Role of RIPK2 in the neuroinflammatory response to ischemic stroke

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Abstract Neuroinflammation after stroke significantly contributes to neuronal damage and neurological impairment. Delayed cell death in the ischemic penumbra is associated with glial activation and recruitment and infiltration of peripheral immune cells to the brain. This is triggered by the production of pro-inflammatory cytokines and chemokines, contributing to cell death and blood-brain barrier (BBB) permeability after stroke. Dying cells in the penumbra also release pro-inflammatory signals and damage-associated molecular patterns (DAMPs) that activate resident microglia toward a pro-inflammatory phenotype, thus further contributing to brain injury. Our overall goal is to reduce the spread of stroke damage by limiting neuroinflammation. Receptor interacting serine/threonine protein kinase 2 (RIPK2) is a critical mediator of inflammation via its activation of multiple pro-inflammatory and cell death pathways. Inhibition of RIPK2’s kinase activity abolishes its signaling to alleviate inflammatory conditions in the periphery. The role of RIPK2 in ischemic stroke remains unexplored; however, our pilot data shows a substantial reduction in infarct size and improvement in post-stroke functional outcomes, both acutely and long-term, in Ripk2 knockout (Ripk2-/-) mice compared to wild-type (Ripk2+/+) mice. We propose that RIPK2 is an essential initiator and propagator of pro-inflammatory pathways in ischemic stroke. Our main objective is to attenuate its activity and assess the specific role of RIPK2 in vivo as it relates to stroke pathology. We hypothesize that RIPK2 signaling is detrimental in ischemic stroke, and RIPK2 degradation/inhibition or selective ablation in myeloid cells will improve outcomes. Aim 1 will determine the neuroprotective effect of RIPK2 blockade after ischemia using a highly selective RIPK2 inhibitor and a proteolysis-targeting chimera (PROTAC) that specifically degrades RIPK2 in vivo. We will utilize aged mice of both sexes subjected to ischemic stroke and investigate the effects of RIPK2 blockade on infarct size and long-term behavioral outcomes. In Aim 2, we will determine the impact of RIPK2 blockade on stroke-induced neuroinflammation and investigate neuroprotection mechanisms. In Aim 3, we will dissect the cell-specific role of RIPK2 in the neuroinflammatory process after stroke by using Ripk2 floxed mice crossed with lines producing Cre recombinase in specific cell types. We will study the contribution of RIPK2 from myeloid- lineage cells and brain-resident microglia to stroke injury. This project will leverage our expertise and unique tools (Ripk2 floxed mice, PROTAC, and selective inhibitors) to understand the mechanisms of RIPK2-driven inflammation in the context of ischemic stroke. This research may lead to identifying RIPK2 as a new therapeutic target to block neuroinflammation and promote neuronal survival in the aftermath of an ischemic stroke.