δ-Catenin is genetically and biologically associated with cortical cataract and future Alzheimer-related structural and functional brain changes

Multiple lines of evidence suggest that specific subtypes of age-related cataract (ARC) and Alzheimer disease (AD) are related etiologically. To identify shared genetic factors for ARC and AD, we estimated co-heritability of quantitative measures of cataract subtypes with AD-related brain MRI traits among 1,249 members of the Framingham Eye Study who had a brain MRI scan approximately ten years after the eye exam. Cortical cataract (CC) was found to be co-heritable with future development of AD and with several MRI traits, especially temporal horn volume (THV, ρ = 0.24, P<10(-4)). A genome-wide association study using 187,657 single nucleotide polymorphisms (SNPs) for the bivariate outcome of CC and THV identified genome-wide significant association with CTNND2 SNPs rs17183619, rs13155993 and rs13170756 (P<2.6 × 10(-7)). These SNPs were also significantly associated with bivariate outcomes of CC and scores on several highly heritable neuropsychological tests (5.7 × 10(-9) ≤ P<3.7 × 10(-6)). Statistical interaction was demonstrated between rs17183619 and APP SNP rs2096488 on CC (P = 0.0015) and CC-THV (P = 0.038). A rare CTNND2 missense mutation (G810R) 249 base pairs from rs17183619 altered δ-catenin localization and increased secreted amyloid-β(1-42) in neuronal cell culture. Immunohistopathological analysis of lens tissue obtained from two autopsy-confirmed AD subjects and two non-AD controls revealed elevated expression of δ-catenin in epithelial and cortical regions of lenses from AD subjects compared to controls. Our findings suggest that genetic variation in delta catenin may underlie both cortical lens opacities in mid-life and subsequent MRI and cognitive changes that presage the development of AD.

Cell membrane expression of cardiac sodium channel Na(v)1.5 is modulated by alpha-actinin-2 interaction

Cardiac sodium channel Na(v)1.5 plays a critical role in heart excitability and conduction. The molecular mechanism that underlies the expression of Na(v)1.5 at the cell membrane is poorly understood. Previous studies demonstrated that cytoskeleton proteins can be involved in the regulation of cell surface expression and localization of several ion channels. We performed a yeast two-hybrid screen to identify Na(v)1.5-associated proteins that may be involved in channel function and expression. We identified alpha-actinin-2 as an interacting partner of the cytoplasmic loop connecting domains III and IV of Na(v)1.5 (Na(v)1.5/LIII-IV). Co-immunoprecipitation and His(6) pull-down assays confirmed the physical association between Na(v)1.5 and alpha-actinin-2 and showed that the spectrin-like repeat domain is essential for binding of alpha-actinin-2 to Na(v)1.5. Patch-clamp studies revealed that the interaction with alpha-actinin-2 increases sodium channel density without changing their gating properties. Consistent with these findings, coexpression of alpha-actinin-2 and Na(v)1.5 in tsA201 cells led to an increase in the level of expression of Na(v)1.5 at the cell membrane as determined by cell surface biotinylation. Lastly, immunostaining experiments showed that alpha-actinin-2 was colocalized with Na(v)1.5 along the Z-lines and in the plasma membrane. Our data suggest that alpha-actinin-2, which is known to regulate the functional expression of the potassium channels, may play a role in anchoring Na(v)1.5 to the membrane by connecting the channel to the actin cytoskeleton network.

Presence and active synthesis of the 67 kDa elastin-receptor in human circulating white blood cells

Early after the identification of the elastin-receptor (El-R) on mesenchymal cells, it was demonstrated that phagocytic cells and lymphocytes could also respond to elastin peptides. Nevertheless, the level of El-R expression has never been demonstrated on immune cells and no data exist whether these cells actively synthesize this El-R. Thus, our aim in the present work was to study the expression and number of El-R on white blood cells (WBC) using a specific 67 kDa El-R antibody and to demonstrate the presence of mRNA corresponding to the gene coding for El-R. Our results show that messenger RNA corresponding to the presumptive gene coding for the 67 kDa El-R subunit could be detected in all three WBC-types investigated. On all of these WBC, the presence of El-R could be demonstrated, however their number and their function varied following the cell type. The presence of El-R is very important for the interaction of circulating cell with the matrix as these cells intervene during atherosclerosis and in host defence.

Dissociated phenotypes in presenilin transgenic mice define functionally distinct gamma-secretases

Gamma-secretase depends on presence of presenilins (PS), Nct, Aph-1, and PEN-2 within a core complex. This endoproteolytic activity cleaves within transmembrane domains of amyloid-beta precursor protein (APP) and Notch, and familial Alzheimer's disease (FAD) mutations in PS1 or PS2 genes shift APP cleavage from production of amyloid-beta (Abeta) 40 peptide to greater production of Abeta42. Although studies in PS1/PS2-deficient embryonic cells define overlapping activities for these proteins, in vivo complementation of PS1-deficient animals described here reveals an unexpected spectrum of activities dictated by PS1 and PS2 alleles. Unlike PS1 transgenes, wild-type PS2 transgenes expressed in the mouse CNS support little Abeta40 or Abeta42 production, and FAD PS2 alleles support robust production of only Abeta42. Although wild-type PS2 transgenes failed to rescue Notch-associated skeletal defects in PS1 hypomorphs, a "gained" competence in this regard was apparent for FAD alleles of PS2. The range of discrete and divergent processing activities in mice reconstituted with different PS genes and alleles argues against gamma-secretase being a single enzyme with intrinsically relaxed substrate and cleavage site specificities. Instead, our studies define functionally distinct gamma-secretase variants. We speculate that extrinsic components, in combination with core complexes, may tailor functional variants of this enzyme to their preferred substrates.

Normal brain development in PS1 hypomorphic mice with markedly reduced gamma-secretase cleavage of betaAPP

Presenilin 1-null mice die at birth from brain and skeletal developmental deformities due to disrupted Notch signaling. Presenilin 1-null mice also have severely reduced gamma-secretase cleavage of betaAPP. The assumption has been that facilitation of Notch signaling and betaAPP processing by presenilin 1 are analogous functions. Here we describe a presenilin 1-targetted mouse model that expresses extremely low levels ( approximately 1% of normal) of mutant PS1-M146L. Homozygous mice have significantly reduced viability due to a Notch-like phenotype. The animals that survive have severe axial skeletal deformities and markedly diminished gamma-secretase activity and accumulation of betaAPP-C100, but no obvious abnormalities in brain development. These results suggest that, in mice, a marked reduction of PS1-facilitated gamma-secretase activity is not detrimental to normal brain development.

Protein thioacylation: 2. Reagent stability in aqueous media and thioacylation kinetics

Several thioacylating reagents have been tested toward hydrolysis under conditions suitable for protein modifications: 20-35 degrees C and buffered solutions at pH 7.5-8.5. Aliphatic dithioesters are sufficiently stable in aqueous media at room temperature (or below) if protein modification reaction time does not exceed 24 h, whereas at 35 degrees C reaction times must be limited to a few hours. Kinetic data obtained in gelatin thioacylation at room temperature using aliphatic dithioesters and dithio acid are consistent with a second-order reaction rate with respect to amine concentration. The pH dependence of the second-order reaction rate constants indicate that dithioester reacts exclusively with the free amine form of lysine residue, whereas dithiocarboxylate ion reacts with both amine and ammonium ion, probably through a more complex mechanism. Interestingly thioacylation using dithio acids may be obtained in pH near neutrality or in slightly acidic media, thus offering protein modification possibilities at pH 5-9. Thioacylation reaction rates may be expressed as R = -(dAt/dt) = k[H3O+](-b)At2[thioacylating agent] in which At is the amine concentration at time t, constants k and b depending on the reagent nature.

Protein thioacylation. 1. Reagents design and synthesis

Thioacylation is a new way for protein chemical modification. Carboxylic dithioesters and -acids react selectively and rapidly at room temperature with aliphatic amines such as lysine epsilon-amino groups leading to thioamide formation, without any other reagent or catalyst. Various thioacylating reagents were synthesized: monofunctional dithioesters bearing on the acylating end various chemical groups such as: aliphatic chains, phenyl group, mono- and dicarboxylic acids, dialkylphosphonic ester, phosphonic acid, thiol, phenol, or quaternary ammonium group. Bifunctional dithioesters containing either a polymethylene chain or an ethylene oxide oligomer as spacer group as well as some mono- and bis(dithio acids) are described. Applications of thioacylation may be involved either in enzyme chemical modifications or in the obtention of new materials from proteins. Bifunctional reagents might be used as cross-linking or coupling reagents.

Carboxyl-terminal fragments of Alzheimer beta-amyloid precursor protein accumulate in restricted and unpredicted intracellular compartments in presenilin 1-deficient cells

Absence of functional presenilin 1 (PS1) protein leads to loss of gamma-secretase cleavage of the amyloid precursor protein (betaAPP), resulting in a dramatic reduction in amyloid beta peptide (Abeta) production and accumulation of alpha- or beta-secretase-cleaved COOH-terminal fragments of betaAPP (alpha- or beta-CTFs). The major COOH-terminal fragment (CTF) in brain was identified as betaAPP-CTF-(11-98), which is consistent with the observation that cultured neurons generate primarily Abeta-(11-40). In PS1(-/-) murine neurons and fibroblasts expressing the loss-of-function PS1(D385A) mutant, CTFs accumulated in the endoplasmic reticulum, Golgi, and lysosomes, but not late endosomes. There were some subtle differences in the subcellular distribution of CTFs in PS1(-/-) neurons as compared with PS1(D385A) mutant fibroblasts. However, there was no obvious redistribution of full-length betaAPP or of markers of other organelles in either mutant. Blockade of endoplasmic reticulum-to-Golgi trafficking indicated that in PS1(-/-) neurons (as in normal cells) trafficking of betaAPP to the Golgi compartment is necessary before alpha- and beta-secretase cleavages occur. Thus, although we cannot exclude a specific role for PS1 in trafficking of CTFs, these data argue against a major role in general protein trafficking. These results are more compatible with a role for PS1 either as the actual gamma-secretase catalytic activity or in other functions indirectly related to gamma-secretase catalysis (e.g. an activator of gamma-secretase, a substrate adaptor for gamma-secretase, or delivery of gamma-secretase to betaAPP-containing compartments).

Presenilins interact with armadillo proteins including neural-specific plakophilin-related protein and beta-catenin

Missense substitutions in the presenilin 1 (PS1) and presenilin 2 (PS2) proteins are associated with early-onset familial Alzheimer's disease. We have used yeast-two-hybrid and coimmunoprecipitation methods to show that the large cytoplasmic loop domains of PS1 and PS2 interact specifically with three members of the armadillo protein family, including beta-catenin, p0071, and a novel neuronal-specific armadillo protein--neural plakophilin-related armadillo protein (NPRAP). The PS1:NPRAP interaction occurs between the arm repeats of NPRAP and residues 372-399 at the C-terminal end of the large cytoplasmic loop of PS1. The latter residues contain a single arm-like domain and are highly conserved in the presenilins, suggesting that they form a functional armadillo protein binding site for the presenilins.

Presenilin mutations associated with Alzheimer disease cause defective intracellular trafficking of beta-catenin, a component of the presenilin protein complex

The presenilin proteins are components of high-molecular-weight protein complexes in the endoplasmic reticulum and Golgi apparatus that also contain beta-catenin. We report here that presenilin mutations associated with familial Alzheimer disease (but not the non-pathogenic Glu318Gly polymorphism) alter the intracellular trafficking of beta-catenin after activation of the Wnt/beta-catenin signal transduction pathway. As with their effect on betaAPP processing, the effect of PS1 mutations on trafficking of beta-catenin arises from a dominant 'gain of aberrant function' activity. These results indicate that mistrafficking of selected presenilin ligands is a candidate mechanism for the genesis of Alzheimer disease associated with presenilin mutations, and that dysfunction in the presenilin-beta-catenin protein complexes is central to this process.

Evidence for an Alzheimer disease susceptibility locus on chromosome 12 and for further locus heterogeneity

CONTEXT

Alzheimer disease (AD) susceptibility genes have been identified on chromosomes 1, 14, 19, and 21, and a recent study has suggested a locus on chromosome 12.

OBJECTIVE

To confirm or refute the existence of a familial AD susceptibility locus on chromosome 12 in an independent sample of familial AD cases.

DESIGN

Retrospective cohort study. DNA data for 6 chromosome 12 genetic markers were evaluated using parametric lod score and nonparametric linkage methods and linkage heterogeneity tests. The latter include the admixture test of homogeneity in the total group of families and the predivided sample test in families stratified by the presence or absence of an apolipoprotein E (APOE) epsilon4 allele among affected members. Parametric analyses were repeated assuming autosomal dominant inheritance of AD and either age- and sex-dependent penetrance or zero penetrance for the analysis of unaffected relatives.

SETTING

Clinical populations in the continental United States, Canada, Argentina, and Italy.

PATIENTS

Fifty-three white families composed of multiple members affected with AD, from whom DNA samples were obtained from 173 patients with AD whose conditions were diagnosed using established criteria and from 146 nondemented relatives.

MAIN OUTCOME MEASURE

Presence of an APOE epsilon4 allele among affected family members.

RESULTS

Using parametric methods, no evidence for linkage to the region spanned by the chromosome 12 markers could be detected if familial AD is assumed to arise from the same genetic locus in all 53 families. However, significant evidence for linkage was detected in the presence of locus heterogeneity using the admixture test (odds ratio, 15, 135:1). The estimated proportion of linked families within the 53 families examined varied between 0.40 and 0.65, depending on the genetic model assumed and APOE status. The precise location of the AD gene could not be determined, but includes the entire region suggested previously. Nonparametric linkage analysis confirmed linkage to chromosome 12 with the strongest evidence at D12S96 (P<.001).

CONCLUSIONS

Our data provide independent confirmation of the existence of an AD susceptibility locus on chromosome 12 and suggest the existence of AD susceptibility genes on other chromosomes. Screening a larger set of families with additional chromosome markers will be necessary for identifying the chromosome 12 AD gene.

Additive effects of PS1 and APP mutations on secretion of the 42-residue amyloid beta-protein

Humans harboring missense mutations in the presenilin 1 (PS1) gene undergo progressive cerebral deposition of the 42-residue amyloid beta-protein (A beta 42) at an early age and develop severe Alzheimer's disease. A beta 42 is selectively elevated in the conditioned media of cells expressing mutant but not wild-type PS1, indicating that presenilin mutations alter APP processing. Here we analyze the effects of various PS1 mutant constructs on the cellular production of A beta 42. A construct expressing only the PS1 N-terminal endoproteolytic fragment with the mutation Y115H causes no significant increase in A beta 42, whereas a full-length PS1 construct with the same mutation does. This result suggests that the pathogenic effect of mutant presenilins is produced by the full-length molecule even though only a minor proportion of total PS1 occurs as holoprotein in tissues and cell lines. We demonstrate that the effects of two different PS1 mutations are additive when engineered into the same PS1 molecule. Therefore, two mutations alter gamma-secretase processing of APP more than one and the PS1 mutations described to date do not cause the maximum possible PS1-mediated rise in A beta 42. When a PS1 mutation was expressed in cells carrying the APPV717I mutation, A beta 42 rose dramatically to become the predominant secreted A beta species, an observation of interest for transgenic modeling of AD. Our results are consistent with the hypothesis that presenilin is a major regulator of the proteolytic processing of APP by gamma-secretases.

Absence of association between Alzheimer disease and the -491 regulatory region polymorphism of APOE

A novel polymorphism (-491 A/T) within the regulatory region on the apolipoprotein E gene has recently been reported to be associated with risk for Alzheimer disease (AD). To test this association in an independent data set, we have examined this polymorphism in a sample of 88 well-characterized AD cases and compared the allele frequency and genotype frequencies for this polymorphism with those observed in 112 cognitively normal subjects drawn from the same ethnic group. These results suggest that in the current data set at least, the -491 A/T polymorphism is not associated with risk for AD, but may be in partial linkage disequilibrium with the APOE epsilon2/epsilon3/epsilon4 polymorphism.

The presenilin 1 protein is a component of a high molecular weight intracellular complex that contains beta-catenin

The presenilin (PS) genes associated with Alzheimer disease encode polytopic transmembrane proteins which undergo physiologic endoproteolytic cleavage to generate stable NH2- and COOH-terminal fragments (NTF or CTF) which co-localize in intracellular membranes, but are tightly regulated in their stoichiometry and abundance. We have used linear glycerol velocity and discontinuous sucrose gradient analysis to investigate the distribution and native conformation of PS1 and PS2 during this regulated processing in cultured cells and in brain. The PS1 NTF and CTF co-localize in the endoplasmic reticulum (ER) and in the Golgi apparatus, where they are components of a approximately 250-kDa complex. This complex also contains beta-catenin but not beta-amyloid precursor protein (APP). In contrast, the PS1 holoprotein precursor is predominantly localized to the rough ER and smooth ER, where it is a component of a approximately 180-kDa native complex. PS2 forms similar but independent complexes. Restricted incorporation of the presenilin NTF and CTF along with a potentially functional ligand (beta-catenin) into a multimeric complex in the ER and Golgi apparatus may provide an explanation for the regulated accumulation of the NTF and CTF.

Amyloid-beta-protein isoforms in brain of subjects with PS1-linked, beta APP-linked and sporadic Alzheimer disease

To determine whether similar abnormalities of various soluble full-length and N-terminal truncated Abeta peptides occur in postmortem cerebral cortex of affected PS1 mutation carriers, we examined the amounts of two amyloid species ending at residue 40 or at residues 42(43) using sandwich ELISA systems. Our results indicate that PS1 mutations effect a dramatic accumulation in brain of the highly insoluble potentially neurotoxic long-tailed isoforms of the Abeta peptide such as Abeta1-42(43) and Abetax-42(43). This enhancing effect of PS1 mutation on Abetax-42(43) deposition was highly similar to that of a betaAPP mutation (Val717Ile) but the effects on Abetax-40 production were significantly different between these two causal genes. In contrast to previous studies of soluble Abeta in plasma and in supernatants from cultured fibroblasts of subjects with PS1 mutations, our studies also show that there is an increase in insoluble Abetax-40 peptides in brain of subjects with PS1 mutations.

Analysis of the butyrylcholinesterase gene and nearby chromosome 3 markers in Alzheimer disease

The K-variant of butyrylcholinesterase (BCHE-K) recently has been reported to be associated with Alzheimer disease (AD) in carriers of the epsilon4 allele of the apolipoprotein E (APOE) gene. We have re-examined the frequency of the BCHE-K allele in a large data set of both sporadic and familial cases of AD disease, and we have also examined the segregation of three genetic markers on chromosome 3 near BCHE . Our data neither support an association of BCHE-K with sporadic or familial AD, nor do they suggest the existence of another gene nearby on chromosome 3 as a common cause of familial AD.

Presenilin 1 is actively degraded by the 26S proteasome

The metabolic pathways governing the turnover of presenilin 1 (PS1) have been incompletely worked out. The PS1 holoprotein has low abundance in many cells and appears to undergo endoproteolytic cleavage near residue 298. We provide evidence that one mechanism by which the PS1 holoprotein is degraded is through the action of the 26S proteasome. We also show that the proteasome does not participate in the endoproteolytic cleavage.

Analysis of the 5' sequence, genomic structure, and alternative splicing of the presenilin-1 gene (PSEN1) associated with early onset Alzheimer disease

Mutations in the human presenilin genes (PSEN1 and PSEN2) are associated with early onset familial Alzheimer disease. The presenilin genes encode integral membrane proteins with similar structures, which suggests that they may have closely related, but as yet unknown functions. Analysis of the 5' upstream sequence and the structure of the PSEN1 gene reveals that the 5' sequence contains multiple putative transcription regulatory elements including clusters of STAT elements involved in transcriptional activation in response to signal transduction. The first four exons contain untranslated sequences, with Exons 1 and 2 representing alternate initial transcription sites. The function of these alternate initial exons is unclear. Exon 4 bears the first ATG sequence. The last 12 bp of Exon 4 is used as an alternative splice donor site. Exon 9 is alternately spliced in leukocytes, but not in most other tissues. Splicing of Exon 9 is predicted to cause significant structural changes to the protein. The majority of transcripts expressed in most tissues are polyadenylated 1127 bp from the TAG stop codon in Exon 13. A small proportion of transcripts contain the same 5'UTR and ORF but are polyadenylated 4435 bp from the stop codon. The longer polyadenylated transcripts contain three additional palindromes and at least one additional stem-loop structure with stabilities greater than -16 kcal/mol.

Mutant presenilins of Alzheimer's disease increase production of 42-residue amyloid beta-protein in both transfected cells and transgenic mice

The mechanism by which mutations in the presenilin (PS) genes cause the most aggressive form of early-onset Alzheimer's disease (AD) is unknown, but fibroblasts from mutation carriers secrete increased levels of the amyloidogenic A beta 42 peptide, the main component of AD plaques. We established transfected cell and transgenic mouse models that coexpress human PS and amyloid beta-protein precursor (APP) genes and analyzed quantitatively the effects of PS expression on APP processing. In both models, expression of wild-type PS genes did not alter APP levels, alpha- and beta-secretase activity and A beta production. In the transfected cells, PS1 and PS2 mutations caused a highly significant increase in A beta 42 secretion in all mutant clones. Likewise, mutant but not wildtype PS1 transgenic mice showed significant overproduction of A beta 42 in the brain, and this effect was detectable as early as 2-4 months of age. Different PS mutations had differential effects on A beta generation. The extent of A beta 42 increase did not correlate with presenilin expression levels. Our data demonstrate that the presenilin mutations cause a dominant gain of function and may induce AD by enhancing A beta 42 production, thus promoting cerebral beta-amyloidosis.

Presenilin proteins undergo heterogeneous endoproteolysis between Thr291 and Ala299 and occur as stable N- and C-terminal fragments in normal and Alzheimer brain tissue

Humans inheriting missense mutations in the presenilin (PS)1 and -2 genes undergo progressive cerebral deposition of the amyloid beta-protein at an early age and develop a clinically and pathologically severe form of familial Alzheimer's disease (FAD). Because PS1 mutations cause the most aggressive known form of AD, it is important to elucidate the structure and function of this multitransmembrane protein in the brain. Using a panel of region-specific PS antibodies, we characterized the presenilin polypeptides in mammalian tissues, including brains of normal, AD, and PS1-linked FAD subjects, and in transfected and nontransfected cell lines. Very little full-length PS1 or -2 was detected in brain and untransfected cells; instead the protein occurred as a heterogeneous array of stable N- and C-terminal proteolytic fragments that differed subtly among cell types and mammalian tissues. Sequencing of the major C-terminal fragment from PS1-transfected human 293 cells showed that the principal endoproteolytic cleavage occurs at and near Met298 in the proximal portion of the large hydrophilic loop. Full-length PS1 in these cells is quickly turned over (T1/2 approximately 60 min), in part to the two major fragments. The sizes and amounts of the PS fragments were not significantly altered in four FAD brains with the Cys410Tyr PS1 missense mutation. Our results indicate that presenilins are rapidly processed to N- and C-terminal fragments in both neural and nonneural cells and that interference with this processing is not an obligatory feature of FAD-causing mutations.

Alzheimer's disease associated with mutations in presenilin 2 is rare and variably penetrant

Missense mutations in the presenilin 2 (PS-2) gene on chromosome 1 were sought by direct nucleotide sequence analysis of the open reading frame of 60 pedigrees with familial Alzheimer's disease (FAD). In the majority of these pedigrees, PS-1 and beta-amyloid precursor protein (beta APP) gene mutations had been excluded. While no additional PS-2 pathogenic mutations were detected, four silent nucleotide substitutions and alternative splicing of nucleotides 1338-1340 (Glu325) were observed. Analysis of additional members of a pedigree known to segregate a Met239Val mutation in PS-2 revealed that the age of onset of symptoms is highly variable (range 45-88 years). This variability is not attributable to differences in ApoE genotypes. These results suggest (i) that, in contrast to mutations in PS-1, mutations in PS-2 are a relatively rare cause of FAD; (ii) that other genetic or environmental factor modify the AD phenotype associated with PS-2 mutations; and (iii) that still other FAD susceptibility genes remain to be identified.

Failure to detect missense mutations in the S182 gene in a series of late-onset Alzheimer's disease cases

The possibility of an interaction of multiple genes has been speculated in pathogenesis of Alzheimer's disease (AD). Because we have recently cloned a novel gene S182 bearing five different missense mutations which segregate with early-onset familial AD, we sought the frequency of these mutations in familial and sporadic late-onset AD to clarify the incidence of these mutations in the disease. The current study showed lack of these mutations in 118 independent subjects affected with late-onset Alzheimer's disease.

Familial Alzheimer's disease in kindreds with missense mutations in a gene on chromosome 1 related to the Alzheimer's disease type 3 gene

We report the cloning of a novel gene (E5-1) encoded on chromosome 1 which has substantial nucleotide and amino-acid sequence similarity to the S182 gene on chromosome 14q24.3. Mutations, including three new missense mutations in the S182 gene, are associated with the AD3 subtype of early-onset familial Alzheimer's disease (AD). Both the E5-1 and the S182 proteins are predicted to be integral membrane proteins with seven membrane-spanning domains, and a large exposed loop between the sixth and seventh transmembrane domains. Analysis of the nucleotide sequence of the open reading frame (ORF) of the E5-1 gene led to the discovery of two missense substitutions at conserved amino-acid residues in affected members of pedigrees with a form of familial AD that has a later age of onset than the AD3 subtype (50-70 years versus 30-60 years for AD3). These observations imply that the E5-1 gene on chromosome 1 and the S182 gene on chromosome 14q24.3 are members of a family of genes (presenilins) with related functions, and indicates that mutations in conserved residues of E5-1 could also play a role in the genesis of AD. Our results also indicate that still other AD susceptibility genes exist.

Cloning of a gene bearing missense mutations in early-onset familial Alzheimer's disease

Some cases of Alzheimer's disease are inherited as an autosomal dominant trait. Genetic linkage studies have mapped a locus (AD3) associated with susceptibility to a very aggressive form of Alzheimer's disease to chromosome 14q24.3. We have defined a minimal cosegregating region containing the AD3 gene, and isolated at least 19 different transcripts encoded within this region. One of these transcripts (S182) corresponds to a novel gene whose product is predicted to contain multiple transmembrane domains and resembles an integral membrane protein. Five different missense mutations have been found that cosegregate with early-onset familial Alzheimer's disease. Because these changes occurred in conserved domains of this gene, and are not present in normal controls, they are likely to be causative of AD3.

Application of the reaction of dithioesters with epsilon-amino groups in lysine to the chemical modification of proteins

The reaction of lysine with dithioesters was applied to horseradish peroxidase donor: hydrogen-peroxide oxidoreductase, EC 1.11.1.7) using carboxymethyl dithiotridecanoate: three to four lysine residues were modified. The modified enzyme was soluble and active in diethyl ether. Papain (EC 3.4.22.2) was modified with carboxymethyl dithiobenzoate: two lysine residues were modified. The modified enzyme was soluble and active in dimethylsulfoxide. From these results it is concluded that dithioesters are efficient reagents for the modification of peripheral lysine residues of proteins. Aromatic dithioesters, less reactive but more selective, should be recommended for thiol-dependent enzymes such as papain.

Epileptic discharges induced by intermittent light stimulation in photosensitive baboons: a current source density study

The current source density (CSD) method was applied to the study of paroxysmal discharges (PDs) induced by intermittent light stimulation (ILS) in Papio papio baboons made photosensitive by a subconvulsant dose of allylglycine. CSD was studied in the motor and premotor areas (4 and 6). Laminar profiles of sinks and sources are similar in both areas. Nevertheless, the motor area seems to become involved first since it shows the earliest and most prominent sink in layer III. Such a sink, correlated with the PD spike, moves progressively upward to the cortical surface. The localization and other experimental arguments obtained by the same method suggest that this sink could be mainly of dendritic origin. The cortico-cortical afferents to the superficial layers of the motor area might thus determine the generation of this sink. A smaller sink, detected at the same latency between layers V and VI could correspond to synaptic activations due to thalamo-cortical afferents probably arriving on the pyramidal cells which project to the spinal cord. Intense sinks correlated with the PD wave in layer V could be passive, due to active sources lying just above and/or below, because in previous studies an inhibition of the cellular discharges was always observed in correlation with the wave. It is suggested that ILS triggered PDs involve visual cortico-cortical afferents directed mainly to the superficial layers of the motor area provoking an intense synaptic activation of the cellular elements situated at this level.

Effects of trichothecenes (T-2 toxin) on protein synthesis in vitro by brain polysomes and messenger RNA

The effects of T-2 toxin on protein synthesis were tested in two reticulocyte lysate in vitro systems pretreated with micrococcal nuclease. One of the test systems contained purified globin mRNA and was initiation dependent. The other contained rat brain polysomes and incorporated amino acids by an elongation dependent process. T-2 toxin inhibited the translation of globin mRNA at all concentrations tested, from 10(-8) M to 10(-4) M. Rat brain polysomes were much less sensitive to T-2 toxin than globin mRNA. While high concentrations of the toxin (10(-4) M) led to partial inhibition of protein synthesis by polysomes, low concentrations (10(-8) M and 10(-6) M) stimulated protein synthesis. Comparison of the above results with those obtained by other workers suggest that the T-2 toxin may inhibit not only the initiation step of translation, but also elongation and termination, depending upon the concentration of the toxin and the nature of the translation system. A similar mechanism may operate for all the trichothecene toxins that exert their effect through binding to ribosomal peptidyl transferase.

Possible involvement of the amygdaloid complex in morphine analgesia as studied by electrolytic lesions in rats

The analgesic effects of morphine (5 mg/kg i.p.) were studied in biamygalectomized rats. (1) Using the tail-flick test neither withdrawal latencies nor morphine time-course and efficacy were affected by the lesions. (2) The threshold for vocalization to electrical stimulation of the tail was greatly increased in lesioned rats; however, statistical analysis revealed no significant change in the analgesic efficacy of morphine.