Large-scale, multicenter study of cerebrospinal fluid tau protein phosphorylated at serine 199 for the antemortem diagnosis of Alzheimer's disease

We surveyed a total of 570 cerebrospinal fluid (CSF) samples from a variety of diseases, including Alzheimer's disease (AD; n = 236), non-AD-demented and nondemented diseases (n = 239), and normal controls (n = 95) to quantitate levels of tau protein phosphorylated at serine 199 (CSF/phospho-tau199) by a recently established sandwich ELISA. The CSF/phospho-tau199 levels in the AD group were significantly elevated compared to those in all the other non-AD groups. Receiver operating characteristics curves showed that the diagnostic sensitivity and specificity for the AD group vs all the other non-AD groups using the CSF/phospho-tau199 were 85.2% and 85.0%, respectively. Furthermore, there was a significant positive correlation between CSF/phospho-tau199 and CSF/total-tau levels in the AD group. Elevated CSF/phospho-tau199 in the AD group was noted irrespective of age, gender, dementia severity, and number of apolipoprotein E4 alleles. Thus, we suggest that CSF/phospho-tau199 may be a novel and logical biomarker in supporting antemortem diagnosis of AD.

CSF phosphorylated tau protein and mild cognitive impairment: a prospective study

Cerebrospinal fluid (CSF) tau protein phosphorylated at both Thr231 and Ser235 sites (CSF/phospho-tau(231-235)) and total tau (CSF/total-tau) were quantified by sandwich ELISA in 20 patients with mild cognitive impairment (MCI) who eventually developed AD on follow-up as well as seven memory complainers with no objective memory loss. 13/20 (65%) of the MCI patients had high CSF/total-tau and detectable levels of CSF/phospho-tau(231-235), whereas these markers were low and under a detectable level in all of the memory complainers. Although either a total-tau, phospho-tau measurement or a combination of these can help in predicting if MCI will develop AD, our results suggest that the pathogenic steps of AD may be at the stage that finally leads to an accumulation of abnormally phosphorylated tau and neuron death, at least in some brain areas, when MCI patients present with the earliest detectable clinical symptoms of dementia.

Phosphorylated tau in human cerebrospinal fluid is a diagnostic marker for Alzheimer's disease

Microtubule-associated protein tau in cerebrospinal fluid (CSF) has been proposed as a diagnostic marker for Alzheimer's disease (AD), but there is overlap between AD patients and non-AD controls. To improve the diagnostic accuracy, we measured phosphorylated tau in CSF, because phosphorylated tau accumulates as pathological paired helical filaments in neurons of the AD brain. Immunoblot showed that CSF contained a 32 kDa N-terminal fragment of tau that was partially phosphorylated on Ser199, Thr231 and Ser235. A sandwich enzyme immunoassay revealed that phosphorylated CSF-tau levels were significantly higher in AD patients than those in non-AD controls. Discrimination between the two groups was clearer in phosphorylated CSF-tau than in total CSF-tau. The data indicate that elevated phosphorylated CSF-tau level is a more specific diagnostic marker for AD.

Phosphatidic acid-dependent phosphorylation of a 29-kDa protein by protein kinase Calpha in bovine brain cytosol

Activation of phospholipase D (PLD) is involved in receptor-mediated signal transduction responses. Signaling from PLD to a downstream molecule(s) appears to be mediated by the PLD product phosphatidic acid (PA). A target molecule(s) of PA, however, has not yet been identified. The present study sought to define such a target molecule(s) of PA. In bovine brain cytosol, proteins with apparent molecular weights of 29,000 (p29) and 32,000 (p32) were prominently phosphorylated in the presence of PA, but not in its absence, indicating that there is a PA-regulated protein kinase (PARK) in bovine brain that phosphorylates p29 and p32. One of these substrates, p29, was purified to near homogeneity. Its partial amino acid sequence was determined and found to be identical to that of a known brain-specific 25-kDa protein (p25). The purified p29 was also readily recognized by and immunoprecipitated with an anti-p25 antibody. These results suggest that p29 is very similar to or identical with p25. Using the purified p29 as a substrate, PARK was purified to near homogeneity. The purified PARK had an apparent molecular weight of 80,000, was strongly recognized by an antiprotein kinase C (PKC)alpha antibody, and was activated by phosphatidylserine (PS) as well as PA. The PA- and PS-stimulated PARK activity was extremely augmented by the presence of 1 microM free Ca2+. In the presence of 1 mM EGTA, phorbol 12-myristate 13-acetate activated PARK synergistically with PA or PS. Similar results were obtained with the purified recombinant PKCalpha. From these results, it is suggested that the PARK activity purified might be attributed to PKCalpha. In p25-depleted bovine brain cytosol, which was prepared by treatment of bovine brain cytosol with the anti-p25 antibody, PA-dependent phosphorylation of p29, but not p32, was almost completely eliminated. When PKCalpha in bovine brain cytosol was depleted by its precipitation with the anti-PKCalpha antibody, neither p29 nor p32 in this PKCalpha-depleted cytosol was phosphorylated in the presence of PA. These results indicate that in bovine brain cytosol PA activates PKCalpha, which, in turn, phosphorylates p29, which may be identical with p25.

Characterization of tau phosphorylation in glycogen synthase kinase-3beta and cyclin dependent kinase-5 activator (p23) transfected cells

One of the histopathological markers in Alzheimer's disease is the accumulation of hyperphosphorylated tau in neurons called neurofibrillary tangles (NFT) composing paired helical filaments (PHF). Combined tau protein kinase II (TPK II), which consists of CDK5 and its activator (p23), and glycogen synthase kinase-3beta (GSK-3beta) phosphorylate tau to the PHF-form in vitro. To investigate tau phosphorylation by these kinases in intact cells, the phosphorylation sites were examined in detail using well-characterized phosphorylation-dependent anti-tau antibodies after overexpressing the kinases in COS-7 cells with a human tau isoform. The overexpression of tau in COS-7 cells showed extensive phosphorylation at Ser-202 and Ser-404. The p23 overexpression induced a mobility shift of tau, but most of the phosphorylation sites overlapped the endogenous phosphorylation sites. GSK-3beta transfection showed the phosphorylation at Ser-199, Thr-231, Ser-396, and Ser-413. Triplicated transfection resulted in phosphorylation of tau at 8 observed sites (Ser-199, Ser-202, Thr-205, Thr-231, Ser-235, Ser-396, Ser-404, and Ser-413).

Immunocytochemistry of formalin-fixed human brain tissues: microwave irradiation of free-floating sections

Formalin fixation, the chemical process in which formaldehyde binds to cells and tissues, is widely used to preserve human brain specimens from autolytic decomposition. Ultrastructure of cellular and mitochondrial membranes is markedly altered by vesiculation, but this does not interfere with diagnostic evaluation of neurohistology by light microscopy. Serious difficulties are encountered, however, when immunocytochemical staining is attempted. Antigens that are immunoreactive in unfixed frozen sections and protein extracts appear to be concealed or destroyed in formalin-fixed tissues. In dilute aqueous solution, formaldehyde is in equilibrium with methylene glycol and its polymeric hydrates, the balance by far in favor of methylene glyco. Carbonylic formaldehyde is a reactive electrophilic species well known for crosslinking functional groups in tissue proteins, nucleic acids, and polysaccharides. Some of its methylene crosslinks are readily hydrolyzed. Others are stable and irreversible. During immunostaining reactions, intra- and inter-molecular links between macromolecules limit antibody permeation of tissue sections, alter protein secondary structure, and reduce accessibility of antigenic determinants . Accordingly, immunoreactivity is diminished for many antigens. Tissues are rapidly penetrated by methylene glycol, but formaldehyde binding to cellular constituents is relatively slow, increasing progressively until equilibrium is reached. In addition, prolonged storage in formalin may result in acidification of human brain specimens. Low pH favors dissociation of methylene glycol into formaldehyde, further reducing both classical staining and antigen detectability. Various procedures have been devised to counter the antigen masking effects of formaldehyde. Examples include pretreatment of tissue sections with proteases, formic acid, or ultrasound. Recently, heating of mounted sections in ionic salt solution by microwave energy was found to restore many antigens. Theory and practice of microwave antigen retrieval are covered extensively in the handbook Microwave Cookbook for Microscopists. A concise overview of microwave methods in the neurosciences has been published, and clinical applications have been reviewed. In this context, it should be noted that fresh tissues may be stabilized for immunocytochemistry by reversible, non-chemical binding processes such as cryosectioning after microwave treatment and freeze-drying. Thus, it may be possible to enhance immunostaining for some antigens by microwave irradiation of unfixed as well as fixed specimens. Parameters to be optimized for microwave retrieval of specific antigens include temperature, irradiation time, tissue buffer composition, salt concentration, and pH. Temperature, irradiation time, and pH are key variables. With this in mind, an optimal method was developed for retrieval of a wide variety of antigens in human brain tissues. Typical microwave protocols employ elevated temperatures that may reach 100 degrees C, where denaturation causes irreversible uncoiling and disruption of protein secondary and tertiary structures. Under these conditions, stable covalent bonds securing methylene crosslinks between polypeptides remain intact, but more reactive links formed by Schiff bases may be hydrolyzed. Resultant conformational changes presumably expose buried loops of continuous amino acids and protruding regions, increasing accessibility of their epitopes. Protein denaturation seems to be a reasonable explanation for the effects of microwaves on antigen retrieval. This idea is supported by the observation that denaturing solutions such as 6 M urea increase immunoreactivity of some antigens. Still, the molecular basis of these effects remains unresolved, in part due to the complex chemistry of formaldehyde reactions with tissue constituents. Indeed, some methylene bridges between similar groups such as NH2 and NH may be hydrolyzed by washing fixed tissues in distilled wa

Possible role of tau protein kinases in pathogenesis of Alzheimer's disease

Tau protein kinases (TPK) I and II were isolated as candidate enzymes responsible for the hyperphosphorylation observed in PHF-tau. Four phosphorylation sites of tau were identified for each kinase, accounting for most, but not all, of the major phosphorylation sites of PHF-tau. Immunostaining with anti-TPKI antibody indicated that this kinase is up-regulated in AD brain. Such up-regulation of TPKI and phosphorylatioin of tau were reproduced by treating cultured hippocampal cells with amyloid beta (Abeta) protein. In addition, we found that TPKI can phosphorylate and inactivate pyruvate dehydrogenase (PDH), which is expected to result in depletion of acetyl-CoA, a key substrate of acetyl choline synthesis. Indeed, when septum cells were treated with Abeta, the level of acetyl choline decreased dramatically.

Cloning of cDNA and expression of the gene encoding rat presenilin-2

We have cloned the rat homologue of the presenilin-2 (PS-2) cDNA. PS-2 is responsible for chromosome 1-linked familial Alzheimer's disease. Sequence analysis predicted that the rat PS-2 encodes a 448 amino acid (aa) protein, and there was a very high degree of amino acid identity between rat and human PS-2 (95%). All the mutated codons in PS-2 and PS-1 in chromosome 1- or 14-linked familial Alzheimer's disease patients were conserved in rat PS-2. The expression of PS-2 was weaker than that of PS-1. The alternatively spliced short form of PS-2 mRNA, which was detected in human tissues was not detected in various rat tissues. During brain development, the expression level of both PS-2 and PS-1 increased but decreased in the adult. No remarkable change was observed in neural differentiation of PC12 cells.

Physiology and pathology of tau protein kinases in relation to Alzheimer's disease

Alzheimer's disease (AD) is characterized by neuronal cell death and two kinds of deposits, neurofibrillary tangles (NFT) and senile plaques. The main component of NFT is paired helical filaments (PHF), which mainly consist of hyperphosphorylated tau protein. Tau protein kinases I and II were found as candidate enzymes responsible for hyperphosphorylation of tau to induce the formation of PHF. Since prior phosphorylation of tau by TPKII strongly enhanced the action of TPKI, it was thought that TPKII was involved in the formation of PHF-tau in concert with TPKI. After cloning, TPKI was found to be identical with glycogen synthase kinase 3 beta (GSK3 beta), while TPKII consists of a novel 23 kDa protein activator and a catalytic subunit that is identical with cyclin-dependent kinase 5 (CDK5). The phosphorylation sites on tau by TPKI and TPKII could account for the most, but not all, of the major phosphorylation sites of fetal tau and PHF-tau. An antibody for a site specifically phosphorylated by TPKI (Ser413) could identify all three neurofibrillary lesions in the AD brain, and double staining for either TPKI or TPKII and NFT in the brain of Down's syndrome patients clearly demonstrated that TPKI and TPKII are both associated with NFT in vivo, suggesting that the level of TPKI or TPKII is elevated in AD brain by some mechanism. On the other hand, the levels of both TPKs change developmentally, being high in the neonatal period when the phosphorylation of fetal tau proceeds actively, suggesting that the TPKI/TPKII cooperative system has an important physiological role in the formation of neural networks. In AD brain, aberrant accumulation of amyloid-beta protein (A beta) occurs ahead of the accumulation of PHF in NFT. When a primary culture of embryonic rat hippocampus was treated with 20 microM A beta, induction of TPKI, extensive phosphorylation of tau and then programmed cell death were observed, indicating that TPKI induced by A beta phosphorylates tau, followed by disruption of axonal transportation and finally cell death. By using a yeast two hybrid system, TPKI was found to interact with pyruvate dehydrogenase (PDH), which is a key enzyme in the glycolytic pathway. PDH was phosphorylated in vitro by TPKI to reduce the activity converting pyruvate into acetyl-CoA, which is required for acetylcholine synthesis. In a primary culture of rat hippocampal cells treated with A beta, PDH was inactivated in inverse relation to the activation of TPKI, resulting in accumulation of pyruvate or lactate, energy failure induced by the disturbance of glucose metabolism, and a shortage of acetylcholine owing to deficiency of acetyl-CoA, all of which are characteristic of AD brain. In cholinergic neurons such as those of the septum, non-aggregated A beta, specifically A beta (1-42), not A beta (1-40), caused a shortage of acetylcholine by activation of TPKI and inactivation of PDH without cell death.

Nontoxic amyloid beta peptide 1-42 suppresses acetylcholine synthesis. Possible role in cholinergic dysfunction in Alzheimer's disease

We show here that amyloid beta peptide1-42 (Abeta1-42) may play a key role in the pathogenesis of the cholinergic dysfunction seen in Alzheimer's disease (AD), in addition to its putative role in amyloid plaque formation. Abeta1-42 freshly solubilized in water (non-aged Abeta1-42), which was not neurotoxic without preaggregation, suppressed acetylcholine (ACh) synthesis in cholinergic neurons at very low concentrations (10-100 nM), although non-aged Abeta1-40 was ineffective. Non-aged Abeta1-42 impaired pyruvate dehydrogenase (PDH) activity by activating mitochondrial tau protein kinase I/glycogen synthase kinase-3beta, as we have already shown in hippocampal neurons (Hoshi, M., Takashima, A., Noguchi, K., Murayama, M., Sato, M., Kondo, S., Saitoh, Y., Ishiguro, K., Hoshino, T., and Imahori, K. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 2719-2723). Neither choline acetyltransferase activity nor choline metabolism was affected. Therefore, the major cause of reduced ACh synthesis was considered to be an inadequate supply of acetyl-CoA owing to PDH impairment. Soluble Abeta1-42 increases specifically in AD brain (Kuo, Y.-M., Emmerling, M. R., Vigo-Pelfrey, C., Kasunic, T. C., Kirkpatrick, J. B., Murdoch, G. H., Ball, M. J., and Roher, A. E. (1996) J. Biol. Chem. 271, 4077-4081). This increase in soluble Abeta1-42 may disturb cholinergic function, leading to the deterioration of memory and cognitive function that is characteristic of AD.

Immunocytochemistry of tau phosphoserine 413 and tau protein kinase I in Alzheimer pathology

One unique phosphorylation site consistently found in paired helical filament tau, serine 413, is modified by tau protein kinase I/glycogen synthase kinase-3 beta but no other known tau kinase. Here we present immunocytochemistry from Alzheimer's disease brains showing that focal subpopulations of hippocampal CA1 pyramidal neurons and neuritic plaques are strongly reactive for tau protein kinase I/glycogen synthase kinase-3 beta and tau phosphoserine 413 in early stages of pathology. Colocalization of these epitopes suggests that tau protein kinase I/glycogen synthase kinase-3 beta abnormally phosphorylates tau and is in a position to disrupt neuronal metabolism in anatomical areas vulnerable to Alzheimer's disease.

Preferential labeling of Alzheimer neurofibrillary tangles with antisera for tau protein kinase (TPK) I/glycogen synthase kinase-3 beta and cyclin-dependent kinase 5, a component of TPK II

Using immunohistochemistry, we examined the localization of four types of proline-directed kinases in the brains of control rats and in the brains of non-demented aged human subjects, subjects with Alzheimer's disease and those with Down's syndrome. The four kinases were: cyclin-dependent kinase (cdk) 5, a component of tau protein kinase (TPK) II; TPK I/glycogen synthase kinase (GSK)-3 beta; GSK-3 alpha; and mitogen-activated protein kinase (MAPK/ERK2). Each of these kinases has been reported to promote the hyperphosphorylation of tau protein in vitro. The kinases were located essentially in neurons, although the intensity and distribution of labeling varied. Antiserum for cdk5 showed the most preferential and consistent labeling of intraneuronal neurofibrillary tangles (NFT). Antiserum for TPK I/GSK-3 beta also labeled intraneuronal NFT. Double immunolabeling for TPK I/GSK-3 beta and tau 1 showed that TPK I/GSK-3 beta was closely associated with NFT. Antiserum for GSK-3 alpha labeled neurons weakly, and the intensity of labeling did not differ between neurons with and without NFT. Antiserum for MAPK labeled neurons in superficial cortical layers, but NFT appeared in both superficial and deep cortical layers. These findings suggest that cdk5 and TPK I/GSK-3 beta are the critically important kinases for the generation in vivo of hyperphosphorylated tau, the main component of the paired helical filaments in NFT.

Characterization of human presenilin 1 using N-terminal specific monoclonal antibodies: Evidence that Alzheimer mutations affect proteolytic processing

The majority of cases of early-onset familial Alzheimer disease are caused by mutations in the recently identified presenilin 1 (PS1) gene, located on chromosome 14. PS1, a 467 amino acid protein, is predicted to be an integral membrane protein containing seven putative transmembrane domains and a large hydrophilic loop between the sixth and seventh membrane-spanning domain. We produced 7 monoclonal antibodies that react with 3 non-overlapping epitopes on the N-terminal hydrophilic tail of PS1. The monoclonal antibodies can detect the full-size PS1 at Mr 47000 and a more abundant Mr 28000 product in membrane extracts from human brain and human cell lines. PC12 cells transiently transfected with PS1 constructs containing two different Alzheimer mutations fail to generate the 28 kDa degradation product in contrast to PC12 cells transfected with wild-type PS1. Our results indicate that missense mutations in this form of familial Alzheimer disease may act via a mechanism of impaired proteolytic processing of PS1.

Regulation of mitochondrial pyruvate dehydrogenase activity by tau protein kinase I/glycogen synthase kinase 3beta in brain

According to the amyloid hypothesis for the pathogenesis of Alzheimer disease, beta-amyloid peptide (betaA) directly affects neurons, leading to neurodegeneration and tau phosphorylation. In rat hippocampal culture, betaA exposure activates tau protein kinase I/glycogen synthase kinase 3beta (TPKI/GSK-3beta), which phosphorylates tau protein into Alzheimer disease-like forms, resulting in neuronal death. To elucidate the mechanism of betaA-induced neuronal death, we searched for substrates of TPKI/GSK-3beta in a two-hybrid system and identified pyruvate dehydrogenase (PDH), which converts pyruvate to acetyl-CoA in mitochondria. PDH was phosphorylated and inactivated by TPKI/GSK-3beta in vitro and also in betaA-treated hippocampal cultures, resulting in mitochondrial dysfunction, which would contribute to neuronal death. In cholinergic neurons, betaA impaired acetylcholine synthesis without affecting choline acetyltransferase activity, which suggests that PDH is inactivated by betaA-induced TPKI/GSK-3beta. Thus, TPKI/GSK-3beta regulates PDH and participates in energy metabolism and acetylcholine synthesis. These results suggest that TPKI/GSK-3beta plays a key role in the pathogenesis of Alzheimer disease.

Molecular cloning and expression of the rat homologue of presenilin-1

The rat homologue of the presenilin-1 (PS-1) gene, which is responsible for early-onset familial Alzheimer's disease linked to chromosome 14, was cloned and sequenced. The predicted amino acid sequence showed quite high homology among rat, mouse, and human PS-1. Especially, the amino acid sequences of the putative transmembrane domains were highly conserved among the three species. The expression ĺevel of the PS-1 gene increased during brain development and the number of transcripts of the PS-1 gene changed during brain development. We found one transcript of the PS-1 gene in embryonic day 12 (E12)-E15 rat brain and two transcripts in E18-adult rat brain. Therefore, PS-1 may play a role in neurogenesis.

Exposure of rat hippocampal neurons to amyloid beta peptide (25-35) induces the inactivation of phosphatidyl inositol-3 kinase and the activation of tau protein kinase I/glycogen synthase kinase-3 beta

Exposure of rat hippocampal neurons to the peptide amyloid beta (A beta) (25-35) as well as A beta (1-40) peptides enhances phosphorylation of tau to a paired helical filament (PHF)-state through activation of tau protein kinase I (TPK I)/glycogen synthase kinase-3 beta (GSK-3 beta) [Busciglio, J., Lorenzo, A., Yeh, J. and Yankner, B.A., Neuron, 14 (1995) 879-888; Takashima, A., Ishiguro, K., Noguchi, K., Michel, G., Hoshi, M., Sato, K., Takahashi, M., Hoshino, T., Uchida, T. and Imahori, K., Neurosci. Meeting Abstr., 671 (1995) 17]. In order to examine the effects of A beta treatment on intracellular signaling mechanism, we have investigated the role of phosphatidyl inositol-3 (PI-3) kinase in the phosphorylation of tau. A beta (25-35) exposure induced an inactivation of PI-3 kinase and an activation of TPK I/GSK-3 beta in rat hippocampal culture. Wortmannin, an inhibitor of PI-3 kinase, also activated TPK I/GSK-3 beta, leading to an enhancement of tau phosphorylation and neuronal death in hippocampal culture. These results suggest that A beta (25-35) inhibition of PI-3 kinase results in the activation of TPK I/GSK-3 beta, the phosphorylation of tau, and resultant neuronal death in rat hippocampal neurons.

Analysis of phosphorylation of tau with antibodies specific for phosphorylation sites

Previously, we determined sites of tau protein phosphorylation by tau protein kinase (TPK) I/glycogen synthase kinase 3 beta (GSK-3 beta) and TPKII/(cyclin-dependent kinase 5 (CDK5) + p23). We prepared antibodies specific for these sites of tau phosphorylated by TPKI and TPKII, using chemically synthesized phosphopeptides as antigens. Each antibody specifically reacts with each phosphorylation site. With these antibodies, it was confirmed that TPKI and TPKII are responsible for these phosphorylation sites, as reported previously, except that Ser404 is also weakly phosphorylated by TPKI alone. It was also observed that TPKII-phosphorylation enhances TPKI-phosphorylation. These results indicate that these antibodies are useful tools for investigation of the phosphorylation of tau by TPKI and TPKII.

Correlation among secondary structure, amyloid precursor protein accumulation, and neurotoxicity of amyloid beta(25-35) peptide as analyzed by single alanine substitution

Structure-neurotoxicity relationships of amyloid beta (25-35) peptide were studied by replacing each amino acid with Ala. In contrast to the general tendency in hydrophobicity-toxicity relationships, replacement of Asn27 yielded a more hydrophobic but less toxic analog and that of Met35 gave a less hydrophobic but more toxic one. Sedimentation profiles and CD spectra indicated that peptide aggregation via intermolecular beta-sheet formation is essential for the neurotoxicity of amyloid beta (25-35) peptide. The correlation between neurotoxicity and amyloid precursor protein accumulation suggested that the latter is one of the pathways of the neuronal death caused by amyloid beta protein.

Tau protein immunoreactivity in muscle fibers with rimmed vacuoles differs from that in regenerating muscle fibers

To determine whether tau protein found in muscle fibers with rimmed vacuoles and in regenerating fibers was phosphorylated, we examined eight muscle biopsy samples containing rimmed vacuoles (from five patients with distal myopathy with rimmed vacuole formation and three patients with inclusion body myositis) and three muscle biopsy samples from patients with Duchenne muscular dystrophy containing numerous regenerating fibers. Although both rimmed vacuolated and regenerating fibers had increased immunoreactivity against tubulin and tau protein, tau protein in the former was more highly phosphorylated than that in the latter. While very few microtubules in muscle fibers with rimmed vacuoles were recognizable by electron microscopy, regenerating fibers, especially immature ones, contained numerous microtubules. Since tau protein found in vacuolated fibers is hyperphosphorylated, it can be considered to have reduced ability to bind tubulin molecules. Thus, the tau protein cannot stabilize microtubules, resulting in their depolymerization even in the presence of tubulin molecules.

Different localization of tau protein kinase I/glycogen synthase kinase-3 beta from glycogen synthase kinase-3 alpha in cerebellum mitochondria

We examined the subcellular distribution of two glycogen synthase kinase-3 (GSK-3) isoforms in rat cerebellum. Results from immunoelectron microscopy and subcellular fractionation revealed that one isoform, tau protein kinase I/GSK-3 beta (TPKI/GSK-3 beta), was present in mitochondria, but GSK-3 alpha was not. Although the two GSK-3 isoforms seem to have similar properties, the difference of subcellular localization observed here suggests that TPKI/GSK-3 beta fulfills some specific function in mitochondria.

Amyloid beta peptide induces cytoplasmic accumulation of amyloid protein precursor via tau protein kinase I/glycogen synthase kinase-3 beta in rat hippocampal neurons

Exogenous application of synthetic amyloid beta protein (A beta) is known to induce neurotoxic effects in rat hippocampal culture. We report here that A beta (25-35) induces accumulation of amyloid precursor protein (APP) derivatives in the cytoplasm of neurons. At the same time, the level of the secreted form of APP released into the culture medium decreases. Tau protein kinase I/glycogen synthase kinase-3 beta (TPK I/GSK-3 beta) antisense oligonucleotide blocked APP accumulation and prevented neuronal death. These results provide evidence that APP accumulation after A beta treatment is regulated by TPK I/GSK-3 beta. A beta neurotoxicity is probably mediated via phosphorylation of tau by TPK I/GSK-3 beta, resulting in an impairment of axonal transport, and cytoplasmic accumulation of APP.

cDNA cloning of a novel brain-specific protein p25

A cDNA for a bovine brain-specific protein p25 which had been originally found as a major protein in a partially purified fraction of tau protein kinases was cloned. The deduced amino-acid sequence consists of 218 amino acids (M(r) 23,472) and has no significant homology with previously reported proteins. p25 is a basic protein and has a consensus sequence for ATP-binding in the C-terminal region.

Involvement of tau protein kinase I in paired helical filament-like phosphorylation of the juvenile tau in rat brain

tau protein kinase I (TPKI) phosphorylates tau and forms paired helical filament epitopes in vitro. We studied temporal expression and histochemical distribution of tau phosphoserine epitopes at sites known to be phosphorylated by TPKI. Antibodies directed against phosphorylated Ser199 (anti-PS 199) or phosphorylated Ser396 (C5 or anti-PS 396) were used. TPKI is abundantly expressed in the young rat brain and the highly phosphorylated juvenile form of tau occurs in the same period. The activity peak of TPKI coincided with the high level of phosphorylation of Ser199 and Ser396 in juvenile tau at around postnatal day 8. By immunohistochemistry on the hippocampus and neocortex of 3-11-day-old rats, phosphorylated Ser396 was found in young axonal tracts and neuropil, where TPKI immunoreactivity was also detected. TPKI and phospho-Ser199 immunoreactivities were also detected in the perikarya of pyramidal neurons. TPKI immunoreactivity had declined to a low level and phosphorylated serine immunoreactivities were undetectable in the sections of adult brain. These findings implicate TPKI in paired helical filament-like phosphorylation of juvenile form of tau in the developing brain.

Precursor of cdk5 activator, the 23 kDa subunit of tau protein kinase II: its sequence and developmental change in brain

Tau protein kinase II (TPKII) is shown by immunoprecipitation to be a complex composed of two subunits, a catalytic subunit, cdk5, and regulatory subunit, p23. By sequence analysis of p23 cDNA, p23 was found to occupy a region from the 99th amino acid residue to the C-terminus of a novel protein with a molecular weight of 34,000 Da, suggesting that this 34 kDa protein is a precursor of p23 (pre-p23). These findings suggest that p23 results from the processing of the precursor protein, pre-p23. The precursor mRNA was expressed most abundantly in rat brain just before and after birth. Expression of pre-p23, but not of cdk5, mRNA changed, coinciding with the developmental change of TPKII activity, suggesting that its expression controls the phosphorylation of tau by the TPKII/TPKI system in the neonatal brain. p23 appears to be a cdk5 activator in neuronal cells.

Localization and developmental changes of tau protein kinase I/glycogen synthase kinase-3 beta in rat brain

tau protein kinase I (TPKI) purified from bovine brain extract has been shown to phosphorylate tau and to form paired helical filament (PHF) epitopes and was found recently to be identical to glycogen synthase kinase -3 beta (GSK-3 beta). Before elucidating a role of TPKI/GSK-3 beta in PHF formation, it is necessary to investigate the normal function of the enzyme. To study the distribution and developmental changes of the enzyme, specific polyclonal antibodies were prepared against TPKI and GSK-3 alpha. Immunoblot analysis demonstrated that TPKI was nearly specifically localized in the brain of adult rats. The level of TPKI in the rat brain was high at gestational day 18, peaked on postnatal day 8, and then decreased rapidly to a low level, which was sustained up to 2 years. Immunohistochemistry indicated primarily neuronal localization of TPKI. Growing axons were stained most intensely in the developing cerebellum, but the immunoreactivity became restricted to the gray matter in the mature tissue. Parallel fibers had a high level of TPKI and also stained intensely for tau. These findings indicate that tau is one of the physiological substrates of TPKI and suggest that the enzyme plays an important role in the growth of axons during development of the brain.

Identification of the 23 kDa subunit of tau protein kinase II as a putative activator of cdk5 in bovine brain

Tau protein kinase II (TPKII) was reported previously to be composed of a neuron-rich cdc2-related kinase (PSSALRE/cdk5) and 23 kDa subunit. Here we show that the 23 kDa subunit is a putative activator for the kinase activity. Amino acid sequence analysis revealed that the protein was novel and included a partial similarity of amino acids to a cyclin box important for the interaction with cdc2-related kinase. These results suggest that the 23 kDa subunit, but not cyclin, activates cdk5 in neuronal cells, which no longer exhibit cell cycling but are terminally differentiated cells.

A cdc2-related kinase PSSALRE/cdk5 is homologous with the 30 kDa subunit of tau protein kinase II, a proline-directed protein kinase associated with microtubule

We previously reported that tau protein kinase II (TPKII) from bovine brain was composed of 30 kDa and 23 kDa subunits. The 30 kDa subunit of TPKII can be regarded as a catalytic subunit because of its ATP-binding activity. Antibodies directed against TPKII-phosphorylated tau also reacted with tau phosphorylated by cdc2 kinase obtained from starfish oocytes, indicating that TPKII and cdc2 kinase phosphorylate the same sites. We determined the amino acid sequence of the 30 kDa subunit and found it to be homologous with a cdc2-related kinase, PSSALRE/cdk5. Moreover, an antibody against PSSALRE/cdk5 reacted with the 30 kDa subunit. These results indicate that the 30 kDa subunit of TPKII is bovine homologue of PSSALRE/cdk5. Expression of the 30 kDa subunit mRNA was enhanced in juvenile rat brain. This result supports our previous hypothesis that the kinase works actively in juvenile brain.

Tau protein kinase I is essential for amyloid beta-protein-induced neurotoxicity

Pathological changes of Alzheimer disease are characterized by cerebral cortical atrophy as a result of degeneration and loss of neurons. Typical histological lesions include numerous senile plaques composed of deposits of amyloid beta-protein and neurofibrillary tangles consisting predominantly of ubiquitin and highly phosphorylated tau proteins. Previously, tau protein kinase I (TPK I) was purified and its cDNA was cloned. To examine the biological role of this enzyme in neurons, we have studied the induction of its kinase activity in primary cultures of embryonic rat hippocampal neurons. Treatment of cultures with amyloid beta-protein significantly increased TPK I activity and induced the appearance of tau proteins recognized by the Alz-50 monoclonal antibody. In addition, though amyloid beta-protein was neurotoxic, either cycloheximide or actinomycin D prevented neuronal death. Death was also prevented by TPK I antisense oligonucleotides but not by sense oligonucleotides. These observations suggest that rat hippocampal neurons undergo programmed cell death in response to amyloid beta-protein and that TPK I is a key enzyme in this process.

Glycogen synthase kinase 3 beta is identical to tau protein kinase I generating several epitopes of paired helical filaments

We previously reported that tau protein kinase I (TPKI) induced normal tau protein into a state of paired helical filaments (PHF); this is further confirmed here by immunoblot analysis using several antibodies. We also present the amino acid sequence of TPKI, which is identical to glycogen synthase kinase 3 beta (GSK3 beta). Moreover, we found that TPKI activity was inseparable from GSK3 activity throughout the purification procedure. These results indicate that TPKI is identical to GSK3 beta.

Tau protein kinase II is involved in the regulation of the normal phosphorylation state of tau protein

To study the phosphorylation state of tau in vivo, we have prepared antisera by immunizing rabbits with synthetic phosphopeptides containing phosphoamino acids at specific sites that are potential targets for tau protein kinase II. Immunoblot experiments using these antisera demonstrated that tau in microtubule-associated proteins is phosphorylated at Ser144 and at Ser315. Almost all tau variants separated on two-dimensional gel electrophoresis were phosphorylated at Ser144 and nearly one-half of them at Ser315. Phosphorylation at Ser144 and at Thr147 of tau isolated from heat-stable brain extracts was shown to be developmentally regulated, with the highest level of phosphorylation found at postnatal week 1. In vitro phosphorylation of tau by tau protein kinase I, a kinase responsible for abnormal phosphorylation of tau found in paired helical filaments of patients with Alzheimer's disease, was enhanced by prior phosphorylation of tau by tau protein kinase II. Thus, we suggest that tau protein kinase II is indirectly involved, at least in part, in the regulation of the phosphorylation state of tau in neuronal cells.

A brain-specific protein p25 is localized and associated with oligodendrocytes, neuropil, and fiber-like structures of the CA3 hippocampal region in the rat brain

Developmental expression and cellular localization of a novel brain-specific 25-kDa protein (p25), a substrate of tau protein kinase II, were investigated in the rat brain using polyclonal antibodies raised against peptides synthesized based on the p25 amino acid sequence. By western immunoblotting, p25 was found to be expressed only slightly in the embryonic period; the expression increased from 11 days up to 5 weeks of age, and continued to increase gradually until 1-2 years of age. Immunohistochemistry revealed distinct staining of glial cells in most regions of the central nervous system in the adult rat brain. These positively immunostained cells were especially abundant in the white matter, such as the corpus callosum, cingulum, external capsule, and internal capsule. The glial cells were identified as oligodendrocytes, and the nuclei of the cells remained unstained. Whereas the neuropil in most parts of the brain was immunostained less intensely than glias, the neuropil in the first and second layers of the cerebral cortex and the dentate gyrus was relatively strongly stained. Fiber-like structures were also stained in the CA3 region of hippocampus.

Phosphorylation sites on tau by tau protein kinase I, a bovine derived kinase generating an epitope of paired helical filaments

Tau protein kinase I (TPKI) isolated from bovine brain has been determined to phosphorylate tau at four distinct sites by detecting modified Ser and Thr residues with protein sequencer. Ser199, Thr231, Ser396 and Ser413 were all found to have been phosphorylated by TPKI (numbering of amino acids was done in relation to the longest human tau [Neuron, 3 (1989) 519-526]). These phosphorylations generate an epitope of PHF (paired helical filaments) and eliminate the recognition of tau by the monoclonal antibody, tau-1. These results suggested that TPKI might be responsible for at least some of the phosphorylation of tau to induce PHF formation.

Tau protein kinase I converts normal tau protein into A68-like component of paired helical filaments

From bovine brain microtubules we purified tau protein kinase I (TPKI, Mr 45,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and tau protein kinase II (TPKII) whose activity was attributed to a 30-kDa protein on SDS-PAGE by affinity-labeling using an ATP analog. Both kinases were activated by tubulin. TPKII, but not TPKI, phosphorylated tau fragment peptides previously used for detection of a Ser/ThrPro kinase activity. Therefore, TPKII was considered to be the Ser/ThrPro kinase. TPKI was more effective than TPKII for producing the decrease of tau-1 immunoreactivity and mobility shift of tau on SDS-PAGE. Moreover, TPKI, but not TPKII nor other well-known protein kinases, generated an epitope present on paired helical filaments. These findings suggested that tau phosphorylated by TPKI resembled A-68, a component of paired helical filaments.

A novel brain-specific 25 kDa protein (p25) is phosphorylated by a Ser/Thr-Pro kinase (TPK II) from tau protein kinase fractions

A novel brain-specific 25 kDa protein (p25) was purified from a bovine brain extract. The protein was phosphorylated by Ser/Thr-Pro kinase (TPK II) in tau protein kinase fractions at the Ser residues of Ser-Pro sequences. Using immunoblot analysis, the protein was found only in brain extracts, and was most abundant in the brain regions such as cerebrum and hippocampus, but less abundant in cerebellum, medulla oblongata and olfactory bulb. The protein was detected in rat, bovine and human brain extracts, indicating that this protein specifically exists in mammalian brain tissues.

A serine/threonine proline kinase activity is included in the tau protein kinase fraction forming a paired helical filament epitope

Previously we partially purified a novel protein kinase which phosphorylated tau and formed a paired helical filament (PHF) epitope. In this paper we show that the kinase fraction contains a protein kinase activity recognizing serine/threonine proline sequence. The kinase phosphorylated tau at the tau-1 site previously reported as one of the phosphorylation sites on PHF by other groups. The kinase also phosphorylated extraordinarily insoluble portion located on C-terminal region of tau in PHF. It is worth considering that tau phosphorylated by this kinase activity is incorporated into PHF.

A novel tubulin-dependent protein kinase forming a paired helical filament epitope on tau

From rat brain microtubule proteins, we purified a protein kinase that phosphorylated tau, one of microtubule-associated proteins. The electrophoretic mobility of the phosphorylated tau on SDS-polyacrylamide gel decreased. The enzyme was not activated by cyclic nucleotides, calmodulin, or phospholipids, and was inhibited by the calcium ions. The kinase bound to tau. The phosphorylation of tau was stimulated by tubulin under the condition of microtubule formation. From these results we propose an idea that the phosphorylation could occur concomitantly with microtubule formation in the brain. Human tau phosphorylated by the kinase carried an epitope of the paired helical filaments that accumulate in the brain in Alzheimer's disease.

Tissue distribution of calcium-activated neutral proteinases in rat

A simple separation method involving a minimum number of essential steps was established to separate the two kinds of calcium-activated neutral proteinase (CANP) activity from each other and from endogenous CANP inhibitor activity. Determination of CANP activity in rat tissues using this method revealed a ubiquitous distribution of two CANPs. The level of CANP activity, however, differs between tissues. Low-calcium-requiring CANP (microCANP) is plentiful in spleen and kidney, while high-calcium-requiring CANP (mCANP) is plentiful in lung and brain. In all of the tissues examined, mCANP activity predominates over microCANP activity.

Effect of perfringolysin O on the lateral diffusion constant of membrane proteins of hepatocytes as revealed by fluorescence recovery after photobleaching

Perfringolysin O is a thiol-activated cytolytic exotoxin the primary receptor of which is the membrane cholesterol on the cell surface. The effect of perfringolysin O was tested in various hepatocyte preparations. (i) Smears of fresh liver exposed to a mild H2O2 (1.0 mM) injury for 10 min at 37 degrees C, develop a 'peroxide-induced autofluorescence' (PIAF) on the membrane proteins. PIAF is suitable for measuring the average lateral diffusion constant (D) of the membrane proteins by means of fluorescence recovery after photobleaching technique (FRAP). Incubation for 5 min with 600 or 2000 units/ml of the perfringolysin O resulted in a significant increase (32 and 46%, respectively) of D as compared to the controls of the same age group (13-14 months). Various tests like heat denaturation of cholesterol saturation of perfringolysin O before its application as well as thiol-activation of the smears with dithiothreitol revealed that the increase of D is a specific toxin effect due mot probably to the reaction of perfringolysin O with cholesterol. (ii) Isolated hepatocytes were exposed to perfringolysin O and their viability as well as the release of two cytosolic enzymes (lactate dehydrogenase and glutamic-pyruvic transaminase) were measured; 40-60 units/ml of perfringolysin O in 30 min reduced the viability of the hepatocytes to zero and caused a release of about 70% of both cytosolic enzymes. The significance of the results is discussed from the points of view of both the toxin-effect and the FRAP method.

Tissue distribution of an endogenous inhibitor of calcium-activated neutral protease and age-related changes in its activity in rats

1. The distribution of an endogenous inhibitor of calcium-activated neutral protease (CANP) and age-related changes in its activity were studied in male and female rats of different ages by a fluorometric assay on tissue extracts after heat treatment. 2. Ubiquitous distribution of CANP inhibitor in brain, cardiac muscle, lung, spleen, liver, skeletal muscle, kidney and testis and its abundance in spleen, liver and kidney was demonstrated. 3. Comparison in terms of units/ml of crude extracts showed that the level of CANP inhibitor exceeded that of CANP in most tissues and that the relative content of CANP inhibitor to mCANP and microCANP differed greatly among tissues. 4. Sex and species differences in CANP inhibitor activity in each tissue were of little significance. 5. Changes in CANP inhibitor during aging from 6 to 12 months was not obvious but senescent rats showed a tendency toward increased inhibitor activity. This increase was especially evident in the testis.

Thiol protease-specific inhibitor E-64 arrests human epidermoid carcinoma A431 cells at mitotic metaphase

E-64-d (ethyl (2S, 3S)-3-[(S)-3-methyl-1-(3-methylbutylcarbamoyl) butylcarbamoyl]oxirane-2-carboxylate), a membrane-permeant derivative of the thiol protease-specific inhibitor E-64, was found to arrest human epidermoid carcinoma A431 cells at mitotic metaphase. This effect was dose-dependent with a threshold of 20 micrograms/ml in chemically defined culture medium. Cell cycle analysis by flow cytometry showed that the relative proportion of the G2/M population increased 2.5-fold after treatment of the cells with E-64 (100 micrograms/ml) for 5 hr. In addition, time-lapse video analysis showed that E-64-treated cells remained at metaphase for an extended period after rounding-up, whereas untreated cells completed mitosis within 42.0 +/- 5.7 min. Some treated cells were able to complete mitosis, while others did not do so within the limits of our observation. As an approach to the molecular basis of this phenomenon, we have shown that several cellular proteins can be labeled by incubation of cells with radioactive E-64-d.

Possibilities and limitations of the smearing technique for cellular studies in compact tissues: a transmission electron microscopic analysis of liver smears

During the last decade a sophisticated biophysical technique called fluorescence recovery after photobleaching (FRAP) has become available for the measurement of lateral diffusion constants of lipids and proteins in the cell membrane. The information obtainable by this method is of great importance; however, the applicability of this method is seriously hindered by the fact that it has been elaborated mostly for isolated, individual cells. On the other hand, the use of freshly prepared cells from compact tissues for such studies is highly desirable. Therefore, a special smearing method was devised (using liver cells) for this purpose. The present paper describes (i) the method of standardization of the smearing technique, (ii) the ultrastructural features of the liver cells when studying the liver smears by means of transmission electron microscopy. The possibilities and limitations of this method are discussed. According to the observations, under well-defined conditions the structural integrity of hepatocytes is maintained in the liver smears to such an extent that they are suitable for FRAP experiments.