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C L Masters

Publications and source records attributed to C L Masters.

At least 163 records · Page 9Linked to original sources
PubMed1995

Cells from peripheral tissues that exhibit high APP expression are characterized by their high membrane fusion activity.

The amyloid precursor protein of Alzheimer's disease (APP) is ubiquitously expressed suggesting a general function throughout the organism. We have used APP-specific antibodies to investigate the expression and localization of APP in different tissues from rat (testis, ovary, liver, kidney, spleen, pancreas, salivary gland). Immunohistochemistry demonstrated that APP is highly expressed in Sertoli cells, follicle cells, secretory cells, podocytes and macrophages. Features common to these cells include their high membrane turnover and their functional characteristics of endocytic and phagocytic retrieval and exocytosis. This suggests APP may participate in interactions of cells of the mononuclear phagocytic system, and function in relation to tissue maintenance and repair.

Amyloid beta-Protein Precursor↗
PubMed1995

Affinity purification of proteoglycans that bind to the amyloid protein precursor of Alzheimer's disease.

The binding of the amyloid protein precursor (APP) to heparan sulfate proteoglycans has been shown to stimulate the neurite-promoting activity of APP. In this study, proteoglycans that bind with high affinity to APP were characterized. Conditioned medium from cultures of postnatal day 3 mouse brain cells was applied to an affinity column containing a peptide homologous to a heparin-binding domain of APP. A fraction 17-fold enriched in proteoglycans was recovered by elution with a salt gradient. APP bound saturably and with high affinity to the affinity-purified proteoglycan fraction. Scatchard analysis of the binding showed that APP bound to high- and low-affinity sites with equilibrium dissociation constants of 1.4 x 10(-11) and 6.5 x 10(-10) M, respectively. APP, in conjunction with the affinity-purified proteoglycan fraction, promoted neurite outgrowth. The affinity-purified proteoglycan fraction contained a heparan sulfate proteoglycan and a chondroitin sulfate proteoglycan. Digestion of the affinity-purified fraction with heparitinase I revealed a core protein of 63-69-kDa molecular mass, whereas digestion with chondroitinase ABC revealed a core protein of 100-110 kDa. The results suggest that expression of specific APP-binding proteoglycans may be an important step in the regulation of the neurite outgrowth-promoting activity of APP.

Alzheimer Disease↗
PubMed1995

The nosology of Creutzfeldt-Jakob disease and conditions related to the accumulation of PrPCJD in the nervous system.

Although typical cases of Creutzfeldt-Jakob disease are readily recognized pathologically and clinically, variant forms often pose a diagnostic challenge. From the 1920's, when this disease was first characterized, until quite recently diagnosis relied heavily on morphologic changes. New advances in immunoassays and PrP gene analysis now provide important adjuncts in recognizing the spectrum of disorders of PrP metabolism associated with these transmissible encephalopathies.

Brain↗
PubMed1995

Neurodegeneration and dementia. Alzheimer's disease as a model.

The common feature in neurodegeneration with dementia is neuronal dysfunction which is mainly and primarily expressed as synaptic dysfunction. The consequence of this dysfunction is neuronal disconnection and dementia if the corresponding hippocampal, basal forebrain and cortical structures are damaged. Neuronal loss is not necessarily a prerequisite for dementia, although it may be observed in some neurodegenerative diseases. If neuronal loss is not the major cause of the symptoms, in principle non-invasive treatment with the aim of cure should be possible, provided intervention occurs early enough. In dementias in which neuronal loss is a major event implantation of nerve cells may become an important aspect in treatment. The latter may apply to vascular dementia (VaD). In contrast neuronal dysfunction may apply for the most common form of dementia, Alzheimer's disease (AD). AD shares some of the characteristic clinical features of VaD, the second most prominent cause of dementia, in which mental deterioration affecting normal brain leads to a loss or impairment of intellectual functions of memory, power of reason and intelligence with interference with patient's conduct of the customary affairs of life. As we begin to understand some of the underlying pathogenetic mechanisms and causes of AD, this most frequent dementing condition is well suited to serve as model system to study the common principles of neurodegenerative diseases. Much of the present knowledge on the molecular and genetic processes that occur in AD came directly or indirectly from the identification of the beta A4 (A beta, beta) amyloid protein and its precursor which is termed amyloid precursor protein, and abbreviated as APP.(ABSTRACT TRUNCATED AT 250 WORDS)

Alzheimer Disease↗
PubMed1995

Molecular neuropathology of Alzheimer's disease.

Alzheimer's disease (AD) is caused by the aberrant metabolism of the amyloid precursor protein (APP) and is consequently associated with the accumulation of one of its degradation products, the beta A4 amyloid protein. The proteases (secretases) which generate beta A4 from APP are now being defined, as is the normal function of APP. How neurons degenerate in AD remains unexplained, but is of central importance in developing new therapeutic approaches. While the genetic factors which contribute to the aberrant metabolism of APP are now being elucidated, the environmental factors which exacerbate this process are unknown.

Alzheimer Disease↗
PubMed1995

Transmissibility of Creutzfeldt-Jakob disease and related disorders.

The spongiform encephalopathies occur in both animals and humans, with kuru, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, and Fatal Familial Insomnia constituting the currently recognised spectrum of such disorders in man. All have proven to be transmissible, including familial cases. Important determinants of transmissibility include the route of inoculation (intracerebral is most effective) and the titre of the inoculated material (brain and spinal cord have greatest infectivity). However, in familial cases, the pathogenic mutations in the PrP gene additionally influence the efficacy of transmission. Recent progress in the molecular biological basis of these diseases suggests that most of the infectivity resides in an abnormal, relatively protease resistant, isoform of the constitutively expressed PrP. The abnormal isoform is postulated to serve as a template for auto-catalytic polymerisation and the consequent deposition of amyloid. Extensions of this hypothesis attempt to reconcile the paradox of how these disorders can be both infectious and also inherited in an autosomal dominant fashion.

Animals↗
PubMed1994

Interaction between the zinc (II) and the heparin binding site of the Alzheimer's disease beta A4 amyloid precursor protein (APP).

The Alzheimer's disease beta A4 amyloid precursor protein (APP) has been suggested to be involved in regulation of cell growth, neurite outgrowth and adhesiveness through binding to heparin sulfate proteoglycans. In order to unravel the molecular mechanisms underlying those functions in vitro we show that APP binds in a time dependent and saturable manner to the glycosaminoglycan side-chains of proteoglycans but not to chondroitinsulfate. We also demonstrate an interaction between the high affinity heparin binding site within the carbohydrate domain of APP and the zinc(II) binding site of APP. We show that the affinity for heparin is increased two- to four-fold in the presence of micromolar zinc(II). Thus micromolar concentrations of zinc(II) appear to be able to modulate the binding of APP to heparin side-chains of proteoglycans and as shown previously [Science 265 (1994) 1464-1467] to induce the aggregation of soluble amyloid beta A4 protein.

Allosteric Site↗
PubMed1994

Complete nucleotide and deduced amino acid sequence of rat amyloid protein precursor-like protein 2 (APLP2/APPH): two amino acids length difference to human and murine homologues.

We present the cDNA sequence of the rat amyloid precursor-like protein 2 (APLP2) comprising the complete coding sequence of 765 amino acid residues. By alternative splicing of two exons, transcripts encoding for 753, 709 and 697 amino acids are also generated. The derived amino acid sequence displays a sequence identity to human APLP2 of approx. 92% and to murine CDEI binding protein of approx. 95%, but differs from both by a deletion of 2 amino acids and an insertion of 4 amino acids within the acidic domain.

Alternative Splicing↗
PubMed1994

Rapid induction of Alzheimer A beta amyloid formation by zinc.

A beta 1-40, a major component of Alzheimer's disease cerebral amyloid, is present in the cerebrospinal fluid and remains relatively soluble at high concentrations (less than or equal to 3.7 mM). Thus, physiological factors which induce A beta amyloid formation could provide clues to the pathogenesis of the disease. It has been shown that human A beta specifically and saturably binds zinc. Here, concentrations of zinc above 300 nM rapidly destabilized human A beta 1-40 solutions, inducing tinctorial amyloid formation. However, rat A beta 1-40 binds zinc less avidly and is immune to these effects, perhaps explaining the scarcity with which these animals form cerebral A beta amyloid. These data suggest a role for cerebral zinc metabolism in the neuropathogenesis of Alzheimer's disease.

Alzheimer Disease↗
PubMed1994

The beta A4 amyloid precursor protein binding to copper.

Previously it has been shown that the extracellular domain of transmembrane beta A4 amyloid precursor protein (APP) includes binding sites for zinc(II) and for molecules of the extracellular matrix such as collagen, laminin and the heparin sulfate chains of proteoglycans (HSPGs). Here we report that APP also binds copper ions. A copper type II binding site was located within residues 135-155 of the cysteine-rich domain of APP695 which is present in all eight APP splice isoforms known so far. The two essential histidines in the type II copper binding site of APP are conserved in the related protein APLP2. Copper(II) binding is shown to inhibit homophilic APP binding. The identification of a copper(II) binding site in APP suggests that APP and APLP2 may be involved in electron transfer and radical reactions.

Amino Acid Sequence↗
PubMed1994

Membrane-associated forms of the beta A4 amyloid protein precursor of Alzheimer's disease in human platelet and brain: surface expression on the activated human platelet.

The amyloid protein precursor (APP) of Alzheimer's disease (AD) is abundantly expressed in platelets, where its primary function remains undetermined. As an integral transmembrane protein, the release of APP from the membrane may be a critical event in AD. We examined the association of APP with human platelet membranes using a combination of alkali treatment and immunoprecipitation of the carboxyl-terminus of APP. Most of the platelet membrane-associated APP (APPMem) with molecular mass of 100 to 130 kD is removed with alkali treatment and is also truncated at the carboxyl-terminus. APPMem is present at least in part on the surface of the platelet. The full-length transmembrane form of APP, as a 140- to 150-kD minor species, is alkali resistant and is also present on the plasma membrane. In contrast, most of the APPMem from brain is full-length (possessing the carboxyl-terminus) with a molecular mass of 105 to 130 kD and is resistant to alkali treatment. Immunoelectron microscopy shows platelet APP to be localized to the alpha-granule. Activation of platelets results in a threefold increase in surface APP detectability. In plasma, the 130-kD APP-reactive band is increased in AD. We find that in the gray platelet syndrome, platelets contain reduced amounts of APP, with a corresponding reduction in plasma APP levels, suggesting that platelets are the major source of plasma APP. Our studies also identify an interaction of APP with platelet membranes which differs from that found in the brain, and raise the possibility of a receptor for APP in platelet membranes. Quantitative differences in the amounts of APPMem in platelets compared with brain also indicate regulation of the pathways that determine the cleavage of APP near its transmembrane domain. These pathways are a therapeutic target in AD, and may be easily amenable to investigation in platelets.

Alzheimer Disease↗
PubMed1994

Secretion of nerve growth factor from septum stimulates neurite outgrowth and release of the amyloid protein precursor of Alzheimer's disease from hippocampal explants.

Alzheimer's disease (AD) is characterized by the deposition of amyloid in the extracellular and intracellular compartments of the cerebral cortex. The extracellular amyloid consists of a protein (beta A4) which is derived from a larger precursor, the amyloid protein precursor (APP). Several studies have implicated APP in the regulation of neurite outgrowth during development, although the precise function of APP remains unknown. To examine the role of APP in the regulation of neurite outgrowth from hippocampal neurons, an explant culture system was developed. Explants of E18 mouse hippocampus were found to extend neurites when co-cultured with explants of E18 mouse septum. This finding demonstrated that the septum can release a neurite outgrowth-promoting factor (NOPF). As nerve growth factor (NGF) was also able to stimulate neurite outgrowth from the hippocampal explants, this suggested that the NOPF might be NGF. Immunoprecipitation of NGF from septal conditioned medium using a specific monoclonal antibody (27/21) completely blocked the neurite outgrowth-promoting effect, supporting this conclusion. Concomitant with its ability to stimulate neurite outgrowth, NGF stimulated the release of APP from the hippocampal explants. As previous studies have suggested that the binding of APP to heparan sulfate proteoglycans (HSPGs) in the extracellular matrix might be an important step in the regulation of neurite outgrowth by NGF, we examined the effect of APP on neurite outgrowth from dissociated hippocampal cells cultured on various protein substrates. When cells were cultured on a substrate of APP and HSPG, neurite outgrowth was markedly stimulated. No stimulation of neurite outgrowth was seen when neurons were cultured on substrates of either APP or HSPG alone. The results suggest that secreted forms of APP may be involved in stimulating neurite outgrowth from hippocampal neurons and that interactions between APP and HSPG may be important for a neurite outgrowth-promoting function.

Amyloid beta-Protein Precursor↗
PubMed1994

Similar alternative splicing of a non-homologous domain in beta A4-amyloid protein precursor-like proteins.

The beta A4-amyloid protein precursor (APP) is a transmembrane glycoprotein that is the source of the characteristic beta A4-amyloid deposits found in Alzheimer brains. It is expressed in several isoforms generated by alternative splicing of exons 7, 8, and 15, of which the leukocyte-derived APP mRNAs lacking exon 15 are significantly expressed in non-neuronal tissues, but not in neurons. The recent finding of APP-like proteins prompted us to analyze alternative splicing of the nearest relative of APP, the amyloid protein precursor homologue (APPH) or amyloid precursor-like protein 2 (APLP2). We were able to show that there are two alternatively spliced inserts, i.e. the Kunitz protease inhibitor domain and a 12-amino-acid-encoding region on the NH2-terminal side of the transmembrane domain, which is part of the region of highest divergence between APP and APLP2/APPH. Analysis of the tissue-specific differential expression of the resulting four APLP2/APPH mRNA isoforms revealed that isoforms lacking the latter, non-homologous insert are highly expressed in non-neuronal tissues, but only weakly in neurons. While this resembles the tissue-specific alternative splicing of exon 15 of APP, expression of the Kunitz protease inhibitor-encoding exon of APLP2/APPH is abundant in both neuronal and non-neuronal tissues and thus differs from APP. Because of the similar regulation of alternative splicing of exon 15 of APP and the described APLP2/APPH insert, and because of structural similarities of the sequences and the predicted secondary structures, a functional homology of alternatively spliced isoforms of APP and APLP2/APPH is suggested.

Alternative Splicing↗
PubMed1994

Transforming growth factor beta mediates increase of mature transmembrane amyloid precursor protein in microglial cells.

By using the immortalized microglial cell line BV-2, we show that the high expression of the beta A4 amyloid precursor protein (APP), its biogenesis and metabolism is modulated by TGF beta, a cytokine with immunosuppressive activity, and by the microglia-stimulating agent LPS. TGF beta induces accumulation of cellular mature APP, the putative precursor of the amyloid subunit of Alzheimer's disease. LPS leads to an increase in cellular immature, non-amyloidogenic APP and secretion of also non-amyloidogenic APP fragments. We also demonstrate a functional involvement of ECM molecules in the regulation of microglial APP expression at mRNA and protein level by TGF beta and LPS.

Amyloid beta-Protein Precursor↗
PubMed1994

Beta A4-amyloid protein precursor mRNA isoforms without exon 15 are ubiquitously expressed in rat tissues including brain, but not in neurons.

The beta A4-amyloid protein precursor (APP), the source of the beta A4-amyloid deposits found in Alzheimer brains, constitutes a family of transmembrane glycoproteins generated by alternative splicing. While exon 7 and exon 8 are well known to be alternatively spliced, APP mRNA isoforms without exon 15 were only recently identified in leukocytes and rat brain microglial cells and therefore denoted as L-APP mRNAs. In order to perform a detailed analysis of individual L-APP mRNA isoforms in perfused rat tissues, we developed a quantitative polymerase chain reaction assay from reverse transcribed RNA allowing us to analyze the alternatively spliced region in between exon 6 and 16. In all peripheral tissues examined, L-APP mRNA isoforms were detected comprising between 25% (skeletal muscle) and about 70% (aorta, pancreas) of total APP transcripts. All four possible APP mRNA isoforms without exon 15 were shown to exist, i.e. L-APP752, L-APP733, L-APP696, and L-APP677. L-APP expression in the central nervous system (approximately 4% of total APP mRNA) was then studied in more detail by analyzing different brain regions and tissues and primary cultured brain cells. The only cell type which was shown not to express L-APP mRNA to a detectable level is the neuronal cell. Ubiquitous expression of APP mRNAs lacking exon 15 except for neurons indicates an important function in non-neuronal cells and is especially remarkable since neurons are the primarily affected cells in Alzheimer's disease.

Alternative Splicing↗
PubMed1994

APP gene family: unique age-associated changes in splicing of Alzheimer's betaA4-amyloid protein precursor.

The betaA4-amyloid protein precursor (APP) is a transmembrane glycoprotein that is the source of the characteristic betaA4-amyloid deposits of Alzheimer brains. It exists in eight isoforms generated by alternative splicing of exons 7, 8 and 15, of which the L-APP mRNAs lacking exon 15 are significantly expressed in non-neuronal cells and tissues, but not in neurones. Recently, it was shown that APP is a member of a multigene family of which the amyloid precursor-like protein 2 (APLP2) is the nearest relative. Analysis of APLP2 expression revealed regulated alternative splicing of the Kunitz protease inhibitor domain (KPI, homologous to exon 7 of APP) and a non-homologous insert of 12 amino acids on the NH2-terminal side of the transmembrane domain. While expression of the KPI encoding exon of APLP2 is abundant in neurones and thus differs from APP, L-APLP2 mRNA isoforms lacking the latter, non-homologous insert show a tissue-specific expression pattern similar to that of exon 15 of APP. Comparison of alternatively spliced APP and APLP2 mRNA isoforms in rat brain regions from early post-natal and adult rats revealed significantly higher relative amounts of KPI-encoding APP isoforms in the adult rat brain and an even more pronounced augmentation of L-APP mRNAs. Both effects were not observed for APLP2. This indicates an APP-specific age-associated regulation pattern within the APP gene family which has intriguing implications for the development of Alzheimer's disease in humans.

Age Factors↗