Synaptic Proteostasis in Health and Disease

Neurons rely on tightly coordinated mechanisms of protein synthesis and degradation to maintain cellular homeostasis, a process known as proteostasis. Given their highly polarised and compartmentalised nature, regulation of proteostasis is especially important at neuronal synapses, which are spatially distant from the soma yet require rapid on-demand adaptation of the synaptic proteome. Neurons meet their demand for synaptic proteostasis through localised mRNA transport and translation, alongside specialised pathways for protein degradation. Recent advances reveal that thousands of transcripts localise to distal neuronal compartments and that their distribution may be shaped by RNA stability, RNA dynamics, and organelle-hitchhiking transport mechanisms. In parallel, processes such as synaptic autophagy and endolysosomal trafficking are crucial for maintaining synaptic structure and neurotransmission. Disruptions in these finely balanced mechanisms are a common underlying feature of various neurological disorders, including fragile X syndrome, amyotrophic lateral sclerosis, Parkinson's disease, and Alzheimer's disease. This overview highlights key milestones and remaining questions in synaptic proteostasis, focusing on how local protein synthesis and degradation work together to preserve synaptic integrity and how their dysregulation can lead to disease.