Intracellular distribution of amyloid beta peptide and its relationship to the lysosomal system

Background:Amyloid beta peptide(Aβ)is the main component of extraneuronal senile plaques typical of Alzheimer’s disease(AD)brains.Although Aβis produced by normal neurons,it is shown to accumulate in large amounts within neuronal lysosomes in AD.We have recently shown that under normal conditions the majority of Aβis localized extralysosomally,while oxidative stress significantly increases intralysosomal Aβcontent through activation of macroautophagy.It is also suggested that impaired Aβsecretion and resulting intraneuronal increase of Aβcan contribute to AD pathology.However,it is not clear how Aβis distributed inside normal neurons,and how this distribution is effected when Aβsecretion is inhibited.Methods:Using retinoic acid differentiated neuroblastoma cells and neonatal rat cortical neurons,we studied intracellular distribution of Aβby double immunofluorescence microscopy for Aβ40 or Aβ42 and different organelle markers.In addition,we analysed the effect of tetanus toxin-induced exocytosis inhibition on the intracellular distribution of Aβ.Results:Under normal conditions,Aβwas found in the small cytoplasmic granules in both neurites and perikarya.Only minor portion of Aβwas colocalized with trans-Golgi network,Golgi-derived vesicles,early and late endosomes,lysosomes,and synaptic vesicles,while the majority of Aβgranules were not colocalized with any of these structures.Furthermore,treatment of cells with tetanus toxin significantly increased the amount of intracellular Aβin both perikarya and neurites.Finally,we found that tetanus toxin increased the levels of intralysosomal Aβalthough the majority of Aβstill remained extralysosomally.Conclusion:Our results indicate that most Aβis not localized to Golgi-related structures,endosomes,lysosomes secretory vesicles or other organelles,while the suppression of Aβsecretion increases intracellular intra-and extralysosomal Aβ.