Overexpression Of PS1 Research Articles

YY-1224, a terpene trilactone-strengthened Ginkgo biloba, attenuates neurodegenerative changes induced by \u03b2-amyloid (1-42) or double transgenic overexpression of APP and PS1 via inhibition of cyclooxygenase-2

BackgroundGinkgo biloba has been reported to possess free radical-scavenging antioxidant activity and anti-inflammatory properties. In our pilot study, YY-1224, a terpene trilactone-strengthened extract of G. biloba, showed anti-inflammatory, neurotrophic, and antioxidant effects.ResultsWe investigated the pharmacological potential of YY-1224 in β-amyloid (Aβ) (1-42)-induced memory impairment using cyclooxygenase-2 (COX-2) knockout (−/−) and APPswe/PS1dE9 transgenic (APP/PS1 Tg) mice. Repeated treatment with YY-1224 significantly attenuated Aβ (1-42)-induced memory impairment in COX-2 (+/+) mice, but not in COX-2 (−/−) mice. YY-1224 significantly attenuated Aβ (1-42)-induced upregulation of platelet-activating factor (PAF) receptor gene expression, reactive oxygen species, and pro-inflammatory factors. In addition, YY-1224 significantly inhibited Aβ (1-42)-induced downregulation of PAF-acetylhydrolase-1 (PAF-AH-1) and peroxisome proliferator-activated receptor γ (PPARγ) gene expression. These changes were more pronounced in COX-2 (+/+) mice than in COX-2 (−/−) mice. YY-1224 significantly attenuated learning impairment, Aβ deposition, and pro-inflammatory microglial activation in APP/PS1 Tg mice, whereas it significantly enhanced PAF-AH and PPARγ expression. A preferential COX-2 inhibitor, meloxicam, did not affect the pharmacological activity by YY-1224, suggesting that the COX-2 gene is a critical mediator of the neuroprotective effects of YY-1224. The protective activity of YY-1224 appeared to be more efficacious than a standard G. biloba extract (Gb) against Aβ insult.ConclusionsOur results suggest that the protective effects of YY-1224 against Aβ toxicity may be associated with its PAF antagonistic- and PPARγ agonistic-potential as well as inhibition of the Aβ-mediated pro-inflammatory switch of microglia phenotypes through suppression of COX-2 expression.

New pathway links γ‐secretase to inflammation and memory while sparing notch

New pathway links γ‐secretase to inflammation and memory while sparing notch

Alzheimer's Disease-Linked Presenilin Mutation (PS1M146L) Induces Filamin Expression and γ-Secretase Independent Redistribution

Presenilin mutations are linked to the early onset familial Alzheimer's disease (FAD) and lead to a range of neuronal changes, indicating that presenilins interact with multiple cellular pathways to regulate neuronal functions. In this report, we demonstrate the effects of FAD-linked presenilin 1 mutation (PS1M146L) on the expression and distribution of filamin, an actin cross-linking protein that interacts with PS1 both physically and genetically. By using immunohistochemical methods, we evaluated hippocampal dentate gyrus for alterations of proteins involved in synaptic plasticity. Among many proteins expressed in the hippocampus, calretinin, glutamic acid decarboxylase (GAD67), parvalbumin, and filamin displayed distinct changes in their expression and/or distribution patterns. Striking anti-filamin immunoreactivity was associated with the polymorphic cells of hilar region only in transgenic mice expressing PS1M146L. In over 20% of the PS1M146L mice, the hippocampus of the left hemisphere displayed more pronounced upregulation of filamin than that of the right hemisphere. Anti-filamin labeled the hilar neurons only after the PS1M146L mice reached after four months of age. Double labeling immunohistochemical analyses showed that anti-filamin labeled neurons partially overlapped with cholecystokinin (CCK), somatostatin, GAD67, parvalbumin, and calretinin immunoreactive neurons. In cultured HEK293 cells, PS1 overexpression resulted in filamin redistribution from near cell peripheries to cytoplasm. Treatment of CHO cells stably expressing PS1 with WPE-III-31C or DAPT, selective γ-secretase inhibitors, did not suppress the effects of PS1 overexpression on filamin. These studies support a γ-secretase-independent role of PS1 in modulation of filamin-mediated actin cytoskeleton.

Nuclear translocation and signalling of L1-CAM in human carcinoma cells requires ADAM10 and presenilin/γ-secretase activity

L1-CAM (L1 cell-adhesion molecule), or more simply L1, plays an important role in the progression of human carcinoma. Overexpression promotes tumour-cell invasion and motility, growth in nude mice and tumour metastasis. It is feasible that L1-dependent signalling contributes to these effects. However, little is known about its mechanism in tumour cells. We reported previously that L1 is cleaved by ADAM (a disintegrin and metalloprotease) and that the cytoplasmic part is essential for L1 function. Here we analysed more closely the role of proteolytic cleavage in L1-mediated nuclear signalling. Using OVMz carcinoma cells and L1-transfected cells as a model, we found that ADAM10-mediated cleavage of L1 proceeds in lipid raft and non-raft domains. The cleavage product, L1-32, is further processed by PS (presenilin)/γ-secretase to release L1-ICD, an L1 intracellular domain of 28 kDa. Overexpression of dominant-negative PS1 or use of a specific γ-secretase inhibitor leads to an accumulation of L1-32. Fluorescence and biochemical analysis revealed a nuclear localization for L1-ICD. Moreover, inhibition of ADAM10 and/or γ-secretase blocks nuclear translocation of L1-ICD and L1-dependent gene regulation. Overexpression of recombinant L1-ICD mediates gene regulation in a similar manner to full-length L1. Our results establish for the first time that regulated proteolytic processing by ADAM10 and PS/γ-secretase is essential for the nuclear signalling of L1 in human carcinoma cell lines.

Hyperhomocysteinemia Increases β-Amyloid by Enhancing Expression of γ-Secretase and Phosphorylation of Amyloid Precursor Protein in Rat Brain

Hyperhomocysteinemia and beta-amyloid (Abeta) overproduction are critical etiological and pathological factors in Alzheimer disease, respectively; however, the intrinsic link between them is still missing. Here, we found that Abeta levels increased and amyloid precursor protein (APP) levels simultaneously decreased in hyperhomocysteinemic rats after a 2-week induction by vena caudalis injection of homocysteine. Concurrently, both the mRNA and protein levels of presenilin-1, a component of gamma-secretase, were elevated, whereas the expression levels of beta-secretase and presenilin-2 were not altered. We also observed that levels of phosphorylated APP at threonine-668, a crucial site facilitating the amyloidogenic cleavage of APP, increased in rats with hyperhomocysteinemia, although the phosphorylation per se did not increase the binding capacity of pT668-APP to the secretases. The enhanced phosphorylation of APP in these rats was not relevant to either c-Jun N-terminal kinase or cyclin-dependent kinase-5. A prominent spatial memory deficit was detected in rats with hyperhomocysteinemia. Simultaneous supplementation of folate and vitamin-B12 attenuated the hyperhomocysteinemia-induced abnormal processing of APP and improved memory. Our data revealed that hyperhomocysteinemia could increase Abeta production through the enhanced expression of gamma-secretase and APP phosphorylation, causing memory deficits that could be rescued by folate and vitamin-B12 treatment in these rats. It is suggested that hyperhomocysteinemia may serve as an upstream factor for increased Abeta production as seen in patients with Alzheimer disease.

NGF and BDNF signaling control amyloidogenic route and Aβ production in hippocampal neurons

Here, we report that interruption of NGF or BDNF signaling in hippocampal neurons rapidly activates the amyloidogenic pathway and causes neuronal apoptotic death. These events are associated with an early intracellular accumulation of PS1 N-terminal catalytic subunits and of APP C-terminal fragments and a progressive accumulation of intra- and extracellular Abeta aggregates partly released into the culture medium. The released pool of Abeta induces an increase of APP and PS1 holoprotein levels, creating a feed-forward toxic loop that might also cause the death of healthy neurons. These events are mimicked by exogenously added Abeta and are prevented by exposure to beta- and gamma-secretase inhibitors and by antibodies directed against Abeta peptides. The same cultured neurons deprived of serum die, but APP and PS1 overexpression does not occur, Abeta production is undetectable, and cell death is not inhibited by anti-Abeta antibodies, suggesting that hippocampal amyloidogenesis is not a simple consequence of an apoptotic trigger but is due to interruption of neurotrophic signaling.

Enhancing Channel Activity

Alzheimer’s disease (AD) is associated with the accumulation of amyloid β (Aβ) plaques and neurofibrillary tangles in the brain, but whether Aβ is responsible for triggering AD is unclear. Excessive Ca 2+ signaling, which is very toxic to neurons, is another potential culprit. The γ secretase complex, whose core components are the presenilin (PS) proteins, processes the amyloid precursor protein (APP) to produce Aβ. Cells containing mutant PS proteins associated with familial AD (FAD) exhibit excessive Ca 2+ signaling. Because the inositol 1,4,5-trisphosphate receptor (IP 3 R) is the channel responsible for Ca 2+ egress from the endoplasmic reticulum (ER), Cheung et al . investigated a role for PS proteins in modulating IP 3 R activity. Coimmunoprecipitation assays showed the physical association of either wild-type or FAD PS proteins with IP 3 Rs in mouse brain lysates. Single-channel patch-clamp current recordings showed that basal and IP 3 -stimulated channel activity in chick DT40 cells overexpressing FAD PS proteins was enhanced compared with that in cells expressing wild-type PS proteins and was more sensitive to lower concentrations of IP 3 . The increased Ca 2+ flux in FAD PS–expressing cells was associated with the IP 3 R being in an open state for longer durations than was the case in wild-type PS-expressing cells. Similar electrophysiological experiments showed that FAD PS1 enhanced IP 3 R-mediated Ca 2+ signaling in transfected mouse brain cortical neurons. Although overexpression of FAD PS1 increased Aβ production by APP-expressing DT40 cells compared with that observed when wild-type PS1 was overexpressed, this enhancement of APP processing was blocked in DT40 cells deficient in all IP 3 R isoforms. Together, these data suggest that increased Ca 2+ signaling through mutant PS-mediated enhancement of IP 3 R activity may play a role in the pathogenesis of AD. K.-H. Cheung, D. Shineman, M. Müller, C. Cárdenas, L. Mei, J. Yang, T. Tomita, T. Iwatsubo, V. M.-Y. Lee, J. K. Foskett, Mechanism of Ca 2+ disruption in Alzheimer’s disease by presenilin regulation of InsP 3 receptor channel gating. Neuron 58 , 871-883 (2008). [PubMed]

P4-191: PS1 promoter is regulated by methylation

Although there are a crescent number of studies on the significance of high homocysteine levels in Alzheimer, the existence of a causal correlation is still far to be ascertained. Years ago we postulated a molecular mechanism responsible for amyloid accumulation in AD, involving changes in methylation of specific genes. We evidenced that a nutritional model of homocysteine cycle alteration could lead to increase amyloid production both in SK-N-BE neuroblastoma cells and in TgCRND8 mice (carrying a double mutated APP). Amyloid increase was due to PS1 and BACE over-expression and the consequent increase in secretase activity. Our hypothesis is that nutritional factors causing vitamin B and folate deficiency and homocysteine cycle alterations could induce a decrease in sequence-specific DNA methylation and the “aberrant” activation of genes involved in amyloid processing. The aim of the present study is to verify the hypothesised hypomethylation of PS1 promoter in SK-N-BE neuroblastoma cells and in TgCRND8 mice, in conditions of vitamin B (folate, B12 and B6) deficiency. Supplementation with S-adenosylmethionine as methyl donor represents the tentative to reverse this effect. DNA is extracted both from SK-N-BE neuroblastoma cells cultured either in control or vitamin B deficient, with or without S-adenosylmethionine 100 μM and from brains collected from TgCRND8 or wt 129SV mice grown either with control or vitamin B deficient diet, with or without oral supplementation of S-adenosylmethionine 400 μg/day. Methylation status of PS1 promoter is evaluated through bisulphite modification and genomic sequencing. Deficiency of folate, vitamin B12 and vitamin B6 induces the hypomethylation of specific CpG moieties in the 5'-flanking region of PS1 promoter with no changes in overall DNA methylation. S-adenosylmethionine is able to prevent the observed sequence-specific hypomethylation without increase in overall DNA methylation. PS1 promoter methylation status appears to be correlated with the level of gene expression. This finding allows to directly correlating the vitamin B-dependent alteration of homocysteine cycle with DNA methylation and clearly evidences that PS1 promoter is regulated by methylation status of specific CpG moieties.

SERCA pump activity is physiologically regulated by presenilin and regulates amyloid β production

In addition to disrupting the regulated intramembraneous proteolysis of key substrates, mutations in the presenilins also alter calcium homeostasis, but the mechanism linking presenilins and calcium regulation is unresolved. At rest, cytosolic Ca2+ is maintained at low levels by pumping Ca2+ into stores in the endoplasmic reticulum (ER) via the sarco ER Ca2+-ATPase (SERCA) pumps. We show that SERCA activity is diminished in fibroblasts lacking both PS1 and PS2 genes, despite elevated SERCA2b steady-state levels, and we show that presenilins and SERCA physically interact. Enhancing presenilin levels in Xenopus laevis oocytes accelerates clearance of cytosolic Ca2+, whereas higher levels of SERCA2b phenocopy PS1 overexpression, accelerating Ca2+ clearance and exaggerating inositol 1,4,5-trisphosphate–mediated Ca2+ liberation. The critical role that SERCA2b plays in the pathogenesis of Alzheimer's disease is underscored by our findings that modulating SERCA activity alters amyloid β production. Our results point to a physiological role for the presenilins in Ca2+ signaling via regulation of the SERCA pump.

Non-cognitive behaviours in an APP/PS1 transgenic model of Alzheimer's disease

Alzheimer's disease (AD) is characterised by progressive cognitive impairment with neuropsychiatric symptoms such as anomalous motor behaviour, depression, anxiety, weight loss, irritability and agitation. The effect of hAPP and PS1 overexpression on cognition has been well characterised in a variety of transgenic mouse models, however, non-cognitive behaviours have not been considered as systematically. The non-cognitive behaviour of the hAPP/PS1 transgenic mouse model (TASTPM) was observed at ages spanning the rapid progression of amyloid neuropathology. TASTPM transgenic mice, of both genders, exhibited decreased spontaneous motor activity, disinhibition, increased frequency and duration of feeding bouts, reduced body weight and, by 10 months, increased activity over a 24 h period. In addition to the aforementioned behaviours, male transgenic mice also displayed enhanced aggression relative to wildtype controls. These data reveal previously unreported disease relevant behavioural changes that demonstrate the value of measuring behaviour in APP/PS1 transgenic models. These behavioural readouts could be useful in screening putative drug treatments for AD.

Where the actions of environment (nutrition), gene and protein meet: Beneficial role of fruit and vegetable juices in potentially delaying the onset of Alzheimer's disease

The present commentary is based on a thought – provoking and experiment – driven manuscript entitled “Supplementation with apple juice attenuates presenilin – 1 overexpression during dietary and genetically – induced oxidative stress” by A. Chan and T.B. Shea (University of Massachusetts Lowell, Lowell, MA) [2]. The manuscript’s highlights are discussed, with a short review of the current perspective on the important topic of the effects of dietary supplementation on Alzheimer’s disease (AD). The manuscript is focused to how apple juice concentrate (AJC) modulates the expression of the important AD – related protein presenilin (PS-1). This is a well – focused and well – defined study that tests a specific hypothesis in a potentially fruitful fashion. Using an interesting animal model, the investigators in the present work have examined the effect of dietary supplementation of AJC on the overexpression of PS-1, whose variant form participates in the overproduction of amyloid β-peptide (Aβ), a major hallmark of AD. Notably, this work shows that AJC attenuates PS-1 overexpression during dietary and

Co-expression of Nicastrin and Presenilin Rescues a Loss of Function Mutant of APH-1

gamma-Secretase is an intramembrane-cleaving aspartyl protease complex that mediates the final cleavage of beta-amyloid precursor protein to liberate the neurotoxic amyloid-beta peptide implicated in Alzheimer's disease. The four proteins presenilin (PS), nicastrin (NCT), APH-1, and PEN-2 are sufficient to reconstitute gamma-secretase activity in yeast. Although PS seems to contribute the catalytic core of the gamma-secretase complex, no distinct function could be attributed to the other components so far. In Caenorhabditis elegans, mutation of a glycine to an aspartic acid within a conserved GXXXG motif in the fourth transmembrane domain of APH-1 causes a loss of function phenotype. Surprisingly, we now found that the human homologue APH-1a carrying the equivalent mutation G122D is fully active in yeast co-expressing PS1, NCT, and PEN-2. To address this discrepancy, we expressed APH-1a G122D in HEK293 cells. As reported previously, overexpressed APH-1a G122D was not incorporated into the gamma-secretase complex. Separate overexpression of PS1, NCT, or PEN-2 together with APH-1a G122D allowed the formation of heterodimers lacking the other endogenous components. Only the combined overexpression of PS1 and NCT together with APH-1a G122D facilitated the formation of a fully active gamma-secretase complex. Under these conditions, APH-1a G122D supported the production of normal amounts of Abeta. We conclude that cooperative effects may stabilize a trim-eric complex of APH-1a G122D together with PS1 and NCT. Upon successful complex assembly, the GXXXG motif becomes dispensable for gamma-secretase activity.

Characterisation of cytoskeletal abnormalities in mice transgenic for wild-type human tau and familial Alzheimer's disease mutants of APP and presenilin-1

To study the role of Aβ amyloid deposits in the generation of cytoskeletal lesions, we have generated a transgenic mouse line coexpressing in the same neurons a wild-type human tau isoform (0N3R), a mutant form of APP (751SL) and a mutant form of PS1 (M146L). These mice developed early cerebral extracellular deposits of Aβ, starting at 2.5 months. A somatodendritic neuronal accumulation of transgenic tau protein was observed in tau only and in tau/PS1/APP transgenic mice, including in neurons adjacent to Aβ deposits. The phosphorylation status of this somatodendritic tau was similar in the two transgenic lines. The Aβ deposits were surrounded by a neuritic reaction composed of axonal dystrophic processes, immunoreactive for many phosphotau epitopes and for the human tau transgenic protein. Ultrastructural observation showed in these dystrophic neurites a disorganisation of the microtubule and the neurofilament network but animals that were observed up to 18 months of age did not develop neurofibrillary tangles. These results indicate that overexpression of mutant PS1, mutant APP and of wild-type human tau were not sufficient per se to drive the formation of neurofibrillary tangles in a transgenic model. The Aβ deposits, however, were associated to marked changes in cytoskeletal rganisation and in tau phosphorylation in adjacent dystrophic neurites.

Calpain inhibitors: a treatment for Alzheimer's disease.

Activation of the calpain system might contribute to the impairment of synaptic transmission in Alzheimer's disease (AD) (Liu et al., 1999; Rapoport, 1999; Selkoe, 1994). Calpains regulate the function of many proteins by limited proteolysis and initiate the complete degradation of other proteins. In particular, they modulate processes that govern the function and metabolism of proteins key to the pathogenesis of AD, including tau and amyloid precursor protein (APP). (Xie and Johnson, 1998; Wang, 2000). We have found that overexpression of APP(K670M:N671L) and PS1(M146L) proteins in hippocampal cultures derived from transgenic mice causes an increase in the frequency of spontaneous release of neurotransmitter. We have also found that calpain immunoreactive clusters are co-localized with immunoreactivity for the vesicle-associated presynaptic marker, synaptophysin. Moreover, application of calpain inhibitor reduces the frequency of spontaneous release of neurotransmitter. Therefore, we have hypothesized that calpains might contribute to the increase in transmitter release. Based on this hypothesis, we propose to test whether it is possible to restore normal synaptic transmission between cells derived from the transgenic model of AD by using calpain inhibitors. The transgenic mouse model also shows spatial learning impairment, a phenomenon that is thought to be associated with plastic changes at synaptic level. Therefore, we will also test whether we can rescue the learning impairment through a treatment with calpain inhibitors.

Increased Expression of Presenilin 2 Inhibits Protein Synthesis

Mutations in the presenilin genes PS1 and PS2 are a major cause of early onset familial Alzheimer's disease (AD). Previous studies have suggested that presenilins have several functions, including γ-secretase activity. It was also shown that presenilin expression is increased in the brains of some AD patients and ischemic rodents. The present study examines the effect of increased presenilin expression on protein synthesis. We show here that overexpression of wild-type PS2 (PS2wt) or PS2 mutant containing the FAD mutation N141I (PS2mut) in various cell lines inhibits the synthesis of coexpressed reporter and endogenous proteins. Furthermore, endogenous PS2 seems to be needed for translation inhibition since PS2 null fibroblasts were translationally more active than PS2+/+ fibroblasts under conditions known to inhibit translation. Overexpression of PS1 also appeared to cause inhibition of protein synthesis, but its effect was much weaker than that of PS2. Taken together, the results suggest that increased expression of PS2 and possibly also of PS1 inhibits translation and that presenilins may function as regulators of protein synthesis.

Characterization of the in vivo acceptors of the mycoloyl residues transferred by the corynebacterial PS1 and the related mycobacterial antigens 85.

Mycolic acids, long-chain (C70-C90) alpha-alkyl, beta-hydroxy fatty acids, are characteristic cell envelope components of mycobacteria; similar but shorter-chain substances occur in corynebacteria and related taxa. These compounds apparently play an important role in the physiology of these bacteria. The deduced N-terminal region of PS1, one of the two major secreted proteins of Corynebacterium glutamicum encoded by the csp1 gene, is similar to the antigens 85 complex of Mycobacterium tuberculosis which has been shown to be associated in vitro with a mycoloyltransferase activity onto trehalose. Overexpression of PS1 in the wild-type strain of C. glutamicum suggested the implication of the protein in the transfer of corynomycolates, evidenced by an increase esterification of the cell wall arabinogalactan with corynomycolic acid residues and an accumulation of trehalose dicorynomycolates. Overexpression of truncated forms of PS1 demonstrated that the crucial region for transfer activity of the protein involves all the region of homology with antigens 85. To establish the putative mycoloyltransferase activity of PS1, a csp1-inactivated mutant of C. glutamicum was biochemically characterized. Inactivation of the gene resulted in: (i) a 50% decrease in the cell wall corynomycolate content; (ii) the alteration of the permeability of the C. glutamicum cell envelope; (iii) the decrease of the trehalose dicorynomycolate content; (iv) the accumulation of trehalose monocorynomycolate; and (v) the appearance of a glycolipid identified as 6-corynomycoloylglucose. Complementation of the mutant by the csp1 gene fully restored the wild-type phenotype. Finally, a mycoloyltransferase assay established that PS1 possesses a trehalose mycoloyltransferase activity. To define the in vivo function of antigens 85, the csp1-inactivated mutant was complemented with the fbpA, fbpB or fbpC genes. Complementation with the different fbp genes restored the normal cell wall corynomycolate content and permeability, but did not affect either the fate of trehalose corynomycolates or the occurrence of glucose corynomycolate. Thus, PS1 is one of the enzymes that transfer corynomycoloyl residues onto both the cell wall arabinogalactan and trehalose monocorynomycolate, whereas in the whole bacterium the mycobacterial antigens 85A, 85B and 85C can transfer mycolates only onto the cell wall acceptor in C. glutamicum.

Processing of wild-type and mutant familial Alzheimer's disease-associated presenilin-1 in cultured neurons.

Mutations of presenilin (PS)-1, an endoplasmic reticulum/Golgi transmembrane protein, have been associated with early-onset familial Alzheimer's disease (FAD). In mammalian brain, PS1 exists primarily as its processed fragments; however, the role of this cleavage event in PS1 function remains unclear. Although some investigators have shown that mutant PS1 processing is unaltered (with the exception of PS1-deltaE9, which lacks the cleavage site) in stably transfected cells and PS1-FAD transgenic mice, other investigators have reported altered FAD mutant PS1 and PS2 protein processing in transiently transfected cells and human FAD patients. The present study uses recombinant replication-defective adenoviral vectors to transiently express wild-type (WT) or mutant PS1 in various cells, including primary cultured hippocampal neurons. We show that in contrast to PS1-WT, overexpression of mutant PS1 results in an increased ratio of mutant holoprotein to endoproteolytic products that is dependent on cell type and differentiation state. In addition, mutant PS1 overexpression leads to an increase in caspase-type protease derived fragments above that seen with PS1-WT overexpression. Furthermore, overexpression of at least one mutant significantly alters the processing of coexpressed PS1-WT, suggesting that mutant PS1 may affect PS1-WT function. These findings suggest that a defect in PS1 holoprotein stability may be a general defect seen in cells expressing mutant PS1, especially neuronal cells, and may play a critical role in the pathogenesis of FAD.

Interaction of Presenilins with the Filamin Family of Actin-Binding Proteins

Mutations in presenilin genes PS1 and PS2 account for approximately 50% of early-onset familial Alzheimer's disease (FAD). The PS1 and PS2 genes encode highly homologous transmembrane proteins related to the Caenorhabditis elegans sel-12 and spe-4 gene products. A hydrophilic loop region facing the cytoplasmic compartment is likely to be functionally important because at least 14 mutations in FAD patients have been identified in this region. We report here that the loop regions of PS1 and PS2 interact with nonmuscle filamin (actin-binding protein 280, ABP280) and a structurally related protein (filamin homolog 1, Fh1). Overexpression of PS1 appears to modify the distribution of ABP280 and Fh1 proteins in cultured cells. A monoclonal antibody recognizing ABP280 and Fh1 binds to blood vessels, astrocytes, neurofibrillary tangles, neuropil threads, and dystrophic neurites in the AD brain. Detection of ABP280/Fh1 proteins in these structures suggests that these presenilin-interacting proteins may be involved in the development of AD and that interactions between presenilins and ABP280/Fh1 may be functionally significant. The ABP280 gene is located on the human X chromosome, whereas the newly identified Fh1 gene maps to human chromosome 3. These results provide a new basis for understanding the function of presenilin proteins and further implicate cytoskeletal elements in AD pathogenesis.

Alpha-secretase-derived product of beta-amyloid precursor protein is decreased by presenilin 1 mutations linked to familial Alzheimer's disease.

Recent reports indicate that missense mutations on presenilin (PS) 1 are likely responsible for the main early-onset familial forms of Alzheimer's disease (FAD). Consensual data obtained through distinct histopathological, cell biology, and molecular biology approaches have led to the conclusion that these PS1 mutations clearly trigger an increased production of the 42-amino-acid-long species of beta-amyloid peptide (A beta). Here we show that overexpression of wild-type PS1 in HK293 cells increases A beta40 secretion. By contrast, FAD-linked mutants of PS1 trigger increased secretion of both A beta40 and A beta42 but clearly favor the production of the latter species. We also demonstrate that overexpression of the wild-type PS1 augments the alpha-secretase-derived C-terminally truncated fragment of beta-amyloid precursor protein (APP alpha) recovery, whereas transfectants expressing mutated PS1 secrete drastically lower amounts of APP alpha when compared with cells expressing wild-type PS1. This decrease was also observed when comparing double transfectants overexpressing wild-type beta-amyloid precursor protein and either PS1 or its mutated congener M146V-PS1. Altogether, our data indicate that PS mutations linked to FAD not only trigger an increased ratio of A beta42 over total A beta secretion but concomitantly down-regulate the production of APP alpha.

Evidence That Levels of Presenilins (PS1 and PS2) Are Coordinately Regulated by Competition for Limiting Cellular Factors

Mutations in two related genes, PS1 and PS2, account for the majority of early onset cases of familial Alzheimer's disease. PS1 and PS2 are homologous polytopic membrane proteins that are processed endoproteolytically into two fragments in vivo. In the present report we examine the fate of endogenous PS1 and PS2 after overexpression of human PS1 or PS2 in mouse N2a neuroblastoma cell lines and human PS1 in transgenic mice. Remarkably, in N2a cell lines and in brains of transgenic mice expressing human PS1, accumulation of human PS1 derivatives is accompanied by a compensatory, and highly selective, decrease in the steady-state levels of murine PS1 and PS2 derivatives. Similarly, the levels of murine PS1 derivatives are diminished in cultured cells overexpressing human PS2. To define the minimal sequence requirements for "replacement" we expressed familial Alzheimer's disease-linked and experimental deletion variants of PS1. These studies revealed that compromised accumulation of murine PS1 and PS2 derivatives resulting from overexpression of human PS1 occurs in a manner independent of endoproteolytic cleavage. Our results are consistent with a model in which the abundance of PS1 and PS2 fragments is regulated coordinately by competition for limiting cellular factor(s).