Ultrasound-mediated augmented exosome release from astrocytes alleviates amyloid-beta-induced neurotoxicity

Background: Extracellular vesicles, including exosomes, are secreted by a variety of cell types in the central nervous system. Exosomes play a role in removing intracellular materials from the endosomal system. Alzheimer's disease (AD) is caused by an overproduction or reduced amyloid-beta (A beta) peptide clearance. Increased A beta levels in the brain may impair the exosome-mediated A beta clearance pathway. Therapeutic ultrasound stimulation demonstrated its potential for promoting A beta degradation efficiency in clinical trials. However, the underlying mechanism of ultrasound stimulation is still unclear. Methods: In this study, astrocytes, the most abundant glial cells in the brain, were used for exosome production. Post insonation, exosomes from ultrasound-stimulated HA cells (US-HA-Exo) were collected, nanoparticle tracking analysis and protein analysis were used to measure and characterize exosomes. Neuroprotective effect of US-HA-Exo in oligomeric A beta 42 toxicated SH-SY5Y cells was tested. Cellular uptake and distribution of exosomes were observed by flow cytometry and confocal laser scanning microscopy. Focused ultrasound (FUS) with microbubbles was employed for blood-brain-barrier opening to achieve brain-targeted exosome delivery. After US-HA-Exo/FUS treatment, amyloid-beta plaque in APP/PS1 mice were evaluated by A beta immunostaining and thioflavin-S staining. Results: We showed that ultrasound resulted in an almost 5-fold increase in the exosome release from human astrocytes. Exosomes were rapidly internalized in SH-SY5Y cells, and colocalized with FITC-A beta 42, causing a decreased uptake of FITC-A beta 42. CCk-8 test results showed that US-HA-Exo could mitigate A beta toxicity to neurons in vitro. The therapeutic potential of US-HA-Exo/FUS delivery was demonstrated by a decrease in thioflavin-S-positive amyloid plaques and A beta immuno-staining, a therapeutic target for AD in APP/PS1 transgenic mice. The iTRAQ-based proteomic quantification was performed to gain mechanistic insight into the ultrasound effect on astrocyte-derived exosomes and their ability to alleviate A beta neurotoxicity. Conclusion: Our results imply that US-HA-Exo have the potential to provide neuroprotective effects to reverse oligomeric amyloid-beta-induced cytotoxicity in vitro and, when combined with FUS-induced BBB opening, enable the clearance of amyloid-beta plaques in vivo.

Automated summary

The study showed that ultrasound stimulation can enhance the release of exosomes from astrocytes, which have neuroprotective effects against Aβ toxicity. When combined with ultrasound-induced blood-brain-barrier opening, it enables the clearance of Aβ plaques in the brain.