Functional Analysis of Late-Onset Alzheimer's Disease Risk Genes in Caenorhabditis elegans Identifies Regulators of Neuronal Aging.

Abstract

Genome-wide studies in late-onset Alzheimer's disease (LOAD) have uncovered many risk loci, yet identifying the causal genes and clarifying how these genetic signals connect to molecular and cellular mechanisms relevant to AD pathogenesis in vivo remains challenging. Using Caenorhabditis elegans as a model to identify LOAD-associated genes that drive neurodegenerative processes, we focused on 14 understudied genes and their homologs: ABI3/abi-1 , B4GALT3/bre-4 , CCDC6/T09B9.4 , CLPTM1 (two homologs C36B7.6 and R166.2 ), CNN2/cpn-2 , DMWD/wdr-20 , ECHDC3/ech-2 , MADD/aex-3 , NCK2/nck-1 , RABEP1/rabn-5 , RIN3/rin-1 , SLC39A13/zipt-13 , TRAM1/tram-1 , and USP6NL/tbc-17 . We knocked down these genes by RNAi and quantified lifespan, aging-associated degeneration of two neuron classes, PVD and PLM, and associative learning and short-term memory. Lifespan was unaffected by most knockdowns, and only nck-1 and tbc-17 shortened lifespan. Across neuronal assays, multiple homologs modulated aging with clear neuron-class selectivity. Knockdown of aex-3 , C36B7.6 , cpn-2 , ech-2 , rabn-5 , rin-1 , T09B9.4 , and zipt-13 attenuated late-life PVD degeneration, whereas R166.2 and tram-1 accelerated early PVD aging. Only two genes affected PLM aging: R166.2 knockdown exacerbated degeneration, while tbc-17 knockdown attenuated it despite its lifespan-shortening effect. In PLM neurons, tbc-17 knockdown, targeting a Rab GTPase-activating protein, also preserved mitochondrial architecture during early aging and shifted heat stress-induced mitochondrial remodeling toward a pattern consistent with improved quality control. In behavioral assays, ech-2 knockdown, targeting an enoyl-CoA-hydratase, enhanced short-term memory during early stages of aging. To further assess how LOAD-linked genes interact with Aβ-driven neurodegeneration, we developed a model that combines the PVD aging assay with a background expressing human Aβ 1-42 pan-neuronally. In this model, Aβ expression accelerated age-dependent PVD degeneration, whereas ech-2 knockdown abolished this Aβ-induced effect. Our findings show that conserved homologs of several understudied LOAD risk genes causally modulate neuronal aging in vivo in a neuron-class-selective manner, often dissociable from organismal longevity. This C. elegans framework translates human genetic associations into quantitative, aging-linked neuronal phenotypes, and our results further emphasize early endosomal and lipid-related processes as key pathways that warrant functional testing in neuronal aging. This study also provides a tractable platform to prioritize targets for cross-species validation and to test synergy with established LOAD risk genes.