Gary R Lewin’s research while affiliated with Charité Universitätsmedizin Berlin and other places

A gentle touch or a painful pinch are relayed to the brain and spinal cord by rapidly conducting myelinated sensory neurons1,2. These sensory neurons possess mechanically activated ion channels like PIEZO2 and ELKIN1 that can be gated by small movements of the substrate3-6. This gating mechanism has been proposed to involve extracellular tether proteins that may transfer force from the matrix to the channel7, the so-called force from tether model8. The molecular nature of such tethers has, however, remained elusive. Here we identify the type II membrane protein Teneurin-4 (TENM4) as an essential component for mechanosensory transduction in the vast majority of cutaneous mechanoreceptors, including fast conducting nociceptors. Sensory neuron specific genetic ablation of Tenm4 in mice led to profound touch insensitivity. We devised a strategy to rapidly and reversibly disassemble the TENM4 protein at sensory endings, demonstrating its direct involvement in sensory transduction. TENM4 has been primarily studied in the context of neural development, but here we provide evidence that it transfers force to mechanically activated channels like PIEZO2 and ELKIN1, with which it associates. The identification of TENM4 as an essential component of fast somatic sensation including fast mechanical nociception is a major step towards identifying treatments for sensory disorders including pain.

Oxygen deprivation or hypoxia is poorly dealt with by most terrestrial species and often leads to permanent tissue damage and death. One prominent exception is the naked mole-rat (Heterocephalus glaber) which is remarkably adapted to withstand prolonged periods (~18 mins) of severe hypoxia, a trait likely driven by its crowded underground lifestyle. Other African mole-rat species are less social or entirely solitary like the Cape mole-rat (Georychus capensis). Here, we asked whether cellular and molecular adaptations to hypoxia map to social traits. We discovered that at the cellular level naked mole-rat fibroblasts survive >30 hours in 1% oxygen, while fibroblasts from terrestrial or non-social mole-rat species (human, mouse and Cape mole-rat) die rapidly under hypoxic conditions. We further show that naked mole-rat mitochondria have evolved morphological, functional and proteomic adaptations crucial for hypoxia resistance, remaining unaffected after long periods of severe hypoxia. We identify the mitochondrial protein Optic Atrophy 1 (OPA1) as a key player in naked mole-rat hypoxia resilience. Naked mole-rat mitochondria not only express more protective forms of OPA1, but also harbor a structurally unique isoform that likely protects cells from hypoxic damage. We show that evolutionary changes including the functionalization of a unique Opa1 exon support mitochondrial mediated cellular protection. Indeed, knockdown of OPA1 in naked mole-rat cells is sufficient to render them equally susceptible to hypoxia as human cells or cells from non-social African species. Our study demonstrates how molecular evolution drives unique adaptations that enable cells to achieve unprecedented resistance to hypoxic damage. We also show that molecular changes at the level of mitochondria are crucial in conferring hypoxia resistance. Our results thus chart a novel molecular path to understand how robust cellular hypoxia resistance can be achieved. Such knowledge may eventually inspire novel strategies to circumvent the consequences of hypoxic-damage in humans.

The coronary arteries develop under substantial mechanical loads. However, the role of mechanosensitive ion channels has barely been addressed in this system. Here we demonstrate the expression of the mechanosensitive ion channel PIEZO2 in specific coronary endothelial cell populations during a crucial phase of vascular modeling. Piezo2 positive coronary endothelial cells display distinct transcriptional profiles and have mechanically activated ionic currents. Strikingly, Piezo2 -/- mouse embryos and mice with human pathogenic variants of PIEZO2 display coronary vessel malformations and left ventricular hyperplasia. We conclude that an optimal balance of PIEZO2 channel function is indispensable for coronary vessel formation, integrity, and remodeling and likely for proper cardiac function.

PIEZO2 is a trimeric mechanically-gated ion channel expressed by most sensory neurones in the dorsal root ganglia. Mechanosensitive PIEZO2 channels are also genetically required for normal touch sensation in both mice and humans. We previously showed that PIEZO2 channels are also strongly modulated by membrane voltage. Specifically, it is only at very positive voltages that all channels are available for opening by mechanical force. Conversely, most PIEZO2 channels are blocked at normal negative resting membrane potentials. The physiological function of this unusual biophysical property of PIEZO2 channels, however, remained unknown. We characterized the biophysical properties of three PIEZO2 ion channel mutations at an evolutionarily conserved Arginine (R2756). Using genome engineering in mice we generated Piezo2R2756H/R2756H and Piezo2R2756K/R2756K knock-in mice to characterize the physiological consequences of altering PIEZO2 voltage sensitivity in vivo. We measured endogenous mechanosensitive currents in sensory neurones isolated from the dorsal root ganglia and characterized mechanoreceptor and nociceptor function using electrophysiology. Mice were also assessed behaviourally and morphologically. Mutations at the conserved Arginine (R2756) dramatically changed the biophysical properties of the channel relieving voltage block and lowering mechanical thresholds for channel activation. Piezo2R2756H/R2756H and Piezo2R2756K/R2756K knock-in mice that were homozygous for gain of function mutations were viable and were tested for sensory changes. Surprisingly, mechanosensitive currents in nociceptors, neurones that detect noxious mechanical stimuli, were substantially sensitized in Piezo2 knock-in mice, but mechanosensitive currents in most mechanoreceptors that underlie touch sensation were only mildly affected by the same mutations. Single-unit electrophysiological recordings from sensory neurones innervating the glabrous skin revealed that rapidly-adapting mechanoreceptors that innervate Meissner’s corpuscles exhibited slightly decreased mechanical thresholds in Piezo2 knock-in mice. Consistent with measurements of mechanically activated currents in isolated sensory neurones essentially all cutaneous nociceptors, both fast conducting Aδ-mechanonociceptors and unmyelinated C-fibre nociceptors were substantially more sensitive to mechanical stimuli and indeed acquired receptor properties similar to ultrasensitive touch receptors in Piezo2 knock-in mice. Mechanical stimuli also induced enhanced ongoing activity in cutaneous nociceptors in Piezo2 knock-in mice and hyper-sensitive PIEZO2 channels were sufficient alone to drive ongoing activity, even in isolated nociceptive neurones. Consistently, Piezo2 knock-in mice showed substantial behaviourally hypersensitivity to noxious mechanical stimuli. Our data indicate that ongoing activity and sensitization of nociceptors, phenomena commonly found in human chronic pain syndromes, can be driven by relieving the voltage-block of PIEZO2 ion channels. Indeed, membrane depolarization caused by multiple noxious stimuli may sensitize nociceptors by relieving voltage-block of PIEZO2 channels.

As a subterranean eusocial mammal, the naked mole-rat faces a particularly challenging environment characterised by patchily available food, low O2 and high CO2 levels. In response, naked mole-rats have evolved a suite of molecular and physiological adaptations to survive extreme hypoxia. Yet, how naked mole-rats rewire their metabolism to protect the heart has not been comprehensively addressed. Here, we performed comparative analyses of naked mole-rat and mouse organs exposed to ischaemic conditions. We show that naked mole-rats have retained features of foetal cardiac metabolism replacing fatty acid utilisation for a unique type of carbohydrate metabolism largely dependent on glycogen. We found that naked mole-rats have co-opted specialised liver-like glycogen handling mechanisms in the heart. Amongst these is the expression of liver-specific enzyme isoforms and amylase, a digestive enzyme known for starch breakdown in saliva and intestine but whose biological role in glycogen processing has not been fully recognised. We show that amylase is rapidly activated in ischaemia and hydrolyses internal glycosidic bonds for more efficient downstream processing. This biochemical adaptation occurred in both mouse and naked mole-rat livers but exclusively in the naked mole-rat heart, which retained higher ATP levels by maintaining an increased glycolytic flux in an amylase-dependent mechanism. Overall, we discovered a previously unknown type of glycogen metabolism in the naked mole-rat that holds relevance to pathologies where glycogen plays a role. Furthermore, we describe a novel type of metabolic plasticity in the heart which may be harnessed for cardiac disease.

Touch perception is enabled by mechanically activated ion channels, the opening of which excites cutaneous sensory endings to initiate sensation. In this study, we identify ELKIN1 as an ion channel likely gated by mechanical force, necessary for normal touch sensitivity in mice. Touch insensitivity in Elkin1 −/− mice was caused by a loss of mechanically activated currents (MA currents) in around half of all sensory neurons activated by light touch (low-threshold mechanoreceptors). Reintroduction of Elkin1 into sensory neurons from Elkin1 −/− mice restored MA currents. Additionally, small interfering RNA–mediated knockdown of ELKIN1 from induced human sensory neurons substantially reduced indentation-induced MA currents, supporting a conserved role for ELKIN1 in human touch. Our data identify ELKIN1 as a core component of touch transduction in mice and potentially in humans.

Touch sensation is primarily encoded by mechanoreceptors, called low-threshold mechanoreceptors (LTMRs), with their cell bodies in the dorsal root ganglia. Because of their great diversity in terms of molecular signature, terminal endings morphology, and electrophysiological properties, mirroring the complexity of tactile experience, LTMRs are a model of choice to study the molecular cues differentially controlling neuronal diversification. While the transcriptional codes that define different LTMR subtypes have been extensively studied, the molecular players that participate in their late maturation and in particular in the striking diversity of their end-organ morphological specialization are largely unknown. Here we identified the TALE homeodomain transcription factor Meis2 as a key regulator of LTMRs target-field innervation in mice. Meis2 is specifically expressed in cutaneous LTMRs, and its expression depends on target-derived signals. While LTMRs lacking Meis2 survived and are normally specified, their end-organ innervations, electrophysiological properties, and transcriptome are differentially and markedly affected, resulting in impaired sensory-evoked behavioral responses. These data establish Meis2 as a major transcriptional regulator controlling the orderly formation of sensory neurons innervating peripheral end organs required for light touch.

Previous work identified nociceptive Schwann cells that can initiate pain. Consistent with the existence of inherently mechanosensitive sensory Schwann cells, we found that in mice, the mechanosensory function of almost all nociceptors, including those signaling fast pain, were dependent on sensory Schwann cells. In polymodal nociceptors, sensory Schwann cells signal mechanical, but not cold or heat pain. Terminal Schwann cells also surround mechanoreceptor nerve-endings within the Meissner’s corpuscle and in hair follicle lanceolate endings that both signal vibrotactile touch. Within Meissner´s corpuscles, two molecularly and functionally distinct sensory Schwann cells positive for Sox10 and Sox2 differentially modulate rapidly adapting mechanoreceptor function. Using optogenetics we show that Meissner’s corpuscle Schwann cells are necessary for the perception of low threshold vibrotactile stimuli. These results show that sensory Schwann cells within diverse glio-neural mechanosensory end-organs are sensors for mechanical pain as well as necessary for touch perception.

Touch sensation is primarily encoded by mechanoreceptors, called Low-Threshold Mechanoreceptors (LTMRs), with their cell bodies in the Dorsal Root Ganglia (DRG). Because of their great diversity in terms of molecular signature, terminal endings morphology and electrophysiological properties, mirroring the complexity of tactile experience, LTMRs are a model of choice to study the molecular cues differentially controlling neuronal diversification. While the transcriptional codes that define different LTMR subtypes have been extensively studied, the molecular players that participate in their late maturation and in particular in the striking diversity of their end-organ morphological specialization are largely unknown. Here we identified the TALE homeodomain transcription factor Meis2 as a key regulator of LTMRs target-field innervation. Meis2 is specifically expressed in cutaneous LTMRs and its expression depends on target-derived signals. While LTMRs lacking Meis2 survived and are normally specified, their end-organ innervations, electrophysiological properties and transcriptome are differentially and markedly affected, resulting in impaired sensory-evoked behavioral responses. These data establish Meis2 as a major transcriptional regulator controlling the orderly formation of sensory neurons innervating peripheral end-organs required for light touch.

Touch sensation is primarily encoded by mechanoreceptors, called Low-Threshold Mechanoreceptors (LTMRs), with their cell bodies in the Dorsal Root Ganglia. Because of their great diversity in terms of molecular signature, terminal endings morphology and electrophysiological properties, mirroring the complexity of tactile experience, LTMRs are a model of choice to study the molecular cues differentially controlling neuronal diversification. While the transcriptional codes that define different LTMR subtypes have been extensively studied, the molecular players that participate in their late maturation and in particular in the striking diversity of their end-organ morphological specialization are largely unknown. Here we identified the TALE homeodomain transcription factor Meis2 as a key regulator of LTMRs target-field innervation. Meis2 is specifically expressed in cutaneous LTMRs and its expression depends on target-derived signals. While LTMRs lacking Meis2 survived and are normally specified, their end-organ innervations, electrophysiological properties and transcriptome are differentially and markedly affected, resulting in impaired sensory-evoked behavioral responses. These data establish Meis2 as a major transcriptional regulator controlling the orderly formation of sensory neurons innervating peripheral end-organs required for light touch.