Circulatory extracellular vesicles transport complement C1q for promoting neuronal amyloid-β production in Alzheimer's disease.

Alzheimer’s disease (AD) is the most common type of dementia. A major pathological feature of AD is the aggregation of amyloid-β (Aβ), primarily driven by β-secretase (BACE1) activity. However, the mechanisms underlying continuous Aβ accumulation remain unclear. Circulating extracellular vesicles (EVs) may play a crucial role in AD progression. Here, we investigate whether circulating EVs in AD promote Aβ generation and aggregation. In this study, we found that compared to WTEVs (circulating EVs isolated from WT mice), APPEVs (circulating EVs isolated from APP/PS1 mice) showed higher concentrations and activated the JAK2-STAT1 pathway in neurons, upregulating BACE1 expression and activity. This cascade promoted amyloid precursor protein (APP) β-cleavage in lipid rafts, inducing substantial Aβ generation. Proteomic analysis revealed complement C1q in APPEVs as a key protein activating the JAK2-STAT1-BACE1 pathway. Furthermore, in vivo experiments demonstrated that intravenously injected APPEVs crossed the blood-brain barrier without damaged the epithelial tight junction, promoting BACE1 expression in neurons, and enhancing Aβ production and aggregation in brain. Inhibition of C1q mitigated these effects in both in vitro and in vivo experiments. In conclusion, during the progression of AD, circulating EVs containing complement C1q are delivered to neurons, activating their JAK2-STAT1 signaling pathway. This activation upregulates the expression of BACE1, subsequently enhancing the β-cleavage of APP in lipid rafts. These events lead to a substantial increase in Aβ production, exacerbating the pathological progression of AD.