Alterations of Neuronal Lysosomes in Alzheimer's Disease and in APPxPS1-KI Mice

Background: The cellular and molecular alterations associated with synapse and neuron loss in Alzheimer's disease (AD) remain unclear. In transgenic mouse models that express mutations responsible for familial AD, neuronal and synaptic losses occur in populations that accumulate fibrillar amyloid-beta 42 (A beta(42)) intracellularly. Objective: We aimed to study the subcellular localization of these fibrillar accumulations and whether such intraneuronal assemblies could be observed in the human pathology. Methods: We used immunolabeling and various electron microscopy techniques on APP x presenilin1 - knock-in mice and on human cortical biopsies and postmortem samples. Results: We found an accumulation of A beta fibrils in lipofuscin granule-like organelles in APP x presenilinl - knock-in mice. Electron microscopy of human cortical biopsies also showed an accumulation of undigested material in enlarged lipofuscin granules in neurons from AD compared to age-matched non-AD patients. However, in those biopsies or in postmortem samples we could not detect intraneuronal accumulations of A beta fibrils, neither in the lipofuscin granules nor in other intraneuronal compartments. Conclusion: The intralysosomal accumulation of A beta fibrils in specific neuronal populations in APPxPS1-KI mice likely results from a high concentration of A beta(42) in the endosome-lysosome system due to the high expression of the transgene in these neurons.

Automated summary

This study investigates the subcellular localization of Aβ fibrils in transgenic mouse models and human brain tissue of Alzheimer's disease (AD). Results show the accumulation of Aβ fibrils in intralysosomal lipofuscin granules in mice and undigested material in enlarged lipofuscin granules in human cortical biopsies. However, no intraneuronal accumulations of Aβ fibrils were detected in the examined samples.