Faculty Bibliography

Individuals with Down syndrome develop beta-amyloid deposition characteristic of early-onset Alzheimer's disease (AD) in mid-life, presumably because of an extra copy of the chromosome 21-located amyloid precursor protein (App) gene. App mRNA and APP metabolite levels were assessed in the brains of Ts65Dn mice, a mouse model of Down syndrome, using quantitative PCR, western blot analysis, immunoprecipitation, and ELISAs. In spite of the additional App gene copy, App mRNA, APP holoprotein, and all APP metabolite levels in the brains of 4-month-old trisomic mice were not increased compared with the levels seen in diploid littermate controls. However starting at 10 months of age, brain APP levels were increased proportional to the App gene dosage imbalance reflecting increased App message levels in Ts65Dn mice. Similar to APP levels, soluble amino-terminal fragments of APP (sAPPalpha and sAPPbeta) were increased in Ts65Dn mice compared with diploid mice at 12 months but not at 4 months of age. Brain levels of both Abeta40 and Abeta42 were not increased in Ts65Dn mice compared with diploid mice at all ages examined. Therefore, multiple mechanisms contribute to the regulation towards diploid levels of APP metabolites in the Ts65Dn mouse brain

In vivo quantitative magnetic resonance imaging (MRI) was employed to detect brain pathology and map its distribution within control, disomic mice (2N) and in Ts65Dn and Ts1Cje trisomy mice with features of human Down syndrome (DS). In Ts65Dn, but not Ts1Cje mice, transverse proton spin-spin (T(2)) relaxation time was selectively reduced in the medial septal nucleus (MSN) and in brain regions that receive cholinergic innervation from the MSN, including the hippocampus, cingulate cortex, and retrosplenial cortex. Basal forebrain cholinergic neurons (BFCNs) in the MSN, identified by choline acetyltransferase (ChAT) and nerve growth factor receptors p75(NTR) and TrkA immunolabeling were reduced in Ts65Dn brains and in situ acetylcholinesterase (AChE) activity was depleted distally along projecting cholinergic fibers, and selectively on pre- and postsynaptic profiles in these target areas. T(2) effects were negligible in Ts1Cje mice that are diploid for App and lack BFCN neuropathology, consistent with the suspected relationship of this pathology to increased App dosage. These results establish the utility of quantitative MRI in vivo for identifying Alzheimer's disease-relevant cholinergic changes in animal models of DS and characterizing the selective vulnerability of cholinergic neuron subpopulations

Downregulation of brain-derived neurotrophic factor (BDNF) in the cortex occurs early in the progression of Alzheimer's disease (AD). Since BDNF plays a critical role in neuronal survival, synaptic plasticity, and memory, BDNF reduction may contribute to synaptic and cellular loss and memory deficits characteristic of AD. In vitro evidence suggests that amyloid-beta (A beta) contributes to BDNF downregulation in AD, but the specific A beta aggregation state responsible for this downregulation in vivo is unknown. In the present study, we examined cortical levels of BDNF mRNA in three different transgenic AD mouse models harboring mutations in APP resulting in A beta overproduction, and in a genetic mouse model of Down syndrome. Two of the three A beta transgenic strains (APP(NLh) and TgCRND8) exhibited significantly decreased cortical BDNF mRNA levels compared with wild-type mice, whereas neither the other strain (APP(swe)/PS-1) nor the Down syndrome mouse model (Ts65Dn) was affected. Only APP(NLh) and TgCRND8 mice expressed high A beta(42)/A beta(40) ratios and larger SDS-stable A beta oligomers (approximately 115 kDa). TgCRND8 mice exhibited downregulation of BDNF transcripts III and IV; transcript IV is also downregulated in AD. Furthermore, in all transgenic mouse strains, there was a correlation between levels of large oligomers, A beta(42)/A beta(40), and severity of BDNF decrease. These data show that the amount and species of A beta vary among transgenic mouse models of AD and are negatively correlated with BDNF levels. These findings also suggest that the effect of A beta on decreased BDNF expression is specific to the aggregation state of A beta and is dependent on large oligomers

OBJECTIVE: To examine alpha7 nicotinic acetylcholine receptor (nAChR) binding and beta-amyloid (Abeta) peptide load in superior frontal cortex (SFC) across clinical and neuropathological stages of Alzheimer disease (AD). DESIGN: Quantitative measures of alpha7 nAChR by [(3)H]methyllycaconitine binding and Abeta concentration by enzyme-linked immunosorbent assay in SFC were compared across subjects with antemortem clinical classification of no cognitive impairment, mild cognitive impairment, or mild to moderate AD, and with postmortem neuropathological diagnoses. SETTING: Academic medical center. Subjects Twenty-nine elderly retired clergy. MAIN OUTCOME MEASURES: Quantitative measures of alpha7 nAChR binding and Abeta peptide concentration in SFC. RESULTS: Higher concentrations of total Abeta peptide in SFC were associated with clinical diagnosis of mild to moderate AD (P = .02), lower Mini-Mental State Examination scores (P = .003), presence of cortical Abeta plaques (P = .02), and likelihood of AD diagnosis by the National Institute on Aging-Reagan criteria (P = .002). Increased alpha7 nAChR binding was associated with National Institute on Aging-Reagan diagnosis (P = .02) and, albeit weakly, the presence of cortical Abeta plaques (P = .08). There was no correlation between the 2 biochemical measures. CONCLUSIONS: These observations suggest that during the clinical progression from normal cognition to neurodegenerative disease state, total Abeta peptide concentration increases while alpha7 nAChRs remain relatively stable in SFC. Regardless of subjects' clinical status, however, elevated alpha7 nAChR binding is associated with increased Abeta plaque pathology, supporting the hypothesis that cellular expression of these receptors may be upregulated selectively in Abeta plaque-burdened brain areas.

Terminal continuation (TC) RNA amplification was developed originally to reproducibly and inexpensively amplify RNA. The TC RNA amplification method has been improved further by obviating second strand DNA synthesis, a cost-effective protocol that takes less time to perform with fewer manipulations required for RNA amplification. Results demonstrate that TC RNA amplification without second strand synthesis does not differ from the original protocol using RNA harvested from mouse brain and from hippocampal neurons obtained via laser capture microdissection from postmortem human brains. The modified TC RNA amplification method can discriminate single cell gene expression profiles between normal control and Alzheimer's disease hippocampal neurons indistinguishable from the original protocol. Thus, TC RNA amplification without second strand synthesis is a reproducible, time- and cost-effective method for RNA amplification from minute amounts of input RNA, and is compatible with microaspiration strategies and subsequent microarray analysis as well as quantitative real-time PCR