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Paul M Mathews

Publications and source records attributed to Paul M Mathews.

28 records · Page 2Linked to original sources
PubMed2004

Overexpression of human cystatin C in transgenic mice does not affect levels of endogenous brain amyloid Beta Peptide.

Cystatin C, an inhibitor of cysteine proteases, colocalizes with amyloid beta (Abeta) in parenchymal and vascular amyloid deposits in brains of Alzheimer's disease (AD) patients, suggesting that cystatin C has a role in AD. Cystatin C also colocalizes with beta amyloid precursor protein (betaAPP) in transfected cultured cells. In vitro analysis of the association between the two proteins revealed that binding of cystatin C to full-length betaAPP does not affect the level of Abeta secretion. Here we studied the effect of in vivo overexpression of cystatin C on the levels of endogenous brain Abeta. We have generated lines of transgenic mice expressing either wild-type human cystatin C or the Leu68Gln variant that forms amyloid deposits in the cerebral vessels of Icelandic patients with hereditary cerebral hemorrhage, under control sequences of the human cystatin C gene. Western blot analysis of brain homogenates was used to select lines of mice expressing various levels of the transgene. Analysis of Abeta40 and Abeta42 concentrations in the brain showed no difference between transgenic mice and their nontransgenic littermates. Thus, in vivo overexpression of human cystatin C does not affect Abeta levels in mice that do not deposit Abeta.

Alzheimer Disease↗
PubMed2003

In vivo reduction of amyloid-beta by a mutant copper transporter.

Cu ions have been suggested to enhance the assembly and pathogenic potential of the Alzheimer's disease amyloid-beta (Abeta) peptide. To explore this relationship in vivo, toxic-milk (txJ) mice with a mutant ATPase7b transporter favoring elevated Cu levels were analyzed in combination with the transgenic (Tg) CRND8 amyloid precursor protein mice exhibiting robust Abeta deposition. Unexpectedly, TgCRND8 mice homozygous for the recessive txJ mutation examined at 6 months of age exhibited a reduced number of amyloid plaques and diminished plasma Abeta levels. In addition, homozygosity for txJ increased survival of young TgCRND8 mice and lowered endogenous CNS Abeta at times before detectable increases in Cu in the CNS. These data suggest that the beneficial effect of the txJ mutation on CNS Abeta burden may proceed by a previously undescribed mechanism, likely involving increased clearance of peripheral pools of Abeta peptide.

Adenosine Triphosphatases↗
PubMed2003

Presenilin redistribution associated with aberrant cholesterol transport enhances beta-amyloid production in vivo.

Epidemiology, in vitro, and in vivo studies strongly implicate a role for cholesterol in the pathogenesis of Alzheimer's disease (AD). We have examined the impact of aberrant intracellular cholesterol transport on the processing of the amyloid precursor protein (APP) in a mouse model of Niemann-Pick type C (NPC) disease. In the NPC mouse brain, cholesterol accumulates in late endosomes/lysosomes. This was associated with the accumulation of beta-C-terminal fragments (CTFs) of APP, but the level of beta-secretase and its activity were not affected. Alpha-secretase activity and secreted APPalpha generation were also not affected, suggesting CTFs increased because of decreased clearance. The level of presenilin-1 (PS-1) was unchanged, but gamma-secretase activity was greatly enhanced, which correlated with an increase in Abeta40 and Abeta42 levels. These events were associated with abnormal distribution of PS-1 in the endosomal system. Our results show that aberrant cholesterol trafficking is associated with the potentiation of APP processing components in vivo, leading to an overall increase in Abeta levels.

Amyloid Precursor Protein Secretases↗
PubMed2003

Rab5-stimulated up-regulation of the endocytic pathway increases intracellular beta-cleaved amyloid precursor protein carboxyl-terminal fragment levels and Abeta production.

We previously identified abnormalities of the endocytic pathway in neurons as the earliest known pathology in sporadic Alzheimer's disease (AD) and Down's syndrome brain. In this study, we modeled aspects of these AD-related endocytic changes in murine L cells by overexpressing Rab5, a positive regulator of endocytosis. Rab5-transfected cells exhibited abnormally large endosomes immunoreactive for Rab5 and early endosomal antigen 1, resembling the endosome morphology seen in affected neurons from AD brain. The levels of both Abeta40 and Abeta42 in conditioned medium were increased more than 2.5-fold following Rab5 overexpression. In Rab5 overexpressing cells, the levels of beta-cleaved amyloid precursor protein (APP) carboxyl-terminal fragments (betaCTF), the rate-limiting proteolytic intermediate in Abeta generation, were increased up to 2-fold relative to APP holoprotein levels. An increase in beta-cleaved soluble APP relative to alpha-cleaved soluble APP was also observed following Rab5 overexpression. BetaCTFs were co-localized by immunolabeling to vesicular compartments, including the early endosome and the trans-Golgi network. These results demonstrate a relationship between endosomal pathway activity, betaCTF generation, and Abeta production. Our findings in this model system suggest that the endosomal pathology seen at the earliest stage of sporadic AD may contribute to APP proteolysis along a beta-amyloidogenic pathway.

Alzheimer Disease↗
PubMed2003

Extracellular amyloid formation and associated pathology in neural grafts.

Amyloid precursor protein (APP) processing and the generation of beta-amyloid peptide (Abeta) are important in the pathogenesis of Alzheimer's 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 Abeta in the extracellular space is involved in the spread of Abeta pathology, and that extracellular amyloid formation can lead to neurodegeneration.

Alzheimer Disease↗
PubMed2002

Alleles at the Nicastrin locus modify presenilin 1- deficiency phenotype.

Presenilin 1 (PS1), presenilin 2, and nicastrin form high molecular weight complexes that are necessary for the endoproteolysis of several type 1 transmembrane proteins, including amyloid precursor protein (APP) and the Notch receptor, by apparently similar mechanisms. The cleavage of the Notch receptor at the "S3-site" releases a C-terminal cytoplasmic fragment (Notch intracellular domain) that acts as the intracellular transduction molecule for Notch activation. Missense mutations in the presenilins cause familial Alzheimer's disease by augmenting the "gamma-secretase" cleavage of APP and overproducing one of the proteolytic derivatives, the Abeta peptide. Null mutations in PS1 inhibit both gamma-secretase cleavage of APP and S3-site cleavage of the Notch receptor. Mice lacking PS1 function have defective Notch signaling and die perinatally with severe skeletal and brain deformities. We report here that a genetic modifier on mouse distal chromosome 1, coinciding with the locus containing Nicastrin, influences presenilin-mediated Notch S3-site cleavage and the resultant Notch phenotype without affecting presenilin-mediated APP gamma-site cleavage. Two missense substitutions of residues conserved among vertebrates have been identified in nicastrin. These results indicate that Notch S3-site cleavage and APP gamma-site cleavage are distinct presenilin-dependent processes and support a functional interaction between nicastrin and presenilins in vertebrates. The dissociation of Notch S3-site and APP gamma-site cleavage activities will facilitate development of gamma-secretase inhibitors for treatment of Alzheimer's disease.

Alleles↗
PubMed2002

Calpain activity regulates the cell surface distribution of amyloid precursor protein. Inhibition of calpains enhances endosomal generation of beta-cleaved C-terminal APP fragments.

In murine L cells, treatment with calpeptin or calpain inhibitor III increased Abeta42, but not Abeta40, secretion in a dose-dependent fashion. This correlated with an increase in the levels of amyloid precursor protein (APP) carboxyl-terminal fragments (CTFs). Immunoprecipitation with novel mAbs directed against the carboxyl-terminus of APP or specific for the beta-cleaved CTF showed that generation of both alpha- and beta-cleaved CTFs increase proportionately following inhibition of calpains. Pulse-chase metabolic labeling confirmed that inhibiting calpains increases the production of alpha- and beta-cleaved APP metabolites. Immunolabeling showed greater betaCTF signal in calpeptin-treated cells, primarily in small vesicular compartments that were shown to be predominantly endosomal by colocalization with early endosomal antigen 1. A second mAb, which recognizes an extracellular/luminal epitope found on both APP and betaCTFs, gave more cell surface labeling of calpeptin-treated cells than control cells. Quantitative binding of this antibody confirmed that inhibiting calpains caused a partial redistribution of APP to the cell surface. These results demonstrate that 1) calpain inhibition results in a partial redistribution of APP to the cell surface, 2) this redistribution leads to an increase in both alpha- and beta-cleavage without changing the ratio of alphaCTFs/betaCTFs, and 3) the bulk of the betaCTFs in the cell are within early endosomes, confirming the importance of this compartment in APP processing.

Amyloid beta-Protein Precursor↗
PubMed2002

Mature glycosylation and trafficking of nicastrin modulate its binding to presenilins.

Nicastrin is an integral component of the high molecular weight presenilin complexes that control proteolytic processing of the amyloid precursor protein and Notch. We report here that nicastrin is most probably a type 1 transmembrane glycoprotein that is expressed at moderate levels in the brain and in cultured neurons. Immunofluorescence studies demonstrate that nicastrin is localized in the endoplasmic reticulum, Golgi, and a discrete population of vesicles. Glycosidase analyses reveal that endogenous nicastrin undergoes a conventional, trafficking-dependent maturation process. However, when highly expressed in transfected cells, there is a disproportionate accumulation of the endo-beta-N-acetylglucosaminidase H-sensitive, immature form, with no significant increase in the levels of the fully mature species. Immunoprecipitation revealed that presenilin-1 interacts preferentially with mature nicastrin, suggesting that correct trafficking and co-localization of the presenilin complex components are essential for activity. These findings demonstrate that trafficking and post-translational modifications of nicastrin are tightly regulated processes that accompany the assembly of the active presenilin complexes that execute gamma-secretase cleavage. These results also underscore the caveat that simple overexpression of nicastrin in transfected cells may result in the accumulation of large amounts of the immature protein, which is apparently unable to assemble into the active complexes capable of processing amyloid precursor protein and Notch.

Alzheimer Disease↗
PubMed2001

Alzheimer's disease-related overexpression of the cation-dependent mannose 6-phosphate receptor increases Abeta secretion: role for altered lysosomal hydrolase distribution in beta-amyloidogenesis.

Prominent endosomal and lysosomal changes are an invariant feature of neurons in sporadic Alzheimer's disease (AD). These changes include increased levels of lysosomal hydrolases in early endosomes and increased expression of the cation-dependent mannose 6-phosphate receptor (CD-MPR), which is partially localized to early endosomes. To determine whether AD-associated redistribution of lysosomal hydrolases resulting from changes in CD-MPR expression affects amyloid precursor protein (APP) processing, we stably transfected APP-overexpressing murine L cells with human CD-MPR. As controls for these cells, we also expressed CD-MPR trafficking mutants that either localize to the plasma membrane (CD-MPRpm) or to early endosomes (CD-MPRendo). Expression of CD-MPR resulted in a partial redistribution of a representative lysosomal hydrolase, cathepsin D, to early endosomal compartments. Turnover of APP and secretion of sAPPalpha and sAPPbeta were not altered by overexpression of any of the CD-MPR constructs. However, secretion of both human Abeta40 and Abeta42 into the growth media nearly tripled in CD-MPR- and CD-MPRendo-expressing cells when compared with parental or CD-MPRpm-expressing cells. Comparable increases were confirmed for endogenous mouse Abeta40 in L cells expressing these CD-MPR constructs but not overexpressing human APP. These data suggest that redistribution of lysosomal hydrolases to early endocytic compartments mediated by increased expression of the CD-MPR may represent a potentially pathogenic mechanism for accelerating Abeta generation in sporadic AD, where the mechanism of amyloidogenesis is unknown.

Alzheimer Disease↗