Neurons Export Extracellular Vesicles Enriched in Cysteine String Protein and Misfolded Protein Cargo

The fidelity of synaptic transmission depends on the integrity of the protein machinery at the synapse. Unfolded synaptic proteins undergo refolding or degradation in order to maintain synaptic proteostasis and preserve synaptic function, and buildup of unfolded/toxic proteins leads to neuronal dysfunction. Many molecular chaperones contribute to proteostasis, but one in particular, cysteine string protein (CSP alpha), is critical for proteostasis at the synapse. In this study we report that exported vesicles from neurons contain CSP alpha. Extracellular vesicles (EV's) have been implicated in a wide range of functions. However, the functional significance of neural EV's remains to be established. Here we demonstrate that co-expression of CSP alpha with the disease-associated proteins, polyglutamine expanded protein 72Q huntingtin(exon1) or superoxide dismutase-1 (SOD-1(G93A)) leads to the cellular export of both 72Q huntingtin(exon1) and SOD-1(G93A) via EV's. In contrast, the inactive CSP alpha(HPD-AAA) mutant does not facilitate elimination of misfolded proteins. Furthermore, CSP alpha-mediated export of 72Q huntingtin(exon1) is reduced by the polyphenol, resveratrol. Our results indicate that by assisting local lysosome/proteasome processes, CSP alpha-mediated removal of toxic proteins via EVs plays a central role in synaptic proteostasis and CSP alpha thus represents a potential therapeutic target for neurodegenerative diseases.