Transient receptor potential ankyrin 1 channel: An evolutionarily tuned thermosensor

Human Transient Receptor Potential Ankyrin 1 Channel: Structure, Function, and Physiology

The transient receptor potential ion channel TRPA1 is a Ca2+-permeable nonselective cation channel widely expressed in sensory neurons, but also in many nonneuronal tissues typically possessing barrier functions, such as the skin, joint synoviocytes, cornea, and the respiratory and intestinal tracts. Here, the primary role of TRPA1 is to detect potential danger stimuli that may threaten the tissue homeostasis and the health of the organism. The ability to directly recognize signals of different modalities, including chemical irritants, extreme temperatures, or osmotic changes resides in the characteristic properties of the ion channel protein complex. Recent advances in cryo-electron microscopy have provided an important framework for understanding the molecular basis of TRPA1 function and have suggested novel directions in the search for its pharmacological regulation. This chapter summarizes the current knowledge of human TRPA1 from a structural and functional perspective and discusses the complex allosteric mechanisms of activation and modulation that play important roles under physiological or pathophysiological conditions. In this context, major challenges for future research on TRPA1 are outlined.

TRPA1 rare variants in chronic neuropathic and nociplastic pain patients

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TRPA1 gene is significantly enriched of rare variants in neuropathic pain and fibromyalgia patients, with itch or cold-induced pain as the most common features, opening new treatment opportunities.

Missing aspects of the heritability of chronic neuropathic pain, as a complex adult-onset trait, may be hidden within rare variants with low effect on disease risk, unlikely to be resolved by a single-variant approach. To identify new risk genes, we performed a next-generation sequencing of 107 pain genes and collapsed the rare variants through gene-wise aggregation analysis. The optimal unified sequence kernel association test was applied to 169 patients with painful neuropathy, 223 patients with nociplastic pain (82 diagnosed with chronic widespread pain and 141 with fibromyalgia), and 216 healthy controls. Frequency and features of variants in TRPA1 , which was the most significant gene, were further validated in 2 independent cohorts of 140 patients with chronic pain (90 with painful neuropathy and 50 with chronic widespread pain) and 34 with painless neuropathy. The effect of aminoacidic changes were modeled in silico according to physicochemical characteristics. TRPA1 was significantly enriched of rare variants which significantly discriminated chronic pain patients from healthy controls after Bonferroni correction (P = 6.7 × 10−4, ρ = 1), giving a risk of 4.8-fold higher based on the simple burden test (P = 0.0015, OR = 4.8). Among the 32 patients harboring TRPA1 variants, 24 (75%) were diagnosed with nociplastic pain, either fibromyalgia (12; 37.5%) or chronic widespread pain (12; 37.5%), whereas 8 (25%) with painful neuropathy. Irrespective of the clinical diagnosis, 12 patients (38%) complained of itch and 10 (31.3%) of cold-induced or cold-accentuated pain, mostly episodic. Our study widens the spectrum of channelopathy-related chronic pain disorders and contributes to bridging the gap between phenotype and targeted therapies based on patients' molecular profile.

1_tzjjvsic Kaltura

North African fox genomes show signatures of repeated introgression and adaptation to life in deserts

Elucidating the evolutionary process of animal adaptation to deserts is key to understanding adaptive responses to climate change. Here we generated 82 individual whole genomes of four fox species (genus Vulpes) inhabiting the Sahara Desert at different evolutionary times. We show that adaptation of new colonizing species to a hot arid environment has probably been facilitated by introgression and trans-species polymorphisms shared with older desert resident species, including a putatively adaptive 25 Mb genomic region. Scans for signatures of selection implicated genes affecting temperature perception, non-renal water loss and heat production in the recent adaptation of North African red foxes (Vulpes vulpes), after divergence from Eurasian populations approximately 78 thousand years ago. In the extreme desert specialists, Rueppell's fox (V. rueppellii) and fennec (V. zerda), we identified repeated signatures of selection in genes affecting renal water homeostasis supported by gene expression and physiological differences. Our study provides insights into the mechanisms and genetic underpinnings of a natural experiment of repeated adaptation to extreme conditions.

Transient Receptor Potential Ankyrin 1 (TRPA1) Channel as a Sensor of Oxidative Stress in Cancer Cells

Moderate levels of reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂), fuel tumor metastasis and invasion in a variety of cancer types. Conversely, excessive ROS levels can impair tumor growth and metastasis by triggering cancer cell death. In order to cope with the oxidative stress imposed by the tumor microenvironment, malignant cells exploit a sophisticated network of antioxidant defense mechanisms. Targeting the antioxidant capacity of cancer cells or enhancing their sensitivity to ROS-dependent cell death represent a promising strategy for alternative anticancer treatments. Transient Receptor Potential Ankyrin 1 (TRPA1) is a redox-sensitive non-selective cation channel that mediates extracellular Ca²⁺ entry upon an increase in intracellular ROS levels. The ensuing increase in intracellular Ca²⁺ concentration can in turn engage a non-canonical antioxidant defense program or induce mitochondrial Ca²⁺ dysfunction and apoptotic cell death depending on the cancer type. Herein, we sought to describe the opposing effects of ROS-dependent TRPA1 activation on cancer cell fate and propose the pharmacological manipulation of TRPA1 as an alternative therapeutic strategy to enhance cancer cell sensitivity to oxidative stress.

Endogenous Inflammatory Mediators Produced by Injury Activate TRPV1 and TRPA1 Nociceptors to Induce Sexually Dimorphic Cold Pain That Is Dependent on TRPM8 and GFRα3

The detection of environmental temperatures is critical for survival, yet inappropriate responses to thermal stimuli can have a negative impact on overall health. The physiological effect of cold is distinct among somatosensory modalities in that it is soothing and analgesic, but also agonizing in the context of tissue damage. Inflammatory mediators produced during injury activate nociceptors to release neuropeptides, such as calcitonin gene-related peptide (CGRP) and substance P, inducing neurogenic inflammation, which further exasperates pain. Many inflammatory mediators induce sensitization to heat and mechanical stimuli but, conversely, inhibit cold responsiveness, and the identity of molecules inducing cold pain peripherally is enigmatic, as are the cellular and molecular mechanisms altering cold sensitivity. Here, we asked whether inflammatory mediators that induce neurogenic inflammation via the nociceptive ion channels TRPV1 (vanilloid subfamily of transient receptor potential channel) and TRPA1 (transient receptor potential ankyrin 1) lead to cold pain in mice. Specifically, we tested cold sensitivity in mice after intraplantar injection of lysophosphatidic acid or 4-hydroxy-2-nonenal, finding that each induces cold pain that is dependent on the cold-gated channel transient receptor potential melastatin 8 (TRPM8). Inhibition of CGRP, substance P, or toll-like receptor 4 (TLR4) signaling attenuates this phenotype, and each neuropeptide produces TRPM8-dependent cold pain directly. Further, the inhibition of CGRP or TLR4 signaling alleviates cold allodynia differentially by sex. Last, cold pain induced by both inflammatory mediators and neuropeptides requires TRPM8, as well as the neurotrophin artemin and its receptor GDNF receptor α3 (GFRα3). These results are consistent with artemin-induced cold allodynia requiring TRPM8, demonstrating that neurogenic inflammation alters cold sensitivity via localized artemin release that induces cold pain via GFRα3 and TRPM8.SIGNIFICANCE STATEMENT The cellular and molecular mechanisms that generate pain are complex with a diverse array of pain-producing molecules generated during injury that act to sensitize peripheral sensory neurons, thereby inducing pain. Here we identify a specific neuroinflammatory pathway involving the ion channel TRPM8 (transient receptor potential cation channel subfamily M member 8) and the neurotrophin receptor GFRα3 (GDNF receptor α3) that leads to cold pain, providing select targets for potential therapies for this pain modality.

The role of TRPA1 channels in thermosensation

Transient receptor potential ankyrin 1 (TRPA1) is a polymodal nonselective cation channel sensitive to different physical and chemical stimuli. TRPA1 is associated with many important physiological functions in different species and thus is involved in different degrees of evolution. TRPA1 acts as a polymodal receptor for the perceiving of irritating chemicals, cold, heat, and mechanical sensations in various animal species. Numerous studies have supported many functions of TRPA1, but its temperature-sensing function remains controversial. Although TRPA1 is widely distributed in both invertebrates and vertebrates, and plays a crucial role in tempreture sensing, the role of TRPA1 thermosensation and molecular temperature sensitivity are species-specific. In this review, we summarize the temperature-sensing role of TRPA1 orthologues in terms of molecular, cellular, and behavioural levels.

The human TRPA1 intrinsic cold and heat sensitivity involves separate channel structures beyond the N-ARD domain

TRP channels sense temperatures ranging from noxious cold to noxious heat. Whether specialized TRP thermosensor modules exist and how they control channel pore gating is unknown. We studied purified human TRPA1 (hTRPA1) truncated proteins to gain insight into the temperature gating of hTRPA1. In patch-clamp bilayer recordings, ∆1-688 hTRPA1, without the N-terminal ankyrin repeat domain (N-ARD), was more sensitive to cold and heat, whereas ∆1-854 hTRPA1, also lacking the S1-S4 voltage sensing-like domain (VSLD), gained sensitivity to cold but lost its heat sensitivity. In hTRPA1 intrinsic tryptophan fluorescence studies, cold and heat evoked rearrangement of VSLD and the C-terminus domain distal to the transmembrane pore domain S5-S6 (CTD). In whole-cell electrophysiology experiments, replacement of the CTD located cysteines 1021 and 1025 with alanine modulated hTRPA1 cold responses. It is proposed that hTRPA1 CTD harbors cold and heat sensitive domains allosterically coupled to the S5-S6 pore region and the VSLD, respectively.