Mechanosensitive ion channels and the peptide inhibitor GsMTx-4: history, properties, mechanisms and pharmacology

The Mechanosensitive PIEZO1 Channel Contributes to the Reaction of RAW264.7 Macrophages to Mechanical Strain

The mechanosensitive channel 'piezo type mechanosensitive ion channel component 1' (PIEZO1) plays a regulatory role in the response of periodontal ligament fibroblasts (PDLFs) to the mechanical strain that occurs during orthodontic tooth movement. In addition to PDLFs, immune cells such as macrophages are also exposed to mechanical stimuli. Macrophages respond to mechanical strain with increased expression of inflammatory mediators. The role of PIEZO1 in this response remains elusive. To investigate the effect of PIEZO1 activation, RAW264.7 macrophages were stimulated with the PIEZO1 activator YODA1 without concurrent application of pressure. To further examine the specific role of PIEZO1 during mechanical strain, RAW264.7 macrophages were exposed to mechanical strain without and with simultaneous inhibition of PIEZO1 either by chemical inhibition (GsMTx4) or siRNA silencing. The expression of genes and proteins involved in orthodontic tooth movement was examined by quantitative PCR, western blot, and enzyme-linked immunosorbent assay (ELISA). Activation of PIEZO1 by YODA1 or mechanical strain increased the expression of inflammatory cytokines and osteoprotegerin (Opg), which is critically involved in bone remodeling processes. Conversely, inhibition of the PIEZO1 channel attenuates the effects of mechanical stress. In conclusion, our data demonstrate that the PIEZO1 channel is a major contributor to the response of macrophages to mechanical strain encountered during orthodontic tooth movement and affects the expression of inflammatory and bone remodeling factors.

Opposing Calcium-Dependent Effects of GsMTx4 in Acute Lymphoblastic Leukemia: In Vitro Proliferation vs. In Vivo Survival Advantage

Mechanogated (MG) ion channels play a crucial role in mechano-transduction and immune cell regulation, yet their impact on blood cancers, particularly acute lymphoblastic leukemia (ALL), remains poorly understood. This study investigates the pharmacological effects of GsMTx4, an MG channel inhibitor, in human ALL cells both in vitro and in vivo. Unexpectedly, we found that GsMTx4 remarkably increased basal calcium (Ca2+) levels in ALL cells through constitutive Ca2+ entry and enhanced store-operated Ca2⁺ influx upon thapsigargin stimulation. This increase in basal Ca2+ signaling promoted ALL cell viability and proliferation in vitro. Notably, chelating intracellular Ca2+ with BAPTA-AM reduces GsMTx4-mediated leukemia cell viability and proliferation. However, in vivo, GsMTx4 decreases cytosolic Ca2+ levels in Nalm-6 GFP⁺ cells isolated from mouse blood, effectively countering leukemia progression and significantly extending survival in NSG mice transplanted with leukemia cells (median survival: GsMTx4 vs. control, 37.5 days vs. 29 days, p = 0.0414). Our results highlight the different properties of GsMTx4 activity in in vitro and in vivo models. They also emphasize that Ca2+ signaling is a key vulnerability in leukemia, where its precise modulation dictates disease progression. Thus, targeting Ca2+ channels could offer a novel therapeutic strategy for leukemia by exploiting Ca2+ homeostasis.

Mechanical cues rewire lipid metabolism and support chemoresistance in epithelial ovarian cancer cell lines OVCAR3 and SKOV3

Epithelial ovarian cancer (EOC) is one of the deadliest cancers in women, and acquired chemoresistance is a major contributor of aggressive phenotypes. Overcoming treatment failure and disease recurrence is therefore an ambitious goal. Ovarian cancer develops in a biophysically challenging environment where the cells are constantly exposed to mechanical deformation originating in the abdomen and shear stress caused by the accumulation of ascitic fluid in the peritoneal cavity. Therefore, mechanical stimulation can be seen as an inseparable part of the tumor microenvironment. The role of biomechanics in shaping tumor metabolism is emerging and promises to be a real game changer in the field of cancer biology. Focusing on two different epithelial ovarian cancer cell lines (SKOV3 and OVCAR3), we explored the impact of shear stress on cellular behavior driven by mechanosensitive transcription factors (TFs). Here, we report data linking physical triggers to the alteration of lipid metabolism, ultimately supporting increased chemoresistance. Mechanistically, shear stress induced adaptation of cell membrane and actin cytoskeleton which were accompanied by the regulation of nuclear translocation of SREBP2 and YAP1. This was associated with increased cholesterol uptake/biosynthesis and decreased sensitivity to the ruthenium-based anticancer drug BOLD-100. Overall, the present study contributes to shedding light on the molecular pathways connecting mechanical cues, tumor metabolism and drug responsiveness.

Lysosome and plasma membrane Piezo channels of Trypanosoma cruzi are essential for proliferation, differentiation and infectivity

Trypanosoma cruzi, the causative agent of Chagas disease, is a parasitic protist that affects millions of people worldwide. Currently there are no fully effective drugs or vaccines available. Contact of T. cruzi infective forms with their host cells or with the extracellular matrix increases their intracellular Ca2+ concentration suggesting a mechano-transduction process. We report here that T. cruzi possesses two distinct mechanosensitive Piezo channels, named TcPiezo1 and TcPiezo2, with different subcellular localizations but similarly essential for normal proliferation, differentiation, and infectivity. While TcPiezo1 localizes to the plasma membrane, TcPiezo2 localizes to the lysosomes. Downregulation of TcPiezo1 expression by a novel ligand-regulated hammerhead ribozyme (HHR) significantly inhibited Ca2+ entry in cells expressing a genetically encoded Ca2+ indicator while downregulation of TcPiezo2 expression inhibited Ca2+ release from lysosomes, which are now identified as novel acidic Ca2+ stores in trypanosomes. The channels are activated by contact with extracellular matrix and by hypoosmotic stress. The results establish the essentiality of Piezo channels for the life cycle and Ca2+ homeostasis of T. cruzi and a novel lysosomal localization for a Piezo channel in eukaryotes.

Applying Ultrasound to Mechanically and Noninvasively Sensitize Prostate Tumors to TRAIL-Mediated Apoptosis

Non-surgical and safe prostate cancer (PCa) therapies are in demand. Soluble tumor necrosis factor (TNF-α) related apoptosis inducing ligand (TRAIL), a cancer-specific drug, shows preclinical efficacy but has a short circulation half-life. This research has shown that physiological fluid shear stress activates mechanosensitive ion channels (MSCs), such as Piezo1, enhancing TRAIL-mediated apoptosis in cancer cells. Herein, noninvasive, focal ultrasound (FUS) is implemented to augment the pro-apoptotic effects of TRAIL. Using thermally safe FUS parameters, it is observed that TRAIL sensitivity increases with higher FUS pressure in PCa cells, mediated by Piezo1. This is confirmed by examining the effects of calcium chelation, MSC inhibitors, and PIEZO knockdown. In vivo, a multi-dose study with 10 min FUS exposure shows that 0 and 4-h intervals between TRAIL and FUS significantly reduce tumor burden, with an increase in apoptosis evident by enhanced cleaved-caspase 3 expression. This mechanotherapy offers a clinically translatable approach by utilizing widely available FUS technology, applicable to treat additional cancer types.

Human TMC1 and TMC2 are mechanically gated ion channels

Mammalian transmembrane channel-like proteins 1 and 2 (TMC1 and TMC2) have emerged as very promising candidate mechanotransduction channels in hair cells. However, controversy persists because the heterogeneously expressed TMC1/2 in cultured cells lack evidence of mechanical gating, primarily due to their absence from the plasma membrane. By employing domain swapping with OSCA1.1 and subsequent point mutations, we successfully identified membrane-localized mouse TMC1/2 mutants, demonstrating that they are mechanically gated in heterologous cells. Further, whole-genome CRISPRi screening enabled wild-type human TMC1/2 localization in the plasma membrane, where they responded robustly to poking stimuli. In addition, wild-type human TMC1/2 showed stretch-activated currents and clear single-channel current activities. Deafness-related TMC1 mutations altered the reversal potential of TMC1, indicating that TMC1/2 are pore-forming mechanotransduction channels. In summary, our study provides evidence that human TMC1/2 are pore-forming, mechanically activated ion channels, supporting their roles as mechanotransduction channels in hair cells.

Monocyte-derived extracellular vesicles, stimulated by Trypanosoma cruzi, enhance cellular invasion in vitro via activated TGF-β1

During cell invasion, large Extracellular Vesicle (lEV) release from host cells was dose-dependently triggered by Trypanosoma cruzi metacyclic trypomastigotes (Mtr). This lEV release was inhibited when IP3-mediated Ca2+ exit from the ER and further Ca2+ entry from plasma membrane channels was blocked, but whilst any store-independent Ca2+ entry (SICE) could continue unabated. That lEV release was equally inhibited if all entry from external sources was blocked by chelation of external Ca2+ points to the major contributor to Mtr-triggered host cell lEV release being IP3/store-mediated Ca2+ release, SICE playing a minor role. Host cell lEVs were released through Mtr interaction with host cell lipid raft domains, integrins, and mechanosensitive ion channels, whereupon [Ca2+]cyt increased (50 to 750 nM) within 15 s. lEV release and cell entry of T. cruzi, which increased up to 30 and 60 mpi, respectively, as well as raised actin depolymerization at 60 mpi, were all reduced by TRPC inhibitor, GsMTx-4. Vesicle release and infection was also reduced with RGD peptide, methyl-β-cyclodextrin, knockdown of calpain and with the calpain inhibitor, calpeptin. Restoration of lEV levels, whether with lEVs from infected or uninfected epithelial cells, did not restore invasion, but supplementation with lEVs from infected monocytes, did. We provide evidence of THP-1 monocyte-derived lEV interaction with Mtr (lipid mixing by R18-dequenching; flow cytometry showing transfer to Mtr of R18 from R18-lEVs and of LAP(TGF-β1). Active, mature TGF-β1 (at 175 pg/×105 in THP-1 lEVs) was detected in concentrated lEV-/cell-free supernatant by western blotting, only after THP-1 lEVs had interacted with Mtr. The TGF-β1 receptor (TβRI) inhibitor, SB-431542, reduced the enhanced cellular invasion due to monocyte-lEVs.

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.

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.

Are Aminoglycoside Antibiotics TRPing Your Metabolic Switches?

Transient receptor potential (TRP) channels are broadly implicated in the developmental programs of most tissues. Amongst these tissues, skeletal muscle and adipose are noteworthy for being essential in establishing systemic metabolic balance. TRP channels respond to environmental stimuli by supplying intracellular calcium that instigates enzymatic cascades of developmental consequence and often impinge on mitochondrial function and biogenesis. Critically, aminoglycoside antibiotics (AGAs) have been shown to block the capacity of TRP channels to conduct calcium entry into the cell in response to a wide range of developmental stimuli of a biophysical nature, including mechanical, electromagnetic, thermal, and chemical. Paradoxically, in vitro paradigms commonly used to understand organismal muscle and adipose development may have been led astray by the conventional use of streptomycin, an AGA, to help prevent bacterial contamination. Accordingly, streptomycin has been shown to disrupt both in vitro and in vivo myogenesis, as well as the phenotypic switch of white adipose into beige thermogenic status. In vivo, streptomycin has been shown to disrupt TRP-mediated calcium-dependent exercise adaptations of importance to systemic metabolism. Alternatively, streptomycin has also been used to curb detrimental levels of calcium leakage into dystrophic skeletal muscle through aberrantly gated TRPC1 channels that have been shown to be involved in the etiology of X-linked muscular dystrophies. TRP channels susceptible to AGA antagonism are critically involved in modulating the development of muscle and adipose tissues that, if administered to behaving animals, may translate to systemwide metabolic disruption. Regenerative medicine and clinical communities need to be made aware of this caveat of AGA usage and seek viable alternatives, to prevent contamination or infection in in vitro and in vivo paradigms, respectively.

The role of the Piezo1 channel in osteoblasts under cyclic stretching: A study on osteogenic and osteoclast factors

OBJECTIVES

Orthodontic tooth movement is a mechanobiological reaction induced by appropriate forces, including bone remodeling. The mechanosensitive Piezo channels have been shown to contribute to bone remodeling. However, information about the pathways through which Piezo channels affects osteoblasts remains limited. Thus, we aimed to investigate the influence of Piezo1 on the osteogenic and osteoclast factors in osteoblasts under mechanical load.

MATERIALS AND METHODS

Cyclic stretch (CS) experiments on MC3T3-E1 were conducted using a BioDynamic mechanical stretching device. The Piezo1 channel blocker GsMTx4 and the Piezo1 channel agonist Yoda1 were used 12 h before the application of CS. MC3T3-E1 cells were then subjected to 15% CS, and the expression of Piezo1, Piezo2, BMP-2, OCN, Runx2, RANKL, p-p65/p65, and ALP was measured using quantitative real-time polymerase chain reaction, western blot, alkaline phosphatase staining, and immunofluorescence staining.

RESULTS

CS of 15% induced the highest expression of Piezo channel and osteoblast factors. Yoda1 significantly increased the CS-upregulated expression of Piezo1 and ALP activity but not Piezo2 and RANKL. GsMTx4 downregulated the CS-upregulated expression of Piezo1, Piezo2, Runx2, OCN, p-65/65, and ALP activity but could not completely reduce CS-upregulated BMP-2.

CONCLUSIONS

The appropriate force is more suitable for promoting osteogenic differentiation in MC3T3-E1. The Piezo1 channel participates in osteogenic differentiation of osteoblasts through its influence on the expression of osteogenic factors like BMP-2, Runx2, and OCN and is involved in regulating osteoclasts by influencing phosphorylated p65. These results provide a foundation for further exploration of osteoblast function in orthodontic tooth movement.

Dissecting cell membrane tension dynamics and its effect on Piezo1-mediated cellular mechanosensitivity using force-controlled nanopipettes

The dynamics of cellular membrane tension and its role in mechanosensing, which is the ability of cells to respond to physical stimuli, remain incompletely understood, mainly due to the lack of appropriate tools. Here, we report a force-controlled nanopipette-based method that combines fluidic force microscopy with fluorescence imaging for precise manipulation of the cellular membrane tension while monitoring the impact on single-cell mechanosensitivity. The force-controlled nanopipette enables control of the indentation force imposed on the cell cortex as well as of the aspiration pressure applied to the plasma membrane. We show that this setup can be used to concurrently monitor the activation of Piezo1 mechanosensitive ion channels via calcium imaging. Moreover, the spatiotemporal behavior of the tension propagation is assessed with the fluorescent membrane tension probe Flipper-TR, and further dissected using molecular dynamics modeling. Finally, we demonstrate that aspiration and indentation act independently on the cellular mechanobiological machinery, that indentation induces a local pre-tension in the membrane, and that membrane tension stays confined by links to the cytoskeleton.

Multiplex, high-throughput method to study cancer and immune cell mechanotransduction

Studying cellular mechanoresponses during cancer metastasis is limited by sample variation or complex protocols that current techniques require. Metastasis is governed by mechanotransduction, whereby cells translate external stimuli, such as circulatory fluid shear stress (FSS), into biochemical cues. We present high-throughput, semi-automated methods to expose cells to FSS using the VIAFLO96 multichannel pipetting device custom-fitted with 22 G needles, increasing the maximum FSS 94-fold from the unmodified tips. Specifically, we develop protocols to semi-automatically stain live samples and to fix, permeabilize, and intracellularly process cells for flow cytometry analysis. Our first model system confirmed that the pro-apoptotic effects of TRAIL therapeutics in prostate cancer cells can be enhanced via FSS-induced Piezo1 activation. Our second system implements this multiplex methodology to show that FSS exposure (290 dyn cm-2) increases activation of murine bone marrow-derived dendritic cells. These methodologies greatly improve the mechanobiology workflow, offering a high-throughput, multiplex approach.

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.

Extracellular Matrix Cues Regulate Mechanosensing and Mechanotransduction of Cancer Cells

Extracellular biophysical properties have particular implications for a wide spectrum of cellular behaviors and functions, including growth, motility, differentiation, apoptosis, gene expression, cell-matrix and cell-cell adhesion, and signal transduction including mechanotransduction. Cells not only react to unambiguously mechanical cues from the extracellular matrix (ECM), but can occasionally manipulate the mechanical features of the matrix in parallel with biological characteristics, thus interfering with downstream matrix-based cues in both physiological and pathological processes. Bidirectional interactions between cells and (bio)materials in vitro can alter cell phenotype and mechanotransduction, as well as ECM structure, intentionally or unintentionally. Interactions between cell and matrix mechanics in vivo are of particular importance in a variety of diseases, including primarily cancer. Stiffness values between normal and cancerous tissue can range between 500 Pa (soft) and 48 kPa (stiff), respectively. Even the shear flow can increase from 0.1-1 dyn/cm2 (normal tissue) to 1-10 dyn/cm2 (cancerous tissue). There are currently many new areas of activity in tumor research on various biological length scales, which are highlighted in this review. Moreover, the complexity of interactions between ECM and cancer cells is reduced to common features of different tumors and the characteristics are highlighted to identify the main pathways of interaction. This all contributes to the standardization of mechanotransduction models and approaches, which, ultimately, increases the understanding of the complex interaction. Finally, both the in vitro and in vivo effects of this mechanics-biology pairing have key insights and implications for clinical practice in tumor treatment and, consequently, clinical translation.

Autophagy modulation changes mechano-chemical sensitivity of T24 bladder cancer cells

Bladder cancer cells possess unique adaptive capabilities: shaped by their environment, cells face a complex chemical mixture of metabolites and xenobiotics accompanied by physiological mechanical cues. These responses might translate into resistance to chemotherapeutical regimens and can largely rely on autophagy. Considering molecules capable of rewiring tumor plasticity, compounds of natural origin promise to offer valuable options. Fungal derived metabolites, such as bafilomycin and wortmannin are widely acknowledged as autophagy inhibitors. Here, their potential to tune bladder cancer cells´ adaptability to chemical and physical stimuli was assessed. Additionally, dietary occurring mycotoxins were also investigated, namely deoxynivalenol (DON, 0.1-10 µM) and fusaric acid (FA, 0.1-1 mM). Endowing a Janus' face behavior, DON and FA are on the one side described as toxins with detrimental health effects. Concomitantly, they are also explored experimentally for selective pharmacological applications including anticancer activities. In non-cytotoxic concentrations, bafilomycin (BAFI, 1-10 nM) and wortmannin (WORT, 1 µM) modified cell morphology and reduced cancer cell migration. Application of shear stress and inhibition of mechano-gated PIEZO channels reduced cellular sensitivity to BAFI treatment (1 nM). Similarly, for FA (0.5 mM) PIEZO1 expression and inhibition largely aligned with the modulatory potential on cancer cells motility. Additionally, this study highlighted that the activity profile of compounds with similar cytotoxic potential (e.g. co-incubation DON with BAFI or FA with WORT) can diverge substantially in the regulation of cell mechanotransduction. Considering the interdependence between tumor progression and response to mechanical cues, these data promise to provide a novel viewpoint for the study of chemoresistance and associated pathways.

Beyond matrix stiffness: targeting force-induced cancer drug resistance

During tumor progression, mechanical abnormalities in the tumor microenvironment (TME) trigger signaling pathways in cells that activate cellular programs, resulting in tumor growth and drug resistance. In this review, we describe mechanisms of action for anti-cancer therapies and mechanotransduction programs that regulate cellular processes, including cell proliferation, apoptosis, survival and phenotype switching. We discuss how the therapeutic response is impacted by the three main mechanical TME abnormalities: high extracellular matrix (ECM) composition and stiffness; interstitial fluid pressure (IFP); and elevated mechanical forces. We also review drugs that normalize these abnormalities or block mechanosensors and mechanotransduction pathways. Finally, we discuss current challenges and perspectives for the development of new strategies targeting mechanically induced drug resistance in the clinic.

Dual action of Dooku1 on PIEZO1 channel in human red blood cells

PIEZO1 is a mechanosensitive non-selective cation channel, present in many cell types including Red Blood Cells (RBCs). Together with the Gárdos channel, PIEZO1 forms in RBCs a tandem that participates in the rapid adjustment of the cell volume. The pharmacology allowing functional studies of the roles of PIEZO1 has only recently been developed, with Yoda1 as a widely used PIEZO1 agonist. In 2018, Yoda1 analogues were developed, as a step towards an improved understanding of PIEZO1 roles and functions. Among these, Dooku1 was the most promising antagonist of Yoda1-induced effects, without having any ability to activate PIEZO1 channels. Since then, Dooku1 has been used in various cell types to antagonize Yoda1 effects. In the present study using RBCs, Dooku1 shows an apparent IC₅₀ on Yoda1 effects of 90.7 µM, one order of magnitude above the previously reported data on other cell types. Unexpectedly, it was able, by itself, to produce entry of calcium sufficient to trigger Gárdos channel activation. Moreover, Dooku1 evoked a rise in intracellular sodium concentrations, suggesting that it targets a non-selective cation channel. Dooku1 effects were abolished upon using GsMTx4, a known mechanosensitive channel blocker, indicating that Dooku1 likely targets PIEZO1. Our observations lead to the conclusion that Dooku1 behaves as a PIEZO1 agonist in the RBC membrane, similarly to Yoda1 but with a lower potency. Taken together, these results show that the pharmacology of PIEZO1 in RBCs must be interpreted with care especially due to the unique characteristics of RBC membrane and associated cytoskeleton.

Macrophages induce gingival destruction via Piezo1-mediated MMPs-degrading collagens in periodontitis

Macrophages are an integral part of the innate immune response in periodontal tissue and play a crucial role in the progression of periodontitis. Here we reported that macrophages also provoke periodontitis-induced gingival destruction through Piezol-mediated collagen degradation. We discovered that the PIEZO1 expression was markedly elevated in patients with periodontitis through transcriptomic profiling. Moreover, Piezo1 promoted macrophage polarization toward the M1 type in response to lipopolysaccharide (LPS) and induced production of proinflammatory cytokines, which in turn stimulated production of matrix metalloproteinases (MMPs) leading to collagen degradation. Our study suggests that Piezol might be a potential therapeutic target for treating periodontitis-induced gingival destruction.

Sensory Neurons, PIEZO Channels and PAC1 Receptors Regulate the Mechanosensitive Release of Soluble Ectonucleotidases in the Murine Urinary Bladder Lamina Propria

The urinary bladder requires adequate concentrations of extracellular adenosine 5'-triphosphate (ATP) and other purines at receptor sites to function properly. Sequential dephosphorylation of ATP to ADP, AMP and adenosine (ADO) by membrane-bound and soluble ectonucleotidases (s-ENTDs) is essential for achieving suitable extracellular levels of purine mediators. S-ENTDs, in particular, are released in the bladder suburothelium/lamina propria (LP) in a mechanosensitive manner. Using 1,N⁶-etheno-ATP (eATP) as substrate and sensitive HPLC-FLD methodology, we evaluated the degradation of eATP to eADP, eAMP and eADO in solutions that were in contact with the LP of ex vivo mouse detrusor-free bladders during filling prior to substrate addition. The inhibition of neural activity with tetrodotoxin and ω-conotoxin GVIA, of PIEZO channels with GsMTx4 and D-GsMTx4 and of the pituitary adenylate cyclase-activating polypeptide type I receptor (PAC1) with PACAP6-38 all increased the distention-induced but not spontaneous release of s-ENTDs in LP. It is conceivable, therefore, that the activation of these mechanisms in response to distention restricts the further release of s-ENTDs and prevents excessive hydrolysis of ATP. Together, these data suggest that afferent neurons, PIEZO channels, PAC1 receptors and s-ENTDs form a system that operates a highly regulated homeostatic mechanism to maintain proper extracellular purine concentrations in the LP and ensure normal bladder excitability during bladder filling.

Vascular mechanotransduction

This review aims to survey the current state of mechanotransduction in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), including their sensing of mechanical stimuli and transduction of mechanical signals that result in the acute functional modulation and longer-term transcriptomic and epigenetic regulation of blood vessels. The mechanosensors discussed include ion channels, plasma membrane-associated structures and receptors, and junction proteins. The mechanosignaling pathways presented include the cytoskeleton, integrins, extracellular matrix, and intracellular signaling molecules. These are followed by discussions on mechanical regulation of transcriptome and epigenetics, relevance of mechanotransduction to health and disease, and interactions between VSMCs and ECs. Throughout this review, we offer suggestions for specific topics that require further understanding. In the closing section on conclusions and perspectives, we summarize what is known and point out the need to treat the vasculature as a system, including not only VSMCs and ECs but also the extracellular matrix and other types of cells such as resident macrophages and pericytes, so that we can fully understand the physiology and pathophysiology of the blood vessel as a whole, thus enhancing the comprehension, diagnosis, treatment, and prevention of vascular diseases.

Functional maturation of kidney organoid tubules: PIEZO1-mediated Ca2+ signaling

Kidney organoids cultured on adherent matrices in the presence of superfusate flow generate vascular networks and exhibit more mature podocyte and tubular compartments compared with static controls (Homan KA, Gupta N, Kroll KT, Kolesky DB, Skylar-Scott M, Miyoshi T, Mau D, Valerius MT, Ferrante T, Bonventre JV, Lewis JA, Morizane R. Nat Methods 16: 255-262, 2019; Takasato M, Er PX, Chiu HS, Maier B, Baillie GJ, Ferguson C, Parton RG, Wolvetang EJ, Roost MS, Chuva de Sousa Lopes SM, Little MH. Nature 526: 564-568, 2015.). However, their physiological function has yet to be systematically investigated. Here, we measured mechano-induced changes in intracellular Ca2+ concentration ([Ca2+]i) in tubules isolated from organoids cultured for 21-64 days, microperfused in vitro or affixed to the base of a specimen chamber, and loaded with fura-2 to measure [Ca2+]i. A rapid >2.5-fold increase in [Ca2+]i from a baseline of 195.0 ± 22.1 nM (n = 9; P ≤ 0.001) was observed when microperfused tubules from organoids >40 days in culture were subjected to luminal flow. In contrast, no response was detected in tubules isolated from organoids <30 days in culture. Nonperfused tubules (41 days) subjected to a 10-fold increase in bath flow rate also exhibited a threefold increase in [Ca2+]i from baseline (P < 0.001). Mechanosensitive PIEZO1 channels contribute to the flow-induced [Ca2+]i response in mouse distal tubule (Carrisoza-Gaytan R, Dalghi MG, Apodaca GL, Kleyman TR, Satlin LM. The FASEB J 33: 824.25, 2019.). Immunodetectable apical and basolateral PIEZO1 was identified in tubular structures by 21 days in culture. Basolateral PIEZO1 appeared to be functional as basolateral exposure of nonperfused tubules to the PIEZO1 activator Yoda 1 increased [Ca2+]i (P ≤ 0.001) in segments from organoids cultured for >30 days, with peak [Ca2+]i increasing with advancing days in culture. These results are consistent with a maturational increase in number and/or activity of flow/stretch-sensitive Ca2+ channels, including PIEZO1, in tubules of static organoids in culture.

Piezo1 activation induces relaxation of the pudendal artery and corpus cavernosum

Piezo1 channel is a sensor for shear-stress in the vasculature. Piezo1 activation induces vasodilation, and its deficiency contributes to vascular disorders, such as hypertension. In this study, we aimed to determine whether Piezo1 channel has a functional role in the dilation of pudendal arteries and corpus cavernosum (CC). For this, male Wistar rats were used, and the relaxation of the pudendal artery and CC was obtained using the Piezo1 activator, Yoda1, in the presence and absence of Dooku (Yoda1 antagonist), GsMTx4 (non-selective mechanosensory channel inhibitor) and L-NAME (nitric oxide synthase inhibitor). In the CC, Yoda1 was also tested in the presence of indomethacin (non-selective COX inhibitor) and tetraethylammonium (TEA, non-selective potassium channel inhibitor). The expression of Piezo1 was confirmed by Western blotting. Our data show that Piezo1 activation leads to the relaxation of the pudendal artery and CC as the chemical activator of Piezo1, Yoda1, relaxed the pudendal artery (47%) and CC (41%). This response was impaired by L-NAME and abolished by Dooku and GsMTx4 in the pudendal artery only. Indomethacin and TEA did not affect the relaxation induced by Yoda1 in the CC. Limited tools to explore this channel prevent further investigation of its underlying mechanisms of action. In conclusion, our data demonstrate that Piezo1 is expressed and induced the relaxation of the pudendal artery and CC. Further studies are necessary to determine its role in penile erection and if erectile dysfunction is associated with Piezo1 deficiency.

Infection-induced membrane ruffling initiates danger and immune signaling via the mechanosensor PIEZO1

Microorganisms are generally sensed by receptors recognizing microbial molecules, which evoke changes in cellular activities and gene expression. Bacterial pathogens induce secretion of the danger signal ATP as an early alert response of intestinal epithelial cells, initiating overt inflammation. However, what triggers ATP secretion during infection is unclear. Here we show that the inherently mechanosensitive plasma membrane channel PIEZO1 acts as a sensor for bacterial entry. PIEZO1 is mechanically activated by invasion-induced membrane ruffles upstream of Ca²⁺ influx and ATP secretion. Mimicking mechanical stimuli of pathogen uptake with sterile beads equally elicits ATP secretion. Chemical or genetic PIEZO1 inactivation inhibits mechanically induced ATP secretion. Moreover, chemical or mechanical PIEZO1 activation evokes gene expression in immune and barrier pathways. Thus, mechanosensation of invasion-induced plasma membrane distortion initiates immune signaling upon infection, independently of detection of microbial molecules. Hence, PIEZO1-dependent detection of infection is driven by physical signals instead of chemical ligands.

Cationic Mechanosensitive Channels Mediate Trabecular Meshwork Responses to Cyclic Mechanical Stretch

The trabecular meshwork (TM) is responsible for intraocular pressure (IOP) homeostasis in the eye. The tissue senses IOP fluctuations and dynamically adapts to the mechanical changes to either increase or decrease aqueous humor outflow. Cationic mechanosensitive channels (CMCs) have been reported to play critical roles in mediating the TM responses to mechanical forces. However, how CMCs influence TM cellular function affect aqueous humor drainage is still elusive. In this study, human TM (HTM) cells were collected from a Chinese donor and subjected to cyclically equiaxial stretching with an amplitude of 20% at 1 Hz GsMTx4, a non-selective inhibitor for CMCs, was added to investigate the proteomic changes induced by CMCs in response to mechanical stretch of HTM. Gene ontology enrichment analysis demonstrated that inhibition of CMCs significantly influenced several biochemical pathways, including store-operated calcium channel activity, microtubule cytoskeleton polarity, toll-like receptor signaling pathway, and neuron cell fate specification. Through heatmap analysis, we grouped 148 differentially expressed proteins (DEPs) into 21 clusters and focused on four specific patterns associated with Ca²⁺ homeostasis, autophagy, cell cycle, and cell fate. Our results indicated that they might be the critical downstream signals of CMCs adapting to mechanical forces and mediating AH outflow.

Mechanistic insights into ultrasonic neurostimulation of disconnected neurons using single short pulses

Ultrasonic neurostimulation is a potentially potent noninvasive therapy, whose mechanism has yet to be elucidated. We designed a system capable of applying ultrasound with minimal reflections to neuronal cultures. Synaptic transmission was pharmacologically controlled, eliminating network effects, enabling examination of single-cell processes. Short single pulses of low-intensity ultrasound were applied, and time-locked responses were examined using calcium imaging. Low-pressure (0.35MPa) ultrasound directly stimulated ∼20% of pharmacologically disconnected neurons, regardless of membrane poration. Stimulation was resistant to the blockade of several purinergic receptor and mechanosensitive ion channel types. Stimulation was blocked, however, by suppression of action potentials. Surprisingly, even extremely short (4μs) pulses were effective, stimulating ∼8% of the neurons. Lower-pressure pulses (0.35MPa) were less effective than higher-pressure ones (0.65MPa). Attrition effects dominated, with no indication of compromised viability. Our results detract from theories implicating cavitation, heating, non-transient membrane pores >1.5nm, pre-synaptic release, or gradual effects. They implicate a post-synaptic mechanism upstream of the action potential, and narrow down the list of possible targets involved.

The Role of Mechanically-Activated Ion Channels Piezo1, Piezo2, and TRPV4 in Chondrocyte Mechanotransduction and Mechano-Therapeutics for Osteoarthritis

Mechanical factors play critical roles in the pathogenesis of joint disorders like osteoarthritis (OA), a prevalent progressive degenerative joint disease that causes debilitating pain. Chondrocytes in the cartilage are responsible for extracellular matrix (ECM) turnover, and mechanical stimuli heavily influence cartilage maintenance, degeneration, and regeneration via mechanotransduction of chondrocytes. Thus, understanding the disease-associated mechanotransduction mechanisms can shed light on developing effective therapeutic strategies for OA through targeting mechanotransducers to halt progressive cartilage degeneration. Mechanosensitive Ca2+-permeating channels are robustly expressed in primary articular chondrocytes and trigger force-dependent cartilage remodeling and injury responses. This review discusses the current understanding of the roles of Piezo1, Piezo2, and TRPV4 mechanosensitive ion channels in cartilage health and disease with a highlight on the potential mechanotheraputic strategies to target these channels and prevent cartilage degeneration associated with OA.

Mechanosensitive calcium flashes promote sustained RhoA activation during tight junction remodeling

Epithelial cell–cell junctions remodel in response to mechanical stimuli to maintain barrier function. Previously, we found that local leaks in tight junctions (TJs) are rapidly repaired by local, transient RhoA activation, termed “Rho flares,” but how Rho flares are regulated is unknown. Here, we discovered that intracellular calcium flashes and junction elongation are early events in the Rho flare pathway. Both laser-induced and naturally occurring TJ breaks lead to local calcium flashes at the site of leaks. Additionally, junction elongation induced by optogenetics increases Rho flare frequency, suggesting that Rho flares are mechanically triggered. Depletion of intracellular calcium or inhibition of mechanosensitive calcium channels (MSCs) reduces the amplitude of calcium flashes and diminishes the sustained activation of Rho flares. MSC-dependent calcium influx is necessary to maintain global barrier function by regulating reinforcement of local TJ proteins via junction contraction. In all, we uncovered a novel role for MSC-dependent calcium flashes in TJ remodeling, allowing epithelial cells to repair local leaks induced by mechanical stimuli.

Intrinsic mechanical sensitivity of mammalian auditory neurons as a contributor to sound-driven neural activity

Mechanosensation – by which mechanical stimuli are converted into a neuronal signal – is the basis for the sensory systems of hearing, balance, and touch. Mechanosensation is unmatched in speed and its diverse range of sensitivities, reaching its highest temporal limits with the sense of hearing; however, hair cells (HCs) and the auditory nerve (AN) serve as obligatory bottlenecks for sounds to engage the brain. Like other sensory neurons, auditory neurons use the canonical pathway for neurotransmission and millisecond-duration action potentials (APs). How the auditory system utilizes the relatively slow transmission mechanisms to achieve ultrafast speed, and high audio-frequency hearing remains an enigma. Here, we address this paradox and report that the mouse, and chinchilla, AN are mechanically sensitive, and minute mechanical displacement profoundly affects its response properties. Sound-mimicking sinusoidal mechanical and electrical current stimuli affect phase-locked responses. In a phase-dependent manner, the two stimuli can also evoke suppressive responses. We propose that mechanical sensitivity interacts with synaptic responses to shape responses in the AN, including frequency tuning and temporal phase locking. Combining neurotransmission and mechanical sensation to control spike patterns gives the mammalian AN a secondary receptor role, an emerging theme in primary neuronal functions.

Mechanosensitive Piezo1 channels mediate renal fibrosis

Kidney fibrosis is the final common pathway of progressive kidney diseases, the underlying mechanisms of which is not fully understood. The purpose of the current study is to investigate a role of Piezo1, a mechanosensitive nonselective cation channel, in kidney fibrosis. In human fibrotic kidneys, Piezo1 protein expression was markedly upregulated. The abundance of Piezo1 protein in kidneys of mice with UUO or with folic-acid treatment was significantly increased. Inhibition of Piezo1 with GsMTx4 markedly ameliorated UUO or folic acid-induced kidney fibrosis. Mechanical stretch, compression or stiffness induced Piezo1 activation and pro-fibrotic responses in human HK2 cells and primary cultured mouse proximal tubular cells (mPTCs), which were greatly prevented by inhibition or silence of Piezo1. TGFβ-1 induced increased Piezo1 expression and pro-fibrotic phenotypic alterations in HK2 cells and mPTCs, which was again markedly prevented by inhibition of Piezo1. Activation of Piezo1 by Yoda1, a Piezo1 agonist, caused calcium influx and profibrotic responses in HK2 cells and induced calpain2 activation, followed by talin1 cleavage and upregulation of integrinβ1. Also, Yoda1 promoted the link between ECM and integrinβ1. In conclusion, Piezo1 is involved in the progression of kidney fibrosis and pro-fibrotic alterations in renal proximal tubular cells, likely through activating calcium-calpain2-integrinβ1 pathway.

Pain-related toxins in scorpion and spider venoms: a face to face with ion channels

Pain is a common symptom induced during envenomation by spiders and scorpions. Toxins isolated from their venom have become essential tools for studying the functioning and physiopathological role of ion channels, as they modulate their activity. In particular, toxins that induce pain relief effects can serve as a molecular basis for the development of future analgesics in humans. This review provides a summary of the different scorpion and spider toxins that directly interact with pain-related ion channels, with inhibitory or stimulatory effects. Some of these toxins were shown to affect pain modalities in different animal models providing information on the role played by these channels in the pain process. The close interaction of certain gating-modifier toxins with membrane phospholipids close to ion channels is examined along with molecular approaches to improve selectivity, affinity or bioavailability in vivo for therapeutic purposes.

SLO2.1/NALCN a sodium signaling complex that regulates uterine activity

Depolarization of the myometrial smooth muscle cell (MSMC) resting membrane potential is necessary for the uterus to transition from a quiescent state to a contractile state. The molecular mechanisms involved in this transition are not completely understood. Here, we report that a coupled system between the Na+-activated K+ channel (SLO2.1) and the non-selective Na+ leak channel (NALCN) determines the MSMC membrane potential. Our data indicate that Na+ entering through NALCN acts as an intracellular signaling molecule that activates SLO2.1. Potassium efflux through SLO2.1 hyperpolarizes the membrane. A decrease in SLO2.1/NALCN activity induces membrane depolarization, triggering Ca2+ entry through voltage-dependent Ca2+ channels and promoting contraction. Consistent with functional coupling, our data show that NALCN and SLO2.1 are in close proximity in human MSMCs. We propose that these arrangements of SLO2.1 and NALCN permit these channels to functionally regulate MSMC membrane potential and cell excitability and modulate uterine contractility.

Hair shaft miniaturization causes stem cell depletion through mechanosensory signals mediated by a Piezo1-calcium-TNF-α axis

In aging, androgenic alopecia, and genetic hypotrichosis disorders, hair shaft miniaturization is often associated with hair follicle stem cell (HFSC) loss. However, the mechanism causing this stem cell depletion in vivo remains elusive. Here we show that hair shaft loss or a reduction in diameter shrinks the physical niche size, which results in mechanical compression of HFSCs and their apoptotic loss. Mechanistically, cell compression activates the mechanosensitive channel Piezo1, which triggers calcium influx. This confers tumor necrosis factor alpha (TNF-α) sensitivity in a hair-cycle-dependent manner in otherwise resistant HFSCs and induces ectopic apoptosis. Persistent hair shaft miniaturization during aging and genetic hypotrichosis disorders causes long-term HFSC loss by inducing continuous ectopic apoptosis through Piezo1. Our results identify an unconventional role of the inert hair shaft structure as a functional niche component governing HFSC survival and reveal a mechanosensory axis that regulates physical-niche-atrophy-induced stem cell depletion in vivo.

ASIC1a is required for neuronal activation via low-intensity ultrasound stimulation in mouse brain

Accumulating evidence has shown transcranial low-intensity ultrasound can be potentially a non-invasive neural modulation tool to treat brain diseases. However, the underlying mechanism remains elusive and the majority of studies on animal models applying rather high-intensity ultrasound that cannot be safely used in humans. Here, we showed low-intensity ultrasound was able to activate neurons in the mouse brain and repeated ultrasound stimulation resulted in adult neurogenesis in specific brain regions. In vitro calcium imaging studies showed that a specific ultrasound stimulation mode, which combined with both ultrasound-induced pressure and acoustic streaming mechanotransduction, is required to activate cultured cortical neurons. ASIC1a and cytoskeletal proteins were involved in the low-intensity ultrasound-mediated mechanotransduction and cultured neuron activation, which was inhibited by ASIC1a blockade and cytoskeleton-modified agents. In contrast, the inhibition of mechanical-sensitive channels involved in bilayer-model mechanotransduction like Piezo or TRP proteins did not repress the ultrasound-mediated neuronal activation as efficiently. The ASIC1a-mediated ultrasound effects in mouse brain such as immediate response of ERK phosphorylation and DCX marked neurogenesis were statistically significantly compromised by ASIC1a gene deletion. Collated data suggest that ASIC1a is the molecular determinant involved in the mechano-signaling of low-intensity ultrasound that modulates neural activation in mouse brain.

Mechanosensitive cation channel Piezo1 contributes to ventilator-induced lung injury by activating RhoA/ROCK1 in rats

Background

Mechanical ventilation can induce or aggravate lung injury, which is termed ventilator-induced lung injury (VILI). Piezo1 is a key element of the mechanotransduction process and can transduce mechanical signals into biological signals by mediating Ca²⁺ influx, which in turn regulates cytoskeletal remodeling and stress alterations. We hypothesized that it plays an important role in the occurrence of VILI, and investigated the underlying mechanisms.

Methods

High tidal volume mechanical ventilation and high magnitude cyclic stretch were performed on Sprague–Dawley rats, and A549 and human pulmonary microvascular endothelial cells, respectively, to establish VILI models. Immunohistochemical staining, flow cytometry, histological examination, enzyme-linked immunosorbent assay, western blotting, quantitative real-time polymerase chain reaction and survival curves were used to assess the effect of Piezo1 on induction of lung injury, as well as the signaling pathways involved.

Results

We observed that Piezo1 expression increased in the lungs after high tidal volume mechanical ventilation and in cyclic stretch-treated cells. Mechanistically, we observed the enhanced expression of RhoA/ROCK1 in both cyclic stretch and Yoda1-treated cells, while the deficiency or inhibition of Piezo1 dramatically antagonized RhoA/ROCK1 expression. Furthermore, blockade of RhoA/ROCK1 signaling using an inhibitor did not affect Piezo1 expression. GSMTx4 was used to inhibit Piezo1, which alleviated VILI-induced pathologic changes, water content and protein leakage in the lungs, and the induction of systemic inflammatory mediators, and improved the 7-day mortality rate in the model rats.

Conclusions

These findings indicate that Piezo1 affects the development and progression of VILI through promotion of RhoA/ROCK1 signaling.

Fast desensitization of acetylcholine receptors induced by a spider toxin

Nicotinic acetylcholine receptors (nAChRs) are members of the “cys-loop” ligand-gated ion channel superfamily that play important roles in both the peripheral and central system. At the neuromuscular junction, the endplate current is induced by ACh binding and nAChR activation, and then, the current declines to a small steady state, even though ACh is still bound to the receptors. The kinetics of nAChRs with high affinity for ACh but no measurable ion conductance is called desensitization. This adopted desensitization of nAChR channel currents might be an important mechanism for protecting cells against uncontrolled excitation. This study aimed to show that Grammostola spatulata toxin (GsMTx4), which was first purified and characterized from the venom of the tarantula Grammostola spatulata (now genus Phixotricus), can facilitate the desensitization of nAChRs in murine C2C12 myotubes. To examine the details, muscle-type nAChRs, which are expressed heterologously in HEK293T cells, were studied. A single channel current was recorded under the cell-attached configuration, and the channel activity (NP_o) decayed much faster after the addition of GsMTx-4 to the pipette solution. The channel kinetics were further analyzed, and GsMTx-4 affected the channel activity of nAChRs by prolonging the closing time without affecting channel conductance or opening activity. The interaction between nAChRs embedded in the lipid membrane and toxin inserted into the membrane may contribute to the conformational change in the receptor and thus change the channel activity. This new property of GsMTx-4 may lead to a better understanding of the desensitization of ligand-gated channels and disease therapy.

Biomechanical micromotion at the neural interface modulates intracellular membrane potentialsin vivo

Objective. Respiration and vascular pulsation cause relative micromotion of brain tissue against stationary implants resulting in repetitive displacements of 2-4µm (due to vascular pulsation) and 10-30µm (due to breathing) in rats. However, the direct functional impact of such tissue micromotion on the cells at the neural interface remains unknown. This study aims to test the hypothesis that micromotion in brain tissue causes changes in membrane potentials (MPs) through the activation of mechanosensitive ion channels.Approach. Intracellular MPs were recorded from Aplysia ganglion cells (n= 8) and cortical cells (n= 15)in vivoinn= 7 adult rats. Cyclic stresses between 0.2 and 4 kPa repeated at 1 Hz were tested in Aplysia ganglion cells. For thein vivoexperiments, 30μM of gadolinium chloride (Gd³⁺), a non-selective blocker of mechanosensitive ion channels, was used to assess the role of such ion channels.Main results. In Aplysia ganglion cells, there were no MP changes for <1.5 kPa, and action potentials were observed at >3.1 kPa. Drug studies utilizing 5-HT showed an 80% reduction in firing frequency from controls. Inin vivoexperiments, periodic pulsations (1-10 mV) were observed in the MPs of cells that corresponded to breathing and heart-rate. In response to the addition of 30µM Gd³⁺, we observed a significant reduction (0.5-3 mV) in the periodic pulsations in MP in all cortical cells across four different rats, suggesting the role of mechanosensitive ion channels in mediating MP fluctuations due to tissue micromotion at the neural interface.Significance.Under chronic conditions, the tissue at the interface stiffens due to scar tissue formation, which is expected to increase the likelihood of recruiting stretch-receptors due to tissue micromotion. It is speculated that such chronic sub-threshold pulsations in MPs might trigger the immune response at the neural interface.

Trends in Piezo Channel Research Over the Past Decade: A Bibliometric Analysis

Purpose: We used bibliometric methods to evaluate the global scientific output of research on Piezo channels and explore the current status and trends in this field over the past decade. Methods: Piezo channel-related studies published in 2010-2020 were retrieved from Web of Science. The R bibliometrix package was used for quantitative and qualitative analyses of publication outputs and author contributions. VOSviewer was used to construct networks based on co-authorship of countries/institutions/authors, co-citation analysis of journals/references, citation analysis of documents, and co-occurrence of keywords. Results: In total, 556 related articles and reviews were included in the final analysis. The number of publications has increased substantially with time. The country and institution contributing the most to this field was the United States and Scripps Research Institute, respectively. Ardem Patapoutian was the most productive author and ranked first among the cited authors, h-index, and m-index. The top cited reference was the article published by Coste B et al. in Science (2010) that identified Piezo1/2 in mammalian cells. The top journals in terms of the number of selected articles and citations were Nature Communications and Nature, respectively. The co-occurrence analysis revealed that Piezo channels are involved a variety of cell types (Merkel cells, neurons, endothelial cells, red blood cells), physiological processes (touch sensation, blood pressure, proprioception, vascular development), related ion channels (transient receptor potential, Gardos), and diseases (pain, distal arthrogryposis, dehydrated hereditary stomatocytosis, cancer), and pharmacology (Yoda1, GsMTx-4). Conclusion: Our bibliometric analysis shows that Piezo channel research continues to be a hotspot. The focus has evolved from Piezo identification to architecture, activation mechanism, roles in diseases, and pharmacology.

TRPC channel-derived calcium fluxes differentially regulate ATP and flow-induced activation of eNOS

Endothelial dysfunction, characterised by impaired nitric oxide (NO) bioavailability, arises in response to a variety of cardiovascular risk factors and precedes atherosclerosis. NO is produced by tight regulation of endothelial nitric oxide synthase (eNOS) activity in response to vasodilatory stimuli. This regulation of eNOS is mediated in part by store-operated calcium entry (SOCE). We hypothesized that both ATP- and flow-induced eNOS activation are regulated by SOCE derived from Orai1 channels and members of the transient receptor potential canonical (TRPC) channel family. Bovine aortic endothelial cells (BAECs) were pre-treated with pharmacological inhibitors of TRPC channels and Orai1 to examine their effect on calcium signaling and eNOS activation in response to flow and ATP. The peak and sustained ATP-induced calcium signal and the resulting eNOS activation were attenuated by inhibition of TRPC3, which we found to be store operated. TRPC4 blockade reduced the transient peak in calcium concentration following ATP stimulation, but did not significantly reduce eNOS activity. Simultaneous TRPC3 & 4 inhibition reduced flow-induced NO production via alterations in phosphorylation-mediated eNOS activity. Inhibition of TRPC1/6 or Orai1 failed to lower ATP-induced calcium entry or eNOS activation. Our results suggest that TRPC3 is a store-operated channel in BAECs and is the key regulator of ATP-induced eNOS activation, whereas flow stimulation also recruits TRPC4 into the pathway for the synthesis of NO.

A role of PIEZO1 in iron metabolism in mice and humans

Iron overload causes progressive organ damage and is associated with arthritis, liver damage, and heart failure. Elevated iron levels are present in 1%-5% of individuals; however, iron overload is undermonitored and underdiagnosed. Genetic factors affecting iron homeostasis are emerging. Individuals with hereditary xerocytosis, a rare disorder with gain-of-function (GOF) mutations in mechanosensitive PIEZO1 ion channel, develop age-onset iron overload. We show that constitutive or macrophage expression of a GOF Piezo1 allele in mice disrupts levels of the iron regulator hepcidin and causes iron overload. We further show that PIEZO1 is a key regulator of macrophage phagocytic activity and subsequent erythrocyte turnover. Strikingly, we find that E756del, a mild GOF PIEZO1 allele present in one-third of individuals of African descent, is strongly associated with increased plasma iron. Our study links macrophage mechanotransduction to iron metabolism and identifies a genetic risk factor for increased iron levels in African Americans.

Reproducible Quantitative Stimulation Allows New Analysis of Crayfish Muscle Receptor Organ Responses

The crustacean muscle receptor organ (MRO) has provided a particularly accessible preparation for the study of sensory coding, which has been widely used in introductory laboratory courses incorporating extracellular recording from sensory nerves in living preparations. We describe three innovations to the standard laboratory exercise using the MRO: (1) a new form of suction electrode to facilitate extracellular recording; (2) a new, Arduino-driven actuator to allow reproducible and quantifiable mechanical stimulation of the MRO; and (3) a new approach to the crayfish abdomen preparation that allows linear extension of the MRO muscles. These novel approaches allow the collection of data sets comprised of sensory cell spike trains under software control as important mechanical stimulus parameters are varied systematically through software. This additional level of user control facilitates a more robust quantitative approach to the analysis of MRO sensory neuron spike trains, which is facilitated by training in data analysis using python.

Rat Auditory Inner Hair Cell Mechanotransduction and Stereociliary Membrane Diffusivity Are Similarly Modulated by Calcium

The lipid bilayer plays a pivotal role in force transmission to many mechanically-gated channels. We developed the technology to monitor membrane diffusivity in order to test the hypothesis positing that Ca²⁺ regulates open probability (P _o) of cochlear hair cell mechanotransduction (MET) channels via the plasma membrane. The stereociliary membrane was more diffusive (9x) than the basolateral membrane. Elevating intracellular Ca²⁺ buffering or lowering extracellular Ca²⁺ reduced stereociliary diffusivity and increased MET P _o. In contrast, prolonged depolarization increased stereociliary diffusivity and reduced MET P _o. No comparable effects were noted for soma measurements. Although MET channels are located in the shorter stereocilia rows, both rows had similar baseline diffusivity and showed similar responses to Ca²⁺ manipulations and MET channel blocks, suggesting that diffusivity is independent of MET. Together, these data suggest that the stereociliary membrane is a component of a calcium-modulated viscoelastic-like element regulating hair cell mechanotransduction.

Transgenic Tarantula Toxin: A novel tool to study mechanosensitive ion channels in Drosophila

The tarantula venom toxin GsMTx4 is the only known specific inhibitor of cation-selective mechanosensitive ion channels (MSCs). Its specificity, potency, and ease of use on isolated tissues and cells have made it a powerful pharmacological tool to identify and probe the physiological function of MSCs. In some contexts, however, it would be desirable to deliver the toxin in a controlled way in vivo. Here we describe a novel tool to allow spatial and temporal control of GsMTx4 delivery in vivo in Drosophila. To test the tool, we targeted MSCs required for mechanical nociception in a specific subset of sensory neurons in intact larvae. Expression of GsMTx4 in these neurons results in robust inhibition of mechanical nociception, demonstrating the toxin is active when expressed in vivo. The tool will be particularly useful to manipulate MSC activity in a spatially and temporally-controlled manner to study their role in development, physiology and behaviour in intact, free moving animals.

Mechanical activation of TRPV4 channels controls albumin reabsorption by proximal tubule cells

Defects in protein reabsorption by the proximal tubule are toxic for epithelial cells in the nephron and may result in nephropathy. In this study, we showed that the ion channel TRPV4 modulated the endocytosis of albumin and low–molecular weight proteins in the proximal tubule. TRPV4 was found at the basolateral side of proximal tubule cells, and its mechanical activation by cell stretching induced Ca2+ entry into the cytosol, which promoted endocytosis. Trpv4−/− mice presented with mild proximal tubule dysfunction under basal conditions. To challenge endocytic function, the permeability of the glomerular filter was altered by systemic delivery of angiotensin II. The proteinuria induced by this treatment was more severe in Trpv4−/− than in Trpv4+/+ mice. Injecting antibodies against the glomerular basement membrane to induce glomerulonephritis is a more pathophysiologically relevant method of impairing glomerular filter permeability. Albuminuria was more severe in mice that lacked TRPV4 specifically in the proximal tubule than in control mice. These results emphasize the importance of TRPV4 in sensing pressure in the proximal tubule in response to variations in the amount of ultrafiltrate and unveil a mechanism that controls protein reabsorption.

Cardiac Mechano-Electric Coupling: Acute Effects of Mechanical Stimulation on Heart Rate and Rhythm

The heart is vital for biological function in almost all chordates, including humans. It beats continually throughout our life, supplying the body with oxygen and nutrients while removing waste products. If it stops, so does life. The heartbeat involves precise coordination of the activity of billions of individual cells, as well as their swift and well-coordinated adaption to changes in physiological demand. Much of the vital control of cardiac function occurs at the level of individual cardiac muscle cells, including acute beat-by-beat feedback from the local mechanical environment to electrical activity (as opposed to longer term changes in gene expression and functional or structural remodeling). This process is known as mechano-electric coupling (MEC). In the current review, we present evidence for, and implications of, MEC in health and disease in human; summarize our understanding of MEC effects gained from whole animal, organ, tissue, and cell studies; identify potential molecular mediators of MEC responses; and demonstrate the power of computational modeling in developing a more comprehensive understanding of ‟what makes the heart tick.ˮ.

Progesterone and estrogen regulate NALCN expression in human myometrial smooth muscle cells

During pregnancy, the uterus transitions from a quiescent state to an excitable, highly contractile state to deliver the fetus. Two important contributors essential for this transition are hormones and ion channels, both of which modulate myometrial smooth muscle cell (MSMC) excitability. Recently, the sodium (Na⁺) leak channel, nonselective (NALCN), was shown to contribute to a Na⁺ leak current in human MSMCs, and mice lacking NALCN in the uterus had dysfunctional labor. Microarray data suggested that the proquiescent hormone progesterone (P4) and the procontractile hormone estrogen (E2) regulated this channel. Here, we sought to determine whether P4 and E2 directly regulate NALCN. In human MSMCs, we found that NALCN mRNA expression decreased by 2.3-fold in the presence of E2 and increased by 5.6-fold in the presence of P4. Similarly, E2 treatment decreased, and P4 treatment restored NALCN protein expression. Additionally, E2 significantly inhibited, and P4 significantly enhanced an NALCN-dependent leak current in MSMCs. Finally, we identified estrogen response and progesterone response elements (EREs and PREs) in the NALCN promoter. With the use of luciferase assays, we showed that the PREs, but not the ERE, contributed to regulation of NALCN expression. Our findings reveal a new mechanism by which NALCN is regulated in the myometrium and suggest a novel role for NALCN in pregnancy.

Suppression of hypersynchronous network activity in cultured cortical neurons using an ultrasoft silicone scaffold

The spontaneous activity pattern of cortical neurons in dissociated culture is characterized by burst firing that is highly synchronized among a wide population of cells. The degree of synchrony, however, is excessively higher than that in cortical tissues. Here, we employed polydimethylsiloxane (PDMS) elastomers to establish a novel system for culturing neurons on a scaffold with an elastic modulus resembling brain tissue, and investigated the effect of the scaffold's elasticity on network activity patterns in cultured rat cortical neurons. Using whole-cell patch clamp to assess the scaffold effect on the development of synaptic connections, we found that the amplitude of excitatory postsynaptic current, as well as the frequency of spontaneous transmissions, was reduced in neuronal networks grown on an ultrasoft PDMS with an elastic modulus of 0.5 kPa. Furthermore, the ultrasoft scaffold was found to suppress neural correlations in the spontaneous activity of the cultured neuronal network. The dose of GsMTx-4, an antagonist of stretch-activated cation channels (SACs), required to reduce the generation of the events below 1.0 event per min on PDMS substrates was lower than that for neurons on a glass substrate. This suggests that the difference in the baseline level of SAC activation is a molecular mechanism underlying the alteration in neuronal network activity depending on scaffold stiffness. Our results demonstrate the potential application of PDMS with biomimetic elasticity as cell-culture scaffold for bridging the in vivo-in vitro gap in neuronal systems.