Modulation of PHF-like tau phosphorylation in cultured neurones and transfected cells.

Two cellular systems have been used to investigate the modulation of tau hyperphosphorylation. In the first system, the effects of the excitatory amino acid glutamate, the microtubule destabilising agent colchicine, and beta 25-35-amyloid peptide on tau phosphorylation were studied in rat cortical neurones in primary culture. Using immunocytochemistry and western blot analysis, we demonstrated that tau in these cultures is normally highly phosphorylated, but a proportion becomes rapidly dephosphorylated following treatment of the cultures with glutamate or colchicine. These changes in tau phosphorylation occurred prior to cell death. In the second system, the ability of p42 MAP and p44 MAP kinases, glycogen synthase kinases 3 alpha and 3 beta (GSK-3 alpha and GSK-3 beta) to phosphorylate tau in transfected COS cells was investigated. Both GSK-3 alpha and GSK-3 beta phosphorylated tau to produce a PHF-like state of phosphorylation but the MAP kinases failed to induce such a transformation in tau. These results suggest that aberrant regulation of GSK-3 alpha/beta may be a pathogenic mechanism in Alzheimer's disease.

Isolation of cDNAs coding for epitopes shared by microtubule-associated proteins and neurofibrillary tangle in Alzheimer's disease.

5 cross-hybridizing cDNA clones of sizes 2.2 (3 cDNAs), 1.3 and 0.8 kb corresponding to tau microtubule-associated protein have been isolated from a rat brain lambda gt11 expression library. Antibodies affinity-purified using the fusion protein encoded by the cDNAs were observed to label tau polypeptides on Western blots and Alzheimer's neurofibrillary tangles.

Distribution of the phosphorylated microtubule-associated protein tau in developing cortical neurons.

During brain development, the microtubule-associated protein tau presents a transient state of high phosphorylation. We have investigated the developmental distribution of the phosphorylated fetal-type tau in the developing rat cortex and in cultures of embryonic cortical neurons, using antibodies which react with tau in a phosphorylation-dependent manner. The phosphorylated fetal-type tau was present in the developing cortex at 20 days but not at 18 days of embryonic life and was not detected before four to five days in neuronal culture. The cyclin-dependent kinase p34cdc2 was expressed only in germinal layers in the embryonic brain and was not co-localized with phosphorylated tau. After 10 days of postnatal life, the phosphorylated tau progressively disappeared from cortical neurons, disappearing first from the deepest cortical layers where neurons are ontogenetically the oldest. Phosphorylated tau was found in axons and dendrites of cortical neurons at all developmental stages whereas unphosphorylated tau tended to disappear from dendrites during development. The timing of appearance of phosphorylated tau in the cortex, by comparison with the expression of other developmental markers, indicates that phosphorylated tau is present at a high level only during the period of intense neuritic outgrowth and that it disappears during the period of neurite stabilization and synaptogenesis, concomitantly to the expression of adult tau isoforms. In control cultures and in cultures treated with colchicine, the phosphorylated tau was not associated to cold-stable and to colchicine-resistant microtubules. These in vivo results suggest that the high expression of phosphorylated tau species is correlated with the presence of a dynamic microtubule network during a period of high plasticity in the developing brain.

Heterogeneity of ubiquitin immunoreactivity in neurofibrillary tangles of Alzheimer's disease.

The immunoreactivity of neurofibrillary tangles (bundles of abnormal filaments) in Alzheimer's disease was compared in photonic and electron microscopy using antisera against the microtubule- associated protein tau, against isolated tangles, against ubiquitin and using monoclonal antibodies against neurofilament proteins. Only a sub-population of tangles is labeled in situ by the anti-ubiquitin serum and some tangles are unlabeled by any of the antibodies used. Double immunolabeling in electron microscopy shows, however, that ubiquitin epitopes can coexist with tau and neurofilament epitopes on a same abnormal filament. These results indicate that in situ ubiquitin immunoreactivity (and to a lesser extent tau and neurofilament immunoreactivity) is not an obligatory feature of these abnormal filaments and suggest that their antigenic composition could evolve in affected neurons.

Synaptophysin and chromogranin A immunoreactivities in senile plaques of Alzheimer's disease.

Immunolabelling for synaptophysin and chromogranin A, two polypeptides associated with small clear and large dense core synaptic vesicles respectively, has been performed on tissue sections of the temporal cortex in Alzheimer's disease in combination with anti-A4 amyloid labelling. The dystrophic neurites in many senile plaques were observed to be labelled by the anti-synaptophysin or anti-chromogranin A antibodies. Some diffuse amyloid deposits, demonstrated by antibodies against synthetic amyloid A4 peptides, were associated with a punctuate increase in synaptophysin or chromogranin A immunoreactivity. The labelling of dystrophic plaque neurites may reflect the accumulation in these processes of synaptic vesicles or material derived from them. We suggest also that the punctuate increase in synaptophysin and chromogranin A immunoreactivities associated with some A4 amyloid deposits may be an early event reflecting neuronal dysfunction.

Accumulation of smooth endoplasmic reticulum in Alzheimer's disease: new morphological evidence of axoplasmic flow disturbances.

Numerous enlarged neurites and presynaptic terminals containing tubulovesicular profiles of smooth endoplasmic reticulum (SER) were observed in frontal biopsies from six patients with Alzheimer's disease. These accumulations of SER probably reflect disturbances of axoplasmic flows. In addition, curvilinear tubular inclusions similar to those characteristic of Farber's disease were found in one patient. Finally, accumulation of glycogen within neurites and enlarged mitochondria were observed in all patients.

Cortical and brainstem-type Lewy bodies are immunoreactive for the cyclin-dependent kinase 5.

The immunoreactivity of cortical and brainstem-type Lewy bodies has been investigates with antibodies to the cyclin-dependent kinase 5 (cdk5), to the extracellular regulated kinase 1 (ERK-1), and to the cdc2p34 kinase and with antibodies specific for phosphorylation epitopes typical of paired helical filament-tau (PHF-tau). Both cortical and brainstem-type Lewy bodies in diffuse Lewy body disease and brainstem-type Lewy bodies in Parkinson's disease were found to be immunoreactive for cdk5 but not for cdc2p34 or ERK-1 or with the PHF-tau antibodies. Double immunolabeling showed that cdk5-positive Lewy bodies were also ubiquitin immunoreactive and that cdk5 antibodies labeled as many Lewy bodies as ubiquitin antibodies in adequately fixed tissue. The cdk5 immunoreactivity of Lewy bodies was abolished by preabsorption of the antibody with a cdk5 peptide. The antibodies to cdk5 labeled a single 33-kd species on Western blots of human brain homogenates, with a similar intensity in control, diffuse Lewy body disease, and Alzheimer's disease, and this cdk5 species was found mainly in the particulate fraction of brain homogenates. This observation suggests that cdk5 might be a protein kinase involved in the phosphorylation of a molecular component of Lewy bodies, for example, neurofilament proteins known to be present in these inclusions.

Spongiform alterations in brain biopsies of presenile dementia.

Spongiform lesions were observed in close association with typical presenile alterations in three of six frontal lobe biopsies taken in presenile demented patients without any familial relationship. These findings are discussed in relation with recent investigations indicating the production of spongiform lesions after inoculation of nervous tissue from an Alzheimer patient to animals and the effects of saline extract of such material on cultured nerve cells.

Ultrastructural study of enriched fractions of "tangles" from human patients with senile dementia of the Alzheimer type.

Enriched fractions of "tangles" obtained from cases of Alzheimer's disease have been observed by negative staining and platinum: iridium shadowing, and also after treatment with sodium dodecyl sulfate and urea. Abnormal filaments with a 80-nm periodic constriction exhibited a substructure consisting of six protofilaments. They also showed a periodic right-handed twist. Some fibrils with a 160-nm periodic constriction were made up of four protofilaments. These features are discussed in view of known fibrous protein models, especially neurofilaments.

Calcineurin (phosphatase 2B) is present in neurons containing neurofibrillary tangles and in a subset of senile plaques in Alzheimer's disease.

The accumulation of hyperphosphorylated tau species in neurons in Alzheimer's disease (AD) might result from a relative decrease in their content of protein phosphatases. In this study we have investigated the immunocytochemical distribution of calcineurin (phosphatase 2B) in the hippocampus and temporal cortex of human control subjects and in AD. Calcineurin was strongly expressed in neuronal perikarya and dendrites but only weakly in white matter tracts, both in controls and in AD. The distribution of calcineurin was preserved in AD. By double-immunolabelling with calcineurin antibodies and the AT8 antibody to paired helical filament-tau, it was observed that a strong calcineurin immunoreactivity was still present in many neurons containing neurofibrillary tangles (NFT). Calcineurin was present in dystrophic neurites in some senile plaques (SP) located in the hippocampal formation but more rarely in neocortical areas; this calcineurin immunoreactivity did not always overlap with the tau immunoreactivity in SP. These results suggest that development of NFT in most neurons does not result from a major decrease of calcineurin expression.

Studies on the transport of secretory granules in the magnocellular hypothalamic neurons of the rat. II. Action of vincristine on axonal flow and neurotubules in the paraventricular and supraoptic nuclei.

Intrathecal administration of 20 mug of vincristine sulphate in the rat induced in vivo the formation of paracrystalline inclusions mainly in axonal processes. This is associated with an impairment in the migration of neurosecretory granules as shown by their accumulation in the perikarya of the magnocellular neurons. The granules are intermixed with numerous dense bodies of various shape, sometimes with a fibrillar content, and probably of lysosomal origin. In addition to the impairment of the flow of neurosecretory granules, there is also a striking accumulation of mitochondria and synaptic vesicles, and an apparent proliferation of the smooth endoplasmic reticulum. In the posterior lobe, the axonal endings contain a large number of neurosecretory granules, intermingled with bodies of varying shapes and electron density. Occasionally, a dense membrane surrounding a group of elementary granules is observed, reacting positively for acid phosphatase. This suggests an attempted crinophagia.

Demonstration of prolactin at the ultrastructural level in a pituitary adenoma by the use of colloidal gold labelling.

A prolactin-secreting pituitary adenoma was removed in a 38-year-old man. The tumor was classified as a chromophobe adenoma on the basis of tinctorial staining, but immunocytochemistry revealed that cells reacted with anti-PRL serum. Electron microscopy showed secretory granules and evidence of high metabolic activity (well developed Golgi apparatus and rough endoplasmic reticulum). Immunoelectron microscopy by the immunogold staining method allowed a clear definition of prolactin containing granules.

Neurofilament monoclonal antibodies RT97 and 8D8 recognize different modified epitopes in paired helical filament-tau in Alzheimer's disease.

Neurofibrillary tangles in Alzheimer's disease have been previously found to be labeled by some neurofilament antibodies that also recognize tau proteins. We have studied the reactivity of two such monoclonal antibodies, RT97 and 8D8, and of an anti-ubiquitin serum with the abnormal paired helical filaments (PHF)-tau (A68) polypeptides known to be the main component of the PHFs constituting the neurofibrillary tangles. 8D8 recognized the three major PHF-tau polypeptides, but RT97 reacted only with the two larger PHF-tau species. PHF-tau polypeptides were labeled by 8D8 and RT97 much more strongly than normal human tau and this labeling was decreased after alkaline phosphatase treatment. Anti-ubiquitin and anti-phosphotyrosine antibodies did not label PHF-tau polypeptides. The immunoreactivity of proteolytic fragments of PHF-tau polypeptides was studied with RT97, 8D8, and a panel of tau antibodies. The epitope for 8D8 on PHF-tau was localized between amino acids 222 and 427 in the carboxyl half of tau. The RT97 epitope on PHF-tau was localized in the amino domain of tau, probably in the 29-amino-acid insertion (insert 1) found towards the amino terminus of some tau isoforms. These results show that the basis for the labeling of neurofibrillary tangles by antibodies 8D8 and RT97 to neurofilament is their ability to react with PHF-tau polypeptides by recognizing sites specifically modified on PHF-tau, including a site specific to some tau isoforms.

Developmental changes in tau phosphorylation: fetal tau is transiently phosphorylated in a manner similar to paired helical filament-tau characteristic of Alzheimer's disease.

Rat and human fetal brain tau were probed with a panel of monoclonal antibodies (tau-1, AT8, 8D8, RT97, SMI31, SMI34) that distinguish between paired helical filament (PHF)-tau of Alzheimer's disease and normal adult brain tau. These antibodies discriminate between normal and PHF-tau because their epitopes are phosphorylated in PHF-tau. Although only one molecular isoform of tau was shown to be expressed in fetal brain, two fetal tau species could be distinguished on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the slower migrating species was recognized by all of the PHF-tau-specific antibodies. Moreover, this immunoreactivity was shown to be phosphorylation dependent. Our observations suggest that the abnormal phosphorylation of tau in Alzheimer's disease may be the result of reactivation of pathways governing the phosphorylation of tau in the developing brain.

Neurofibrillary tangles of Alzheimer's disease: an immunohistochemical study.

The reactivity of neurofibrillary tangles (NFT) of Alzheimer's disease with several antisera has been studied by immunocytochemistry. They were heavily labelled by an antiserum prepared against isolated NFT; the latter also remained stainable by Bodian-silver method. Some NFT were labelled on vibratome sections by an antimicrotubular protein but remained able to be counterstained by Congo Red, suggesting this labelling could demonstrate material trapped in NFT. The immunoelectron labelling shows that the abnormal filaments, straight as well as 'twisted', are the only structures recognised by the anti-NFT serum. This labelling was prevented only by pre-incubation with fractions enriched in NFT, confirming the presence of unique antigenic determinants in the latter.

A68 proteins in Alzheimer's disease are composed of several tau isoforms in a phosphorylated state which affects their electrophoretic mobilities.

The tau-immunoreactive A68 polypeptides found in brains from patients with Alzheimer's disease have been studied by Western blotting using (1) antibodies to synthetic peptides corresponding to sequences that span the complete human tau molecule, and (2) antibodies specific for inserts 1 and 2 found towards the N-terminus of some tau isoforms. The three major A68 polypeptides were labelled by all of the antibodies to sequences common to all tau isoforms, but the faster-migrating A68 polypeptides was not labelled by either of the two antibodies specific for inserts 1 and 2. Treatment with alkaline phosphatase of non-solubilized A68 did not change its electrophoretic mobility on SDS/PAGE under the conditions described here. However, A68 that was solubilized before treating it with alkaline phosphatase was found to move faster on SDS/PAGE than untreated A68, to a position similar to that of normal tau. We also confirmed that A68 preparations contain numerous paired helical filaments (PHF). These PHF were labelled by all anti-tau antibodies, including insert-specific antibodies. Our results further support the notion that PHF contain abnormally phosphorylated tau in an aggregated state, and indicate that these abnormally phosphorylated tau forms are composed of several tau isoforms and that the full length of the tau molecule is present in these polypeptides.

Transmission and scanning electron-microscopic observations on tanycytes in the mediobasal hypothalamus and the median eminence of adrenalectomized rats.

Tanycytes in the median eminence (ME) of the rat exhibit morphological features suggesting their possible participation in transport phenomena. After adrenalectomy, which modifies the hypothalamo-hypophyseal axis, they undergo morphological changes characterized by an accumulation of lipid droplets, an increased number of bleb-like protrusions at their apex, as well as an increased pinocytosis of intraventricularly injected horseradish peroxidase (HRP). In addition, after adrenalectomy an increased number of vacuoles appears at the level of the tubero-infundibular sulci. Their intracellular location in the tanycytes is demonstrated by an intraventricular injection of HRP. The significance of these vacuoles is discussed in relation to the hydroelectrolytic modifications associated with the state of adrenalectomy.

Tau in Alzheimer neurofibrillary tangles. N- and C-terminal regions are differentially associated with paired helical filaments and the location of a putative abnormal phosphorylation site.

To investigate the extent to which whole tau proteins, structurally abnormal tau and fragments of tau are incorporated into neurofibrillary tangles in Alzheimer's disease, an immunocytochemical mapping study using a panel of antibodies to several synthetic human tau peptides has been performed. Neurofibrillary tangles were immunolabelled in situ, and paired helical filaments (PHF), the principal structural component of tangles, were immunolabelled after isolation and Pronase treatment. N-Terminal and C-terminal domains of tau were found to be present in tangles in situ. SDS-treated PHF were found to contain most of the C-terminal half of tau and were also labelled by antibodies to ubiquitin. Only some of these PHF were labelled by antisera to tau sequences towards the N-terminus, and this enabled the identification of a region of tau in which proteolytic cleavage may occur. The ultrastructural appearance of the immunolabelling suggested that both the N- and C-terminal domains of tau extend outwards from the axis of PHF. After Pronase treatment. PHF were strongly labelled only by an antiserum to PHF and by the antiserum to the most C-terminal tau synthetic peptide. The latter antiserum also strongly labelled extracellular tangles in situ, whereas these extracellular tangles were poorly labelled by the antisera to the other synthetic peptides. One anti-(tau peptide) serum labelled a population of neurofibrillary tangles in situ only after alkaline phosphatase pretreatment of tissue sections. Our results show that, although peptides along the length of the tau molecule are associated with neurofibrillary tangles in situ, only the C-terminal one-third of the molecule is tightly associated with PHF, since this region of tau is resistant to SDS treatment of PHF. We also report the existence in PHF in situ of a masked tau epitope which is partially unmasked by dephosphorylation. These results are indicative of post-translational changes in tangle-associated tau in degenerating neurons in Alzheimer's disease.

Transplantation of human cortex with Alzheimer's disease into rat occipital cortex; a model for the study of Alzheimer disease.

Senile dementia of the Alzheimer type (SDAT) is a major problem in the human senescent population. As this pathology cannot be reproduced in animals, research into its development is greatly impeded. The technique of implantation of the nervous tissue has been utilized in order to establish an animal model and to test the possible existence of a transmissible agent. When human temporal cortex with Alzheimer's disease is implanted in the occipital cortex of 7-week-old rats, human cerebral tissue containing abundant tangles induces in the receiver cortex a reactive fibrous gliosis. In the processes of the astrocytes, twisted filaments are evident among bundles of normal filaments. These alterations could be induced by the metabolising of abnormal filament subunits or by some infectious agent introduced by the implant.