Different pathways of molecular pathophysiology underlie cognitive and motor tauopathy phenotypes in transgenic models for Alzheimer's disease and frontotemporal lobar degeneration.

A poorly understood feature of the tauopathies is their very different clinical presentations. The frontotemporal lobar degeneration (FTLD) spectrum is dominated by motor and emotional/psychiatric abnormalities, whereas cognitive and memory deficits are prominent in the early stages of Alzheimer's disease (AD). We report two novel mouse models overexpressing different human tau protein constructs. One is a full-length tau carrying a double mutation [P301S/G335D; line 66 (L66)] and the second is a truncated 3-repeat tau fragment which constitutes the bulk of the PHF core in AD corresponding to residues 296-390 fused with a signal sequence targeting it to the endoplasmic reticulum membrane (line 1; L1). L66 has abundant tau pathology widely distributed throughout the brain, with particularly high counts of affected neurons in hippocampus and entorhinal cortex. The pathology is neuroanatomically static and declines with age. Behaviourally, the model is devoid of a higher cognitive phenotype but presents with sensorimotor impairments and motor learning phenotypes. L1 displays a much weaker histopathological phenotype, but shows evidence of neuroanatomical spread and amplification with age that resembles the Braak staging of AD. Behaviourally, the model has minimal motor deficits but shows severe cognitive impairments affecting particularly the rodent equivalent of episodic memory which progresses with advancing age. In both models, tau aggregation can be dissociated from abnormal phosphorylation. The two models make possible the demonstration of two distinct but nevertheless convergent pathways of tau molecular pathogenesis. L1 appears to be useful for modelling the cognitive impairment of AD, whereas L66 appears to be more useful for modelling the motor features of the FTLD spectrum. Differences in clinical presentation of AD-like and FTLD syndromes are therefore likely to be inherent to the respective underlying tauopathy, and are not dependent on presence or absence of concomitant APP pathology.

Addictive-like behaviours to ultraviolet light among frequent indoor tanners.

BACKGROUND: Frequent, purposeful exposure to ultraviolet (UV) light may induce a compulsive desire to tan despite the negative consequences being known, suggesting a behavioural complex similar to addictive disorders. AIM: To assess the presence of addictive-like behaviours in subjects using indoor tanning salons. METHODS: Subjects (n = 100) were surveyed by two questionnaires: a modified CAGE questionnaire to assess behaviours consistent with problem tanning and a modified Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) ('substance dependence' criteria) to assess behaviours consistent with a dependence-like disorder. RESULTS: In total, 41% of subjects met criteria consistent with a 'tanning addictive disorder', and an additional 33% met criteria for problematic tanning behaviour based on the modified CAGE criteria or subthreshold criteria on the modified DSM-IV criteria. Female gender and early age of onset were associated with meeting tanning addiction criteria. CONCLUSION: A high percentage of subjects who tan frequently in indoor salons experience behaviours and consequences to their tanning consistent with other identified addictive disorders.

Loss of synaptic but not cytoskeletal proteins in the cerebellum of chronic schizophrenics.

The pathobiology of schizophrenia is poorly understood, and many neuroanatomical domains have been considered to underlie the pathophysiology of the disease. There is considerable clinical and neuroradiological evidence to support cerebellar involvement in the schizophrenic illness. We have analysed the changes in synaptic and cytoskeletal proteins in the cerebellum associated with schizophrenia. The cerebellar expression of tau and MAP2 proteins is similar in schizophrenia to that detected in age-matched controls, whereas the level of SNAP-25 is significantly depleted in the schizophrenic cerebellum. Other synaptic proteins, such as synaptophysin and syntaxin, are not affected. This provides evidence that alterations of the cerebellar synaptic network occur in schizophrenia. These changes may influence cerebellar-forebrain connections, especially those with the frontal lobes, and give rise to the cognitive dysmetria that is characteristic of the clinical phenotype in schizophrenia.

Accumulation of C-terminally truncated tau protein associated with vulnerability of the perforant pathway in early stages of neurofibrillary pathology in Alzheimer's disease.

Neurofibrillary pathology is a characteristic hallmark of Alzheimer's disease that is closely correlated with cognitive decline. We have analysed the density and distribution of neurofibrillary tangles (NFTs) that are immunoreactive with the monoclonal antibody (mAb) 423 in a prospectively analysed population of Alzheimer's disease (AD) cases and age-matched controls. NFTs were examined in allocortical and isocortical areas and correlated with Braak pathological stage and clinical severity of dementia. The mAb 423 was used as it recognises a C-terminally truncated tau fragment that is a major constituent of NFTs. Our results show that extracellular NFTs and, to a lesser extent, intracellular NFTs, correlated significantly with both Braak stages and the clinical index of severity. Furthermore, a differential distribution of the two types of tangles indicates that layer II of the entorhinal cortex and the transentorhinal area are particularly vulnerable to neurofibrillary degeneration. These areas serve as a point of connection between isocortex and hippocampus. Our findings, therefore, suggest that the perforant pathway may be substantially affected by the accumulation of truncated tau protein in AD and that this represents a neuropathological predictor for the clinical severity of dementia. When neurofibrillary pathology was examined by combined labelling with mAbs 423 and Alz-50 and the dye thiazin red, we were able to demonstrate various stages of tau aggregation. The different stages may represent a sequence of conformational changes that tau proteins undergo during tangle formation in the allocortex during the early development of dementia in AD.

Staging of cytoskeletal and beta-amyloid changes in human isocortex reveals biphasic synaptic protein response during progression of Alzheimer's disease.

We have examined the relationships between dementia, loss of synaptic proteins, changes in the cytoskeleton, and deposition of beta-amyloid plaques in the neocortex in a clinicopathologically staged epidemiological cohort using a combination of biochemical and morphometric techniques. We report that loss of synaptic proteins is a late-stage phenomenon, occurring only at Braak stages 5 and 6, or at moderate to severe clinical grades of dementia. Loss of synaptic proteins was seen only after the emergence of the full spectrum of tau and beta-amyloid pathology in the neocortex at stage 4, but not in the presence of beta-amyloid plaques alone. Contrary to previous studies, we report increases in the levels of synaptophysin, syntaxin, and SNAP-25 at stage 3 and of alpha-synuclein and MAP2 at stage 4. Minimal and mild clinical grades of dementia were associated with either unchanged or elevated levels of synaptic proteins in the neocortex. Progressive aggregation of paired helical filament (PHF)-tau protein could be detected biochemically from stage 2 onwards, and this was earliest change relative to the normal aging background defined by Braak stage 1 that we were able to detect in the neocortex. These results are consistent with the possibility that failure of axonal transport associated with early aggregation of tau protein elicits a transient adaptive synaptic response to partial de-afferentation that may be mediated by trophic factors. This early abnormality in cytoskeletal function may contribute directly to the earliest clinically detectable stages of dementia.

Lack of an association of estrogen receptor alpha gene polymorphisms and transcriptional activity with Alzheimer disease.

BACKGROUND: Long-term cognitive decline in postmenopausal women is associated with aging and Alzheimer disease (AD). Estrogen replacement therapy has been reported to reduce the risk of developing AD. The distribution of estrogen receptors (ERs) in neurons overlaps that of the brain neurons known to develop AD. Estrogen increases the secretion and metabolism of amyloid precursor protein, may help synapse formation, and is reported to protect neurons from toxins. Restriction fragment length polymorphisms (RFLPs) of the ERalpha gene at intron 1 and exon 2 were associated with a low bone mineral density in postmenopausal women and also with AD in a Japanese population. OBJECTIVE: To determine whether ERalpha gene polymorphisms are associated with transcriptional activity and AD. METHODS: A luciferase reporter assay analyzed enhancer activity of the ERalpha gene at intron 1 and exon 2. This activity was evaluated according to the RFLPs. The RFLPs of the ERalpha gene were determined in Japanese patients clinically diagnosed as having AD, white patients diagnosed as having AD at autopsy, and corresponding healthy control subjects. The RFLPs were also evaluated for the contribution of the ERalpha gene RFLPs to AD. RESULTS: We found weak (about 2-fold) enhancer activity of the ERalpha gene, which differed among RFLPs. Although there were racial differences in these polymorphisms, we could not confirm the previously reported association between ERalpha gene polymorphisms and AD. CONCLUSION: Regulatory element of the ERalpha gene was found in intron 1, but we found no association between ERalpha gene polymorphisms and AD.

The CCTTT polymorphism in the NOS2A gene is associated with dementia with Lewy bodies.

We report the analysis of the allele distribution of a (CCTTT)n pentanucleotide repeat within the promoter region of the NOS2A gene in DNA samples from patients with autopsy confirmed Alzheimer's disease (AD) and dementia with Lewy bodies (DLB) type. A significant difference was observed in the allelic distribution between the control group and the DLB group (chi2 = 15.175, df = 5; p<0.01), with an increased occurrence of the eight and nine repeat alleles, and a marked under representation of the 11 repeat allele. Genotype frequencies in the DLB group also differed significantly from controls (p<0.012). These results suggest that variations in the NOS2A gene may predispose to the development of DLB.

Presence of the apolipoprotein E type epsilon 4 allele is not associated with neurofibrillary pathology or biochemical changes to tau protein.

Alzheimer's disease (AD) represents a heterogeneous disorder, and several factors have been associated with its development. The presence of the apolipoprotein E type (APOE) epsilon 4 allele has been proposed as a risk factor for AD, but how it influences the development of the characteristic hallmarks of the disease remains unknown. In the present study, the neuropathological changes and levels of both core PHF-tau and normal tau protein in 4 neocortical areas, cerebellum and medial temporal cortex were determined in 18 AD cases. The extent of these changes was compared between 10 cases possessing an epsilon 4 allele and 8 cases without. These two groups were indistinguishable in terms of neurofibrillary pathology, whereas cases with an epsilon 4 allele had more diffuse plaques, particularly in the temporal neocortex. Biochemically, there was no difference in the levels of PHF-tau protein between the two groups. These data indicate that APOE epsilon 4 allele may influence deposition of diffuse amyloid, but altered tau protein processing, which underlies the development of the neurofibrillary pathology in AD, is not influenced by this allele.

Presenilin-1 intron 8 polymorphism is not associated with autopsy-confirmed late-onset Alzheimer's disease.

Mutations in the presenilin-1 (PS-1) gene may account for the majority of familial early-onset Alzheimer's disease (EOAD) cases. However, there is controversy as to whether the bi-allelic intron 8 PS-1 polymorphism plays a role in late-onset AD (LOAD). As previous association studies with this polymorphism have all investigated clinically diagnosed LOAD cases, we have analysed the frequency of the PS-1 intronic polymorphism in a series of autopsy-confirmed early- (n = 54) and late-onset (n = 199) cases and a large control population of non-demented, aged individuals (n = 215). Our sample size should have had the power to reveal effects of the size previously reported for the PS-1 polymorphism, but we detected no significant increase in the 1/1 risk genotype distribution in EOAD or LOAD cases. Thus, we have been unable to find an association between the PS-1 intronic polymorphism and early- or late-onset AD within this autopsy-confirmed population.

Evolution of a homopurine-homopyrimidine pentanucleotide repeat sequence upstream of the human inducible nitric oxide synthase gene.

We have identified a highly polymorphic pentanucleotide repeat (CCTTT)n within the 5'-putative promoter region of the human inducible nitric oxide synthase gene (iNOS, NOS2). Using a pair of specific primers derived from the human iNOS gene, we have also amplified this iNOS repeat in DNA from the following species: chimpanzee, gorilla, orangutan and macaque. As is found in man, both chimpanzees and gorillas are polymorphic at this locus. In contrast, the locus is monomorphic in macaques and orangutans. While the average number of repeats is similar in gorilla and man, there are considerably fewer repeats in chimpanzees. A comparison of the sequences flanking the (CCTTT)n repeats among these closely related species demonstrates the presence of long stretches of homopurine-homopyrimidine residues. Similar polypurine/polypyrimidine stretches have been identified in the promoter regions of a number of other vertebrate genes where they have been associated with transcriptional regulation, although a role for the (CCTTT)n repeat array in the human iNOS gene has not yet been demonstrated.

Selective inhibition of Alzheimer disease-like tau aggregation by phenothiazines.

In Alzheimer disease (AD) the microtubule-associated protein tau is redistributed exponentially into paired helical filaments (PHFs) forming neurofibrillary tangles, which correlate with pyramidal cell destruction and dementia. Amorphous neuronal deposits and PHFs in AD are characterized by aggregation through the repeat domain and C-terminal truncation at Glu-391 by endogenous proteases. We show that a similar proteolytically stable complex can be generated in vitro following the self-aggregation of tau protein through a high-affinity binding site in the repeat domain. Once started, tau capture can be propagated by seeding the further accumulation of truncated tau in the presence of proteases. We have identified a nonneuroleptic phenothiazine previously used in man (methylene blue, MB), which reverses the proteolytic stability of protease-resistant PHFs by blocking the tau-tau binding interaction through the repeat domain. Although MB is inhibitory at a higher concentration than may be achieved clinically, the tau-tau binding assay was used to identify desmethyl derivatives of MB that have Ki values in the nanomolar range. Neuroleptic phenothiazines are inactive. Tau aggregation inhibitors do not affect the tau-tubulin interaction, which also occurs through the repeat domain. Our findings demonstrate that biologically selective pharmaceutical agents could be developed to facilitate the proteolytic degradation of tau aggregates and prevent the further propagation of tau capture in AD.

Apolipoprotein E genotype in the prediction of cognitive decline and dementia in a prospectively studied elderly population.

An increased apolipoprotein E (ApoE) type epsilon 4 allele frequency is associated with both sporadic and familial late-onset Alzheimer's disease (AD). The age of onset of disease in patients homozygous for the epsilon 4 allele appears to be decreased by approximately 15 years compared with E2/3 individuals. In order to assess the influence of this allele on both dementia and cognitive decline in the elderly we have determined the ApoE genotype of 150 individuals over the age of 75 years who have taken part in a longitudinal study. Homozygosity for the epsilon 4 allele was rare. Of the 2 homozygotes, 1 was severely demented but the other did not receive a clinical diagnosis of dementia. The latter individual did demonstrate marked cognitive decline over a 28-month period. There was a consistent association between the presence of an epsilon 4 allele and both the clinical diagnosis of dementia and cognitive decline. These findings confirm a genetic heterogeneity in late-onset sporadic AD and prompt caution in the use of ApoE genotype to predict an elderly individual's susceptibility to either dementia or cognitive decline.

Alterations in tau protein metabolism during normal aging.

It is unknown whether aging and Alzheimer's disease (AD) are on the same continuum, or whether they are qualitatively distinct. Tau protein has been identified as a major constituent of paired helical filaments (PHFs) and AD is characterised by a major redistribution of the normal tau protein pool into PHFs. Little is known about the changes in tau protein distribution that occur in the course of normal aging. We have examined PHF-bound and normal tau fractions in frontal, temporal, parietal and occipital neocortex, cerebellum, hippocampus and entorhinal cortex in 15 cognitively unimpaired individuals aged 19-88 years at death. Insoluble tau protein in the PHF fraction did not increase with aging in any brain region, despite the appearance of neurofibrillary pathology at low density in the more elderly cases. By contrast, normal tau protein decreased with aging (r = 0.32, p < 0.001), with an average loss of 14% of soluble tau per decade after the age of 20 years. This was unrelated either to neurofibrillary or beta-amyloid pathology. Frontal grey matter and hippocampus were most vulnerable to age-related tau loss, decreasing by as much as 90% in the older subgroup. These findings contrast with those we have previously reported in AD, where the redistribution of tau protein into the PHF-bound fraction was highly correlated with the extent of neurofibrillary pathology, and suggest that the mechanisms of tau loss in aging and AD are distinct. Age-related tau loss may underlie the neuropsychological impairments seen in the non-demented elderly.

The role of the Maillard reaction in other pathologies: Alzheimer's disease.

Many approaches have and are being undertaken to treat Alzheimer's disease but, as yet, no therapy is available with any established efficacy. Given the heterogeneity of the aetiological factors involved in Alzheimer's disease and the difficulties encountered in the clinical diagnosis, the lack of pharmacological success is not surprising. Furthermore, the lack of an adequate animal model of Alzheimer's disease has delayed the development of novel therapeutic strategies. At present, and with the exception of the rarer forms of familial Alzheimer's disease, the need remains to treat the symptoms rather than the causes of the disease, primarily because the pathogenesis of Alzheimer's disease is still unknown. The evidence for the role of glycation and advanced glycation end-products (AGEs) in the formation of neurofibrillary tangles and neuritic plaques, the characteristic histopathological lesions of Alzheimer's disease, is briefly reviewed. While the role of glycation in the pathogenesis of Alzheimer's disease is not yet unequivocally proven, it is the only single protein modification that would explain the formation of both the characteristic histopathological lesions first described by Alois Alzheimer in 1907. With our improved understanding of the molecular basis for the clinical symptoms of dementia, it is hoped that the aetiological causes will afford more suitable targets for therapeutic intervention. In this respect it is interesting to note that the anti-inflammatory compounds indomethacin and acetylsalicylic acid, both inhibitors of the Maillard reaction, have been reported to have therapeutic potential and the nootropic agent tenilsetam inhibits protein cross-linking by AGEs.

Staging the pathological assembly of truncated tau protein into paired helical filaments in Alzheimer's disease.

Tau protein, which is incorporated into the core of paired helical filaments (PHFs) in Alzheimer's disease (AD), can be characterised immunochemically by C-terminal truncation at Glu-391 recognised by monoclonal antibody (mAb) 423, and acid-reversible occlusion of a generic tau epitope in the tandem repeat region recognised by mAb 7.51. PHFs are also characterised by the presence of binding sites for a fluorescent dye (thiazin red) which can be used to differentiate between amorphous and fibrillar states of tau and beta-amyloid proteins in AD. We have used double labelling confocal microscopy to investigate that state of aggregation of the tau antigens associated with the core structure of the PHF at early stages of neurofibrillary pathology. We report that the early abnormal tau deposits in cells vulnerable to neurofibrillary degeneration are characterised by C-terminal truncation at Glu-391, acid-reversible occlusion of the mAb 7.51 epitope, and the absence of binding sites for thiazin red, consistent with the amorphous non-fibrillar structure demonstrated by immunoelectron microscopy. Transition to the fibrillar state in the PHF is associated with acid-reversible occlusion of both mAb 7.51 and 423 epitopes, and acquisition of binding sites for thiazin red. In neurites, the transition between the two states of aggregation shows distal to proximal polarity, with the fibrillar state found nearest the cell body. These findings demonstrate that the assembly of tau protein into the PHF occurs in at least two stages, an amorphous stage characterised by C-terminal truncation and occlusion of sites within the tandem repeat region, and a fibrillar stage characterised by acid-reversible occlusion of both epitopes via addition of intact tau molecules in the fuzzy coat of the PHF.

The relationship between clinical dementia and neuropathological staging (Braak) in a very elderly community sample.

The neuropathological staging model proposed by Braak and Braak (1991) implies that the evolution of neurofibrillary pathology follows a predictable sequence and can be ordered in a regular regional hierarchy. A total of 42 cases of an elderly population sample, which had been prospectively clinically assessed, were examined. Clinical diagnosis was made according to the CAMDEX criteria, and the sample reported here did not include cases were vascular dementia according to the criteria proposed by Chui et al. (1991). The neuropathological staging procedure was applied as originally proposed by Braak and Braak (1991). In addition, in all cortical laminae and regions which are essential for the staging model neurofibrillary tangles were quantified. Demented cases had significantly more areas involved and more advanced neuropathological stages. Cases with stages 1-3 tended to be non-demented, and cases with stages 4-6 tended to be demented. However, there was a considerable degree of overlap and no clear-cut threshold could be established. This brings into question the diagnostic value of the staging model.

Apolipoprotein E type epsilon 4 allele frequency is increased in patients with schizophrenia.

Apolipoprotein E type epsilon 4 alleles are increased in both Alzheimer's disease (AD) and cortical Lewy body dementia, while the epsilon 2 allele has been associated as a protective factor against the development of dementia in AD. We have determined APOE genotype in schizophrenic patients coming to autopsy (age range 19-95 years). The allele frequencies in this group were: epsilon 2, 6.0%; epsilon 3, 67.9%; and epsilon 4, 26.2%. Three patients (14%) were homozygous for the epsilon 4 allele. Thus, schizophrenia is associated with an increased epsilon 4 allele frequency, as compared with controls (P = 0.01), that was indistinguishable from that found in either AD or Lewy body dementia. The increased epsilon 4 allele frequency was not associated with increased age of schizophrenia patient, indicating that it was not due to the co-existence of AD.