Leptin induces proliferation of neuronal progenitors and neuroprotection in a mouse model of Alzheimer's disease.

Alzheimer's disease (AD) is a progressive neurodegenerative disease associated with senile amyloid-ß (Aß) plaques, neuronal death, and cognitive decline. Neurogenesis in the adult hippocampus, which is notably affected by progressive neurodegeneration and Aß pathology, is implicated in learning and memory regulation. Human postmortem brains of AD patients and AßPP/PS1 double transgenic mice show increased neurodegeneration. Leptin, an adipose-derived hormone, promotes neurogenesis in the adult hippocampus, but the way in which this process occurs in the AD brain is still unknown. Thus, we sought to determine if leptin stimulated the proliferation of neuronal precursors in AßPP/PS1 mice. We estimated the number proliferating hippocampal cells after intracerebroventricular administration of a lentiviral vector encoding leptin. After 3 months of treatment with leptin we observed an increase in the number of BrdU-positive cells in the subgranular zone of the dentate gyrus, as shown by morphometric analysis. This increase resulted mainly from an increased proliferation of neuronal precursors. Additionally, leptin led to an attenuation of Aß-induced neurodegeneration, as revealed by Fluoro-Jade staining. Our results suggest that in AßPP/PS1 mice, leptin exerts changes resembling acute neurotrophic and neuroprotective effects. These effects could serve as the basis for the design of future treatment strategies in AD.

IGF-I gene variability is associated with an increased risk for AD.

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 (Aß) 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 GG 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 IGF-I levels, and confirm the physiological role IGF-I in the pathogenesis of AD.

Saliva levels of Abeta1-42 as potential biomarker of Alzheimer's disease: a pilot study.

BACKGROUND: Simple, non-invasive tests for early detection of degenerative dementia by use of biomarkers are urgently required. However, up to the present, no validated extracerebral diagnostic markers for the early diagnosis of Alzheimer disease (AD) are available. The clinical diagnosis of probable AD is made with around 90% accuracy using modern clinical, neuropsychological and imaging methods. A biochemical marker that would support the clinical diagnosis and distinguish AD from other causes of dementia would therefore be of great value as a screening test. A total of 126 samples were obtained from subjects with AD, and age-sex-matched controls. Additionally, 51 Parkinson's disease (PD) patients were used as an example of another neurodegenerative disorder. We analyzed saliva and plasma levels of ß amyloid (Aß) using a highly sensitive ELISA kit. RESULTS: We found a small but statistically significant increase in saliva Aß42 levels in mild AD patients. In addition, there were not differences in saliva concentration of Aß42 between patients with PD and healthy controls. Saliva Aß40 expression was unchanged within all the studied sample. The association between saliva Aß42 levels and AD was independent of established risk factors, including age or Apo E, but was dependent on sex and functional capacity. CONCLUSIONS: We suggest that saliva Aß42 levels could be considered a potential peripheral marker of AD and help discrimination from other types of neurodegenerative disorders. We propose a new and promising biomarker for early AD.

PLA2G3, a gene involved in oxidative stress induced death, is associated with Alzheimer's disease.

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.

Megalin interacts with APP and the intracellular adapter protein FE65 in neurons.

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 ß-peptide (Aß) 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 Aß-mediated neurotoxicity, and therefore may be involved in the neurodegenerative processes that occur in AD.

Gelsolin restores A beta-induced alterations in choroid plexus epithelium.

Histologically, Alzheimer's disease (AD) is characterized by senile plaques and cerebrovascular amyloid deposits. In previous studies we demonstrated that in AD patients, amyloid-beta (A beta) peptide also accumulates in choroid plexus, and that this process is associated with mitochondrial dysfunction and epithelial cell death. However, the molecular mechanisms underlying A beta accumulation at the choroid plexus epithelium remain unclear. A beta clearance, from the brain to the blood, involves A beta carrier 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 A beta-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 A beta-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.

A megalin polymorphism associated with promoter activity and Alzheimer's disease risk.

Elevated cerebral levels of amyloid beta-protein (Abeta) occur in Alzheimer's disease (AD), yet only a few patients show evidence of increased Abeta production. This observation suggests that many, perhaps most, cases of AD are caused by faulty clearance of Abeta. Megalin, which plays an important role in mediating Abeta 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.

Abeta accumulation in choroid plexus is associated with mitochondrial-induced apoptosis.

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.

Cytoplasmic gelsolin increases mitochondrial activity and reduces Abeta burden in a mouse model of Alzheimer's disease.

Accumulation of amyloid-beta (Abeta) peptides is thought to be a critical event in the pathology of Alzheimer's disease (AD), because they induce multiple neurotoxic effects, including mitochondrial dysfunction and apoptotic cell death. Therefore the reduction of Abeta is considered a primary therapeutic target. Gelsolin, an Abeta binding protein, has been shown to inhibit apoptosis, although the underlying mechanism is unclear. To clarify these effects, we manipulated cytoplasmic gelsolin levels through viral-directed overexpression in the brain of APP/Ps1 transgenic mice. We observed that gelsolin reduces brain Abeta burden in the APP/Ps1 mice, possibly by enhancing Abeta clearance via megalin. The reduction in brain Abeta levels was accompanied by an inhibition of nitric oxide production and cell death, not only in the choroid plexus but also in the cerebral cortex. Notably, overexpressed gelsolin restored the impaired mitochondrial activity in the APP/Ps1 mice, resulting in the increase of cytochrome c oxidase activity. By contrast, RNA interference to block gelsolin expression, confirmed that cytoplasmic gelsolin acts as a modulator of brain Abeta levels and its neurotoxic effects. We conclude that gelsolin might prevent brain amyloidosis and Abeta-induced apoptotic mitochondrial changes. These findings make cytoplasmic gelsolin a potential therapeutic strategy in AD.