SMPD3 and Alzheimer disease: Inhibiting the synthesis or secretion of exosomes prevents the aggregation of tau protein in the brain.336–338 Inhibition of exosome biosynthesis by blocking the activity of a key enzyme regulating ceramide biosynthesis, neutral sphingomyelinase 2, reduced the proliferation of Aβ plaque and tau in AD mouse model.339 Some enzymes carried in exosomes, such as neprilysin and insulin-degrading enzymes, reduce intracellular and extracellular Aβ levels.340 In summary, exosomes participate in the pathogenesis of AD by transmitting different substances or information.