RESUMO
UNLABELLED: Recent evidence implicates exosomes in the aggregation of Aß and spreading of tau in Alzheimer's disease. In neural cells, exosome formation can be blocked by inhibition or silencing of neutral sphingomyelinase-2 (nSMase2). We generated genetically nSMase2-deficient 5XFAD mice (fro;5XFAD) to assess AD-related pathology in a mouse model with consistently reduced ceramide generation. We conducted in vitro assays to assess Aß42 aggregation and glial clearance with and without exosomes isolated by ultracentrifugation and determined exosome-induced amyloid aggregation by particle counting. We analyzed brain exosome content, amyloid plaque formation, neuronal degeneration, sphingolipid, Aß42 and phospho-tau levels, and memory-related behaviors in 5XFAD versus fro;5XFAD mice using contextual and cued fear conditioning. Astrocyte-derived exosomes accelerated aggregation of Aß42 and blocked glial clearance of Aß42 in vitro Aß42 aggregates were colocalized with extracellular ceramide in vitro using a bifunctional ceramide analog preloaded into exosomes and in vivo using anticeramide IgG, implicating ceramide-enriched exosomes in plaque formation. Compared with 5XFAD mice, the fro;5XFAD mice had reduced brain exosomes, ceramide levels, serum anticeramide IgG, glial activation, total Aß42 and plaque burden, tau phosphorylation, and improved cognition in a fear-conditioned learning task. Ceramide-enriched exosomes appear to exacerbate AD-related brain pathology by promoting the aggregation of Aß. Reduction of exosome secretion by nSMase2 loss of function improves pathology and cognition in the 5XFAD mouse model. SIGNIFICANCE STATEMENT: We present for the first time evidence, using Alzheimer's disease (AD) model mice deficient in neural exosome secretion due to lack of neutral sphingomyelinase-2 function, that ceramide-enriched exosomes exacerbate AD-related pathologies and cognitive deficits. Our results provide rationale to pursue a means of inhibiting exosome secretion as a potential therapy for individuals at risk for developing AD.
