Presenilin-1 protein expression in familial and sporadic Alzheimer's disease

γ-secretase binding sites in aged and Alzheimer's disease human cerebrum: the choroid plexus as a putative origin of CSF Aβ

Deposition of β -amyloid (Aβ) peptides, cleavage products of β-amyloid precursor protein (APP) by β-secretase-1 (BACE1) and γ-secretase, is a neuropathological hallmark of Alzheimer's disease (AD). γ-Secretase inhibition is a therapeutical anti-Aβ approach, although changes in the enzyme's activity in AD brain are unclear. Cerebrospinal fluid (CSF) Aβ peptides are thought to derive from brain parenchyma and thus may serve as biomarkers for assessing cerebral amyloidosis and anti-Aβ efficacy. The present study compared active γ-secretase binding sites with Aβ deposition in aged and AD human cerebrum, and explored the possibility of Aβ production and secretion by the choroid plexus (CP). The specific binding density of [(3) H]-L-685,458, a radiolabeled high-affinity γ-secretase inhibitor, in the temporal neocortex and hippocampal formation was similar for AD and control cases with similar ages and post-mortem delays. The CP in post-mortem samples exhibited exceptionally high [(3) H]-L-685,458 binding density, with the estimated maximal binding sites (Bmax) reduced in the AD relative to control groups. Surgically resected human CP exhibited APP, BACE1 and presenilin-1 immunoreactivity, and β-site APP cleavage enzymatic activity. In primary culture, human CP cells also expressed these amyloidogenic proteins and released Aβ40 and Aβ42 into the medium. Overall, our results suggest that γ-secretase activity appears unaltered in the cerebrum in AD and is not correlated with regional amyloid plaque pathology. The CP appears to be a previously unrecognised non-neuronal contributor to CSF Aβ, probably at reduced levels in AD.

Comparative distribution of protein components of the A20 ubiquitin-editing complex in normal human brain

Activation of innate and adaptive immune responses is tightly regulated, as insufficient activation could result in defective clearance of pathogens, while excessive activation might lead to lethal systemic inflammation or autoimmunity. A20 functions as a negative regulator of innate and adaptive immunity by inhibiting NF-κB activation. A20 mediates its inhibitory function in a complex with other proteins including RNF11 and Itch, both E3 ubiquitin ligases and TAX1BP1, an adaptor protein. Since NF-κB has been strongly implicated in various neuronal functions, we predict that its inhibitor, the A20 complex, is also present in the nervous system. In efforts to better understand the role of A20 complex and NF-κB signaling pathway, we determined regional distribution of A20 mRNA as well as protein expression levels and distribution of RNF11, TAX1BP1 and Itch, in different brain regions. The distribution of TRAF6 was also investigated since TRAF6, also an E3 ligase, has an important role in NF-κB signaling pathway. Our investigations, for the first time, describe and demonstrate that the essential components of the A20 ubiquitin-editing complex are present and mainly expressed in neurons. The A20 complex components are also differentially expressed throughout the human brain. This study provides useful information about region specific expression of the A20 complex components that will be invaluable while determining the role of NF-κB signaling pathway in neuronal development and degeneration.

Control of intracellular calcium signaling as a neuroprotective strategy

Both acute and chronic degenerative diseases of the nervous system reduce the viability and function of neurons through changes in intracellular calcium signaling. In particular, pathological increases in the intracellular calcium concentration promote such pathogenesis. Disease involvement of numerous regulators of intracellular calcium signaling located on the plasma membrane and intracellular organelles has been documented. Diverse groups of chemical compounds targeting ion channels, G-protein coupled receptors, pumps and enzymes have been identified as potential neuroprotectants. The present review summarizes the discovery, mechanisms and biological activity of neuroprotective molecules targeting proteins that control intracellular calcium signaling to preserve or restore structure and function of the nervous system. Disease relevance, clinical applications and new technologies for the identification of such molecules are being discussed.

Presenilin 1 interacts with acetylcholinesterase and alters its enzymatic activity and glycosylation

Presenilin 1 (PS1) plays a critical role in the gamma-secretase processing of the amyloid precursor protein to generate the beta-amyloid peptide, which accumulates in plaques in the pathogenesis of Alzheimer's disease (AD). Mutations in PS1 cause early onset AD, and proteins that interact with PS1 are of major functional importance. We report here the coimmunoprecipitation of PS1 and acetylcholinesterase (AChE), an enzyme associated with amyloid plaques. Binding occurs through PS1 N-terminal fragment independent of the peripheral binding site of AChE. Subcellular colocalization of PS1 and AChE in cultured cells and coexpression patterns of PS1 and AChE in brain sections from controls and subjects with sporadic or familial AD indicated that PS1 and AChE are located in the same intracellular compartments, including the perinuclear compartments. A PS1-A246E pathogenic mutation expressed in transgenic mice leads to decreased AChE activity and alteration of AChE glycosylation and the peripheral binding site, which may reflect a shift in protein conformation and disturbed AChE maturation. In both the transgenic mice and humans, mutant PS1 impairs coimmunoprecipitation with AChE. The results indicate that PS1 can interact with AChE and influence its expression, supporting the notion of cholinergic-amyloid interrelationships.

Presenilin immunoreactivity in Alzheimer's disease

The role of presenilin (PS) mutations in familial Alzheimer's disease (AD) may be as a toxic gain of function, but in sporadic disease their contribution is more difficult to understand. In this study, we investigated PS proteins in sporadic AD by comparing the immunocytochemical profiles in sporadic AD with control brains using a quantitative immunocytochemical approach to both the N- and C-terminals of PS1 and PS2. Ten patients with pathologically proven AD (using modified Consortium to Establish a Registry for Alzheimer's Disease [CERAD] criteria) and 10 controls were age- and sex-matched. The immunocytochemical primary antibodies were affinity-purified goat polyclonal antibodies and the secondary antibodies were biotinylated donkey anti-goat to the N- and C-terminal of both PS1 and PS2. The number of PS-containing neurones was quantified manually and without the knowledge of the diagnosis. We found no significant differences in the number of PS1- and PS2-containing neurones in three anatomical regions for both N- and C-terminals between AD and controls. Our findings argue in favour of functional changes in PS molecules contributing to the pathogenesis of AD and are consistent with the hypothesis of dysfunction of the entire gamma-secretase complex, of which PS proteins are a constituent.

Induction of pro-apoptotic calsenilin/DREAM/KChIP3 in Alzheimer's disease and cultured neurons after amyloid-beta exposure

Calsenilin/DREAM/KChIP3 was identified as a calcium-binding protein that interacts with presenilins, serves as a transcription repressor, and binds to the A-type potassium channel. In this study, we hypothesized that calsenilin might be involved in the neurodegeneration of Alzheimer's disease and examined calsenilin expression in Alzheimer's disease. Calsenilin levels were elevated in the cortex region of Alzheimer's patient brains and in the neocortex and the hippocampus of Swedish mutant beta-amyloid precursor protein transgenic mice brains. Induction of calsenilin was also observed in the activated astroglia as well as in the neurons surrounding beta-amyloid (Abeta)- and Congo red-positive plaques. Exposing cultured cortical and hippocampal neurons to Abeta42, an amyloid-beta peptide whose deposition in the brain is a characteristic of Alzheimer's disease, induced both calsenilin protein and mRNA expression, and cell death. Moreover, blocking the calsenilin expression protected the neuronal cells from Abeta toxicity. These findings suggest that chronic up-regulation of calsenilin may be a risk factor for developing Alzheimer's disease, perhaps by facilitating calsenilin-mediated neurodegeneration.

Alternative transcripts of presenilin-1 associated with frontotemporal dementia

We have analyzed the expression of Alzheimer's disease-associated presenilin 1 (PS1) in various neurodegenerative disorders. Western blotting identified PS1 N- and C-terminal fragments similarly in the cortex of controls, Parkinson, Huntington and schizophrenia subjects. Additional PS1 immunoreactive species of 42 and 46 kDa were present in six out of seven cases of sporadic frontotemporal dementia (FTD) and these were particularly prominent in two cases. RT-PCR analysis using nested primers showed the presence of PS1 gene products with deletions within the exon 4-8 region. Our results suggest that alternative transcription of PS1 may be associated with FTD.

Alternative transcripts of presenilin-1 associated with frontotemporal dementia

We have analyzed the expression of Alzheimer's disease-associated presenilin 1 (PS1) in various neurodegenerative disorders. Western blotting identified PS1 N- and C-terminal fragments similarly in the cortex of controls, Parkinson, Huntington and schizophrenia subjects. Additional PS1 immunoreactive species of 42 and 46 kDa were present in six out of seven cases of sporadic frontotemporal dementia (FTD) and these were particularly prominent in two cases. RT-PCR analysis using nested primers showed the presence of PS1 gene products with deletions within the exon 4-8 region. Our results suggest that alternative transcription of PS1 may be associated with FTD.

Amyloid angiopathy and variability in amyloid beta deposition is determined by mutation position in presenilin-1-linked Alzheimer's disease

The presenilins (PSs) are components of large molecular complexes that contain beta-catenin and function as gamma-secretase. We report here a striking correlation between amyloid angiopathy and the location of mutation in PS-1 linked Alzheimer's disease. The amount of amyloid beta protein, Abeta(42(43)), but not Abeta(40,) deposited in the frontal cortex of the brain is increased in 54 cases of early-onset familial Alzheimer's disease, encompassing 25 mutations in the presenilin-1 (PS-1) gene, compared to sporadic Alzheimer's disease. The amount of Abeta(40) in PS-1 Alzheimer's disease varied according to the copy number of epsilon4 alleles of the Apolipoprotein E gene. Although the amounts of Abeta(40) and Abeta(42(43)) deposited did not correlate with the genetic location of the mutation in a strict linear sense, the histological profile did so vary. Cases with mutations between codon 1 and 200 showed, in frontal cortex, many diffuse plaques, few cored plaques, and mild or moderate amyloid angiopathy. Cases with mutations occurring after codon 200 also showed many diffuse plaques, but the number and size of cored plaques were increased (even when epsilon4 allele was not present) and these were often clustered around blood vessels severely affected by amyloid angiopathy. Similarly, diverging histological profiles, mainly according to the degree of amyloid angiopathy, were seen in the cerebellum. Mutations in the PS-1 gene may therefore alter the topology of the PS-1 protein so as to favor Abeta formation and deposition, generally, but also to facilitate amyloid angiopathy particularly in cases in which the mutation lies beyond codon 200. Finally we report that the amount of Abeta(42(43)) deposited in the brain correlated with the amount of this produced in culture by cells bearing the equivalent mutations.

Alzheimer's disease presenilin-1 expression modulates the assembly of neurofilaments

Mutations in presenilin-1 gene are responsible for the majority of early-onset familial Alzheimer's disease cases. The function of this protein and the mechanism underlying the pathogenicity of its mutations are still unclear. To elucidate the role of presenilin-1 in the Alzheimer's disease pathology, we tested two such mutations (P117L and M146L) for their effect in stably transfected mouse neuroblastoma cell lines. Over-expression of the wild-type presenilin-1 gene induced formation of a well-extended, orderly organized network consisting of neurofilaments assembled from the L and H subunits, while in cells with the mutant gene this network was markedly reduced to short filaments concentrated in structures resembling cups. Cells expressing the mutant gene displayed altered processing of the transgene protein and neurofilament-H, suggesting that presenilin-1 is the mediator of changes targeted at neurofilaments. The two different mutations produced similar alterations, implying that this is a common pathogenic mechanism. Presenilin-1, neurofilament-H and tau proteins showed co-localization as evidenced by confocal microscopy, suggesting a possible physiological connection between these three proteins. Presenilin-1 appears to influence assembly of the H subunit into neurofilaments and the subsequent formation of new neurites. Mutations impair this function of presenilin-1, resulting in inhibition of neurite outgrowth. That presenilin-1 influences the assembly of neurofilaments may represent a novel pathway through which presenilin-1 mutations are involved in Alzheimer's disease pathology. In this hypothesis, presenilin-1 mutations will be associated with aberrant sprouting leading to synaptic loss, a key neuropathological feature of Alzheimer's disease.

Endogenous presenilin-1 targets to endocytic rather than biosynthetic compartments

Presenilin-1 (PS1), which is linked to familial Alzheimer's disease, participates in the proteolytic processing of Notch and amyloid-beta precursor protein (APP) by an unknown mechanism. Reports of PS1 localization to the endoplasmic reticulum (ER) and Golgi apparatus have focused attention on the early biosynthetic pathway as the site of PS1 function. However, it is unclear how Notch cleavage and APP processing events which occur at or near the cell surface are influenced by PS1. In contrast to some earlier studies, examination of endogenously expressed PS1 in PC12 cells by subcellular fractionation and immunofluorescence microscopy revealed a distribution distinct from that of ER and Golgi markers. Rather, PS1 colocalized with transferrin receptor, a marker for early endosomes. In addition, electron microscopic examination of intact vesicles immunoisolated with PS1 antibodies allowed visualization of endocytic tracer in endosomes. These findings identify an early endosomal pool of PS1 and suggest alternative mechanisms for PS1 interactions with APP and Notch.

Proteolytic processing and degradation of human presenilin-1 expressed in yeast

Numerous mutations causing early-onset familial Alzheimer's disease have been identified in the presenilin-1 gene. Presenilin-1 protein is produced as a 47 kDa holoprotein and proteolytically processed to an N-terminal 28 kDa and a C-terminal 19 kDa fragments by unidentified presenilinase in mammalian cells. We have demonstrated that this proteolytic processing also occurs in yeast. We also show that degradation of C-terminal fragment of presenilin-1 is dependent of proteasomal function. This yeast system will be a good tool to identify presenilinase and to study the role of presenilin-1 in amyloid precursor protein processing.

Molecules of the brain

Progress against a range of brain disorders is being sustained by the use of genetic research techniques to identify specific molecules involved in brain disease, and by the realization that the identified molecules may disclose novel therapeutic targets. Both strategies are illustrated by recent insights and interventions in Alzheimer's disease and Parkinson's disease.

Presenilin 1 controls gamma-secretase processing of amyloid precursor protein in pre-golgi compartments of hippocampal neurons

Mutations of presenilin 1 (PS1) causing Alzheimer's disease selectively increase the secretion of the amyloidogenic betaA4(1-42), whereas knocking out the gene results in decreased production of both betaA4(1-40) and (1-42) amyloid peptides (De Strooper et al. 1998). Therefore, PS1 function is closely linked to the gamma-secretase processing of the amyloid precursor protein (APP). Given the ongoing controversy on the subcellular localization of PS1, it remains unclear at what level of the secretory and endocytic pathways PS1 exerts its activity on APP and on the APP carboxy-terminal fragments that are the direct substrates for gamma-secretase. Therefore, we have reinvestigated the subcellular localization of endogenously expressed PS1 in neurons in vitro and in vivo using confocal microscopy and fine-tuned subcellular fractionation. We show that uncleaved PS1 holoprotein is recovered in the nuclear envelope fraction, whereas the cleaved PS fragments are found mainly in post-ER membranes including the intermediate compartment (IC). PS1 is concentrated in discrete sec23p- and p58/ERGIC-53-positive patches, suggesting its localization in subdomains involved in ER export. PS1 is not found to significant amounts beyond the cis-Golgi. Surprisingly, we found that APP carboxy-terminal fragments also coenrich in the pre-Golgi membrane fractions, consistent with the idea that these fragments are the real substrates for gamma-secretase. Functional evidence that PS1 exerts its effects on gamma-secretase processing of APP in the ER/IC was obtained using a series of APP trafficking mutants. These mutants were investigated in hippocampal neurons derived from transgenic mice expressing PS1wt or PS1 containing clinical mutations (PS1(M146L) and PS1(L286V)) at physiologically relevant levels. We demonstrate that the APP-London and PS1 mutations have additive effects on the increased secretion of betaA4(1-42) relative to betaA4(1-40), indicating that both mutations operate independently. Overall, our data clearly establish that PS1 controls gamma(42)-secretase activity in pre-Golgi compartments. We discuss models that reconcile this conclusion with the effects of PS1 deficiency on the generation of betaA4(1-40) peptide in the late biosynthetic and endocytic pathways.

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.

Analysis of presenilin 1 and presenilin 2 expression and processing by newly developed monoclonal antibodies

Because distinct mutations in presenilin 1 and presenilin 2 are a major cause of early-onset familial Alzheimer's disease, we generated four monoclonal antibodies for the identification, localization, and investigation of presenilins in various cell lines and tissues from patients and controls. We show that these antibodies are specific for the N- and C-terminal domains of human presenilin 1 and presenilin 2. They recognize presenilin full-length proteins and their approximately 28-35 kDa N-terminal fragments and approximately 18-20 kDa C-terminal fragments. None of the antibodies showed cross-reaction in their specific detection ability. We demonstrated that presenilin 1 and presenilin 2 are proteolytically processed in human glioma cell lines, transfected and untransfected human neuroblastoma SH-SY5Y cells, COS-7 cells, rat cerebellar neuronal ST15 cells, mouse and human brain. Remarkably, we observed that presenilin 2 is alternatively cleaved during apoptosis, producing smaller C-terminal fragments. By analyzing the subcellular distribution of presenilins, we found reticular and fine vesicular staining throughout the cell bodies. In addition, staining of Golgi compartments and the perinuclear envelope was observed. Alzheimer's disease brain showed strong immunoreactivity of presenilin 1 in reactive astrocytes and senile plaques. This high expression of presenilin 1 may explain the increased production and accumulation of the amyloid-beta peptide in patients with sporadic Alzheimer's disease in the absence of familial presenilin mutation.

Carboxyl-terminal fragments of presenilin-1 are closely related to cytoskeletal abnormalities in Alzheimer's brains

To clarify the role of presenilin-1 (PS-1) in the pathology of Alzheimer's disease (AD), we tested four antisera to PS-1. The specific antisera to the N-terminus (HSN-2) and C-terminus (HS-C) of PS-1 detected a 44/40kD holoprotein, a 25kD N-terminal fragment (NTF) and a 16kD C-terminal fragment (CTF) of PS-1 in COS-7 cells. The 25kD NTF and 16kD CTF were observed in human brains, and their amounts were not significantly different between the control and AD brains. The antibody HS-C labeled extensive neurofibrillary tangles, dystrophic neurites and curly fibers in the AD brains. In the paired helical filament (PHF) fraction containing A68 protein from AD brains, a smear pattern of CTFs was revealed. Antisera (HS-L292 and HS-L300) to cleavage sites of PS-1 also revealed immunoreactive neurofibrillary tangles in the AD brain sections and the smear pattern of CTFs of A68 protein fraction. The CTFs of PS-1 accumulate with PHF tau, suggesting a close relationship between PS-1 and cytoskeletal abnormalities in AD brains.

Impaired proteolytic processing of presenilin-1 in chromosome 14-linked familial Alzheimer's disease patient lymphocytes

Many cases of early-onset familial Alzheimer's disease (FAD) are caused by mutations in the presenilin 1 (PS1) and PS2 genes. PS1 protein is generated as a 47 kDa protein and is endoproteolytically cleaved into N-terminal 28 kDa and C-terminal 19 kDa fragments in vivo. To examine whether mutated PS1 protein is abnormally metabolized, we performed immunoblot analysis of lymphoblasts from familial Alzheimer's disease patients and controls. More full-length PS1 was apparently detected in samples from PS1 mutants than those from PS2 mutant and controls. This result suggests that impaired proteolysis of PS1 may be associated with the pathogenesis of FAD. Moreover, our simple test using lymphocytes from FAD patients might be useful from a diagnostic point of view.

Sporadic inclusion-body myositis and its similarities to Alzheimer disease brain. Recent approaches to diagnosis and pathogenesis, and relation to aging

Sporadic inclusion-body myositis (s-IBM) is the most common, debilitating and progressive muscle disease beginning at the age 50 or later. The most characteristic pathologic feature is vacuolar degeneration of muscle fibers accompanied by intrafiber congophilia and clusters ("tangles") of paired-helical filaments, containing phosphorylated tau. An unusual feature of sporadic inclusion-body myositis is accumulation within its abnormal muscle fibers of several proteins that are characteristic of Alzheimer disease brain, including epitopes of beta-amyloid precursor protein (betaAPP), phosphorylated tau, alpha-1-antichymotrypsin, apolipoprotein E, and presenilin-1. Indicators of oxidative stress are also present within abnormal s-IBM muscle fibers. In this review, we describe new advances seeking the pathogenic mechanism of sporadic inclusion-body myositis. We hypothesize on the possible pathogenic role of abnormally accumulated proteins, and we propose that important contributory factors leading to inclusion-body myositis are the milieu of muscle-fiber aging and oxidative stress. In addition, we present evidence that overexpression of adenovirus-transferred betaAPP gene in cultured human muscle fibers induces aspects of the inclusion-body myositis phenotype, and suggest that betaAPP-overexpression is an early event in the pathogenic cascade causing inclusion-body myositis.

Presenilin 1 associates with glycogen synthase kinase-3beta and its substrate tau

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 beta protein (Abeta1-42). 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 3beta (GSK-3beta). Deletion studies show that both tau and GSK-3beta 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-3beta into close proximity suggests that PS1 may regulate the interaction of tau with GSK-3beta. Mutations in PS1 that cause Alzheimer's disease increase the ability of PS1 to bind GSK-3beta and, correspondingly, increase its tau-directed kinase activity. We propose that the increased association of GSK-3beta with mutant PS1 leads to increased phosphorylation of tau.

Localization and possible functions of presenilins in brain

Presenilin-1 (PS-1) is localized to chromosome 14 and presenilin-2 (PS-2) to chromosome 1. Mutations in these genes, primarily in PS-1, account for an estimated 60% of early onset familial Alzheimer's disease cases (FAD), while FAD cases account for about 10% of all Alzheimer's disease (AD) cases. The mutations are minor but are 100% penetrant, suggesting that the proteins have acquired a toxic gain in function. The proteins have multiple transmembrane domains and have been reported to be localized to the Golgi apparatus, endoplasmic reticulum, nuclear membranes and cell surface membranes. They are thought to have functions associated with vesicular trafficking, Notch signaling and apoptosis. PS mutants show relative increases in the amount of A beta42/43 compared with A beta40 in plasma, fibroblasts and brain, observations which have been taken as a possible mechanism of their role in AD. In brain, the mRNAs for these two genes are localized primarily in neurons, with the strongest in situ hybridization signals being observed in the hippocampus, cerebellum and cerebral cortex. In AD, signals detected in the hippocampus are weaker than those in normals, while signals in the cerebellum are comparable. Immunohistochemical localization of the proteins is also primarily in neurons, and, at least for PS-1, is reduced in AD affected areas. PS-1 is localized to granular structures which are most abundant in cell bodies and dendrites. The functions of the presenilins are not yet known, but available evidence points to pyramidal neurons as the most logical site for pathological change in AD.

Lack of specific association of presenilin 1 (PS-1) protein with plaques and tangles in Alzheimer's disease

Missense mutations in the presenilin-1 (PS-1) gene are causally related to the majority of familial early-onset Alzheimer's disease (FAD). PS-1 immunohistochemical expression in normal human brain and in brains with Alzheimer's disease (AD) has so far been controversial. Here, we report a study of PS-1 expression in brains, cell lines and peripheral blood mononuclear cells using a panel of well characterized PS-1-specific antibodies. These antibodies were characterized by immunofluorescent staining of PS-1 transfectants followed by flow cytometric analysis. In human brain, widespread neuronal staining was observed. PS-1 immunoreactivity was primarily confined to neuronal cell bodies and proximal dendrites. Weaker staining of microglia was also detected, in accord with the finding of PS-1 immunoreactivity in monocytes. PS-1 expression is not particularly associated with neurons either containing or spared from neurofibrillary tangles, nor with senile plaques. The level of PS-1 expression does not differ between normal and AD brains. Immunoprecipitation from AD, FAD and control brains revealed only a 32 kDa N-terminal fragment and an 18-20 kDa C-terminal fragment. Little or no full length PS-1 was detected. The enriched presence of PS-1 in neurons implies an important role in neuronal function, however, the lack of apparent association of its expression with AD pathology signifies the need for a better understanding of its pathophysiological role.

Biology of A beta amyloid in Alzheimer's disease

The genetic associations with the pathological features of AD are diverse: A rapidly growing number of mutations in presenilin 1 and 2 on chromosomes 14 and 1, respectively, are found in many early-onset FAD patients (Lendon et al., 1997). In addition, beta PP mutations are found in a small percentage of early-onset FAD kindreds. The apoE4 allele on chromosome 19 is associated with the presence of the most common form of AD, sporadic AD (Wisniewski & Frangione, 1992; Namba et al., 1991). However, it is clear that other proteins are also involved in the pathogenesis of AD, since some early-onset FAD kindreds do not have linkage to PS1, PS2, apoE, or beta PP, while at least 50% of late-onset AD is unrelated to apoE. Other proteins which have been implicated in the formation of senile plaques, but so far are not known to have any genetic linkage to AD, include proteoglycans (Snow et al., 1987), apoA1 (Wisniewski et al., 1995a), alpha 1-antichymotrypsin (Abraham et al., 1988), HB-GAM (Wisniewski et al., 1996a), complement components (McGeer & Rogers, 1992), acetylcholinesterase (Friede, 1965), and NAC (Ueda et al., 1993). Which of these proteins will be the most important for the etiology of the most common form of AD, late-onset sporadic AD, remains an open question. Three of the genes which are now known to be linked to AD, including PS1, beta PP, and apoE, have been established immunohistochemically and biochemically to be components of senile plaques (see Fig. 1). This raises at least two possibilities: either each of these proteins is part of one pathway with A beta-related amyloid formation as a final causative pathogenic event or amyloid deposition in AD is a reactive process related to dysfunction of a number of different CNS proteins. Whether or not amyloid formation is directly causative in the pathogenesis of AD, current data suggest that new therapeutic approaches which may inhibit the aggregation and/or the conformational change of sA beta to A beta fibrils (Soto et al., 1996) have the greatest likelihood to make a significant impact on controlling amyloid accumulation in AD.

Light and electron microscopic localization of presenilin-1 in primate brain

Several genes have been implicated in the pathogenesis of early-onset familial Alzheimer's disease. A majority of the autosomal dominant cases are linked to recently identified mutations in the presenilin-1 gene on chromosome 14. The native presenilin-1 protein in primates has not been well characterized, and its precise localization is unknown. We have studied the native presenilin-1 protein in monkey brain and peripheral tissues by using a monoclonal antibody specific for the N-terminal domain of human presenilin-1. Western blots detect polypeptide species of approximately 49 and approximately 32 kDa from COS-7 and PC12 cells transfected with full-length human presenilin-1 cDNA and from in vitro translations of the normal human presenilin-1 mRNA. A 32 kDa polypeptide is detected in monkey peripheral tissues, with the highest expression in testis and lung. In all brain regions the 32 kDa band is the predominant form of presenilin-1, and it is found in particulate subfractions. Light microscopic immunocytochemistry reveals presenilin-1 staining in all brain regions, with the strongest labeling in neurons and neuropil. In addition, weaker immunoreactivity is also present in glia and blood vessels. Neuronal staining shows significant variability, with particularly intense labeling of certain cell types, including large neocortical and hippocampal pyramidal neurons, magnocellular basal forebrain neurons, brainstem motoneurons, and some populations of interneurons. By electron microscopic immunocytochemistry, highly selective presenilin-1 staining is seen on the cytoplasmic surfaces of membranous organelles, which suggest localization to the endoplasmic reticulum-Golgi intermediate compartment, a subdomain of the endoplasmic reticulum, and some coated transport vesicles.