No abstract

Flaviviruses including Dengue virus (DENV), Yellow fever virus (YFV), West Nile virus (WNV), and Japanese encephalitis virus (JEV) are global health problems that caused several serious diseases such as fever, hemorrhagic fever, and encephalitis in the past century. Recently, Zika virus (ZIKV) which spreads from Asia to American and causes millions of infections emerges as a new dangerous member of the genus of Flavivirus. Unlike other well-known flaviviruses, ZIKV can be transmitted sexually and infect testes in murine models. Its impacts on sperm functions, and the exact susceptible cells, however, are not entirely clear. To investigate these issues, we infected interferon α/β and γ receptors deficient AG6 mice with ZIKV and examined the outcomes of infection using an assortment of physiological, histopathological, immunological, and virological techniques. We found that infected mice displayed signs of reproductive system disorder, altered androgen levels in serum, and high viral load in semen and testes. Additionally, histopathological examinations revealed marked atrophy of seminiferous tubules and significant reduction in lumen size. Notably, these were accompanied by positive staining of ZIKV antigens on sertoli cells, detection of viral particles and vacuole changes within cytoplasm of sertoli cells. The susceptibility of sertoli cells to ZIKV was further validated in vitro study using cell lines. Importantly, the disruption of tight junctions within testis and altered sperm morphology were also observed in ZIKV infected mice. It is well-known that tight junctions formed by adjacent sertoli cells are major component of blood testis barrier, which plays important roles in maintenance of microenvironment for spermagenesis in testis. Taken together, these results demonstrate that sertoli cells are susceptible to ZIKV infection, which results in the disruption of tight junctions in testis and causes abnormal spermatogenesis in mice. These results also imply that long-term impact of ZIKV infection on human male reproductive system requires close monitoring.

BackgroundIncreased vascular permeability is a hallmark feature in severe dengue virus (DV) infection, and dysfunction of endothelial cells has been speculated to contribute in the pathogenesis of dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). Rho-family GTPase Rac1 is a significant element of endothelial barrier function regulation and has been implicated in the regulation of actin remodeling and intercellular junction formation. Yet there is little evidence linking Rac1 GTPase to alteration in endothelial cell function induced by DV infection.Methods and FindingsHere, we showed that actin is essential for DV serotype 2 (DV2) entry into and release from ECV304 cells, and Rac1 signaling is involved these processes. At early infection, actin cytoskeleton rearranged significantly during 1 hour post infection, and disrupting actin filament dynamics with jasplakinolide or cytochalasin D reduced DV2 entry. DV2 entry induced reduction of Rac1 activity within 1 hour post infection. The expression of dominant-negative forms of Rac1 established that DV2 entry is negatively regulated by Rac1. At late infection, actin drugs also inhibited the DV2 release and induced accumulation of viral proteins in the cytoplasm. Meanwhile, the activity of Rac1 increased significantly with the progression of DV2 infection and was up-regulated in transfected cells expressing E protein. Confocal microscopy showed that DV2 E protein was closely associated with either actin or Rac1 in DV2-infected cells. The interaction between E protein and actin was further confirmed by co-immunoprecipitation assay.ConclusionsThese results defined roles for actin integrity in DV2 entry and release, and indicated evidence for the participation of Rac1 signaling pathways in DV2-induced actin reorganizations and E-actin interaction. Our results may provide further insight into the pathogenesis of DHF/DSS.

Recently, Zika virus (ZIKV) outbreak has been associated with a sharp increase in cases of Guillain–Barré syndrome and severe fetal abnormalities. However, the mechanism underlying the interaction of ZIKV with host cells is not yet clear. Axl, a receptor tyrosine kinase, is postulated as a receptor for ZIKV entry; however, its in vivo role during ZIKV infection and its impact on the outcome of the disease have not been fully characterized and evaluated. Moreover, there are contradictory results on its involvement in ZIKV infection. Here we utilized Axl-deficient mice (Axl−/−) and their littermates (Axl+/−) to study the in vivo role of Axl in ZIKV infection. Our results showed that both Axl+/− and Axl−/− suckling mice supported the replication of ZIKV and presented clinical manifestations. No significant difference has been found between Axl-deficient mice and their littermates in terms of the survival rate, clinical manifestations, viral load, ZIKV distribution and histopathological changes in major organs. These results therefore indicate that Axl is not an indispensable factor for ZIKV infection in mice.

Dengue viruses (DENVs) and Japanese encephalitis virus (JEV) are closely related mosquito-borne flaviviruses that cause very high global disease burdens. Although cross-reactivity and cross-protection within flaviviruses have been demonstrated, the effect of JEV vaccination on susceptibility to DENV infection has not been well elucidated. In this study, we found that vaccination with the JEV inactivated vaccine (INV) and live attenuated vaccine (LAV) could induce cross-immune responses and cross-protection against DENV1-4 in mice. Despite the theoretical risk of immune enhancement, no increased mortality was observed in our mouse model. Additionally, low but consistently detectable cross-neutralizing antibodies against DENV2 and DENV3 were also observed in the sera of JEV vaccine-immunized human donors. The results suggested that both JEV-LAV and JEV-INV could elicit strong cross-immunity and protection against DENVs, indicating that inoculation with JEV vaccines may influence the distribution of DENVs in co-circulated areas and that the cross-protection induced by JEV vaccines against DENVs might provide important information in terms of DENV prevention.