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Perdita L Pugh,
Martin P Vidgeon-Hart,
Tracey Ashmeade, Ainsley A Culbert,
Zoe Seymour,
Marion J Perren,
Flora Joyce,
Simon T Bate,
Anna Babin,
David J Virley,
Jill C Richardson,
Neil Upton,
David Sunter
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ABSTRACT: Data indicates anti-oxidant, anti-inflammatory and pro-cognitive properties of noradrenaline and analyses of post-mortem brain of Alzheimer's disease (AD) patients reveal major neuronal loss in the noradrenergic locus coeruleus (LC), the main source of CNS noradrenaline (NA). The LC has projections to brain regions vulnerable to amyloid deposition and lack of LC derived NA could play a role in the progression of neuroinflammation in AD. Previous studies reveal that intraperitoneal (IP) injection of the noradrenergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) can modulate neuroinflammation in amyloid over-expressing mice and in one study, DSP-4 exacerbated existing neurodegeneration.
TASTPM mice over-express human APP and beta amyloid protein and show age related cognitive decline and neuroinflammation. In the present studies, 5 month old C57/BL6 and TASTPM mice were injected once monthly for 6 months with a low dose of DSP-4 (5 mg kg-1) or vehicle. At 8 and 11 months of age, mice were tested for cognitive ability and brains were examined for amyloid load and neuroinflammation.
At 8 months of age there was no difference in LC tyrosine hydroxylase (TH) across all groups and cortical NA levels of TASTPM/DSP-4, WT/Vehicle and WT/DSP-4 were similar. NA levels were lowest in TASTPM/Vehicle. Messenger ribonucleic acid (mRNA) for various inflammatory markers were significantly increased in TASTPM/Vehicle compared with WT/Vehicle and by 8 months of age DSP-4 treatment modified this by reducing the levels of some of these markers in TASTPM. TASTPM/Vehicle showed increased astrocytosis and a significantly larger area of cortical amyloid plaque compared with TASTPM/DSP-4. However, by 11 months, NA levels were lowest in TASTPM/DSP-4 and there was a significant reduction in LC TH of TASTPM/DSP-4 only. Both TASTPM groups had comparable levels of amyloid, microglial activation and astrocytosis and mRNA for inflammatory markers was similar except for interleukin-1 beta which was increased by DSP-4. TASTPM mice were cognitively impaired at 8 and 11 months but DSP-4 did not modify this.
These data reveal that a low dose of DSP-4 can have varied effects on the modulation of amyloid plaque deposition and neuroinflammation in TASTPM mice dependent on the duration of dosing.
Journal of Neuroinflammation 02/2007; 4:8. · 3.83 Impact Factor
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ABSTRACT: FRAT1, like its Xenopus homolog glycogen synthase kinase-3 (GSK-3)-binding protein, is known to inhibit GSK-3-mediated phosphorylation of beta-catenin. It is currently unknown how FRAT-GSK-3-binding protein activity toward GSK-3 is regulated. FRAT1 has recently been shown to be a phosphoprotein in vivo; however, the responsible kinase(s) have not been determined. In this study, we identified Ser188 as a phosphorylated residue in FRAT1. The identity of the kinase that catalyzes Ser188 phosphorylation and the significance of this phosphorylation to FRAT1 function were investigated. Protein kinase A (PKA) was found to phosphorylate Ser188 in vitro as well as in intact cells. Importantly, activation of endogenous cAMP-coupled beta-adrenergic receptors with norepinephrine stimulated the phosphorylation of FRAT1 at Ser188. GSK-3 was also able to phosphorylate FRAT1 at Ser188 and other residues in vitro or when overexpressed in intact cells. In contrast, endogenous GSK-3 did not lead to significant FRAT1 phosphorylation in cells, suggesting that GSK-3 is not a major FRAT1 kinase in vivo. Phosphorylation of Ser188 by PKA inhibited the ability of FRAT1 to activate beta-catenin-dependent transcription. In conclusion, PKA phosphorylates FRAT1 in vitro as well as in intact cells and may play a role in regulating the inhibitory activity of FRAT1 toward GSK-3.
Journal of Biological Chemistry 12/2006; 281(46):35021-9. · 4.77 Impact Factor
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ABSTRACT: MAPK-activated protein kinase 2 (MAPKAP K2 or MK2) is one of several kinases directly regulated by p38 MAPK. A role for p38 MAPK in the pathology of Alzheimer disease (AD) has previously been suggested. Here, we provide evidence to suggest that MK2 also plays a role in neuroinflammatory and neurodegenerative pathology of relevance to AD. MK2 activation and expression were increased in lipopolysaccharide (LPS) + interferon gamma-stimulated microglial cells, implicating a role for MK2 in eliciting a pro-inflammatory response. Microglia cultured ex vivo from MK2-deficient (MK2-/-) mice demonstrated significant inhibition in release of tumor necrosis factor alpha, KC (mouse chemokine with highest sequence identity to human GROs and interleukin-8), and macrophage inflammatory protein 1alpha on stimulation with LPS + interferon gamma or amyloid-beta peptide (1-42) compared with MK2+/+ wild-type microglia. Consistent with an inhibition in pro-inflammatory mediator release, cortical neurons co-cultured with LPS + interferon gamma-stimulated or amyloid-beta peptide (1-42)-stimulated MK2-/- microglia were protected from microglial-mediated neuronal cell toxicity. In a transgenic mouse model of AD in which amyloid precursor protein and presenilin-1 harboring familial AD mutations are overexpressed in specific regions of the brain, elevated activation and expression of MK2 correlated with beta-amyloid deposition, microglial activation, and up-regulation of tumor necrosis factor alpha, macrophage inflammatory protein 1alpha, and KC gene expression in the same brain regions. Our data propose a role for MK2 in AD brain pathology, for which neuroinflammation involving cytokines and chemokines and overt neuronal loss have been documented.
Journal of Biological Chemistry 09/2006; 281(33):23658-67. · 4.77 Impact Factor
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ABSTRACT: The P2X(7) receptor has been implicated in the release of cytokines and in the induction of cell death, and is up-regulated in a transgenic mouse model of Alzheimer's disease. Using cocultures of rat cortical neurons and microglia, we show that ATP and the more potent P2X(7) agonist benzoylbenzoyl-ATP (BzATP) cause neuronal cell injury. The deleterious effects of BzATP-treated microglia were prevented by nonselective P2X antagonists (PPADS and oxidized ATP) and by the more selective P2X(7) antagonist Brilliant Blue G. Similar concentrations of BzATP caused release of superoxide and nitric oxide from isolated microglia, and neuronal cell injury was attenuated by a superoxide dismutase mimetic and by a peroxynitrite decomposition catalyst, suggesting a role for reactive oxide species. Cocultures composed of wild-type cortical neurons, and microglia from P2X(7) receptor-deficient mice failed to exhibit neuronal cell injury in the presence of BzATP, but retained sensitivity to injury when microglia were derived from genotypically matched normal (P2X(7) (+/+) mice), thereby establishing P2X(7) involvement in the injury process. P2X(7) receptor activation on microglia thus appears necessary for microglial-mediated injury of neurons, and proposes that targeting P2X(7) receptors may constitute a novel approach for the treatment of acute and chronic neurodegenerative disorders where a microglial component is evident.
Glia 09/2006; 54(3):234-42. · 4.82 Impact Factor
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ABSTRACT: Insulin regulates the activity of the AP-1 (activator protein-1) transcriptional complex in several cell types. One component of the AP-1 complex is the transcription factor Fra-1 (fos-related antigen-1), and we have demonstrated previously that insulin stimulates the expression of Fra-1 mRNA in CHO.T cells [Griffiths, Black, Culbert, Dickens, Shaw, Gillespie and Tavaré (1998) Biochem. J. 335, 19-26]. Here we demonstrate that insulin stimulates the activity of a fra-1 promoter linked to a luciferase reporter gene, indicating that the ability of insulin to induce expression of Fra-1 mRNA is due, at least in part, to an increase in gene transcription. Furthermore, we found that insulin induces the serine phosphorylation of Fra-1 and reduces its mobility during SDS/PAGE as a result of phosphorylation. The ability of insulin to induce the accumulation of Fra-1 mRNA, stimulate the fra-1 promoter and stimulate phosphorylation of Fra-1 all require the mitogen-activated protein (MAP) kinase cascade, which leads to the activation of extracellular-signal-regulated kinase (Erk) 1/2. Consequently, our results demonstrate that the Erk cascade plays a dual role in the co-ordinated regulation of the transcription and the phosphorylation of Fra-1 by insulin.
Biochemical Journal 01/2003; 368(Pt 2):573-80. · 4.90 Impact Factor
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ABSTRACT: In differentiated 3T3-L1 adipocytes, insulin stimulated the expression of the mRNA for the genes encoding Fra-1 (>100-fold), which is a component of the AP-1 transcriptional complex, beta-actin (6.0-fold) and hexokinase II (2.4-fold). We have examined the signalling pathways involved in these effects of insulin. Rapamycin, which binds to FRAP/mTOR and completely suppressed the activation of p70S6 kinase by insulin, almost completely blocked the induction of the hexokinase II gene, and caused an approximately 50% inhibition of the induction of the Fra-1 gene. PD98059, which completely blocks MAP kinase activation by insulin, inhibited insulin-induced Fra-1 and beta-actin gene expression by approximately 70% and 40%, respectively. These findings suggest that a FRAP/mTOR-dependent pathway is responsible for the induction of hexokinase II expression, and that MAP kinase is required, at least in part, for the stimulation of beta-actin gene expression. However, the induction of Fra-1 gene expression by insulin requires both the FRAP/mTOR and MAP kinase pathways.
Biochimica et Biophysica Acta 10/2002; 1578(1-3):43-50. · 4.66 Impact Factor
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ABSTRACT: Glycogen synthase kinase-3 (GSK-3) is a serine-threonine kinase that is involved in multiple cellular signaling pathways, including the Wnt signaling cascade where it phosphorylates beta-catenin, thus targeting it for proteasome-mediated degradation. Unlike phosphorylation of glycogen synthase, phosphorylation of beta-catenin by GSK-3 does not require priming in vitro, i.e. it is not dependent on the presence of a phosphoserine, four residues C-terminal to the GSK-3 phosphorylation site. Recently, a means of dissecting GSK-3 activity toward primed and non-primed substrates has been made possible by identification of the R96A mutant of GSK-3beta. This mutant is unable to phosphorylate primed but can still phosphorylate unprimed substrates (Frame, S., Cohen, P., and Biondi R. M. (2001) Mol. Cell 7, 1321-1327). Here we have investigated whether phosphorylation of Ser(33), Ser(37), and Thr(41) in beta-catenin requires priming through prior phosphorylation at Ser(45) in intact cells. We have shown that the Arg(96) mutant does not induce beta-catenin degradation but instead stabilizes beta-catenin, indicating that it is unable to phosphorylate beta-catenin in intact cells. Furthermore, if Ser(45) in beta-catenin is mutated to Ala, beta-catenin is markedly stabilized, and phosphorylation of Ser(33), Ser(37), and Thr(41) in beta-catenin by wild type GSK-3beta is prevented in intact cells. In addition, we have shown that the L128A mutant, which is deficient in phosphorylating Axin in vitro, is still able to phosphorylate beta-catenin in intact cells although it has reduced activity. Mutation of Tyr(216) to Phe markedly reduces the ability of GSK-3beta to phosphorylate and down-regulate beta-catenin. In conclusion, we have found that the Arg(96) mutant has a dominant-negative effect on GSK-3beta-dependent phosphorylation of beta-catenin and that targeting of beta-catenin for degradation requires prior priming through phosphorylation of Ser(45).
Journal of Biological Chemistry 07/2002; 277(26):23330-5. · 4.77 Impact Factor
