in vivo CRISPR screen identifies novel regulators of microglia state in Alzheimer’s disease 9094

Abstract Description Genome-wide association studies (GWAS) in Alzheimer’s disease (AD) have identified over 200 diseased-associated genes that are predominantly expressed in microglia. While these studies implicate microglia in AD pathogenesis, the intrinsic role of AD risk genes in regulating microglia phenotype and function is unknown. Recent work has shown that microglia acquire a protective Disease-associated state, also known as DAM/MGnD when associated with Aβ-plaques. To identify how these GWAS-associated genes may regulate DAM/MGnD state, we developed an in vivo CRISPR screen that ex vivo introduces pools of sgRNAs into CAS9-GFP donor stem cells before intrathecal injecting these cells into P2-P4 5xFAD pups lacking microglia. After two months, these perturbed cells differentiated into functional microglia and completely repopulated the CNS, providing us with an ideal system to interrogate microglial biology in AD at scale. Our screen identified regulators of DAM/MGnD state, notably highlighting the known role of Tgfbr1, Mertk and Clec7a as potent inducers of this phenotype. Genetic deletion of Tim3, an immune checkpoint and recently identified AD-GWAS hit, showed a major effect in inducing a partial DAM/MGnD phenotype with reduction in plaque load and increase in synapse density. These studied validate our perturbation platform and provide a means by which to identify the role of other GWAS hits in microglial development and function in vivo. Topic Categories Neuroimmunology (NEUR)