Distinct Mechanisms Account for In Vitro Activation and Sensitization of TRPV1 by the Porphyrin Hemin.

Natalie E Palmaers,Steffen B Wiegand,Frank G Echtermeyer,Mirjam J Eberhardt,Andreas Leffler,Christine Herzog

doi:10.3390/ijms221910856

Natalie E Palmaers, Steffen B Wiegand + Show 4 more

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https://doi.org/10.3390/ijms221910856

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Abstract

TRPV1 mediates pain occurring during sickling episodes in sickle cell disease (SCD). We examined if hemin, a porphyrin released during intravascular hemolysis modulates TRPV1. Calcium imaging and patch clamp were employed to examine effects of hemin on mouse dorsal root ganglion (DRG) neurons and HEK293t cells expressing TRPV1 and TRPA1. Hemin induced a concentration-dependent calcium influx in DRG neurons which was abolished by the unspecific TRP-channel inhibitor ruthenium red. The selective TRPV1-inhibitor BCTC or genetic deletion of TRPV1 only marginally impaired hemin-induced calcium influx in DRG neurons. While hTRPV1 expressed in HEK293 cells mediated a hemin-induced calcium influx which was blocked by BCTC, patch clamp recordings only showed potentiated proton- and heat-evoked currents. This effect was abolished by the PKC-inhibitor chelerythrine chloride and in protein kinase C (PKC)-insensitive TRPV1-mutants. Hemin-induced calcium influx through TRPV1 was only partly PKC-sensitive, but it was abolished by the reducing agent dithiothreitol (DTT). In contrast, hemin-induced potentiation of inward currents was not reduced by DTT. Hemin also induced a redox-dependent calcium influx, but not inward currents on hTRPA1. Our data suggest that hemin induces a PKC-mediated sensitization of TRPV1. However, it also acts as a photosensitizer when exposed to UVA-light used for calcium imaging. The resulting activation of redox-sensitive ion channels such as TRPV1 and TRPA1 may be an in vitro artifact with limited physiological relevance.

Highlights

The ability of sensory neurons to detect painful noxae largely depends on irritant receptors such as the capsaicin receptor TRPV1 which is gated by several exogenous and endogenous substances [1]
We started this study by exploring the effects of hemin on mouse dorsal root ganglion (DRG) neurons by means of ratiometric calcium imaging recordings
Data are shown as mean ± S.E.M. *** denotes p < 0.001. In this mechanistic in vitro study, we demonstrate that the porphyrin hemin is able to sensitize the capsaicin receptor TRPV1 in a protein kinase C (PKC)-dependent manner

Summary

Introduction

The ability of sensory neurons to detect painful noxae largely depends on irritant receptors such as the capsaicin receptor TRPV1 (transient receptor potential cation channel subfamily V member 1) which is gated by several exogenous and endogenous substances [1]. In addition to mediating pain, TRPV1-expressing sensory neurons seem to maintain organ function and to fulfil protective effects in several disorders [4,5,6,7,8,9,10]. A recent study from Xu and colleagues describes that TRPV1-expressing sensory neurons have an important protective role in the hematologic disorder sickle cell disease (SCD) [4]. In a mouse model of SCD, the ablation of TRPV1-expressing sensory neurons resulted in an aggravated phenotype with more severe vaso-occlusive episodes, resulting in organ dysfunction and an increased lethality. Among several proalgesic cytokines which are released from mast cells, tryptase may sensitize TRPV1 by activating the PAR2 receptor expressed in sensory neurons. Sadler et al found that increased levels of chemokine ligand 2 lead to a sensitization of TRPV1 via the chemokine receptor 2 [14]

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