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Biomedical subjects

R E Tanzi

Publications and source records attributed to R E Tanzi.

At least 37 records · Page 2Linked to original sources
PubMed2000

Genomic structure, expression pattern, and chromosomal localization of the human calsenilin gene: no association between an exonic polymorphism and Alzheimer's disease.

Calsenilin is a recently-identified member of the neuronal calcium sensor family. Like other members of this family, it is found in the brain and binds calcium. Calsenilin was discovered by virtue of its interaction with both presenilin-1 and -2, proteins that are involved in the etiology of Alzheimer's disease. Because calsenilin may play a role in Alzheimer's disease and other disease with alterations in calcium homeostasis, we characterized the human gene. The gene, which we localized to chromosome 2, extends over a region of at least 74 kb and includes nine exons. Interestingly, the ninth exon of calsenilin contains a highly polymorphic CA repeat, adjacent to the stop codon. In a study of Alzheimer patients and their unaffected siblings, there was no evidence of association of AD with any calsenilin allele. This CA repeat will be useful for linkage and linkage disequilibrium studies to determine whether calsenilin variants contribute to risk in other diseases.

Alleles↗
PubMed2000

Mutant presenilin 2 transgenic mice. A large increase in the levels of Abeta 42 is presumably associated with the low density membrane domain that contains decreased levels of glycerophospholipids and sphingomyelin.

The N141I mutation in presenilin (PS) 2 is tightly linked with a form of autosomal dominant familial Alzheimer's disease in the Volga German families. We previously reported that mouse brains harboring mutant PS2 contained increased levels of amyloid beta protein (Abeta) 42 in the Tris-saline-soluble fraction (Oyama, F., Sawamura, N., Kobayashi, K., Morishima-Kawashima, M., Kuramochi, T., Ito, M., Tomita, T., Maruyama, K., Saido, T. C., Iwatsubo, T., Capell, A., Walter, J., Grünberg, J., Ueyama, Y., Haass, C. and Ihara, Y. (1998) J. Neurochem. 71, 313-322). Here, using a new extraction protocol, we quantitated the Abeta40 and Abeta42 levels in the Tris-saline-insoluble fraction. The insoluble Abeta levels were found to be higher than the soluble Abeta levels, and the insoluble Abeta42 levels were markedly increased in mutant PS2 transgenic mice. To investigate the origin of the insoluble Abeta42, we prepared the detergent-insoluble, low density membrane fraction. This fraction from two independent lines of mutant PS2 transgenic mice contained remarkably increased levels of Abeta42 and significantly low levels of glycerophospholipids and sphingomyelin. This unexpected finding suggests that a large increase in the levels of Abeta42 in mutant PS2 mice is presumably induced through alterations of the lipid composition in the low density membrane domain in the brain.

Amino Acid Substitution↗
PubMed2000

3-Hydroxykynurenine and 3-hydroxyanthranilic acid generate hydrogen peroxide and promote alpha-crystallin cross-linking by metal ion reduction.

The kynurenine pathway catabolite 3-hydroxykynurenine (3HK) and redox-active metals such as copper and iron are implicated in cataractogenesis. Here we investigate the reaction of kynurenine pathway catabolites with copper and iron, as well as interactions with the major lenticular structural proteins, the alpha-crystallins. The o-aminophenol kynurenine catabolites 3HK and 3-hydroxyanthranilic acid (3HAA) reduced Cu(II)>Fe(III) to Cu(I) and Fe(II), respectively, whereas quinolinic acid and the nonphenolic kynurenine catabolites kynurenine and anthranilic acid did not reduce either metal. Both 3HK and 3HAA generated superoxide and hydrogen peroxide in a copper-dependent manner. In addition, 3HK and 3HAA fostered copper-dependent alpha-crystallin cross-linking. 3HK- or 3HAA-modifed alpha-crystallin showed enhanced redox activity in comparison to unmodified alpha-crystallin or ascorbate-modified alpha-crystallin. These data support the possibility that 3HK and 3HAA may be cofactors in the oxidative damage of proteins, such as alpha-crystallin, through interactions with redox-active metals and especially copper. These findings may have relevance for understanding cataractogenesis and other degenerative conditions in which the kynurenine pathway is activated.

3-Hydroxyanthranilic Acid↗
PubMed2000

Presenilin 2 interacts with sorcin, a modulator of the ryanodine receptor.

Perturbed Ca(2+) homeostasis is a common molecular consequence of familial Alzheimer's disease-linked presenilin mutations. We report here the molecular interaction of the large hydrophilic loop region of presenilin 2 (PS2) with sorcin, a penta-EF-hand Ca(2+)-binding protein that serves as a modulator of the ryanodine receptor intracellular Ca(2+) channel. The association of endogenous sorcin and PS2 was demonstrated in cultured cells and human brain tissues. Membrane-associated sorcin and a subset of the functional PS2 complexes were co-localized to a novel subcellular fraction that is distinctively positive for calcineurin B. Sorcin was found to interact with PS2 endoproteolytic fragments but not full-length PS2, and the sorcin/PS2 interaction was greatly enhanced by treatment with the Ca(2+) ionophore A23187. Our findings reveal a molecular link between PS2 and intracellular Ca(2+) channels (i.e. ryanodine receptor) and substantiate normal and/or pathological roles of PS2 in intracellular Ca(2+) homeostasis.

Amino Acid Sequence↗
PubMed2000

Modulation of beta-amyloid precursor protein processing by the low density lipoprotein receptor-related protein (LRP). Evidence that LRP contributes to the pathogenesis of Alzheimer's disease.

Beta-amyloid peptide (Abeta), which plays a central role in the pathogenesis of Alzheimer's disease, is derived from the transmembrane beta-amyloid precursor protein (APP) by proteolytic processing. Although mechanisms associated with Abeta generation are not fully understood, it is known that Abeta can be generated within endosomal compartments upon internalization of APP from the cell surface. The low density lipoprotein receptor-related protein (LRP) was previously shown to mediate the endocytosis of APP isoforms containing the Kunitz proteinase inhibitor domain (Kounnas, M. Z., Moir, R. D., Rebeck, G. W., Bush, A. I., Argraves, W. S., Tanzi, R. E., Hyman, B. T., and Strickland, D. K. (1995) Cell 82, 331-340; Knauer, M. F., Orlando, R. A., and Glabe, C. G. (1996) Brain Res. 740, 6-14). The objective of the current study was to test the hypothesis that LRP-mediated internalization of cell surface APP can modulate APP processing and thereby affect Abeta generation. Here, we show that long term culturing of cells in the presence of the LRP-antagonist RAP leads to increased cell surface levels of APP and a significant reduction in Abeta synthesis. Further, restoring LRP function in LRP-deficient cells results in a substantial increase in Abeta production. These findings demonstrate that LRP contributes to Abeta generation and suggest novel pharmacological approaches to reduce Abeta levels based on selective LRP blockade.

Alzheimer Disease↗
PubMed2000

Inhibitors of beta-amyloid formation based on the beta-secretase cleavage site.

A series of inhibitors of beta-amyloid formation have been developed based on the beta-secretase cleavage site (VNL-DA) of the Swedish mutant Amyloid Precursor Protein. A simple tripeptide aldehyde was found to be the most potent (IC(50) = 700 nM) in the series displaying an inhibitory profile which is different from reported inhibitors of beta-amyloid formation.

Aldehydes↗
PubMed2000

Chelation and intercalation: complementary properties in a compound for the treatment of Alzheimer's disease.

Selective application of metal chelators to homogenates of human Alzheimer's disease (AD) brain has led us to propose that the architecture of aggregated beta-amyloid peptide, whether in the form of plaques or soluble oligomers, is determined at least in part by high-affinity binding of transition metals, especially copper and zinc. Of the two metals, copper is implicated in reactive oxygen species generating reactions, while zinc appears to be associated with conformational and antioxidant activity. We tested the copper chelators trientine, penicillamine, and bathophenanthroline for their ability to mobilize brain Abeta as measured against our benchmark compound bathocuproine (BC). All of these agents were effective in solubilizing brain Abeta, although BC was the most consistent across the range of AD brain tissue samples tested. Similarly, all of the copper chelators depleted copper in the high-speed supernatants. BC alone had no significant effect upon zinc levels in the soluble fraction. BC extraction of brain tissue from C100 transgenic mice (which express human Abeta but do not develop amyloid) revealed SDS-resistant dimers as Abeta was mobilized from the sedimentable to the soluble fraction. NMR analysis showed that, in addition to its copper chelating properties, BC interacts with Abeta to form a complex independent of the presence of copper. Such hybrid copper chelating and "chain breaking" properties may form the basis of a rational design for a therapy for Alzheimer's disease.

Alzheimer Disease↗
PubMed2000

Presenilin-mediated modulation of capacitative calcium entry.

We studied a novel function of the presenilins (PS1 and PS2) in governing capacitative calcium entry (CCE), a refilling mechanism for depleted intracellular calcium stores. Abrogation of functional PS1, by either knocking out PS1 or expressing inactive PS1, markedly potentiated CCE, suggesting a role for PS1 in the modulation of CCE. In contrast, familial Alzheimer's disease (FAD)-linked mutant PS1 or PS2 significantly attenuated CCE and store depletion-activated currents. While inhibition of CCE selectively increased the amyloidogenic amyloid beta peptide (Abeta42), increased accumulation of the peptide had no effect on CCE. Thus, reduced CCE is most likely an early cellular event leading to increased Abeta42 generation associated with FAD mutant presenilins. Our data indicate that the CCE pathway is a novel therapeutic target for Alzheimer's disease.

Alzheimer Disease↗
PubMed2000

Uptake of HIV-1 tat protein mediated by low-density lipoprotein receptor-related protein disrupts the neuronal metabolic balance of the receptor ligands.

Neurological disorders develop in most people infected with human immunodeficiency virus type 1 (HIV-1). However, the underlying mechanisms remain largely unknown. Here we report that binding of HIV-1 transactivator (Tat) protein to low-density lipoprotein receptor-related protein (LRP) promoted efficient uptake of Tat into neurons. LRP-mediated uptake of Tat was followed by translocation to the neuronal nucleus. Furthermore, the binding of Tat to LRP resulted in substantial inhibition of neuronal binding, uptake and degradation of physiological ligands for LRP, including alpha2-macroglobulin, apolipoprotein E4, amyloid precursor protein and amyloid beta-protein. In a model of macaques infected with a chimeric strain of simian-human immunodeficiency virus, increased staining of amyloid precursor protein was associated with Tat expression in the brains of simian-human immunodeficiency virus-infected macaques with encephalitis. These results indicate that HIV-1 Tat may mediate HIV-1-induced neuropathology through a pathway involving disruption of the metabolic balance of LRP ligands and direct activation of neuronal genes.

AIDS Dementia Complex↗
PubMed2000

Characterization of copper interactions with alzheimer amyloid beta peptides: identification of an attomolar-affinity copper binding site on amyloid beta1-42.

Cu and Zn have been shown to accumulate in the brains of Alzheimer's disease patients. We have previously reported that Cu(2+) and Zn(2+) bind amyloid beta (Abeta), explaining their enrichment in plaque pathology. Here we detail the stoichiometries and binding affinities of multiple cooperative Cu(2+)-binding sites on synthetic Abeta1-40 and Abeta1-42. We have developed a ligand displacement technique (competitive metal capture analysis) that uses metal-chelator complexes to evaluate metal ion binding to Abeta, a notoriously self-aggregating peptide. This analysis indicated that there is a very-high-affinity Cu(2+)-binding site on Abeta1-42 (log K(app) = 17.2) that mediates peptide precipitation and that the tendency of this peptide to self-aggregate in aqueous solutions is due to the presence of trace Cu(2+) contamination (customarily approximately 0.1 microM). In contrast, Abeta1-40 has much lower affinity for Cu(2+) at this site (estimated log K(app) = 10.3), explaining why this peptide is less self-aggregating. The greater Cu(2+)-binding affinity of Abeta1-42 compared with Abeta1-40 is associated with significantly diminished negative cooperativity. The role of trace metal contamination in inducing Abeta precipitation was confirmed by the demonstration that Abeta peptide (10 microM) remained soluble for 5 days only in the presence of high-affinity Cu(2+)-selective chelators.

Amyloid beta-Peptides↗
PubMed2000

Alzheimer's disease, beta-amyloid protein and zinc.

Alzheimer's disease (AD) is characterized by amyloid deposits within the neocortical parenchyma and the cerebrovasculature. The main component of these predominantly extracellular collections, Abeta, which is normally a soluble component of all biological fluids, is cleaved out of a ubiquitously expressed parent protein, the amyloid protein precursor (APP), one of the type 1 integral membrane glycoproteins. Considerable evidence has indicated that there is zinc dyshomeostasis and abnormal cellular zinc mobilization in AD. We have characterized both APP and Abeta as copper/zinc metalloproteins. Zinc, copper and iron have recently been reported to be concentrated to 0.5 to 1 mmol/L in amyloid plaque. In vitro, rapid Abeta aggregation is mediated by Zn(II), promoted by the alpha-helical structure of Abeta, and is reversible with chelation. In addition, Abeta produces hydrogen peroxide in a Cu(II)/Fe(III)-dependent manner, and the hydrogen peroxide formation is quenched by Zn(II). Moreover, zinc preserves the nontoxic properties of Abeta. Although the zinc-binding proteins apolipoprotein E epsilon4 allele and alpha(2)-macroglobulin have been characterized as two genetic risk factors for AD, zinc exposure as a risk factor for AD has not been rigorously studied. Based on our findings, we envisage that zinc may serve twin roles by both initiating amyloid deposition and then being involved in mechanisms attempting to quench oxidative stress and neurotoxicity derived from the amyloid mass. Hence, it remains debatable whether zinc supplementation is beneficial or deleterious for AD until additional studies clarify the issue.

Alzheimer Disease↗
PubMed2000

GSK3 beta forms a tetrameric complex with endogenous PS1-CTF/NTF and beta-catenin. Effects of the D257/D385A and FAD-linked mutations.

We have previously shown that the endogenous C-terminal fragment of presenilin 1 co-immunoprecipitates with endogenous beta-catenin. Since PS1 has been suggested to be involved in beta-catenin stabilization, we further investigated whether GSK3 beta, responsible for beta-catenin phosphorylation and degradation, is part of the PS1/beta-catenin complex. In naïve H4 and CHO cells, PS1 co-immunoprecipitated with both endogenous beta-catenin and GSK3 beta. In addition, GSK3 beta endogenously binds to the PS1-CTF/NTF complex and beta-catenin in naïve CHO cells. GSK3 beta also co-immunoprecipitated with PS1 full length in CHO cell lines overexpressing PS1 wild type. Given that it has been recently shown that PS1 mutations of aspartate 257 or 385 result in prevention of PS1 endoproteolysis and inhibition of gamma-secretase activity, we also tested whether PS1 endoproteolysis is required for beta-catenin/GSK3 beta/PS1 binding and whether PS1 FAD-linked mutations affect GSK3 beta recruitment in the PS1/beta-catenin complex. GSK3 beta was detected in PS1 immunoprecipitates from H4 cell lines overexpressing PS1 wild type, delta E10, A286E, L246V and in CHO cell lines overexpressing aspartate or M146L mutations. The latter data show that the absence of PS1 endoproteolysis (D257A/D385A and delta E10) or the presence of PS1-FAD mutations does not interfere with beta-catenin/GSK3 beta/PS1 complex formation.

Animals↗
PubMed2000

Metal chelation as a potential therapy for Alzheimer's disease.

Alzheimer's disease is a rapidly worsening public health problem. The current lack of effective treatments for Alzheimer's disease makes it imperative to find new pharmacotherapies. At present, the treatment of symptoms includes use of acetylcholinesterase inhibitors, which enhance acetylcholine levels and improve cognitive functioning. Current reports provide evidence that the pathogenesis of Alzheimer's disease is linked to the characteristic neocortical amyloid-beta deposition, which may be mediated by abnormal metal interaction with A beta as well as metal-mediated oxidative stress. In light of these observations, we have considered the development of drugs that target abnormal metal accumulation and its adverse consequences, as well as prevention or reversal of amyloid-beta plaque formation. This paper reviews recent observations on the possible etiologic role of A beta deposition, its redox activity, and its interaction with transition metals that are enriched in the neocortex. We discuss the effects of metal chelators on these processes, list existing drugs with chelating properties, and explore the promise of this approach as a basis for medicinal chemistry in the development of novel Alzheimer's disease therapeutics.

Alzheimer Disease↗
PubMed2000

Copper catalyzed oxidation of Alzheimer Abeta.

Abeta derived from amyloid plaques of Alzheimer's disease-affected brain contain several oxidative posttranslational modifications. In this study we have characterized the amino acid content of human amyloid-derived Abeta and compared it with that of human synthetic Abeta subjected to metal-catalyzed oxidation. Human amyloid derived Abeta has an increased content of arginine (46%) and glutamate/glutamine residues (28%), but a decreased content of histidine residues (-32%) as compared to the expected amino acid content. Incubation of synthetic human Abeta with Cu(II), but not Fe(III), in the presence of H2O2 similarly induced a decrease in histidine residues (-79%), but also a decrease in tyrosine residues (-28%). Our results suggest that histidine and tyrosine are most vulnerable to metal mediated oxidative attack, consistent with our earlier findings that Cu coordinated via histidine residues is redox competent. Our results suggest that the loss of histidine residues in human amyloid-derived Abeta may be a result of Cu oxidation, and that unidentified post-translational mechanisms operate to modify other amino acids of Abeta in vivo.

Alzheimer Disease↗
PubMed1999

Cu(II) potentiation of alzheimer abeta neurotoxicity. Correlation with cell-free hydrogen peroxide production and metal reduction.

Oxidative stress markers as well as high concentrations of copper are found in the vicinity of Abeta amyloid deposits in Alzheimer's disease. The neurotoxicity of Abeta in cell culture has been linked to H(2)O(2) generation by an unknown mechanism. We now report that Cu(II) markedly potentiates the neurotoxicity exhibited by Abeta in cell culture. The potentiation of toxicity is greatest for Abeta1-42 > Abeta1-40 >> mouse/rat Abeta1-40, corresponding to their relative capacities to reduce Cu(II) to Cu(I), form H(2)O(2) in cell-free assays and to exhibit amyloid pathology. The copper complex of Abeta1-42 has a highly positive formal reduction potential ( approximately +500-550 mV versus Ag/AgCl) characteristic of strongly reducing cuproproteins. These findings suggest that certain redox active metal ions may be important in exacerbating and perhaps facilitating Abeta-mediated oxidative damage in Alzheimer's disease.

Amyloid beta-Peptides↗