A β1/2 adrenergic receptor-sensitive intracellular signaling pathway modulates CCL2 production in cultured spinal astrocytes.

The phosphorylation of c-jun N-terminal kinase (JNK) and the subsequent production of C-C chemokine CCL2 (monocyte chemoattractant protein; MCP-1) in spinal astrocytes contribute to the initiation of neurological disorders including chronic pain. Astrocytes express neurotransmitter receptors which could be targeted to ameliorate neurological disorders. In the current study, the involvement of the β-adrenergic system in the regulation of JNK activity and CCL2 production after stimulation with tumor necrosis factor (TNF)-α, one of many initiators of neuroinflammation, was elucidated. Treatment of cultured spinal astrocytes with isoproterenol (a β-adrenergic receptor agonist; 1 µM) reduced both TNF-α-induced JNK1 phosphorylation, as observed by Western blotting, and the subsequent increase of both CCL2 mRNA expression and CCL2 production, which were measured by real time-PCR and ELISA, respectively. The effects of isoproterenol were completely blocked by pretreatment with either propranolol (a β-adrenoceptor antagonist) or H89 (a protein kinase A [PKA] inhibitor). The current study revealed that the regulation of glycogen synthase kinase-3β (GSK-3β) activity is a crucial factor in the inhibitory action of isoproterenol. The TNF-α-induced JNK1 phosphorylation was significantly blocked by treatment with GSK-3β inhibitors (either LiCl or TWS119), and stimulation of β-adrenergic receptors induced the inhibition of GSK-3β through the phosphorylation of Ser(9) . Moreover, treatment with isoproterenol markedly suppressed the TNF-α-induced increase of CCL2 mRNA expression and CCL2 production through a β-adrenergic receptor-PKA pathway mediated by GSK-3β regulation. Thus, activation of β1/2 adrenergic receptors expressed in spinal astrocytes could be a novel method of moderating neurological disorders with endogenous catecholamines or selective agonists.