TRPV4 inhibition prevents paclitaxel-induced neurotoxicity in preclinicalmodels

Wolfgang Boehmerlea,b,c,⁎,1, Petra Huehnchena,b,c,1, Sabrina Lin Lin Leeb,d, Christoph Harmsa,b,c,d,1, Matthias Endresa,b,c,d,e,f,1

Paclitaxel is a cytotoxic drug which frequently causes sensory peripheral neuropathy in patients. Increasing
evidence suggests that altered intracellular calcium (Ca2+) signals play an important role in the pathogenesis of
this condition. In the present study, we examined the interplay between Ca2+ release channels in the endoplasmic reticulum (ER) and Ca2+ permeable channels in the plasma membrane in the context of paclitaxel
mediated neurotoxicity. We observed that in small to medium size dorsal root ganglia neurons (DRGN) the
inositol-trisphosphate receptor (InsP3R) type 1 was often concentrated in the periphery of cells, which is in
contrast to homogenous ER distribution. G protein-coupled designer receptors were used to further elucidate
phosphoinositide mediated Ca2+ signaling: This approach showed strong InsP3 mediated Ca2+ signals close to
the plasma membrane, which can be amplified by Ca2+ entry through TRPV4 channels. In addition, our results
support a physical interaction and partial colocalization of InsP3R1 and TRPV4 channels. In the context of
paclitaxel-induced neurotoxicity, blocking Ca2+ influx through TRPV4 channels reduced cell death in cultured
DRGN. Pretreatment of mice with the pharmacological TRPV4 inhibitor HC067047 prior to paclitaxel injections
prevented electrophysiological and behavioral changes associated with paclitaxel-induced neuropathy.
In summary, these results underline the relevance of TRPV4 signaling for the pathogenesis of paclitaxelinduced neuropathy and suggest novel preventive strategies

Keywords: Paclitaxel, Neuropathy, Calcium, TRPV4, Inositol-trisphosphate receptor

Presenter: Hye In Kim

A re‐innervated in vitro skin model of non‐histaminergic itch and skin neurogenic inflammation: PAR2‐, TRPV1‐ and TRPA1‐agonist induced functionality

N. Lebonvallet, J. W. Fluhr, C. Le Gall‐Ianotto, R. Leschiera, M. Talagas, J.‐L. Carré, A. Reux, L. Misery, A. Bataille, C. Brun3, T. Oddos3, J.‐P. Pennec4

• Published in:- Skin Health and Disease

Abstract

Background: Skin, and epidermis, is innervated by sensory nerve fibres. Interactions between them and signal transduction are only partially eluci- dated in physiological/pathological conditions, especially in pruritus.

Objectives: To study the mechanisms involved in pruritus in vitro, we developed a skin explant model re‐innervated by sensory neurons.

Methods: This model is based on the co‐culture of human skin explants and sensory neurons from dorsal root ganglia of rats. Innervation and the expression of protease activated receptor 2 (PAR2), transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential ankyrin one (TRPA1) was analysed by immunostaining. The response of the model to TRPV1, PAR2 and TRPA1 agonists was analysed by patch‐clamp, qPCR and enzyme‐linked immunosorbent assay.

Results: After 5 days of re‐innervating nerve fibres was evidenced in the epidermis. Re‐innervation was correlated with decrease of epidermal thickness and the number of apoptotic cells in the tissue. The major actors of non‐histaminergic itch (PAR‐2, thymic stromal lymphopoietin [TSLP], TSLP‐R, TRPA1 and TRPV1) were expressed in neurons and/or epidermal cells of skin explants. After topical exposure of TRPV1‐(Capsaicin), TRPA1‐ (Polygodial) and PAR2‐agonist (SLIGKV‐NH2) activation of reinnervating neurons could be shown in patch‐clamp analysis. The release of TSLP was increased with capsaicin or SLIGKV but decreased with polygodial. Release of CGRP was increased by capsaicin and polygodial but decreased with SLIGKV. Activation by SLIGKV showed a decrease of VEGF; polygodial induced an increase of TSLP, Tumour necrosis factor (TNF) and nerve growth factor and capsaicin lead to a decrease of sema3 and TNF expression.

Conclusion: The present model is suitable for studying itch and neurogenic inflammation pathways in vitro. We observed that activation of TRPV1, TRPA1 and PAR‐2 leads to different response profiles in re‐innervated skin explants.

The role of Na _v 1.7 and methylglyoxal-mediated activation of TRPA1 in itch and hypoalgesia in a murine model of type 1 diabetes

Ruo-Xiao Cheng, Yu Feng, Di Liu, Zhi-Hong Wang, Jiang-Tao Zhang, Li-Hua Chen, Cun-Jin Su, Bing Wang, Ya Huang, Ru-Rong Ji, Ji Hu, Tong Liu

Abstract

Methylglyoxal (MGO), an endogenous reactive carbonyl compound, plays a key role in the pathogenesis of diabetic neuropathy. The aim of this study is to investigate the role of MGO in diabetic itch and hypoalgesia, two common symptoms associated with diabetic neuropathy. 

Methods: Scratching behavior, mechanical itch (alloknesis), and thermal hypoalgesia were quantified after intradermal (i.d.) injection of MGO in naïve mice or in diabetic mice induced by intraperitoneal (i.p.) injection of streptozotocin (STZ). Behavioral testing, patch-clamp recording, transgenic mice, and gene expression analysis were used to investigate the mechanisms underlying diabetic itch and hypoalgesia in mice. 

Results: I.d. injection of MGO evoked dose-dependent scratching in normal mice. Addition of MGO directly activated transient receptor potential ankyrin 1 (TRPA1) to induce inward currents and calcium influx in dorsal root ganglia (DRG) neurons or in TRPA1-expressing HEK293 cells. Mechanical itch, but not spontaneous itch was developed in STZ-induced diabetic mice. Genetic ablation of Trpa1 (Trpa1^-/- ), pharmacological blockade of TRPA1 and Na_v1.7, antioxidants, and mitogen-activated protein kinase kinase enzyme (MEK) inhibitor U0126 abrogated itch induced by MGO or in STZ-induced diabetic mice. Thermal hypoalgesia was induced by intrathecal (i.t.) injection of MGO or in STZ-induced diabetic mice, which was abolished by MGO scavengers, intrathecal injection of TRPA1 blockers, and in Trpa1^-/- mice. 

Conclusion: This study revealed that Na_v1.7 and MGO-mediated activation of TRPA1 play key roles in itch and hypoalgesia in a murine model of type 1 diabetes. Thereby, we provide a novel potential therapeutic strategy for the treatment of itch and hypoalgesia induced by diabetic neuropathy.

Keywords: Diabetes; Hypoalgesia; Itch; Methylglyoxal; TRPA1.

The Role of Transient Receptor Potential A1 and G Protein-Coupled Receptor 39 in Zinc-Mediated Acute and Chronic Itch in Mice

Yue Hu^1†, Qing-Yue Fu^1†, Dan-Ni Fu^1†, Xue-Long Wang^2†, Zhi-Hong Wang¹, Jiang-Tao Zhang³, Wen-Jing Xu³, Guo-Kun Zhou³, Li-Hua Chen^4* and Tong Liu^3,5,6*

• ¹Jiangsu Key Laboratory of Neuropsychiatric Diseases and Institute of Neuroscience, Soochow University, Suzhou, China
• ²Department of Thoracic Surgery, Capital Medical University Electric Power Teaching Hospital Beijing, Beijing, China
• ³Institute of Pain Medicine and Special Environmental Medicine, Nantong University, Nantong, China
• ⁴Department of Nutrition and Food Hygiene, School of Public Health, Nantong University, Nantong, China
• ⁵College of Life Sciences, Yanan University, Yan’an, China
• ⁶Suzhou Key Laboratory of Intelligent Medicine and Equipment, Soochow University, Suzhou, China

Itching is a common symptom of many skin or systemic diseases and has a negative impact on the quality of life. Zinc, one of the most important trace elements in an organism, plays an important role in the regulation of pain. Whether and how zinc regulates itching is largely unclear. Herein, we explored the role of Zn²⁺ in the regulation of acute and chronic itch in mice. It is found that intradermal injection (i.d.) of Zn²⁺ dose-dependently induced acute itch and transient receptor potential A1 (TRPA1) participated in Zn²⁺-induced acute itch in mice. Moreover, the pharmacological analysis showed the involvement of histamine, mast cells, opioid receptors, and capsaicin-sensitive C-fibers in Zn²⁺-induced acute itch in mice. Systemic administration of Zn²⁺ chelators, such as N,N,N′,N′-Tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), pyrithione, and clioquinol were able to attenuate both acute itch and dry skin-induced chronic itch in mice. Quantitative polymerase chain reaction (Q-PCR) analysis showed that the messenger RNA (mRNA) expression levels of zinc transporters (ZIPs and ZnTs) significantly changed in the dorsal root ganglia (DRG) under dry skin-induced chronic itch condition in mice. Activation of extracellular signal-regulated kinase (ERK) pathway was induced in the DRG and skin by the administration of zinc or under dry skin condition, which was inhibited by systemic administration of Zn²⁺ chelators. Finally, we found that the expression of GPR39 (a zinc-sensing GPCR) was significantly upregulated in the dry skin mice model and involved in the pathogenesis of chronic itch. Together, these results indicated that the TRPA1/GPR39/ERK axis mediated the zinc-induced itch and, thus, targeting zinc signaling may be a promising strategy for anti-itch therapy.

Keywords: GPR39; Itch; TRPA1; Zn2+; p-ERK.