TRPM3 Is Expressed in Afferent Bladder Neurons and Is Upregulated during Bladder Inflammation.

Matthias Vanneste,Marie Mulier,Axelle Kerstens,Ana Nogueira Freitas,Nele Van Ranst,Thomas Voets,Wouter Everaerts

doi:10.3390/ijms23010107

Abstract

The cation channel TRPM3 is activated by heat and the neurosteroid pregnenolone sulfate. TRPM3 is expressed on sensory neurons innervating the skin, where together with TRPV1 and TRPA1, it functions as one of three redundant sensors of acute heat. Moreover, functional upregulation of TRPM3 during inflammation contributes to heat hyperalgesia. The role of TRPM3 in sensory neurons innervating internal organs such as the bladder is currently unclear. Here, using retrograde labeling and single-molecule fluorescent RNA in situ hybridization, we demonstrate expression of mRNA encoding TRPM3 in a large subset of dorsal root ganglion (DRG) neurons innervating the mouse bladder, and confirm TRPM3 channel functionality in these neurons using Fura-2-based calcium imaging. After induction of cystitis by injection of cyclophosphamide, we observed a robust increase of the functional responses to agonists of TRPM3, TRPV1, and TRPA1 in bladder-innervating DRG neurons. Cystometry and voided spot analysis in control and cyclophosphamide-treated animals did not reveal differences between wild type and TRPM3-deficient mice, indicating that TRPM3 is not critical for normal voiding. We conclude that TRPM3 is functionally expressed in a large proportion of sensory bladder afferent, but its role in bladder sensation remains to be established.

Highlights

Publisher’s Note: MDPI stays neutralThe urinary bladder enables us to store urine effortlessly, until it reaches a certain filling state, and we perceive an urge to void
Since these ganglia contain cell bodies of sensory neurons projecting to other organs, including the bowel and the skin, we injected the fluorescent label Wheat Germ Agglutinin-conjugated (WGA)-AF647 into the bladder wall 7 days prior to dorsal root ganglion (DRG) isolation, allowing specific identification of bladder-innervating neurons
Whereas TRPM3 deletion fully abrogates inflammatory heat hyperalgesia in the skin [9,12], we found here that TRPM3-deficient mice develop cyclophosphamide cystitisinduced voiding dysfunction of a similar severity as wild-type animals. These results indicate that upregulation of TRPM3 is not a key driver of bladder overactivity in this model, and that other channels such as TRPV1 and TRPA1 may contribute to the cystitis phenotype

Summary

Introduction

Publisher’s Note: MDPI stays neutralThe urinary bladder enables us to store urine effortlessly, until it reaches a certain filling state, and we perceive an urge to void. Functional bladder disorders, like overactive bladder (OAB) and interstitial cystitis/bladder pain syndrome (IC/BPS) affect up to 10% of the Western population and negatively impact the quality of life of patients while imposing high socioeconomical costs on society [1,2]. The bladder is innervated by sensory nerves that have their cell bodies in the thoracolumbar (T10-L2) and lumbosacral (L5-S1) dorsal root ganglia (DRG). These spinal afferents have specialized peripheral nerve endings within the bladder mucosa and the detrusor muscle, which express a myriad of ion channels and receptors allowing them to determine the content of the bladder. Several members of the Transient Receptor Potential with regard to jurisdictional claims in published maps and institutional affiliations

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