Involvement of P2 receptors in the modulation of nociceptive afferent stimuli
Final Report Abstract
P2 purinergic receptors respond to the extracellular signaling molecule ATP. Homomeric P2X3 and heteromeric P2X2/3 receptors are ligand-gated cationic channels, located at the nerve terminals and cell bodies of sensory neurons. They participate in the transformation of tissue damage into painful stimuli at the levels of peripheral tissues and the spinal cord. Based on a homology model of the P2X3 receptor structure, we identified groups of amino acids which are involved in the binding of ATP to the agonist binding jaw. Further, it was demonstrated that the uninhibited flexibility of the upper and lower lips of this jaw are a prerequisite for gating movements of the receptor channel and the subsequent flux of ions initiating action potentials. We constructed a kinetic model for the simulation of ATP-induced currents and their desensitization behavior. Later this model was extended to describe the kinetics of both agonist and antagonist binding to the receptor. Since P2X3 receptors cause rapidly desensitizing currents, their effects are necessarily complemented by the slowly desensitizing P2X2/3 receptors. It was interesting to clarify that the P2X2 subunit may associate with either P2X3 or P2X6 subunits to heteromers and that the stoichiometry of this association is governed by the law of mass action, rather than by specific binding sites between the individual subunits. Eventually, the ATP-gated P2X7 receptors, originally described to be present at immunocytes (e.g. macrophages, microglia) were shown to be located also on astrocytes in the pain-relevant layer II of the spinal cord dorsal horn. The activation of this receptor type induced negligible astrocytic currents, which were however markedly potentiated in a low cation-containing extracellular medium. It was found that the stimulation of P2X7 receptors at astrocytes releases glutamate and nitric oxide onto the neighboring neurons and thereby might intensify pain sensation. In conclusion, neuronal P2X3 and P2X2/3 as well as astrocytic P2X7 receptors modulate a wide range of painful stimuli. We are confident that our results are supportive to understand the mechanism of action of these receptor sites both at the molecular and cellular level and in consequence alleviate the search for new analgesic compounds with relatively modest side effects.
Publications
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Amino acid residues constituting the agonist binding site of the human P2X3 receptor. J Biol Chem. 2011; 286: 2739–49
Bodnar M, Wang H, Riedel T, Hintze S, Kato E, Fallah G, Gröger-Arndt H, Giniatullin R, Grohmann M, Hausmann R, Schmalzing G, Illes P, Rubini P
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Clemastine potentiates the human P2X7 receptor by sensitizing it to lower ATP concentrations. J Biol Chem. 2011; 286: 11067–81
Nörenberg W, Hempel C, Urban N, Sobottka H, Illes P, Schaefer M
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Molecular determinants of potent P2X2 antagonism identified by functional analysis, mutagenesis and homology docking. Mol Pharmacol. 2011; 79: 649–61
Wolf C, Rosefort C, Fallah G, Kassack MU, Hamacher A, Bodnar M, Wang H, Illes P, Kless A, Bahrenberg G, Schmalzing G, Hausmann R
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Different subunit stoichiometry of functional P2X2/3 and P2X2/6 receptors. J Biol Chem. 2012; 287: 13930–43
Hausmann R, Bodnar M, Woltersdorf R, Wang H, Fuchs M, Messemer N, Qin Y, Riedel T, Grohmann M, Nieber K, Schmalzing G, Rubini P, Illes P
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Effects of nucleotide analogues at the human P2X3 receptor and its mutants identify the agonist binding pouch. Mol Pharmacol. 2012; 82: 80–9
Riedel T, Wiese S, Leichsenring A, Illes P
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Kinetic analysis of the binding of antagonistic drugs to the fast desensitizing P2X3 receptor by means of a Markov model. PLoS One. 2013; 8: e79213
Helms N, Kowalski M, Illes P, Riedel T
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Astrocyte-neuron interaction in the substantia gelatinosa of the spinal cord dorsal horn via P2X7 receptor-mediated release of glutamate and reactive oxygen species. Glia. 2014; 62: 1671–86
Ficker C, Rozmer K, Kato E, Ando RD, Schumann L, Krügel U, Franke H, Sperlagh B, Riedel T, Illes P
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Conformational flexibility of the agonist binding jaw of the hP2X3 receptor is a prerequisite for channel opening. Br J Pharmacol. 2014; 171: 5093–112
Kowalski M, Hausmann R, Grohmann M, Dopychai A, Franke H, Nieber K, Schmalzing G, Illes P, Riedel T
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The P2X7 receptor: an emerging target in CNS diseases. Trends Pharmacol Sci. 2014; 35: 537–47
Sperlagh B, Illes P
