Iowa variant of familial Alzheimer's disease: accumulation of posttranslationally modified AbetaD23N in parenchymal and cerebrovascular amyloid deposits.

Mutations within the amyloid-beta (Abeta) sequence, especially those clustered at residues 21-23, which are linked to early onset familial Alzheimer's disease (AD), are primarily associated with cerebral amyloid angiopathy (CAA). The basis for this predominant vascular amyloid burden and the differential clinical phenotypes of cerebral hemorrhage/stroke in some patients and dementia in others remain unknown. The AbetaD23N Iowa mutation is associated with progressive AD-like dementia, often without clinically manifested intracerebral hemorrhage. Neuropathologically, the disease is characterized by predominant preamyloid deposits, severe CAA, and abundant neurofibrillary tangles in the presence of remarkably few mature plaques. Biochemical analyses using a combination of immunoprecipitation, mass spectrometry, amino acid sequence, and Western blot analysis performed after sequential tissue extractions to separately isolate soluble components, preamyloid, and fibrillar amyloid species indicated that the Iowa deposits are complex mixtures of mutated and nonmutated Abeta molecules. These molecules exhibited various degrees of solubility, were highly heterogeneous at both the N- and C-termini, and showed partial aspartate isomerization at positions 1, 7, and 23. This collection of Abeta species-the Iowa brain Abeta peptidome-contained clear imprints of amyloid clearance mechanisms yet highlighted the unique neuropathological features shared by a non-Abeta cerebral amyloidosis, familial Danish dementia, in which neurofibrillary tangles coexist with extensive pre-amyloid deposition in the virtual absence of fibrillar lesions. These data therefore challenge the importance of neuritic plaques as the sole contributors for the development of dementia.

RAGE mediates amyloid-beta peptide transport across the blood-brain barrier and accumulation in brain.

Amyloid-beta peptide (Abeta) interacts with the vasculature to influence Abeta levels in the brain and cerebral blood flow, providing a means of amplifying the Abeta-induced cellular stress underlying neuronal dysfunction and dementia. Systemic Abeta infusion and studies in genetically manipulated mice show that Abeta interaction with receptor for advanced glycation end products (RAGE)-bearing cells in the vessel wall results in transport of Abeta across the blood-brain barrier (BBB) and expression of proinflammatory cytokines and endothelin-1 (ET-1), the latter mediating Abeta-induced vasoconstriction. Inhibition of RAGE-ligand interaction suppresses accumulation of Abeta in brain parenchyma in a mouse transgenic model. These findings suggest that vascular RAGE is a target for inhibiting pathogenic consequences of Abeta-vascular interactions, including development of cerebral amyloidosis.

CEREBRAL AMYLOID ANGIOPATHY AND ALZHEIMER'S DISEASE.

Cerebral amyloid angiopathy (CAA) is increasingly recognized as a major contributor of Alzheimer's disease (AD) pathogenesis. To date, vascular deposits and not parenchymal plaques appear more sensitive predictors of dementia. Amyloid deposition in and around cerebral blood vessels plays a central role in a series of response mechanisms that lead to changes in the integrity of the blood-brain barrier, extravasations of plasma proteins, edema formation, release of inflammatory mediators and matrix metalloproteases which, in turn, produce partial degradation of the basal lamina with the potential to develop hemorrhagic complications. The progressive buildup of amyloid deposits in and around blood vessels chronically limits blood supply and causes focal deprivation of oxygen, triggering a secondary cascade of metabolic events several of which involve the generation of nitrogen and oxygen free radicals with consequent oxidative stress and cell toxicity. Many aspects of CAA in early- and late-onset AD -the special preference of Aß40 to deposit in the vessel walls, the favored vascular compromise associated with many Aß genetic variants, the puzzling observation that some of these vasculotropic variants solely manifest with recurrent hemorrhagic episodes while others are mainly associated with dementia- await clarification. Non-Aß cerebral amyloidoses reinforce the viewpoint that plaque burden is not indicative of dementia while highlighting the relevance of nonfibrillar lesions and vascular involvement in the disease pathogenesis. The lessons learned from the comparative study of Aß and non-Aß cerebral amyloidosis provide new avenues and alternative models to study the role of amyloid in the molecular basis of neurodegeneration.

PYROGLUTAMATE FORMATION AT THE N-TERMINI OF ABRI MOLECULES IN FAMILIAL BRITISH DEMENTIA IS NOT RESTRICTED TO THE CENTRAL NERVOUS SYSTEM.

Amyloid molecules harboring pyroglutamate (pGlu) residue at the N-termini are considered to be important for the development of cerebral amyloidosis such as Alzheimer's disease and thought to be either spontaneously generated or being catalyzed by glutaminyl cyclase. Familial British dementia (FBD) is an autosomal dominant form of dementia neuropathologically characterized by parenchymal amyloid and preamyloid deposits, extensive cerebral amyloid angiopathy, and neurofibrillary tangles. FBD is caused by a stop to Arg mutation in the BRI2 gene, generating de novo created amyloid molecule ABri which accumulates in FBD brains but is not present in the normal population. Soluble ABri molecules present in the circulation of carriers of the BRI2 mutation are 34 amino acids long exclusively harboring Glu residue at the N-termini (ABri1-34E), whereas water- and formic acid-soluble ABri molecules extracted from FBD brains have abundant ABri species bearing pGlu residue (ABri1-34pE), suggesting that pyroglutamate formation occurs at the site of deposition. In order to further clarify the mechanism (s) of ABri deposition, we studied whether pyroglutamate formation indeed occurs outside the central nervous system taking advantage that FBD is also a systemic amyloidosis. Soluble and fibrillar ABri molecules extracted from systemic organs and analyzed biochemically using a combination of immunoprecipitation, mass spectrometry, and western blot analysis were oligomeric in size and contained a large proportion of ABri1-34pE. The data indicate that pyroglutamate formation at the N-termini of ABri molecules is an early step in the process of FBD amyloid deposition, and its formation is not restricted to the central nervous system.

Genetics and molecular pathogenesis of sporadic and hereditary cerebral amyloid angiopathies.

In cerebral amyloid angiopathy (CAA), amyloid fibrils deposit in walls of arteries, arterioles and less frequently in veins and capillaries of the central nervous system, often resulting in secondary degenerative vascular changes. Although the amyloid-beta peptide is by far the commonest amyloid subunit implicated in sporadic and rarely in hereditary forms of CAA, a number of other proteins may also be involved in rare familial diseases in which CAA is also a characteristic morphological feature. These latter proteins include the ABri and ADan subunits in familial British dementia and familial Danish dementia, respectively, which are also known under the umbrella term BRI2 gene-related dementias, variant cystatin C in hereditary cerebral haemorrhage with amyloidosis of Icelandic-type, variant transthyretins in meningo-vascular amyloidosis, disease-associated prion protein (PrP(Sc)) in hereditary prion disease with premature stop codon mutations and mutated gelsolin (AGel) in familial amyloidosis of Finnish type. In this review, the characteristic morphological features of the different CAAs is described and the implication of the biochemical, genetic and transgenic animal data for the pathogenesis of CAA is discussed.

Novel prion protein conformation and glycotype in Creutzfeldt-Jakob disease.

OBJECTIVE: To describe a novel molecular and pathological phenotype of Creutzfeldt-Jakob disease. Patient A 69-year-old woman with behavioral and personality changes followed by rapidly evolving dementia. RESULTS: Postmortem examination of the brain showed intracellular prion protein deposition and axonal swellings filled with amyloid fibrils. Biochemical analysis of the pathological prion protein disclosed a previously unrecognized PrP(Sc) tertiary structure lacking diglycosylated species. Genetic analysis revealed a wild-type prion protein gene. The prion agent responsible for this atypical phenotype was successfully passaged to bank voles. CONCLUSION: To our knowledge, our results define a new human prion disorder characterized by intracellular accumulation of a novel type of pathological prion protein.

A primer of amyloid nomenclature.

The increasing knowledge of the exact biochemical nature of the localized and systemic amyloid disorders has made a logical and easily understood nomenclature absolutely necessary. Such a nomenclature, biochemically based, has been used for several years but the current literature is still mixed up with many clinical and histochemically based designations from the time when amyloid in general was poorly understood. All amyloid types are today preferably named by their major fibril protein. This makes a simple and rational nomenclature for the increasing number of amyloid disorders known in humans and animals.

Preferential association of serum amyloid P component with fibrillar deposits in familial British and Danish dementias: similarities with Alzheimer's disease.

Two hereditary forms of cerebrovascular amyloidosis, familial British and Danish dementias (FBD and FDD), share striking similarities with Alzheimer's disease (AD) despite structural differences among their amyloid subunits (ABri in FBD, ADan in FDD, and Abeta in AD). Neuropathological lesions in these disorders include neurofibrillary tangles, parenchymal amyloid and pre-amyloid deposits and overwhelming cerebral amyloid angiopathy co-localizing with reactive microglia and multiple amyloid associated proteins including activation products of the complement cascade. Immunohistochemical analysis of FBD and FDD brain lesions unveiled the presence of serum amyloid P-component (SAP) primarily associated with thioflavin positive amyloid deposits in spite of the significant pre-amyloid burden existing in both disorders. Using affinity chromatography and ELISA binding assays we demonstrated specific, calcium-dependent, saturable, high affinity binding interactions between SAP and ABri/ADan peptides, with dissociation constant values in the sub-nanomolar range and within the same order of magnitude as those resulting from the interaction of SAP with Alzheimer's Abeta1-40 and Abeta1-42. The preferential association of SAP with fibrillar amyloid lesions and not with non-fibrillar pre-amyloid deposits is puzzling, suggesting that SAP modulates the assembly and stability of the final fibril rather than participating in the early steps of protein misfolding and oligomerization.

Plaque-associated overexpression of insulin-degrading enzyme in the cerebral cortex of aged transgenic tg2576 mice with Alzheimer pathology.

It was proposed that insulin-degrading enzyme (IDE) participates in the clearance of amyloid beta (Abeta) in the brain, and its low expression or activity may be relevant for the progression of Alzheimer disease. We performed a longitudinal study of brain level, activity, and distribution of IDE in transgenic mice (Tg2576) expressing the Swedish mutation in human Abeta precursor protein. At 16 months of age, Tg2576 showed a significant 2-fold increment in IDE protein level as compared with 4.5- and 11-month-old animals. The peak of IDE was in synchrony with the sharp accumulation of sodium dodecyl sulfate-soluble Abeta and massive Abeta deposition into plaques. At this stage, IDE appeared surrounding Abeta fibrillar deposits within glial fibrillar acidic protein-positive astrocytes, suggesting that it was locally overexpressed during the Abeta-mediated inflammation process. When primary astrocytes were exposed to fibrillar Abeta in vitro, IDE protein level increased as compared with control, and this effect was reduced by the addition of U0126, a specific inhibitor of the ERK1/2 mitogen-activated protein kinase cascade. We propose that in Tg2576 mice and in contrast to its behavior in Alzheimer brains, active IDE increases with age around plaques as a component of astrocyte activation as a result of Abeta-triggered inflammation.

Studies on the first described Alzheimer's disease amyloid beta mutant, the Dutch variant.

Amyloid protein deposited in cerebral vessel walls and diffuse plaques of patients with hereditary cerebral hemorrhage with amyloidosis, Dutch type (HCHWA-D), is similar to the 40-42 residues amyloid beta (Abeta) in vessel walls and senile plaques in brains of patients with Alzheimer's disease (AD), Down's syndrome, and familial and sporadic cerebral amyloid angiopathy (CAA). In 1990 we sequenced the amyloid beta-protein precursor (AbetaPP) gene from HCHWA-D patients revealing a single mutation that results in an amino acid substitution, Abeta E22Q. Subsequent identification of additional mutations in the AbetaPP gene in familial AD (FAD) pedigrees revealed that whereas substitutions in the middle of Abeta, residues Abeta21-23, are predominantly vasculotropic, those found amino- or carboxyl-terminal to the Abeta sequence within AbetaPP enhance amyloid parenchymal plaque deposition. Studies of transfected cells showed that substitutions amino- or carboxyl-terminal to Abeta lead to either greater Abeta production or to enhanced secretion of the more hydrophobic thus more fibrillogenic Abeta1-42. Substitutions in the center of Abeta facilitate rapid aggregation and fibrillization, slower clearance across the blood-brain barrier and perivascular drainage to the systemic circulation, possibly higher resistance to proteolysis, and enhanced toxicity towards endothelial and smooth muscle cells. However, most AD patients have no genetic defects in AbetaPP, indicating that other factors may alter Abeta production, conformation, and/or clearance initiating the disease process.

Clusterin and Alzheimer's disease.

Clusterin (apolipoprotein J) is a ubiquitous multifunctional glycoprotein with the capability to interact with a broad spectrum of molecules, among them the Alzheimer's Abeta peptide. Due to its co-localization with fibrillar deposits in systemic and cerebral amyloid disorders, clusterin is also considered an amyloid-associated protein. Although no genuine function has been attributed to this protein so far, it has been implicated in a wide variety of physiological and pathological processes, a role that may vary according to the protein maturation, sub-cellular localization, and the presence of certain tissue- or cell-specific factors. This review focuses on the importance of clusterin in health and disease conditions, with particular emphasis in its role in Abeta amyloidosis and other disorders of protein folding.

An attenuated immune response is sufficient to enhance cognition in an Alzheimer's disease mouse model immunized with amyloid-beta derivatives.

Immunization with amyloid-beta (Abeta) 1-42 has been shown to reduce amyloid burden and improve cognition in Alzheimer's disease (AD) model mice. In a human trial, possible cognitive benefit was found but in association with significant toxicity in a minority of patients. We proposed that immunization with nonfibrillogenic Abeta derivatives is much less likely to produce toxicity and have previously shown that one such derivative (K6Abeta1-30) can reduce amyloid burden in mice to a similar extent as Abeta1-42. Here, we immunized AD model mice (Tg2576) with Abeta1-30[E18E19] or with K6Abeta1-30[E18E19]. These peptides were designed to be nontoxic and to produce less T-cell response, which has been linked to toxicity. K6Abeta1-30[E18E19] induced primarily an IgM response, whereas Abeta1-30[E18E19] induced an IgG titer that was lower than previously seen with K6Abeta1-30 or Abeta1-42. However, both treated animal groups performed better than Tg controls in the radial arm maze. Amyloid burden was similar in Abeta1-30[E18E19]-vaccinated mice and their Tg controls, whereas the number of medium and small sized plaques was reduced (29-34%) in K6Abeta1-30[E18E19]-immunized mice compared with Tg controls. Amyloid burden in these mice correlated inversely with plasma IgM levels. The cognitive benefit and amyloid reduction in the K6Abeta1-30[E18E19]-vaccinated mice are likely to be related to peripheral clearance of Abeta, because IgM does not cross the blood-brain barrier because of its large size. Our results indicate that these nontoxic Abeta derivatives produce an attenuated antibody response, which is less likely to be associated with negative side effects while having cognitive benefits.

Immunological and anti-chaperone therapeutic approaches for Alzheimer disease.

Alzheimer disease (AD) is the most common cause of dementia. Currently available therapies only provide symptomatic relief. A number of therapeutic approaches are under development that aim to increase the clearance of brain Abeta peptides. These include immune mediated clearance of Abeta and the inhibition of the interaction between Abeta and its pathological chaperones. Both active and passive immunization has been shown to have robust effects in transgenic mouse models of AD on amyloid reduction and behavioral improvements. However, a human trial of active immunization has been associated with significant toxicity in a minority of patients. New generation vaccines are being developed which likely will reduce the potential for cell-mediated toxicity. In addition, the recent development of anti-chaperone therapy opens a new therapeutic avenue which is unlikely to be associated with toxicity.

Infectivity of amyloid diseases.

To date, transmissibility of amyloid diseases has not been thoroughly investigated. Although only some of these conformational disorders are considered infectious, all amyloid diseases could be infectious under certain conditions. For transmissibility, endogenous expression of an amyloidogenic peptide required, as well as the presence of an inoculum that is rich in amyloid fibrils and/or their precursors. Notably, administration of one type of amyloid might result in deposition of a different amyloid. Various cofactors could be essential for transmission - some might chaperone the amyloid peptides and/or fibrils, thereby directly facilitating their propagation; others might indirectly stabilize and/or increase levels of conformers with a high beta-sheet content. It is possible that these chaperones are induced by inflammation, which itself can lead to secondary amyloidosis. Thus, amyloid-related therapeutic approaches should not be based on administration of amyloidogenic peptides in conjunction with an inflammatory stimulus, such as in a recently halted clinical trial for Alzheimer's disease.

Amyloid: toward terminology clarification. Report from the Nomenclature Committee of the International Society of Amyloidosis.

The modern nomenclature of amyloidosis now includes 25 human and 8 animal fibril proteins. To be included in the list, the protein has to be a major fibril protein in extracellular deposits, which have the characteristics of amyloid, including affinity for Congo red with resulting green birefringence. Synthetic fibrils with amyloid properties are best named 'amyloid-like'. With increasing knowledge, however, the borders between different protein aggregates tend to become less sharp.

Axonal transport of British and Danish amyloid peptides via secretory vesicles.

The ABri and ADan amyloid peptides deposited in familial British and Danish neurodegenerative disorders are generated by processing mutant forms of the precursor protein BRI2. Although the pathogenic process that leads to deposition of amyloid in the brains of patients has been studied extensively, the cellular processes and normal function of the precursor protein did not receive much attention. We observed in a variety of transfected cell lines the presence of two independent proteolytic processing events. In addition to the previously described cleavage, which results in the production of carboxyl-terminal approximately 3 kDa wild-type peptide or approximately 4 kDa ABri or ADan peptides, we describe a novel amino-terminal cleavage site within BRI2. Both cleavages occur within the cis- or medial-Golgi. Following cleavage, the BRI2-derived carboxyl-terminal peptides are transported via a regulated secretory pathway into secretory vesicles in neuronal cells. Worth noting is that expression of wild-type British or Danish mutants of BRI2, in mouse neuroblastoma N2a cells that do not express endogenous BRI2, induces elongation of neurites, which suggests a role for this protein in differentiation of neuronal cells.

Diversity of senile plaques in Alzheimer's disease as revealed by a new monoclonal antibody that recognizes an internal sequence of the Abeta peptide.

In order to have more specific tools available to approach amyloidogenesis in Alzheimer's disease (AD), we have produced several polyclonal and monoclonal antibodies that recognize specific sequences of the amyloid beta (Abeta) peptide. Here we present results that demonstrate that our monoclonal antibody EM5 recognizes an internal sequence (residues 11-16) of the Abeta peptide. This strategic localization of the epitope allowed us to employ this antibody, together with two previously reported polyclonal antibodies (EM2 and EM3, specific for AbetaX-40 and AbetaX-42, respectively), in an immunohistochemical study aimed at exploring the differential distribution of longer (AbetaX-40/42) and shorter (Abeta17-X) peptides along the various types of amyloid deposits of AD. This antibody panel was used in six AD brains, on sections from associative neocortex, striatum and cerebellar cortex. Single and double immunostaining revealed specific staining of vascular amyloid deposits and neuritic plaques by EM5 antibody, with high co-localization of EM2. Our results suggest that EM5 antibody recognizes pathogenic forms of Abeta deposits (amyloid angiopathy and neuritic plaques) and reveals the existence of a subset of plaques with a profile similar to vascular deposits. Additionally, our results show that diffuse plaques in AD brains may contain Abeta17-X peptides as its principal component. EM5 may be a useful tool in research both on human and transgenic mice tissue that may aid in the study of molecular heterogeneity of plaques in AD.

Purification of human wild-type or variant cystatin C from conditioned media of transfected cells.

The characterization of proteins in their native state is essential for the understanding of patho-genic isoforms. A variant of the cysteine protease inhibitor cystatin C is the major constituent of the amyloid deposited in the cerebral vasculature of patients with the Icelandic form of hereditary cerebral hemorrhage with amyloidosis (HCHWA-I). In order to study the nature of the bio-physical changes owing to the Leu68Gln substitution in cystatin C, we have developed a purification procedure of human cystatin C in its native state. The protein is isolated from media of stably transfected tissue culture cells using physiological conditions that preclude protein denaturation. The importance of mild purification conditions is underscored by the finding that denaturation of the wild-type and variant proteins facilitates a similar folding of both molecules, diminishing their differences in structure and biophysical properties. Following native purification conditions, variant cystatin C has a distinct structure compared to the wild-type protein.

Clearance systems in the brain-implications for Alzheimer disease.

Accumulation of toxic protein aggregates-amyloid-ß (Aß) plaques and hyperphosphorylated tau tangles-is the pathological hallmark of Alzheimer disease (AD). Aß accumulation has been hypothesized to result from an imbalance between Aß production and clearance; indeed, Aß clearance seems to be impaired in both early and late forms of AD. To develop efficient strategies to slow down or halt AD, it is critical to understand how Aß is cleared from the brain. Extracellular Aß deposits can be removed from the brain by various clearance systems, most importantly, transport across the blood-brain barrier. Findings from the past few years suggest that astroglial-mediated interstitial fluid (ISF) bulk flow, known as the glymphatic system, might contribute to a larger portion of extracellular Aß (eAß) clearance than previously thought. The meningeal lymphatic vessels, discovered in 2015, might provide another clearance route. Because these clearance systems act together to drive eAß from the brain, any alteration to their function could contribute to AD. An understanding of Aß clearance might provide strategies to reduce excess Aß deposits and delay, or even prevent, disease onset. In this Review, we describe the clearance systems of the brain as they relate to proteins implicated in AD pathology, with the main focus on Aß.

Amyloidosis and Alzheimer's disease.

Alzheimer's disease (AD) is the most frequent type of amyloidosis in humans and the commonest form of dementia. Extracellular Abeta amyloid deposits in the form of amyloid plaques and cerebral amyloid angiopathy as well as intraneuronal neurofibrillary tangles co-exist in the brain parenchyma of AD patients, the cognitive areas being the most severely affected. This review focuses on the potential role of amyloid in the development of neurodegeneration and presents studies of AD and other unrelated inherited dementia syndromes associated with neuronal loss and amyloid deposition in the brain.