Masato Hasegawa

|[alpha]|-Synuclein is phosphorylated in synucleinopathy lesions

The deposition of the abundant presynaptic brain protein α-synuclein as fibrillary aggregates in neurons or glial cells is a hallmark lesion in a subset of neurodegenerative disorders. These disorders include Parkinsons disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy, collectively referred to as synucleinopathies. Importantly, the identification of missense mutations in the α-synuclein gene in some pedigrees of familial PD has strongly implicated α-synuclein in the pathogenesis of PD and other synucleinopathies. However, specific post-translational modifications that underlie the aggregation of α-synuclein in affected brains have not, as yet, been identified. Here, we show by mass spectrometry analysis and studies with an antibody that specifically recognizes phospho-Ser 129 of α-synuclein, that this residue is selectively and extensively phosphorylated in synucleinopathy lesions. Furthermore, phosphorylation of α-synuclein at Ser 129 promoted fibril formation in vitro. These results highlight the importance of phosphorylation of filamentous proteins in the pathogenesis of neurodegenerative disorders.

Ubiquitin is conjugated with amino-terminally processed tau in paired helical filaments

We have investigated ubiquitinated paired helical filaments, which produce a proteinaceous smear in SDS-polyacrylamide gel electrophoresis and immunoblotting. The smear consisted largely of the carboxy-terminal portion of tau and ubiquitin. The ubiquitin-targeted protein was identified as tau in paired helical filaments, and the conjugation sites were localized to the microtubule-binding region. Most ubiquitin in paired helical filaments occurred as a monoubiquitinated form, and only a small proportion of ubiquitin formed multiubiquitin chains. There was a ubiquitin-negative smear, in which tau was much less processed in the amino-terminal portion. This strongly suggests that the amino-terminal processing of tau in paired helical filaments precedes its ubiquitination.

Hyperphosphorylation and insolubility of α‐synuclein in transgenic mouse oligodendrocytes

(Oligodendro)glial cytoplasmic inclusions composed of α‐synuclein (αSYN) characterize multiple system atrophy (MSA). Mature oligodendrocytes (OLs) do not normally express αSYN, so MSA pathology may arise from aberrant expression of αSYN in OLs. To study pathological deposition of αSYN in OLs, transgenic mice were generated in which human wild‐type αSYN was driven by a proteolipid protein promoter. Transgenic αSYN was detected in OLs but no other brain cell type. At the light microscopic level, the transgenic αSYN profiles resembled glial cytoplasmic inclusions. Strikingly, the diagnostic hyperphosphorylation at S129 of αSYN was reproduced in the transgenic mice. A significant proportion of the transgenic αSYN was detergent insoluble, as in MSA patients. The histological and biochemical abnormalities were specific for the disease‐relevant αSYN because control green fluorescent protein was fully soluble and evenly distributed throughout OL cell bodies and processes. Thus, ectopic expression αSYN in OLs might initiate salient features of MSA pathology.

Age-Related Amyloid β Deposition in Transgenic Mice Overexpressing Both Alzheimer Mutant Presenilin 1 and Amyloid β Precursor Protein Swedish Mutant Is Not Associated with Global Neuronal Loss

To analyze the relationship between the deposition of amyloid beta peptides (Abeta) and neuronal loss in transgenic models of Alzheimers disease (AD), we examined the frontal neocortex (Fc) and CA1 portion of hippocampus (CA1) in PSAPP mice doubly expressing AD-associated mutant presenilin 1 (PS1) and Swedish-type mutant beta amyloid precursor protein (APPsw) by morphometry of Abeta burden and neuronal counts. Deposition of Abeta was detected as early as 3 months of age in the Fc and CA1 of PSAPP mice and progressed to cover 28.3% of the superior frontal cortex and 18.4% of CA1 at 12 months: approximately 20- (Fc) and approximately 40- (CA1) fold greater deposition than in APPsw mice. There was no significant difference in neuronal counts in either CA1 or the frontal cortex between nontransgenic (non-tg), PS1 transgenic, APPsw, and PSAPP mice at 3 to 12 months of age. In the PSAPP mice, there was disorganization of the neuronal architecture by compact amyloid plaques, and the average number of neurons was 8 to 10% fewer than the other groups (NS, P > 0.10) in CA1 and 2 to 20% fewer in frontal cortex (NS, P = 0.31). There was no loss of total synaptophysin immunoreactivity in the Fc or dentate gyrus molecular layer of the 12-month-old PSAPP mice. Thus, although co-expression of mutant PS1 with Swedish mutant betaAPP leads to marked cortical and limbic Abeta deposition in an age-dependent manner, it does not result in the dramatic neuronal loss in hippocampus and association cortex characteristic of AD.

Tau gene mutation G389R causes a tauopathy with abundant pick body-like inclusions and axonal deposits.

Exonic and intronic mutations in Tau cause familial neurodegenerative syndromes characterized by frontotemporal dementia and dysfunction of multiple cortical and subcortical circuits. Here we describe a G389R mutation in exon 13 of Tau. When 38 years old, the proband presented with progressive aphasia and memory disturbance, followed by apathy, indifference, and hyperphagia. Repeated magnetic resonance imaging showed the dramatic progression of cerebral atrophy. Positron emission tomography revealed marked glucose hypometabolism that was most severe in left frontal, temporal, and parietal cortical regions. Rigidity, pyramidal signs and profound dementia progressed until death at 43 years of age. A paternal uncle, who had died at 43 years of age, had presented with similar symptoms. The probands brain showed numerous tau-immunoreactive Pick body-like inclusions in the neocortex and the fascia dentata of the hippocampus. In addition, large numbers of tau-positive filamentous inclusions were present in axons in the frontal, temporal, and parietal lobes. Immunoblot analysis of sarkosyl-insoluble tau showed 2 major bands of 60 and 64 kDa. Upon dephosphorylation, these bands resolved into 4 bands consisting of three- and four-repeat tau isoforms. Most isolated tau filaments were straight and resembled filaments found in Alzheimer disease and some frontotemporal dementias with tau mutations. A smaller number of twisted filaments was also observed. Biochemically, recombinant tau proteins with the G389R mutation showed a reduced ability to promote microtubule assembly, suggesting that this may be the primary effect of the mutation. Taken together, the present findings indicate that the G389R mutation in Tau can cause a dementing condition that closely resembles Picks disease.

Hyperphosphorylation of Tau in PHF

Tau in PHF is known to be highly phosphorylated and immunochemical study has indicated the similarity of the phosphorylation between PHF-tau and fetal tau. We have determined the exact phosphorylation sites in both PHF-tau and fetal rat tau by ion-spray mass spectrometry and sequencing of ethanethiol-modified peptides. In PHF-tau, 19 sites have been identified; all the phosphorylation sites except for Ser-262 are localized to the amino- and carboxyl-terminal flanking regions of the microtubule-binding domain. Half of them are shared by fetal tau. Thus, PHF-tau is much more phosphorylated. Whereas most of the sites in fetal tau are proline-directed, half of them in PHF-tau are nonproline-directed. Overall, the hyperphosphorylation of PHF-tau can be considered to consist of fetal-type phosphorylation and additional proline-directed and nonproline-directed phosphorylation. This extraphosphorylation may provide PHF-tau with the unusual characteristics including assembly incompetence.

Characterization of mAb AP422, a novel phosphorylation-dependent monoclonal antibody against tau protein

A monoclonal antibody (AP422) specific for phosphoserine 422 in microtubule‐associated protein tau has been produced. It strongly labels paired helical filament (PHF) tau from Alzheimers disease brain in a phosphorylation‐dependent manner. By contrast, AP422 only labels a small fraction of fetal tau and a very small fraction of tau from adult brain. The amount of tau phosphorylated at Ser‐422 in normal brain is minor relative to that phosphorylated at sites recognized by other phosphorylation‐dependent anti‐tau antibodies of known epitope. It follows that AP422 is the most specific anti‐tau antibody available for detecting the neurofibrillary lesions of Alzheimers disease. We also show that Ser‐422 in tau is a good in vitro substrate for mitogen‐activated protein kinase, but not for glycogen synthase kinase‐3 or neuronal cdc2‐like kinase.

Calpain-mediated degradation of p35 to p25 in postmortem human and rat brains

Tau in Alzheimer neurofibrillary tangles has been shown to be hyperphosphorylated and CDK5, GSK3, MAP kinase and SAP kinases are the candidate kinases for the phosphorylation of tau. Recently, it was reported that the conversion of p35, the activator of CDK5, to p25 was upregulated in Alzheimers disease (AD) brains, and that p35 is cleaved to yield p25 by calpain. Here we show that p35 is rapidly cleaved to p25 in rat and human brains within a short postmortem delay and that the conversion of p35 to p25 is partially dependent on calpain activity. Immunoblot analysis of brains prepared from patients with AD or age‐matched control individuals with a short postmortem delay revealed no specific increase in the levels of p25 in AD brains, whereas the levels of active form of calpain were increased in AD brains compared to the those in controls. These observations suggest that the conversion of p35 to p25 is a postmortem degradation event and may not be upregulated in AD brains.

Pick's disease is associated with mutations in the tau gene

Recently, mutations within the tau gene have been associated with some familial forms of frontotemporal dementia. To investigate whether tau gene mutations are also associated with Picks disease, we analyzed the tau gene in 30 cases of pathologically confirmed Picks disease. Two coding mutations were identified in separate cases of Picks disease. A glycine‐to‐arginine mutation at codon 389 was detected in 1 case and a lysine‐to‐threonine mutation at codon 257 was identified in another. Analysis of dephosphorylated tau from the brain of the patient with the codon 389 mutation revealed a prominent band representing tau, with four microtubule‐binding domains and no amino terminal inserts. This is in contrast to Picks disease without any tau gene mutations, which consist of tau with mainly three microtubule‐binding domains and only a trace of tau, with four microtubule‐binding domains. Functional analysis of tau with these two mutations demonstrated a reduced ability of tau to promote microtubule assembly. Surprisingly, these mutations increased taus susceptibility to calpain I digestion, suggesting that this feature may be related to the formation of a Pick type of histology. Moreover, these data suggest that Picks disease is not a separate entity but part of the frontotemporal dementia disease spectrum. Ann Neurol 2000;48:859–867

Characterization of Two Distinct Monoclonal Antibodies to Paired Helical Filaments: Further Evidence for Fetal-Type Phosphorylation of the τ in Paired Helical Filaments

Abstract: Two monoclonal antibodies C5 and M4 raised against Sarkosyl‐insoluble paired helical filaments (PHF) specifically labeled fetal τ, but hardly labeled normal adult τ. C5 immunoreactivity was eliminated by alkaline phosphatase treatment at 37°C, whereas M4 reactivity could be removed only by the treatment at 67°C. Epitope analysis showed that C5 and M4 recognition sites are in residues 386–406 and 198–250, respectively, according to the numbering of the longest human τ isoform. Thus, the phosphorylation sites are located in the amino‐ and carboxyl‐terminal portions of the microtubule‐binding region. These two well‐characterized monoclonals should be valuable in the identification of a protein kinase(s) that converts normal τ into PHF‐τ.