Gene regulation and DNA damage in the ageing human brain

Aging of the brain, neurotrophin signaling, and Alzheimer's disease: is IGF1-R the common culprit?

The last decade has revealed that the lifespan of an organism can be modulated by the signaling pathway that acts downstream of the insulin/insulin-like growth factor 1 receptors (IR/IGF1-R), indicating that there is a "program" that drives the process of aging. New results have now linked the same pathway to the neurogenic capacities of the aging brain, to neurotrophin signaling, and to the molecular pathogenesis of Alzheimer's disease. Therefore, a common signaling cascade now seems to link aging to age-associated pathologies of the brain, suggesting that pharmacologic approaches aimed at the modulation of this pathway can serve to delay the onset of age-associated disorders and improve the quality of life. Work from a wide range of fields performed with different approaches has already identified some of the signaling molecules that act downstream of IGF1-R, and has revealed that a delicate checkpoint exists to balance excessive growth/"immortality" and reduced growth/"senescence" of a cell. Future research will determine how far the connection goes and how much of it we can influence.

Innate immune receptor expression in normal brain aging

Brain aging often results in cognitive impairment and is considered to be a major risk factor for neurodegenerative diseases. Earlier studies reported inflammatory responses in aged brain that could contribute to age-related neurodegeneration. Recently, innate immune receptors such as toll-like receptors (TLRs), so far implicated in defense against microorganisms, have been linked to pathogenesis of Alzheimer's disease. Therefore, we asked whether the transcription of TLRs (1-9) and CD14, could also be altered in physiological brain aging. Using real-time polymerase chain reaction (PCR), we indeed observed that TLR1, TLR2, TLR4, TLR5, TLR7 and CD14 expression was up-regulated in mouse brain in correlation with age. In contrast, transcriptions of TLR3, TLR6 and TLR8 were unchanged and the one of TLR9 was down-regulated. In situ hybridization further confirmed these results and identified the cellular source of TLR2 and TLR7 as mononuclear phagocytes. Together, this first systematic analysis demonstrates altered regulation of those innate immune receptors even in normal brain aging, which might be of relevance for understanding susceptibility to neurodegenerative processes associated with aging.

β-Amyloid increases somatostatin expression in cultured cortical neurons

In beta-amyloid (Abeta)-induced neurotoxicity, activation of the NMDA receptor, increased Ca2+ and oxidative stress are intimately associated with neuronal cell death as normally seen in NMDA-induced neurotoxicity. We have recently shown selective sparing of somatostatin (SST)-positive neurons and increased SST expression in NMDA agonist-induced neurotoxicity. Accordingly, the present study was undertaken to determine the effect of Abeta25-35-induced neurotoxicity on the expression of SST in cultured cortical neurons. Cultured cortical cells were exposed to Abeta25-35 and processed to determine the cellular content and release of SST into medium by radioimmunoassay and SST mRNA by RT-PCR. Abeta25-35 induces neuronal cell death in a concentration- and time-dependent fashion, increases SST mRNA synthesis and induces an augmentation in the cellular content of SST. No significant changes were seen on SST release at any concentration of Abeta25-35 after 24 h of treatment. However, Abeta25-35 induces a significant increase of SST release into medium only after 12 h in comparison with other time points. Most significantly, SST-positive neurons are selectively spared in the presence of a lower concentration of Abeta25-35, whereas, in the presence of higher concentrations of Abeta25-35 for extended time periods, SST-positive neurons decrease gradually. Furthermore, Abeta25-35 induces apoptosis at lower concentrations (5 and 10 micromol/L) and necrosis at higher concentrations (20 and 40 micromol/L). Consistent with the increased accumulation of SST, these data suggest that Abeta25-35 impairs cell membrane permeability. Selective sparing of SST-positive neurons at lower concentrations of Abeta25-35 at early time points directly correlates with the pathophysiology of Alzheimer's disease.

Calorie restriction in nonhuman primates: assessing effects on brain and behavioral aging

Dietary caloric restriction (CR) is the only intervention repeatedly demonstrated to retard the onset and incidence of age-related diseases, maintain function, and extend both lifespan and health span in mammals, including brain and behavioral function. In 70 years of study, such beneficial effects have been demonstrated in rodents and lower animals. Recent results emerging from ongoing studies of CR in humans and nonhuman primates suggest that many of the same anti-disease and anti-aging benefits observed in rodent studies may be applicable to long-lived species. Results of studies in rhesus monkeys indicate that CR animals (30% less than controls) are healthier than fully-fed counterparts based on reduced incidence of various diseases, exhibit significantly better indices of predisposition to disease and may be aging at a slower rate based on analysis of selected indices of aging. The current review discusses approaches taken in studies of rhesus monkeys to analyze age-related changes in brain and behavioral function and the impact of CR on these changes. Approaches include analyses of gross and fine locomotor performance as well as brain imaging. In a related study it was observed that short-term CR (6 months) in adult rhesus monkeys can provide protection against a neurotoxic insult. Increasing interest in the CR paradigm will expand its role in demonstrating how nutrition can modulate the rate of aging and the mechanisms responsible for this modulation.

[Oxidative stress in human diseases]

Oxidative stress is an abnormal phenomenon occurring inside our cells or tissues when production of oxygen radicals exceeds their antioxidant capacity. Excess of free radicals damage essential macromolecules of the cell, leading to abnormal gene expression, disturbance in receptor activity, proliferation or cell dye, immunity perturbation, mutagenesis, protein or lipofushin deposition. Numerous human diseases involve during the pathological process such a stress, localized or general (in the same way as inflammation). In many serious diseases such as cancer, ocular degeneration (age related macular degeneration or cataract), neurodegenerative diseases (ataxia, amyotrophic lateral sclerosis, Alzheimer's disease) stress is the factor original. In familial amyotrophic lateral sclerosis the genetic abnormality occurred an abnormal coding for an antioxidant enzyme, copper-zinc super oxide dismutase. In various other diseases oxidative stress occur secondary to the initial disease but plays an important in role immune or vascular complications. This is the case in infectious disease such as AIDS or septic shock, Parkinson's disease or renal failure. So antioxidant treatment seems logical to be tested in these pathologies. But they have to be applied early in the process, before irreversible mechanisms. They need also to be prescribed at low doses as baseline free radical production have to be preserved to maintain useful activity that cannot be suppressed.

DNA repair in neurons: so if they don't divide what's to repair?

Neuronal DNA repair remains one of the most exciting areas for investigation, particularly as a means to compare the DNA repair response in mitotic (cancer) vs. post-mitotic (neuronal) cells. In addition, the role of DNA repair in neuronal cell survival and response to aging and environmental insults is of particular interest. DNA damage caused by reactive oxygen species (ROS) such as generated by mitochondrial respiration includes altered bases, abasic sites, and single- and double-strand breaks which can be prevented by the DNA base excision repair (BER) pathway. Oxidative stress accumulates in the DNA of the human brain over time especially in the mitochondrial DNA (mtDNA) and is proposed to play a critical role in aging and in the pathogenesis of several neurological disorders including Parkinson's disease, ALS, and Alzheimer's diseases. Because DNA damage accumulates in the mtDNA more than nuclear DNA, there is increased interest in DNA repair pathways and the consequence of DNA damage in the mitochondria of neurons. The type of damage that is most likely to occur in neuronal cells is oxidative DNA damage which is primarily removed by the BER pathway. Following the notion that the bulk of neuronal DNA damage is acquired by oxidative DNA damage and ROS, the BER pathway is a likely area of focus for neuronal studies of DNA repair. BER variations in brain aging and pathology in various brain regions and tissues are presented. Therefore, the BER pathway is discussed in greater detail in this review than other repair pathways. Other repair pathways including direct reversal, nucleotide excision repair (NER), mismatch repair (MMR), homologous recombination and non-homologous end joining are also discussed. Finally, there is a growing interest in the role that DNA repair pathways play in the clinical arena as they relate to the neurotoxicity and neuropathy associated with cancer treatments. Among the numerous side effects of cancer treatments, major clinical effects include neurocognitive dysfunction and peripheral neuropathy. These symptoms occur frequently and have not been effectively studied at the cellular or molecular level. Studies of DNA repair may help our understanding of how those cells that are not dividing could succumb to neurotoxicity with the clinical manifestations discussed in the following article.

Different DNA repair strategies to combat the threat from 8-oxoguanine

Oxidative DNA damage is one of the most common threats to genome stability and DNA repair enzymes provide protection from the effects of oxidized DNA bases. In mammalian cells, base excision repair (BER) mediated by the OGG1 and MYH DNA glycosylases prevents the accumulation of 8-oxoguanine (8-oxoG) in DNA. When steady-state levels of DNA 8-oxoG were measured in myh(-/-) and myh(-/-)/ogg1(-/-) mice, an age-dependent accumulation of the oxidized purine was found in lung and small intestine of doubly defective myh(-/-)/ogg1(-/-) mice. Since there is an increased incidence of lung and small intestinal cancer in myh(-/-)/ogg1(-/-) mice, these findings are consistent with a causal role for unrepaired oxidized DNA bases in cancer development. We previously presented in vitro evidence that mismatch repair (MMR) participates in the repair of oxidative DNA damage and msh2(-/-) mouse embryo fibroblasts also have increased steady state levels of DNA 8-oxoG. To investigate whether DNA 8-oxoG also accumulates in vivo, basal levels were measured in several organs of 4-month-old msh2(-/-) mice and their wild-type counterparts. Msh2(-/-) mice had significantly increased levels of DNA 8-oxoG in spleen, heart, liver, lung, kidney and possibly small intestine but not in bone marrow, thymus or brain. The tissue-specificity of DNA 8-oxoG accumulation in msh2(-/-) and other DNA repair defective mice suggests that DNA protection of different organs is mediated by different combinations of repair pathways.

The aging brain: Accumulation of DNA damage or neuron loss?

Age-related molecular and cellular alterations in the central nervous system are known to show selectivity for certain cell types and brain regions. Among them age-related accumulation of nuclear (n) DNA damage can lead to irreversible loss of genetic information content. In the present study on the aging mouse brain, we observed a substantial increase in the amount of nDNA single-strand breaks in hippocampal pyramidal and granule cells as well as in cerebellar granule cells but not in cerebellar Purkinje cells. The reverse pattern was found for age-related reductions in total numbers of neurons. Only the total number of cerebellar Purkinje cells was significantly reduced during aging whereas the total numbers of hippocampal pyramidal and granule cells as well as of cerebellar granule cells were not. This formerly unknown inverse relation between age-related accumulation of nDNA damage and age-related loss of neurons may reflect a fundamental process of aging in the central nervous system.

2-DE profiling of GDNF overexpression-related proteome changes in differentiating ST14A rat progenitor cells

Targeted differentiation of neural progenitor cells (NPCs) is a challenge for treatment of neurodegenerative diseases by cell replacement therapy and cell signalling manipulation. Here, we applied a proteome profiling approach to the rat striatal progenitor model cell line ST14A in order to elucidate cellular differentiation processes. Native cells and cells transfected with the glial cell line-derived neurotrophic factor (GDNF) gene were investigated at the proliferative state and at seven time points up to 72 h after induction of differentiation. 2-DE combined with MALDI-MS was used to create a reference 2-DE-map of 652 spots of which 164 were identified and assigned to 155 unique proteins. For identification of protein expression changes during cell differentiation, spot patterns of triplicate gels were matched to the 2-DE-map. Besides proteins that display expression changes in native cells, we also noted 43 protein-spots that were differentially regulated by GDNF overexpression in more than four time points of the experiment. The expression patterns of putative differentiation markers such as annexin 5 (ANXA5), glucosidase II beta subunit (GLU2B), phosphatidylethanolamine-binding protein 1 (PEBP1), myosin regulatory light chain 2-A (MLRA), NASCENT polypeptide-associated complex alpha (NACA), elongation factor 2 (EF2), peroxiredoxin-1 (PRDX1) and proliferating cell nuclear antigen (PCNA) were verified by Western blotting. The results reflect the large rearrangements of the proteome during the differentiation process of NPCs and their strong modification by neurotrophic factors like GDNF.

Aging and its differential effects on consolidated memory forms in Drosophila

Aging is known to be associated with a decrease of learning and memory. Little is known on the specificity of this process. In Drosophila, two forms of consolidated memory have been observed. Anesthesia-resistant memory (ARM) is formed after one or several consecutive training sessions whereas long-term memory (LTM) is formed only after multiple training sessions separated in time. Both memory forms last more than 24 h. In the present experiment I, address the question of the effect of aging on the formation of each memory form. Twenty four hours after being conditioned, old flies show similar ARM as young flies but LTM was completely abolished. Age memory impairment seems therefore to be specific to one consolidated memory form.

Caenorhabditis elegans as a model system to study aging of learning and memory

The nematode Caenorhabditis elegans is an excellent model organism to study biological processes relevant to a wide variety of human and rodent disease systems. Previous studies have suggested that mutants of the insulin/insulin-like growth factor-1 pathway show life extension and increased stress resistance in various species, including C. elegans, the fruit fly, and the mouse. It has recently been shown that the life-extending mutants, including the age-1 phosphatidylinositol- 3 OH kinase mutants and the daf-2 insulin-like receptor mutants, display improvement in a type of associative learning behavior called thermotaxis learning behavior. The age-1 mutant shows a dramatic threefold extension of the health-span that ensures thermotaxis learning behavior, suggesting strong neuroprotective actions during aging. The age-1 and daf-2 mutants show resistance to multiple forms of stress and upregulates the genes involved in reactive oxygen species scavenging, heat shock, and P450 drug-detoxification. The life-extending mutants may confer resistance to various stress and diseases in neurons. Therefore, C. elegans provides an emerging system for the prevention of age-related deficits in the nervous system and in learning behaviors. This article discusses the aging of learning and memory and the neuroprotection effects of life-extending mutants on learning behaviors.

Prolonged stress will induce Alzheimer’s disease in elderly people by increased release of homocysteic acid

Recently, many papers have reported the physiological functions of amyloid beta and amyloid precursor protein (APP). In particular, one of its functions is of importance for synaptic plasticity. Extracellular amyloid beta may suppress synaptic plasticity or inhibit long-term potentiation (LTP) from outside the cell. LTP is now considered the molecular basis of memory. Amyloid beta may induce the inhibition or loss of memory. We propose that suppression of LTP by amyloid beta induces a kind of physiological forgetfulness. On the other hand, homocysteic acid (HA) which is released from astrocytes under stress conditions accumulates the amyloid beta into neuronal cell, which consequently induces the inhibition of amyloid beta physiological function and induces strong LTP. We propose that HA induces strong unforgetful memory under stress condition such as PTSD and emotional depression. The situation is different in the elderly people. Prolonged stress in the elderly people may induce neurodegenerative diseases such as Alzheimer's disease. We observed that in the presence of excess methionine, HA induced alpha-synuclein protein in cultured cells, suggesting a hypermethylation model in vivo. Usually hypermethylation is observed in the ageing process. We have shown that HA promotes the accumulation of amyloid beta in cells, and that the production of alpha-synuclein, which induces the aggregation of amyloid beta, impairing the cell function. LTP is inhibited by deficient cellular function, which means that memories cannot be formed. In fact, there is confusion of memories in the early stages of Alzheimer's disease. Finally, the aggregated alpha-synuclein induces tau pathology, which induces cell death, leading to Alzheimer's pathology. In conclusion, we propose that HA induces Alzheimer's pathology in the elderly people because of prolonged stress.

Application of advanced technologies in ageing research

Several technologies that emerged in the post-genomic era have been particularly useful in dissecting the molecular mechanisms of complex biological processes through the systems approach. Here, we review how three of these technologies, namely transcriptional profiling, large-scale RNA interference (RNAi) and genome-wide location analysis of protein-DNA interactions, have been used in the study of ageing in metazoans. We also highlight recent developments of these three technologies and how these developments are applicable to ageing research.

Validation of endogenous controls for quantitative gene expression analysis: application on brain cortices of human chronic alcoholics

Real-time PCR is frequently used for gene expression quantification due to its methodological sensitivity and reproducibility. The gene expression is quantified by normalization to one or more reference genes, usually beta-actin (ACTB), glyceraldehyde-3-phosphate dehydrogenase (GAPD) or to ribosomal RNA (18S). However, different environmental or pathological conditions might also influence the expression of normalizing genes, which could severely skew the interpretation of quantitative results. This study evaluates whether 16 genes frequently used as endogenous controls in expression studies, can serve as such for comparison of human brain tissues of chronic alcoholics and control subjects. The prefrontal and motor cortices that are affected differently by chronic alcohol consumption were analyzed. The reference genes that have no or small differences in expression in alcoholics and control subjects, were found to be specific for each region: beta-actin (ACTB) and ribosomal large P0 (RPLP0) for the prefrontal cortex while importin 8 (IPO8) and RNA polymerase II (POLR2A) for the motor cortex. Four out of sixteen analyzed genes demonstrated significant differences in expression between alcoholics and controls: phosphoglycerate kinase (PGK1), hypoxanthine phosphoribosyl transferase (HPRT1) and peptidylprolyl isomerase A (PPIA) in the motor cortex and beta-2-microglobulin (B2M) in the prefrontal cortex. Our study demonstrates the importance of validation of endogenous control genes prior to real-time PCR analysis of human brain tissues. Prescribed and non-prescribed drugs, pathological or environmental conditions along with alcohol abuse may differentially influence expression of reference genes.

Multivariate regression analysis of distance matrices for testing associations between gene expression patterns and related variables

A fundamental step in the analysis of gene expression and other high-dimensional genomic data is the calculation of the similarity or distance between pairs of individual samples in a study. If one has collected N total samples and assayed the expression level of G genes on those samples, then an N x N similarity matrix can be formed that reflects the correlation or similarity of the samples with respect to the expression values over the G genes. This matrix can then be examined for patterns via standard data reduction and cluster analysis techniques. We consider an alternative to conventional data reduction and cluster analyses of similarity matrices that is rooted in traditional linear models. This analysis method allows predictor variables collected on the samples to be related to variation in the pairwise similarity/distance values reflected in the matrix. The proposed multivariate method avoids the need for reducing the dimensions of a similarity matrix, can be used to assess relationships between the genes used to construct the matrix and additional information collected on the samples under study, and can be used to analyze individual genes or groups of genes identified in different ways. The technique can be used with any high-dimensional assay or data type and is ideally suited for testing subsets of genes defined by their participation in a biochemical pathway or other a priori grouping. We showcase the methodology using three published gene expression data sets.

Aging and visual motion discrimination in normal adults and schizophrenia patients

Motion perception is impaired in many neuropathological conditions, including schizophrenia. Motion perception also declines in the course of normal aging. In this study, we ask whether aging is an additive factor in the motion-discrimination deficits of schizophrenia patients. We examined motion perception in schizophrenia patients (n=44) and non-psychiatric controls (n=40) whose ages ranged from 18 to 55. The tasks included velocity discrimination and contrast detection. Thresholds for each of the two tasks were determined for each subject using psychophysical methods. Schizophrenia patients showed significantly increased thresholds (degraded performance) for velocity discrimination compared with the controls. Degraded performance in patients was not related to age. In controls, however, velocity discrimination thresholds were significantly increased beginning by age 45. Performance on a contrast-detection task, which does not require precise discrimination of motion signals, was not significantly affected by age in either group. Aging, even in its early stages, degrades motion discrimination in normal adults. Aging, however, does not adversely affect motion-discrimination deficits in schizophrenia patients through age 55. A similar motion-discrimination deficit in schizophrenia patients and aging normal adults suggests that the mechanisms underlying motion processing in schizophrenia and normal aging may be associated.

Mitochondrial dysfunction and oxidative stress in neurodegenerative diseases

Many lines of evidence suggest that mitochondria have a central role in ageing-related neurodegenerative diseases. Mitochondria are critical regulators of cell death, a key feature of neurodegeneration. Mutations in mitochondrial DNA and oxidative stress both contribute to ageing, which is the greatest risk factor for neurodegenerative diseases. In all major examples of these diseases there is strong evidence that mitochondrial dysfunction occurs early and acts causally in disease pathogenesis. Moreover, an impressive number of disease-specific proteins interact with mitochondria. Thus, therapies targeting basic mitochondrial processes, such as energy metabolism or free-radical generation, or specific interactions of disease-related proteins with mitochondria, hold great promise.

Identification of the proliferation/differentiation switch in the cellular network of multicellular organisms

The protein-protein interaction networks, or interactome networks, have been shown to have dynamic modular structures, yet the functional connections between and among the modules are less well understood. Here, using a new pipeline to integrate the interactome and the transcriptome, we identified a pair of transcriptionally anticorrelated modules, each consisting of hundreds of genes in multicellular interactome networks across different individuals and populations. The two modules are associated with cellular proliferation and differentiation, respectively. The proliferation module is conserved among eukaryotic organisms, whereas the differentiation module is specific to multicellular organisms. Upon differentiation of various tissues and cell lines from different organisms, the expression of the proliferation module is more uniformly suppressed, while the differentiation module is upregulated in a tissue- and species-specific manner. Our results indicate that even at the tissue and organism levels, proliferation and differentiation modules may correspond to two alternative states of the molecular network and may reflect a universal symbiotic relationship in a multicellular organism. Our analyses further predict that the proteins mediating the interactions between these modules may serve as modulators at the proliferation/differentiation switch.

Hypoxia facilitates Alzheimer's disease pathogenesis by up-regulating BACE1 gene expression

The molecular mechanism underlying the pathogenesis of the majority of cases of sporadic Alzheimer's disease (AD) is unknown. A history of stroke was found to be associated with development of some AD cases, especially in the presence of vascular risk factors. Reduced cerebral perfusion is a common vascular component among AD risk factors, and hypoxia is a direct consequence of hypoperfusion. Previously we showed that expression of the beta-site beta-amyloid precursor protein (APP) cleavage enzyme 1 (BACE1) gene BACE1 is tightly controlled at both the transcriptional and translational levels and that increased BACE1 maturation contributes to the AD pathogenesis in Down's syndrome. Here we have identified a functional hypoxia-responsive element in the BACE1 gene promoter. Hypoxia up-regulated beta-secretase cleavage of APP and amyloid-beta protein (Abeta) production by increasing BACE1 gene transcription and expression both in vitro and in vivo. Hypoxia treatment markedly increased Abeta deposition and neuritic plaque formation and potentiated the memory deficit in Swedish mutant APP transgenic mice. Taken together, our results clearly demonstrate that hypoxia can facilitate AD pathogenesis, and they provide a molecular mechanism linking vascular factors to AD. Our study suggests that interventions to improve cerebral perfusion may benefit AD patients.

IntNetDB v1.0: an integrated protein-protein interaction network database generated by a probabilistic model

Background

Although protein-protein interaction (PPI) networks have been explored by various experimental methods, the maps so built are still limited in coverage and accuracy. To further expand the PPI network and to extract more accurate information from existing maps, studies have been carried out to integrate various types of functional relationship data. A frequently updated database of computationally analyzed potential PPIs to provide biological researchers with rapid and easy access to analyze original data as a biological network is still lacking.

Results

By applying a probabilistic model, we integrated 27 heterogeneous genomic, proteomic and functional annotation datasets to predict PPI networks in human. In addition to previously studied data types, we show that phenotypic distances and genetic interactions can also be integrated to predict PPIs. We further built an easy-to-use, updatable integrated PPI database, the Integrated Network Database (IntNetDB) online, to provide automatic prediction and visualization of PPI network among genes of interest. The networks can be visualized in SVG (Scalable Vector Graphics) format for zooming in or out. IntNetDB also provides a tool to extract topologically highly connected network neighborhoods from a specific network for further exploration and research. Using the MCODE (Molecular Complex Detections) algorithm, 190 such neighborhoods were detected among all the predicted interactions. The predicted PPIs can also be mapped to worm, fly and mouse interologs.

Conclusion

IntNetDB includes 180,010 predicted protein-protein interactions among 9,901 human proteins and represents a useful resource for the research community. Our study has increased prediction coverage by five-fold. IntNetDB also provides easy-to-use network visualization and analysis tools that allow biological researchers unfamiliar with computational biology to access and analyze data over the internet. The web interface of IntNetDB is freely accessible at . Visualization requires Mozilla version 1.8 (or higher) or Internet Explorer with installation of SVGviewer.

Age-dependent decline of neprilysin in Alzheimer's disease and normal brain: inverse correlation with A beta levels

Brain deposition of amyloid-beta (A beta) is a pathological hallmark of Alzheimer disease (AD) but A beta is also detected in non-demented elderly individuals. Neprilysin has been shown to be an important enzyme to degrade A beta in brain. We investigated whether decreased neprilysin levels contributes to the accumulation of A beta in AD and in normal aging. No difference in neprilysin protein and mRNA levels were found between AD subjects and age-matched controls. Protein levels of neprilysin were reduced with age in the temporal and frontal cortex of AD and normal brain. A significant positive correlation between insoluble A beta 40 and A beta 42 with age was found in cortex of normal brain whereas in AD brain the correlation between age and A beta was weaker. Our findings of an inverse correlation between neprilysin and insoluble A beta levels in both groups suggest that neprilysin is involved in the clearance of A beta. The observed age-dependent decline in neprilysin may be related to the increased A beta levels during normal aging. The similar rate of decline in neprilysin with age may not be the major cause of the high levels of A beta associated with AD but is likely to be a trigger of AD pathology.

Detrimental deletions: mitochondria, aging and Parkinson's disease

As individuals enter their 80s, they are inevitably confronted with the problem of neuronal loss in the brain. The incidence of the common movement disorder 'mild parkinsonian signs' (MPS) is approximately 50% over the age of 85 years. It has long been known that the loss of dopaminergic neurons in the substantia nigra pars compacta is a neuropathological hallmark of Parkinson's disease (PD). Recently, two papers present clear evidence for a high burden of mitochondrial DNA deletions within substantia nigra neurons in aged individuals and individuals with PD, pointing towards a common pathway inevitably leading to neuronal dysfunction and death.

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitor Atorvastatin mediated effects depend on the activation status of target cells in PLP-EAE

The effect of Atorvastatin on transcriptional activity in murine experimental autoimmune encephalomyelitis (EAE) induced by PLP peptide 139-151 was analyzed by DNA microarray technique in lymph nodes and spinal cord at onset (10 days), height (20 days) and first remission (30 days) of disease. Fourteen genes were selectively influenced by Atorvastatin in EAE mice. They are mainly related to immune cell functions and regulation of cell-to-cell interaction. Interestingly, seven genes were also differentially regulated in CFA-injected control mice. But qualitative and quantitative differences to EAE mice argue for a dependency of statin effects on the activation status of target cells. Differential regulation of the newly detected candidate genes of statin effects COX-1 and HSP-105 and the previously known statin-responsive genes ICAM-1 and CD86 was confirmed by Western blot and immunohistochemistry. Flow cytometric analysis of lymph node cells revealed that the effect of Atorvastatin treatment in non-immunized healthy animals resembled the effect of immunization with PLP peptide regarding changes of T helper cells, activated B cells and macrophages. In EAE mice, these effects were partially reversed by Atorvastatin treatment. Monitoring of expression of the newly identified candidate genes and patterns of lymphocyte subpopulations might predict the responsiveness of multiple sclerosis patients to statin treatment.

Genotoxicants target distinct molecular networks in neonatal neurons

BACKGROUND

Exposure of the brain to environmental agents during critical periods of neuronal development is considered a key factor underlying many neurologic disorders.

OBJECTIVES

In this study we examined the influence of genotoxicants on cerebellar function during early development by measuring global gene expression changes.

METHODS

We measured global gene expression in immature cerebellar neurons (i.e., granule cells) after treatment with two distinct alkylating agents, methylazoxymethanol (MAM) and nitrogen mustard (HN2). Granule cell cultures were treated for 24 hr with MAM (10-1,000 microM) or HN2 (0.1-20 microM) and examined for cell viability, DNA damage, and markers of apoptosis.

RESULTS

Neuronal viability was significantly reduced (p < 0.01) at concentrations > 500 microM for MAM and > 1.0 microM for HN2; this correlated with an increase in both DNA damage and markers of apoptosis. Neuronal cultures treated with sublethal concentrations of MAM (100 microM) or HN2 (1.0 microM) were then examined for gene expression using large-scale mouse cDNA microarrays (27,648). Gene expression results revealed that a) global gene expression was predominantly up-regulated by both genotoxicants; b) the number of down-regulated genes was approximately 3-fold greater for HN2 than for MAM; and c) distinct classes of molecules were influenced by MAM (i.e, neuronal differentiation, the stress and immune response, and signal transduction) and HN2 (i.e, protein synthesis and apoptosis).

CONCLUSIONS

These studies demonstrate that individual genotoxicants induce distinct gene expression signatures. Further study of these molecular networks may explain the variable response of the developing brain to different types of environmental genotoxicants.

Early neuropathology of somatostatin/NPY GABAergic cells in the hippocampus of a PS1×APP transgenic model of Alzheimer's disease

At advanced stages, Alzheimer's disease (AD) is characterized by an extensive neuronal loss. However, the early neurodegenerative deficiencies have not been yet identified. Here we report an extensive, selective and early neurodegeneration of the dendritic inhibitory interneurons (oriens-lacunosum moleculare, O-LM, and hilar perforant path-associated, HIPP, cells) in the hippocampus of a transgenic PS1xAPP AD model. At 6 months of age, from 22 different pre- and postsynaptic mRNA markers tested (including GABAergic, glutamatergic and cholinergic markers), only the expression of somatostatin (SOM) and NPY neuropeptides (O-LM and HIPP markers) displayed a significant decrease. Stereological cell counting demonstrated a profound diminution (50-60%) of SOM-immunopositive neurons, preceding the pyramidal cell loss in this AD model. SOM population co-expressing NPY was the most damaged cell subset. Furthermore, a linear correlation between SOM and/or NPY deficiency and Abeta content was also observed. Though the molecular mechanism of SOM neuronal loss remains to be determined, these findings might represent an early hippocampal neuropathology. Therefore, SOM and NPY neuropeptides could constitute important biomarkers to assess the efficacy of potential early AD treatments.

Systems approaches to the networks of aging

The aging of an organism is the result of complex changes in structure and function of molecules, cells, tissues, and whole body systems. To increase our understanding of how aging works, we have to analyze and integrate quantitative evidence from multiple levels of biological organization. Here, we define a broader conceptual framework for a quantitative, computational systems biology approach to aging. Initially, we consider fractal supply networks that give rise to scaling laws relating body mass, metabolism and lifespan. This approach provides a top-down view of constrained cellular processes. Concomitantly, multi-omics data generation build such a framework from the bottom-up, using modeling strategies to identify key pathways and their physiological capacity. Multiscale spatio-temporal representations finally connect molecular processes with structural organization. As aging manifests on a systems level, it emerges as a highly networked process regulated through feedback loops between levels of biological organization.

The age-related attenuation in long-term potentiation is associated with microglial activation

It is well established that inflammatory changes contribute to brain ageing, and an increased concentration of proinflammatory cytokine, interleukin-1beta (IL-1beta), has been reported in the aged brain associated with a deficit in long-term potentiation (LTP) in rat hippocampus. The precise age at which changes are initiated is unclear. In this study, we investigate parallel changes in markers of inflammation and LTP in 3-, 9- and 15-month-old rats. We report evidence of increased hippocampal concentrations of the proinflammatory cytokines IL-1alpha, IL-18 and interferon-gamma (IFNgamma), which are accompanied by deficits in LTP in the older rats. We also show an increase in expression of markers of microglial activation, CD86, CD40 and intercellular adhesion molecules (ICAM). Associated with these changes, we observed a significant impairment of hippocampal LTP in the same rats. The importance of microglial activation in the attenuation of long-term potentiation (LTP) was demonstrated using an inhibitor of microglial activation, minocycline; partial restoration of LTP in 15-month-old rats was observed following administration of minocycline. We propose that signs of neuroinflammation are observed in middle age and that these changes, which are characterized by microglial activation, may be triggered by IL-18.

The Application of Microarray Technology to Neuropathology: Cutting Edge Tool With Clinical Diagnostics Potential or Too Much Information?

Microarray technology is a tremendously powerful method for simultaneously monitoring the expression of thousands of species of nucleic acids, usually cellular mRNA, producing a high-resolution representation of the genes encoded or expressed in a cell. As such, microarray technology has great potential for impacting research and clinical approaches to treatment. However, this complex technology has been challenging to apply as a result of difficulties discerning biologic variation from technologic issues, therefore slowing the application of the technology to human diagnostics. Nevertheless, significant advances in microarray technology, improvements that avoid potential pitfalls, and a wider spectrum of application are making this technology easier to apply. Indeed, microarray technology has provided valuable insights into mechanisms involving gene regulation and expression in Alzheimer disease, and it remains a powerful tool to identify biomarkers for disease diagnosis. Ultimately, the most robust markers will enable the application of more specific treatments particular to disease stages or subcategories. Currently, no widely applicable molecular test is available to identify those at risk for developing Alzheimer disease or those who have early markers of pathology but show discernible cognitive impairment. The progression of this technology will lead to earlier detection of the disease through enhanced understanding of disease onset and progression.

Gene expression profiles in anatomically and functionally distinct regions of the normal aged human brain

In this article, we have characterized and compared gene expression profiles from laser capture microdissected neurons in six functionally and anatomically distinct regions from clinically and histopathologically normal aged human brains. These regions, which are also known to be differentially vulnerable to the histopathological and metabolic features of Alzheimer's disease (AD), include the entorhinal cortex and hippocampus (limbic and paralimbic areas vulnerable to early neurofibrillary tangle pathology in AD), posterior cingulate cortex (a paralimbic area vulnerable to early metabolic abnormalities in AD), temporal and prefrontal cortex (unimodal and heteromodal sensory association areas vulnerable to early neuritic plaque pathology in AD), and primary visual cortex (a primary sensory area relatively spared in early AD). These neuronal profiles will provide valuable reference information for future studies of the brain, in normal aging, AD and other neurological and psychiatric disorders.

Diminished lifespan and acute stress-induced death in DNA-PKcs-deficient mice with limiting telomeres

An adequate and appropriate response to physiological and pathophysiological stresses is critical for long-term homeostasis and viability of the aging organism. Previous work has pointed to the immune system, telomeres and DNA repair pathways as important and distinct determinants of a normal healthy lifespan. In this study, we explored the genetic interactions of telomeres and DNA-PKcs, a protein involved in non-homologous end-joining (NHEJ) and immune responses, in the context of a key aspect of aging and lifespan--the capacity to mount an acute and appropriate immune-mediated stress response. We observed that the combination of DNA-PKcs deficiency and telomere dysfunction resulted in a shortened lifespan that was reduced further following viral infection or experimental activation of the innate immune response. Analysis of the innate immune response in the DNA-PKcs-deficient mice with short dysfunctional telomeres revealed high basal serum levels of tumor necrosis factor alpha (TNFalpha) and hyper-active cytokine responses upon challenge with polyinosinic-polycytidylic acid (poly-IC). We further show that serum cytokine levels become elevated in telomere dysfunctional mice as a function of age. These results raise speculation that these genetic factors may contribute to misdirected immune responses of the aged under conditions of acute and chronic stress.

Xenobiotic- and vitamin D-responsive induction of the steroid/bile acid-sulfotransferase Sult2A1 in young and old mice: the role of a gene enhancer in the liver chromatin

The xenobiotic-activated nuclear receptors PXR (pregnane X receptor) and CAR (constitutive androstane receptor) and the vitamin D(3)-activated nuclear receptor VDR regulate steroid and xenobiotic metabolism by inducing the phase I cytochrome P450 monooxygenases, phase II conjugating transferases, and the phase III transporters, which mediate the efflux of water-soluble lipid metabolites from cells. Metabolic stress due to the deviant expression of steroid- and xenobiotic-metabolizing enzymes is known to have severe health consequences including accelerated aging, and increased expression of these enzymes is associated with extended longevity [Gachon, F, Olela, FF, Schaad, O, Descombes, P and Schibler, U, 2006. The circadian PAR-domain basic leucine zipper transcription factors DBP, TEF, and HLF modulate basal and inducible xenobiotic detoxification. 4, 25-36.; McElwee, JJ, Schuster, E, Blanc, E, Thomas, JH and Gems, D, 2004. Shared Transcriptional Signature in Caenorhabditis elegans Dauer Larvae and Long-lived daf-2 Mutants Implicates Detoxification System in Longevity Assurance. J. Biol. Chem., 279, 44533-43.]. Information on the similarities and dissimilarities in drug metabolism between the young and old, as may be uncovered by studying aging regulation of the genes relevant to steroid and xenobiotic metabolism, is likely to have clinical significance. In this report, we examined the VDR- and PXR-mediated gene induction of the phase II sulfotransferase Sult2A1 in the livers of 4-month- and 20-month-old mice. Sult2A1 converts bile acids, steroids and a number of drugs to the corresponding sulfated metabolites, which are readily eliminated from the body due to increased water solubility. In RT-PCR assay, aging did not change the induction of Sult2A1 mRNAs by the hormonally active vitamin D(3) and the catatoxic synthetic steroid PCN (pregnenolone-16alpha-carbonitrile). Chromatin immunoprecipitation (ChIP) from liver nuclei showed that aging had no effect on the activity of an IR0 enhancer in the Sult2A1 chromatin to recruit VDR, RXR-alpha (retinoid X receptor) and PXR in mice injected with D(3) or PCN. Thus, mice in late life are as competent as those in early life in responding to the hormonal and xenobiotic signaling for Sult2A1 induction. This is the first report describing the role of aging in the functional response of an enhancer in the liver chromatin to the nuclear receptor-dependent signaling.

Amyloid-beta-(1-42) increases ryanodine receptor-3 expression and function in neurons of TgCRND8 mice

Disruption of intracellular calcium homeostasis precedes the neurodegeneration that occurs in Alzheimer disease (AD). Of the many neuronal calcium-regulating proteins, we focused on endoplasmic reticulum (ER)-resident ryanodine receptors (RyRs) because they are increased in the hippocampus of mice expressing mutant presenilin-1 and are associated with neurotoxicity. Others have observed that ryanodine binding is elevated in human postmortem hippocampal regions suggesting that RyR(s) are involved in AD pathogenesis. Here we report that extracellular amyloid-beta(Abeta)-(1-42) specifically increased RyR-3, but not RyR-1 or RyR-2, gene expression in cortical neurons from C57Bl6 mice. Furthermore, endogenously produced Abeta-(1-42) increased RyR-3 mRNA and protein in cortical neurons from transgenic (Tg)CRND8 mice, a mouse model of AD. Increased RyR-3 mRNA and protein was also observed in brain tissue from 4- to 4.5-month-old Tg animals compared with non-Tg littermate controls. In experiments performed in nominal extracellular calcium, neurons from Tg mice had significant increases in intracellular calcium following ryanodine or glutamate treatment compared with littermate controls, which was abolished by treatment with small interfering RNA directed to RyR-3, indicating that the higher levels of calcium originated from RyR-3-regulated stores. Taken together, these observations suggest that Abeta-(1-42)-mediated changes in intracellular calcium homeostasis is regulated in part through a direct increase of RyR-3 expression and function.

Long-lived C. elegans mitochondrial mutants as a model for human mitochondrial-associated diseases

Mitochondria play a pivotal role in the life of cells, controlling diverse processes ranging from energy production to the regulation of cell death. In humans, numerous pathological conditions have been linked to mitochondrial dysfunction. Cancer, diabetes, obesity, neurodegeneration, cardiomyopathy and even aging are all associated with mitochondrial dysfunction. Over 400 mutations in mitochondrial DNA result directly in pathology and many more disorders associated with mitochondrial dysfunction arise from mutations in nuclear DNA. It is counter-intuitive then, that a class of mitochondrially defective mutants in the nematode Caenorhabditis elegans, the so called Mit (Mitochondrial) mutants, in fact live longer than wild-type animals. In this review, we will reconcile this paradox and provide support for the idea that the Mit mutants are in fact an excellent model for studying human mitochondrial associated diseases (HMADs). In the context of the 'Mitochondrial Threshold Effect Theory', we propose that the kinds of processes induced to counteract mitochondrial mutations in the Mit mutants (and which mediate their life extension), are very likely the same ones activated in many HMADs to delay disease appearance. The identification of such compensatory pathways opens a window of possibility for future preventative therapies for many HMADs. They may also provide a way of potentially extending human life span.

Functional roles of the NTS2 and NTS3 receptors

Neurotensin exerts its actions in the central nervous system and the periphery through three identified receptors. Two of them, the NTS2 and NTS3, display unusual properties either because of their complex signal transduction mechanisms (NTS2) or because of their structural composition as a non-G-protein-coupled receptor (NTS3). Here, we review the transduction mechanisms, cellular trafficking, and potential physiological roles of these two unconventional receptors.

The effect of chronic lorazepam administration in aging mice

To assess benzodiazepine tolerance in aged animals, lorazepam or vehicle was administered chronically to male Crl: CD-1(ICR)BR mice. Pharmacodynamic and neurochemical endpoints were examined on days 1 and 14 of drug administration. There was no age-related significant difference in plasma lorazepam levels. Young and middle-aged animals demonstrated behavioral tolerance to lorazepam, while the aged animals showed a similar trend which failed to reach significance. In addition, aged animals also showed a trend toward tolerance to the anticonvulsant effects of lorazepam. There were no changes in alpha1 mRNA levels in cortex or hippocampus following administration of lorazepam when compared to vehicle-treated animals in any age group. Aged animals, however, had an initial increase in alpha1 mRNA expression in cortex and hippocampus on day 1 of vehicle treatment followed by decreased expression on day 14. These age-related changes were abolished by lorazepam administration. In summary, age-related sensitivity to the effects of lorazepam was not demonstrated in the present study. However, comparison of these data to other studies indicates that the effect of chronic benzodiazepine treatment may be specific to the benzodiazepine administered, the technique used to quantify mRNA expression changes, the subunits of the GABA(A) receptor investigated and the brain region analyzed. The phenomenon of benzodiazepine sensitivity in the elderly is an area of research which remains controversial and may well be compound specific. Determining benzodiazepines that do not produce pharmacodynamic sensitivity, such as lorazepam, may allow more careful prescribing and dosing of these drugs, and perhaps even the development of specific agents which could avoid this sensitivity.

Transcriptional profiling of Alzheimer blood mononuclear cells by microarray

We evaluated pathomechanisms and systemic manifestations of Alzheimer disease (AD), an aging-related dementing neurodegenerative disorder, by expression profiling. Blood mononuclear cell (BMC) transcriptomes of sporadic AD subjects and aged-matched normal elderly controls (NEC) were compared using the human NIA microarray. Relative to the NEC samples, the Alzheimer BMC exhibited a significant decline in the expression of genes concerned with cytoskeletal maintenance, cellular trafficking, cellular stress response, redox homeostasis, transcription and DNA repair. We observed decreased expression of several genes which may impact amyloid-beta production and the processing of the microtubule-associated protein tau. The microarray results were validated by quantitative real time PCR and revealed gender differences in the levels of altered gene expression. Our findings attest to the systemic nature of gene dys-regulation in sporadic AD, implicate disruption of cytoskeletal integrity, DNA repair mechanisms and cellular defenses in this condition, and suggest novel pathways of beta-amyloid deposition in this disease. BMC are highly accessible and may reflect molecular events germane to the neuropathophysiology of AD.

Daily consumption of green tea catechin delays memory regression in aged mice

Almost all elderly people show brain atrophy and cognitive dysfunction, even if they are saved from illness, such as cardiac disease, malignancy and diabetes. Prevention or delay of brain senescence would therefore enhance the quality of life for older persons. Because oxidative stress has been implicated in brain senescence, we investigated the effects of green tea catechin (GT-catechin), a potential antioxidant, in senescence-accelerated (SAMP10) mice. The mouse is a model of brain senescence with short life span, cerebral atrophy and cognitive dysfunction. Mice were fed water containing 0.02% GT-catechin from 1- to 15-month-old. The mean dose was about 35 mg/kg/day. We found that daily consumption of GT-catechin prevented memory regression and DNA oxidative damage in these mice. GT-catechin did not prolong the lifetime of SAMP10 mice, but it did delay brain senescence. These findings suggest that continued intake of GT-catechin might promote healthy ageing of the brain in older persons.

Inflammatory processes in the aging mouse brain: participation of dendritic cells and T-cells

Increased inflammatory activity accompanies normal brain aging. Whereas local glial cell activation, upregulation of cytokines and transcriptional alterations of inflammatory factors are well-documented components of this complex process, it is unclear whether blood-derived leukocytes also contribute to the age-related changes. The present study of normal mouse brain applied single and double immunohistochemistry to reveal for the first time that dendritic cells (DCs) and T-cells are important components of the general increased inflammatory state, which was documented by upregulation of reactive astrocytes and microglia. B-cells and mast cells do not contribute to this inflammatory response. Dendritic cells and T-cells appeared at about 12 months of age and their number increased further during aging. In 24-month-old animals a dense network of DCs interspersed with T-cells pervaded brain areas where substantial histopathological changes and a volumetric decrease have been reported. All CD11c(+)-DCs displayed the typical dendritic shape and expressed the myeloid specific integrin CD11b. Some of the DCs were also CD205- or MIDC8-immunoreactive and expressed the cathepsins S and X. The emergence and prolonged presence of leukocytes might indicate a crucial role of these cells in local, age-related immune responses in the brain.

Oxidative stress in the brain at early preclinical stages of mouse scrapie

Oxidative stress has been shown to be involved in the pathogenesis of neurodegenerative diseases including prion diseases. Although a growing body of evidence suggests direct involvement of oxidative stress in the pathogenesis of prion diseases, it is still not clear whether oxidative stress is a causative early event in these conditions or a secondary phenomenon commonly found in the progression of neurodegenerative diseases. Using a mouse scrapie model, we assessed oxidative stress in the brain at various stages of the disease progression and observed significantly increased concentration of lipid peroxidation markers, malondialdehyde and 4-hydroxyalkenals, and mRNA level of an oxidative stress response enzyme, heme oxygenase-1, at early preclinical stages of scrapie. The changes preceded dramatic synaptic loss demonstrated by immunohistochemical staining of a synaptic protein, synaptophysin. These findings imply that the brain undergoes oxidative stress even from an early stage of prion invasion into the brain. Given the well-known deleterious effects of reactive-oxygen-species-mediated damage in the brain, it is considered that the oxidative stress at the preclinical stage of prion diseases may predispose the brain to neurodegenerative mechanisms that characterize the diseases.

Base excision repair and the central nervous system

Reactive oxygen species generated during normal cellular metabolism react with lipids, proteins, and nucleic acid. Evidence indicates that the accumulation of oxidative damage results in cellular dysfunction or deterioration. In particular, oxidative DNA damage can induce mutagenic replicative outcomes, leading to altered cellular function and/or cellular transformation. Additionally, oxidative DNA modifications can block essential biological processes, namely replication and transcription, triggering cell death responses. The major pathway responsible for removing oxidative DNA damage and restoring the integrity of the genome is base excision repair (BER). We highlight herein what is known about BER protein function(s) in the CNS, which in cooperation with the peripheral nervous system operates to control physical responses, motor coordination, and brain operation. Moreover, we describe evidence indicating that defective BER processing can promote post-mitotic (i.e. non-dividing) neuronal cell death and neurodegenerative disease. The focus of the review is on the core mammalian BER participants, i.e. the DNA glycosylases, AP endonuclease 1, DNA polymerase beta, X-ray cross-complementing 1, and the DNA ligases.

Tertiary structural rearrangements upon oxidation of Methionine145 in calmodulin promotes targeted proteasomal degradation

The selectivity underlying the recognition of oxidized calmodulin (CaM) by the 20S proteasome in complex with Hsp90 was identified using mass spectrometry. We find that degradation of oxidized CaM (CaMox) occurs in a multistep process, which involves an initial cleavage that releases a large N-terminal fragment (A1-F92) as well as multiple smaller carboxyl-terminus peptides ranging from 17 to 26 amino acids in length. These latter small peptides are enriched in methionine sulfoxides (MetO), suggesting a preferential degradation around MetO within the carboxyl-terminal domain. To confirm the specificity of CaMox degradation and to identify the structural signals underlying the preferential recognition and degradation by the proteasome/Hsp90, we have investigated how the oxidation of individual methionines affect the degradation of CaM using mutants in which all but selected methionines in CaM were substituted with leucines. Substitution of all methionines with leucines except Met144 and Met145 has no detectable effect on the structure of CaM, permitting a determination of how site-specific substitutions and the oxidation of Met144 and Met145 affects the recognition and degradation of CaM by the proteasome/Hsp90. Comparable rates of degradation are observed upon the selective oxidation of Met144 and Met145 in CaM-L7 relative to that observed upon oxidation of all nine methionines in wild-type CaM. Substitution of leucines for either Met144 or Met145 promotes a limited recognition and degradation by the proteasome that correlates with decreases in the helical content of CaM. The specific oxidation of Met144 has little effect on rates of proteolytic degradation by the proteasome/Hsp90 or the structure of CaM. In contrast, the specific oxidation of Met145 results in both large increases in the rate of degradation by the proteasome/Hsp90 and significant circular dichroic spectral shape changes that are indicative of changes in tertiary rather than secondary structure. Thus, tertiary structural changes resulting from the site-specific oxidation of a single methionine (i.e., Met145) promote the degradation of CaM by the proteasome/Hsp90, suggesting a mechanism to regulate cellular metabolism through the targeted modulation of CaM abundance in response to oxidative stress.

Acceleration of amyloid beta-peptide aggregation by physiological concentrations of calcium

Alzheimer disease is characterized by the accumulation of aggregated amyloid beta-peptide (Abeta) in the brain. The physiological mechanisms and factors that predispose to Abeta aggregation and deposition are not well understood. In this report, we show that calcium can predispose to Abeta aggregation and fibril formation. Calcium increased the aggregation of early forming protofibrillar structures and markedly increased conversion of protofibrils to mature amyloid fibrils. This occurred at levels 20-fold below the calcium concentration in the extracellular space of the brain, the site at which amyloid plaque deposition occurs. In the absence of calcium, protofibrils can remain stable in vitro for several days. Using this approach, we directly compared the neurotoxicity of protofibrils and mature amyloid fibrils and demonstrate that both species are inherently toxic to neurons in culture. Thus, calcium may be an important predisposing factor for Abeta aggregation and toxicity. The high extracellular concentration of calcium in the brain, together with impaired intraneuronal calcium regulation in the aging brain and Alzheimer disease, may play an important role in the onset of amyloid-related pathology.

Changes in transcription within the CA1 field of the hippocampus are associated with age-related spatial learning impairments

Aged rats display a broad range of behavioral performance in spatial learning. The aim of this study was to identify candidate genes that are associated with learning and memory impairments. We first categorized aged-superior learners and age learning-impaired rats based on their performance in the Morris water maze (MWM) and then isolated messenger RNA from the CA1 hippocampal region of each animal to interrogate Affymetrix microarrays. Microarray analysis identified a set of 50 genes that was transcribed differently in aged-superior learners that had successfully learned the spatial strategy in the MWM compared to aged learning-impaired animals that were unable to learn and a variety of groups designed to control for all non-learning aspects of exposure to the water maze paradigm. A detailed analysis of the navigation patterns of the different groups of animals during acquisition and probe trials of the MWM task was performed. Young animals used predominantly an allocentric (spatial) search strategy and aged-superior learners appeared to use a combination of allocentric and egocentric (response) strategies, whereas aged-learning impaired animals displayed thigmotactic behavior. The significant 50 genes that we identified were tentatively classified into four groups based on their putative role in learning: transcription, synaptic morphology, ion conductivity and protein modification. Thus, this study has potentially identified a set of genes that are responsible for the learning impairments in aged rats. The role of these genes in the learning impairments associated with aging will ultimately have to be validated by manipulating gene expression in aged rats. Finally, these 50 genes were functioning in the context of an aging CA1 region where over 200 genes was found to be differentially expressed compared to a young CA1.

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

In this paper, we review experimental advances in molecular neurobiology of Alzheimer's 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.

Patterns of gene expression in the frontal cortex discriminate alcoholic from nonalcoholic individuals

Alcohol dependence is characterized by tolerance, physical dependence, and craving. The neuroadaptations underlying these effects of chronic alcohol abuse are likely due to altered gene expression. Previous gene expression studies using human post-mortem brain demonstrated that several gene families were altered by alcohol abuse. However, most of these changes in gene expression were small. It is not clear if gene expression profiles have sufficient power to discriminate control from alcoholic individuals and how consistent gene expression changes are when a relatively large sample size is examined. In the present study, microarray analysis (approximately 47,000 elements) was performed on the superior frontal cortex of 27 individual human cases (14 well characterized alcoholics and 13 matched controls). A partial least squares statistical procedure was applied to identify genes with altered expression levels in alcoholics. We found that genes involved in myelination, ubiquitination, apoptosis, cell adhesion, neurogenesis, and neural disease showed altered expression levels. Importantly, genes involved in neurodegenerative diseases such as Alzheimer's disease were significantly altered suggesting a link between alcoholism and other neurodegenerative conditions. A total of 27 genes identified in this study were previously shown to be changed by alcohol abuse in previous studies of human post-mortem brain. These results revealed a consistent re-programming of gene expression in alcohol abusers that reliably discriminates alcoholic from non-alcoholic individuals.

Insulin resistance and atherosclerosis

Considerable evidence supports the association between insulin resistance and vascular disease, and this has led to wide acceptance of the clustering of hyperlipidemia, glucose intolerance, hypertension, and obesity as a clinical entity, the metabolic syndrome. While insulin resistance, by promoting dyslipidemia and other metabolic abnormalities, is part of the proatherogenic milieu, it is possible that insulin resistance itself in the vascular wall does not promote atherosclerosis. Recent findings suggest that insulin resistance and atherosclerosis could represent independent and ultimately maladaptive responses to the disruption of cellular homeostasis caused by the excess delivery of fuel.

Mitochondrial dysfunction and increased sensitivity to excitotoxicity in mice deficient in DNA mismatch repair

The expression profile in the hippocampus of mice lacking one allele of the MutS homologue (Msh2), gene, which is one of the most representative components of the DNA mismatch repair system, was analysed to understand whether defects in the repair or in response to DNA damage could impact significantly on brain function. The overall results suggested a reduction in mitochondrial function as indicated by gene expression analysis, biochemical and behavioural studies. In the hippocampus of Msh2+/- mice, array data, validated by RT-PCR and western blot analysis, showed reduced expression levels of genes for cytochrome c oxidase subunit 2 (CoxII), ATP synthase subunit beta and superoxide dismutase 1. Biochemically, mitochondria from the hippocampus and cortex of these mice show reduced CoxII and increased aconitase activity. Behaviourally, these alterations resulted in mice with increased vulnerability to kainic acid-induced epileptic seizures and hippocampal neuronal loss. These data suggest that lack of an efficient system involved in recognizing and repairing DNA damage may generate a brain mitochondriopathy.