Dietary fatty acids fine-tune Piezo1 mechanical response

Mechanosensitive ion channels in apoptosis and ferroptosis: focusing on the role of Piezo1

Mechanosensitive ion channels sense mechanical stimuli applied directly to the cellular membranes or indirectly through their tethered components, provoking cellular mechanoresponses. Among others, Piezo1 mechanosensitive ion channel is a relatively novel Ca2+-permeable channel that is primarily present in non-sensory tissues. Recent studies have demonstrated that Piezo1 plays an important role in Ca2+-dependent cell death, including apoptosis and ferroptosis, in the presence of mechanical stimuli. It has also been proven that cancer cells are sensitive to mechanical stresses due to higher expression levels of Piezo1 compared to normal cells. In this review, we discuss Piezo1-mediated cell death mechanisms and therapeutic strategies to inhibit or induce cell death by modulating the activity of Piezo1 with pharmacological drugs or mechanical perturbations induced by stretch and ultrasound. [BMB Reports 2023; 56(3): 145-152].

Gsmtx4 Alleviated Osteoarthritis through Piezo1/Calcineurin/NFAT1 Signaling Axis under Excessive Mechanical Strain

Excessive mechanical strain is the prominent risk factor for osteoarthritis (OA), causing cartilage destruction and degeneration. However, the underlying molecular mechanism contributing to mechanical signaling transduction remains unclear in OA. Piezo type mechanosensitive ion channel component 1 (Piezo1) is a calcium-permeable mechanosensitive ion channel and provides mechanosensitivity to cells, but its role in OA development has not been determined. Herein, we found up-regulated expression of Piezo1 in OA cartilage, and that its activation contributes to chondrocyte apoptosis. The knockdown of Piezo1 could protect chondrocytes from apoptosis and maintain the catabolic and anabolic balance under mechanical strain. In vivo, Gsmtx4, a Piezo1 inhibitor, markedly ameliorated the progression of OA, inhibited the chondrocyte apoptosis, and accelerated the production of the cartilage matrix. Mechanistically, we observed the elevated activity of calcineurin (CaN) and the nuclear transfection of nuclear factor of activated T cells 1 (NFAT1) under mechanical strain in chondrocytes. Inhibitors of CaN or NFAT1 rescued the pathologic changes induced by mechanical strain in chondrocytes. Overall, our findings revealed that Piezo1 was the essential molecule response to mechanical signals and regulated apoptosis and cartilage matrix metabolism via the CaN/NFAT1 signaling axis in chondrocytes, and that Gsmtx4 could be an attractive therapeutic drug for OA treatment.

Regulation of membrane protein structure and function by their lipid nano-environment

Transmembrane proteins comprise ~30% of the mammalian proteome, mediating metabolism, signalling, transport and many other functions required for cellular life. The microenvironment of integral membrane proteins (IMPs) is intrinsically different from that of cytoplasmic proteins, with IMPs solvated by a compositionally and biophysically complex lipid matrix. These solvating lipids affect protein structure and function in a variety of ways, from stereospecific, high-affinity protein-lipid interactions to modulation by bulk membrane properties. Specific examples of functional modulation of IMPs by their solvating membranes have been reported for various transporters, channels and signal receptors; however, generalizable mechanistic principles governing IMP regulation by lipid environments are neither widely appreciated nor completely understood. Here, we review recent insights into the inter-relationships between complex lipidomes of mammalian membranes, the membrane physicochemical properties resulting from such lipid collectives, and the regulation of IMPs by either or both. The recent proliferation of high-resolution methods to study such lipid-protein interactions has led to generalizable insights, which we synthesize into a general framework termed the 'functional paralipidome' to understand the mutual regulation between membrane proteins and their surrounding lipid microenvironments.

PIEZO1-Related Physiological and Pathological Processes in CNS: Focus on the Gliomas

PIEZO1 is ubiquitously expressed in cells in different kinds of tissues throughout the body, which can sense physical or mechanical stimuli and translate them into intracellular electrochemical signals to regulate organism functions. In particular, PIEZO1 appears in complex interactive regulatory networks as a central node, governing normal and pathological functions in the body. However, the effect and mechanism of the activation or expression of PIEZO1 in diseases of the central nervous system (CNS) remain unclear. On one hand, in CNS diseases, pathophysiological processes in neurons and glial are often accompanied by variations in the mechanical properties of the cellular and extracellular matrix stiffness. The expression of PIEZO1 can therefore be upregulated, in responding to mechanical stimulation, to drive the biological process in cells, which in turns indirectly affects the cellular microenvironment, resulting in alterations of the cellular status. On the other hand, it may have contradictory effects with the change of active patterns and/or subcellular location. This review highlights the biological processes involved with PIEZO1 in CNS cells, with special emphasis on its multiple roles in glioma-associated phenotypes. In conclusion, PIEZO1 can be used as an indicator to assess the malignancy and prognosis of patients with gliomas, as well as a therapeutic target for clinical application following fully exploring the potential mechanism of PIEZO1 in CNS diseases.

Mechanosensitive Ion Channels and Their Role in Cancer Cells

Mechanical forces are an inherent element in the world around us. The effects of their action can be observed both on the macro and molecular levels. They can also play a prominent role in the tissues and cells of animals due to the presence of mechanosensitive ion channels (MIChs) such as the Piezo and TRP families. They are essential in many physiological processes in the human body. However, their role in pathology has also been observed. Recent discoveries have highlighted the relationship between these channels and the development of malignant tumors. Multiple studies have shown that MIChs mediate the proliferation, migration, and invasion of various cancer cells via various mechanisms. This could show MIChs as new potential biomarkers in cancer detection and prognosis and interesting therapeutic targets in modern oncology. Our paper is a review of the latest literature on the role of the Piezo1 and TRP families in the molecular mechanisms of carcinogenesis in different types of cancer.

Excessive mechanotransduction in sensory neurons causes joint contractures

Distal arthrogryposis (DA) is a collection of rare disorders that are characterized by congenital joint contractures. Most DA mutations are in muscle- and joint-related genes, and the anatomical defects originate cell-autonomously within the musculoskeletal system. However, gain-of-function mutations in PIEZO2, a principal mechanosensor in somatosensation, cause DA subtype 5 (DA5) through unknown mechanisms. We show that expression of a gain-of-function PIEZO2 mutation in proprioceptive sensory neurons that mainly innervate muscle spindles and tendons is sufficient to induce DA5-like phenotypes in mice. Overactive PIEZO2 causes anatomical defects through increased activity within the peripheral nervous system during postnatal development. Furthermore, botulinum toxin (Botox) and a dietary fatty acid that modulates PIEZO2 activity reduce DA5-like deficits. This reveals a role for somatosensory neurons: Excessive mechanosensation within these neurons disrupts musculoskeletal development.

Mechanotransductive Receptor Piezo1 as a Promising Target in the Treatment of Neurological Diseases

In recent years, increasing attention has been paid to the role of physical factors in biological processes. This direction was ultimately confirmed by the recent 2021 Nobel Prize in medicine and physiology awarded in ½ to Ardem Patapoutian for his discovery of Piezo1 and Piezo2 mechanosensitive receptors. Among them, Piezo2 is responsible for sensing touch, while Piezo1 is engaged in a variety of mechanotransduction events. Piezo1 is expressed in various central nervous system cells, while its expression may be affected in the course of various pathological conditions. Recently, thanks to the development of Piezo1 modulators (i.e. Yoda1, Jedi1/2 and Dooku2), it is possible to study the role of Piezo1 in the pathogenesis of various neurological diseases including ischemia, glioma, and age-related dementias. The results obtained in this field suggest that proper modulation of Piezo1 receptor might be beneficial in the course of various neurological diseases.

Omega-3 fatty acids and atrial fibrillation

Although some clinical trials have demonstrated reduced incidence of cardiovascular disease with the use of omega-3 fatty acids, others have found an increased risk of atrial fibrillation (AF). AF is the most common sustained cardiac arrhythmia worldwide. It is associated with high morbidity and mortality rates and significant public health burden. Previous studies of the effect of omega-3 fatty acids on AF occurrence have reported contradictory results. Here we reviewed the effect of omega-3 fatty acids on the risk of AF.

Importance of molecular dynamics equilibrium protocol on protein-lipid interaction near channel pore

Multiscale molecular dynamics simulations using Martini coarse-grained (CG) and all-atom (AA) force fields are commonly used in membrane protein studies. In particular, reverse mapping an equilibrated CG model to an AA model offers an efficient way for preparing large membrane protein systems with complex protein shapes and lipid compositions. Here, we report that this hybrid CG-equilibrium-AA-production protocol may artificially increase lipid density and decrease hydration in ion channel pores walled with transmembrane gaps. To understand the origin of this conundrum, we conducted replicas of CG, AA, and CG reverse-mapped AA simulations of the pore domain of the mechanosensitive Piezo1 channel in a nonconducting conformation. Lipid/water density analysis and free energy calculations reveal that the lack of initial pore hydration allows excessive lipids to enter the upper pore lumen through gaps between pore helices during CG simulation. Due to the mismatch between CG and AA lipid kinetics, these pore lipids remain trapped in the subsequent AA simulations, despite unfavorable binding free energy. We tested several CG equilibrium protocols and found that a protocol restraining the whole lipid produces pore hydration consistent with AA results, thus eliminating this artifact for further studies of lipid gating and protein-lipid interactions.

Mechanosensitive Ion Channel PIEZO1 Signaling in the Hall-Marks of Cancer: Structure and Functions

Simple Summary

Tumor cells obtain various unique characteristics, which known as hallmarks of cancers, including sustained proliferative signaling, apoptosis resistance, and metastasis. These characteristics are crucial for tumor cells survival and for supporting their rapid growth. Studies have revealed that tumorigenesis is also accompanied by alteration in mechanical properties. Tumor cells could sense various mechanical forces, such as compressive force, shear stress, and portal vein pressure, which in turn could affect tumor progression. Piezo1 is a mechanically sensitive ion channel protein that can be activated mechanically, and is closely related to various diseases. Recent studies showed that Piezo1 is overexpressed in numerous tumors and is associated with poor prognosis. Furthermore, previous studies revealed that Piezo1 mediates these cancer hallmarks, and thus links up mechanical forces with tumor progression. Therefore, the discovery of Piezo1 provides a new insight for elucidating the mechanism of tumor progression under a mechanical microenvironment.

Abstract

Tumor cells alter their characteristics and behaviors during tumorigenesis. These characteristics, known as hallmarks of cancer, are crucial for supporting their rapid growth, need for energy, and adaptation to tumor microenvironment. Tumorigenesis is also accompanied by alteration in mechanical properties. Cells in tumor tissue sense mechanical signals from the tumor microenvironment, which consequently drive the acquisition of hallmarks of cancer, including sustained proliferative signaling, evading growth suppressors, apoptosis resistance, sustained angiogenesis, metastasis, and immune evasion. Piezo-type mechanosensitive ion channel component 1 (Piezo1) is a mechanically sensitive ion channel protein that can be activated mechanically and is closely related to various diseases. Recent studies showed that Piezo1 mediates tumor development through multiple mechanisms, and its overexpression is associated with poor prognosis. Therefore, the discovery of Piezo1, which links-up physical factors with biological properties, provides a new insight for elucidating the mechanism of tumor progression under a mechanical microenvironment, and suggests its potential application as a tumor marker and therapeutic target. In this review, we summarize current knowledge regarding the role of Piezo1 in regulating cancer hallmarks and the underlying molecular mechanisms. Furthermore, we discuss the potential of Piezo1 as an antitumor therapeutic target and the limitations that need to be overcome.

Piezo1 in vascular remodeling of atherosclerosis and pulmonary arterial hypertension: A potential therapeutic target

Vascular remodeling (VR) is a structural and functional change of blood vessels to adapt to the changes of internal and external environment. It is one of the common pathological features of many vascular proliferative diseases. The process of VR is mainly manifested in the changes of vascular wall structure and function, including intimal hyperplasia, thickening or thinning of media, fibrosis of adventitia, etc. These changes are also the pathological basis of aging and various cardiovascular diseases. Mechanical force is the basis of cardiovascular biomechanics, and the newly discovered mechanical sensitive ion channel Piezo1 is widely distributed in the whole cardiovascular system. Studies have confirmed that Piezo1, a mechanically sensitive ion channel, plays an important role in cardiovascular remodeling diseases. This article reviews the molecular mechanism of Piezo1 in atherosclerosis, hypertension and pulmonary hypertension, in order to provide a theoretical basis for the further study of vascular remodeling.

MRTF may be the missing link in a multiscale mechanobiology approach toward macrophage dysfunction in space

Macrophages exhibit impaired phagocytosis, adhesion, migration, and cytokine production in space, hindering their ability to elicit immune responses. Considering that the combined effect of spaceflight microgravity and radiation is multiscale and multifactorial in nature, it is expected that contradictory findings are common in the field. This theory paper reanalyzes research on the macrophage spaceflight response across multiple timescales from seconds to weeks, and spatial scales from the molecular, intracellular, extracellular, to the physiological. Key findings include time-dependence of both pro-inflammatory activation and integrin expression. Here, we introduce the time-dependent, intracellular localization of MRTF-A as a hypothetical confounder of macrophage activation. We discuss the mechanosensitive MRTF-A/SRF pathway dependence on the actin cytoskeleton/nucleoskeleton, microtubules, membrane mechanoreceptors, hypoxia, oxidative stress, and intracellular/extracellular crosstalk. By adopting a multiscale perspective, this paper provides the first mechanistic answer for a three-decade-old question regarding impaired cytokine secretion in microgravity—and strengthens the connection between the recent advances in mechanobiology, microgravity, and the spaceflight immune response. Finally, we hypothesize MRTF involvement and complications in treating spaceflight-induced cardiovascular, skeletal, and immune disease.

Piezo1 regulates cholesterol biosynthesis to influence neural stem cell fate during brain development

Mechanical forces and tissue mechanics influence the morphology of the developing brain, but the underlying molecular mechanisms have been elusive. Here, we examine the role of mechanotransduction in brain development by focusing on Piezo1, a mechanically activated ion channel. We find that Piezo1 deletion results in a thinner neuroepithelial layer, disrupts pseudostratification, and reduces neurogenesis in E10.5 mouse embryos. Proliferation and differentiation of Piezo1 knockout (KO) mouse neural stem cells (NSCs) isolated from E10.5 embryos are reduced in vitro compared to littermate WT NSCs. Transcriptome analysis of E10.5 Piezo1 KO brains reveals downregulation of the cholesterol biosynthesis superpathway, in which 16 genes, including Hmgcr, the gene encoding the rate-limiting enzyme of the cholesterol biosynthesis pathway, are downregulated by 1.5-fold or more. Consistent with this finding, membrane lipid composition is altered, and the cholesterol levels are reduced in Piezo1 KO NSCs. Cholesterol supplementation of Piezo1 KO NSCs partially rescues the phenotype in vitro. These findings demonstrate a role for Piezo1 in the neurodevelopmental process that modulates the quantity, quality, and organization of cells by influencing cellular cholesterol metabolism. Our study establishes a direct link in NSCs between PIEZO1, intracellular cholesterol levels, and neural development.

Genetic- and diet-induced ω-3 fatty acid enrichment enhances TRPV4-mediated vasodilation in mice

TRPV4 channel activation in endothelial cells leads to vasodilation, while impairment of TRPV4 activity is implicated in vascular dysfunction. Strategies that increase TRPV4 activity could enhance vasodilation and ameliorate vascular disorders. Here, we show that supplementation with eicosapentaenoic acid (EPA), an ω-3 polyunsaturated fatty acid known to have beneficial cardiovascular effects, increases TRPV4 activity in human endothelial cells of various vascular beds. Mice carrying the C. elegans FAT-1 enzyme, which converts ω-6 to ω-3 polyunsaturated fatty acids, display higher EPA content and increased TRPV4-mediated vasodilation in mesenteric arteries. Likewise, mice fed an EPA-enriched diet exhibit enhanced and prolonged TRPV4-dependent vasodilation in an endothelial cell-specific manner. We also show that EPA supplementation reduces TRPV4 desensitization, which contributes to the prolonged vasodilation. Neutralization of positive charges in the TRPV4 N terminus impairs the effect of EPA on channel desensitization. These findings highlight the beneficial effects of manipulating fatty acid content to enhance TRPV4-mediated vasodilation.

The Janus-faced role of Piezo1 in cardiovascular health under mechanical stimulation

In recent years, cardiovascular health problems are becoming more and more serious. At the same time, mechanical stimulation closely relates to cardiovascular health. In this context, Piezo1, which is very sensitive to mechanical stimulation, has attracted our attention. Here, we review the critical significance of Piezo1 in mechanical stimulation of endothelial cells, NO production, lipid metabolism, DNA damage protection, the development of new blood vessels and maturation, narrowing of blood vessels, blood pressure regulation, vascular permeability, insulin sensitivity, and maintenance of red blood cell function. Besides, Piezo1 may participate in the occurrence and development of atherosclerosis, diabetes, hypertension, and other cardiovascular diseases. It is worth noting that Piezo1 has dual effects on maintaining cardiovascular health. On the one hand, the function of Piezo1 is necessary to maintain cardiovascular health; on the other hand, under some extreme mechanical stimulation, the overexpression of Piezo1 may bring adverse factors such as inflammation. Therefore, this review discusses the Janus-faced role of Piezo1 in maintaining cardiovascular health and puts forward new ideas to provide references for gene therapy or nanoagents targeting Piezo1.

Lipid redistribution in the highly curved footprint of Piezo1

We investigate the effects on the distribution of lipids in the plasma membrane that are caused by the insertion of a protein, Piezo1, that significantly distorts the membrane toward the cytosol. From coarse-grained molecular dynamics simulations, we find that the major effects occur in the outer, extracellular, leaflet. The mol fraction of cholesterol increases significantly in the curved region of the membrane close to Piezo1, while those of phosphatidylcholine and of sphingomyelin decrease. In the inner leaflet, mol fractions of cholesterol and of phosphatidylethanolamine decrease slightly as the protein is approached, while that of phosphatidylserine increases slightly. The mol fraction of phosphatidylcholine decreases markedly as the protein is approached. Most of these results are understood in the context of a theoretical model that utilizes two elements; (i) a coupling between the leaflets' actual curvatures and their compositionally-dependent spontaneous curvatures and, (ii) the dependence of the spontaneous curvatures not only on the mol fractions of the phospholipids, but also on the effect that cholesterol has on the spontaneous curvatures of the phospholipids.

Characterizing the lipid fingerprint of the mechanosensitive channel Piezo2

Piezo2 is a mechanosensitive ion channel that plays critical roles in sensing touch and pain, proprioception, and regulation of heart rate. Global knockout of Piezo2 leads to perinatal lethality in mice, and Piezo2 gain-of-function mutations are associated with distal arthrogryposis, a disease characterized by congenital joint contractures. Emerging evidence suggests that Piezo channels (Piezo1 and Piezo2) can be regulated by their local membrane environment and particularly by cholesterol and phosphoinositides. To characterize the local Piezo2 lipid environment and investigate key lipid-protein interactions, we carried out coarse-grained molecular dynamics simulations of Piezo2 embedded in a complex mammalian membrane containing >60 distinct lipid species. We show that Piezo2 alters its local membrane composition such that it becomes enriched with specific lipids, such as phosphoinositides, and forms specific, long-term interactions with a variety of lipids at functionally relevant sites.

TMEM120A/TACAN inhibits mechanically activated PIEZO2 channels

PIEZO2 channels mediate rapidly adapting mechanically activated currents in peripheral sensory neurons of the dorsal root ganglia (DRG), and they are indispensable for light touch and proprioception. Relatively little is known about what other proteins regulate PIEZO2 activity in a cellular context. TMEM120A (TACAN) was proposed to act as a high threshold mechanically activated ion channel in nociceptive DRG neurons. Here, we find that Tmem120a coexpression decreased the amplitudes of mechanically activated PIEZO2 currents and increased their threshold of activation. TMEM120A did not inhibit mechanically activated PIEZO1 and TREK1 channels and TMEM120A alone did not result in the appearance of mechanically activated currents above background. Tmem120a and Piezo2 expression in mouse DRG neurons overlapped, and siRNA-mediated knockdown of Tmem120a increased the amplitudes of rapidly adapting mechanically activated currents and decreased their thresholds to mechanical activation. Our data identify TMEM120A as a negative modulator of PIEZO2 channel activity, and do not support TMEM120A being a mechanically activated ion channel.

Physics of mechanotransduction by Piezo ion channels

Piezo ion channels are sensors of mechanical forces and mediate a wide range of physiological mechanotransduction processes. More than a decade of intense research has elucidated much of the structural and mechanistic principles underlying Piezo gating and its roles in physiology, although wide gaps of knowledge continue to exist. Here, we review the forces and energies involved in mechanical activation of Piezo ion channels and their functional modulation by other chemical and physical stimuli including lipids, voltage, and temperature. We compare the three predominant mechanisms likely to explain Piezo activation—the force-from-lipids mechanism, the tether model, and the membrane footprint theory. Additional sections shine light on how Piezo ion channels may affect each other through spatial clustering and functional cooperativity, and how substantial functional heterogeneity of Piezo ion channels arises as a byproduct of the precise physical environment each channel experiences. Finally, our review concludes by pointing out major research questions and technological limitations that future research can address.

Asymmetric effects of amphipathic molecules on mechanosensitive channels

Mechanosensitive (MS) ion channels are primary transducers of mechanical force into electrical and/or chemical intracellular signals. Many diverse MS channel families have been shown to respond to membrane forces. As a result of this intimate relationship with the membrane and proximal lipids, amphipathic compounds exert significant effects on the gating of MS channels. Here, we performed all-atom molecular dynamics (MD) simulations and employed patch-clamp recording to investigate the effect of two amphipaths, Fluorouracil (5-FU) a chemotherapy agent, and the anaesthetic trifluoroethanol (TFE) on structurally distinct mechanosensitive channels. We show that these amphipaths have a profound effect on the bilayer order parameter as well as transbilayer pressure profile. We used bacterial mechanosensitive channels (MscL/MscS) and a eukaryotic mechanosensitive channel (TREK-1) as force-from-lipids reporters and showed that these amphipaths have differential effects on these channels depending on the amphipaths' size and shape as well as which leaflet of the bilayer they incorporate into. 5-FU is more asymmetric in shape and size than TFE and does not penetrate as deep within the bilayer as TFE. Thereby, 5-FU has a more profound effect on the bilayer and channel activity than TFE at much lower concentrations. We postulate that asymmetric effects of amphipathic molecules on mechanosensitive membrane proteins through the bilayer represents a general regulatory mechanism for these proteins.

The State of the Art of Piezo1 Channels in Skeletal Muscle Regeneration

Piezo1 channels are highly mechanically-activated cation channels that can sense and transduce the mechanical stimuli into physiological signals in different tissues including skeletal muscle. In this focused review, we summarize the emerging evidence of Piezo1 channel-mediated effects in the physiology of skeletal muscle, with a particular focus on the role of Piezo1 in controlling myogenic precursor activity and skeletal muscle regeneration and vascularization. The disclosed effects reported by pharmacological activation of Piezo1 channels with the selective agonist Yoda1 indicate a potential impact of Piezo1 channel activity in skeletal muscle regeneration, which is disrupted in various muscular pathological states. All findings reported so far agree with the idea that Piezo1 channels represent a novel, powerful molecular target to develop new therapeutic strategies for preventing or ameliorating skeletal muscle disorders characterized by an impairment of tissue regenerative potential.

Förster Resonance Energy Transfer-Based Single-Cell Imaging Reveals Piezo1-Induced Ca2+ Flux Mediates Membrane Ruffling and Cell Survival

A mechanosensitive ion channel, Piezo1 induces non-selective cation flux in response to various mechanical stresses. However, the biological interpretation and underlying mechanisms of cells resulting from Piezo1 activation remain elusive. This study elucidates Piezo1-mediated Ca²⁺ influx driven by channel activation and cellular behavior using novel Förster Resonance Energy Transfer (FRET)-based biosensors and single-cell imaging analysis. Results reveal that extracellular Ca²⁺ influx via Piezo1 requires intact caveolin, cholesterol, and cytoskeletal support. Increased cytoplasmic Ca²⁺ levels enhance PKA, ERK, Rac1, and ROCK activity, which have the potential to promote cancer cell survival and migration. Furthermore, we demonstrate that Piezo1-mediated Ca²⁺ influx upregulates membrane ruffling, a characteristic feature of cancer cell metastasis, using spatiotemporal image correlation spectroscopy. Thus, our findings provide new insights into the function of Piezo1, suggesting that Piezo1 plays a significant role in the behavior of cancer cells.

Force From Filaments: The Role of the Cytoskeleton and Extracellular Matrix in the Gating of Mechanosensitive Channels

The senses of proprioception, touch, hearing, and blood pressure on mechanosensitive ion channels that transduce mechanical stimuli with high sensitivity and speed. This conversion process is usually called mechanotransduction. From nematode MEC-4/10 to mammalian PIEZO1/2, mechanosensitive ion channels have evolved into several protein families that use variant gating models to convert different forms of mechanical force into electrical signals. In addition to the model of channel gating by stretching from lipid bilayers, another potent model is the opening of channels by force tethering: a membrane-bound channel is elastically tethered directly or indirectly between the cytoskeleton and the extracellular molecules, and the tethering molecules convey force to change the channel structure into an activation form. In general, the mechanical stimulation forces the extracellular structure to move relative to the cytoskeleton, deforming the most compliant component in the system that serves as a gating spring. Here we review recent studies focusing on the ion channel mechanically activated by a tethering force, the mechanotransduction-involved cytoskeletal protein, and the extracellular matrix. The mechanosensitive channel PIEZO2, DEG/ENaC family proteins such as acid-sensing ion channels, and transient receptor potential family members such as NompC are discussed. State-of-the-art techniques, such as polydimethylsiloxane indentation, the pillar array, and micropipette-guided ultrasound stimulation, which are beneficial tools for exploring the tether model, are also discussed.

Inhibiting Endocannabinoid Hydrolysis as Emerging Analgesic Strategy Targeting a Spectrum of Ion Channels Implicated in Migraine Pain

Migraine is a disabling neurovascular disorder characterized by severe pain with still limited efficient treatments. Endocannabinoids, the endogenous painkillers, emerged, alternative to plant cannabis, as promising analgesics against migraine pain. In this thematic review, we discuss how inhibition of the main endocannabinoid-degrading enzymes, monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), could raise the level of endocannabinoids (endoCBs) such as 2-AG and anandamide in order to alleviate migraine pain. We describe here: (i) migraine pain signaling pathways, which could serve as specific targets for antinociception; (ii) a divergent distribution of MAGL and FAAH activities in the key regions of the PNS and CNS implicated in migraine pain signaling; (iii) a complexity of anti-nociceptive effects of endoCBs mediated by cannabinoid receptors and through a direct modulation of ion channels in nociceptive neurons; and (iv) the spectrum of emerging potent MAGL and FAAH inhibitors which efficiently increase endoCBs levels. The specific distribution and homeostasis of endoCBs in the main regions of the nociceptive system and their generation ‘on demand’, along with recent availability of MAGL and FAAH inhibitors suggest new perspectives for endoCBs-mediated analgesia in migraine pain.

An extensional strain sensing mechanosome drives adhesion-independent platelet activation at supraphysiological hemodynamic gradients

Background

Supraphysiological hemodynamics are a recognized driver of platelet activation and thrombosis at high-grade stenosis and in blood contacting circulatory support devices. However, whether platelets mechano-sense hemodynamic parameters directly in free flow (in the absence of adhesion receptor engagement), the specific hemodynamic parameters at play, the precise timing of activation, and the signaling mechanism(s) involved remain poorly elucidated.

Results

Using a generalized Newtonian computational model in combination with microfluidic models of flow acceleration and quasi-homogenous extensional strain, we demonstrate that platelets directly mechano-sense acute changes in free-flow extensional strain independent of shear strain, platelet amplification loops, von Willebrand factor, and canonical adhesion receptor engagement. We define an extensional strain sensing “mechanosome” in platelets involving cooperative Ca²⁺ signaling driven by the mechanosensitive channel Piezo1 (as the primary strain sensor) and the fast ATP gated channel P2X1 (as the secondary signal amplifier). We demonstrate that type II PI3 kinase C2α activity (acting as a “clutch”) couples extensional strain to the mechanosome.

Conclusions

Our findings suggest that platelets are adapted to rapidly respond to supraphysiological extensional strain dynamics, rather than the peak magnitude of imposed wall shear stress. In the context of overall platelet activation and thrombosis, we posit that “extensional strain sensing” acts as a priming mechanism in response to threshold levels of extensional strain allowing platelets to form downstream adhesive interactions more rapidly under the limiting effects of supraphysiological hemodynamics.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01274-7.

Intrinsically disordered intracellular domains control key features of the mechanically-gated ion channel PIEZO2

A central question in mechanobiology is how mechanical forces acting in or on cells are transmitted to mechanically-gated PIEZO channels that convert these forces into biochemical signals. Here we examined the role of the intracellular domains of PIEZO2, which account for 25% of the channel, and demonstrate that these domains fine-tune properties such as poking and stretch-sensitivity, velocity coding and single channel conductance. Moreover, we show that the intrinsically disordered linker between the transmembrane helices twelve and thirteen (IDR5) is required for the activation of PIEZO2 by cytoskeleton-transmitted forces. The deletion of IDR5 abolishes PIEZO2-mediated inhibition of neurite outgrowth, while it only partially affected its sensitivity to cell indentation and does not alter its stretch sensitivity. Thus, we propose that PIEZO2 is a polymodal mechanosensor that detects different types of mechanical stimuli via different force transmission pathways, which highlights the importance of utilizing multiple complementary assays when investigating PIEZO function.

A key question in mechanobiology is how mechanical forces are transmitted to PIEZO ion channels. Here, Verkest et al. identify an intracellular channel domain that is required for the activation of PIEZO2 by cytoskeleton-transmitted forces.

Distinct mechanoreceptor pezo-1 isoforms modulate food intake in the nematode Caenorhabditis elegans

Two PIEZO mechanosensitive cation channels, PIEZO1 and PIEZO2, have been identified in mammals, where they are involved in numerous sensory processes. While structurally similar, PIEZO channels are expressed in distinct tissues and exhibit unique properties. How different PIEZOs transduce force, how their transduction mechanism varies, and how their unique properties match the functional needs of the tissues they are expressed in remain all-important unanswered questions. The nematode Caenorhabditis elegans has a single PIEZO ortholog (pezo-1) predicted to have 12 isoforms. These isoforms share many transmembrane domains but differ in those that distinguish PIEZO1 and PIEZO2 in mammals. We used transcriptional and translational reporters to show that putative promoter sequences immediately upstream of the start codon of long pezo-1 isoforms predominantly drive green fluorescent protein (GFP) expression in mesodermally derived tissues (such as muscle and glands). In contrast, sequences upstream of shorter pezo-1 isoforms resulted in GFP expression primarily in neurons. Putative promoters upstream of different isoforms drove GFP expression in different cells of the same organs of the digestive system. The observed unique pattern of complementary expression suggests that different isoforms could possess distinct functions within these organs. We used mutant analysis to show that pharyngeal muscles and glands require long pezo-1 isoforms to respond appropriately to the presence of food. The number of pezo-1 isoforms in C. elegans, their putative differential pattern of expression, and roles in experimentally tractable processes make this an attractive system to investigate the molecular basis for functional differences between members of the PIEZO family of mechanoreceptors.

Piezo1 Channels as Force Sensors in Mechanical Force-Related Chronic Inflammation

Mechanical damage is one of the predisposing factors of inflammation, and it runs through the entire inflammatory pathological process. Repeated or persistent damaging mechanical irritation leads to chronic inflammatory diseases. The mechanism of how mechanical forces induce inflammation is not fully understood. Piezo1 is a newly discovered mechanically sensitive ion channel. The Piezo1 channel opens in response to mechanical stimuli, transducing mechanical signals into an inflammatory cascade in the cell leading to tissue inflammation. A large amount of evidence shows that Piezo1 plays a vital role in the occurrence and progression of chronic inflammatory diseases. This mini-review briefly presents new evidence that Piezo1 responds to different mechanical stresses to trigger inflammation in various tissues. The discovery of Piezo1 provides new insights for the treatment of chronic inflammatory diseases related to mechanical stress. Inhibiting the transduction of damaging mechanical signals into inflammatory signals can inhibit inflammation and improve the outcome of inflammation at an early stage. The pharmacology of Piezo1 has shown bright prospects. The development of tissue-specific Piezo1 drugs for clinical use may be a new target for treating chronic inflammation.

Erythrocyte Membrane Nanomechanical Rigidity Is Decreased in Obese Patients

This work intends to describe the physical properties of red blood cell (RBC) membranes in obese adults. The hypothesis driving this research is that obesity, in addition to increasing the amount of body fat, will also modify the lipid composition of membranes in cells other than adipocytes. Forty-nine control volunteers (16 male, 33 female, BMI 21.8 ± 5.6 and 21.5 ± 4.2 kg/m², respectively) and 52 obese subjects (16 male and 36 female, BMI 38.2± 11.0 and 40.7 ± 8.7 kg/m², respectively) were examined. The two physical techniques applied were atomic force microscopy (AFM) in the force spectroscopy mode, which allows the micromechanical measurement of penetration forces, and fluorescence anisotropy of trimethylammonium diphenylhexatriene (TMA-DPH), which provides information on lipid order at the membrane polar–nonpolar interface. These techniques, in combination with lipidomic studies, revealed a decreased rigidity in the interfacial region of the RBC membranes of obese as compared to control patients, related to parallel changes in lipid composition. Lipidomic data show an increase in the cholesterol/phospholipid mole ratio and a decrease in sphingomyelin contents in obese membranes. ω-3 fatty acids (e.g., docosahexaenoic acid) appear to be less prevalent in obese patient RBCs, and this is the case for both the global fatty acid distribution and for the individual major lipids in the membrane phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylserine (PS). Moreover, some ω-6 fatty acids (e.g., arachidonic acid) are increased in obese patient RBCs. The switch from ω-3 to ω-6 lipids in obese subjects could be a major factor explaining the higher interfacial fluidity in obese patient RBC membranes.

C. elegans PEZO-1 is a mechanosensitive ion channel involved in food sensation

PIEZO channels are force sensors essential for physiological processes, including baroreception and proprioception. The Caenorhabditis elegans genome encodes an orthologue gene of the Piezo family, pezo-1, which is expressed in several tissues, including the pharynx. This myogenic pump is an essential component of the C. elegans alimentary canal, whose contraction and relaxation are modulated by mechanical stimulation elicited by food content. Whether pezo-1 encodes a mechanosensitive ion channel and contributes to pharyngeal function remains unknown. Here, we leverage genome editing, genetics, microfluidics, and electropharyngeogram recording to establish that pezo-1 is expressed in the pharynx, including in a proprioceptive-like neuron, and regulates pharyngeal function. Knockout (KO) and gain-of-function (GOF) mutants reveal that pezo-1 is involved in fine-tuning pharyngeal pumping frequency, as well as sensing osmolarity and food mechanical properties. Using pressure-clamp experiments in primary C. elegans embryo cultures, we determine that pezo-1 KO cells do not display mechanosensitive currents, whereas cells expressing wild-type or GOF PEZO-1 exhibit mechanosensitivity. Moreover, infecting the Spodoptera frugiperda cell line with a baculovirus containing the G-isoform of pezo-1 (among the longest isoforms) demonstrates that pezo-1 encodes a mechanosensitive channel. Our findings reveal that pezo-1 is a mechanosensitive ion channel that regulates food sensation in worms.

Emerging Piezo1 signaling in inflammation and atherosclerosis; a potential therapeutic target

Purpose of Review: Atherosclerosis is the principal cause of cardiovascular diseases (CVDs) which are the major cause of death worldwide. Mechanical force plays an essential role in cardiovascular health and disease. To bring the awareness of mechanosensitive Piezo1 role in atherosclerosis and its therapeutic potentials we review recent literature to highlight its involvement in various mechanisms of the disease. Recent Findings: Recent studies reported Piezo1 channel as a sensor, and transducer of various mechanical forces into biochemical signals, which affect various cellular activities such as proliferation, migration, apoptosis and vascular remodeling including immune/inflammatory mechanisms fundamental phenomenon in atherogenesis. Summary: Numerous evidences suggest Piezo1 as a player in different mechanisms of cell biology, including immune/inflammatory and other cellular mechanisms correlated with atherosclerosis. This review discusses mechanistic insight about this matter and highlights the drugability and therapeutic potentials consistent with emerging functions Piezo1 in various mechanisms of atherosclerosis. Based on the recent works, we suggest Piezo1 as potential therapeutic target and a valid candidate for future research. Therefore, a deeper exploration of Piezo1 biology and translation towards the clinic will be a novel strategy for treating atherosclerosis and other CVDs.

DHA-phospholipids control membrane fusion and transcellular tunnel dynamics

Metabolic studies and animal knockout models point to the critical role of polyunsaturated docosahexaenoic acid (22:6, DHA)-containing phospholipids (PLs) in physiology. Here, we investigated the impact of DHA-PLs on the dynamics of transendothelial cell macroapertures (TEMs) triggered by RhoA inhibition-associated cell spreading. Lipidomic analyses show that human umbilical vein endothelial cells (HUVECs) subjected to DHA-diet undergo a 6-fold enrichment in DHA-PLs at plasma membrane (PM) at the expense of monounsaturated OA-PLs. Consequently, DHA-PLs enrichment at the PM induces a reduction of cell thickness and shifts cellular membranes towards a permissive mode of membrane fusion for transcellular tunnel initiation. We provide evidence that a global homeostatic control of membrane tension and cell cortex rigidity minimizes overall changes of TEM area through a decrease of TEM size and lifetime. Conversely, low DHA-PL levels at the PM leads to the opening of unstable and wider TEMs. Together, this provides evidence that variations of DHA-PLs levels in membranes affect cell biomechanical properties.

"Time window" effect of Yoda1-evoked Piezo1 channel activity during mouse skeletal muscle differentiation

Aim

Mechanosensitive Piezo1 ion channels emerged recently as important contributors to various vital functions including modulation of the blood supply to skeletal muscles. The specific Piezo1 channel agonist Yoda1 was shown to regulate the tone of blood vessels similarly to physical exercise. However, the direct role of Piezo1 channels in muscle function has been little studied so far. We therefore investigated the action of Yoda1 on the functional state of skeletal muscle precursors (satellite cells and myotubes) and on adult muscle fibres.

Methods

Immunostaining, electrophysiological intracellular recordings and Ca²⁺ imaging experiments were performed to localize and assess the effect of the chemical activation of Piezo1 channels with Yoda1, on myogenic precursors, adult myofibres and at the adult neuromuscular junction.

Results

Piezo1 channels were detected by immunostaining in satellite cells (SCs) and myotubes as well as in adult myofibres. In the skeletal muscle precursors, Yoda1 treatment stimulated the differentiation and cell fusion rather than the proliferation of SCs. Moreover, in myotubes, Yoda1 induced significant [Ca²⁺]_i transients, without detectable [Ca²⁺]_i response in adult myofibres. Furthermore, although expression of Piezo1 channels was detected around the muscle endplate region, Yoda1 application did not alter either the nerve‐evoked or spontaneous synaptic activity or muscle contractions in adult myofibres.

Conclusion

Our data indicate that the chemical activation of Piezo1 channels specifically enhances the differentiation of skeletal muscle precursors, suggesting a possible new strategy to promote muscle regeneration.

Mechanosensing by Piezo1 and its implications for physiology and various pathologies

Piezo1 is a mechanosensitive ion channel with essential roles in cardiovascular, lung, urinary, and immune functions. Piezo1 is widely distributed in different tissues in the human body and its specific roles have been identified following a decade of research; however, not all are well understood. Many structural and functional characteristics of Piezo1 have been discovered and are known to differ greatly from the characteristics of other mechanosensitive ion channels. Understanding the mechanisms by which this ion channel functions may be useful in determining its physiological roles in various organ systems. This review provides insight into the signalling pathways activated by mechanical stimulation of Piezo1 in various organ systems and cell types. We discuss downstream targets of Piezo1 and the overall effects resulting from Piezo1 activation, which may provide insights into potential treatment targets for diseases involving this ion channel.

Tug-of-war: molecular dynamometers against living cells for analyzing sub-piconewton interaction of a specific protein with the cell membrane

Protein–membrane interactions play important roles in signal transductions and functional regulation of membrane proteins. Here, we design a molecular dynamometer (MDM) for analyzing protein–membrane interaction on living cells. The MDM is constructed by assembling an artificial lipid bilayer and alkylated Cy3-DNA azide (azide-Cy3-Cx) on a silica bubble. After a functional aptamer is covalently anchored onto the corresponding target protein on a living cell through UV irradiation, azide-Cy3-Cx is conjugated with the aptamer through a click reaction to produce a “tug-of-war” between the MDM and the cell due to the buoyancy of the silica bubble. This induces the detachment of the protein from the cell membrane or the alkane terminal from the MDM enabling sub-piconewton embedding force measurement by changing the alkane chain length and simple fluorescence analysis. The successful analysis of embedding force variation of a protein on the cell membrane upon post-translational modifications demonstrates the practicability and expansibility of this method for mechanics-related research in biological systems.

A molecular dynamometer is designed to analyze the variation of sub-piconewton interaction between a specific protein and the membrane on living cells.

Hereditary Xerocytosis: Differential Behavior of PIEZO1 Mutations in the N-Terminal Extracellular Domain Between Red Blood Cells and HEK Cells

Hereditary Xerocytosis, a rare hemolytic anemia, is due to gain of function mutations in PIEZO1, a non-selective cation channel activated by mechanical stress. How these PIEZO1 mutations impair channel function and alter red blood cell (RBC) physiology, is not completely understood. Here, we report the characterization of mutations in the N-terminal part of the protein (V598M, F681S and the double mutation G782S/R808Q), a part of the channel that was subject of many investigations to decipher its role in channel gating. Our data show that the electrophysiological features of these PIEZO1 mutants expressed in HEK293T cells are different from previously characterized PIEZO1 mutations that are located in the pore or at the C-terminal extracellular domain of the protein. Although RBC with PIEZO1 mutations showed a dehydrated phenotype, the activity of V598M, F681S or R808Q in response to stretch was not significantly different from the WT channels. In contrast, the G782S mutant showed larger currents compared to the WT PIEZO1. Interestingly, basal activity of all the mutated channels was not significantly altered at the opposite of what was expected according to the decreased water and cation contents of resting RBC. In addition, the features of mutant PIEZO1 expressed in HEK293 cells do not always correlate with the observation in RBC where PIEZO1 mutations induced a cation leak associated with an increased conductance. Our work emphasizes the role of the membrane environment in PIEZO1 activity and the need to characterize RBC permeability to assess pathogenicity to PIEZO1 mutants associated with erythrocyte diseases.

The Diverse Physiological Functions of Mechanically Activated Ion Channels in Mammals

Many aspects of mammalian physiology are mechanically regulated. One set of molecules that can mediate mechanotransduction are the mechanically activated ion channels. These ionotropic force sensors are directly activated by mechanical inputs, resulting in ionic flux across the plasma membrane. While there has been much research focus on the role of mechanically activated ion channels in touch sensation and hearing, recent data have highlighted the broad expression pattern of these molecules in mammalian cells. Disruption of mechanically activated channels has been shown to impact (a) the development of mechanoresponsive structures, (b) acute mechanical sensing, and (c) mechanically driven homeostatic maintenance in multiple tissue types. The diversity of processes impacted by these molecules highlights the importance of mechanically activated ion channels in mammalian physiology. Expected final online publication date for the Annual Review of Physiology, Volume 84 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Molecular mechanism in trigeminal nerve and treatment methods related to orthodontic pain

BACKGROUND

Orthodontic treatment is the main treatment approach for malocclusion. Orthodontic pain is an inevitable undesirable adverse reaction during orthodontic treatment. It is reported orthodontic pain has become one of the most common reason that patients withdraw from orthodontic treatment. Therefore, understanding the underlying mechanism and finding treatment of orthodontic pain are in urgent need.

AIMS

This article aims to sort out the mechanisms and treatments of orthodontic pain, hoping to provide some ideas for future orthodontic pain relief.

MATERIALS

Tooth movement will cause local inflammation. Certain inflammatory factors and cytokines stimulating the trigeminal nerve and further generating pain perception, as well as drugs and molecular targeted therapy blocking nerve conduction pathways, will be reviewed in this article.

METHOD

We review and summaries current studies related to molecular mechanisms and treatment approaches in orthodontic pain control.

RESULTS

Orthodontics pain related influencing factors and molecular mechanisms has been introduced. Commonly used clinical methods in orthodontic pain control has been evaluated.

DISCUSSION

With the clarification of more molecular mechanisms, the direction of orthodontic pain treatment will shift to targeted drugs.

Sphingomyelinase Disables Inactivation in Endogenous PIEZO1 Channels

Endogenous PIEZO1 channels of native endothelium lack the hallmark inactivation often seen when these channels are overexpressed in cell lines. Because prior work showed that the force of shear stress activates sphingomyelinase in endothelium, we considered if sphingomyelinase is relevant to endogenous PIEZO1. Patch clamping was used to quantify PIEZO1-mediated signals in freshly isolated murine endothelium exposed to the mechanical forces caused by shear stress and membrane stretch. Neutral sphingomyelinase inhibitors and genetic disruption of sphingomyelin phosphodiesterase 3 (SMPD3) cause PIEZO1 to switch to profoundly inactivating behavior. Ceramide (a key product of SMPD3) rescues non-inactivating channel behavior. Its co-product, phosphoryl choline, has no effect. In contrast to ceramide, sphingomyelin (the SMPD3 substrate) does not affect inactivation but alters channel force sensitivity. The data suggest that sphingomyelinase activity, ceramide, and sphingomyelin are determinants of native PIEZO gating that enable sustained activity.

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SMPD3 sphingomyelinase enables long-lasting PIEZO1 activity in response to force

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Ceramide, a key lipid product of SMPD3, promotes long-lasting activity

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Sphingomyelin, the SMPD3 substrate, does not affect the duration of activity

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Sphingomyelin alters PIEZO1 force sensitivity

Modified N-linked glycosylation status predicts trafficking defective human Piezo1 channel mutations

Mechanosensitive channels are integral membrane proteins that sense mechanical stimuli. Like most plasma membrane ion channel proteins they must pass through biosynthetic quality control in the endoplasmic reticulum that results in them reaching their destination at the plasma membrane. Here we show that N-linked glycosylation of two highly conserved asparagine residues in the 'cap' region of mechanosensitive Piezo1 channels are necessary for the mature protein to reach the plasma membrane. Both mutation of these asparagines (N2294Q/N2331Q) and treatment with an enzyme that hydrolyses N-linked oligosaccharides (PNGaseF) eliminates the fully glycosylated mature Piezo1 protein. The N-glycans in the cap are a pre-requisite for N-glycosylation in the 'propeller' regions, which are present in loops that are essential for mechanotransduction. Importantly, trafficking-defective Piezo1 variants linked to generalized lymphatic dysplasia and bicuspid aortic valve display reduced fully N-glycosylated Piezo1 protein. Thus the N-linked glycosylation status in vitro correlates with efficient membrane trafficking and will aid in determining the functional impact of Piezo1 variants of unknown significance.

Disruption of membrane cholesterol organization impairs the activity of PIEZO1 channel clusters

The human mechanosensitive ion channel PIEZO1 is gated by membrane tension and regulates essential biological processes such as vascular development and erythrocyte volume homeostasis. Currently, little is known about PIEZO1 plasma membrane localization and organization. Using a PIEZO1-GFP fusion protein, we investigated whether cholesterol enrichment or depletion by methyl-β-cyclodextrin (MBCD) and disruption of membrane cholesterol organization by dynasore affects PIEZO1-GFP's response to mechanical force. Electrophysiological recordings in the cell-attached configuration revealed that MBCD caused a rightward shift in the PIEZO1-GFP pressure-response curve, increased channel latency in response to mechanical stimuli, and markedly slowed channel inactivation. The same effects were seen in native PIEZO1 in N2A cells. STORM superresolution imaging revealed that, at the nanoscale, PIEZO1-GFP channels in the membrane associate as clusters sensitive to membrane manipulation. Both cluster distribution and diffusion rates were affected by treatment with MBCD (5 mM). Supplementation of polyunsaturated fatty acids appeared to sensitize the PIEZO1-GFP response to applied pressure. Together, our results indicate that PIEZO1 function is directly dependent on the membrane composition and lateral organization of membrane cholesterol domains, which coordinate the activity of clustered PIEZO1 channels.

Role of mechanosensitive ion channel Piezo1 in tumors

A better understanding of mechanotransduction mechanisms is the key to exploring biomechanical signal-regulated tumor malignant characteristics, and it is also the theoretical and practical basis for effective intervention from the upstream of mechanical cues. The discovery of the novel mechanosensitive ion channel protein Piezo1 (piezo type mechanosensitive ion channel component 1) provides a new perspective for the study of mechanotransduction mechanism in tumors. This article summarizes some of the latest research progress of Piezo1 in modulating tumor progression, including inducing cell carcinogenesis; regulating cell cycle, proliferation, invasion, and metastasis; influencing tumor stemness and angiogenesis; as well as reprogramming tumor immune microenvironment, etc.