Human delta opioid receptors stimulate AMP-activated protein kinase through coincident signaling with Gq/11-coupled receptors

The heterotrimeric AMP-activated protein kinase (AMPK) is activated under conditions of metabolic stress, such as glucose deprivation and hypoxia/ischemia, and it may play a neuroprotective role. We previously reported that activation of delta opioid receptors (DOR) stably expressed in CHO cells rapidly stimulated Thr172 phosphorylation of AMPK and increased the enzyme activity through a signaling pathway involving Gi/o proteins and Ca2+/calmodulin-dependent protein kinase kinase β (CaMKKβ). In the present study we have further characterized this regulatory pathway by examining the possible occurrence of DOR interaction with Gq/11-coupled receptors. We found that in CHO cells DOR activation of AMPK was prevented by cell treatment with apyrase, which hydrolyzes extracellular ATP and ADP, and attenuated by either PPADS, a non-selective P2 purinergic receptor antagonist, or MRS 2179, a selective P2Y1 receptor antagonist. Apyrase treatment markedly depressed DOR enhancement of intracellular free Ca2+, whereas MRS 2179 blocked DOR stimulation of phospholipase C activity. Moreover, cell treatment with the Gq/11 antagonist YM-254890 inhibited DOR stimulation of AMPK phosphorylation. In human SH-SY5Y neuroblastoma cells, the DOR agonist SNC 80 failed to affect AMPK phosphorylation but significantly enhanced the stimulatory effect elicited by activation of M3 muscarinic receptors. These data indicate that in different cell systems DOR activation regulates AMPK through a synergistic interaction with Gq/11-coupled receptors, which leads to enhancement of intracellular free Ca2+ and AMPK phosphorylation by CaMKKβ. This mechanism of AMPK regulation may participate in DOR-induced neuroprotection against metabolic insults.