Exosome-dependent trafficking of insulin degrading enzyme (IDE) modulates amyloid ß (Aß) degradation.

BULLOJ A; LEAL MC; XU H; CASTAÑO EM; MORELLI L

Mar del Plata

Congreso; SAIB 43th Annual Meeting.; 2007

Sociedad Argentina de Bioquímica y Biología Molecular

Insulin Degrading Enzyme (IDE) degrades  Amyloid â (Ab) in the brain and its expression/activity is impaired in Alzheimer’s disease. IDE lacks typical signal peptide needed for secretory pathway but was detected extracellularly. IDE is located in lipid rafts and its secretion is stimulated by calcium without the involvement of ER-Golgi pathway, mechanism compatible with exosomes (EX)-mediated release. Here we detected in living N2a cells by laser confocal microscopy IDE associated to multivesicular bodies (MVB) labeled with a fluorescent lipid (NR-h-PE). MVB are intracellular structures containing EX.  EX isolated from N2a conditioned supernatants by sequential ultra-centrifugation contained IDE (detected by immunoelectron microscopy and western-blotting). EX-associated IDE degraded 125I-Ab. Stable transfection with Rab11wt or Rab11S25N (which unable the fusion of MVB to the plasma membrane) showed that EX are mainly involved in IDE secretion and that impairment of EX release significantly reduces Ab clearance. The amount of EX was quantified by acetylcholynesterase activity assay. N2a cell were exposed to acute hypoxia (0.1%O2) and IDE was quantified intra- and extra-cellularly. Our results show under hypoxia the size of MVBs and the release of EX increase but the secretion of IDE is impaired suggesting that stress factors may directly impact on the translocation of IDE to EX and its further proteolytic activity.