Expression of Transient Receptor Potential Ankyrin 1 (TRPA1) and Its Role in Insulin Release from Rat Pancreatic Beta Cells

De-Shou Cao,Linlin Zhong,Lauren Hughes,Mruvil Abooj,Mahendra Bishnoi,Louis S Premkumar,Tsung-Han Hsieh,Alexander G Obukhov

doi:10.1371/journal.pone.0038005

Abstract

ObjectiveSeveral transient receptor potential (TRP) channels are expressed in pancreatic beta cells and have been proposed to be involved in insulin secretion. However, the endogenous ligands for these channels are far from clear. Here, we demonstrate the expression of the transient receptor potential ankyrin 1 (TRPA1) ion channel in the pancreatic beta cells and its role in insulin release. TRPA1 is an attractive candidate for inducing insulin release because it is calcium permeable and is activated by molecules that are produced during oxidative glycolysis.MethodsImmunohistochemistry, RT-PCR, and Western blot techniques were used to determine the expression of TRPA1 channel. Ca2+ fluorescence imaging and electrophysiology (voltage- and current-clamp) techniques were used to study the channel properties. TRPA1-mediated insulin release was determined using ELISA.ResultsTRPA1 is abundantly expressed in a rat pancreatic beta cell line and freshly isolated rat pancreatic beta cells, but not in pancreatic alpha cells. Activation of TRPA1 by allyl isothiocyanate (AITC), hydrogen peroxide (H2O2), 4-hydroxynonenal (4-HNE), and cyclopentenone prostaglandins (PGJ2) and a novel agonist methylglyoxal (MG) induces membrane current, depolarization, and Ca2+ influx leading to generation of action potentials in a pancreatic beta cell line and primary cultured pancreatic beta cells. Activation of TRPA1 by agonists stimulates insulin release in pancreatic beta cells that can be inhibited by TRPA1 antagonists such as HC030031 or AP-18 and by RNA interference. TRPA1-mediated insulin release is also observed in conditions of voltage-gated Na+ and Ca2+ channel blockade as well as ATP sensitive potassium (KATP) channel activation.ConclusionsWe propose that endogenous and exogenous ligands of TRPA1 cause Ca2+ influx and induce basal insulin release and that TRPA1-mediated depolarization acts synergistically with KATP channel blockade to facilitate insulin release.

Highlights

The Transient Receptor Potential (TRP) channels TRPC, TRPV, TRPM, TRPP, TRPML, and TRPA are involved in diverse functions that include transduction of sensory information, cell growth/death, and neurotransmitter/hormone release [1]
Activation of transient receptor potential ankyrin 1 (TRPA1) by allyl isothiocyanate (AITC), hydrogen peroxide (H2O2), 4-hydroxynonenal (4HNE), and cyclopentenone prostaglandins (PGJ2) and a novel agonist methylglyoxal (MG) induces membrane current, depolarization, and Ca2+ influx leading to generation of action potentials in a pancreatic beta cell line and primary cultured pancreatic beta cells
Expression of TRPA1 in pancreatic beta cells Using RT-PCR technique, the presence of TRPA1 channel was detected in dorsal root ganglion (DRG), pancreas (Pan) and pancreatic islets (Isl), and in rat pancreatic beta cell line RINm5F (RIN), but not in a hamster pancreatic alpha cell line, INR1G9 (INR) (Fig. 1a)

Summary

Introduction

The Transient Receptor Potential (TRP) channels TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPP (polycystin), TRPML (mucolipin), and TRPA (ankyrin) are involved in diverse functions that include transduction of sensory information, cell growth/death, and neurotransmitter/hormone release [1]. TRPM4 has been shown to control insulin secretion in pancreatic beta cells [13,14], and recently, a role for TRPM5 was indicated by the finding of altered Ca2+ oscillations in beta cells from TRPM5 knockout animals [15]. These TRP channels are expressed in pancreatic beta cells and are associated with insulin release, the efficacy and the endogenous ligands for these channels are far from clear

Methods

Results

Conclusion