-
[show abstract]
[hide abstract]
ABSTRACT: Accumulating evidence continues to underpin the role of the innate immune system in pathologies associated with neuroinflammation. Innate immunity is regulated by pattern recognition receptors that detect pathogens and, in the case of Gram-positive bacteria, binding of bacterial lipopeptides to toll-like receptor (TLR)2 is emerging as an important mechanism controlling glial cell activation. In the present study, we employed the use of the synthetic bacterial lipoprotein and a selective TLR2 agonist, Pam3CSK4, to induce inflammatory signaling in microglia and astrocytes. The adaptor proteins, downstream of kinase (Dok)1 and Dok2, are known to have a role in negatively regulating the Ras-ERK signaling cascade, with downstream consequences on pro-inflammatory cytokine expression. Data presented herein demonstrate that TLR2 enhanced the tyrosine phosphorylation of Dok1 and Dok2 in astrocytes and microglia, and that knockdown of these adaptors using small interfering RNA robustly elevated TLR2-induced ERK activation. Importantly, TLR2-induced NF-κB activation and IL-6 production was exacerbated in astrocytes transfected with Dok1 and Dok2 siRNA, indicating that both Dok proteins negatively regulate TLR2-induced inflammatory signaling in astrocytes. In contrast, Dok1 knockdown attenuated TLR2-induced NF-κB activation and IL-6 production in microglia, while Dok2 siRNA failed to affect TLR2-induced NF-κB activity and subsequent cytokine expression in this cell type. Overall this indicates that Dok1 and Dok2 are novel adaptors for TLR2 in glial cells and, importantly, indicates that Dok1 and Dok2 differentially regulate TLR2-induced pro-inflammatory signaling in astrocytes and microglia.
Molecular and Cellular Neuroscience 05/2013; · 3.66 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: BACKGROUND: The interaction between the membrane glycoprotein, CD200 and its cognate receptor CD200 receptor (CD200R), has been shown to play a role in maintaining microglia in a quiescent state. There is evidence of increased activation under resting and stimulated conditions in microglia prepared from CD200-deficient mice compared with wild-type mice, whereas activation of the receptor by CD200 fusion protein (CD200Fc) ameliorates inflammatory changes which are evident in the central nervous system (CNS) of the mouse model of multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE) and also in the hippocampus of aged rats. Additionally, an inverse relationship between microglial activation and expression of CD200 has been observed in animals treated with lipopolysaccharide (LPS) or amyloid-beta (Abeta). METHODS: We assessed the effect of CD200R activation by CD200Fc on Abeta-induced production of the pro-inflammatory cytokines, interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNFalpha) and the expression of microglial activation markers, CD68 and CD40 in cultured glia. The role played by downstream of tyrosine kinase 2 (Dok2) phosphorylation in mediating the effects of CD200R activation was evaluated by siRNA knockdown of Dok2. To further examine the impact of inflammatory changes on synaptic plasticity, the effect of CD200Fc on Abeta-induced impairment of long-term potentiation (LTP) in the CA1 region of hippocampal slices was also investigated. RESULTS: We demonstrate that Abeta-induced increases in IL-1beta, TNFalpha, CD68 and CD40 were inhibited by CD200Fc. The evidence suggests that Dok2 phosphorylation is a key factor in mediating the effect of CD200Fc, since Dok2 knockdown by siRNA abrogated its effects on microglial activation and inflammatory cytokine production. Consistent with evidence that inflammatory changes negatively impact on LTP, we show that the Abeta-induced impairment of LTP was attenuated by CD200Fc. CONCLUSIONS: The findings suggest that activation of CD200R and Dok2 is a valuable strategy for modulating microglial activation and may have therapeutic potential in neurodegenerative conditions.
Journal of Neuroinflammation 05/2012; 9(1):107. · 3.83 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Marijuana and hashish consist of at least 66 distinctive plant-derived (phyto-) cannabinoid compounds, with tetrahydrocannabinoids proving the most effective phytocannabinoid psychotropically. Despite the known pharmacological effects of phytocannabinoids, their role in controlling the cell survival/death decision in cells of the CNS continues to be unravelled.
In this review, we examine the influence of phytocannabinoids on neural cell fate, with particular emphasis on how the time of marijuana exposure (neonatal vs. pubertal vs. adult) might influence the neurotoxic activities of phytocannabinoid compounds.
Evidence in the literature indicates that exposure to phytocannabinoids during the prenatal period, in addition to the adolescent period, can alter the temporally ordered sequence of events that occur during neurotransmitter development, in addition to negatively impacting neural cell survival and maturation. Regarding the effect of marijuana consumption on brain composition in adults the evidence is contradictory.
Exposure to marijuana during pregnancy might impact negatively on brain structure in the first years of postnatal life. Furthermore, early-onset (before age 17) marijuana use might also have damaging effects on brain composition.
The neonatal and immature CNS is more susceptible to phytocannabinoid damage. In the adult CNS the data are conflicting and the continued development of methods to assess whether marijuana consumption results in brain atrophy or morphometric changes will determine if structural changes are occurring.
Drug and Alcohol Review 01/2010; 29(1):91-8. · 1.55 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Several neurodegenerative disorders are associated with evidence of inflammation, one feature of which is increased activation of microglia, the most likely cellular source of inflammatory cytokines like interleukin-1β. It is now recognized that interaction of microglia with other cells contributes to maintenance of microglia in a quiescent state and the complementary distribution of the chemokine, fractalkine (CX3CL1) on neurons and its receptor (CX3CR1) on microglia, suggests that this interaction may play a role in modulating microglial activation. Here we demonstrate that both soluble and membrane-bound fractalkine attenuate lipopolysaccharide-induced microglial activation in vitro. We also show that fractalkine expression is reduced in the brain of aged rats and this is accompanied by an age-related increase in microglial activation. Treatment of aged rats with fractalkine attenuates the age-related increase in microglial activation and the evidence indicates that fractalkine-induced activation of the phosphatidylinositol-3 kinase pathway is required to maintain microglia in a quiescent state both in vivo and in vitro.
Journal of Neurochemistry 08/2009; 110(5):1547 - 1556. · 4.06 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Several neurodegenerative disorders are associated with evidence of inflammation, one feature of which is increased activation of microglia, the most likely cellular source of inflammatory cytokines like interleukin-1beta. It is now recognized that interaction of microglia with other cells contributes to maintenance of microglia in a quiescent state and the complementary distribution of the chemokine, fractalkine (CX(3)CL1) on neurons and its receptor (CX(3)CR1) on microglia, suggests that this interaction may play a role in modulating microglial activation. Here we demonstrate that both soluble and membrane-bound fractalkine attenuate lipopolysaccharide-induced microglial activation in vitro. We also show that fractalkine expression is reduced in the brain of aged rats and this is accompanied by an age-related increase in microglial activation. Treatment of aged rats with fractalkine attenuates the age-related increase in microglial activation and the evidence indicates that fractalkine-induced activation of the phosphatidylinositol-3 kinase pathway is required to maintain microglia in a quiescent state both in vivo and in vitro.
Journal of Neurochemistry 08/2009; 110(5):1547-56. · 4.06 Impact Factor
-
Anthony Lyons,
Keith McQuillan,
Brian F Deighan,
Julie-Ann O'Reilly, Eric J Downer,
Aine C Murphy,
Melanie Watson,
Alessia Piazza,
Florence O'Connell,
Rebecca Griffin,
Kingston H G Mills,
Marina A Lynch
[show abstract]
[hide abstract]
ABSTRACT: Maintenance of the balance between pro- and anti-inflammatory cytokines in the brain, which is affected by the activation state of microglia, is important for maintenance of neuronal function. Evidence has suggested that IL-4 plays an important neuromodulatory role and has the ability to decrease lipopolysaccharide-induced microglial activation and the production of IL-1beta. We have also demonstrated that CD200-CD200R interaction is involved in immune homeostasis in the brain. Here, we investigated the anti-inflammatory role of IL-4 and, using in vitro and in vivo analysis, established that the effect of lipopolysaccharide was more profound in IL-4(-/-), compared with wildtype, mice. Intraperitoneal injection of lipopolysaccharide exerted a greater inhibitory effect on exploratory behaviour in IL-4(-/-), compared with wildtype, mice and this was associated with evidence of microglial activation. We demonstrate that the increase in microglial activation is inversely related to CD200 expression. Furthermore, CD200 was decreased in neurons prepared from IL-4(-/-) mice, whereas stimulation with IL-4 enhanced CD200 expression. Importantly, neurons prepared from wildtype, but not from IL-4(-/-), mice attenuated the lipopolysaccharide-induced increase in pro-inflammatory cytokine production by glia. These findings suggest that the neuromodulatory effect of IL-4, and in particular its capacity to maintain microglia in a quiescent state, may result from its ability to upregulate CD200 expression on neurons.
Brain Behavior and Immunity 07/2009; 23(7):1020-7. · 4.72 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Microglial cell activity increases in the rat hippocampus during normal brain aging. The neural cell adhesion molecule (NCAM)-derived mimetic peptide, FG loop (FGL), acts as an anti-inflammatory agent in the hippocampus of the aged rat, promoting CD200 ligand expression while attenuating glial cell activation and subsequent pro-inflammatory cytokine production. The aim of the current study was to determine if FGL corrects the age-related imbalance in hippocampal levels of insulin-like growth factor-1 (IGF-1) and pro-inflammatory interferon-gamma (IFNgamma), and subsequently attenuates the glial reactivity associated with aging. Administration of FGL reversed the age-related decline in IGF-1 in hippocampus, while abrogating the age-related increase in IFNgamma. FGL robustly promotes IGF-1 release from primary neurons and IGF-1 is pivotal in FGL induction of neuronal Akt phosphorylation and subsequent CD200 ligand expression in vitro. In addition, FGL abrogates both age- and IFNgamma-induced increases in markers of glial cell activation, including major histocompatibility complex class II (MHCII) and CD40. Finally, the proclivity of FGL to attenuate IFNgamma-induced glial cell activation in vitro is IGF-1-dependent. Overall, these findings suggest that FGL, by correcting the age-related imbalance in hippocampal levels of IGF-1 and IFNgamma, attenuates glial cell activation associated with aging. These findings also highlight a novel mechanism by which FGL can impact on neuronal CD200 ligand expression and subsequently on glial cell activation status.
Journal of Neurochemistry 04/2009; 109(5):1516-25. · 4.06 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Age-related cognitive deficits in hippocampus are correlated with neuroinflammatory changes, typified by increased pro-inflammatory cytokine production and microglial activation. We provide evidence that the neural cell adhesion molecule (NCAM)-derived mimetic peptide, FG loop (FGL), acts as a novel anti-inflammatory agent. Administration of FGL to aged rats attenuated the increased expression of markers of activated microglia, the increase in pro-inflammatory interleukin-1beta (IL-1beta) and the impairment in long-term potentiation (LTP). We report that the age-related increase in microglial activation was accompanied by decreased expression of neuronal CD200, and suggest that the proclivity of FGL to suppress microglial activation is due to its stimulatory effect on neuronal CD200. We demonstrate that FGL enhanced interleukin-4 (IL-4) release from glial cells and IL-4 in turn enhanced neuronal CD200 in vitro. We provide evidence that the increase in CD200 is reliant on IL-4-induced extracellular signal-regulated kinase (ERK) signal transduction. These findings provide the first evidence of a role for FGL as an anti-inflammatory agent and identify a mechanism by which FGL controls microglial activation.
Neurobiology of aging 06/2008; 31(1):118-28. · 5.94 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The majority of neurodegenerative diseases are associated with excessive glutamatergic transmission, oxidative stress and/or
inflammatory changes that lead to activation of the apoptotic cascade and subsequent neuronal demise. Cannabinoids have been
demonstrated to confer neuroprotection both in vitro and in a number of in vivo paradigms of neurodegeneration including cerebral
ischemia, hypoxia, seizures and experimental autoimmune encephalitis. The molecular mechanisms underlying cannabinoid-mediated
protection involve both CB1 receptor-dependent and receptor-independent events. Anti-oxidant activities and the proclivity to reduce excessive glutamatergic
synaptic activity underlie some of the neuroprotective effects of cannabinoids. The attenuation of pro-inflammatory signalling
coupled with an induction of pro-survival growth factors and enhanced mitogen-activated protein kinase (MAPK) and phosphatidylinositol
3-kinase (PI3K) activities have also been implicated in the ability of exogenous and endogenous cannabinoids to provide neuroprotection.
12/2007: pages 317-329;
-
[show abstract]
[hide abstract]
ABSTRACT: The maternal use of cannabis during pregnancy results in a number of cognitive deficits in the offspring that persist into adulthood. The endocannabinoid system has a role to play in neurodevelopmental processes such as neurogenesis, migration and synaptogenesis. However, exposure to phytocannabinoids, such as Delta(9)-tetrahydrocannabinol, during gestation may interfere with these events to cause abnormal patterns of neuronal wiring and subsequent cognitive impairments. Aberrant cell death evoked by Delta(9)-tetrahydrocannabinol may also contribute to cognitive deficits and in cultured neurones Delta(9)-tetrahydrocannabinol induces apoptosis via the CB(1) cannabinoid receptor. In this study we report that Delta(9)-tetrahydrocannabinol (5-50 microM) activates the stress-activated protein kinase, c-jun N-terminal kinase, and the pro-apoptotic protease, caspase-3, in in vitro cerebral cortical slices obtained from the neonatal rat brain. The proclivity of Delta(9)-tetrahydrocannabinol to impact on these pro-apoptotic signalling molecules was not observed in in vitro cortical slices obtained from the adult rat brain. In vivo, subcutaneous administration of Delta(9)-tetrahydrocannabinol (1-30 mg/kg) activated c-jun N-terminal kinase, caspase-3 and cathepsin-D, and induced DNA fragmentation in the cerebral cortex of neonatal rats. In contrast, in vivo administration of Delta(9)-tetrahydrocannabinol to adult rats was not associated with the apoptotic pathway in the cerebral cortex. The data provide evidence which supports the hypothesis that the neonatal rat brain is more vulnerable to the neurotoxic influence of Delta(9)-tetrahydrocannabinol, suggesting that the cognitive deficits that are observed in humans exposed to marijuana during gestation may be due, in part, to abnormal engagement of the apoptotic cascade during brain development.
Brain Research 11/2007; 1175:39-47. · 2.73 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Deficits in cognitive function are associated with neuroinflammatory changes, typified by activation of glial cells and an alteration of the pro- and anti-inflammatory cytokine balance in the brain. Although there is evidence to suggest that activation of microglia is regulated by interaction with other cell types in the brain, the mechanism(s) involved is poorly understood. Here, we provide evidence that interaction between CD200 and its receptor plays a role in modulating microglial activation under conditions of chronic and acute inflammation of the brain. We report that interleukin-4 (IL-4) plays a central role in modulating expression of CD200 and identify a mechanism by which IL-4 directly controls microglial cell activation. Our findings provide the first demonstration of a role for IL-4 in modulating CD200 expression and suggest a mechanism for regulation of microglial activation in the intact CNS under inflammatory conditions.
Journal of Neuroscience 09/2007; 27(31):8309-13. · 7.11 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Cannabis is the most commonly used illegal drug of abuse in Western society. Delta(9)-tetrahydrocannabinol, the psychoactive ingredient of marijuana, regulates a variety of neuronal processes including neurotransmitter release and synaptic transmission. An increasing body of evidence suggests that cannabinoids play a key role in the regulation of neuronal viability. In cortical neurons tetrahydrocannabinol has a neurodegenerative effect, the mechanisms of which are poorly understood, but involve the cannabinoid receptor subtype, CB(1). In this study we report that tetrahydrocannabinol (5 muM) evokes a rapid phosphorylation, and thus activation, of the tumour suppressor protein, p53, in a manner involving the cannabinoid CB(1) receptor, and the stress-activated protein kinase, c-jun N-terminal kinase, in cultured cortical neurons. Tetrahydrocannabinol increased expression of the p53-transcriptional target, Bax and promoted Bcl phosphorylation. These events were abolished by the p53 inhibitor, pifithrin-alpha (100 nM). The tetrahydrocannabinol-induced activation of the pro-apoptotic cysteine protease, caspase-3, and DNA fragmentation was also blocked by pifithrin-alpha. A siRNA knockdown of p53 further verified the role of p53 in tetrahydrocannabinol-induced apoptosis. This study demonstrates a novel cannabinoid signalling pathway involving p53 that culminates in neuronal apoptosis.
European Journal of Pharmacology 07/2007; 564(1-3):57-65. · 2.52 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Delta9-Tetrahydrocannabinol (THC), the main psychoactive ingredient of marijuana, induces apoptosis in cultured cortical neurons. THC exerts its apoptotic effects in cortical neurons by binding to the CB1 cannabinoid receptor. The CB1 receptor has been shown to couple to the stress-activated protein kinase, c-Jun N-terminal kinase (JNK). However, the involvement of specific JNK isoforms in the neurotoxic properties of THC remains to be established. The present study involved treatment of rat cultured cortical neurons with THC (0.005-50 microM), and combinations of THC with the CB1 receptor antagonist, AM 251 (10 microM) and pertussis toxin (PTX; 200 ng ml-1). Antisense oligonucleotides (AS) were used to deplete neurons of JNK1 and JNK2 in order to elucidate their respective roles in THC signalling. Here we report that THC induces the activation of JNK via the CB1 receptor and its associated G-protein, Gi/o. Treatment of cultured cortical neurons with THC resulted in a differential timeframe of activation of the JNK1 and JNK2 isoforms. Use of specific JNK1 and JNK2 AS identified activation of caspase-3 and DNA fragmentation as downstream consequences of JNK1 and JNK2 activation. The results from this study demonstrate that activation of the CB1 receptor induces JNK and caspase-3 activation, an increase in Bax expression and DNA fragmentation. The data demonstrate that the activation of both JNK1 and JNK2 isoforms is central to the THC-induced activation of the apoptotic pathway in cortical neurons.
British Journal of Pharmacology 11/2003; 140(3):547-57. · 4.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: beta-Amyloid (A beta) peptide has been shown to induce neuronal apoptosis; however, the mechanisms underlying A beta-induced neuronal cell death remain to be fully elucidated. The stress-activated protein kinase, c-Jun N-terminal kinase (JNK), is activated in response to cellular stress and has been identified as a proximal mediator of cell death. In the present study, expression of active JNK was increased in the nucleus and cytoplasm of A beta-treated cells. Evaluation of the nature of the JNK isoforms activated by A beta revealed a transient increase in JNK1 activity that reached its peak at 1 h and a later activation (at 24 h) of JNK2. The tumour suppressor protein, p53, is a substrate for JNK and can serve as a signalling molecule in apoptosis. In cultured cortical neurons, we found that A beta increased p53 protein expression and phosphorylation of p53 at Ser(15). Thus it appears that A beta increases p53 expression via phosphorylation-mediated stabilization of the protein. Given the lack of availability of a JNK inhibitor that can distinguish between JNK1- and JNK2-mediated effects, we employed antisense technology to deplete cells of JNK1 or JNK2 selectively. Using this strategy, the respective roles of JNK1 and JNK2 on the A beta-mediated activation of the apoptotic cascade (i.e. p53 stabilization, caspase 3 activation and DNA fragmentation) were examined. The results obtained demonstrate a role for JNK1 in the A beta-induced stabilization of p53, activation of caspase 3 and DNA fragmentation. In contrast, depletion of JNK2 had no effect on the proclivity of A beta to activate capase 3 or induce DNA fragmentation. These results demonstrate a significant role for JNK1 in A beta-mediated induction of the apoptotic cascade in cultured cortical neurons.
Biochemical Journal 06/2003; 371(Pt 3):789-98. · 4.90 Impact Factor
