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Colin L Masters

Publications and source records attributed to Colin L Masters.

90 records · Page 5Linked to original sources
PubMed2002

Overexpression of Alzheimer's disease amyloid-beta opposes the age-dependent elevations of brain copper and iron.

Increased brain metal levels have been associated with normal aging and a variety of diseases, including Alzheimer's disease (AD). Copper and iron levels both show marked increases with age and may adversely interact with the amyloid-beta (Abeta) peptide causing its aggregation and the production of neurotoxic hydrogen peroxide (H(2)O(2)), contributing to the pathogenesis of AD. Amyloid precursor protein (APP) possesses copper/zinc binding sites in its amino-terminal domain and in the Abeta domain. Here we demonstrate that overexpression of the carboxyl-terminal fragment of APP, containing Abeta, results in significantly reduced copper and iron levels in transgenic mouse brain, while overexpression of the APP in Tg2576 transgenic mice results in significantly reduced copper, but not iron, levels prior to the appearance of amyloid neuropathology and throughout the lifespan of the mouse. Concomitant increases in brain manganese levels were observed with both transgenic strains. These findings, complemented by our previous findings of elevated copper levels in APP knock-out mice, support roles for APP and Abeta in physiological metal regulation.

Aging↗
PubMed2002

Metalloenzyme-like activity of Alzheimer's disease beta-amyloid. Cu-dependent catalytic conversion of dopamine, cholesterol, and biological reducing agents to neurotoxic H(2)O(2).

Beta-amyloid (Abeta) 1-42, implicated in the pathogenesis of Alzheimer's disease, forms an oligomeric complex that binds copper at a CuZn superoxide dismutase-like binding site. Abeta.Cu complexes generate neurotoxic H(2)O(2) from O(2) through Cu(2+) reduction, but the reaction mechanism has been unclear. We now report that Abeta1-42, when binding up to 2 eq of Cu(2+), generates the H(2)O(2) catalytically by recruiting biological reducing agents as substrates under conditions where the Cu(2+) or reducing agents will not form H(2)O(2) themselves. Cholesterol is an important substrate for this activity, as are vitamin C, L-DOPA, and dopamine (V(max) for dopamine = 34.5 nm/min, K(m) = 8.9 microm). The activity was inhibited by anti-Abeta antibodies, Cu(2+) chelators, and Zn(2+). Toxicity of Abeta in neuronal culture was consistent with catalytic H(2)O(2) production. Abeta was not toxic in cell cultures in the absence of Cu(2+), and dopamine (5 microm) markedly exaggerated the neurotoxicity of 200 nm Abeta1-42.Cu. Therefore, microregional catalytic H(2)O(2) production, combined with the exhaustion of reducing agents, may mediate the neurotoxicity of Abeta in Alzheimer's disease, and inhibitors of this novel activity may be of therapeutic value.

Alzheimer Disease↗
PubMed2002

Evidence for a copper-binding superfamily of the amyloid precursor protein.

The amyloid precursor protein (APP) copper-binding domain (CuBD) has been shown to reduce Cu(II) to Cu(I) and to mediate copper-induced oxidation in vitro. However, little is known about copper binding to the homologous domains of APP and APP family paralogs and orthologs (including amyloid precursor-like proteins from Drosophila melanogaster, Xenopus laevis, and Caenorhabditis elegans) and their effects on Cu-induced oxidation and Cu(I) formation. Here, we show that APP homologues with and without conserved histidine residues at positions 147, 149, and 151 all bind Cu(II). Oxidized peptides were the kinetically favored products of the redox reaction of CuBDs promoting the reduction of Cu(II) to Cu(I). These results reveal a molecular phylogeny-based divergence that has taken place between the ancestral Drosophila APPL and C. elegans APL-1 and the recently evolved APP lineage of CuBDs. Whereas higher species CuBDs have a decreased affinity for Cu(II) and high Cu(II) reducing activities, ancestral CuBDs form very tight binding sites for Cu(II) ions and have low Cu(II) reducing activities. Thus, the APP lineage displays a gain in activity toward promoting Cu(II) reduction and Cu(I) release. The findings suggests that the Cu(II)-binding equilibrium at the phylogenetic stage of Drosophila APPL and C. elegans APL-1 is shifted from the exchangeable Cu(II) pool to the tightly bound, nonexchangeable pool and that ancestral CuBDs may exert antioxidation activities in vivo. The more recently evolved homologues of human APP appear to take advantage of unique redox properties for yet unknown biological functions.

Amino Acid Sequence↗
PubMed2002

Oligodendrocytes from neural stem cells express alpha-synuclein: increased numbers from presenilin 1 deficient mice.

alpha-Synuclein normally a synaptic vesicle-associated cytoplasmic protein is the major component of filamentous inclusions of neurons in Parkinson's disease and dementia with Lewy bodies. It is also the major component of glial inclusions of multiple system atrophy. In characterizing cells derived from embryonic neural stem cells we found all oligodendrocytes had strong cytoplasmic expression of alpha-synuclein. Comparison of cells from presenilin 1 (PS1)-deficient mice with wild type revealed a 7-fold increase in oligodendrocytes. Western blotting analysis indicated the cells contained alpha-synuclein monomers and SDS-stable dimers and trimers. This cell system of oligodendroglial alpha-synuclein expression is a useful system to study alpha-synuclein metabolism in the cell type affected in multiple system atrophy. Increased oligodendroglial cell numbers from PS1-deficient cells provides further evidence for a role of PS1-dependent Notch signalling in cell fate decisions.

Animals↗
PubMed2002

Alzheimer's disease amyloid beta and prion protein amyloidogenic peptides promote macrophage survival, DNA synthesis and enhanced proliferative response to CSF-1 (M-CSF).

Microglial cells, macrophage-lineage cells in the brain, are increased in amyloid-containing plaques in Alzheimer's disease (AD) and in the lesions of prion diseases. Recent studies suggest that microglia have a central role in turnover of amyloid in these diseases. We report here that synthetic amyloid beta (Abeta) 1-42 and prion protein (PrP) 106-126 peptides promote macrophage survival; they also induce macrophage DNA synthesis, particularly in the presence of sub-optimal concentrations of the growth factor, macrophage-colony stimulating factor (M-CSF or CSF-1). These responses are proposed to provide a means to increase brain microglia/macrophage numbers thereby enhancing subsequent inflammatory/immune responses. These fibrillogenic peptides join the list of aggregates having these effects on macrophages, indicating the generality of this type of response.

Amyloid beta-Peptides↗
PubMed2002

Alternative transcripts of presenilin-1 associated with frontotemporal dementia.

We have analyzed the expression of Alzheimer's disease-associated presenilin 1 (PS1) in various neurodegenerative disorders. Western blotting identified PS1 N- and C-terminal fragments similarly in the cortex of controls, Parkinson, Huntington and schizophrenia subjects. Additional PS1 immunoreactive species of 42 and 46 kDa were present in six out of seven cases of sporadic frontotemporal dementia (FTD) and these were particularly prominent in two cases. RT-PCR analysis using nested primers showed the presence of PS1 gene products with deletions within the exon 4-8 region. Our results suggest that alternative transcription of PS1 may be associated with FTD.

Adult↗
PubMed2002

Alternative transcripts of presenilin-1 associated with frontotemporal dementia.

We have analyzed the expression of Alzheimer's disease-associated presenilin 1 (PS1) in various neurodegenerative disorders. Western blotting identified PS1 N- and C-terminal fragments similarly in the cortex of controls, Parkinson, Huntington and schizophrenia subjects. Additional PS1 immunoreactive species of 42 and 46 kDa were present in six out of seven cases of sporadic frontotemporal dementia (FTD) and these were particularly prominent in two cases. RT-PCR analysis using nested primers showed the presence of PS1 gene products with deletions within the exon 4-8 region. Our results suggest that alternative transcription of PS1 may be associated with FTD.

Alternative Splicing↗
PubMed2002

A novel epsilon-cleavage within the transmembrane domain of the Alzheimer amyloid precursor protein demonstrates homology with Notch processing.

Proteolytic processing of the transmembrane domain of the amyloid precursor protein (APP) is a key component of Alzheimer's disease pathogenesis. Using C-terminally tagged APP derivatives, we have identified by amino-terminal sequencing a novel cleavage site of APP, at Leu-49, distal to the gamma-secretase site. This was termed -cleavage. Brefeldin A treatment and pulse-chase experiments indicate that this cleavage occurs late in the secretory pathway. The level of -cleavage is decreased by expression of presenilin-1 mutants known to impair Abeta formation, and it is sensitive to the gamma-secretase inhibitors MDL28170 and L-685,458. Remarkably, it shares similarities with site 3 cleavage of Notch-1: membrane topology, cleavage before a valine, dependence on presenilins, and inhibition profile.

Alzheimer Disease↗
PubMed2002

The intramembrane cleavage site of the amyloid precursor protein depends on the length of its transmembrane domain.

Proteolytic processing of the amyloid precursor protein by beta-secretase generates C99, which subsequently is cleaved by gamma-secretase, yielding the amyloid beta peptide (A beta). This gamma-cleavage occurs within the transmembrane domain (TMD) of C99 and is similar to the intramembrane cleavage of Notch. However, Notch and C99 differ in their site of intramembrane cleavage. The main gamma-cleavage of C99 occurs in the middle of the TMD, whereas the cleavage of Notch occurs close to the C-terminal end of the TMD, making it unclear whether both are cleaved by the same protease. To investigate whether gamma-cleavage always occurs in the middle of the TMD of C99 or may also occur at the end of the TMD, we generated C99-mutants with an altered length of the TMD and analyzed their gamma-cleavage in COS7 cells. The C terminus of A beta and thus the site of gamma-cleavage were determined by using monoclonal antibodies and mass spectrometry. Compared with C99-wild type (wt), most mutants with an altered length of the TMD changed the cleavage site of gamma-secretase, whereas control mutants with mutations outside the TMD did not. Thus, the length of the whole TMD is a major determinant for the cleavage site of gamma-secretase. Moreover, the C99-mutants were not only cleaved at one site but at two sites within their TMD. One cleavage site was located around the middle of the TMD, regardless of its actual length. An additional cleavage occurred within the N-terminal half of their TMD and thus at the opposite side of the Notch cleavage site.

Amino Acid Sequence↗
PubMed2002

Contrasting, species-dependent modulation of copper-mediated neurotoxicity by the Alzheimer's disease amyloid precursor protein.

The amyloid precursor protein (APP) of Alzheimer's disease (AD) has a copper binding domain (CuBD) located in the N-terminal cysteine-rich region that can strongly bind copper(II) and reduce it to Cu(I) in vitro. The CuBD sequence is similar among the APP family paralogs [amyloid precursor-like proteins (APLP1 and APLP2)] and its orthologs (including Drosophila melanogaster, Xenopus laevis, and Caenorhabditis elegans), suggesting an overall conservation in its function or activity. The APP CuBD is involved in modulating Cu homeostasis and amyloid beta peptide production. In this paper, we demonstrate for the first time that Cu-metallated full-length APP ectodomain induces neuronal cell death in vitro. APP Cu neurotoxicity can be induced directly or potentiated through Cu(I)-mediated oxidation of low-density lipoprotein, a finding that may have important implications for the role of lipoproteins and membrane cholesterol composition in AD. Cu toxicity induced by human APP, Xenopus APP, and APLP2 CuBDs is dependent on conservation of histidine residues at positions corresponding to 147 and 151 of human APP. Intriguingly, APP orthologs with different amino acid residues at these positions had dramatically altered Cu phenotypes. The corresponding C. elegans APL-1 CuBD, which has tyrosine and lysine residues at positions 147 and 151, respectively, strongly protected against Cu-mediated lipid peroxidation and neurotoxicity in vitro. Replacement of histidines 147 and 151 with tyrosine and lysine residues conferred this neuroprotective Cu phenotype to human APP, APLP2, and Xenopus APP CuBD peptides. Moreover, we show that the toxic and protective CuBD phenotypes are associated with differences in Cu binding and reduction. These studies identify a significant evolutionary change in the function of the CuBD in modulating Cu metabolism. Our findings also suggest that targeting of inhibitors to histidine residues at positions 147 and 151 of APP could significantly alter the oxidative potential of APP.

Alzheimer Disease↗
PubMed2002

Increased expression of the amyloid precursor beta-secretase in Alzheimer's disease.

Beta-secretase cleavage represents the first step in the generation of Abeta polypeptides and initiates the amyloid cascade that leads to neurodegeneration in Alzheimer's disease. By comparative Western blot analysis, we show a 2.7-fold increase in protein expression of the beta-secretase enzyme BACE in the brain cortex of Alzheimer's disease patients as compared to age-matched controls. Similarly, we found the levels of the amyloid precursor protein C-terminal fragment produced by beta-secretase to be increased by nearly twofold in Alzheimer's disease cortex.

Adult↗
PubMed2002

Creutzfeldt-Jakob disease cluster in an Australian rural city.

Through the Australian National Creutzfeldt-Jakob Disease Registry, 6 pathologically confirmed sporadic cases were recognized over a 13-year period in persons who had been long-term residents of a moderate-sized rural city, whereas the expected number was 0.923. An extensive investigation could not find any point-source or case-to-case transmission links. This occurrence is highly statistically significant (p = 0.0027) when viewed in isolation and remains significant (p < 0.02) when only the cases that arose after the cluster was recognized were taken into account. However, a more conservative statistical analysis suggests that such a grouping could have arisen by chance in at least one population group of this size when the whole country is taken into consideration.

Aged↗
PubMed2002

Quinacrine does not prolong survival in a murine Creutzfeldt-Jakob disease model.

Paramount among issues relating to the transmissible spongiform encephalopathies (also known as prion diseases) is the absence of any effective therapy. This need has been heightened by the substantial European and emerging global problem of bovine spongiform encephalopathy and consequent variant Creutzfeldt-Jakob disease. Stimulated by the recent reports of a potent antiprion effect in cell culture-based clearance assays, we studied the utility of quinacrine in a well-characterized in vivo model of mouse-adapted transmissible spongiform encephalopathy. Our results failed to show any evidence that quinacrine is effective when using the simple but objective measure of survival prolongation.

Animals↗
PubMed2002

Toxicity of substrate-bound amyloid peptides on vascular smooth muscle cells is enhanced by homocysteine.

Tauhe main component of cerebral amyloid angiopathy (CAA) in Alzheimer's disease is the amyloid-beta protein (Abeta), a 4-kDa polypeptide derived from the beta-amyloid protein precursor (APP). The accumulation of Abeta in the basement membrane has been implicated in the degeneration of adjacent vascular smooth muscle cells (VSMC). However, the mechanism of Abeta toxicity is still unclear. In this study, we examined the effect of substrate-bound Abeta on VSMC in culture. The use of substrate-bound proteins in cell culture mimics presentation of the proteins to cells as if bound to the basement membrane. Substrate-bound Abeta peptides were found to be toxic to the cells and to increase the rate of cell death. This toxicity was dependent on the length of time the peptide was allowed to 'age', a process by which Abeta is induced to aggregate over several hours to days. Oxidative stress via hydrogen peroxide (H2O2) release was not involved in the toxic effect, as no decrease in toxicity was observed in the presence of catalase. However, substrate-bound Abeta significantly reduced cell adhesion compared to cells grown on plastic alone, indicating that cell-substrate adhesion may be important in maintaining cell viability. Abeta also caused an increase in the number of apoptotic cells. This increase in apoptosis was accompanied by activation of caspase-3. Homocysteine, a known risk factor for cerebrovascular disease, increased Abeta-induced toxicity and caspase-3 activation in a dose-dependent manner. These studies suggest that Abeta may activate apoptotic pathways to cause loss of VSMC in CAA by inhibiting cell-substrate interactions. Our studies also suggest that homocysteine, a known risk factor for other cardiovascular diseases, could also be a risk factor for hemorrhagic stroke associated with CAA.

Amyloid beta-Peptides↗
PubMed2002

Altered glycosylation of acetylcholinesterase in APP (SW) Tg2576 transgenic mice occurs prior to amyloid plaque deposition.

Previous studies have shown that a minor glycoform of acetylcholinesterase (AChE) is increased in Alzheimer's disease brain and cerebrospinal fluid. This glycoform can be distinguished from other AChE species by its lack of binding to concanavalin A (Con A). In this study, the temporal relationship between AChE glycosylation and Abeta deposition was examined in Tg2576 mice. There was a significant (p < 0.05) difference in AChE glycosylation in Tg2576 mice compared with age-matched background strain control mice at 4 months of age. This difference in glycosylation was also observed in 8- and 12-month-old Tg2576 mice. In contrast, Abeta plaques were only seen in the Tg2576 mice at 12 months of age, and were not detected at 4 and 8 months of age. Soluble human-sequence Abeta was detected as early as 4 months of age in the transgenic mice. The altered AChE glycosylation was due to an increase in a minor AChE isoform, which did not bind Con A, similar to that previously observed to be increased in Alzheimer's disease brain and cerebrospinal fluid. The results demonstrate that in transgenic mice altered AChE glycosylation is associated with very early events in the development of AD-like pathology. The study supports the possibility that glycosylation may also be a useful biomarker of AD.

Acetylcholinesterase↗
PubMed2002

Platelet alpha- and gamma-synucleins in Parkinson's disease and normal control subjects.

Alpha-synuclein (alphaSN) has been implicated in Parkinson's Disease (PD) and alphaSN is a major component of Lewy bodies (LBs). This study explored platelets as a model system for study of alphaSN metabolism and platelet alphaSN as a diagnostic marker for PD. We used Western blot analysis to characterize and compare platelet and brain alpha-, beta- and gammaSN; and to quantitate alphaSN levels in platelets from PD and age-matched controls. We found that platelets contain full-length alphaSN and 6 and 12 kDa fragments, and gammaSN-like protein. alphaSN and gammaSN were not secreted by thrombin-activated platelets. Furthermore, we also found that the alphaSN and gammaSN levels in sporadic PD patients and age-matched normal controls were not significantly different. This indicates that platelet alphaSN or gammaSN is not a suitable peripheral diagnostic marker for PD. Platelets may be used for study of alphaSN and gammaSN metabolism, and may give some broad insight into the normal functions of alphaSN and gammaSN.

Biomarkers↗
PubMed2002

Mechanisms of peripheral microvascular dysfunction in transgenic mice overexpressing the Alzheimer's disease amyloid Abeta protein.

Freshly prepared soluble amyloid (Abeta) peptide has been reported to have vascular actions both in vitro and in vivo. This study was designed to examine the in vivo microvascular effects of beta in two skin microvascular model systems that might reflect possible short and long-term vascular effects of this peptide. Short-term vascular effects were examined using freshly prepared soluble Abeta(1-40) peptide superfused over naive rat skin microvasculature for 15 min. Peripheral microvascular functional changes in 9-months-old transgenic (Tg) mice overexpressing soluble beta in the brain, peripheral circulation and other tissues, were also examined. Microvascular responses were monitored using laser Doppler flowmetry from the base of a blister raised on the hind footpad of the animals. Endothelial-dependent and independent vasodilatation responses (VD) were examined using acetylcholine (ACh) and sodium nitroprusside (SNP) respectively. The exposure of naïve rat skin microvasculature to Abeta(1-40) resulted in an immediate vasoconstriction (VC) that prevented ACh but not SNP from inducing a subsequent VD response. The vascular effects of Abeta(1-40) were reversed by antioxidants (superoxide dismutase and catalase) and an endothelin A (ETA) receptor antagonist (BQ-123). Tg mice overexpressing soluble Abeta and C100 showed significant reductions in both endothelial-dependent and endothelial-independent VD that were also reversed by antioxidants and BQ-123. In conclusion, this study provided evidence to support the notion of peripheral vascular effects of Abeta in vivo and present novel evidence for alterations in endothelial and smooth muscle cell function in peripheral skin microvasculature in Tg mice overexpressing Abeta and C100. We suggest that skin microvasculature is a useful model to examine the mechanisms underlying the vascular actions of the Abeta protein.

Acetylcholine↗