Native Piezo2 Interactomics Identifies Pericentrin as a Novel Regulator of Piezo2 in Somatosensory Neurons

Piezo1 and Piezo2 channels in retinal ganglion cells and the impact of Piezo1 stimulation on light-dependent neural activity

Piezo channels are associated with neuropathology in diseases like traumatic brain injury and glaucoma, but pathways linking tissue stretch to aberrant neural signaling remain unclear. The present study demonstrates that Piezo1 activation increases action potential frequency in response to light and the spontaneous dark signal from mouse retinal explants. Piezo1 stimulation was sufficient to increase cytoplasmic Ca 2+ in soma and neurites, while stretch increased spiking activity in current clamp recordings from of isolated retinal ganglion cells (RGCs). Axon-marker beta-tubulin III colocalized with both Piezo1 and Piezo2 protein in the mouse optic nerve head, while RGC nuclear marker BRN3A colocalized with Piezo channels in the soma. Piezo1 was also present on GFAP-positive regions in the optic nerve head and colocalized with glutamine synthetase in the nerve fiber layer, suggesting expression in optic nerve head astrocytes and Müller glia end feet, respectively. Human RGCs from induced pluripotent stem cells also expressed Piezo1 and Piezo2 in soma and axons, while staining patterns in rats resembled those in mice. mRNA message for Piezo1 was greatest in the RPE/choroid tissue, while Piezo2 levels were highest in the optic nerve, with both channels also expressed in the retina. Increased expression of Piezo1 and Piezo2 occurred both 1 and 10 days after a single stretch in vivo; this increase suggests a potential role in rising sensitivity to repeated nerve stretch. In summary, Piezo1 and Piezo2 were detected in the soma and axons of RGCs, and stimulation affected the light-dependent output of RGCs. The rise in RGCs excitability induced by Piezo stimulation may have parallels to the early disease progression in models of glaucoma and other retinal degenerations.

Highlights

Activation of Piezo1 excites retinal ganglion cells, paralleling the early neurodegenerative progression in glaucoma mouse models and retinal degeneration.Piezo1 and Piezo2 were expressed in axons and soma of retinal ganglion cells in mice, rats, and human iPSC-RGCs.Functional assays confirmed Piezo1 in soma and neurites of neurons. Sustained elevation of Piezo1 and Piezo2 occurred after a single transient stretch may enhance damage from repeated traumatic nerve injury.

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Caldendrin Is a Repressor of PIEZO2 Channels and Touch Sensation in Mice

The sense of touch is crucial for cognitive, emotional, and social development and relies on mechanically activated (MA) ion channels that transduce force into an electrical signal. Despite advances in the molecular characterization of these channels, the physiological factors that control their activity are poorly understood. Here, we used behavioral assays, electrophysiological recordings, and various mouse strains (males and females analyzed separately) to investigate the role of the calmodulin-like Ca2+ sensor, caldendrin, as a key regulator of MA channels and their roles in touch sensation. In mice lacking caldendrin (Cabp1 KO), heightened responses to tactile stimuli correlate with enlarged MA currents with lower mechanical thresholds in dorsal root ganglion neurons (DRGNs). The expression pattern of caldendrin in the DRG parallels that of the major MA channel required for touch sensation, PIEZO2. In transfected cells, caldendrin interacts with and inhibits the activity of PIEZO2 in a manner that requires an alternatively spliced sequence in the N-terminal domain of caldendrin. Moreover, targeted genetic deletion of caldendrin in Piezo2-expressing DRGNs phenocopies the tactile hypersensitivity of complete Cabp1 KO mice. We conclude that caldendrin is an endogenous repressor of PIEZO2 channels and their contributions to touch sensation in DRGNs.

Piezo2 Contributes to Traumatic Brain Injury by Activating the RhoA/ROCK1 Pathways

Traumatic brain injury (TBI) can lead to short-term and long-term physical and cognitive impairments, which have significant impacts on patients, families, and society. Currently, treatment outcomes for this disease are often unsatisfactory, due at least in part to the fact that the molecular mechanisms underlying the development of TBI are largely unknown. Here, we observed significant upregulation of Piezo2, a key mechanosensitive ion channel protein, in the injured brain tissue of a mouse model of TBI induced by controlled cortical impact. Pharmacological inhibition and genetic knockdown of Piezo2 after TBI attenuated neuronal death, brain edema, brain tissue necrosis, and deficits in neural function and cognitive function. Mechanistically, the increase in Piezo2 expression contributed to TBI-induced neuronal death and subsequent production of TNF-α and IL-1β, likely through activation of the RhoA/ROCK1 pathways in the central nervous system. Our findings suggest that Piezo2 is a key player in and a potential therapeutic target for TBI.

Piezo2 Channel Upregulation is Involved in Mechanical Allodynia in CYP-Induced Cystitis Rats

Mechanical sensing Piezo2 channel in primary sensory neurons has been shown contribute to mechanical allodynia in somatic chronic pain conditions. Interstitial cystitis (IC)-associated pain is often triggered by bladder filling, a presentation that mimics the mechanical allodynia. In the present study, we aimed to examine the involvement of sensory Piezo2 channel in IC-associated mechanical allodynia using a commonly employed cyclophosphamide (CYP)-induced IC model rat. Piezo2 channels in dorsal root ganglia (DRGs) was knocked down by intrathecal injections of Piezo2 anti-sense oligodeoxynucleotides (ODNs) in CYP-induced cystitis rats, and mechanical stimulation-evoked referred bladder pain was measured in the lower abdomen overlying the bladder using von Frey filaments. Piezo2 expression at the mRNA, protein, and functional levels in DRG neurons innervating the bladder was detected by RNA-fluorescence in situ hybridization, western blotting, immunofluorescence, and Ca2+ imaging, respectively. We found that Piezo2 channels were expressed on most (> 90%) of the bladder primary afferents, including afferents that express CGRP, TRPV1 and stained with isolectin B4. CYP-induced cystitis was associated with Piezo2 upregulation in bladder afferent neurons at the mRNA, protein, and functional levels. Knockdown of Piezo2 expression in DRG neurons significantly suppressed mechanical stimulation-evoked referred bladder pain as well as bladder hyperactivity in CYP rats compared to CYP rats treated with mismatched ODNs. Our results suggest upregulation of Piezo2 channels is involved in the development of bladder mechanical allodynia and bladder hyperactivity in CYP-induced cystitis. Targeting Piezo2 might be an attractive therapeutic approach for IC-related bladder pain.

Role of TMEM100 in mechanically insensitive nociceptor un-silencing

Mechanically silent nociceptors are sensory afferents that are insensitive to noxious mechanical stimuli under normal conditions but become sensitized to such stimuli during inflammation. Using RNA-sequencing and quantitative RT-PCR we demonstrate that inflammation upregulates the expression of the transmembrane protein TMEM100 in silent nociceptors and electrophysiology revealed that over-expression of TMEM100 is required and sufficient to un-silence silent nociceptors in mice. Moreover, we show that mice lacking TMEM100 do not develop secondary mechanical hypersensitivity-i.e., pain hypersensitivity that spreads beyond the site of inflammation-during knee joint inflammation and that AAV-mediated overexpression of TMEM100 in articular afferents in the absence of inflammation is sufficient to induce mechanical hypersensitivity in remote skin regions without causing knee joint pain. Thus, our work identifies TMEM100 as a key regulator of silent nociceptor un-silencing and reveals a physiological role for this hitherto enigmatic afferent subclass in triggering spatially remote secondary mechanical hypersensitivity during inflammation.

Intestinal enteroendocrine cells rely on ryanodine and IP3 calcium store receptors for mechanotransduction

Enteroendocrine cells (EECs) are specialized sensors of luminal forces and chemicals in the gastrointestinal (GI) epithelium that respond to stimulation with a release of signalling molecules such as serotonin (5-HT). For mechanosensitive EECs, force activates Piezo2 channels, which generate a very rapidly activating and inactivating (∼10 ms) cationic (Na+ , K+ , Ca2+ ) receptor current. Piezo2 receptor currents lead to a large and persistent increase in intracellular calcium (Ca2+ ) that lasts many seconds to sometimes minutes, suggesting signal amplification. However, intracellular calcium dynamics in EEC mechanotransduction remain poorly understood. The aim of this study was to determine the role of Ca2+ stores in EEC mechanotransduction. Mechanical stimulation of a human EEC cell model (QGP-1) resulted in a rapid increase in cytoplasmic Ca2+ and a slower decrease in ER stores Ca2+ , suggesting the involvement of intracellular Ca2+ stores. Comparing murine primary colonic EECs with colonocytes showed expression of intercellular Ca2+ store receptors, a similar expression of IP3 receptors, but a >30-fold enriched expression of Ryr3 in EECs. In mechanically stimulated primary EECs, Ca2+ responses decreased dramatically by emptying stores and pharmacologically blocking IP3 and RyR1/3 receptors. RyR3 genetic knockdown by siRNA led to a significant decrease in mechanosensitive Ca2+ responses and 5-HT release. In tissue, pressure-induced increase in the Ussing short circuit current was significantly decreased by ryanodine receptor blockade. Our data show that mechanosensitive EECs use intracellular Ca2+ stores to amplify mechanically induced Ca2+ entry, with RyR3 receptors selectively expressed in EECs and involved in Ca2+ signalling, 5-HT release and epithelial secretion. KEY POINTS: A population of enteroendocrine cells (EECs) are specialized mechanosensors of the gastrointestinal (GI) epithelium that respond to mechanical stimulation with the release of important signalling molecules such as serotonin. Mechanical activation of these EECs leads to an increase in intracellular calcium (Ca2+ ) with a longer duration than the stimulus, suggesting intracellular Ca2+ signal amplification. In this study, we profiled the expression of intracellular Ca2+ store receptors and found an enriched expression of the intracellular Ca2+ receptor Ryr3, which contributed to the mechanically evoked increases in intracellular calcium, 5-HT release and epithelial secretion. Our data suggest that mechanosensitive EECs rely on intracellular Ca2+ stores and are selective in their use of Ryr3 for amplification of intracellular Ca2+ . This work advances our understanding of EEC mechanotransduction and may provide novel diagnostic and therapeutic targets for GI motility disorders.

Comparative Genomics Provides Insights into Adaptive Evolution in Tactile-Foraging Birds

Tactile-foraging birds have evolved an enlarged principal sensory nucleus (PrV) but smaller brain regions related to the visual system, which reflects the difference in sensory dependence. The “trade-off” may exist between different senses in tactile foragers, as well as between corresponding sensory-processing areas in the brain. We explored the mechanism underlying the adaptive evolution of sensory systems in three tactile foragers (kiwi, mallard, and crested ibis). The results showed that olfaction-related genes in kiwi and mallard and hearing-related genes in crested ibis were expanded, indicating they may also have sensitive olfaction or hearing, respectively. However, some genes required for visual development were positively selected or had convergent amino acid substitutions in all three tactile branches, and it seems to show the possibility of visual degradation. In addition, we may provide a new visual-degradation candidate gene PDLIM1 who suffered dense convergent amino acid substitutions within the ZM domain. At last, two genes responsible for regulating the proliferation and differentiation of neuronal progenitor cells may play roles in determining the relative sizes of sensory areas in brain. This exploration offers insight into the relationship between specialized tactile-forging behavior and the evolution of sensory abilities and brain structures.

Deep proteome profiling reveals signatures of age and sex differences in paw skin and sciatic nerve of naïve mice

The age and sex of studied animals profoundly impact experimental outcomes in biomedical research. However, most preclinical studies in mice use a wide-spanning age range from 4 to 20 weeks and do not assess male and female mice in parallel. This raises concerns regarding reproducibility and neglects potentially relevant age and sex differences, which are largely unknown at the molecular level in naïve mice. Here, we employed an optimized quantitative proteomics workflow in order to deeply profile mouse paw skin and sciatic nerves (SCN) - two tissues implicated in nociception and pain as well as diseases linked to inflammation, injury, and demyelination. Remarkably, we uncovered significant differences when comparing male and female mice at adolescent (4 weeks) and adult (14 weeks) age. Our analysis deciphered protein subsets and networks that were correlated with the age and/or sex of mice. Notably, among these were proteins/biological pathways with known (patho)physiological relevance, e.g., homeostasis and epidermal signaling in skin, and, in SCN, multiple myelin proteins and regulators of neuronal development. Extensive comparisons with available databases revealed that various proteins associated with distinct skin diseases and pain exhibited significant abundance changes in dependence on age and/or sex. Taken together, our study uncovers hitherto unknown sex and age differences at the level of proteins and protein networks. Overall, we provide a unique proteome resource that facilitates mechanistic insights into somatosensory and skin biology, and integrates age and sex as biological variables - a prerequisite for successful preclinical studies in mouse disease models.

Generation of hiPSC-derived low threshold mechanoreceptors containing axonal termini resembling bulbous sensory nerve endings and expressing Piezo1 and Piezo2

Somatosensory low threshold mechanoreceptors (LTMRs) sense innocuous mechanical forces, largely through specialized axon termini termed sensory nerve endings, where the mechanotransduction process initiates upon activation of mechanotransducers. In humans, a subset of sensory nerve endings is enlarged, forming bulb-like expansions, termed bulbous nerve endings. There is no in vitro human model to study these neuronal endings. Piezo2 is the main mechanotransducer found in LTMRs. Recent evidence shows that Piezo1, the other mechanotransducer considered absent in dorsal root ganglia (DRG), is expressed at low level in somatosensory neurons. We established a differentiation protocol to generate, from iPSC-derived neuronal precursor cells, human LTMR recapitulating bulbous sensory nerve endings and heterogeneous expression of Piezo1 and Piezo2. The derived neurons express LTMR-specific genes, convert mechanical stimuli into electrical signals and have specialized axon termini that morphologically resemble bulbous nerve endings. Piezo2 is concentrated within these enlarged axon termini. Some derived neurons express low level Piezo1, and a subset co-express both channels. Thus, we generated a unique, iPSCs-derived human model that can be used to investigate the physiology of bulbous sensory nerve endings, and the role of Piezo1 and 2 during mechanosensation.

Piezo2 Knockdown Inhibits Noxious Mechanical Stimulation and NGF-Induced Sensitization in A-Delta Bone Afferent Neurons

Piezo2 is a mechanically gated ion-channel that has a well-defined role in innocuous mechanical sensitivity, but recently has also been suggested to play a role in mechanically induced pain. Here we have explored a role for Piezo2 in mechanically evoked bone nociception in Sprague Dawley rats. We have used an in vivo electrophysiological bone-nerve preparation to record the activity of single Aδ bone afferent neurons in response to noxious mechanical stimulation, after Piezo2 knockdown in the dorsal root ganglia with intrathecal injections of Piezo2 antisense oligodeoxynucleotides, or in control animals that received mismatch oligodeoxynucleotides. There were no differences in the number of Aδ bone afferent neurons responding to the mechanical stimulus, or their threshold for mechanical activation, in Piezo2 knockdown animals compared to mismatch control animals. However, bone afferent neurons in Piezo2 knockdown animals had reduced discharge frequencies and took longer to recover from stimulus-evoked fatigue than those in mismatch control animals. Piezo2 knockdown also prevented nerve growth factor (NGF)-induced sensitization of bone afferent neurons, and retrograde labeled bone afferent neurons that expressed Piezo2 co-expressed TrkA, the high affinity receptor for NGF. Our findings demonstrate that Piezo2 contributes to the response of bone afferent neurons to noxious mechanical stimulation, and plays a role in processes that sensitize them to mechanical stimulation.

The Form and Function of PIEZO2

Mechanosensation is the ability to detect dynamic mechanical stimuli (e.g., pressure, stretch, and shear stress) and is essential for a wide variety of processes, including our sense of touch on the skin. How touch is detected and transduced at the molecular level has proved to be one of the great mysteries of sensory biology. A major breakthrough occurred in 2010 with the discovery of a family of mechanically gated ion channels that were coined PIEZOs. The last 10 years of investigation have provided a wealth of information about the functional roles and mechanisms of these molecules. Here we focus on PIEZO2, one of the two PIEZO proteins found in humans and other mammals. We review how work at the molecular, cellular, and systems levels over the past decade has transformed our understanding of touch and led to unexpected insights into other types of mechanosensation beyond the skin.

The effect of IL-6/Piezo2 on the trigeminal neuropathic pain

The nature of trigeminal neuropathic pain (TN) attacks is regarded as the ignition of ectopic action potentials from the trigeminal root following vascular compression, which seemed to be related to transmembrane proteins and inflammation factors. This study focused on the mechanosensitive channel Piezo2 and cytokine IL-6. The chronic constriction injury of infraorbital nerve in SD rats was used to establish the TN model. The trigeminal ganglion was then achieved to perform immunocytochemistry studies. A significant upregulation of Piezo2 and IL-6 was showed in the TN model rats. The Piezo2 positive accounted for 72.3±9.5% in those IL-6 positive neurons. The Piezo2 co-localized with CGRP, IB4 and NF-200 but not with GFAP, which implied that it was expressed in both the C-type and the A-type neurons. After administration of GsMTx4 or anti-rat IL-6 antibody in the TN model, the dynamic allodynia and pinprick hyperalgesia scores as well as the mechanical threshold changed significantly. In the sham-operation rates, with local administration of IL-6, an upregulation of Piezo2 was also exhibited. Our study demonstrated that the up-regulation of Piezo2 in the pain afferent neurons following trigeminal nerve injury may play a role in the development of the neuralgia. Meanwhile, the expression of Piezo2 may be modulated by inflammatory cytokines, such as IL-6.

Role of ion channels during cell division

Ion channels are transmembrane proteins whose canonical function is the transport of ions across the plasma membrane to regulate cell membrane potential and play an essential role in neural communication, nerve conduction, and muscle contraction. However, over the last few years, non-canonical functions have been identified for many channels, having active roles in phagocytosis, invasiveness, proliferation, among others. The participation of some channels in cell proliferation has raised the question of whether they may play an active role in mitosis. There are several reports showing the participation of channels during interphase, however, the direct participation of ion channels in mitosis has received less attention. In this article, we summarize the current evidence on the participation of ion channels in mitosis. We also summarize some tools that would allow the study of ion channels and cell cycle regulatory molecules in individual cells during mitosis.

Maturational Changes in Mouse Cutaneous Touch and Piezo2-Mediated Mechanotransduction

The age of studied animals has a profound impact on experimental outcomes in animal-based research. In mice, age influences molecular, morphological, physiological, and behavioral parameters, particularly during rapid postnatal growth and maturation until adulthood (at 12 weeks of age). Despite this knowledge, most biomedical studies use a wide-spanning age range from 4 to 12 weeks, raising concerns about reproducibility and potential masking of relevant age differences. Here, using mouse behavior and electrophysiology in cultured dorsal root ganglia (DRG), we reveal a decline in behavioral cutaneous touch sensitivity and Piezo2-mediated mechanotransduction in vitro during mouse maturation but not thereafter. In addition, we identify distinct transcript changes in individual Piezo2-expressing mechanosensitive DRG neurons by combining electrophysiology with single-cell RNA sequencing (patch-seq). Taken together, our study emphasizes the need for accurate age matching and uncovers hitherto unknown maturational plasticity in cutaneous touch at the level of behavior, mechanotransduction, and transcripts.

Levering Mechanically Activated Piezo Channels for Potential Pharmacological Intervention

The mechanically activated Piezo channels, including Piezo1 and Piezo2 in mammals, function as key mechanotransducers for converting mechanical force into electrochemical signals. This review highlights key evidence for the potential of Piezo channel drug discovery. First, both mouse and human genetic studies have unequivocally demonstrated the prominent role of Piezo channels in various mammalian physiologies and pathophysiologies, validating their potential as novel therapeutic targets. Second, the cryo-electron microscopy structure of the 2,547-residue mouse Piezo1 trimer has been determined, providing a solid foundation for studying its structure-function relationship and drug action mechanisms and conducting virtual drug screening. Third, Piezo1 chemical activators, named Yoda1 and Jedi1/2, have been identified through high-throughput screening assays, demonstrating the drugability of Piezo channels. However, the pharmacology of Piezo channels is in its infancy. By establishing an integrated drug discovery platform, we may hopefully discover and develop a fleet of Jedi masters for battling Piezo-related human diseases.

Vti1b promotes TRPV1 sensitization during inflammatory pain

Sensitization of the transient receptor potential ion channel vanilloid 1 (TRPV1) is critically involved in inflammatory pain. To date, manifold signaling cascades have been shown to converge onto TRPV1 and enhance its sensitization. However, many of them also play a role for nociceptive pain, which limits their utility as targets for therapeutic intervention. Here, we show that the vesicle transport through interaction with t-SNAREs homolog 1B (Vti1b) protein promotes TRPV1 sensitization upon inflammation in cell culture but leaves normal functioning of TRPV1 intact. Importantly, the effect of Vti1b can be recapitulated in vivo: Virus-mediated knockdown of Vti1b in sensory neurons attenuated thermal hypersensitivity during inflammatory pain without affecting mechanical hypersensitivity or capsaicin-induced nociceptive pain. Interestingly, TRPV1 and Vti1b are localized in close vicinity as indicated by proximity ligation assays and are likely to bind to each other, either directly or indirectly, as suggested by coimmunoprecipitations. Moreover, using a mass spectrometry-based quantitative interactomics approach, we show that Vti1b is less abundant in TRPV1 protein complexes during inflammatory conditions compared with controls. Alongside, we identify numerous novel and pain state-dependent binding partners of native TRPV1 in dorsal root ganglia. These data represent a unique resource on the dynamics of the TRPV1 interactome and facilitate mechanistic insights into TRPV1 regulation. We propose that inflammation-related differences in the TRPV1 interactome identified here could be exploited to specifically target inflammatory pain in the future.

Cell-Type-Specific Splicing of Piezo2 Regulates Mechanotransduction

Piezo2 is a mechanically activated ion channel required for touch discrimination, vibration detection, and proprioception. Here, we discovered that Piezo2 is extensively spliced, producing different Piezo2 isoforms with distinct properties. Sensory neurons from both mice and humans express a large repertoire of Piezo2 variants, whereas non-neuronal tissues express predominantly a single isoform. Notably, even within sensory ganglia, we demonstrate the splicing of Piezo2 to be cell type specific. Biophysical characterization revealed substantial differences in ion permeability, sensitivity to calcium modulation, and inactivation kinetics among Piezo2 splice variants. Together, our results describe, at the molecular level, a potential mechanism by which transduction is tuned, permitting the detection of a variety of mechanosensory stimuli.

Myotubularin related protein-2 and its phospholipid substrate PIP2 control Piezo2-mediated mechanotransduction in peripheral sensory neurons

Piezo2 ion channels are critical determinants of the sense of light touch in vertebrates. Yet, their regulation is only incompletely understood. We recently identified myotubularin related protein-2 (Mtmr2), a phosphoinositide (PI) phosphatase, in the native Piezo2 interactome of murine dorsal root ganglia (DRG). Here, we demonstrate that Mtmr2 attenuates Piezo2-mediated rapidly adapting mechanically activated (RA-MA) currents. Interestingly, heterologous Piezo1 and other known MA current subtypes in DRG appeared largely unaffected by Mtmr2. Experiments with catalytically inactive Mtmr2, pharmacological blockers of PI(3,5)P₂ synthesis, and osmotic stress suggest that Mtmr2-dependent Piezo2 inhibition involves depletion of PI(3,5)P₂. Further, we identified a PI(3,5)P₂ binding region in Piezo2, but not Piezo1, that confers sensitivity to Mtmr2 as indicated by functional analysis of a domain-swapped Piezo2 mutant. Altogether, our results propose local PI(3,5)P₂ modulation via Mtmr2 in the vicinity of Piezo2 as a novel mechanism to dynamically control Piezo2-dependent mechanotransduction in peripheral sensory neurons.

We often take our sense of touch for granted. Yet, our every-day life greatly depends on the ability to perceive our environment to alert us of danger or to further social interactions, such as mother-child bonding. Our sense of touch relies on the conversion of mechanical stimuli to electrical signals (this is known as mechanotransduction), which then travel to brain to be processed. This task is fulfilled by specific ion channels called Piezo2, which are activated when cells are exposed to pressure and other mechanical forces. These channels can be found in sensory nerves and specialized structures in the skin, where they help to detect physical contact, roughness of surfaces and the position of our body parts.

It is still not clear how Piezo2 channels are regulated but previous research by several laboratories suggests that they work in conjunction with other proteins. One of these proteins is the myotubularin related protein-2, or Mtmr2 for short. Now, Narayanan et al. – including some of the researchers involved in the previous research – set out to advance our understanding of the molecular basis of touch and looked more closely at Mtmr2.

To test if Mtmr2 played a role in mechanotransduction, Narayanan et al. both increased and reduced the levels of this protein in sensory neurons of mice grown in the laboratory. When Mtmr2 levels were low, the activity of Piezo2 channels increased. However, when the protein levels were high, Piezo2 channels were inhibited. These results suggest that Mtmr2 can control the activity of Piezo2. Further experiments, in which Mtmr2 was genetically modified or sensory neurons were treated with chemicals, revealed that Mtmr2 reduces a specific fatty acid in the membrane of nerve cells, which in turn attenuates the activity of Piezo2.

This study identified Mtmr2 and distinct fatty acids in the cell membrane as new components of the complex setup required for the sense of touch. A next step will be to test if these molecules also influence the activity of Piezo2 when the skin has become injured or upon inflammation.

Piezos thrive under pressure: mechanically activated ion channels in health and disease

Cellular mechanotransduction, the process of translating mechanical forces into biological signals, is crucial for a wide range of physiological processes. A role for ion channels in sensing mechanical forces has been proposed for decades, but their identity in mammals remained largely elusive until the discovery of Piezos. Recent research on Piezos has underscored their importance in somatosensation (touch perception, proprioception and pulmonary respiration), red blood cell volume regulation, vascular physiology and various human genetic disorders.

Genetic Diseases of PIEZO1 and PIEZO2 Dysfunction

Mutations in the genes encoding the mechanosensitive cation channels PIEZO1 and PIEZO2 are responsible for multiple hereditary human diseases. Loss-of-function mutations in the human PIEZO1 gene cause autosomal recessive congenital lymphatic dysplasia. Gain-of-function mutations in the human PIEZO1 gene cause the autosomal dominant hemolytic anemia, hereditary xerocytosis (also known as dehydrated stomatocytosis). Loss-of-function mutations in the human PIEZO2 gene cause an autosomal recessive syndrome of muscular atrophy with perinatal respiratory distress, arthrogryposis, and scoliosis. Gain-of-function mutations in the human PIEZO2 gene cause three clinical types of autosomal dominant distal arthrogryposis. This chapter will review the hereditary diseases caused by mutations in the PIEZO genes and will discuss additional physiological systems in which PIEZO channel dysfunction may contribute to human disease pathophysiology.

Piezo2 in Cutaneous and Proprioceptive Mechanotransduction in Vertebrates

Mechanosensitivity is a fundamental physiological capacity, which pertains to all life forms. Progress has been made with regard to understanding mechanosensitivity in bacteria, flies, and worms. In vertebrates, however, the molecular identity of mechanotransducers in somatic and neuronal cells has only started to appear. The Piezo family of mechanogated ion channels marks a pivotal milestone in understanding mechanosensitivity. Piezo1 and Piezo2 have now been shown to participate in a number of processes, ranging from arterial modeling to sensing muscle stretch. In this review, we focus on Piezo2 and its role in mediating mechanosensation and proprioception in vertebrates.