The early endosome is the first vacuolar compartment along the endocytic pathway. It is the site of internalization and initial processing of amyloid precursor protein (APP) and apolipoprotein E (ApoE), two proteins of etiological importance in Alzheimer's disease, and a putative site of ␤-amyloid peptide (A␤) formation. Here, we identify early endosomes in human pyramidal neurons, using specific compartmental markers and morphometry, and show that in Alzheimer's disease individual endosomes display up to 32-fold larger volumes than the normal average. Endosomal enlargement contributed to an average 2.5-fold larger total endosomal volume per neuron, implying a marked increase in endocytic activity. Endosomal alterations were evident in most pyramidal neurons in Alzheimer brain, detectable at early stages of the disease but absent in several other neurodegenerative disorders examined. In addition, mature and proenzyme forms of the proteases cathepsin B and cathepsin D, a candidate APP secretase, were identified in most early endosomes in Alzheimer brains but were detectable in only a minor proportion of endosomes in normal brain. Expression of the cation-dependent 46 kDa mannose 6-phosphate receptor was elevated in pyramidal neurons of Alzheimer brains, which could be a possible basis for the altered cathepsin trafficking pattern. Enhanced endocytic activity, coupled with increased trafficking to endosomes of proteases, which may have the ability under pathological conditions to generate A␤, constitutes a potential mechanism by which ␤-amyloidogenesis may become accelerated in sporadic AD and also be subject to influences by ApoE.

Cyclooxygenase-2 (COX-2), a key enzyme in prostanoid biosynthesis, may represent an important therapeutic target in Alzheimer's disease (AD). In the present study, we explored the regulation of COX-2 in the hippocampal formation in sporadic AD. Using semiquantitative immunocytochemical techniques, we found that in AD cases (vs. age-matched controls) neurons of the CA1-CA4 subdivisions of the hippocampal pyramidal layer showed elevation of COX-2 signal; COX-2 levels correlated with amyloid plaque density. In contrast, the level of COX-2 immunostaining in the dentate gyrus granule neurons was not elevated in AD. No expression of COX-2 in cells with glial morphology was found in any case examined. In parallel, in vitro studies found that neurons derived from transgenic mice with neuronal overexpression of COX-2 are more susceptible to beta-amyloid (Abeta) toxicity, with potentiation of redox impairment. The results indicate elevated expression of neuronal COX-2 in subregions of the hippocampal formation in AD and that such elevation may potentiate Abeta-mediated oxidative stress.

Cyclooxygenase-2 (COX-2), a key enzyme in prostanoid biosynthesis, may represent an important therapeutic target in Alzheimer's disease (AD). In the present study, we explored the regulation of COX-2 in the hippocampal formation in sporadic AD. Using semiquantitative immunocytochemical techniques, we found that in AD cases (vs. age-matched controls) neurons of the CA1-CA4 subdivisions of the hippocampal pyramidal layer showed elevation of COX-2 signal; COX-2 levels correlated with amyloid plaque density. In contrast, the level of COX-2 immunostaining in the dentate gyrus granule neurons was not elevated in AD. No expression of COX-2 in cells with glial morphology was found in any case examined. In parallel, in vitro studies found that neurons derived from transgenic mice with neuronal overexpression of COX-2 are more susceptible to beta-amyloid (Abeta) toxicity, with potentiation of redox impairment. The results indicate elevated expression of neuronal COX-2 in subregions of the hippocampal formation in AD and that such elevation may potentiate Abeta-mediated oxidative stress.

The crystal structure of intercellular adhesion molecule-2 (ICAM-2) revealed significant differences in the presentation of the critical acidic residue important for integrin binding between I and non-I-domain integrin ligands. Based on this crystal structure, we mutagenized ICAM-2 to localize the binding site for the integrin lymphocyte functionassociated antigen-1 (LFA-1). The integrin binding site runs diagonally across the GFC ␤-sheet and includes residues on the CD edge of the ␤-sandwich.