Microglial MARCO facilitates Varicella zoster virus uptake and triggers TLR2-mediated neuroinflammation

Varicella zoster virus (VZV) is a human neurotropic virus that can establish latency in sensory neurons. Microglia play a complex role during neurotropic virus infections; however, their role during VZV infection remains to be determined. In the present study, we explored the role of VZV-induced alterations in the morphodynamics and function of microglia in triggering neuroinflammation.

We prepared cell-free VZV and compared replication efficiencies of wild-type (YC01) and attenuated (MAV/06, MAV) VZV in two transformed human microglial cell lines (HMC3 and HIM) and human embryonic stem cell (ESC)-derived microglia (ESC-MG). Bulk RNA sequencing was used to assess molecular signatures of microglia following VZV infection in ESC-MG, and cytokine profiles were determined to further investigate neuroinflammation. To further examine the impact of VZV-induced microglial inflammation on neuronal responses, we generated ESC-derived sensory neurons (ESC-SN) and evaluated nociceptor expression and calcium flux as a readout for SN activities following microglial secretome treatment.

VZV upregulates its gene and protein expression and triggered morphological changes in various microglia cultures. Transcriptomic analysis of YC01-infected ESC-MG revealed a robust induction of genes associated with antiviral innate immunity, alongside a pronounced upregulation of macrophage receptor with collagenous structure (MARCO). Functional studies demonstrated that MARCO facilitates VZV uptake in microglia by binding to the viral glycoprotein E (gE) via its C-terminal scavenger receptor cysteine-rich (SRCR) domain, thereby promoting viral entry and phagocytosis. Moreover, VZV infection elicited neuroinflammation in an ORF62-dependent manner, while MARCO activation triggered toll-like receptor 2 (TLR2)-mediated inflammatory signaling. This cascade further amplified the expression of pain-associated molecular mediators in an ESC-SN model, highlighting a potential mechanistic link between microglial MARCO and VZV-triggered neuropathic processes.

Our results show, for the first time, that microglia are susceptible to VZV infection and identify MARCO as an important mediator for regulating TLR2-mediated neuroinflammation and promoting an upregulation of factors associated with neuropathic pain.