Cultured hippocampal slices prepared from apolipoprotein E (apoE)-deficient mice were exposed to an inhibitor of cathepsins B and L and then processed for an ultrastructural analysis of neuronal features for pyramidal cell bodies. Electron microscopy showed that the nuclei of pyramidal cells from treated hippocampal slices were more eccentrically located than those from untreated slices. In addition, increased numbers of vesicles were associated with the Golgi complex while microtubules were less frequent in the proximal dendrites. Consistent with previous studies in rats, treated apoE-deficient slices had increased numbers of lysosomes and multivesicular bodies. Finally, there were reductions in the number of synapses around the cell body, a finding similar to that found in the brains from Alzheimer's disease patients. These results provide ultrastructural data indicating that partial lysosomal dysfunction in apoE-deficient brains rapidly induces characteristic features of the aged human brain.

An inhibitor of cathepsins B and L was used to test if lysosomal dysfunction in cultured slices of rat frontal cortex induces pathological features that develop in the human cortex during aging and Alzheimer's disease (AD). Incubation for 6 days with N-CBZ-L-phenylalanyl-L-alanine-diazomethylketone (ZPAD) resulted in a massive proliferation of endosomes-lysosomes in all cortical layers. Slices additionally exposed to a washout of 4 days had numerous meganeurites, blister-like structures in the region of the axon hillock, in layer III but not in other cortical laminae. Meganeurites are a characteristic feature of the human frontal cortex after age 50 and are largely restricted to layer III. Tests for apoptosis were carried out at two intervals following meganeurite formation. TUNEL-labeled neurons were confined to layers II/III on the surface of the slices but there was no evidence for a ZPAD effect. In all, 6 days of lysosomal dysfunction reproduces characteristic effects of normal aging in neocortex without generating some key features of AD.