Infection and injury of human astrocytes by tick-borne encephalitis virus

Abstract

Tick-borne encephalitis (TBE), a disease caused by tick-borne encephalitis virus (TBEV), represents the most important flaviviral neural infection in Europe and north-eastern Asia. In the central nervous system (CNS), neurons are the primary target for TBEV infection; however, infection of non-neuronal CNS cells, such as astrocytes, is not well understood. In this study, we investigated the interaction between TBEV and primary human astrocytes. We report for the first time, to the best of our knowledge, that primary human astrocytes are sensitive to TBEV infection, although the infection did not affect their viability. The infection induced a marked increase in the expression of glial fibrillary acidic protein, a marker of astrocyte activation. In addition, expression of matrix metalloproteinase 9 and several key pro-inflammatory cytokines/chemokines (e.g. tumour necrosis factor a, interferon a, interleukin (IL)-1b, IL-6, IL-8, interferon c-induced protein 10, macrophage inflammatory protein, but not monocyte chemotactic protein 1) was upregulated. Moreover, we present a detailed description of morphological changes in TBEV-infected cells, as investigated using three-dimensional electron tomography. Several novel ultrastructural changes were observed, including the formation of unique tubule-like structures of 17.9 ±0.15 nm diameter with associated viral particles and/or virus-induced vesicles and located in the rough endoplasmic reticulum of the TBEV-infected cells. This is the first demonstration that TBEV infection activates primary human astrocytes. The infected astrocytes might be a potential source of pro-inflammatory cytokines in the TBEV-infected brain, and might contribute to the TBEVinduced neurotoxicity and blood-brain barrier breakdown that occurs during TBE. The neuropathological significance of our observations is also discussed.

Electron Tomography Analysis of Tick-Borne Encephalitis Virus Infection in Human Neurons

“…3B,4A–D). Similar structures were previously demonstrated in the RER of other vertebrate or arthropod cells infected with TBEV19, Langat virus20, and mosquito-borne flaviviruses162122. In a previous study, we observed virus-induced vesicles and viral particles directly attached to tubule-like structures in the RER of TBEV-infected human primary astrocytes19.…”

“…Previous studies reported tubule-like structures that ranged from 50 to 100 nm in diameter and from 100 nm to 3.5 μm in length20212223. In TBEV-infected human astrocytes, we previously observed tubule-like structures of 17.9 nm (±0.2 nm) in diameter19. The function of tubule-like structures is not clear.…”

Encephalitic Arboviruses: Emergence, Clinical Presentation, and Neuropathogenesis

“…Consistent with this, it has been shown that increased expression of TNF-α after infection with WNV and JEV is correlated with neuronal death [154,195], and that neutralizing antibodies specific for IL-1β and TNF-α protected neurons from WNV-induced cell death [195]. The release of inflammatory cytokines by neurons can trigger gliosis (i.e., microglial and astrocyte activation), which is one of the major hallmarks of arboviral neuropathogenesis [154,186,198].…”

“…Activated astrocytes and microglia play an important role in inflammatory responses during natural infection with encephalitic flaviviruses, namely JEV [200], WNV [201], and TBEV [198], as well as encephalitic alphaviruses [186]. Upon activation, astrocytes and microglia release several chemokines and cytokines such as TNF-α, IL-6, C-X-C motif chemokine ligand (CXCL)10, chemokine (C-C motif) ligand 2, monocyte chemoattractant protein-1, RANTES, IFN-γ-induced protein 10, and matrix metalloproteinases [154,195,[202][203][204].…”

Prevalence of Neurotropic Viruses in Malignant Glioma and Their Onco-Modulatory Potential

“…In the present study, human enteroviruses (hEV) and tick-borne encephalitis virus (TBEV) were included, as they are both neurotropic, although not oncogenic, in order to define their possible association with brain tumours. TBEV can cause the relatively common flaviviral infection in Europe, including Slovenia (32), and Palus et al (33) reported on the link between TBEV infection and astrocyte injury. Taken together, the presence of this plethora of viruses in glioma, their carcinogenic activities, and their roles in glioma progression all remain unclear.…”