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Oxidative stress, which plays a critical role in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD), is intimately linked to aging, the best established risk factor for AD. Studies in neuronal cells subjected to oxidative stress, mimicking such stress in AD brains, are therefore of great interest. PLA2G3 is the most overexpressed gene in a human neuronal model of oxidative stress induced by the free radical-generating xanthine/xanthine oxidase (X-XOD) system, which provokes apoptotic cell death. In this work, we describe that PLA2G3 gene silencing produced a marked inhibition of X-XOD induced cell death, and that PLA2G3 polymorphisms are associated with AD in a Spanish case-control sample. The capacity to respond to oxidative stress may therefore modulate the risk of AD, and PLA2G3 is a potential target to regulate neuronal damage induced by free radicals.

Increasing evidence has implicated megalin, a low-density lipoprotein receptor-related protein, in the pathogenesis of Alzheimer's disease (AD). In the brain, megalin is expressed in brain capillaries, ependymal cells and choroid plexus, where it participates in the clearance of brain amyloid β-peptide (Aβ) complex. Recently, megalin has also been detected in oligodendrocytes and astrocytes. In this study we demonstrate that megalin is widely distributed in neurons throughout the brain. Additionally, given that FE65 mediates the interaction between the low density lipoprotein receptor-related protein-1 and the amyloid precursor protein (APP) to modulate the rate of APP internalization from the cell surface, we hypothesize that megalin could also interact with APP in neurons. Our results confirm that megalin interacts with APP and FE65, suggesting that these three proteins form a tripartite complex. Moreover, our findings imply that megalin may participate in neurite branching. Taken together, these results indicate that megalin has an important role in Aβ-mediated neurotoxicity, and therefore may be involved in the neurodegenerative processes that occur in AD.

Elevated cerebral levels of amyloid beta-protein (Aβ) occur in Alzheimer's disease (AD), yet only a few patients show evidence of increased Aβ production. This observation suggests that many, perhaps most, cases of AD are caused by faulty clearance of Aβ. Megalin, which plays an important role in mediating Aβ clearance, is an attractive candidate gene for genetic association with AD. To investigate this hypothesis, we analyzed the megalin gene in a population of 2,183 subjects. Genetic analysis indicated that the rs3755166 (G/A) polymorphism located in the megalin promoter associated with risk for AD, dependently of apolipoprotein E genotype. The rs3755166 AA genotype frequency was significantly greater in AD patients than in control subjects. Furthermore, the luciferase reporter assay indicated that the rs3755166 A variant has 20% less transcriptional activity than the rs3755166 G variant. This study provides strong evidence that this megalin polymorphism confers a greater risk for AD, and supports a biological role for megalin in the neurodegenerative processes involved in AD, This work was supported by grants from Fondo de Investigación Sanitaria (FIS) (CP04/00179, PI060155), Fundación Investigación Médica Mutua Madrileña (2006.125), CIBERNED, Obra Social Caja Madrid, Comunidad Autónoma de Madrid (GR/SAL/0783/2004). We thank Drs. P. Gil, P. Coria, and A. Labad-Alquézar for their cooperation in the generation of the case–control samples

Histologically, Alzheimer's disease (AD) is characterized by senile plaques and cerebrovascular amyloid deposits. In previous studies we demonstrated that in AD patients, amyloid-β(Aβ) peptide also accumulates in choroid plexus, and that this process is associated with mitochondrial dysfunction and epithelial cell death. However, the molecular mechanisms underlying Aβaccumulation at the choroid plexus epithelium remain unclear. Aβclearance, from the brain to the blood, involves Aβcarrier proteins that bind to megalin, including gelsolin, a protein produced specifically by the choroid plexus epithelial cells. In this study, we show that treatment with gelsolin reduces Aβ-induced cytoskeletal disruption of blood-cerebrospinal fluid (CSF) barrier at the choroid plexus. Additionally, our results demonstrate that gelsolin plays an important role in decreasing Aβ-induced cytotoxicity by inhibiting nitric oxide production and apoptotic mitochondrial changes. Taken together, these findings make gelsolin an appealing tool for the prophylactic treatment of AD.

One of the possible mechanisms involved in beta-amyloid (Abeta)-induced neuronal damage is blood-cerebrospinal fluid barrier dysfunction. Recently, we have demonstrated that Alzheimer patients have an elevated expression of Abeta in the choroid plexus (CP), where it could impair the physiological functions of CP epithelium. We investigated whether these alterations were mediated by mitochondrial dysfunction, a common early pathomechanism in Alzheimer's disease. Our main observations were: high Abeta levels; increased nitric oxide levels; impairment of the activity and assembly of mitochondrial respiratory chain complexes I and IV; and a significant increase in reactive oxygen species and caspase expression in CP epithelial cells treated with Abeta. Our results also demonstrate a direct relationship between Abeta toxicity, increased expression of matrix metalloproteinase-9, and blood-cerebrospinal fluid barrier disruption. We propose a sequence of pathological steps that link Abeta accumulation in CP epithelium with an enhanced nitric oxide production, mitochondrial dysfunction, and up-regulation of matrix metalloproteinase-9, which ultimately lead to cell death, and probably to CSF barrier dysfunction.

Insulin-like growth factor I (IGF-I), a neuroprotective factor with a wide spectrum of actions in the adult brain is involved in the pathogenesis of Alzheimer's disease (AD). Circulating levels of IGF-I change in AD patients and are implicated in the clearance of brain amyloid beta (Lambda beta) complexes. To investigate this hypothesis, we screened the IGF-I gene for various well known single nucleotide polymorphisms (SNPs) covering % of the gene variability in a population of 2352 individuals. Genetic analysis indicated different distribution of genotypes of 1 single nucleotide polymorphism., and 1 extended haplotype in the AD population compared with healthy control subjects. In particular, the frequency of rs972936 GC, genotype was significantly greater in AD patients than in control subjects (63% vs. 55%). The rs972936 GG genotype was associated with an increased risk for disease, independently of apolipoprotein E genotype, and with enhanced circulating levels of IGF-I. These findings suggest that polymorphisms within the IGF-I gene could infer greater risk for AD through their effect on ICE-I levels, and confirm the physiological role IGF-I in the pathogenesis of AD. (C) 2011 IBRO All rights reserved.