Functional and biochemical interaction between PPARα receptors and TRPV1 channels: Potential role in PPARα agonists-mediated analgesia

Abstract

Transient receptor potential vanilloid type-1 (TRPV1) channels expressed in primary afferent neurons play a critical role in nociception triggered by endogenous and exogenous compounds. In the present study, the functional and biochemical interaction between TRPV1 channels and type-α peroxisome proliferator-activated receptors (PPARα) has been investigated. In TRPV1-expressing CHO cells, patch-clamp studies revealed that acute application of the PPARα agonists clofibrate (CLO; 0.1–100μM), WY14643 (1–300μM), or GW7647 (0.1–100nM) activated TRPV1 currents in a concentration-dependent manner, with EC50s of 5.3±0.8μM, 13.0±1.2μM, and 12.7±0.3nM, respectively. The role of PPARα in these pharmacological responses was confirmed by the ability of the PPARα antagonist GW6471 (10μM) to block CLO-, WY14643- and GW7647-induced TRPV1 activation, and by the observation that modulation of PPARα levels via siRNA-mediated suppression or PPARα over-expression affected TRPV1 channel activation by PPARα agonists accordingly. In cells cotransfected with PPARα and TRPV1, PPARα receptors were detected in TRPV1-immunoprecipitated fractions. When compared to capsaicin (CAP), TRPV1 currents activated by PPARα agonists showed a higher degree of acute desensitization and tachyphylaxis; moreover, GW7647, when pre-incubated at a concentration (1nM) unable to activate TRPV1 currents per se, desensitized CAP-induced TRPV1 currents. Finally, a sub-effective concentration of each PPARα agonist inhibited TRPV1-dependent bradykinin-induced [Ca2+]i transients in sensory neurons. Collectively, these results provide evidence for a PPARα-mediated pathway triggering TRPV1 channel activation and desensitization, and highlight a novel mechanism which might contribute to the analgesic effects shown by PPARα agonists in vivo.