The Proteostasis Network in Proteinopathies: Mechanisms and Interconnections

Proteinopathies are neurodegenerative disorders that are characterized by accumulation of misfolded toxic protein aggregates that lead to synaptic and neuronal dysfunction. Although genetically, clinically, and pathologically distinct, a common feature of these diseases is disruption of protein homeostasis (proteostasis), which causes accumulation of misfolded proteins. The machinery mediating proteostasis exquisitely balances and interlaces protein synthesis, protein folding and trafficking, and protein degradation processes within the proteostasis network to maintain homeostasis. The proteostasis network governs a functional and dynamic proteome by modulating the timing, location, and stoichiometry of protein expression, surveillance, and maintenance of protein folding and removal of misfolded or excess proteins. Although a functional proteome is essential for the health of all cell types, this is especially true for neurons, which are prone to enhanced cellular stress. Aging is the most important risk factor for proteostasis decline and the development of proteinopathies. However, germline and somatic mutations can also functionally impair components of the proteostasis network. Post-mitotic cells, particularly neurons, are rendered further susceptible to proteostasis dysfunction because of their extended lifespan. This review discusses the interconnections between the functional components mediating proteostasis in neuronal cells and how aberrations in proteostasis contribute to neuronal dysfunction and disease.