Chronic itch is a common symptom and complaint for many dermatological patients. While some patients find relief with antihistamines, many do not, and the underlying pathways responsible for itch are poorly understood. In this episode, Martin Steinhoff details the identification of endothelin–converting enzyme 1 (ECE-1) as a key regulator of endothelin (ET-1), which evokes a histamine-independent pruritus through activation of ERK1/2. In murine itch models, scratching behavior was enhanced by pharmacological inhibition of ECE-1 and ameliorated by administration of an ERK1/2 inhibitor. Furthermore, this ECE-1/ER-1/ERK1/2 axis was upregulated in patients with prurigo nodularis, suggesting that this pathway has potential as a therapeutic target to relieve chronic itch.
In humans, pruritus (itch) is a common but poorly understood symptom in numerous skin and systemic diseases. Endothelin 1 (ET-1) evokes histamine-independent pruritus in mammals through activation of its cognate G protein–coupled receptor endothelin A receptor (ETAR). Here, we have identified neural endothelin–converting enzyme 1 (ECE-1) as a key regulator of ET-1–induced pruritus and neural signaling of itch. We show here that ETAR, ET-1, and ECE-1 are expressed and colocalize in murine dorsal root ganglia (DRG) neurons and human skin nerves. In murine DRG neurons, ET-1 induced internalization of ETAR within ECE-1–containing endosomes. ECE-1 inhibition slowed ETAR recycling yet prolonged ET-1–induced activation of ERK1/2, but not p38. In a murine itch model, ET-1–induced scratching behavior was substantially augmented by pharmacological ECE-1 inhibition and abrogated by treatment with an ERK1/2 inhibitor. Using iontophoresis, we demonstrated that ET-1 is a potent, partially histamine-independent pruritogen in humans. Immunohistochemical evaluation of skin from prurigo nodularis patients confirmed an upregulation of the ET-1/ETAR/ECE-1/ERK1/2 axis in patients with chronic itch. Together, our data identify the neural peptidase ECE-1 as a negative regulator of itch on sensory nerves by directly regulating ET-1–induced pruritus in humans and mice. Furthermore, these results implicate the ET-1/ECE-1/ERK1/2 pathway as a therapeutic target to treat pruritus in humans.
Makiko Kido-Nakahara, Jörg Buddenkotte, Cordula Kempkes, Akihiko Ikoma, Ferda Cevikbas, Tasuku Akiyama, Frank Nunes, Stephan Seeliger, Burcu Hasdemir, Christian Mess, Timo Buhl, Mathias Sulk, Frank-Ulrich Müller, Dieter Metze, Nigel W. Bunnett, Aditi Bhargava, Earl Carstens, Masutaka Furue, Martin Steinhoff