Piezo1 Channels Contribute to the Regulation of Human Atrial Fibroblast Mechanical Properties and Matrix Stiffness Sensing

Fibroblast and myofibroblast activation in normal tissue repair and fibrosis

The term 'fibroblast' often serves as a catch-all for a diverse array of mesenchymal cells, including perivascular cells, stromal progenitor cells and bona fide fibroblasts. Although phenotypically similar, these subpopulations are functionally distinct, maintaining tissue integrity and serving as local progenitor reservoirs. In response to tissue injury, these cells undergo a dynamic fibroblast-myofibroblast transition, marked by extracellular matrix secretion and contraction of actomyosin-based stress fibres. Importantly, whereas transient activation into myofibroblasts aids in tissue repair, persistent activation triggers pathological fibrosis. In this Review, we discuss the roles of mechanical cues, such as tissue stiffness and strain, alongside cell signalling pathways and extracellular matrix ligands in modulating myofibroblast activation and survival. We also highlight the role of epigenetic modifications and myofibroblast memory in physiological and pathological processes. Finally, we discuss potential strategies for therapeutically interfering with these factors and the associated signal transduction pathways to improve the outcome of dysregulated healing.

Effect of extracellular matrix stiffness on efficacy of Dapagliflozin for diabetic cardiomyopathy

BACKGROUND

Extracellular matrix (ECM) stiffness is closely related to the progress of diabetic cardiomyopathy (DCM) and the response of treatment of DCM to anti-diabetic drugs. Dapagliflozin (Dapa) has been proven to have cardio-protective efficacy for diabetes and listed as the first-line drug to treat heart failure. But the regulatory relationship between ECM stiffness and treatment efficacy of Dapa remains elusive.

MATERIALS AND METHODS

This work investigated the effect of ECM stiffness on DCM progression and Dapa efficacy using both in vivo DCM rat model and in vitro myocardial cell model with high glucose injury. First, through DCM rat models with various levels of myocardial injury and administration with Dapa treatment for four weeks, the levels of myocardial injury, myocardial oxidative stress, expressions of AT1R (a mechanical signal protein) and the stiffness of myocardial tissues were obtained. Then for mimicking the stiffness of myocardial tissues at early and late stages of DCM, we constructed cell models through culturing H9c2 myocardial cells on the polyacrylamide gels with two stiffness and exposed to a high glucose level and without/with Dapa intervention. The cell viability, reactive oxygen species (ROS) levels and expressions of mechanical signal sensitive proteins were obtained.

RESULTS

The DCM progression is accompanied by the increased myocardial tissue stiffness, which can synergistically exacerbate myocardial cell injury with high glucose. Dapa can improve the ECM stiffness-induced DCM progression and its efficacy on DCM is more pronounced on the soft ECM, which is related to the regulation pathway of AT1R-FAK-NOX2. Besides, Dapa can inhibit the expression of the ECM-induced integrin β1, but without significant impact on piezo 1.

CONCLUSIONS

Our study found the regulation and effect of biomechanics in the DCM progression and on the Dapa efficacy on DCM, providing the new insights for the DCM treatment. Additionally, our work showed the better clinical prognosis of DCM under early Dapa intervention.

The mechanosensitive Piezo1 channel exacerbates myocardial ischaemia/reperfusion injury by activating caspase-8-mediated PANoptosis

PANoptosis is a newly discovered type of cell death characterized by pyroptosis, apoptosis and/or necroptosis and has been implicated in the inflammatory response. Piezo1 is a mechanosensitive ion channel that plays important roles in physiological development and various diseases. However, whether cardiomyocytes undergo PANoptosis during myocardial ischaemia/reperfusion (I/R) injury and the role of Piezo1 in this process remain largely unexplored. In this study, our results revealed that the expression levels of the main components of the PANoptosome, including caspase-8, caspase-3, NLRP3, caspase-1, GSDMD, RIPK1, RIPK3 and MLKL, were significantly upregulated in I/R heart tissues over time, indicating the occurrence of PANoptosis in I/R hearts. Accordingly, Piezo1 expression was significantly upregulated in I/R-injured hearts and hypoxia/reoxygenation (H/R)-treated cardiomyocytes. In contrast, pharmacological inhibition of Piezo1 by the inhibitor GsMTx4 in mice markedly attenuated the I/R-mediated decline in cardiac contractile function and increases in infarct size, apoptosis, oxidative stress and inflammation accompanied by the inhibition of PANoptosis-related mediators in I/R hearts. Consistently, the effects of Piezo1 on calcium influx and PANoptosis were further verified by GsMTx4 and Piezo1 activator Yoda1 in H/R-treated cardiomyocytes in vitro. Moreover, caspase-8 rather than calcium influx was required for H/R-induced PANoptosis in vitro. Mechanistically, Piezo1 interacts with caspase-8, a key initial activator of the PANoptosome complex, which subsequently activates cardiomyocyte PANoptosis, leading to cardiac dysfunction. In summary, these data suggest that Piezo1 is a new cardiac mechanosensor that promotes cardiac I/R injury possibly through the caspase-8-mediated activation of cardiomyocyte PANoptosis and highlight that Piezo1 may represent a new target for treating ischaemic heart disease.

Alteration of Piezo1 signaling in type 2 diabetic mice: focus on endothelium and BKCa channel

Piezo1 mechanosensitive ion channel plays a important role in vascular physiology and disease. This study aimed to elucidate the altered signaling elicited by Piezo1 activation in the arteries of type 2 diabetes. Ten- to 12-week-old male C57BL/6 (control) and type 2 diabetic mice (db-/db-) were used. The second-order mesenteric arteries (~ 150 μm) were used for isometric tension experiments. Western blot analysis and immunofluorescence staining were performed to observe protein expression. Piezo1 was significantly decreased in mesenteric arteries of type 2 diabetic mice compared to control mice, as analyzed by western blot and immunofluorescence staining. Piezo1 agonist, Yoda1, concentration-dependently induced relaxation of mesenteric arteries in both groups. Interestingly, the relaxation response was significantly greater in control mice than in db-/db- mice. The removal of endothelium reduced relaxation responses induced by Yoda1, which was greater in control mice than db-/db- mice. Furthermore, the relaxation response was reduced by pre-treatment with various types of K+ channel blockers in endothelium-intact arteries in control mice. In endothelium-denuded arteries, pre-incubation with charybdotoxin, an Ca2+-activated K+ channel (BKCa channel) blocker, significantly attenuated Yoda1-induced relaxation in db-/db- mice, while there was no effect in control mice. Co-immunofluorescence staining showed co-localization of Piezo1 and BKCa channel was more pronounced in db-/db- mice than in control mice. These results indicate that the vascular responses induced by Piezo1 activation are different in the mesenteric resistance arteries in type 2 diabetic mice.

Cyclic strain alters the transcriptional and migratory response of scleral fibroblasts to TGFβ

In glaucoma, scleral fibroblasts are exposed to IOP-associated mechanical strain and elevated TGFβ levels. These stimuli, in turn, lead to scleral remodeling. Here, we examine the scleral fibroblast migratory and transcriptional response to these stimuli to better understand mechanisms of glaucomatous scleral remodeling. Human peripapillary scleral (PPS) fibroblasts were cultured on parallel grooves, treated with TGFβ (2 ng/ml) in the presence of vehicle or TGFβ signaling inhibitors, and exposed to uniaxial strain (1 Hz, 5%, 12-24 h). Axis of cellular orientation was determined at baseline, immediately following strain, and 24 h after strain cessation with 0° being completely aligned with grooves and 90° being perpendicular. Fibroblasts migration in-line and across grooves was assessed using a scratch assay. Transcriptional profiling of TGFβ-treated fibroblasts with or without strain was performed by RT-qPCR and pERK, pSMAD2, and pSMAD3 levels were measured by immunoblot. Pre-strain alignment of TGFβ-treated cells with grooves (6.2 ± 1.5°) was reduced after strain (21.7 ± 5.3°, p < 0.0001) and restored 24 h after strain cessation (9.5 ± 2.6°). ERK, FAK, and ALK5 inhibition prevented this reduction; however, ROCK, YAP, or SMAD3 inhibition did not. TGFβ-induced myofibroblast markers were reduced by strain (αSMA, POSTN, ASPN, MLCK1). While TGFβ-induced phosphorylation of ERK and SMAD2 was unaffected by cyclic strain, SMAD3 phosphorylation was reduced (p = 0.0004). Wound healing across grooves was enhanced by ROCK and SMAD3 inhibition but not ERK or ALK5 inhibition. These results provide insight into the mechanisms by which mechanical strain alters the cellular response to TGFβ and the potential signaling pathways that underlie scleral remodeling.

MiR-214-3p Regulates Piezo1, Lysyl Oxidases and Mitochondrial Function in Human Cardiac Fibroblasts

Cardiac fibroblasts are pivotal regulators of cardiac homeostasis and are essential in the repair of the heart after myocardial infarction (MI), but their function can also become dysregulated, leading to adverse cardiac remodelling involving both fibrosis and hypertrophy. MicroRNAs (miRNAs) are noncoding RNAs that target mRNAs to prevent their translation, with specific miRNAs showing differential expression and regulation in cardiovascular disease. Here, we show that miR-214-3p is enriched in the fibroblast fraction of the murine heart, and its levels are increased with cardiac remodelling associated with heart failure, or in the acute phase after experimental MI. Tandem mass tagging proteomics and in-silico network analyses were used to explore protein targets regulated by miR-214-3p in cultured human cardiac fibroblasts from multiple donors. Overexpression of miR-214-3p by miRNA mimics resulted in decreased expression and activity of the Piezo1 mechanosensitive cation channel, increased expression of the entire lysyl oxidase (LOX) family of collagen cross-linking enzymes, and decreased expression of an array of mitochondrial proteins, including mitofusin-2 (MFN2), resulting in mitochondrial dysfunction, as measured by citrate synthase and Seahorse mitochondrial respiration assays. Collectively, our data suggest that miR-214-3p is an important regulator of cardiac fibroblast phenotypes and functions key to cardiac remodelling, and that this miRNA represents a potential therapeutic target in cardiovascular disease.

Piezo1-mediated regulation of smooth muscle cell volume in response to enhanced extracellular matrix rigidity

BACKGROUND AND PURPOSE

Decreased aortic compliance is a precursor to numerous cardiovascular diseases. Compliance is regulated by the rigidity of the aortic wall and the vascular smooth muscle cells (VSMCs). Extracellular matrix stiffening, observed during ageing, reduces compliance. In response to increased rigidity, VSMCs generate enhanced contractile forces that result in VSMC stiffening and a further reduction in compliance. Mechanisms driving VSMC response to matrix rigidity remain poorly defined.

EXPERIMENTAL APPROACH

Human aortic-VSMCs were seeded onto polyacrylamide hydrogels whose rigidity mimicked either healthy (12 kPa) or aged/diseased (72 kPa) aortae. VSMCs were treated with pharmacological agents prior to agonist stimulation to identify regulators of VSMC volume regulation.

KEY RESULTS

On pliable matrices, VSMCs contracted and decreased in cell area. Meanwhile, on rigid matrices VSMCs displayed a hypertrophic-like response, increasing in area and volume. Piezo1 activation stimulated increased VSMC volume by promoting calcium ion influx and subsequent activation of PKC and aquaporin-1. Pharmacological blockade of this pathway prevented the enhanced VSMC volume response on rigid matrices whilst maintaining contractility on pliable matrices. Importantly, both piezo1 and aquaporin-1 gene expression were up-regulated during VSMC phenotypic modulation in atherosclerosis and after carotid ligation.

CONCLUSIONS AND IMPLICATIONS

In response to extracellular matrix rigidity, VSMC volume is increased by a piezo1/PKC/aquaporin-1 mediated pathway. Pharmacological targeting of this pathway specifically blocks the matrix rigidity enhanced VSMC volume response, leaving VSMC contractility on healthy mimicking matrices intact. Importantly, upregulation of both piezo1 and aquaporin-1 gene expression is observed in disease relevant VSMC phenotypes.

Piezo1-Mediated Neurogenic Inflammatory Cascade Exacerbates Ventricular Remodeling After Myocardial Infarction

BACKGROUND

Heart failure is associated with a high rate of mortality and morbidity, and ventricular remodeling invariably precedes heart failure. Ventricular remodeling is fundamentally driven by mechanotransduction that is regulated by both the nervous system and the immune system. However, it remains unknown which key molecular factors govern the neuro/immune/cardio axis that underlies mechanotransduction during ventricular remodeling. Here, we investigated whether the mechanosensitive Piezo cation channel-mediated neurogenic inflammatory cascade underlies ventricular remodeling-related mechanotransduction.

METHODS

By ligating the left coronary artery of rats to establish an in vivo model of chronic myocardial infarction (MI), lentivirus-mediated thoracic dorsal root ganglion (TDRG)-specific Piezo1 knockdown rats and adeno-associated virus-PHP.S-mediated TDRG neuron-specific Piezo1 knockout mice were used to investigate whether Piezo1 in the TDRG plays a functional role during ventricular remodeling. Subsequently, neutralizing antibody-mediated TDRG IL-6 (interleukin-6) inhibition rats and adeno-associated virus-PHP.S-mediated TDRG neuron-specific IL-6 knockdown mice were used to determine the mechanism underlying neurogenic inflammation. Primary TDRG neurons were used to evaluate Piezo1 function in vitro.

RESULTS

Expression of Piezo1 and IL-6 was increased, and these factors were functionally activated in TDRG neurons at 4 weeks after MI. Both knockdown of TDRG-specific Piezo1 and deletion of TDRG neuron-specific Piezo1 lessened the severity of ventricular remodeling at 4 weeks after MI and decreased the level of IL-6 in the TDRG or heart. Furthermore, inhibition of TDRG IL-6 or knockdown of TDRG neuron-specific IL-6 also ameliorated ventricular remodeling and suppressed the IL-6 cascade in the heart, whereas the Piezo1 level in the TDRG was not affected. In addition, enhanced Piezo1 function, as reflected by abundant calcium influx induced by Yoda1 (a selective agonist of Piezo1), led to increased release of IL-6 from TDRG neurons in mice 4 weeks after MI.

CONCLUSIONS

Our findings point to a critical role for Piezo1 in ventricular remodeling at 4 weeks after MI and reveal a neurogenic inflammatory cascade as a previously unknown facet of the neuronal immune signaling axis underlying mechanotransduction.

Divergent and Compensatory Effects of BMP2 and BMP4 on the VSMC Phenotype and BMP4's Role in Thoracic Aortic Aneurysm Development

Vascular smooth muscle cells (VSMCs) play a key role in aortic aneurysm formation. Bone morphogenetic proteins (BMPs) have been implicated as important regulators of VSMC phenotype, and dysregulation of the BMP pathway has been shown to be associated with vascular diseases. The aim of this study was to investigate for the first time the effects of BMP-4 on the VSMC phenotype and to understand its role in the development of thoracic aortic aneurysms (TAAs). Using the angiotensin II (AngII) osmotic pump model in mice, aortas from mice with VSMC-specific BMP-4 deficiency showed changes similar to AngII-infused aortas, characterised by a loss of contractile markers, increased fibrosis, and activation of matrix metalloproteinase 9. When BMP-4 deficiency was combined with AngII infusion, there was a significantly higher rate of apoptosis and aortic dilatation. In vitro, VSMCs with mRNA silencing of BMP-4 displayed a dedifferentiated phenotype with activated canonical BMP signalling. In contrast, BMP-2-deficient VSMCs exhibited the opposite phenotype. The compensatory regulation between BMP-2 and BMP-4, with BMP-4 promoting the contractile phenotype, appeared to be independent of the canonical signalling pathway. Taken together, these results demonstrate the impact of VSMC-specific BMP-4 deficiency on TAA development.

The mechanisms of exercise improving cardiovascular function by stimulating Piezo1 and TRP ion channels: a systemic review

Mechanosensitive ion channels are widely distributed in the heart, lung, bladder and other tissues, and plays an important role in exercise-induced cardiovascular function promotion. By reviewing the PubMed databases, the results were summarized using the terms "Exercise/Sport", "Piezo1", "Transient receptor potential (TRP)" and "Cardiovascular" as the keywords, 124-related papers screened were sorted and reviewed. The results showed that: (1) Piezo1 and TRP channels play an important role in regulating blood pressure and the development of cardiovascular diseases such as atherosclerosis, myocardial infarction, and cardiac fibrosis; (2) Exercise promotes cardiac health, inhibits the development of pathological heart to heart failure, regulating the changes in the characterization of Piezo1 and TRP channels; (3) Piezo1 activates downstream signaling pathways with very broad pathways, such as AKT/eNOS, NF-κB, p38MAPK and HIPPO-YAP signaling pathways. Piezo1 and Irisin regulate nuclear localization of YAP and are hypothesized to act synergistically to regulate tissue mechanical properties of the cardiovascular system and (4) The cardioprotective effects of exercise through the TRP family are mostly accomplished through Ca2+ and involve many signaling pathways. TRP channels exert their important cardioprotective effects by reducing the TRPC3-Nox2 complex and mediating Irisin-induced Ca2+ influx through TRPV4. It is proposed that exercise stimulates the mechanosensitive cation channel Piezo1 and TRP channels, which exerts cardioprotective effects. The activation of Piezo1 and TRP channels and their downstream targets to exert cardioprotective function by exercise may provide a theoretical basis for the prevention of cardiovascular diseases and the rehabilitation of clinical patients.

PIEZO Ion Channels in Cardiovascular Functions and Diseases

The cardiovascular system provides blood supply throughout the body and as such is perpetually applying mechanical forces to cells and tissues. Thus, this system is primed with mechanosensory structures that respond and adapt to changes in mechanical stimuli. Since their discovery in 2010, PIEZO ion channels have dominated the field of mechanobiology. These have been proposed as the long-sought-after mechanosensitive excitatory channels involved in touch and proprioception in mammals. However, more and more pieces of evidence point to the importance of PIEZO channels in cardiovascular activities and disease development. PIEZO channel-related cardiac functions include transducing hemodynamic forces in endothelial and vascular cells, red blood cell homeostasis, platelet aggregation, and arterial blood pressure regulation, among others. PIEZO channels contribute to pathological conditions including cardiac hypertrophy and pulmonary hypertension and congenital syndromes such as generalized lymphatic dysplasia and xerocytosis. In this review, we highlight recent advances in understanding the role of PIEZO channels in cardiovascular functions and diseases. Achievements in this quickly expanding field should open a new road for efficient control of PIEZO-related diseases in cardiovascular functions.

Cell-cell and cell-matrix adhesion regulated by Piezo1 is critical for stiffness-dependent DRG neuron aggregation

The dorsal root ganglion (DRG) is characterized by the dense clustering of primary sensory neuron bodies, with their axons extending to target tissues for sensory perception. The close physical proximity of DRG neurons facilitates the integration and amplification of somatosensation, ensuring normal physiological functioning. However, the mechanism underlying DRG neuron aggregation was unclear. In our study, we culture DRG neurons from newborn rats on substrates with varying stiffness and observe that the aggregation of DRG neurons is influenced by mechanical signals arising from substrate stiffness. Moreover, we identify Piezo1 as the mechanosensor responsible for DRG neurons' ability to sense different substrate stiffness. We further demonstrate that the Piezo1-calpain-integrin-β1/E-cadherin signaling cascade regulates the aggregation of DRG neurons. These findings deepen our understanding of the mechanisms involved in histogenesis and potential disease development, as mechanical signals arising from substrate stiffness play a crucial role in these processes.

Transcriptomic profile of the mechanosensitive ion channelome in human cardiac fibroblasts

Human cardiac fibroblasts (HCFs) have mRNA transcripts that encode different mechanosensitive ion channels and channel regulatory proteins whose functions are not known yet. The primary goal of this work was to define the mechanosensitive ion channelome of HCFs. The most common type of cationic channel is the transient receptor potential (TRP) family, which is followed by the TWIK-related K+ channel (TREK), transmembrane protein 63 (TMEM63), and PIEZO channel (PIEZO) families. In the sodium-dependent NON-voltage-gated channel (SCNN) subfamily, only SCNN1D was shown to be highly expressed. Particular members of the acid-sensing ion channel (ASIC) (ASIC1 and ASIC3) subfamilies were also significantly expressed. The transcripts per kilobase million (TPMs) for Piezo 2 were almost 100 times less abundant than those for Piezo 1. The tandem of P domains in a weak inward rectifying K+ channel (TWIK)-2 channel, TWIK-related acid-sensitive K+ channel (TASK)-5, TASK-1, and the TWIK-related K1 (TREK-1) channel were the four most prevalent types in the K2P subfamily. The highest expression in the TRPP subfamily was found for PKD2 and PKD1, while in the TRPM subfamily, it was found for TRPM4, TRPM7, and TRPM3. TRPV2, TRPV4, TRPV3, and TRPV6 (all members of the TRPV subfamily) were also substantially expressed. A strong expression of the TRPC1, TRPC4, TRPC6, and TRPC2 channels and all members of the TRPML subfamily (MCOLN1, MCOLN2, and MCOLN3) was also shown. In terms of the transmembrane protein 16 (TMEM16) family, the HCFs demonstrated significant expression of the TMEM16H, TMEM16F, TMEM16J, TMEM16A, and TMEM16G channels. TMC3 is the most expressed channel in HCFs of all known members of the transmembrane channel-like protein (TMC) family. This analysis of the mechanosensitive ionic channel transcriptome in HCFs: (1) agrees with previously documented findings that all currently identified mechanosensitive channels play a significant and well recognized physiological function in elucidating the mechanosensitive characteristics of HCFs; (2) supports earlier preliminary reports that point to the most common expression of the TRP mechanosensitive family in HCFs; and (3) points to other new mechanosensitive channels (TRPC1, TRPC2, TWIK-2, TMEM16A, ASIC1, and ASIC3).

Piezo1：the potential new therapeutic target for fibrotic diseases

Fibrosis is a pathological process that occurs in various organs, characterized by excessive deposition of extracellular matrix (ECM), leading to structural damage and, in severe cases, organ failure. Within the fibrotic microenvironment, mechanical forces play a crucial role in shaping cell behavior and function, yet the precise molecular mechanisms underlying how cells sense and transmit these mechanical cues, as well as the physical aspects of fibrosis progression, remain less understood. Piezo1, a mechanosensitive ion channel protein, serves as a pivotal mediator, converting mechanical stimuli into electrical or chemical signals. Accumulating evidence suggests that Piezo1 plays a central role in ECM formation and hemodynamics in the mechanical transduction of fibrosis expansion. This review provides an overview of the current understanding of the role of Piezo1 in fibrosis progression, encompassing conditions such as myocardial fibrosis, pulmonary fibrosis, renal fibrosis, and other fibrotic diseases. The main goal is to pave the way for potential clinical applications in the field of fibrotic diseases.

Joining forces: crosstalk between mechanosensitive PIEZO1 ion channels and integrin-mediated focal adhesions

Both integrin-mediated focal adhesions (FAs) and mechanosensitive ion channels such as PIEZO1 are critical in mechanotransduction processes that influence cell differentiation, development, and cancer. Ample evidence now exists for regulatory crosstalk between FAs and PIEZO1 channels with the molecular mechanisms underlying this process remaining unclear. However, an emerging picture is developing based on spatial crosstalk between FAs and PIEZO1 revealing a synergistic model involving the cytoskeleton, extracellular matrix (ECM) and calcium-dependent signaling. Already cell type, cell contractility, integrin subtypes and ECM composition have been shown to regulate this crosstalk, implying a highly fine-tuned relationship between these two major mechanosensing systems. In this review, we summarize the latest advances in this area, highlight the physiological implications of this crosstalk and identify gaps in our knowledge that will improve our understanding of cellular mechanosensing.

Atrial Fibrillation: Rate Versus Rhythm Control

Description Atrial fibrillation (AF) remains the most common arrhythmia worldwide and is expected to affect approximately 12 million individuals in the United States alone by 2030. Thromboembolic events remain a feared complication of AF and should be treated and risk-stratified utilizing the CHA2DS2-VASc scoring system. Other complications of AF span a wide spectrum from impaired quality of life (QoL) to an increase in all-cause mortality. Rate control strategies consist of controlling the ventricular rate and have been shown to be a safe and effective strategy for asymptomatic AF patients. In patients who are plagued with symptoms leading to impaired QoL or a decrease in exercise capacity, rhythm control with antiarrhythmic drugs or catheter ablation may be suitable options. Mortality benefits when comparing rate versus rhythm control remain equivocal when comparing multiple studies over the past decade.

PIEZO1 expression at the glio-vascular unit adjusts to neuroinflammation in seizure conditions

Mechanosensors are emerging players responding to hemodynamic and physical inputs. Their significance in the central nervous system remains relatively uncharted. Using human-derived brain specimens or cells and a pre-clinical model of mesio-temporal lobe epilepsy (MTLE), we examined how the mRNA levels of the mechanosensitive channel PIEZO1 adjust to disease-associated pro-inflammatory trajectories. In brain tissue micro-punches obtained from 18 drug-resistant MTLE patients, PIEZO1 expression positively correlated with pro-inflammatory biomarkers TNFα, IL-1β, and NF-kB in the epileptogenic hippocampus compared to the adjacent amygdala and temporal cortex tissues. In an experimental MTLE model, hippocampal Piezo1 and cytokine expression levels were increased post-status epilepticus (SE) and during epileptogenesis. Piezo1 expression positively correlated with Tnfα, Il1β, and Nf-kb in the hippocampal foci. Next, by combining RNAscope with immunohistochemistry, we identified Piezo1 in glio-vascular cells. Post-SE and during epileptogenesis, ameboid IBA1 microglia, hypertrophic GFAP astrocytes, and damaged NG2DsRed pericytes exhibited time-dependent patterns of increased Piezo1 expression. Digital droplet PCR analysis confirmed the Piezo1 trajectory in isolated hippocampal microvessels in the ipsi and contralateral hippocampi. The combined examinations performed in this model showed Piezo1 expression returning towards basal levels after the epileptogenesis-associated peak inflammation. From these associations, we next asked whether pro-inflammatory players directly regulate PIEZO1 expression. We used human-derived brain cells and confirmed that endothelium, astrocytes, and pericytes expressed PIEZO1. Exposure to human recombinant TNFα or IL1β upregulated NF-kB in all cells. Furthermore, TNFα induced PIEZO1 expression in a dose and time-dependent manner, primarily in astrocytes. This exploratory study describes a spatiotemporal dialogue between PIEZO1 brain cell-mechanobiology and neuro-inflammatory cell remodeling. The precise functional mechanisms regulating this interplay in disease conditions warrant further investigation.

Mechanotransductive receptor Piezo1 as a promising target in the treatment of fibrosis diseases

Fibrosis could happen in every organ, leading to organic malfunction and even organ failure, which poses a serious threat to global health. Early treatment of fibrosis has been reported to be the turning point, therefore, exploring potential correlates in the pathogenesis of fibrosis and how to reverse fibrosis has become a pressing issue. As a mechanism-sensitive cationic calcium channel, Piezo1 turns on in response to changes in the lipid bilayer of the plasma membrane. Piezo1 exerts multiple biological roles, including inhibition of inflammation, cytoskeletal stabilization, epithelial-mesenchymal transition, stromal stiffness, and immune cell mechanotransduction, interestingly enough. These processes are closely associated with the development of fibrotic diseases. Recent studies have shown that deletion or knockdown of Piezo1 attenuates the onset of fibrosis. Therefore, in this paper we comprehensively describe the biology of this gene, focusing on its potential relevance in pulmonary fibrosis, renal fibrosis, pancreatic fibrosis, and cardiac fibrosis diseases, except for the role of drugs (agonists), increased intracellular calcium and mechanical stress using this gene in alleviating fibrosis.

Effect of whole body vibration therapy in the rat model of steroid-induced osteonecrosis of the femoral head

Background: Steroid-induced Osteonecrosis of the Femoral Head (SIONFH) is a skeletal disease with a high incidence and a poor prognosis. Whole body vibration therapy (WBVT), a new type of physical training, is known to promote bone formation. However, it remains unclear whether WBVT has a therapeutic effect on SIONFH. Materials and methods: Thirty adult male and female Sprague-Dawley (SD) rats were selected and randomly assigned to three experimental groups: the control group, the model group, and the mechanical vibration group, respectively. SIONFH induction was achieved through the combined administration of lipopolysaccharides (LPS) and methylprednisolone sodium succinate for injection (MPS). The femoral head samples underwent hematoxylin and eosin (H&E) staining to visualize tissue structures. Structural parameters of the region of interest (ROI) were compared using Micro-CT analysis. Immunohistochemistry was employed to assess the expression levels of Piezo1, BMP2, RUNX2, HIF-1, VEGF, CD31, while immunofluorescence was used to examine CD31 and Emcn expression levels. Results: The H&E staining results revealed a notable improvement in the ratio of empty lacuna in various groups following WBVT intervention. Immunohistochemical analysis showed that the expression levels of Piezo1, BMP2, RUNX2, HIF-1, VEGF, and CD31 in the WBVT group exhibited significant differences when compared to the Model group (p < 0.05). Additionally, immunofluorescence analysis demonstrated statistically significant differences in CD31 and Emcn expression levels between the WBVT group and the Model group (p < 0.05). Conclusion: WBVT upregulates Piezo1 to promote osteogenic differentiation, potentially by enhancing the HIF-1α/VEGF axis and regulating H-vessel angiogenesis through the activation of the Piezo1 ion channel. This mechanism may lead to improved blood flow supply and enhanced osteogenic differentiation within the femoral head.

Macrophages and fibroblasts in foreign body reactions: How mechanical cues drive cell functions?

Biomaterials, when implanted in the human body, can induce a series of cell- and cytokine-related reactions termed foreign body reactions (FBRs). In the progression of FBRs, macrophages regulate inflammation and healing by polarizing to either a pro-inflammatory or pro-healing phenotype and recruit fibroblasts by secreting cytokines. Stimulated by the biomaterials, fibrotic capsule is formed eventually. The implant, along with its newly formed capsule, introduces various mechanical cues that influence cellular functions. Mechanosensing proteins, such as integrins or ion channels, transduce extracellular mechanical signals into cytoplasm biochemical signals in response to mechanical stimuli. Consequently, the morphology, migration mode, function, and polarization state of the cells are affected. Modulated by different intracellular signaling pathways and their crosstalk, the expression of fibrotic genes increases with fibroblast activation and fibroblast to myofibroblast transition under stiff or force stimuli. However, summarized in most current studies, the outcomes of macrophage polarization in the effect of different mechanical cues are inconsistent. The underlying mechanisms should be investigated with more advanced technology and considering more interfering aspects. Further research is needed to determine how to modulate the progression of fibrotic capsule formation in FBR artificially.

Novel approaches to target fibroblast mechanotransduction in fibroproliferative diseases

The ability of cells to sense and respond to changes in mechanical environment is vital in conditions of organ injury when the architecture of normal tissues is disturbed or lost. Among the various cellular players that respond to injury, fibroblasts take center stage in re-establishing tissue integrity by secreting and organizing extracellular matrix into stabilizing scar tissue. Activation, activity, survival, and death of scar-forming fibroblasts are tightly controlled by mechanical environment and proper mechanotransduction ensures that fibroblast activities cease after completion of the tissue repair process. Conversely, dysregulated mechanotransduction often results in fibroblast over-activation or persistence beyond the state of normal repair. The resulting pathological accumulation of extracellular matrix is called fibrosis, a condition that has been associated with over 40% of all deaths in the industrialized countries. Consequently, elements in fibroblast mechanotransduction are scrutinized for their suitability as anti-fibrotic therapeutic targets. We review the current knowledge on mechanically relevant factors in the fibroblast extracellular environment, cell-matrix and cell-cell adhesion structures, stretch-activated membrane channels, stress-regulated cytoskeletal structures, and co-transcription factors. We critically discuss the targetability of these elements in therapeutic approaches and their progress in pre-clinical and/or clinical trials to treat organ fibrosis.

Nonmyocytes as electrophysiological contributors to cardiac excitation and conduction

Although cardiac action potential (AP) generation and propagation have traditionally been attributed exclusively to cardiomyocytes (CM), other cell types in the heart are also capable of forming electrically conducting junctions. Interactions between CM and nonmyocytes (NM) enable and modulate each other's activity. This review provides an overview of the current understanding of heterocellular electrical communication in the heart. Although cardiac fibroblasts were initially thought to be electrical insulators, recent studies have demonstrated that they form functional electrical connections with CM in situ. Other NM, such as macrophages, have also been recognized as contributing to cardiac electrophysiology and arrhythmogenesis. Novel experimental tools have enabled the investigation of cell-specific activity patterns in native cardiac tissue, which is expected to yield exciting new insights into the development of novel or improved diagnostic and therapeutic strategies.

Cellular mechanosignaling for sensing and transducing matrix rigidity

The mechanisms by which cells sense their mechanical environment and transduce the signal through focal adhesions and signaling pathways to the nucleus is an area of key focus for the field of mechanobiology. In the past two years, there has been expansion of our knowledge of commonly studied pathways, such as YAP/TAZ, FAK/Src, RhoA/ROCK, and Piezo1 signaling, as well as the discovery of new interactions, such as the effect of matrix rigidity of cell mitochondrial function and metabolism, which represent a new and exciting direction for the field as a whole. This review covers the most recent advances in the field of substrate stiffness sensing as well as perspective on future directions.

The Role of the Piezo1 Mechanosensitive Channel in Heart Failure

Mechanotransduction (MT) is inseparable from the pathobiology of heart failure (HF). However, the effects of mechanical forces on HF remain unclear. This review briefly describes how Piezo1 functions in HF-affected cells, including endothelial cells (ECs), cardiac fibroblasts (CFs), cardiomyocytes (CMs), and immune cells. Piezo1 is a mechanosensitive ion channel that has been extensively studied in recent years. Piezo1 responds to different mechanical forces and converts them into intracellular signals. The pathways that modulate the Piezo1 switch have also been briefly described. Experimental drugs that specifically activate Piezo1-like proteins, such as Yoda1, Jedi1, and Jedi2, are available for clinical studies to treat Piezo1-related diseases. The only mechanosensitive ion-channel-specific inhibitor available is GsMTx4, which can turn off Piezo1 by modulating the local membrane tension. Ultrasound waves can modulate Piezo1 switching in vitro with the assistance of microbubbles. This review provides new possible targets for heart failure therapy by exploring the cellular functions of Piezo1 that are involved in the progression of the disease. Modulation of Piezo1 activity may, therefore, effectively delay the progression of heart failure.

Epithelial cells sense local stiffness via Piezo1 mediated cytoskeletal reorganization

Local substrate stiffness is one of the major mechanical inputs for tissue organization during its development and remodeling. It is widely recognized that adherent cells use transmembrane proteins (integrins) at focal adhesions to translate ECM mechanical cues into intracellular bioprocess. Here we show that epithelial cells respond to substrate stiffening primarily via actin cytoskeleton organization, that requires activation of mechanosensitive Piezo1 channels. Piezo1 Knockdown cells eliminated the actin stress fibers that formed on stiff substrates, while it had minimal effect on cell morphology and spreading area. Inhibition of Piezo1 channels with GsMTx4 also significantly reduced stiffness-induced F-actin reorganization, suggesting Piezo1 mediated cation current plays a role. Activation of Piezo1 channels with specific agonist (Yoda1) resulted in thickening of F-actin fibers and enlargement of FAs on stiffer substrates, whereas it did not affect the formation of nascent FAs that facilitate spreading on the soft substrates. These results demonstrate that Piezo1 functions as a force sensor that couples with actin cytoskeleton to distinguish the substrate stiffness and facilitate epithelial adaptive remodeling.

Cell response to mechanical microenvironment cues via Rho signaling: From mechanobiology to mechanomedicine

Mechanical cues in the cell microenvironment such as those from extracellular matrix properties, stretching, compression and shear stress, play a critical role in maintaining homeostasis. Upon sensing mechanical stimuli, cells can translate these external forces into intracellular biochemical signals to regulate their cellular behaviors, but the specific mechanisms of mechanotransduction at the molecular level remain elusive. As a subfamily of the Ras superfamily, Rho GTPases have been recognized as key intracellular mechanotransduction mediators that can regulate multiple cell activities such as proliferation, migration and differentiation as well as biological processes such as cytoskeletal dynamics, metabolism, and organ development. However, the upstream mechanosensors for Rho proteins and downstream effectors that respond to Rho signal activation have not been well illustrated. Moreover, Rho-mediated mechanical signals in previous studies are highly context-dependent. In this review, we systematically summarize the types of mechanical cues in the cell microenvironment and provide recent advances on the roles of the Rho-based mechanotransduction in various cell activities, physiological processes and diseases. Comprehensive insights into the mechanical roles of Rho GTPase partners would open a new paradigm of mechanomedicine for a variety of diseases. STATEMENT OF SIGNIFICANCE: In this review, we highlight the critical role of Rho GTPases as signal mediators to respond to physical cues in microenvironment. This article will add a distinct contribution to this set of knowledge by intensively addressing the relationship between Rho signaling and mechanobiology/mechanotransduction/mechanomedcine. This topic has not been discussed by the journal, nor has it yet been developed by the field. The comprehensive picture that will develop, from molecular mechanisms and engineering methods to disease treatment strategies, represents an important and distinct contribution to the field. We hope that this review would help researchers in various fields, especially clinicians, oncologists and bioengineers, who study Rho signal pathway and mechanobiology/mechanotransduction, understand the critical role of Rho GTPase in mechanotransduction.

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.

Fibrous Matrix Architecture-Dependent Activation of Fibroblasts with a Cancer-Associated Fibroblast-like Phenotype

Cancer-associated fibroblasts (CAFs) are one of the most prevalent cell types within the tumor microenvironment (TME). While several physicochemical cues from the TME, including growth factors, cytokines, and ECM specificity, have been identified as essential factors for CAF activation, the precise mechanism of how the ECM architecture regulates CAF initiation remains elusive. Using a gelatin-based electrospun fiber mesh, we examined the effect of matrix fiber density on CAF activation induced by MCF-7 conditioned media (CM). A less dense (3D) gelatin mesh matrix facilitated better activation of dermal fibroblasts into a CAF-like phenotype in the CM than a highly dense (3D) gelatin mesh matrix. In addition, it was discovered that CAF activation on the less dense (LD) matrix is dependent on the cell size-related AKT/mTOR signaling cascade, accompanied by an increase in intracellular tension within the well-spread fibroblasts.

Quantitative Live-Cell Ca2+ Imaging During Isotropic Cell Stretch

Cell viability of many cell types strongly relies on their ability to adjust to mechanical conditions and alterations. Cellular mechanisms for sensing and responding to mechanical forces and pathophysiological variations in these processes have become an emerging research field in recent years. An important signaling molecule involved in mechanotransduction as in many cellular processes is Ca²⁺. New experimental methods to probe cellular Ca²⁺ signaling live under conditions of mechanical stimulation facilitate new insights into previously overlooked aspects of mechanical regulation of cells.Here, we describe a protocol for using Ca²⁺ imaging in combination with a cell stretching device, the IsoStretcher. Cells grown on elastic membranes can be isotopically stretched in-plane, and their intracellular Ca²⁺ level can be accessed online on the single cell level using fluorescent calcium indicator dyes. We show a protocol for functional screening of mechanosensitive ion channels and related drug screenings using BJ cells, a foreskin fibroblast cell line that strongly reacts to acute mechanical stimulation.

Simultaneous assessment of radial and axial myocyte mechanics by combining atomic force microscopy and carbon fibre techniques

Cardiomyocytes sense and shape their mechanical environment, contributing to its dynamics by their passive and active mechanical properties. While axial forces generated by contracting cardiomyocytes have been amply investigated, the corresponding radial mechanics remain poorly characterized. Our aim is to simultaneously monitor passive and active forces, both axially and radially, in cardiomyocytes freshly isolated from adult mouse ventricles. To do so, we combine a carbon fibre (CF) set-up with a custom-made atomic force microscope (AFM). CF allows us to apply stretch and to record passive and active forces in the axial direction. The AFM, modified for frontal access to fit in CF, is used to characterize radial cell mechanics. We show that stretch increases the radial elastic modulus of cardiomyocytes. We further find that during contraction, cardiomyocytes generate radial forces that are reduced, but not abolished, when cells are forced to contract near isometrically. Radial forces may contribute to ventricular wall thickening during contraction, together with the dynamic re-orientation of cells and sheetlets in the myocardium. This new approach for characterizing cell mechanics allows one to obtain a more detailed picture of the balance of axial and radial mechanics in cardiomyocytes at rest, during stretch, and during contraction. This article is part of the theme issue 'The cardiomyocyte: new revelations on the interplay between architecture and function in growth, health, and disease'.

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.

A positive mechanobiological feedback loop controls bistable switching of cardiac fibroblast phenotype

Cardiac fibrosis is associated with activation of cardiac fibroblasts (CFs), a pathological, phenotypic transition that is widely believed to be irreversible in the late stages of disease development. Sensing of a stiffened mechanical environment through regulation of integrin-based adhesion plaques and activation of the Piezo1 mechanosensitive ion channel is known to factor into this transition. Here, using integrated in vitro and in silico models, we discovered a mutually reinforcing, mechanical positive feedback loop between integrin β1 and Piezo1 activation that forms a bistable switch. The bistable switch is initiated by perturbations in matrix elastic modulus that amplify to trigger downstream signaling involving Ca²⁺ and YAP that, recursively, leads fibroblasts to further stiffen their environment. By simultaneously interfering with the newly identified mechanical positive feedback loop and modulating matrix elastic modulus, we reversed markers of phenotypical transition of CF, suggesting new therapeutic targets for fibrotic disease.

Piezo1 Channel as a Potential Target for Hindering Cardiac Fibrotic Remodeling

Fibrotic tissues share many common features with neoplasms where there is an increased stiffness of the extracellular matrix (ECM). In this review, we present recent discoveries related to the role of the mechanosensitive ion channel Piezo1 in several diseases, especially in regulating tumor progression, and how this can be compared with cardiac mechanobiology. Based on recent findings, Piezo1 could be upregulated in cardiac fibroblasts as a consequence of the mechanical stress and pro-inflammatory stimuli that occurs after myocardial injury, and its increased activity could be responsible for a positive feedback loop that leads to fibrosis progression. The increased Piezo1-mediated calcium flow may play an important role in cytoskeleton reorganization since it induces actin stress fibers formation, a well-known characteristic of fibroblast transdifferentiation into the activated myofibroblast. Moreover, Piezo1 activity stimulates ECM and cytokines production, which in turn promotes the phenoconversion of adjacent fibroblasts into new myofibroblasts, enhancing the invasive character. Thus, by assuming the Piezo1 involvement in the activation of intrinsic fibroblasts, recruitment of new myofibroblasts, and uncontrolled excessive ECM production, a new approach to blocking the fibrotic progression can be predicted. Therefore, targeted therapies against Piezo1 could also be beneficial for cardiac fibrosis.

Benchmarking of Cph1 Mutants and DrBphP for Light-Responsive Phytochrome-Based Hydrogels with Reversibly Adjustable Mechanical Properties

In the rapidly expanding field of molecular optogenetics, the performance of the engineered systems relies on the switching properties of the underlying genetically encoded photoreceptors. In this study, the bacterial phytochromes Cph1 and DrBphP are engineered, recombinantly produced in Escherichia coli, and characterized regarding their switching properties in order to synthesize biohybrid hydrogels with increased light-responsive stiffness modulations. The R472A mutant of the cyanobacterial phytochrome 1 (Cph1) is identified to confer the phytochrome-based hydrogels with an increased dynamic range for the storage modulus but a different light-response for the loss modulus compared to the original Cph1-based hydrogel. Stiffness measurements of human atrial fibroblasts grown on these hydrogels suggest that differences in the loss modulus at comparable changes in the storage modulus affect cell stiffness and thus underline the importance of matrix viscoelasticity on cellular mechanotransduction. The hydrogels presented here are of interest for analyzing how mammalian cells respond to dynamic viscoelastic cues. Moreover, the Cph1-R472A mutant, as well as the benchmarking of the other phytochrome variants, are expected to foster the development and performance of future optogenetic systems.

Global PIEZO1 Gain-of-Function Mutation Causes Cardiac Hypertrophy and Fibrosis in Mice

PIEZO1 is a subunit of mechanically-activated, nonselective cation channels. Gain-of-function PIEZO1 mutations are associated with dehydrated hereditary stomatocytosis (DHS), a type of anaemia, due to abnormal red blood cell function. Here, we hypothesised additional effects on the heart. Consistent with this hypothesis, mice engineered to contain the M2241R mutation in PIEZO1 to mimic a DHS mutation had increased cardiac mass and interventricular septum thickness at 8–12 weeks of age, without altered cardiac contractility. Myocyte size was greater and there was increased expression of genes associated with cardiac hypertrophy (Anp, Acta1 and β-MHC). There was also cardiac fibrosis, increased expression of Col3a1 (a gene associated with fibrosis) and increased responses of isolated cardiac fibroblasts to PIEZO1 agonism. The data suggest detrimental effects of excess PIEZO1 activity on the heart, mediated in part by amplified PIEZO1 function in cardiac fibroblasts.

Atomic Force Microscopy (AFM) Applications in Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is an inherited heart muscle disorder characterized by progressive replacement of cardiomyocytes by fibrofatty tissue, ventricular dilatation, cardiac dysfunction, arrhythmias, and sudden cardiac death. Interest in molecular biomechanics for these disorders is constantly growing. Atomic force microscopy (AFM) is a well-established technic to study the mechanobiology of biological samples under physiological and pathological conditions at the cellular scale. However, a review which described all the different data that can be obtained using the AFM (cell elasticity, adhesion behavior, viscoelasticity, beating force, and frequency) is still missing. In this review, we will discuss several techniques that highlight the potential of AFM to be used as a tool for assessing the biomechanics involved in ACM. Indeed, analysis of genetically mutated cells with AFM reveal abnormalities of the cytoskeleton, cell membrane structures, and defects of contractility. The higher the Young’s modulus, the stiffer the cell, and it is well known that abnormal tissue stiffness is symptomatic of a range of diseases. The cell beating force and frequency provide information during the depolarization and repolarization phases, complementary to cell electrophysiology (calcium imaging, MEA, patch clamp). In addition, original data is also presented to emphasize the unique potential of AFM as a tool to assess fibrosis in cardiac tissue.

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.

A Review on the Design of Hydrogels With Different Stiffness and Their Effects on Tissue Repair

Tissue repair after trauma and infection has always been a difficult problem in regenerative medicine. Hydrogels have become one of the most important scaffolds for tissue engineering due to their biocompatibility, biodegradability and water solubility. Especially, the stiffness of hydrogels is a key factor, which influence the morphology of mesenchymal stem cells (MSCs) and their differentiation. The researches on this point are meaningful to the field of tissue engineering. Herein, this review focus on the design of hydrogels with different stiffness and their effects on the behavior of MSCs. In addition, the effect of hydrogel stiffness on the phenotype of macrophages is introduced, and then the relationship between the phenotype changes of macrophages on inflammatory response and tissue repair is discussed. Finally, the future application of hydrogels with a certain stiffness in regenerative medicine and tissue engineering has been prospected.

Bioprinting of Collagen Type I and II via Aerosol Jet Printing for the Replication of Dense Collagenous Tissues

Collagen has grown increasingly present in bioprinting, however collagen bioprinting has mostly been limited to the extrusion printing of collagen type I to form weak collagen hydrogels. While these weak collagen hydrogels have their applications, synthetic polymers are often required to reinforce gel-laden constructs that aim to replicate dense collagenous tissues found in vivo. In this study, aerosol jet printing (AJP) was used to print and process collagen type I and II into dense constructs with a greater capacity to replicate the dense collagenous ECM found in connective tissues. Collagen type I and II was isolated from animal tissues to form solutions for printing. Collagen type I and II constructs were printed with 576 layers and measured to have average effective elastic moduli of 241.3 ± 94.3 and 196.6 ± 86.0 kPa (±SD), respectively, without any chemical modification. Collagen type II solutions were measured to be less viscous than type I and both collagen type I and II exhibited a drop in viscosity due to AJP. Circular dichroism and SDS-PAGE showed collagen type I to be more vulnerable to structural changes due to the stresses of the aerosol formation step of aerosol jet printing while the collagen type II triple helix was largely unaffected. SEM illustrated that distinct layers remained in the aerosol jet print constructs. The results show that aerosol jet printing should be considered an effective way to process collagen type I and II into stiff dense constructs with suitable mechanical properties for the replication of dense collagenous connective tissues.

Channeling the Force: Piezo1 Mechanotransduction in Cancer Metastasis

Cancer metastasis is one of the leading causes of death worldwide, motivating research into identifying new methods of preventing cancer metastasis. Recently there has been increasing interest in understanding how cancer cells transduce mechanical forces into biochemical signals, as metastasis is a process that consists of a wide range of physical forces. For instance, the circulatory system through which disseminating cancer cells must transit is an environment characterized by variable fluid shear stress due to blood flow. Cancer cells and other cells can transduce physical stimuli into biochemical responses using the mechanosensitive ion channel Piezo1, which is activated by membrane deformations that occur when cells are exposed to physical forces. When active, Piezo1 opens, allowing for calcium flux into the cell. Calcium, as a ubiquitous second-messenger cation, is associated with many signaling pathways involved in cancer metastasis, such as angiogenesis, cell migration, intravasation, and proliferation. In this review, we discuss the roles of Piezo1 in each stage of cancer metastasis in addition to its roles in immune cell activation and cancer cell death.

High-Resolution Bioprinting of Recombinant Human Collagen Type III

The development of commercial collagen inks for extrusion-based bioprinting has increased the amount of research on pure collagen bioprinting, i.e., collagen inks not mixed with gelatin, alginate, or other more common biomaterial inks. New printing techniques have also improved the resolution achievable with pure collagen bioprinting. However, the resultant collagen constructs still appear too weak to replicate dense collagenous tissues, such as the cornea. This work aims to demonstrate the first reported case of bioprinted recombinant collagen films with suitable optical and mechanical properties for corneal tissue engineering. The printing technology used, aerosol jet® printing (AJP), is a high-resolution printing method normally used to deposit conductive inks for electronic printing. In this work, AJP was employed to deposit recombinant human collagen type III (RHCIII) in overlapping continuous lines of 60 µm to form thin layers. Layers were repeated up to 764 times to result in a construct that was considered a few hundred microns thick when swollen. Samples were subsequently neutralised and crosslinked using EDC:NHS crosslinking. Nanoindentation and absorbance measurements were conducted, and the results show that the AJP-deposited RHCIII samples possess suitable mechanical and optical properties for corneal tissue engineering: an average effective elastic modulus of 506 ± 173 kPa and transparency ≥87% at all visible wavelengths. Circular dichroism showed that there was some loss of helicity of the collagen due to aerosolisation. SDS-PAGE and pepsin digestion were used to show that while some collagen is degraded due to aerosolisation, it remains an inaccessible substrate for pepsin cleavage.

Piezo1-Mediated Mechanotransduction Promotes Cardiac Hypertrophy by Impairing Calcium Homeostasis to Activate Calpain/Calcineurin Signaling

[Figure: see text].

Piezo1 Mechanosensitive Ion Channel Mediates Stretch-Induced Nppb Expression in Adult Rat Cardiac Fibroblasts

In response to stretch, cardiac tissue produces natriuretic peptides, which have been suggested to have beneficial effects in heart failure patients. In the present study, we explored the mechanism of stretch-induced brain natriuretic peptide (Nppb) expression in cardiac fibroblasts. Primary adult rat cardiac fibroblasts subjected to 4 h or 24 h of cyclic stretch (10% 1 Hz) showed a 6.6-fold or 3.2-fold (p < 0.05) increased mRNA expression of Nppb, as well as induction of genes related to myofibroblast differentiation. Moreover, BNP protein secretion was upregulated 5.3-fold in stretched cardiac fibroblasts. Recombinant BNP inhibited TGFβ1-induced Acta2 expression. Nppb expression was >20-fold higher in cardiomyocytes than in cardiac fibroblasts, indicating that cardiac fibroblasts were not the main source of Nppb in the healthy heart. Yoda1, an agonist of the Piezo1 mechanosensitive ion channel, increased Nppb expression 2.1-fold (p < 0.05) and significantly induced other extracellular matrix (ECM) remodeling genes. Silencing of Piezo1 reduced the stretch-induced Nppb and Tgfb1 expression in cardiac fibroblasts. In conclusion, our study identifies Piezo1 as mediator of stretch-induced Nppb expression, as well as other remodeling genes, in cardiac fibroblasts.

Heterogeneity and Remodeling of Ion Currents in Cultured Right Atrial Fibroblasts From Patients With Sinus Rhythm or Atrial Fibrillation

Cardiac fibroblasts express multiple voltage-dependent ion channels. Even though fibroblasts do not generate action potentials, they may influence cardiac electrophysiology by electrical coupling via gap junctions with cardiomyocytes, and through fibrosis. Here, we investigate the electrophysiological phenotype of cultured fibroblasts from right atrial appendage tissue of patients with sinus rhythm (SR) or atrial fibrillation (AF). Using the patch-clamp technique in whole-cell mode, we observed steady-state outward currents exhibiting either no rectification or inward and/or outward rectification. The distributions of current patterns between fibroblasts from SR and AF patients were not significantly different. In response to depolarizing voltage pulses, we measured transient outward currents with fast and slow activation kinetics, an outward background current, and an inward current with a potential-dependence resembling that of L-type Ca²⁺ channels. In cell-attached patch-clamp mode, large amplitude, paxilline-sensitive single channel openings were found in ≈65% of SR and ∼38% of AF fibroblasts, suggesting the presence of “big conductance Ca²⁺-activated K⁺ (BK_Ca)” channels. The open probability of BK_Ca was significantly lower in AF than in SR fibroblasts. When cultured in the presence of paxilline, the shape of fibroblasts became wider and less spindle-like. Our data confirm previous findings on cardiac fibroblast electrophysiology and extend them by illustrating differential channel expression in human atrial fibroblasts from SR and AF tissue.

Channelling the Force to Reprogram the Matrix: Mechanosensitive Ion Channels in Cardiac Fibroblasts

Cardiac fibroblasts (CF) play a pivotal role in preserving myocardial function and integrity of the heart tissue after injury, but also contribute to future susceptibility to heart failure. CF sense changes to the cardiac environment through chemical and mechanical cues that trigger changes in cellular function. In recent years, mechanosensitive ion channels have been implicated as key modulators of a range of CF functions that are important to fibrotic cardiac remodelling, including cell proliferation, myofibroblast differentiation, extracellular matrix turnover and paracrine signalling. To date, seven mechanosensitive ion channels are known to be functional in CF: the cation non-selective channels TRPC6, TRPM7, TRPV1, TRPV4 and Piezo1, and the potassium-selective channels TREK-1 and KATP. This review will outline current knowledge of these mechanosensitive ion channels in CF, discuss evidence of the mechanosensitivity of each channel, and detail the role that each channel plays in cardiac remodelling. By better understanding the role of mechanosensitive ion channels in CF, it is hoped that therapies may be developed for reducing pathological cardiac remodelling.