Molecular cloning of cDNA encoding an unrecognized component of amyloid in Alzheimer disease

Protein precipitation: a common etiology in neurodegenerative disorders?

Molecular genetic analyses have elucidated a class of inherited neurodegenerative disorders caused by expanded CAG repeats encoding polyglutamines (e.g. Huntington disease and Machado-Joseph disease). Proteins containing expanded polyglutamine repeats appear to precipitate by self-aggregation and, as a result, produce a core disease-related phenotype: neuronal cell death or degeneration. In other neurodegenerative disorders, such as Alzheimer disease, prion disease, Parkinson disease and amyotrophic lateral sclerosis, precipitation of abnormal proteins is also now considered to play a key role. These observations might lead to the elucidation of universal mechanisms for neurodegeneration and to effective treatments for many neurodegenerative disorders.

Mutation in the alpha-synuclein gene and sporadic Parkinson's disease, Alzheimer's disease, and dementia with lewy bodies

Recently, alpha-synuclein attracted attention when Polymeropoulos and colleagues identified a missense mutation of this gene (Science 276:2045-2047, 1997), which is responsible for a form of early-onset familial Parkinson's disease (PD). Immunohistochemically, alpha-synuclein is localized in Lewy bodies, characteristic brain pathology of PD, dementia with Lewy bodies (DLB), and Alzheimer's disease (AD), suggesting that this protein may link these common neurological diseases. Exploration of the possibility that the same mutation of the alpha-synuclein gene as that in familial PD (Ala53Thr) may also confer susceptibility to sporadic PD, DLB, and AD revealed the mutation in none of the samples of 329 cases and 230 controls examined, suggesting that this mutation is not involved in these neurological diseases.

The synuclein family

The synuclein gene family recently came into the spotlight, when one of its members, alpha-synuclein, was found to be mutated in several families with autosomal dominant Parkinson's disease (PD). A peptide of the alpha-synuclein protein had been characterized previously as a major component of amyloid plaques in brains of patients with Alzheimer's disease (AD). The mechanism by which this presynaptic protein is involved in the two most common neurodegenerative disorders, AD and PD, remains unclear. Remarkably, another member of this gene family, gamma-synuclein, has been shown to be overexpressed in breast carcinomas and may also be overexpressed in ovarian cancer. The possible involvement of the synuclein proteins in the etiology of common human diseases has raised exciting questions and is the subject of intense investigation. Details of the properties of any member of the synuclein family may provide useful information for understanding the characteristics and function of other family members. The present review offers a synopsis of the current state of knowledge of all synuclein family members in different species.

Glial cytoplasmic inclusions in white matter oligodendrocytes of multiple system atrophy brains contain insoluble alpha-synuclein

Recently, alpha-synuclein was shown to be a structural component of the filaments in Lewy bodies (LBs) of Parkinson's disease (PD), dementia with LBs (DLB) as well as the LB variant of Alzheimer's disease, and this suggests that alpha-synuclein could play a mechanistic role in the pathogenesis of these disorders. To determine whether alpha-synuclein is a building block of inclusions in other neurodegenerative movement disorders, we examined brains from patients with multiple system atrophy (MSA) and detected alpha-synuclein, but not beta- or gamma-synuclein, in glial cytoplasmic inclusions (GCIs) throughout the MSA brain. In MSA white matter, alpha-synuclein-positive GCIs were restricted to oligodendrocytes, and alpha-synuclein was localized to the filaments in GCIs by immunoelectron microscopy. Finally, we demonstrated that insoluble alpha-synuclein accumulated selectively in MSA white matter with alpha-synuclein-positive GCIs. Taken together with evidence that LBs contain insoluble alpha-synuclein, our data suggest that a reduction in the solubility of alpha-synuclein may induce this protein to form filaments that aggregate into cytoplasmic inclusions, which contribute to the dysfunction or death of glial cells as well as neurons in neurodegenerative disorders with different phenotypes.

The native form of alpha-synuclein is not found in the cerebrospinal fluid of patients with Parkinson's disease or normal controls

Alpha-synuclein has recently been shown to be a major constituent of Lewy bodies in Parkinson's disease (PD). This observation led us to investigate the possibility that its detection in the cerebrospinal fluid (CSF) could be used as a marker for Lewy bodies in the central nervous system. In this study we determined the pattern of expression of alpha-synuclein in patients with sporadic Parkinson's disease (PD) and normal controls, using western immunoblotting in conjunction with an antibody that recognizes the carboxyl terminal of alpha-synuclein protein. The native 19 kDa band normally seen in brain homogenates was not found in the CSF of either parkinsonian patients or control subjects. However, a novel band was observed, which migrated at a position in the range of 42 kDa in CSF from both patients and controls. We conclude that alpha-synuclein cannot be used as a biomarker for Lewy bodies during life. However, further characterization of the 42 kDa protein may be of interest.

Failure to replicate a protective effect of allele 2 of NACP/alpha-synuclein polymorphism in Alzheimer's disease: an association study

Recently, a dinucleotide repeat polymorphism was identified in the promoter of the nonamyloid component of plaques (NACP) gene, and it was shown that the NACP allele 2 was significantly associated with healthy elderly control individuals with at least one apolipoprotein E epsilon4 allele, suggesting a protective role for this allele in Alzheimer's disease. We genotyped the same NACP polymorphism in a comparable number of individuals diagnosed with dementia of the Alzheimer's type and in healthy, elderly controls. In our analysis, however, no protective effect for NACP allele 2, or any of the other NACP alleles, was observed.

Human recombinant NACP/alpha-synuclein is aggregated and fibrillated in vitro: relevance for Lewy body disease

The precursor of non-amyloid beta protein component of Alzheimer's disease amyloid (NACP/alpha-synuclein) is aggregated and fibrillated under certain conditions, i.e., increasing time lag, high temperature and low pH. These in vitro aggregates form Thioflavine-S-positive filamentous structures, reminiscent of amyloid-like fibrils. Since some Lewy bodies in Parkinson's disease display Thioflavine-S reactivity, our results may suggest that amyloidogenic properties of NACP/alpha-synuclein may play a crucial role in pathogenesis of disorders with Lewy bodies such as Parkinson's disease.

Apoptosis in Degenerative Diseases of the Basal Ganglia

Degenerative disorders of the basal ganglia are characterized by disturbances of motor control. Prototypic examples are Parkinson's disease, which is caused by degeneration of dopamine neurons of the substantia nigra, and Huntington's disease, which is caused by degeneration of neurons of the striatum. In recent years, it has been postulated that some of these disorders may be caused by programmed cell death or apoptosis, a genetically regulated form of cell death. There is clear evidence that apoptosis occurs in neurons of the basal ganglia during normal development, that it can be regulated, and that it can be induced in some animal models of these disorders. Although there is some suggestive direct evidence that apoptosis may occur in the human brain in these disorders, the evidence to date is partial and not yet compelling. Nevertheless, programmed cell death is an important new hypothesis for the pathogenesis of these disorders and warrants vigorous further investigation, particularly with molecular markers in addition to classic morphological markers. The concept of programmed cell death is relevant not only to the pathogenesis of these diseases but also to therapeutic issues, such as transplantation approaches.

Alpha-synuclein immunoreactivity in glial cytoplasmic inclusions in multiple system atrophy

Lewy bodies in Parkinson' s disease (PD) are strongly immunoreactive with antibodies against alpha-synuclein, which is mutated in some familial cases of the disease. We carried out immunohistochemical examinations of the brains of multiple system atrophy (MSA) patients using anti-alpha-synuclein antibodies. Strong alpha-synuclein immunoreactivity was found in glial cytoplasmic inclusions (GCIs), which are of oligodendroglial origin and occur exclusively in MSA. Alpha-synuclein-immunoreactive neuronal cytoplasmic inclusions (NCIs) were also found occasionally in the substantia nigra, pontine and inferior olivary nuclei, and dentate fascia. These findings indicate that alpha-synuclein is also a major component of GCIs and NCIs in MSA and strongly suggest that alpha-synuclein aggregation is a common process in certain neurodegenerative diseases, including PD and MSA.

Amyloid beta neurotoxicity in the cholinergic but not in the serotonergic phenotype of RN46A cells

Neuropathological examination of brains from AD patients has documented that distinct areas and nuclei are differently affected by the disease. It is unknown as to what extent the neurochemical phenotype plays a role in this process, but particularly acetylcholine (Ach) neurons in the basal forebrain are lost during the progress of the disease. The exact molecular mechanism by which the neuronal death is induced remains unclear, but the amyloid beta peptide (A beta) is cytotoxic in vitro and may be important for the neuronal cell death in vivo. Previous reports have demonstrated that an immortalized neuronal cell line (RN46A) derived from rat raphe nucleus differentiate in the presence of ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) to a cholinergic and a serotonergic phenotype, respectively [J.S. Rudge et al., Mol. Cell Neurosci. 7 (1996) 204-221]. This study takes advantage of the RN46A cell line to investigate whether the sensitivity to A beta is dependent on cell differentiation and neurochemical phenotype. We found that cellular reduction of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) could be inhibited 30-40% by A beta in undifferentiated cells. The cholinergic phenotype induced by CNTF remained sensitive to A beta whereas the serotonergic phenotype induced by BDNF was unaffected by concentrations of A beta up to 10 microM. These findings suggest that differentiation and neurochemical phenotype may play a role for A beta induced lesions in Alzheimer's disease.

The synucleins: a family of proteins involved in synaptic function, plasticity, neurodegeneration and disease

Synuclein proteins are produced, in vertebrates, by three genes. They share structural resemblance to apolipoproteins, but are abundant in the neuronal cytosol and present in enriched amounts at presynaptic terminals. Synucleins have been specifically implicated in three diseases:Alzheimer's (AD), Parkinson's (PD) and breast cancer. In AD, a peptide derived from alpha-synuclein forms an intrinsic component of plaque amyloid. In PD, an alpha-synuclein allele is genetically linked to several independent familial cases, and the protein appears to accumulate in Lewy bodies. In breast cancer, increased expression of gamma-synuclein correlates with disease progression. In songbirds, alpha-synuclein expression is correlated with plasticity in the developing song control system. Although the normal function of synucleins is unknown, a role in membrane plasticity seems likely.

Distribution of PNP 14 (beta-synuclein) in neuroendocrine tissues: localization in Sertoli cells

Phosphoneuroprotein (PNP 14) is abundant in the central nervous system and is localized at nerve endings but not in synaptic vesicles. In this study, we examined the presence of PNP 14 in various endocrine tissues of the rat. PNP 14 was not detected in the endocrine cells of the intestine, testes, or adrenal gland, but it was present in axon terminals in both the medulla of the adrenal gland and the anterior pituitary gland. When testes were stained with PNP 14-specific antibodies by an indirect immunofluorescence method, PNP 14 was found in Sertoli cells of the testes, associated with fibrillar structures. PNP 14 was also detected in cultured Sertoli cells with a fibrillar pattern in the cytoplasm and around the nuclei. The fibrillar structure did not resemble actin stress fibers, microtubules, or intermediate filaments. The amount of PNP 14 in the testis changed with development. It increased markedly during the first 4 weeks after birth and then decreased. During the first 4 weeks after birth, spermatogonia undergo two rounds of meiosis. It is possible, therefore, that PNP 14 might be a factor related to meiosis.

Stabilization of alpha-synuclein secondary structure upon binding to synthetic membranes

alpha-Synuclein is a highly conserved presynaptic protein of unknown function. A mutation in the protein has been causally linked to Parkinson's disease in humans, and the normal protein is an abundant component of the intraneuronal inclusions (Lewy bodies) characteristic of the disease. alpha-Synuclein is also the precursor to an intrinsic component of extracellular plaques in Alzheimer's disease. The alpha-synuclein sequence is largely composed of degenerate 11-residue repeats reminiscent of the amphipathic alpha-helical domains of the exchangeable apolipoproteins. We hypothesized that alpha-synuclein should associate with phospholipid bilayers and that this lipid association should stabilize an alpha-helical secondary structure in the protein. We report that alpha-synuclein binds to small unilamellar phospholipid vesicles containing acidic phospholipids, but not to vesicles with a net neutral charge. We further show that the protein associates preferentially with vesicles of smaller diameter (20-25 nm) as opposed to larger (approximately 125 nm) vesicles. Lipid binding is accompanied by an increase in alpha-helicity from 3% to approximately 80%. These observations are consistent with a role in vesicle function at the presynaptic terminal.

Dementia with Lewy bodies. A distinct non-Alzheimer dementia syndrome?

Lewy body formation is central to the pathological phenotype of a spectrum of disorders. The most familiar of these is the extrapyramidal syndrome of idiopathic Lewy-body Parkinson's disease (PD). Studies of dementia in the elderly suggest that another manifestation of Lewy body pathology is equally or more common than Parkinson's disease. This syndrome of Dementia with Lewy bodies (DLB) has been given a number of diagnostic labels and is characterised by dementia, relatively mild parkinsonism, visual hallucinations, and fluctuations in conscious level. Although many of these features can arise in Parkinson's disease, the patients with DLB tend to have early neuropsychiatric features which predominate the clinical picture, and the diagnosis of the syndrome in practice is more concerned with the differential diagnosis of Alzheimer's disease (AD). Distinction from AD has clinical importance because of potentially differing therapeutic implications. Diagnostic guidelines for the clinical diagnosis and pathological evaluation of DLB are reviewed. Research into the disorder has centered around characterising the clinical, neuropsychological, pathological, neurochemical and genetic relationships with Alzheimer's disease on the one hand, and Parkinson's disease on the other. Many cases of DLB have prominent pathological features of AD and there are some shared genetic risk factors. Differences from the pathology of PD are predominantly quantitative rather than qualitative and evidence is discussed which suggests that DLB represents a clinicopathological syndrome within the spectrum of Lewy body disorders. The possibility that the syndrome represents a chance association of PD and AD is not supported by published studies.

Changes in presynaptic protein NACP/alpha-synuclein in an ischemic gerbil hippocampus

We observed temporal changes in NACP (precursor protein of non-Abeta component of Alzheimer's disease amyloid), a presynaptic protein a.k. a. alpha-synuclein, in the hippocampus after 5 min ischemia. Intense NACP immunoreactivity was seen transiently around cerebral blood vessels in the CA1 subfield on day 4, and NACP-positive unusual tubal and chain-like structures developed on month 6. We suggest that the changes in NACP may play an important role in the ischemic pathogenesis.

Abnormal accumulation of NACP/alpha-synuclein in neurodegenerative disorders

The precursor of the non-Abeta component of Alzheimer's disease amyloid (NACP) (also known as a-synuclein) is a presynaptic terminal molecule that accumulates in the plaques of Alzheimer's disease. Recent studies have shown that a mutation in NACP is associated with familial Parkinson's disease, and that Lewy bodies are immunoreactive with antibodies against this molecule. To clarify the patterns of accumulation and differences in abnormal compartmentalization, we studied NACP immunoreactivity using double immunolabeling and laser scanning confocal microscopy in the cortex of patients with various neurodegenerative disorders. In Lewy body variant of Alzheimer's disease, diffuse Lewy body disease, and Parkinson's disease, NACP was found to immunolabel cortical Lewy bodies, abnormal neurites, and dystrophic neurites in the plaques. Double-labeling studies showed that all three of these neuropathological structures also contained ubiquitin, synaptophysin, and neurofilament (but not tau) immunoreactivity. In contrast, neurofibrillary tangles, neuropil threads, Pick bodies, ballooned neurons, and glial tangles (most of which were tau positive) were NACP negative. These results support the view that NACP specifically accumulates in diseases related to Lewy bodies such as Lewy body variant of Alzheimer's disease, diffuse Lewy body disease, and Parkinson's disease and suggests a role for this synaptic protein in the pathogenesis of neurodegeneration.

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.

MARCKS, a major protein kinase C substrate, assumes non-helical conformations both in solution and in complex with Ca2+-calmodulin

MARCKS, a major cellular substrate for protein kinase C, plays important roles in various cellular functions and its functions are regulated by calmodulin. We have studied the conformational properties of recombinant human MARCKS in solution and in complex with calmodulin. Circular dichroism (CD) spectra showed a high content of random coil in physiological solution. When MARCKS or MARCKS-derived calmodulin-binding peptide was complexed with Ca2+-calmodulin, little change was observed in the CD spectra, suggesting that MARCKS binds with calmodulin in a non-helical conformation, which is unique among the calmodulin-binding proteins.

Self-oligomerization of NACP, the precursor protein of the non-amyloid beta/A4 protein (A beta) component of Alzheimer's disease amyloid, observed in the presence of a C-terminal A beta fragment (residues 25-35)

NACP, the precursor protein of the non-amyloid beta/A4 protein (A beta) component of Alzheimer's disease (AD) amyloid, also known as alpha-synuclein, was suggested to seed amyloid plaque formation in AD by stimulating A beta aggregation. We have demonstrated that NACP experienced self-oligomerization only in the presence of a modified A beta fragment (A beta25-35) by using dicyclohexylcarbodiimide. This NACP oligomerization, appearing as a discrete ladder on a Tricine SDS-PAGE, was not observed with other A beta peptides such as the reverse peptide A beta35-25 and A beta1-40, indicating this process was specific not only for the C-terminal peptide sequence of the A beta but also for its orientation. It might be, therefore, suggested that the NACP self-oligomers formed only in the presence of a N-terminally truncated A beta peptide could act as a nucleation center for plaque formation during AD development.

NACP, a presynaptic protein, immunoreactivity in Lewy bodies in Parkinson's disease

NACP, originally identified as a precursor of the non-Abeta component of Alzheimer's disease amyloid (NAC), is now known to be identical to alpha-synuclein, a presynaptic protein in the human brain. Recently, a mutation in the alpha-synuclein gene in families with autosomal dominant Parkinson's disease (PD) was identified. We carried out immunohistochemical examinations of the brains of sporadic PD patients using anti-NACP and anti-ubiquitin antibodies. Consistent with previous studies, the anti-NACP antibody immunostained the neuropil in a punctate pattern throughout the brain. Moreover, much stronger NACP immunoreactivity was found in Lewy bodies and degenerating neurites in the brainstem. Serial sections immunolabeled with anti-ubiquitin or anti-NACP showed that all ubiquitin-immunoreactive LBs were also NACP-immunoreactive. These findings suggest that alteration of NACP metabolism is involved in the pathogenesis of PD, particularly in Lewy body formation, leading to neurodegeneration.

Synelfin regulation during the critical period for song learning in normal and isolated juvenile zebra finches

Male zebra finches (Taeniopygia guttata) learn to sing during a critical period in adolescence. We previously described a presynaptic protein, synelfin, whose mRNA is increased early in this critical period in a brain nucleus specifically implicated in song learning, lateral MAN (lMAN). In the current study, in situ hybridization was used to map this change in gene expression to the subregion of lMAN that projects to the robust nucleus of the archistriatum (RA), the principal motor output of the telencephalic circuit that controls song production. Using confocal immunofluorescence microscopy, we detected numerous puncta of synelfin immunoreactivity that apparently represent presynaptic terminals from lMAN in the RA of young males. Synelfin immunoreactivity in RA declined abruptly between 40 and 45 days of age, a time of major synaptic reorganization in RA. This change did not occur until about 10 days after the decline in synelfin mRNA in cell bodies within lMAN, indicating a relatively slow turnover of the protein in presynaptic terminals and suggesting that some of the functional changes that occur during the critical period may arise from regulatory decisions that were initiated a week or more earlier. Depriving birds of tutoring did not halt or delay the decline of synelfin mRNA in lMAN. This change in gene expression must not be a consequence of early song learning, but may reflect an innate or programmed step in song circuit development.

NACP, a synaptic protein involved in Alzheimer's disease, is differentially regulated during megakaryocyte differentiation

Non-amyloid-beta component precursor (NACP) is a presynaptic protein which may play a role in amyloidogenesis in Alzheimer's disease (AD). Since an abnormal function of platelets has been demonstrated in AD, platelets could be used as a model to investigate the role of NACP in this disease. We characterized the patterns of NACP and beta-synuclein expression in a megakaryocyte-platelet system (K562). In this hematopoietic cell line, NACP expression was up-regulated during phorbol ester-induced megakaryocytic differentiation, while beta-synuclein was down-regulated. Consistent with this, NACP but not beta-synuclein was abundantly expressed in platelets. Immunogold electron microscopy of platelets showed that NACP is loosely associated with the plasma membrane, the endomembrane system and, occasionally, with the membrane of secretory alpha-granules. These findings suggest that coordinate expression of the synuclein family members may play a critical role during hematopoietic cell differentiation. Additionally, expression of the synuclein family members may be developmentally regulated during neural differentiation.

Aluminum-induced structural alterations of the precursor of the non-A beta component of Alzheimer's disease amyloid

The precursor of the non-A beta component of Alzheimer's disease amyloid (NACP) is a presynaptic protein whose function has been suspected to be tightly involved in neuronal biogenesis including synaptic regulations. NACP was suggested to seed the neuritic plaque formation in the presence of A beta during the development of Alzheimer's disease (AD). Recombinant NACP purified through heat treatment, DEAE-Sephacel anion-exchange, Sephacryl S-200 size-exclusion, and S-Sepharose cation-exchange chromatography steps appeared as a single band on SDS-PAGE with Mr of 19 kDa. Its N-terminal amino acid sequence clearly confirmed that the protein was NACP. Interestingly, however, the protein was split into a doublet on a nondenaturing (ND)-PAGE with equal intensities. The doublet was located slightly above a 45-kDa marker protein on a 12.5% ND-PAGE. In addition, the size of NACP was more carefully estimated as 53 kDa with high-performance gel-permeation chromatography using a TSK G3000sw size-exclusion column. Recently, Lansbury and his colleagues (Biochemistry 35, 13709-13715) have reported that NACP exists as an elongated "natively unfolded" structure which would make the protein more actively involved in protein-protein interactions and Kim (Mol. Cells 7, 78-83) has also shown that the natively unfolded protein is extremely sensitive to proteases. Here, we report that the structure of NACP could be altered by certain environmental factors. Aluminum, a suspected risk factor for AD, converged the doublet of NACP into a singlet with slightly lower mobility on ND-PAGE. Spectroscopic analysis employing uv absorption, intrinsic fluorescence, and circular dichroism indicated that NACP experienced the structural alterations in the presence of aluminum such as the secondary structure transition to generate about 33% alpha-helix. This altered structure of NACP became resistant to proteases such as trypsin, alpha-chymotrypsin, and calpain. Therefore, it is suggested that aluminum, which influences two pathologically critical processes in AD such as the protein turnover and the protein aggregation via the structural modifications, could participate in the disease.

Mutation in the alpha-synuclein gene identified in families with Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder with a lifetime incidence of approximately 2 percent. A pattern of familial aggregation has been documented for the disorder, and it was recently reported that a PD susceptibility gene in a large Italian kindred is located on the long arm of human chromosome 4. A mutation was identified in the alpha-synuclein gene, which codes for a presynaptic protein thought to be involved in neuronal plasticity, in the Italian kindred and in three unrelated families of Greek origin with autosomal dominant inheritance for the PD phenotype. This finding of a specific molecular alteration associated with PD will facilitate the detailed understanding of the pathophysiology of the disorder.

Binding of Abeta to alpha- and beta-synucleins: identification of segments in alpha-synuclein/NAC precursor that bind Abeta and NAC

NAC, a 35-residue peptide derived from the neuronal protein alpha-synuclein/NAC precursor, is tightly associated with Abeta fibrils in Alzheimer's disease amyloid, and alpha-synuclein has recently been shown to bind Abeta in vitro. We have studied the interaction between Abeta and synucleins, aiming at determining segments in alpha-synuclein that can account for the binding, as well as identifying a possible interaction between Abeta and the beta-type synuclein. We report that Abeta binds to native and recombinant alpha-synuclein, and to beta-synuclein in an SDS-sensitive interaction (IC50 approx. 20 microM), as determined by chemical cross-linking and solid-phase binding assays. alpha-Synuclein and beta-synuclein were found to stimulate Abeta-aggregation in vitro to the same extent. The synucleins also displayed Abeta-inhibitable binding of NAC and they were capable of forming dimers. Using proteolytic fragmentation of alpha-synuclein and cross-linking to 125I-Abeta, we identified two consecutive binding domains (residues 1-56 and 57-97) by Edman degradation and mass spectrometric analysis, and a synthetic peptide comprising residues 32-57 possessed Abeta-binding activity. To test further the possible significance in pathology, alpha-synuclein was biotinylated and shown to bind specifically to amyloid plaques in a brain with Alzheimer's disease. It is proposed that the multiple Abeta-binding sites in alpha-synuclein are involved in the development of amyloid plaques.

Delayed localization of synelfin (synuclein, NACP) to presynaptic terminals in cultured rat hippocampal neurons

Synelfin is a presynaptic protein of unknown function that is differentially regulated in the avian song control circuit during the critical period for song learning; in humans, it gives rise to an amyloidogenic peptide found in senile plaques of Alzheimer's disease. To gain insight into the potential involvement of synelfin in synapse development, we investigated its expression in neurons cultured from the embryonic rat hippocampus. These neurons express a variety of defined synaptic proteins, and form numerous synaptic connections after several days in culture. Synapsin I, a synaptic vesicle-associated protein, was detected within one day after the neurons were put in culture, but significant immunoreactivity for synelfin was not detected until approximately 5 days in vitro (DIV). By 3 DIV, synapsin-positive puncta (previously shown to correspond to presynaptic specializations) were detected surrounding the soma and proximal dendritic processes, whereas comparable aggregations of synelfin did not appear until several days later. By 14 DIV the punctate concentrations of synelfin and synapsin overlapped completely. Thus synelfin is expressed in these cultured neurons and eventually becomes localized to presynaptic terminals, but it is absent from these specializations when they first form. We conclude that presynaptic terminals can change in molecular composition, and that synelfin is associated with later stages in synaptic development or modulation.

Isoform-specific binding of human apolipoprotein E to the non-amyloid beta component of Alzheimer's disease amyloid

The non-A beta component (NAC) of Alzheimer's disease amyloid is a newly discovered 35 amino acid peptide found to be closely linked to the beta-amyloid fibrils in senile plaques. Apolipoprotein E (apoE) is another prominent constituent of senile plaques. In vitro studies have shown that apoE binds beta-amyloid (A beta) with high avidity, but it is unknown to what extent apoE interacts with NAC. We examined the interactions between apoE and NAC and found that apoE bound synthetic NAC, forming a complex that resisted reducing agents and separation on SDS-PAGE. The complex could be formed using apoE from either purified human very low density lipoprotein (VLDL) particles, unfractionated human cerebrospinal fluid (CSF), or recombinant protein. The binding was established within 15 min upon mixing, and the interaction between NAC and apoE was dose-dependent and specific as revealed by competition experiments. The NAC-apoE complex was affected by non-physiological pH, but not by reducing agents such as DTT or beta-mercaptoethanol. ApoE exists in different isoforms of which the apoE3 genotype is the most frequent. Notably, the apoE4 genotype has been linked to late-onset Alzheimer's disease. This study presents evidence that apoE3 as well as apoE4 bind NAC, but the binding to apoE4 is about twice as strong as to apoE3. The isoform-specific binding of NAC to apoE may thus play an important role in amyloidogenesis and in the sequestering of apoE in senile plaques during the progress of Alzheimer's disease.

Brain beta-spectrin is a component of senile plaques in Alzheimer's disease

Spectrin is a multifunctional cortical membrane skeleton protein. We report here that the beta-subunit of spectrin is an integral component of beta-amyloid plaques in Alzheimer's disease (AD). We prepared anti-beta-spectrin antibodies by using synthetic peptides corresponding to the N-terminal and C-terminal domains of beta-spectrin variants. When tissues from post-mortem AD brains were immunostained with these domain-specific affinity purified beta-spectrin antibodies, beta-amyloid plaques were specifically stained in the cortical parenchyma in approximately one third of the cases. The staining was unaffected by preadsorption of beta-spectrin antibodies with A4/beta 1-40 peptide. The sodium dodecyl sulfate-insoluble amyloids were also stained by the beta-spectrin antibodies. The anti-alpha-spectrin antibody stained neuronal processes, but not amyloid plaques. The presence of beta-spectrin in the amyloid plaques in a subset of sporadic AD cases suggests that distinct biochemical pathways are involved in the formation or deposition of beta-amyloid plaques, and that an abnormality of beta-spectrin structure or function may be involved in the formation or deposition of beta-amyloid plaques in this subset of AD cases.

Genetic studies in Alzheimer's disease with an NACP/alpha-synuclein polymorphism

The non-Abeta component of Alzheimer's disease amyloid (NAC) is copurified with amyloid from the brain tissue of Alzheimer's disease victims and is immunohistochemically localized to amyloid fibrils. NAC is a hydrophobic peptide fragment from the NAC precursor protein (NACP/alpha-synuclein) that is localized to presynaptic terminals. We used a polymorphic dinucleotide repeat sequence in a genomic clone of NACP for genetic association and linkage studies. Screening of Alzheimer's disease families failed to establish linkage between NACP and Alzheimer's disease. Nevertheless, one of the NACP polymorphisms (NACP allele 2) was shown to have significant association with healthy elderly control individuals with apolipoprotein E risk. This may indicate a possible protective function of the allele.

The serpin-enzyme complex receptor recognizes soluble, nontoxic amyloid-beta peptide but not aggregated, cytotoxic amyloid-beta peptide

There is now extensive evidence that amyloid-beta peptide is toxic to neurons and that its cytotoxic effects can be attributed to a domain corresponding to amyloid-beta 25-35, GSNKGAIIGLM. We have shown recently that the serine proteinase inhibitor (serpin)-enzyme complex receptor (SEC-R), a receptor initially identified for binding of alpha1-antitrypsin (alpha1-AT) and other serine protease inhibitors, also recognizes the amyloid-beta 25-35 domain. In fact, by recognizing the amyloid-beta 25-35 domain, SEC-R mediates cell surface binding, internalization, and degradation of soluble amyloid-beta peptide. In this study, we examined the possibility that SEC-R mediates the neurotoxic effect of amyloid-beta peptide. A series of peptides based on the sequences of amyloid-beta peptide and alpha1-AT was prepared soluble in dimethyl sulfoxide or insoluble in water and examined in assays for SEC-R binding, for cytotoxicity in neuronal PC12 cells and murine cortical neurons in primary culture, and for aggregation in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. The results show that amyloid-beta peptide 25-35 and amyloid-beta peptide 1-40 prepared soluble in dimethyl sulfoxide compete for binding to SEC-R, are nontoxic, and migrate as monomers in SDS-PAGE analysis. In contrast, the same peptides aged in water did not compete for binding to SEC-R but were toxic and migrated as aggregates in SDS-PAGE. An all-D-amyloid-beta 25-35 peptide was not recognized at all by SEC-R but retained full toxic/aggregating properties. Using a series of deleted, substituted, and chimeric ambeta/alpha1-AT peptides, toxicity correlated well with aggregation but poorly with SEC-R recognition. In a subclone of PC12 cells which developed resistance to the toxic effect of aggregated amyloid-beta 25-35 there was a 2.5-3-fold increase in the number of SEC-R molecules/cell compared with the parent PC12 cell line. These data show that SEC-R does not mediate the cytotoxic effect of aggregated amyloid-beta peptide. Rather, SEC-R could play a protective role by mediating clearance and catabolism of soluble, monomeric amyloid-beta peptide, if soluble amyloid-beta peptide proves to be an in vivo precursor of the insoluble, toxic peptide.

Altered presynaptic protein NACP is associated with plaque formation and neurodegeneration in Alzheimer's disease

We have recently identified, in the brain tissue of patients afflicted with Alzheimer's disease (AD), the non-A beta component of AD amyloid (NAC) as a new constituent of amyloid. NAC is derived from a larger precursor, NACP, a presynaptic protein. To better understand the role of NACP/NAC in the pathogenesis of AD, we used semiquantitative immunoblotting and combined double-immunocytochemistry/laser scanning confocal microscopy to study the concentration and distribution of NACP/NAC in human brain, and compared them to the concentration and distribution of the presynaptic marker synaptophysin and the amyloid marker A beta. The semiquantitative immunoblotting demonstrated that the NACP concentration is slightly increased in the AD frontal cortex without statistical significance, whereas synaptophysin was reduced in its levels in AD. Consequently the proportion of NACP/synaptophysin was more than double in the AD frontal cortex as compared with controls. In the AD neocortex, NACP was colocalized with approximately 80% of the synaptophysin-immunoreactive structures (presumably the presynaptic terminals) and with the dystrophic neuritic component of the plaques. Computer-aided analysis showed that numbers of NACP-immunoreactive structures along synaptophysin-immunoreactive structures were significantly diminished (30 to 40%) in AD. Although the overall numbers of NACP-positive structures were decreased, there was a significant increase in the intensity of NACP-immunoreactivity per structure in AD. This increased intensity of NACP immunoreactivity per structure in AD was not observed with anti-synaptophysin, consistent with immunoblotting-based quantification. Antibodies against NAC immunoreacted with amyloid in 35% of the diffuse plaques and 55% of the mature plaques. Normal aged control brains containing small groups of diffuse plaques were negative with anti-NAC. Double-immunolabeling studies with A beta antibodies showed that NAC immunoreactivity is more abundant in the center portion of amyloid rather than in the periphery. These studies suggest that there is a connection between metabolism of presynaptic proteins and amyloid formation, and that NAC might follow diffuse A beta accumulation resulting in the formation of compact amyloid and mature plaques.

The toxicity in vitro of beta-amyloid protein

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NACP, the precursor protein of the non-amyloid beta/A4 protein (A beta) component of Alzheimer disease amyloid, binds A beta and stimulates A beta aggregation

NACP, a 140-amino acid presynaptic protein, is the precursor of NAC [the non-amyloid beta/A4 protein (A beta) component of Alzheimer disease (AD) amyloid], a peptide isolated from and immunologically localized to brain amyloid of patients afflicted with AD. NACP produced in Escherichia coli bound to A beta peptides, the major component of AD amyloid. NACP bound to A beta 1-38 and A beta 25-35 immobilized on nitrocellulose but did not bind to A beta 1-28 on the filter under the same conditions. NACP binding to A beta 1-38 was abolished by addition of A beta 25-35 but not by A beta 1-28, suggesting that the hydrophobic region of the A beta peptide is critical to this binding. NACP-112, a shorter splice variant of NACP containing the NAC sequence, bound to A beta, but NACP delta, a deletion mutant of NACP lacking the NAC domain, did not bind A beta 1-38. Furthermore, binding between NACP-112 and A beta 1-38 was decreased by addition of peptide Y, a peptide that covers the last 15 residues of NAC. In an aqueous solution, A beta 1-38 aggregation was observed when NACP was also present in an incubation mixture at a ratio of 1:125 (NACP/A beta), whereas A beta 1-38 alone or NACP alone did not aggregate under the same conditions, suggesting that the formation of a complex between A beta and NACP may promote aggregation of A beta. Thus, NACP can bind A beta peptides through the specific sequence and can promote A beta aggregation, raising the possibility that NACP may play a role in the development of AD amyloid.

Peripheral nervous system-specific genes identified by subtractive cDNA cloning

An improved method for constructing and screening subtractive cDNA libraries has been used to identify 46 mRNA transcripts that are expressed selectively in neonatal rat dorsal root ganglia (DRG) as judged by Northern blots and in situ hybridization. Sequence analysis demonstrates that both known (e.g. peripherin, calcitonin gene-related peptide, myelin P0) and novel identifiable transcripts (e.g. C-protein-like, synuclein-like, villin-like) are present in the library. Half of the transcripts (23) are undetectable in liver, kidney, heart, spleen, cerebellum, and cerebral cortex. Of the DRG-specific transcripts, 12 contain putative open reading frames that show no identity with known proteins. The construction of such a subtractive library thus provides us with both known and novel markers, and identifies new predicted DRG-specific proteins. In addition, the DRG-specific clones provide probes to define the regulatory elements that specify peripheral nervous-system-specific gene expression.

Residues in the synuclein consensus motif of the alpha-synuclein fragment, NAC, participate in transglutaminase-catalysed cross-linking to Alzheimer-disease amyloid beta A4 peptide

The widespread deposition of amyloid plaques is one of the hallmarks of Alzheimer disease (AD). A recently described component of amyloid plaques is the 35-residue peptide, non-A beta component of AD amyloid, which is derived from a larger intracellular neuronal constituent, alpha-synuclein. We demonstrate that transglutaminase catalyses the formation of the covalent non-A beta component of AD amyloid polymers in vitro as well as polymers with beta-amyloid peptide, the major constituent of AD plaques. The transglutaminase-reactive amino acid residues in the non-A beta component of AD amyloid were identified as Gln79 and Lys80. Lys80 is localized in a consensus motif Lys-Thr-Lys-Glu-Gly-Val, which is conserved in the synuclein gene family. Thus transglutaminase might be involved in the formation of insoluble amyloid deposits and participate in the modification of other members of the synuclein family.

The NACP/synuclein gene: chromosomal assignment and screening for alterations in Alzheimer disease

The major component of the vascular and plaque amyloid deposits in Alzheimer disease is the amyloid beta peptide (A beta). A second intrinsic component of amyloid, the NAC (non-A beta component of amyloid) peptide, has recently been identified, and its precursor protein was named NACP. A computer homology search allowed us to establish that the human NACP gene was homologous to the rat synuclein gene. We mapped the NACP/synuclein gene to chromosome 4 and cloned three alternatively spliced transcripts in lymphocytes derived from a normal subject. We analyzed by RT-PCR and direct sequencing the entire coding region of the NACP/synuclein gene in a group of patients with familial early onset Alzheimer disease. No mutation was found in 26 unrelated patients. Further studies are required to investigate the implication of the NACP/synuclein gene in Alzheimer disease.

Identification of two distinct synucleins from human brain

Two abundant proteins of 140 and 134 amino acids were purified and sequenced from human brain. They were identified through their reactivity on immunoblots with a partially characterised monoclonal antibody that recognises tau protein in a phosphorylation-dependent manner. The 140 amino acid protein is identical with the precursor of the non-A beta component of Alzheimer's disease amyloid which in turn is highly homologous to synuclein from Torpedo electroplaques and rat brain. The 134 amino acid protein is the human homologue of bovine phosphoneuroprotein 14; it is 61% identical in sequence to the 140 amino acid protein. The previously unrecognised homology between these two proteins defines a family of human brain synucleins. We refer to the 140 and 134 amino acid proteins as alpha-synuclein and beta-synuclein, respectively. Both synucleins are expressed predominantly in brain, where they are concentrated in presynaptic nerve terminals.