Yuanyuan Han

Tree shrew, a potential animal model for hepatitis C, supports the infection and replication of HCV in vitro and in vivo

The tree shrew (Tupaia belangeri chinensis), a small animal widely distributed in Southeast Asia and southwest China, has the potential to be developed as an animal model for hepatitis C. To determine the susceptibility of the tree shrew to hepatitis C virus (HCV) infection in vitro and in vivo, a well-established HCV, produced from the J6/JFH1-Huh7.5.1 culture system, was used to infect cultured primary tupaia hepatocytes (PTHs) and tree shrews. The in vitro results showed that HCV genomic RNA and HCV-specific nonstructural protein 5A (NS5A) could be detected in the PTH cell culture from days 3–15 post-infection, although the viral load was lower than that observed in Huh7.5.1 cell culture. The occurrence of five sense mutations [S391A, G397A, L402F and M405T in the hypervariable region 1 (HVR1) of envelope glycoprotein 2 and I2750M in NS5B] suggested that HCV undergoes genetic evolution during culture. Fourteen of the 30 experimental tree shrews (46.7 %) were found to be infected, although the HCV viremia was intermittent in vivo. A positive test for HCV RNA in liver tissue provided stronger evidence for HCV infection and replication in tree shrews. The results of an immunohistochemistry assay also demonstrated the presence of four HCV-specific proteins (Core, E2, NS3/4 and NS5A) in the hepatocytes of infected tree shrews. The pathological changes observed in the liver tissue of infected tree shrews could be considered to be representative symptoms of mild hepatitis. These results revealed that the tree shrew can be used as an animal model supporting the infection and replication of HCV in vitro and in vivo.

CircRNAs in the tree shrew (Tupaia belangeri) brain during postnatal development and aging.

Circular RNAs (circRNAs) are a novel type of non-coding RNA expressed across different species and tissues. At present, little is known about the expression and function of circRNAs in the tree shrew brain. In this study, we used RNA-seq to identify 35,007 circRNAs in hippocampus and cerebellum samples from infant (aged 47–52 days), young (aged 15–18 months), and old (aged 78–86 months) tree shrews. We observed no significant changes in the total circRNA expression profiles in different brain regions over time. However, circRNA tended to be downregulated in the cerebellum over time. Real-time RT-PCR analysis verified the presence of circRNAs. KEGG analysis indicated the occurrence of ubiquitin-mediated proteolysis, the MAPK signaling pathway, phosphatidylinositol signaling system, long-term depression, the rap1 signaling pathway, and long-term potentiation in both brain regions. We also observed that 29,087 (83.1%) tree shrew circRNAs shared homology with human circRNAs. The competing endogenous RNA networks suggested novel_circRNA_007362 potential functions as a 24-miRNAs sponge to regulate UBE4B expression. Thus, we obtained comprehensive circRNA expression profiles in the tree shrew brain during postnatal development and aging, which might help to elucidate the functions of circRNAs during brain aging and in age-related diseases.

Characterization of tree shrew (Tupaia belangeri) interleukin-6 and its expression pattern in response to exogenous challenge

Tree shrews, one of the closest relatives of primates, have attracted increasing attention as a model of human diseases, particularly for viral infections. As the first line of defense against microbial pathogens, the innate immune system is crucial in tree shrews. Interleukin-6 (IL-6) is important in the pathophysiology of infection, inflammation and cancer, where it promotes disease development or sustains immune reactions. The present study aimed to obtain further insight into the tree shrew IL-6 (tsIL-6) system, and the function of tsIL-6 in the antiviral and antibacterial response. In the present study, the mRNA and genomic sequence of the tsIL-6 gene were characterized, and the tissue distribution and expression profile of this gene were analyzed in response to lipopolysaccharide (LPS) and polyinosinic:polycytidylic acid (poly I:C) treatment. The full-length tsIL-6 mRNA consisted of 1,152 bp with an open reading frame of 627 bp encoding 208 amino acids, a 5′-untranslated region (UTR) of 62 bp, and a 3′-UTR of 436 bp. The genome sequence of the tsIL-6 gene was 5,265 bp in length, comprising of five exons and four introns. The predicted tsIL-6 protein contained a 25-amino-acid-long signal peptide and a conserved IL-6 domain. Phylogenetic analysis based on the coding sequences revealed that tsIL-6 was closely related to IL-6 in humans. Residues crucial for receptor binding were completely conserved in the tree shrew protein. Reverse transcription-polymerase chain reaction analysis revealed that tsIL-6 mRNA was expressed in all examined tissues of healthy tree shrews, with high levels in the muscle and spleen. Following poly I:C challenge, the expression levels of tsIL-6 were upregulated in four tissues associated with immune system, the liver, spleen, kidney and intestine. Taken together, the molecular and bioinformatics analyses based on the IL-6 sequence revealed that the tree shrew has a close phylogenetic association with humans. These results provide insight for future investigations on the structure and function of tsIL-6.