Alzheimer's disease: genotypes, phenotypes, and treatments

Structural transitions associated with the interaction of Alzheimer beta-amyloid peptides with gangliosides

Alzheimer's disease is characterized pathologically by the presence of neurofibrillary tangles and amyloid plaques. The principal component of the plaque is the beta-amyloid peptide (Abeta), a 39-43-residue peptide. The conformational change required for the conversion of soluble peptide into amyloid fibrils is modulated by pH, Abeta concentration, addition of kinetic and thermodynamic enhancers, and alterations in the primary sequence of Abeta. We report here the ability of gangliosides to induce an alpha-helical structure in Abeta and thereby diminish fibrillogenesis. Circular dichroism and a fluorescence dye release assay data indicate that gangliosides interact with and induce alpha-helix formation in Abeta. We find that the sialic acid moiety of gangliosides is necessary for the induction of alpha-helical structure. Differences in the amount and the position of the sialic acid on the carbohydrate backbone also affect the conformational switch. The Abeta-ganglioside interaction at pH 7.0, monitored by CD, is stable over time and resistant to high concentrations of NaCl. The induction of alpha-helical structure is greater with Abeta1-40 than Abeta1-42. The ability of gangliosides to sequester Abeta from fibril formation was also evaluated by electron microscopy.

The alternative conformations of amyloidogenic proteins and their multi-step assembly pathways

The conformational change hypothesis postulates that tertiary structural changes under partially denaturing conditions convert one of 17 normally soluble and functional human proteins into an alternative conformation that subsequently undergoes self-assembly into an amyloid fibril, the putative causative agent in amyloid disease. This hypothesis is consistent with Anfinsen's view that the tertiary structure of a protein is determined both by its sequence and the aqueous environment; the latter does not always favor the normally folded state. Unlike sickle cell hemoglobin assembly, where owing to a surface mutation, hemoglobin polymerizes in its normally folded conformation, amyloid proteins self-assemble as a result of the formation of an alternative tertiary structure-a conformational intermediate formed under partially denaturing conditions. The pathway by which an amyloidogenic protein assembles into amyloid fibrils appears to involve quaternary structural intermediates that assemble into increasingly complex quaternary structures, including amyloid protofilaments, which ultimately assemble into amyloid fibrils. Several recent studies have discussed the multi-step assembly pathway(s) characterizing amyloid fibril formation.

Alzheimer's beta-amyloid peptide: affinity for metal chelates

Alzheimer's amyloid peptide, A beta(1-42) and its fragments, A beta(1-28) and A beta(1-16), were chromatographed on IDA-M(II) columns (M: Cu2+, Ni2+ and Zn2+). The retention of A beta(1-42) and its fragments on IDA-Cu(II) could not be reversed in decreasing a gradient of pH, from 7.0 to 4.0. All A beta peptides were recovered from IDA-Ni(II) columns in a decreasing pH gradient from 7.0 to 4.0, within the pH range from 5.6 to 5.1. A beta(1-42) peptide was strongly retained on IDA-Zn(II) at pH 4.0, but its A beta(1-28) and A beta(1-16) were only transiently retained on IDA-Zn(II) columns when applied at pH 6.1. We submit that histidine clusters, residing both in the Alzheimer's beta-amyloid peptide and in most of the APP/APLP superfamily of proteins, constitute high-affinity binding sites for immobilized metal chelates.

Relationship of senescence of cerebrospinal fluid circulatory system to dementias of the aged

In common with other organ systems, the cerebrospinal fluid circulatory system is subject to senescence. Cerebrospinal fluid production and turnover rates decline. The choroid plexus calcifies and its blood supply falters. Microvascular disease violates the integrity of the blood-brain barrier. The arachnoid membranes thicken. Arachnoid villi occlude and degenerate. The consequent functional losses are exacerbated by the deterioration of other interacting organ systems. Eventually, the cerebrospinal fluid circulatory system may fail, resulting in stagnation, contamination, compositional deficiencies, and impaired clearance of noxious substances. The hypothesis is that senescence of the cerebrospinal fluid circulatory system plays a part in some dementias of the aged.

Regulation of amyloid precursor protein catabolism involves the mitogen-activated protein kinase signal transduction pathway

Catabolic processing of the amyloid precursor protein (APP) is subject to regulatory control by protein kinases. We hypothesized that this regulation involves sequential activation of the enzymes mitogen-activated protein kinase kinase (MEK) and extracellular signal-regulated protein kinase (ERK). In the present investigation, we provide evidence that MEK is critically involved in regulating APP processing by both nerve growth factor and phorbol esters. Western blot analysis of the soluble N-terminal APP derivative APPs demonstrated that the synthetic MEK inhibitor PD 98059 antagonized nerve growth factor stimulation of both APPs production and ERK activation in PC12 cells. Moreover, PD 98059 inhibited phorbol ester stimulation of APPs production and activation of ERK in both human embryonic kidney cells and cortical neurons. Furthermore, overexpression of a kinase-inactive MEK mutant inhibited phorbol ester stimulation of APP secretion and activation of ERK in human embryonic kidney cell lines. Most important, PD 98059 antagonized phorbol ester-mediated inhibition of Abeta secretion from cells overexpressing human APP695 carrying the "Swedish mutation." Taken together, these data indicate that MEK and ERK may be critically involved in protein kinase C and nerve growth factor regulation of APP processing. The mitogen-activated protein kinase cascade may provide a novel target for altering catabolic processing of APP.

Estrogens influence growth, maturation, and amyloid beta-peptide production in neuroblastoma cells and in a beta-APP transfected kidney 293 cell line

During development in vivo and in vitro, estrogens: a) increase brain excitability, particularly in limbic structures; b) are responsible for the maturation and cyclicity of limbic-hypothalamic interrelations; c) enhance myelinogenesis; and d) may act with NGF to stimulate neurite formation. In senescence, estrogen administration would improve memory in postmenopausal women. The absence or low levels of estrogens after menopause would increase prevalence of Alzheimer's dementia (AD) more in women than men, irrespective of age or ethnicity. In the present study, addition of 17-beta estradiol to cultured human neuroblastoma cells affected growth slightly, but stimulated cell maturation as shown by increased tyrosine hydroxylase activity. The extracellular deposition in brain tissue and around blood vessels of the amyloid beta-peptide (A beta), a 4.3 kD fragment of the larger integral membrane protein, beta-amyloid precursor protein (beta-APP), is considered an important characteristic of AD. We investigated whether 17-beta estradiol may influence the formation of the A beta (thus the abnormal accumulation of amyloid proteins) in neuroblastoma cells and in a beta-APP transfected human kidney 293 cell line. Two doses of 17 beta-estradiol were added to the cultures of both cell lines. Cells were grown until confluence, metabolically labeled with 35S-methionine, immunoprecipitated with the rabbit antiserum R1282, gel electrophoresed and autoradiographed in order to compare levels of A beta under the different estradiol concentrations. While in neuroblastoma cells, levels of A beta were only slightly reduced after estradiol and a dose-effect relationship with the hormone could not be demonstrated, in the 293 cells, A beta band intensity decreased as concentration of estradiol increased. These data support the role of estrogen in normal and abnormal brain metabolism and suggest potential hormonal interventions which may reduce or prevent the formation of amyloid deposits occur in AD.

The WW domain of neural protein FE65 interacts with proline-rich motifs in Mena, the mammalian homolog of Drosophila enabled

The neural protein FE65 contains two types of protein-protein interaction modules: one WW binding domain and two phosphotyrosine binding domains. The carboxyl-terminal phosphotyrosine binding domain of FE65 interacts in vivo with the beta-amyloid precursor protein, which is implicated in Alzheimer disease. To understand the function of this adapter protein, we identified binding partners for the FE65 WW domain. Proline-rich sequences sharing a proline-proline-leucine-proline core motif were recovered by screening expression libraries for ligands of the FE65 WW domain. Five proteins of molecular masses 60, 75, 80, 140, and 200 kDa could be purified from mouse brain lysates by affinity to the FE65 WW domain. We identified two of these five proteins as the 80- and 140-kDa isoforms encoded by Mena, the mammalian homolog of the Drosophila Enabled gene. Using the SPOTs technique of peptide synthesis, we identified the sequences in Mena that interact with the FE65 WW domain and found that they contain the signature proline-proline-leucine-proline motif. Finally, we demonstrated that Mena binds to FE65 in vivo by coimmunoprecipitation assay from COS cell extracts. The specificity of the Mena-FE65 WW domain association was confirmed by competition assays. Further characterization of the FE65-Mena complex may identify a physiological role for these proteins in beta-amyloid precursor protein biogenesis and may help in understanding the mechanism of molecular changes that underlie Alzheimer disease.

Primate embryonic stem cells

Primate embryonic stem (ES) cells are derived from preimplantation embryos, have a normal karyotype, and are capable of indefinite, undifferentiated proliferation. Even after culture for more than a year, primate ES cells maintain the potential to differentiate to trophoblast and derivatives of embryonic endoderm, mesoderm, and ectoderm. In this review, we compare the characteristics of ES cell lines from two primate species, the rhesus monkey (Macaca mulatta) and the common marmoset (Callithrix jacchus), with the characteristics of mouse ES cells and human embryonal carcinoma cells. We also discuss the implications of using primate ES cells to understand early human development and discuss the practical and ethical implications for the understanding and treatment of human disease.

Low concentrations of estradiol reduce beta-amyloid (25-35)-induced toxicity, lipid peroxidation and glucose utilization in human SK-N-SH neuroblastoma cells

The present studies were undertaken to determine the role of physiologically relevant concentrations of estrogens on amyloid-induced changes in cell viability, metabolic demands, and lipid peroxidation in response to the toxic fragment of beta-amyloid (betaAP 25-35). To this end, SK-N-SH human neuroblastoma cells were exposed to betaAP 25-35 or betaAP 25-35 plus 17beta-estradiol, and cell viability, media glucose use and lactate production were measured at time points ranging from 3 to 15 h for examination of acute effects, or at 48 and 72 h time points for chronic effects. Addition of betaAP 25-35 to SK-N-SH cells decreased the number of viable cells from 5% at 3 h to 35% at 15 h when compared to vehicle controls. Chronic treatment for 48 and 72 h caused decreases in viable cell number of 70% and 65%, respectively. Paradoxically, both glucose utilization and lactate production were found to be increased for the betaAP-treated cells. Concomitant estrogen treatment was found to be neuroprotective, as the severity of the insult on cell viability was decreased by 40% at 15 h and up to 71% at 72 h. Likewise, the addition of 17beta-estradiol decreased both the glucose use and lactate production of the cells. Chronic treatment with betaAP caused increases in lipid peroxidation over vehicle treated controls of 82% and 78% at 48 and 72 h, respectively, while decreases in peroxidation of 48% were seen with simultaneous estrogen treatment. These results indicate that the neuroprotective effects of estrogens against betaAP-induced toxicity are due in part to their capability to decrease lipid peroxidation and may additionally be attributable to decreasing the metabolic load of the cell.

Atomic force microscopic imaging of seeded fibril formation and fibril branching by the Alzheimer's disease amyloid-beta protein

BACKGROUND

Amyloid plaques composed of the fibrillar form of the amyloid-beta protein (Abeta) are the defining neuropathological feature of Alzheimer's disease (AD). A detailed understanding of the time course of amyloid formation could define steps in disease progression and provide targets for therapeutic intervention. Amyloid fibrils, indistinguishable from those derived from an AD brain, can be produced in vitro using a seeded polymerization mechanism. In its simplest form, this mechanism involves a cooperative transition from monomeric Abeta to the amyloid fibril without the buildup of intermediates. Recently, however, a transient species, the Abeta amyloid protofibril, has been identified. Here, we report studies of Abeta amyloid protofibril and its seeded transition into amyloid fibrils using atomic force microscopy.

RESULTS

Seeding of the protofibril-to-fibril transition was observed. Preformed fibrils, but not protofibrils, effectively seeded this transition. The assembly state of Abeta influenced the rate of seeded growth, indicating that protofibrils are fibril assembly precursors. The handedness of the helical surface morphology of fibrils depended on the chirality of Abeta. Finally, branched and partially wound fibrils were observed.

CONCLUSIONS

The temporal evolution of morphologies suggests that the protofibril-to-fibril transition is nucleation-dependent and that protofibril winding is involved in that transition. Fibril unwinding and branching may be essential for the post-nucleation growth process. The protofibrillar assembly intermediate is a potential target for AD therapeutics aimed at inhibiting amyloid formation and AD diagnostics aimed at detecting presymptomatic disease.

Human behavioural genetics of cognitive abilities and disabilities

Although neither the genome nor the environment can be manipulated in research on human behaviour, some of the new tools of molecular genetics can be brought to bear on human behavioural disorders (e.g. cognitive disabilities) and quantitative traits (e.g. cognitive abilities). The inability to manipulate the human genome experimentally has had the positive effect of focusing attention on naturally occurring genetic variation responsible for behavioural differences among individuals in all their complex multifactorial splendour. Genes in such complex multiple-gene systems are called quantitative trait loci (QTLs), which merge the two worlds of genetic research, quantitative genetics and molecular genetics. Although most genetic research on complex human behaviour has focused on severe mental disorders, cognitive abilities and disabilities may be even more immediately relevant to neuroscience. For example, verbal ability and spatial ability are two of the most heritable cognitive abilities, and reading disability is the first behavioural disability for which replicated QTL linkage has been found. The purpose of this essay is to provide an overview of the genetics of cognitive abilities and disabilities as an example of the impending merger of quantitative genetics and molecular genetics in QTL analysis of complex traits.

Aggregated amyloid-beta protein induces cortical neuronal apoptosis and concomitant "apoptotic" pattern of gene induction

To gain a molecular understanding of neuronal responses to amyloid-beta peptide (Abeta), we have analyzed the effects of Abeta treatment on neuronal gene expression in vitro by quantitative reverse transcription-PCR and in situ hybridization. Treatment of cultured rat cortical neurons with Abeta1-40 results in a widespread apoptotic neuronal death. Associated with death is an induction of several members of the immediate early gene family. Specifically, we (1) report the time-dependent and robust induction of c-jun, junB, c-fos, and fosB, as well as transin, which is induced by c-Jun/c-Fos heterodimers and encodes an extracellular matrix protease; these gene inductions appear to be selective because other Jun and Fos family members, i.e., junD and fra-1, are induced only marginally; (2) show that the c-jun induction is widespread, whereas c-fos expression is restricted to a subset of neurons, typically those with condensed chromatin, which is a hallmark of apoptosis; (3) correlate gene induction and neuronal death by showing that each has a similar dose-response to Abeta; and (4) demonstrate that both cell death and immediate early gene induction are dependent on Abeta aggregation state. This overall gene expression pattern during this "physiologically inappropriate" apoptotic stimulus is markedly similar to the pattern we previously identified after a "physiologically appropriate" stimulus, i.e., the NGF deprivation-induced death of sympathetic neurons. Hence, the parallels identified here further our understanding of the genetic alterations that may lead neurons to apoptosis in response to markedly different insults.

Drugs for the prevention and treatment of Alzheimer's disease

Alzheimer's disease affects up to 100,000 people in Australia, but pharmacological treatment has only been available in recent years. Currently available drugs provide modest relief of symptoms for varying periods of time but have no proven preventive action against the disease.

Melatonin alters the metabolism of the beta-amyloid precursor protein in the neuroendocrine cell line PC12

The deposition of amyloid plaques in brain parenchyma is one of the major pathological hallmarks of Alzheimer's disease (AD). The amyloid in senile plaques is composed of the amyloid beta-peptide (A beta) of 39-43 amino acid residues derived from a larger beta-amyloid precursor protein (beta APP). Soluble derivatives of beta APP (sAPP) lacking the cytoplasmic tail, transmembrane domain, and a small portion of the extracellular domain are generated proteolytically by "secretases." Using cell cultures, the authors analyzed the level of sAPP in neuroblastoma and pheochromocytoma (PC12) cells by immunoblotting samples from conditioned media and cell lysates. Normal levels of secretion of sAPP into conditioned media were severely inhibited by treating cells with melatonin (3-4 mM). The inhibitory effect of melatonin on the secretion of sAPP can be reversed. When the cells that were pretreated with melatonin for 10 h were washed, the normal level of secretion of sAPP was restored. Northern blot analyses indicated that the treatment of PC12 cells with melatonin resulted in a significant decrease in the level of mRNA encoding beta APP, beta-actin, and glyceraldehyde-3-phosphate dehydrogenase, and that the treatment of a human neuroblastoma cell line with melatonin resulted in no change in levels of these messages. The secretion of sAPP into the conditioned medium was substantially reduced in the differentiated cells similar to reductions observed in melatonin-treated undifferentiated PC12 cells. Melatonin was found to potentiate the nerve growth factor-mediated differentiation in PC12 cells at 24 h. Taken together, these data suggest that melatonin regulates the metabolism of beta APP and other housekeeping genes in a cell-type specific manner, and that melatonin accelerates the early process of neuronal differentiation.

Accelerated amyloid deposition in the brains of transgenic mice coexpressing mutant presenilin 1 and amyloid precursor proteins

Missense mutations in two related genes, termed presenilin 1 (PS1) and presenilin 2 (PS2), cause dementia in a subset of early-onset familial Alzheimer's disease (FAD) pedigrees. In a variety of experimental in vitro and in vivo settings, FAD-linked presenilin variants influence the processing of the amyloid precursor protein (APP), leading to elevated levels of the highly fibrillogenic Abeta1-42 peptides that are preferentially deposited in the brains of Alzheimer Disease (AD) patients. In this report, we demonstrate that transgenic animals that coexpress a FAD-linked human PS1 variant (A246E) and a chimeric mouse/human APP harboring mutations linked to Swedish FAD kindreds (APP swe) develop numerous amyloid deposits much earlier than age-matched mice expressing APP swe and wild-type Hu PS1 or APP swe alone. These results provide evidence for the view that one pathogenic mechanism by which FAD-linked mutant PS1 causes AD is to accelerate the rate of beta-amyloid deposition in brain.

Current concepts in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) affects a large proportion of the increasingly aging population of this country, with prevalence rates as high as 47% for those >85 years old and a total annual cost approaching $70 billion. There is no currently validated test for detection of dementia of the Alzheimer type (DAT). Because of this and the insidious onset of the disease, the diagnosis may be missed by primary care physicians. Cerebral extracellular beta-amyloid deposition as senile plaques and intraneuronal neurofibrillary tangles appear to represent critical processes in the development of AD; however, whether and the extent to which these may also occur in nondemented aging is uncertain. Tangles occur primarily in medial temporal lobe structures (hippocampus, entorhinal cortex, and amygdala), and tangle density correlates with dementia severity. Plaques are diffusely distributed throughout the cerebral cortex, and are the neuropathologic hallmark of the disease. Aging is the primary risk factor for AD. After controlling for differential life expectancy, female sex still appears to be an additional risk factor. There may be a genetic component, in some cases based on family and twin studies. Allelic variation in the apolipoprotein E (Apo E) gene located on chromosome 19 represents another important risk factor. However, the diversity of gene mutations apparently responsible for the various forms of AD suggest that the disease is genetically heterogeneous. AD may be conceptualized as an imbalance between neuronal injury and repair. Oxygen free radicals may be involved in the cross-linking process of beta-amyloid aggregation, and antioxidants may represent a potential intervention. There may be a role for heavy metals in the pathogenesis of AD, but this remains controversial. Work continues toward possibly a cure or prevention, but more likely palliation, of AD, and the results of trials of anti-inflammatory agents, estrogen, and antioxidant therapy are anticipated in the near future.

What does cell death have to do with aging?

When Lockshin and Zakeri discussed the relevance of apoptosis to aging 7 years ago, the common view was that apoptosis would have primarily a negative impact on aging by destroying essential and often irreplaceable cells. That view has now changed to one that acknowledges that there are two general ways in which apoptosis can play a role in aging: (1) elimination of damaged and presumably dysfunctional cells (e.g., fibroblasts, hepatocytes), which can then be replaced by cell proliferation, thereby maintaining homeostasis, and (2) elimination of essential post-mitotic cells (e.g., neurons, cardiac myocytes), which cannot be replaced, thereby leading to pathology. Evidence exists in two systems (fibroblasts and thymocytes/lymphocytes) that there are age-related decreases in the potential for apoptosis, although the molecular bases for the decreases in these two systems appear to differ. Upon becoming senescent, fibroblasts lose the ability to down-regulate expression of the bcl-2 gene in response to an apoptotic signal; thus, apoptosis is blocked even though an initiating signal has been received. In contrast, thymocytes/lymphocytes lack the ability to initiate the signal because of down-regulation of the cell surface receptor Fas. There is limited information available for other tissue types, and nothing is known about why and how age-related changes occur. An interesting observation is that the frequency of up-regulation of the bcl-2 gene as a result of chromosome translocation in otherwise normal B cells increases with age; the functional consequences of this phenomenon during aging are not known. The role of apoptosis in regulating cell number is also a promising area of research. The studies on liver damage and neoplastic lesions suggest an extremely important role for apoptosis in controlling cancer. This may be particularly important in the prostate where hypertrophy and/or cancer are a virtual certainty with ever-increasing age. It is not known whether the ability to undergo apoptosis declines in the prostate with increasing age, but it appears possible that it may, thus explaining the loss of control over cell number in this tissue. A particularly important area of research is whether apoptosis plays a role in the changing balance between bone formation and resorption observed during osteoporosis. Monica Driscoll has already pointed out that, "regulation and execution of cell death is an absolutely critical process that interfaces with nearly every aspect of life. Future investigation of the links of cell death to cellular aging and the aging of organisms should be an exciting enterprise." The results currently available do suggest that apoptosis is a process that may be important in aging, at least in some tissues, and the mechanism of its regulation, in particular, needs to be understood. Several tumor suppressor gene and oncogene products are involved in signal transduction associated with apoptosis, but it remains to be shown which of these, if any, are actually involved in "on-off" switches for apoptosis. Where great progress has been made is in understanding the events occurring after binding of either Fas ligand or tumor necrosis factor to their respective receptors. However, one area about which little is known is the identity of the signals that initiate this process in response to intracellular damage. Through continuing research on cell death mechanisms, funded by the NIA, we hope to provide answers to such fundamental questions as: 1. Are there age-related changes in apoptosis, and what role, if any, do these have in the aging process? 2. If age-related changes in apoptosis do occur, what molecular mechanisms are altered to produce these changes? 3. Can approaches be developed to improve the detection and elimination of damaged cells in vivo in tissues where cell replacement is possible? 4. Can death of damaged cells be attenuated or delayed in nonrenewable tissues, and, if so, is it advantageous to the org

Inhibition of amyloid formation: a strategy to delay the onset of Alzheimer's disease

Converging evidence suggests that the formation of amyloid plaques may play a central role in the pathogenesis of Alzheimer's disease and that blocking amyloid formation may be an effective therapeutic strategy.

Kinetic theory of fibrillogenesis of amyloid beta-protein

Prior quasielastic light scattering (QLS) studies of fibrillogenesis of synthetic amyloid beta-protein (Abeta)-(1-40) at low pH have suggested a kinetic model in which: (i) fibrillogenesis requires a nucleation step; (ii) nuclei are produced by Abeta micelles in addition to seeds initially present; and (iii) fibril elongation occurs by irreversible binding of Abeta monomers to the fibril ends. Here we present the full mathematical formulation of this model. We describe the temporal evolution of the concentrations of Abeta monomers and micelles as well as the concentration and size distribution of fibrils. This formulation enables deduction of the fundamental parameters of the model-e.g., the nucleation and elongation rate constants kn and ke-from the time dependency of the apparent diffusion coefficient measured by QLS. The theory accurately represents the experimental observations for Abeta concentrations both below and above c*, the critical concentration for Abeta micelle formation. We suggest that the method of QLS in combination with this theory can serve as a powerful tool for understanding the molecular factors that control Abeta plaque formation.

Interaction between amyloid precursor protein and presenilins in mammalian cells: implications for the pathogenesis of Alzheimer disease

Mutations in the presenilin 1 (PS1) and presenilin 2 (PS2) genes increase the production of the highly amyloidogenic 42-residue form of amyloid beta-protein (Abeta42) in a variety of cell lines and transgenic mice. To elucidate the molecular mechanism of this effect, wild-type (wt) or mutant PS1 and PS2 genes were stably transfected into Chinese hamster ovary cells expressing endogenous or transfected beta-amyloid precursor protein (APP). By immunoprecipitation/Western blot analysis, APP was consistently found to coimmunoprecipitate with PS1 or PS2 proteins. Several distinct PS1, PS2, or APP antibodies precipitated PS-APP complexes that were detectable by blotting with either APP or PS antibodies. Importantly, complex formation could be detected at endogenous protein levels in nontransfected cells. In various Chinese hamster ovary cell lines, the amounts of APP coprecipitated by PS antibodies were proportional to the expression levels of both APP and PS. APP-PS complexes also were recovered from human 293 and HS683 cells. Full maturation of APP was not required for the interaction; most APP molecules complexed with PS were solely N-glycosylated. Treatment of cells with brefeldin A or incubation at 20 degrees C did not block complex formation, suggesting that the association between APP and PS occurs in part in the endoplasmic reticulum. Complex formation was detected for both wt and mutant PS and APP proteins. Deletion of the APP C-terminal domain did not abrogate complex formation, suggesting that the interaction does not occur in the cytoplasmic domains of the proteins. Our results demonstrate that wt and mutant PS1 and PS2 proteins form complexes with APP in living cells, strongly supporting the hypothesis that mutant PS interacts with APP in a way that enhances the intramembranous proteolysis of the latter by a gamma-secretase cleaving at Abeta42.

Beta APP gene transfer into cultured human muscle induces inclusion-body myositis aspects

Direct transfer of the beta-amyloid precursor protein (beta APP) gene into cultured normal human muscle, using recombinant adenovirus vector, was sufficient to induce several of the typical light microscopic, electron microscopic (EM), and EM-immunochemical aspects of the inclusion-body myositis (IBM) phenotype, including congophilia, clusters of amyloid-beta-positive 6-10 nm filaments, and 15-21 nm tubulofilamentous inclusions in the nuclei. Our results suggest that excessive production of intracellular beta APP may play an important role in the pathogenic cascade leading to the IBM phenotype.