Molecular Signalling Mediating the Protective Effect of A₁Adenosine and mGlu3 Metabotropic Glutamate Receptor Activation against Apoptosis by Oxygen/Glucose Deprivation in Cultured Astrocytes

Abstract

Astrocyte death may occur in neurodegenerative disorders and complicates the outcome of brain ischemia, a condition associated with high extracellular levels of adenosine and glutamate. We show that pharmacological activation of A 1 adenosine and mGlu3 metabotropic glutamate receptors with N 6 -chlorocyclopentyladenosine (CCPA) and (Ϫ)2-oxa-4-aminocyclo-[3.1.0]hexane-4,6-dicarboxylic acid (LY379268), respectively, protects cultured astrocytes against apoptosis induced by a 3-h exposure to oxygen/glucose deprivation (OGD). Protection by CCPA and LY379268 was less than additive and was abrogated by receptor blockade with selective competitive antagonists or pertussis toxin. Both in control astrocytes and in astrocytes exposed to OGD, CCPA and LY379268 induced a rapid activation of the phosphatidylinositol-3-kinase (PI3K) and extracellular signal-regulated kinases 1 and 2 (ERK1/2)/mitogen-activated protein kinase (MAPK) pathways, which are known to support cell survival. In cultures exposed to OGD, CCPA and LY379268 reduced the activation of c-Jun N-terminal kinase and p38/MAPK, reduced the levels of the proapoptotic protein Bad, increased the levels of the antiapoptotic protein Bcl-X L , and were highly protective against apoptotic death, as shown by nuclear 4Ј-6-diamidino-2-phenylindole staining and measurements of caspase-3 activity. All of these effects were attenuated by treatment with 1,4-diamino-2,3-dicyano-1,4-bis(methylthio)butadiene (U0126) and 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride (LY294002), which inhibit the MAPK and the PI3K pathways, respectively. These data suggest that pharmacological activation of A 1 and mGlu3 receptors protects astrocytes against hypoxic/ischemic damage by stimulating the PI3K and ERK1/2 MAPK pathways.Astrocytes, the most abundant glial cell types in the brain, provide metabolic and trophic support to neurons by several mechanisms that include the clearance of ions and environmental toxins, the supply of energy substrates, and the production of trophic factors, and modulate synaptic activity (Volterra and Meldolesi, 2005). Impairments in these functions critically affect neuronal survival.Recent studies have shown that ischemic and inflammatory insults induce astrocyte apoptotic death, and this contributes to the pathophysiology of short-and long-term neurodegenerative disorders (Takuma et al., 2004). Apoptotic astrocytes are found in Alzheimer's disease (Kobayashi et al., ABBREVIATIONS: CCPA, N 6 -chlorocyclopentyladenosine; ASK1, apoptosis-signal-regulating kinase 1; DAPI, 4Ј-6-diamidino-2-phenylindole; DMEM, Dulbecco's modified Eagle's medium; DPCPX, 1,3-dipropyl-8-cyclopentyl xanthine; ERK1/2, extracellular signal-regulated kinases 1 and 2; HRP, horseradish peroxidase; JNK, c-Jun N-terminal kinase; LY294002, 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride; LY341495, (2S,1ЈS,2ЈS)-2(9-xanthylmethyl)-2-(2Ј-carboxycyclo-propyl)glycine; LY379268, (Ϫ)2-oxa-4-aminocyclo-[3.1.0] hexane-4,6-dicarboxylic acid; MAPK, mitogen-activated p...

Purinergic Mechanisms in Epilepsy

“…Activation of the A1 adenosine receptor has been shown to powerfully protect astrocytes from apoptosis [23,24]. Supporting these results Bjorklund et al [25] found that both A1 and A3 adenosine receptors were implicated in protecting astrocytes from injury.…”

Activation of Type 4 Metabotropic Glutamate Receptor Attenuates Oxidative Stress-Induced Death of Neural Stem Cells with Inhibition of JNK and p38 MAPK Signaling

“…Future studies should include the identification of these possible molecules, which might be used as targets for protecting cells from apoptosis through inhibiting the JNK and p38 signaling pathways. JNK and p38 MAPKs are also referred to various types of mGluRs in regulating cell apoptosis and survival in CNS insults [64][65][66]. The present study showed that mGluR4 activation attenuated the JNK and p38 phosphorylation induced by H 2 O 2 in cultured NSCs and the action is possibly linked with the inhibition of procaspase-3cleavage and the suppression of NSC apoptosis, suggesting mGluR4-mediated protection of NSCs might be due to the inhibition of JNK/p38 MAPKs.…”

Gliopreventive effects of guanosine against glucose deprivation in vitro

“…Here, guanosine reversed the decrease in glutamate uptake caused by glucose deprivation; however, this effect was abolished by the p38 MAPK and ERK specific inhibitors. Additionally, the activation of MAPK/ERK is considered one of the major protective pathways in glucose deprivation [108,109].…”