Abstract
The distinction between normal brain aging and neurodegeneration has traditionally been viewed as a binary classification, yet emerging evidence reveals a complex continuum of shared genetic mechanisms underlying both processes. This review synthesises current understanding of conserved molecular pathways that contribute to age-related neural decline across the spectrum from healthy aging to pathological neurodegeneration. We examine how fundamental cellular processes including protein quality control, mitochondrial dysfunction, inflammation, and synaptic maintenance are genetically regulated and become progressively dysregulated during aging. Key genetic pathways, such as insulin/IGF signalling, autophagy-lysosomal networks, and stress response mechanisms demonstrate remarkable conservation from model organisms to humans, suggesting evolutionary constraints on neural aging processes. The review highlights how genetic variants in these pathways can determine individual trajectories along the aging-neurodegeneration continuum, influencing susceptibility to diseases like Alzheimer's, Parkinson's, and ALS. We discuss evidence from comparative studies in C. elegans, Drosophila, rodents, and human populations that illuminate shared vulnerability genes and protective factors. Understanding these convergent mechanisms offers unprecedented opportunities for therapeutic intervention, as strategies targeting fundamental aging processes may simultaneously address multiple neurodegenerative conditions. This integrated perspective challenges traditional disease-centric approaches and supports the development of unified therapeutic strategies for promoting healthy brain aging while preventing neurodegeneration.
