A myeloid trisomy 21-associated gene variant is protective from Alzheimer's disease [WGS]

While challenging, identifying individuals displaying resilience to Alzheimer's disease (AD) and understanding the underlying mechanism holds great promise for the development of new therapeutic interventions to effectively treat AD. Recent studies indicate that somatic mutations in hematopoietic cells may lead to both the instigation and resilience to neurodegeneration. Down syndrome (DS), or trisomy 21, is the most significant genetic risk factor for AD. Interestingly, some DS individuals show resilience to AD neuropathology and do not exhibit dementia signs. Notably, DS individuals face a heightened risk of myeloid leukemia due to somatic mutations in hematopoietic cells. Microglia dysfunction is a central mechanism in AD etiology. Here we hypothesize that somatic mutations associated with DS myeloid leukemia may impart resilience to microglia against AD. Using CRISPR-Cas9 gene editing, we introduce a DS-linked hotspot CSF2RB A455D mutation into human pluripotent stem cell (hPSC) lines derived from both DS and healthy individuals. Employing hPSC-based in vitro microglia culture and in vivo human microglia chimeric mouse brain models, we show that in response to pathological tau, the CSF2RB A455D mutation suppresses type-1 interferon signaling in both DS and control human microglia, independent of trisomy 21 genetic background. This mutation also reduces neuroinflammation and enhances phagocytic and autophagy functions, ameliorating senescent and dystrophic changes in human microglia. Furthermore, the CSF2RB A455D mutation promotes the development of a microglia subcluster with tissue repair properties. Importantly, human microglia carrying CSF2RB A455D provide protection to neuronal function, such as neurogenesis and synaptic plasticity. When co-transplanted into the same mouse brains, human microglia with CSF2RB A455D mutation phagocytize, outcompete, and gradually replace human microglia carrying the wildtype CSF2RB gene following pathological tau treatment. Our findings suggest the potential use of hPSC-derived CSF2RB A455D microglia to develop effective microglial replacement therapy for AD and other age-related neurodegenerative diseases, even without the need of depleting endogenous senescent microglia prior to cell transplantation. Overall design: To accurately assign cell identities in the CAGG-WT and Cont-A455D microglia co-transplanted scRNA-seq samples, we conducted whole genome sequencing (WGS) on their respective pluripotent stem cell lines. Single nucleotide polymorphisms (SNPs) were identified from the aligned WGS data and used to assign identities to individual cells.