Intracellular metalloprotease activity controls intraneuronal Aβ aggregation and limits secretion of Aβviaexosomes

Abstract

Accumulating evidence suggests that the abnormal aggregation of amyloid‐β (Aβ) peptide in Alzheimer's disease (AD) begins intraneuronally, within vesicles of the endosomal‐lysosomal pathway where Aβ is both generated and degraded. Metalloproteases, including endothelin‐converting enzyme (ECE)‐1 and ‐2, reside within these vesicles and normally limit the accumulation of intraneuronally produced Aβ. In this study, we determined whether disruption of Aβ catabolism could trigger Aβ aggregation within neurons and increase the amount of Aβ associated with exosomes, small extracellular vesicles derived from endosomal multivesicular bodies. Using cultured cell lines, primary neurons, and organotypic brain slices from an AD mouse model, we found that pharmacological inhibition of the ECE family of metalloproteases increased intracellular and extracellular Aβ levels and promoted the intracellular formation of Aβ oligomers, a process that did not require internalization of secreted Aβ. In vivo, the accumulation of intraneuronal Aβ aggregates was accompanied by increased levels of both extracellular and exosome‐associated Aβ, including oligomeric species. Neuronal exosomes were found to contain both ECE‐1 and ‐2 activities, suggesting that multivesicular bodies are intracellular sites of Aβ degradation by these enzymes. ECE dysfunction could lead to the accumulation of intraneuronal Aβ aggregates and their subsequent release into the extracellular space via exosomes.—Pacheco‐Quinto, J., Clausen, D., Pérez‐González, R., Peng, H., Meszaros, A., Eckman, C. B., Levy, E., Eckman, E. A. Intracellular metalloprotease activity controls intraneuronal Aβ aggregation and limits secretion of Aβ via exosomes. FASEB J. 33, 3758–3771 (2019). http://www.fasebj.org

Extracellular vesicles: where the amyloid precursor protein carboxyl‐terminal fragments accumulate and amyloid‐β oligomerizes

“…The level of Aβ42 was below the assay detection level (data not shown). The reduction in Aβ level could be due to the activity of EV‐associated Aβ‐degrading enzymes such as neprilysin, 47 insulin‐degrading enzyme (IDE), 48 or endothelin‐converting enzymes‐1 and −2 (ECE‐1 and ECE‐2), 49 suggested to be active in the extracellular space 50 . Thus, we pretreated the brain EVs with the metalloprotease inhibitors phosphoramidon and thiorphan, in order to inhibit the activities of these enzymes.…”

Diagnostic and therapeutic potential of exosomes in Alzheimer’s disease

“…Furthermore, treatment of BV‐2 cells with statins enhanced exosome secretion carrying IDE, contributing to Aβ clearance, although the underlying mechanisms remain unclear (Tamboli et al., 2010). Endothelin‐converting enzymes 1/2 and metalloproteinases, are also capable of degrading Aβ, and are likewise found into exosomes (Pacheco‐Quinto et al., 2018).…”

<p>Targetting Exosomes as a New Biomarker and Therapeutic Approach for Alzheimer’s Disease</p>

“…Aβ and exosomes were also found to co-localize inside neurons, thus suggesting that exosomes participate in Aβ sorting and oligomerization. 65 Tau is a core protein associated with the pathogenesis of AD and is secreted in exosomes. 66 Our previous study showed that the up-regulation of mTOR facilitates the release of tau into the extracellular space in an exosome-independent fashion in SH-SY5Y cells.…”