Specific spatial learning deficits become severe with age in beta -amyloid precursor protein transgenic mice that harbor diffuse beta -amyloid deposits but do not form plaques

Memory impairment progressing to dementia is the main clinical symptom of Alzheimer's disease (AD). AD is characterized histologically by the presence of beta-amyloid (Abeta) plaques and neurofibrillary tangles in specific brain regions. Although Abeta derived from the Abeta precursor protein (beta-APP) is believed to play a central etiological role in AD, it is not clear whether soluble and/or fibrillar forms are responsible for the memory deficit. We have generated and previously described mice expressing human wild-type beta-APP(751) isoform in neurons. These transgenic mice recapitulate early histopathological features of AD and form Abeta deposits but no plaques. Here we describe a specific and progressive learning and memory impairment in these animals. In the Morris water maze, a spatial memory task sensitive to hippocampal damage, one pedigree already showed significant differences in acquisition in 3-month-old mice that increased in severity with age and were expressed clearly in 6-month- and 2-year-old animals. The second transgenic pedigree displayed a milder impairment with a later age of onset. Performance deficits significantly decreased during the 6 days of training in young but not in aged transgenic animals. Both pedigrees of the transgenic mice differed from wild-type mice by less expressed increase of escape latencies after the platform position had been changed in the reversal experiment and by failure to prefer the goal quadrant in probe trials. Both pedigrees performed at wild-type level in a number of other tests (open field exploration and passive and active place avoidance). The results suggest that plaque formation is not a necessary condition for the neuronal beta-APP(751) transgene-induced memory impairment, which may be caused by beta-APP overexpression, isoform misexpression, or elevated soluble Abeta.

Neuronal DNA damage correlates with overexpression of interleukin-1beta converting enzyme in APPV717F mice

Transgenic APPV717F mice, homozygous for a human minigene encoding the V717F familial Alzheimer's disease mutation, develop Abeta plaques similar to those seen in Alzheimer patients and show evidence of neuronal cell drop out in CA2-3 regions of the hippocampus at 8 months of age and older. Interleukin-1 (IL-1)beta (IL-1beta) converting enzyme (ICE) is a cysteine protease (caspase-1) that processes inactive (33 kDa) pro-IL-1beta to the active (17 kDa) inflammatory cytokine. We used immunohistochemistry, RT-PCR, and DNA cleavage (TUNEL) analysis to show progressive, age-associated increases in ICE mRNA levels, in the numbers of ICE-immunoreactive glia, and in the numbers of neurons showing evidence of DNA damage in APPV717F mice that commenced months prior to the appearance of Abeta plaques. Moreover, there were significant correlations between these parameters over an age range of 1-17 months. These findings are consistent with the idea that increases in ICE activity and expression contribute to neuronal injury in Alzheimer's disease.

Glycogen synthase kinase-3beta regulates presenilin 1 C-terminal fragment levels

The majority of familial Alzheimer's disease cases have been attributed to mutations in the presenilin 1 (PS1) gene. PS1 is synthesized as an inactive holoprotein that undergoes endoproteolytic processing to generate a functional N- and C-terminal heterodimer (NTF and CTF, respectively). We identified a single residue in PS1, Ser(397), which regulates the CTF levels in a population of dimer that has a rapid turnover. This residue is part of a highly conserved glycogen synthase kinase-3beta (GSK-3beta) consensus phosphorylation site within the loop domain of PS1. Site-directed mutagenesis at the Ser(397) position increased levels of PS1 CTF but not NTF or holoprotein. Similar increases in only CTF levels were seen when cells expressing wild type PS1 were treated with lithium chloride, an inhibitor of GSK-3beta. Both wild type and PS1 S397A CTF displayed a biphasic turnover, reflecting rapidly degraded and stable populations. Rapid turnover was delayed for mutant PS1 S397A, causing increased CTF. These data demonstrate that PS1 NTF.CTF endoproteolytic fragments are generated in excess, that phosphorylation at Ser(397) by GSK-3beta regulates the discard of excess CTF, and that the disposal of surplus NTF is mediated by an independent mechanism. Overall, the results indicate that production of active NTF.CTF dimer is more complex than limited endoproteolysis of PS1 holoprotein and instead involves additional regulatory events.

Conversion of brain apolipoprotein E to an insoluble form in a mouse model of Alzheimer disease

A beta deposition in the APPV717F transgenic model of Alzheimer's pathology involves apolipoprotein E (apoE). We measured soluble and insoluble apoE in brain region extracts at an early and late stage of plaque development. The apoE levels in the insoluble fraction were greatly elevated in the hippocampus and cortex of aged transgenic animals but were unchanged in wild type or young APPV717F animals. Soluble apoE levels were unaltered. A beta levels were also measured and a positive correlation between apoE and A beta in the insoluble fraction was observed. ApoE transcription was increased approximately 3-fold in the hippocampus of 17-month-old APPV717F mice, suggesting a region-specific upregulation of apoE transcription in the brains of APPV717F mice to compensate for apoE sequestered with fibrillar A beta.

Novel functional assay for proteases and modulators. Application in beta-secretase studies

Proteases play a critical role in many cellular functions and have been an attractive therapeutic target due to their involvement in a number of disease processes. One prominent example is the secretases responsible for the generation of amyloid beta peptide, which is believed to be central for the development of Alzheimer's disease. It is therefore desirable to identify and characterize these proteases. We have developed a novel functional approach for identification of proteases and modulators by coupling the protease activity to caspase-mediated apoptosis. Here we show the proof of principle for this approach using beta-secretase as an example. We provide data showing that 1. A modified caspase-3 containing beta-secretase cleavage site induces apoptosis in 293T cells. 2. The modified caspase-3 induced apoptosis is correlated with the susceptibility of beta-secretase recognition sequence to beta-secretase. 3. In vivo beta-secretase competitors BACE2 and BACE2(D110A) prevent the modified caspase-3 induced cell death. Therefore, this approach can be a useful tool in studies of proteolytic cleavage provided only that the protease recognition sequence is known.

Beta-amyloid precursor detected in human cerebral cortex

1. Amyloid deposition is one of the pathologic hallmarks of Alzheimer's disease. Since the isolation of the beta-amyloid gene, which revealed that the amyloid forming 4 kD protein is part of a larger precursor, interest has focused on the process by which amyloid is generated and deposited. 2. The authors have developed an immunologic means of detecting amyloid precursor proteins in human brain. 3. The method involves the expression of human beta-amyloid precursor cDNA in a recombinant vaccinia virus, so that antibodies are produced against the precursor proteins in their native forms. 4. By using this expression system, the amyloid precursor immunogens incorporate post-translational modifications that normally occur in vivo; this cannot be achieved with small synthetic peptides. 5. Using antibodies to the 695 residue amyloid precursor, we have detected using Western blot analysis a protein of approximately 120 kD in samples of cerebral cortex from three subjects with Alzheimer's disease and one control subject. 6. Additional antibodies to other amyloid-related proteins have been developed. These are being used to assess the differential expression of the various amyloid precursors and subdomains in additional cases.

Substitution of a glycogen synthase kinase-3beta phosphorylation site in presenilin 1 separates presenilin function from beta-catenin signaling

The majority of cases with early onset familial Alzheimer's disease have been attributed to mutations in the presenilin 1 (PS1) gene. PS1 protein is a component of a high molecular weight membrane-bound complex that also contains beta-catenin. The physiological relevance of the association between PS1 and beta-catenin remains controversial. In this study, we report the identification and functional characterization of a highly conserved glycogen synthase kinase-3beta consensus phosphorylation site within the hydrophilic loop domain of PS1. Site-directed mutagenesis, together with in vitro and in vivo phosphorylation assays, indicates that PS1 residues Ser(353) and Ser(357) are glycogen synthase kinase-3beta targets. Substitution of one or both of these residues greatly reduces the ability of PS1 to associate with beta-catenin. By disrupting this interaction, we demonstrate that the association between PS1 and beta-catenin has no effect on Abeta peptide production, beta-catenin stability, or cellular susceptibility to apoptosis. Significantly, in the absence of PS1/beta-catenin association, we found no alteration in beta-catenin signaling using induction of this pathway by exogenous expression of Wnt-1 or beta-catenin and a Tcf/Lef transcriptional assay. These results argue against a pathologically relevant role for the association between PS1 and beta-catenin in familial Alzheimer's disease.

Pathology of early-onset Alzheimer's disease cases bearing the Thr113-114ins presenilin-1 mutation

Most cases of familial presenile Alzheimer's disease are caused by mutations in the presenilin-1 (PSEN-1) gene, most of these mutations being missense mutations. A mutation in the splice donor site of intron 4 of PSEN-1 has been described recently which results in aberrant splicing of PSEN-1 mRNA, causing insertion of an additional amino acid, Thr113-114ins, into the protein. We studied the neuropathology of four cases bearing this mutation in an attempt to clarify the pathology of this hereditary form of Alzheimer's disease and to determine whether it differs from other familial forms of the disease. The disease presented as a progressive cognitive decline, myoclonus and seizures developing later in the disease, a feature common to PSEN-1-linked Alzheimer's disease. The course of the disease was relatively rapid, death occurring approximately 6 years after onset. Pathology in the intron 4 cases demonstrated a severe Alzheimer's disease pathology with abundant deposition of ss-amyloid (Ass) 1-42 senile plaques and the formation of neurofibrillary tangles. Amyloid angiopathy was present in these cases and was readily demonstrated by Ass 1-40 staining, particularly in the cerebellum. Cases with the intron 4 mutation appear clinically and pathologically similar to other cases of early-onset Alzheimer's disease bearing PSEN-1 mutations.

Presenilin-1 and -2 are molecular targets for gamma-secretase inhibitors

Presenilins are integral membrane protein involved in the production of amyloid beta-protein. Mutations of the presenilin-1 and -2 gene are associated with familial Alzheimer's disease and are thought to alter gamma-secretase cleavage of the beta-amyloid precursor protein, leading to increased production of longer and more amyloidogenic forms of A beta, the 4-kDa beta-peptide. Here, we show that radiolabeled gamma-secretase inhibitors bind to mammalian cell membranes, and a benzophenone analog specifically photocross-links three major membrane polypeptides. A positive correlation is observed among these compounds for inhibition of cellular A beta formation, inhibition of membrane binding and cross-linking. Immunological techniques establish N- and C-terminal fragments of presenilin-1 as specifically cross-linked polypeptides. Furthermore, binding of gamma-secretase inhibitors to embryonic membranes derived from presenilin-1 knockout embryos is reduced in a gene dose-dependent manner. In addition, C-terminal fragments of presenilin-2 are specifically cross-linked. Taken together, these results indicate that potent and selective gamma-secretase inhibitors block A beta formation by binding to presenilin-1 and -2.

Isolation and characterization of apolipoproteins from murine microglia. Identification of a low density lipoprotein-like apolipoprotein J-rich but E-poor spherical particle

Amyloid Abeta deposition is a neuropathologic hallmark of Alzheimer's disease. Activated microglia are intimately associated with plaques and appear to facilitate Abeta deposition, an event believed to contribute to pathogenesis. It is unclear if microglia can modulate pathogenesis of Alzheimer's disease by secreting lipoprotein particles. Here we show that cultured BV2 murine microglial cells, like astrocytes, secrete apolipoprotein E (apoE) and apolipoprotein J (apoJ) in a time-dependent manner. To isolate and identify BV2 microglial particles, gel filtration chromatography was employed to fractionate BV2-conditioned medium. Analyses by Western blot, lipid determination, electron microscopy, and native gel electrophoresis demonstrate that BV2 microglial cells release spherical low density lipoprotein (LDL)-like lipid-containing particles rich in apoJ but poor in apoE. These microglial particles are dissimilar in size, shape, and lipoprotein composition to astrocyte-derived particles. The microglial-derived particles were tested for functional activity. Under conditions of suppressed de novo cholesterol synthesis, the LDL-like particles effectively rescued primary rat cortical neurons from mevastatin-induced neurotoxicity. The particles were also shown to bind Abeta. We speculate that the LDL-like apoJ-rich apoE-poor microglial lipoproteins preferentially bind the lipoprotein receptor, recognizing apoJ, which is abundant in the choroid plexus, facilitating Abeta clearance from the brain. BV2 cells also secrete an apoE-rich lipid-poor species that binds Abeta. Consistent with the role of apoE in Abeta fibril formation and deposition, this microglial species may promote plaque formation.

Expression of macrophage colony-stimulating factor receptor is increased in the AbetaPP(V717F) transgenic mouse model of Alzheimer's disease

Inflammation is an important neuropathological change in Alzheimer's disease (AD). However, the pathophysiological factors that initiate and maintain the inflammatory response in AD are unknown. We examined AbetaPP(V717F) transgenic mice, which show numerous brain amyloid-beta (Abeta) deposits, for expression of the macrophage colony-stimulating factor (M-CSF) and its receptor (M-CSFR). M-CSF is increased in the brain in AD and dramatically augments the effects of Abeta on cultured microglia. AbetaPP(V717F) animals 12 months of age showed large numbers of microglia strongly labeled with an M-CSFR antibody near Abeta deposits. M-CSFR mRNA and protein levels were also increased in brain homogenates from AbetaPP(V717F) animals. Dystrophic neurites and astroglia showed no M-CSFR labeling in the transgenic animals. A M-CSF antibody decorated neuritic structures near hippocampal Abeta deposits in transgenic animals. M-CSF mRNA was also increased in AbetaPP(V717F) animals in comparison with wild-type controls. Simultaneous overexpression of M-CSFR and its ligand in AbetaPP(V717F) animals could result in augmentation of Abeta-induced activation of microglia. Because chronic activation of microglia is thought to result in neuronal injury, the M-CSF system may be a potential target for therapeutic intervention in AD.

Behavioral disturbances without amyloid deposits in mice overexpressing human amyloid precursor protein with Flemish (A692G) or Dutch (E693Q) mutation

The contribution of mutations in the amyloid precursor protein (APP) gene known as Flemish (APP/A692G) and Dutch (APP/E693Q) to the pathogenesis of Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis of the Dutch type, respectively, was studied in transgenic mice that overexpress the mutant APP in brain. These transgenic mice showed the same early behavioral disturbances and defects and increased premature death as the APP/London (APP V717I), APP/Swedish (K670N, M671L), and other APP transgenic mice described previously. Pathological changes included intense glial reaction, extensive microspongiosis in the white matter, and apoptotic neurons in select areas of the brain, while amyloid deposits were absent, even in mice over 18 months of age. This contrasts with extensive amyloid deposition in APP/London transgenic mice and less pronounced amyloid deposition in APP/Swedish transgenic mice generated identically. It demonstrated, however, that the behavioral deficiencies and the pathological changes in brain resulting from an impaired neuronal function are caused directly by APP or its proteolytic derivative(s). These accelerate or impinge on the normal process of aging and amyloid deposits per se are not essential for this phenotype.

Alpha2 macroglobulin and the risk of Alzheimer's disease

BACKGROUND

alpha2 Macroglobulin is a panproteinase inhibitor that is found immunohistochemically in neuritic plaques, a requisite neuropathologic feature of AD. Recently, a pentanucleotide deletion near the 5' end of the "bait region" of the alpha2 macroglobulin (A2M) gene was reported to be associated with AD in a large cohort of sibpairs, in which the mutation conferred a similar odds ratio with AD as the APOE-epsilon4 allele for carriers of at least one copy of the A2M gene (Mantel-Haenszel odds ratio, 3.56).

METHODS

We studied three independent association samples of AD patients (n = 309) with an age range of 50 to 94 years and representative controls (n = 281) to characterize the allele frequency of the pentanucleotide deletion in this cohort. We detected the mutation near the 5' splice site of exon 18 using standard PCR and restriction fragment length polymorphism methods. The results were adjusted for age, gender, education, and APOE polymorphism.

RESULTS

We found that the A2M gene polymorphism conferred an increased risk for AD, with an estimated Mantel-Haenszel ratio of 1.5 (95% CI 1.1 to 2.2; p = 0.025). There was no age- or gender-dependent increase in A2M gene allele frequencies in AD patients compared with controls. The combined sample showed the expected association between AD and APOE-epsilon 4. In one of our three samples there was an interaction between the A2M and APOE-epsilon4 genes, but the other two samples showed no interaction between the two risk factors.

CONCLUSIONS

Our data support an association between the A2M gene and AD. This association is less pronounced, however, in our cohort than in the previously reported sample of sibpairs.

Overexpression of the neuritotrophic cytokine S100beta precedes the appearance of neuritic beta-amyloid plaques in APPV717F mice

Homozygous APPV717F transgenic mice overexpress a human beta-amyloid precursor protein (betaAPP) minigene encoding a familial Alzheimer's disease mutation. These mice develop Alzheimer-type neuritic beta-amyloid plaques surrounded by astrocytes. S100beta is an astrocyte-derived cytokine that promotes neurite growth and promotes excessive expression of betaAPP. S100beta overexpression in Alzheimer's disease correlates with the proliferation of betaAPP-immunoreactive neurites in beta-amyloid plaques. We found age-related increases in tissue levels of both betaAPP and S100beta mRNA in transgenic mice. Neuronal betaAPP overexpression was found in cell somas in young mice, whereas older mice showed betaAPP overexpression in dystrophic neurites in plaques. These age-related changes were accompanied by progressive increases in S100beta expression, as determined by S100beta load (percent immunoreactive area). These increases were evident as early as 1 and 2 months of age, months before the appearance of beta-amyloid deposits in these mice. Such precocious astrocyte activation and S100beta overexpression are similar to our earlier findings in Down's syndrome. Accelerated age-related overexpression of S100beta may interact with age-associated overexpression of mutant betaAPP in transgenic mice to promote development of Alzheimer-like neuropathological changes.

A combinatorial approach to the identification of dipeptide aldehyde inhibitors of beta-amyloid production

In an effort to rapidly identify potent inhibitors of Abeta production and to probe the amino acid sequence specificity of the protease(s) responsible for the production of this peptide, a large number of dipeptide aldehydes were combinatorially synthesized and manually evaluated for their inhibitory properties. The starting point for this study was the dipeptide aldehyde carbobenzoxyl-valinyl-phenylalanal previously shown to inhibit the production of Abeta in CHO cells stably transfected with the cDNA encoding betaAPP695. Pools of related dipeptide aldehydes were combinatorially synthesized, and the most active pool was deconvoluted, resulting in the identification of the most active inhibitor of this pool. Systematic optimization of this inhibitor resulted in a series of dipeptide aldehydes with enhanced potencies relative to carbobenzoxyl-valinyl-phenylalanal. The most active dipeptide aldehydes were those that possessed hydrophobic amino acids at both the P1 and P2 positions. The most potent compound identified in this study was 3, 5-dimethoxycinnamamide-isoleucinyl-leucinal with an IC(50) of 9.6 microM, approximately 10-fold more active than carbobenzoxyl-valinyl-phenylalanal. In immunoprecipitation experiments using antibodies directed toward either Abeta1-40 or Abeta1-42, 3,5-dimethoxycinnamamide-isoleucinyl-leucinal, like carbobenzoxyl-valinyl-phenylalanal, preferentially inhibited the shorter 1-40 form of Abeta, whereas the longer 1-42 form was not as strongly inhibited. These results suggest that dipeptide aldehydes related to carbobenzoxyl-valinyl-phenylalanal inhibit Abeta through similar mechanisms and demonstrate the utility of a combinatorial synthesis approach to rapidly identify potent inhibitors of Abeta production.

Early phenotypic changes in transgenic mice that overexpress different mutants of amyloid precursor protein in brain

Transgenic mice overexpressing different forms of amyloid precursor protein (APP), i.e. wild type or clinical mutants, displayed an essentially comparable early phenotype in terms of behavior, differential glutamatergic responses, deficits in maintenance of long term potentiation, and premature death. The cognitive impairment, demonstrated in F1 hybrids of the different APP transgenic lines, was significantly different from nontransgenic littermates as early as 3 months of age. Biochemical analysis of secreted and membrane-bound APP, C-terminal "stubs," and Abeta(40) and Abeta(42) peptides in brain indicated that no single intermediate can be responsible for the complex of phenotypic dysfunctions. As expected, the Abeta(42) levels were most prominent in APP/London transgenic mice and correlated directly with the formation of amyloid plaques in older mice of this line. Plaques were associated with immunoreactivity for hyperphosphorylated tau, eventually signaling some form of tau pathology. In conclusion, the different APP transgenic mouse lines studied display cognitive deficits and phenotypic traits early in life that dissociated in time from the formation of amyloid plaques and will be good models for both early and late neuropathological and clinical aspects of Alzheimer's disease.

Macrophage colony-stimulating factor augments beta-amyloid-induced interleukin-1, interleukin-6, and nitric oxide production by microglial cells

In Alzheimer's disease (AD), a chronic cerebral inflammatory state is thought to lead to neuronal injury. Microglia, intrinsic cerebral immune effector cells, are likely to be key in the pathophysiology of this inflammatory state. We showed that macrophage colony-stimulating factor, a microglial activator found at increased levels in the central nervous system in AD, dramatically augments beta-amyloid peptide (betaAP)-induced microglial production of interleukin-1, interleukin-6, and nitric oxide. In contrast, granulocyte macrophage colony-stimulating factor, another hematopoietic cytokine found in the AD brain, did not augment betaAP-induced microglial secretory activity. These results indicate that increased macrophage colony-stimulating factor levels in AD could magnify betaAP-induced microglial inflammatory cytokine and nitric oxide production, which in turn could intensify the cerebral inflammatory state by activating astrocytes and additional microglia, as well as directly injuring neurons.

Empowerment as a source of healing: redefining the art of nursing management

Empowerment amounts to a social process of recognizing, promoting and enhancing staff nurse abilities to meet self needs, solve their own problems and mobilize the necessary resources to gain mastery over their own professional lives. Healing, to be made whole, is a process of getting in touch with that which is impeding our realization of wholeness. Empowerment as a source of organizational healing conveys the message that in order to realize wholeness, nurses are dependent upon personal and organizational resources. As nurses learn multiple ways to interact with the work environment, they find the path to a wholeness that incorporates physical, emotional, intellectual, and spiritual aspects of themselves. As the value of wholeness is realized individually, interactions with the environment spontaneously manifest these attributes and the message permeates the nursing community. As the nursing community is empowered, it is increasingly able to empower the individual. This expanding energy can result in a synergistic pattern that brings phenomena together, and interrelates them, creating a new and greater whole from the disparate, seemingly conflicting parts. When nurses as individuals and groups are able and willing (empowered) to invest energy to that which impacts their lives so that they can move toward wholeness (heal), positive energy exponentially intensifies and permeates the environment to envelop all.

Phosphorylation, subcellular localization, and membrane orientation of the Alzheimer's disease-associated presenilins

Presenilins 1 and 2 are unglycosylated proteins with apparent molecular mass of 45 and 50 kDa, respectively, in transfected COS-1 and Chinese hamster ovary cells. They colocalize with proteins from the endoplasmic reticulum and the Golgi apparatus in transfected and untransfected cells. In COS-1 cells low amounts of intact endogeneous presenilin 1 migrating at 45 kDa are detected together with relative larger amounts of presenilin 1 fragments migrating between 18 and 30 kDa. The presenilins have a strong tendency to form aggregates (mass of 100-250 kDa) in SDS-polyacrylamide gel electrophoresis, which can be partially resolved when denatured by SDS at 37 degrees C instead of 95 degrees C. Sulfation, glycosaminoglycan modification, or acylation of the presenilins was not observed, but both proteins are posttranslationally phosphorylated on serine residues. The mutations Ala-246 --> Glu or Cys-410 --> Tyr that cause Alzheimer's disease do not interfere with the biosynthesis or phosphorylation of presenilin 1. Finally, using low concentrations of digitonin to selectively permeabilize the cell membrane but not the endoplasmic reticulum membrane, it is demonstrated that the two major hydrophilic domains of presenilin 1 are oriented to the cytoplasm. The current investigation documents the posttranslational modifications and subcellular localization of the presenilins and indicates that postulated interactions with amyloid precursor protein metabolism should occur in the early compartments of the biosynthetic pathway.

Inhibition of beta-amyloid formation by haloperidol: a possible mechanism for reduced frequency of Alzheimer's disease pathology in schizophrenia

Several reports have suggested that the frequency of Alzheimer's disease (AD) neuropathology is significantly reduced in elderly individuals with schizophrenia (SZ), and it has been proposed that medications used for treatment of SZ may be responsible. A central event in AD pathology is the formation of beta-amyloid (A beta) peptide, which is derived by enzymatic processing of its precursor protein. Haloperidol, an antipsychotic medication commonly used in the treatment of SZ, can act as an inhibitor of select proteinases; hence, we examined the ability of this compound to inhibit A beta formation by cultured cells. Haloperidol and, to a lesser extent, droperidol inhibited A beta in a dose-dependent manner. These results may explain the apparent reduction of AD neuropathological changes in elderly patients with SZ as well as provide a possible mechanism for this difference.

Processing of beta-amyloid precursor protein by cathepsin D

The events leading to the formation of beta-amyloid (betaA4) from its precursor (betaAPP) involve proteolytic cleavages that produce the amino and carboxyl termini of betaA4. The enzyme activities responsible for these cleavages have been termed beta- and gamma-secretase, respectively, although these protease(s) have not been identified. Since betaA4 is known to possess heterogeneity at both the amino and carboxyl termini, beta- and gamma-secretases may actually be a collection of proteolytic activities or perhaps a single proteolytic enzyme with broad amino acid specificity. We investigated the role of cathepsin D in the processing of betaAPP since this enzyme has been widely proposed as a gamma-secretase candidate. Treatment of a synthetic peptide that spans the gamma-secretase site of betaAPP with human cathepsin D resulted in the cleavage of this substrate at Ala42-Thr43. A sensitive liquid chromatography/mass spectrometry technique was also developed to further investigate the ability of cathepsin D to process longer recombinant betaAPP substrates (156 and 100 amino acids of betaAPP carboxyl terminus) in vitro. The precise cathepsin D cleavage sites within these recombinant betaAPP substrates were identified using this technique. Both recombinant substrates were cleaved at the following sites: Leu49-Val50, Asp68-Ala69, Phe93-Phe94. No cleavages were observed at putative gamma-secretase sites: Val40-Ile41 or Ala42-Thr43, suggesting that cathepsin D is not gamma-secretase as defined by these betaA4 termini. Under conditions where the betaAPP156 substrate was first denatured prior to cathepsin D digestion, two additional cleavage sites near the amino terminus of betaA4, Glu-3-Val-2 and Glu3-Phe4, were observed, indicating that cathepsin D cleavage of betaAPP is influenced by the structural integrity of the substrate. Taken together, these results indicate that in vitro, cathepsin D is unlikely to function as gamma-secretase; however, the ability of this enzyme to efficiently cleave betaAPP substrates at nonamyloidogenic sites within the molecule may reflect a role in betaAPP catabolism.

Genetically Engineered Animal Models of Alzheimer's Disease

The application of transgenic research has proven to be a powerful and popular tool for investigating the contribution of specific genes known or suspected to be involved in the pathology of Alzheimer's disease. Many different experimental approaches have been pursued in an effort to mimic one or more of the numerous and diverse features characterizing Alzheimer's disease. Results have been variable but not without successes. Some of the cardinal hallmarks of this disorder have been recapitulated through the manipulation of a single gene, providing information on the interrelationship between several pathological events. Also, through the generation of such transgenic animals, potential models are being established for this disease that will be valuable for development of intervention strategies.

Antibodies to presenilin proteins detect neurofibrillary tangles in Alzheimer's disease

Mutations in the presenilin (PS)-1 and PS-2 genes have been shown to be linked with the development of Alzheimer's disease (AD). We examined Alzheimer's brain tissue by immunohistochemistry using a set of antibodies raised to sequences shared between PS-1 and PS-2 proteins. These antibodies reacted exclusively with a subset of neurofibrillary tangles and not with neuropil threads or dystrophic neurites. Detection of the presenilin epitope in neurofibrillary tangles was observed in sporadic Alzheimer's disease brain samples and in samples from individuals carrying PS-1 and PS-2 mutations with no qualitative difference. These data indicate that both wild-type and mutant PS proteins are involved in a common pathogenic pathway in AD.

Beta-amyloid precursor protein. Location of transmembrane domain and specificity of gamma-secretase cleavage

The formation of beta-amyloid by processing of its precursor protein is a characteristic of Alzheimer's disease. Two proteolytic cleavages produce the amino and carboxyl termini of beta-amyloid, with the latter cleavage site located within the transmembrane domain. Using DNA mutagenesis, we investigated the membrane position and sequence requirements for carboxyl-terminal processing of the beta-amyloid domain. Substitution of negatively charged residues across positions 40-46 of the beta-amyloid domain precluded both beta-amyloid formation and precursor maturation associated with secretory protein transport. In contrast, identical substitutions from positions 48-50 had no adverse effects. Since charged residues typically prevent protein membrane insertion, these data define the membrane boundary to position 46/47, a location allowing greater access to carboxyl-terminal processing of beta-amyloid, possibly without membrane destruction. Deletions within the carboxyl-terminal domain, including 4 residues spanning positions 39-42 of beta-amyloid, resulted in formation of the beta-amyloid peptide. Substituting residues 38-47 or 39-56 of the beta-amyloid domain in the precursor with a transmembrane sequence from another protein yielded a approximately 4-kDa beta-amyloid peptide, reflecting a loose residue specificity for carboxyl-terminal processing to beta-amyloid.

P3 beta-amyloid peptide has a unique and potentially pathogenic immunohistochemical profile in Alzheimer's disease brain

The presence of beta-amyloid in brain tissue is characteristic of Alzheimer's disease (AD). A naturally occurring derivative of the beta-amyloid peptide, p3, possesses all of the structural determinants required for fibril assembly and neurotoxicity. p3-specific antibodies were used to examine the distribution of this peptide in brain. p3 reactivity was absent or sparse in aged non-AD brains but was prevalent in selected areas of AD brain in diffuse deposits and in a subset of dystrophic neurites. p3-reactive dystrophic neurites were found both independent in the neuropil and associated with plaques. Little or no reactivity was observed to amyloid cores in classical plaques or to amyloid in the cerebral vasculature. The exclusive appearance of p3 reactivity in AD brain plus the selective localization of p3 reactivity to abnormal structures in the temporal lobe limbic system suggests that p3 may be a contributing factor to AD pathology.

Beta-amyloid peptide secretion by a microglial cell line is induced by beta-amyloid-(25-35) and lipopolysaccharide

beta-Amyloid protein (betaAP) deposition is a neuropathologic hallmark of Alzheimer's disease (AD). Yet, the source of cerebral betaAP in AD is controversial. We examined the production of betaAP by the BV-2 immortalized microglial cell line using a sensitive enzyme immunoassay. Constitutive production of betaAP was detected in conditioned media from unstimulated BV-2 cells. Further, production of betaAP was induced by treatment of cultures by lipopolysaccharide (LPS) or betaAP-(25-35) and was inhibited by the calpain protease inhibitor MDL 28170. Treatment of BV-2 cells with LPS or betaAP-(25-35) did not affect cell-associated beta-amyloid precursor protein levels. These findings suggest that microglia may be an important source of betaAP in AD, and that microglial production of betaAP may be augmented by proinflammatory stimuli or by betaAP itself.

Age-related learning deficits in transgenic mice expressing the 751-amino acid isoform of human beta-amyloid precursor protein

The beta-amyloid precursor protein (beta-APP), from which the beta-A4 peptide is derived, is considered to be central to the pathogenesis of Alzheimer disease (AD). Transgenic mice expressing the 751-amino acid isoform of human beta-APP (beta-APP751) have been shown to develop early AD-like histopathology with diffuse deposits of beta-A4 and aberrant tau protein expression in the brain, particularly in the hippocampus, cortex, and amygdala. We now report that beta-APP751 transgenic mice exhibit age-dependent deficits in spatial learning in a water-maze task and in spontaneous alternation in a Y maze. These deficits were mild or absent in 6-month-old transgenic mice but were severe in 12-month-old transgenic mice compared to age-matched wild-type control mice. No other behavioral abnormalities were observed. These mice therefore model the progressive learning and memory impairment that is a cardinal feature of AD. These results provide evidence for a relationship between abnormal expression of beta-APP and cognitive impairments.

Genetically engineered animal models of human neurodegenerative diseases

The influence of a single gene, engineered to be normally or abnormally expressed, can be evaluated in vivo through the development of transgenic animals. Application of this approach in the study of human neurological problems is contributing to an increased understanding of the pathogenic components operative in a variety of disorders. These include Alzheimer's disease, prion encephalopathies, motor neuron disease such as amyotrophic lateral sclerosis, and fragile X syndrome, as well as a number of viral-mediated neurological disorders. These transgenic animals can also serve as models to investigate the possible involvement of additional genetic and environmental factors on the disease state. Moreover, transgenic animals can be used in the development of intervention strategies. The application of this powerful and increasingly popular tool to investigate neurodegenerative disorders is reviewed.

Early Alzheimer disease-like histopathology increases in frequency with age in mice transgenic for beta-APP751

beta-Amyloid deposition and neurofibrillary tangle formation are two histopathological features of Alzheimer disease. We have previously reported that beta-amyloid immunoreactive deposits form in the brains of transgenic mice programmed for neuronal expression of the 751-amino acid isoform of human beta-amyloid precursor protein (beta-APP751) and now describe that these animals also display Alz50 intraneuronal immunoreactivity similar to that seen in early Alzheimer disease. This suggests that abnormal beta-APP expression and/or beta-amyloid deposition promotes pathogenic alterations in tau protein. The frequency of both beta-amyloid deposition and Alz50-positive neurons was twice as prevalent in brains from old (22 months) as compared to young (2-3 months) beta-APP751 transgenic mice. This increase in histopathology with age in beta-APP751 transgenic mice parallels the time-dependent progression seen in the human disease.

Transgenic mice and modeling Alzheimer's disease

The etiology of Alzheimer's disease (AD) is poorly understood, and no effective therapies are available. Although histopathology of the disease has been studied thoroughly, the relationship of various AD lesions to pathological processes and to dementia are debated. Progress would be greatly enhanced by existence of manipulable small animal models of the disease. Recently, transgenic strategies to developing such a model have been extensively explored. The approach has proved to be difficult and has yielded some disappointments, but also some encouraging results. Transgenic strategies for obtaining a model for AD are surveyed in this review and, as an illustration, early AD-like features of transgenic mice produced in our laboratory are described.

Inhibition of beta-amyloid formation identifies proteolytic precursors and subcellular site of catabolism

Cerebral deposition of beta-amyloid protein is a pathological feature central to Alzheimer's disease. Production of beta-amyloid by proteolytic processing of the beta-amyloid precursor protein (beta APP) is a critical initial step in beta-amyloidogenesis. We use an inhibitor of beta APP processing to block beta-amyloid peptide formation. Application of the inhibitor to cultured cells results in an accumulation of proteolytic intermediates of beta APP, enabling a precursor-product relationship between beta APP carboxy-terminal fragments and beta-amyloid peptides to be demonstrated directly. In the presence of inhibitor, these amyloidogenic carboxy-terminal fragments can be degraded to nonamyloidogenic products. The catabolism of beta APP carboxy-terminal intermediates and the formation of beta-amyloid peptides are likely to involve an early endosomal compartment as the subcellular site of processing.

beta-Amyloid peptide produced in vitro is degraded by proteinases released by cultured cells

The primary histopathological feature of Alzheimer's disease is the accumulation of beta-amyloid in the brains of afflicted individuals. This peptide has been shown to be produced and liberated both in vitro and in vivo by normal physiological processes. The mechanism by which beta-amyloid is formed, as well as that by which it may be cleared, are events likely to impact on the development and progression of this disease. Thus, the fate of beta-amyloid peptides secreted by cultured mammalian cells was investigated. It was found that levels of the soluble peptide are reduced over time due to the activity of multiple types of proteinases including those from the metallo, aspartyl, and thiol classes. Inhibitors to each class of proteinase can only partially block beta-amyloid degradation, but, if used in combination, they can fully prevent its catabolism. The Kunitz serine proteinase inhibitor domain, present on two beta-amyloid precursor protein isoforms, was found to be an effective inhibitor of beta-amyloid peptide degradation. These data indicate that modulations in expression of secreted proteinases and/or beta-amyloid precursor isoforms may influence levels of beta-amyloid.

Cultural Diversity and Patient Teaching

Cultural diversity challenges health care providers to facilitate bridging cross-cultural gaps with clients. It is through providing culturally relevant care that health care practitioners truly serve the needs of all clients in our diverse society. A theory of Cultural Care Diversity and Universality offers a framework for building linkages of clinical knowledge to cultural care. A four-step approach to providing culturally sensitive patient teaching is described: (1) health care providers should assess their own cultural beliefs and be aware of general ethnic, regional, and religious beliefs and practices in their area; (2) develop a teaching plan; (3) implement the plan; (4) evaluate the success of the teaching-learning process and make alterations based on evaluation. When providers assess clients' beliefs and practices and incorporate them into the teaching plan design, teaching becomes more relevant and clients become more successful at learning.

Transgenic mouse brain histopathology resembles early Alzheimer's disease

Transgenic mice expressing the 751-amino acid form of the human amyloid precursor protein develop extracellular beta-amyloid protein (A beta)-immunoreactive deposits that increase in frequency with age. Here we show that the appearance and histological profile of deposits in the transgenic mice closely resemble those of preamyloid deposits in the brains of young adults with Down's syndrome, who presumably have the pathology of early-stage Alzheimer's disease. Specific monoclonal antibodies reveal that material in the deposits has the free carboxyl terminus of A beta 1-42, and that the deposits contain material which, by immunohistochemical analysis, apparently originates from the human beta-amyloid precursor protein (beta PP) transgene. In rare cases, the transgenic mouse brains contain several different histopathological characteristics of Alzheimer lesions. These features include dense A beta immunoreactivity which co-localizes with gliosis and with Alz50-immunoreactive structures resembling swollen boutons of dystrophic neurites. These observations demonstrate that the murine brain is capable of reproducing several typical features of Alzheimer histopathology.

Development of a monoclonal antibody specific for the COOH-terminal of beta-amyloid 1-42 and its immunohistochemical reactivity in Alzheimer's disease and related disorders

The beta-amyloid peptide (beta AP) has been characterized by protein sequencing techniques as a 39-43 amino acid protein with heterogeneous COOH-termini. Controversy exists regarding the predominant form of beta AP in neuritic plaques (NP) and cerebral vasculature of Alzheimer's disease (AD) brain. A monoclonal antibody was developed that selectively recognizes the free COOH-terminal of beta AP 1-42 but not beta AP species with shorter or longer COOH-termini. Brain sections from AD and related disorders were examined using this antibody. In AD samples, the antibody stained diffuse amyloid and NP cores, many intraneuronal and extraneuronal neurofibrillary tangles (NFT), but not cerebrovascular amyloid. Pick and Lewy bodies lacked immunoreactivity. These findings suggest that beta AP 1-42 is present in early and mature amyloid deposits and NFT, but that species of beta AP other than 1-42 comprise human vascular deposits.

Increased amyloid production from aberrant beta-amyloid precursor proteins

The 4-kDa beta-amyloid protein that forms fibrillar deposits in Alzheimer's diseased brains is derived from a large precursor, the beta-amyloid precursor protein (beta-APP). Recently, it has been reported that beta-amyloid is normally produced and secreted by cultured mammalian cells. In our studies involving recombinant expression of beta-APP, increased yields of beta-amyloid were associated with expression of aberrant beta-APP molecules. Deletion mutations within the beta-amyloid domain, incorrect beta-APP isoform expression in fibroblasts or neuronal cells, or excess amounts of beta-APP all led to increases in beta-amyloid production. Aberrant beta-APP appears to be diverted from the secretory pathway and then degraded to beta-amyloid.

Secretion of beta-amyloid precursor protein involves multiple cleavage sites

A major histopathological feature of Alzheimer's disease is deposits of a approximately 4-kDa beta-amyloid peptide derived by proteolytic processing from a precursor, the beta-amyloid precursor protein (beta-APP). Proteolytic cleavage of beta-APP within the approximately 4-kDa beta-amyloid domain permits the secretion of the amino-terminal portion of beta-APP while concomitantly producing a membrane bound approximately 9-kDa carboxyl-terminal fragment. We have characterized the proteolytic cleavage site for beta-APP secretion by amino acid sequence analysis of the approximately 9-kDa beta-APP carboxyl-terminal cleavage product produced by recombinant and native expression systems. Recombinant beta-APP was generated by a vaccinia virus expression system in CV-1 monkey fibroblasts; endogenous beta-APP was obtained using a fibroblast line derived from an individual with Down's syndrome. The sequences of both unlabeled and metabolically radiolabeled approximately 9-kDa fragment from CV-1 cells reveal that the major (60%) secretory cleavage site is after Lys16 of the beta-amyloid domain as reported previously; however, an additional cleavage site is seen after Phe19 (40%). Radiosequence analysis of the carboxyl-terminal fragment purified from Down's syndrome fibroblasts indicates cleavage sites after Phe19, Glu22, and Gly25 and not after Lys16. CV-1 cells expressing beta-APP mutants lacking 4 and 6 amino acids adjacent to Lys16 yielded approximately 9-kDa fragments with two identical cleavage sites, neither of which occurred after the retained Lys16 but were after Glu11 and His13. These data suggest that secretion of beta-APP involves multiple proteinases and that the composition of these proteinases may vary within different cell backgrounds.

Transgenic mice expressing human beta-APP751, but not mice expressing beta-APP695, display early Alzheimer's disease-like histopathology

Mice transgenic for the 751 amino acid isoform of the human beta-amyloid precursor protein (beta-APP) driven by the rat neuron specific enolase (NSE) promoter (NSE:beta-APP751) show features of early Alzheimer's disease (AD) pathology. These features, which were evident in multiple pedigrees, include: 1) preamyloid deposits which stain with antibodies that are specific for the beta-amyloid peptide and stain AD amyloid deposits and plaques, and 2) neuronal soma and processes which stain with an antibody (Alz50) that detects abnormal isoforms of tau which are characteristic of AD. The quality and distribution of both types of immunoreactivity revealed in the NSE:beta-APP751 mouse brains most closely resemble those seen in brains of young adults with Down's syndrome. Both structures are rarely, if ever, observed in brains from mice transgenic for the 695 amino acid isoform of beta-APP (NSE:beta-APP695) or in wild type mice.

Total quality management and quality assurance: discussing the differences

Total Quality Management and Continuous Quality Improvement have become the "buzz" phrase for the 1990s. Everyone seems to be jumping on the band wagon. But what is it, and is it right for your organization? We believe that Total Quality Management is superior to many Quality Assurance programs currently in use. There are, however, many considerations to take into account before implementing a Total Quality Management program. The purpose of this article is to explain the pros and cons of Total Quality Management and standard Quality Assurance programs and to compare and contrast these two approaches. This article focuses on barriers to successful implementation and presents several questions organizations can utilize in assessing readiness for a quality management program.

Sequence analysis and editing of the phosphoprotein (P) gene of rinderpest virus

We have cloned the cDNA of the phosphoprotein (P) gene of the virulent (Kabete "O") strain of rinderpest virus and provided a comparative analysis of its sequence with that of the P genes of measles, canine distemper, and phocid distemper viruses. The gene encodes two overlapping open reading frames of 1521 and 531 nucleotides. Use of the first ATG would produce a P polypeptide of 507 amino acids with a calculated molecular weight of 54,344. The second ATG would produce a C polypeptide of 177 residues with a predicted molecular weight of 19,927. In addition, the insertion of a G residue at position 740 generates an alternative mRNA potentially encoding the V polypeptide of rinderpest virus. The homology comparisons in P amino acid sequences between rinderpest and measles, between rinderpest and canine distemper, and between rinderpest and phocid distemper viruses are 60, 44, and 46%, respectively. A four-way comparison shows an identity of 34%. Similar homology comparisons with the C amino acid sequence between rinderpest and measles, rinderpest and canine distemper, and rinderpest and phocid distemper viruses are 56, 42, and 40%, respectively. A homology of 31% is found in a four-way comparison for the C polypeptide. From the point of the insertion of the G residue, there is a homology of 78% between the V polypeptides of rinderpest and measle viruses.

Expression cloning of neurotrophic factors using Xenopus oocytes

We have explored the potential for cloning novel neurotrophic factor cDNAs via assay of neurotrophic activities following expression in Xenopus oocytes. In this report, we describe the successful application of the method to tract rat ciliary neurotrophic factor (CNTF) activity from mRNA purified from cultured cells and from mRNA synthesized by in vitro transcription of a cDNA library. Rat C6 glioma cells, which had been previously shown to have CNTF-like activity (Westermann et al., 1988), were used as source material. We tested protein extracts of C6 cells using an in vitro assay of primary neurons from the chick ciliary ganglion (CCG assay) and detected a CNTF-like activity. RNA isolated from C6 cells was shown to direct the synthesis of the activity following microinjection into Xenopus oocytes and one-step fractionation of Xenopus extract. C6 mRNA was size-fractionated, and fractions encoding CNTF-like activity were cloned into a lambda phage vector at a site distal to a T7 promoter. Synthetic RNA transcribed from total library DNA was injected into Xenopus oocytes, and a CNTF-like activity in the oocyte extract was detected by the CCG assay. Further fractionation of library clones narrowed the presence of the clone encoding the CNTF-like activity to a pool containing 20,000 members. The presence of a full-length CNTF cDNA clone in this pool and partial clones in other pools was confirmed by Polymerase Chain Reaction (PCR) using oligonucleotides from the rabbit CNTF cDNA (Lin et al., 1989) as primers.(ABSTRACT TRUNCATED AT 250 WORDS)