Summary/Abstract Down Syndrome (DS) affects over 200,000 individuals in the United States and is the most common genetic cause of intellectual and developmental disabilities in children and young adults. Down Syndrome arises from an extra third copy of chromosome 21, encompassing over 200 genes, which leads to genome wide transcriptional disruption. The brain cell-type specific contribution to DS neurodevelopmental deficits and the interaction between cognitive and immune dysfunction in DS are poorly understood. DS has been difficult to model due to limitations in murine orthologs and inadequacies of in vitro systems in modeling complex cellular interactions. Microglial pathology has been identified in individuals with DS, but the extent to which microglial dystrophy contributes to neurodevelopmental deficits is unknown. There is increasing evidence for the impact of microglia on brain development and microglia have been suggested as a novel therapeutic target in DS. This proposal is built around the central hypothesis that trisomy 21 causes microglial dysfunction and thereby contributes to the pathogenesis of intellectual and developmental disability in DS. Motivated by our strong preliminary data that in vitro microglia exhibit altered gene expression and functional phenotypes in neurodegenerative diseases and psychiatric disorders, we developed novel organoid microglia cocultures and a chimeric human microglia mouse model, whereby 80% of microglia are human in origin. Here we apply innovative in vitro and in vivo methods to ascertain the contribution of human DS microglia in neurodevelopment, neuronal function, and cognition. The project goal is to test the hypothesis that isolated trisomy 21 in human microglia and microglia-cerebral organoid cocultures in vitro (Aim 1) and in a xenotransplantation model of human microglia in vivo (Aim 2) results in microglial pathology, neuropathological defects, and behavioral deficits. Delineating genome wide transcriptional disruption and genome wide reorganization will uncover DS associated transcriptional dysregulation and expand our knowledge of DS associated genes. The long-term goal is to generate and validate in vitro and in vivo DS microglial models that can be employed for drug screening and to generate preclinical data. A deeper understanding of the contribution and molecular regulation of microglia in DS will lay the groundwork to ultimately identify novel potential therapeutic targets to improve the outcomes for individuals with DS.

Narrative Down Syndrome is primarily caused by trisomy of chromosome 21, resulting in an extra copy of over 200 genes and significant intellectual and developmental disability. Generating translational models and identifying the brain cell type specific contribution to Down Syndrome pathophysiology has been difficult and has hampered development and screening of new treatments. This project is relevant to the NIH’s mission to enhance life and reduce disability, aiming to understand how human microglia contribute to the neurodevelopmental pathogenesis of Down Syndrome with a goal of identifying novel treatment targets and screening methodologies.