Tree Shrew Is a Suitable Animal Model for the Study of Epstein Barr Virus

Epstein-Barr virus (EBV) is a human herpesvirus that latently infects approximately 95% of adults and is associated with a spectrum of human diseases including Infectious Mononucleosis and a variety of malignancies. However, understanding the pathogenesis, vaccines and antiviral drugs for EBV-associated disease has been hampered by the lack of suitable animal models. Tree shrew is a novel laboratory animal with a close phylogenetic relationship to primates, which is a critical advantage for many animal models for human disease, especially viral infections. Herein, we first identified the key residues in the CR2 receptor that bind the gp350 protein and facilitate viral entry. We found that tree shrew shares 100% sequence identity with humans in these residues, which is much higher than rabbits (50%) and rats (25%). In vitro analysis showed that B lymphocytes of tree shrews are susceptible to EBV infection and replication, as well as EBV-enhanced cell proliferation. Moreover, results of in vivo experiments show that EBV infection in tree shrews resembles EBV infection in humans. The infected animals exhibited transient fever and loss of weight accompanied by neutropenia and high viremia levels during the acute phase of the viral infection. Thereafter, tree shrews acted as asymptomatic carriers of the virus in most cases that EBV-related protein could be detected in blood and tissues. However, a resurgence of EBV infection occurred at 49 dpi. Nanopore transcriptomic sequencing of peripheral blood in EBV-infected animals revealed the dynamic changes in biological processes occurring during EBV primary infection. Importantly, we find that neutrophil function was impaired in tree shrew model as well as human Infectious Mononucleosis datasets (GSE85599 and GSE45918). In addition, retrospective case reviews suggested that neutropenia may play an important role in EBV escaping host innate immune response, leading to long-term latent infection. Our findings demonstrated that tree shrew is a suitable animal model to evaluate the mechanisms of EBV infection, and for developing vaccines and therapeutic drugs against EBV.

Infection of the Asian gray shrew Crocidura attenuata (Insectivora: Soricidae) with Sarcocystis attenuati n. sp. (Apicomplexa: Sarcocystidae) in China

Background Data on the genus Sarcocystis in insectivores are limited. The Asian gray shrew Crocidura attenuata is one of the most common species of the insectivore family Soricidae in South Asia and Southeast Asia. To our knowledge, species of Sarcocystis have never been recorded previously in this host. Methods Tissues were obtained from 42 Asian gray shrews caught in 2017 and 2018 in China. Sarcocysts were observed using light microscopy (LM) and transmission electron microscopy (TEM). To describe the parasite life cycle, muscle tissues of the host infected with sarcocysts were force-fed to two beauty rat snakes Elaphe taeniura. Individual sarcocysts from different Asian gray shrews, and oocysts/sporocysts isolated from the small intestines and feces of the experimental snakes, were selected for DNA extraction, and seven genetic markers, namely, two nuclear loci [18S ribosomal DNA (18S rDNA) and internal transcribed spacer region 1 (ITS1)], three mitochondrial genes [cytochrome oxidase subunit 1 (cox1), cox3 and cytochrome b], and two apicoplast genes (RNA polymerase beta subunit and caseinolytic protease C), were amplified, sequenced and analyzed. Results Sarcocysts were found in 17 of the 42 (40.5%) Asian gray shrews. Under LM, the microscopic sarcocysts showed saw- or tooth-like protrusions measuring 3.3–4.5 μm. Ultrastructurally, the sarcocyst wall contained numerous lancet- or leaf-like villous protrusions, similar to those described for type 9h of the common cyst wall classification. The experimental beauty rat snakes shed oocysts/sporocysts measuring 11.9–16.7 × 9.2–10.6 μm with a prepatent period of 10–11 days. Comparison of the newly obtained sequences with those previously deposited in GenBank revealed that those of 18S rDNA and cox1 were most similar to those of Sarcocystis scandentiborneensis recorded in the tree shrews Tupaia minor and Tupaiatana (i.e., 97.6–98.3% and 100% identity, respectively). Phylogenetic analysis based on 18S rDNA or ITS1 sequences placed this parasite close to Sarcocystis spp. that utilize small animals as intermediate hosts and snakes as the known or presumed definitive host. On the basis of morphological and molecular characteristics and host specificity, the parasite was proposed as a new species, named Sarcocystis attenuati. Conclusions Sarcocysts were recorded in Asian gray shrews, to our knowledge for the first time. Based on morphological and molecular characterization, a new species of parasite is proposed: Sarcocystisattenuati. According to the LM and TEM results, S. attenuati sarcocysts are distinct from those of Sarcocystis spp. in other insectivores and those of S. scandentiborneensis in tree shrews. The 18S rDNA or cox1 sequences of Sarcocystis attenuati shared high similarity with those of Sarcocystisscandentiborneensis, Sarcocystis zuoi, Sarcocystis cf. zuoi in the Malayan field rat, and Sarcocystis sp. in the greater white-toothed shrew. Therefore, we suggest that more research on the relationships of these closely related taxa should be undertaken in the future. Graphical abstract

Glucose sparing by glycogenolysis (GSG) determines the relationship between brain metabolism and neurotransmission

Over the last two decades, it has been established that glucose metabolic fluxes in neurons and astrocytes are proportional to the rates of the glutamate/GABA-glutamine neurotransmitter cycles in close to 1:1 stoichiometries across a wide range of functional energy demands. However, there is presently no mechanistic explanation for these relationships. We present here a theoretical meta-analysis that tests whether the brain’s unique compartmentation of glycogen metabolism in the astrocyte and the requirement for neuronal glucose homeostasis lead to the observed stoichiometries. We found that blood-brain barrier glucose transport can be limiting during activation and that the energy demand could only be met if glycogenolysis supports neuronal glucose metabolism by replacing the glucose consumed by astrocytes, a mechanism we call Glucose Sparing by Glycogenolysis (GSG). The predictions of the GSG model are in excellent agreement with a wide range of experimental results from rats, mice, tree shrews, and humans, which were previously unexplained. Glycogenolysis and glucose sparing dictate the energy available to support neuronal activity, thus playing a fundamental role in brain function in health and disease.

A Novel Tree Shrew Model of Diabetic Retinopathy

Existing animal models with rod-dominant retinas have shown that hyperglycemia injures neurons, but it is not yet clearly understood how blue cone photoreceptors and retinal ganglion cells (RGCs) deteriorate in patients because of compromised insulin tolerance. In contrast, northern tree shrews (Tupaia Belangeri), one of the closest living relatives of primates, have a cone-dominant retina with short wave sensitivity (SWS) and long wave sensitivity (LWS) cones. Therefore, we injected animals with a single streptozotocin dose (175 mg/kg i.p.) to investigate whether sustained hyperglycemia models the features of human diabetic retinopathy (DR). We used the photopic electroretinogram (ERG) to measure the amplitudes of A and B waves and the photopic negative responses (PhNR) to evaluate cone and RGC function. Retinal flat mounts were prepared for immunohistochemical analysis to count the numbers of neurons with antibodies against cone opsins and RGC specific BRN3a proteins. The levels of the proteins TRIB3, ISR-1, and p-AKT/p-mTOR were measured with western blot. The results demonstrated that tree shrews manifested sustained hyperglycemia leading to a slight but significant loss of SWS cones (12%) and RGCs (20%) 16 weeks after streptozotocin injection. The loss of BRN3a-positive RGCs was also reflected by a 30% decline in BRN3a protein expression. These were accompanied by reduced ERG amplitudes and PhNRs. Importantly, the diabetic retinas demonstrated increased expression of TRIB3 and level of p-AKT/p-mTOR axis but reduced level of IRS-1 protein. Therefore, a new non-primate model of DR with SWS cone and RGC dysfunction lays the foundation to better understand retinal pathophysiology at the molecular level and opens an avenue for improving the research on the treatment of human eye diseases.

AA-amyloidosis in captive northern tree shrews (Tupaia belangeri)

A high prevalence of AA-amyloidosis was identified in a breeding colony of northern tree shrews ( Tupaia belangeri) in a retrospective analysis, with amyloid deposits in different organs being found in 26/36 individuals (72%). Amyloid deposits, confirmed by Congo red staining, were detected in kidneys, intestines, skin, and lymph nodes, characteristic of systemic amyloidosis. Immunohistochemically, the deposited amyloid was intensely positive with anti-AA-antibody (clone mc4), suggesting AA-amyloidosis. The kidneys were predominantly affected (80%), where amyloid deposits ranged from mild to severe and was predominantly located in the renal medulla. In addition, many kidneys contained numerous cysts with atrophy of the renal parenchyma. There was no significant association between concurrent neoplastic or inflammatory processes and amyloidosis. The lack of distinctive predisposing factors suggests a general susceptibility of captive T. belangeri to develop amyloidosis. Clinical and laboratory findings of a female individual with pronounced kidney alterations were indicative of renal failure. The observed tissue tropism with pronounced kidney alterations, corresponding renal dysfunction, and an overall high prevalence suggests amyloidosis as an important disease in captive tree shrews.

Animal Models in Human Adenovirus Research

Human adenovirus (HAdV) infections cause a wide variety of clinical symptoms, ranging from mild upper respiratory tract disease to lethal outcomes, particularly in immunocompromised individuals. To date, neither widely available vaccines nor approved antiadenoviral compounds are available to efficiently deal with HAdV infections. Thus, there is a need to thoroughly understand HAdV-induced disease, and for the development and preclinical evaluation of HAdV therapeutics and/or vaccines, and consequently for suitable standardizable in vitro systems and animal models. Current animal models to study HAdV pathogenesis, persistence, and tumorigenesis include rodents such as Syrian hamsters, mice, and cotton rats, as well as rabbits. In addition, a few recent studies on other species, such as pigs and tree shrews, reported promising data. These models mimic (aspects of) HAdV-induced pathological changes in humans and, although they are relevant, an ideal HAdV animal model has yet to be developed. This review summarizes the available animal models of HAdV infection with comprehensive descriptions of virus-induced pathogenesis in different animal species. We also elaborate on rodent HAdV animal models and how they contributed to insights into adenovirus-induced cell transformation and cancer.

Tree Shrew Umbilical Cord Mesenchymal Stem Cells Labeled with the Dark Red Fluorescent Dye DIR and Small Animal Live Imager Observation

Background: Umbilical cord mesenchymal stem cell transplantation can treat metabolic syndrome, but the tracing of cells in the body after transplantation has always been a problem. Tree shrew umbilical cord mesenchymal stem cells were labeled with the dark red fluorescent dye DIR and a metabolic syndrome model in tree shrew was generated. The migration, distribution, colonization and survival of the cells were observed. Methods: Tree shrew umbilical cord mesenchymal stem cells were labeled with the dark red fluorescent dye DIR. Three days after the tree shrew model was generated, the pancreas, kidney and liver were placed in a small animal live imager to observe the distribution of the labeled cells. Result: The labeled cells showed deep red fluorescence in the live imager. After treatment with the transplanted cells, dark red fluorescent signals were observed in the liver, kidney and pancreas of the tree shrews but not in the untreated group and no dark red fluorescent signal was observed in the cell distribution.

Whole-Brain Afferent Inputs to the Caudate Nucleus, Putamen, and Accumbens Nucleus in the Tree Shrew Striatum

Day-active tree shrews have a well-developed internal capsule (ic) that clearly separates the caudate nucleus (Cd) and putamen (Pu). The striatum consists of the Cd, ic, Pu, and accumbens nucleus (Acb). Here, we characterized the cytoarchitecture of the striatum and the whole-brain inputs to the Cd, Pu, and Acb in tree shrews by using immunohistochemistry and the retrograde tracer Fluoro-Gold (FG). Our data show the distribution patterns of parvalbumin (PV), nitric oxide synthase (NOS), calretinin (CR), and tyrosine hydroxylase (TH) immunoreactivity in the striatum of tree shrews, which were different from those observed in rats. The Cd and Pu mainly received inputs from the thalamus, motor cortex, somatosensory cortex, subthalamic nucleus, substantia nigra, and other cortical and subcortical regions, whereas the Acb primarily received inputs from the anterior olfactory nucleus, claustrum, infralimbic cortex, thalamus, raphe nucleus, parabrachial nucleus, ventral tegmental area, and so on. The Cd, Pu, and Acb received inputs from different neuronal populations in the ipsilateral (60, 67, and 63 brain regions, respectively) and contralateral (23, 20, and 36 brain regions, respectively) brain hemispheres. Overall, we demonstrate that there are species differences between tree shrews and rats in the density of PV, NOS, CR, and TH immunoreactivity in the striatum. Additionally, we mapped for the first time the distribution of whole-brain input neurons projecting to the striatum of tree shrews with FG injected into the Cd, Pu, and Acb. The similarities and differences in their brain-wide input patterns may provide new insights into the diverse functions of the striatal subregions.

Re-descriptions of eight chigger mite species (Acariformes: Trombiculidae) of the Leptotrombidium generic complex from Vietnam

Six mite species of the genus Leptotrombidium Nagayo, Miyagawa, Mitamura and Imamura, 1916 and one species from each of the genera Lorillatum Nadchatram, 1963 and Trombiculindus Radford, 1948, incompletely described by Schluger et al. (1960b, 1963) from rodents and tree shrews in North Vietnam, are re-described based on type series. Lectotypes and paralectotypes have been designated for all redescribed species. Two new synonyms have been established: Leptotrombidium magnum (Schluger, 1960) (= Leptotrombidium dooleyi Nadchatram, 1970, syn. nov.; = Leptotrombidium submagnum Wang, Li and Shi, 1988, syn. nov.).