Feedback regulation of IFN-α/β signaling by Axl receptor tyrosine kinase modulates HBV immunity: Immunity to infection

Decreased CSTB, RAGE, and Axl Receptor Are Associated with Zika Infection in the Human Placenta

Zika virus (ZIKV) compromises placental integrity, infecting the fetus. However, the mechanisms associated with ZIKV penetration into the placenta leading to fetal infection are unknown. Cystatin B (CSTB), the receptor for advanced glycation end products (RAGE), and tyrosine-protein kinase receptor UFO (AXL) have been implicated in ZIKV infection and inflammation. This work investigates CSTB, RAGE, and AXL receptor expression and activation pathways in ZIKV-infected placental tissues at term. The hypothesis is that there is overexpression of CSTB and increased inflammation affecting RAGE and AXL receptor expression in ZIKV-infected placentas. Pathological analyses of 22 placentas were performed to determine changes caused by ZIKV infection. Quantitative proteomics, immunofluorescence, and western blot were performed to analyze proteins and pathways affected by ZIKV infection in frozen placentas. The pathological analysis confirmed decreased size of capillaries, hyperplasia of Hofbauer cells, disruption in the trophoblast layer, cell agglutination, and ZIKV localization to the trophoblast layer. In addition, there was a significant decrease in CSTB, RAGE, and AXL expression and upregulation of caspase 1, tubulin beta, and heat shock protein 27. Modulation of these proteins and activation of inflammasome and pyroptosis pathways suggest targets for modulation of ZIKV infection in the placenta.

Axl-/- neurons promote JEV infection by dampening the innate immunity

Japanese encephalitis virus (JEV) causes the most commonly diagnosed viral encephalitis in Asia. JEV is a highly neurotropic flavivirus that can replicate efficiently in the brain. Axl belongs to the TAM (Tyro3, Axl, Mer) family, a group of tyrosine kinase receptors involved in the viral entry, micked as apoptotic bodies and regulation of innate immunity. However, the underlying mechanisms on its regulation in the neurons for JEV are unclear. Here, we found that Axl was upregulated in neurons after JEV infection. Unexpectedly, Axl deficient (Axl^-/-) mice were more susceptible to JEV infection with increased viral loads in neurons. The RNA-sequencing analysis between the wild type neurons and Axl^-/- neurons infected with JEV showed that many interferon-stimulated genes were downregulated in the Axl^-/- neurons which innate immunity was attenuated largely. The rescue experiment in Axl^-/- neurons indicated that Axl may be positively involved in the regulation of antiviral immunity. Taken together, our data demonstrated that Axl may play an antiviral role in JEV replication within neurons by modulating neuronal innate immunity.

Intrinsic and Extrinsic Control of Hepatocellular Carcinoma by TAM Receptors

Simple Summary

Tyro3, Axl, and MerTK are receptor tyrosine kinases of the TAM family, which are activated by their ligands Gas6 and Protein S. TAM receptors have large physiological implications, including the removal of dead cells, activation of immune cells, and prevention of bleeding. In the last decade, TAM receptors have been suggested to play a relevant role in liver fibrogenesis and the development of hepatocellular carcinoma. The understanding of TAM receptor functions in tumor cells and their cellular microenvironment is of utmost importance to advances in novel therapeutic strategies that conquer chronic liver disease including hepatocellular carcinoma.

Abstract

Hepatocellular carcinoma (HCC) is the major subtype of liver cancer, showing high mortality of patients due to limited therapeutic options at advanced stages of disease. The receptor tyrosine kinases Tyro3, Axl and MerTK—belonging to the TAM family—exert a large impact on various aspects of cancer biology. Binding of the ligands Gas6 or Protein S activates TAM receptors causing homophilic dimerization and heterophilic interactions with other receptors to modulate effector functions. In this context, TAM receptors are major regulators of anti-inflammatory responses and vessel integrity, including platelet aggregation as well as resistance to chemotherapy. In this review, we discuss the relevance of TAM receptors in the intrinsic control of HCC progression by modulating epithelial cell plasticity and by promoting metastatic traits of neoplastic hepatocytes. Depending on different etiologies of HCC, we further describe the overt role of TAM receptors in the extrinsic control of HCC progression by focusing on immune cell infiltration and fibrogenesis. Additionally, we assess TAM receptor functions in the chemoresistance against clinically used tyrosine kinase inhibitors and immune checkpoint blockade in HCC progression. We finally address the question of whether inhibition of TAM receptors can be envisaged for novel therapeutic strategies in HCC.

Simultaneous or prior activation of intrahepatic type I interferon signaling leads to hepatitis B virus persistence in a mouse model

It remains controversial how interferon (IFN) response contributes to hepatitis B virus (HBV) control and pathogenesis. A previous study identified that hydrodynamic injection (HI) of type I IFN (IFN-I) inducer polyinosinic-polycytidylic acid (poly(I:C)) leads to HBV clearance in a chronic HBV mouse model. However, recent studies have suggested that premature IFN-I activation in the liver may facilitate HBV persistence. In the present study, we investigated how the early IFN-I response induces an immunosuppressive signaling cascade and thus causes HBV persistence. We performed HI of the plasmid adeno-associated virus (pAAV)/HBV 1.2 into adult BALB/c mice to establish an adult acute HBV replication model. Activation of the IFN-I signaling pathway following poly(I:C) stimulation or murine cytomegalovirus (MCMV) infection resulted in subsequent HBV persistence. HI of poly(I:C) with the pAAV/HBV 1.2 plasmid resulted in not only the production of IFN-I and the anti-inflammatory cytokine interleukin (IL)-10 but also the expansion of intrahepatic regulatory T cells (Tregs), Kupffer cells (KCs) and myeloid-derived suppressor cells (MDSCs), all of which impaired the T cell response. However, when poly(I:C) was injected at day 14 after the HBV plasmid injection, it significantly enhanced HBV specific T cell responses. In addition, interferon-alpha/beta receptor (IFNAR) blockade rescued T cell response by downregulating of IL-10 expression and decreasing Treg and KC expansion. Consistently, Treg depletion or IL-10 blockade also controlled HBV replication. Importance: IFN-I plays a double-edged sword role during chronic HBV infection. Here, we identified that application of IFN-I at different time points causes contrast outcome. Activation of the IFN-I pathway before HBV replication induces an immunosuppressive signaling cascade in the liver, and consequently caused HBV persistence while IFN-I activation post HBV infection enhances HBV-specific T cell responses and thus promote HBV clearance. This result provided an important clue to the mechanism of HBV persistence in adult individuals.

Total saponins extracted from Abrus cantoniensis Hance suppress hepatitis B virus replication in vitro and in rAAV8-1.3HBV transfected mice

ETHNOPHARMACOLOGICAL RELEVANCE

Hepatitis B, an infectious disease caused by hepatitis B virus (HBV), is still a serious problem affecting global public health. Abrus cantoniensis Hance (AC), a traditional Chinese medicinal herb, has been used as a folk medicine for treating hepatitis in China from ancient times. However, its active ingredients are still unclear.

AIM OF STUDY

Our previous study indicated that saponins extracted from AC (ACS) were the active anti-HBV ingredients in AC. This study aimed to further investigate the anti-HBV effect of ACS in vitro and in vivo.

MATERIALS AND METHODS

HepG2.2.15 cells which consecutively produce HBV DNA and HBV antigens were used for in vitro test, and C57BL/6 mice infected by a recombinant adeno-associated virus 8 vector carrying 1.3 copies of HBV genome (rAAV8-HBV1.3) were used for in vivo test. The histopathological changes and the immune indices were evaluated in mice model. Genechip was conducted to identify genes and pathways regulated by ACS in HepG2.2.15 cells.

RESULTS

In this study, we confirmed that ACS treatment prominently inhibited production of HBV DNA, Hepatitis Be Antigen (HBeAg), and Hepatitis B surface antigen (HBsAg) in HepG2.2.15 cells. ACS treatment also decreased serum HBsAg, HBeAg, and HBV DNA level in rAAV8-1.3HBV transfected mice, which is in accordance with the in vitro results. Moreover, HBV infection-induced liver inflammation was significantly relieved by ACS, which could be observed in H&E staining and immunohistochemistry of HBcAg. ACS treatment elevated IFN-γ level in mice serum and increased CD4⁺ T cell percentage in splenocytes. KEGG pathway analysis showed that phenylalanine metabolism pathway and tyrosine metabolism pathway were greatly regulated by ACS treatment.

CONCLUSION

ACS exerted potent inhibitory effects on HBV replication both in vivo and in vitro, which may provide basis for its potential clinical usage.

Viral receptors for flaviviruses: Not only gatekeepers

Arboviruses have been a huge threat for human health since the discovery of yellow fever virus in 1901. Arboviruses are arthropod born viruses, mainly transmitted by mosquitoes and ticks, responsible for more than thousands of deaths annually. The Flavivirideae family is probably the most clinically relevant, as it is composed of very important agents, such as dengue, yellow fever, West Nile, Japanese encephalitis, and, recently, Zika virus. Intriguingly, despite their structural and genomic similarities, flaviviruses may cause conditions ranging from mild infections with fever, cutaneous rash, and headache, to very severe cases, such as hemorrhagic fever, encephalitis, Guillain-Barré syndrome, and microcephaly. These differences may greatly rely on viral burden, tissue tropism, and mechanisms of immune evasion that may depend on both viral and host genetic factors. Unfortunately, very little is known about the biology of these factors, and how they orchestrate these differences. In this context, viral structural proteins and host cellular receptors may have a great relevance, as their interaction dictates not only viral tissue tropism, but also a plethora on intracellular mechanisms that may greatly account for either failure or success of infection. A great number of viral receptors have been described so far, although there is still a huge gap in understanding their overall role during infection. Here we discuss some important aspects triggered after the interaction of flaviviruses and host membrane receptors, and how they change the overall outcome of the infection.

Intrahepatic innate immune response pathways are downregulated in untreated chronic hepatitis B

BACKGROUND & AIMS

Hepatitis B virus (HBV) persistence and the pathobiology of chronic HBV (CHB) infections result from the interplay between viral replication and host immune responses. We aimed to comprehensively analyse the expression of intrahepatic host genes as well as serum and liver HBV markers in a large cohort of untreated CHB patients.

METHODS

One-hundred and five CHB patients untreated at the time of liver biopsy (34 HBeAg[+] and 71 HBeAg[-]) were analysed for the intrahepatic expression profile of 67 genes belonging to multiple innate immunity pathways. Results were correlated to serological (quantification of HBsAg [qHBsAg] and HBV DNA) and intrahepatic viral markers (total HBV DNA, pre-genomic RNA and covalently closed circular HBV DNA).

RESULTS

Intrahepatic gene expression profiling revealed a strong downregulation of antiviral effectors, interferon stimulated genes, Toll-like and pathogen recognition receptor pathways in CHB patients as compared to non-infected controls, which was not directly correlated to HBV replication. A subset of genes [CXCL10, GBP1, IFITM1, IFNB1, IL10, IL6, ISG15, TLR3, SOCS1, SOCS3] was more repressed in HBeAg(-) respect to HBeAg(+) patients (median of serum HBV DNA 7.9×10³vs. 7.9×10⁷IU/ml, respectively). Notably, HBeAg(-) patients with lower qHBsAg (<5×10³IU/ml) showed a relief of repression of genes belonging to multiple pathways.

CONCLUSIONS

Our results show a strong impairment of innate immune responses in the liver of CHB patients. The association of low levels of qHBsAg with gene repression, if confirmed, might prove useful for the identification of patients who would most benefit from immune-modulators and/or HBsAg targeting agents as strategies to restore immune responsiveness.

LAY SUMMARY

Chronic hepatitis B virus (HBV) infections represent a major public health problem worldwide. Over 200 million people are chronically infected and at risk of developing chronic hepatitis, liver cirrhosis and cancer. Our work aimed to understand the molecular consequences of chronic hepatitis B in the infected liver. It was conducted in a large cohort of untreated chronically infected HBV patients and analysed the expression of immunity and liver disease-related genes in the liver, with respect to markers of viral replication and persistence. Our results indicate that chronic HBV infection has a suppressive effect on immune responses, which was more pronounced with high levels of hepatitis B virus surface antigen (HBsAg). These data provide novel insight into the mechanisms of HBV persistence in the liver and suggest that approaches aimed at reducing HBsAg levels, may restore immune responsiveness against the virus.