Kazutomo Imahori

Glycogen synthase kinase 3β 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 3β (GSK3β). Moreover, we found that TPKI activity was inseparable from GSK3 activity throughout the purification procedure. These results indicate that TPKI is identical to GSK3β.

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.

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

Abstract 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)-3β; GSK-3α; 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-3β also labeled intraneuronal NFT. Double immunolabeling for TPK I/GSK-3β and tau1 showed that TPK I/GSK-3β was closely associated with NFT. Antiserum for GSK-3α 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-3β are the critically important kinases for the generation in vivo of hyperphosphorylated tau, the main component of the paired helical filaments in NFT.

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 Alzheimers 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 versus 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.

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 Alzheimers 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.

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.

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.

Nontoxic Amyloid β Peptide1-42 Suppresses Acetylcholine Synthesis POSSIBLE ROLE IN CHOLINERGIC DYSFUNCTION IN ALZHEIMER'S DISEASE

We show here that amyloid β peptide1-42 (Aβ1-42) may play a key role in the pathogenesis of the cholinergic dysfunction seen in Alzheimers disease (AD), in addition to its putative role in amyloid plaque formation. Aβ1-42 freshly solubilized in water (non-aged Aβ1-42), which was not neurotoxic without preaggregation, suppressed acetylcholine (ACh) synthesis in cholinergic neurons at very low concentrations (10-100 nM), although non-aged Aβ1-40 was ineffective. Non-aged Aβ1-42 impaired pyruvate dehydrogenase (PDH) activity by activating mitochondrial τ protein kinase I/glycogen synthase kinase-3β, 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 Aβ1-42 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 Aβ1-42 may disturb cholinergic function, leading to the deterioration of memory and cognitive function that is characteristic 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.

Localization and Developmental Changes of τ Protein Kinase I/Glycogen Synthase Kinase‐3β in Rat Brain

Abstract: τ protein kinase I (TPKI) purified from bovine brain extract has been shown to phosphorylate τ and to form paired helical filament (PHF) epitopes and was found recently to be identical to glycogen synthase kinase‐3β (GSK‐3β). Before elucidating a role of TPKI/GSK‐3β 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‐3α. 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 τ. These findings indicate that τ 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.