Sustained phosphorylation and activation of protein kinase B correlates with brain-derived neurotrophic factor and insulin stimulated survival of cerebellar granule cells

The neurobiology and therapeutic potential of multi-targeting β-secretase, glycogen synthase kinase 3β and acetylcholinesterase in Alzheimer's disease

Alzheimer's Disease (AD) is the most common form of dementia, affecting almost 50 million of people around the world, characterized by a complex and age-related progressive pathology with projections to duplicate its incidence by the end of 2050. AD pathology has two major hallmarks, the amyloid beta (Aβ) peptides accumulation and tau hyperphosphorylation, alongside with several sub pathologies including neuroinflammation, oxidative stress, loss of neurogenesis and synaptic dysfunction. In recent years, extensive research pointed out several therapeutic targets which have shown promising effects on modifying the course of the disease in preclinical models of AD but with substantial failure when transposed to clinic trials, suggesting that modulating just an isolated feature of the pathology might not be sufficient to improve brain function and enhance cognition. In line with this, there is a growing consensus that an ideal disease modifying drug should address more than one feature of the pathology. Considering these evidence, β-secretase (BACE1), Glycogen synthase kinase 3β (GSK-3β) and acetylcholinesterase (AChE) has emerged as interesting therapeutic targets. BACE1 is the rate-limiting step in the Aβ production, GSK-3β is considered the main kinase responsible for Tau hyperphosphorylation, and AChE play an important role in modulating memory formation and learning. However, the effects underlying the modulation of these enzymes are not limited by its primarily functions, showing interesting effects in a wide range of impaired events secondary to AD pathology. In this sense, this review will summarize the involvement of BACE1, GSK-3β and AChE on synaptic function, neuroplasticity, neuroinflammation and oxidative stress. Additionally, we will present and discuss new perspectives on the modulation of these pathways on AD pathology and future directions on the development of drugs that concomitantly target these enzymes.

Relationship between Brain-Derived Neurotrophic Factor and Cognitive Decline in Patients with Mild Cognitive Impairment and Dementia

In the last decade, increasing evidence has emerged linking alterations in the brain-derived neurotrophic factor (BDNF) expression with the development of Alzheimer's disease (AD). Because of the important role of BDNF in cognition and its association with AD pathogenesis, the aim of this study was to evaluate the potential difference in plasma BDNF concentrations between subjects with mild cognitive impairment (MCI; N = 209) and AD patients (N = 295) and to determine the possible association between BDNF plasma levels and the degree of cognitive decline in these individuals. The results showed a significantly higher (p < 0.001) concentration of plasma BDNF in subjects with AD (1.16; 0.13-21.34) compared with individuals with MCI (0.68; 0.02-19.14). The results of the present study additionally indicated a negative correlation between cognitive functions and BDNF plasma concentrations, suggesting higher BDNF levels in subjects with more pronounced cognitive decline. The correlation analysis revealed a significant negative correlation between BDNF plasma levels and both Mini-Mental State Examination (p < 0.001) and Clock Drawing test (p < 0.001) scores. In conclusion, the results of our study point towards elevated plasma BDNF levels in AD patients compared with MCI subjects, which may be due to the body's attempt to counteract the early and middle stages of neurodegeneration.

Dietary Macronutrients Do Not Differently Influence Postprandial Serum and Plasma Brain-Derived Neurotrophic Factor Concentrations: A Randomized, Double-Blind, Controlled Cross-Over Trial

Objectives: Brain-derived neurotrophic factor (BDNF) plays a role in cognition and metabolism. Specific nutrients can affect fasting BDNF concentrations, which are potentially mediated by insulin and/or glucose. Since macronutrients trigger each a different insulin and glucose response, we examined postprandial effects of meals rich in fat, carbohydrates, or protein on BDNF concentrations. BDNF was analyzed in serum and plasma, since concentration differences can be found between matrices.

Methods: Healthy overweight/obese male participants (n = 18) participated in this randomized, double-blind, cross-over trial consisting of three test days with 1 week wash-out periods. Either a high-fat (En% fat, carbohydrates, protein: 52.3, 39.2, 8.0), high-carbohydrate (En% 9.6, 81.5, 8.6) or high-protein meal (En% 10.6, 51.5, 36.9) was consumed on each test day. BDNF concentrations were measured after 0, 60, and 240 min. Glucose and insulin concentrations were measured after 0, 15, 30, 45, 60, 90, 120, and 240 min.

Results: BDNF concentrations were higher in serum compared with plasma (P < 0.001). Postprandial BDNF concentrations in serum decreased significantly after the high-fat (P = 0.013) and high-carbohydrate meals (P = 0.040), and showed a trend after the high-protein meal (P = 0.076). No differences were found between meals (P = 0.66). Postprandial BDNF concentrations measured in plasma did not significantly change after the different meals (P = 0.47). As total area under the curve (AUC) for glucose was significantly higher after the high-carbohydrate meal compared with the high-fat (P = 0.003) and high-protein meals (P < 0.001), and the total AUC for insulin was higher after the high-carbohydrate (P < 0.001) and high-protein meals (P < 0.001) compared with the high-fat meal, it seems that acute changes in glucose and insulin do not affect postprandial BDNF concentrations. However, after the high-protein meal, the higher total AUC for glucose correlated with lower serum BDNF concentrations, and a higher maximal increase in glucose correlated with a lower maximal increase in plasma BDNF concentrations. There were no correlations with insulin concentrations after either meal.

Conclusion: Serum BDNF concentrations were higher than plasma concentrations. Since postprandial BDNF responses were not different between the meals, we conclude that there is no role for insulin or glucose in regulating postprandial BDNF concentrations.

Clinical Trial Registration: [www.ClinicalTrials.gov], identifier [NCT03139890].

Insulin attenuates apoptosis in neuronal cells by an integrin-linked kinase-dependent mechanism

Insulin promotes neuronal survival by activating a phosphatidylinositol 3-kinase (PI 3-kinase)/AKT-dependent signaling pathway and reducing caspase activation. We investigated a role for integrin-linked kinase (ILK) in insulin-mediated cell survival in cultured neurons and differentiated R28 cells. We used a serum and depolarization withdrawal model to induce apoptosis in cerebellar granule neurons and a serum withdrawal model to induce apoptosis in differentiated R28 cells. ILK knock-out decreased insulin-mediated protection as did the addition of pharmacological inhibitors of ILK, KP-392 or QLT-0267. Prosurvival effects of insulin were rescued by Boc-Asp (O-methyl)-CH₂F (BAF), a pancaspase inhibitor, in the presence of KP-392. Insulin and IGF-1 decreased caspase-3 activation, an effect that was inhibited by KP-392 and QLT-0267. Western blot analysis indicates that insulin-induced stimulation of AKT Ser-473 phosphorylation was decreased after the ILK gene was conditionally knocked-out, following overexpression of AKT-DN or in the presence of QLT-0267. Insulin and IGF-1 stimulated ILK kinase activity in primary neurons and this was inhibited following ILK-DN overexpression. Western blot analysis indicates that insulin exposure upregulated the expression of the cellular inhibitor of apoptosis protein c-IAP2 in an extracellular matrix-dependent manner, an effect blocked by KP-392. These results indicate that ILK is an important effector in insulin-mediated neuroprotection.

The Protective Effect of Insulin on Rat Cortical Neurons in Oxidative Stress and Its Dependence on the Modulation of Akt, GSK-3beta, ERK1/2, and AMPK Activities

Insulin is a promising drug for the treatment of diseases associated with brain damage. However, the mechanism of its neuroprotective action is far from being understood. Our aim was to study the insulin-induced protection of cortical neurons in oxidative stress and its mechanism. Immunoblotting, flow cytometry, colorimetric, and fluorometric techniques were used. The insulin neuroprotection was shown to depend on insulin concentration in the nanomolar range. Insulin decreased the reactive oxygen species formation in neurons. The insulin-induced modulation of various protein kinase activities was studied at eight time-points after neuronal exposure to prooxidant (hydrogen peroxide). In prooxidant-exposed neurons, insulin increased the phosphorylation of GSK-3beta at Ser⁹ (thus inactivating it), which resulted from Akt activation. Insulin activated ERK1/2 in neurons 5–30 min after cell exposure to prooxidant. Hydrogen peroxide markedly activated AMPK, while it was for the first time shown that insulin inhibited it in neurons at periods of the most pronounced activation by prooxidant. Insulin normalized Bax/Bcl-2 ratio and mitochondrial membrane potential in neurons in oxidative stress. The inhibitors of the PI3K/Akt and MEK1/2/ERK1/2 signaling pathways and the AMPK activator reduced the neuroprotective effect of insulin. Thus, the protective action of insulin on cortical neurons in oxidative stress appear to be realized to a large extent through activation of Akt and ERK1/2, GSK-3beta inactivation, and inhibition of AMPK activity increased by neuronal exposure to prooxidant.

Neuroprotective Effects of Forced Exercise and Bupropion on Chronic Methamphetamine-induced Cognitive Impairment via Modulation of cAMP Response Element-binding Protein/Brain-derived Neurotrophic Factor Signaling Pathway, Oxidative Stress, and Inflammatory Biomarkers in Rats

Background

Forced exercise can act as non-pharmacologic neuroprotective agent. In current study, we tried the involved molecular mechanisms of protective effects of forced exercise against methamphetamine induced neurodegeneration.

Materials and Methods

Forty adult male rats were divided to Group 1 and 2 which received normal saline and methamphetamine (10 mg/kg) respectively for 30 days. Groups 3, 4 and 5 were treated with methamphetamine for first 15 days and then were treated by forced exercise, bupropion (20 mg/kg/day) or combination of them for the following 15 days. Between 26^th and 30^th days, Morris Water Maze (MWM) was used to evaluate the cognition. On day 31, hippocampus was isolated from each rat and oxidative, antioxidant and inflammatory factors also the level of total and phosphorylated forms of cAMP response element-binding protein (CREB) and brain derived neurotrophic factor (BDNF) proteins were also evaluated.

Results

Chronic abuse of methamphetamine could decreases cognition and increase malondialdehyde (MDA), Tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β), while caused decreases in superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione reductase (GR) activities all these changes was significant (P < 0.001) in compared to control group while treatment with bupropion, forced exercise and bupropion in combination with forced exercise could prevent all these malicious effects of methamphetamine (P < 0.001). Bupropion, forced exercise and bupropion in combination with forced exercise could activate CREB (both forms) and activates BDNF proteins' expression with P < 0.001 in methamphetamine treated rats.

Conclusions

P-CREB/BDNF signaling pathways might have critical role in forced exercise protective effects against methamphetamine induced neurodegeneration.

GSK3β: a plausible mechanism of cognitive and hippocampal changes induced by erythropoietin treatment in mood disorders?

Mood disorders are associated with significant psychosocial and occupational disability. It is estimated that major depressive disorder (MDD) will become the second leading cause of disability worldwide by 2020. Existing pharmacological and psychological treatments are limited for targeting cognitive dysfunctions in mood disorders. However, growing evidence from human and animal studies has shown that treatment with erythropoietin (EPO) can improve cognitive function. A recent study involving EPO-treated patients with mood disorders showed that the neural basis for their cognitive improvements appeared to involve an increase in hippocampal volume. Molecular mechanisms underlying hippocampal changes have been proposed, including the activation of anti-apoptotic, antioxidant, pro-survival and anti-inflammatory signalling pathways. The aim of this review is to describe the potential importance of glycogen synthase kinase 3-beta (GSK3β) as a multi-potent molecular mechanism of EPO-induced hippocampal volume change in mood disorder patients. We first examine published associations between EPO administration, mood disorders, cognition and hippocampal volume. We then highlight evidence suggesting that GSK3β influences hippocampal volume in MDD patients, and how this could assist with targeting more precise treatments particularly for cognitive deficits in patients with mood disorders. We conclude by suggesting how this developing area of research can be further advanced, such as using pharmacogenetic studies of EPO treatment in patients with mood disorders.

Biochemical and Radiological Markers of Alzheimer's Disease Progression

Alzheimer's disease (AD) is a neurodegenerative, inevitably progressive disease with a rate of cognitive, functional, and behavioral decline that varies highly from patient to patient. Although several clinical predictors of AD progression have been identified, to our mind in clinical practice there is a lack of a reliable biomarker that enables one to stratify the risk of deterioration. Identification of biomarkers that allow the monitoring of AD progression could change the way physicians and caregivers make treatment decisions. This review summarizes the results of studies on potential biochemical and radiological markers related to AD progression.

Effects of mood-stabilizing drugs on dendritic outgrowth and synaptic protein levels in primary hippocampal neurons

OBJECTIVES

Mood-stabilizing drugs, such as lithium (Li) and valproate (VPA), are widely used for the treatment of bipolar disorder, a disease marked by recurrent episodes of mania and depression. Growing evidence suggests that Li exerts neurotrophic and neuroprotective effects, leading to an increase in neural plasticity. The present study investigated whether other mood-stabilizing drugs produce similar effects in primary hippocampal neurons.

METHODS

The effects of the mood-stabilizing drugs Li, VPA, carbamazepine (CBZ), and lamotrigine (LTG) on hippocampal dendritic outgrowth were examined. Western blotting analysis was used to measure the expression of synaptic proteins - that is, brain-derived neurotrophic factor (BDNF), postsynaptic density protein-95 (PSD-95), neuroligin 1 (NLG1), β-neurexin, and synaptophysin (SYP). To determine neuroprotective effects, we used a B27-deprivation cytotoxicity model which causes hippocampal cell death upon removal of B27 from the culture medium.

RESULTS

Li (0.5-2.0 mM), VPA (0.5-2.0 mM), CBZ (0.01-0.10 mM), and LTG (0.01-0.10 mM) significantly increased dendritic outgrowth. The neurotrophic effect of Li and VPA was blocked by inhibition of phosphatidylinositol 3-kinase, extracellular signal-regulated kinase, and protein kinase A signaling; the effects of CBZ and LTG were not affected by inhibition of these signaling pathways. Li, VPA, and CBZ prevented B27 deprivation-induced decreases in BDNF, PSD-95, NLG1, β-neurexin, and SYP levels, whereas LTG did not.

CONCLUSIONS

These results suggest that Li, VPA, CBZ, and LTG exert neurotrophic effects by promoting dendritic outgrowth; however, the mechanism of action differs. Furthermore, certain mood-stabilizing drugs may exert neuroprotective effects by enhancing synaptic protein levels against cytotoxicity in hippocampal cultures.

Neuroprotective and anti-apoptotic effects of liraglutide on SH-SY5Y cells exposed to methylglyoxal stress

Glucagon-like peptide 1 (GLP-1) is a growth factor that has demonstrated neuroprotective properties in a range of studies. In an APPswe/PS1ΔE9 mouse model of Alzheimer's disease (AD), we previously found protective effects on memory formation, synaptic plasticity, synapse survival and a reduction of amyloid synthesis and plaque load in the brain. Here, we analyse the neuroprotective properties of the GLP-1 analogue liraglutide in human neuroblastoma cell line SH-SY5Y during methyl glyoxal stress. We show for the first time that cell viability was enhanced by liraglutide (XTT assay) in a dose-dependent way, while cytotoxicity (LDH assay) and apoptosis were reduced. Expression of the pro-survival Mcl1 signaling protein was increased, as was activation of cell survival kinases Akt, MEK1/2 and the transcription factor p90RSK. Liraglutide also decreased pro-apoptotic Bax and Bik expression. In addition, the membrane potential and the influx of calcium into the cell were enhanced by liraglutide. GLP-1 receptor expression was also increased by the drug. The results demonstrate a range of growth factor-related cytoprotective processes induced by liraglutide, which is currently on the market as a treatment for type 2 diabetes (Victoza®). It is also tested in clinical trials in patients with Alzheimer disease.

The study of candidate genes related to the neurodevelopmental hypothesis of anorexia nervosa: classical association study versus decision tree

In this research, we conducted a study of genes connected with the neurodevelopmental hypothesis of anorexia nervosa, using classical statistical and data-mining methods to establish a relationship with disease risk and algorithms to identify the best genetic predictors of anorexia nervosa.

DISC1: Structure, Function, and Therapeutic Potential for Major Mental Illness

Disrupted in schizophrenia 1 (DISC1) is well established as a genetic risk factor across a spectrum of psychiatric disorders, a role supported by a growing body of biological studies, making the DISC1 protein interaction network an attractive therapeutic target. By contrast, there is a relative deficit of structural information to relate to the myriad biological functions of DISC1. Here, we critically appraise the available bioinformatics and biochemical analyses on DISC1 and key interacting proteins, and integrate this with the genetic and biological data. We review, analyze, and make predictions regarding the secondary structure and propensity for disordered regions within DISC1, its protein-interaction domains, subcellular localization motifs, and the structural and functional implications of common and ultrarare DISC1 variants associated with major mental illness. We discuss signaling pathways of high pharmacological potential wherein DISC1 participates, including those involving phosphodiesterase 4 (PDE4) and glycogen synthase kinase 3 (GSK3). These predictions and priority areas can inform future research in the translational and potentially guide the therapeutic processes.

Transcriptomic profiles of Wnt3a and insulin in primary cultured rat cortical neurones

Glycogen synthase kinase 3 (GSK3) is a widely expressed, constitutively active, serine/threonine kinase that is negatively regulated by both Wnt and insulin via two independent signalling pathways. GSK3 is an important mediator in many physiological processes including glycogen metabolism, apoptosis and gene transcription. In addition, GSK3 is implicated in diseases such as Alzheimer's, schizophrenia and cancer, where it exhibits deregulated activity. In this study, we sought to determine the neuronal genes regulated by both Wnt and insulin in an in vitro cell culture model to further elucidate the signalling roles GSK3 plays in the CNS. Affymetrix Rat Genome 230 2.0 whole genome microarrays were used to explore the expression profiles of rat primary cortical neurones treated with recombinant Wnt3a (10 nM) or insulin (50 nM) for 2 h. Following a conservative correction (Bonferroni) for multiple testing, seven genes were identified to be differentially expressed from controls; four of these genes were regulated by insulin and three genes were regulated by both insulin and Wnt3a. The data were also analysed using a false discovery rate cut off, which is a less stringent correction for multiple testing. This approach yielded 105 genes that were differentially regulated from controls; 72 of the gene changes were attributable to insulin treatment, 11 were because of Wnt3a treatment and 22 genes were altered by both insulin and Wnt3a. These data demonstrate that the Wnt and insulin pathways exhibit both divergent and overlapping signalling activities in neuronal cells. The overlapping transcriptional response was not attributable to Wnt3a activating Akt. These findings have ramifications for neurodevelopment and neurological diseases, in which the Wnt and insulin signalling pathways are implicated.

Higher BDNF serum levels predict slower cognitive decline in Alzheimer's disease patients

The neurotrophin brain-derived neurotrophic factor (BDNF) plays a critical role in neuronal survival, synaptic plasticity, and memory. Several recent studies have demonstrated altered BDNF serum levels in Alzheimer's disease (AD) patients. However, the association of BDNF serum levels with the rate of cognitive decline in AD patients is still unclear. We demonstrate that BDNF serum levels are significantly decreased in AD patients with fast cognitive decline [decrease of Mini-Mental State Examination (MMSE) score >4/yr; n=12] compared to AD patients with slow cognitive decline (decrease of MMSE score ≤4/yr, n=28) and show a significant correlation with the rate of cognitive decline during 1 yr follow-up. These results suggest that higher BDNF serum levels are associated with a slower rate of cognitive decline in AD patients. Further longitudinal studies are necessary to elucidate the kinetics and the potential role of serum BDNF as a surrogate marker of disease progression in AD patients.

Genetic association of BDNF val66met and GSK-3beta-50T/C polymorphisms with tardive dyskinesia

AIMS

Neurodegenerative processes may be involved in the pathogenesis of tardive dyskinesia (TD), and a growing body of evidence suggests that brain-derived neurotrophic factor (BDNF) plays a role in both the antipsychotic effects and the pathogenesis of TD. BDNF and glycogen synthase kinase (GSK)-3beta are important in neuronal survival, and thus abnormal regulation of BDNF and GSK-3beta may contribute to TD pathophysiology. This study investigated the relationship between two polymorphisms, val66met in the BDNF coding region and -50T/C in the GSK-3beta promoter, and susceptibility to TD among a matched sample of patients having schizophrenia with TD (n = 83), patients with schizophrenia without TD (n = 78), and normal control subjects (n = 93).

METHODS

All subjects were Korean. The BDNF val66met and GSK-3beta-50T/C genotypes were determined by polymerase chain reaction and restriction fragment length polymorphism analyses.

RESULTS

Polymerase chain reaction analysis revealed no significant difference in the occurrence of the polymorphisms among the TD, non-TD, and control subjects, but a significant interaction was observed among the groups possessing BDNF val allele in compound genotypes (P = 0.001). We found that the schizophrenic subjects with the C/C GSK-3beta genotype, who carry the val allele of the BDNF gene, are expected to have a decreased risk of developing neuroleptic-induced tardive dyskinesia (P < 0.001).

CONCLUSIONS

Our results demonstrate that the GSK-3beta C/C genotype with the BDNF val allele is associated with patients having schizophrenia without TD. This study also suggests that the BDNF and GSK-3beta gene polymorphisms work in combination, but not individually, in predisposing patients with schizophrenia to TD.

Bone marrow stromal cells protect oligodendrocytes from oxygen-glucose deprivation injury

Oligodendrocyte (OLG) damage leads to demyelination, which is frequently observed in ischemic cerebrovascular diseases. In this study, we investigated the effect of bone marrow stromal cells (BMSCs) on OLGs subjected to oxygen-glucose deprivation (OGD). N20.1 cells (mouse OLG cell line) were transferred into an anaerobic chamber for 3 hr in glucose-free and serum-free medium. After OGD incubation, OLG cultures were divided into the following groups: 1) OGD alone, 2) OLG cocultured with BMSCs, 3) treatment with the phosphoinostide 3-kinase (PI3k) inhibitor LY294002, 4) LY294002-treated OLGs with BMSC cocultured, and 5) anti-p75 antibody-treated OLGs. After an additional 3 hr of reoxygenation incubation, OLG viability and apoptosis were measured. The mRNA expression in the BMSCs and OLGs was analyzed using quantitative real-time PCR (RT-PCR). Serine/threonine-specific protein kinase (Akt), phosphorylated Akt (p-Akt), p75, and caspase 3 protein expressions in OLGs were measured by Western blot. Our results suggest that BMSCs produce growth factors, activate the Akt pathway, and increase the survival of OLGs. BMSCs also reduce p75 and caspase 3 expressions in the OGD-OLGs, which leads to decreased OLG apoptosis. BMSCs participate in OLG protection that may occur with promoting growth factors/PI3K/Akt and inhibiting the p75/caspase pathways. Our study provides insight into white matter damage and the therapeutic benefits of BMSC-based remyelinating therapy after stroke and demyelinating diseases.

Increase of BDNF serum concentration during donepezil treatment of patients with early Alzheimer's disease

Alzheimer's disease (AD) can be treated with inhibitors of the enzyme acetylcholinesterase (AChE). Recent pre-clinical and clinical studies gave evidence that AChE-inhibitors have neuroprotective effects and thereby a disease-modifying potential. The mechanism of this action is still discussed. In an animal model oral administration of an AChE-inhibitor lead to an increase of brain derived neurotrophic factor (BDNF) in hippocampus and cortex. Recent studies have found a decrease of BDNF in the serum and brain of AD patients with potentially consecutive lack of neurotrophic support and contribution to progressive neurodegeneration. BDNF serum concentrations were assessed by ELISA in 19 AD patients and 20 age-matched healthy controls at baseline and in the AD patients after 15 months of treatment with donepezil 10 mg per day (one patient received just 5 mg). Before treatment with donepezil we found in AD significantly decreased BDNF serum concentrations (19.2 +/- 3.7 ng/ml) as compared to healthy controls (23.2 +/- 6.0 ng/ml, P = 0.015). After 15 months of treatment the BDNF serum concentration increased significantly in the AD patients (23.6 +/- 7.0 ng/ml, P = 0.001) showing no more difference to the healthy controls (P = 0.882). The results of the present study confirm data of prior investigations that a down-regulation of BDNF in serum and brain of AD patients seems to begin with the first clinical symptoms and to be persistent. A treatment with the AChE-inhibitor donepezil is accompanied with an increase of BDNF serum concentration in AD patients reaching the level of healthy controls. Thus, up-regulation of BDNF might be part of a neuroprotective effect of AChE-inhibitors. The molecular mechanism of this potentially disease-modifying mechanism of action of donepezil should be clarified.

S100A11, an dual mediator for growth regulation of human keratinocytes

We previously revealed a novel signal pathway involving S100A11 for inhibition of the growth of normal human keratinocytes (NHK) caused by high Ca(++) or transforming growth factor beta. Exposure to either agent resulted in transfer of S100A11 to nuclei, where it induced p21(WAF1). In contrast, S100A11 has been shown to be overexpressed in many human cancers. To address this apparent discrepancy, we analyzed possible new functions of S100A11, and we provide herein evidence that 1) S100A11 is actively secreted by NHK; 2) extracellular S100A11 acts on NHK to enhance the production of epidermal growth factor family proteins, resulting in growth stimulation; 3) receptor for advanced glycation end products, nuclear factor-kappaB, Akt, and cAMP response element-binding protein are involved in the S100A11-triggered signal transduction; and 4) production and secretion of S100A11 are markedly enhanced in human squamous cancer cells. These findings indicate that S100A11 plays a dual role in growth regulation of epithelial cells.

BDNF serum and CSF concentrations in Alzheimer's disease, normal pressure hydrocephalus and healthy controls

Alzheimer's disease (AD) and normal pressure hydrocephalus (NPH) are common forms of dementia in the elderly. Recent findings have suggested an involvement of brain-derived neurotrophic factor (BDNF) in the pathogenesis of AD. BDNF is an endogenous protein involved in the maintenance of neuronal function, synaptic plasticity and structural integrity in the adult brain. BDNF serum and cerebrospinal fluid (CSF) concentrations were assessed by a sensitive ELISA in 27 AD patients in comparison to 9 NPH patients and 28 age-matched healthy controls (10 CSF samples). We found a significant decrease of BDNF serum concentration in AD (18.6ng/ml) and NPH patients (18.1ng/ml) as compared to healthy controls (21.3ng/ml; p=0.041/p=0.017). BDNF serum concentrations did not correlate with CSF levels, age or MMSE scores both in AD and NPH patients. In unconcentrated CSF samples, BDNF could be detected in AD patients in 8/27 cases (29.6%; mean of 4.6pg/ml), in NPH patients in 1/9 cases (11.1%; mean of 6.4pg/ml) and in the control subjects in 5/10 cases (50%; mean of 1.6pg/ml) with no significant differences as regards mean concentration and frequency of detectable BDNF in CSF. The decrease of BDNF serum levels in AD and NPH may reflect a lack of trophic support and thus contribute to progressive degeneration in both diseases. In contrast to serum, CSF seems to be no useful source to determine BDNF in AD or NPH because of too low concentrations. Further examinations have to follow to elucidate the potential sources and the meaning of reduced BDNF levels in the blood in AD and NPH.

New polysaccharide from Nerium indicum protects neurons via stress kinase signaling pathway

Most of the polysaccharides purified from Chinese medicinal herbs showed anti-tumor and immune-stimulating effects. However, little is known about their effects on neuroprotection. Our previous study has demonstrated that polysaccharides (J2, J3 and J4) isolated from the flowers of Nerium indicum (Oleander) exert partial protection in cortical neurons stressed by beta-amyloid (Abeta) peptides or deprivation of nutrition from serum. In this study, we have isolated and characterized a new polysaccharide from the flowers of N. indicum (named as J6) and aimed to investigate its neuroprotective effects against Abeta-induced apoptosis. Pretreatment of the polysaccharide J6 significantly decreased the activity of caspase-3 as well as the cytotoxicity triggered by Abeta peptides in a dose-dependent manner. In contrast to the activation of survival signaling such as Akt found in J2, J3 and J4 fractions, neuroprotective effects of J6 markedly inhibited Abeta peptide-stimulated phosphorylation of c-Jun N-terminal kinase (JNK-1) as determined by Western blot analysis. Taken together, the polysaccharide J6 isolated from the flowers of N. indicum can serve as potential neuroprotective agent against neuronal death in Alzheimer's disease and the neuroprotective mechanism may primarily rely on inactivation of JNK signaling pathway.

Neurochemical characterization of insulin receptor-expressing primary sensory neurons in wild-type and vanilloid type 1 transient receptor potential receptor knockout mice

The insulin receptor (IR) is expressed by a subpopulation of primary sensory neurons (PSN), including a proportion of cells expressing the nociceptive transducer vanilloid type 1 transient receptor potential receptor (TRPV1). Recent data suggest functional links between the IR and other receptors, including TRPV1, which could be involved in the development of PSN malfunctions in pathological insulin secretion. Here we used combined immunohistochemical labelling on sections from L4-5 dorsal root ganglia of wild-type (WT) and TRPV1 knockout (KO) mice to examine the neurochemical properties of IR-expressing PSN and the possible effect of deletion of TRPV1 on those characteristics. We found that antibodies raised against the high-molecular-weight neurofilament (NF-200) and the neurofilament protein peripherin distinguished between small and large neurons. We also found that the IR was expressed predominantly by the small peripherin-immunopositive cells both in the WT and in the KO animals. IR expression, however, did not show any preference between the major subpopulations of the small cells, the calcitonin gene-related peptide (CGRP)-expressing and Bandeiraea simplicifolia isolectin B4 (IB4)-binding neurons, either in the WT or in the KO mice. Nevertheless, a significant proportion of the IR-expressing cells also expressed TRPV1. Comparison of the staining pattern of these markers showed no difference between WT and KO animals. These findings indicate that the majority of the IR-expressing PSN are small neurons, which are considered as nociceptive cells. Furthermore, these data show that deletion of the TRPV1 gene does not induce any additional changes in neurochemical phenotype of nociceptive PSN.

Activation of protein kinase B/Akt in the periphery contributes to pain behavior induced by capsaicin in rats

Protein kinase B (PKB/Akt) is a member of the second-messenger regulated subfamily of protein kinases. It is implicated in signaling downstream of growth factors, insulin receptor tyrosine kinases and phosphoinositide 3-kinase (PI3K). Current studies indicate that nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and PI3K help mediate inflammatory hyperalgesia. However, little is known about the role of PKB/Akt in the nociceptive system. In this study, we investigated whether PKB/Akt in primary sensory neurons is activated after noxious stimulation and contributes to pain behavior induced in rats by capsaicin. We demonstrated that phospho-PKB/Akt (p-PKB/Akt) is increased in dorsal root ganglia (DRG) at 5 min after intradermal injection of capsaicin. p-PKB/Akt is distributed predominantly in small- and medium-sized DRG cells. After capsaicin injection, p-PKB/Akt (473) is colocalized with isotectin-B4 (IB4), tyrosine kinase A (TrkA), and calcitonin gene-related peptide (CGRP). Furthermore, most transient receptor potential vanilloid type 1 (TRPV1) positive DRG neurons double label for p-PKB/Akt. Behavioral experiments show that intradermal injection of a PI3K (upstream of PKB/Akt) inhibitor, wortmannin, dose-dependently inhibits the changes in exploratory behavior evoked by capsaicin injection. The PKB/Akt inhibitor, Akt inhibitor IV, has the same effect. The results suggest that the PKB/Akt signaling pathway in the periphery is activated by noxious stimulation and contributes to pain behavior.

Neuroprotection of insulin against oxidative stress-induced apoptosis in cultured retinal neurons: involvement of phosphoinositide 3-kinase/Akt signal pathway

In order to investigate the neuroprotection of insulin in retinal neurons, we used retinal neuronal culture as a model system to study the protective effects of insulin against H2O2-induced cytotoxicity and apoptotic death. Primary retinal neuronal cultures were grown from retinas of 0-2-day old Sprague-Dawley rats. Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide assay. Apoptotic cell death was evaluated by the TdT-mediated digoxigenin-dUTP nick-end labeling assay, and by DNA laddering analysis. Phosphoinositide 3-kinase (PI3K) activity was measured using phosphoinositide 4,5-bisphophate and [gamma-32P]ATP as substrate. Western blot analysis with anti-phospho-Akt (pS473) antibody was performed to examine the level of phosphorylated Akt. We observed that treatment with 100 microM H2O2 for 24 h significantly decreased cell viability and induced apoptotic death of retinal neurons, and that pretreatment with 10 nM insulin significantly inhibited or attenuated H2O2-induced cytotoxicity and apoptosis. Pretreatment with LY294002, a specific PI3K inhibitor, abolished the cytoprotective effect of insulin. Insulin also strongly activated both PI3K and the downstream effector Akt. These results suggest that insulin protects retinal neurons from oxidative stress-induced apoptosis and that the PI3K/Akt signal pathway is involved in insulin-mediated retinal neuroprotection.

Stage-dependent BDNF serum concentrations in Alzheimer’s disease

Alzheimer's disease (AD) is characterized by cognitive decline and loss of neurons in specific brain regions. Recent findings have suggested an involvement of brain-derived neurotrophic factor (BDNF) in the pathogenesis of AD. BDNF is an endogenous protein involved in the maintenance of neuronal function, synaptic plasticity and structural integrity in the adult brain. To our knowledge, the present pilot study assessed for the first time BDNF serum and CSF concentrations in 30 patients with different stages of AD in comparison to 10 age-matched non-demendet controls. AD patients were divided in two groups according to their MMSE score: Group 1 (n = 15) in early stages with MMSE scores >or=21 (mean of 25.5) and Group 2 (n = 15) with more severe stages of dementia with MMSE scores <21 (mean of 13.3). As main results, we found in patients with early stages of probable AD significantly increased BDNF serum concentrations as compared to more severe stages of AD (p < 0.0001) and age-matched healthy controls (p = 0.028). BDNF serum values in all AD patients correlated significantly with MMSE scores (r = 0.486; p < 0.0001). Levels of BDNF were below the detection limit of the assay in unconcentrated CSF samples of AD patients and non-demendet controls.In summary, BDNF serum values are increased in early stages of Alzheimer's disease, which may reflect a compensatory repair mechanism in early neurodegeneration and could also contribute to increased degradation of beta-amyloid (Abeta). During the course of the disease, BDNF is decreasing, which correlates with the severity of dementia. The decrease of BDNF may constitute a lack of trophic support with an increase of Abeta accumulation and thus contribute to progressive degeneration of specific regions in the AD-affected brain. BDNF should be further evaluated as a candidate marker for clinical diagnosis and therapeutic monitoring in Alzheimer's disease.

Continuous exposure to brain-derived neurotrophic factor is required for persistent activation of TrkB receptor, the ERK signaling pathway, and the induction of neuropeptide Y production in cortical cultures

We have previously demonstrated that brain-derived neurotrophic factor (BDNF) induces persistent neuropeptide Y (NPY) production in cortical cultures in an ERK1/2-dependent manner. In some studies, it was shown that BDNF leads to the downregulation of TrkB receptor and some of its downstream responses, whereas in others it does not. We examined whether the BDNF requirement for induction of persistent NPY production correlates with that for induction of phosphorylation of TrkB and ERK1/2. Continuous 24-h exposure to BDNF led to a 2- to 3-fold increase in NPY production (maximal level). While 1 h of BDNF exposure induced NPY production at a half maximal level, 8 h was required for induction of a maximal level. BDNF-induced NPY production was completely inhibited by co-exposure to TrkB-Fc fusion protein (TrkB extracellular domain fused to Fc) and partially inhibited by TrkB-Fc added 1 h after BDNF; TrkC-Fc did not do so. Activation of TrkB receptor was analyzed at two potential tyrosine phosphorylated sites, the activation loop and the Shc binding. BDNF led to coordinated phosphorylation of the two sites that persisted for 6-8 h, and this was not associated with changes in the content of TrkB protein. The presence of BDNF throughout the 6- to 8-h period was required for the persistent phosphorylation of TrkB and ERK1/2. Thus, continuous BDNF activation of TrkB is required for persistent activation of the ERK1/2 pathway and induction of NPY production. We propose that, within the time frame analyzed in this study, BDNF does not lead to the downregulation of TrkB receptor or of the biological responses leading to NPY production.

Glycogen synthase kinase 3beta (GSK3beta) mediates 6-hydroxydopamine-induced neuronal death

The causes of sporadic Parkinson's disease (PD) are poorly understood. 6-Hydroxydopamine (6-OHDA), a PD mimetic, is widely used to model this neurodegenerative disorder in vitro and in vivo; however, the underlying mechanisms remain incompletely elucidated. We demonstrate here that 6-OHDA evoked endoplasmic reticulum (ER) stress, which was characterized by an up-regulation in the expression of GRP78 and GADD153 (Chop), cleavage of procaspase-12, and phosphorylation of eukaryotic initiation factor-2 alpha in a human dopaminergic neuronal cell line (SH-SY5Y) and cultured rat cerebellar granule neurons (CGNs). Glycogen synthase kinase-3 beta (GSK3beta) responds to ER stress, and its activity is regulated by phosphorylation. 6-OHDA significantly inhibited phosphorylation of GSK3beta at Ser9, whereas it induced hyperphosphorylation of Tyr216 with little effect on GSK3beta expression in SH-SY5Y cells and PC12 cells (a rat dopamine cell line), as well as CGNs. Furthermore, 6-OHDA decreased the expression of cyclin D1, a substrate of GSK3beta, and dephosphorylated Akt, the upstream signaling component of GSK3beta. Protein phosphatase 2A (PP2A), an ER stress-responsive phosphatase, was involved in 6-OHDA-induced GSK3beta dephosphorylation (Ser9). Blocking GSK3beta activity by selective inhibitors (lithium, TDZD-8, and L803-mts) prevented 6-OHDA-induced cleavage of caspase-3 and poly(ADP-ribose) polymerase (PARP), DNA fragmentations and cell death. With a tetracycline (Tet)-controlled TrkB inducible system, we demonstrated that activation of TrkB in SH-SY5Y cells alleviated 6-OHDA-induced GSK3beta dephosphorylation (Ser9) and ameliorated 6-OHDA neurotoxicity. TrkB activation also protected CGNs against 6-OHDA-induced damage. Although antioxidants also offered neuroprotection, they had little effect on 6-OHDA-induced GSK3beta activation. These results suggest that GSK3beta is a critical intermediate in pro-apoptotic signaling cascades that are associated with neurodegenerative diseases, thus providing a potential target site amenable to pharmacological intervention.

Ethanol inhibits brain-derived neurotrophic factor-mediated intracellular signaling and activator protein-1 activation in cerebellar granule neurons

Developmental exposure to ethanol causes profound damage to the cerebellum, ranging from aberration in neuronal differentiation to cell loss. As a major neurotrophic factor, brain-derived neurotrophic factor (BDNF) and its receptor TrkB are expressed in the developing, as well as adult, cerebellum. Many neurotrophic effects of BDNF are mediated by gene transcription. We hypothesized that ethanol interfered with BDNF signaling and disrupted BDNF-regulated transcriptional activity. Using a transgenic mouse model expressing an activator protein-1 (AP-1) luciferase reporter construct, we demonstrated that BDNF stimulated AP-1 transactivation in cultured cerebellar granule neurons. This observation was validated by the study using a human neuronal cell line expressing inducible TrkB (TB8 neuroblastoma cells). BDNF induced AP-1 transactivation, as well as increased the binding activity of AP-1 protein complex to a DNA sequence containing AP-1 sites in TB8 cells. BDNF-mediated AP-1 activation was mediated by PI3K/Akt and JNK pathways; BDNF activated Akt and JNKs, and blocking these pathways significantly inhibited BDNF-stimulated AP-1 transactivation. More importantly, ethanol inhibited BDNF-mediated activation of PI3K/Akt and JNKs, and blocked BDNF-stimulated AP-1 activation. Since ethanol did not affect either the expression or autophosphorylation of TrkB, it could be concluded that the site of ethanol action was downstream of TrkB. The present study establishes that this AP-1 reporter transgenic mouse model is valuable for assessing AP-1 activity in the CNS neurons. Our results provide an insight into molecular mechanism(s) of ethanol action.

G protein-coupled chemokine receptors induce both survival and apoptotic signaling pathways

Chemokine receptors are essential for triggering chemotaxis to immune cells; however, a number of them can also mediate death when engaged by nonchemokine ligands. When the chemokine receptor CXCR4 is engaged by stromal cell-derived factor (SDF1)alpha, it triggers cells to chemotax, and in some cell types such as neurons, causes cell death. To elucidate this dual and opposing receptor function, we have investigated whether CXCR4 activation by its chemokine SDF1alpha could lead to the simultaneous activation of both anti- and proapoptotic signaling pathways; the balance ultimately influencing cell survival. CXCR4 activation in CD4 T cells by SDF1alpha led to the activation of the prosurvival second messengers, Akt and extracellular signal-regulated protein kinase. Selective inhibition of each signal demonstrated that extracellular signal-regulated protein kinase is essential for mediating SDF1alpha-triggered chemotaxis but does not confer an antiapoptotic state. In contrast, Akt activation through CXCR4 by SDF1alpha interactions is necessary to confer resistance to apoptosis. The proapoptotic signaling pathway triggered by SDF1alpha-CXCR4 interaction involves the G(ialpha) protein-independent activation of the proapoptotic MAPK (p38). Furthermore, other chemokines and chemokine receptors also signal chemotaxis and proapoptotic effects via similar pathways. Thus, G(ialpha) protein-coupled chemokine receptors can function as death prone receptors and the balance between the above signaling pathways will ultimately mandate the fate of the activated cell.

BDNF-mediated signal transduction is modulated by GSK3beta and mood stabilizing agents

Brain-derived neurotrophic factor (BDNF) is a major neurotrophin in the brain and abnormal regulation of BDNF may contribute to the pathophysiology of mood disorders. In the present study, we examined if alterations in the activity of glycogen synthase kinase-3-beta (GSK3beta) or treatment with mood stabilizers modulated BDNF-mediated signal transduction pathways in differentiated human neuroblastoma SH-SY5Y cells. BDNF increased the phosphorylation of the forkhead transcription factor FKHRL1 through activation of the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway, and the phosphorylation of the cyclic AMP response element binding protein (CREB) through activation of extracellular signal-regulated kinase1/2 (ERK1/2). BDNF also increased serine(9) -phosphorylation of GSK3beta, which inhibits GSK3beta activity. Overexpression of GSK3beta did not affect BDNF-induced phosphorylation of Akt, ERK1/2, or FKHRL1, but abolished CREB phosphorylation induced by BDNF. This inhibition of BDNF-induced CREB phosphorylation in GSK3beta-overexpressing SH-SY5Y cells was blocked by treatment with lithium. In contrast to lithium, sodium valproate and lamotrigine did not affect BDNF-mediated signaling, whereas carbamazepine induced a rapid and prolonged phosphorylation of ERK1/2 and CREB in the absence or the presence of BDNF. Therefore, increased GSK3beta selectively attenuates BDNF-induced CREB phosphorylation, and lithium and carbamazepine can facilitate activation of CREB.

Brain evolution and lifespan regulation: conservation of signal transduction pathways that regulate energy metabolism

Mechanisms for sensing, acquiring, storing and using energy are fundamental to the survival of organisms at all levels of the phylogenetic scale. Single-cell organisms evolved surface receptors that sense an energy source and, via signal transduction pathways that couple the receptors to the cell cytoskeleton move towards the energy source. Mutlicellular organisms evolved under conditions that favored species that developed complex mechanisms for obtaining food, with nervous systems being critical mediators of energy acquisition and regulators of energy metabolism. A conserved signaling system involved in regulating cellular and organismal energy metabolism, and in sensing and responding to energy/food-related environmental signals, involves receptors coupled to the phosphatidylinositol-3-kinase-Akt signaling pathway. Prominent activators of this pathway are insulin, insulin-like growth factors and brain-derived neurotrophic factor (BDNF). Recent studies in diverse organisms including nematodes, flies and rodents have provided evidence that insulin-like signaling in the nervous system can control lifespan, perhaps by modulating stress responses and energy metabolism. Interestingly, the lifespan-extending effect of dietary restriction in rodents is associated with increased BDNF signaling in the brain, and a related increase of peripheral insulin sensitivity, suggesting a mechanism whereby the brain can control lifespan. Thus a prominent evolutionarily conserved function of the nervous system is to regulate food acquisition and energy metabolism, thereby controlling lifespan.

Rapid stimulation of the PI3-kinase/Akt signalling pathway in developing midbrain neurones by oestrogen

Oestrogen promotes the differentiation of neurones in the central nervous system. In the rodent midbrain, the maturation of dopaminergic neurones appears to be under oestrogen control. This is supported by the fact that dopaminergic cells contain nuclear oestrogen receptors-alpha/beta (ER). Second, aromatase is transiently expressed in the developing midbrain. In previous studies, we have shown that oestrogen increases dopamine synthesis and plasticity of dopamine cells. These effects are transmitted through classical nuclear ER but require also the stimulation of nonclassical signalling pathways involving the activation of membrane receptors. This study attempted to identify nonclassical oestrogen-dependent signalling cascades which might be stimulated downstream of membrane ERs. Using cultured mouse midbrain cells, we could demonstrate by Western blotting, that oestrogen rapidly phosphorylates Akt, a kinase which is implicated in the phosphatidylinositol 3 (PI3)-kinase pathway. This effect was only seen in midbrain neurones but not astrocytes. Oestrogen-induced Akt phosphorylation was time- and dose-dependent, showing highest responses after 30 min and at a steroid concentration of 10(-8) and 10(-6) M. Immunocytochemistry for phosphorylated Akt (pAkt) demonstrated that pAkt is predominantly found in a nuclear/perinuclear position and that oestrogen exposure increased the number of pAkt-positive cells. To investigate the mechanisms which are involved in transmitting oestrogen effects on the cellular level, cells were treated with antagonists for distinct signalling pathways. The application of the nuclear ER antagonist ICI 182 780 did not abolish the oestrogen-induced Akt phosphorylation. In contrast, interrupting intracellular calcium signalling with BAPTA completely prevented this effect. The PI3-kinase inhibitor LY294002 also inhibited the activation of Akt by oestrogen. Our study clearly indicates that oestrogen can rapidly stimulate the PI3-kinase/Akt signalling cascade in differentiating midbrain neurones. This effect requires the intermediate activation of calcium-dependent signalling pathways. In conclusion, oestrogen effects in the developing midbrain appear to be connected with the PI3-kinase/Akt signalling mechanism.

Insulin rescues retinal neurons from apoptosis by a phosphatidylinositol 3-kinase/Akt-mediated mechanism that reduces the activation of caspase-3

The ability of insulin to protect neurons from apoptosis was examined in differentiated R28 cells, a neural cell line derived from the neonatal rat retina. Apoptosis was induced by serum deprivation, and the number of pyknotic cells was counted. p53 and Akt were examined by immunoblotting after serum deprivation and insulin treatment, and caspase-3 activation was examined by immunocytochemistry. Serum deprivation for 24 h caused approximately 20% of R28 cells to undergo apoptosis, detected by both pyknosis and activation of caspase-3. 10 nm insulin maximally reduced the amount of apoptosis with a similar potency as 1.3 nm (10 ng/ml) insulin-like growth factor 1, which acted as a positive control. Insulin induced serine phosphorylation of Akt, through the phosphatidylinositol (PI) 3-kinase pathway. Inhibition of PI 3-kinase with wortmannin or LY294002 blocked the ability of insulin to rescue the cells from apoptosis. SN50, a peptide inhibitor of NF-kappaB nuclear translocation, blocked the rescue effect of insulin, but neither insulin or serum deprivation induced phosphorylation of IkappaB. These results suggest that insulin is a survival factor for retinal neurons by activating the PI 3-kinase/Akt pathway and by reducing caspase-3 activation. The rescue effect of insulin does not appear to be mediated by NF-kappaB or p53. These data suggest that insulin provides trophic support for retinal neurons through a PI 3-kinase/Akt-dependent pathway.

Glutaredoxin protects cerebellar granule neurons from dopamine-induced apoptosis by dual activation of the ras-phosphoinositide 3-kinase and jun n-terminal kinase pathways

Glutaredoxin 2 (Grx2) from Escherichia coli protects cerebellar neurons from dopamine-induced apoptosis via nuclear factor kappa B (NF-kappaB) activation, which is mediated by the expression of redox factor-1 (Ref-1). An analysis of the mechanisms underlying Grx2 protective activity revealed dual activation of signal transduction pathways. Grx2 significantly activated the Ras/phosphoinositide 3-kinase/Akt/NF-kappaB cascade in parallel to the Jun N-terminal kinase (JNK)/AP1 cascade. Dopamine, in comparison, down-regulated both pathways. Treatment of neurons with Ref-1 antisense oligonucleotide reduced the ability of Grx2 to activate Akt and AP-1 but had no effect on the phosphorylation of JNK1/2, suggesting that Akt/NF-kappaB and AP-1 are regulated by Ref-1. Exposure of the neurons to JNK1/2 antisense oligonucleotide in the presence of Grx2 significantly reduced AP-1 and NF-kappaB DNA binding activities and abolished Grx2 protection. These results demonstrate that dual activation of Ras/phosphoinositide 3-kinase and AP-1 cascades, which are mediated by Ref-1, is an essential component of the Grx2 mechanism of action.

Role of insulin and insulin receptor in learning and memory

As one of the most extensively studied protein hormones, insulin and its receptor have been known to play key roles in a variety of important biological functions. Until recent years, the functions of insulin and insulin receptor (IR) in the central nervous system (CNS) have largely remained unclear. IR is abundantly expressed in several specific brain regions that govern fundamental behaviors such as food intake, reproduction and high cognition. The IR from the periphery and CNS exhibit differences in both structure and function. In addition to that from the peripheral system, locally synthesized insulin in the brain has also been identified. Accumulated evidence has demonstrated that insulin/IR plays important roles in associative learning, as suggested by results from both interventive and correlative studies. Interruption of insulin production and IR activity causes deficits in learning and memory formation. Abnormal insulin/IR levels and activities are seen in Alzheimer's dementia, whereas administration of insulin significantly improves the cognitive performance of these patients. The synaptic bases for the action of insulin/IR include modifying neurotransmitter release processes at various types of presynaptic terminals and modulating the activities of both excitatory and inhibitory postsynaptic receptors such as NMDA and GABA receptors, respectively. At the molecular level, insulin/IR participates in regulation of learning and memory via activation of specific signaling pathways, one of which is shown to be associated with the formation of long-term memory and is composed of intracellular molecules including the shc, Grb-r/SOS, Ras/Raf, and MEK/MAP kinases. Cross-talk with another IR pathway involving IRS1, PI3 kinase, and protein kinase C, as well as with the non-receptor tyrosine kinase pp60c-src, may also be associated with memory processing.

Developmental mechanisms in the pathogenesis of neurodegenerative diseases

Cellular genes that are mutated in neurodegenerative diseases code for proteins that are expressed throughout neural development. Genetic analysis suggests that these genes are essential for a broad range of normal neurodevelopmental processes. The proteins they code for interact with numerous other cellular proteins that are components of signaling pathways involved in patterning of the neural tube and in regional specification of neuronal subtypes. Further, pathogenetic mutations of these genes can cause progressive, sublethal alterations in the cellular homeostasis of evolving regional neuronal subpopulations, culminating in late-onset cell death. Therefore, as a consequence of the disease mutations, targeted cell populations may retain molecular traces of abnormal interactions with disease-associated proteins by exhibiting changes in a spectrum of normal cellular functions and enhanced vulnerability to a host of environmental stressors. These observations suggest that the normal functions of these disease-associated proteins are to ensure the fidelity and integration of developmental events associated with the progressive elaboration of neuronal subtypes as well as the maintenance of mature neuronal populations during adult life. The ability to identify alterations within vulnerable neuronal precursors present in pre-symptomatic individuals prior to the onset of irrevocable cellular injury may help foster the development of effective therapeutic interventions using evolving pharmacologic, gene and stem cell technologies.

Confocal imaging of the subcellular distribution of phosphatidylinositol 3,4,5-trisphosphate in insulin- and PDGF-stimulated 3T3-L1 adipocytes

The activation of phosphatidylinositol 3-kinase (PI 3-kinase) and production of PtdIns(3,4,5)P(3) is crucial in the actions of numerous extracellular stimuli, including insulin-stimulated glucose uptake. Platelet-derived growth factor (PDGF) also stimulates PI 3-kinase, but only weakly promotes glucose uptake when compared with insulin. Insulin and PDGF have thus been proposed to have differential effects on the subcellular targeting of PI 3-kinase. However, owing to a lack of suitable methodologies, the subcellular localization of the PtdIns(3,4,5)P(3) generated has not been examined. The pleckstrin-homology (PH) domains of the nucleotide exchange factors, ADP-ribosylation factor nucleotide-binding-site opener (ARNO) and general receptor for 3-phosphoinositides (GRP1), which have a high affinity and specificity for PtdIns(3,4,5)P(3), were fused to green fluorescent protein and used to examine the subcellular localization of PtdIns(3,4,5)P(3) generation in living 3T3-L1 adipocytes. PtdIns(3,4,5)P(3) was produced almost exclusively in the plasma membrane in response to both agonists, although the response to insulin was greater in magnitude and occurred in considerably more cells. The results suggest that the greater ability of insulin to stimulate glucose uptake may be the result of its ability to generate significantly more plasma-membrane PtdIns(3, 4,5)P(3) than PDGF. ARNO and GRP1 are nucleotide exchange factors for the small GTP-binding protein ADP-ribosylation factor 6 (ARF6). The inability of a constitutively active GTPase-deficient mutant of ARF6 (ARF6-Q67L; Gln(67)-->Leu) to cause glucose transporter GLUT4 translocation suggests that activation of this pathway is not sufficient to cause GLUT4 translocation.