Paul M. Mathews

The Endosomal-Lysosomal System of Neurons in Alzheimer's Disease Pathogenesis: A Review

A prominent feature of brain pathology in Alzheimers 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 Alzheimers disease provide insight into how β-amyloidogenesis might be promoted in sporadic Alzheimers 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 Alzheimers disease contribute importantly to the neurodegenerative process in Alzheimers disease.

Extracellular amyloid formation and associated pathology in neural grafts

Amyloid precursor protein (APP) processing and the generation of β-amyloid peptide (Aβ) are important in the pathogenesis of Alzheimers disease. Although this has been studied extensively at the molecular and cellular levels, much less is known about the mechanisms of amyloid accumulation in vivo. We transplanted transgenic APP23 and wild-type B6 embryonic neural cells into the neocortex and hippocampus of both B6 and APP23 mice. APP23 grafts into wild-type hosts did not develop amyloid deposits up to 20 months after grafting. In contrast, both transgenic and wild-type grafts into young transgenic hosts developed amyloid plaques as early as 3 months after grafting. Although largely diffuse in nature, some of the amyloid deposits in wild-type grafts were congophilic and were surrounded by neuritic changes and gliosis, similar to the amyloid-associated pathology previously described in APP23 mice. Our results indicate that diffusion of soluble Aβ in the extracellular space is involved in the spread of Aβ pathology, and that extracellular amyloid formation can lead to neurodegeneration.

Elimination of GD3 synthase improves memory and reduces amyloid-β plaque load in transgenic mice

Gangliosides have been shown to be necessary for beta-amyloid (Abeta) binding and aggregation. GD3 synthase (GD3S) is responsible for biosynthesis of the b- and c-series gangliosides, including two of the four major brain gangliosides. We examined Abeta-ganglioside interactions in neural tissue from mice lacking the gene coding for GD3S (St8sia1), and in a double-transgenic (APP/PSEN1) mouse model of Alzheimers disease cross-bred with GD3S-/- mice. In primary neurons and astrocytes lacking GD3S, Abeta-induced cell death and Abeta aggregation were inhibited. Like GD3S-/- and APP/PSEN1 double-transgenic mice, APP/PSEN1/GD3S-/- triple-mutant mice are indistinguishable from wild-type mice on casual examination. APP/PSEN1 double-transgenics exhibit robust impairments on a number of reference-memory tasks. In contrast, APP/PSEN1/GD3S-/- triple-mutant mice performed as well as wild-type control and GD3S-/- mice. Consistent with the behavioral improvements, both aggregated and unaggregated Abeta and associated neuropathology were almost completely eliminated in triple-mutant mice. These results suggest that GD3 synthase may be a novel therapeutic target to combat the cognitive deficits, amyloid plaque formation, and neurodegeneration that afflict Alzheimers patients.

Age-dependent dysregulation of brain amyloid precursor protein in the Ts65Dn Down syndrome mouse model

Individuals with Down syndrome develop β‐amyloid deposition characteristic of early‐onset Alzheimer’s disease (AD) in mid‐life, presumably because of an extra copy of the chromosome 21‐located amyloid precursor protein (App) gene. App mRNA and APP metabolite levels were assessed in the brains of Ts65Dn mice, a mouse model of Down syndrome, using quantitative PCR, western blot analysis, immunoprecipitation, and ELISAs. In spite of the additional App gene copy, App mRNA, APP holoprotein, and all APP metabolite levels in the brains of 4‐month‐old trisomic mice were not increased compared with the levels seen in diploid littermate controls. However starting at 10u2003months of age, brain APP levels were increased proportional to the App gene dosage imbalance reflecting increased App message levels in Ts65Dn mice. Similar to APP levels, soluble amino‐terminal fragments of APP (sAPPα and sAPPβ) were increased in Ts65Dn mice compared with diploid mice at 12u2003months but not at 4u2003months of age. Brain levels of both Aβ40 and Aβ42 were not increased in Ts65Dn mice compared with diploid mice at all ages examined. Therefore, multiple mechanisms contribute to the regulation towards diploid levels of APP metabolites in the Ts65Dn mouse brain.

FE65 as a link between VLDLR and APP to regulate their trafficking and processing

BackgroundSeveral studies found that FE65, a cytoplasmic adaptor protein, interacts with APP and LRP1, altering the trafficking and processing of APP. We have previously shown that FE65 interacts with the ApoE receptor, ApoER2, altering its trafficking and processing. Interestingly, it has been shown that FE65 can act as a linker between APP and LRP1 or ApoER2. In the present study, we tested whether FE65 can interact with another ApoE receptor, VLDLR, thereby altering its trafficking and processing, and whether FE65 can serve as a linker between APP and VLDLR.ResultsWe found that FE65 interacted with VLDLR using GST pull-down and co-immunoprecipitation assays in COS7 cells and in brain lysates. This interaction occurs via the PTB1 domain of FE65. Co-transfection with FE65 and full length VLDLR increased secreted VLDLR (sVLDLR); however, the levels of VLDLR C-terminal fragment (CTF) were undetectable as a result of proteasomal degradation. Additionally, FE65 increased cell surface levels of VLDLR. Moreover, we identified a novel complex between VLDLR and APP, which altered trafficking and processing of both proteins. Furthermore, immunoprecipitation results demonstrated that the presence of FE65 increased the interaction between APP and VLDLR in vitro and in vivo.ConclusionsThese data suggest that FE65 can regulate VLDLR trafficking and processing. Additionally, the interaction between VLDLR and APP altered both proteins trafficking and processing. Finally, our data suggest that FE65 serves as a link between VLDLR and APP. This novel interaction adds to a growing body of literature indicating trimeric complexes with various ApoE Receptors and APP.

Brain-Wide Insulin Resistance, Tau Phosphorylation Changes, and Hippocampal Neprilysin and Amyloid-β Alterations in a Monkey Model of Type 1 Diabetes

Epidemiological findings suggest that diabetic individuals are at a greater risk for developing Alzheimers disease (AD). To examine the mechanisms by which diabetes mellitus (DM) may contribute to AD pathology in humans, we examined brain tissue from streptozotocin-treated type 1 diabetic adult male vervet monkeys receiving twice-daily exogenous insulin injections for 8–20 weeks. We found greater inhibitory phosphorylation of insulin receptor substrate 1 in each brain region examined of the diabetic monkeys when compared with controls, consistent with a pattern of brain insulin resistance that is similar to that reported in the human AD brain. Additionally, a widespread increase in phosphorylated tau was seen, including brain areas vulnerable in AD, as well as relatively spared structures, such as the cerebellum. An increase in active ERK1/2 was also detected, consistent with DM leading to changes in tau-kinase activity broadly within the brain. In contrast to these widespread changes, we found an increase in soluble amyloid-β (Aβ) levels that was restricted to the temporal lobe, with the greatest increase seen in the hippocampus. Consistent with this localized Aβ increase, a hippocampus-restricted decrease in the protein and mRNA for the Aβ-degrading enzyme neprilysin (NEP) was found, whereas various Aβ-clearing and -degrading proteins were unchanged. Thus, we document multiple biochemical changes in the insulin-controlled DM monkey brain that can link DM with the risk of developing AD, including dysregulation of the insulin-signaling pathway, changes in tau phosphorylation, and a decrease in NEP expression in the hippocampus that is coupled with a localized increase in Aβ. SIGNIFICANCE STATEMENT Given that diabetes mellitus (DM) appears to increase the risk of developing Alzheimers disease (AD), understanding the mechanisms by which DM promotes AD is important. We report that DM in a nonhuman primate brain leads to changes in the levels or posttranslational processing of proteins central to AD pathobiology, including tau, amyloid-β (Aβ), and the Aβ-degrading protease neprilysin. Additional evidence from this model suggests that alterations in brain insulin signaling occurred that are reminiscent of insulin signaling pathway changes seen in human AD. Thus, in an in vivo model highly relevant to humans, we show multiple alterations in the brain resulting from DM that are mechanistically linked to AD risk.

P-161: Amyloid beta (Aβ) is unaltered with highly elevated peripheral cholesterol in mice lacking the low-density lipoprotein receptor

satisfaction. The second study used new behavioral measures of self-regulation and estimation procedures based on occupational data (study in progress). Its aim was to study the differential effect of premorbid motivational and cognitive factors to the current cognitive and health status of older people. Results: Measures of motivational competence correlated significantly or highly significantly with satisfaction with life (r .30 .40). In a multiple regression analysis, motivation and decision regulation, self-efficacy and optimism showed to be most important to predict well-being in older age. Results of the second study will also be presented. Conclusions: We conclude suggesting adequate longitudinal studies to further investigate the concept of MR. The hypothesis is that premorbid motivational competence is associated with incidence and progression of Alzheimer’s dementia.

P2-002 : Levels and turnover of endogenous APP metabolites in the wild-type mouse brain

upon symptoms in the Mood cluster at both weeks 12 (P .034) and 24 (P .033), with 65.5% of patients in the memantine group showing a positive response at week 24. Memantine also had a significant effect over placebo (OC) upon symptoms of Psychosis at both weeks 12 (P .006) and 24 (P .001), with 80.7% of patients in the memantine group showing a positive response in this domain at week 24. The response difference (OC) between memantine and placebo patients at week 24 was 12.2% and 18.9% for Mood and Psychosis clusters, respectively. LOCF analysis yielded comparable results. Effects of memantine on Frontal symptoms were not significant, while the effects on Other symptoms were significant at week 24 using LOCF analysis (P .037), but not OC analysis (P .058). Conclusions: Taken together, these results suggest that memantine provides specific behavioral benefits for mood and psychosis-related symptoms associated with AD.

Aβ vaccination of a genetic model of Alzheimer's disease

Abstract Alzheimers disease (AD), the pathological hallmarks of which are amyloid plaques, neurofibrillary tangles and neuronal loss, is the most common dementia in elderly persons. To date, much evidence supports the hypothesis that the excess extracellular deposition of amyloid β-peptide (Aβ) is the most likely initiator of the pathogenesis of the disease. Recently, immunization of Aβ in PDAPP transgenic mouse model of AD was reported to reduce the burden of amyloid in the central nervous system. We show here that immunization results in an ∼50% reduction in dense-core amyloid plaques and an improvement in cognitive impairment in both the young and old TgCRND8 murine model of AD, without changing the total amount of Aβ in the brain. The induced sera had strong immunoreactivity with dense-cored Aβ plaques, not with the amyloid precursor protein, and reduced Aβ fibril formation and cytotoxicity of Aβ in vitro. These findings suggest that immunization may be a potential therapy, although undesirable immune reactions must be avoided.