Proteasome Dysfunction and Aggregation-Prone Proteins in Neurodegenerative Diseases: From Mechanisms to Therapeutic Opportunities

Neurodegenerative diseases are characterized by the accumulation of misfolded and aggregation-prone proteins, reflecting a failure of proteostasis. The ubiquitin–proteasome system (UPS), a major pathway for selective intracellular protein degradation, is essential for maintaining neuronal protein homeostasis. Proteasome dysfunction has been implicated in several major neurodegenerative disorders, including Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington’s disease (HD), although its extent and mechanisms vary across disease contexts. In this review, we examine current evidence for proteasome dysfunction in neurodegeneration and discuss how disease-associated proteins impair proteasome function through direct inhibition, defective substrate processing, and sequestration into protein aggregates. We also address the contribution of oxidative stress, neuroinflammation, and aging to proteasome dysregulation. Finally, we highlight emerging therapeutic strategies aimed at restoring proteasome function, including pharmacological activation, modulation of proteasome assembly and stability, and targeted protein degradation approaches. Understanding the context-dependent nature of proteasome dysfunction will be important for developing effective proteostasis-based therapies.