Cerebral Proteomic Changes in the rTg-D Rat Model of Cerebral Amyloid Angiopathy Type-2 With Cortical Microhemorrhages and Cognitive Impairments.

Cerebral amyloid angiopathy (CAA) is a common disorder of the elderly, a prominent comorbidity of Alzheimer's disease, and causes vascular cognitive impairment and dementia. Previously, we generated a novel transgenic rat model (rTg-D) that produces human familial CAA Dutch E22Q mutant amyloid ß-protein (Aß) in brain and develops arteriolar CAA type-2. Here, we show that deposition of fibrillar Aß promotes arteriolar smooth muscle cell loss and cerebral microhemorrhages that can be detected by magnetic resonance imaging and confirmed by histopathology. Aged rTg-D rats also present with cognitive deficits. Cerebral proteomic analyses revealed 241 proteins that were significantly elevated with an increase of >50% in rTg-D rats presenting with CAA compared to wild-type rats. Fewer proteins were significantly decreased in rTg-D rats. Of note, high temperature requirement peptidase A (HTRA1), a proteinase linked to transforming growth factor beta 1 (TGF-ß1) signaling, was elevated and found to accumulate in cerebral vessels harboring amyloid deposits. Pathway analysis indicated elevation of the TGF-ß1 pathway and increased TGF-ß1 levels were detected in rTg-D rats. In conclusion, the present findings provide new molecular insights into the pathogenesis of CAA and suggest a role for interactions between HTRA1 and TGF-ß1 in the disease process.

Evaluation of Copper Chelation Therapy in a Transgenic Rat Model of Cerebral Amyloid Angiopathy.

Cerebral amyloid angiopathy (CAA) is characterized by the accumulation of the amyloid ß (Aß) protein in blood vessels and leads to hemorrhages, strokes, and dementia in elderly individuals. Recent reports have shown elevated copper levels colocalized with vascular amyloid in human CAA and Alzheimer's disease patients, which have been suggested to contribute to cytotoxicity through the formation of reactive oxygen species. Here, we treated a transgenic rat model of CAA (rTg-DI) with the copper-specific chelator, tetrathiomolybdate (TTM), via intraperitoneal (IP) administration for 6 months to determine if it could lower copper content in vascular amyloid deposits and modify CAA pathology. Results showed that TTM treatment led to elevated Aß load in the hippocampus of the rTg-DI rats and increased microbleeds in the wild type (WT) animals. X-ray fluorescence microscopy was performed to image the distribution of copper and revealed a surprising increase in copper colocalized with Aß aggregates in TTM-treated rTg-DI rats. Unexpectedly, we also found an increase in the copper content in unaffected vessels of both rTg-DI and WT animals. These results show that IP administration of TTM was ineffective in removing copper from vascular Aß aggregates in vivo and increased the development of disease pathology in CAA.

rTg-D: A novel transgenic rat model of cerebral amyloid angiopathy Type-2.

Background: Cerebral amyloid angiopathy (CAA) is common disorder of the elderly, a prominent comorbidity of Alzheimer's disease, and causes vascular cognitive impairment and dementia. Previously, we generated a transgenic rat model of capillary CAA type-1 that develops many pathological features of human disease. However, a complementary rat model of larger vessel CAA type-2 disease has been lacking. Methods: A novel transgenic rat model (rTg-D) was generated that produces human familial CAA Dutch E22Q mutant amyloid ß-protein (Aß) in brain and develops larger vessel CAA type-2. Quantitative biochemical and pathological analyses were performed to characterize the progression of CAA and associated pathologies in aging rTg-D rats. Results: rTg-D rats begin to accumulate Aß in brain and develop varying levels of larger vessel CAA type-2, in the absence of capillary CAA type-1, starting around 18 months of age. Larger vessel CAA was mainly composed of the Aß40 peptide and most prominent in surface leptomeningeal/pial vessels and arterioles of the cortex and thalamus. Cerebral microbleeds and small vessel occlusions were present mostly in the thalamic region of affected rTg-D rats. In contrast to capillary CAA type-1 the amyloid deposited within the walls of larger vessels of rTg-D rats did not promote perivascular astrocyte and microglial responses or accumulate the Aß chaperone apolipoprotein E. Conclusion: Although variable in severity, the rTg-D rats specifically develop larger vessel CAA type-2 that reflects many of the pathological features of human disease and provide a new model to investigate the pathogenesis of this condition.

Human cerebral vascular amyloid contains both antiparallel and parallel in-register Aß40 fibrils.

The accumulation of fibrillar amyloid-ß (Aß) peptides alongside or within the cerebral vasculature is the hallmark of cerebral amyloid angiopathy (CAA). This condition commonly co-occurs with Alzheimer's disease (AD) and leads to cerebral microbleeds, intracranial hemorrhages, and stroke. CAA also occurs sporadically in an age-dependent fashion and can be accelerated by the presence of familial Aß mutant peptides. Recent studies using Fourier transform infrared (FTIR) spectroscopy of vascular Aß fibrils derived from rodents containing the double E22Q/D23N mutations indicated the presence of a novel antiparallel ß-sheet structure. To address whether this structure is associated solely with the familial mutations or is a common feature of CAA, we propagated Aß fibrils from human brain vascular tissue of patients diagnosed with nonfamilial CAA. Aß fibrils were isolated from cerebral blood vessels using laser capture microdissection in which specific amyloid deposits were removed from thin slices of the brain tissue. Transmission electron microscopy revealed that these deposits were organized into a tight meshwork of fibrils, which FTIR measurements showed could serve as seeds to propagate the growth of Aß40 fibrils for structural studies. Solid-state NMR measurements of the fibrils propagated from vascular amyloid showed they contained a mixture of parallel, in-register, and antiparallel ß-sheet structures. The presence of fibrils with antiparallel structure derived from vascular amyloid is distinct from the typical parallel, in-register ß-sheet structure that appears in fibrils derived from parenchymal amyloid in AD. These observations reveal that different microenvironments influence the structures of Aß fibrils in the human brain.

Diffuse white matter loss in a transgenic rat model of cerebral amyloid angiopathy.

Diffuse white matter (WM) disease is highly prevalent in elderly with cerebral small vessel disease (cSVD). In humans, cSVD such as cerebral amyloid angiopathy (CAA) often coexists with Alzheimer's disease imposing a significant impediment for characterizing their distinct effects on WM. Here we studied the burden of age-related CAA pathology on WM disease in a novel transgenic rat model of CAA type 1 (rTg-DI). A cohort of rTg-DI and wild-type rats was scanned longitudinally using MRI for characterization of morphometry, cerebral microbleeds (CMB) and WM integrity. In rTg-DI rats, a distinct pattern of WM loss was observed at 9 M and 11 M. MRI also revealed manifestation of small CMB in thalamus at 6 M, which preceded WM loss and progressively enlarged until the moribund disease stage. Histology revealed myelin loss in the corpus callosum and thalamic CMB in all rTg-DI rats, the latter of which manifested in close proximity to occluded and calcified microvessels. The quantitation of CAA load in rTg-DI rats revealed that the most extensive microvascular Aß deposition occurred in the thalamus. For the first time using in vivo MRI, we show that CAA type 1 pathology alone is associated with a distinct pattern of WM loss.

Voluntary Wheel Running Reduces Amyloid-ß42 and Rescues Behavior in Aged Tg2576 Mouse Model of Alzheimer's Disease.

Exercise has been shown to be protective against the risk of dementias, including Alzheimer's disease (AD). Intervention studies have demonstrated its ability to mitigate cognitive and behavioral impairments and reduce disease in both humans and animals. However, information is lacking in regard to the volume and intensity, as well as timing of exercise onset with respect to disease stage, which produces optimal benefits. Here, utilizing the Tg2576 mouse, a model of AD-like parenchymal amyloid pathology and cognitive impairment, we sought to understand the effects of different lengths of daily access to a running wheel on advanced stage disease. This study is the first to determine the benefits of long-term exercise (4 months of voluntary running) and different periods of daily access to a running wheel (0 h, 1 h, 3 h, and 12 h running wheel access) beginning in 14-month-old Tg2576 mice, an age with significant amyloid pathology. We found that exercising Tg2576 animals showed lower levels of some aspects of AD pathology and reduced behavioral dysfunction compared to sedentary Tg2576 animals. High intensity exercise, rather than high volume exercise, was generally most beneficial in reducing amyloid pathology. Our results suggest that engaging in vigorous exercise programs, even after living a sedentary life, may lead to a measurable reduction in AD pathology and preservation of some cognitive abilities.

A Novel Transgenic Rat Model of Robust Cerebral Microvascular Amyloid with Prominent Vasculopathy.

Accumulation of fibrillar amyloid ß protein in blood vessels of the brain, a condition known as cerebral amyloid angiopathy (CAA), is a common pathology of elderly individuals, a prominent comorbidity of Alzheimer disease, and a driver of vascular cognitive impairment and dementia. Although several transgenic mouse strains have been generated that develop varying levels of CAA, consistent models of associated cerebral microhemorrhage and vasculopathy observed clinically have been lacking. Reliable preclinical animal models of CAA and microhemorrhage are needed to investigate the molecular pathogenesis of this condition. Herein, we describe the generation and characterization of a novel transgenic rat (rTg-DI) that produces low levels of human familial CAA Dutch/Iowa E22Q/D23N mutant amyloid ß protein in brain and faithfully recapitulates many of the pathologic aspects of human small-vessel CAA. rTg-DI rats exhibit early-onset and progressive accumulation of cerebral microvascular fibrillar amyloid accompanied by early-onset and sustained behavioral deficits. Comparable to CAA in humans, the cerebral microvascular amyloid in rTg-DI rats causes capillary structural alterations, promotes prominent perivascular neuroinflammation, and produces consistent, robust microhemorrhages and small-vessel occlusions that are readily detected by magnetic resonance imaging. The rTg-DI rats provide a new model to investigate the pathogenesis of small-vessel CAA and microhemorrhages, to develop effective biomarkers for this condition and to test therapeutic interventions.

Mutation of the Kunitz-type proteinase inhibitor domain in the amyloid ß-protein precursor abolishes its anti-thrombotic properties in vivo.

INTRODUCTION: Kunitz proteinase inhibitor (KPI) domain-containing forms of the amyloid ß-protein precursor (AßPP) inhibit cerebral thrombosis. KPI domain-lacking forms of AßPP are abundant in brain. Regions of AßPP other than the KPI domain may also be involved with regulating cerebral thrombosis. To determine the contribution of the KPI domain to the overall function of AßPP in regulating cerebral thrombosis we generated a reactive center mutant that was devoid of anti-thrombotic activity and studied its anti-thrombotic function in vitro and in vivo. METHODS: To determine the extent of KPI function of AßPP in regulating cerebral thrombosis we generated a recombinant reactive center KPIR13I mutant devoid of anti-thrombotic activity. The anti-proteolytic and anti-coagulant properties of wild-type and R13I mutant KPI were investigated in vitro. Cerebral thrombosis of wild-type, AßPP knock out and AßPP/KPIR13I mutant mice was evaluated in experimental models of carotid artery thrombosis and intracerebral hemorrhage. RESULTS: Recombinant mutant KPIR13I domain was ineffective in the inhibition of pro-thrombotic proteinases and did not inhibit the clotting of plasma in vitro. AßPP/KPIR13I mutant mice were similarly deficient as AßPP knock out mice in regulating cerebral thrombosis in experimental models of carotid artery thrombosis and intracerebral hemorrhage. CONCLUSIONS: We demonstrate that the anti-thrombotic function of AßPP primarily resides in the KPI activity of the protein.

Intensive 'Brain Training' Intervention Fails to Reduce Amyloid Pathologies or Cognitive Deficits in Transgenic Mouse Models of Alzheimer's Disease.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is the leading cause of dementia in the elderly. Amyloid-ß protein (Aß) depositions in both the brain parenchyma and the cerebral vasculature are recognized as important pathological components that contribute to the cognitive impairments found in individuals with AD. Because pharmacological options have been minimally effective in treating cognitive impairment to date, interest in the development of preventative lifestyle intervention strategies has increased in the field. One controversial strategy, cognitive-specific stimulation, has been studied previously in human participants and has been widely commercialized in the form of 'brain-training games.' In the present study, we developed a highly controlled, isolated cognitive training intervention program for mice. Two transgenic mouse lines, one that develops Aß deposition largely in brain parenchyma, and another in the cerebral microvasculature, progressed through a series of domain-specific tasks for an average of 4 months. Despite the high intensity and duration of the intervention, we found little evidence of positive benefits for AD amyloid pathologies and post-training cognitive testing in these two models. Taken together, these results support the current evidence in human studies that cognitive-specific stimulation does not lead to a measurable reduction in AD pathology or an improvement in general brain health.

Cerebral vascular amyloid seeds drive amyloid ß-protein fibril assembly with a distinct anti-parallel structure.

Cerebrovascular accumulation of amyloid ß-protein (Aß), a condition known as cerebral amyloid angiopathy (CAA), is a common pathological feature of patients with Alzheimer's disease. Familial Aß mutations, such as Dutch-E22Q and Iowa-D23N, can cause severe cerebrovascular accumulation of amyloid that serves as a potent driver of vascular cognitive impairment and dementia. The distinctive features of vascular amyloid that underlie its unique pathological properties remain unknown. Here, we use transgenic mouse models producing CAA mutants (Tg-SwDI) or overproducing human wild-type Aß (Tg2576) to demonstrate that CAA-mutant vascular amyloid influences wild-type Aß deposition in brain. We also show isolated microvascular amyloid seeds from Tg-SwDI mice drive assembly of human wild-type Aß into distinct anti-parallel ß-sheet fibrils. These findings indicate that cerebrovascular amyloid can serve as an effective scaffold to promote rapid assembly and strong deposition of Aß into a unique structure that likely contributes to its distinctive pathology.

Mechanism of Nucleated Conformational Conversion of Aß42.

Soluble oligomers and protofibrils of the Aß42 peptide are neurotoxic intermediates in the conversion of monomeric Aß42 into the amyloid fibrils associated with Alzheimer's disease. Nuclear magnetic resonance and Fourier transform infrared spectroscopy, along with single-touch atomic force microscopy, are used to establish the structural transitions involved in fibril formation. We show that under conditions favorable for the nucleated conformation conversion, the Aß42 peptide aggregates into largely unstructured low-molecular weight (MW) oligomers that are able to stack to form high-MW oligomers and to laterally associate to form protofibrils. ß-Sheet secondary structure develops during the irreversible lateral association of the oligomers. The first step in this conversion is the formation of an antiparallel ß-hairpin stabilized by intramonomer hydrogen bonding. The antiparallel ß-hairpins then associate into a cross ß-sheet structure with parallel and in-register ß-strands having intermonomer hydrogen bonding.

N-terminal region of myelin basic protein reduces fibrillar amyloid-ß deposition in Tg-5xFAD mice.

Alzheimer's disease is a progressive neurodegenerative disorder that is characterized by extensive deposition of fibrillar amyloid-ß (Aß) in the brain. Previously, myelin basic protein (MBP) was identified to be a potent inhibitor to Aß fibril formation, and this inhibitory activity was localized to the N-terminal residues 1-64, a fragment designated MBP1. Here, we show that the modest neuronal expression of a fusion protein of the biologically active MBP1 fragment and the enhanced green fluorescent protein (MBP1-EGFP) significantly improved the performance of spatial learning memory in Tg-5xFAD mice, a model of pathologic Aß accumulation in brain. The levels of insoluble Aß and fibrillar amyloid were significantly reduced in bigenic Tg-5xFAD/Tg-MBP1-EGFP mice. Quantitative stereological analysis revealed that the reduction in amyloid was because of a reduction in the size of fibrillar plaques rather than a decrease in plaque numbers. The current findings support previous studies showing that MBP1 inhibits Aß fibril formation in vitro and demonstrate the ability of MBP1 to reduce Aß pathology and improve behavioral performance.

Early-onset formation of parenchymal plaque amyloid abrogates cerebral microvascular amyloid accumulation in transgenic mice.

The fibrillar assembly and deposition of amyloid ß (Aß) protein, a key pathology of Alzheimer disease, can occur in the form of parenchymal amyloid plaques and cerebral amyloid angiopathy (CAA). Familial forms of CAA exist in the absence of appreciable parenchymal amyloid pathology. The molecular interplay between parenchymal amyloid plaques and CAA is unclear. Here we investigated how early-onset parenchymal amyloid plaques impact the development of microvascular amyloid in transgenic mice. Tg-5xFAD mice, which produce non-mutated human Aß and develop early-onset parenchymal amyloid plaques, were bred to Tg-SwDI mice, which produce familial CAA mutant human Aß and develop cerebral microvascular amyloid. The bigenic mice presented with an elevated accumulation of Aß and fibrillar amyloid in the brain compared with either single transgenic line. Tg-SwDI/Tg-5xFAD mice were devoid of microvascular amyloid, the prominent pathology of Tg-SwDI mice, but exhibited larger parenchymal amyloid plaques compared with Tg-5xFAD mice. The larger parenchymal amyloid deposits were associated with a higher loss of cortical neurons and elevated activated microglia in the bigenic Tg-SwDI/Tg-5xFAD mice. The periphery of parenchymal amyloid plaques was largely composed of CAA mutant Aß. Non-mutated Aß fibril seeds promoted CAA mutant Aß fibril formation in vitro. Further, intrahippocampal administration of biotin-labeled CAA mutant Aß peptide accumulated on and adjacent to pre-existing parenchymal amyloid plaques in Tg-5xFAD mice. These findings indicate that early-onset parenchymal amyloid plaques can serve as a scaffold to capture CAA mutant Aß peptides and prevent their accumulation in cerebral microvessels.

Cerebral microvascular rather than parenchymal amyloid-ß protein pathology promotes early cognitive impairment in transgenic mice.

Alzheimer's disease (AD) is an age-dependent neurodegenerative condition that causes a progressive decline in cognitive function. Accumulation of amyloid ß-protein (Aß) in the brain is a prominent feature of AD and related disorders. However, the levels of Aß accumulation alone are not a reliable predictor of cognitive deficits. Aß accumulates in AD brain in the form of parenchymal amyloid plaques and cerebral vascular deposits. Although both types of lesions can contribute to cognitive decline, their temporal impact remains unclear. Moreover, cerebral microvascular pathology is identified as an early driver of cognitive impairment. Here for the first time, we compared two transgenic mouse strains, Tg-5xFAD and Tg-SwDI, which exhibit similar onset and anatomical accumulation of Aß, but with distinct parenchymal and microvascular compartmental deposition, respectively, to assess their impact on cognitive impairment. Cohorts of each line were tested at 3 and 6 months of age to assess the relationship between spatial working memory performance and quantitative pathology. At 3 months of age, Tg-SwDI mice with onset of cerebral microvascular amyloid were behaviorally impaired, while the Tg-5xFAD, which had disproportionately higher levels of total Aß, soluble oligomeric Aß, and parenchymal amyloid were not. However, at 6 months of age, behavioral deficits for both groups of transgenic mice were evident, as the levels of Aß pathologies in the Tg-5xFAD accumulated to extremely high amounts. The present findings suggest early-onset cerebral microvascular amyloid deposition, that precedes high parenchymal levels of Aß, may be an important early factor in the development of cognitive deficits.

Human apolipoprotein E2 promotes parenchymal amyloid deposition and neuronal loss in vasculotropic mutant amyloid-ß protein Tg-SwDI mice.

Human apolipoprotein (ApoE) genotype influences the development of Alzheimer's disease and cerebral amyloid angiopathy (CAA), where the ε4 allele increases and the ε2 allele decreases the risk for developing disease. Specific mutations within the amyloid-ß (Aß) peptide have been identified that cause familial forms of CAA. However, the influence of APOE genotype on accumulation of CAA mutant Aß in brain is not well understood. Earlier, we showed that human ApoE4 redistributes fibrillar amyloid deposition from the cerebral microvasculature to parenchymal plaques in Tg-SwDI mice, a model that accumulates human Dutch/Iowa (E22Q/D23N) CAA mutant Aß in brain (Xu et al., J Neurosci 28, 5312-5320, 2008). Human ApoE2 can reduce Aß pathology in transgenic models of parenchymal plaques. Here we determined if human ApoE2 can influence the location and severity of amyloid pathology in Tg-SwDI mice. Comparing Tg-SwDI mice bred onto a human APOE2/2 or human APOE4/4 background, we found there was no change in the brain levels of total Aß(40) and Aß(42) compared to mice on the endogenous mouse APOE background. In Tg-SwDI mice on either human APOE background, there was a similarly strong reduction in the levels of microvascular CAA and emergence of extensive parenchymal plaque amyloid. In both Tg-SwDI-hAPOE2/2 and Tg-SwDI-hAPOE4/4 mice, the distribution of ApoE proteins and neuronal loss were associated with parenchymal amyloid plaques. These findings suggest that compared with human ApoE4, human ApoE2 does not beneficially influence the quantitative or spatial accumulation of human Dutch/Iowa CAA mutant amyloid or associated pathology in transgenic mice.

Conformational differences between two amyloid ß oligomers of similar size and dissimilar toxicity.

Several protein conformational disorders (Parkinson and prion diseases) are linked to aberrant folding of proteins into prefibrillar oligomers and amyloid fibrils. Although prefibrillar oligomers are more toxic than their fibrillar counterparts, it is difficult to decouple the origin of their dissimilar toxicity because oligomers and fibrils differ both in terms of structure and size. Here we report the characterization of two oligomers of the 42-residue amyloid ß (Aß42) peptide associated with Alzheimer disease that possess similar size and dissimilar toxicity. We find that Aß42 spontaneously forms prefibrillar oligomers at Aß concentrations below 30 µm in the absence of agitation, whereas higher Aß concentrations lead to rapid formation of fibrils. Interestingly, Aß prefibrillar oligomers do not convert into fibrils under quiescent assembly conditions but instead convert into a second type of oligomer with size and morphology similar to those of Aß prefibrillar oligomers. Strikingly, this alternative Aß oligomer is non-toxic to mammalian cells relative to Aß monomer. We find that two hydrophobic peptide segments within Aß (residues 16-22 and 30-42) are more solvent-exposed in the more toxic Aß oligomer. The less toxic oligomer is devoid of ß-sheet structure, insoluble, and non-immunoreactive with oligomer- and fibril-specific antibodies. Moreover, the less toxic oligomer is incapable of disrupting lipid bilayers, in contrast to its more toxic oligomeric counterpart. Our results suggest that the ability of non-fibrillar Aß oligomers to interact with and disrupt cellular membranes is linked to the degree of solvent exposure of their central and C-terminal hydrophobic peptide segments.

N-terminal domain of myelin basic protein inhibits amyloid beta-protein fibril assembly.

Accumulation of amyloid ß-protein (Aß) into brain parenchymal plaques and the cerebral vasculature is a pathological feature of Alzheimer disease and related disorders. Aß peptides readily form ß-sheet-containing oligomers and fibrils. Previously, we reported a strong interaction between myelin basic protein (MBP) and Aß peptides that resulted in potent inhibition of fibril assembly (Hoos, M. D., Ahmed, M., Smith, S. O., and Van Nostrand, W. E. (2007) J. Biol. Chem. 282, 9952-9961; Hoos, M. D., Ahmed, M., Smith, S. O., and Van Nostrand, W. E. (2009) Biochemistry 48, 4720-4727). MBP is recognized as a highly post-translationally modified protein. In the present study, we demonstrate that human MBP purified from either brain or a bacterial recombinant expression system comparably bound to Aß and inhibited Aß fibril assembly indicating that post-translational modifications are not required for this activity. We also show that purified mouse brain MBP and recombinantly expressed mouse MBP similarly inhibited Aß fibril formation. Through a combination of biochemical and ultrastructural techniques, we demonstrate that the binding site for Aß is located in the N-terminal 64 amino acids of MBP and that a stable peptide (MBP1) comprising these residues was sufficient to inhibit Aß fibrillogenesis. Under conditions comparable with those used for Aß, the fibrillar assembly of amylin, another amyloidogenic peptide, was not inhibited by MBP1, although MBP1 still bound to it. This observation suggests that the potent inhibitory effect of MBP on fibril formation is not general to amyloidogenic peptides. Finally, MBP1 could prevent the cytotoxic effects of Aß in primary cortical neurons. Our findings suggest that inhibition of Aß fibril assembly by MBP, mediated through its N-terminal domain, could play a role in influencing amyloid formation in Alzheimer disease brain and corresponding mouse models.

Structural conversion of neurotoxic amyloid-beta(1-42) oligomers to fibrils.

The amyloid-beta(1-42) (Abeta42) peptide rapidly aggregates to form oligomers, protofibils and fibrils en route to the deposition of amyloid plaques associated with Alzheimer's disease. We show that low-temperature and low-salt conditions can stabilize disc-shaped oligomers (pentamers) that are substantially more toxic to mouse cortical neurons than protofibrils and fibrils. We find that these neurotoxic oligomers do not have the beta-sheet structure characteristic of fibrils. Rather, the oligomers are composed of loosely aggregated strands whose C termini are protected from solvent exchange and which have a turn conformation, placing Phe19 in contact with Leu34. On the basis of NMR spectroscopy, we show that the structural conversion of Abeta42 oligomers to fibrils involves the association of these loosely aggregated strands into beta-sheets whose individual beta-strands polymerize in a parallel, in-register orientation and are staggered at an intermonomer contact between Gln15 and Gly37.

Amyloid reduction by amyloid-beta vaccination also reduces mouse tau pathology and protects from neuron loss in two mouse models of Alzheimer's disease.

Shown to lower amyloid deposits and improve cognition in APP transgenic mouse models, immunotherapy appears to be a promising approach for the treatment of Alzheimer's disease (AD). Due to limitations in available animal models, however, it has been unclear whether targeting amyloid is sufficient to reduce the other pathological hallmarks of AD-namely, accumulation of pathological, nonmutated tau and neuronal loss. We have now developed two transgenic mouse models (APPSw/NOS2(-/-) and APPSwDI/NOS2(-/-)) that more closely model AD. These mice show amyloid pathology, hyperphosphorylated and aggregated normal mouse tau, significant neuron loss, and cognitive deficits. A beta(1-42) or KLH vaccinations were started in these animals at 12 months, when disease progression and cognitive decline are well underway, and continued for 4 months. Vaccinated APPSwDI/NOS2(-/-) mice, which have predominantly vascular amyloid pathology, showed a 30% decrease in brain A beta and a 35-45% reduction in hyperphosphorylated tau. Neuron loss and cognitive deficits were partially reduced. In APPSw/NOS2(-/-) vaccinated mice, brain A beta was reduced by 65-85% and hyperphosphorylated tau by 50-60%. Furthermore, neurons were completely protected, and memory deficits were fully reversed. Microhemorrhage was observed in all vaccinated APPSw/NOS2(-/-) mice and remains a significant adverse event associated with immunotherapy. Nevertheless, by providing evidence that reducing amyloid pathology also reduces nonmutant tau pathology and blocks neuron loss, these data support the development of amyloid-lowering therapies for disease-modifying treatment of AD.