Identification of cellular and extracellular sites of amyloid precursor protein extracytoplasmic domain in normal and Alzheimer disease brains

Wasteosomes (corpora amylacea) as a hallmark of chronic glymphatic insufficiency

In different organs and tissues, the lymphatic system serves as a drainage system for interstitial fluid and is useful for removing substances that would otherwise accumulate in the interstitium. In the brain, which lacks lymphatic circulation, the drainage and cleaning function is performed by the glymphatic system, called so for its dependence on glial cells and its similar function to that of the lymphatic system. In the present article, we define glymphatic insufficiency as the inability of the glymphatic system to properly perform the brain cleaning function. Furthermore, we propose that corpora amylacea or wasteosomes, which are protective structures that act as waste containers and accumulate waste products, are, in fact, a manifestation of chronic glymphatic insufficiency. Assuming this premise, we provide an explanation that coherently links the formation, distribution, structure, and function of these bodies in the human brain. Moreover, we open up new perspectives in the study of the glymphatic system since wasteosomes can provide information about which variables have the greatest impact on the glymphatic system and which diseases occur with chronic glymphatic insufficiency. For example, based on the presence of wasteosomes, it seems that aging, sleep disorders, and cerebrovascular pathologies have the highest impact on the glymphatic system, whereas neurodegenerative diseases have a more limited impact. Furthermore, as glymphatic insufficiency is a risk factor for neurodegenerative diseases, information provided by wasteosomes could help to define the strategies and actions that can prevent glymphatic disruptions, thus limiting the risk of developing neurodegenerative diseases.

Lipopolysaccharide, Identified Using an Antibody and by PAS Staining, Is Associated With Corpora amylacea and White Matter Injury in Alzheimer's Disease and Aging Brain

Corpora amylacea (CA) increase in number and size with aging. Their origins and functions remain unknown. Previously, we found that Alzheimer's disease (AD) brains have more CA in the periventricular white matter (PVWM) compared to aging controls. In addition, CA is associated with neurodegeneration as indicated by colocalization of degraded myelin basic protein (dMBP) with periodic acid-Schiff (PAS), a CA marker. We also found that bacterial lipopolysaccharide is present in aging brains, with more LPS in AD compared with controls. Periodic acid-Schiff staining is used to identify CA by virtue of their high polysaccharide content. Despite the growing knowledge of CA as a contributor to AD pathology, the molecules that contribute to the polysaccharides in CA are not known. Notably, lipopolysaccharides (LPS) are important cell-surface polysaccharides found in all Gram-negative bacteria. However, it is unknown whether PAS could detect LPS, whether the LPS found in aging brains contribute to the polysaccharide found in CA, and whether LPS associate with myelin injury. In this study, we found that aging brains had a myelin deficit zone (MDZ) adjacent to the ventricles in PVWM. The MDZ contained vesicles, most of which were CA. LPS and dMBP levels were higher in AD than in control brains. LPS was colocalized with dMBP in the vesicles/CA, linking white matter injury with a bacterial pro-inflammatory molecule. The vesicles also contained oxidized fibers, C-reactive protein, NG2, and GALC, markers of oligodendrocyte precursor cells (OPCs) and oligodendrocyte cells (OLs), respectively. The vesicles/CA were surrounded by dense astrocyte processes in control and AD brains. LPS was co-localized with CA by double staining of PAS with LPS in aging brains. The relationship of LPS with PAS staining was confirmed by PAS staining of purified LPS on nitrocellulose membranes. These findings reveal that LPS is one of the polysaccharides found in CA which can be stained with PAS. In addition, vesicles/CA are associated with oxidized and damaged myelin. The LPS in these vesicles/CA may have contributed to this oxidative myelin damage and may have contributed to oxidative stress to OPCs and OLs which could impair the ability to repair damaged myelin in AD and control brains.

From corpora amylacea to wasteosomes: History and perspectives

Corpora amylacea (CA) have been described in several human organs and have been associated with ageing and several pathological conditions. Although they were first discovered two centuries ago, their function and significance have not yet been identified. Here, we provide a chronological summary of the findings on CA in various organs and identify their similarities. After collecting and integrating these findings, we propose to consider CA as waste containers created by specific cells, which sequester waste products and foreign products, and assemble them within a glycan structure. The containers are then secreted into the external medium or interstitial spaces, in this latter case subsequently being phagocytosed by macrophages. This proposal explains, among others, why CA are so varied in content, why only some of them contain fibrillary amyloid proteins, why all of them contain glycan structures, why some of them contain neo-epitopes and are phagocytosed, and why they can be intracellular or extracellular structures. Lastly, in order to avoid the ambiguity of the term amyloid (which can indicate starch-like structures but also insoluble fibrillary proteins), we propose renaming CA as "wasteosomes", emphasising the waste products they entrap rather than their misleading amyloid properties.

Systematic review of human post-mortem immunohistochemical studies and bioinformatics analyses unveil the complexity of astrocyte reaction in Alzheimer's disease

AIMS

Reactive astrocytes in Alzheimer's disease (AD) have traditionally been demonstrated by increased glial fibrillary acidic protein (GFAP) immunoreactivity; however, astrocyte reaction is a complex and heterogeneous phenomenon involving multiple astrocyte functions beyond cytoskeletal remodelling. To better understand astrocyte reaction in AD, we conducted a systematic review of astrocyte immunohistochemical studies in post-mortem AD brains followed by bioinformatics analyses on the extracted reactive astrocyte markers.

METHODS

NCBI PubMed, APA PsycInfo and WoS-SCIE databases were interrogated for original English research articles with the search terms 'Alzheimer's disease' AND 'astrocytes.' Bioinformatics analyses included protein-protein interaction network analysis, pathway enrichment, and transcription factor enrichment, as well as comparison with public human -omics datasets.

RESULTS

A total of 306 articles meeting eligibility criteria rendered 196 proteins, most of which were reported to be upregulated in AD vs control brains. Besides cytoskeletal remodelling (e.g., GFAP), bioinformatics analyses revealed a wide range of functional alterations including neuroinflammation (e.g., IL6, MAPK1/3/8 and TNF), oxidative stress and antioxidant defence (e.g., MT1A/2A, NFE2L2, NOS1/2/3, PRDX6 and SOD1/2), lipid metabolism (e.g., APOE, CLU and LRP1), proteostasis (e.g., cathepsins, CRYAB and HSPB1/2/6/8), extracellular matrix organisation (e.g., CD44, MMP1/3 and SERPINA3), and neurotransmission (e.g., CHRNA7, GABA, GLUL, GRM5, MAOB and SLC1A2), among others. CTCF and ESR1 emerged as potential transcription factors driving these changes. Comparison with published -omics datasets validated our results, demonstrating a significant overlap with reported transcriptomic and proteomic changes in AD brains and/or CSF.

CONCLUSIONS

Our systematic review of the neuropathological literature reveals the complexity of AD reactive astrogliosis. We have shared these findings as an online resource available at www.astrocyteatlas.org.

Exploring the elusive composition of corpora amylacea of human brain

Corpora amylacea (CA) are polyglucosan bodies that accumulate in the human brain during ageing and are also present in large numbers in neurodegenerative conditions. Theories regarding the function of CA are regularly updated as new components are described. In previous work, we revealed the presence of some neo-epitopes in CA and the existence of some natural IgM antibodies directed against these neo-epitopes. We also noted that these neo-epitopes and IgMs were the cause of false staining in CA immunohistochemical studies, and disproved the proposed presence of β-amyloid peptides and tau protein in them. Here we extend the list of components erroneously attributed to CA. We show that, contrary to previous descriptions, CA do not contain GFAP, S100, AQP4, NeuN or class III β-tubulin, and we question the presence of other components. Nonetheless, we observe that CA contains ubiquitin and p62, both of them associated with processes of elimination of waste substances, and also glycogen synthase, an indispensable enzyme for polyglucosan formation. In summary, this study shows that it is imperative to continue reviewing previous studies about CA but, more importantly, it shows that the vision of CA as structures involved in protective or cleaning mechanisms remains the most consistent theory.

Synaptophysin Is a Reliable Marker for Axonal Damage

Synaptophysin is an abundant membrane protein of synaptic vesicles. The objective of this study was to determine the utility of identifying synaptophysin accumulations (spheroids/ovoids/bulbs) in CNS white matter as an immunohistochemical marker of axonal damage in demyelinating and neuroinflammatory conditions. We studied the cuprizone toxicity and Theiler’s murine encephalomyelitis virus (TMEV) infection models of demyelination and analyzed CNS tissue from patients with multiple sclerosis (MS). Synaptophysin colocalized with the amyloid precursor protein (APP), a well-known marker of axonal damage. In the cuprizone model, numerous pathological synaptophysin/APP-positive spheroids/ovoids were identified in the corpus callosum at the onset of demyelination; the extent of synaptophysin/APP-positive vesicle aggregates correlated with identified reactive microglia; during late and chronic demyelination, the majority of synaptophysin/APP-positive spheroids/ovoids resolved but a few remained, indicating persistent axonal damage; in the remyelination phase, scattered large synaptophysin/APP-positive bulbs persisted. In the TMEV model, only a few large- to medium-sized synaptophysin/APP-positive bulbs were found in demyelinated areas. In MS patient tissue samples, the bulbs appeared exclusively at the inflammatory edges of lesions. In conclusion, our data suggest that synaptophysin as a reliable marker of axonal damage in the CNS in inflammatory/demyelinating conditions.

New perspectives on corpora amylacea in the human brain

Corpora amylacea are structures of unknown origin and function that appear with age in human brains and are profuse in selected brain areas in several neurodegenerative conditions. They are constituted of glucose polymers and may contain waste elements derived from different cell types. As we previously found on particular polyglucosan bodies in mouse brain, we report here that corpora amylacea present some neo-epitopes that can be recognized by natural antibodies, a certain kind of antibodies that are involved in tissue homeostasis. We hypothesize that corpora amylacea, and probably some other polyglucosan bodies, are waste containers in which deleterious or residual products are isolated to be later eliminated through the action of the innate immune system. In any case, the presence of neo-epitopes on these structures and the existence of natural antibodies directed against them could become a new focal point for the study of both age-related and degenerative brain processes.

Disconnection of the ascending arousal system in traumatic coma

Traumatic coma is associated with disruption of axonal pathways throughout the brain, but the specific pathways involved in humans are incompletely understood. In this study, we used high angular resolution diffusion imaging to map the connectivity of axonal pathways that mediate the 2 critical components of consciousness-arousal and awareness-in the postmortem brain of a 62-year-old woman with acute traumatic coma and in 2 control brains. High angular resolution diffusion imaging tractography guided tissue sampling in the neuropathologic analysis. High angular resolution diffusion imaging tractography demonstrated complete disruption of white matter pathways connecting brainstem arousal nuclei to the basal forebrain and thalamic intralaminar and reticular nuclei. In contrast, hemispheric arousal pathways connecting the thalamus and basal forebrain to the cerebral cortex were only partially disrupted, as were the cortical "awareness pathways." Neuropathologic examination, which used β-amyloid precursor protein and fractin immunomarkers, revealed axonal injury in the white matter of the brainstem and cerebral hemispheres that corresponded to sites of high angular resolution diffusion imaging tract disruption. Axonal injury was also present within the gray matter of the hypothalamus, thalamus, basal forebrain, and cerebral cortex. We propose that traumatic coma may be a subcortical disconnection syndrome related to the disconnection of specific brainstem arousal nuclei from the thalamus and basal forebrain.

Reelin immunoreactivity in neuritic varicosities in the human hippocampal formation of non-demented subjects and Alzheimer's disease patients

BACKGROUND

Reelin and its downstream signaling members are important modulators of actin and microtubule cytoskeleton dynamics, a fundamental prerequisite for proper neurodevelopment and adult neuronal functions. Reductions in Reelin levels have been suggested to contribute to Alzheimer's disease (AD) pathophysiology. We have previously reported an age-related reduction in Reelin levels and its accumulation in neuritic varicosities along the olfactory-limbic tracts, which correlated with cognitive impairments in aged mice. Here, we aimed to investigate whether a similar Reelin-associated neuropathology is observed in the aged human hippocampus and whether it correlated with dementia status.

RESULTS

Our immunohistochemical stainings revealed the presence of N- and C-terminus-containing Reelin fragments in corpora amylacea (CAm), aging-associated spherical deposits. The density of these deposits was increased in the molecular layer of the subiculum of AD compared to non-demented individuals. Despite the limitation of a small sample size, our evaluation of several neuronal and glial markers indicates that the presence of Reelin in CAm might be related to aging-associated impairments in neuronal transport leading to accumulation of organelles and protein metabolites in neuritic varicosities, as previously suggested by the findings and discussions in rodents and primates.

CONCLUSIONS

Our results indicate that aging- and disease-associated changes in Reelin levels and proteolytic processing might play a role in the formation of CAm by altering cytoskeletal dynamics. However, its presence may also be an indicator of a degenerative state of neuritic compartments.

Pathogenesis of cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is the result of the deposition of an amyloidogenic protein in cortical and leptomeningeal vessels. The most common type of CAA is caused by amyloid beta-protein (Abeta), which is particularly associated with Alzheimer's disease (AD). Excessive Abeta-CAA formation can be caused by several mutations in the Abeta precursor protein and presenilin genes. The origin of Abeta in CAA is likely to be neuronal, although cerebrovascular cells or the circulation cannot be excluded as a source. Despite the apparent similarity, the pathogenesis of CAA appears to differ from that of senile plaques in several aspects, including the mechanism of Abeta-induced cellular toxicity, the extent of inflammatory reaction and the role of oxidative stress. Therefore, therapeutic strategies for AD should, at least in part, also target CAA. Moreover, CAA and cerebrovascular disease (CVD) may set a lower threshold for AD-like changes to cause dementia and may even cause dementia on its own, since patients with AD and CAA and/or CVD appear to be more cognitively impaired than patients with only AD. In conclusion, the precise impact of CAA on AD or dementia remains unclear, however, its role may have been underestimated in the past, and more extensive studies of in vitro and in vivo models for CAA will be needed to elucidate the importance of CAA-specific approaches in designing intervention strategies for AD.

S100 proteins in Corpora amylacea from normal human brain

Corpora amylacea (C.A.) also named polyglucosan bodies (P.B.) are one of the hallmarks of normal brain aging. Although their functions are not yet clear, C.A. increase in number in patients suffering from neurodegenerative diseases. C.A. contain 88% of hexoses and 4% of proteins. Most of the proteins in C.A. are aging or stress proteins such as heat shock proteins, ubiquitinated proteins and advanced glycation end products which are also proinflammatory products. Stimulated by the potential role played by some S100 proteins in the inflammatory process which may be triggered in C.A., we investigated, by immunohistochemistry, the presence of different S100 proteins (S100A1, S100A2, S100A3, S100A4, S100A5, S100A6, S100A8, S100A9, S100A12 and S100B) in C.A. from normal human brain. Among the ten S100 proteins analyzed, nine (S100A) were detected in C.A. Three S100 proteins (S100A8, S100A9, S100A12) which are highly expressed in activated macrophages and used as inflammatory markers were detected in C.A. S100A8 was, in addition, found in thick neuronal processes from the pons. One (S100B) could not be found in C.A. although it was highly expressed in astrocytes. In C.A., the staining intensity was estimated by computer-assisted microscopy and gave the following order: S100A1 congruent withS100A8 congruent with S100A9>S100A5> or =S100A4>S100A12>S100A6> S100A2=S100A3. The potential inflammatory role played by S100 proteins in C.A. is discussed.

Corpora-amylacea and the family of polyglucosan diseases

The history, characters, composition and topography of corpora amylacea (CA) in man and the analogous polyglucosan bodies (PGB) in other species are documented, noting particularly the wide variation in the numbers found with age and in neurological disease. Their origins from both neurons and glia and their probable migrations and ultimate fate are discussed. Their presence is also noted in other organs, particularly in the heart. The occurrence in isolated cases of occasional 'massive' usually focal accumulations of similar polyglucosan bodies in association with certain chronic neurological diseases is noted and the specific conditions Adult Polyglucosan body disease and type IV glycogenosis where they are found throughout the nervous system in great excess is discussed. The distinctive differences of CA from the PGB of Lafora body disease and Bielschowsky body disease are emphasised. When considering their functional roles, a parallel is briefly drawn on the one hand between normal CA and the bodies in the polyglucosan disorders and on the other with the lysosomal system and its associated storage diseases. It is suggested that these two systems are complementary ways by which large, metabolically active cells such as neurons, astrocytes, cardiac myocytes and probably many other cell types, dispose of the products of stressful metabolic events throughout life and the continuing underlying process of aging and degradation of long lived cellular proteins. Each debris disposal system must be regulated in its own way and must inevitably, a priori, be heir to metabolic defects that give rise in each to its own set of metabolic disorders.

Spinal corpora amylacea and motor neuron disease: a quantitative study

OBJECTIVE

To test the hypothesis that as there is growing evidence that corpora amylacea, or amyloid bodies, in the CNS are derived primarily from neurons, it might be expected that their numbers in the spinal cord would decline with loss of neurons in motor neuron degeneration as they do in the retina on destruction of ganglion cells by glaucoma.

METHODS

The numbers of corpora amylacea were counted in PAS stained transverse sections of the lumbar cord from 27 patients with motor neuron disease and 21 control subjects of similar age and sex mix. The numbers and sizes of corpora amylacea were determined both in the anterior horn grey matter and in the submeningeal white matter regions in each case.

RESULTS

In both groups the total numbers in the white matter and submeningeal regions ranged from 160 to more than 5000/section and there was minimal significant difference between the two groups. No relation with age was found in this narrow age range. The mean diameters of the corpora amylacea were significantly less in the grey matter of both groups than in the submeningeal regions. However, their densities in the grey matter of the anterior horn were significantly reduced in the spinal cord sections in the motor neuron disease group, but only where few motor neurons remained.

CONCLUSIONS

These findings support the view that corpora amylacea may arise from neurons, and suggest that that there may be two compartments, one mobile and one static, the second most likely remaining in the periphery of the spinal cord for prolonged periods.

Immunohistochemical and in situ analysis of amyloid precursor-like protein-1 and amyloid precursor-like protein-2 expression in Alzheimer disease and aged control brains

Amyloid precursor protein (APP) is a ubiquitously expressed membrane spanning glycoprotein which is endoproteolytically processed to Abeta, a 39-43 amino acid peptide that is the main component of senile plaques in Alzheimer Disease (AD). APP is a member of a highly conserved gene family, including Amyloid Precursor-Like Proteins (APLPs) APLP1 and APLP2. We now characterize APLP1 and APLP2 mRNA and protein expression in AD and aged control brains. Using in situ hybridization in hippocampal tissue from control and AD brain, we show that APLP1 and APLP2 mRNA are expressed primarily in the granule cells of the dentate gyrus, in areas CA1-CA3, and subiculum. Immunohistochemistry reveals staining for both APLP1 and APLP2 in neurons and blood vessels in AD and control cases. In addition, in AD brain, large dystrophic neurites in a subset of senile plaques are conspicuously labeled with APLP1 and APLP2 antibodies. The aged control brains have significantly fewer immunoreactive plaques and dystrophic neurites. The regional, cellular, and subcellular distribution of APLP1 and APLP2 overlap with each other and with APP. These observations support the hypothesis that the members of this family of proteins may perform similar functions.

Relative increase in Alzheimer's disease of soluble forms of cerebral Abeta amyloid protein precursor containing the Kunitz protease inhibitory domain

Although a number of studies have examined amyloid precursor protein (APP) mRNA levels in Alzheimer's disease (AD), no clear consensus has emerged as to whether the levels of transcripts for isoforms containing a Kunitz protease inhibitory (KPI)-encoded region are increased or decreased in AD. Here we compare AD and control brain for the relative amounts of APP protein containing KPI to APP protein lacking this domain. APP protein was purified from the soluble subcellular fraction and Triton X-100 membrane pellet extract of one hemisphere of AD (n = 10), normal (n = 7), and neurological control (n = 5) brains. The amount of KPI-containing APP in the purified protein samples was determined using two independent assay methods. The first assay exploited the inhibitory action of KPI-containing APP on trypsin. The second assay employed reflectance analysis of Western blots. The proportion of KPI-containing forms of APP in the soluble subcellular fraction of AD brains is significantly elevated (p < 0.01) compared with controls. Species containing a KPI domain comprise 32-41 and 76-77% of purified soluble APP from control and AD brains, respectively. For purified membrane-associated APP, 72-77 and 65-82% of control and AD samples, respectively, contain a KPI domain. Since KPI-containing species of APP may be more amyloidogenic (Ho, L., Fukuchi, K., and Yonkin, S. G. (1996) J. Biol. Chem. 271, 30929-30934), our findings support an imbalance of isoforms as one possible mechanism for amyloid deposition in sporadic AD.

Oligodendrocytes express different isoforms of beta-amyloid precursor protein in chemically defined cell culture conditions: in situ hybridization and immunocytochemical detection

The expression of beta-amyloid precursor protein (betaAPP) by astrocytes is well documented; however, data concerning oligodendrocytes remain controversial. The main goal of the present study was to determine whether or not oligodendrocytes in culture constitutively express the different betaAPP isoforms. Oligodendrocytes were cultured in a chemically defined medium that avoids putative effects of unknown serum factors on oligodendrocyte development. We have employed immunocytochemistry and in situ hybridization with antibodies and synthetic oligonucleotides recognizing, respectively, specific protein epitopes and mRNA transcripts of rat betaAPP isoforms. Oligodendrocytes, in both mixed primary cultures in the presence of serum or in secondary cultures in defined medium, were clearly labeled by antibodies directed to different betaAPP sequences. Antibodies against the serine protease inhibitor domain of betaAPP, also strongly labelled oligodendrocytes. Immunohistochemistry and in situ hybridization were combined to determine precisely the expression of different isoforms of betaAPP. In situ hybridization revealed the presence in oligodendrocytes of mRNA transcripts coding not only for betaAPP695 but also for betaAPP770 and betaAPP751. This indicates that betaAPP immunoreactivity found in oligodendrocytes corresponds to constitutive expression of betaAPP. Oligodendrocyte cultured in chemically defined medium are able to express not only betaAPP695 but also betaAPP770, betaAPP751 isoforms containing the Kunitz protease inhibitor domain. Although the role of betaAPP in the pathological processes of Alzheimer's disease (AD) remains unknown, possible disturbances of betaAPP processing and/or synthesis in oligodendrocytes may account for some myelin disorders observed in AD and other senile dementias.

Expression of Kunitz protease inhibitor--containing forms of amyloid beta-protein precursor within vascular thrombi

BACKGROUND

The presence of patent neovessels within vascular occlusions in chronic thromboembolic pulmonary hypertension suggests that local mechanisms exist to regulate the coagulation system. This study investigated the expression of a potent inhibitor of Factor IXa and Factor XIa (ie, protease nexin-2/ amyloid beta-protein precursor, A beta PP) in the organized vascular occlusions harvested from patients with this disease.

METHODS AND RESULTS

Immunohistochemical analysis revealed intense immunoreactivity for A beta PP in the single layer of cells that line the neovessels. A positive signal was also detected by in situ hybridization analysis with the use of a 35S-UTP-labeled antisense riboprobe that recognizes the various alternatively spliced mRNA forms of this molecule. To identify the forms of A beta PP produced within the thrombi, total RNA was extracted from the thrombi, reverse transcribed, and subjected to amplification with the use of the polymerase chain reaction (PCR) and primers that flank the region encoding the alternatively spliced 56-amino acid Kunitz-type protease inhibitor (KPI) domain. The major PCR products consisted of 255 bp and 312 bp and corresponded to transcripts encoding this domain (ie, A beta PP751 and A beta PP770). In situ hybridization analysis with the use of a 35S-UTP-labeled antisense riboprobe complementary to the region encoding the KPI domain confirmed the presence of these mRNA species in nucleated cells lining the neovessels.

CONCLUSIONS

The expression of KPI-containing isoforms of A beta PP in thrombus endothelial cells may represent one mechanism utilized in this disease to shift the local hemostatic balance and preserve regional vessel patency.

Expression and distribution of amyloid precursor protein-like protein-2 in Alzheimer's disease and in normal brain

Amyloid precursor-like protein-2 (APLP-2) belongs to a family of homologous amyloid precursor-like proteins. In the present study we report on the expression and distribution of APLP-2 in fetal and adult human brain and in brains of patients with Alzheimer's disease. We demonstrate that APLP-2 mRNAs encoding isoforms predicted to undergo post-translational modification by chondroitin sulfate glycosaminoglycans are elevated in fetal and aging brains relative to the brains of young adults. Immunocytochemical labeling with APLP-2-specific antibodies demonstrates APLP-2 immunoreactivity in cytoplasmic compartments in neurons and astrocytes, in large part overlapping the distribution of the amyloid precursor protein. In Alzheimer's disease brain, APLP-2 antibodies also label a subset of neuritic plaques. APLP-2 immunoreactivity is particularly conspicuous in large dystrophic neurites that also label with antibodies specific for APP and chromogranin A. In view of the age-dependent increase in levels of chondroitin sulfate glycosaminoglycan-modified forms of APLP-2 in aging brain and the accumulation of APLP-2 in dystrophic presynaptic elements, we suggest that APLP-2 may play roles in neuronal sprouting or in the aggregation, deposition, and/or persistence of beta-amyloid deposits.

Distribution of beta/A4 protein and amyloid precursor protein in hereditary cerebral hemorrhage with amyloidosis-Dutch type and Alzheimer's disease

Brain amyloidosis with abundant beta/A4 protein deposition in plaques and cortical and meningeal vessels is found in Alzheimer's disease (AD) and hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D). In contrast to AD, no neuritic pathology or classical congophilic plaques are found in HCHWA-D. Unlike most AD cases, the congophilic angiopathy in HCHWA-D is very severe. It is still unknown whether beta/A4 deposits in plaques and vessels have the same origin. In this study, we have used frozen cortical tissue of HCHWA-D and AD patients to investigate the beta/A4 amyloid protein and the amyloid precursor protein (APP) in different types of plaques and congophilic angiopathy. Immunohistochemical staining was conducted using antibodies against synthetic beta/A4 proteins and antibodies against APP including MAbP2-1, a monoclonal antibody against purified protease nexin-2, which is the secreted form of APP. In contrast to immunohistochemical studies on formalin-fixed, paraffin-embedded tissue, frozen tissue of HCHWA-D patients revealed a very high number of beta/A4 plaques resembling AD. All plaques were of the diffuse type. Double-staining with MabP2-1 and beta/A4 antisera revealed: 1) the presence of APP immunoreactivity in classical plaques and transitional forms; 2) the absence of APP immunoreactivity in diffuse plaques in HCHWA-D and AD; and 3) pronounced APP immunoreactivity in congophilic vessels in HCHWA-D in contrast to weak APP staining in congophilic vessels in AD. Together these findings suggest that: a) the presence of APP in plaques is related to neuritic changes; b) different processes occur in amyloid formation in plaques and vessels; and c) differences exist between the process of amyloid formation in HCHWA-D and AD.

Monoclonal antibody to beta peptide, recognizing amyloid deposits, neuronal cells and lipofuscin pigments in systemic organs

A monoclonal antibody (AmT-1) produced against synthetic amyloid beta peptide (1-28 residues) was revealed to be reactive with amyloid beta peptide blotted on nitrocellulose membrane, but not with that dissolved in sodium dodecyl sulfate and electrophoresed. AmT-1 immunostained senile plaques of typical, primitive and diffuse type, as well as amyloid deposits in cerebral vessels. It also reacted with neuronal and glial cells of normal and Alzheimer's disease (AD) brains. In addition, AmT-1 was also reactive strongly with lipofuscin pigments of adrenal reticular cells, and weakly with those of eccrine glands and liver cells. A rat neural cell line (PC12h) was reactive with AmT-1. By immunoelectron microscopy, a positive reaction was seen in ribosomes along the rough endoplasmic reticulum of nerve cells and PC12h cells. By immunoprecipitation, AmT1 reacted with a band at 36 kDa in the brain homogenates from Ad patients as well as from normal aged subjects. By immunoblotting analysis, AmT1 reacted with a band at 36 kDa in the cytosolic fraction of PC12 cells, and three bands (12-17 kDa) in the lipopigment fraction of the adrenal gland. These findings suggest that the cerebral amyloid deposits contain substance(s) having an epitope common to neuronal cells and lipofuscin pigments. The possible relationship between cerebral amyloid deposits and lipofuscin pigments in systemic organs is discussed.

Molecular and cellular biology of Alzheimer amyloid

Alzheimer's Disease (AD), a disorder of unknown etiology, is the most common form of adult-onset dementia and is characterized by severe intellectual deterioration. The definitive diagnosis of AD is made by postmortem examination of the brain, which reveals large quantities of neurofibrillary tangles (NFT) and senile plaques within the parenchyma. The NFT are composed of paired helical filaments associated with several cytoskeletal proteins. The primary protein component of senile plaques is beta/A4 amyloid, a 42-43 amino acid peptide derived from a much larger molecule, the amyloid precursor protein (APP). Vascular beta/A4 amyloidosis is also prevalent in the disease. The mechanism by which beta/A4 amyloid accumulates in the AD brain is unknown. Recent research has demonstrated that the precursor molecule, APP, is a transmembrane protein with a large extracytoplasmic domain, a membrane spanning region that includes the portion that gives rise to beta/A4 amyloid, and a short intracytoplasmic domain. The precursor has multiple forms among which are those that differ by a variable length insert within the extracytoplasmic domain. The insert has sequence homology to the family of Kunitz protease inhibitor proteins. Cellular and animal models have been developed to study the nature of APP processing and the biological and behavioral consequences of beta/A4 amyloidosis. The results of such studies indicate that the normal processing of APP involves enzymatic cleavage of the molecule within the beta/A4 amyloid region, thus preventing the accumulation of beta/A4 in the normal brain. The factors leading to abnormal processing of APP, and consequent beta/A4 amyloid accumulation within the AD brain, have yet to be identified. In cell culture, the biological effects associated with beta/A4 amyloid include neurotrophic and neurotoxic activities, while the peptide has also been shown to have dramatic behavioral effects in animal models.

Immunohistochemical localization of the proteinase inhibitor region of amyloid precursor proteins in the neocortex of Alzheimer's disease and aged controls

The immunohistochemical localization of the proteinase inhibitor region of amyloid protein precursors (APPI) in the postmortem human neocortex was studied using a polyclonal antibody raised against a purified recombinant human APPI derivative produced by COS-1 cells. APPI-like immunoreactivity (APPI-LI) was found diffusely in the human neocortex. APPI-LI appeared as irregularly shaped granular structures. The size of the APPI-LI structures was 1-4 microns in diameter. APPI-LI usually formed a cluster of 10- to 20-microns diameter in the cortical gray matter and 20- to 40-microns diameter in the subcortical white matter. Double staining for APPI and glial fibrillary acidic protein indicated that APPI-LI in the white matter and molecular layer was localized exclusively in the fibrillary astrocytes. In contrast, APPI-LI was found in neurons as well as in the fibrillary astrocytes in layers II through to VI. Under fluorescence microscopy, APPI-LI in both neurons and fibrillary astrocytes were found in close association with lipofuscin. The present observations indicate that APPI is localized in neurons and astrocytes in the human neocortex and that APPI may be associated with lipofuscin or lysosome in the human neocortex.

Spinal cord vascular and leptomeningeal amyloid beta-protein deposition in a case with cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is characterized by the deposition of amyloid fibrils on leptomeningeal and cortical blood vessels, and the incidence of this disorder increases with age. However, this form of vascular amyloid deposition rarely involves tissues outside of the brain. A 71-year-old woman first developed some deterioration in memory, and soon afterwards suffered from recurrent episodes of subcortical hemorrhage. Histopathological examination of this case revealed typical pathology of Alzheimer's disease with an extensive appearance of beta-protein type CAA, and additionally, the spinal leptomeningeal vessels and the pia-arachnoid membranes were also affected by amyloid beta-protein deposits. The spinal cord involvement associated with CAA and Alzheimer's disease is unusual, and the present case provides additional important information on the pathogenesis of disorders with beta-protein deposition including Alzheimer's disease.

Expression of protease nexin-II in human dorsal root ganglia. A correlative immunocytochemical and in situ hybridization study

Protease nexin-II (PN-II) is a potent chymotrypsin inhibitor that forms SDS-stable inhibitory complexes with epidermal growth factor binding protein, the gamma-subunit of nerve growth factor, and trypsin, and represents the secreted form of the amyloid beta-protein precursor (APP) that contains the Kunitz-type protease inhibitor domain. To determine the expression of PN-II within the peripheral nervous system, human dorsal root ganglia were processed for immunocytochemistry using well-characterized monoclonal antibodies against PN-II and for in situ hybridization studies using 35S-RNA PN-II probes for both APP751 and APP770. Highly specific immunoperoxidase staining of PN-II was demonstrated within the cytoplasm of dorsal root ganglia neurons and their processes in cryostat (fresh frozen) and vibratome (paraformaldehyde-fixed) sections. In situ hybridization using an anti-sense 35S-RNA PN-II probe demonstrated the presence of intense neuronal labeling. Labeling was not observed when the corresponding sense 35S-RNA PN-II probe was used. Although the precise functional role of PN-II/APP is not clear, the accumulation of amyloid beta-protein within the neuropil appears to be one of the earliest events in the pathogenesis of Alzheimer's disease (AD). Thus knowledge of the cell populations expressing the PN-II/APP gene would certainly be helpful for studies of the molecular mechanisms leading to the morphological and functional changes of AD. The results of this study clearly establish the expression of PN-II and its mRNA within the dorsal root ganglia neurons and their processes, and provide another point of departure for studies of the molecular mechanisms underlying the deposition of amyloid beta-protein and its relationships to the formation of neuritic plaques and neurofibrillary tangles.

Immunohistochemical localization of beta-amyloid precursor protein sequences in Alzheimer and normal brain tissue by light and electron microscopy

Immunohistochemical staining with antibodies directed against four segments of the amyloid precursor protein (APP) was studied by light and electron microscopy in normal and Alzheimer (AD) brain tissue. The segments according to the Kang et al. sequence were: 18-38 (T97); 527-540 (R36); 597-620 (1-24 of beta-amyloid protein [BAP], R17); and 681-695 (R37) (Kang et al. [1987]: Nature 325:733-736). The antibodies recognized full length APP in Western blots of extracts of APP transfected cells. They stained cytoplasmic granules in some pyramidal neurons in normal appearing tissue from control and AD cases. In AD affected tissue, the antibodies to amino terminal sections of APP stained tangled neurons and neuropil threads, and intensely stained dystrophic neurites in senile plaques. By electron microscopy, this staining was localized to abnormal filaments. The antibody to the carboxy terminal segment failed to stain neurofibrillary tangles or neuropil threads; it did stain some neurites with globular swellings. It also stained globular and elongated deposits in senile plaque areas. The antibody against the BAP intensely stained extracellular material in senile plaques and diffuse deposits. By electron microscopy, the antibodies all stained intramicroglial deposits. Some of the extracellular and intracellular BAP-positive deposits were fibrillary. Communication between intramicroglial and extracellular fibrils was detected in plaque areas. These data suggest the following sequence of events. APP is normally concentrated in intraneuronal granules. In AD, it accumulates in damaged neuronal fibers. The amino terminal portion binds to abnormal neurofilaments. Major fragments of APP are phagocytosed and processed by microglia with the BAP portion being preserved. The preserved BAP is then extruded and accumulates in extracellular tissue.

Deposition of amyloid beta protein in non-Alzheimer dementias: evidence for a neuronal origin of parenchymal deposits of beta protein in neurodegenerative disease

In two elderly patients with frontal lobe dementia and in two others with progressive aphasia an inverse relationship between the severity of beta protein deposition and the principal pathology of these disorders was noted. Deposition of beta protein occurred only in areas of cortex where functional (viable) neurones were still present and was absent where neuronal decimation had taken place. Such findings suggest that the presence of functional neurones is necessary for beta protein deposition to occur and, therefore, that neurones may be the source of the amyloid protein that is deposited within brain parenchyma not only in these disorders but also in other conditions, particularly Alzheimer's disease.

Immunolocalization of Alzheimer beta-amyloid peptide precursor to cellular membranes in baculovirus expression system

One characteristic of Alzheimer's disease (A beta disease) is the accumulation of amyloid deposits within the extracellular space of the brain and meninges. A 40 amino acid peptide called beta-peptide or A4 protein is the subunit of the amyloid fibrils found in these deposits. The sequence of beta-peptide is contained within those of a family of larger proteins called the Alzheimer beta-amyloid peptide precursor (APP). These APPs contain, in addition to a signal sequence, a hydrophobic sequence that is believed to span cell membranes. Although biochemical studies indicate that some APPs have properties of integral membrane proteins, morphological confirmation of this has not been reported. We recently described an expression system in which human APP751 cDNA was placed under the transcriptional regulation of the polyhedrin gene promoter in the baculovirus Autographica californica infecting a Spodoptera frugiperda cell line (Ramakrishna et al., Biochem Biophys Res Commun 174:983-989, 1991). As part of a larger biochemical and molecular biological study of APP, we have carried out an immunocytochemical study using antibodies directed against several epitopes within APP to reveal, at both the light and the electron microscopic levels, the cellular localization of APP in the baculovirus expression system. These studies demonstrate that APP751 is abundantly synthesized and inserted into certain of the membrane compartments of the cell. As early as 24 hr postinfection, APP751 is found associated with all membrane compartments excepting mitochondrial membranes. The patterns of immunolabeling are consistent with our biochemical findings that the protein is processed in these cells so as to release the extracellular domain and to retain a transmembrane and intracellular segment. These data provide the first morphological demonstration of the membrane location of APP751, its posttranslational processing to a secreted fragment, and its exclusion from the mitochondrial membranes. This system is especially valuable for identifying conditions under which antibodies raised against APP or appropriate synthetic peptides will react with native APP.

In-vitro matured human macrophages express Alzheimer's beta A4-amyloid precursor protein indicating synthesis in microglial cells

Microglia which are consistently associated with Alzheimer's disease (AD) senile plaques are part of the mononuclear phagocyte system. In-vitro matured human monocyte-derived macrophages feature many immunological characteristics of microglia. We found strong constitutive expression of Alzheimer's beta A4-amyloid precursor protein (APP) in human mononuclear phagocytes after terminal in-vitro maturation from monocytes to macrophages. Amyloid has previously been found to be associated with microglia in AD brains, however, it remained unclear whether the material was synthesized in or had been phagocytosed by the cells. The findings presented here support the assumption that brain microglia may contribute to APP synthesis in AD brain.

Amyloid precursor protein in aged nonhuman primates

In individuals with Alzheimer disease and in aged nonhuman primates, deposits of amyloid occur in senile plaques in brain parenchyma and in the walls of some meningeal and cortical vessels. Amyloid is primarily composed of beta/A4, a 4-kDa peptide derived from the transmembrane form of an amyloid precursor protein (APP). We examined the distribution of beta/A4 and APP (outside the beta/A4 domain) in cerebral cortices of monkeys ranging in age from 4 to 41 years. In all animals, APP immunoreactivity was present in cell bodies, proximal dendrites, and axons of cortical neurons. In aged animals, all of which showed senile plaques, large APP-positive axons were conspicuous, and APP immunoreactivity was present in neurites around beta/A4-immunoreactive plaques. In some plaques, APP-immunoreactive elements were located in proximity to deposits of beta/A4. The presence of APP immunoreactivity in neuronal perikarya, dendrites, axons, and in neurites within beta/A4-containing plaques supports the hypothesis that neurons can serve as one source of amyloid deposited in brain parenchyma.

Antibodies to non-beta regions of the beta-amyloid precursor protein detect a subset of senile plaques

A central unresolved issue in Alzheimer's disease is the origin of the extracellular amyloid beta protein (A beta P) found in senile plaques and its relationship to the dystrophic neurites that intimately surround it. Here the presence and distribution within senile plaques of various epitopes of the beta-amyloid precursor protein (APP) are compared with the distribution of A beta P itself and markers for plaque neurites. Several principal findings emerge: 1) antibodies to regions of APP outside of A beta P ('APP antibodies') recognize only a subgroup of senile plaques; 2) within these plaques, APP antibodies label discrete globular and granular structures morphologically resembling neurites; 3) virtually all of the plaques labeled by APP antibodies also contain neurites reactive with antibodies to tau; 4) double labeling with anti-tau and an APP antibody shows that the neuritelike profiles stained by the APP antibody are always closely associated with tau-positive neurites within the same plaque and that a minority of profiles appear to be labeled by both antibodies; and 5) antibodies to different regions throughout APP label the same profiles within plaques, suggesting the presence of the full-length precursor. The authors conclude that only a subgroup of senile plaques contain APP epitopes and that the immunostained structures are neurites. Because many A beta P-containing plaques in neocortex, cerebellum, and striatum were found to be devoid of any APP labeling, as were vascular A beta P deposits, it is unlikely that the extracellular A beta P is principally derived from the APP found within dystrophic neurites. The immunodetection of apparently full-length APP, an axonally transported protein, in selected plaque neurites provides yet another protein marker of neuritic dystrophy, possibly indicative of an aberrant regenerative response.

Colocalization of amino terminal and A4 (beta-amyloid) antigens in Alzheimer plaques: evidence for coordinated processing of the amyloid precursor protein

The mechanism by which the A4 (beta-amyloid) domain of the Alzheimer amyloid precursor protein (APP) is deposited in plaques is unknown, and limited information is available concerning the extent to which other APP sites are associated with plaques. To address these issues, we prepared antiserum to a peptide adjacent to the N-terminus of the APP (referred to as N1) and examined its distribution in brain relative to A4 by double-immunostaining techniques. Anti-N1 localized to both neurons and glia in control and Alzheimer patients. In the Alzheimer brain, anti-N1 detected plaques. Quantitation revealed that 85% of thioflavin-positive plaques, and 91% of A4-positive plaques were also N1 positive. Double-staining methods directly demonstrated colocalization of distant APP sites. The data suggest that suggest that proposed mechanisms for amyloid deposition during plaque formation must take into account the extracytoplasmic domain, in addition to the A4 region, rather than be confined exclusively to the A4 site.

Immunohistological study of senile brains by using a monoclonal antibody recognizing beta amyloid precursor protein: significance of granular deposits in relation with senile plaques

Immunochemical analyses revealed that a monoclonal antibody Am-3 recognized beta amyloid precursor protein (beta APP) in senile plaques extracted from Alzheimer's brain, but did not recognize beta amyloid protein. Immunohistochemically, however, the staining pattern of Am-3 in frozen section of Alzheimer's brain was almost the same with that of rabbit polyclonal antibody to beta amyloid peptide which could recognize both beta amyloid protein and beta APP. In other words, beta APP was present in senile plaques of various types, cerebrovascular amyloid and granular deposits. The granular deposits were 5-10 microns in size and laminarily distributed in the 1st, 3rd and 4th layers of cerebral cortex. They were especially abundant in 1st and 4th layers where senile plaques were usually fewer in number. Although the distribution in the cerebral cortex was different between the senile plaques and the granular deposits, the number of the granular deposits was well correlated with that of senile plaques. The granular deposits were negative in Congo-red birefringence, but contained beta amyloid protein as well as beta APP fragment judging from positive staining by both Am-3 and polyclonal antibody to synthetic beta amyloid peptide. Thus, they could be regarded as "pre-amyloid".

Enzymatically active lysosomal proteases are associated with amyloid deposits in Alzheimer brain

The formation of beta-amyloid in the brains of individuals with Alzheimer disease requires the proteolytic cleavage of a membrane-associated precursor protein. The proteases that may be involved in this process have not yet been identified. Cathepsins are normally intracellular proteolytic enzymes associated with lysosomes; however, when sections from Alzheimer brains were stained by antisera to cathepsin D and cathepsin B, high levels of immunoreactivity were also detected in senile plaques. Extracellular sites of cathepsin immunoreactivity were not seen in control brains from age-matched individuals without neurologic disease or from patients with Huntington disease or Parkinson disease. In situ enzyme histochemistry of cathepsin D and cathepsin B on sections of neocortex using synthetic peptides and protein substrates showed that senile plaques contained the highest levels of enzymatically active cathepsin. At the ultrastructural level, cathepsin immunoreactivity in senile plaques was localized principally to lysosomal dense bodies and lipofuscin granules, which were extracellular. Similar structures were abundant in degenerating neurons of Alzheimer neocortex, and cathepsin-laden neuronal perikarya in various stages of disintegration could be seen within some senile plaques. The high levels of enzymatically competent lysosomal proteases abnormally localized in senile plaques represent evidence for candidate enzymes that may mediate the proteolytic formation of amyloid. We propose that amyloid precursor protein within senile plaques is processed by lysosomal proteases principally derived from degenerating neurons. Escape of cathepsins from the stringently regulated intracellular milieu provides a basis for an abnormal sequence of proteolytic cleavages of accumulating amyloid precursor protein.

Defined neurofilament, tau, and beta-amyloid precursor protein epitopes distinguish Alzheimer from non-Alzheimer senile plaques

Eight antisera and one monoclonal antibody to synthetic peptides that corresponded to domains extending over the entire length of the beta-amyloid precursor protein (beta-APP), and an antiserum to the full-length 695-amino acid form of the beta-APP, were raised to probe the composition of the core and corona of senile plaques (SPs). We localized distinct beta-APP domains, including the beta-amyloid protein or A4 region, within the SPs of 13 end-stage Alzheimer disease (AD) and 13 age-matched control samples of hippocampus and entorhinal cortex. The composition of SPs also was probed with antibodies to defined epitopes in tau (tau) as well as the large and mid-size neurofilament (NF) proteins. The most important observations were that beta-APP domains outside the A4 region were largely restricted to SP coronas in the AD samples, together with tau and NF determinants, whereas the same epitopes were absent from A4-positive blood vessels and exceptionally rare in non-AD SPs. Indeed, samples from a subset of the non-AD cases contained a considerable number of A4-positive SPs totally devoid of any of the other beta-APP, tau, and NF epitopes. These observations suggest that the deposition of the A4 protein in AD SPs results from the local processing of beta-APPs in association with tau and NF protein fragments. It is unclear whether this association is fortuitous or linked by common mechanisms. However, differences between the complement of beta-APP, tau, and NF protein epitopes in AD versus non-AD brains implicate a defect involving one or more steps in the posttranslational modification, degradation, or elimination of these proteins in AD brains, and this may account for the massive numbers of SPs that characterize AD.

Alzheimer cortical neurons containing abundant amyloid mRNA. Relationship to amyloid deposition and senile plaques

Since the detailed molecular events leading to the formation of amyloid-containing senile plaques of the Alzheimer's disease (AD) brain are incompletely understood, the present studies were undertaken to address this issue using a combination of molecular and cytochemical approaches. Amyloid precursor protein riboprobes containing the A4 (beta-amyloid) domain were applied to cortex using the in situ hybridization method to examine the distribution of neuronal amyloid mRNA in relation to the laminar pattern of amyloid deposition and the localization of plaques. The derived data indicated that high levels of amyloid mRNA can be synthesized by AD cortical neurons that appeared to be morphologically intact. The distribution of these cells was not coincident with the cortical laminar pattern that is typical of amyloid deposits observed after immunostaining with anti-A4 monoclonal antibodies. Further, there was no obvious relationship between neurons containing abundant amyloid mRNA and the distribution of plaques identified by thioflavin S staining. While the neuronal synthesis of amyloid may be a significant factor at some point during plaque formation, it may not be the exclusive determinant. The possibility is raised that processes affecting secretion, diffusion, and/or transport of amyloid away from neuronal or non-neuronal cells of origin to sites of deposition may be meaningful aspects of the molecular pathology of Alzheimer's disease.

Alzheimer's disease--neuropathological aspects

Alzheimer's disease is characterized neuropathologically by the progressive atrophy and death of selected neuronal populations. Prominent cytoskeletal changes are also observed, as well as the formation of neuritic plaques associated with the abnormal deposition of amyloid in the brain. The nature, pathogenesis and distribution of these changes are discussed.

Interleukin 1 regulates synthesis of amyloid beta-protein precursor mRNA in human endothelial cells

We have analyzed the modulation of amyloid beta-protein precursor (APP) gene expression in human umbilical vein endothelial cells (HUVEC). The level of the APP mRNA transcripts increased as HUVEC reached confluency. In confluent culture the half-life of the APP mRNA was 4 hr. Treatment of the cells with human-recombinant interleukin 1 (IL-1), phorbol 12-myristate 13-acetate, or heparin-binding growth factor 1 enhanced the expression of APP gene in these cells, but calcium ionophore A23187 and dexamethasone did not. The protein kinase C inhibitor 1-(isoquinolinsulfonyl)-2-methylpiperazine (H7) inhibited IL-1-mediated increase of the level of APP transcripts. To map IL-1-responsive elements of the APP promoter, truncated portions of the APP promoter were fused to the human growth hormone reporter gene. The recombinant plasmids were transfected into mouse neuroblastoma cells, and the cell medium was assayed for the human growth hormone. A 180-base-pair region of the APP promoter located between position -485 and -305 upstream from the transcription start site was necessary for IL-1-mediated induction of the reporter gene. This region contains the upstream transcription factor AP-1 binding site. These results suggest that IL-1 upregulates APP gene expression in HUVEC through a pathway mediated by protein kinase C, utilizing the upstream AP-1 binding site of the APP promoter.