Faculty Bibliography

Much evidence indicates that abnormal processing and extracellular deposition of amyloid-beta peptide (A beta), a proteolytic derivative of the beta-amyloid precursor protein (betaAPP), is central to the pathogenesis of Alzheimer's disease (reviewed in ref. 1). In the PDAPP transgenic mouse model of Alzheimer's disease, immunization with A beta causes a marked reduction in burden of the brain amyloid. Evidence that A beta immunization also reduces cognitive dysfunction in murine models of Alzheimer's disease would support the hypothesis that abnormal A beta processing is essential to the pathogenesis of Alzheimer's disease, and would encourage the development of other strategies directed at the 'amyloid cascade'. Here we show that A beta immunization reduces both deposition of cerebral fibrillar A beta and cognitive dysfunction in the TgCRND8 murine model of Alzheimer's disease without, however, altering total levels of A beta in the brain. This implies that either a approximately 50% reduction in dense-cored A beta plaques is sufficient to affect cognition, or that vaccination may modulate the activity/abundance of a small subpopulation of especially toxic A beta species

The accumulation of neurofilaments required for postnatal radial growth of myelinated axons is controlled regionally along axons by oligodendroglia. Developmentally regulated processes previously suspected of modulating neurofilament number, including heavy neurofilament subunit (NFH) expression, attainment of mature neurofilament subunit stoichiometry, and expansion of interneurofilament spacing cannot be primary determinants of regional accumulation as we show each of these factors precede accumulation by days or weeks. Rather, we find that regional neurofilament accumulation is selectively associated with phosphorylation of a subset of Lys-Ser-Pro (KSP) motifs on heavy neurofilament subunits and medium-size neurofilament subunits (NFMs), rising >50-fold selectively in the expanding portions of optic axons. In mice deleted in NFH, substantial preservation of regional neurofilament accumulation was accompanied by increased levels of the same phosphorylated KSP epitope on NFM. Interruption of oligodendroglial signaling to axons in Shiverer mutant mice, which selectively inhibited this site-specific phosphorylation, reduced regional neurofilament accumulation without affecting other neurofilament properties or aspects of NFH phosphorylation. We conclude that phosphorylation of a specific KSP motif triggered by glia is a key aspect of the regulation of neurofilament number in axons during axonal radial growth

A prominent feature of brain pathology in Alzheimer's disease is a robust activation of the neuronal lysosomal system and major cellular pathways converging on the lysosome, namely, endocytosis and autophagy. Recent studies that identify a disturbance of the endocytic pathway as one of the earliest known manifestation of Alzheimer's disease provide insight into how beta-amyloidogenesis might be promoted in sporadic Alzheimer's disease, the most prevalent and least well understood form of the disease. Primary lysosomal dysfunction has historically been linked to neurodegeneration. New data now directly implicate cathepsins as proteases capable of initiating, as well as executing, cell death programs in certain pathologic states. These and other studies support the view that the progressive alterations of lysosomal function observed during aging and Alzheimer's disease contribute importantly to the neurodegenerative process in Alzheimer's disease

BACKGROUND: Mutations in the presenilin proteins cause early-onset, familial Alzheimer's disease (FAD). MATERIALS AND METHODS: We characterized the cellular localization and endoproteolysis of presenilin 2 (PS2) and presenilin 1 (PS1) in brains from 25 individuals with presenilin-mutations causing FAD, as well as neurologically normal individuals and individuals with sporadic Alzheimer's disease (AD). RESULTS: Amino-terminal antibodies to both presenilins predominantly decorated large neurons. Regional differences between the broad distributions of the two presenilins were greatest in the cerebellum, where most Purkinje cells showed high levels of only PS2 immunoreactivity. PS2 endoproteolysis in brain yielded multiple amino-terminal fragments similar in size to the PS1 amino-terminal fragments detected in brain. In addition, two different PS2 amino-terminal antibodies also detected a prominent 42 kDa band that may represent a novel PS2 form in human brain. Similar to PS1 findings, neither amino-terminal nor antiloop PS2 antibodies revealed substantial full-length PS2 in brain. Immunocytochemical examination of brains from individuals with the N141I PS2 mutation or eight different PS1 mutations, spanning the molecule from the second transmembrane domain to the large cytoplasmic loop domain, revealed immunodecoration of no senile plaques and only neurofibrillary tangles in the M139I PS1 mutation stained with PS1 antibodies. CONCLUSIONS: Overall presenilin expression and the relative abundance of full-length and amino-terminal fragments in presenilin FAD cases were similar to control cases and sporadic AD cases. Thus, accumulation of full-length protein or other gross mismetabolism of neither PS2 nor PS1 is a consequence of the FAD mutations examined

Endocytosis is critical to the function and fate of molecules important to Alzheimer's disease (AD) etiology, including the beta protein precursor (betaPP), amyloid beta (Abeta) peptide, and apolipoprotein E (ApoE). Early endosomes, a major site of Abeta peptide generation, are markedly enlarged within neurons in the Alzheimer brain, suggesting altered endocytic pathway (EP) activity. Here, we show that neuronal EP activation is a specific and very early response in AD. To evaluate endocytic activation, we used markers of internalization (rab5, rabaptin 5) and recycling (rab4), and found that enlargement of rab5-positive early endosomes in the AD brain was associated with elevated levels of rab4 immunoreactive protein and translocation of rabaptin 5 to endosomes, implying that both endocytic uptake and recycling are activated. These abnormalities were evident in pyramidal neurons of the neocortex at preclinical stages of disease when Alzheimer-like neuropathology, such as Abeta deposition, was restricted to the entorhinal region. In Down syndrome, early endosomes were significantly enlarged in some pyramidal neurons as early as 28 weeks of gestation, decades before classical AD neuropathology develops. Markers of EP activity were only minimally influenced by normal aging and other neurodegenerative diseases studied. Inheritance of the epsilon4 allele of APOE, however, accentuated early endosome enlargement at preclinical stages of AD. By contrast, endosomes were normal in size at advanced stages of familial AD caused by mutations of presenilin 1 or 2, indicating that altered endocytosis is not a consequence of Abeta deposition. These results identify EP activation as the earliest known intraneuronal change to occur in sporadic AD, the most common form of AD. Given the important role of the EP in Abeta peptide generation and ApoE function, early endosomal abnormalities provide a mechanistic link between EP alterations, genetic susceptibility factors, and Abeta generation and suggest differences that may be involved in Abeta generation and beta amyloidogenesis in subtypes of AD

We have previously shown that Alzheimer disease (AD) brain exhibits terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) for DNA damage and morphological evidence for apoptosis. Down syndrome (DS) is a neurodegenerative disorder that exhibits significant neuropathological parallels with AD. In accordance with these parallels and the need to clarify the mechanism of cell death in DS and AD, we investigated two principal issues in the present study. First, we investigated the hypothesis that TUNEL labeling for DNA damage and morphological evidence for apoptosis is also present in the DS brain. All DS cases employed had a neuropathological diagnosis of AD. Analysis of these cases showed that DS brain exhibits a significant increase in the number of TUNEL-labeled nuclei relative to controls matched for age, Postmortem Delay, and Archival Length, and that a subset of TUNEL-positive nuclei exhibits apoptotic morphologies. We also report that Archival Length in 10% formalin can significantly affect TUNEL labeling in postmortem human brain, and therefore, that Archival Length must be controlled for as a variable in this type of study. Second, we investigated whether biochemical evidence for the mechanism of cell death in DS and AD could be detected. To address this question we employed pulsed-field gel electrophoresis (PFGE) as a sensitive method to evaluate DNA integrity. Although apoptotic oligonucleosomal laddering has not previously been observed in AD, PFGE of DNA from control, DS and AD brain in the present study revealed evidence of high molecular weight DNA fragmentation indicative of apoptosis. This represents biochemical support for an apoptotic mechanism of cell death in DS and AD