Selective adenosine A2a receptor antagonism reduces JNK activation in oligodendrocytes after cerebral ischaemia

Abstract

Adenosine is a potent biological mediator, the concentration of which increases dramatically following brain ischaemia. During ischaemia, adenosine is in a concentration range (μM) that stimulates all four adenosine receptor subtypes (A1, A2A, A2B and A3). In recent years, evidence has indicated that the A2A receptor subtype is of critical importance in stroke. We have previously shown that 24 h after medial cerebral artery occlusion (MCAo), A2A receptors up-regulate on neurons and microglia of ischaemic striatum and cortex and that subchronically administered adenosine A2A receptor antagonists protect against brain damage and neurological deficit and reduce activation of p38 mitogen-activated protein kinase (MAPK) in microglial cells. The mechanisms by which A2A receptors are noxious during ischaemia still remain elusive. The objective of the present study was to investigate whether the adenosine A2A antagonist SCH58261 affects JNK and MEK1/ERK MAPK activation. A further aim was to investigate cell types expressing activated JNK and MEK1/ERK MAPK after ischaemia. We hereby report that the selective adenosine A2A receptor antagonist, SCH58261, administered subchronically (0.01 mg/kg i.p) 5 min, 6 and 20 h after MCAo in male Wistar rats, reduced JNK MAPK activation (immunoblot analysis: phospho-JNK54 isoform by 81 and phospho-JNK46 isoform by 60) in the ischaemic striatum. Twenty-four hours after MCAo, the Olig2 transcription factor of oligodendroglial progenitor cells and mature oligodendrocytes was highly expressed in cell bodies in the ischaemic striatum. Immunofluorescence staining showed that JNK MAPK is maximally expressed in Olig2-stained oligodendrocytes and in a few NeuN stained neurons. Striatal cell fractioning into nuclear and extra-nuclear fractions demonstrated the presence of Olig2 transcription factor and JNK MAPK in both fractions. The A2A antagonist reduced striatal Olig 2 transcription factor (immunoblot analysis: by 55) and prevented myelin disorganization, assessed by myelin-associated glycoprotein staining. Twenty-four hours after MCAo, ERK1/2 MAPK was highly activated in the ischaemic striatum, mostly in microglia, while it was reduced in the ischaemic cortex. The A2A antagonist did not affect activation of the ERK1/2 pathway. The efficacy of A2A receptor antagonism in reducing activation of JNK MAPK in oligodendrocytes suggests a mechanism of protection consisting of scarring oligodendrocyte inhibitory molecules that can hinder myelin reconstitution and neuron functionality.