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.

Summary How we sense touch remains fundamentally unknown1,2. The Merkel cell-neurite complex is a gentle touch receptor in the skin that mediates slowly-adapting (SA) responses of Aβ sensory fibers to encode fine details of objects3-6. This mechanoreceptor complex was recognized to play an essential role in sensing gentle touch nearly 50 years ago3,4. However, whether Merkel cells or afferent fibers themselves sense mechanical force is still debated, and the molecular mechanism of mechanotransduction is unknown1,2,7-12. Interestingly, synapse-like junctions are observed between Merkel cells and associated afferents6,13-15, and yet it is unclear if Merkel cells are inherently mechanosensitive or whether they can rapidly transmit such information to the neighboring nerve1,2,16,17. Here we show for the first time that Merkel cells produce touch-sensitive currents in vitro. Piezo2, a mechanically-activated (MA) cation channel, is expressed in Merkel cells. We engineered mice deficient in Piezo2 in the skin, but not in sensory neurons, and show that Merkel cell mechanosensitivity completely depends on Piezo2. In these mice, Merkel cell-neurite complex-mediated SA responses in vivo show reduced static firing rates, and moreover, they display moderately decreased behavioral responses to gentle touch. Our results indicate that Piezo2 is the Merkel cell mechanotransduction channel and provide the first line of evidence that Piezos play a physiological role in mechanosensation in mammals. Furthermore, our data present evidence for a two-receptor site model, where both Merkel cells and innervating afferents act in concert as mechanosensors. The two-receptor system could provide this mechanoreceptor complex with a tuning mechanism to achieve highly sophisticated responses to a given mechanical stimulus15,18,19.

Summary Maintenance of a constant cell volume in response to extracellular or intracellular osmotic changes is critical for cellular homeostasis. Activation of a ubiquitous volume-regulated anion channel (VRAC) plays a key role in this process; however, its molecular identity in vertebrates remains unknown. Here, we used a cell-based fluorescence assay and performed a genome-wide RNAi screen to find components of VRAC. We identified SWELL1 (LRRC8A), a member of a four-transmembrane protein family with unknown function, as essential for hypotonicity-induced iodide influx. SWELL1 is localized to the plasma membrane, and its knockdown dramatically reduces endogenous VRAC currents and regulatory cell volume decrease in various cell types. Furthermore, point mutations in SWELL1 cause a significant change in VRAC anion selectivity, demonstrating that SWELL1 is an essential VRAC component. These findings enable further molecular characterization of the VRAC channel complex and genetic studies for understanding the function of VRAC in normal physiology and disease.

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Problem statement: Free radical stress leads to tissue injury and progression of disease conditions such as arthritis, hemorrhagic shock, atherosclerosis, diabetes, hepatic injury, aging and ischemia, reperfusion injury of many tissues, gastritis, tumor promotion, neurodegenerative diseases and carcinogenesis. Safer antioxidants suitable for long term use are needed to prevent or stop the progression of free radical mediated disorders. Approach: Many plants possess antioxidant ingredients that provided efficacy by additive or synergistic activities. A. polystachya bark was a strong astringent, used for the treatment of liver and spleen diseases, rheumatism and tumors. Antioxidant activity of the crude extracts of bark of A. polystachya were assessed using NBT, DPPH, ABTS and FRAP assays. The potent fraction (AP-110/82C) was tested for in vivo efficacy Results: The methanol, aqueous methanol and water extracts exhibited potent antioxidant activity compared to known antioxidants. In vivo studies on potent fraction AP-110/82C demonstrated dose dependent reduction in hepatic malondialdehyde (320.6, 269.3 and 373.69 µM mg −1 protein) with simultaneous improvement in hepatic glutathione (6.9, 17.1 and 5.8 µg mg −1 protein) and catalase levels (668.9, 777.0 and 511.94 µg mg −1 protein) respectively for 50, 100 mg kg −1 doses and control) compared to control group. Conclusion: Due to its natural origin and potent free-radical scavenging ability A. polystachya could be used as a potential preventive intervention for free radical-mediated diseases.