No abstract

Cannabinoids exert pleiotropic actions in the CNS, including the inhibition of inflammatory responses and the enhancement of neuronal survival after injury. Although cannabinoid receptors are distributed widely in brain, their presence has not been investigated previously in oligodendrocytes. This study examined the expression of cannabinoid type 1 (CB1) receptors in rat oligodendrocytes in vivo and in culture and explored their biological function. Expression of CB1 receptors by oligodendrocytes was demonstrated immunocytochemically in postnatal and in adult white matter as well as in oligodendrocyte cultures. Reverse transcription-PCR and Western blotting further confirmed the presence of CB1 receptors. Oligodendrocyte progenitors undergo apoptosis with the withdrawal of trophic support, as determined by TUNEL assay and caspase-3 activation, and both the selective CB1 agonist arachidonyl-2'-chloroethylamide/(all Z)-N-(2-cycloethyl)-5,8,11,14-eicosatetraenamide (ACEA) and the nonselective cannabinoid agonists HU210 and (+)-Win-55212-2 enhanced cell survival. To investigate intracellular signaling involved in cannabinoid protection, we focused on the phosphatidylinositol-3 kinase (PI3K)/Akt pathway. HU210, (+)-Win-55212-2, and ACEA elicited a time-dependent phosphorylation of Akt. Pertussis toxin abolished Akt activation, indicating the involvement of G(i)/G(o)-protein-coupled receptors. The CB1 receptor antagonist SR141716A partially inhibited Akt phosphorylation in response to HU210 and (+)-Win-55212-2 and abolished the effects of ACEA. Trophic support deprivation downregulated Akt activity, and cannabinoids recovered phospho-Akt levels. Inhibition of PI3K abrogated the survival action and the recovery of Akt activity in response to cannabinoids. SR141716A prevented only the protection conferred by ACEA. Nevertheless, SR141716A and the selective CB2 receptor antagonist SR144528 in combination inhibited the prosurvival action of HU210, which is in accordance with the finding of CB2 receptor expression by oligodendroglial cells. These data identify oligodendrocytes as potential targets of cannabinoid action in the CNS.

No abstract

Neurodegenerative disorders include a variety of pathological conditions, which share similar critical metabolic processes such as protein aggregation and oxidative stress, both of which are associated with the involvement of metal ions. In this review Alzheimer's disease and Parkinson's disease are mainly discussed, with the aim of identifying common trends underlying these neurological conditions. Chelation therapy could be a valuable therapeutic approach, since metals are considered to be a pharmacological target for the rationale design of new therapeutic agents directed towards the treatment of neurodegeneration.

Interleukin-1 receptor antagonist (IL-1ra) is an important anti-inflammatory cytokine that blocks all known actions of IL-1 and markedly protects against experimentally induced ischemic, excitotoxic, and traumatic brain insults. Cannabinoids (CBs) also exert potent anti-inflammatory and neuroprotective effects, but the mechanisms of their actions are unknown. Here we tested the hypothesis that the actions of CBs are mediated by endogenous IL-1ra. We report for the first time that both CB1 and CB2 receptors modulate release of endogenous IL-1ra from primary cultured glial cells. Activation of CB1 or CB2 receptors increased lipopolysaccharide-induced IL-1ra release, and specific CB1 or CB2 antagonists blocked lipopolysaccharide-induced production of IL-1ra from glial cells. Comparison of neuronal cultures from wild-type mice and mice lacking IL-1ra (knock-out) indicates that endogenous IL-1ra is essential for the neuro-protective effects of CBs against excessive activation of glutamate receptors (excitotoxicity) in response to S-AMPA or NMDA. Similarly, analysis of mixed glial cultures from IL-1ra knock-out mice indicates that endogenous IL-1ra is required for the CB-induced inhibition of nitric oxide production in response to bacterial lipopolysaccharide. These data suggest a novel neuroprotective mechanism of action for CBs in response to inflammatory or excitotoxic insults that is mediated by both CB1 and CB2 receptor-dependent pathways.

1 Interleukin-1 (IL-1) is an important mediator of immunoin¯ammatory responses in the brain. In the present study, we examined whether prostaglandin E 2 (PGE 2 ) production after IL-1b stimulation is dependent upon activation of protein kinases in astroglial cells. 2 Astrocyte cultures stimulated with IL-1b or the phorbol ester, PMA signi®cantly increased PGE 2 secretion. The stimulatory action of IL-1b on PGE 2 production was totally abolished by NS-398, a speci®c inhibitor of cyclo-oxygenase-2 activity, as well as by the protein synthesis inhibitor cycloheximide, and the glucocorticoid dexamethasone. Furthermore, IL-1b induced the expression of COX-2 mRNA. This occurred early at 2 h, with a maximum at 4 h and declined at 12 h. IL-1 b treatment also induced the expression of COX-2 protein as determined by immunoblot analysis. In that case the expression of the protein remained high at least up to 12 h. 3 Treatment of cells with protein kinase C inhibitors (H-7, bisindolylmaleimide and calphostin C) inhibited IL-1b stimulation of PGE 2 . In addition, PKC-depleted astrocyte cultures by overnight treatment with PMA no longer responded to PMA or IL-1. The ablation of the e ects of PMA and IL-1b on PGE 2 production, likely results from down-regulation of phorbol ester sensitive-PKC isoenzymes. Immunoblot analysis demonstrated the translocation of the conventional isoform cPKC-a from cytosol to membrane following treatment with IL-1b. 4 In addition, IL-1b treatment led to activation of extracellular signal-regulated kinase (ERK1/2) and p38 subgroups of MAP kinases in astroglial cells. Interestingly, the inhibition of ERK kinase with PD 98059, as well as the inhibition of p38 MAPK with SB 203580, prevented IL-1b-induced PGE 2 release. 5 ERK1/2 activation by IL-1b was sensitive to inhibition by the PKC inhibitor bisindolylmaleimide suggesting that ERK phosphorylation is a downstream signal of PKC activation. 6 These results suggest key roles for PKC as well as for ERK1/2 and p38 MAP kinase cascades in the biosynthesis of PGE 2 , likely by regulating the induction of cyclo-oxygenase-2, in IL-1b-stimulated astroglial cells.

Neurospheres are clonal cellular aggregates of neural stem/precursor cells that grow in culture as free-floating clusters. Activation of CB1 cannabinoid receptors, which are expressed by these cells, promotes proliferation. In the present study we investigated the expression of CB2 cannabinoid receptors and the effect of exogenous cannabinoids on neural stem/precursor cell proliferation. Neurospheres containing nestin-positive and sn-1 diacylglycerol lipase alpha-positive cells expressed both CB1 and CB2 receptors, which were maintained through several passages. Application of the non-selective cannabinoid agonist (HU-210, 0.5 microM) stimulated bromodeoxyuridine incorporation and neurosphere formation. This action involved both CB1 and CB2 receptors as neurosphere formation was stimulated by either selective CB1 [arachidonyl-2'chloroethylamide/(all Z)-N-(2-cycloethyl)-5,8,11,14-eicosatetraenamide (ACEA), 200 nM and 1 microM] or CB2 (JWH-056, 0.5 microM) agonists. In addition, CB1 or CB2 antagonists (1 microM SR-141716A and SR-144528, respectively) blocked basal proliferation, suggesting that endogenous cannabinoids are implicated in neurosphere proliferation. In addition, cannabinoid agonist-stimulated proliferation was reduced by the Akt translocation inhibitor BML-257 (12.5 microM), suggesting a role for phosphoinositide-3 kinase signalling. Together, our results suggest that cannabinoids stimulate proliferation of neural stem/precursor cells acting on both CB1 and CB2 cannabinoid receptors through a phosphoinositide-3 kinase/Akt pathway.

The purpose of this study was to investigate the role of the central cannabinoid receptor (CB1) in mediating the actions of the endogenous cannabinoid agonist anandamide and the synthetic cannabinoid CP‐55940. Activation of primary mouse astrocyte cultures by exposure to bacterial lipopolysaccharide (LPS) caused a marked (approximately tenfold) increase in nitric oxide (NO) release. Coincubation with the cannabinoid agonists anandamide or CP‐55940 markedly inhibited release of NO (–12% to –55%). This effect was abolished by SR‐141716A (1 μM), a CB1 receptor antagonist. SR‐141716A alone also significantly increased NO release in response to LPS, suggesting that endogenous cannabinoids modify inflammatory responses. In contrast, coincubation with the CB2 receptor antagonist SR‐144528 (1 μM) abolished the inhibitory effects of the endogenous cannabinoid anandamide on LPS‐induced NO release, although this may reflect nonspecific effects of this ligand or cannabinoid actions through atypical receptors of anandamide. We also showed that endogenous or synthetic cannabinoids inhibit LPS‐induced inducible NO synthase expression (mRNA and protein) in astrocyte cultures. These results indicate that CB1 receptors may promote antiinflammatory responses in astrocytes. © 2002 Wiley‐Liss, Inc.