Basic FGF, NGF, and IGFs protect hippocampal and cortical neurons against iron-induced degeneration

When the Blood Hits Your Brain: The Neurotoxicity of Extravasated Blood

Hemorrhage in the central nervous system (CNS), including intracerebral hemorrhage (ICH), intraventricular hemorrhage (IVH), and aneurysmal subarachnoid hemorrhage (aSAH), remains highly morbid. Trials of medical management for these conditions over recent decades have been largely unsuccessful in improving outcome and reducing mortality. Beyond its role in creating mass effect, the presence of extravasated blood in patients with CNS hemorrhage is generally overlooked. Since trials of surgical intervention to remove CNS hemorrhage have been generally unsuccessful, the potent neurotoxicity of blood is generally viewed as a basic scientific curiosity rather than a clinically meaningful factor. In this review, we evaluate the direct role of blood as a neurotoxin and its subsequent clinical relevance. We first describe the molecular mechanisms of blood neurotoxicity. We then evaluate the clinical literature that directly relates to the evacuation of CNS hemorrhage. We posit that the efficacy of clot removal is a critical factor in outcome following surgical intervention. Future interventions for CNS hemorrhage should be guided by the principle that blood is exquisitely toxic to the brain.

Beyond Trophic Factors: Exploiting the Intrinsic Regenerative Properties of Adult Neurons

Injuries and diseases of the peripheral nervous system (PNS) are common but frequently irreversible. It is often but mistakenly assumed that peripheral neuron regeneration is robust without a need to be improved or supported. However, axonal lesions, especially those involving proximal nerves rarely recover fully and injuries generally are complicated by slow and incomplete regeneration. Strategies to enhance the intrinsic growth properties of reluctant adult neurons offer an alternative approach to consider during regeneration. Since axons rarely regrow without an intimately partnered Schwann cell (SC), approaches to enhance SC plasticity carry along benefits to their axon partners. Direct targeting of molecules that inhibit growth cone plasticity can inform important regenerative strategies. A newer approach, a focus of our laboratory, exploits tumor suppressor molecules that normally dampen unconstrained growth. However several are also prominently expressed in stable adult neurons. During regeneration their ongoing expression “brakes” growth, whereas their inhibition and knockdown may enhance regrowth. Examples have included phosphatase and tensin homolog deleted on chromosome ten (PTEN), a tumor suppressor that inhibits PI3K/pAkt signaling, Rb1, the protein involved in retinoblastoma development, and adenomatous polyposis coli (APC), a tumor suppressor that inhibits β-Catenin transcriptional signaling and its translocation to the nucleus. The identification of several new targets to manipulate the plasticity of regenerating adult peripheral neurons is exciting. How they fit with canonical regeneration strategies and their feasibility require additional work. Newer forms of nonviral siRNA delivery may be approaches for molecular manipulation to improve regeneration.

Mechanisms of Endogenous Neuroprotective Effects of Astrocytes in Brain Injury

Astrocytes, once believed to serve only as "glue" for the structural support of neurons, have been demonstrated to serve critical functions for the maintenance and protection of neurons, especially under conditions of acute or chronic injury. There are at least seven distinct mechanisms by which astrocytes protect neurons from damage; these are (1) protection against glutamate toxicity, (2) protection against redox stress, (3) mediation of mitochondrial repair mechanisms, (4) protection against glucose-induced metabolic stress, (5) protection against iron toxicity, (6) modulation of the immune response in the brain, and (7) maintenance of tissue homeostasis in the presence of DNA damage. Astrocytes support these critical functions through specialized responses to stress or toxic conditions. The detoxifying activities of astrocytes are essential for maintenance of the microenvironment surrounding neurons and in whole tissue homeostasis. Improved understanding of the mechanisms by which astrocytes protect the brain could lead to the development of novel targets for the development of neuroprotective strategies.

Delayed histochemical alterations within the neurovascular unit due to transient focal cerebral ischemia and experimental treatment with neurotrophic factors

Current stroke therapy is focused on recanalizing strategies, but neuroprotective co-treatments are still lacking. Modern concepts of the ischemia-affected neurovascular unit (NVU) and surrounding penumbra emphasize the complexity during the transition from initial damaging to regenerative processes. While early treatment with neurotrophic factors was shown to result in lesion size reduction and blood-brain barrier (BBB) stabilization, cellular consequences from these treatments are poorly understood. This study explored delayed cellular responses not only to ischemic stroke, but also to an early treatment with neurotrophic factors. Rats underwent 60 minutes of focal cerebral ischemia. Fluorescence labeling was applied to sections from brains perfused 7 days after ischemia. Analyses focused on NVU constituents including the vasculature, astrocytes and microglia in the ischemic striatum, the border zone and the contralateral hemisphere. In addition to histochemical signs of BBB breakdown, a strong up-regulation of collagen IV and microglia activation occurred within the ischemic core with simultaneous degradation of astrocytes and their endfeet. Activated astroglia were mainly depicted at the border zone in terms of a glial scar formation. Early treatment with pigment epithelium-derived factor (PEDF) resulted in an attenuation of the usually up-regulated collagen IV-immunoreactivity. However, glial activation was not influenced by treatment with PEDF or the epidermal growth factor (EGF). In conclusion, these data on ischemia-induced cellular reactions within the NVU might help to develop treatments addressing the transition from injury towards regeneration. Thereby, the integrity of the vasculature in close relation to neighboring structures like astrocytes appears as a promising target.

C6 Glioma-Secreted NGF and FGF2 Regulate Neuronal APP Processing Through Up-Regulation of ADAM10 and Down-Regulation of BACE1, Respectively

Excessive accumulation of amyloid-β (Aβ) caused by cleavage of amyloid precursor protein (APP) is thought to be the primary cause of Alzheimer's disease (AD). Two key enzymes ADAM10 and BACE1 are involved in the initial cleavage of APP, resulting in the onset of two pathways, the amyloidogenic pathway and the non-amyloidogenic pathway, respectively. Altering APP metabolism towards the non-amyloidogenic pathway is thought to reduce Aβ production. It has been reported that, in vivo, exogenous neurotrophic factors make APP apt to entering the non-amyloidogenic pathway. Since astrocytes secrete a battery of neurotrophic factors, we investigated the role of astrocyte-derived factors in the dynamics of Aβ generation in neural cells. Results show that C6 glioma cell-conditioned medium (GCM), obtained from cultured astrocyte-derived C6 glioma cells, inhibit Aβ1-42 production and shift APP processing towards the non-amyloidogenic pathway in APPswe-HEK293 cells. Such effect is attributed to two key APP cleavage enzymes, ADAM10 and BACE1. Two neurotrophic factors in the GCM, nerve growth factor and fibroblast growth factor 2, are responsible for the up-regulation of ADAM10 and down-regulation of BACE1, respectively. Our findings enhance our understanding of the relationship between astrocytes and Aβ generation, indicating that stimulation of astrocytic neurotrophic factors could slow AD progression.

bFGF in the CSF and serum of sALS patients

OBJECTIVES

Amyotrophic lateral sclerosis is a fatal neurodegenerative disease characterized by selective motor neuron loss in the brain and spinal cord. The cause of this selective death of motor neurons is still unclear, but among several pathomechanisms that have been discussed, the loss of neurotrophic factors is one hypothesis. Basic fibroblast growth factor 2 (bFGF) may be a potential neurotrophic factor for slowing various neurodegenerative diseases, but its potential role in the prognosis of ALS is not known.

METHODS

To explore the role of bFGF in ALS, we investigated changes in bFGF in the CSF and serum from patients with sALS and from the control group. Furthermore, we analyzed the correlations between bFGF, disease duration, disease progression rate, ALSFRS-r score and survival.

RESULTS

The level of bFGF increased in both the CSF and serum in sALS patients. It was higher in patients with longer durations. It was negatively correlated with disease progression rates, especially in the later stages of sALS, but showed no linear correlation with ALSFRS-r. In an analysis of the relationship between bFGF and survival, we found that sALS patients with high levels of bFGF had significantly higher cumulative survival rates than patients with low levels of bFGF.

DISCUSSION AND CONCLUSION

In conclusion, endogenous bFGF increased both in the CSF and serum of sALS patients and it may be a useful biomarker that could predict disease progression and survival.

Developmental and activity-dependent expression of LanCL1 confers antioxidant activity required for neuronal survival

Production of reactive oxygen species (ROS) increases with neuronal activity that accompanies synaptic development and function. Transcription-related factors and metabolic enzymes that are expressed in all tissues have been described to counteract neuronal ROS to prevent oxidative damage. Here, we describe the antioxidant gene LanCL1 that is prominently enriched in brain neurons. Its expression is developmentally regulated and induced by neuronal activity, neurotrophic factors implicated in neuronal plasticity and survival, and oxidative stress. Genetic deletion of LanCL1 causes enhanced accumulation of ROS in brain, as well as development-related lipid, protein, and DNA damage; mitochondrial dysfunction; and apoptotic neurodegeneration. LanCL1 transgene protects neurons from ROS. LanCL1 protein purified from eukaryotic cells catalyzes the formation of thioether products similar to glutathione S-transferase. These studies reveal a neuron-specific glutathione defense mechanism that is essential for neuronal function and survival.

Neurovascular protection by targeting early blood-brain barrier disruption with neurotrophic factors after ischemia-reperfusion in rats*

The 'new penumbra' concept imbues the transition between injury and repair at the neurovascular unit with profound implications for selecting the appropriate type and timing of neuroprotective interventions. In this conceptual study, we investigated the protective effects of pigment epithelium-derived factor (PEDF) and compared them with the properties of epidermal growth factor (EGF) in a rat model of ischemia-reperfusion injury. We initiated a delayed intervention 3 hours after reperfusion using equimolar amounts of PEDF and EGF. These agents were then administered intravenously for 4 hours following reperfusion after 1 hour of focal ischemia. Magnetic resonance imaging indices were characterized, and imaging was performed at multiple time points post reperfusion. PEDF and EGF reduced lesion volumes at all time points as observed on T2-weighted images (T2-LVs). In addition PEDF selectively attenuated lesion volume expansion at 48 hours after reperfusion and persistently modulated blood-brain barrier (BBB) permeability at all time points. Intervention with peptides is suspected to cause edema formation at distant regions. The observed T2-LV reduction and BBB modulation by these trophic factors is probably mediated through a number of diverse mechanisms. A thorough evaluation of neurotrophins is still necessary to determine their time-dependent contributions against injury and their modulatory effects on repair after stroke.

Metabolic reserve as a determinant of cognitive aging

Mild cognitive impairment (MCI) and Alzheimer's disease (AD) represent points on a continuum of cognitive performance in aged populations. Cognition may be impaired or preserved in the context of brain aging. One theory to account for memory maintenance in the context of extensive pathology involves 'cognitive reserve', or the ability to compensate for neuropathology through greater recruitment of remaining neurons. In this review, we propose a complementary hypothesis of 'metabolic reserve', where a brain with high metabolic reserve is characterized by the presence of neuronal circuits that respond adaptively to perturbations in cellular and somatic energy metabolism and thereby protects against declining cognition. Lifestyle determinants of metabolic reserve, such as exercise, reduced caloric intake, and intake of specific dietary components can promote neuroprotection, while pathological states arising from sedentary lifestyles and excessive caloric intake contribute to neuronal endangerment. This bidirectional relationship between metabolism and cognition may be mediated by alterations in central insulin and neurotrophic factor signaling and glucose metabolism, with downstream consequences for accumulation of amyloid-β and hyperphosphorylated tau. The metabolic reserve hypothesis is supported by epidemiological findings and the spectrum of individual cognitive trajectories during aging, with additional data from animal models identifying potential mechanisms for this relationship. Identification of biomarkers for metabolic reserve could assist in generating a predictive model for the likelihood of cognitive decline with aging.

Efficient cultivation of neural stem cells with controlled delivery of FGF-2

Neural stem cells (NSCs) raised the hope for cell-based therapies in human neurodevelopmental and neurodegenerative diseases. Current research strategies aim to isolate, enrich, and propagate homogeneous populations of neural stem cells. Unfortunately, several concerns with NSC cultures currently may limit their therapeutic promise. Exhaustion of growth factors and/or their uncontrolled release with burst and fall in their concentration may greatly affect the in vitro behavior of NSCs. In this context, we investigate whether a device containing heparan sulfate (HS), which is a co-factor in growth factor-mediated cell proliferation and differentiation, could potentiate and prolong the delivery of fibroblast growth factor-2 (FGF-2) and thus improve in vitro NSC cultivation. We demonstrated that NSCs cultivated in media with a controlled release of FGF-2 from a polyelectrolyte polymer showed a higher proliferation rate, and reduced apoptosis and senescence. In these experimental conditions NSCs preserve their stemness properties for a longer period of time compared with controls. Also of interest is that cell fate properties are conserved as well. The controlled release of FGF-2 reduced the level of oxidative stress and this is associated with a lower level of damaged DNA. This result may explain the reduced level of senescence and apoptosis in NSCs cultivated in the presence of hydrogel-releasing FGF-2.

Exercise-induced cognitive plasticity, implications for mild cognitive impairment and Alzheimer's disease

Lifestyle factors such as intellectual stimulation, cognitive and social engagement, nutrition, and various types of exercise appear to reduce the risk for common age-associated disorders such as Alzheimer’s disease (AD) and vascular dementia. In fact, many studies have suggested that promoting physical activity can have a protective effect against cognitive deterioration later in life. Slowing or a deterioration of walking speed is associated with a poor performance in tests assessing psychomotor speed and verbal fluency in elderly individuals. Fitness training influences a wide range of cognitive processes, and the largest positive impact observed is for executive (a.k.a. frontal lobe) functions. Studies show that exercise improves additional cognitive functions such as tasks mediated by the hippocampus, and result in major changes in plasticity in the hippocampus. Interestingly, this exercise-induced plasticity is also pronounced in APOE ε4 carriers who express a risk factor for late-onset AD that may modulate the effect of treatments. Based on AD staging by Braak and Braak (1991) and Braak et al. (1993) we propose that the effects of exercise occur in two temporo-spatial continua of events. The “inward” continuum from isocortex (neocortex) to entorhinal cortex/hippocampus for amyloidosis and a reciprocal “outward” continuum for neurofibrillary alterations. The exercise-induced hypertrophy of the hippocampus at the core of these continua is evaluated in terms of potential for prevention to stave off neuronal degeneration. Exercise-induced production of growth factors such as the brain-derived neurotrophic factor (BDNF) has been shown to enhance neurogenesis and to play a key role in positive cognitive effects. Insulin-like growth factor (IGF-1) may mediate the exercise-induced response to exercise on BDNF, neurogenesis, and cognitive performance. It is also postulated to regulate brain amyloid β (Aβ) levels by increased clearance via the choroid plexus. Growth factors, specifically fibroblast growth factor and IGF-1 receptors and/or their downstream signaling pathways may interact with the Klotho gene which functions as an aging suppressor gene. Neurons may not be the only cells affected by exercise. Glia (astrocytes and microglia), neurovascular units and the Fourth Element may also be affected in a differential fashion by the AD process. Analyses of these factors, as suggested by the multi-dimensional matrix approach, are needed to improve our understanding of this complex multi-factorial process, which is increasingly relevant to conquering the escalating and intersecting world-wide epidemics of dementia, diabetes, and sarcopenia that threaten the global healthcare system. Physical activity and interventions aimed at enhancing and/or mimicking the effects of exercise are likely to play a significant role in mitigating these epidemics, together with the embryonic efforts to develop cognitive rehabilitation for neurodegenerative disorders.

Therapeutic time window for the neuroprotective effects of NGF when administered after focal cerebral ischemia

In the present study, we evaluated the neuroprotection time window for nerve growth factor (NGF) after ischemia/reperfusion brain injury in rabbits as related to this anti-apoptosis mechanism. Male New Zealand rabbits were subjected to 2 h of middle cerebral artery occlusion (MCAO), followed by 70 h of reperfusion. NGF was administered after injury to evaluate the time window. Neurological deficits, infarct volume, neural cell apoptosis and expressions of caspase-3 and Bcl-2 were measured. Compared to saline-treated control, NGF treatment at 2, 3 and 5 h after MCAO significantly reduced infarct volume, neural cell apoptosis and expression of caspase-3 (P < 0.01), up-regulated the expression of Bcl-2 and improved functional recovery (P < 0.01). However, treatment at latter time points did not produce significant neuroprotection. Neuroprotection treatment with NGF provides an extended time window of up to 5 h after ischemia/reperfusion brain injury, in part by attenuating the apoptosis.

Neuroprotection signaling pathway of nerve growth factor and brain-derived neurotrophic factor against staurosporine induced apoptosis in hippocampal H19-7/IGF-IR [corrected]

Neurotrophins protect neurons against excitotoxicity; however the signaling mechanisms for this protection remain to be fully elucidated. Here we report that activation of the phosphatidyl inositol 3 kinase (PI3K)/Akt pathway is critical for protection of hippocampal cells from staurosporine (STS) induced apoptosis, characterized by nuclear condensation and activation of the caspase cascade. Both nerve growth factor (NGF) and brain-derived growth factor (BDNF) prevent STS-induced apoptotic morphology and caspase-3 activity by upregulating phosphorylation of the tropomyosin receptor kinase (Trk) receptor. Inhibition of Trk receptor by K252a altered the neuroprotective effect of both NGF and BDNF whereas inhibition of the p75 neurotrophin receptor (p75NTR) had no effect. Impairment of the PI3K/Akt pathway or overexpression of dominant negative (DN)-Akt abolished the protective effect of both neurotrophins, while active Akt prevented cell death. Moreover, knockdown of Akt by si-RNA was able to block the survival effect of both NGF and BDNF. Thus, the survival action of NGF and BDNF against STS-induced neurotoxicity was mediated by the activation of PI3K/Akt signaling through the Trk receptor.

Edaravone and carnosic acid synergistically enhance the expression of nerve growth factor in human astrocytes under hypoxia/reoxygenation

Edaravone is a brain-penetrant free radical scavenger that is known to ameliorate postischemic neuronal dysfunction. The transcription factor Nrf2 plays an important role in the coordinated expression of stress-inducible genes. Here we examined the effects of edaravone and carnosic acid (CA), an Nrf2-inducer, on the expression of nerve growth factor (NGF) in human astrocytes exposed to hypoxia/reoxygenation. Cultured astrocytes were exposed to hypoxia for up to 4.5 h and then treated with edaravone and/or CA under normoxia (reoxygenation) for up to 72 h. Edaravone (∼1 mM) and CA (∼50 μM) treatment synergistically enhanced NGF expression. Nrf2 knockdown by siRNA and the inhibition of JNK (c-Jun N-terminal kinase) by SP600125 decreased both CA-induced NGF expression and Nrf2 nuclear accumulation and suppressed their synergistic effect on NGF expression. In contrast, the MEK (mitogen-activated protein kinase/extracellular signal-regulated kinase kinase) inhibitor U0126 suppressed the synergism without inhibiting CA-induced NGF expression. These results suggest that the synergistic effects of CA and edaravone depend, at least partially, on JNK-dependent Nrf2 accumulation (induced by CA) and on MEK-dependent pathways (induced by edaravone). We conclude that the use of edaravone and CA in combination may have therapeutic potential in the treatment of brain damage, particularly ischemia/reperfusion injury.

Expression and Functions of Fibroblast Growth Factor 2 (FGF-2) in Hippocampal Formation

Among the 23 members of the fibroblast growth factor (FGF) family, FGF-2 is the most abundant one in the central nervous system. Its impact on neural cells has been profoundly investigated by in vitro and in vivo studies as well as by gene knockout analyses during the past 2 decades. Key functions of FGF-2 in the nervous system include roles in neurogenesis, promotion of axonal growth, differentiation in development, and maintenance and plasticity in adulthood. From a clinical perspective, its prominent role for the maintenance of lesioned neurons (e.g., ischemia and following transection of fiber tracts) is of particular relevance. In the unlesioned brain, FGF-2 is involved in synaptic plasticity and processes attributed to learning and memory. The focus of this review is on the expression of FGF-2 and its receptors in the hippocampal formation and the physiological and pathophysiological roles of FGF-2 in this region during development and adulthood.

Molecular genetic approaches to understanding the roles and regulation of iron in brain health and disease

Iron is essential in the brain, yet too much iron can be toxic. Tight regulation of iron in the brain may involve intrinsic mechanisms that control internal homeostasis independent of systemic iron status. Iron abnormalities occur in various neurological disorders, usually with symptoms or neuropathology associated with movement impairment or behavioral disturbances rather than cognitive impairment or dementia. Consistent with this, polymorphisms in the HFE gene, associated with the iron overload disorder hemochromatosis, show stronger associations with the movement disorder amyotrophic lateral sclerosis (motor neuron disease) than with cognitive impairment. Such associations may arise because certain brain regions involved in movement or executive control are particularly iron-rich, notably the basal ganglia, and may be highly reliant on iron. Various mechanisms, including iron redistribution causing functional iron deficiency, lysosomal and mitochondrial abnormalities or oxidative damage, could underlie iron-related neuropathogenesis. Clarifying how iron contributes causatively to neurodegeneration may improve treatment options in a range of neurodegenerative disorders. This review considers how modern molecular genetic approaches can be applied to resolve the complex molecular systems and pathways by which brain iron homeostasis is regulated and the molecular changes that occur with iron dyshomeostasis and neuropathogenesis.

Ginsenoside Rb(1) prevents image navigation disability, cortical infarction, and thalamic degeneration in rats with focal cerebral ischemia

Oral administration of red ginseng powder before but not after transient forebrain ischemia prevents delayed neuronal death in gerbils. One neuroprotective molecule within red ginseng powder is ginsenoside Rb(1). The mechanism of action(s) of ginsenoside Rb(1) remains to be determined. We performed intracerebroventricular infusion of 0.6 microg/d ginsenoside Rb(1) before or after permanent occlusion of the left middle cerebral artery in stroke-prone spontaneous hypertensive rats. Ginsenoside Rb(1) significantly decreased escape latency on repeated trials of the Morris water maze test, throughout the first to fourth trial days at 2 and 4 weeks after MCA occlusion (P<.05, P<.01 or P<.001). The ratio of the infarcted area to the left hemispheric area in the groups treated with 0.6 microg/d of ginsenoside Rb(1) was significantly smaller than that in the saline-treated ischemic group (P<.05 or P<.001). The continuous infusion of ginsenoside Rb(1) (0.06 microg/d) was less effective and the other doses examined were ineffective in ameliorating ischemia-induced image navigation disability and reducing cortical infarct size. There were significant differences in neuron numbers in the ventroposterior thalamic nucleus and in the left-to-right ratio of the thalamic area between the saline-infused ischemic group and the ginsenoside Rb(1)-treated ischemic group (P<.05 or P<.01). Moreover, ginsenoside Rb(1) at concentrations of 0.1 to 100 fg/mL (0.09 to 90 fM), facilitated neurite extension and rescued cortical neurons from lethal damage caused by the free radical-promoting agent FeSO(4), in vitro (P<.05 or P<.01). These findings suggest that ginsenoside Rb(1) protects the cerebral cortex against lethal ischemic damage possibly by acting as a neurotrophic factor-like agent and by scavenging free radicals, which are overproduced in situ during and after brain ischemia. The final link between the in vivo neuroprotective action and the in vitro neurotrophic and antioxidant activities of ginsenoside Rb(1) remains to be determined.

Long-term cultivation of a neuroblastoma cell line in medium with reduced serum content as a model system for neuronal aging?

Impaired energy metabolism and increased vulnerability to additional stress are some of the pivotal characteristics of the aging brain. This study was designed to establish a cell culture model for long-term investigations of some mechanisms underlying the process of aging using the neuroblastoma cell line SK-N-MC. As high serum concentrations in the culture medium are a major disadvantage for the investigation of regulatory or toxic influences, the effects of serum reduction in the culture medium on growth, viability and energy metabolism during long-term cultivation were determined. Serum reduction resulted in a decrease in the proliferation rate and in increased vulnerability of the cells, measured as release of lactate dehydrogenase into the culture medium. The rates of glucose consumption and lactate production were elevated, whereas the energetic state was markedly compromised, as was obvious from a 40% reduction of creatine phosphate. The observed increased vulnerability and the decreased energy state of the SK-N-MC cells were even more pronounced after induction of free radicals by addition of FeSO(4) to the medium with reduced serum content. Increased oxidative stress was indicated by elevated cellular contents of glutathione both after serum reduction and after incubation with FeSO(4). It is concluded that the SK-N-MC cells cultured chronically in medium with low serum content display biochemical characteristics that are similar to those observed in aging studies with animal models.

Edaravone improves the expression of nerve growth factor in human astrocytes subjected to hypoxia/reoxygenation

Edaravone (MCI-186, 3-methyl-1-phenyl-2-pyrazolin-5-one), a free radical scavenger, is known to ameliorate postischemic neuronal dysfunction. Nerve growth factor (NGF) is essential for neuronal growth and survival. We have addressed the effect of edaravone on the NGF expression in astrocytes exposed to hypoxia/reoxygenation. Normal human astrocytes in culture were incubated under hypoxia for 3h and then treated with edaravone under normal culture condition for up to 72h. The levels of NGF mRNA were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) or real-time quantitative PCR and NGF protein levels were measured by enzyme-linked immunosorbent assay (ELISA). Edaravone enhanced, in time- and concentration-dependent manners, the expressions of NGF mRNA and protein in astrocytes under reoxygenation condition. After the treatment for 72h, 1mmol/L edaravone enhanced the levels of NGF protein in astrocyte-conditioned media by 1.7-fold of the control. An inhibitor of c-Jun N-terminal kinase (JNK) suppressed the effect of edaravone on the NGF expression, and cellular levels of phospho-JNK were increased in response to edaravone. We conclude that edaravone enhances, via the JNK pathway, NGF expression in astrocytes. This agent may exert a neurotrophic effect in the therapy of brain injury in ischemia/reperfusion.

Amitriptyline is a TrkA and TrkB receptor agonist that promotes TrkA/TrkB heterodimerization and has potent neurotrophic activity

Neurotrophins, the cognate ligands for the Trk receptors, are homodimers and induce Trk dimerization through a symmetric bivalent mechanism. We report here that amitriptyline, an antidepressant drug, directly binds TrkA and TrkB and triggers their dimerization and activation. Amitriptyline, but not any other tricyclic or selective serotonin reuptake inhibitor antidepressants, promotes TrkA autophosphorylation in primary neurons and induces neurite outgrowth in PC12 cells. Amitriptyline binds the extracellular domain of both TrkA and TrkB and promotes TrkA-TrkB receptor heterodimerization. Truncation of amitriptyline binding motif on TrkA abrogates the receptor dimerization by amitriptyline. Administration of amitriptyline to mice activates both receptors and significantly reduces kainic acid-triggered neuronal cell death. Inhibition of TrkA, but not TrkB, abolishes amitriptyline's neuroprotective effect without impairing its antidepressant activity. Thus, amitriptyline acts as a TrkA and TrkB agonist and possesses marked neurotrophic activity.

Adenine nucleotide translocator 1 deficiency increases resistance of mouse brain and neurons to excitotoxic insults

The mitochondrial adenine nucleotide translocators (Ant) are bi-functional proteins that transport ADP and ATP across the mitochondrial inner membrane, and regulate the mitochondrial permeability transition pore (mtPTP) which initiates apoptosis. The mouse has three Ant isoforms: Ant1 expressed in heart, muscle, and brain; Ant2 expressed in all tissues but muscle; and Ant4 expressed primarily in testis. Ant1-deficient mice manifest muscle and heart but not brain pathology. Brain Ant1 is induced by stress, while Ant2 is not. Ant1-deficient mice are resistant to death induced by systemic exposure to the brain excitotoxin, kainic acid (KA), and their hippocampal and cortical neurons are significantly more resistant to neuronal death induced by glutamate, KA, and etoposide. The mitochondrial membrane potential of Ant1-deficient brain mitochondria is increased and the mtPTP is more resistance to Ca(++) induced permeability transition. Hence, Ant1-deficiency may protect the brain from excitotoxicity by desensitizing the mtPTP and by blocking the pro-apoptotic induction of Ant1 by stress.

Growth factor signals in neural cells: coherent patterns of interaction control multiple levels of molecular and phenotypic responses

Individual neurons express receptors for several different growth factors that influence the survival, growth, neurotransmitter phenotype, and other properties of the cell. Although there has been considerable progress in elucidating the molecular signal transduction pathways and physiological responses of neurons and other cells to individual growth factors, little is known about if and how signals from different growth factors are integrated within a neuron. In this study, we determined the interactive effects of nerve growth factor, insulin-like growth factor 1, and epidermal growth factor on the activation status of downstream kinase cascades and transcription factors, cell survival, and neurotransmitter production in neural cells that express receptors for all three growth factors. We document considerable differences in the quality and quantity of intracellular signaling and eventual phenotypic responses that are dependent on whether cells are exposed to a single or multiple growth factors. Dual stimulations that generated the greatest antagonistic or synergistic actions, compared with a theoretically neutral summation of their two activities, yielded the largest eventual change of neuronal phenotype indicated by the ability of the cell to produce norepinephrine or resist oxidative stress. Combined activation of insulin-like growth factor 1 and epidermal growth factor receptors was particularly notable for antagonistic interactions at some levels of signal transduction and norepinephrine production, but potentiation at other levels of signaling and cytoprotection. Our findings suggest that in true physiological settings where multiple growth factors are present, activation of one receptor type may result in molecular and phenotypic responses that are different from that observed in typical experimental paradigms in which cells are exposed to only a single growth factor at a time.

Acrylamide: a dietary carcinogen formed in vivo?

Acrylamide, a chemical formed during heating of human foods, reacts with N-terminal valine in hemoglobin (Hb) and forms stable reaction products (adducts). These adducts to N-terminal valine in Hb have been used to estimate daily intake of acrylamide. Daily intake of acrylamide estimated from Hb adduct levels was higher than daily intake estimated from dietary questionnaires, possibly indicating other sources of exposures. Therefore, in this study the possible endogenous formation of acrylamide was investigated by treating mice with FeSO 4, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-hydrochloric acid (MPTP), or methamphetamine (METH). Acrylamide Hb adducts were determined, and a significant increase ( p < 0.05) in acrylamide Hb adduct levels was observed 24 h following treatment with FeSO 4 and 72 h following treatment with MPTP or METH. The results of this study show that acrylamide Hb adduct levels are increased in mice treated with compounds known to induce free radicals, thus suggesting the endogenous production of acrylamide.

IGF-1 signaling reduces neuro-inflammatory response and sensitivity of neurons to MPTP

Reduced expression of IGF-1R increases lifespan and resistance to oxidative stress in the mouse, raising the possibility that this also confers relative protection against the pro-parkinsonian neurotoxin MPTP, known to involve an oxidative stress component. We used heterozygous IGF-1R(+/-) mice and challenged them with MPTP. Interestingly, MPTP induced more severe lesions of dopaminergic neurons of the substantia nigra, in IGF-1R(+/-) mice than in wild-type animals. Using electron spin resonance, we found that free radicals were decreased in IGF-1R(+/-) mice in comparison with controls, both before and after MPTP exposure, suggesting that the increased vulnerability of dopamine neurons is not caused by oxidative stress. Importantly, we showed that IGF-1R(+/-) mice display a dramatically increased neuro-inflammatory response to MPTP that may ground the observed increase in neuronal death. Microarray analysis revealed that oxidative stress-associated genes, but also several anti-inflammatory signaling pathways were downregulated under control conditions in IGF-1R(+/-) mice compared to WT. Collectively, these data indicate that IGF signaling can reduce neuro-inflammation dependent sensitivity of neurons to MPTP.

Gambogic amide, a selective agonist for TrkA receptor that possesses robust neurotrophic activity, prevents neuronal cell death

Nerve growth factor (NGF) binds to TrkA receptor and triggers activation of numerous signaling cascades, which play critical roles in neuronal plasticity, survival, and neurite outgrowth. To mimic NGF functions pharmacologically, we developed a high-throughput screening assay to identify small-molecule agonists for TrkA receptor. The most potent compound, gambogic amide, selectively binds to TrkA, but not TrkB or TrkC, and robustly induces its tyrosine phosphorylation and downstream signaling activation, including Akt and MAPKs. Further, it strongly prevents glutamate-induced neuronal cell death and provokes prominent neurite outgrowth in PC12 cells. Gambogic amide specifically interacts with the cytoplasmic juxtamembrane domain of TrkA receptor and triggers its dimerization. Administration of this molecule in mice substantially diminishes kainic acid-triggered neuronal cell death and decreases infarct volume in the transient middle cerebral artery occlusion model of stroke. Thus, gambogic amide might not only establish a powerful platform for dissection of the physiological roles of NGF and TrkA receptor but also provide effective treatments for neurodegenerative diseases and stroke.

Electroacupuncture regulates TRPM7 expression through the trkA/PI3K pathway after cerebral ischemia-reperfusion in rats

Recently, it was demonstrated that TRPM7 is an essential mediator of anoxia-induced neuronal death. Meanwhile, nerve growth factor (NGF) is known to have survival and neuroprotective effects by interacting with the high affinity neurotrophin receptor, tropomyosin-related kinase A (trkA). In the present study, we found that electroacupuncture (EA) treatment could up-regulate trkA expression after focal cerebral ischemia in rats. At the same time, EA therapy obviously decreased the high expression of TRPM7 induced by ischemia. Using K252a to inhibit trkA, we found that the EA-mediated down-regulation of TRPM7 was significantly suppressed in rats subjected to cerebral ischemia. TrkA can utilize two distinct signaling pathways: the phosphatidylinositol 3-kinase (PI3K) pathway and the extracellular signal-related kinase (ERK) pathway. We found that the effect of EA on TRPM7 was also inhibited by a PI3K inhibitor, while an ERK inhibitor had no effect. Taken together, our findings suggest that EA can reverse the ischemia-induced increase of TRPM7 levels through the trkA-PI3K pathway.

Brain Iron Toxicity: Differential Responses of Astrocytes, Neurons, and Endothelial Cells

Iron accumulation or iron overload in brain is commonly associated with neurodegenerative disorders such as Parkinson's and Alzheimer's diseases, and also plays a role in cellular damage following hemorrhagic stroke and traumatic brain injury. Despite the brain's highly regulated system for iron utilization and metabolism, these disorders often present following disruptions within iron metabolic pathways. Such dysregulation allows saturation of proteins involved in iron transport and storage, and may cause an increase in free ferrous iron within brain leading to oxidative damage. Not only do astrocytes, neurons, and brain endothelial cells serve unique purposes within the brain, but their individual cell types are equipped with distinct protective mechanisms against iron-induced injury. This review evaluates iron metabolism within the brain under homeostatic and pathological conditions and focuses on the mechanism(s) of brain cellular iron toxicity and differential responses of astrocytes, neurons, and brain vascular endothelial cells to excessive free iron.

Long-term gene expression changes in the cortex following cortical ischemia revealed by transcriptional profiling

Cerebral ischemia evokes changes in gene expression time-dependently after the ischemic event. Most studies on transcriptional changes following ischemia have centered on relatively early postischemic time points, and detected multiple genes relevant to neuronal cell death. However, functional outcome after ischemia depends critically on adaptations of the postischemic brain. Plasticity may derive from network-inherent changes, or from the formation of new nerve cells in the CNS. We have screened for gene expression changes up to 3 weeks following a limited photothrombotic cortical insult in the rat sensorimotor cortex by using the sensitive restriction-mediated differential display (RMDD) technique. A high number of genes were detected as induced at early or intermediate time points in the ipsi- and contralateral cortex (6 and 48 h). Unexpectedly, at the late time point examined (3 weeks), we still detected 40 genes that were changed in their expression. We further characterized the expression of two genes linked to neurogenesis (nestin and stathmin), and two genes likely involved in reconfiguring neuronal networks (semaphorin VIa and synaptotagmin IV). Conclusively, our data highlight the degree of long-term transcriptional changes in the cortex after ischemia, and provide insight into functional pathways of relevance for compensatory recovery mechanisms in neural networks.

A transient treatment of hippocampal neurons with alpha-tocopherol induces a long-lasting protection against oxidative damage via a genomic action

Neuroprotection exerted by alpha-tocopherol against oxidative stress was investigated in cultured rat hippocampal neurons. In addition to its direct action as a radical scavenger revealed at concentrations above 10 microM, a transient application of 1 microM alpha-tocopherol phosphate (alpha-TP) to neurons induced a complete delayed long-lasting protection against oxidative insult elicited by exposure to Fe2+ ions, but not against excitotoxicity. A minimal 16-h application of alpha-TP was required to observe the protection against subsequent oxidative stress. This delayed protection could last up to a week after the application of alpha-TP, even when medium was changed after the alpha-TP treatment. Cycloheximide, added either 2 h before or together with alpha-TP, prevented the delayed neuroprotection, but not the acute. However, cycloheximide applied after the 16-h alpha-TP pretreatment did not alter the delayed neuroprotection. Neither Trolox, a cell-permeant analogue of alpha-tocopherol, nor other antioxidants, such as epigallocatechin-gallate and N-acetyl-L-cysteine, elicited a similar long-lasting protection. Only tert-butylhydroquinone could mimic the alpha-TP effect. Depletion of glutathione (GSH) by L-buthionine sulfoximine did not affect the delayed alpha-TP protection. Thus, in addition to its acute anti-radical action, alpha-TP induces a long-lasting protection of neurons against oxidative damage, via a genomic action on antioxidant defenses apparently unrelated to GSH biosynthesis.

Cardiotrophin-1 protects cortical neuronal cells against free radical-induced injuries in vitro

Cardiotrophin-1 (CT-1) was initially defined as a mediator of cardiomyocyte hypertrophy. Additional studies have showed that CT-1 enhanced survival of differentiated cardiac muscle cells and inhibited cardiac myocyte apoptosis after serum deprivation or cytokine stimulation. Moreover, CT-1 has recently been shown to act as a neuroregulatory cytokine in the peripheral nervous system. However, its effects in the central nervous system have not been determined. In the present study, we evaluated whether CT-1 protects cultured cortical neurons against oxidative injuries caused by the hydroxyl radical-producing agent FeSO4 and by the peroxynitrite-producing agent 3-morpholinosydnonimine (SIN-1). CT-1 reduced neuronal cell death caused by FeSO4 and also attenuated the neurotoxic effect of SIN-1 in a dose-dependent manner. These results indicate that CT-1 is neuroprotective in an in vitro model of cerebral ischemia. This study indicates that further evaluation of CT-1 in acute brain injury should be investigated in vivo.

Insulin neuroprotection against oxidative stress in cortical neurons--involvement of uric acid and glutathione antioxidant defenses

In this study we investigated the effect of insulin on neuronal viability and antioxidant defense mechanisms upon ascorbate/Fe2+-induced oxidative stress, using cultured cortical neurons. Insulin (0.1 and 10 microM) prevented the decrease in neuronal viability mediated by oxidative stress, decreasing both necrotic and apoptotic cell death. Moreover, insulin inhibited ascorbate/Fe2+-mediated lipid and protein oxidation, thus decreasing neuronal oxidative stress. Increased 4-hydroxynonenal (4-HNE) adducts on GLUT3 glucose transporters upon exposure to ascorbate/Fe2+ were also prevented by insulin, suggesting that this peptide can interfere with glucose metabolism. We further analyzed the influence of insulin on antioxidant defense mechanisms in the cortical neurons. Oxidative stress-induced decreases in intracellular uric acid and GSH/GSSG levels were largely prevented upon treatment with insulin. Inhibition of phosphatidylinositol-3-kinase (PI-3K) or mitogen-induced extracellular kinase (MEK) reversed the effect of insulin on uric acid and GSH/GSSG, suggesting the activation of insulin-mediated signaling pathways. Moreover, insulin stimulated glutathione reductase (GRed) and inhibited glutathione peroxidase (GPx) activities under oxidative stress conditions, further supporting that insulin neuroprotection was related to the modulation of the glutathione redox cycle. Thus, insulin may be useful in preventing oxidative stress-mediated injury that occurs in several neurodegenerative disorders.

Neuroprotective role of neurotrophins: Relationship between nerve growth factor and apoptotic cell survival pathway after cerebral ischemia

Neurotrophins provide a neuroprotective effect in a variety of brain diseases. Recent reports demonstrate that neurotrophins play an important role in the regulation of apoptotic neuronal cell death and in the relationship between this machinery and activation of cell survival pathways. The cascade reactions of the two major cell survival pathways, mitogen-activated protein kinase and phosphatidylinositol 3-kinase, are known to play a critical role in the regulation of apoptotic neuronal cell survival pathways. Neurotrophins such as nerve growth factor regulate these two cell survival pathways in in vitro studies. However, the role of neurotrophins in cell survival remains unclear in in vivo apoptotic neuronal cell death. We discuss the mechanism of neuroprotection by neurotrophins and also discuss cell survival effect of nerve growth factor on apoptotic neuronal cell death after in vivo cerebral ischemia.

Platelet-activating factor enhances the expression of nerve growth factor in normal human astrocytes under hypoxia

Nerve growth factor (NGF) is required for the survival of neurons. We have addressed the effect of platelet-activating factor (PAF), one of the mediators of ischemic injury of the brain, on NGF expression in astrocytes. Normal human astrocytes in culture were stimulated with PAF, and levels of NGF mRNA and protein were analyzed by reverse transcription-polymerase chain reaction (RT-PCR), real-time quantitative PCR and enzyme-linked immunosorbent assay (ELISA). PAF increased the expressions of NGF mRNA and protein in astrocytes in time- and concentration-dependent manners. After 48-h stimulation, 10 nmol/L PAF increased the levels of NGF protein in astrocyte-conditioned medium by 1.4-fold. The PAF-induced stimulation of NGF expression was further enhanced (2.1-fold of the control) in the cells under hypoxic culture condition. BN52021 (Ginkgolide B), an antagonist for PAF binding sites, suppressed the effect of PAF. We conclude that PAF enhances NGF gene expression in human astrocytes, and the PAF-induced increase in the expression of NGF under hypoxia may benefit the protection of the nervous tissue by promoting neuronal survival.

Pathogenic factors in vascular dementia and Alzheimer's disease. Multiple actions of heparin that probably are beneficial

The following areas are discussed in this review: atherogenesis; cerebrovascular factors; hypoperfusion; beta-amyloid production; beta-amyloid fibril formation; beta-sheets; metal cations; reactive oxygen species/free radicals; chronic inflammatory factors; endogenous plasma heparin; lipoprotein lipase; polyamines; protein kinase C; casein kinases; phospholipase A2; serine proteases; myeloperoxidase; cyclooxygenase 2; cysteine proteases; caspases; proprotein convertases; aspartic proteases; cyclin proteinases; thrombin; tau hyperphosphorylation; advanced glycosylation end products; activator protein 1; calcium; apolipoprotein E epsilon4; histamine; blood-brain barrier; glutamate; transglutaminase; insulin-like growth factor 1.

The amyloid paradox: amyloid-beta-metal complexes can be neurotoxic and neuroprotective

Senile plaques in the brains of people with Alzheimer disease (AD) are primarily composed of the amyloid-beta (Abeta) peptide and contain substantially elevated levels of iron, copper and zinc. These metals bind to Abeta and have been reported to increase the toxicity of Abeta to cultured neurones. Other reports have demonstrated that Abeta can reduce the neurotoxicity of metal ions, suggesting that the interaction can, under some circumstances, be protective. To investigate these apparently conflicting results, human Abeta1-42 was co-injected with iron, copper or zinc (at the concentrations found in plaques) into rat cerebral cortex, and the resulting numbers of dying neurones were compared. It was found that Abeta complexed with either iron or zinc was more toxic than Abeta alone. In contrast, Abeta-copper complexes were not neurotoxic. Surprisingly, we observed that when iron or copper were combined with Abeta, the neurotoxicity of these metals was substantially reduced, suggesting that Abeta may help to limit the toxicity of redox-active metal ions, thereby assisting the antioxidant defence of the brain. Thus paradoxical effects occur when Abeta complexes with metal ions, where Abeta-metal complexes are capable of being neurotoxic and neuroprotective.

Microglia-derived tumor necrosis factor-α exaggerates death of newborn hippocampal progenitor cells in vitro

Production of new hippocampal neurons continues in adult mammals and different brain insults can significantly increase this process. However, many hippocampal progenitor cells (HPC) die shortly after birth. Here we investigated the possibility that increased release of cytokines by activated microglia contributes to the death of HPC. We showed that addition of tumor necrosis factor-alpha (TNFalpha) to the medium of a cultured HPC line (HiB5) shortly after the cells stopped division causes significant apoptotic cell death. Conditioned medium from an activated microglial cell line (BV-2) had a similar effect, though conditioned medium from nonactivated microglia increased the survival of HPC. Reverse transcription-PCR indicated that HPC and microglial cells express both TNF receptors, TNF-R1 and TNF-R2. Coculturing of HPC with activated microglial cells aggravated death of hippocampal progenitors and also caused death of microglial cells themselves. Our data indicate that activated microglia-released TNFalpha might be an important contributor in inflammation-induced exaggeration of death of newly formed HPC in the adult brain after an insult.

Deposition of amyloid fibrils promotes cell-surface accumulation of amyloid β precursor protein

Amyloid beta protein (Abeta) deposition and neuronal degeneration are characteristic pathological features of Alzheimer's disease (AD). In vitro, Abeta fibrils (fAbeta) induce neuronal degeneration reminiscent to AD, but the mechanism of neurotoxicity is unknown. Here we show that amyloid fibrils increase the level of cell-surface full-length amyloid beta precursor protein (h-AbetaPP) and secreted AbetaPP (s-AbetaPP). Pulse-chase analysis indicated that fAbeta selectively inhibited the turnover of cell-surface AbetaPP, without altering its intracellular levels. FAbeta-induced AbetaPP accumulation was not abrogated by cycloheximide, suggesting that increased protein synthesis is not critically required. Abeta fibrils sequester s-AbetaPP from the culture medium and promote its accumulation at the cell surface, indicating that binding of Abeta fibrils mediates AbetaPP accumulation. A time course analysis of Abeta treatment showed that AbetaPP level is elevated before significant cell death can be detected, while other toxic insults do not augment AbetaPP level, suggesting that AbetaPP may be specifically involved in early stages of Abeta-induced neurodegeneration. Finally, Abeta fibrils promote clustering of h-AbetaPP in abnormal focal adhesion-like (FA-like) structures that mediate neuronal dystrophy, increasing its association with the cytoskeleton. These results indicate that the interaction of Abeta fibrils with AbetaPP is an early event in the mechanism of Abeta-induced neurodegeneration that may play a significant role in AD pathogenesis.

The role of iron neurotoxicity in ischemic stroke

Stroke is the second leading cause of death worldwide, and its incidence is expected to rise with the projected increase in the number of aging population. Disturbances of brain iron homeostasis have been linked to acute neuronal injury following cerebral ischemia. Free iron catalyzes the conversion of superoxide and hydrogen peroxide into hydroxyl radicals, which promote oxidative stress leading to subsequent cell death/apoptosis. In recent years, considerable evidence has emerged regarding the role of iron neurotoxicity following experimental cerebral ischemia. Few clinical studies have also attempted to investigate the role of iron in stroke patients. The present review will examine the currently available evidence for iron-mediated neurotoxicity and the potential mechanisms underlying deregulation of iron homeostasis in the brain following cerebral ischemia. Understanding the changes in brain iron metabolism and its relationship to neuronal injury in ischemic stroke could provide new therapeutic targets to improve the outcome of stroke patients.

The tyrosine phosphatase inhibitor orthovanadate mimics NGF-induced neuroprotective signaling in rat hippocampal neurons

Activation of the high affinity neurotrophin receptor tropomyosin-related kinase A (TrkA) by nerve growth factor (NGF) leads to phosphorylation of intracellular tyrosine residues of the receptor with subsequent activation of signaling pathways involved in neuronal survival such as the phosphoinositide-3-kinase (PI3-K)/protein kinase B (PKB/Akt) pathway and the mitogen-activated protein kinase (MAPK) cascade. In the present study, we tested whether inhibition of protein-tyrosine phosphatases (PTP) by orthovanadate could enhance tyrosine phosphorylation of TrkA thereby stimulating NGF-like survival signaling in embryonic hippocampal neurons. We found that the PTP inhibitor orthovanadate (1 microM) enhanced TrkA phosphorylation and protected neurons against staurosporine (STS)-induced apoptosis in a time-and concentration-dependent manner. Inhibition of PTP enhanced TrkA phosphorylation also in the presence of NGF antibodies indicating that NGF binding to TrkA was not required for the effects of orthovanadate. Moreover, orthovanadate enhanced phosphorylation of Akt and the MAPK Erk1/2 suggesting that the signaling pathways involved in the protective effect were similar to those activated by NGF. Accordingly, inhibition of PI3-K by wortmannin and MAPK-kinase (MEK) inhibition by UO126 abolished the neuroprotective effects. In conclusion, the results indicate that orthovanadate mimics the effect of NGF on survival signaling pathways in hippocampal neurons. Thus, PTP inhibition appears to be an appropriate strategy to trigger neuroprotective signaling pathways downstream of neurotrophin receptors.

Adventures in neural plasticity, aging, and neurodegenerative disorders aboard the CWC beagle

This article recounts some of the scientific endeavors of Carl W. Cotman (CWC) during his journeys through the cellular circuitry of the mammalian brain. I have selected for consideration his findings that have been an important impetus for my own research; in several cases our different experiments have provided complementary data to support an hypothesis. Three examples are (i) Carl's studies of the roles of glutamate in synaptic transmission and plasticity in the adult brain and my studies of how glutamate regulates neurite outgrowth and cell survival in brain development; (ii) his and our studies of the mechanisms whereby amyloid beta-peptide damages and kills neurons; and (iii) Carl's evidence that physical activity regulates neurotrophin levels in the brain and our evidence that dietary restriction has similar effects and is neuroprotective. In case you have not yet realized how I chose a title for this article it is because Carl has a (very distant) connection with Charles Darwin-Darwin sailed on a vessel called the Beagle and Carl has studied beagle dogs, establishing them as a model for understanding the neurobiology of human brain aging.

Forebrain-specific neuronal inhibition of nuclear factor-kappaB activity leads to loss of neuroprotection

The transcription factor Rel/nuclear factor (NF)-kappaB is known for its fundamental role in regulating immune and inflammatory responses. In the brain, constitutive NF-kappaB activity has been detected exclusively in neurons, and a large diversity of stimuli have been reported to induce NF-kappaB activity. Yet the function of this transcription factor in the nervous system remains unclear, and its role in neuroprotection or neurodegeneration is open to debate. Recently it was suggested that kappaB-driven gene expression in neurons is controlled by Sp1-like factors. To clarify such controversy, we have characterized here a novel mouse model in which the entire NF-kappaB-dependent transcriptional response is abolished in the forebrain. Calcium-calmodulin-dependent kinase II alpha promoter-driven tetracycline transactivator was used for regulated expression of a transdominant negative mutant of inhibitor kappaBalpha (super-repressor) together with a green fluorescent protein tracer. Inhibition of expression of a kappaB-dependent lacZ transgene was shown in triple transgenic mice, which correlated with the loss of kappaB-specific DNA binding. In transgenic organotypic hippocampal slice cultures, expression of the super-repressor led to strong cell death after neurotoxic insults. These data demonstrate for the first time that neuron-restricted ablation of NF-kappaB-driven gene expression increases neurodegeneration. This might lead to the path for new treatments of neurodegenerative diseases.

Neurotrophic factor effects on oxidative stress-induced neuronal death

Neurotrophic factors have been shown to potentiate necrotic neuronal death in cortical cultures. In this study we characterized the death induced by various oxidative insults and tested the effects of neurotrophic factors on that death. Treatment with fibroblast growth factor-2, neurotrophin-4, or insulin-like growth factor-1 potentiated neuronal cell death induced by iron-citrate (Fe) or buthionine sulfoximine (BSO), but not ethacrynic acid (EA). Neuronal death induced by each insult was blocked by the free radical scavenger, trolox. An analysis of the death indicated that Fe and BSO induced necrotic cell death, while EA induced apoptotic cell death. BSO and EA caused decreased cellular glutathione levels, whereas Fe had no effect on glutathione levels. Neurotrophic factors had no effect on the changes in glutathione. The results indicate that oxidative insults can induce either apoptotic or necrotic death and that the effects of neurotrophic factors are dependent on the type of cell death.

Nerve growth factor survival signaling in cultured hippocampal neurons is mediated through TrkA and requires the common neurotrophin receptor P75

The role of the common neurotrophin receptor p75 (p75NTR) in neuronal survival and cell death remains controversial. On the one hand, p75NTR provides a positive modulatory influence on nerve growth factor (NGF) signaling through the high affinity neurotrophin receptor TrkA, and hence increases NGF survival signaling. However, p75NTR may also signal independently of TrkA, causing cell death or cell survival, depending on the cell type and stage of development. Here we demonstrate that TrkA is expressed in primary cultures of hippocampal neurons and is activated by NGF within 10 min of exposure. In primary hippocampal cultures neuroprotection by NGF against glutamate toxicity was mediated by NF-kappaB and accompanied by an increased expression of neuroprotective NF-kappaB target genes Bcl-2 and Bcl-xl. In mouse hippocampal cells lacking p75NTR (p75NTR-/-) activation of TrkA by NGF was not detectable. Moreover, neuroprotection by NGF against glutamate toxicity was abolished in p75NTR-/- neurons, and the expression of bcl-2 and bcl-xl was markedly reduced as compared to wildtype cells. NGF increased TrkA phosphorylation in hippocampal neurons and provided protection that required phosphoinositol-3-phosphate (PI3)-kinase activity and Akt phosphorylation, whereas the mitogen-activated protein kinases (MAPK), extracellular-regulated kinases (Erk) 1/2, were not involved. P75NTR signaling independent of TrkA, such as increased neutral sphingomyelinase (NSMase) activity causing enhanced levels of ceramide, were not detected after exposure of hippocampal neurons to NGF. Interestingly, inhibition of sphingosine-kinase blocked the neuroprotective effect of NGF, suggesting that sphingosine-1-phosphate was also involved in NGF-mediated survival in our cultured hippocampal neurons. Overall, our results indicate an essential role for p75NTR in supporting NGF-triggered TrkA signaling pathways mediating neuronal survival in hippocampal neurons.

Up-regulation of cDK5/p35 by oxidative stress in human neuroblastoma IMR-32 cells

Cdk5, a member of the cyclin-dependent kinase (cdk) family, is predominantly active in neurons, where its activity is tightly regulated by the binding of its neuronal activators p35 and p39. Cdk5 is implicated in regulating the proper neuronal function; a deregulation of cdk5 has been found associated with Alzheimer's disease and amyotrophic lateral sclerosis. As oxidative stress products have been seen co-localized with pathological hallmarks of neurodegenerative diseases, we studied the effect of oxidative stress on the cdk5 enzyme in human neuroblastoma IMR-32 cells. We evaluated the effects of 4-hydroxynonenal and Ascorbate plus FeSO(4) on cdk5 activity and on the expression of cdk5 and p35 proteins. We report here that oxidative stress stimulates cdk5 activity and induces an upregulation of its regulatory and catalytic subunit expression in IMR-32 vital cells, showing that the cdk5 enzyme is involved in the signaling pathway activated by oxidative stress.