Mechanical stimuli drive many physiological processes, including touch and pain sensation, hearing, and blood pressure regulation. Mechanically-activated (MA) cation channel activities have been recorded in many cells, but the responsible molecules have not been identified. We characterized a rapidly-adapting MA current in a mouse neuroblastoma cell line. Expression profiling and RNAi knockdown of candidate genes identified Piezo1 (Fam38A) to be required for MA currents in these cells. Piezo1 and related Piezo2 (Fam38B) are vertebrate multipass transmembrane proteins with homologs in invertebrates, plants, and protozoa. Overexpression of mouse Piezo1 or Piezo2 induced two kinetically-distinct MA currents. Piezos are expressed in several tissues, and knockdown of Piezo2 in dorsal root ganglia neurons specifically reduced rapidly-adapting MA currents. We propose that Piezos are components of mechanically-activated cation channels.
The nervous system senses peripheral damage through nociceptive neurons that transmit a pain signal. TRPA1 is a member of the Transient Receptor Potential (TRP) family of ion channels and is expressed in nociceptive neurons. TRPA1 is activated by a variety of noxious stimuli, including cold temperatures, pungent natural compounds, and environmental irritants. How such diverse stimuli activate TRPA1 is not known. We observed that most compounds known to activate TRPA1 are able to covalently bind cysteine residues. Here we use click chemistry to show that derivatives of two such compounds, mustard oil and cinnamaldehyde, covalently bind mouse TRPA1. Structurally unrelated cysteine-modifying agents such as iodoacetamide (IA) and (2-aminoethyl)methanethiosulphonate (MTSEA) also bind and activate TRPA1. We identified by mass spectrometry fourteen cytosolic TRPA1 cysteines labelled by IA, three of which are required for normal channel function. In excised patches, reactive compounds activated TRPA1 currents that were maintained at least 10 min after washout of the compound in calcium-free solutions. Finally, activation of TRPA1 by disulphide-bond-forming MTSEA is blocked by the reducing agent dithiothreitol (DTT). Collectively, our data indicate that covalent modification of reactive cysteines within TRPA1 can cause channel activation, rapidly signalling potential tissue damage through the pain pathway.
Mechanotransduction plays a crucial role in physiology. Biological processes including sensing touch and sound waves require yet unidentified cation channels that detect pressure. Mouse piezo1 (mpiezo1) and mpiezo2 induce mechanically activated cationic currents in cells; however, it is unknown if piezos are pore-forming ion channels or modulate ion channels. We show that Drosophila piezo (dpiezo) also induces mechanically activated currents in cells, but through channels with remarkably distinct pore properties including sensitivity to the pore blocker ruthenium red and single channel conductances. mpiezo1 assembles as a ~1.2 million-Dalton homo-oligomer, with no evidence of other proteins in this complex. Finally, purified mpiezo1 reconstituted into asymmetric lipid bilayers and liposomes forms ruthenium red-sensitive ion channels. These data demonstrate that piezos are an evolutionarily conserved ion channel family involved in mechanotransduction.
Specialized peripheral sensory neurons known as nociceptors alert us to potentially damaging stimuli at the skin by detecting extremes in temperature and pressure and injury-related chemicals, and transducing these stimuli into long-ranging electrical signals that are relayed to higher brain centers. The activation of functionally distinct cutaneous nociceptor populations and the processing of information they convey provide a rich diversity of pain qualities. Current work in this field is providing researchers with a more thorough understanding of nociceptor cell biology at molecular and systems levels and insight that will allow the targeted design of novel pain therapeutics.
Summary The sense of touch provides critical information about our physical environment by transforming mechanical energy into electrical signals1. It is postulated that mechanically activated (MA) cation channels initiate touch sensation, but the identity of these molecules in mammals has been elusive2. Piezo2 is a rapidly adapting (RA) MA ion channel expressed in a subset of sensory neurons of the dorsal root ganglion (DRG) and in cutaneous mechanoreceptors known as Merkel cell-neurite complexes3,4. Merkel cells have been demonstrated to play a role in vertebrate mechanosensation using Piezo2, particularly in shaping the type of current sent by its innervating sensory neuron4-6. 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 (LTMRs) that innervate both hairy and glabrous skin. Most RA MA currents in DRG neuronal cultures are absent in Piezo2CKO mice, and ex vivo skin nerve preparation studies show that mechanosensitivity of LTMRs strongly depends on Piezo2. This striking cellular phenotype correlates with an unprecedented behavioral phenotype: an almost complete deficit in light touch sensation in multiple behavioral assays, without affecting other somatosensory functions. Our results highlight that a single ion channel that displays RA MA currents in vitro is responsible for the mechanosensitivity of most LTMR subtypes involved in innocuous touch sensation. Interestingly, we find that touch and pain sensation are separable, suggesting that yet-unknown MA ion channel(s) must account for noxious (painful) mechanosensation.
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