (HSV-1) and Newcastle disease virus (NDV) infections. Overexpression of tDDIT3 significantly increased the production of HSV-1 and vesicular stomatitis virus (VSV) in tree shrew primary renal cells (TSPRCs), whereas tDDIT3 knockout in tree shrew stable cell line (TSR6 cells) had an inhibitory effect on virus production. The enhanced effect on viral infection by tDDIT3 was not associated with the three PSSs. Mechanistically, tDDIT3 overexpression inhibited type I IFN signaling. tDDIT3 interacted with tMAVS through CARD and PRR domains, but not with other immune-related factors such as tMDA5, tSTING and tTBK1. Collectively, our results revealed tDDIT3 as a negative regulator for virus infection.

Tupaia GBP1 Interacts with STING to Initiate Autophagy and Restrict Herpes Simplex Virus Type 1 Infection

Stimulator of IFN genes (STING) is a key molecule that binds to cyclic dinucleotides produced by the cyclic GMP-AMP synthase to activate IFN expression and autophagy in the fight against microbial infection. The regulation of STING in the activation of IFN expression has been extensively reported, whereas the regulation of STING in the initiation of autophagy is still insufficiently determined. IFN-inducible guanylate-binding proteins (GBPs) are central to the cell-autonomous immunity in defending a host against viral, bacterial, and protozoan infections. In this study using the Chinese tree shrew (Tupaia belangeri chinensis), which is genetically close to primates, we found that Tupaia GBP1 (tGBP1) combines with Tupaia STING (tSTING), promotes autophagy, and moderately inhibits HSV type 1 (HSV-1) infection. The antiviral effects of tGBP1 are IFN independent. Mechanistically, tGBP1 interacted with tSTING, Tupaia sequestosome 1, and Tupaia microtubule associated protein 1 L chain 3, forming a complex which promotes autophagy in response to HSV-1 infection. This function of tGBP1 against HSV-1 infection was lost in tSTING knockout cells. Overexpression of either tSTING or its mutant tSTING-ΔCTT that can only activate autophagy rescued the anti-HSV-1 activity of tGBP1 in tSTING knockout cells. Our study not only elucidated the underlying mechanism of tGBP1 antiviral activity against HSV-1 infection, but also uncovered the regulation of tSTING in the initiation of autophagy in response 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.

COVID-19-like symptoms observed in Chinese tree shrews infected with SARS-CoV-2

The coronavirus disease 2019 (COVID-19) pandemic continues to pose a global threat to the human population. Identifying animal species susceptible to infection with the SARS-CoV-2/ HCoV-19 pathogen is essential for controlling the outbreak and for testing valid prophylactics or therapeutics based on animal model studies. Here, different aged Chinese tree shrews (adult group, 1 year old; old group, 5-6 years old), which are close relatives to primates, were infected with SARS-CoV-2. X-ray, viral shedding, laboratory, and histological analyses were performed on different days post-inoculation (dpi). Results showed that Chinese tree shrews could be infected by SARS-CoV-2. Lung infiltrates were visible in X-ray radiographs in most infected animals. Viral RNA was consistently detected in lung tissues from infected animals at 3, 5, and 7 dpi, along with alterations in related parameters from routine blood tests and serum biochemistry, including increased levels of aspartate aminotransferase (AST) and blood urea nitrogen (BUN). Histological analysis of lung tissues from animals at 3 dpi (adult group) and 7 dpi (old group) showed thickened alveolar septa and interstitial hemorrhage. Several differences were found between the two different aged groups in regard to viral shedding peak. Our results indicate that Chinese tree shrews have the potential to be used as animal models for SARS-CoV-2 infection.

Establishment and transcriptomic features of an immortalized hepatic cell line of the Chinese tree shrew

BACKGROUND

The Chinese tree shrew (Tupaia belangeri chinesis) is a rising experimental animal and has been used for studying a variety of human diseases, such as metabolic and viral infectious diseases.

METHODS

In this study, we established an immortalized tree shrew hepatic cell line, ITH6.1, by introducing the simian virus 40 large T antigen gene into primary tree shrew hepatocytes (PTHs).

RESULTS

The ITH6.1 cell line had a stable cell morphology and proliferation activity. This cell line could be infected by enterovirus 71 (EV71), but not hepatitis C virus (HCV), although the known HCV entry factors, including CD81, SR-BI, CLDN1 and OCLN, were all expressed in the PTHs and ITH6.1 of different passages. Comparison of the transcriptomic features of the PTHs and different passages of the ITH6.1 cells revealed the dynamic gene expression profiles during the transformation. We found that the DNA replication- and cell cycle-related genes were upregulated, whereas the metabolic pathway-related genes were downregulated in early passages of immortalized hepatocytes compared to the PTHs. Furthermore, expression of hepatocytes function-related genes were repressed in ITH6.1 compared to that of PTHs.

CONCLUSION

We believe these cellular expression alterations might cause the resistance of the ITH6.1 cell to HCV infection. This tree shrew liver cell line may be a good resource for the field.

KEY POINTS

• A tree shrew hepatic cell line (ITH6.1) was established. • ITH6.1 cells could be infected by EV71, but not HCV. • ITH6.1 had an altered expression profiling compared to the primary hepatocytes.