Mechanically Activated Ion Channels

Effects of Panax notoginseng saponins on alleviating low shear induced endothelial inflammation and thrombosis via Piezo1 signalling

ETHNOPHARMACOLOGICAL RELEVANCE

Panax notoginseng saponins (PNS) are the major effective components of Panax notoginseng (burk) F.H.Chen which is one of the classic promoting blood circulation herbs in traditional Chinese medicine. PNS is widely used in China for the treatment of cerebral ischemic stroke. Pathological low shear stress is a causal factor in endothelial inflammation and thrombosis. However, the mechanism of PNS against low shear related endothelial inflammation is still unclear.

AIM TO THE STUDY

This study aims to investigate the effects of PNS against endothelial inflammation induced by low shear stress and to explore the underlying mechanical and biological mechanisms.

MATERIALS AND METHODS

Mouse model of carotid partial ligation for inducing low endothelial shear stress was established, the pharmacodynamic effect and mechanism of PNS against endothelial inflammation induced by low shear stress through Piezo1 were explored. Yoda1-evoked Piezo1 activation and expression in human umbilical vein endothelial cells (HUVECs) were determined at static condition. Microfluidic channel systems were used to apply shear stress on HUVECs and Piezo1 siRNA HUVECs to determine PECAM-1, p-YAP and VCAM-1 expression. And platelet rich plasma (PRP) was introduced to low shear treated endothelial cells surface to observe the adhesion and activation by fluorescence imaging and flowcytometry.

RESULTS

PNS attenuated endothelial inflammation and improved blood flow in a reasonable dose response pattern in carotid partial ligation mouse model by influencing Piezo1 and PECAM-1 expression, while suppressing yes-associated protein (YAP) nuclear translocation. We found Piezo1 sensed abnormal shear stress and transduced these mechanical signals by different pathways in HUVECs, and PNS relieved endothelial inflammation induced by low shear stress through Piezo1. We also found Piezo1 signalling has interaction with PECAM-1 under low shear stress, which were involved in platelets adhesion to endothelial cells. Low shear stress increased YAP nuclear translocation and increased VCAM-1 expression in HUVECs which might activate platelets. PNS inhibited low shear induced Piezo1 and PECAM-1 expression and YAP nuclear translocation in HUVECs, furthermore inhibited platelet adhesion and activation on dysfunctional endothelial cells induced by low shear stress.

CONCLUSION

PNS ameliorated endothelial inflammation and thrombosis induced by low shear stress through modulation of the Piezo1 channel, PECAM-1 expression, and YAP nuclear translocation. PNS might serve as a potential therapeutic candidate for ameliorating endothelial inflammation induced by abnormal blood shear stress.

Piezoelectric biomaterials with embedded ionic liquids for improved orthopedic interfaces through osseointegration and antibacterial dual characteristics

Orthopedic implant failures, primarily attributed to aseptic loosening and implant site infections, pose significant challenges to patient recovery and lead to revision surgeries. Combining piezoelectric materials with ionic liquids as interfaces for orthopedic implants presents an innovative approach to addressing both issues simultaneously. In this study, films of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) incorporated with 1-ethyl-3-methylimidazolium hydrogen sulfate ([Emim][HSO4]) ionic liquid were developed. These films exhibited strong antibacterial properties, effectively reducing biofilm formation, thereby addressing implant-related infections. Furthermore, stem cell-based differentiation assays exposed the potential of the composite materials to induce osteogenesis. Interestingly, our findings also revealed the upregulation of calcium channel expression as a result of electromechanical stimulation, pointing to a mechanistic basis for the observed biological effects. This work highlights the potential of piezoelectric materials with ionic liquids to improve the longevity and biocompatibility of orthopedic implants. Offering dual-functionality for infection prevention and bone integration, these advancements hold significant potential for advancing orthopedic implant technologies and improving patient outcomes.

Cyclic tensile stress promotes osteogenic differentiation via upregulation of Piezo1 in human dental follicle stem cells

As periodontal progenitor cells, human dental follicle stem cells (hDFCs) play an important role in regenerative medicine research. Mechanical stimuli exert different regulatory effects on various functions of stem cells. Mechanosensitive ion channels can perceive and transmit mechanical signals. Piezo1 is a novel mechanosensitive cation channel dominated by Ca2+ permeation. The yes-associated protein 1 (YAP1) and mitogen-activated protein kinase (MAPK) pathways can respond to mechanical stimuli and play important roles in cell growth, differentiation, apoptosis, and cell cycle regulation. In this study, we demonstrated that Piezo1 was able to transduce cyclic tension stress (CTS) and promote the osteogenic differentiation of hDFCs by applying CTS of 2000 μstrain to hDFCs. Further investigation of this mechanism revealed that CTS activated Piezo1 in hDFCs and resulted in increased levels of intracellular Ca2+, YAP1 nuclear translocation, and phosphorylated protein expression levels of extracellular signalling-associated kinase 1/2 (ERK 1/2) and Jun amino-terminal kinase 1/2/3 (JNK 1/3) of the MAPK pathway family. However, when Piezo1 was knocked down in the hDFCs, all these increases disappeared. We conclude that CTS activates Piezo1 expression and promotes its osteogenesis via Ca2+/YAP1/MAPK in hDFCs. Appropriate mechanical stimulation promotes the osteogenic differentiation of hDFCs via Piezo1. Targeting Piezo1 may be an effective strategy to regulate the osteogenic differentiation of hDFCs, contributing to MSC-based therapies in the field of bone tissue engineering.

Progress in Noninvasive Low-Intensity Focused Ultrasound Neuromodulation

Low-intensity focused ultrasound represents groundbreaking medical advancements, characterized by its noninvasive feature, safety, precision, and broad neuromodulatory capabilities. This technology operates through mechanisms, for example, acoustic radiation force, cavitation, and thermal effects. Notably, with the evolution of medical technology, ultrasound neuromodulation has been gradually applied in treating central nervous system diseases, especially stroke. Furthermore, burgeoning research areas such as sonogenetics and nanotechnology show promising potential. Despite the benefit of low-intensity focused ultrasound the precise biophysical mechanism of ultrasound neuromodulation still need further exploration. This review discusses the recent and ongoing developments of low-intensity focused ultrasound for neurological regulation, covering the underlying rationale to current utility and the challenges that impede its further development and broader adoption of this promising alternative to noninvasive therapy.

Piezo ion channels: long-sought-after mechanosensors mediating hypertension and hypertensive nephropathy

Recent advances in mechanobiology and the discovery of mechanosensitive ion channels have opened a new era of research on hypertension and related diseases. Piezo1 and Piezo2, first reported in 2010, are regarded as bona fide mechanochannels that mediate various biological and pathophysiological phenomena in multiple tissues and organs. For example, Piezo channels have pivotal roles in blood pressure control, triggering shear stress-induced nitric oxide synthesis and vasodilation, regulating baroreflex in the carotid sinus and aorta, and releasing renin from renal juxtaglomerular cells. Herein, we provide an overview of recent literature on the roles of Piezo channels in the pathogenesis of hypertension and related kidney damage, including our experimental data on the involvement of Piezo1 in podocyte injury and that of Piezo2 in renin expression and renal fibrosis in animal models of hypertensive nephropathy. The mechanosensitive ion channels Piezo1 and Piezo2 play various roles in the pathogenesis of systemic hypertension by acting on vascular endothelial cells, baroreceptors in the carotid artery and aorta, and the juxtaglomerular apparatus. Piezo channels also contribute to hypertensive nephropathy by acting on mesangial cells, podocytes, and perivascular mesenchymal cells.

Conducting polymer hydrogels for biomedical application: Current status and outstanding challenges

Conducting polymer hydrogels (CPHs) are composite polymeric materials with unique properties that combine the electrical capabilities of conducting polymers (CPs) with the excellent mechanical properties and biocompatibility of traditional hydrogels. This review aims to highlight how the unique properties CPHs have from combining their two constituent materials are utilized within the biomedical field. First, the synthesis approaches and applications of non-CPH conductive hydrogels are discussed briefly, contrasting CPH-based systems. The synthesis routes of hydrogels, CPs, and CPHs are then discussed. This review also provides a comprehensive overview of the recent advancements and applications of CPHs in the biomedical field, encompassing their applications as biosensors, drug delivery scaffolds (DDSs), and tissue engineering platforms. Regarding their applications within tissue engineering, a comprehensive discussion of the usage of CPHs for skeletal muscle prosthetics and regeneration, cardiac regeneration, epithelial regeneration and wound healing, bone and cartilage regeneration, and neural prosthetics and regeneration is provided. Finally, critical challenges and future perspectives are also addressed, emphasizing the need for continued research; however, this fascinating class of materials holds promise within the vastly evolving field of biomedicine.

Downregulation of PIEZO2 in the Detrusor of Men With Bladder Outlet Obstruction and Its Association With Urinary Retention and Decreased Bladder Compliance

PURPOSE

Recent research has highlighted the mechanotransducer PIEZO2 as a crucial factor in lower urinary tract function, demonstrating associations with bladder compliance (BC), bladder wall thickening, and elevated bladder pressure. We explored the hypothesis that PIEZO2 expression may be associated with lower urinary tract dysfunction in men with bladder outlet obstruction (BOO) due to benign prostatic hyperplasia (BPH).

METHODS

The study included a consecutive series of patients undergoing open prostatectomy for BPH at our hospital between September 2014 and January 2016. All participants underwent comprehensive preoperative evaluations, including urodynamic assessments. During prostatectomy, a full-thickness fragment of the bladder wall was obtained for subsequent PIEZO2 gene expression analysis. Cadaveric organ donors served as the control group.

RESULTS

PIEZO2 expression was downregulated in the detrusor muscle of men with BPH compared to the control group. Among patients with BPH, those experiencing urinary retention and requiring an indwelling catheter exhibited significantly lower PIEZO2 messenger RNA (mRNA) expression than patients capable of spontaneous voiding. PIEZO2 mRNA expression was similar in men with and without detrusor overactivity. Additionally, a positive correlation was found between PIEZO2 mRNA expression levels and BC.

CONCLUSION

Our findings indicate that PIEZO2 is downregulated in the detrusor muscle of men with BPH, particularly in those experiencing urinary retention and those with reduced BC. These results suggest a potential role for PIEZO2 in BOOinduced bladder dysfunction. Further research is required to clarify the role of PIEZO mechanotransducers in the bladder and to explore their therapeutic implications.

The pyrexia channel remodels egg-laying of Liriomyza huidobrensis in response to temperature change

BACKGROUND

The pea leafminer, Liriomyza huidobrensis, is one of the most important insect pests on vegetables and ornamentals. The survival and egg-laying behavior of leafminers are markedly affected by the environment temperature. However, the mechanisms underlying the relationship between egg-laying and temperature are still largely unknown.

RESULTS

Here, we find that leafminers have evolved an adaptive strategy to overcome the stress from high or low temperature by regulating oviposition-punching plasticity. We further show that this oviposition-punching plasticity is mediated by the expression of pyx in the ovipositor when subjected to disadvantageous temperature. Specifically, down-regulation of pyx expression in leafminers under low temperature stress led to a significant decrease in the swing numbers of ovipositor and puncture area of the egg spot, and consequently the lower amount of egg-laying compared to leafminers at ambient temperature. Conversely, activation of pyx expression under high temperature stress increased the swing numbers and puncture area, still resulting in a reduction of egg-laying amount.

CONCLUSION

Thereby, leafminers are able to coordinate pyx channel expression level and accordingly depress the oviposition. Our study uncovers a molecular mechanism underlying the adaptive strategy in insects that can avoid disadvantageous temperature for reproducing offspring. © 2024 Society of Chemical Industry.

Localization of Piezo 1 and Piezo 2 in Lateral Line System and Inner Ear of Zebrafish (Danio rerio)

Piezo proteins have been identified as mechanosensitive ion channels involved in mechanotransduction. Several ion channel dysfunctions may be associated with diseases (including deafness and pain); thus, studying them is critical to understand their role in mechanosensitive disorders and to establish new therapeutic strategies. The current study investigated for the first time the expression patterns of Piezo proteins in zebrafish octavolateralis mechanosensory organs. Piezo 1 and 2 were immunoreactive in the sensory epithelia of the lateral line system and the inner ear. Piezo 1 (28.7 ± 1.55 cells) and Piezo 2 (28.8 ± 3.31 cells) immunopositive neuromast cells were identified based on their ultrastructural features, and their overlapping immunoreactivity to the s100p specific marker (28.6 ± 1.62 cells), as sensory cells. These findings are in favor of Piezo proteins' potential role in sensory cell activation, while their expression on mantle cells reflects their implication in the maintenance and regeneration of the neuromast during cell turnover. In the inner ear, Piezo proteins' colocalization with BDNF introduces their potential implication in neuronal plasticity and regenerative events, typical of zebrafish mechanosensory epithelia. Assessing these proteins in zebrafish could open up new scenarios for the roles of these important ionic membrane channels, for example in treating impairments of sensory systems.

Role of Piezo1 in modulating the RANKL/OPG ratio in mouse osteoblast cells exposed to Porphyromonas gingivalis lipopolysaccharide and mechanical stress

AIMS

Excessive occlusal force with periodontitis leads to rapid alveolar bone resorption. However, the molecular mechanism by which inflammation and mechanical stress cause bone resorption remains unclear. We examined the role of Piezo1, a mechanosensitive ion channel expressed on osteoblasts, in the changes in the receptor activator of nuclear factor-kappa B ligand (RANKL)/osteoprotegerin (OPG) ratio in mouse MC3T3-E1 osteoblast-like cells under Porphyromonas gingivalis lipopolysaccharide (P.g.-LPS) and mechanical stress.

METHODS

To investigate the effect of P.g.-LPS and mechanical stress on the RANKL/OPG ratio and Piezo1 expression, we stimulated MC3T3-E1 cells with P.g.-LPS. After 3 days in culture, shear stress, a form of mechanical stress, was applied to the cells using an orbital shaker. Subsequently, to investigate the role of Piezo1 in the change of RANKL/OPG ratio, we inhibited Piezo1 function by knockdown via Piezo1 siRNA transfection or by adding GsMTx4, a Piezo1 antagonist.

RESULTS

The RANKL/OPG ratio significantly increased in MC3T3-E1 cells cultured in a medium containing P.g.-LPS and undergoing mechanical stress compared to cells treated with P.g.-LPS or mechanical stress alone. However, the expression of Piezo1 was not increased by P.g.-LPS and mechanical stress. In addition, phosphorylation of MEK/ERK was induced in the cells under P.g.-LPS and mechanical stress. MC3T3-E1 cells treated with P.g.-LPS and mechanical stress when cocultured with RAW264.7 cells induced their differentiation into osteoclast-like cells. The increased RANKL/OPG ratio was suppressed by either Piezo1 knockdown or the addition of GsMTx4. Furthermore, GsMTx4 inhibited the phosphorylation of MEK/ERK.

CONCLUSION

These findings suggest that P.g.-LPS and Piezo1-mediated mechanical stress induce MEK/ERK phosphorylation and increase RANKL expression in osteoblasts. Consequently, this leads to the differentiation of osteoclast precursor cells into osteoclasts.

Tentonin 3 is a pore-forming subunit of a slow inactivation mechanosensitive channel

Mechanically activating (MA) channels transduce numerous physiological functions. Tentonin 3/TMEM150C (TTN3) confers MA currents with slow inactivation kinetics in somato- and barosensory neurons. However, questions were raised about its role as a Piezo1 regulator and its potential as a channel pore. Here, we demonstrate that purified TTN3 proteins incorporated into the lipid bilayer displayed spontaneous and pressure-sensitive channel currents. These MA currents were conserved across vertebrates and differ from Piezo1 in activation threshold and pharmacological response. Deep neural network structure prediction programs coupled with mutagenetic analysis predicted a rectangular-shaped, tetrameric structure with six transmembrane helices and a pore at the inter-subunit center. The putative pore aligned with two helices of each subunit and had constriction sites whose mutations changed the MA currents. These findings suggest that TTN3 is a pore-forming subunit of a distinct slow inactivation MA channel, potentially possessing a tetrameric structure.

The emerging role of Piezo1 in the musculoskeletal system and disease

Piezo1, a mechanosensitive ion channel, has emerged as a key player in translating mechanical stimuli into biological signaling. Its involvement extends beyond physiological and pathological processes such as lymphatic vessel development, axon growth, vascular development, immunoregulation, and blood pressure regulation. The musculoskeletal system, responsible for structural support, movement, and homeostasis, has recently attracted attention regarding the significance of Piezo1. This review aims to provide a comprehensive summary of the current research on Piezo1 in the musculoskeletal system, highlighting its impact on bone formation, myogenesis, chondrogenesis, intervertebral disc homeostasis, tendon matrix cross-linking, and physical activity. Additionally, we explore the potential of targeting Piezo1 as a therapeutic approach for musculoskeletal disorders, including osteoporosis, muscle atrophy, intervertebral disc degeneration, and osteoarthritis.

TMC6 functions as a GPCR-like receptor to sense noxious heat via Gαq signaling

Thermosensation is vital for the survival, propagation, and adaption of all organisms, but its mechanism is not fully understood yet. Here, we find that TMC6, a membrane protein of unknown function, is highly expressed in dorsal root ganglion (DRG) neurons and functions as a Gαq-coupled G protein-coupled receptor (GPCR)-like receptor to sense noxious heat. TMC6-deficient mice display a substantial impairment in noxious heat sensation while maintaining normal perception of cold, warmth, touch, and mechanical pain. Further studies show that TMC6 interacts with Gαq via its intracellular C-terminal region spanning Ser780 to Pro810. Specifically disrupting such interaction using polypeptide in DRG neurons, genetically ablating Gαq, or pharmacologically blocking Gαq-coupled GPCR signaling can replicate the phenotype of TMC6 deficient mice regarding noxious heat sensation. Noxious heat stimulation triggers intracellular calcium release from the endoplasmic reticulum (ER) of TMC6- but not control vector-transfected HEK293T cell, which can be significantly inhibited by blocking PLC or IP3R. Consistently, noxious heat-induced intracellular Ca2+ release from ER and action potentials of DRG neurons largely reduced when ablating TMC6 or blocking Gαq/PLC/IP3R signaling pathway as well. In summary, our findings indicate that TMC6 can directly function as a Gαq-coupled GPCR-like receptor sensing noxious heat.

Axonal and Glial PIEZO1 and PIEZO2 Immunoreactivity in Human Clitoral Krause's Corpuscles

Krause's corpuscles are typical of cutaneous mucous epithelia, like the lip vermillion or the glans clitoridis, and are associated with rapidly adapting low-threshold mechanoreceptors involved in gentle touch or vibration. PIEZO1 and PIEZO2 are transmembrane mechano-gated proteins that form a part of the cationic ion channels required for mechanosensitivity in mammalian cells. They are involved in somatosensitivity, especially in the different qualities of touch, but also in pain and proprioception. In the present study, immunohistochemistry and immunofluorescence were used to analyze the occurrence and cellular location of PIEZO1 and PIEZO2 in human clitoral Krause's corpuscles. Both PIEZO1 and PIEZO2 were detected in Krause's corpuscles in both the axon and the terminal glial cells. The presence of PIEZOs in the terminal glial cells of Kraus's corpuscles is reported here for the first time. Based on the distribution of PIEZO1 and PIEZO2, it may be assumed they could be involved in mechanical stimuli, sexual behavior, and sexual pleasure.

Microelectrochemical Sensor Reveals Tunneling Nanotube-Mediated Intercellular Communication of Endothelial Mechanotransduction

The intercellular communication of mechanotransduction has a significant impact on various cellular processes. Tunneling nanotubes (TNTs) have been documented to possess the capability of transmitting mechanical stimulation between cells, thereby triggering an influx of Ca2+ ions. However, the related kinetic information on the TNT-mediated intercellular mechanotransduction communication is still poorly explored. Herein, we developed a classic and sensitive Pt-functionalized carbon fiber microelectrochemical sensor (Pt/CF) to study the intercellular communication of endothelial mechanotransduction through TNTs. The experimental findings demonstrate that the transmission of mechanical stimulation from stimulated human umbilical vein endothelial cells (HUVECs) to recipient HUVECs connected by TNTs occurred quickly (<100 ms) and effectively promoted nitric oxide (NO) production in the recipient HUVECs. The kinetic profile of NO release exhibited remarkable similarity in stimulated and recipient HUVECs. But the production of NO in the recipient cell is significantly attenuated (16.3%) compared to that in the stimulated cell, indicating a transfer efficiency of approximately 16.3% for TNTs. This study unveils insights into the TNT-mediated intercellular communication of mechanotransduction.

Krause corpuscles are genital vibrotactile sensors for sexual behaviours

Krause corpuscles, which were discovered in the 1850s, are specialized sensory structures found within the genitalia and other mucocutaneous tissues1-4. The physiological properties and functions of Krause corpuscles have remained unclear since their discovery. Here we report the anatomical and physiological properties of Krause corpuscles of the mouse clitoris and penis and their roles in sexual behaviour. We observed a high density of Krause corpuscles in the clitoris compared with the penis. Using mouse genetic tools, we identified two distinct somatosensory neuron subtypes that innervate Krause corpuscles of both the clitoris and penis and project to a unique sensory terminal region of the spinal cord. In vivo electrophysiology and calcium imaging experiments showed that both Krause corpuscle afferent types are A-fibre rapid-adapting low-threshold mechanoreceptors, optimally tuned to dynamic, light-touch and mechanical vibrations (40-80 Hz) applied to the clitoris or penis. Functionally, selective optogenetic activation of Krause corpuscle afferent terminals evoked penile erection in male mice and vaginal contraction in female mice, while genetic ablation of Krause corpuscles impaired intromission and ejaculation of males and reduced sexual receptivity of females. Thus, Krause corpuscles of the clitoris and penis are highly sensitive mechanical vibration detectors that mediate sexually dimorphic mating behaviours.

Design of neural organoids engineered by mechanical forces

Neural organoids consist of three-dimensional tissue derived from pluripotent stem cells that could recapitulate key features of the human brain. During the past decade, organoid technology has evolved in the field of human brain science by increasing the quality and applicability of its products. Among them, a novel approach involving the design of neural organoids engineered by mechanical forces has emerged. This review describes previous approaches for the generation of neural organoids, the engineering of neural organoids by mechanical forces, and future challenges for the application of mechanical forces in the design of neural organoids.

Single-molecule magnetic tweezers to probe the equilibrium dynamics of individual proteins at physiologically relevant forces and timescales

The reversible unfolding and refolding of proteins is a regulatory mechanism of tissue elasticity and signalling used by cells to sense and adapt to extracellular and intracellular mechanical forces. However, most of these proteins exhibit low mechanical stability, posing technical challenges to the characterization of their conformational dynamics under force. Here, we detail step-by-step instructions for conducting single-protein nanomechanical experiments using ultra-stable magnetic tweezers, which enable the measurement of the equilibrium conformational dynamics of single proteins under physiologically relevant low forces applied over biologically relevant timescales. We report the basic principles determining the functioning of the magnetic tweezer instrument, review the protein design strategy and the fluid chamber preparation and detail the procedure to acquire and analyze the unfolding and refolding trajectories of individual proteins under force. This technique adds to the toolbox of single-molecule nanomechanical techniques and will be of particular interest to those interested in proteins involved in mechanosensing and mechanotransduction. The procedure takes 4 d to complete, plus an additional 6 d for protein cloning and production, requiring basic expertise in molecular biology, surface chemistry and data analysis.

The fallacy of functional nomenclature in the kingdom of biological multifunctionality: physiological and evolutionary considerations on ion channels

Living organisms are multiscale complex systems that have evolved high degrees of multifunctionality and redundancy in the structure-function relationship. A number of factors, only in part determined genetically, affect the jobs of proteins. The overall structural organization confers unique molecular properties that provide the potential to perform a pattern of activities, some of which are co-opted by specific environments. The variety of multifunctional proteins is expanding, but most cases are handled individually and according to the still dominant 'one structure-one function' approach, which relies on the attribution of canonical names typically referring to the first task identified for a given protein. The present topical review focuses on the multifunctionality of ion channels as a paradigmatic example. Mounting evidence reports the ability of many ion channels (including members of voltage-dependent, ligand-gated and transient receptor potential families) to exert biological effects independently of their ion conductivity. 'Functionally based' nomenclature (the practice of naming a protein or family of proteins based on a single purpose) is a conceptual bias for three main reasons: (i) it increases the amount of ambiguity, deceiving our understanding of the multiple contributions of biomolecules that is the heart of the complexity; (ii) it is in stark contrast to protein evolution dynamics, largely based on multidomain arrangement; and (iii) it overlooks the crucial role played by the microenvironment in adjusting the actions of cell structures and in tuning protein isoform diversity to accomplish adaptational requirements. Biological information in protein physiology is distributed among different entwined layers working as the primary 'locus' of natural selection and of evolutionary constraints.

Neural mechanisms of respiratory interoception

Respiratory interoception is one of the internal bodily systems that is comprised of different types of somatic and visceral sensations elicited by different patterns of afferent input and respiratory motor drive mediating multiple respiratory modalities. Respiratory interoception is a complex system, having multiple afferents grouped into afferent clusters and projecting into both discriminative and affective centers that are directly related to the behavioral assessment of breathing. The multi-afferent system provides a spectrum of input that result in the ability to interpret the different types of respiratory interceptive sensations. This can result in a response, commonly reported as breathlessness or dyspnea. Dyspnea can be differentiated into specific modalities. These respiratory sensory modalities lead to a general sensation of an Urge-to-Breathe, driven by a need to compensate for the modulation of ventilation that has occurred due to factors that have affected breathing. The multiafferent system for respiratory interoception can also lead to interpretation of the sensory signals resulting in respiratory related sensory experiences, including the Urge-to-Cough and Urge-to-Swallow. These behaviors are modalities that can be driven through the differentiation and integration of multiple afferent input into the respiratory neural comparator. Respiratory sensations require neural somatic and visceral interoceptive elements that include gated attention and detection leading to respiratory modality discrimination with subsequent cognitive decision and behavioral compensation. Studies of brain areas mediating cortical and subcortical respiratory sensory pathways are summarized and used to develop a model of an integrated respiratory neural network mediating respiratory interoception.

Immunolocalization of the mechanogated ion channels PIEZO1 and PIEZO2 in human and mouse dental pulp and periodontal ligament

PIEZO1 and PIEZO2 are essential components of mechanogated ion channels, which are required for mechanotransduction and biological processes associated with mechanical stimuli. There is evidence for the presence of PIEZO1 and PIEZO2 in teeth and periodontal ligaments, especially in cell lines and mice, but human studies are almost nonexistent. Decalcified permanent human teeth and mouse molars were processed for immunohistochemical detection of PIEZO1 and PIEZO2. Confocal laser microscopy was used to examine the co-localization of PIEZO 1 and PIEZO2 with vimentin (a marker of differentiated odontoblasts) in human teeth. In the outer layer of the human dental pulp, abundant PIEZO1- and PIEZO2-positive cells were found that had no odontoblast morphology and were vimentin-negative. Based on their morphology, location, and the absence of vimentin positivity, they were identified as dental pulp stem cells or pre-odontoblasts. However, in mice, PIEZO1 and PIEZO2 were ubiquitously detected and colocalized in odontoblasts. Intense immunoreactivity of PIEZO1 and PIEZO2 has been observed in human and murine periodontal ligaments. Our findings suggest that PIEZO1 and PIEZO2 may be mechanosensors/mechanotransducers in murine odontoblasts, as well as in the transmission of forces by the periodontal ligament in humans and mice.

TMC7 functions as a suppressor of Piezo2 in primary sensory neurons blunting peripheral mechanotransduction

The transmembrane channel-like (TMC) protein family comprises eight members, with TMC1 and TMC2 being extensively studied. This study demonstrates substantial co-expression of TMC7 with the mechanosensitive channel Piezo2 in somatosensory neurons. Genetic deletion of TMC7 in primary sensory ganglia neurons in vivo enhances sensitivity in both physiological and pathological mechanosensory transduction. This deletion leads to an increase in proportion of rapidly adapting (RA) currents conducted by Piezo2 in dorsal root ganglion (DRG) neurons and accelerates RA deactivation kinetics. In HEK293 cells expressing both proteins, TMC7 significantly suppresses the current amplitudes of co-expressed Piezo2. Our findings reveal that TMC7 and Piezo2 exhibit physical interactions, and both proteins also physically interact with cytoskeletal β-actin. We hypothesize that TMC7 functions as an inhibitory modulator of Piezo2 in DRG neurons, either through direct inhibition or by disrupting the transmission of mechanical forces from the cytoskeleton to the channel.

Tension activation of mechanosensitive two-pore domain K+ channels TRAAK, TREK-1, and TREK-2

TRAAK, TREK-1, and TREK-2 are mechanosensitive two-pore domain K+ (K2P) channels that contribute to action potential propagation, sensory transduction, and muscle contraction. While structural and functional studies have led to models that explain their mechanosensitivity, we lack a quantitative understanding of channel activation by membrane tension. Here, we define the tension response of mechanosensitive K2Ps using patch-clamp recording and imaging. All are low-threshold mechanosensitive channels (T10%/50% 0.6-2.7 / 4.4-6.4 mN/m) with distinct response profiles. TRAAK is most sensitive, TREK-1 intermediate, and TREK-2 least sensitive. TRAAK and TREK-1 are activated broadly over a range encompassing nearly all physiologically relevant tensions. TREK-2, in contrast, activates over a narrower range like mechanosensitive channels Piezo1, MscS, and MscL. We further show that low-frequency, low-intensity focused ultrasound increases membrane tension to activate TRAAK and MscS. This work provides insight into tension gating of mechanosensitive K2Ps relevant to understanding their physiological roles and potential applications for ultrasonic neuromodulation.

Biomimetic Electronic Skin Based on a Stretchable Ionogel Mechanoreceptor Composed of Crumpled Conductive Rubber Electrodes for Synchronous Strain, Pressure, and Temperature Detection

Electronic skin (e-skin) is showing a huge potential in human-computer interaction, intelligent robots, human health, motion monitoring, etc. However, it is still challenging for e-skin to realize distinguishable detection of stretching strain, vertical pressure, and temperature through a simple noncoupling structure design. Here, a stretchable multimodal biomimetic e-skin was fabricated by integrating layer-by-layer self-assembled crumpled reduced graphene oxide/multiwalled carbon nanotubes film on natural rubber (RGO/MWCNTs@NR) as stretchable conductive electrodes and polyacrylamide/NaCl ionogel as a dielectric layer into an ionotropic capacitive mechanoreceptor. Unlike natural skin receptors, the sandwich-like stretchable ionogel mechanoreceptor possessed a distinct ionotropic capacitive behavior for strain and pressure detection. The results showed that the biomimetic e-skin displayed a negative capacitance change with superior stretchability (0-300%) and a high gauge factor of 0.27 in 180-300% strain, while exhibiting a normal positive piezo-capacitance behavior in vertical pressure range of 0-15 kPa with a maximal sensitivity of 1.759 kPa-1. Based on this feature, the biomimetic e-skin showed an excellent synchronous detection capability of planar strain and vertical pressure in practical wearable applications such as gesture recognition and grasping movement detection without a complicated mathematical or signal decoupling process. In addition, the biomimetic e-skin exhibited a quantifiable linear responsiveness to temperature from 20-90 °C with a temperature coefficient of 0.55%/°C. These intriguing properties gave the biomimetic e-skin the ability to perform a complete function similar to natural skin but beyond its performance for future wearable devices and artificial intelligence devices.

Structure-guided mutagenesis of OSCAs reveals differential activation to mechanical stimuli

The dimeric two-pore OSCA/TMEM63 family has recently been identified as mechanically activated ion channels. Previously, based on the unique features of the structure of OSCA1.2, we postulated the potential involvement of several structural elements in sensing membrane tension (Jojoa-Cruz et al., 2018). Interestingly, while OSCA1, 2, and 3 clades are activated by membrane stretch in cell-attached patches (i.e. they are stretch-activated channels), they differ in their ability to transduce membrane deformation induced by a blunt probe (poking). Here, in an effort to understand the domains contributing to mechanical signal transduction, we used cryo-electron microscopy to solve the structure of Arabidopsis thaliana (At) OSCA3.1, which, unlike AtOSCA1.2, only produced stretch- but not poke-activated currents in our initial characterization (Murthy et al., 2018). Mutagenesis and electrophysiological assessment of conserved and divergent putative mechanosensitive features of OSCA1.2 reveal a selective disruption of the macroscopic currents elicited by poking without considerable effects on stretch-activated currents (SAC). Our results support the involvement of the amphipathic helix and lipid-interacting residues in the membrane fenestration in the response to poking. Our findings position these two structural elements as potential sources of functional diversity within the family.

Analysis of pressure-activated Piezo1 open and subconductance states at a single channel level

Mechanically activated Piezo1 channels undergo transitions from closed to open-state in response to pressure and other mechanical stimuli. However, the molecular details of these mechanosensitive gating transitions are unknown. Here, we used cell-attached pressure-clamp recordings to acquire single channel data at steady-state conditions (where inactivation has settled down), at various pressures and voltages. Importantly, we identify and analyze subconductance states of the channel which were not reported before. Pressure-dependent activation of Piezo1 increases the occupancy of open and subconductance state at the expense of decreased occupancy of shut-states. No significant change in the mean open time of subconductance states was observed with increasing negative pipette pressure or with varying voltages (ranging from -40 to -100 mV). Using Markov-chain modeling, we identified a minimal four-states kinetic scheme, which recapitulates essential characteristics of the single channel data, including that of the subconductance level. This study advances our understanding of Piezo1-gating mechanism in response to discrete stimuli (such as pressure and voltage) and paves the path to develop cellular and tissue level models to predict Piezo1 function in various cell types.

A mouse DRG genetic toolkit reveals morphological and physiological diversity of somatosensory neuron subtypes

Dorsal root ganglia (DRG) somatosensory neurons detect mechanical, thermal, and chemical stimuli acting on the body. Achieving a holistic view of how different DRG neuron subtypes relay neural signals from the periphery to the CNS has been challenging with existing tools. Here, we develop and curate a mouse genetic toolkit that allows for interrogating the properties and functions of distinct cutaneous targeting DRG neuron subtypes. These tools have enabled a broad morphological analysis, which revealed distinct cutaneous axon arborization areas and branching patterns of the transcriptionally distinct DRG neuron subtypes. Moreover, in vivo physiological analysis revealed that each subtype has a distinct threshold and range of responses to mechanical and/or thermal stimuli. These findings support a model in which morphologically and physiologically distinct cutaneous DRG sensory neuron subtypes tile mechanical and thermal stimulus space to collectively encode a wide range of natural stimuli.

Structure-guided mutagenesis of OSCAs reveals differential activation to mechanical stimuli

The dimeric two-pore OSCA/TMEM63 family has recently been identified as mechanically activated ion channels. Previously, based on the unique features of the structure of OSCA1.2, we postulated the potential involvement of several structural elements in sensing membrane tension1. Interestingly, while OSCA1, 2, and 3 clades are activated by membrane stretch in cell-attached patches (i.e., they are stretch-activated channels), they differ in their ability to transduce membrane deformation induced by a blunt probe (poking). In an effort to understand the domains contributing to mechanical signal transduction, we used cryo-electron microscopy to solve the structure of Arabidopsis thaliana (At) OSCA3.1, which, unlike AtOSCA1.2, only produced stretch- but not poke-activated currents in our initial characterization2. Mutagenesis and electrophysiological assessment of conserved and divergent putative mechanosensitive features of OSCA1.2 reveal a selective disruption of the macroscopic currents elicited by poking without considerable effects on stretch-activated currents (SAC). Our results support the involvement of the amphipathic helix and lipid-interacting residues in the membrane fenestration in the response to poking. Our findings position these two structural elements as potential sources of functional diversity within the family.

Ultrasound Modulates Calcium Activity in Cultured Neurons, Glial Cells, Endothelial Cells and Pericytes

OBJECTIVE

Ultrasound is being researched as a method to modulate the brain. Studies of the interaction of sound with neurons support the hypothesis that mechanosensitive ion channels play an important role in ultrasound neuromodulation. The response of cells other than neurons (e.g., astrocytes, pericytes and endothelial cells) have not been fully characterized, despite playing an important role in brain function.

METHODS

To address this gap in knowledge, we examined cultured murine primary cortical neurons, astrocytes, endothelial cells and pericytes in an in vitro widefield microscopy setup during application of a 500 ms burst of 250 kHz focused ultrasound over a pressure range known to elicit neuromodulation. We examined cell membrane health in response to a range of pulses and used optical calcium indicators in conjunction with pharmacological antagonists to selectively block different groups of thermo- and mechanosensitive ion channels known to be responsive to ultrasound.

RESULTS

All cell types experienced an increase in calcium fluorescence in response to ultrasound. Gadolinium (Gad), 2-aminoethoxydiphenyl borate (2-APB) and ruthenium red (RR) reduced the percentage of responding neurons and magnitude of response. The percentage of astrocytes responding was significantly lowered only by Gad, whereas both 2-APB and Gad decreased the amplitude of the fluorescence response. 2-APB decreased the percentage of responding endothelial cells, whereas only Gad reduced the magnitude of responses. Pericytes exposed to RR or Gad were less likely to respond to stimulation. RR had no detectable effect on the magnitude of the pericyte responses while 2-APB and Gad significantly decreased the fluorescence intensity, despite not affecting the percentage responding.

CONCLUSION

Our study highlights the role of non-neuronal cells during FUS neuromodulation. All of the investigated cell types are sensitive to mechanical ultrasound stimulation and rely on mechanosensitive ion channels to undergo ultrasound neuromodulation.

Role of mechanically-sensitive cation channels Piezo1 and TRPV4 in trabecular meshwork cell mechanotransduction

Glaucoma is one of the leading causes of irreversible blindness in developed countries, and intraocular pressure (IOP) is primary and only treatable risk factor, suggesting that to a significant extent, glaucoma is a disease of IOP disorder and pathological mechanotransduction. IOP-lowering ways are limited to decreaseing aqueous humour (AH) production or increasing the uveoscleral outflow pathway. Still, therapeutic approaches have been lacking to control IOP by enhancing the trabecular meshwork (TM) pathway. Trabecular meshwork cells (TMCs) have endothelial and myofibroblast properties and are responsible for the renewal of the extracellular matrix (ECM). Mechanosensitive cation channels, including Piezo1 and TRPV4, are abundantly expressed in primary TMCs and trigger mechanostress-dependent ECM and cytoskeletal remodelling. However, prolonged mechanical stimulation severely affects cellular biosynthesis through TMC mechanotransduction, including signaling, gene expression, ECM remodelling, and cytoskeletal structural changes, involving outflow facilities and elevating IOP. As for the functional coupling relationship between Piezo1 and TRPV4 channels, inspired by VECs and osteoblasts, we hypothesized that Piezo1 may also act upstream of TRPV4 in glaucomatous TM tissue, mediating the activation of TRPV4 via Ca2+ inflow or Ca2+ binding to phospholipase A2(PLA2), and thus be involved in increasing TM outflow resistance and elevated IOP. Therefore, this review aims to help identify new potential targets for IOP stabilization in ocular hypertension and primary open-angle glaucoma by understanding the mechanical transduction mechanisms associated with the development of glaucoma and may provide ideas into novel treatments for preventing the progression of glaucoma by targeting mechanotransduction.

Mechanical activation of TWIK-related potassium channel by nanoscopic movement and rapid second messenger signaling

Rapid conversion of force into a biological signal enables living cells to respond to mechanical forces in their environment. The force is believed to initially affect the plasma membrane and then alter the behavior of membrane proteins. Phospholipase D2 (PLD2) is a mechanosensitive enzyme that is regulated by a structured membrane-lipid site comprised of cholesterol and saturated ganglioside (GM1). Here we show stretch activation of TWIK-related K+ channel (TREK-1) is mechanically evoked by PLD2 and spatial patterning involving ordered GM1 and 4,5-bisphosphate (PIP2) clusters in mammalian cells. First, mechanical force deforms the ordered lipids, which disrupts the interaction of PLD2 with the GM1 lipids and allows a complex of TREK-1 and PLD2 to associate with PIP2 clusters. The association with PIP2 activates the enzyme, which produces the second messenger phosphatidic acid (PA) that gates the channel. Co-expression of catalytically inactive PLD2 inhibits TREK-1 stretch currents in a biological membrane. Cellular uptake of cholesterol inhibits TREK-1 currents in culture and depletion of cholesterol from astrocytes releases TREK-1 from GM1 lipids in mouse brain. Depletion of the PLD2 ortholog in flies results in hypersensitivity to mechanical force. We conclude PLD2 mechanosensitivity combines with TREK-1 ion permeability to elicit a mechanically evoked response.

Piezo1 as a potential player in intracranial hemorrhage: from perspectives on biomechanics and hematoma metabolism

Intracranial hemorrhage (ICH) causes numerous neurological deficits and deaths worldwide each year, leaving a significant health burden on the public. The pathophysiology of ICH is complicated, and involves both primary and secondary injury. Hematoma, as the prime pathology of ICH, undergoes metabolism and triggers biochemical and biomechanical alterations in the brain, leading to secondary injury. Past endeavors mainly aimed at biochemical-initiated mechanisms for causing secondary injury have made limited progress in recent years, although ICH itself is also highly biomechanics-related. The discovery of the mechanical-activated cation channel Piezo1 provides a new avenue to further explore underlying mechanisms of secondary injury. The current article reviews the structure and gating mechanisms of Piezo1, its roles in the physiology/pathophysiology of neurons, astrocytes, microglia, and bone-marrow-derived macrophages, and especially its roles in erythrocytic turnover and iron metabolism, revealing a potential interplay between the biomechanics and biochemistry of hematoma in ICH. Collectively, these advances provide deeper insights into the secondary injury of ICH and lay the foundations for future research.

[Role of Piezo mechanosensitive ion channels in the osteoarticular system]

Objective

To summarize the role of Piezo mechanosensitive ion channels in the osteoarticular system, in order to provide reference for subsequent research.

Methods

Extensive literature review was conducted to summarize the structural characteristics, gating mechanisms, activators and blockers of Piezo ion channels, as well as their roles in the osteoarticular systems.

Results

The osteoarticular system is the main load-bearing and motor tissue of the body, and its ability to perceive and respond to mechanical stimuli is one of the guarantees for maintaining normal physiological functions of bones and joints. The occurrence and development of many osteoarticular diseases are closely related to abnormal mechanical loads. At present, research shows that Piezo mechanosensitive ion channels differentiate towards osteogenesis by responding to stretching stimuli and regulating cellular Ca 2+ influx signals; and it affects the proliferation and migration of osteoblasts, maintaining bone homeostasis through cellular communication between osteoblasts-osteoclasts. Meanwhile, Piezo1 protein can indirectly participate in regulating the formation and activity of osteoclasts through its host cells, thereby regulating the process of bone remodeling. During mechanical stimulation, the Piezo1 ion channel maintains bone homeostasis by regulating the expressions of Akt and Wnt1 signaling pathways. The sensitivity of Piezo1/2 ion channels to high strain mechanical signals, as well as the increased sensitivity of Piezo1 ion channels to mechanical transduction mediated by Ca 2+ influx and inflammatory signals in chondrocytes, is expected to become a new entry point for targeted prevention and treatment of osteoarthritis. But the specific way mechanical stimuli regulate the physiological/pathological processes of bones and joints still needs to be clarified.

Conclusion

Piezo mechanosensitive ion channels give the osteoarticular system with important abilities to perceive and respond to mechanical stress, playing a crucial mechanical sensing role in its cellular fate, bone development, and maintenance of bone and cartilage homeostasis.

Beyond Natural Channel Proteins: Recent Advances in Fluorinated Nanochannels

Inspired by the structures and functions of natural channel proteins that selectively permeate ions and molecules across biological membranes, synthetic molecules capable of self-assembling into supramolecular nanotubes within the hydrophobic layer of the membranes have been designed and their material permeation properties have been studied. More recently, synthetic chemists have ventured to incorporate fluorine atoms, elements rarely found in natural proteins, into the structure of synthetic channels and discovered anomalous transmembrane material permeation properties. In this Perspective, the author provides a brief overview of recent advances in the development of fluorinated nanochannels and possible directions for the future.

The role of mechanically sensitive ion channel Piezo1 in bone remodeling

Piezo1 (2010) was identified as a mechanically activated cation channel capable of sensing various physical forces, such as tension, osmotic pressure, and shear force. Piezo1 mediates mechanosensory transduction in different organs and tissues, including its role in maintaining bone homeostasis. This review aimed to summarize the function and possible mechanism of Piezo1 in the mechanical receptor cells in bone tissue. We found that it is a potential therapeutic target for the treatment of bone diseases.

Mechanics in the nervous system: From development to disease

Physical forces are ubiquitous in biological processes across scales and diverse contexts. This review highlights the significance of mechanical forces in nervous system development, homeostasis, and disease. We provide an overview of mechanical signals present in the nervous system and delve into mechanotransduction mechanisms translating these mechanical cues into biochemical signals. During development, mechanical cues regulate a plethora of processes, including cell proliferation, differentiation, migration, network formation, and cortex folding. Forces then continue exerting their influence on physiological processes, such as neuronal activity, glial cell function, and the interplay between these different cell types. Notably, changes in tissue mechanics manifest in neurodegenerative diseases and brain tumors, potentially offering new diagnostic and therapeutic target opportunities. Understanding the role of cellular forces and tissue mechanics in nervous system physiology and pathology adds a new facet to neurobiology, shedding new light on many processes that remain incompletely understood.

Structure of mechanically activated ion channel OSCA2.3 reveals mobile elements in the transmembrane domain

Members of the OSCA/TMEM63 family are mechanically activated ion channels and structures of some OSCA members have revealed the architecture of these channels and structural features that are potentially involved in mechanosensation. However, these structures are all in a similar state and information about the motion of different elements of the structure is limited, preventing a deeper understanding of how these channels work. Here, we used cryoelectron microscopy to determine high-resolution structures of Arabidopsis thaliana OSCA1.2 and OSCA2.3 in peptidiscs. The structure of OSCA1.2 matches previous structures of the same protein in different environments. Yet, in OSCA2.3, the TM6a-TM7 linker adopts a different conformation that constricts the pore on its cytoplasmic side. Furthermore, coevolutionary sequence analysis uncovered a conserved interaction between the TM6a-TM7 linker and the beam-like domain (BLD). Our results reveal conformational heterogeneity and differences in conserved interactions between the TMD and BLD among members of the OSCA family.

Stretch response of the mechano-gated channel TMEM63A in membrane patches and single cells

The recently discovered ion channel TMEM63A has biophysical features distinctive for mechano-gated cation channels, activating at high pressures with slow kinetics while not inactivating. However, some biophysical properties are less clear, including no information on its function in whole cells. The aim of this study is to expand the TMEM63A biophysical characterization and examine the function in whole cells. Piezo1-knockout HEK293T cells were cotransfected with human TMEM63A and green fluorescent protein (GFP), and macroscopic currents in cell-attached patches were recorded by high-speed pressure clamp at holding voltages from -120 to -20 mV with 0-100 mmHg patch suction for 1 s. HEK293 cells cotransfected with TMEM63A and GCaMP5 were seeded onto polydimethylsiloxane (PDMS) membrane, and the response to 3-12 s of 1%-15% whole cell isotropic (equi-biaxial) stretch induced by an IsoStretcher was measured by the change in intracellular calcium ([Ca2+]i) and presented as (ΔF/F0 > 1). Increasing patch pressures activated TMEM63A currents with accelerating activation kinetics and current amplitudes that were pressure dependent but voltage independent. TMEM63A currents were plateaued within 2 s, recovered quickly, and were sensitive to Gd3+. In whole cells stretched on flexible membranes, radial stretch increased the [Ca2+]i responses in a larger proportion of cells cotransfected with TMEM63A and GCaMP5 than GCaMP5-only controls. TMEM63A currents are force activated and voltage insensitive, have a high threshold for pressure activation with slow activation and deactivation, and lack inactivation over 5 s. TMEM63A has the net polarity and kinetics that would depolarize plasma membranes and increase inward currents, contributing to a sustained [Ca2+]i increase in response to high stretch.NEW & NOTEWORTHY TMEM63A has biophysical features distinctive for mechano-gated cation channels, but some properties are less clear, including no functional information in whole cells. We report that pressure-dependent yet voltage-independent TMEM63A currents in cell membrane patches correlated with cell size. In addition, radial stretch of whole cells on flexible membranes increased the [Ca2+]i responses more in TMEM63A-transfected cells. Inward TMEM63A currents in response to high stretch can depolarize plasma membranes and contribute to a sustained [Ca2+]i increase.

LHFPL5 is a key element in force transmission from the tip link to the hair cell mechanotransducer channel

During auditory transduction, sound-evoked vibrations of the hair cell stereociliary bundles open mechanotransducer (MET) ion channels via tip links extending from one stereocilium to its neighbor. How tension in the tip link is delivered to the channel is not fully understood. The MET channel comprises a pore-forming subunit, transmembrane channel-like protein (TMC1 or TMC2), aided by several accessory proteins, including LHFPL5 (lipoma HMGIC fusion partner-like 5). We investigated the role of LHFPL5 in transduction by comparing MET channel activation in outer hair cells of Lhfpl5-/- knockout mice with those in Lhfpl5+/- heterozygotes. The 10 to 90 percent working range of transduction in Tmc1+/+; Lhfpl5+/- was 52 nm, from which the single-channel gating force, Z, was evaluated as 0.34 pN. However, in Tmc1+/+; Lhfpl5-/- mice, the working range increased to 123 nm and Z more than halved to 0.13 pN, indicating reduced sensitivity. Tip link tension is thought to activate the channel via a gating spring, whose stiffness is inferred from the stiffness change on tip link destruction. The gating stiffness was ~40 percent of the total bundle stiffness in wild type but was virtually abolished in Lhfpl5-/-, implicating LHFPL5 as a principal component of the gating spring. The mutation Tmc1 p.D569N reduced the LHFPL5 immunolabeling in the stereocilia and like Lhfpl5-/- doubled the MET working range, but other deafness mutations had no effect on the dynamic range. We conclude that tip-link tension is transmitted to the channel primarily via LHFPL5; residual activation without LHFPL5 may occur by direct interaction between PCDH15 and TMC1.

Exploring the Alternative Conformation of a Known Protein Structure Based on Contact Map Prediction

The rapid development of deep learning-based methods has considerably advanced the field of protein structure prediction. The accuracy of predicting the 3D structures of simple proteins is comparable to that of experimentally determined structures, providing broad possibilities for structure-based biological studies. Another critical question is whether and how multistate structures can be predicted from a given protein sequence. In this study, analysis of tens of two-state proteins demonstrated that deep learning-based contact map predictions contain structural information on both states, which suggests that it is probably appropriate to change the target of deep learning-based protein structure prediction from one specific structure to multiple likely structures. Furthermore, by combining deep learning- and physics-based computational methods, we developed a protocol for exploring alternative conformations from a known structure of a given protein, by which we successfully approached the holo-state conformations of multiple representative proteins from their apo-state structures.

Experimental modulation of physiological force application on leg joint neurons in intact Drosophila melanogaster

The study of how mechanical forces affect biological events in living tissue is important for the understanding of a multitude of physiogical and pathophysiological phenomena. However, these investigations are often impeded by insufficient knowledge about force parameters, inadequate experimental administration of force stimuli and lack of noninvasive means to record their molecular and cellular effects. We therefore introduced a procedure to study the impact of force stimulation on adhesion G-protein-coupled receptor dissociation in mechanosensory neurons. Here, we detail a procedure to harness the mechanical force spectrum that emerges during the natural flexion-extension cycle of the femorotibial joint of adult fruit flies (Drosophila melanogaster). Mechanical load generated during the joint's motion is transmitted to specialized mechanosensory neurons residing close to the joint axis, which serve as proprioceptive sensors in the peripheral nervous system of the animal. Temporary immobilization of the joint by a restraint made of a human hair allows for the observation of transgenic mechanosensitive reporters by using fluorescent readout in the neurons before, during and after cessation of mechanical stimulation. The assay harnesses physiologically adequate stimuli for joint flexion and extension, can be conducted noninvasively in live specimens and is compatible with various transgenic reporter systems beyond the initially conceived strategy and mechanobiological hypotheses tested. The application of the protocol requires knowledge in Drosophila genetics, husbandry and fluorescence imaging and micromanipulation skills. The experimental procedure can be completed in 10 h and requires an additional 30 min in advance for fly fixation and leg immobilization. The apple agar cooking and heptane glue preparation requires a maximum of 30 min on the day before the experiment is conducted.

Stem cells and pain

Pain can be defined as an unpleasant sensory and emotional experience caused by either actual or potential tissue damage or even resemble that unpleasant experience. For years, science has sought to find treatment alternatives, with minimal side effects, to relieve pain. However, the currently available pharmacological options on the market show significant adverse events. Therefore, the search for a safer and highly efficient analgesic treatment has become a priority. Stem cells (SCs) are non-specialized cells with a high capacity for replication, self-renewal, and a wide range of differentiation possibilities. In this review, we provide evidence that the immune and neuromodulatory properties of SCs can be a valuable tool in the search for ideal treatment strategies for different types of pain. With the advantage of multiple administration routes and dosages, therapies based on SCs for pain relief have demonstrated meaningful results with few downsides. Nonetheless, there are still more questions than answers when it comes to the mechanisms and pathways of pain targeted by SCs. Thus, this is an evolving field that merits further investigation towards the development of SC-based analgesic therapies, and this review will approach all of these aspects.

TMEM63 mechanosensitive ion channels: Activation mechanisms, biological functions and human genetic disorders

The transmembrane 63 (TMEM63) family of proteins are originally identified as homologs of the osmosensitive calcium-permeable (OSCA) channels in plants. Mechanosensitivity of OSCA and TMEM63 proteins are recently demonstrated in addition to their proposed activation mechanism by hyper/hypo-osmolarity. TMEM63 proteins exist in all animals, with a single member in Drosophila (TMEM63) and three members in mammals (TMEM63 A/B/C). In humans, monoallelic variants of TMEM63A have been reported to cause transient hypomyelination during infancy, or severe hypomyelination and global developmental delay. Heterozygous variants of TMEM63B are found in patients with intellectual disability and abnormal motor function and brain morphology. Biallelic variants of TMEM63C are associated with hereditary spastic paraplegias accompanied by mild or no intellectual disability. Physiological functions of TMEM63 proteins clearly recognized so far include detecting food grittiness and environmental humidity in Drosophila, and supporting hearing in mice by regulating survival of cochlear hair cells. In this review, we summarize current knowledge about the activation mechanisms and biological functions of TMEM63 channels, and provide a concise reference for researchers interested in investigating more physiological and pathogenic roles of this family of proteins with ubiquitous expression in the body.

Harnessing mechanobiology for kidney organoid research

Recently, organoids have emerged as revolutionizing tools with the unprecedented potential to recreate organ-specific microanatomy in vitro. Upon their derivation from human pluripotent stem cells (hPSCs), organoids reveal the blueprints of human organogenesis, further allowing the faithful recapitulation of their physiology. Nevertheless, along with the evolution of this field, advanced research exposed the organoids' shortcomings, particularly regarding poor reproducibility rates and overall immatureness. To resolve these challenges, many studies have started to underscore the relevance of mechanical cues as a relevant source to induce and externally control hPSCs differentiation. Indeed, established organoid generation protocols from hPSCs have mainly relyed on the biochemical induction of fundamental signalling pathways present during kidney formation in mammals, whereas mechanical cues have largely been unexplored. This review aims to discuss the pertinence of (bio) physical cues within hPSCs-derived organoid cultures, while deciphering their effect on morphogenesis. Moreover, we will explore state-of-the-art mechanobiology techniques as revolutionizing means for understanding the underlying role of mechanical forces in biological processes in organoid model systems.

Mechanically-primed voltage-gated proton channels from angiosperm plants

Voltage-gated and mechanically-gated ion channels are distinct classes of membrane proteins that conduct ions across gated pores and are turned on by electrical or mechanical stimuli, respectively. Here, we describe an Hv channel (a.k.a voltage-dependent H+ channel) from the angiosperm plant A. thaliana that gates with a unique modality as it is turned on by an electrical stimulus only after exposure to a mechanical stimulus, a process that we call priming. The channel localizes in the vascular tissue and has homologs in vascular plants. We find that mechanical priming is not required for activation of non-angiosperm Hvs. Guided by AI-generated structural models of plant Hv homologs, we identify a set of residues playing a crucial role in mechanical priming. We propose that Hvs from angiosperm plants require priming because of a network of hydrophilic/charged residues that locks the channels in a silent resting conformation. Mechanical stimuli destabilize the network allowing the conduction pathway to turn on. In contrast to many other channels and receptors, Hv proteins are not thought to possess mechanisms such as inactivation or desensitization. Our findings demonstrate that angiosperm Hv channels are electrically silent until a mechanical stimulation turns on their voltage-dependent activity.

Mechanical stimulation from the surrounding tissue activates mitochondrial energy metabolism in Drosophila differentiating germ cells

In multicellular lives, the differentiation of stem cells and progenitor cells is often accompanied by a transition from glycolysis to mitochondrial oxidative phosphorylation (OXPHOS). However, the underlying mechanism of this metabolic transition remains largely unknown. In this study, we investigate the role of mechanical stress in activating OXPHOS during differentiation of the female germline cyst in Drosophila. We demonstrate that the surrounding somatic cells flatten the 16-cell differentiating cyst, resulting in an increase of the membrane tension of germ cells inside the cyst. This mechanical stress is necessary to maintain cytosolic Ca2+ concentration in germ cells through a mechanically activated channel, transmembrane channel-like. The sustained cytosolic Ca2+ triggers a CaMKI-Fray-JNK signaling relay, leading to the transcriptional activation of OXPHOS in differentiating cysts. Our findings demonstrate a molecular link between cell mechanics and mitochondrial energy metabolism, with implications for other developmentally orchestrated metabolic transitions in mammals.

Deciphering the role of mechanosensitive channels in plant root biology: perception, signaling, and adaptive responses

MAIN CONCLUSION

Mechanosensitive channels are integral membrane proteins that rapidly translate extrinsic or intrinsic mechanical tensions into biological responses. They can serve as potential candidates for developing smart-resilient crops with efficient root systems. Mechanosensitive (MS) calcium channels are molecular switches for mechanoperception and signal transduction in all living organisms. Although tremendous progress has been made in understanding mechanoperception and signal transduction in bacteria and animals, this remains largely unknown in plants. However, identification and validation of MS channels such as Mid1-complementing activity channels (MCAs), mechanosensitive-like channels (MSLs), and Piezo channels (PIEZO) has been the most significant discovery in plant mechanobiology, providing novel insights into plant mechanoperception. This review summarizes recent advances in root mechanobiology, focusing on MS channels and their related signaling players, such as calcium ions (Ca2+), reactive oxygen species (ROS), and phytohormones. Despite significant advances in understanding the role of Ca2+ signaling in root biology, little is known about the involvement of MS channel-driven Ca2+ and ROS signaling. Additionally, the hotspots connecting the upstream and downstream signaling of MS channels remain unclear. In light of this, we discuss the present knowledge of MS channels in root biology and their role in root developmental and adaptive traits. We also provide a model highlighting upstream (cell wall sensors) and downstream signaling players, viz., Ca2+, ROS, and hormones, connected with MS channels. Furthermore, we highlighted the importance of emerging signaling molecules, such as nitric oxide (NO), hydrogen sulfide (H2S), and neurotransmitters (NTs), and their association with root mechanoperception. Finally, we conclude with future directions and knowledge gaps that warrant further research to decipher the complexity of root mechanosensing.

Modulation of Mechanosensitive Potassium Channels by a Membrane-targeted Nongenetic Photoswitch

Mechanosensitive ion channels are present in the plasma membranes of all cells. They play a fundamental role in converting mechanical stimuli into biochemical signals and are involved in several physiological processes such as touch sensation, hearing, and blood pressure regulation. This protein family includes TWIK-related arachidonic acid-stimulated K+ channel (TRAAK), which is specifically implicated in the maintenance of the resting membrane potential and in the regulation of a variety of important neurobiological functions. Dysregulation of these channels has been linked to various diseases, including blindness, epilepsy, cardiac arrhythmia, and chronic pain. For these reasons, mechanosensitive channels are targets for the treatment of several diseases. Here, we propose a new approach to investigate TRAAK ion channel modulation that is based on nongenetic photostimulation. We employed an amphiphilic azobenzene, named Ziapin2. In the dark, Ziapin2 preferentially dwells in the plasma membrane, causing a thinning of the membrane. Upon light irradiation, an isomerization occurs, breaking the dimers and inducing membrane relaxation. To study the effect of Ziapin2 on the mechanosensitive channels, we expressed human TRAAK (hTRAAK) channels in HEK293T cells. We observed that Ziapin2 insertion in the membrane is able per se to recruit hTRAAK, permitting the exit of K+ ions outside the cells with a consequent hyperpolarization of the cell membrane. During light stimulation, membrane relaxation induces hTRAAK closure, generating a consistent and compensatory depolarization. These results add information to the Ziapin2 mechanism and suggest that membrane deformation can be a tool for the nonselective modulation of mechanosensitive channels.

Selective RNAi-silencing of Schwann cell Piezo1 alleviates mechanical hypersensitization following peripheral nerve injury

We previously reported functional Piezo1 expression in Schwann cells of the peripheral nervous system. This study is designed to further investigate the role of Schwann cell Piezo1 in peripheral nociception. We first developed an adeno-associated viral (AAV) vector that has primary Schwann cell tropism after delivery into the sciatic nerve. This was achieved by packing AAV-GFP transcribed by a hybrid CMV enhancer/chicken β-actin (CBA) promoter using a capsid AAVolig001 to generate AAVolig001-CBA-GFP. Five weeks after intrasciatic injection of AAVolig001-CBA-GFP in naïve rats, GFP expression was detected selectively in the Schwann cells of the sciatic nerve. A short hairpin RNA against rat Piezo1 (PZ1shRNA) was designed that showed efficient physical and functional knockdown of Piezo1 in NG108 neuronal cells. A dual promoter and bidirectional AAV encoding a U6-driven PZ1shRNA and CBA-transcribed GFP was packed with capsid olig001 (AAVolig001-PZ1shRNA), and AAV was injected into unilateral sciatic nerve immediately after induction of common peroneal nerve injury (CPNI). Results showed that the development of mechanical hypersensitivity in the CPNI rats injected with AAVolig001-PZ1shRNA was mitigated, compared to rats subjected with AAVolig001-scramble. Selective in vivo Schwann cell transduction and functional block of Piezo1 channel activity of primary cultured Schwann cells was confirmed. Together, our data demonstrate that 1) AAVolig001 has unique and selective primary tropism to Schwann cells via intrasciatic delivery and 2) Schwann cell Piezo1 contributes to mechanical hypersensitivity following nerve injury.