Activation of α7 nicotinic acetylcholine receptor by nicotine selectively up-regulates cyclooxygenase-2 and prostaglandin E(2 )in rat microglial cultures

BACKGROUND: Nicotinic acetylcholine (Ach) receptors are ligand-gated pentameric ion channels whose main function is to transmit signals for the neurotransmitter Ach in peripheral and central nervous system. However, the α7 nicotinic receptor has been recently found in several non-neuronal cells and described as an important regulator of cellular function. Nicotine and ACh have been recently reported to inhibit tumor necrosis factor-α (TNF-α) production in human macrophages as well as in mouse microglial cultures. In the present study, we investigated whether the stimulation of α7 nicotinic receptor by the specific agonist nicotine could affect the functional state of activated microglia by promoting and/or inhibiting the release of other important pro-inflammatory and lipid mediator such as prostaglandin E(2). METHODS: Expression of α7 nicotinic receptor in rat microglial cell was examined by RT-PCR, immunofluorescence staining and Western blot. The functional effects of α7 receptor activation were analyzed in resting or lipopolysaccharide (LPS) stimulated microglial cells pre-treated with nicotine. Culture media were assayed for the levels of tumor necrosis factor, interleukin-1β, nitric oxide, interleukin-10 and prostaglandin E(2). Total RNA was assayed by RT-PCR for the expression of COX-2 mRNA. RESULTS: Rat microglial cells express α7 nicotinic receptor, and its activation by nicotine dose-dependently reduces the LPS-induced release of TNF-α, but has little or no effect on nitric oxide, interleukin-10 and interleukin-1β. By contrast, nicotine enhances the expression of cyclooxygenase-2 and the synthesis of one of its major products, prostaglandin E(2). CONCLUSIONS: Since prostaglandin E(2 )modulates several macrophage and lymphocyte functions, which are instrumental for inflammatory resolution, our study further supports the existence of a brain cholinergic anti-inflammatory pathway mediated by α7 nicotinic receptor that could be potentially exploited for novel treatments of several neuropathologies in which local inflammation, sustained by activated microglia, plays a crucial role

Branched-chain amino acids influence the immune properties of microglial cells and their responsiveness to pro-inflammatory signals

AbstractThe branched-chain amino acids (BCAAs) valine, leucine and isoleucine are essential amino acids involved in several important brain functions. Although commonly used as nutritional supplements, excessive intake of BCAAs might favour the establishment of neurotoxic conditions as indicated by the severe neurological symptoms characterising inherited disorders of BCAA catabolism such as maple syrup urine disease (MSUD). Recent evidence indicates that BCAAs induce excitotoxicity through mechanisms that require the presence of astrocytes. In the present study, we evaluated the effects of BCAAs on microglia, the main immune cells of the brain. As an experimental model we used primary microglial cells harvested from mixed glial cultures that had been kept in normal or high BCAA medium (H-BCAA). We show that H-BCAA microglial cells exhibit a peculiar phenotype characterized by a partial skewing toward the M2 state, with enhanced IL-10 expression and phagocytic activity but also increased free radical generation and decreased neuroprotective functions. We suggest that such an intermediate M1/M2 phenotype might result in a less efficient microglial response, which would promote the establishment of a low grade chronic inflammation and increase the likelihood of neurodegeneration. Although based on in vitro evidence, our study adds on to an increasing literature indicating that the increasing use of dietary integrators might deserve consideration for the possible drawbacks. In addition to excitotoxicity, the altered immune profile of microglia might represent a further mechanism by which BCAAs might turn into toxicants and facilitate neurodegeneration

Critical role of maternal selenium nutrition in neurodevelopment: Effects on offspring behavior and neuroinflammatory profile

Research in both animals and humans shows that some nutrients are important in pregnancy and during the first years of life to support brain and cognitive development. Our aim was to evaluate the role of selenium (Se) in supporting brain and behavioral plasticity and maturation. Pregnant and lactating female rats and their offspring up to postnatal day 40 were fed isocaloric diets differing in Se content - i.e., Optimal, SubOptimal, and Deficient - and neurodevelopmental, neu-roinflammatory, and anti-oxidant markers were analyzed. We observed early adverse behavioral changes in juvenile rats only in SubOptimal offspring. In addition, SubOptimal, more than Deficient supply reduced basal glial reactivity in sex dimorphic and brain-area specific fashion. In female offspring, Deficient and SubOptimal diets reduced the antioxidant Glutathione peroxidase (GPx) activity in the cortex and in the liver, the latter being the key organ regulating Se metabo-lism and homeostasis. The finding that Se SubOptimal was more detrimental than Se Deficient diet may suggest that maternal Se Deficient diet, leading to a lower Se supply at earlier stages of fetal development, stimulated homeostatic mechanisms in the offspring that were not initiated by SubOptimal Se. Our observations demonstrate that even moderate Se deficiency during early life negatively may affect, in a sex-specific manner, optimal brain development

Non-Steroidal Anti-Inflammatory Drugs and Brain Inflammation: Effects on Microglial Functions

The term NSAID refers to structurally diverse chemical compounds that share the ability to inhibit the activity of the prostaglandin (PG) biosynthetic enzymes, the cyclooxygenase (COX) isoforms 1 and 2. The suppression of PG synthesis at sites of inflammation has been regarded as primarily responsible for the beneficial properties of NSAIDs, but several COX-independent effects have been described in recent years. Epidemiological studies indicate that NSAIDs are neuroprotective, although the mechanisms underlying their beneficial effect remain largely unknown. Microglial cells play a major role in brain inflammation and are often viewed as major contributors to the neurodegeneration. Therefore, microglia represent a likely target for NSAIDs within the brain. In the present review, we focused on the direct effects of NSAIDs and selective COX-2 inhibitors on microglial functions and discuss the potential efficacy in controlling brain inflammation

Brain inflammation and the neuronal fate: from neurogenesis to neurodegeneration

Inflammation is a self-defensive reaction that may develop into a chronic state and become a causative factor in the pathogenesis of a broad range of disabling diseases. Similar to peripheral inflammation, brain inflammation is increasingly being viewed as a target for treating neurological diseases, not only infectious and immune-mediated disorders such as meningitis or multiple sclerosis but also stroke, trauma, and neurodegenerative diseases that were originally not considered to be inflammatory. Microglial cells, the resident macrophages of brain parenchyma, are generally viewed as major sources of pro-inflammatory and potentially neurotoxic molecules in the damaged brain, However, a direct link between activated microglia and tissue damage has not been univocally demonstrated in vivo, and recent studies have rather documented exacerbation of injury following selective microglial ablation or anti-inflammatory treatments. Recent studies have implicated inflammation in the regulation of adult neurogenesis, thus broadening the therapeutic potential of strategies aimed at controlling neuroinflammation. This chapter summarizes the main evidence supporting both detrimental and protective roles of inflammation in acute and chronic brain disease

Pro-gliogenic effect of IL-1α in the differentiation of embryonic neural precursor cells in vitro

Inflammation is regarded as a main obstacle to brain regeneration. Major detrimental effects are attributed to microglial/macrophagic products, such as TNF-α and interleukin (IL)-6. The role of cytokines of the IL-1 family, particularly of IL-1α, in the modulation of neural precursor cell (NPC) properties is less characterized. IL-1α is one of the most abundant cytokines released upon acute stimulation of microglia with lipopolysaccharide and is down-regulated upon chronic stimulation. As we recently demonstrated, acutely activated microglia reduces NPC survival, prevent neuronal differentiation and promote glial differentiation. Chronically activated microglia are instead permissive to NPC survival and neuronal differentiation, and less effective in promoting astrocytic differentiation. We thus investigated whether IL-1α could contribute to the effects of acutely activated microglia on NPC. We found that NPC express functional IL-1 receptors and that exposure to recombinant IL-1α strongly enhances NPC differentiation into astrocytes, without affecting cell viability and neuronal differentiation. In the same conditions, recombinant IL-1β has pro-gliogenic effects at concentrations 10-fold higher than those found in activated microglial conditioned media. Interestingly, immunodepletion of IL-1α in activated microglial conditioned media fails to revert microglial pro-gliogenic action and slightly enhances neuronal differentiation, revealing that other microglial-derived factors contribute to the modulation of NPC properties. © 2010 International Society for Neurochemistry

In vitro neuronal and glial differentiation from embryonic or adult neural precursor cells are differently affected by chronic or acute activation of microglia

The contribution of microglia to the modulation of neurogenesis under pathological conditions is unclear. Both pro- and anti-neurogenic effects have been reported, likely reflecting the complexity of microglial activation process. We previously demonstrated that prolonged (72 hr) in vitro exposure to lipopolysaccharide (LPS) endows microglia with a potentially neuroprotective phenotype, here referred as to "chronic". In the present study we further characterized the chronic phenotype and investigated whether it might differently regulate the properties of embryonic and adult neural precursor cells (NPC) with respect to the "acute" phenotype acquired following a single (24 hr) LPS stimulation. We show that the LPS-dependent induction of the proinflammatory cytokines interleukin (IL)-1 alpha, IL-1 beta, IL-6, and tumor necrosis factor (TNF)-alpha was strongly reduced after chronic stimulation of microglia, as compared with acute stimulation. Conversely, the synthesis of the anti-inflammatory cytokine IL-10 and the immunomodulatory prostaglandin E-2 (PGE(2)) was still elevated or further increased, after chronic LPS exposure, as revealed by real time PCR and ELISA techniques. Acutely activated microglia, or their conditioned medium, reduced NPC survival, prevented neuronal differentiation and strongly increased glial differentiation, likely through the release of proinflammatory cytokines, whereas chronically activated microglia were permissive to neuronal differentiation and cell survival, and still supported glial differentiation. Our data suggest that, in a chronically altered environment, persistently activated microglia can display protective functions that favor rather than hinder brain repair processes. (c) 2008 Wiley-Liss, Inc

Inflammatory Signatures of Maternal Obesity as Risk Factors for Neurodevelopmental Disorders: Role of Maternal Microbiota and Nutritional Intervention Strategies

Obesity is a main risk factor for the onset and the precipitation of many non-communicable diseases. This condition, which is associated with low-grade chronic systemic inflammation, is of main concern during pregnancy leading to very serious consequences for the new generations. In addition to the prominent role played by the adipose tissue, dysbiosis of the maternal gut may also sustain the obesity-related inflammatory milieu contributing to create an overall suboptimal intrauterine environment. Such a condition here generically defined as “inflamed womb” may hold long-term detrimental effects on fetal brain development, increasing the vulnerability to mental disorders. In this review, we will examine the hypothesis that maternal obesity-related gut dysbiosis and the associated inflammation might specifically target fetal brain microglia, the resident brain immune macrophages, altering neurodevelopmental trajectories in a sex-dependent fashion. We will also review some of the most promising nutritional strategies capable to prevent or counteract the effects of maternal obesity through the modulation of inflammation and oxidative stress or by targeting the maternal microbiota

Prostaglandin E(2) and BDNF levels in rat hippocampus are negatively correlated with status epilepticus severity: No impact on survival of seizure-generated neurons.

Partial and generalized status epilepticus (pSE and gSE) trigger the same level of progenitor cell proliferation in adult dentate gyrus, but survival of new neurons is poor after gSE. Here, we show markedly elevated levels of prostaglandin E-2 (PGE(2)) and brain-derived neurotrophic factor (BDNF) in rat hippocampal formation at 7 days following pSE but not gSE. Administration of the cyclooxygenase (COX) inhibitor flurbiprofen for 1 week, starting at day 8 post-SE, abated PGE(2) and decreased BDNF levels, but did not affect survival of new neurons a weeks later. Thus, high PGE(2) and BDNF levels induced by pSE are probably not of major importance for survival of new neurons during the first days after formation. We propose that they modulate other aspects of synaptic and cellular plasticity, and thereby may influence epileptogenesis