Immunohistochemical evidence for macroautophagy in neurones and endothelial cells in Alzheimer's disease

Aim: To determine the pathological structures associated with macroautophagy in Alzheimer's disease (AD) and any relationship to disease progression. Methods: Immunohistochemistry using antibodies to beclin-1, Atg5 and Atg12, early macroautophagy markers and LC3, the mammalian homologue of the later macroautophagy marker Atg8, were localized in formalin-fixed, paraffin-embedded medial temporal lobe sections of AD cases at variable neuritic disease stages. Double immunofluorescence labelling was used to co-localize these macroautophagy markers with A beta and phospho-tau (AT8) and correlations performed using Spearman rank tests. Results: Atg12 immunoreactivity in AD was either dispersed in the soma and dendrites or concentrated in tau-immunoreactive dystrophic neurites and some neurofibrillary tangles. Fewer Atg12-immunopositive neurones were observed with longer disease durations. Atg12-immunoreactive endothelial cells were found spatially associated with A beta-positive plaques, with more Atg12-immunoreactive capillary endothelial cells with higher neuritic disease stage. These findings were confirmed by the other autophagy markers beclin-1, Atg5 and LC3. Conclusion: The data confirm that macroautophagy occurs in neurones undergoing neuritic degeneration in AD, identified early macroautophagy markers in capillary endothelial cells in close proximity to A beta plaques, and found that evidence for macroautophagy changes with disease progression.