Kathryn J. Elliott

Genome-wide association analysis reveals putative Alzheimer's disease susceptibility loci in addition to APOE.

Alzheimers disease (AD) is a genetically complex and heterogeneous disorder. To date four genes have been established to either cause early-onset autosomal-dominant AD (APP, PSEN1, and PSEN2(1-4)) or to increase susceptibility for late-onset AD (APOE5). However, the heritability of late-onset AD is as high as 80%, (6) and much of the phenotypic variance remains unexplained to date. We performed a genome-wide association (GWA) analysis using 484,522 single-nucleotide polymorphisms (SNPs) on a large (1,376 samples from 410 families) sample of AD families of self-reported European descent. We identified five SNPs showing either significant or marginally significant genome-wide association with a multivariate phenotype combining affection status and onset age. One of these signals (p = 5.7 x 10(-14)) was elicited by SNP rs4420638 and probably reflects APOE-epsilon4, which maps 11 kb proximal (r2 = 0.78). The other four signals were tested in three additional independent AD family samples composed of nearly 2700 individuals from almost 900 families. Two of these SNPs showed significant association in the replication samples (combined p values 0.007 and 0.00002). The SNP (rs11159647, on chromosome 14q31) with the strongest association signal also showed evidence of association with the same allele in GWA data generated in an independent sample of approximately 1,400 AD cases and controls (p = 0.04). Although the precise identity of the underlying locus(i) remains elusive, our study provides compelling evidence for the existence of at least one previously undescribed AD gene that, like APOE-epsilon4, primarily acts as a modifier of onset age.

Comparative structure of human neuronal α2–α7 and β2–β4 nicotinic acetylcholine receptor subunits and functional expression of the α2, α3, α4, α7, β2, and β4 subunits

AbstractcDNA clones encoding human neuronal nicotinic acetylcholine receptor α2, α3, α4, α5, α6, α7, β2, β3, and β4 subunits were isolated from brainstem, hippocampus, prefrontal cortex, substantia nigra, thalamus, and IMR32 libraries. Human α2 and α6 and full-length β3 and β4 clones have not been previously reported. Deduced amino acid sequences of the α2, α6, β3, and β4 predicted mature peptides are 503 residues (56.9 kDa), 464 residues (53.7 kDa), 440 residues (50.8 kDa), and 477 residues (54.1 kDa), respectively. These sequences show 84 (α2), 87 (α6), 89 (β3), and 84% (β4) identity to the corresponding rat sequences. The amino termini of the human α2 and β3 mature peptides contain 23 and six additional residues, respectively, compared to those of rat α2 and β3. Recombinant receptors were expressed inXenopus laevis oocytes injected with in vitro transcripts encoding either α7 alone or α2, α3, or α4 in pairwise combination with β2 or β4. Inward currents were elicited by the application of acetylcholine (1–100 µM) and other agonists; these responses were blocked 65–97% by application of 10 µM d-tubocurare, confirming functional expression of human nicotinic receptors.

6-hydroxydopamine lesion of rat nigrostriatal dopaminergic neurons differentially affects nicotinic acetylcholine receptor subunit mRNA expression

AbstractNicotinic acetylcholine receptor (nAChR) subunit mRNA expression in the rat substantia nigra (SN) was assayed by semiquantitative RT-PCR following 6-hydroxydopamine (6-OHDA) lesion of nigrostriatal dopaminergic neurons. Six months after unilateral injection of 6-OHDA or saline into the SN, total RNA was isolated from ipsilateral and contralateral tissue samples. RT-PCR amplifications were performed with template titration using primers specific for sequences encoding1.nAChR α2–α7 and β2–β4 subunits2.Glutamic acid decarboxylase3.Glyceraldehyde 3-phosphate dehydrogenase for normalization of template mass. PCR products specific for α3, α4, α5, α6, α7, β2, β3, and glutamic acid decarboxylase were detected in the reactions containing SN RNA. This is the first evidence that α7 may be expressed in the SN. α2 and β4 PCR products were not detected in SN reactions, although they were observed in hippocampus and thalamus control reactions. A comparison of ipsilateral and contralateral SN RT-PCR reaction products showed substantial decreases in α5, α6, and β3 product yields following 6-OHDA, but not sham treatment. Neither the SN of sham-lesioned rats nor the thalamus of 6-OHDA-lesioned rats yielded similar results, indicating that the effects observed in 6-OHDA-treated SN were not caused by local mechanical damage or a nonspecific response, respectively. Effects of 6-OHDA treatment on α3, α4, α7, β2, or glutamic acid decarboxylase product yields from SN samples were small or undetectable. The results suggest that α5, β6, and β3 subunit-encoding mRNAs are expressed at substantially higher levels in dopaminergic than in nondopaminergic cell bodies in the SN.