Genetics of familial and sporadic Alzheimer's disease.

Alzheimer's disease (AD) is an age-related progressive neurodegenerative disorder. A majority of cases manifest as a late onset sporadic form but genetically the disease is divided into familial cases and sporadic cases. The familial form is due to mutations in three major genes (amyloid precursor protein (APP) gene, presenilin1 (PSEN1) gene and presenilin 2 (PSEN2) gene). In contrast, many genetic and environmental factors may contribute to determining the sporadic AD form. Despite many years of research and great progress in the knowledge of the molecular pathogenesis of AD, a full understanding of the etiology of the sporadic form is still not yet in reach. Genome-wide association studies (GWASs) revealed the genetic complexity of the disease and recent studies suggested that epigenetic mechanisms may play an essential role in disease development. This review provides an overview of all the milestones in AD genetic research, as well as the new and promising approach, in order to better understand the genetic profile for predicting the risk of AD

Association Study of Genetic Variants in CDKN2A/CDKN2B Genes/Loci with Late-Onset Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia clinically characterized by progressive impairment of memory and other cognitive functions. Many genetic researches in AD identified one common genetic variant (ε4) in Apolipoprotein E (APOE) gene as a risk factor for the disease. Two independent genome-wide studies demonstrated a new locus on chromosome 9p21.3 implicated in Late-Onset Alzheimer's Disease (LOAD) susceptibility in Caucasians. In the present study, we investigated the role of three SNP's in the CDKN2A gene (rs15515, rs3731246, and rs3731211) and one in the CDKN2B gene (rs598664) located in 9p21.3 using an association case-control study carried out in a group of Caucasian subjects including 238 LOAD cases and 250 controls. The role of CDKN2A and CDKN2B genetic variants in AD is not confirmed in our LOAD patients, and further studies are needed to elucidate the role of these genes in the susceptibility of AD

Specific Silencing of L392V PSEN1 Mutant Allele by RNA Interference

RNA interference (RNAi) technology provides a powerful molecular tool to reduce an expression of selected genes in eukaryotic cells. Short interfering RNAs (siRNAs) are the effector molecules that trigger RNAi. Here, we describe siRNAs that discriminate between the wild type and mutant (1174 C→G) alleles of human Presenilin1 gene (PSEN1). This mutation, resulting in L392V PSEN1 variant, contributes to early onset familial Alzheimer's disease. Using the dual fluorescence assay, flow cytometry and fluorescent microscopy we identified positions 8th–11th, within the central part of the antisense strand, as the most sensitive to mismatches. 2-Thiouridine chemical modification introduced at the 3′-end of the antisense strand improved the allele discrimination, but wobble base pairing adjacent to the mutation site abolished the siRNA activity. Our data indicate that siRNAs can be designed to discriminate between the wild type and mutant alleles of genes that differ by just a single nucleotide

Increased susceptibility to amyloid toxicity in familial Alzheimer's fibroblasts

Much experimental evidence suggests that an imbalance in cellular redox status is a major factor in the pathogenesis of Alzheimer's disease (AD). Our previous data showed a marked increase in membrane lipoperoxidation in primary fibroblasts from familial AD (FAD) patients. In the present study, we demonstrate that when oligomeric structures of A beta 1-40 and A beta 1-42 are added to the culture media, they accumulate quicker near the plasma membrane, and are internalized faster and mostly in APPV717I fibroblasts than in age-matched healthy cells; this results in an earlier and sharper increase in the production of reactive oxygen species (ROS). Higher ROS production leads in turn to an increase in membrane oxidative-injury and significant impairment of cellular antioxidant capacity, giving rise to apoptotic cascade activation and finally to a necrotic outcome. In contrast, healthy fibroblasts appear more resistant to amyloid oxidative-attack, possibly as a result of their plasma membrane integrity and powerful antioxidant capacity. Our data are consistent with increasing evidence that prefibrillar aggregates, compared to mature fibrils, are likely the more toxic species of the peptides. These findings provide compelling evidence that cells bearing increased membrane lipoperoxidation are more susceptible to aggregate toxicity as a result of their reduced ability to counteract amyloid oligomeric attack

Tumor Necrosis Factor α Influences Phenotypic Plasticity and Promotes Epigenetic Changes in Human Basal Forebrain Cholinergic Neuroblasts.

TNFα is the main proinflammatory cytokine implicated in the pathogenesis of neurodegenerative disorders, but it also modulates physiological functions in both the developing and adult brain. In this study, we investigated a potential direct role of TNFα in determining phenotypic changes of a recently established cellular model of human basal forebrain cholinergic neuroblasts isolated from the nucleus basalis of Meynert (hfNBMs). Exposing hfNBMs to TNFα reduced the expression of immature markers, such as nestin and β-tubulin III, and inhibited primary cilium formation. On the contrary, TNFα increased the expression of TNFα receptor TNFR2 and the mature neuron marker MAP2, also promoting neurite elongation. Moreover, TNFα affected nerve growth factor receptor expression. We also found that TNFα induced the expression of DNA-methylation enzymes and, accordingly, downregulated genes involved in neuronal development through epigenetic mechanisms, as demonstrated by methylome analysis. In summary, TNFα showed a dual role on hfNBMs phenotypic plasticity, exerting a negative influence on neurogenesis despite a positive effect on differentiation, through mechanisms that remain to be elucidated. Our results help to clarify the complexity of TNFα effects in human neurons and suggest that manipulation of TNFα signaling could provide a potential therapeutic approach against neurodegenerative disorders