Characterization of AD-related endolysosomal dysfunction in human neural cells

Project Summary Alzheimer’s disease (AD) is a major leading cause of death in the developed world and there are few preventative or disease-modifying treatments. Genetics and cell biology point to deficiencies in the endo-lysosomal network as a driving factor in AD pathogenesis. Therefore, this proposal is in response to NOSI (NOT-AG-21-034): Genetic Underpinnings of Endosomal Trafficking as a Pathological Hub in AD/ADRD. We will use human induced pluripotent cell lines (hiPSC) and patient tissue to define how endo-lysosomal dysfunction impacts cell- type specific functions and how high genetic burden of risk in endo-lysosomal pathways manifests in the AD brain. In Aims 1 and 2 we will perform experiments in neurons and microglia harboring AD-associated variants in the endosomal gene SORL1. SORL1 is a highly pathogenic AD risk gene and mutations in SORL1 that lead to haploinsufficiency are considered causal for AD. SORL1 is also a strong risk factor late onset AD. The protein product of the SORL1 gene, SORL1/SORLA interacts with the multi-protein sorting complex retromer to traffic various cargo essential for cellular function. Understanding the impact of SORL1-retromer trafficking in diverse cell types of the central nervous system is essential to determine whether this is a valid therapeutic pathway. We will differentiate neurons and microglia from hiPSCs harboring AD-associated variants in SORL1, along with isogenic controls. In these cells we will perform assays to specifically interrogate neuronal and microglial functions that rely on efficient endo-lysosomal trafficking. For neurons we will test neuronal synaptic function and analysis of protein-protein interactions at the neuronal synapse. For microglia we will test phagocytosis, lysosomal degradation, receptor recycling and cytokine levels. In both cell types, we will test whether aberrant phenotypes can be rescued by using small molecules that enhance retromer function and by genetically expressing specific components of the SORL1-retromer pathway. For Aim 3 we have also generated a cohort of patient-derived hiPSC lines from late onset AD subjects and controls and matched brain tissue stratified by polygenic risk in the endo-lysosomal network (ePRS). We will analyze endo-lysosomal phenotypes in brain tissue as well as in neural cells differentiated from the matched hiPSC lines. We will test whether rescue of ELN trafficking via the SORL1-retromer pathway will also be beneficial in these cell lines. These experiments will significantly advance knowledge in this area by generating patient-specific data on global gene expression and morphology in a cohort representative of the genomes of at- risk individuals. These experiments will also be critical in determining whether this pathway can be a strong target for AD therapeutic development.