The ability to sense temperature is essential for organism survival and efficient metabolism. Body temperatures profoundly affect many physiological functions, including immunity. Transient receptor potential melastatin 2 (TRPM2) is a thermosensitive, Ca 2+ -permeable cation channel expressed in a wide range of immunocytes. TRPM2 is activated by adenosine diphosphate ribose and hydrogen peroxide (H 2 O 2 ), although the activation mechanism by H 2 O 2 is not well understood. Here we report a unique activation mechanism in which H 2 O 2 lowers the temperature threshold for TRPM2 activation, termed “sensitization,” through Met oxidation and adenosine diphosphate ribose production. This sensitization is completely abolished by a single mutation at Met-214, indicating that the temperature threshold of TRPM2 activation is regulated by redox signals that enable channel activity at physiological body temperatures. Loss of TRPM2 attenuates zymosan-evoked macrophage functions, including cytokine release and fever-enhanced phagocytic activity. These findings suggest that redox signals sensitize TRPM2 downstream of NADPH oxidase activity and make TRPM2 active at physiological body temperature, leading to increased cytosolic Ca 2+ concentrations. Our results suggest that TRPM2 sensitization plays important roles in macrophage functions.

Key pointsr Lysophosphatidic acid (LPA) is an itch mediator, but not a pain mediator by a cheek injection model.r Dorsal root ganglion neurons directly respond to LPA depending on transient receptor potential ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1).r LPA-induced itch-related behaviours are decreased in TRPA1-knockout (KO), TRPV1KO or TRPA1TRPV1 double KO mice. Abstract Intractable and continuous itch sensations often accompany diseases such as atopic dermatitis, neurogenic lesions, uremia and cholestasis. Lysophosphatidic acid (LPA) is an itch mediator found in cholestatic itch patients and it induces acute itch and pain in experimental rodent models. However, the molecular mechanism by which LPA activates peripheral sensory neurons remains unknown. In this study, we used a cheek injection method in mice to reveal that LPA induced itch-related behaviours but not pain-related behaviours. The LPA-induced itch behaviour and cellular effects were dependent on transient receptor potential ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1), which are important for itch signal transduction. We also found that, among the six LPA receptors, the LPA 5 receptor had the greatest involvement in itching. Furthermore, we demonstrated that phospholipase D (PLD) plays a critical role downstream of LPA 5 and that LPA directly and intracellularly activates TRPA1 and TRPV1. These results suggest a unique mechanism by which cytoplasmic LPA produced de novo could activate TRPA1 and TRPV1. We conclude that LPA-induced itch is mediated by LPA 5 , PLD, TRPA1 and TRPV1 signalling, and thus targeting TRPA1, TRPV1 or PLD could be effective for cholestatic itch interventions.

Transient Receptor Potential (TRP) channels serve as temperature receptors in a wide variety of animals and must have played crucial roles in thermal adaptation. The TRP vanilloid (TRPV) subfamily contains several temperature receptors with different temperature sensitivities. The TRPV3 channel is known to be highly expressed in skin, where it is activated by warm temperatures and serves as a sensor to detect ambient temperatures near the body temperature of homeothermic animals such as mammals. Here we performed comprehensive comparative analyses of the TRPV subfamily in order to understand the evolutionary process; we identified novel TRPV genes and also characterized the evolutionary flexibility of TRPV3 during vertebrate evolution. We cloned the TRPV3 channel from the western clawed frog Xenopus tropicalis to understand the functional evolution of the TRPV3 channel. The amino acid sequences of the N- and C-terminal regions of the TRPV3 channel were highly diversified from those of other terrestrial vertebrate TRPV3 channels, although central portions were well conserved. In a heterologous expression system, several mammalian TRPV3 agonists did not activate the TRPV3 channel of the western clawed frog. Moreover, the frog TRPV3 channel did not respond to heat stimuli, instead it was activated by cold temperatures. Temperature thresholds for activation were about 16 °C, slightly below the lower temperature limit for the western clawed frog. Given that the TRPV3 channel is expressed in skin, its likely role is to detect noxious cold temperatures. Thus, the western clawed frog and mammals acquired opposite temperature sensitivity of the TRPV3 channel in order to detect environmental temperatures suitable for their respective species, indicating that temperature receptors can dynamically change properties to adapt to different thermal environments during evolution.