Humberto Arboleda

Synaptic dysfunction and oxidative stress in Alzheimer's disease: Emerging mechanisms

In this paper, we review experimental advances in molecular neurobiology of Alzheimers disease (AD), with special emphasis on analysis of neural function of proteins involved in AD pathogenesis, their relation with several signaling pathways and with oxidative stress in neurons. Molecular genetic studies have found that mutations in APP, PS1 and PS2 genes and polymorphisms in APOE gene are implicated in AD pathogenesis. Recent studies show that these proteins, in addition to its role in beta‐amyloid processing, are involved in several neuroplasticity‐signaling pathways (NMDA‐PKA‐CREB‐BDNF, reelin, wingless, notch, among others). Genomic and proteomic studies show early synaptic protein alterations in AD brains and animal models. DNA damage caused by oxidative stress is not completely repaired in neurons and is accumulated in the genes of synaptic proteins. Several functional SNPs in synaptic genes may be interesting candidates to explore in AD as genetic correlates of this synaptopathy in a “synaptogenomics” approach. Thus, experimental evidence shows that proteins implicated in AD pathogenesis have differential roles in several signaling pathways related to neuromodulation and neurotransmission in adult and developing brain. Genomic and proteomic studies support these results. We suggest that oxidative stress effects on DNA and inherited variations in synaptic genes may explain in part the synaptic dysfunction seen in AD.

Regulation of ceramide-induced neuronal death: Cell metabolism meets neurodegeneration

The present review explores the role of ceramides in neuronal apoptosis, as well as the recent discovery of the signaling pathways involved in this process placing particular emphasis on the correlation between cellular metabolism and neuronal death. Endogenous levels of ceramides are increased following various pro-apoptotic stimuli which have been identified as potential causes of chronic and acute neurodegenerative diseases. Ceramides induce changes in multiple enzymes and cell signaling components. The early inhibition of the neuronal survival pathway regulated by phosphatidil-inositol-3-kinase/protein kinase B or AKT mediated by ceramide may be a relevant early event in the decision of neuronal survival/death. It may perturb several molecular and metabolic functions. In particular it might decrease glycolysis through rapid modulation of hexokinase activity. This would in turn generate limited amounts of mitochondrial substrates leading to mitochondrial dysfunction and neuronal apoptosis. Subtle and early metabolic alterations caused by inhibition of the PI3K/AKT pathway mediated by ceramide may potentially work with genes associated with neurodegenerative diseases such as Parkinsons and Alzheimers disease. Together they may be determinant steps in downstream events leading to neuronal apoptosis. Therefore, reinforcement of the PI3K/AKT pathway could constitute an important neuroprotective strategy.

Optimizing methodologies for PCR-based DNA methylation analysis

Comprehensive analysis of DNA methylation patterns is critical for understanding the molecular basis of many human diseases. While hundreds of PCR-based DNA methylation studies are published every year, the selection and implementation of appropriate methods for these studies can be challenging for molecular genetics researchers not yet familiar with methylation analysis. Here we review the most commonly used PCR-based DNA methylation analysis techniques: bisulfite sequencing PCR (BSP), methylation specific PCR (MSP), MethyLight, and methylation-sensitive high resolution melting (MS-HRM). We provide critical analysis of the strengths and weaknesses of each approach as well as a series of guidelines to assist in selecting and implementing an appropriate method.

Sexually dimorphic effect of the Val66Met polymorphism of BDNF on susceptibility to Alzheimer's disease: New data and meta-analysis.

Conflicting results have been reported as to whether genetic variations (Val66Met and C270T) of the brain‐derived neurotrophic factor gene (BDNF) confer susceptibility to Alzheimers disease (AD). We genotyped these polymorphisms in a Japanese sample of 657 patients with AD and 525 controls, and obtained weak evidence of association for Val66Met (P = 0.063), but not for C270T. After stratification by sex, we found a significant allelic association between Val66Met and AD in women (P = 0.017), but not in men. To confirm these observations, we collected genotyping data for each sex from 16 research centers worldwide (4,711 patients and 4,537 controls in total). The meta‐analysis revealed that there was a clear sex difference in the allelic association; the Met66 allele confers susceptibility to AD in women (odds ratio = 1.14, 95% CI 1.05–1.24, P = 0.002), but not in men. Our results provide evidence that the Met66 allele of BDNF has a sexually dimorphic effect on susceptibility to AD.

Analysis of functional polymorphisms in three synaptic plasticity-related genes (BDNF, COMT AND UCHL1) in Alzheimer's disease in Colombia.

In recent years, it has been proposed that synaptic dysfunction may be an important etiological factor for Alzheimers disease (AD). This hypothesis has important implications for the analysis of AD genetic risk in case-control studies. In the present work, we analyzed common functional polymorphisms in three synaptic plasticity-related genes (brain-derived neurotrophic factor, BDNF Val66Met; catechol-O-methyl transferase, COMT Val158; ubiquitin carboxyl-terminal hydroxylase, UCHL1 S18Y) in a sample of 102 AD cases and 168 age and sex matched controls living in Bogotá, Colombia. There was not association between UCHL1 polymorphism and AD in our sample. We have found an initial association with BDNF polymorphism in familial cases and with COMT polymorphism in male and sporadic patients. These initial associations were lost after Bonferroni correction for multiple testing. Unadjusted results may be compatible with the expected functional effect of variations in these genes on pathological memory and cognitive dysfunction, as has been implicated in animal and cell models and also from neuropsychological analysis of normal subjects carriers of the AD associated genotypes. An exploration of functional variants in these and in other synaptic plasticity-related genes (a synaptogenomics approach) in independent larger samples will be important to discover new genes associated with AD.

Exploration of genetic susceptibility factors for Parkinson’s disease in a South American sample

1Neurosciences Research Group, School of Medicine and Institute of Genetics, Universidad Nacional de Colombia, Bogota, Colombia 2Department of Internal Medicine, 3Department of Pediatrics, 4Department of Pathology, School of Medicine, Universidad Nacional de Colombia, Bogota, Colombia 5MSc Program in Neurosciences, Universidad Nacional de Colombia, Bogota, Colombia 6Present address: Biomedical Science Research Group, School of Medicine, Universidad Antonio Narino, Bogota, Colombia

Differential regulation of AKT, MAPK and GSK3β during C2-ceramide-induced neuronal death

Evidence has implicated apoptosis as a mechanism underlying cell demise in diverse neurodegenerative diseases including Parkinsons disease (PD). Endogenous toxins and other stress signals activate the sphingomyelin pathway increasing the levels of ceramide, an important regulator of cell death. In the present paper we have analysed the contribution of PI3K/AKT-GSK3β and MAPK (ERK and JNK) pathways to cell death in a catecholaminergic cell line following exposure to C(2)-ceramide. We also explored the potential neuroprotective action of insulin-like growth factor-1 (IGF-1) and neurotrophin-3 (NT3). We demonstrated that C(2)-ceramide-induced cell death is associated to an early decrease in phosphorylation (inhibition) of PI3K/AKT and ERK, followed by phosphorylation (activation) of JNK and de-phosphorylation (activation) of glycogen synthase kinase-3 beta (GSK3β). NT3 and IGF-1 increased survival at early time points, but only IGF-1 is capable to attenuate C(2)-ceramide-mediated neuronal death, and this neuroprotection is associated to strong and permanent activation of AKT and inhibition of GSK3β. In conclusion, C(2)-ceramide initiates a series of events including an early inactivation of PI3K/AKT and ERK pathways followed by activation of JNK and activation of GSK3β and neuronal death, changes that are counteracted by IGF-1.

Global Long Interspersed Nuclear Element 1 DNA Methylation in a Colombian Sample of Patients With Late-Onset Alzheimer’s Disease

Alterations in DNA methylation have implicated as an epigenetic event in the pathogenesis of late-onset Alzheimer’s disease (LOAD). The objective of this work was to evaluate global DNA methylation levels for long interspersed nuclear element 1 (LINE-1) repetitive sequences in Colombian patients with LOAD and controls. The LINE-1 DNA methylation levels in peripheral blood samples from 28 Colombian patients with LOAD and 30 healthy participants were assessed using a methylation-sensitive high-resolution melting (MS-HRM) quantitative assay. We did not find differences in LINE-1 methylation levels between patients with Alzheimer’s disease (AD; median 76.2%, interquartile range [IQR]: 69.8-81.9) and control participants (median 79.8%, IQR: 73.2-83.8; P = .3). Additional stratified analyses did not show differences in LINE-1 methylation levels for male or female patients versus controls nor for apolipoprotein E4 carriers and noncarriers. This is the first report of LINE-1 methylation levels in patients with LOAD using the cost-effective MS-HRM technique, and this is the first global DNA methylation study in Latin American patients with AD.

Apolipoprotein E genotyping in a sample of Colombian patients with Alzheimer's disease

Abstract Apolipoprotein E e4 (APOEe4) allele has been associated with an increased risk for Alzheimers disease (AD) in diverse populations. Few studies have been carried out in Hispano-Americans and results are inconclusive due to ethnic diversity. This study determined the frequency of APOE alleles in a group of 61 Caucasian-Mestizos patients with probable AD, and 61 age- and sex-matched controls. APOEe4 frequency was 36.8% for patients, and 8.2% for controls (P

The neonatal progeroid syndrome (Wiedemann–Rautenstrauch): A model for the study of human aging?

The Wiedemann-Rautenstrauch syndrome (WRS) characterises a premature aging syndrome in which several features of human aging are apparent at birth therefore allowing their grouping as a neonatal progeroid condition. This differentiates WRS from other progeroid entities such as Hutchinson-Gilford progeria syndrome (HGPS) in which characteristics of premature aging become apparent some time after birth. The etiology of WRS remains unknown. Some studies have observed an autosomal recessive mode of inheritance. Several studies analysing telomere length and lamin A gene have not revealed any alterations. However, mutations in LMNA have been reported in several other atypical progeroid syndromes. Based on these observations, several hypothesis could be withdrawn concerning the etiology of WRS. The study of genes associated with lamin A metabolism, such as Zmpste24, and the metabolic pathways associated with insulin, such as protein kinase B or AKT, are of particular interest. We believe that WRS characteristics indicate that discovery of the gene and the metabolic pathway associated with this syndrome will most likely lead to new knowledge about the physiopathology of human aging.