The capsaicin receptor TRPV1 ion channel is a polymodal nociceptor that responds to heat with exquisite sensitivity through an unknown mechanism. Here we report the identification of a novel toxin, RhTx, from the venom of the Chinese red-headed centipede that potently activates TRPV1 to produce excruciating pain. RhTx is a 27-amino-acid small peptide that forms a compact polarized molecule with very rapid binding kinetics and high affinity for TRPV1. We show that RhTx targets the channel’s heat activation machinery to cause powerful heat activation at body temperature. The RhTx–TRPV1 interaction is mediated by the toxin’s highly charged C terminus, which associates tightly to the charge-rich outer pore region of the channel where it can directly interact with the pore helix and turret. These findings demonstrate that RhTx binding to the outer pore can induce TRPV1 heat activation, therefore providing crucial new structural information on the heat activation machinery.

Anoctamin 1 (ANO1) or TMEM16A gene encodes a member of Ca2+ activated Cl– channels (CaCCs) that are critical for physiological functions, such as epithelial secretion, smooth muscle contraction and sensory signal transduction. The attraction and interest in ANO1/TMEM16A arise from a decade long investigations that abnormal expression or dysfunction of ANO1 is involved in many pathological phenotypes and diseases, including asthma, neuropathic pain, hypertension and cancer. However, the lack of specific modulators of ANO1 has impeded the efforts to validate ANO1 as a therapeutic target. This review focuses on the recent progress made in understanding of the pathophysiological functions of CaCC ANO1 and the current modulators used as pharmacological tools, hopefully illustrating a broad spectrum of ANO1 channelopathy and a path forward for this target validation.

Temperature-sensitive and calcium-permeable transient receptor potential vanilloid 3 (TRPV3) channel abundantly expressed in the keratinocyte plays important functions in the skin physiology. Dysfunctional gain-of-function mutations of TRPV3 cause genetic Olmsted Syndrome (OS) characterized by palmoplantar and periorificial keratoderma, inflammation and severe itch, suggesting that pharmacological inhibition of overactive TRPV3 may be beneficial for therapy of pruritus or skin disorders. To test this hypothesis, we identified a natural compound forsythoside B as an inhibitor of TRPV3 through a screen of HEK293 cells expressing human TRPV3 channels in calcium fluorescent assay. Whole-cell patch clamp recordings further confirmed that forsythoside B selectively inhibited TRPV3 current activated by TRP channel agonist 2-APB (50-->µ<--M) in dose-dependent manner with an IC50 value of 6.7-->± <--0.7 µM. In vivo evaluation of scratching behavior demonstrates that inhibition of TRPV3 by forsythoside B significantly attenuated acute itch induced by either TRPV3 agonist carvacrol or pruritogen histamine, and also chronic itch of dry skin induced by acetone-ether-water (AEW) in mice. Furthermore, forsythoside B is able to prevent cell death of HEK293 cells and native HaCaT cells from human keratinocytes expressing gain-of-function TRPV3 G573S mutant or in the presence of TRPV3 agonist carvacrol. Taken together, our findings demonstrate the crucial role of TRPV3 in pruritus and keratinocyte toxicity, and specific inhibition of overactive TRPV3 by natural forsythoside B may possess therapeutic potential for chronic pruritus, skin allergy or inflammation-related skin diseases.

Coumarin osthole is a dominant bioactive ingredient of natural Cnidium monnieri plant commonly used as traditional Chinese herbal medicines for therapies and treatments including antipruritus and antidermatitis. However, the molecular mechanism underlying the action of osthole remains unclear. In this study we report that osthole exerts antipruritic effect through selective inhibition of Ca2+-permeable and thermosensitive TRPV3 cation channels that are primarily expressed in the keratinocytes of the skin. Coumarin osthole was identified as an inhibitor of TRPV3 channels transiently expressed in HEK293 cells in the calcium fluorescent FlexStation assay. Inhibition of TRPV3 current by osthole and its selectivity were further confirmed by whole-cell patch clamp recordings of TRPV3 expressing HEK293 cells and mouse primary cultured keratinocytes. Behavioral evaluation demonstrated that inhibition of TRPV3 by osthole or silencing by knockout of TRPV3 gene significantly reduced the scratching induced by either acetone-ether-water (AEW) or histamine in localized rostral neck skin in mice. Taken together, our findings provide a molecular basis for use of natural coumarin osthole from C. monnieri plant in antipruritic or skin care therapy, thus establishing a significant role of TRPV3 channel in chronic itch signaling or acute histamine-dependent itch sensation.