The interplay between autophagy and unconventional secretion in neurodegeneration

Within neurons, the misfolding and aggregation of certain proteins has been identified as a common feature of many late-onset neurodegenerative diseases (NDs). These aggregate-prone proteins include tau (in both primary tauopathies and in Alzheimer's disease) and alpha-synuclein in Parkinson's disease. There is strong experimental evidence that the upregulation of intracellular clearance pathways (autophagy and ubiquitin-proteasome pathways) can clear aggregate-prone proteins in experimental models. When the flux through these pathways is increased, the levels of aggregate-prone proteins are reduced, resulting in improved cell survival in both cell-based and animal models of ND. More recently, a third strategy for clearing proteins from cells has been identified, via the unconventional secretion of proteins out of the cell. However, secretion may also facilitate the spreading and propagation of disease through a prion-like process. This review explains how the autophagy and unconventional secretion pathways interact and how these impact ND.