Molecular mechanisms involved in the adenosine A(1) and A(2A) receptor-induced neuronal differentiation in neuroblastoma cells and striatal primary cultures

Adenosine A(1) receptors (A(1)Rs) and adenosine A(2A) receptors (A(2A)Rs) are the major mediators of the neuromodulatory actions of adenosine in the brain. In the striatum A(1)Rs and A(2A)Rs are mainly co-localized in the GABAergic striatopallidal neurons. In this paper we show that agonist-induced stimulation of A(1)Rs and A(2A)Rs induces neurite outgrowth processes in the human neuroblastoma cell line SH-SY5Y and also in primary cultures of striatal neuronal precursor cells. The kinetics of adenosine-mediated neuritogenesis was faster than that triggered by retinoic acid. The triggering of the expression of TrkB neurotrophin receptor and the increase of cell number in the G(1) phase by the activation of adenosine receptors suggest that adenosine may participate in early steps of neuronal differentiation. Furthermore, protein kinase C (PKC) and extracellular regulated kinase-1/2 (ERK-1/2) are involved in the A(1)R- and A(2A)R-mediated effects. Inhibition of protein kinase A (PKA) activity results in a total inhibition of neurite outgrowth induced by A(2A)R agonists but not by A(1)R agonists. PKA activation is therefore necessary for A(2A)R-mediated neuritogenesis. Co-stimulation does not lead to synergistic effects thus indicating that the neuritogenic effects of adenosine are mediated by either A1 or A(2A) receptors depending upon the concentration of the nucleoside. These results are relevant to understand the mechanisms by which adenosine receptors modulate neuronal differentiation and open new perspectives for considering the use of adenosine agonists as therapeutic agents in diseases requiring neuronal repair.