Direct Activation of Transient Receptor Potential Vanilloid 1(TRPV1) by Diacylglycerol (DAG)

Abstract

The capsaicin receptor, known as transient receptor potential channel vanilloid subtype 1 (TRPV1), is activated by a wide range of noxious stimulants and putative ligands such as capsaicin, heat, pH, anandamide, and phosphorylation by protein kinase C (PKC). However, the identity of endogenous activators for TRPV1 under physiological condition is still debated. Here, we report that diacylglycerol (DAG) directly activates TRPV1 channel in a membrane-delimited manner in rat dorsal root ganglion (DRG) neurons. 1-oleoyl-2-acetyl-sn-glycerol (OAG), a membrane-permeable DAG analog, elicited intracellular Ca 2+ transients, cationic currents and cobalt uptake that were blocked by TRPV1-selective antagonists, but not by inhibitors of PKC and DAG lipase in rat DRG neurons or HEK 293 cells heterologously expressing TRPV1. OAG induced responses were about one fifth of capsaicin induced signals, suggesting that OAG displays partial agonism. We also found that endogenously produced DAG can activate rat TRPV1 channels. Mutagenesis of rat TRPV1 revealed that DAG-binding site is at Y511, the same site for capsaicin binding, and PtdIns(4,5)P 2 binding site may not be critical for the activation of rat TRPV1 by DAG in heterologous system. We propose that DAG serves as an endogenous ligand for rat TRPV1, acting as an integrator of G q/11 -coupled receptors and receptor tyrosine kinases that are linked to phospholipase C.

Membrane-Delimited Coupling of TRPV1 and mGluR5 on Presynaptic Terminals of Nociceptive Neurons

“…Although lipid metabolite products such as hydroperoxyeicosatetraenoic acid and anandamide have been suggested as candidate molecules for mediating GPCR activation of TRPV1 (Hwang et al, 2000;van der Stelt et al, 2005), the identities of endogenous ligands for TRPV1 at the pathophysiological conditions, especially in the central neurons, are still debated. We have recently demonstrated that DAG is a novel endogenous ligand of TRPV1 (Woo et al, 2008). In the present study, we provide further strong evidences that group l mGluR5 activates the TRPV1 channel in a membrane-delimited manner and DAG mediates functional coupling of group l mGluR5 and TRPV1 on central presynaptic terminals of sensory neurons.…”

“…To provide further evidences on the membrane-delimited activation of TRPV1, we used Ca 2ϩ imaging in the present study. As indicated in our previous study (Woo et al, 2008), one possible mechanism of this pathway would be direct interaction between DAG and TRPV1. To investigate this possibility, we used Y511A mutants of TRPV1 (Jordt and Julius, 2002) transiently expressed in HEK293 cells.…”

“…We also demonstrated the mechanisms by which DAG activates TRPV1 using whole-cell patch-clamp recording in a heterologous expression system (Woo et al, 2008). To provide further evidences on the membrane-delimited activation of TRPV1, we used Ca 2ϩ imaging in the present study.…”

“…These results indicated that downstream signaling molecules of PLC mediated DHPG-induced Ca 2ϩ transients and that these effects were a result of a protein kinase-and DAG lipase-independent activation of TRPV1, implying DAG as the most plausible candidate molecule. Indeed, we have recently shown that OAG, a membrane-permeable analog of DAG, directly activates TRPV1 (Woo et al, 2008). We further found in the present study that bath application of OAG produced a Ca 2ϩ transient that was blocked by capsazepine (2.68 Ϯ 0.73%; n ϭ 12; p Ͻ 0.001), but not by staurosporine and RHC80267 (80.85 Ϯ 3.32%; n ϭ 12; p Ͼ 0.001), in DRG neurons (Fig.…”

TRPV1-expressing primary afferents generate behavioral responses to pruritogens via multiple mechanisms

“…However, histamine-induced itch appears to require both PLC␤3 and TRPV1, which suggests that TRPV1 can function as an effector molecule downstream of PLC␤3. In support of this proposal, a recent electrophysiological study (25) demonstrated that TRPV1 is directly activated by diacylglycerol (DAG), which is produced by hydrolysis of PIP 2 , a substrate of PLC␤3. There may be other mechanisms as well for TRPV1 activation in histamine-mediated signaling (10).…”