Zakrzewicz_2017_Front.Cell.Neurosci_11_189

Recently, we discovered a cholinergic mechanism that inhibits the adenosine triphosphate (ATP)-dependent release of interleukin-1beta (IL-1beta) by human monocytes via nicotinic acetylcholine receptors (nAChRs) composed of alpha7, alpha9 and/or alpha10 subunits. Furthermore, we identified phosphocholine (PC) and dipalmitoylphosphatidylcholine (DPPC) as novel nicotinic agonists that elicit metabotropic activity at monocytic nAChR. Interestingly, PC does not provoke ion channel responses at conventional nAChRs composed of subunits alpha9 and alpha10. The purpose of this study is to determine the composition of nAChRs necessary for nicotinic signaling in monocytic cells and to test the hypothesis that common metabolites of phosphatidylcholines, lysophosphatidylcholine (LPC) and glycerophosphocholine (G-PC), function as nAChR agonists. In peripheral blood mononuclear cells from nAChR gene-deficient mice, we demonstrated that inhibition of ATP-dependent release of IL-1beta by acetylcholine (ACh), nicotine and PC depends on subunits alpha7, alpha9 and alpha10. Using a panel of nAChR antagonists and siRNA technology, we confirmed the involvement of these subunits in the control of IL-1beta release in the human monocytic cell line U937. Furthermore, we showed that LPC (C16:0) and G-PC efficiently inhibit ATP-dependent release of IL-1beta. Of note, the inhibitory effects mediated by LPC and G-PC depend on nAChR subunits alpha9 and alpha10, but only to a small degree on alpha7. In Xenopuslaevis oocytes heterologously expressing different combinations of human alpha7, alpha9 or alpha10 subunits, ACh induced canonical ion channel activity, whereas LPC, G-PC and PC did not. In conclusion, we demonstrate that canonical nicotinic agonists and PC elicit metabotropic nAChR activity in monocytes via interaction of nAChR subunits alpha7, alpha9 and alpha10. For the metabotropic signaling of LPC and G-PC, nAChR subunits alpha9 and alpha10 are needed, whereas alpha7 is virtually dispensable. Furthermore, molecules bearing a PC group in general seem to regulate immune functions without perturbing canonical ion channel functions of nAChR.