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PubMed1996

Missense mutations associated with familial Alzheimer's disease in Sweden lead to the production of the amyloid peptide without internalization of its precursor.

Production of soluble amyloid peptide precursor (APP) and amyloid peptide (A beta) was measured in CHO cells transfected by the wild-type APP 695 cDNA sequence or by the same sequence carrying missense mutations associated with familial Alzheimer's disease in Sweden. Deletion of the C-terminal domain of the protein corresponding to residues 654 to 695 of APP 695 not only inhibited very significantly the internalization of APP at 37 degrees C, but also led to the secretion of an uncleaved APP in the culture medium of CHO cells. This deletion did not affect A beta production from the Swedish APP but was able to inhibit the production of the wild-type APP. These results demonstrate that, in CHO cells, the internalization of the wild-type APP is needed for A beta production, while the production of the amyloid peptide from Swedish APP is independent of the internalization process.

Alzheimer Disease↗

PubMed2000

Possible role of calpain in normal processing of beta-amyloid precursor protein in human platelets.

Abnormal proteolytic processing of beta-amyloid precursor protein (APP) underlies the formation of amyloid plaques in aging and Alzheimer's disease. The proteases involved in the process have not been identified. Here we found that spontaneous proteolysis of intact APP in detergent-lysed human platelets generated a N-terminal fragment that was immunologically indistinguishable from secreted APP, reminiscent of the action of a putative alpha-secretase. This proteolysis of APP was inhibited by EDTA, suggesting that a metal-dependent protease was involved. Among the several metals tested, calcium was the only one that enhanced APP proteolysis and the reaction was blocked by EGTA as well as by several calpain inhibitors. The APP fragments generated by spontaneous proteolysis in platelet lysates were identical to those produced by exposure of partially purified APP to exogenous calpain. Finally, the secretion of APP from intact platelets was inhibited by cell-permeable calpain inhibitors. Taken together, these results suggest that normal processing of APP in human platelets is mediated by a calcium-dependent protease that exhibits calpain-like properties.

Amyloid beta-Peptides↗

PubMed1994

Regulation of proteolytic processing of the amyloid beta-protein precursor of Alzheimer's disease in transfected cell lines and in brain slices.

beta A4 is the principal component of Alzheimer's disease brain amyloid. It is derived from proteolytic processing of amyloid beta-protein precursors (APP), a family of transmembrane glycoproteins. Secretion of APPs, a secreted proteolytic derivative that is cleaved within the beta A4 domain of APP, is increased many-fold by the activation of cell-surface receptors, like the muscarinic m1 and m3 receptor subtypes, which are coupled to protein kinase C. Concomitantly, their activation decreases the formation of both secreted soluble beta A4 and of endosomal-lysosomal C-terminal APP derivatives. These data suggest that muscarinic m1 and m3 receptors accelerate non-amyloidogenic APP processing and depress the formation of potentially amyloidogenic derivatives. Other receptors that stimulate APPs secretion include those for bradykinin, vasopressin, and interleukin-1 receptors. A similar control mechanism is present in rat brain tissue slices, in which the release of both APPs and endogenous neurotransmitters is increased by electrical depolarization. This increase is tetrodotoxin-sensitive and frequency-dependent, suggesting that APPs release may normally depend on neuronal activity. Taken together, our findings suggest that specific receptor agonists might be effective in reducing the formation of potentially amyloidogenic APP derivatives in vivo.

Alzheimer Disease↗

PubMed1994

Modulation of the PC12 cell response to nerve growth factor by antisense oligonucleotide to amyloid precursor protein.

1. The amyloid precursor protein (APP) is widely distributed among eukaryotic cells, however, its precise role in cellular functioning is not fully clarified. APP is glycoprotein membrane constituent and it may facilitate membrane associated functions. 2. The aim of the present study was to examine the possibility that APP may play a role in mediating cellular trophic responses. The methods made use of an antisense oligonucleotide that was prepared to the 5' terminus of APP and shown specifically to reduce the level of APP isoforms. 3. In sequential mixing experiments it was observed that the APP antisense oligonucleotide did not significantly modify the trophic response of PC12 cells pretreated with nerve growth factor (NGF). However, pretreatment of cells with the antisense oligonucleotide diminished NGF-induced increases in cellular size and neurite length. 4. These observations suggest that APP may play a role in modulating the trophic response. The combined use of APP antisense oligonucleotides and neurotrophic agents may find clinical utility in the treatment of Alzheimer-type dementia since it is known that NGF normally causes increases in APP levels.

Alzheimer Disease↗

PubMed1991

"Secretase," Alzheimer amyloid protein precursor secreting enzyme is not sequence-specific.

The major pathological change in Alzheimer's disease is the deposition of amyloid beta/A4-protein (beta P) in the brain. beta P is derived from a small part of the much larger amyloid protein precursor (APP). In the normal condition, APP is cleaved in the interior of beta P, preventing the formation of beta P, by a hypothetical proteinase "secretase". To characterize this enzyme, APP and mutated APPs were expressed by cDNA transfection in COS-1 cells, a monkey kidney fibroblast derived cell line. The mutant APPs with the mutations of the proposed cleavage site (Gln686-Lys687) were processed in the same way as wild APP. The deleted mutant APP (deletion of Arg676-Asp694) was also cleaved in a similar way to wild APP. The cleavage site of this deletion mutant was located at the 12 amino acid residues from the predicted membrane spanning domain. Hence, "secretase" cleaves APP, depending not on its specific amino acid sequence, but probably on the relative conformation with plasma membrane.

Alzheimer Disease↗

PubMed1992

Senile plaques in cerebral amyloid angiopathy show accumulation of amyloid precursor protein without cytoskeletal abnormalities.

The abnormal neurites that surround beta-amyloid in senile plaques (SP) in Alzheimer disease contain beta-amyloid precursor protein (beta APP) or abnormal filaments which react with antibodies to tau. Occasionally, beta APP and abnormal filaments are present in the same neurite. Whether both types of abnormal neurites are reactive to the presence of beta-amyloid or they are instead independent from each other is unknown. To begin to clarify this issue, we comparatively studied beta APP and tau-epitopes in SP from cases of classical Alzheimer disease and cases of cerebral amyloid angiopathy, with SP but without neurofibrillary pathology. In subjects with cerebral amyloid angiopathy, about one-third of SP, the same percentage as in Alzheimer disease, were beta APP reactive in the absence of tau-reactivity. beta APP epitopes were ultrastructurally localized in dense bodies of probable lysosomal origin, adjacent to the core of SP. These results demonstrate that beta APP and tau-reactive cytoskeletal alterations occur independently in the neurites of SP. The presence of beta APP in dystrophic neurites of SP and the localization of beta APP in lysosomes suggest that beta APP containing dystrophic neurites may play a role in the extracellular deposition of amyloid.

Alzheimer Disease↗

PubMed1995

The muscarinic M1 agonist xanomeline increases soluble amyloid precursor protein release from Chinese hamster ovary-m1 cells.

The functionally selective M1 agonist xanomeline, which is currently undergoing clinical trials as a therapy for Alzheimer's disease, was compared to the muscarinic agonist carbachol for effects on secretion of soluble amyloid precursor protein (APPs) from Chinese hamster ovary cells transfected with the human m1 receptor (CHO-m1). Release of APPs from CHO-m1 cells was increased maximally (4-10 fold) by 100 microM carbachol (EC50 = 11 microM) and by 100 nM xanomeline (EC50 = 10 nM). Stimulation of APPs secretion by xanomeline and carbachol was blocked by preincubation with 1 microM atropine. Carbachol did not stimulate APPs secretion from non-transfected CHO cells. Pilocarpine at 1 mM also increased APPs release. The efficacy of carbachol, xanomeline and pilocarpine for stimulating APPs secretion did not differ significantly. Activation of protein kinase C (PKC) in m1 transfected cell lines by 1 microM phorbol dibutyrate (PDBu) increased APPs release, and this was inhibited 97% by the PKC inhibitor bisindolemalemide. The PKC inhibitor decreased xanomeline and carbachol-stimulated APPs secretion by only 25-30%. These results demonstrate that xanomeline increased APPs release by activation of m1 muscarinic receptors and support the possibility that cholinergic replacement therapy for Alzheimer's Disease may reduce amyloid deposition.

Amyloid beta-Protein Precursor↗

PubMed1987

Human acid beta-glucosidase: use of inhibitors, alternative substrates and amphiphiles to investigate the properties of the normal and Gaucher disease active sites.

Comparative studies with lipoidal inhibitors and alternative substrates were conducted to investigate the properties of the active site of human acid beta-glucosidase (D-glucosyl-N-acylsphingosine glucohydrolase, EC 3.2.1.45) from normal placenta and spleens of Type 1 Ashkenazi Jewish Gaucher disease (AJGD) patients. With the normal enzyme, the inhibitory potencies of series of alkyl(Cn; n = 0-18)amines, alkyl beta-glucosides and alkyl-1-deoxynojirimycins were a biphasic function of increasing chain length: i.e., large decreases in Ki,app or IC50 were found only with n greater than 4 and limiting values were approached with n = 12-14. This biphasic function of alkyl chain length was observed in the presence or absence of detergents and/or negatively charged lipids. In the presence of Triton X-100 concentrations greater than the critical micellar concentration, the relative (to deoxynojirimycin) inhibitory potencies of the N-Cn-deoxynojirimycins (n greater than 4) were decreased about 3-5-fold, due to an energy requirement to extract the inhibitors from Triton X-100 micelles. The Ki,app or IC50 of N-hexylglucosylsphingosine was inversely related to the Triton X-100 concentration and was not affected by the presence of 'co-glucosidase'. The mutual exclusion of glucon, N-Cn-deoxynojirimycin and sphingosine derivatives from the normal enzyme suggested a shared region for binding in the active site. Increasing the fatty-acid acyl chain length of glucosyl ceramide from 1 to 24 carbons had minor effects on Km,app ( = Kis,app) (8-40 microM), but increased Vmax,app up to 13-fold. With the AJGD enzyme, the inhibitor and alternative substrate findings were similar to those with the normal enzyme, except that Kis,app(AJGD)/Kis,app(normal) = 4 to 11 for the Cn-glycons and sphingosine derivatives. These results indicated that (1) the Ki,app or Km,app values for amphiphilic inhibitors or substrates reflect a balance of binding energies for two hydrophobic subsites within the enzyme's active site and Triton X-100 micelles and (2) the abnormal properties of the AJGD enzyme result from an amino-acid alteration(s) within or near a hydrophilic region which is shared by the glycon-binding site and the two hydrophobic sites of the active site.

1-Deoxynojirimycin↗

PubMed1993

Alzheimer's amyloid precursor protein mRNA without exon 15 is ubiquitously expressed except in the rat central nervous system.

The expression of L-beta A4 amyloid precursor protein (L-APP) mRNA, which is a splicing product excluding exon 15 of the APP gene, was investigated in various tissues of adult rats by a polymerase chain reaction analysis of reverse-transcribed RNA (RT-PCR). L-APP mRNA was ubiquitously expressed in all the examined tissues including the liver, kidney, heart, skeletal muscle, spleen, thymus, adrenal, stomach, submandibular gland, testis and ovary, except for the central nervous system (CNS) tissues such as the brain and spinal cord. The DNA sequence analysis of the RT-PCR products from adult rat liver showed an L-APP cDNA form, in which exon 14 was spliced from exon 14 to exon 16, and exon 15 of the APP gene was excluded. In addition, regarding as the brain and liver, L-APP mRNA expression was examined during the development of the embryonic stage. In the brain, no L-APP mRNA expression was detected even in the embryonic stage, whereas L-APP mRNA expression of the liver was still found in the embryonic stage. These results suggest that the splicing event excluding exon 15, which is exactly adjacent to exon 16 and exon 17 encoding the beta A4 protein, would probably occur very rarely in the CNS and that the splicing of L-APP might already be regulated in the embryonic stage.

Amyloid beta-Protein Precursor↗

PubMedDate not supplied

Detection of distinct isoform patterns of the beta-amyloid precursor protein in human platelets and lymphocytes.

Cerebral deposition of the amyloid beta-protein (A beta P), approximately 40 residue fragment of the integral membrane protein, beta-amyloid precursor protein (beta APP), has been implicated as the probable cause of some cases of familial Alzheimer's disease (AD). The parallels between A beta P deposition in AD and the deposition of certain plasma proteins in systemic amyloid diseases has heightened interest in the analysis of beta APP in circulating cells and plasma. Here, we describe distinct isoform patterns of beta APP in peripheral platelets and lymphocytes. PCR-mediated amplification of mRNA from purified platelets demonstrated the expression of all three major beta APP transcripts (beta APP770,751,695). The full-length, approximately 140 kDa form of beta APP751,770 was detected in membranes of resting and activated platelets but very little immature, approximately 122 kDa beta APP751,770 was found, suggesting a different processing of beta APP in platelets than that described in a variety of cultured cells and tissues. Platelets stimulated with thrombin, calcium ionophore, or collagen released the soluble, carboxyl-truncated form of beta APP (protease nexin-II), but no evidence for the shedding of full-length beta APP associated with platelet microparticles was found, in contrast to previous reports. As a positive control marker for microparticles, the fibrinogen receptor subunit, GPIIIa, was readily detected in platelet releasates. Resting and activated platelets contained similar amounts of the approximately 10 kDa carboxyl terminal beta APP fragment that is retained in platelet membranes following the constitutive cleavage of protease nexin-II. Nonstimulated peripheral B and T lymphocytes contained small amounts of membrane-associated mature and immature beta APP751,770. The potentially amyloidogenic full-length beta APP molecules present in circulating platelets and lymphocytes but not in microparticles could serve as a source of the microvascular A beta P deposited during aging and particularly in AD.

Adult↗

PubMed1990

Differential expression of amyloid precursor protein mRNAs in cases of Alzheimer's disease and in aged nonhuman primates.

Senile plaques are a characteristic feature in brains of individuals with Alzheimer's disease (AD) and aged monkeys. The principal component of amyloid in senile plaques is beta/A4, a peptide derived from a larger amyloid precursor protein (APP). To date, several alternatively spliced APP transcripts have been described. The relationship between levels of these APP mRNAs and amyloid deposition is unclear. In this study, we directly measured the relative levels of APP transcripts that lack the protease inhibitor domain (APP-695) and transcripts that encode the inhibitor sequences (APP-751/770). Our results indicate that the expression of APP mRNAs is not selectively altered in AD cortex. Moreover, the differential expression of APP transcripts is not correlated with the deposition of amyloid in cases of AD and aged monkeys. These findings suggest that other factors, not directly related to the relative expression of APP mRNAs, may contribute to amyloidogenesis in the brain.

Aging↗

PubMed1993

Activation of protein kinase C increases the extracellular release of the transmembrane amyloid protein precursor of Alzheimer's disease.

The beta A4 peptide is the major constituent of the amyloid core of abundant senile plaques found in the cerebral cortex of patients with Alzheimer's disease. This amyloid peptide is synthesized as part of a large transmembrane amyloid protein precursor or APP. In addition to the highly expressed transmembrane APP isoforms, an mRNA encoding a secreted APP lacking the transmembrane domain has been identified. A cleavage of the transmembrane protein also yields an extracellular soluble APP fragment. The effect of phorbol esters on the release of the extracellular APP was studied in transfected Chinese hamster ovary cells which stably express either a transmembrane or a secreted APP isoform. The activation of protein kinase C by phorbol-12,13-dibutyrate increased the extracellular release of the transmembrane APP resulting from its proteolytic cleavage, while 4-beta-phorbol, which does not activate protein kinase C, did not significantly affect the recovery of the soluble APP. On the contrary, the recovery of APP secreted in the culture medium without proteolytic cleavage was not increased by protein kinase C-mediated phosphorylation.

Alkaloids↗

PubMed1996

Differential effects of trilostane and cyanoketone on the 3 beta-hydroxysteroid dehydrogenase-isomerase reactions in androgen and 16-androstene biosynthetic pathways in the pig testis.

3 beta-Hydroxysteroid dehydrogenase-isomerase (3 beta-HSD-I) activity in the pig testis is responsible for the conversion of dehydroepiandrosterone (DHA) to 4-androstenedione and also for the conversion of 5,16-androstadien-3 beta-ol (andien-beta) to 4, 16-androstadien-3-one (dienone). Therefore, 3 beta-HSD-I plays an essential role in the biosynthesis of hormonally and pheromonally active steroids. Previous studies from this laboratory have suggested that the 3 beta-HSD-I reactions in the androgen and 16-androstene biosynthetic pathways may be catalysed by different enzymes with selective substrate specificities [3, 4]. The aim of the present studies was to investigate the reactions further by examining the effects of two classical steroidal inhibitors of 3 beta-HSD-I, trilostane (WIN 24540) and cyanoketone (WIN 19578), on the kinetic parameters of the 3 beta-HSD-I reactions in immature (< 3 weeks) pig testis microsomes. In kinetic analyses of the conversion of DHA to 4-androstenedione, both trilostane and cyanoketone caused increases in the Km(app) for DHA which at the highest concentration used, were 15-fold the control Km(app) of 1.4 mumol/l. No effect on the Vmax(app) (6.55 +/- 0.74 nmol/h/mg protein) was observed, demonstrating that competitive inhibition was evident. Slope and intercept replots confirmed the competitive nature of the inhibition and Ki(app) values of 0.16 mumol/l for trilostane and 0.20 mumol/l for cyanoketone were respectively 9 and 7-fold lower than the Km(app) value. In contrast, trilostane and cyanoketone had no effect on the Km(app) for andien-beta (0.26 mumol/l). The Vmax(app) (1.12 nmol/h/mg protein) was decreased by 40-50% only by trilostane at the highest concentration used, demonstrating a very low affinity for the andien-beta active site. Ki(app) values for trilostane and cyanoketone, obtained from slope and intercept replots were, respectively 1.1 and 1.6 mumol/l, which were 4 and 6-fold greater than the Km(app) for andien-beta. Therefore, trilostane and cyanoketone were powerful competitive inhibitors of the conversion of DHA to 4-androstenedione but were weak non-competitive inhibitors of the conversion of andien-beta to dienone. The selective effects of trilostane and cyanoketone on the 3 beta-HSD-Is involved in the androgen and 16-androstene biosynthetic pathways strongly suggest that the reactions are catalysed by separate enzymes, or at least separate, non-interacting active sites on a single enzyme.

Androstadienes↗

PubMed2003

Enhancement of proteolytic processing of the beta-amyloid precursor protein by hyperforin.

We studied the effect of hyperforin, a component of St. John's wort (Hypericum perforatum) extracts, on the processing of the amyloid precursor protein (APP) in rat pheochromocytoma PC12 cells, stably transfected with human wildtype APP. We observed transiently increased release of secretory APP fragments upon hyperforin treatment. Unique features, like a strong reduction of intracellular APP and the time course of soluble APP release, distinguished the effects of hyperforin from those of alkalizing agents and phorbol esters, well known activators of secretory processing of APP. Carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP), a protonophore, induced an almost identical decrease in intracellular pH in PC12 cells as does hyperforin. Despite this, FCCP induced a less pronounced release of soluble APP fragments and only slightly reduced intracellular APP levels. These results suggest that hyperforin is an activator of secretory processing of APP with a novel mechanism of action not solely dependent on its effects on intracellular pH.

Amyloid beta-Protein Precursor↗

PubMed2005

Restraint stress induces beta-amyloid precursor protein mRNA expression in the rat basolateral amygdala.

Several studies have shown the involvement of beta-amyloid precursor proteins (APP) isoforms in physiological process like development of the central nervous system (CNS), functional roles in mature brain, and in pathological process like Alzheimer's disease, neuronal experimental damage, and stress, among others. However, the APP functions are still not clear. In the brain, APP(695) isoform is predominantly found in neurons while APP(751/770) isoforms are predominantly found in astroglial cells and have been associated to neurodegenerative processes. Acute or chronic stress in rats may trigger specific response mechanisms in several brain areas such as amygdala, hippocampus and cortex with the involvement of multiple neurotransmitters. Chronic stress may also induce neuronal injury in rat hippocampus. In situ hybridization (ISH) was used to investigate the expression of APP(695) and APP(751/770) mRNA in amygdala and hippocampus of male Wistar rats (n=4-6 per group) after acute (2 or 6h) or chronic (2h daily/7 days or 6h daily/21 days) restraint stress. Only the APP(695) mRNA expression was significantly increased in the basolateral amygdaloid nuclei following acute or chronic restraint. No APP isoform changed in hippocampus after any stress condition. These results suggest that restraint stress induces changes in gene expression of APP(695) in basolateral amygdaloid nucleus, an area related to stress response.

Amygdala↗

PubMed2006

Allele-specific silencing of Alzheimer's disease genes: the amyloid precursor protein genes with Swedish or London mutations.

Alzheimer's disease (AD) is the most common cause of dementia in humans. A pathological hallmark in the brain of an AD patient is extracellular amyloid plaques formed by accumulated beta-amyloid protein (Abeta), a metabolic product of amyloid precursor protein (APP). Studies have revealed a strong genetic linkage in the early-onset familial form (<60 years old) of AD. For example, some mutant APPs are transmitted dominantly and are segregated with inheritance of early onset AD. These mutants facilitate Abeta production. The "Swedish" mutations (APP(SW)) and the "London" mutation (APP(LON)) are examples of these mutants. Selective silencing of these mutant alleles holds therapeutic promise for AD. Here we show that the expression of the mutant APPs was selectively inhibited by RNA interference. The best selectivity was obtained when the mismatches were centrally placed in the antisense strand of small interfering RNAs. Introducing an additional mismatch in the antisense strand may improve the selectivity. The addition of a G at 5' end of the antisense strand may enhance the efficacy of gene silencing by RNA interference. Our results illustrate the guiding principles for selection of targeted sequences to achieve allele-specific silencing. The sequences that are effective to silence APP(SW) and APP(LON) as identified in this study may be useful in both in vivo and in vitro studies to investigate the pathophysiological role of APP(SW) and APP(LON) in AD development.

Alleles↗

PubMed2006

Expression cloning screen for modifiers of amyloid precursor protein shedding.

Ectodomain shedding of the amyloid precursor protein (APP) is a key regulatory step in the generation of the amyloid beta peptide (Abeta), which is thought to provoke the pathogenesis of Alzheimer's disease. To better understand the cellular processes that regulate ectodomain shedding of APP we used human embryonic kidney 293 cells and applied a sib-selection expression cloning approach. In addition to a known activator of APP shedding -- protein kinase A -- the following cDNAs were identified: the endocytic proteins endophilin A1 and A3, the metabotropic glutamate receptor 3 (mGluR3), palmitoyl-protein thioesterase 1 (PPT1), Numb-like and the kinase MEKK2. Endophilins A1 and A3, as well as mGluR3 activated APP shedding relatively specifically. They had little or no effect on the shedding of the unrelated membrane proteins TNF receptor 2 and P-selectin glycoprotein ligand-1. In contrast, MEKK2 and PKA also increased shedding of TNF receptor 2, suggesting that these kinases contribute to a general program regulating ectodomain shedding. The strongest activator of APP shedding, endophilin A3, reduced the rate of APP endocytosis and specifically increased APP shedding by the protease alpha-secretase, as measured in an antibody uptake assay and by immunoblot analysis. This suggests that endophilin A3 is a novel modulator of APP trafficking affecting access of APP to alpha-secretase. In summary, this study shows that expression cloning is a suitable way to identify proteins controlling ectodomain shedding of membrane proteins.

Acyltransferases↗

PubMed2006

Muscarinic acetylcholine receptor inhibition in transgenic Alzheimer-like Tg2576 mice by scopolamine favours the amyloidogenic route of processing of amyloid precursor protein.

The molecular mechanisms of the interrelationship between cholinergic neurotransmission, processing of amyloid precursor protein (APP) and beta-amyloid (Abeta) production in vivo are still less understood. To reveal any effect of cholinergic dysfunction on APP processing in vivo, 11-month-old transgenic Tg2576 mice with Abeta plaque pathology received intraperitoneal injections of scopolamine at a daily dosage of 2mg/kg body weight for 14 days in order to suppress cortical cholinergic transmission by chronic inhibition of muscarinic acetylcholine receptors. Scopolamine treatment of transgenic Tg2576 mice resulted in increased levels of fibrillar Abeta(1-40) and Abeta(1-42), while the soluble, SDS-extractable Abeta level remained unchanged as compared to vehicle-injected Tg2576 mice. alpha-Secretase activity determined in cortical tissue from scopolamine-treated Tg2576 mice was lower by about 30% as compared to that assayed in control mice, while beta-secretase activity and BACE1 protein expression appeared unaffected by scopolamine treatment. The amount of sAPPalpha, the product secreted by alpha-secretase-mediated APP cleavage, and the unprocessed APP were assayed in the soluble and membrane fraction, respectively, of cortical tissue preparations from treated and control mice by Western blotting. Using the anti antibody 6E10 which specifically labels human sAPPalpha and full length APP in transgenic Tg2576, an enhanced APP level was detected in the membrane fraction from treated mice as compared to controls, while in the soluble fraction scopolamine treatment did not affect the protein level of sAPPalpha. These data indicate an accumulation of APP in cortical membrane fraction in scopolamine-treated Tg2576 mice presumably due to the decreased level of alpha-secretase-mediated APP cleavage, and further suggest that chronic suppression of cortical muscarinic cholinergic transmission may alter the balance between alpha- and beta-secretory APP processing by favouring the amyloidogenic route.

Alzheimer Disease↗