Production of paired helical filament, tau-like proteins by PC12 cells: a model of neurofibrillary degeneration.

Neuron-like cells derived from a rat pheochromocytoma cell line (PC12) and differentiated with nerve growth factor produce a paired helical filament (PHF)-like antigen when they are subjected to heat shock (Wallace et al.: Mol Brain Res 19:149-155, 1993). It accumulates in a localized region of the perinuclear cytoplasm and reacts with monoclonal antitau antibodies, which identify epitopes in the N- and C-terminal halves and the microtubule-binding domain of tau protein. The observed profile of immunoreactivity suggests the presence of full-length and C-terminally truncated tau in a region of perinuclear cytoplasm in which no structurally intact PHFs could be demonstrated by conventional transmission electron microscopy. The accumulated tau protein colocalized with antibodies raised against mitochondrial outer membrane proteins and was associated with the presence of numerous mitochondrial profiles that were demonstrated with electron microscopy. Because differentiated PC12 cells pretreated with colcemid or Taxol prior to heat shock fail to exhibit perinuclear PHF-like immunoreactivity, the reported response to heat shock appears to require an intact system of intracellular microtubules. This PC12 system provides a model in which the metabolic and molecular biological underpinnings of neuronal degeneration in Alzheimer's disease can be manipulated. The system may eventually be applicable to the development of pharmaceutical agents that interfere with formation and/or degeneration of PHF-tau in Alzheimer's disease.

Evidence for association of HLA-A2 allele with onset age of Alzheimer's disease.

Our earlier studies had suggested a possible association between the HLA-A2 allele and Alzheimer's disease (AD). In the present study we tested the hypothesis that A2 is associated with earlier AD onset. We performed two independent studies: a collaborative study with 111 patients and a confirmatory study with 96 patients. We found similar patterns of reduced age at onset as a function of A2 in both data sets. Overall, A2 was associated with a significant 3-year shift to earlier onset. The effects of A2 and epsilon 4 on age at onset appeared additive. Our results suggest A2, or a closely linked gene, modulates onset age of AD. Association with A2 would suggest an immune/inflammatory response mechanism for AD.

D2 dopamine receptor A1 allele in Alzheimer disease and aging.

BACKGROUND: The apolipoprotein E4 (APOE*4) allele is a major risk factor for the common forms of late-onset Alzheimer disease (AD), but does not account for all the genetic variation in late-onset AD; hence, other genetic markers must be examined. The D2 dopamine receptor (DRD2) A1 allele is associated with abnormal brain function and decreased DRD2s. These receptors are decreased in hippocampus and amygdala in AD, and allele frequencies may vary with age. OBJECTIVE: To study APOE and DRD2 genotypes in patients with AD and cognitively intact controls of varying ages. DESIGN: The DRD2 and APOE genotypes were examined in 832 unrelated white subjects, including 554 patients with AD (486 sporadic; 68 familial) and 278 controls. Logistic regressions tested A1 allele effects on disease status and age, and DRD2 linkage with AD was investigated in 60 families with late-onset AD. SETTING: University medical centers. SUBJECTS: Patients (mean +/- SD age, 74.6 +/- 8.1 years; range, 52-98 years) had probable AD, according to standard consensus diagnostic criteria; controls (mean +/- SD age, 69.2 +/- 8.6 years; range, 50-93 years) were cognitively intact. MAIN OUTCOME MEASURES: Disease status, age, and DRD2 linkage with AD. RESULTS: No association between the DRD2 and APOE alleles was found, and the presence of the A1 allele did not increase the risk for AD. There was also no evidence of linkage between DRD2 and AD. Age analyses, including both patients and controls, indicated a decrease in A1 allele frequency with age. CONCLUSIONS: The A1 allele does not contribute to AD risk, alone or in combination with the APOE*4 allele. The DRD2 A1 allele frequencies decrease with age in both patients and controls. Thus, studies of DRD2 disease association need to control for age.

Tetraethylammonium-induced calcium concentration changes in skin fibroblasts from patients with Alzheimer disease.

Potassium (K+) channel dysfunction in fibroblasts was recently proposed as a potential diagnostic marker for Alzheimer disease (AD). We utilized a microspectrofluorometric method with Fura-2AM to measure intracellular free calcium ([Ca2+]i) following depolarization with the K+ channel blocker tetraethylammonium (TEA) in seven AD and seven control fibroblast cultures. Contrary to our expectation, 43% of the AD and 36% of the control fibroblast plated coverglasses responded with an increase in [Ca2+]i on addition of 100 mM TEA. The data suggest that the TEA-elicited [Ca2+]i response is not a useful AD screening test.

Cognitive changes in young-old adults: effect of family history of dementia.

Cognitive performance of 40 first-degree relatives of patients with probable Alzheimer disease was compared to that of 24 matched controls without a family history of dementia. Across a test-retest interval ranging from 1 to 6 years, relatives more often showed evidence of cognitive decline, and in multivariate analyses of memory and intelligence measures, relatives of patients with early-onset dementia (< 67 years) showed greater decline than controls or relatives of patients with late-onset dementia. All changes observed to date are in the subclinical range, and further follow-up will be needed to determine the reliability of change trajectories. However, the findings suggest that family history of dementia may be worthy of monitoring in research on normal cognitive aging.

Tau-like immunoreactivity in Alzheimer and control skin fibroblasts.

The presence of the microtubule-associated protein tau in skin fibroblasts derived from Alzheimer patients and normal controls was investigated using a panel of well-characterized anti-tau antibodies against epitopes spanning the tau protein from the amino to the carboxyl end. The antibodies immunolabeled a fine, fibrillar cytoplasmic network in all skin fibroblasts. Disruption of the microtubule network with colchicine did not affect the immunolabeling of the fibrillar network nor did treatment with cytochalasin B known to disrupt the microfilament network. Immunoelectron microscopy with the anti-tau antibodies revealed colocalization of the label with the 10 nm intermediate filaments. Furthermore, immunoblots found no reactivity against purified vimentin, suggesting that the antibodies recognize an intermediate filament-associated protein. The findings indicate the presence of tau or a protein with considerable homology to tau in fibroblasts associated with intermediate filaments and not microtubules.

Clinical, neuroimaging, and environmental risk differences in monozygotic female twins appearing discordant for dementia of the Alzheimer type.

OBJECTIVE: The study of monozygotic twins can elucidate possible environmental causes for a disease in genetically identical subjects. To this end, we studied a pair of monozygotic female twins appearing discordant for dementia of the Alzheimer type (DAT). DESIGN: Clinical and neuroimaging findings were compared in terms of potential environmental risk factors. SETTING: University referral center. PARTICIPANTS: An 81-year-old female monozygotic twin pair. OUTCOME MEASURES: Clinical assessments, standardized rating scales, and brain imaging studies, including magnetic resonance imaging, positron emission tomography, and electroencephalography, were performed. Neuropsychological tests were performed initially and after 1 year. RESULTS: Although DAT was confirmed clinically in only one twin, neuropsychological and brain imaging studies suggested that the unaffected twin may be developing the prodrome of DAT. The twins' varied life histories suggest that environmental risk factors may contribute to apparent discordance for DAT and possible delay in disease onset for the currently nondemented twin. CONCLUSIONS: These results suggest that both genetic and nongenetic factors influence disease onset and expression. Moreover, review of previous reports of monozygotic twin pairs concordant or discordant for Alzheimer's disease, with adequate family history data, suggest a pattern indicating interactions among age at dementia onset, sex, and familiarity. Such patterns point to hypotheses regarding neurobiologically meaningful Alzheimer's disease subgroups.

Cognitive performance in relatives of patients with probable Alzheimer disease: an age at onset effect?

Cognitive performance of 32 siblings and children of patients with probable Alzheimer disease was assessed longitudinally over an interval averaging 4 years. Mean scores were within normal limits for age on all measures at both test times. However, relatives of patients with early-onset dementia (less than or equal to 67 years) were more likely to show a decline in performance from the first to second testing than relatives of patients with late-onset dementia. Additional follow-up will be needed to determine the reliability of performance trajectories and to assess whether mild cognitive changes are related to future dementia. However, findings suggest that it may be important to consider family history of dementia in studies of normal cognitive aging.

Commingling analysis of memory performance in offspring of Alzheimer patients.

Dementia of the Alzheimer type (DAT) is a neurodegenerative disorder which afflicts approximately 3% of the population. Genetic influences are indicated from twin and family studies although genetic heterogeneity has been suggested from both pedigree analyses and linkage investigations. Autosomal dominant inheritance with age-dependent penetrance has been suggested in at least some families with DAT. In the present investigation, we examine memory and nonmemory task performance in 106 asymptomatic offspring (mean age 40.6 years) of 54 DAT probands. Intraclass sibling correlations revealed little evidence of sibling similarity for performance on three memory tasks which have been reported to be relatively sensitive to the memory losses accompanying DAT. Subsequent investigations of the distributions of the cognitive task scores in the offspring revealed evidence for a commingling of two distributions for the three memory tasks but not for the nonmemory measures. These findings are consistent with a hypothesis that these distributions reflect genotypic subgroups, carriers, and noncarriers, of a presumed DAT gene.

Variable association of HLA-A2 in men with early-onset Alzheimer disease.

In the present study, we attempted to replicate the finding of an increased frequency of HLA-A2 in men with early-onset (less than or equal to 60 years) Alzheimer disease (AD). HLA data obtained on 167 patients (including 19 men with early-onset AD) from three geographic regions (North Carolina, Great Britain, and Finland) failed to replicate the result. A recent prospective study from Oregon, however, confirmed the association. Studies demonstrating the association suggest its presence in sporadic rather than familial AD. These results indicate a variable HLA/AD association, with some factor such as geographic region or disease familiality contributing to this variability.

Hypothesis: microtubules, a key to Alzheimer disease.

Alzheimer disease (AD) is a clinicopathologic syndrome of unknown etiology with numerous abnormalities in neuronal and nonneuronal cells. A review of the literature suggests that a common basic intracellular defect may underlie many of the reported abnormalities. We hypothesize impairment of the microtubule (MT) system as one explanation for the pathogenesis of AD. Evidence in support of the hypothesis includes the following: MTs are ubiquitous and vital cell components, unequally distributed, with the highest concentration in the brain; various abnormalities, including the key neuropathologic lesions, can be explained by impairments of the MT system; and experiments utilizing pharmacologic agents known to disrupt MTs have reproduced certain abnormalities observed in AD. The hypothesis provides a framework for systematic investigations of MTs at the cellular and molecular levels as well as the basis for in vivo diagnostic tests for AD.

HLA antigens in depressed, demented, and nondemented elderly.

To identify HLA antigen associations with geriatric depression, the authors typed 36 elderly patients with major depression and, for comparison, 36 patients with Alzheimer-type dementia and 29 nondemented elderly controls. The frequency for antigen Aw32 was significantly higher in the group of patients with major depression (14%) than in the demented (0%) and control (3%) groups. The frequencies for antigens Aw32 (22%) and Bw51 (22%) were significantly higher in the subgroup of 23 patients with endogenous depression than in the demented (Aw32 = 0%; Bw51 = 11%) and the control (Aw32 = 3%; Bw51 = 0%) groups. Although these results were derived from a relatively small sample (n = 101) and become nonsignificant when corrected for multiple comparisons, they suggest that HLA antigen associations may be present for only certain depressive subtypes in geriatric depression.

Sister chromatid exchanges and dementia of the Alzheimer type.

Sister chromatid exchange (SCE) analysis was carried out on ten patients with the clinical diagnosis of dementia of the Alzheimer type (DAT) and 11 cognitively-intact controls of a comparable age. There was no significant difference between patient and control groups in either the mean baseline SCE frequency or the SCE frequency following in vitro exposure to mitomycin-C. The present results, based on the largest sample (n = 21) published to date, fail to confirm the single positive report in the literature of an increased baseline SCE frequency in DAT patients compared to controls.

Variation in DNA content of mononuclear cells of patients with dementia of the Alzheimer type.

Flow cytometry studies to measure mean DNA content and intercellular variability around the mean were performed on mononuclear blood cells obtained from 21 patients with a clinical diagnosis of dementia of the Alzheimer type (DAT) and 25 cognitively intact individuals. There was no difference in the mean DNA content between both groups. However, patients with DAT had significantly increased intercellular variability compared to controls (3.52 vs. 3.06, respectively). These results are consistent with the reports of increased aneuploidy associated with DAT found on cytogenetic examination.

Relatives' descriptions of changes in symptoms of dementia of the Alzheimer type: a comparison of retrospective and concurrent ratings.

Although relatives' retrospective reports are often used in characterizing the onset and progression of symptoms in dementia of the Alzheimer type (DAT), little is known about the accuracy of these accounts. The primary purpose of this paper is to summarize preliminary data obtained from relatives in an ongoing family study of DAT. Preliminary findings suggest there is rough reliability to relatives' recall of the progression of symptoms over time. This observation is discussed in relation to literature from other areas (e.g. child development, psychopathology) where the reliability of relatives' retrospection has been more thoroughly examined.

HLA-A2 as a possible marker for early-onset Alzheimer disease in men.

We performed HLA typing on 36 patients with clinically diagnosed Alzheimer disease and 25 controls. Antigen A2 was present in all ten men (100%) with early-onset (less than 60 years) dementia, a frequency significantly higher than the 30% frequency found in the cognitively intact men of a comparable age (p = 0.009, corrected). This increased A2 frequency was also significantly greater than the frequencies for all other patient subgroups, including late-onset men (40%, p = 0.008), early-onset women (44%, p = 0.004), and late-onset women (42%, p = 0.028). Our findings, if repeated in future studies with larger samples, suggest that HLA-A2 positive men may comprise a subgroup with increased susceptibility to early-onset disease.

Haptoglobin phenotypes in dementia of the Alzheimer type.

Previous investigations of the association of haptoglobin (Hp) with dementia of the Alzheimer type (DAT) have reported contradictory results. In the present study, we phenotyped 69 patients clinically diagnosed as having DAT and, for comparison, 64 cognitively intact individuals. We failed to find a significant association between either of the Hp alleles and DAT. Instead, we observed a nonsignificant decrease in the Hp-1 gene frequency in the DAT population (0.34) as compared to our normal elderly comparison group (0.41).

Philothermal response, microtubules and dementia.

The role of microtubules in the philothermal response of polymorphonuclear leukocytes (PMNs) was examined using colchicine, a known microtubule disrupting agent. Colchicine inhibited PMN migration in a dose dependent fashion. Spatial distribution analysis of the responding cell population revealed a preferential inhibition of distal cell migration, a pattern similar to that found for PMNs obtained from patients with dementia of the Alzheimer type (DAT). The result is consistent with the known role of microtubules in directed cell migration and the hypothesized microtubular defect in DAT. Further investigations of microtubules may provide insight into the etiology and pathogenesis of DAT.