Piezo2 is the major transducer of mechanical forces for touch sensation in mice

Abstract

Mice lacking the mechanically activated ion channel Piezo2 in both sensory neurons and Merkel cells are almost totally incapable of light-touch sensation while other somatosensory functions, such as mechanical nociception, remain intact, implying that other mechanically activated ion channels must now be identified to account for painful touch sensation. Recent decades have seen the mechanisms of sensing photons (vision), chemicals (olfaction, taste) and temperature (thermosensation) elucidated in some detail. The sense of touch, implying the transduction of mechanical forces into electrical signals, is less well understood. Here Ardem Patapoutian and colleagues show that mice lacking the mechanically activated ion channel Piezo2 in both sensory neurons and in Merkel cells, a type of modified skin cell, are almost totally incapable of light-touch sensation. As the mice are intact in other somatosensory functions such as mechanical nociception, the work implies that other mechanically activated ion channels must now be identified to account for painful touch sensation. The sense of touch provides critical information about our physical environment by transforming mechanical energy into electrical signals1. It is postulated that mechanically activated cation channels initiate touch sensation, but the identity of these molecules in mammals has been elusive2. Piezo2 is a rapidly adapting, mechanically activated ion channel expressed in a subset of sensory neurons of the dorsal root ganglion and in cutaneous mechanoreceptors known as Merkel-cell–neurite complexes3,4. It has been demonstrated that Merkel cells have a role in vertebrate mechanosensation using Piezo2, particularly in shaping the type of current sent by the innervating sensory neuron4,5,6; however, major aspects of touch sensation remain intact without Merkel cell activity4,7. Here we show that mice lacking Piezo2 in both adult sensory neurons and Merkel cells exhibit a profound loss of touch sensation. We precisely localize Piezo2 to the peripheral endings of a broad range of low-threshold mechanoreceptors that innervate both hairy and glabrous skin. Most rapidly adapting, mechanically activated currents in dorsal root ganglion neuronal cultures are absent in Piezo2 conditional knockout mice, and ex vivo skin nerve preparation studies show that the mechanosensitivity of low-threshold mechanoreceptors strongly depends on Piezo2. This cellular phenotype correlates with an unprecedented behavioural phenotype: an almost complete deficit in light-touch sensation in multiple behavioural assays, without affecting other somatosensory functions. Our results highlight that a single ion channel that displays rapidly adapting, mechanically activated currents in vitro is responsible for the mechanosensitivity of most low-threshold mechanoreceptor subtypes involved in innocuous touch sensation. Notably, we find that touch and pain sensation are separable, suggesting that as-yet-unknown mechanically activated ion channel(s) must account for noxious (painful) mechanosensation.