siRNA-mediated Knockdown of INPP5D to Modulate Microglia Activity for the Treatment of Alzheimer's Disease

ABSTRACT Alzheimer's disease (AD) is a progressive and fatal neurodegenerative disorder characterized by β-amyloid (Aβ) plaques, neurofibrillary tau tangles (NFTs), and cognitive decline. Despite recent approvals of anti-amyloid antibodies, there remains a significant unmet need for more effective, safer, and more convenient therapeutics. Recent human genetic evidence highlights the critical role of microglia in AD etiology. INPP5D, identified as a risk gene for AD, encodes SHIP1, a phosphatase that regulates pathways downstream of immune receptors like TREM2 expressed on microglia. Our research has shown a positive correlation between INPP5D levels and Aβ plaques in human AD cases, findings that we replicated in an amyloidosis mouse model of AD. Additionally, we demonstrated that reduced Inpp5d expression improves cognition, reduces plaque burden, and lowers cytokine levels in this mouse model of AD. We have developed and validated a library of fully modified oligonucleotides optimized for broad and efficient RNAi knockdown of INPP5D. Our long-term goal is to slow or halt AD progression by modifying microglial function through siRNA-mediated knockdown of INPP5D. However, various transcriptional isoforms of Inpp5d identified in mouse models of AD have complicated efforts to validate INPP5D as a therapeutic target. To address this gap in knowledge, we will identify and characterize Inpp5d transcriptional variants in murine cellular and animal models using genetic analysis tools. In parallel, we will design and validate self-delivering siRNA oligonucleotides, suitable for animal studies, that efficiently and specifically knockdown Inpp5d isoforms in mouse microglia. These siRNAs will be tested in AD mouse models to demonstrate that Inpp5d knockdown shifts microglial states, reduces Aβ plaque levels and cytokines, and promotes a resilient brain resistant to neurodegeneration. Ultimately, by validating INPP5D as a therapeutic target with an siRNA design suitable for clinical studies, we aim to shift microglial states in humans into an overall protective phenotype that clears harmful proteins and supports brain health, potentially leading to a new treatment that harnesses the brain's immune cells to resist neurodegeneration and offer hope to patients affected by this debilitating disease.