Amyloid precursor-like protein 1 accumulates in neuritic plaques in Alzheimer’s disease

The Alzheimer’s disease (AD) β-amyloid precursor protein (APP) and the amyloid precursor-like protein 1 (APLP1) and 2 (APLP2) are members of a superfamily of proteins that appear functionally related. Although APLPs are highly homologous to APP in the N- and C-terminal domains, they lack the βA4/amyloid peptide, i.e., the main constituent of neuritic plaques in AD. To assess a potential role of APLP1 in AD, we have determined its immunohistochemical distribution in human hippocampal formation, a structure which is strongly affected in AD, and compared it with APP immunoreactivity. There was a considerable overlap of APP and APLP1 regional expression patterns. Significant APLP1 immunoreactivity was observed in neuritic plaques. Large pyramidal neurons of the subiculum showed an accumulation of APLP1 protein in their dendritic compartment. Some astrocytes elicited perinuclear APLP1 staining, but this was observed in both AD and control brains. These findings raise the possibility that APLP1 may contribute to the pathogenesis of AD-associated neurodegeneration. Received: 28 July 1997 / Revised: 28 August 1997 / Accepted: 8 September 1997     

Presenile Alzheimer dementia characterized by amyloid angiopathy and large amyloid core type senile plaques in the APP 692Ala→Gly mutation

Mutations at codons 717 and 670/671 in the amyloid precursor protein (APP) are rare genetic causes of familial Alzheimer’s disease (AD). A mutation at codon 693 of APP has also been described as the genetic defect in hereditary cerebral hemorrhage with amyloidosis of the Dutch type (HCHWA-D). We have reported a APP692Ala→Gly (Flemish) mutation as a cause of intracerebral hemorrhage and presenile dementia diagnosed as probable AD in a Dutch family. We now describe the post-mortem examination of two demented patients with the APP692 mutation. The neuropathological findings support the diagnosis of AD. Leptomeningial and parenchymal vessels showed extensive deposition of Aβ amyloid protein. Numerous senile plaques consisted of large Aβ amyloid cores, often measuring more than 30 μm in diameter and were surrounded by a fine meshwork of dystrophic neurites. In addition, there were a large number of paired helical filaments in pyramidal neurons and dystrophic neurites. Our findings show that the APP692 mutation leads to morphological abnormalities that are similar to AD, but the morphology of senile plaques is clearly distinct from that described in sporadic and chromosome 14-linked AD patients, in patients with APP717 mutations causing familial, presenile AD and in patients with the APP693 mutation causing HCHWA-D. Received: 11 August 1997 / Revised, accepted: 9 February 1998     

Nicotine modulates expression of amyloid precursor protein and amyloid precursor-like protein 2 in mouse brain and in SH-SY5Y neuroblastoma cells

Epidemiological studies indicate that tobacco smoking can be protective against neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). The objective of the present study was to examine the changes in gene expression induced by chronic oral nicotine administration (100 mug/ml in 2% saccharin for 14 days), with special emphasis on amyloid precursor protein (APP) and its homologue, amyloid precursor-like protein 2 (APLP2), in different brain regions of C57BL/6 mice using a pathway-focused microarray. Our results revealed that nicotine stimulated mRNA expression of APP in the amygdala (64%; P = 0.003) and hippocampus (32%; P = 0.034) and of APLP2 in the amygdala (39%; P = 0.002). These results were verified by quantitative real-time RT-PCR except that expression of APLP2 was also significantly upregulated by nicotine in the hippocampus. In addition, in vitro nicotine treatment of SH-SY5Y neuroblastoma cells resulted in a significant increase in expression of APP protein, soluble APP, and APLP2, whereas co-treatment with mecamylamine (an antagonist of nicotinic acetylcholine receptors) attenuated the stimulating effect of nicotine on APP and APLP2 expression. These findings suggest that nicotine treatment facilitates the increase in the expression of mRNA and protein of the APP and APLP2 genes in rat brain and SH-SY5Y neuroblastoma cells.     

Distribution of amyloid beta protein precursor in the Alzheimer's disease brain

In order to clarify the distribution and pathological changes of the amyloid beta protein precursor (betaAPP), 10 Alzheimer's disease (AD) brains and seven normal control brains were examined by immunocytochemistry and in situ hybridization histochemistry. All betaAPP isoforms were distributed evenly in neuronal cell bodies and their axons and dendrites. The betaAPP-positive neuronal processes showed mesh-like networks. In AD brains, betaAPP-positive neurons and mesh-like networks were generally decreased in spite of some intensely labeled neurons. All betaAPP isoforms accumulated in neuronal processes, dystrophic neurites and senile plaques. In situ hybridization histochemistry confirmed that all isoforms of betaAPP were expressed in neurons in control brains. In AD brains, the betaAPP mRNA signal was generally decreased besides some intense signal neurons corresponding to immunostaining findings. Few astrocytes expressed betaAPP. Thus, uniform expression and distribution of betaAPP were disturbed in AD brains showing uneven decreases or increases of neuronal betaAPP expression in individual neurons and betaAPP accumulation in neurons, neuronal processes and abnormal structures including dystrophic neurites, senile plaques and neurofibrillary tangles.     

Plaque biogenesis in brain aging and Alzheimer's disease. I. Progressive changes in phosphorylation states of paired helical filaments and neurofilaments

Paired helical filament (PHF)/tau immunoreactive dystrophic neurites are a common pathological feature in the brain of patients with Alzheimer's disease. Recent studies suggest that swollen neurofilament-immunoreactive neurites are also present in senile plaques. In the present study, we investigated whether PHF/tau-positive dystrophic neurites are located in all subtypes of plaques and whether swollen neurofilament-immunoreactive neurites are hyper-phosphorylated, using a battery of antibodies to PHF/tau, neurofilament, and β-amyloid protein. PHF/tau-positive dystrophic neurites were present in and around nearly all subtypes of plaques, including small amyloid deposits, diffuse plaques, and perivascular plaques in the hippocampal formation of Alzheimer brain. The earlier changes were detectable with AT8 antibody and later changes with PHF-1 antibody. Plaque-associated PHF/tau-positive dystrophic neurites were rare or absent in the hippocampal formation of normal aged brain. Swollen neurofilament-positive neurites appeared to be hyper-phosphorylated in Alzheimer's disease and to a lesser degree in aged control brains. Neurites that contained hyper-phosphorylated tau as well as neurofilament were strongly argentophilic because both populations of dystrophic neurites stained with silver stains. Swollen neurofilament-positive plaque-associated neurites were often present in the absence of PHF/tau-positive plaque-associated dystrophic neurites. These data suggest that PHF/tau-positive dystrophic neurites are a common component of all subtypes of plaques in Alzheimer brain and neurofilament protein in swollen neurites, like tau protein, is hyper-phosphorylated. Hyper-phosphorylated neurofilaments in plaque-associated neurites may represent one of the earliest cytoskeletal changes in vulnerable neurons in Alzheimer's disease and aged control brains.     

The distribution of amyloid beta precursor protein in canine brain

The distribution of amyloid beta precursor protein (APP) in canine brain was investigated. By immunoblot analysis, APP-positive bands corresponding to proteins of 105–120 kilodalton were recognized in all canine brains regardless of the individual age of the dogs. Bands of similar molecular mass were also detected in the meninges, cerebrospinal fluid, and several visceral organs. Immunohistochemical studies were performed using cryostat and paraffin-embedded sections pretreated with formic acid or by the hydrated autoclave method. In the normal canine brain, APP was found to be distributed in the neurons and vascular system. In the brains with SP, obvious accumulation of APP was observed in swollen neurites within amyloid plaques, although the relationship between APP and diffuse plaques was unclear. APP accumulation in swollen axons was also seen around necrotic foci in the brain of one dog with necrotizing purulent encephalitis. These studies revealed the distribution of APP in canine tissues, especially in the brain, and the accumulation of APP in swollen neurites or axons.     

Plaque biogenesis in brain aging and Alzheimer’s disease. II. Progressive transformation and developmental sequence of dystrophic neurites

Plaque-associated dystrophic neurites are a common pathological feature in the brains of patients with Alzheimer’s disease (AD). In the present study, we investigated the relative abundance and progressive transformation of the amyloid precursor protein (APP), neurofilament (NF) and paired helical filament (PHF) tau-positive dystrophic neurites, within plaques in non-demented controls versus plaque-associated dystrophic neurites in mild or severe AD using double and triple immunolabeling. We also determined the argentophilia of the various sub-populations of dystrophic neurites. In aged non-demented brain, approximately half of the APP-positive plaques contained NF-immunopositive dystrophic neurites; rarely were PHF/tau-positive dystrophic neurites detectable. In contrast, in the AD brain, three-fourths of the APP-positive plaques contained NF-positive dystrophic neurites and half contained PHF/tau neurites. We also observed focal patches of hyper-phosphorylated NF and/or PHF/tau within APP-immunopositive dystrophic neurites, which appeared similar to retrograde degeneration, whereas we never observed focal accumulations of APP within NF- or PHF/tau-positive fibers. We hypothesize that plaque-associated dystrophic neurites within plaques develop in a particular sequence: APP-positive dystrophic neurites appear first and are non-argentophilic. This is followed by the appearance of NF-positive dystrophic neurites, where a subset of NF-positive dystrophic neurites are lightly argentophilic. Over time, PHF/tau-positive dystrophic neurites develop and are strongly argentophilic. These data suggest that dystrophic neurites can develop retrogradely from focal plaque damage to induce somatic and dendritic degeneration and potentially contribute to neurofibrillary tangle formation. Received: 22 September 1997 / Revised, accepted: 15 April 1998     

Accumulation of the amyloid precursor-like protein APLP2 and reduction of APLP1 in retinoic acid-differentiated human neuroblastoma cells upon curcumin-induced neurite retraction

Amyloid precursor protein (APP) belongs to a conserved gene family, also including the amyloid precursor-like proteins, APLP1 and APLP2. The function of these three proteins is not yet fully understood. One of the proposed roles of APP is to promote neurite outgrowth. The aim of this study was to investigate the regulation of the expression levels of APP family members during neurite outgrowth. We observed that retinoic acid (RA)-induced neuronal differentiation of human SH-SY5Y cells resulted in increased expression of APP, APLP1 and APLP2. We also examined the effect of the NFkappaB, AP-1 and c-Jun N-terminal kinase inhibitor curcumin (diferuloylmethane) on the RA-induced expression levels of these proteins. We found that treatment with curcumin counteracted the RA-induced mRNA expression of all APP family members. In addition, we observed that curcumin treatment resulted in neurite retraction without any effect on cell viability. Surprisingly, curcumin had differential effects on the APLP protein levels in RA-differentiated cells. RA-induced APLP1 protein expression was blocked by curcumin, while the APLP2 protein levels were further increased. APP protein levels were not affected by curcumin treatment. We propose that the sustained levels of APP and the elevated levels of APLP2, in spite of the reduced mRNA expression, are due to altered proteolytic processing of these proteins. Furthermore, our results suggest that APLP1 does not undergo the same type of regulated processing as APP and APLP2.     

Amyloid beta-protein precursor accumulates in dystrophic neurites of senile plaques in Alzheimer-type dementia

We raised two rabbit antisera against synthetic peptides corresponding to the carboxyl- and amino-terminal regions of the predicted amyloid beta-protein precursor (APP). Both antisera recognized the same 106-135 kDa proteins of human brain extract by immunoblot analysis. Immunocytochemical studies showed that these antisera both reacted with the same dystrophic neurites within the senile plaques of Alzheimer brains. These results indicated that APP accumulated in the dystrophic neurites of the senile plaques.     

Ultrastructural localization of Alzheimer amyloid β/A4 protein precursor in the cytoplasm of neurons and senile plaque-associated astrocytes

Summary The ultrastructural localization of amyloid /A4 protein precursor (APP) in the brains of control and Alzheimer's disease patients was examined immunohistochemically using antisera against the N and C termini of APP. In both control and Alzheimer brains, immunoreaction for APP was seen in the cytoplasm of most neurons, on plasma membranes, outer membrane of mitochondria, granular substance and neurofilaments. Cell bodies and foot processes of astrocytes, containing glial filaments, were also labeled. In primitive and classic type senile plaques, APP immunoreaction products were localized in the astroglial processes that surrounded the amyloid mass of the senile plaques. Swollen degenerating neurites in the senile plaques were also labeled. Amyloid fibrils were negative with APP antisera.Supported by Grant-in-Aid for Scientific Research on Priority Area 02240105 from the Ministry of Education, Science, and Culture, Japan     

Accumulation of cellular prion protein within dystrophic neurites of amyloid plaques in the Alzheimer's disease brain

Amyloid plaques, a well‐known hallmark of Alzheimer's disease (AD), are formed by aggregated β‐amyloid (Aβ). The cellular prion protein (PrPc) accumulates concomitantly with Aβ in amyloid plaques. One type of amyloid plaque, classified as a neuritic plaque, is composed of an amyloid core and surrounding dystrophic neurites. PrPc immunoreactivity reminiscent of dystrophic neurites is observed in neuritic plaques. Proteinase K treatment prior to immunohistochemistry removes PrPc immunoreactivity from amyloid plaques, whereas Aβ immunoreactivity is enhanced by this treatment. In the present study, we used a chemical pretreatment by a sarkosyl solution (0.1% sarkosyl, 75 mM NaOH, 2% NaCl), instead of proteinase K treatment, to evaluate PrPc accumulation within amyloid plaques. Since PrPc within amyloid plaques is removed by this chemical pretreatment, we can recognize that the PrP species deposits within amyloid plaques were PrPc. We could observe that PrPc accumulation in dystrophic neurites occurred differently compared with Aβ or hyperphosphorylated tau aggregation in the AD brain. These results could support the hypothesis that PrPc accumulation in dystrophic neurites reflects a response to impairments in cellular degradation, endocytosis, or transport mechanisms associated with AD rather than a non‐specific cross‐reactivity between PrPc and aggregated Aβ or tau.     

Phosphorylated tau in neuritic plaques of APP<Superscript>sw</Superscript>/Tau<Superscript>vlw</Superscript> transgenic mice and Alzheimer disease

We have previously reported that double-transgenic APP(SW)/Tau(VLW) mice show enhanced amyloid deposition, stronger tau hyperphosphorylation, increased sarkosyl tau polymers, and wider tau filaments when compared to simple mutant models. To validate these transgenic mice as models of Alzheimer disease pathology, in the present study we analyze tau phosphorylation at 12E8 and AT-8 epitopes in amyloid plaques. In APP(SW) mice, phospho-tau in plaque-associated neurites suggests a local direct effect of plaque-amyloid (and/or APP(SW)) on tau phosphorylation. In vitro, attempts to identify which kinases are induced by fibrillar amyloid reveal to Protein Kinase C as responsible for phosphorylation at the 12E8 epitope. Tau(VLW) mice, without plaques, show increased tau phosphorylation at the 12E8 epitope, particularly in pyramidal neurons. APP(SW)/Tau(VLW) mice show earlier and stronger 12E8 tau phosphorylation. Ultrastructurally, the same two types of neurites are found in plaques from APP(SW)/Tau(VLW) and Alzheimer disease (AD) brains: (a) dystrophic giant neurites filled with degenerating organelles and/or phospho-tau-positive filaments and (b) non-dystrophic phospho-tau-positive small punctiform neurites. Both types of plaque-associated neurites are AT-8 positive in APP(SW)/Tau(VLW) mice and AD, but 12E8-positive dystrophic neurites are only detected in AD. We conclude that the simultaneous presence of human mutated Tau(VLW) and plaque-amyloid (and/or APP(SW)) potentiates and anticipates tau phosphorylation at the 12E8 epitope, intensifying pyramidal neuron immunostaining and tau filament formation in this double-transgenic model. Thus, the APP(SW)/Tau(VLW) mouse is a useful model to study neuritic plaques, since they reproduce most of the characteristics that these structures have in AD.     

Deletion of the amyloid precursor-like protein 2 (APLP2) does not affect hippocampal neuron morphology or function

Amyloid precursor protein (APP), the parent molecule to amyloid β peptide, is part of a larger gene family with two mammalian homologues, amyloid precursor-like protein 1 (APLP1) and amyloid precursor-like protein 2 (APLP2). Initial knock-out studies demonstrated that while single APP family gene deletions produced relatively mild phenotypes, deficiency of APLP2 and one other member of the gene family resulted in perinatal lethality, suggesting vital roles masked by functional redundancy of the other homologues. Because of the importance of APP in Alzheimer's disease, the vast majority of studies to date have concentrated on the neuronal functions of APP, leaving limited data on its homologues. APLP2 is of particular interest as it contains high sequence homology with APP, is processed similarly, is expressed in overlapping spatial and temporal patterns, and is obligatory for lethality when combined with deficiency of either APLP1 or APP but does not contain the toxic amyloid β sequence. Here we sought to test the role of APLP2 on neuronal structure and function using a combined approach involving in vitro and in vivo techniques in young and aged animals. Surprisingly, we found that unlike APP, APLP2 appears not to be essential for maintenance of dendritic structure, spine density, or synaptic function. Thus, there is clear divergence in the functional redundancy between APP and APLP2.     

Proteomic identification of less oxidized brain proteins in aged senescence-accelerated mice following administration of antisense oligonucleotide directed at the Abeta region of amyloid precursor protein

Amyloid beta-peptide (Abeta) is the major constituent of senile plaques, a pathological hallmark of Alzheimer's disease (AD) brain. It is generally accepted that Abeta plays a central role in the pathophysiology of AD. Abeta is released from cells under entirely normal cellular conditions during the internalization and endosomal processing of amyloid precursor protein (APP). However, accumulation of Abeta can induce neurotoxicity. Our previous reports showed that decreasing the production of Abeta by giving an intracerebroventricular injection of a 42-mer phosphorothiolated antisense oligonucleotide (AO) directed at the Abeta region of the APP gene reduces lipid peroxidation and protein oxidation and improves cognitive deficits in aged senescence-accelerated mice prone 8 (SAMP8) mice. In order to investigate how Abeta level reduction improves learning and memory performance of SAMP8 mice through reduction of oxidative stress in brains, we used proteomics to identify the proteins that are less oxidized in 12-month-old SAMP8 mice brains treated with AO against the Abeta region of APP (12 mA) compared to that of the age-control SAMP8 mice. We found that the specific protein carbonyl levels of aldoase 3 (Aldo3), coronin 1a (Coro1a) and peroxiredoxin 2 (Prdx2) are significantly decreased in the brains of 12 mA SAMP8 mice compared to the age-controlled SAMP8 treated with random AO (12 mR). We also found that the expression level of alpha-ATP synthase (Atp5a1) was significantly decreased, whereas the expression of profilin 2 (Pro-2) was significantly increased in brains from 12 mA SAMP8 mice. Our results suggest that decreasing Abeta levels in aged brain in aged accelerated mice may contribute to the mechanism of restoring the learning and memory improvement in aged SAMP8 mice and may provide insight into the role of Abeta in the memory and cognitive deficits in AD.     

Current advances on different kinases involved in tau phosphorylation, and implications in Alzheimer's disease and tauopathies

Hyperphosphorylation and accumulation of tau in neurons (and glial cells) is one the main pathologic hallmarks in Alzheimer's disease (AD) and other tauopathies, including Pick's disease (PiD), progressive supranuclear palsy, corticobasal degeneration, argyrophilic grain disease and familial frontotemporal dementia and parkinsonism linked to chromosome 17 due to mutations in the tau gene (FTDP-17-tau). Hyperphosphorylation of tau is regulated by several kinases that phosphorylate specific sites of tau in vitro. GSK-3-immunoprecipitated sarcosyl-insoluble fractions in AD have the capacity to phosphorylate recombinant tau. In addition, GSK-3 phosphorylated at Ser9, that inactivates GSK-3, is found in the majority of neurons with neurofibrillary tangles and dystrophic neurites of senile plaques in AD, and in Pick bodies and other phospho-tau-containing neurons and glial cells in other tauopathies. Increased expression of active kinases, including stress-activated kinase, c-Jun N-terminal kinase (SAPK/JNK) and kinase p38 has been found in brain homogenates in all the tauopathies. Strong active SAPK/JNK and p38 immunoreactivity has been observed restricted to neurons and glial cells containing hyperphosphorylated tau, as well as in dystrophic neurites of senile plaques in AD. Moreover, SAPK/JNK- and p38-immunoprecipitated sub-cellular fractions enriched in abnormal hyperphosphorylated tau have the capacity to phosphorylate recombinant tau and c-Jun and ATF-2 which are specific substrates of SAPK/JNK and p38 in AD and PiD. Interestingly, increased expression of phosphorylated (active) SAPK/JNK and p38 and hyperphosphorylated tau containing neurites have been observed around betaA4 amyloid deposits in the brain of transgenic mice (Tg 2576) carrying the double APP Swedish mutation. These findings suggest that betaA4 amyloid has the capacity to trigger the activation of stress kinases which, in turn, phosphorylate tau in neurites surrounding amyloid deposits. Complementary findings have been reported from the autopsy of two AD patients who participated in an amyloid-beta immunization trial and died during the course of immunization-induced encephalitis. The neuropathological examination of the brain showed massive focal reduction of amyloid plaques but not of neurofibrillary degeneration. Activation of SAPK/JNK and p38 were reduced together with decreased tau hyperphosphorylation of aberrant neurites in association with decreased amyloid plaques in both Tg2576 mice and human brains. These findings support the amyloid cascade hypothesis of tau phosphorylation mediated by stress kinases in dystrophic neurites of senile plaques but not that of neurofibrillary tangles and neuropil threads in AD.     

Diverse fibrillar peptides directly bind the Alzheimer's amyloid precursor protein and amyloid precursor-like protein 2 resulting in cellular accumulation

The Alzheimer's disease Abeta peptide can increase the levels of cell-associated amyloid precursor protein (APP) in vitro. To determine the specificity of this response for Abeta and whether it is related to cytotoxicity, we tested a diverse range of fibrillar peptides including amyloid-beta (Abeta), the fibrillar prion peptides PrP106-126 and PrP178-193 and human islet-cell amylin. All these peptides increased the levels of APP and amyloid precursor-like protein 2 (APLP2) in primary cultures of astrocytes and neurons. Specificity was shown by a lack of change to amyloid precursor-like protein 1, tau-1 and cellular prion protein (PrP(c)) levels. APP and APLP2 levels were elevated only in cultures exposed to fibrillar peptides as assessed by electron microscopy and not in cultures treated with non-fibrillogenic peptide variants or aggregated lipoprotein. We found that PrP106-126 and the non-toxic but fibril-forming PrP178-193 increased APP levels in cultures derived from both wild-type and PrP(c)-deficient mice indicating that fibrillar peptides up-regulate APP through a non-cytotoxic mechanism and irrespective of parental protein expression. Fibrillar PrP106-126 and Abeta peptides bound recombinant APP and APLP2 suggesting the accumulation of these proteins was mediated by direct binding to the fibrillated peptide. This was supported by decreased APP accumulation following extensive washing of the cultures to remove fibrillar aggregates. Pre-incubation of fibrillar peptide with recombinant APP18-146, the putative fibril binding site, also abrogated the accumulation of APP. These findings show that diverse fibrillogenic peptides can induce accumulation of APP and APLP2 and this mechanism could contribute to pathogenesis in neurodegenerative disorders.     

Homer2 and Homer3 interact with amyloid precursor protein and inhibit Abeta production

The study of Amyloid Precursor Protein (APP) processing has been the focus of considerable interest, since it leads to Aβ peptide generation, the main constituent of neuritic plaques found in brains of Alzheimer's disease patients. Therefore, the identification of novel APP binding partners that regulate Aβ peptide production represents a pharmaceutical target aiming at reducing Αβ pathology. In this study, we provide evidence that Homer2 and Homer3 but not Homer1 proteins interact specifically with APP. Their expression inhibits APP processing and reduces secretion of Aβ peptides. In addition, they decrease the levels of cell surface APP and inhibit maturation of APP and β-secretase (BACE1). The effects of Homer2 and Homer3 on APP trafficking to the cell surface and/or on APP and BACE1 maturation could be part of the mechanism by which the expression of these proteins leads to the significant reduction of Aβ peptide production.     

Differential pattern of β-amyloid, amyloid precursor protein and apolipoprotein E expression in cortical senile plaques

Regional differences in senile plaques immunostained by antibodies against β-amyloid A4 (β-A4), amyloid precursor protein 695 (APP) and apolipoprotein E (apo E) were studied in the hippocampus and the entorhinal, temporal and occipital cortices both quantitatively and semiquantitatively with respect to the laminar cortical distribution of the plaques. These patterns were related to the staging of Alzheimer’s disease in regard to the distribution of neurofibrillary tangles [Braak and Braak (1991) Acta Neuropathol 82: 239–259]. In the hippocampus and especially in sector CA 1, no significant differences in the number of plaques visualized by the different antibodies were found. In contrast, there was a striking difference in neocortical regions. Here, significantly higher numbers of plaques positive for β-A4 than that for APP and apo E were present in all stages, except in the stages I and VI, and for apo E in stage II. The highest densities of β-A4-positive plaques were found in the isocortical layers III and V and in the entorhinal pre-α, pre-γ, pri-α and pri-β layers. The preferentially affected area, showing plaques positive for all three antibodies, was the entorhinal-hippocampal circuit with early affection of CA 1, which represents the direct and indirect target of the entorhinal neurons of the upper layers. Therefore, we suggest that plaques with dystrophic neurites, positive for APP, seem to be generated secondarily in afferent areas such as the hippocampus, which is the main afferent target of the entorhinal region. Diffuse plaques, negative for APP and apo E, are virtually absent in the CA 1 and seem to originate independently of afferent neuronal dysfunction, as indicated by neurofibrillary tangles. Received: 21 January 1996 / Revised: 18 July 1996, 13 November 1996 / Accepted: 27 November 1996     

The widespread alteration of neurites in Alzheimer's disease may be unrelated to amyloid deposition

The structural changes of Alzheimer's disease (AD) include a widespread alteration of neuronal cell processes in addition to senile plaques and neurofibrillary tangles. Since the antigenic characteristics of these abnormal neurites are similar to those of the abnormal neurites associated with the senile plaques, the question has been raised as to whether the widespread neuritic alteration is secondary to the deposition of amyloid. To answer this question, we examined brains from 2 subjects with a longer-lasting form of subacute sclerosing panencephalitis (SSPE) characterized by the presence of numerous neurofibrillary tangles but no senile plaques, 3 subjects with AD, and 2 age-matched controls. Light and electron immunocytochemical analyses revealed that abnormal neurites are present diffusely in SSPE cerebral cortex in the absence of amyloid deposits. These abnormal neurites were qualitatively identical to the widespread abnormal neurites of AD. The abnormal neurites, in contrast to the neurites of control brains, immunoreacted with antibodies to tau and ubiquitin. These distinctive antigenic features were due to the presence in these abnormal neurites of straight filaments, 14 to 16 nm in diameter, mixed with a few paired helical filaments. The spatial distribution of the widespread neuritic alteration correlated with that of neurofibrillary tangles in both conditions, but not with that of senile plaques in AD. The present findings demonstrate that a diffuse alteration of neurites similar to that present in AD takes place independently of the deposition of amyloid in SSPE, and they are consistent with the hypothesis that in AD, also, this alteration is not secondary to the deposition of amyloid.(ABSTRACT TRUNCATED AT 250 WORDS)