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 (muM) that stimulates all four adenosine receptor subtypes (A(1), A(2A), A(2B) and A(3)). In recent years, evidence has indicated that the A(2A) receptor subtype is of critical importance in stroke. We have previously shown that 24 h after medial cerebral artery occlusion (MCAo), A(2A) receptors up-regulate on neurons and microglia of ischaemic striatum and cortex and that subchronically administered adenosine A(2A) 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 A(2A) receptors are noxious during ischaemia still remain elusive. The objective of the present study was to investigate whether the adenosine A(2A) 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 A(2A) 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 A(2A) 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 A(2A) antagonist did not affect activation of the ERK1/2 pathway. The efficacy of A(2A) 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.

Role of The Purinergic Neuromodulation System in Epilepsy

“…Thus, A 2A R are also located in astrocytes and microglia cells [238][239][240], where they can control glutamate clearance [94,241], the expression and action of trophic factors [242][243][244][245] and neuroinflammation [238,244,246,247]. Furthermore, A 2A R were also recently found to be present in oligodendrocytes, controlling their degeneration upon ischemia [248]. Probably both neuronal and non-neuronal mechanisms contribute to the ability of A 2A R to control neurodegeneration, according to their temporal pattern of recruitment: for instance, using the MPTP animal model of Parkinson's disease, it has been shown that damage caused by administration of higher doses of MPTP (causing a rapid neurodegeneration) is prevented by non-neuronal A 2A R blockade [240], whereas damage caused by administration of lower doses of MPTP (causing a slow and insidious neurodegeneration) is instead prevented by the genetic deletion of neuronal A 2A R [249].…”

Purinergic Signaling and Blood Vessels in Health and Disease

“…It has been claimed that A 2A receptor-stimulated cascade in bone marrow-derived cells is an important modulator of ischemic brain injury (Yu et al, 2004). A 2A receptor antagonism reduced JNK MAPK activation in oligodendrocytes after cerebral ischemia (Melani et al, 2010). In A 2A receptor knockout mice there was a decrease in early ischemic vascular injury after subarachnoid hemorrhage (Sehba et al, 2010).…”

Protecting White Matter From Stroke Injury

“…10 However, adenosine acting through A 2A receptors on oligodendrocytes could also have deleterious effects. 22 Paradoxically, both agonists and antagonists of α2 noradrenergic receptors improve WM recovery after ischemic/reperfusion injury, apparently by reducing axonal Na + and Ca 2+ accumulation. 14 Complex, but plausible, actions of these agents might explain these strange results.…”

“…This review summarizes current knowledge of the molecular mechanisms of ischemic injury to WM and discusses its translational implications for the treatment of stroke (Table). [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] …”