Phosphatidylinositol-3-OH kinase regulatory subunits are differentially expressed during development of the rat cerebellum

Developing Novel Experimental Models of m-TORopathic Epilepsy and Related Neuropathologies: Translational Insights from Zebrafish

The mammalian target of rapamycin (mTOR) is an important molecular regulator of cell growth and proliferation. Brain mTOR activity plays a crucial role in synaptic plasticity, cell development, migration and proliferation, as well as memory storage, protein synthesis, autophagy, ion channel expression and axonal regeneration. Aberrant mTOR signaling causes a diverse group of neurological disorders, termed 'mTORopathies'. Typically arising from mutations within the mTOR signaling pathway, these disorders are characterized by cortical malformations and other neuromorphological abnormalities that usually co-occur with severe, often treatment-resistant, epilepsy. Here, we discuss recent advances and current challenges in developing experimental models of mTOR-dependent epilepsy and other related mTORopathies, including using zebrafish models for studying these disorders, as well as outline future directions of research in this field.

Targeting PI3K-AKT/mTOR signaling in the prevention of autism

PI3K-AKT/mTOR signaling pathway represents an essential signaling mechanism for mammalian enzyme-related receptors in transducing signals or biological processes such as cell development, differentiation, cell survival, protein synthesis, and metabolism. Upregulation of the PI3K-AKT/mTOR signaling pathway involves many human brain abnormalities, including autism and other neurological dysfunctions. Autism is a neurodevelopmental disorder associated with behavior and psychiatric illness. This research-based review discusses the functional relationship between the neuropathogenic factors associated with PI3K-AKT/mTOR signaling pathway. Ultimately causes autism-like conditions associated with genetic alterations, neuronal apoptosis, mitochondrial dysfunction, and neuroinflammation. Therefore, inhibition of the PI3K-AKT/mTOR signaling pathway may have an effective therapeutic value for autism treatment. The current review also summarizes the involvement of PI3K-AKT/mTOR signaling pathway inhibitors in the treatment of autism and other neurodegenerative disorders.

Intergenerational transmission of the positive effects of physical exercise on brain and cognition

Physical exercise has positive effects on cognition, but very little is known about the inheritance of these effects to sedentary offspring and the mechanisms involved. Here, we use a patrilineal design in mice to test the transmission of effects from the same father (before or after training) and from different fathers to compare sedentary- and runner-father progenies. Behavioral, stereological, and whole-genome sequence analyses reveal that paternal cognition improvement is inherited by the offspring, along with increased adult neurogenesis, greater mitochondrial citrate synthase activity, and modulation of the adult hippocampal gene expression profile. These results demonstrate the inheritance of exercise-induced cognition enhancement through the germline, pointing to paternal physical activity as a direct factor driving offspring's brain physiology and cognitive behavior.

PI3K Signaling in Neurons: A Central Node for the Control of Multiple Functions

Phosphoinositide 3-kinase (PI3K) signaling contributes to a variety of processes, mediating many aspects of cellular function, including nutrient uptake, anabolic reactions, cell growth, proliferation, and survival. Less is known regarding its critical role in neuronal physiology, neuronal metabolism, tissue homeostasis, and the control of gene expression in the central nervous system in healthy and diseased states. The aim of the present work is to review cumulative evidence regarding the participation of PI3K pathways in neuronal function, focusing on their role in neuronal metabolism and transcriptional regulation of genes involved in neuronal maintenance and plasticity or on the expression of pathological hallmarks associated with neurodegeneration.

Changes in phosphatidylinositol 3-kinase 55 kDa gamma expression and subcellular localization may be caspase 6 dependent in paraquat-induced SH-SY5Y apoptosis

The neurotoxin paraquat (PQ) causes apoptosis of dopaminergic neurons in mammalian cell culture and animal models, mimicking an important pathological feature of Parkinson's disease (PD). The phosphoinositide 3-kinase (PI3K)/Akt pathway is critical for several major survival signals in central nervous system neurons. Phosphatidylinositol 3-kinase 55 kDa gamma (p55PIK) is a regulatory subunit of PI3Ks with important roles in cell proliferation, antiapoptosis, and cell cycle progression. However, p55PIK involvement in mechanisms regarding progression and maintenance of neurodegenerative diseases is largely undetermined. We used PQ-induced apoptosis in human dopaminergic SH-SY5Y cells to investigate the association between p55PIK expression levels, subcellular location, and apoptosis. p55PIK expression was reduced in SH-SY5Y cells and p55PIK messenger RNA and protein expression levels were decreased after PQ treatment. Apoptosis induced by PQ was associated with caspase activation and decreased p55PIK expression. Restoration of p55PIK expression was observed after coincubation with a caspase inhibitor. Overexpressed full-length p55PIK in SH-SY5Y and human embryonic kidney 293 cells showed specific distribution in the nucleus and was cleaved in vitro by recombinant caspase 6 (C6), but not C3 and C7. A p55PIK construct lacking 24 N-terminal amino acids (N24) was tested for the presence of a potential C6-recognizable sequence and was found to express its proteins outside the nucleus. The results suggest that p55PIK may be involved in PQ-induced apoptosis signal transduction and that N24 is crucial for p55PIK subcellular localization. Thus, p55PIK could be a substrate of activated C6 during apoptosis, leading to loss of original biological functions and redistribution to disturb cell cycle progression.

The Phosphatidylinositol 3-Kinase/mTor Pathway as a Therapeutic Target for Brain Aging and Neurodegeneration

Many pathological conditions are associated with phosphatidylinositol 3-kinase (PI3K) dysfunction, providing an incentive for the study of the effects of PI3K modulation in different aspects of diabetes, cancer, and aging. The PI3K/AKT/mTOR pathway is a key transducer of brain metabolic and mitogenic signals involved in neuronal proliferation, differentiation, and survival. In several models of neurodegenerative diseases associated with aging, the PI3K/AKT pathway has been found to be dysregulated, suggesting that two or more initiating events may trigger disease formation in an age-related manner. The search for chemical compounds able to modulate the activity of the PI3K/AKT/mTOR pathway is emerging as a potential therapeutic strategy for the treatment and/or prevention of some metabolic defects associated with brain aging. In the current review, we summarize some of the critical actions of PI3K in brain function as well as the evidence of its involvement in aging and Alzheimer's disease.

Blockade of insulin-like growth factor-I has complex effects on structural plasticity in the hippocampus

Physical exercise enhances adult neurogenesis in the hippocampus. Running induces the uptake of blood insulin-like growth factor-I (IGF-I) into the brain. A causal link between these two phenomena has been reported; running-induced increases in adult neurogenesis can be blocked by peripheral infusion of anti-IGF-I. Running also alters other aspects of hippocampal structure, including dendritic spine density. It remains unclear, however, whether these effects are also mediated through an IGF-I mechanism. To examine this possibility, we blocked peripheral IGF-I and examined adult neurogenesis and dendritic spine density in treadmill running mice. Two weeks of running resulted in an increase in cell proliferation in the dentate gyrus (DG) as well as an increase in dendritic spine density on DG granule cells and basal dendrites of CA1 pyramidal neurons, while having no effect on apical or basal dendritic spine density of CA3 pyramidal neurons. IGF-I blockade reduced cell proliferation in both sedentary and running mice, but by contrast, this treatment had no effect on granule cell or CA3 pyramidal cell dendritic spine density in sedentary or running mice. However, IGF-I antibody treatment seemed to prevent the running-induced increase in spine density on basal dendrites of CA1 pyramidal cells. These results suggest that IGF-I exerts a complex influence over hippocampal structure and that its effects are not restricted to those induced by running.

Exercise modulates insulin-like growth factor 1-dependent and -independent effects on adult hippocampal neurogenesis and behaviour

While physical exercise clearly has beneficial effects on the brain, fomenting neuroprotection as well as promoting neural plasticity and behavioural modifications, the cellular and molecular mechanisms mediating these effects are not yet fully understood. We have analyzed sedentary and exercised animals to examine the effects of activity on behaviour (spatial memory and anxiety--as measured by a fear/exploration conflict test), as well as on adult hippocampal neurogenesis (a well-known form of neural plasticity). We have found that the difference in activity between sedentary and exercised animals induced a decrease in the fear/exploration conflict scores (a measure usually accepted as an anxiolytic effect), while no changes are evident in terms of spatial memory learning. The short-term anxiolytic-like effect of exercise was IGF1-dependent and indeed, the recall of hippocampus-dependent spatial memory is impaired by blocking serum IGF1 (as observed by measuring serum IGF levels in the same animals used to analyze the behaviour), irrespective of the activity undertaken by the animals. On the other hand, activity affected neurogenesis as reflected by counting the numbers of several cell populations, while the dependence of this effect on IGF1 varied according to the differentiation state of the new neurons. Hence, while proliferating precursors and postmitotic immature neurons (measured by means of doublecortin and calretinin) are influenced by serum IGF1 levels in both sedentary and exercised animals, premitotic immature neurons (an intermediate stage) respond to exercise independently of serum IGF1. Therefore, we conclude that physical exercise has both serum IGF1-independent and -dependent effects on neural plasticity. Furthermore, several effects mediated by serum IGF1 are induced by physical activity while others are not (both in terms of behaviour and neural plasticity). These findings help to delimit the role of serum IGF1 as a mediator of the effects of exercise, as well as to extend the role of serum IGF1 in the brain in basal conditions. Moreover, these data reveal the complexity of the interaction between neurogenesis, behaviour, and IGF1 under different levels of physical activity.

The neurodevelopmental implications of PI3K signaling

Our understanding of the mechanisms involved in the formation of the complex arrangement of neurons and their interconnections within the brain has made significant progress in recent years. Current research has uncovered a network of intracellular signaling events that provide precise coordination of a diverse array of cellular responses, including trafficking events, cytoskeletal remodeling, gene transcription, and protein ubiquitination and translation. This chapter considers the specific cellular responses controlled by the phosphatidylinositol 3-kinase (PI3K) signaling pathway, which is instructive with regard to a number of important steps involved in the development of the brain. These range from the mediation of extrinsic signals - such as growth factors, axon guidance cues, and extracellular matrix components - to intrinsic effectors, such as downstream signaling components that act, for example, at the translation level. PI3K signaling is, consequently, at the heart of controlling neuronal migration and neuronal morphogenesis, as well as dendrite and synapse development. Many neurobehavioral disorders arise as a consequence of subtle developmental abnormalities. Unsurprisingly, therefore, aberrant PI3K signaling has been indicated by many studies to be a contributing factor to the pathophysiology of disorders such as schizophrenia and autism. In this chapter, we will focus on the specific, yet divergent, cellular processes that are achieved through PI3K signaling in neurons and are key to brain development.

The insulin-like growth factor family: molecular mechanisms, redox regulation, and clinical implications

Insulin-like growth factor (IGF)-induced signaling networks are vital in modulating multiple fundamental cellular processes, such as cell growth, survival, proliferation, and differentiation. Aberrations in the generation or action of IGF have been suggested to play an important role in several pathological conditions, including metabolic disorders, neurodegenerative diseases, and multiple types of cancer. Yet the exact mechanism involved in the pathogenesis of these diseases by IGFs remains obscure. Redox pathways involving reactive oxygen species (ROS) and reactive nitrogen species (RNS) contribute to the pathogenetic mechanism of various diseases by modifying key signaling pathways involved in cell growth, proliferation, survival, and apoptosis. Furthermore, ROS and RNS have been demonstrated to alter IGF production and/or action, and vice versa, and thereby have the ability to modulate cellular functions, leading to clinical manifestations of diseases. In this review, we provide an overview on the IGF system and discuss the potential role of IGF-1/IGF-1 receptor and redox pathways in the pathophysiology of several diseases.

PI3K signaling effects in hypothalamic neurons mediated by estrogen

Multiple mechanisms mediate the effects of estrogen in the central nervous system, including signal transduction pathways such as protein kinase A, protein kinase C, and phosphatidylinositol 3-kinase (PI3K) pathways. Previously we demonstrated that estrogen regulates a number of PI3K-related genes in the hypothalamus, including the PI3K p55gamma regulatory subunit. We hypothesized that PI3K activation is critical for the effects of estrogen and that the p55gamma subunit may be more prevalent than the p85alpha regulatory subunit in the hypothalamus. Therefore, in the present study, we compared the mRNA distribution of the p55gamma and p85alpha regulatory subunits by using in situ hybridization in guinea pig. Expression level of p55gamma mRNA was greater than p85alpha in most hypothalamic nuclei. Twenty-four hours of estrogen treatment increased p55gamma mRNA expression in the paraventricular, suprachiasmatic, arcuate, and ventromedial nuclei, and little or no change was observed for p85alpha mRNA. Quantitative real-time PCR confirmed the in situ hybridization results. Next, we investigated the general role of PI3K signaling in the estrogen-mediated changes of arcuate proopiomelanocortin (POMC) neuronal excitability by using whole-cell recording. One cellular mechanism by which estrogen increases neuronal excitability is to desensitize (uncouple) gamma-aminobutyric acid type B (GABA(B)) receptors from their G-protein-gated inwardly rectifying K(+) channels in hypothalamic neurons. We found that the PI3K inhibitors wortmannin and LY294002 significantly reduced the estrogen-mediated GABA(B) receptor desensitization in POMC arcuate neurons, suggesting that PI3K signaling is a critical downstream mediator of the estrogen-mediated rapid effects. Collectively, these data suggest that the interplay between estrogen and PI3K occurs at multiple levels, including transcriptional and membrane-initiated signaling events that ultimately lead to changes in homeostatic function.

The effects of exercise on spatial learning and anxiety-like behavior are mediated by an IGF-I-dependent mechanism related to hippocampal neurogenesis

Knowledge about the effects of physical exercise on brain is accumulating although the mechanisms through which exercise exerts these actions remain largely unknown. A possible involvement of adult hippocampal neurogenesis (AHN) in the effects of exercise is debated while the physiological and pathological significance of AHN is under intense scrutiny. Recently, both neurogenesis-dependent and independent mechanisms have been shown to mediate the effects of physical exercise on spatial learning and anxiety-like behaviors. Taking advantage that the stimulating effects of exercise on AHN depend among others, on serum insulin-like growth factor I (IGF-I), we now examined whether the behavioral effects of running exercise are related to variations in hippocampal neurogenesis, by either increasing or decreasing it according to serum IGF-I levels. Mutant mice with low levels of serum IGF-I (LID mice) had reduced AHN together with impaired spatial learning. These deficits were not improved by running. However, administration of exogenous IGF-I ameliorated the cognitive deficit and restored AHN in LID mice. We also examined the effect of exercise in LID mice in the novelty-suppressed feeding test, a measure of anxiety-like behavior in laboratory animals. Normal mice, but not LID mice, showed reduced anxiety after exercise in this test. However, after exercise, LID mice did show improvement in the forced swim test, a measure of behavioral despair. Thus, many, but not all of the beneficial effects of exercise on brain function depend on circulating levels of IGF-I and are associated to increased hippocampal neurogenesis, including improved cognition and reduced anxiety.

Identification of IGF2 signaling through phosphoinositide-3-kinase regulatory subunit 3 as a growth-promoting axis in glioblastoma

Amplification or overexpression of growth factor receptors is a frequent occurrence in malignant gliomas. Using both expression profiling and in situ hybridization, we identified insulin-like growth factor 2 (IGF2) as a marker for a subset of glioblastomas (GBMs) that lack amplification or overexpression of EGF receptor. Among 165 primary high-grade astrocytomas, 13% of grade IV tumors and 2% of grade III tumors expressed IGF2 mRNA levels >50-fold the sample population median. IGF2-overexpressing tumors frequently displayed PTEN loss, were highly proliferative, exhibited strong staining for phospho-Akt, and belonged to a subclass of GBMs characterized by poor survival. Using a serum-free culture system, we discovered that IGF2 can substitute for EGF to support the growth of GBM-derived neurospheres. The growth-promoting effects of IGF2 were mediated by the insulin-like growth factor receptor 1 and phosphoinositide-3-kinase regulatory subunit 3 (PIK3R3), a regulatory subunit of phosphoinositide 3-kinase that shows genomic gains in some highly proliferative GBM cases. PIK3R3 knockdown inhibited IGF2-induced growth of GBM-derived neurospheres. The current results provide evidence that the IGF2-PIK3R3 signaling axis is involved in promoting the growth of a subclass of highly aggressive human GBMs that lack EGF receptor amplification. Our data underscore the importance of the phosphoinositide 3-kinase/Akt pathway for growth of high-grade gliomas and suggest that multiple molecular alterations that activate this signaling cascade may promote tumorigenesis. Further, these findings highlight the parallels between growth factors or receptors that are overexpressed in GBMs and those that support in vitro growth of tumor-derived stem-like cells.

Insulin signaling in the central nervous system: Learning to survive

Insulin is best known for its role in peripheral glucose homeostasis. Less studied, but not less important, is its role in the central nervous system. Insulin and its receptor are located in the central nervous system and are both implicated in neuronal survival and synaptic plasticity. Interestingly, over the past few years it has become evident that the effects of insulin, on neuronal survival and synaptic plasticity, are mediated by a common signal transduction cascade, which has been identified as "the PI3K route". This route has turned out to be a major integrator of insulin signaling in the brain. A pronounced feature of this insulin-activated route is that it promotes survival by directly inactivating the pro-apoptotic machinery. Interestingly, it is this same route that is required for the induction of long-term potentiation and depression, basic processes underlying learning and memory. This leads to the hypothesis that the PI3K route forms a direct link between learning and memory and neuronal survival. The implications of this hypothesis are far reaching, since it provides an explanation why insulin has beneficial effects on learning and memory and how synaptic activity can prevent cellular degeneration. Applying this knowledge may provide novel therapeutic approaches in the treatment of neurodegenerative diseases such as Alzheimer's disease.

Pronounced individual variation in the response to the stimulatory action of exercise on immature hippocampal neurons

In the adult hippocampus, neurogenesis is influenced both by external stimuli, such as physical exercise, and by intrinsic conditions like age and disease. However, the way in which many of these external and internal cues interact in this process remains poorly understood. We have used a new, more precise, stereological cell counting method that involves confocal microscopy to analyze the effects of exercise on adult neurogenesis in the mouse. We found that treadmill exercise increases the number of differentiating neurons (doublecortin/calretinin cells) in the granule cell layer of the mouse hippocampus in a manner that is directly related to the size of the mature granule cell population. More immature neurons were found after exercise in animals that had a larger dentate gyrus (DG), while no changes were observed in those with a smaller DG. This differential response to physical exercise suggests that the pre-existing neuronal population regulates the neurogenic response in the DG to external stimuli. These data raise the possibility of anticipating an individuals' response to therapeutic interventions (like exercise) aimed at augmenting dentate neurogenesis and alleviating or preventing cognitive decline.

Estradiol inhibits GSK3 and regulates interaction of estrogen receptors, GSK3, and beta-catenin in the hippocampus

Estrogens regulate a wide set of neuronal functions such as gene expression, survival and differentiation in a manner not very different from that exerted by neurotrophins or by growth factors. The best-studied hormonal action is the transcriptional activation mediated by estrogen receptors. However, the direct effects of estrogen on growth factor signaling have not been well clarified. The present data show that estradiol, in vivo, induces a transient activation of GSK3 in the adult female rat hippocampus, followed by a more sustained inhibition, as inferred from phosphorylation levels of Tau. Similar data was obtained from cultured hippocampal neurons when treated with the hormone. The transient activation was confirmed by direct measure of GSK3 kinase activity. In addition, our results show a novel complex of estrogen receptor alpha, GSK3, and beta-catenin. The presence of the hormone removes beta-catenin from this complex. There is a second complex, also affected by estradiol, in which Tau is associated with GSK3, beta-catenin, and elements of the PI3 kinase complex. Considering the role of GSK3 in neurodegeneration, our data suggest that part of the neuroprotective effects of estrogen may be due to the control of GSK3.

Glutamate excitotoxicity attenuates insulin-like growth factor-I prosurvival signaling

Recent evidence suggests that impaired insulin/insulin-like growth factor I (IGF-I) input may be associated to neurodegeneration. Several major neurodegenerative diseases involve excitotoxic cell injury whereby excess glutamate signaling leads to neuronal death. Recently it was shown that glutamate inactivates Akt, a serine-kinase crucially involved in the prosurvival actions of IGF-I. We now report that excitotoxic doses of glutamate antagonize Akt activation by IGF-I and inhibit the neuroprotective effects of this growth factor on cultured neurons. Glutamate induces loss of sensitivity to IGF-I by phosphorylating the IGF-I receptor docking protein insulin-receptor-substrate (IRS)-1 in Ser(307) through a pathway involving activation of PKA and PKC in a hierarchical fashion. Administration of Ro320432, a selective PKC inhibitor, abrogates the inhibitory effects of glutamate on IGF-I-induced Akt activation in vitro and in vivo and is sufficient to block the neurotoxic action of glutamate on cultured neurons. Notably, administration of Ro320432 after ischemic insult, a major form of excitotoxic injury in vivo, results in a marked decrease ( approximately 50%) in infarct size. Therefore, uncoupling of IGF-I signaling by glutamate may constitute an additional route contributing to excitotoxic neuronal injury. Further work should determine the potential use of PKC inhibitors as a novel therapeutic strategy in ischemia and other excitotoxic insults.

Estrogen receptor alpha forms estrogen-dependent multimolecular complexes with insulin-like growth factor receptor and phosphatidylinositol 3-kinase in the adult rat brain

Estradiol and insulin-like growth factor-I (IGF-I) have numerous functional interactions in the brain, including the regulation of neuroendocrine events, the control of reproductive behavior and the promotion of synaptic plasticity and neuronal survival. To explore the mechanisms involved in these interdependent actions of estradiol and IGF-I in the adult brain, the potential interactions of estrogen receptors with components of the IGF-I signaling system were assessed in this study. Systemic estradiol administration resulted in a transient immunocoprecipitation of the IGF-I receptor with the estrogen receptor alpha and in a transient increase in tyrosine phosphorylation of the IGF-I receptor in the hypothalamus of adult ovariectomized Wistar rats. Both effects were coincident in time, with a peak between 1 and 3 h after systemic estradiol administration. Three hours after estradiol treatment, there was an enhanced immunocoprecipitation of estrogen receptor alpha with p85 subunit of phosphatidylinositol 3-kinase, as well as an enhanced immunocoprecipitation of p85 with insulin receptor substrate-1. The interaction with the IGF-I receptor was specific for the alpha form of the estrogen receptor and was also induced by intracerebroventricular injection of IGF-I. These hormonal actions may be part of the mechanism by which estradiol activates IGF-I receptor signaling pathways in the brain and may explain the interdependence of estrogen receptors and the IGF-I receptor in synaptic plasticity, neuroprotection and other neural events.

A Role for phosphoinositide 3-kinase in the control of cell division and survival during retinal development

Neurogenesis in the retina requires the concerted action of three different cellular processes: proliferation, differentiation, and apoptosis. Class IA phosphoinositide 3-kinase (PI3K) is a heterodimer composed of a p85 regulatory and a p110 catalytic subunit. p110alpha has been shown to regulate cell division and survival. Little is known of its function in development, however, as p110alpha knockout mice exhibit CNS defects, but death at early embryonic stages impairs further study. Here, we examine the role of PI3K in mouse retina development by expressing an activating form of PI3K regulatory subunit, p65(PI3K), as a transgene in the retina. Mice expressing p65(PI3K) showed severely disrupted retina morphogenesis, with ectopic cell masses in the neuroepithelium that evolved into infoldings of adult retinal cell layers. These changes correlated with an altered cell proliferation/cell death balance at early developmental stages. Nonetheless, the most affected cell layer in adult retina was that of photoreceptors, which correlated with selectively increased survival of these cells at developmental stages at which cell division has ceased. These results demonstrate the relevance of accurate PI3K regulation for normal retinal development, supporting class IA PI3K involvement in induction of cell division at early stages of neurogenesis. These data also show that, even after cell division decline, PI3K activation mediates survival of differentiated neurons in vivo.

Functions of PI 3-kinase in development of the nervous system

In the nervous system, receptor regulated phosphoinositide (PI) 3-kinases (PI 3-kinases) participate in fundamental cellular activities that underlie development. Activated by trophic factors, growth factors, neuregulins, cytokines, or neurotransmitters, PI 3-kinases have been implicated in neuronal and glial survival and differentiation. PI 3-kinases produce inositol lipid second messengers that bind to pleckstrin homology (PH) domains in diverse groups of signal transduction proteins, and control their enzymatic activities, subcellular membrane localization, or both. Downstream targets of the inositol lipid messengers include protein kinases and regulators of small GTPases. The kinase Akt/PKB functions as a key component of the PI 3-kinase dependent survival pathway through its phosphorylation and regulation of apoptotic proteins and transcription factors. Furthermore, since members of the Rho GTPase and Arf GTPase families have been implicated in regulation of the actin cytoskeleton, vesicular trafficking, and transcription, the downstream targets of PI 3-kinase that control these GTPases are excellent candidates to mediate aspects of PI 3-kinase dependent neuronal and glial differentiation.

Interleukin-4 and interleukin-10 modulate nuclear factor kappaB activity and nitric oxide synthase-2 expression in Theiler's virus-infected brain astrocytes

In brain astrocytes, nuclear factor kappaB (NF-kappaB) is activated by stimuli that produce cellular stress causing the expression of genes involved in defence, including the inducible nitric oxide synthase (NOS-2). Theiler's murine encephalomyelitis virus (TMEV) induces a persistent CNS infection and chronic immune-mediated demyelination, similar to human multiple sclerosis. The cytokines interleukin (IL)-4 and IL-10 inhibit the expression of proinflammatory cytokines, counteracting the inflammatory process. Our study reports that infection of cultured astrocytes with TMEV resulted in a time-dependent phosphorylation of IkappaBalpha, degradation of IkappaBalpha and IkappaBbeta, activation of NF-kappaB and expression of NOS-2. The proteasome inhibitor MG-132 blocked TMEV-induced nitrite accumulation, NOS-2 mRNA expression and phospho-IkappaBalpha degradation, suggesting NF-kappaB-dependent NOS-2 expression. Pretreatment of astrocytes with IL-4 or IL-10 decreased p65 nuclear translocation, NF-kappaB binding activity and NOS-2 transcription. IL-4 and IL-10 caused an accumulation of IkappaBalpha in TMEV-infected astrocytes without affecting IkappaBbeta levels. The IkappaB kinase activity and the degradation rate of both IkappaBs were not modified by either cytokine, suggesting de novo synthesis of IkappaBalpha. Indeed, IL-4 or IL-10 up-regulated IkappaBalpha mRNA levels after TMEV infection. Therefore, the accumulation of IkappaBalpha might impair the translocation of the NF-kappaB to the nucleus, mediating the inhibition of NF-kappaB activity. Overall, these data suggest a novel mechanism of action of IL-4 and IL-10, which abrogates NOS-2 expression in viral-infected glial cells.