Epistasis between APOE and nicotinic receptor gene CHRNA4 in age related cognitive function and decline

Cholinergic Pathway SNPs and Postural Control in 477 Older Adults

Objective: To determine whether single nucleotide polymorphisms (SNPs) of the cholinergic system and quantitative parameters of postural control are associated in healthy older adults. This is a cross-sectional analysis from the TREND study.

Methods: All participants performed a static postural control task for 30 s on a foam pad in semitandem stance and eyes closed. We analyzed mean power frequency (MPF), area, acceleration, jerk, and velocity from a mobile sensor worn at the lower back using a validated algorithm. Genotypes of four SNPs in genes involved in the cholinergic system (SLC5A7, CHAT, BCHE, CHRNA4) were extracted from the NeuroX chip. All participants present a normal neurological examination and a Minimental state examination score >24.

Results: Four hundred and seventy seven participants were included. Mean age was 69 years, 41% were female. One SNP of the cholinergic pathway was significantly associated with a quantitative postural control parameter. The minor allele of rs6542746 in SLC5A7 was associated with lower MPF (4.04 vs. 4.22 Hz; p = 3.91 × 10^-4). Moreover, the following associations showed trends toward significance: minor allele of rs6542746 in SLC5A7 with higher anteroposterior acceleration (318 vs. 287 mG; p = 0.005), and minor allele of rs3810950 in CHAT with higher mediolateral acceleration [1.77 vs. 1.65 log(mG); p = 0.03] and velocity [1.83 vs. 1.74 log(mm/s); p = 0.019]. Intraindividual occurrence of rs6542746 and rs3810950 minor alleles was dose-dependently related with lower MPF (p = 0.004).

Conclusion: This observational study suggests an influence of SNPs of the cholinergic pathway on postural control in older adults.

Varenicline, the clinically effective smoking cessation agent, restores probabilistic response reversal performance during withdrawal from nicotine

There is recognition that cognitive problems can contribute to renewed drug taking in former addicts. Our previous work has indicated that current smokers show reduced performance on a probabilistic reversal learning (PRL) task, relative to former smokers. To further explore PRL performance and its relevance to smoking, in addition to the role of nicotine, we developed a model of nicotine withdrawal-induced deficits in rodents. A second goal was to test varenicline, an α4β2 partial agonist, for its ability to restore any cognitive impairment. Acute effects of nicotine and varenicline on PRL performance in non-dependent animals were minimal and confined to speed of responding. When rats were made dependent on nicotine via osmotic minipumps implanted for 7 days (3.16 mg/kg/day), repeated tests at specified withdrawal time points revealed PRL disruption peaking at 12 and 24 hours following surgical removal of minipumps. Withdrawal was characterized by significant deficits in the number of reversals (P < 0.05), speed of responding (P < 0.01) and increases in omissions (P < 0.05). Nicotine (0.2 mg/kg SC) or varenicline (0.3 and 1.0 mg/kg SC) administered 10-minute prior to PRL test sessions during withdrawal, relieved the performance deficits. At 24-hour withdrawal, nicotine and varenicline (1 mg/kg) prevented decrements in reversals, in addition to ameliorating slower speed of responding. The high dose of varenicline only reduced omissions. These results confirm the role of nicotine in withdrawal-induced disruption of PRL performance and suggest that the model may be useful for investigating efficacy of potential new treatments for smoking cessation.

A draft network of ligand-receptor-mediated multicellular signalling in human

Cell-to-cell communication across multiple cell types and tissues strictly governs proper functioning of metazoans and extensively relies on interactions between secreted ligands and cell-surface receptors. Herein, we present the first large-scale map of cell-to-cell communication between 144 human primary cell types. We reveal that most cells express tens to hundreds of ligands and receptors to create a highly connected signalling network through multiple ligand-receptor paths. We also observe extensive autocrine signalling with approximately two-thirds of partners possibly interacting on the same cell type. We find that plasma membrane and secreted proteins have the highest cell-type specificity, they are evolutionarily younger than intracellular proteins, and that most receptors had evolved before their ligands. We provide an online tool to interactively query and visualize our networks and demonstrate how this tool can reveal novel cell-to-cell interactions with the prediction that mast cells signal to monoblastic lineages via the CSF1-CSF1R interacting pair.

Global view of transcriptome in the brains of aged NR2B transgenic mice

NR2B subunits are involved in regulating aging, in particular, age-related learning and memory deficits. We examined 19-month-old NR2B transgenic mice and their littermate controls. First, we detected expression of the NR2B subunit gene, Grin2b, in the neocortex of transgenic mice using real-time PCR. Next, we used microarrays to examine differences in neocortical gene expression. Pathway and signal-net analyses identified multiple pathways altered in the transgenic mice, including the P53, Jak-STAT, Wnt, and Notch pathways, as well as regulation of the actin cytoskeleton and neuroactive ligand-receptor interactions. Further signal-net analysis highlighted the P53 and insulin-like growth factor pathways as key regulatory pathways. Our results provide new insight into understanding the molecular mechanisms of NR2B regulated age-related memory storage, normal organismal aging and age-related disease.

Synergy effects of HbA1c and variants of APOE and BDNFVal66Met explains individual differences in memory performance

We aimed at exploring if synergy effects of Brain-Derived Neurotrophic Factor (BDNF) Val(66)Met, Apolipoprotein E (APOE) and HbA1c (glycated haemoglobin) could explain individual differences in memory performance over 10 years in a population based sample of nondemented adults (N=888, 35-85 years at baseline). Episodic memory was affected by such agents, wheras semantic memory was spared. Both age and HbA1c were associated with episodic memory decline. BDNF(66)Met carriers with higher HbA1c levels evidenced slope decline in episodic recall. We found support for joint effects of BDNFVal(66)Met×APOE×HbA1c and BDNFVal(66)Met×APOE×age on rates of episodic memory change over ten years, after controlling for age, sex, education and cardiovascular diseases. We conclude that variants of genetic polymorphisms act in synergy with long-term blood glucose control in shaping patterns of cognitive aging.

Imaging and Cognitive Genetics: The Norwegian Cognitive NeuroGenetics Sample

Data collection for the Norwegian Cognitive NeuroGenetics sample (NCNG) was initiated in 2003 with a research grant (to Ivar Reinvang) to study cognitive aging, brain function, and genetic risk factors. The original focus was on the effects of aging (from middle age and up) and candidate genes (e.g., APOE, CHRNA4) in cross-sectional and longitudinal designs, with the cognitive and MRI-based data primarily being used for this purpose. However, as the main topic of the project broadened from cognitive aging to imaging and cognitive genetics more generally, the sample size, age range of the participants, and scope of available phenotypes and genotypes, have developed beyond the initial project. In 2009, a genome-wide association (GWA) study was undertaken, and the NCNG proper was established to study the genetics of cognitive and brain function more comprehensively. The NCNG is now controlled by the NCNG Study Group, which consists of the present authors. Prominent features of the NCNG are the adult life-span coverage of healthy participants with high-dimensional imaging, and cognitive data from a genetically homogenous sample. Another unique property is the large-scale (sample size 300–700) use of experimental cognitive tasks focusing on attention and working memory. The NCNG data is now used in numerous ongoing GWA-based studies and has contributed to several international consortia on imaging and cognitive genetics. The objective of the following presentation is to give other researchers the information necessary to evaluate possible contributions from the NCNG to various multi-sample data analyses.

The apolipoprotein e antagonistic pleiotropy hypothesis: review and recommendations

Research on apolipoprotein E (APOE) has consistently revealed a relationship between the gene's ε4 allele and risk for development of Alzheimer's disease (AD). However, research with younger populations of ε4 carriers has suggested that the APOE ε4 allele may in fact be beneficial in earlier ages and may only confer risk of cognitive decline later in life. Accordingly, we and others have proposed that APOE may represent an example of antagonistic pleiotropy. Antagonistic pleiotropy is an evolutionary biology concept that proposes certain genes or alleles that may differentially impact fitness during different life stages. We critically review this hypothesis in light of new research of the impact of APOE on cognition and neural integrity across the lifespan. We provide recommendations for the revision of the antagonistic pleiotropy hypothesis of APOE and suggest important avenues for future research in this area.

Neurogenetic effects on cognition in aging brains: a window of opportunity for intervention?

Knowledge of genetic influences on cognitive aging can constrain and guide interventions aimed at limiting age-related cognitive decline in older adults. Progress in understanding the neural basis of cognitive aging also requires a better understanding of the neurogenetics of cognition. This selective review article describes studies aimed at deriving specific neurogenetic information from three parallel and interrelated phenotype-based approaches: psychometric constructs, cognitive neuroscience-based processing measures, and brain imaging morphometric data. Developments in newer genetic analysis tools, including genome wide association, are also described. In particular, we focus on models for establishing genotype-phenotype associations within an explanatory framework linking molecular, brain, and cognitive levels of analysis. Such multiple-phenotype approaches indicate that individual variation in genes central to maintaining synaptic integrity, neurotransmitter function, and synaptic plasticity are important in affecting age-related changes in brain structure and cognition. Investigating phenotypes at multiple levels is recommended as a means to advance understanding of the neural impact of genetic variants relevant to cognitive aging. Further knowledge regarding the mechanisms of interaction between genetic and preventative procedures will in turn help in understanding the ameliorative effect of various experiential and lifestyle factors on age-related cognitive decline.