Yasushi Tomidokoro

Combination assay of CSF Tau, Aβ1-40 and Aβ1-42(43) as a biochemical marker of Alzheimer's disease

Cerebrospinal fluid samples from a total of 157 subjects consisting of 55 patients with sporadic Alzheimers disease (AD), 34 normal controls, 23 patients with non-AD dementia, and 45 with other neurological diseases were examined by ELISA of tau, Aβ1-40, and Aβ1-42(43). The AD group had a significantly higher level of tau than the normal control group (P<0.001), and the diagnostic sensitivity was 31% and specificity was 94%. CSF Aβ1-40 levels did not show any significant differences. Although the level of Aβ1-42(43) was decreased significantly in the AD group compared to the control group (P<0.005), the overlap of Aβ1-42(43) levels among all groups meant that none of the AD samples exceeded the cut-off value, the mean 2SD of normal control subjects. Reduction of Aβ1-42(43) levels in AD resulted in a significant increase in the ratio of Aβ1-40 to Aβ1-42(43) (Aβ ratio) as an improved marker. The diagnostic sensitivity and specificity of Aβ ratio were 51% and 82% respectively. The three indexes, using the tau level and Aβ ratio (tau or Aβ ratio, deviation score and tau×Aβ ratio), showed better sensitivity (58%, 67%, 69%) and specificity (82%, 86%, 88%) than previously reported methods. Combination assay for CSF tau, Aβ1-40 and Aβ1-42(43) in CSF is a biological marker of AD and may be useful to biochemically monitor subjects under treatment.

Aβ amyloidosis induces the initial stage of tau accumulation in APPSW mice

Abstract To clarify how Aβ deposits induce secondary tauopathy, the presence of phosphorylated tau, glycogen synthase kinase 3α (GSK3α), GSK3β, cyclin-dependent kinase 5 (CDK5), mitogen-activated protein kinase (MAPK) and fyn were examined in the Tg2576 brain showing substantial brain Aβ amyloidosis and behavioral abnormalities. Phosphorylated tau at Ser199, Thr231/Ser235, Ser396 and Ser413 accumulated in the dystrophic neurites of senile plaques. The major kinase for tau phosphorylation was GSK3β. Smaller contributions of GSK3α, CDK5 and MAPK were suggested. Thus, brain Aβ amyloidosis has a potential role in the induction of tauopathy leading to the mental disturbances of Alzheimers disease.

Lipoprotein-free amyloidogenic peptides in plasma are elevated in patients with sporadic Alzheimer's disease and Down's syndrome

About 90% of the soluble amyloid β (sAβ) that circulates in normal human plasma is associated with lipoprotein particles. In sporadic Alzheimers disease patients, free sAβ42 but not sAβ40 is increased approximately 2.3‐fold compared with age‐matched controls, although a more marked elevation (approximately 8‐fold for free sAβ40 and about 20‐fold for sAβ42) is found in Downs syndrome patients. The data suggest that lipoprotein‐sAβ dissociation may contribute to the influx of sAβ into the brain as a result of decreased plasma clearance. Ann Neurol 1999;45:537–541

Accumulation of Filamentous Tau in the Cerebral Cortex of Human Tau R406W Transgenic Mice

Missense mutations of the tau gene cause autosomal dominant frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), an illness characterized by progressive personality changes, dementia, and parkinsonism. There is prominent frontotemporal lobe atrophy of the brain accompanied by abundant tau accumulation with neurofibrillary tangles and neuronal cell loss. Using a hamster prion protein gene expression vector, we generated several independent lines of transgenic (Tg) mice expressing the longest form of the human four-repeat tau with the R406W mutation associated with FTDP-17. The TgTauR406W 21807 line showed tau accumulation beginning in the hippocampus and amygdala at 6 months of age, which subsequently spread to the cortices and subcortical areas. The accumulated tau was phosphorylated, ubiquitinated, conformationally changed, argyrophilic, and sarcosyl-insoluble. Activation of GSK-3beta and astrocytic induction of mouse tau were observed. Astrogliosis and microgliosis correlated with prominent tau accumulation. Electron microscopic examination revealed the presence of straight filaments. Behavioral tests showed motor disturbances and progressive acquired memory loss between 10 to 12 months of age. These findings suggested that TgTauR406W mice would be a useful model in the study of frontotemporal dementia and other tauopathies such as Alzheimers disease (AD).

Familial Danish dementia: co-existence of Danish and Alzheimer amyloid subunits (ADan AND A{beta}) in the absence of compact plaques.

Familial Danish dementia is an early onset autosomal dominant neurodegenerative disorder linked to a genetic defect in the BRI2 gene and clinically characterized by dementia and ataxia. Cerebral amyloid and preamyloid deposits of two unrelated molecules (Danish amyloid (ADan) and β-amyloid (Aβ)), the absence of compact plaques, and neurofibrillary degeneration indistinguishable from that observed in Alzheimer disease (AD) are the main neuropathological features of the disease. Biochemical analysis of extracted amyloid and preamyloid species indicates that as the solubility of the deposits decreases, the heterogeneity and complexity of the extracted peptides exponentially increase. Nonfibrillar deposits were mainly composed of intact ADan-(1-34) and its N-terminally modified (pyroglutamate) counterpart together with Aβ-(1-42) and Aβ-(4-42) in ∼1:1 mixture. The post-translational modification, glutamate to pyroglutamate, was not present in soluble circulating ADan. In the amyloid fractions, ADan was heavily oligomerized and highly heterogeneous at the N and C terminus, and, when intact, its N terminus was post-translationally modified (pyroglutamate), whereas Aβ was mainly Aβ-(4-42). In all cases, the presence of Aβ-(X-40) was negligible, a surprising finding in view of the prevalence of Aβ40 in vascular deposits observed in sporadic and familial AD, Down syndrome, and normal aging. Whether the presence of the two amyloid subunits is imperative for the disease phenotype or just reflects a conformational mimicry remains to be elucidated; nonetheless, a specific interaction between ADan oligomers and Aβ molecules was demonstrated in vitro by ligand blot analysis using synthetic peptides. The absence of compact plaques in the presence of extensive neuro fibrillar degeneration strongly suggests that compact plaques, fundamental lesions for the diagnosis of AD, are not essential for the mechanism of dementia.

Complement Activation in Chromosome 13 Dementias SIMILARITIES WITH ALZHEIMER'S DISEASE

Chromosome 13 dementias, familial British dementia (FBD) and familial Danish dementia (FDD), are associated with neurodegeneration and cerebrovascular amyloidosis, with striking neuropathological similarities to Alzheimers disease (AD). Despite the structural differences among the amyloid subunits (ABri in FBD, ADan in FDD, and Aβ in AD), these disorders are all characterized by the presence of neurofibrillary tangles and parenchymal and vascular amyloid deposits co-localizing with markers of glial activation, suggestive of local inflammation. Proteins of the complement system and their pro-inflammatory activation products are among the inflammation markers associated with AD lesions. Immunohistochemistry of FBD and FDD brain sections demonstrated the presence of complement activation components of the classical and alternative pathways as well as the neo-epitope of the membrane attack complex. Hemolytic experiments and enzyme-linked immunosorbent assays specific for the activation products iC3b, C4d, Bb, and C5b-9 indicated that ABri and ADan are able to fully activate the complement cascade at levels comparable to those generated by Aβ1–42. ABri and ADan specifically bound C1q with high affinity and formed stable complexes in physiological conditions. Activation proceeds ∼70–75% through the classical pathway while only ∼25–30% seems to occur through the alternative pathway. The data suggest that the chronic inflammatory response generated by the amyloid peptides in vivo might be a contributing factor for the pathogenesis of FBD and FDD and, in more general terms, to other neurodegenerative conditions.

Cerebrospinal fluid tau in dementia disorders: a large scale multicenter study by a Japanese study group

A large scale multicenter study of cerebrospinal fluid (CSF) tau levels was conducted to determine the cut-off value, sensitivity and specificity for clinical usage as a biomarker of Alzheimers disease (AD). Its use for early and differential diagnosis and the factors that increase CSF tau levels were also examined. CSF samples from a total of 1,031 subjects including 366 patients with AD, 168 patients with non-Alzheimer type dementia (NA), 316 patients with non-dementia neurological diseases (ND) and 181 normal controls (NC) were measured using ELISA for tau. The cut-off value of tau, 375 pg/ml, showed 59.1% sensitivity and 89.5% specificity for diagnosis of AD compared with the other groups. The tau levels were increased from the early to late stages of AD. Elevation of CSF tau in the non-tauopathy and tauopathy dementia groups, chronic and acute damage to the cerebrum, and meningeal disturbance were other factors that required attention for clinical practice. Measurement of CSF tau was useful as a biomarker for early and differential diagnosis of AD.

Brain Aβ amyloidosis in APPsw mice induces accumulation of presenilin‐1 and tau

APPsw transgenic mice (Tg2576) overproducing mutant amyloid β protein precursor (βAPP) show substantial brain Aβ amyloidosis and behavioural abnormalities. To clarify the subsequent abnormalities, the disappearance of neurons and synapses and dystrophic neurite formation with accumulated proteins including hyperphosphorylated tau were examined. Tg2576 demonstrated substantial giant core plaques and diffuse plaques. The number of neurons was significantly decreased in the areas containing the amyloid cores compared with all other areas and corresponding areas in non‐transgenic littermates in sections visualized by Nissl plus Congo red double staining (p<0.001). The presynaptic protein α‐synuclein and postsynaptic protein drebrin were also absent in the amyloid cores. βAPP and presenilin‐1 were accumulated in dystrophic neurites in and around the core plaques. Tau phosphorylated at five independent sites was detected in the dystrophic neurites in the amyloid cores. Thus, the giant core plaques replaced normal brain tissues and were associated with subsequent pathological features such as dystrophic neurites and the appearance of hyperphosphorylated tau. These findings suggest a potential role for brain Aβ amyloidosis in the induction of secondary pathological steps leading to mental disturbance in Alzheimers disease. Copyright

The levels of cerebrospinal fluid Aβ40 and Aβ42(43) are regulated age-dependently

Decreased levels of cerebrospinal fluid (CSF) Abeta42 is a diagnostic marker of Alzheimers disease. To clarify the biological basis of this marker, the physiological alterations of CSF Abeta40 and Abeta42 by aging were studied. CSF samples from 92 normal subjects between 8 and 89 years old were measured using a specific ELISA for Abeta40 and Abeta42(43). High concentrations of Abeta40 and Abeta42(43) in the young group, under 29 years old, changed to be at low concentrations in the adult group between 30 and 59 years old. Subsequently, the levels increased again with age. Third order regression analysis showed a significant correlation between the levels of Abeta40 and age (Y = - 169 X(3) + 3.1X(2)- 0.02X + 4135; P < 0.034) and between the levels of Abeta42(43) and age (Y = - 46 X(3) + 0.9 X(2)- 0.005X + 992; P < 0.005). The levels of CSF Abeta40 and Abeta42(43) were physiologically regulated to show a U-shaped natural course in normal aging. These findings suggested that the physiological increase of Abeta42(43) over 59 years of age is selectively inhibited in Alzheimers disease.

Decreased level of brain acetylcholine and memory disturbance in APPsw mice

To clarify whether amyloid beta protein (Abeta) amyloidosis induces a disturbance of cholinergic system leading to long-term memory deficits, we continuously examined memory disturbance using the passive-avoidance task, and measured Abeta burden and concentrations of acetylcholine in the brain of APPsw transgenic mice. Repetitive retention trials of the passive-avoidance task showed that the long-term memory impairment in APPsw mice appeared from approximately 7.75 months old and progressively advanced. Significant decreases in acetylcholine levels were found in the brains of 10-month-old mice. A few senile plaques appeared in the cerebral cortex and the hippocampus at 8 months old, and increased in size and number with aging. The concentrations of brain Abeta40/42(43) gradually increased from 8 months old and exponentially increased thereafter. Advance of long-term memory disturbance was closely correlated with Abeta40/42(43) burden. These findings suggested that Abeta accumulation induced long-term memory impairment and disturbance of the cholinergic system, and that the passive-avoidance task and measuring acetylcholine were useful methods for evaluating this mouse model as well as Abeta accumulation.