Missense mutations in the human presenilin-1 (PS1) gene, which is found on chromosome 14, cause early-onset familial Alzheimer's disease (FAD). FAD-linked PS1 variants alter proteolytic processing of the amyloid precursor protein and cause an increase in vulnerability to apoptosis induced by various cell stresses. However, the mechanisms responsible for these phenomena are not clear. Here we report that mutations in PS1 affect the unfolded-protein response (UPR), which responds to the increased amount of unfolded proteins that accumulate in the endoplasmic reticulum (ER) under conditions that cause ER stress. PS1 mutations also lead to decreased expression of GRP78/Bip, a molecular chaperone, present in the ER, that can enable protein folding. Interestingly, GRP78 levels are reduced in the brains of Alzheimer's disease patients. The downregulation of UPR signalling by PS1 mutations is caused by disturbed function of IRE1, which is the proximal sensor of conditions in the ER lumen. Overexpression of GRP78 in neuroblastoma cells bearing PS1 mutants almost completely restores resistance to ER stress to the level of cells expressing wild-type PS1. These results show that mutations in PS1 may increase vulnerability to ER stress by altering the UPR signalling pathway.

Families bearing mutations in the presenilin 1 (PS1) gene develop Alzheimer's disease. Previous studies have shown that the Alzheimer-associated mutations in PS1 increase production of amyloid ␤ protein (A␤ 1-42 ). We now show that PS1 also regulates phosphorylation of the microtubule-associated protein tau. PS1 directly binds tau and a tau kinase, glycogen synthase kinase 3␤ (GSK-3␤). Deletion studies show that both tau and GSK-3␤ bind to the same region of PS1, residues 250-298, whereas the binding domain on tau is the microtubule-binding repeat region. The ability of PS1 to bring tau and GSK-3␤ into close proximity suggests that PS1 may regulate the interaction of tau with GSK-3␤. Mutations in PS1 that cause Alzheimer's disease increase the ability of PS1 to bind GSK-3␤ and, correspondingly, increase its tau-directed kinase activity. We propose that the increased association of GSK-3␤ with mutant PS1 leads to increased phosphorylation of tau.The neuropathological diagnosis of Alzheimer's disease (AD) requires the presence of both senile plaques and neurofibrillary tangles (NFT) (1). Senile plaques are largely composed of amyloid ␤ protein (A␤), whereas NFT are composed of hyperphosphorylated tau organized into filamentous structures termed paired helical filaments (2-4). Mutations on the presenilin 1 (PS1) gene cause an early onset form of AD with an autosomal dominant inheritance pattern (5-7). The role of PS1 in AD is particularly interesting because it has a strong causal relationship to the disease; genetic studies show that mutations for PS1 exhibit 100% penetrance in causing AD (8). Although, the mechanism through which PS1 causes AD is unclear. Mutations in presenilins affect A␤ processing. Recent studies indicate that cell lines, transgenic mice, or patients expressing mutant forms of PS1 show a selective increase in production of A␤ 1-42 (9-12). Mutations in the presenilins also activate apoptotic pathways and render neurons more vulnerable to stressors, such as A␤ neurotoxicity (13-16). The ability of PS1 to potentiate A␤ toxicity raises the possibility that PS1 interacts with glycogen synthase kinase 3␤ (GSK-3␤), which we previously have shown to be involved in A␤-mediated cell death (17-20). The enzyme GSK-3␤ also has been implicated in AD because this kinase is one of a group of proline-directed kinases that can phosphorylate the microtubule-associated protein tau, to generate a precursor to NFTs, termed paired helical filaments-tau (21,22). PS1 (23-26) and GSK-3␤ (27, 28) can be found in association with NFTs in the Alzheimer brain, which further suggests that there may be a physiological connection between PS1, GSK-3␤, and tau. To pursue these intriguing connections, we investigated whether PS1 might directly associate with GSK-3␤ and tau. MATERIALS AND METHODSPreparation of Brain Samples. Human brain cortex was obtained at autopsy from patients ranging in age from 44 to 88 years old. Twenty-one samples, from donors age 44-79, showed no evidence of neurological disorders, whereas two sa...

Amyloid-␤ protein (A␤) aggregates in the brain to form senile plaques. By using thioflavin T, a dye that specifically binds to fibrillar structures, we found that metals such as Zn(II) and Cu(II) normally inhibit amyloid ␤-aggregation. Another method for detecting A␤, which does not distinguish the types of aggregates, showed that these metals induce a non-␤-sheeted aggregation, as reported previously. Secondary structural analysis and microscopic studies revealed that metals induced A␤ to make non-fibrillar aggregates by disrupting ␤-sheet formation. These non-fibrillar A␤ aggregates displayed much weaker Congo Red birefringence, and in separate cell culture experiments, were less toxic than self ␤-aggregates, as demonstrated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. The toxicity of soluble A␤ was enhanced in the presence of Cu(II), which suggests the previously hypothesized role of A␤ in generating oxidative stress. Finally, under an acidic condition, similar to that in the inflammation associated with senile plaques, ␤-aggregation was robustly facilitated at one specific concentration of Zn(II) in the presence of heparin. However, because a higher concentration of Zn(II) virtually abolished this abnormal phenomenon, and at normal pH any concentrations strongly inhibit ␤-aggregation and its associated cytotoxicity, including its anti-oxidative nature we suggest that Zn(II) has an overall protective effect against ␤-amyloid toxicity. Amyloid-␤ protein (A␤)1 is one of the main components of senile plaques, a pathological hallmark of Alzheimer's disease (AD) (1, 2). Although A␤ is undisputedly associated with the pathology of AD, it is still an open question as to what specific aspects of A␤ and its processing are the important variables in the pathophysiology of the disease. For example, fibrillar A␤, but not non-amyloidogenic, amorphous aggregates of A␤, was reported to cause neuronal cell death in primary rat hippocampal cultures (3), and soluble monomeric species of A␤ are relatively nontoxic as compared with fibrillar A␤ (4). Thus, these in vitro studies suggest that the degree of ␤-aggregation is particularly important for neurotoxicity to occur (5-8). However, many controversial results from in vivo studies have been reported concerning the pathological role of plaque formation in AD. Irizarry et al. (9) reported that transgenic (TG) mice expressing human A␤ failed to exhibit neuronal loss despite depositing substantial amounts of A␤. On the other hand, TG mice that express Swedish mutant amyloid precursor protein (APP) formed plaques that were detected by both an anti-APP antibody and a ␤-sheet specific dye (10). Moreover, these APP TG mice also displayed memory deficits. Taken together, these results indicate that, although the plaque assembly process may require further investigation, amyloid ␤-aggregation certainly is an essential event in the pathogenesis of AD.Based on these lines of evidence, the search for a compound that interrupts ␤-aggregation and thus protects agai...

Alzheimer's disease (AD) brains contain neurofibrillary tangles (NFTs) composed of abnormally hyperphosphorylated tau protein.Regional reductions in cerebral glucose metabolism correlating to NFT densities have been reported in AD brains. Assuming that reduced glucose metabolism might cause abnormal tau hyperphosphorylation, we induced in vivo alterations of glucose metabolism in mice by starvation or intraperitoneal injections of either insulin or deoxyglucose. We found that the treatments led to abnormal tau hyperphosphorylation with patterns resembling those in early AD brains and also resulted in hypothermia. Surprisingly, tau hyperphosphorylation could be traced down to a differential effect of low temperatures on kinase and phosphatase activities. These data indicate that abnormal tau hyperphosphorylation is associated with altered glucose metabolism through hypothermia. Our results imply that serine-threonine protein phosphatase 2A plays a major role in regulating tau phosphorylation in the adult brain and provide in vivo evidence for its crucial role in abnormal tau hyperphosphorylation in AD.

Families bearing mutations in the presenilin-1 (PS1) gene develop Alzheimer's disease (AD). However, the mechanism through which PS1 causes AD is unclear. The co-immunoprecipitation with PS1 in transfected COS-7 cells indicates that PS1 directly interacts with endogenous L L-catenin, and the interaction requires residues 322^450 of PS1 and 445^676 of L L-catenin. Both proteins are co-localized in the endoplasmic reticulum. Over-expression of PS1 reduces the level of cytoplasmic L Lcatenin, and inhibits L L-catenin-T cell factor-regulated transcription. These results indicate that PS1 plays a role as inhibitor of the L L-catenin signal, which may be connected with the AD dysfunction.z 1998 Federation of European Biochemical Societies.

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The mutation L271V in exon 8 of the presenilin-1 (PS-1) gene was detected in an Alzheimer's disease pedigree. Neuropathological examination of affected individuals identified variant, large, non-cored plaques without neuritic dystrophy, reminiscent of cotton wool plaques. Biochemical analysis of L271V mutation showed that it increased secretion of the 42-amino acid amyloid-␤ peptide, suggesting a pathogenic mutation. Analysis of PS-1 transcripts from the brains of two mutation carriers revealed a 17-50% increase in PS-1 transcripts with deletion of exon 8 (PS-1⌬exon8) compared with unrelated Alzheimer's disease brains. Exon trapping analysis confirmed that L271V mutation enhanced the deletion of exon 8. Western blots of brain lysates indicated that PS-1⌬exon8 was overexpressed in an affected individual. Biochemical analysis of PS-1⌬exon8 in COS and BD8 cells indicate the splice isoform is not intrinsically active but interacts with wild-type PS-1 to generate amyloid-␤. Western blots of cell lysates immunoprecipitated with anti-Tau or anti-GSK-3␤ antibodies indicated that PS-1⌬exon8, unlike wild-type PS-1, does not interact directly with Tau or GSK-3␤, potential modifiers of neuritic dystrophy. We postulate that variant plaques observed in this family are due in part to the effects of PS-1⌬exon8 and that interaction between PS-1 and various protein complexes are necessary for neuritic plaque formation.The presence of senile plaques is one of the key neuropathological features of familial as well as sporadic forms of Alzheimer's disease (AD).1 Senile plaques are extracellular deposits composed mainly of the amyloid-␤ peptide (A␤), which is cleaved by a series of secretases from the amyloid precursor protein (APP) (1). Mutations in any of three genes, APP, presenilin-1 (PS-1), or presenilin-2 (PS-2), give rise to early onset familial AD (EOFAD). Mutations in the PS-1 gene are associated with severe neuropathology. Typically, the brains of affected individuals have a large number of diffuse as well as cored neuritic plaques that are deposited in the cerebral cortex and in regions not normally involved in AD, such as the cerebellum (2). Moreover, there is intense Tau pathology with neuritic dystrophy around the plaques and neurofibrillary tangles (3, 4). However, four mutations in PS-1, an in-frame deletion of the exon 9 sequence (PS1⌬exon9) (5, 6), a two-amino acid deletion (⌬I83/⌬M84) (7), a P436Q (8), and a E280G (9), have been shown to be associated with a variant "cotton wool" plaque pathology. Brains from individuals carrying these specific mutations have extensive deposition of large spherical plaques that lack distinctive cores and neuritic pathology. Biochemical analysis of cells transfected with PS-1 cDNAs, carrying any of these mutations, secrete exceptionally high levels of 〈␤1Ϫ42 (8). This suggests that PS-1 has a role not only in determining the levels of different A␤ species but also in the morphology of the plaques and neuritic dystrophy. The range of functions of the wild-type PS-1 protein are still ...