Single-stranded telomeric DNA tends to form a four-base-paired planar structure termed G-quadruplex. This structure was easily formed in vitro in the presence of monovalent cations. However, the existence of this structure in native human telomeres is unclear. Here we address this important question through the distinctive properties of 3,6-bis(1-methyl-4-vinylpyridinium)carbazole diiodide (BMVC) upon binding to various DNA structures. Although the fluorescence of BMVC increases significantly in the presence of DNA, BMVC has high sensitivity and binding preference to quadruplex d(T(2)AG(3))(4) over duplex DNA. In addition, the fluorescent emissions were characterized around 575 nm for quadruplex d(T(2)AG(3))(4) and 545 nm for most of duplex DNA. The 575-nm fluorescence emissions were detected in the mixtures of 2 nM BMVC with the chromosomal DNA that were extracted from human cells, suggesting the presence of quadruplex structure in human nucleus. Further analyzing the BMVC fluorescence at the ends of metaphase chromosomes and other regions of chromosomes, we detected the quadruplex-binding BMVC fluorescence at telomere-proximal regions. Together these results provide the first evidence for the presence of quadruplex structures in human telomeres.

The minor allele of rs11136000 within CLU is strongly associated with reduced Alzheimer's disease (AD) risk. The mechanism underlying this association is unclear. Here, we report that CLU1 and CLU2 are the two primary CLU isoforms in human brain; CLU1 and CLU2 share exons 2–9 but differ in exon 1 and proximal promoters. The expression of both CLU1 and CLU2 was increased in individuals with significant AD neuropathology. However, only CLU1 was associated with the rs11136000 genotype, with the minor “protective” rs11136000T allele being associated with increased CLU1 expression. Since CLU1 and CLU2 are predicted to encode intracellular and secreted proteins, respectively, we compared their expression; for both CLU1 and CLU2 transfected cells, clusterin is present in the secretory pathway, accumulates in the extracellular media, and is similar in size to clusterin in human brain. Overall, we interpret these results as indicating that the AD-protective minor rs11136000T allele is associated with increased CLU1 expression. Since CLU1 and CLU2 appear to produce similar proteins and are increased in AD, the AD-protection afforded by the rs11136000T allele may reflect increased soluble clusterin throughout life.

Since apoE allele status is the predominant Alzheimer's disease (AD) genetic risk factor, functional single nucleotide polymorphisms (SNPs) in brain apoE receptors represent excellent candidates for association with AD. Recently, we identified a SNP, rs688, as modulating the splicing efficiency of low-density lipoprotein receptor (LDLR) exon 12 in female human liver and in minigene-transfected HepG2 cells. Moreover, the rs688T minor allele was associated with significantly higher LDL and total cholesterol in women within the Framingham Offspring Study cohort. Since LDLR is a major apoE receptor in the brain, we hypothesized that rs688 modulates LDLR splicing in neural tissues and associates with AD. To evaluate this hypothesis, we first transfected LDLR minigenes into SH-SY5Y neuroblastoma cells and found that the rs688T allele reduces exon 12 inclusion in this neural model. We then evaluated the association of rs688 allele with exon 12 splicing efficiency in vivo by quantifying LDLR splicing in human anterior cingulate tissue obtained at autopsy; the rs688T allele is associated with decreased LDLR exon 12 splicing efficiency in aged males, but not females. Lastly, we evaluated whether rs688 associates with AD by genotyping DNA from 1457 men and 2055 women drawn from three case-control series. The rs688T/T genotype was associated with increased AD odds in males [recessive model, odds ratio (OR) of 1.49, 95% confidence interval (CI) of 1.13-1.97, uncorrected P = 0.005], but not in females. In summary, these studies identify a functional apoE receptor SNP that is associated with AD in a sex-dependent fashion.

Background: Variations in sortilin-related receptor (SORL1) expression and function have been implicated in Alzheimers Disease (AD). Here, to gain insights into SORL1, we evaluated SORL1 expression and splicing as a function of AD and AD neuropathology, neural gene expression and a candidate single nucleotide polymorphism (SNP).