An immunohistochemical study of beta-protein in Alzheimer-type dementia brains

Alzheimer's disease, brain immune privilege and memory: a hypothesis

The most distinctive feature of Alzheimer's disease (AD) is the specific degeneration of the neurons involved in memory consolidation, storage, and retrieval. Patients suffering from AD forget basic information about their past, loose linguistic and calculative abilities and communication skills. Thus, understanding the etiology of AD may provide insights into the mechanisms of memory and vice versa. The brain is an immunologically privileged site protected from the organism's immune reactions by the blood-brain barrier (BBB). All risk factors for AD (both cardiovascular and genetic) lead to destruction of the BBB. Evidence emerging from recent literature indicates that AD may have an autoimmune nature associated with BBB impairments. This hypothesis suggests that the process of memory consolidation involves the synthesis of novel macromolecules recognized by the immune system as "non-self" antigens. The objective of this paper is to stimulate new approaches to studies of neural mechanisms underpinning memory consolidation and its breakdown during AD. If the hypothesis on the autoimmune nature of AD is correct, the identification of the putative antigenic macromolecules might be critical to understanding the etiology and prevention of AD, as well as for elucidating cellular mechanisms of learning and memory.

Dense-core plaques in Tg2576 and PSAPP mouse models of Alzheimer's disease are centered on vessel walls

Occurrence of amyloid beta (Abeta) dense-core plaques in the brain is one of the chief hallmarks of Alzheimer's disease (AD). It is not yet clear what factors are responsible for the aggregation of Abeta in the formation of these plaques. Using Tg2576 and PSAPP mouse models that exhibit age-related development of amyloid plaques similar to that observed in AD, we showed that approximately 95% of dense plaques in Tg2576 and approximately 85% in PSAPP mice are centered on vessel walls or in the immediate perivascular regions. Stereoscopy and simulation studies focusing on smaller plaques suggested that vascular associations for both Tg2576 and PSAPP mice were dramatically higher than those encountered by chance alone. We further identified ultrastructural microvascular abnormalities occurring in association with dense plaques. Although occurrence of gross cerebral hemorrhage was infrequent, we identified considerable infiltration of the serum proteins immunoglobulin and albumin in association with dense plaques. Together with earlier evidence of vascular clearance of Abeta, our data suggest that perturbed vascular transport and/or perivascular enrichment of Abeta leads to the formation of vasocentric dense plaques in Tg2576 and PSAPP mouse models of AD.

Dense-core senile plaques in the Flemish variant of Alzheimer's disease are vasocentric

Alzheimer's disease (AD) is characterized by deposition of beta-amyloid (Abeta) in diffuse and senile plaques, and variably in vessels. Mutations in the Abeta-encoding region of the amyloid precursor protein (APP) gene are frequently associated with very severe forms of vascular Abeta deposition, sometimes also accompanied by AD pathology. We earlier described a Flemish APP (A692G) mutation causing a form of early-onset AD with a prominent cerebral amyloid angiopathy and unusually large senile plaque cores. The pathogenic basis of Flemish AD is unknown. By image and mass spectrometric Abeta analyses, we demonstrated that in contrast to other familial AD cases with predominant brain Abeta42, Flemish AD patients predominantly deposit Abeta40. On serial histological section analysis we further showed that the neuritic senile plaques in APP692 brains were centered on vessels. Of a total of 2400 senile plaque cores studied from various brain regions from three patients, 68% enclosed a vessel, whereas the remainder were associated with vascular walls. These observations were confirmed by electron microscopy coupled with examination of serial semi-thin plastic sections, as well as three-dimensional observations by confocal microscopy. Diffuse plaques did not associate with vessels, or with neuritic or inflammatory pathology. Together with earlier in vitro data on APP692, our analyses suggest that the altered biological properties of the Flemish APP and Abeta facilitate progressive Abeta deposition in vascular walls that in addition to causing strokes, initiates formation of dense-core senile plaques in the Flemish variant of AD.

Brain parenchymal and microvascular amyloid in Alzheimer's disease

Brains of patients with Alzheimer disease/senile dementia of Alzheimer type (AD/SDAT) develop a progressive accumulation of amyloid, which deposits primarily in the form of characteristic parenchymal 'plaques' (senile or neuritic plaques/SP's) and as mural deposits in the walls of capillaries and arterioles (cerebral amyloid angiopathy /CAA). A major component of this amyloid is a small and unique peptide composed of 39-43 amino acids, beta/A4, which is cleaved from a much larger precursor protein (APP) that has several isoforms. Brain amyloid can be detected in autopsy or biopsy brain tissue by classical, immunohistochemical and ultrastructural (including immuno-electron microscopic) methods of varying sensitivity and specificity. Beta/A4 amyloid deposition is remarkably variable (e.g. predominantly parenchymal or vascular, or a mixture of parenchymal and vascular) among patients with AD/SDAT. Despite its abundance in the brains of AD/SDAT patients, the precise role of beta/A4 in the pathogenesis of the neurological deficit, neocortical atrophy and progressive synapse loss associated with AD/SDAT has yet to be determined. However, mutations in the gene that encodes APP are clearly associated with familial AD syndromes in which there is significant brain amyloid deposition. CAA, in addition to its association with AD/SDAT, can result in hemorrhagic and (possibly) ischemic forms of stroke. Work with recently developed transgenic mice which express large amounts of beta/A4 in the central nervous system is likely to elucidate mechanisms by which the protein is selectively or deposited in the brain in a parenchymal or microvascular form, and how it contributes to the pathogenesis of neurodegeneration.

Severe cardiovascular disease and Alzheimer's disease: senile plaque formation in cortical areas

The main objectives of this study were to analyze the distribution of senile plaques (SP) and neurofibrillary tangles (NFT) in different cortical areas of patients suffering from severe cardiovascular diseases (CVD) and to compare them with Alzheimer's disease (AD) cases. Forty brains were divided into three groups: an AD group (n = 12), a CVD group (n = 17), and a nonheart disease control group (n = 11). The cortical areas examined were the middle frontal gyrus, the superior and inferior watershed areas, the hippocampal formation with the transentorhinal cortex, and the primary visual cortex. SP and NFT were counted in Bielschowsky-stained sections from all cortical areas and from the hippocampal formation and the transentorhinal cortex, respectively. Patients with severe CVD occupied an intermediate position in the spectrum of SP formation between AD and nonheart disease patients. The CVD group showed a higher prevalence of SP than the control group, and SP counts were significantly larger in the inferior watershed area, dentate gyrus, subiculum, and transentorhinal cortex. The distribution of SP was similar in CVD and AD patients. Control and CVD patients showed no difference regarding the number of NFT. The existence of a possible cardiovascular component in the genesis of SP is discussed.

Demonstration of CRP immunoreactivity in brains of Alzheimer's disease: immunohistochemical study using formic acid pretreatment of tissue sections

C-reactive protein (CRP) is a well-known serum protein which increases during inflammation and deposits in damaged tissues. To establish whether CRP appears in brain of Alzheimer's disease (AD), we immunohistochemically investigated tissue sections which were pretreated with formic acid. Positive immunostaining by anti-CRP antibodies was clearly recognized in senile plaques (SP) in the pretreated tissue sections, with very weak immunostaining in non-treated sections. These findings may suggest that the formation process of SP includes an acute-phase inflammatory state.

Microvascular pathology and vascular basement membrane components in Alzheimer's disease

Several factors have highlighted the vasculature in Alzheimer's disease (AD): Cerebral amyloid angiopathy (CAA) is common, amyloid fibrils emanate from the vascular basement membrane (VBM), and similar forms of beta-amyloid are found in vascular and parenchymal amyloid accumulations. The present article discusses the presence of microvascular pathology in AD. Microangiopathy, in addition to neurofibrillary tangles, senile plaques, and CAA, is a common pathologic hallmark of AD. VBM components are associated with amyloid plaques, and nonamyloidotic alterations of the VBM occur in brain regions susceptible to AD lesions. Also, intra-VBM perivascular cells (traditionally called pericytes), a subset of which share the immunophenotype of microglia and other mononuclear phagocytic system (MPS) cells, have been implicated in vascular alterations and cerebrovascular amyloid deposition. Perivascular and parenchymal MPS cells have access to several sources of the beta-amyloid protein precursor, including platelets, circulating white cells, and neurons. MPS cells would thus be ideally situated to uptake and process the precursor, and deposit beta-amyloid in a fashion analogous to that seen in other forms of systemic and cerebral amyloidoses.

Microvasculature in brain biopsy specimens from patients with Alzheimer's disease: an immunohistochemical and ultrastructural study

Brain biopsy specimens from five patients with Alzheimer's disease obtained in the course of a trial of intracerebroventricular bethanechol were studied by immunohistochemical (antibody to A4 peptide) and ultrastructural techniques, with particular emphasis on the microvessels. In some cases, numbers of A4-immunoreactive lesions (senile plaques) correlated well with numbers of plaques demonstrable by silver stains. Prominent A4-immunoreactive amyloid angiopathy was seen in one patient. The patient with severe cerebral amyloid angiopathy (CAA) showed extensive arteriolar deposition of amyloid filaments with apparent destruction of the media but remarkably intact endothelium. A cell of origin for amyloid filaments was not apparent, although close proximity to smooth muscle cell remnants in the arteriolar media suggested this as one possible cell of origin. Frequent vessels showed medial or adventitial collagen deposition, even when the amount of amyloid was minimal or negligible. Thus relatively severe CAA can exist in the absence of overt endothelial injury, although related studies on this tissue indicate definite abnormalities of the blood-brain barrier. Conversely, destruction of smooth muscle cells and collagen deposition in vessel walls may be the cellular correlates of arteriolar weakening that can lead to CAA-related brain hemorrhage.

Amyloid-P-component-like immunoreactivity in beta/A4-immunoreactive deposits in Alzheimer-type dementia brains

An immunohistochemical study using the mirror-image technique was performed in order to establish whether amyloid P component is involved in the mechanism of deposition of amyloid fibrils in senile plaques (SPs) in Alzheimer-type dementia (ATD). Ninety percent of beta/A4 protein-immunoreactive SPs were also stained by the anti-amyloid P component immunohistochemistry, and this applied to all of the diffuse, primitive and classical types of beta/A4 deposits. These findings may suggest an involvement of amyloid P component in the formation of amyloid fibrils in senile plaques in ATD brains.

Astrocytosis, beta A4-protein deposition and paired helical filament formation in Alzheimer's disease

Alzheimer's disease (AD) temporal cortex (Brodmann area 22) was investigated using stains for astrocytes (GFAP immunohistochemistry), paired helical filaments (Gallyas silver impregnation) and beta A4-protein deposition (beta A4-protein immunohistochemistry). Paired helical filament formation (PHF), as demonstrated by neurofibrillary tangle (NFT) and neuritic plaque (NP) density, was greatest in the pyramidal cell layers III and V. beta A4-protein deposition was greatest in layer III but was present in all neocortical layers. In a regression analysis, astrocyte density was significantly correlated with beta A4-protein deposition (R2 = 0.35, P = 0.02). Astrocyte density was also positively correlated with PHF formation as measured by NFT (R2 = 0.16, P = 0.14) and NP (R2 = 0.25, P = 0.06) density, but this was less significant. This quantitative study demonstrates that both beta A4-protein deposits and PHF formation are positively correlated with the severity of astrocytosis and that damage to the brain parenchyma in temporal cortex in AD may be slightly more strongly associated with beta A4-protein deposition than paired helical filament formation. These results demonstrate the close association of astrocytes with beta A4-protein deposition and neuritic change in AD.

Beta A4 deposition in the temporal cortex of adults with Down's syndrome

The deposition of beta A4 has been quantified in the temporal cortex of 9 adults (4 male, 5 female) with Down's syndrome (DS), mean age (+/- SD) 54.7 +/- 8.8 years (range 41-67 years) at the time of death. Immunostaining with antibodies, raised to different portions of the beta A4 protein, showed a greater number of deposits than were seen with traditional silver impregnation or amyloid stains. Antibody to beta A4(1-10) identified fewer plaques than the antibody to beta A4(12-28), the mean ratio of beta A4(1-10)/beta A4(12-28) plaques being 0.30 +/- 0.10 (mean +/- SD). Morphologically, 'diffuse' and 'neuritic' deposits could be distinguished but there was no significant difference in the beta A4(1-10)/beta A4(12-28) ratio according to plaque morphology, nor did the ratio change with age. Quantitatively, the beta A4(12-28) load in the temporal cortex of DS patients was high, occupying some 14% of the field area, and it was not related to the age of the subject over the range studied. Similarly, the total beta A4(12-28) plaque count was high and not age-related. The proportion of morphological plaque types visualised by the Glees and Marsland silver impregnation and by beta A4(12-28) immunostaining were compared. In both techniques 'diffuse' plaques (D) were predominant in the younger subjects and the proportion of 'neuritic' plaques (N) increased with age. The relative proportions of cored plaques (Cp) and plaque cores (C) did not change significantly with age.(ABSTRACT TRUNCATED AT 250 WORDS)

Association between vascular basement membrane components and the lesions of Alzheimer's disease

A relationship between the microvasculature and Alzheimer senile plaques has been suggested by several lines of evidence. Besides close anatomic and biochemical relationships, both extrinsic (fibronectin) and intrinsic [heparan sulfate proteoglycan (HSPG)] components of the vascular basement membrane (VBM) have been colonized with amyloid plaques. The present study was designed to examine the association between three intrinsic components of the VBM [HSPG, collagen type IV (CIV), and laminin] and the histopathologic lesions of Alzheimer's disease (AD). Six cases with neuropathologically confirmed AD were immunocytochemically labeled for the presence of HSPG, CIV, laminin, or tau-2 (a marker for degenerating neurites) and examined at the light and electron microscopic levels. For light microscopic analyses, sections were counterstained with a fluorescent marker for amyloid. The present study illustrates an involvement of VBM components in the lesions associated with AD. First, we replicate our previous finding that HSPG antibodies immunolabel a subset of neurons; ultrastructural analyses indicate that at least some of these are actually extracellular neurofibrillary tangles. Second, we report that CIV and laminin immunoreaction product was not associated with neurons but did label several perivascular cells with the morphologic characteristics of microglia. Finally, we demonstrate that all three intrinsic VBM components, CIV and laminin as well as HSPG, are localized to senile plaques. Both light and electron microscopic studies indicate that the VBM components are associated with amyloid rather than degenerating neurites. These findings suggest that the VBM or its components may play a role in the AD pathogenetic cascade.

A quantitative study of the coincidence of blood vessels and A4 protein deposits in Alzheimer's disease

The spatial relationship between A4 protein deposits and blood vessels in the brains of 6 elderly cases of Alzheimer's disease has been investigated. Sections were taken from medial temporal cortex and were double immunostained for A4 protein and type IV collagen, the latter being employed as a marker of blood vessels. By comparing the observed area of vessel overlying A4 deposit with that predicted from the product of A4 deposit and blood vessel area fractions it is shown that, contrary to expectations, the likelihood of a vessel co-inciding with an A4 deposit is less than would be expected by chance. It would therefore appear that the previously described positive association between A4 deposits and blood vessels reflects the abundance of A4 and the high vascularity of the cortex rather than any specific correlation between the two features.

Antibodies raised against different portions of A4 protein identify a subset of plaques in Down's syndrome

Antisera were raised to peptides corresponding to residues 1-10 and 12-28 of the published sequence of A4 protein, a 42/43 amino acid long peptide isolated from the brains of patients with Down's syndrome and Alzheimer's disease. Immunohistochemical studies performed on sections of temporal lobe from 12 cases of Down's syndrome showed that the number of senile plaques in the molecular layer of the dentate gyrus which were identified by antibody to A4(1-10) was only 23% (range 11-53%) of that recognised by antibody to A4(12-28). This observation has important consequences for both the diagnosis and the pathogenesis of Down's syndrome and Alzheimer's disease.

Cell membrane changes in brains manifesting senile plaques: an immunohistochemical study of GM1 membranous ganglioside

To investigate structural changes in cell membranes of the Alzheimer-type dementia (ATD) brain, we immunostained for GM1 ganglioside which is a major component of the cell membrane. Our results have shown that astrocytic membranes and senile plaques (SPs) have the same immunoreactivity against the monoclonal anti-ganglioside GM1 antibody. Moreover, the astrocytic processes within the SPs were altered and their abnormal membranes seemed to contribute to the formation of SPs.