Kariwa, H. | Search bioRxiv

bioRxiv2026

Interleukin-34 Promotes Activation of Disease-associated Microglia-like Cells and Attenuates Disease Progression in West Nile Virus Infection

West Nile virus (WNV) is a mosquito-borne orthoflavivirus that causes severe encephalitis, for which no approved antiviral therapies or human vaccines are currently available. Disease-associated microglia (DAM) represent a microglial state associated with neuroprotective functions in neurodegenerative diseases. We previously showed that DAM-like cells are localized in the vicinity of WNV-infected cells in the mouse brain and surmised that these cells may respond to WNV-infected cells. However, the functional significance of this spatial association has since remained unclear. Given the previous reports linking interleukin-34 (IL-34) to the activation of DAM-like cells, we investigated whether IL-34 promotes DAM-like responses and whether these responses are associated with protection against WNV infection. Transcriptomic analysis of IL-34-treated HMC3 human microglial cells revealed upregulation of markers characteristic of DAM, including TREM2, APOE, FABP5, and FTH1. IL-34-treated HMC3 cells suppressed WNV replication in co-culture with WNV-infected SH-SY5Y human neuroblastoma cells apparently in a cell-cell contact-dependent manner, independent of secreted factors. In WNV-infected mice, IL-34 administration improved survival, reduced viral titers, and decreased neuronal apoptosis. IL-34 also increased the abundance of CD11c- and SPP1-positive DAM-like cells, predominantly in the vicinity of WNV-infected cells, in the mouse brain. These findings indicate that IL-34 promotes the activation of DAM-like cells and enhances protective responses in WNV encephalitis. IMPORTANCEWest Nile virus (WNV) is a major cause of viral encephalitis worldwide, with no approved antiviral treatment or human vaccine currently available. Microglia, the resident immune cells of the brain, play key roles in responding to viral infection. However, the mechanism through which specific microglial activation states contribute to protection in viral encephalitis remains poorly understood. In this study, we show that interleukin-34 promotes microglial responses resembling disease-associated microglia (DAM) and is associated with enhanced protection against WNV infection in cell culture and mouse models. The study findings suggest that activation of DAM-like cells may contribute to protective host responses against neurotropic viral infection and provide new insights into the role of specific microglial states in viral encephalitis.

microbiology↗

bioRxiv2026

West Nile virus capsid protein promotes viral replication and pathogenesis through PKCα-dependent lamin phosphorylation and nuclear deformation

The genus Orthoflavivirus comprises several medically important pathogens such as the West Nile virus (WNV), which causes encephalitis in humans. Although viral replication occurs in the cytoplasm, the capsid (C) protein of the orthoflavivirus is localized to both the cytoplasm and nucleus. Nuclear C protein contributes to viral replication and disease progression. However, the underlying mechanisms remain unclear. Here, we investigated whether the WNV C protein induces nuclear deformation and examined the underlying mechanism. We also assessed the contribution of this deformation to viral replication and pathogenesis. WNV infection and C protein expression induced morphological alterations in the nuclear lamina, leading to nuclear deformation. C protein expression enhanced lamin phosphorylation and the disassembly of the polymerized lamin network. In addition, C protein interacted with protein kinase C alpha (PKC) and localized PKC near the nuclear lamina. Downregulation of PKC expression inhibited C protein-induced lamin phosphorylation and nuclear deformation. In addition, both the downregulation of PKC expression and pharmacological inhibition of PKC reduced WNV replication. In contrast, the expression of phosphorylation-deficient lamin mutants attenuated the inhibitory effect of downregulated PKC expression on WNV replication. Furthermore, the pharmacological inhibition of PKC increased the survival rate of WNV-infected mice and suppressed both viral replication and nuclear deformation in the brain. Collectively, these results demonstrate that C protein remodels the nuclear lamina architecture through the PKC-lamin pathway, and that virus-induced nuclear deformation contributes to WNV replication and pathogenesis. Author summaryThe West Nile virus (WNV), a neurotropic orthoflavivirus, causes severe neurological diseases in humans. In host cells, orthoflaviviruses exclusively replicate in the cytoplasm. However, their capsid (C) proteins are localized to both the nucleus and cytoplasm. Although the nuclear C protein has been implicated in viral replication and disease progression, its underlying mechanisms remain unclear. Here, we demonstrate that the WNV C protein induces nuclear deformation, accompanied by the phosphorylation of lamin and disassembly of the nuclear lamina, a structural scaffold that maintains the nuclear shape. The C protein promotes the localization of PKC, a host kinase protein, near the nuclear lamina. Suppression of PKC expression or activity reduces lamin phosphorylation, nuclear deformation, and WNV replication. Importantly, pharmacological inhibition of PKC in WNV-infected mice reduced nuclear deformation and viral replication in the brain and improved survival rates. Collectively, our findings identify the host nucleus as an important site of WNV-host interaction and provide a new perspective that WNV, despite replicating in the cytoplasm, remodels host nuclear architecture to promote viral replication and pathogenesis.

microbiology↗