Defining the Role of Hsa21 Gene Overexpression in Aging-Associated and Aβ-Induced Neurodegeneration in C. elegans - PROJECT SUMMARY Down syndrome (DS), caused by an extra copy of chromosome 21 (Hsa21), is the most common genetic cause of intellectual disability and is also strongly linked to dementia. About 75% of DS individuals eventually develop Alzheimer’s disease (AD)-like symptoms, with amyloid-beta (Aβ) plaques emerging decades earlier than in typical AD patients. APP, an Hsa21 gene almost universally overexpressed in DS, has long been considered a key driver of these pathological changes. However, dementia onset varies widely, with some individuals developing symptoms in their 40s, while others remain unaffected into their 60s or beyond. Given that Hsa21 contains over 200 protein-coding genes, this variability suggests that genetic factors beyond APP may contribute to dementia risk and neurodegeneration progression in DS. Identifying these additional factors is crucial for understanding DS-AD pathogenesis and developing early interventions. While some Hsa21 genes have been linked to DS traits, a systematic mapping of most Hsa21 genes to DS phenotypes, especially aging- related, is lacking. Investigating numerous Hsa21 genes in mammalian models is particularly challenging due to time and cost constraints. To overcome this, we will leverage Caenorhabditis elegans as an efficient and genetically tractable in vivo system to study aging. Our preliminary investigation, based on existing genetic and functional data, identified that C. elegans have orthologs for over 50 Hsa21 genes, many of which are highly conserved in protein sequence and biological function. However, for most, their roles in neuronal health post- development remain unclear. This project will investigate how overexpression of Hsa21 orthologs affects neurodegeneration specifically during aging, using an integrated approach combining genetics, cell biology, biochemistry, and behavioral analysis. Overexpression will be induced via traditional transgenic approaches as well as CRISPR-based gene activation, the latter enabling controlled, physiologically relevant expression increases (~50%), similar to those seen in DS. Aim 1 will identify individual Hsa21 orthologs that accelerate or exacerbate neuronal aging using our well-characterized neurodegeneration models. We will also examine potential synergistic interactions among genes with highly correlated expression patterns in DS individuals, addressing whether combinatorial effects contribute to neurodegeneration progression. Recognizing that Aβ accumulation also occurs in healthy aging, Aim 2 will determine whether specific Hsa21 orthologs interact with Aβ to mediate neurotoxicity, using established C. elegans Aβ models. Successful completion of this project will identify key Hsa21 genes that contribute to neurodegeneration and generate a comprehensive set of relevant Hsa21 overexpression strains and reagents as a widely accessible resource for the research community. These findings and resources will facilitate future mechanistic studies and validation in mammalian systems, ultimately informing the development of preventive and therapeutic strategies to improve care for DS individuals, while also uncovering novel genetic factors potentially relevant to sporadic AD.
