THE SELECTIVE ADENOSINE A2A RECEPTOR AGONIST CGS 21680 REDUCES JNK MAPK ACTIVATION IN OLIGODENDROCYTES IN INJURED SPINAL CORD

Permanent functional deficit after spinal cord injury (SCI) arises from both mechanical injury and from secondary tissue reactions involving inflammation. Adenosine is an important regulator of inflammatory mechanisms. Although functional studies indicate a protective effect of adenosine A(2A) receptor agonists in SCI, the basic molecular mechanisms accounting for the their protective effects from SCI have to be fully elucidated. In this study, we investigated if the selective A(2A) receptor agonist 2-[p-(2-carboxyethyl)-phenethylamino]-5'-N-ethylcarboxamidoadenosine (CGS 21680) administered after SCI has protective effects against tissue damage, motor deficit, and different inflammatory readouts. Spinal cord injury was induced in mice by extradural compression of a section of the SC exposed via a four-level T5-T8 laminectomy. CGS 21680, administered by subcutaneously implanted osmotic minipumps after SCI, clearly reduced motor deficit for up to 19 days after operation. The drug repeatedly administered intraperitoneally after SCI reduced tissue damage, influx of myeloperoxidase-positive leukocytes, nuclear factor-kappa B activation and iNOS expression in injured spinal cord tissue 24 h after SCI. Enhanced immunoreactivity of microglia, astrocytes, and oligodendrocytes (stained by anti-CD11/B, anti-filial fibrillary acidic protein, and anti-Olig2 antibodies, respectively) was also observed 24 h after SCI. Neurons lose immunoreactivity in the nucleus. c-Jun amino-terminal kinase (JNK) mitogen-activated protein kinase, quantified by Western blot, was definitely activated in injured tissue. CGS 21680 treatment significantly reduced JNK phosporylation. Phospho-JNK mitogen-activated protein kinase was de novo expressed selectively in oligodendrocytes. CGS 21680 reduced phospho-JNK immunostaining in oligodendrocytes. Data indicate that protection by the A(2A) agonist is secondary to reduced leukocyte recruitment in the damaged area. A reducing effect of JNK activation in oligodendrocytes might account for protective effect of the A(2A) agonist against SCI-induced demyelination.