Trk and cAMP-dependent survival activity of adenosine A2A agonist CGS21680 on rat motoneurons in culture

The survival activity of adenosine A_2A agonist CGS21680 on motoneurons in culture through the transactivation of neurotrophin receptor TrkB has been reported previously; however, since adenosine A_2A receptor belongs to a Gs-protein-coupled receptor, we investigated the involvement of the cAMP pathway in the survival activity of CGS21680 using purified motoneurons in culture. CGS21680 alone showed only small survival activity, but the activity was significantly enhanced by the addition of a phosphodiesterase inhibitor, IBMX. This survival activity was partially inhibited by a protein kinase A inhibitor H89 or a neurotrophin receptor tyrosine kinase inhibitor K252a, and was completely inhibited by their combination. These results indicate that the survival activity of CGS21680 on motoneurons is exerted by the mixed effect of the adenylate cyclase–cAMP–PKA pathway and transactivation of Trk neurotrophin receptor. Under conditions in which the maximum survival of motoneurons was supported by sufficient concentrations of brain-derived neurotrophic factor (BDNF), a TrkB ligand, the addition of 100 μM AMPA for 3 days led to significant cell death. Treatment with CGS21680 and IBMX protected motoneurons from the toxicity of AMPA, further supporting the presence of a TrkB-independent pathway of CGS21680 activity and suggesting a novel therapeutic approach to motoneuron diseases such as amyotrophic lateral sclerosis.