Unraveling microglial NOD2/RIPK2 signaling: Implications for neuroinflammation and neurodegeneration in Alzheimer's disease

Johns Hopkins University, Baltimore MD

Investigators

Abstract

PROJECT SUMMARY Neuroinflammation, particularly triggered by amyloid-β (Aβ) aggregates, plays a pivotal role in Alzheimer’s disease (AD) pathophysiology. Despite significant research, the precise mechanisms underlying Aβ oligomer (Aβo)-induced microglial activation and neurotoxicity remain elusive. Our study aimed to fill this gap by investigating the involvement of the NOD2/RIPK2 signaling pathway in neuroinflammation and neurodegeneration in AD. Utilizing Stable Isotope Labeling with Amino acids in Cell culture (SILAC) combined proteome analysis, we identified RIPK2 as a key mediator of Aβo-induced microglial activation. We observed substantial accumulation of NOD2 and RIPK2 proteins in the hippocampal tissues of AD patients, supporting their pathological relevance. Furthermore, we demonstrated the interaction between Aβo and NOD2 leading to NOD2/RIPK2-mediated neuroinflammatory responses via MAPK and NF-kB activation in microglia. Building on these findings, our study aims to characterize the role of NOD2/RIPK2 signaling in AD and explore its therapeutic potential through molecular and biophysical assessments. Additionally, we will investigate the effects of selectively removing microglial NOD2 and RIPK2 and pharmacologically inhibiting RIPK2 on Aβo-induced pathology, neuroinflammation, and neurodegeneration in AD mouse models. These insights could pave the way for novel AD treatments targeting microglial NOD2/RIPK2 signaling. In Aim 1: To elucidate the mechanisms driving microglial activation by Aβo and assess the involvement of NOD2/RIPK2 signaling, we will conduct detailed molecular and biophysics analyses. Our preliminary findings indicate significant NOD2 and RIPK2 accumulation in the hippocampus of AD postmortem tissues, suggesting their role in Aβo-induced microglial activation. We will explore the binding kinetics and domain in Aβo-NOD2 interaction and its downstream effects on microglial activation pathways, including RIPK2-mediated ubiquitination and NF-kB activation. In Aim 2: To determine the impact of selectively removing microglial NOD2/RIPK2 signaling on microglia activation and neurodegeneration in AD, we will utilize genetically modified AD mouse models. By generating 5xTg mice with microglia-specific NOD2 or RIPK2 depletion, we aim to assess their specific contributions to Aβo-induced pathology. Behavioral tests, plaque assays, synaptic dysfunction analysis, gliosis evaluation, neuronal loss assessment, and characterization of disease-associated microglia populations will be conducted at 8 months to comprehensively evaluate neurodegenerative changes. In Aim 3: Building on our promising findings with the RIPK2 inhibitor CMPD0673, we will investigate its neuroprotective effects in AD. Oral administration of CMPD0673 to 5xTg mice will be conducted for 4 months, followed by comprehensive assessments at 8 months. Behavioral tests, plaque assays, synaptic function analysis, gliosis evaluation, neuronal loss assessment, and characterization of disease-associated microglia populations will be performed to evaluate the efficacy of RIPK2 inhibition as a potential therapeutic strategy for AD and related dementias.