RIP3 mediated restriction of neuropathogenesis during viral encephalitis

Receptor interacting protein kinase-3 (RIPK3) has been extensively characterized in vitro as the key initiator of necroptosis, a non-apoptotic form of programmed cell death1. However, the physiological role of necroptosis, and by extension of RIPK3, has remained elusive2. The goal of this proposal is to uncover novel functions for RIPK3 signaling in the central nervous system (CNS) and to define the unique nature of RIPK3 signaling in this tissue. In pursuit of this, we will assess the role of RIPK3 in mediating neuroprotective responses to Zika virus (ZIKV) infection, as well as establish the nature of cell-specific transcriptional programs engaged by RIPK3 signaling in the CNS. As opposed to canonical apoptosis, necroptosis is highly immunogenic and has been shown contribute to antiviral responses to diverse viruses3-5. However, emerging evidence also suggests that RIPK3 can induce inflammatory gene expression through signaling pathways that are independent of its canonical role in cell death6-9. Our recent study (in revision) identified a death-independent role for RIPK3 in coordinating protective neuroinflammation during WNV encephalitis. However, the unique features of this unexpected signaling program in the CNS have not yet been fully defined. Moreover, the potential for RIPK3 to promote protective responses to other neuroinvasive infections of global concern is unknown. Since its recent introduction to the Western hemisphere, ZIKV infection has become a significant threat to public health10. Among the outcomes of ZIKV infection are severe birth abnormalities characterized by neuropathological damage during development followed by lifelong functional and cognitive impairments10,11. Though rare, symptomatic infections in adults can lead to chronic neuropathy and potentially fatal meningoencephalitis12. In the absence of any approved vaccines or disease-specific therapies, there is an urgent need to identify host factors that contribute to disease pathogenesis and protection during neuroinvasive ZIKV infection13. In preliminary studies, we demonstrate that RIPK3 is a critical host factor in the restriction of ZIKV pathogenesis, as Ripk3-/- mice exhibit ascending motor impairments and increased viral burden in the spinal cord compared to WT controls. In in vitro studies, we observed a unique induction of inflammatory chemokine expression that was dependent on the kinase activities of both RIPK1 and RIPK3. However, this signaling appeared unique to neurons and did not occur in either peripheral or resident CNS myeloid cells, suggesting that RIPK3 engagement may have different functional outcomes in CNS cells of distinct developmental ontogenies. In these proposed studies, we will define cell- and lineage-specific functions for RIPK3 signaling in the CNS, and establish how these functions coordinate neuroprotective responses to ZIKV infection.