Iodoacetate protects hippocampal neurons against excitotoxic and oxidative injury: involvement of heat-shock proteins and Bcl-2

The Ethanolic Extract of Caesalpinia sappan Heartwood Inhibits Cerebral Ischemia/Reperfusion Injury in a Rat Model Through a Multi-Targeted Pharmacological Mechanism

Background: Caesalpinia sappan L. (C. sappan) is a traditional Chinese medicinal plant. The dried heartwood of C. sappan (also known as Sappan wood) has been widely used for the folkloric medical treatment of ischemic cerebral stroke in China. However, the detailed underlying pharmacological mechanism still remains largely unexplored. Methods: In this study, a middle cerebral artery occlusion (MCAO) rat model was employed to elucidate the mechanism of the anti-cerebral ischemic effects of C. sappan ethanolic extract (CEE). Moreover, systemic multi-target identification coupled with gene ontology biological process (GO BP) and reactome pathway analysis was used to investigate the potential neuroprotective mechanism. Furthermore, the presumed mechanism was confirmed through biological analysis by determining the effects of CEE on the identified signaling pathways in PC12 cells model-induced by oxygen-glucose deprivation/reperfusion (OGD/R). Results: Our study demonstrates that CEE (both through in vivo administration at a dosage of 300 mg/kg and through in vitro incubation at a dosage of 2.4 μg/mL) is a neuroprotective agent that can effectively inhibit neuronal damage, promote synaptic generation, and suppress the activation of neutrophils, microglia, and astrocytes. Moreover, the neuroprotective mechanism of CEE is mediated via regulating 150 potential target proteins, which are associated with 6 biological processes and 10 pathways, including JAK-STAT, HSP90 and DNA damage/telomere stress. Conclusion: CEE can exert neuroprotective effect through multi-target pharmacological mechanisms to prevent ischemia/reperfusion-induced cerebral injury.

Hormesis, cell death, and regenerative medicine for neurode-generative diseases

Although the adult human brain has a small number of neural stem cells, they are insufficient to repair the damaged brain to achieve significant functional recovery for neurodegenerative diseases and stroke. Stem cell therapy, by either enhancing endogenous neurogenesis, or transplanting stem cells, has been regarded as a promising solution. However, the harsh environment of the diseased brain posts a severe threat to the survival and correct differentiation of those new stem cells. Hormesis (or preconditioning, stress adaptation) is an adaptation mechanism by which cells or organisms are potentiated to survive an otherwise lethal condition, such as the harsh oxidative stress in the stroke brain. Stem cells treated by low levels of chemical, physical, or pharmacological stimuli have been shown to survive better in the neurodegenerative brain. Thus combining hormesis and stem cell therapy might improve the outcome for treatment of these diseases. In addition, since the cell death patterns and their underlying molecular mechanism may vary in different neurodegenerative diseases, even in different progression stages of the same disease, it is essential to design a suitable and optimum hormetic strategy that is tailored to the individual patient.

L-DOPA: a scapegoat for accelerated neurodegeneration in Parkinson's disease?

There is consensus that amelioration of the motor symptoms of Parkinson's disease is most effective with L-DOPA (levodopa). However, this necessary therapeutic step is biased by an enduring belief that L-DOPA is toxic to the remaining substantia nigra dopaminergic neurons by itself, or by specific metabolites such as dopamine. The concept of L-DOPA toxicity originated from pre-clinical studies conducted mainly in cell culture, demonstrating that L-DOPA or its derivatives damage dopaminergic neurons due to oxidative stress and other mechanisms. However, the in vitro data remain controversial as some studies showed neuroprotective, rather than toxic action of the drug. The relevance of this debate needs to be considered in the context of the studies conducted on animals and in clinical trials that do not provide convincing evidence for L-DOPA toxicity in vivo. This review presents the current views on the pathophysiology of Parkinson's disease, focusing on mitochondrial dysfunction and oxidative/proteolytic stress, the factors that can be affected by L-DOPA or its metabolites. We then critically discuss the evidence supporting the two opposing views on the effects of L-DOPA in vitro, as well as the animal and human data. We also address the problem of inadequate experimental models used in these studies. L-DOPA remains the symptomatic 'hero' of Parkinson's disease. Whether it contributes to degeneration of nigral dopaminergic neurons, or is a 'scapegoat' for explaining undesirable or unexpected effects of the treatment, remains a hotly debated topic.

Impaired adaptive cellular responses to oxidative stress and the pathogenesis of Alzheimer's disease

As is generally true with other age-related diseases, Alzheimer's disease (AD) involves oxidative damage to cellular components in the affected tissue, in this case the brain. The causes and consequences of oxidative stress in neurons in AD are not fully understood, but considerable evidence points to important roles for accumulation of amyloid β-peptide upstream of oxidative stress and perturbed cellular Ca(2+) homeostasis and energy metabolism downstream of oxidative stress. The identification of mutations in the β-amyloid precursor protein and presenilin-1 as causes of some cases of early onset inherited AD, and the development of cell culture and animal models based on these mutations has greatly enhanced our understanding of the AD process, and has greatly expanded opportunities for preclinical testing of potential therapeutic interventions. In this regard, and of particular interest to us, is the elucidation of adaptive cellular stress response pathways (ACSRP) that can counteract multiple steps in the AD neurodegenerative cascades, thereby limiting oxidative damage and preserving cognitive function. ACSRP can be activated by factors ranging from exercise and dietary energy restriction, to drugs and phytochemicals. In this article we provide an overview of oxidative stress and AD, with a focus on ACSRP and their potential for preventing and treating AD.

Glycolytic inhibition as a strategy for developing calorie restriction mimetics

Calorie restriction (CR) remains the most robust environmental intervention for altering aging processes and increasing healthspan and lifespan. Emerging from progress made in many nonhuman models, current research has expanded to formal, controlled human studies of CR. Since long-term CR requires a major commitment of will power and long-term negative consequences remain to be determined, the concept of a calorie restriction mimetic (CRM) has become a new area of investigation within gerontology. We have proposed that a CRM is a compound that mimics metabolic, hormonal, and physiological effects of CR, activates stress response pathways observed in CR and enhances stress protection, produces CR-like effects on longevity, reduces age-related disease, and maintains more youthful function, all without significantly reducing food intake. Over 12 years ago, we introduced the concept of glycolytic inhibition as a strategy for developing mimetics of CR. We have argued that inhibiting energy utilization as far upstream as possible might offer a broader range of CR-like effects as opposed to targeting a singular molecular target downstream. As the first candidate CRM, 2-deoxyglucose, a known anti-glycolytic, provided a remarkable phenotype of CR, but turned out to produce cardiotoxicity in rats. Since the introduction of 2DG as a candidate CRM, many different targets for development have now been proposed at more downstream sites, including insulin receptor sensitizers, sirtuin activators, and inhibitors of mTOR. This review discusses these various strategies to assess their current status and future potential for this emerging research field.

Strategies for the discovery of anti-aging compounds

IMPORTANCE OF THE FIELD

Life expectancy has increased across the globe and the number of aged people is increasing rapidly. With the rise in the average age of people, the prevalence of age related pathologies has also increased and thus the strategies to find anti-aging molecules assume significance. Anti-aging basically concerns the prevention or delaying the alterations taking place as a function of age which are manifested as age-associated illnesses.

AREAS COVERED IN THIS REVIEW

This review covers anti-aging strategies involving supplementation of dietary antioxidants such as polyphenols, vitamins E and C, lipoic acid, acetyl carnitine, carnosine and cysteine along with the application of mammalian target of rapamycin inhibitors and plasma membrane redox system activators. It also presents the use of different hormone supplementation, for example, melatonin, dehydroepiandrosterone, growth hormone and sex hormones as a tool against aging. The use of caloric restriction and calorie restriction mimetics as an anti-aging intervention is also reviewed.

WHAT THE READER WILL GAIN

The concept, use and efficacy of different anti-aging approaches.

TAKE HOME MESSAGE

Despite a lot of research and sustained ongoing efforts, finding a viable anti-aging therapy which can extend the maximum human lifespan remains elusive. However, several interventions aimed towards a longer healthy life seem promising.

Hsp90-mediated inhibition of FKBP38 regulates apoptosis in neuroblastoma cells

The FK506-binding protein 38 (FKBP38) is a pro-apoptotic regulator of Bcl-2 in neuroblastoma cells. Hsp90 inhibits the pro-apoptotic FKBP38/CaM/Ca(2+) complex and thus prevents interactions between FKBP38 and Bcl-2. Here we show that Hsp90 increases cell survival rates of neuroblastoma cells after apoptosis induction. Depletion of FKBP38 by short interference RNA significantly decreased the anti-apoptotic effect of Hsp90 expression. In addition, the influence of high cellular Hsp90 levels was only observed in post-stimulation apoptosis that is sensitive to selective FKBP38 active site inhibition. Similar anti-apoptotic effects in neuroblastoma cells were observed after stimulation of endogenous Hsp90 expression. Hence, the inhibition of FKBP38 by Hsp90 participates in programmed cell death control of neuroblastoma cells.

The Bcl-2 Regulator FKBP38-Calmodulin-Ca2+ Is Inhibited by Hsp90

FKBP38 is a negative effector of the anti-apoptotic Bcl-2 protein in neuroblastoma cells. The interaction with Bcl-2 and the enzyme activity of FKBP38 depend on prior binding of calmodulin-Ca(2+) (CaM-Ca(2+)) at high Ca(2+) concentrations. The FKBP38 protein structure contains three tetratricopeptide repeat (TPR) motifs corresponding to the Hsp90 interaction sites of other immunophilins. In this study we show that the TPR domain of FKBP38 interacts with the C-terminal domain of Hsp90, but only if the FKBP38-CaM-Ca(2+) complex is preformed. Hence, FKBP38 is the first example of a TPR-containing immunophilin that interacts cofactor-dependently with Hsp90. In the ternary Hsp90-FKBP38-CaM-Ca(2+) complex the active site of FKBP38 is blocked, thus preventing interactions with Bcl-2. The dual control of the active site cleft of FKBP38 by CaM-Ca(2+) and Hsp90 highlights the importance of the enzyme activity of the FKBP38-CaM-Ca(2+) complex in the regulation of programmed cell death.

Caloric restriction mimetics: a novel approach for biogerontology

Caloric restriction remains the only nongenetic intervention that has been consistently and reproducibly shown to extend both average and maximal lifespan in a wide variety of species. If shown to be applicable to human aging, it is unlikely that most people would be able to maintain the 30-40% reduction in food intake apparently required for this intervention. Therefore, an alternative approach is needed. We first proposed the concept of caloric restriction (CR) mimetics in 1998. Since its introduction, this research area has witnessed a significant expansion of interest in academic, government, and private sectors. CR mimetics target alteration of pathways of energy metabolism to potentially mimic the beneficial health-promoting and anti-aging effects of CR without the need to reduce food intake significantly. To date, a number of candidate CR mimetics including glycolytic inhibitors, antioxidants and specific gene-modulators have been investigated and appear to validate the potential of this approach.

The heat-shock protein 90 inhibitor 17-allylamino-17-demethoxygeldanamycin suppresses glial inflammatory responses and ameliorates experimental autoimmune encephalomyelitis

The heat-shock response (HSR), a highly conserved cellular response, is characterized by rapid expression of heat-shock proteins (HSPs), and inhibition of other synthetic activities. The HSR can attenuate inflammatory responses, via suppression of transcription factor activation. A HSR can be induced pharmacologically by HSP90 inhibitors, through activation of the transcription factor Heat Shock Factor 1 (HSF1). In the present study we characterized the effects of 17-allylamino-17-demethoxygeldanamycin (17-AAG), a less toxic derivative of the naturally occurring HSP90 inhibitor geldanamycin, on glial inflammatory responses and the development of experimental autoimmune encephalomyelitis. In primary enriched glial cultures, 17-AAG dose dependently reduced lipopolysaccharide-dependent expression and activity of inducible nitric oxide synthase, attenuated interleukin (IL)-1beta expression and release, increased inhibitor of kappaB protein levels, and induced HSP70 expression. 17-AAG administration to mice immunized with myelin oligodendrocyte glycoprotein peptide prevented disease onset when given at an early time, and reduced clinical symptoms when given during ongoing disease. T cells from treated mice showed a reduced response to immunogen re-stimulation, and 17-AAG reduced CD3- and CD28-dependent IL-2 production. Together, these data suggest that HSP90 inhibitors could represent a new approach for therapeutic intervention in autoimmune diseases such as multiple sclerosis.

NAD(P)H fluorescence transients after synaptic activity in brain slices: predominant role of mitochondrial function

Excitatory stimulation in hippocampal slices results in biphasic NAD(P)H fluorescence transients. Previous studies using differing stimulus protocols agreed that the oxidation phase is a consequence of mitochondrial metabolism, but the reduction phase has been attributed to (1) mitochondrial nicotinamide adenine dinucleotide (NADH) generation or (2) astrocytic glycolysis triggered by glutamate uptake. In an attempt to reconcile these two views, the present study examined NAD(P)H signals evoked by a wide range of stimulus durations (40 ms to 20 secs). A combination of ionotropic glutamate receptor (iGluR) antagonists (6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), 2-amino-5-phosphonopentanoic acid (APV)) virtually abolished responses to brief stimuli (40 to 200 ms, 50 Hz), but a significant fraction of the signal elicited by extended stimulation (20 secs, 32 Hz) was resistant to CNQX/APV. Glycolysis was inhibited by removal of glucose and addition of 2-deoxyglucose (2DG) (10 mmol/L) or iodoacetic acid (IAA, 1 mmol/L). Pyruvate was provided as an alternative substrate for oxidative phosphorylation and the A1 receptor antagonist 1,3-Dipropyl-8-cyclopentylxanthine (DPCPX) included to prevent decreases in synaptic efficacy. If sufficient pyruvate was supplied, responses to brief and extended stimuli were unaffected by glycolytic inhibition and not significantly reduced by an inhibitor of glucose uptake (3-O-methyl glucose, 3 mmol/L). When timed to arrive at the peak of overshoots generated by extended synaptic stimulation, brief pyruvate applications (10 mmol/L, 2 mins) had little effect on evoked NAD(P)H increases. Flavoprotein autofluorescence transients after extended stimuli matched (with inverted sign) NAD(P)H responses. Responses to extended stimuli were not reduced by a nonselective inhibitor of glutamate uptake DL-Threo-beta-benzyloxyaspartic acid (TBOA). These results suggest that NAD(P)H transients report mitochondrial dynamics, rather than recruitment of glycolytic metabolism, over a wide range of stimulus intensities.

Hormesis/preconditioning mechanisms, the nervous system and aging

Throughout life, organisms and their cells are subjected to various stressors which they must respond to adaptively in order to avoid disease and death. Accordingly, cells possess a variety of stress-responsive signaling pathways that are coupled to kinase cascades and transcription factors that induce the expression of genes that encode cytoprotective proteins such as protein chaperones (PC), growth factors and antioxidant enzymes. Emerging findings suggest that many of the environmental factors that improve health and so prolong lifespan (for example, dietary restriction, exercise and cognitive stimulation) exert their beneficial effects through a hormesis-like mechanism. Here we describe data supporting the hormesis hypothesis of disease resistance and longevity, with a focus on findings from studies of the nervous system in this laboratory.

Calorie restriction mimetics: an emerging research field

When considering all possible aging interventions evaluated to date, it is clear that calorie restriction (CR) remains the most robust. Studies in numerous species have demonstrated that reduction of calories 30-50% below ad libitum levels of a nutritious diet can increase lifespan, reduce the incidence and delay the onset of age-related diseases, improve stress resistance, and decelerate functional decline. A current major focus of this research area is whether this nutritional intervention is relevant to human aging. Evidence emerging from studies in rhesus monkeys suggests that their response to CR parallels that observed in rodents. To assess CR effects in humans, clinical trials have been initiated. However, even if results from these studies could eventually substantiate CR as an effective pro-longevity strategy for humans, the utility of this intervention would be hampered because of the degree and length of restriction required. As an alternative strategy, new research has focused on the development of 'CR mimetics'. The objective of this strategy is to identify compounds that mimic CR effects by targeting metabolic and stress response pathways affected by CR, but without actually restricting caloric intake. For example, drugs that inhibit glycolysis (2-deoxyglucose), enhance insulin action (metformin), or affect stress signaling pathways (resveratrol), are being assessed as CR mimetics (CRM). Promising results have emerged from initial studies regarding physiological responses which resemble those observed in CR (e.g. reduced body temperature and plasma insulin) as well as protection against neurotoxicity (e.g. enhanced dopamine action and up-regulated neurotrophic factors). Ultimately, lifespan analyses in addition to expanded toxicity studies must be accomplished to fully assess the potential of any CRM. Nonetheless, this strategy clearly offers a very promising and expanding research endeavor.

Hippocampal infusions of pyruvate reverse the memory-impairing effects of septal muscimol infusions

Hippocampal infusions of glucose reverse memory deficits in spontaneous alternation and in a continuous multiple trial inhibitory avoidance task. The current experiments tested whether glucose metabolism may participate in these effects of glucose. Specifically, these experiments determined whether the glycolytic metabolite pyruvate would mimic these effects of glucose. Male Sprague-Dawley rats were given septal infusions of vehicle or the gamma-aminobutyric acid (GABA) receptor agonist muscimol (0.15 nmol for spontaneous alternation or 5 nmol for continuous multiple trial inhibitory avoidance) combined with hippocampal infusions of vehicle or pyruvate (200 nmol) 15 min prior to assessing spontaneous alternation or training in a continuous multiple trial inhibitory avoidance task. The infusions of muscimol decreased percent alternation scores and continuous multiple trial inhibitory avoidance retention latencies tested 48 h after training. More importantly, hippocampal infusions of pyruvate reversed the deficits produced by septal infusions of muscimol on both tasks. These findings show for the first time that hippocampal infusions of pyruvate influence memory and suggest that glucose may affect memory via glycolytic metabolism.

Depletion of reduced glutathione precedes inactivation of mitochondrial enzymes following limbic status epilepticus in the rat hippocampus

The time course and critical determinants of mitochondrial dysfunction and oxidative stress following limbic status epilepticus (SE) were investigated in hippocampal sub-regions of an electrical stimulation model in rats, at time points 4-44h after status. Mitochondrial and cytosolic enzyme activities were measured spectrophotometrically, and reduced glutathione (GSH) concentrations by HPLC, and compared to results from sham controls. The earliest change in any sub-region was a fall in GSH, appearing as early as 4h in CA3 (-13%, p<0.05), and persisting at all time points. This was followed by a transient fall in complex I activity (CA3, 16h, -13%, p<0.05), and later changes in aconitase (CA1,-18% and CA3, -22% at 44h, p<0.05). The activity of the cytosolic enzyme glyceraldehyde-3-phosphate-dehydrogenase was unaffected at all time points. It is known that GSH levels are dependent both on redox status, and on the availability of the precursor cysteine, in turn dependent on the cysteine/glutamate antiporter, for which extracellular glutamate concentrations are rate limiting. Both mechanisms are likely to contribute indirectly to GSH depletion following seizures. That a relative deficiency in GSH precedes later changes in the activities of complex I and aconitase in vulnerable hippocampal sub-regions, occurring within a clinically relevant therapeutic time window, suggests that strategies to boost GSH levels and/or otherwise reduce oxidative stress following seizures, deserve further study, both in terms of preventing the biochemical consequences of SE and the neuronal dysfunction and clinical consequences.

Caloric restriction in humans: potential pitfalls and health concerns

To date, the only intervention that has consistently been shown to slow the rate of aging, and to increase mean and maximum lifespan in short-lived species, is life-long calorie restriction. It is yet unclear whether long-term calorie restriction in longer lived species (i.e. primates and humans) will have a similar effect. In humans, several studies investigating short-term calorie restriction or "weight loss" programs suggest beneficial outcomes on parameters of cardiovascular disease. Studies on long-term calorie restriction are performed on a self-selected group of human subjects and show similar effects. However, few studies are currently investigating the quality of life and potential pitfalls of long-term calorie restriction in humans. It is likely that some of the physiological and psychological effects of caloric restriction that occur in animals may impact the human life very differently. For certain, calorie restriction has a plethora of health benefits in mammals, such as a reduction in age-related diseases such as cancer. However, despite the "magic" of CR, this intervention in humans may present itself with a number of health concerns, which may not be applicable to or impact the life of experimental animals, but may do so in humans. These potential pitfalls and "side effects" are not clearly addressed in the literature and will be a focus of this review.

Homologous adaptation to oxidative stress induced by the photosensitized Pd-bacteriochlorophyll derivative (WST11) in cultured endothelial cells

Various forms of cellular stress induce adaptive responses through poorly understood mechanisms. In maintaining homeostasis, endothelial cells respond and adapt to changes in oxidative stress that prevail in the circulation. Endothelial cells are also the target of many oxidative stress-based vascular therapies. The objectives of this study were to determine whether endothelial cells adapt to oxidative stress induced upon the photosensitization of WST11 (a water-soluble Pd-bacteriochlorophyll derivative being developed as a photodynamic agent) and to study possible cellular mechanisms involved. The hallmark of WST11-based photodynamic therapy is the in situ generation of cytotoxic reactive oxygen species causing vascular shutdown, hypoxia, and tumor eradication. Here we demonstrated that photodynamic therapy also induces adaptive responses and tolerance following a sublethal preconditioning of endothelial cells with the same (homologous) or different (heterologous) stressor. A link among p38 MAPK activity, expression of hsp70 and hsp27, and homologous adaptation to reactive oxygen species induced by photosensitized WST11 was established. In addition to characterization of some key proteins involved, our observations provide a beneficial new working tool for the studies of mechanisms involved in oxidative stress and adaptation using light-controlled photosensitization.

Development of Calorie Restriction Mimetics as a Prolongevity Strategy

By applying calorie restriction (CR) at 30-50% below ad libitum levels, studies in numerous species have reported increased life span, reduced incidence and delayed onset of age-related diseases, improved stress resistance, and decelerated functional decline. Whether this nutritional intervention is relevant to human aging remains to be determined; however, evidence emerging from CR studies in nonhuman primates suggests that response to CR in primates parallels that observed in rodents. To evaluate CR effects in humans, clinical trials have been initiated. Even if evidence could substantiate CR as an effective antiaging strategy for humans, application of this intervention would be problematic due to the degree and length of restriction required. To meet this challenge for potential application of CR, new research to create "caloric restriction mimetics" has emerged. This strategy focuses on identifying compounds that mimic CR effects by targeting metabolic and stress response pathways affected by CR, but without actually restricting caloric intake. Microarray studies show that gene expression profiles of key enzymes in glucose (energy) handling pathways are modified by CR. Drugs that inhibit glycolysis (2-deoxyglucose) or enhance insulin action (metformin) are being assessed as CR mimetics. Promising results have emerged from initial studies regarding physiological responses indicative of CR (reduced body temperature and plasma insulin) as well as protection against neurotoxicity, enhanced dopamine action, and upregulated brain-derived neurotrophic factor. Further life span analyses in addition to expanded toxicity studies must be completed to assess the potential of any CR mimetic, but this strategy now appears to offer a very promising and expanding research field.

Akt-directed glucose metabolism can prevent Bax conformation change and promote growth factor-independent survival

The serine/threonine kinase Akt is a component of many receptor signal transduction pathways and can prevent cell death following growth factor withdrawal. Here, we show that Akt inhibition of cell death is not dependent on new protein translation. Instead, Akt inhibition of cell death requires glucose hydrolysis through glycolysis. Akt was found to regulate multiple steps in glycolysis via posttranscriptional mechanisms that included localization of the glucose transporter, Glut1, to the cell surface and maintenance of hexokinase function in the absence of extrinsic factors. To test the role of glucose uptake and phosphorylation in growth factor-independent survival, cells were transfected with Glut1 and hexokinase 1 (Glut1/HK1) cells. Glut1/HK1 cells accumulated Glut1 on the cell surface and had high glucose uptake capacity similar to that of cells with constitutively active Akt (mAkt). Unlike mAkt-expressing cells, however, they did not consume more glucose, did not maintain prolonged phosphofructokinase-1 protein levels and activity, and did not maintain pentose phosphate shuttle activity in the absence of growth factor. Nevertheless, expression of Glut1 and HK1 promoted increased cytosolic NADH and NADPH levels relative to those of the control cells upon growth factor withdrawal, prevented activation of Bax, and promoted growth factor-independent survival. These data indicate that Bax conformation is sensitive to glucose metabolism and that maintaining glucose uptake and phosphorylation can promote cell survival in the absence of growth factor. Furthermore, Akt required glucose and the ability to perform glycolysis to prevent Bax activation. The prevention of Bax activation by posttranscriptional regulation of glucose metabolism may, therefore, be a required aspect of the ability of Akt to maintain long-term cell survival in the absence of growth factors.

Oxidative stress-mediated down-regulation of bcl-2 promoter in hippocampal neurons

Generation of oxidative stress/reactive oxygen species (ROS) is one of the causes of neuronal apoptosis. We have examined the effects of ROS at the transcriptional level in an immortalized hippocampal neuronal cell line (H19-7) and in rat primary hippocampal neurons. Treatment of H19-7 cells with hydrogen peroxide (150 micro m) resulted in a 40% decrease in Bcl-2 protein and a parallel decrease in bcl-2 mRNA levels. H19-7 cells overexpressing bcl-2 were found to be resistant to ROS-induced apoptosis. We had previously shown that bcl-2 promoter activity is positively regulated by the transcription factor cyclic AMP response element binding protein (CREB) in neurons. In the present study, we demonstrate that ROS decreases the activity of luciferase reporter gene driven by a cyclic AMP response element site containing bcl-2 promoter. Exposure of neurons to ROS for 6 h resulted in basal and fibroblast growth factor-2-stimulated phosphorylation/activation of CREB. Chronic 24 h treatment with ROS led to a significant (p < 0.01) decrease in CREB protein and CREB mRNA levels. Adenoviral overexpression of wild type CREB in H19-7 cells resulted in significant (p < 0.01) protection against ROS-induced apoptosis through up-regulation of Bcl-2 expression whereas dominant negative CREB exaggerated the injury. These findings demonstrate that loss of CREB function contributes to oxidative stress-induced neuronal dysfunction.

Meal size and frequency affect neuronal plasticity and vulnerability to disease: cellular and molecular mechanisms

Although all cells in the body require energy to survive and function properly, excessive calorie intake over long time periods can compromise cell function and promote disorders such as cardiovascular disease, type-2 diabetes and cancers. Accordingly, dietary restriction (DR; either caloric restriction or intermittent fasting, with maintained vitamin and mineral intake) can extend lifespan and can increase disease resistance. Recent studies have shown that DR can have profound effects on brain function and vulnerability to injury and disease. DR can protect neurons against degeneration in animal models of Alzheimer's, Parkinson's and Huntington's diseases and stroke. Moreover, DR can stimulate the production of new neurons from stem cells (neurogenesis) and can enhance synaptic plasticity, which may increase the ability of the brain to resist aging and restore function following injury. Interestingly, increasing the time interval between meals can have beneficial effects on the brain and overall health of mice that are independent of cumulative calorie intake. The beneficial effects of DR, particularly those of intermittent fasting, appear to be the result of a cellular stress response that stimulates the production of proteins that enhance neuronal plasticity and resistance to oxidative and metabolic insults; they include neurotrophic factors such as brain-derived neurotrophic factor (BDNF), protein chaperones such as heat-shock proteins, and mitochondrial uncoupling proteins. Some beneficial effects of DR can be achieved by administering hormones that suppress appetite (leptin and ciliary neurotrophic factor) or by supplementing the diet with 2-deoxy-d-glucose, which may act as a calorie restriction mimetic. The profound influences of the quantity and timing of food intake on neuronal function and vulnerability to disease have revealed novel molecular and cellular mechanisms whereby diet affects the nervous system, and are leading to novel preventative and therapeutic approaches for neurodegenerative disorders.

Mice expressing human mutant presenilin-1 exhibit decreased activation of NF-kappaB p50 in hippocampal neurons after injury

Mutations in the presenilin-1 (mutPS-1) gene, a cause of familial Alzheimer's disease, increase the susceptibility of neurons to apoptotic death. Using the trimethyltin model of hippocampal neurodegeneration, mice expressing the human mutPS-1 gene (M146L) exhibited increased neurodegeneration and mortality relative to non-transgenic littermates. Activation of NF-kappaB p50 was found to be impaired in transgenic mice with unaltered expression levels suggesting that mutPS-1 expression inhibits p50 activation to adversely affect neuronal resistance to injury.

Caloric restriction and aging in primates: Relevance to humans and possible CR mimetics

For nearly 70 years it has been recognized that reduction in caloric intake by 30-40% from ad libitum levels leads to a significant extension of mean and maximal lifespan in a variety of short-lived species. This effect of caloric restriction (CR) on lifespan has been reported in nearly all species tested and has been reproduced hundreds of times under a variety of different laboratory conditions. In addition to prolonging lifespan, CR also prevents or delays the onset of age-related disease and maintains many physiological functions at more youthful levels. Studies in longer-lived species, specifically rhesus and squirrel monkeys, have been underway since the late 1980s. The studies in nonhuman primates are beginning to yield valuable information suggesting that the effect of CR on aging is universal across species and that this nutritional paradigm will have similar effects in humans. Even if CR can be shown to impact upon human aging, it is unlikely that most people will be able to maintain the strict dietary control required for this regimen. Thus, elucidation of the biological mechanisms of CR and development of alternative strategies to yield similar benefits is of primary importance. CR mimetics, or interventions that "mimic" certain protective effects of CR, may represent one such alternative strategy.