Neurotoxicity of acetylcholinesterase amyloid beta-peptide aggregates is dependent on the type of Abeta peptide and the AChE concentration present in the complexes.

Alzheimer's disease (AD) is a neurodegenerative disorder whose hallmark is the presence of senile plaques and neurofibrillary tangles. Senile plaques are mainly composed of amyloid beta-peptide (Abeta) fibrils and several proteins including acetylcholinesterase (AChE). AChE has been previously shown to stimulate the aggregation of Abeta1-40 into amyloid fibrils. In the present work, the neurotoxicity of different amyloid aggregates formed in the absence or presence of AChE was evaluated in rat pheochromocytoma PC12 cells. Stable AChE-Abeta complexes were found to be more toxic than those formed without the enzyme, for Abeta1-40 and Abeta1-42, but not for amyloid fibrils formed with AbetaVal18-Ala, a synthetic variant of the Abeta1-40 peptide. Of all the AChE-Abeta complexes tested the one containing the Abeta1-40 peptide was the most toxic. When increasing concentrations of AChE were used to aggregate the Abeta1-40 peptide, the neurotoxicity of the complexes increased as a function of the amount of enzyme bound to each complex. Our results show that AChE-Abeta1-40 aggregates are more toxic than those of AChE-Abeta1-42 and that the neurotoxicity depends on the amount of AChE bound to the complexes, suggesting that AChE may play a key role in the neurodegeneration observed in Alzheimer brain.     

The beta-amyloid protein of Alzheimer's disease binds to membrane lipids but does not bind to the alpha7 nicotinic acetylcholine receptor

Accumulation of the amyloid protein (Abeta) in the brain is an important step in the pathogenesis of Alzheimer's disease. However, the mechanism by which Abeta exerts its neurotoxic effect is largely unknown. It has been suggested that the peptide can bind to the alpha7 nicotinic acetylcholine receptor (alpha7nAChR). In this study, we examined the binding of Abeta1-42 to endogenous and recombinantly expressed alpha7nAChRs. Abeta1-42 did neither inhibit the specific binding of alpha7nAChR ligands to rat brain homogenate or slice preparations, nor did it influence the activity of alpha7nAChRs expressed in Xenopus oocytes. Similarly, Abeta1-42 did not compete for alpha-bungarotoxin-binding sites on SH-SY5Y cells stably expressing alpha7nAChRs. The effect of the Abeta1-42 on tau phosphorylation was also examined. Although Abeta1-42 altered tau phosphorylation in alpha7nAChR-transfected SH-SY5Y cells, the effect of the peptide was unrelated to alpha7nAChR expression or activity. Binding studies using surface plasmon resonance indicated that the majority of the Abeta bound to membrane lipid, rather than to a protein component. Fluorescence anisotropy experiments indicated that Abeta may disrupt membrane lipid structure or fluidity. We conclude that the effects of Abeta are unlikely to be mediated by direct binding to the alpha7nAChR. Instead, we speculate that Abeta may exert its effects by altering the packing of lipids within the plasma membrane, which could, in turn, influence the function of a variety of receptors and channels on the cell surface.     

beta-Amyloid(1-42) binds to alpha7 nicotinic acetylcholine receptor with high affinity. Implications for Alzheimer's disease pathology

Alzheimer's disease pathology is characterized by the presence of neuritic plaques and the loss of cholinergic neurons in the brain. The underlying mechanisms leading to these events are unclear, but the 42-amino acid beta-amyloid peptide (Abeta(1-42)) is involved. Immunohistochemical studies on human sporadic Alzheimer's disease brains demonstrate that Abeta(1-42) and a neuronal pentameric cation channel, the alpha7 nicotinic acetylcholine receptor (alpha7nAChR), are both present in neuritic plaques and co-localize in individual cortical neurons. Using human brain tissues and cells that overexpress either alpha7nAChR or amyloid precursor protein as the starting material, Abeta(1-42) and alpha7nAChR can be co-immunoprecipitated by the respective specific antibodies, suggesting that they are tightly associated. The formation of the alpha7nAChR.Abeta(1-42) complex can be efficiently suppressed by Abeta(12-28), implying that this Abeta sequence region contains the binding epitope. Receptor binding experiments show that Abeta(1-42) and alpha7nAChR bind with high affinity, and this interaction can be inhibited by alpha7nAChR ligands. Human neuroblastoma cells overexpressing alpha7nAChR are readily killed by Abeta(1-42), whereas alpha7nAChR agonists such as nicotine and epibatidine offered protection. Because Abeta(1-42) inhibits alpha7nAChR-dependent calcium activation and acetylcholine release, two processes critically involved in memory and cognitive functions, and the distribution of alpha7nAChR correlates with neuritic plaques in Alzheimer's disease brains, we propose that interaction of the alpha7nAChR and Abeta(1-42) is a pivotal mechanism involved in the pathophysiology of Alzheimer's disease.     

Immunohistochemical investigation of amyloid beta-protein (Abeta) in the brain of aged cats

To clarify the immunohistochemical features of amyloid deposits and cerebral amyloid angiopathy (CAA), the distribution of the amyloid beta-protein subtypes Abeta40, Abeta42, Abeta43 and Abeta precursor protein (APP) were examined in the brains of fourteen aged cats (7.5-21 year-old). Two types of plaques were detected. The first type was characterized by Ass positive antigenic material and detected in the cortical layers of the frontal and parietal lobes of all examined cats. The second type was characterized by diffuse positive immune staining representing diffuse plaques, which were detected only in the very aged cats (17-21 years old) and distributed throughout the cortical layers of the parietal lobes. Vascular amyloid and the amyloid deposits were strongly positive-stained with the antibody Abeta42. APP was exhibited in neurons and axons while the staining was stronger in the very aged cats (17-21 years old). Our findings suggest that the feline forms a spontaneous model for understanding the early changes of normal brain aging and the early stage of amyloid beta-protein deposition.     

Amyloid peptide Abeta(1-42) binds selectively and with picomolar affinity to alpha7 nicotinic acetylcholine receptors

We have recently reported evidence that a very high affinity interaction between the beta-amyloid peptide Abeta(1-42) and the alpha7 nicotinic acetylcholine receptor (alpha7nAChR) may be a precipitating event in the formation of amyloid plaques in Alzheimer's disease. In the present study, the kinetics for the binding of Abeta(1-42) to alpha7nAChR and alpha4beta2nAChR were determined using the subtype-selective nicotinic receptor ligands [(3)H]methyllycaconitine and [(3)H]cytisine. Synaptic membranes prepared from rat and guinea pig cerebral cortex and hippocampus were used as the source of receptors. Abeta(1-42) bound to the alpha7nAChR with exceptionally high affinity, as indicated by K(i) values of 4.1 and 5.0 pM for rat and guinea pig receptors, respectively. When compared with the alpha7nAChR, the affinity of Abeta(1-42) for the alpha4beta2nAChR was approximately 5,000-fold lower, as indicated by corresponding K(i) values of 30 and 23nM. The results of this study support the concept that an exceptionally high affinity interaction between Abeta(1-42) and alpha7nAChR could serve as a precipitating factor in the formation of amyloid plaques and thereby contribute to the selective degeneration of cholinergic neurons that originate in the basal forebrain and project to the cortex and hippocampus.     

Apolipoprotein E and low density lipoprotein receptor-related protein facilitate intraneuronal Abeta42 accumulation in amyloid model mice

The low density lipoprotein receptor-related protein (LRP) is highly expressed in the brain and has been shown to alter the metabolism of amyloid precursor protein and amyloid-beta peptide (Abeta) in vitro. Previously we developed mice that overexpress a functional LRP minireceptor (mLRP2) in their brains and crossed them to the PDAPP mouse model of Alzheimer disease. Overexpression of mLRP2 in 22-month-old PDAPP mice with amyloid plaques increased a pool of carbonate-soluble Abeta in the brain and worsened memory-related behavior. In the current study, we examined the effects of mLRP2 overexpression on 3-month-old PDAPP mice that had not yet developed amyloid plaques. We found significantly higher levels of membrane-associated Abeta42 in the hippocampus of mice that overexpressed mLRP2. Using immunohistochemical methods, we observed significant intraneuronal Abeta42 in the hippocampus and frontal cortex of PDAPP mice, which frequently co-localized with the lysosomal marker LAMP-1. Interestingly, PDAPP mice lacking apolipoprotein E (apoE) had much less intraneuronal Abeta42. We also found that PC12 cells overexpressing mLRP2 cleared Abeta42 and Abeta40 more rapidly from media than PC12 cells transfected with the vector only. Preincubation of apoE3 or apoE4 with Abeta42 increased the rate of Abeta clearance, and this effect was partially blocked by receptor-associated protein. Our results support the hypothesis that LRP binds and endocytoses Abeta42 both directly and via apoE but that endocytosed Abeta42 is not completely degraded and accumulates in intraneuronal lysosomes.     

Expression of nicotinic receptors on primary cultures of rat astrocytes and up-regulation of the alpha7, alpha4 and beta2 subunits in response to nanomolar concentrations of the beta-amyloid peptide(1-42)

Neuronal nicotinic acetylcholine receptors (nAChRs) are thought to be involved in the pathogenesis of Alzheimer's disease (AD). Interestingly, in the brains of patients with this disease, losses of several subtypes of nAChRs on neurons have been reported, while an increase in alpha7 nAChRs was recently detected in the astrocytes. However, little is presently known about the expressions of individual subunits of nAChR on rat astrocytes in primary culture or the possible influence of exposure to beta-amyloid peptide (Abeta), a neuropathological hallmark of AD, on this expression. Thus, in the present investigation the levels of individual nAChR subunits on primary rat astrocytes and the possible direct influence of Abetas on the receptors were examined by RT-PCR, Western blotting, monitoring intracellular free calcium and immunohistochemistry. The alpha4, alpha7, beta2 and beta3 subunits and related calcium channel responses were found in these cells, whereas neither alpha2 nor alpha3 could be detected. Elevation in the levels of alpha7, alpha4 and beta2 mRNAs and proteins were observed in astrocytes exposed to 0.1-100nM Abeta(1-42). In contrast, incubation with 1muM Abeta(1-42) or Abeta(35-25) did not affect these levels. We propose that the enhanced expression of alpha7, alpha4 and beta2 nAChRs by astrocytes stimulated directly by nanomolar concentrations of Abeta(1-42) might be related to ongoing defensive or compensative mechanisms.     

RAC1 inhibition targets amyloid precursor protein processing by gamma-secretase and decreases Abeta production in vitro and in vivo

beta-Amyloid peptides (Abeta) that form the senile plaques of Alzheimer disease consist mainly of 40- and 42-amino acid (Abeta 40 and Abeta 42) peptides generated from the cleavage of the amyloid precursor protein (APP). Generation of Abeta involves beta-secretase and gamma-secretase activities and is regulated by membrane trafficking of the proteins involved in Abeta production. Here we describe a new small molecule, EHT 1864, which blocks the Rac1 signaling pathways. In vitro, EHT 1864 blocks Abeta 40 and Abeta 42 production but does not impact sAPPalpha levels and does not inhibit beta-secretase. Rather, EHT 1864 modulates APP processing at the level of gamma-secretase to prevent Abeta 40 and Abeta 42 generation. This effect does not result from a direct inhibition of the gamma-secretase activity and is specific for APP cleavage, since EHT 1864 does not affect Notch cleavage. In vivo, EHT 1864 significantly reduces Abeta 40 and Abeta 42 levels in guinea pig brains at a threshold that is compatible with delaying plaque accumulation and/or clearing the existing plaque in brain. EHT 1864 is the first derivative of a new chemical series that consists of candidates for inhibiting Abeta formation in the brain of AD patients. Our findings represent the first pharmacological validation of Rac1 signaling as a target for developing novel therapies for Alzheimer disease.     

Intraneuronal amyloid-beta1-42 production triggered by sustained increase of cytosolic calcium concentration induces neuronal death

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the presence in the brain of senile plaques which contain an amyloid core made of beta-amyloid peptide (Abeta). Abeta is produced by the cleavage of the amyloid precursor protein (APP). Since impairment of neuronal calcium signalling has been causally implicated in ageing and AD, we have investigated the influence of an influx of extracellular calcium on the metabolism of human APP in rat cortical neurones. We report that a high cytosolic calcium concentration, induced by neuronal depolarization, inhibits the alpha-secretase cleavage of APP and triggers the accumulation of intraneuronal C-terminal fragments produced by the beta-cleavage of the protein (CTFbeta). Increase in cytosolic calcium concentration specifically induces the production of large amounts of intraneuronal Abeta1-42, which is inhibited by nimodipine, a specific antagonist of l-type calcium channels. Moreover, calcium release from endoplasmic reticulum is not sufficient to induce the production of intraneuronal Abeta, which requires influx of extracellular calcium mediated by the capacitative calcium entry mechanism. Therefore, a sustained high concentration of cytosolic calcium is needed to induce the production of intraneuronal Abeta1-42 from human APP. Our results show that this accumulation of intraneuronal Abeta1-42 induces neuronal death, which is prevented by a functional gamma-secretase inhibitor.     

Neuroserpin binds Abeta and is a neuroprotective component of amyloid plaques in Alzheimer disease

Alzheimer disease is characterized by extracellular plaques composed of Abeta peptides. We show here that these plaques also contain the serine protease inhibitor neuroserpin and that neuroserpin forms a 1:1 binary complex with the N-terminal or middle parts of the Abeta(1-42) peptide. This complex inactivates neuroserpin as an inhibitor of tissue plasminogen activator and blocks the loop-sheet polymerization process that is characteristic of members of the serpin superfamily. In contrast neuroserpin accelerates the aggregation of Abeta(1-42) with the resulting species having an appearance that is distinct from the mature amyloid fibril. Neuroserpin reduces the cytotoxicity of Abeta(1-42) when assessed using standard cell assays, and the interaction has been confirmed in vivo in novel Drosophila models of disease. Taken together, these data show that neuroserpin interacts with Abeta(1-42) to form off-pathway non-toxic oligomers and so protects neurons in Alzheimer disease.     

Characterization of amyloid beta peptides from brain extracts of transgenic mice overexpressing the London mutant of human amyloid precursor protein

Alzheimer's disease (AD) is marked by the presence of neurofibrillary tangles and amyloid plaques in the brain of patients. To study plaque formation, we report on further quantitative and qualitative analysis of human and mouse amyloid beta peptides (Abeta) from brain extracts of transgenic mice overexpressing the London mutant of human amyloid precursor protein (APP). Using enzyme-linked immunosorbant assays (ELISAs) specific for either human or rodent Abeta, we found that the peptides from both species aggregated to form plaques. The ratios of deposited Abeta1-42/1-40 were in the order of 2-3 for human and 8-9 for mouse peptides, indicating preferential deposition of Abeta42. We also determined the identity and relative levels of other Abeta variants present in protein extracts from soluble and insoluble brain fractions. This was done by combined immunoprecipitation and mass spectrometry (IP/MS). The most prominent peptides truncated either at the carboxyl- or the amino-terminus were Abeta1-38 and Abeta11-42, respectively, and the latter was strongly enriched in the extracts of deposited peptides. Taken together, our data indicate that plaques of APP-London transgenic mice consist of aggregates of multiple human and mouse Abeta variants, and the human variants that we identified were previously detected in brain extracts of AD patients.     

Antiamyloidogenic and neuroprotective functions of cathepsin B: implications for Alzheimer's disease

Alzheimer's disease (AD) may result from the accumulation of amyloid-beta (Abeta) peptides in the brain. The cysteine protease cathepsin B (CatB) is associated with amyloid plaques in AD brains and has been suspected to increase Abeta production. Here, we demonstrate that CatB actually reduces levels of Abeta peptides, especially the aggregation-prone species Abeta1-42, through proteolytic cleavage. Genetic inactivation of CatB in mice with neuronal expression of familial AD-mutant human amyloid precursor protein (hAPP) increased the relative abundance of Abeta1-42, worsening plaque deposition and other AD-related pathologies. Lentivirus-mediated expression of CatB in aged hAPP mice reduced preexisting amyloid deposits, even thioflavin S-positive plaques. Under cell-free conditions, CatB effectively cleaved Abeta1-42, generating C-terminally truncated Abeta peptides that are less amyloidogenic. Thus, CatB likely fulfills antiamyloidogenic and neuroprotective functions. Insufficient CatB activity might promote AD; increasing CatB activity could counteract the neuropathology of this disease.     

Aggressive amyloidosis in mice expressing human amyloid peptides with the Arctic mutation

The Arctic mutation within the amyloid-beta (Abeta) peptide causes Alzheimer disease. In vitro, Arctic-mutant Abeta forms (proto)fibrils more effectively than wild-type Abeta. We generated transgenic mouse lines expressing Arctic-mutant human amyloid precursor proteins (hAPP). Amyloid plaques formed faster and were more extensive in Arctic mice than in hAPP mice expressing wild-type Abeta, even though Arctic mice had lower Abeta(1-42/1-40) ratios. Thus, the Arctic mutation is highly amyloidogenic in vivo.     

Familial Danish dementia: co-existence of Danish and Alzheimer amyloid subunits (ADan AND A{beta}) in the absence of compact plaques

Familial Danish dementia is an early onset autosomal dominant neurodegenerative disorder linked to a genetic defect in the BRI2 gene and clinically characterized by dementia and ataxia. Cerebral amyloid and preamyloid deposits of two unrelated molecules (Danish amyloid (ADan) and beta-amyloid (Abeta)), the absence of compact plaques, and neurofibrillary degeneration indistinguishable from that observed in Alzheimer disease (AD) are the main neuropathological features of the disease. Biochemical analysis of extracted amyloid and preamyloid species indicates that as the solubility of the deposits decreases, the heterogeneity and complexity of the extracted peptides exponentially increase. Nonfibrillar deposits were mainly composed of intact ADan-(1-34) and its N-terminally modified (pyroglutamate) counterpart together with Abeta-(1-42) and Abeta-(4-42) in approximately 1:1 mixture. The post-translational modification, glutamate to pyroglutamate, was not present in soluble circulating ADan. In the amyloid fractions, ADan was heavily oligomerized and highly heterogeneous at the N and C terminus, and, when intact, its N terminus was post-translationally modified (pyroglutamate), whereas Abeta was mainly Abeta-(4-42). In all cases, the presence of Abeta-(X-40) was negligible, a surprising finding in view of the prevalence of Abeta40 in vascular deposits observed in sporadic and familial AD, Down syndrome, and normal aging. Whether the presence of the two amyloid subunits is imperative for the disease phenotype or just reflects a conformational mimicry remains to be elucidated; nonetheless, a specific interaction between ADan oligomers and Abeta molecules was demonstrated in vitro by ligand blot analysis using synthetic peptides. The absence of compact plaques in the presence of extensive neuro fibrillar degeneration strongly suggests that compact plaques, fundamental lesions for the diagnosis of AD, are not essential for the mechanism of dementia.     

Abeta42 is essential for parenchymal and vascular amyloid deposition in mice

Considerable circumstantial evidence suggests that Abeta42 is the initiating molecule in Alzheimer's disease (AD) pathogenesis. However, the absolute requirement for Abeta42 for amyloid deposition has never been demonstrated in vivo. We have addressed this by developing transgenic models that express Abeta1-40 or Abeta1-42 in the absence of human amyloid beta protein precursor (APP) overexpression. Mice expressing high levels of Abeta1-40 do not develop overt amyloid pathology. In contrast, mice expressing lower levels of Abeta1-42 accumulate insoluble Abeta1-42 and develop compact amyloid plaques, congophilic amyloid angiopathy (CAA), and diffuse Abeta deposits. When mice expressing Abeta1-42 are crossed with mutant APP (Tg2576) mice, there is also a massive increase in amyloid deposition. These data establish that Abeta1-42 is essential for amyloid deposition in the parenchyma and also in vessels.     

Acetylcholinesterase triggers the aggregation of PrP 106-126

Acetylcholinesterase (AChE), a senile plaque component, promotes amyloid-beta-protein (Abeta) fibril formation in vitro. The presence of prion protein (PrP) in Alzheimer's disease (AD) senile plaques prompted us to assess if AChE could trigger the PrP peptides aggregation as well. Consequently, the efficacy of AChE on the PrP peptide spanning-residues 106-126 aggregation containing a coumarin fluorescence probe (coumarin-PrP 106-126) was studied. Kinetics of coumarin-PrP 106-126 aggregation showed a significant increase of maximum size of aggregates (MSA), which was dependent on AChE concentration. AChE-PrP 106-126 aggregates showed the tinctorial and optical amyloid properties as determined by polarized light and electronic microscopy analysis. A remarkable inhibition of MSA was obtained with propidium iodide, suggesting that AChE triggers PrP 106-126 and Abeta aggregation through a similar mechanism. Huprines (AChE inhibitors) also significantly decreased MSA induced by AChE as well, unveiling the potential interest for some AChE inhibitors as a novel class of potential anti-prion drugs.     

TGF-beta1 promotes microglial amyloid-beta clearance and reduces plaque burden in transgenic mice

Abnormal accumulation of the amyloid-beta peptide (Abeta) in the brain appears crucial to pathogenesis in all forms of Alzheimer disease (AD), but the underlying mechanisms in the sporadic forms of AD remain unknown. Transforming growth factor beta1 (TGF-beta1), a key regulator of the brain's responses to injury and inflammation, has been implicated in Abeta deposition in vivo. Here we demonstrate that a modest increase in astroglial TGF-beta1 production in aged transgenic mice expressing the human beta-amyloid precursor protein (hAPP) results in a three-fold reduction in the number of parenchymal amyloid plaques, a 50% reduction in the overall Abeta load in the hippocampus and neocortex, and a decrease in the number of dystrophic neurites. In mice expressing hAPP and TGF-beta1, Abeta accumulated substantially in cerebral blood vessels, but not in parenchymal plaques. In human cases of AD, Abeta immunoreactivity associated with parenchymal plaques was inversely correlated with Abeta in blood vessels and cortical TGF-beta1 mRNA levels. The reduction of parenchymal plaques in hAPP/TGF-beta1 mice was associated with a strong activation of microglia and an increase in inflammatory mediators. Recombinant TGF-beta1 stimulated Abeta clearance in microglial cell cultures. These results demonstrate that TGF-beta1 is an important modifier of amyloid deposition in vivo and indicate that TGF-beta1 might promote microglial processes that inhibit the accumulation of Abeta in the brain parenchyma.     

Aurones serve as probes of beta-amyloid plaques in Alzheimer's disease

A novel series of aurone derivatives for in vivo imaging of beta-amyloid plaques in the brain of Alzheimer's disease (AD) were synthesized and characterized. When in vitro binding studies using Abeta(1-42) aggregates were carried out with aurone derivatives, they showed high binding affinities for Abeta(1-42) aggregates at the K(i) values ranging from 1.2 to 6.8 nM. When in vitro plaque labeling was carried out using double transgenic mice brain sections, the aurone derivatives intensely stained beta-amyiloid plaques. Biodistribution studies in normal mice after i.v. injection of the radioiodinated aurones displayed high brain uptake (1.9-4.6% ID/g at 2 min) and rapid clearance from the brain (0.11-0.26% ID/g at 60 min), which is highly desirable for amyloid imaging agents. The results in this study suggest that novel radiolabeled aurones may be useful amyloid imaging agents for detecting beta-amyloid plaques in the brain of AD.     

Roles of amyloid beta-peptide-associated oxidative stress and brain protein modifications in the pathogenesis of Alzheimer's disease and mild cognitive impairment

Oxidative stress has been implicated to play a crucial role in the pathogenesis of a number of diseases, including neurodegenerative disorders, cancer, and ischemia, just to name a few. Alzheimer disease (AD) is an age-related neurodegenerative disorder that is recognized as the most common form of dementia. AD is histopathologically characterized by the presence of extracellular amyloid plaques, intracellular neurofibrillary tangles, the presence of oligomers of amyloid beta-peptide (Abeta), and synapse loss. In this review we discuss the role of Abeta in the pathogenesis of AD and also the use of redox proteomics to identify oxidatively modified brain proteins in AD and mild cognitive impairment. In addition, redox proteomics studies in in vivo models of AD centered around human Abeta(1-42) are discussed.     

Amino-terminally truncated Abeta peptide species are the main component of cotton wool plaques

Cotton wool plaques (CWPs) are round lesions that lack a central amyloid core. CWPs have been observed in individuals affected by early-onset familial Alzheimer disease (FAD) associated with mutations in the presenilin 1 (PSEN1) gene. Here we present the characterization of the amyloid-beta (Abeta) peptides deposited in the brain of an individual affected by FAD carrying the novel missense (V261I) mutation in the PSEN1 gene. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry was used to determine the Abeta peptide species present in the cerebral and cerebellar cortices, in leptomeningeal vessels, and in CWPs isolated by laser microdissection (LMD). Our results indicate that amino-terminally truncated Abeta peptide species ending at residues 42 and 43 are the main Abeta peptides deposited in brain parenchyma and LMD-CWPs in association with the PSEN1 V261I mutation. Full-length Abeta1-42 and Abeta1-43 peptide species were underrepresented. CWPs were not found to be associated with vessels and did not contain Abeta1-40 peptides, the main component of the vascular deposits. Although Abeta deposits were present mostly in the form of CWPs in the cerebral cortex and as diffuse deposits in the cerebellar cortex, a similar array of amino-terminally truncated Abeta peptide species was seen in both cases. The biochemical data support the concept that parenchymal and vascular amyloid deposits are associated with a different array of Abeta peptide species. The generation and parenchymal deposition of highly insoluble amino-terminally truncated Abeta peptides may play an important role in the pathogenesis of AD and must be taken into consideration in developing new diagnostic and therapeutic strategies.