Suppression of hepatitis B virus replication in Tupaia hepatocytes by tumor necrosis factor alpha of Tupaia belangeri

Role of the CXCR3‑mediated TLRs/MyD88 signaling pathway in promoting the development of hepatitis B into cirrhosis and liver cancer

Chronic hepatitis B can lead to liver cirrhosis and primary hepatocellular carcinoma. The present study aimed to investigate whether C‑X‑C motif chemokine receptor 3 (CXCR3) regulates the genes in Toll‑like receptors (TLRs)/myeloid differentiation primary response protein 88 (MyD88) signaling pathway in the development of hepatitis B into cirrhosis and liver cancer in vitro. A hepatitis B virus (HBV) overexpression lentivirus was constructed and infected into a LX‑2 cell line to obtain stable HBV‑overexpressing cells (named HBV‑LX‑2 cells). The CXCR3 gene was knocked down using small interfering RNA in HBV‑LX‑2 cells. Cell Counting Kit‑8 assays, cell scratch tests and flow cytometry were used to detect cell proliferation, migration and apoptosis, respectively. The levels of IL‑1β and IL‑6 in serum samples of patients with liver cancer were measured via ELISA, and the collagen content in liver cancer tissues was detected using Masson staining. Western blotting was used to detect the expression levels of proteins in the TLRs/MyD88 signaling pathway. Excessive fibrosis was identified in the liver cancer tissues, and the serum levels of IL‑6 and IL‑1β were abnormally increased in patients with liver cancer. It was found that interfering with CXCR3 inhibited cell proliferation and migration, as well as promoted the apoptosis of HBV‑LX‑2 cells. Moreover, interfering with CXCR3 inhibited the expression levels of collagen type I α 1 chain and the proteins in the TLRs/MyD88 pathway. In conclusion, CXCR3 knockdown could inhibit the expression levels of proteins in the TLR4/MyD88 signaling pathway, decrease cell proliferation and migration, and promote cell apoptosis, thus inhibiting the development of liver cirrhosis to liver cancer.

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.

Macrophage Phenotypes and Hepatitis B Virus Infection

Globally, hepatitis B virus (HBV) infection and its related liver diseases account for 780,000 deaths every year. Outcomes of HBV infection depend on the interaction between the virus and host immune system. It is becoming increasingly apparent that Kupffer cells (KCs), the largest population of resident and monocyte-derived macrophages in the liver, contribute to HBV infection in various aspects. These cells play an important role not only in the anti-HBV immunity including virus recognition, cytokine production to directly inhibit viral replication and recruitment and activation of other immune cells involved in virus clearance but also in HBV outcome and progression, such as persistent infection and development of end-stage liver diseases. Since liver macrophages play multiple roles in HBV infection, they are directly targeted by HBV to benefit its life cycle. In the present review, we briefly outline the current advances of research of macrophages, especially the studies of their phenotypes, in chronic HBV infection.

Characteristics of olfactory ensheathing cells and microarray analysis in Tupaia belangeri (Wagner, 1841)

Tree shrews are most closely related to the primates and so possess a number of advantages in experimental studies; they have been used as an animal model in bacterial and virus infection, cancer, endocrine system disease, and certain nervous system diseases. Their olfactory ensheathing cells (OECs) are able to release several cytokines to promote neuronal survival, regeneration and remyelination. The present study used western blot analysis to identify antibody specificity in protein extracts from whole tree shrew brains to identify the specificity of p75 nerve growth factor receptor (NGFR) derived from rabbits (75 kDa). OECs were cultured and isolated, then stained and identified using the antibodies for p75NGFR. To investigate the capacity of OECs to express cytokines and growth factors, microarray technology was used, and the analysis revealed that OECs were able to express 9,821 genes. Of these genes, 44 genes were from the neurotrophic factor family, which may indicate their potential in transplantation in vivo. The present study considered the function of OECs as revealed by other studies, and may contribute to future research.

The tree shrew as a model for infectious diseases research

Despite major advances in medicine, infectious diseases still pose a significant threat to humanity. Mammalian models of disease have proved extremely useful in adding to the understanding of infectious diseases and the development of prophylactic and/or therapeutic interventions. Arguably the most important considerations of any animal model are (I) the similarity of the model to humans with respect to anatomy, physiology, immunology and disease progression, and (II) the expense of conducting experiments using the model organism. Often the choice of a model represents a compromise between these factors. Here we review the Northern Tree shrew (Tupaia belangeri), or tupaia, as a useful model for the study of infectious diseases. Tupaias are non-human primates similar in size to squirrels that are indigenous to Asia. Their genome has been sequenced and, overall, shows relatively high similarity to humans. There is also a close homology of many aspects of tupaia biology with human biology. Importantly, from an infectious diseases viewpoint, tupaias are susceptible to infection with unadapted human pathogens and manifest clinical signs akin to human infections. Overall, the relatively small size of the tupaia, their homology to humans and their susceptibility to human pathogens make them a useful model for the study of infectious diseases.

Tree shrew (Tupaia belangeri) as a novel laboratory disease animal model

The tree shrew (Tupaia belangeri) is a promising laboratory animal that possesses a closer genetic relationship to primates than to rodents. In addition, advantages such as small size, easy breeding, and rapid reproduction make the tree shrew an ideal subject for the study of human disease. Numerous tree shrew disease models have been generated in biological and medical studies in recent years. Here we summarize current tree shrew disease models, including models of infectious diseases, cancers, depressive disorders, drug addiction, myopia, metabolic diseases, and immune-related diseases. With the success of tree shrew transgenic technology, this species will be increasingly used in biological and medical studies in the future.

Interferon-β response is impaired by hepatitis B virus infection in Tupaia belangeri

To date, the chimpanzee has been used as the natural infection model for hepatitis B virus (HBV). However, as this model is very costly and difficult to use because of ethical and animal welfare issues, we aimed to establish the tupaia (Tupaia belangeri) as a new model for HBV infection and characterized its intrahepatic innate immune response upon HBV infection. First, we compared the propagation of HBV genotypes A2 and C in vivo in tupaia hepatocytes. At 8-10days post infection (dpi), the level of HBV-A2 propagation in the tupaia liver was found to be higher than that of HBV-C. Abnormal architecture of liver cell cords and mitotic figures were also observed at 8 dpi with HBV-A2. Moreover, we found that HBV-A2 established chronic infection in some tupaias. We then aimed to characterize the intrahepatic innate immune response in this model. First, we infected six tupaias with HBV-A2 (strains JP1 and JP4). At 28 dpi, intrahepatic HBV-DNA and serum hepatitis B surface antigens (HBsAg) were detected in all tupaias. The levels of interferon (IFN)-β were found to be significantly suppressed in the three tupaias infected with HBV A2_JP4, while no significant change was observed in the three infected with HBV A2_JP1. Expression of toll-like receptor (TLR) 1 was suppressed, while that of TLR3 and TLR9 were induced, in HBV A2_JP1-infected tupaias. Expression of TLR8 was induced in all tupaias. Next, we infected nine tupaias with HBV-A2 (JP1, JP2, and JP4), and characterized the infected animals after 31 weeks. Serum HBsAg levels were detected at 31 weeks post-infection (wpi) and IFN-β was found to be significantly suppressed in all tupaias. TLR3 was not induced, except in tupaia #93 and #96. Suppression of TLR9 was observed in all tupaias, except tupaia #93. Also, we investigated the expression levels of cyclic GMP-AMP synthase, which was found to be induced in all tupaias at 28 dpi and in four tupaias at 31 wpi. Additionally, we evaluated the expression levels of sodium-taurocholate cotransporting polypeptide, which was found to be suppressed during chronic HBV infection. Thus, the tupaia infection model of HBV clearly indicated the suppression of IFN-β at 31 wpi, which might have contributed to the establishment of chronic HBV infection.

The role of tumour necrosis factor in hepatitis B infection: Jekyll and Hyde

Chronic hepatitis B (CHB) is a major health problem worldwide and is associated with significant long-term morbidity and mortality. The hepatitis B virus (HBV) is a hepatotropic virus that is capable of integrating in the host nucleus permanently resulting in lifelong infection. To date, there is no definitive cure for HBV, as our current treatments cannot eradicate the viral reservoir that has integrated in the liver. Elucidating the immunopathogenesis is key to finding a therapeutic target for HBV as the virus is not in itself cytopathic but the immune response to the virus causes the majority of the cellular injury. In most cases, the virus reaches a state of equilibrium with low viral replication constrained by host immunity. Multiple cytokines have been implicated in the pathogenesis of CHB. Tumor necrosis factor (TNF) has emerged as a key player; on one hand it can facilitate immune-mediated virological control but on the other hand it can cause collateral hepatocyte damage, cirrhosis and possibly promote hepatocellular carcinoma. In this review, we discuss the current understanding of the immunopathogenesis of HBV, focusing on TNF and whether it can be harnessed in therapeutic strategies to cure HBV infection.

Toll-like receptor (TLR)-mediated innate immune responses in the control of hepatitis B virus (HBV) infection

The role of adaptive immune responses in the control of hepatitis B virus (HBV) infection is well accepted. The contribution of innate immune responses to the viral control is recognized but yet not fully understood. Toll-like receptors (TLRs) sense pathogen-associated molecule patterns and activate antiviral mechanisms including the intracellular antiviral pathways and the production of antiviral effectors like interferons (IFNs) and pro-inflammatory cytokines. Activation of the TLR3 pathway and the production of IFN-β represent one of the major mechanisms leading to the suppression of HBV replication in the liver, as shown in different in vitro and in vivo models. TLR4 signaling and TLR2 signaling result in the activation of intracellular pathways including MAPK and PI-3 K/Akt in hepatocytes and reduce HBV replication in an IFN-independent manner. HBV is able to counteract the actions of TLR3 and TLR2/4 through downregulation of TLR expression and attenuation of the cellular signaling pathways. Thus, TLR ligands are promising candidates as immunomodulators and therapeutics for the treatment of chronic HBV infection. Specific antiviral treatment against HBV could recover the TLR functions in chronic HBV infection and increase the effectiveness of therapeutic approaches based on TLR activation.

Inhibitory effects of human immunodeficiency virus gp120 and Tat on CpG-A-induced inflammatory cytokines in plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs), not only inhibit viral replication, but also play an essential role in linking the innate and adaptive immune system. In this study, we explored the effects of human immunodeficiency virus (HIV) gp120 and tat on CpG-A-induced inflammatory cytokines in pDCs. The results provided fundamental insights into HIV pathogenesis that may hold promise for preventative and even curative strategies. pDCs were isolated using blood DC antigen 4 (BDCA-4) DC isolation kit, and the purity was analyzed using BDCA-2 antibody by flow cytometry. pDCs and peripheral blood mononuclear cells (PBMCs) were stimulated by either CpG-A (5 µg/ml), gp120 (0.5 µg/ml), tat (0.5 µg/ml), or CpG-A treatment combined with gp120 or tat. The production of type I interferons (IFNs) and other inflammatory cytokines, including tumor necrosis factor-alpha (TNF-α), interlukine-6 (IL-6), and interferon-gamma-inducible protein-10 (IP-10) in the culture supernatant, was determined by enzyme-linked immunosorbent assay. The results showed that CpG-A induced high levels of type I IFNs and other inflammatory cytokines, including TNF-α, IL-6, and IP-10, in pDCs. Concomitant treatment with gp120 reduced the levels of IFN-α, IFN-β, TNF-α, IL-6, and IP-10 induced by CpG-A in pDCs by 79%, 53%, 60%, 50%, and 34%, respectively, while tat suppressed them by 88%, 66%, 71%, 64%, and 53%, respectively. Similar results were demonstrated in CpG-A-treated PBMCs. In conclusion, gp120 and tat are effective inhibitors of the CpG-A-mediated induction of type I IFNs and other inflammatory cytokines from pDCs and PBMCs.