Involvement of TRPV4 in serotonin-evoked scratching

Several thermo-sensitive TRP channels (TRPV1, -3; TRPA1) have been implicated in itch. In contrast, the role of transient receptor potential vanilloid type-4 (TRPV4) in itch is unknown. Therefore, we investigated if TRPV4, a temperature-sensitive cation channel, plays an important role in acute itch in mice. Four different pruritogens including serotonin (5-hydroxytrytamine, 5-HT), histamine, SLIGRL (PAR2/MrgprC11 agonist) and chloroquine (MrgprA3 agonist) were intradermally injected and itch-related scratching behavior was assessed. TRPV4 knockout (TRPV4KO) mice exhibited significantly fewer 5-HT-evoked scratching bouts compared to wild-type (WT) mice. Notably, no differences between TRPV4KO and WT mice were observed in the number of scratch bouts elicited by SLIGRL and histamine. Pretreatment with a TRPV4 antagonist significantly attenuated 5-HT-evoked scratching in vivo. Using calcium imaging in cultured primary murine dorsal root ganglion (DRG) neurons, the response of neurons after 5-HT application, but not other pruritogens, was significantly lower in TRPV4KO compared to WT mice. A TRPV4 antagonist significantly suppressed 5-HT-evoked responses in DRG cells from WT mice. Approximately 90% of 5-HT-sensitive DRG neurons were immunoreactive for an antibody to TRPV4, as assessed by calcium imaging. These results indicate that serotonin-induced itch is linked to TRPV4.