Cysteine string protein α and a link between rare and common neurodegenerative dementias.

The maintenance of protein homeostasis and overall protein quality control dysfunction are associated with dementia. Cysteine string protein α (CSPα) is an endolysosomal cochaperone that facilitates the fusion of secretory and synaptic vesicles to the cell membrane. CSPα interacts with multiple proteins related to the proteostasis network and exocytic pathways and is often dysfunctional in synaptopathies. Since the initial discovery of CSPα 30 years ago, subsequent research has demonstrated a protective role of CSPα, especially in synaptic maintenance. However, the discovery of heterozygous CSPα mutations in 2011 causing adult-onset neuronal ceroid lipofuscinosis (ANCL) shifted the back-then prevalent dogma of unique synaptic function to include an endolysosomal role for CSPα. Recently, CSPα has been involved in the exocytosis of aggregate-prone proteins through either the misfolding-associated protein secretion (MAPS) or unconventional secretory pathways linking the molecular mechanism of rare and common neurodegenerative diseases. Here, we propose a novel molecular and pathophysiological model of CSPα-associated dementia, outline the increasing evidence of a broader role of CSPα in neurodegeneration, propose the role of CSPα in the synaptic secretion of neurodegenerative-associated proteins, and discuss the modulation of CSPα as a molecular target for common dementias.