Abstract
Membrane remodeling by inflammatory mediators influences the function of sensory ion channels. The capsaicin- and heat-activated TRPV1 channel contributes to neurogenic inflammation and pain hypersensitivity, in part due to its potentiation downstream of phospholipase C-coupled receptors that regulate phosphoinositide lipid content. Here, we determined the effect of phosphoinositide lipids on TRPV1 function by combining genetic dissection, diet supplementation, behavioral, biochemical, and functional analyses in Caenorhabditis elegans. As capsaicin elicits hot and pain sensation in mammals, transgenic TRPV1 worms exhibit an aversive response to capsaicin. TRPV1 worms with low levels of phosphoinositide lipids display an enhanced response to capsaicin, whereas phosphoinositide lipid supplementation reduces TRPV1-mediated responses. A worm carrying a TRPV1 construct lacking the distal C-terminal domain features an enhanced response to capsaicin, independent of the phosphoinositide lipid content. Our results demonstrate that TRPV1 activity is enhanced when the phosphoinositide lipid content is reduced, and the C-terminal domain is key to determining agonist response in vivo.
SIGNIFICANCE STATEMENT
TRPV1 is an essential protein for the mechanism whereby noxious stimuli, such as high temperatures and chemicals, cause pain. TRPV1 undergoes sensitization, a process in which inflammatory molecules enhance its response to other stimuli, thereby promoting pain hypersensitivity. Proalgesic agents produced in response to tissue injury activate PLC-coupled receptors and alter the membrane phosphoinositide lipid content. The mechanism by which phosphoinositide lipids modulate TRPV1 function has remained controversial. Determining whether membrane phosphoinositides are positive or negative regulators of TRPV1 function is critical for developing therapeutic strategies to ameliorate TRPV1-mediated inflammatory pain. We address the role of phosphoinositide lipids on TRPV1 function using an in vivo approach and report that phosphoinositide lipids reduce TRPV1 activity in vivo.
Footnotes
The authors declare no competing financial interests.
The authors thank Dr. Avi Priel for kindly providing purified DkTx, and Dr. E. Cao for critically reading the manuscript, and Dr. C. Bargmann for providing worm strains. Channel constructs and worm strains DNA were sequenced at the Molecular Resource Center of Excellence at The University of Tennessee Health Science Center with the assistance of Dr. Tom Cunningham. Lipid analyses were provided by the Mass Spectrometry Lipidomics Core Facility at Wayne State University (supported, in part, by the National Center for Research Resources, National Institutes of Health grant S10RR027926) and the University of Colorado Anschutz Medical Campus in Aurora, Colorado.
This work was supported by the National Institutes of Health (R01GM133845 to V.V. and R01GM125629 to J.F.C.-M.), the United States-Israel Binational Science Foundation (2015221 to V.V.), the American Heart Association (16SDG26700010 to V.V. and 15SDG25700146 to J.F.C.-M.), and the Neuroscience Institute at UTHSC (Postdoctoral Matching Salary Support to R.C. and J.L.).
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