Pathological modeling of TBEV infection reveals differential innate immune responses in human neurons and astrocytes that correlate with their susceptibility to infection

Abstract

Tick-borne encephalitis virus (TBEV) is a member of the Flaviviridae family, Flavivirus genus, which includes several important human pathogens. It is responsible for neurological symptoms that may cause permanent disability or death, and, from a medical point of view, is the major arbovirus in Central/Northern Europe and North-eastern Asia. TBEV tropism is critical for neuropathogenesis, yet, little is known about the molecular mechanisms that govern the susceptibility of human brain cells to the virus. In this study, we sought to establish and characterize a new in vitro model of TBEV infection in the human brain and to decipher cell type-specific innate immunity and its relation to TBEV tropism and neuropathogenesis. We showed that infection of neuronal/glial cultures derived from human fetal neural progenitor cells (hNPCs) mimicked three major hallmarks of TBEV infection in the human brain, namely, preferential neuronal tropism, neuronal death and astrogliosis. We also showed that these cells had conserved their capacity to build an antiviral response against TBEV. TBEV-infected neuronal/glial cells, therefore, represented a highly relevant pathological model. By enriching the cultures in either human neurons or astrocytes, we further demonstrated qualitative and quantitative differential innate immune responses in the two cell types that correlated with their particular susceptibility to TBEV. Our results thus reveal that cell type-specific innate immunity is likely to contribute to shaping TBEV tropism for human brain cells. They offer a new in vitro model to further study TBEV-induced neuropathogenesis and improve our understanding of the mechanisms by which neurotropic viruses target and damage human brain cells.Author summaryTick-borne encephalitis virus (TBEV), a neurotropic Flavivirus that is responsible for encephalitis in humans, is of growing concern in Europe. Indeed, over the last two decades the number of reported cases has continuously increased and the virus has spread into new geographical areas. Whereas it is well established that neurons are the main target of TBEV in the human brain, the mechanisms that underlie this preferential tropism have not yet been elucidated. Here, we used neuronal/glial cells derived from human fetal neural progenitors to establish and characterize a new in vitro pathological model that mimics major hallmarks of TBEV infection in vivo; namely, neuronal tropism, neuronal death and astrogliosis. Using this highly relevant model, we showed that human neurons and astrocytes were both capable of developing an innate immune response against TBEV, but with dissimilar magnitudes that correlated with differential susceptibility to TBEV. Our results thus revealed that TBEV tropism for subsets of human brain cells is likely to depend on cell-type specific innate immunity. This improves our understanding of the mechanisms by which neurotropic viruses target and damage human brain cells and may help guide development of future therapies.

Sequential MAVS- and MyD88/TRIF-signaling triggers anti-viral responses of tick-borne encephalitis virus-infected murine astrocytes

“…al. showed that at early stages of the infection human TBEV infected astrocytes show TLR3 expression that is close to basal levels, whereas at 24 hpi TLR3 expression is significantly enhanced (57). We also observed induction of TLR3 upon infection of both, WT and MAVS ko astrocytes.…”

“…During TBEV infection of human astrocytes, the RLRs RIG-I and MDA5, but not TLR3, sense TBEV NS5 and activate IRF-3 signaling, which leads to the production of CCL5 (58). A recent study analyzing RNA expression profiles of TBEV infected human neuro-glia cultures, i.e., neuron and astrocyte cocultures, showed that in astrocytes the transcripts of Ddx58, Oas2, IFN-β, Mx1, Trim5a and Rasd2 were even more abundantly induced than in neurons (57). We also observed upregulation of these transcripts in TBEV infected WT astrocytes, whereas in MAVS ko astrocytes the induction of the respective transcripts was significantly decreased.…”

Sequential MAVS and MyD88/TRIF signaling triggers anti‐viral responses of tick‐borne encephalitis virus‐infected murine astrocytes

“…During TBEV infection of human astrocytes, the RLRs RIG‐I and MDA5, but not TLR3, sense TBEV NS5 and activate IRF‐3 signaling, which leads to the production of CCL5 (Zheng et al, 2018). A recent study analyzing RNA expression profiles of TBEV‐infected human neuro‐glia cultures, that is, neuron and astrocyte cocultures, showed that in astrocytes the transcripts of Ddx58, Oas2, IFN‐ β , Mx1, Trim5a , and Rasd2 were even more abundantly induced than in neurons (Fares et al., 2020). We also observed upregulation of these transcripts in TBEV‐infected WT astrocytes, whereas in MAVS ko astrocytes the induction of the respective transcripts was significantly decreased.…”

“…Fares et al showed that at early stages of the infection, human TBEV‐infected astrocytes show TLR3 expression that is close to basal levels, whereas at 24 hpi TLR3 expression is significantly enhanced (Fares et al., 2020). We also observed induction of TLR3 upon infection of both, WT and MAVS ko astrocytes.…”

“…While neurons were more susceptible to the infection and showed reduced immune responsiveness, astrocytes were more resistant to the infection and mounted stronger anti‐viral responses. Moreover, astrocytes contributed to neuronal protection against TBEV infection (Fares et al., 2020; Pokorna Formanova et al., 2019). During TBEV infection of human astrocytes, the RLRs RIG‐I and MDA5, but not TLR3, sense TBEV NS5 and activate IRF‐3 signaling, which leads to the production of CCL5 (Zheng et al, 2018).…”