Investigating Complement Component 3a Signaling in Viral Neuroinflammatory Responses.

Project Summary The goal of this proposal is to determine the role of complement in West Nile neuroinvasive disease (WNND). West Nile virus (WNV) is the most common mosquito born virus in the United States 1. Infected individuals can experience febrile illness and approximately 1 out of 150 WNV infected individuals develop severe neuro-inva- sive disease (meningitis, encephalitis, acute flaccid paralysis) 54. In addition to the acute neuroinvasive syn- dromes patients that recover from WNND may also experience significant cognitive dysfunction, high rates of memory impairment and difficulties in executive function 2-11. Complement proteins are ancient components of innate immunity that have emerged as critical regulators of neural networks. Complement proteins are classically thought of as peripheral proteins, produced in the liver, circulating in the bloodstream, and activated upon challenge by pathogens in order to induce chemotaxis, opso- nization and lysis that results in removal of pathogens 28. Since discovery of central nervous system (CNS) pro- duction of complement and complement-mediated synaptic pruning 29,56, complement proteins have been impli- cated in several neurological diseases 12-17, suggesting there are generalizable mechanisms that contribute to diseases of cognitive impairment. Complement component 3a receptor (C3aR) is a G protein coupled receptor present on antigen presenting cells, that aids in the recruitment of immune cells to sites of infection 28. The re- ceptor has been shown to be upregulated on infiltrating immune cells and microglia (the resident immune cell of the brain) during CNS inflammatory states 18-23. Our laboratory has demonstrated a role for C3aR in elimination of presynaptic termini within the hippocampus, a key brain region involved in spatial learning 24. In a murine model of WNND, we found that loss of C3aR leads to decreased engulfment of presynaptic material by activated mi- croglia at 7 days post infection (dpi) 24. Still, there remains questions as to whether complement proteins are neuroprotective or induce a damaging inflammatory response. Studying the cascade in the context of WNND and uncovering the mechanism behind complement mediated neuroinflammation and synaptic elimination will lead to the discovery of therapeutic targets as well as offer insight into complements role in CNS disease states. This study will utilize experiments to analyze inflammatory infiltrates, T cell-microglial interactions, and microglial activation in C3aR knock-out (C3ar-/-) animals, and to analyze C3aR mediated deficits in spatial learn- ing and memory and neural correlates of learning. Completion of this study will define the roles of C3aR in acute neuroinflammation, synapse elimination, and cognitive impairment during WNND.