The Molecular Basis for Species-specific Activation of Human TRPA1 Protein by Protons Involves Poorly Conserved Residues within Transmembrane Domains 5 and 6

• Published in: The Journal of biological chemistry 2013-07, Vol.288 (28), p.20280-20292
• Main Authors: de la Roche, Jeanne, Eberhardt, Mirjam J., Klinger, Alexandra B., Stanslowsky, Nancy, Wegner, Florian, Koppert, Wolfgang, Reeh, Peter W., Lampert, Angelika, Fischer, Michael J.M., Leffler, Andreas
• Format: Article
• Language: English
• Subjects: Acid-sensing Ion Channels (ASIC); Acidosis; Animals; Binding Sites - genetics; Calcium - metabolism; Calcium Channels - genetics; Calcium Channels - metabolism; Capsaicin - pharmacology; Cells, Cultured; Cymenes; Ganglia, Spinal - cytology; Ganglia, Spinal - metabolism; HEK293 Cells; Humans; Hydrogen-Ion Concentration; Ionomycin - pharmacology; Macaca mulatta; Membrane Biology; Membrane Potentials - drug effects; Mice; Mice, Inbred C57BL; Mice, Knockout; Monoterpenes - pharmacology; Mutation; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - metabolism; Neurons - drug effects; Neurons - metabolism; Neurons - physiology; Nociceptor; Pain; Patch Clamp; Potassium - pharmacology; Protons; Rats; Species Specificity; Transient Receptor Potential Channels - genetics; Transient Receptor Potential Channels - metabolism; TRP Channels; TRPA1 Cation Channel
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M113.479337

The surveillance of acid-base homeostasis is concerted by diverse mechanisms, including an activation of sensory afferents. Proton-evoked activation of rodent sensory neurons is mainly mediated by the capsaicin receptor TRPV1 and acid-sensing ion channels. In this study, we demonstrate that extracellular acidosis activates and sensitizes the human irritant receptor TRPA1 (hTRPA1). Proton-evoked membrane currents and calcium influx through hTRPA1 occurred at physiological acidic pH values, were concentration-dependent, and were blocked by the selective TRPA1 antagonist HC030031. Both rodent and rhesus monkey TRPA1 failed to respond to extracellular acidosis, and protons even inhibited rodent TRPA1. Accordingly, mouse dorsal root ganglion neurons lacking TRPV1 only responded to protons when hTRPA1 was expressed heterologously. This species-specific activation of hTRPA1 by protons was reversed in both mouse and rhesus monkey TRPA1 by exchange of distinct residues within transmembrane domains 5 and 6. Furthermore, protons seem to interact with an extracellular interaction site to gate TRPA1 and not via a modification of intracellular N-terminal cysteines known as important interaction sites for electrophilic TRPA1 agonists. Our data suggest that hTRPA1 acts as a sensor for extracellular acidosis in human sensory neurons and should thus be taken into account as a yet unrecognized transduction molecule for proton-evoked pain and inflammation. The species specificity of this property is unique among known endogenous TRPA1 agonists, possibly indicating that evolutionary pressure enforced TRPA1 to inherit the role as an acid sensor in human sensory neurons. Background: Extracellular acidosis mediates pain and inflammation by activating sensory afferent neurons. Results: Protons activate and sensitize human TRPA1 in a strongly species-specific manner encoded by transmembrane domains 5 and 6. Conclusion: Our data identify TRPA1 as an ion channel likely to mediate acid-induced pain in humans. Significance: Protons are the first known endogenous agonists of TRPA1 with species-specificity for human TRPA1.