Exosome-associated cargo is linked to familial Alzheimer's disease-associated phenotypes in vitro

The propagation of pathological proteins such as tau and amyloid-beta (Aβ) in Alzheimer's disease (AD) is poorly understood. Here, we developed a human-relevant in vitro conditioned medium (CM)-based model using human neural progenitor ReN cells carrying Familial AD (FAD) mutations in amyloid precursor protein (APP Sw/Lo) and presenilin 1 (PSEN1ΔE9). Healthy ReN-derived neurons and astrocytes treated with FAD-CM for nine weeks exhibited AD features, including cellular toxicity, neuro-glial alterations, and mitochondrial dysfunction. Exogenous Aβ42 further induced neuroglial and mitochondrial damage. Exosomes released by FAD cells and -to a lesser extent- by CM-treated healthy cells showed elevated Aβ42/40 ratios. Proteomic analysis also revealed that exosomes from FAD-cells carried a distinct content, including overrepresentation of proteins linked to inflammation, extracellular matrix remodelling, synaptic dysfunction, and Aβ processing, as well as Calmodulin-like protein 3. Moreover, exosomes were actively internalized by healthy cells through an actin-dependent mechanism. In summary, these findings support a model based on FAD-associated APP/PSEN1 mutations in which exosome-associated cargo alongside soluble and non-vesicular factors contribute to the transfer of AD-associated cellular phenotypes.