Piezo1 protein induces the apoptosis of human osteoarthritis-derived chondrocytes by activating caspase-12, the signaling marker of ER stress

Characterization of mechanical stress in the occurrence of cortical opacification in age-related cataracts using three-dimensional finite element model of the human lens and RNA-seq

Cataract is the leading cause of blindness across the world. Age-related cataract (ARC) is the most common type of cataract, but its pathogenesis is not fully understood. Using three-dimensional finite element modeling combining experimental biotechnology, our study demonstrates that external forces during accommodation cause mechanical stress predominantly in lens cortex, basically matching the localization of opacities in cortical ARCs. We identified the cellular senescence and upregulation of PIEZO1 mRNA in HLECs under mechanical stretch. This mechano-induced senescence in HLECs might be mediated by PIEZO1-related pathways, portraying a potential biomechanical cause of cortical ARCs. Our study updates the fundamental insight towards cataractogenesis, paving the way for further exploration of ARCs pathogenesis and nonsurgical treatment.

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

Objective

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

Methods

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

Results

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

Conclusion

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

Activation of Piezo1 channels in compressed red blood cells augments platelet-driven contraction of blood clots

BACKGROUND

Piezo1 is a mechanosensitive cationic channel that boosts intracellular [Ca2+]i. Compression of red blood cells (RBCs) during platelet-driven contraction of blood clots may cause the activation of Piezo1.

OBJECTIVES

To establish relationships between Piezo1 activity and blood clot contraction.

METHODS

Effects of a Piezo1 agonist, Yoda1, and antagonist, GsMTx-4, on clot contraction in vitro were studied in human blood containing physiological [Ca2+]. Clot contraction was induced by exogenous thrombin. Activation of Piezo1 was assessed by Ca2+ influx in RBCs and with other functional and morphologic features.

RESULTS

Piezo1 channels in compressed RBCs are activated naturally during blood clot contraction and induce an upsurge in the intracellular [Ca2+]i, followed by phosphatidylserine exposure. Adding the Piezo1 agonist Yoda1 to whole blood increased the extent of clot contraction due to Ca2+-dependent volumetric shrinkage of RBCs and increased platelet contractility due to their hyperactivation by the enhanced generation of endogenous thrombin on activated RBCs. Addition of rivaroxaban, the inhibitor of thrombin formation, or elimination of Ca2+ from the extracellular space abrogated the stimulating effect of Yoda1 on clot contraction. The Piezo1 antagonist, GsMTx-4, caused a decrease in the extent of clot contraction relative to the control both in whole blood and in platelet-rich plasma. Activated Piezo1 in compressed and deformed RBCs amplified the platelet contractility as a positive feedback mechanism during clot contraction.

CONCLUSION

The results obtained demonstrate that the Piezo1 channel expressed on RBCs comprises a mechanochemical modulator of blood clotting that may be considered a potential therapeutic target to correct hemostatic disorders.

The functional effects of Piezo channels in mesenchymal stem cells

Mesenchymal stem cells (MSCs) are widely used in cell therapy, tissue engineering, and regenerative medicine because of their self-renewal, pluripotency, and immunomodulatory properties. The microenvironment in which MSCs are located significantly affects their physiological functions. The microenvironment directly or indirectly affects cell behavior through biophysical, biochemical, or other means. Among them, the mechanical signals provided to MSCs by the microenvironment have a particularly pronounced effect on their physiological functions and can affect osteogenic differentiation, chondrogenic differentiation, and senescence in MSCs. Mechanosensitive ion channels such as Piezo1 and Piezo2 are important in transducing mechanical signals, and these channels are widely distributed in sites such as skin, bladder, kidney, lung, sensory neurons, and dorsal root ganglia. Although there have been numerous studies on Piezo channels in MSCs in recent years, the function of Piezo channels in MSCs is still not well understood, and there has been no summary of their relationship to illustrate which physiological functions of MSCs are affected by Piezo channels and the possible underlying mechanisms. Therefore, based on the members, structures, and functions of Piezo ion channels and the fundamental information of MSCs, this paper focused on summarizing the advances in Piezo channels in MSCs from various tissue sources to provide new ideas for future research and practical applications of Piezo channels and MSCs.

Aberrant mechanical loading induces annulus fibrosus cells apoptosis in intervertebral disc degeneration via mechanosensitive ion channel Piezo1

BACKGROUND

Intervertebral disc degeneration (IVDD) is closely associated with the structural damage in the annulus fibrosus (AF). Aberrant mechanical loading is an important inducement of annulus fibrosus cells (AFCs) apoptosis, which contributes to the AF structural damage and aggravates IVDD, but the underlying mechanism is still unclear. This study aims to investigate the mechanism of a mechanosensitive ion channel protein Piezo1 in aberrant mechanical loading-induced AFCs apoptosis and IVDD.

METHODS

Rats were subjected to lumbar instability surgery to induce the unbalanced dynamic and static forces to establish the lumbar instability model. MRI and histological staining were used to evaluate the IVDD degree. A cyclic mechanical stretch (CMS)-stimulated AFCs apoptosis model was established by a Flexcell system in vitro. Tunel staining, mitochondrial membrane potential (MMP) detection, and flow cytometry were used to evaluate the apoptosis level. The activation of Piezo1 was detected using western blot and calcium fluorescent probes. Chemical activator Yoda1, chemical inhibitor GSMTx4, and a lentiviral shRNA-Piezo1 system (Lv-Piezo1) were utilized to regulate the function of Piezo1. High-throughput RNA sequencing (RNA-seq) was used to explore the mechanism of Piezo1-induced AFCs apoptosis. The Calpain activity and the activation of Calpain2/Bax/Caspase3 axis were evaluated by the Calpain activity kit and western blot with the siRNA-mediated Calapin1 or Calpain2 knockdown. Intradiscal administration of Lv-Piezo1 was utilized to evaluate the therapeutic effect of Piezo1 silencing in IVDD rats.

RESULTS

Lumbar instability surgery promoted the expression of Piezo1 in AFCs and stimulated IVDD in rats 4 weeks after surgery. CMS elicited distinct apoptosis of AFCs, with enhanced Piezo1 activation. Yoda1 further promoted CMS-induced apoptosis of AFCs, while GSMTx4 and Lv-Piezo1 exhibited opposite effects. RNA-seq showed that knocking down Piezo1 inhibited the calcium signaling pathway. CMS enhanced Calpain activity and elevated the expression of BAX and cleaved-Caspase3. Calpain2, but not Calpain1 knockdown, inhibited the expression of BAX and cleaved-Caspase3 and alleviated AFCs apoptosis. Lv-Piezo1 significantly alleviated the progress of IVDD in rats after lumbar instability surgery.

CONCLUSIONS

Aberrant mechanical loading induces AFCs apoptosis to promote IVDD by activating Piezo1 and downstream Calpain2/BAX/Caspase3 pathway. Piezo1 is expected to be a potential therapeutic target in treating IVDD.

The Role of the Piezo1 Mechanosensitive Channel in the Musculoskeletal System

Since the recent discovery of the mechanosensitive Piezo1 channels, many studies have addressed the role of the channel in various physiological or even pathological processes of different organs. Although the number of studies on their effects on the musculoskeletal system is constantly increasing, we are still far from a precise understanding. In this review, the knowledge available so far regarding the musculoskeletal system is summarized, reviewing the results achieved in the field of skeletal muscles, bones, joints and cartilage, tendons and ligaments, as well as intervertebral discs.

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].

Mechanical stretching induces fibroblasts apoptosis through activating Piezo1 and then destroying actin cytoskeleton

The anatomical positions of pelvic floor organs are maintained by ligaments and muscles. Stress urinary incontinence (SUI) occurs when the pelvic floor tissues are repeatedly stimulated by excessive mechanical tension that exceeds the bearing capacity of ligaments or muscles. Besides, cells respond mechanically to mechanical stimulation by reconstituting the Piezo1 and cytoskeletal system. The aim of this study is to determine how Piezo1 and actin cytoskeleton are involved in the mechanized stretch (MS) induced apoptosis of human anterior vaginal wall fibroblasts (hAVWFs) and the mechanism. A four-point bending device was used to provide mechanical stretching to establish a cellular mechanical damage model. The apoptosis of hAVWFs cells in non-SUI patients was significantly increased by MS, which exhibited apoptosis rates comparable to those of SUI patients. Based on these findings, Piezo1 connects the actin cytoskeleton to the apoptosis of hAVWFs cells, providing an idea for the clinical diagnosis and treatment of SUI. However, the disassembly of the actin cytoskeleton suppressed the protective effect of Piezo1 silencing on MS. Based on these findings, Piezo1 connects the actin cytoskeleton to apoptosis of hAVWFs, providing new insight for the clinical diagnosis and treatment of SUI.

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.

Effects of ACE2/GHRL Axis on Proliferation, Apoptosis and Inflammatory Factor Levels of Synovial Cells in Osteoarthritis

We aimed to assess the effects of ACE2/GHRL on the proliferation and apoptosis of synovial cells in osteoarthritis (OA). 20 healthy mice were randomly assigned into blank group and experimental group (ACE2 was knocked down). In addition, 30 mice were subdivided into 3 group (n = 10) and treated with saline solution, GHRL (auxin), and GHRL+CHPAA (Auxin inhibitor) followed by analysis of synovial cell proliferation, apoptosis and inflammatory factor level by Western blot analysis, MTT and flow cytometry. Experimental group exhibited decreased cell proliferation, increased apoptosis upon silencing of ACE2 (p < 0.05) along with elevated expressions of Caspase3 and Bax protein and decreased Bcl-2, inflammatory factors and the GHRL level (p < 0.05). Treatment with GHRL increased cell proliferation cells and decreased apoptosis. Meanwhile, Bcl-2 expression and IL-1β, IL-6 and IL-8 levels in GHRL group were significantly lower than other two groups whilst Caspase-3 and Bax level was significantly higher (p < 0.05). After CHPAA treatment, ACE2 expression in CHPAA group was dramatically declined (p < 0.01). In conclusion, ACE2/GHRL might alleviate OA progression through regulation of cell proliferation, apoptosis and inflammation of synoviocytes, providing insight into a therapeutic target for treating OA.

Laser Reconstruction of Spinal Discs Experiments and Clinic

Degenerative disease of the intervertebral discs (DDD) is currently a serious problem facing the world community. The surgical methods and conservative therapy used today, unfortunately, do not stop the pathological process, but serve as a palliative method that temporarily relieves pain and improves the patient’s quality of life. Therefore, at present, there is an active search for new methods of treating DDD. Among new techniques of treatment, biological methods, and minimally invasive surgery, including the use of laser radiation, which, depending on the laser parameters, can cause ablative or modifying effects on the disc tissue, have acquired considerable interest. Here, we analyze a new approach to solving the DDD problem: laser tissue modification. This review of publications is focused on the studies of the physicochemical foundations and clinical applications of a new method of laser reconstruction of intervertebral discs. Thermomechanical action of laser radiation modifies tissue and leads to its regeneration as well as to a long-term restoration of disc functions, elimination of pain and the return of patients to normal life.

Mechanosensory and mechanotransductive processes mediated by ion channels in articular chondrocytes: Potential therapeutic targets for osteoarthritis

Articular cartilage consists of an extracellular matrix including many proteins as well as embedded chondrocytes. Articular cartilage formation and function are influenced by mechanical forces. Hind limb unloading or simulated microgravity causes articular cartilage loss, suggesting the importance of the healthy mechanical environment in articular cartilage homeostasis and implying a significant role of appropriate mechanical stimulation in articular cartilage degeneration. Mechanosensitive ion channels participate in regulating the metabolism of articular chondrocytes, including matrix protein production and extracellular matrix synthesis. Mechanical stimuli, including fluid shear stress, stretch, compression and cell swelling and decreased mechanical conditions (such as simulated microgravity) can alter the membrane potential and regulate the metabolism of articular chondrocytes via transmembrane ion channel-induced ionic fluxes. This process includes Ca2+ influx and the resulting mobilization of Ca2+ that is due to massive released Ca2+ from stores, intracellular cation efflux and extracellular cation influx. This review brings together published information on mechanosensitive ion channels, such as stretch-activated channels (SACs), voltage-gated Ca2+ channels (VGCCs), large conductance Ca2+-activated K+ channels (BKCa channels), Ca2+-activated K+ channels (SKCa channels), voltage-activated H+ channels (VAHCs), acid sensing ion channels (ASICs), transient receptor potential (TRP) family channels, and piezo1/2 channels. Data based on epithelial sodium channels (ENaCs), purinergic receptors and N-methyl-d-aspartate (NMDA) receptors are also included. These channels mediate mechanoelectrical physiological processes essential for converting physical force signals into biological signals. The primary channel-mediated effects and signaling pathways regulated by these mechanosensitive ion channels can influence the progression of osteoarthritis during the mechanosensory and mechanoadaptive process of articular chondrocytes.

Roles of mechanosensitive channel Piezo1/2 proteins in skeleton and other tissues

Mechanotransduction is a fundamental ability that allows living organisms to receive and respond to physical signals from both the external and internal environments. The mechanotransduction process requires a range of special proteins termed mechanotransducers to convert mechanical forces into biochemical signals in cells. The Piezo proteins are mechanically activated nonselective cation channels and the largest plasma membrane ion channels reported thus far. The regulation of two family members, Piezo1 and Piezo2, has been reported to have essential functions in mechanosensation and transduction in different organs and tissues. Recently, the predominant contributions of the Piezo family were reported to occur in the skeletal system, especially in bone development and mechano-stimulated bone homeostasis. Here we review current studies focused on the tissue-specific functions of Piezo1 and Piezo2 in various backgrounds with special highlights on their importance in regulating skeletal cell mechanotransduction. In this review, we emphasize the diverse functions of Piezo1 and Piezo2 and related signaling pathways in osteoblast lineage cells and chondrocytes. We also summarize our current understanding of Piezo channel structures and the key findings about PIEZO gene mutations in human diseases.

G protein coupled estrogen receptor attenuates mechanical stress-mediated apoptosis of chondrocyte in osteoarthritis via suppression of Piezo1

BACKGROUND

Apoptosis of chondrocyte is involved in osteoarthritis (OA) pathogenesis, and mechanical stress plays a key role in this process by activation of Piezo1. However, the negative regulation of signal conduction mediated by mechanical stress is still unclear. Here, we elucidate that the critical role of G protein coupled estrogen receptor (GPER) in the regulation of mechanical stress-mediated signal transduction and chondrocyte apoptosis.

METHODS

The gene expression profile was detected by gene chip upon silencing Piezo1. The expression of GPER in cartilage tissue taken from the clinical patients was detected by RT-PCR and Western blot as well as immunohistochemistry, and the correlation between GPER expression and OA was also investigated. The chondrocytes exposed to mechanical stress were treated with estrogen, G-1, G15, GPER-siRNA and YAP (Yes-associated protein)-siRNA. The cell viability of chondrocytes was measured. The expression of polymerized actin and Piezo1 as well as the subcellular localization of YAP was observed under laser confocal microscope. Western blot confirmed the changes of YAP/ Rho GTPase activating protein 29 (ARHGAP29) /RhoA/LIMK /Cofilin pathway. The knee specimens of osteoarthritis model were stained with safranin and green. OARSI score was used to evaluate the joint lesions. The expressions of GPER and YAP were detected by immunochemistry.

RESULTS

Expression profiles of Piezo1- silenced chondrocytes showed that GPER expression was significantly upregulated. Moreover, GPER was negatively correlated with cartilage degeneration during OA pathogenesis. In addition, we uncovered that GPER directly targeted YAP and broadly restrained mechanical stress-triggered actin polymerization. Mechanism studies revealed that GPER inhibited mechanical stress-mediated RhoA/LIMK/cofilin pathway, as well as the actin polymerization, by promoting expression of YAP and ARHGAP29, and the YAP nuclear localization, eventually causing the inhibition of Piezo1. YAP was obviously decreased in degenerated cartilage. Silencing YAP caused significantly increased actin polymerization and activation of Piezo1, and an increase of chondrocyte apoptosis. In addition, intra-articular injection of G-1 to OA rat effectively attenuated cartilage degeneration.

CONCLUSION

We propose a novel regulatory mechanism underlying mechanical stress-mediated apoptosis of chondrocyte and elucidate the potential application value of GPER as therapy targets for OA.

Grape seed proanthocyanidin extract ameliorates cisplatin-induced testicular apoptosis via PI3K/Akt/mTOR and endoplasmic reticulum stress pathways in rats

Testicular toxicity is an adverse reaction of the effective chemotherapy drug cisplatin (CIS). Our previous study found that grape seed proanthocyanidin extract (GSPE) had a protective effect on CIS-induced testicular toxicity. However, the protective mechanism of GSPE against CIS-induced testicular toxicity remains unknown. In this study, we aimed to investigate whether GSPE can reduce CIS-induced testicular toxicity and its potential mechanism in rats. The results showed that GSPE ameliorated CIS-induced the apoptosis of testicular cells and inhibited the protein levels of Bad, Cyt c, caspase-9, caspase-3, caspase-12, GRP78, CHOP, IRE1α, p-IRE1α, XBP-1S, PERK, p-PERK, eIF2α, and p-eIF2α. Besides, GSPE reversed the downregulation of PI3K, p-PI3K, Akt, p-Akt, mTOR, and p-mTOR protein expression induced by CIS. These results indicated that GSPE can improve CIS-induced testicular cells apoptosis via activating PI3K/Akt/mTOR and inhibiting Bad/Cyt c/caspase-9/caspase-3 pathways. And GSPE relieved endoplasmic reticulum stress-mediated apoptosis via inhibiting PREK/eIF2α and IRE1α/XBP-1S/caspase-12 pathways. In conclusion, the evidence suggested that GSPE can act as a protective agent against testicular toxicity induced by CIS. PRACTICAL APPLICATIONS: Testicular toxicity was a well-known adverse effect of cisplatin (CIS) in cancer treatment. Grape seed proanthocyanidin extract (GSPE) has been reported to serve as one of the most therapeutic potentials agents. In present study, we explored the regulatory effects of GSPE on the apoptosis induced by CIS, which involved testicular apoptosis mechanisms in rats. Our results indicated that CIS caused testicular toxicity via PI3K/AKT/mTOR and ERS mediated apoptosis pathway in rats. This toxicity was attenuated by GSPE treatment via activated PI3K/Akt/mTOR pathway, and inhibiting Bad/CytC/caspase-9/caspase-3 as well as PREK/eIF2α, IRE1α/XBP-1S/caspase-12 pathways. Our findings suggest that GSPE may be a novel protective agent against testicular toxicity induced by CIS.

Piezo Channels: Awesome Mechanosensitive Structures in Cellular Mechanotransduction and Their Role in Bone

Piezo channels are mechanosensitive ion channels located in the cell membrane and function as key cellular mechanotransducers for converting mechanical stimuli into electrochemical signals. Emerged as key molecular detectors of mechanical forces, Piezo channels' functions in bone have attracted more and more attention. Here, we summarize the current knowledge of Piezo channels and review the research advances of Piezo channels' function in bone by highlighting Piezo1's role in bone cells, including osteocyte, bone marrow mesenchymal stem cell (BM-MSC), osteoblast, osteoclast, and chondrocyte. Moreover, the role of Piezo channels in bone diseases is summarized.

Piezo-type mechanosensitive ion channel component 1 (Piezo1) in human cancer

Piezo-type mechanosensitive ion channel component 1 (Piezo1) is a mechanosensitive ion channel protein that is evolutionarily conserved and multifunctional. It plays an important role as an oncogenic mediator in several malignant tumors. It mediates the proliferation, migration, and invasion of a variety of cancer cells through various mechanisms. Multiple studies have shown that the expression of Piezo1 is related to the clinical characteristics of senescence and cancer patients, making Piezo1 useful as a new biomarker for the diagnosis and prognosis of a variety of human cancers. Manipulating the expression or function of Piezo1 is a potential therapeutic strategy for different diseases. Piezo1 may be a promising tumor biomarker and therapeutic target. Here we review the biological function, mechanism of action, and potential clinical significance of Piezo1 in oncogenesis and progression.

Mechanosensitive Ion Channel Piezo1 Activated by Matrix Stiffness Regulates Oxidative Stress-Induced Senescence and Apoptosis in Human Intervertebral Disc Degeneration

Mechanical stimulation plays a crucial part in the development of intervertebral disc degeneration (IDD). Extracellular matrix (ECM) stiffness, which is a crucial mechanical microenvironment of the nucleus pulposus (NP) tissue, contributes to the pathogenesis of IDD. The mechanosensitive ion channel Piezo1 mediates mechanical transduction. This study purposed to investigate the function of Piezo1 in human NP cells under ECM stiffness. The expression of Piezo1 and the ECM elasticity modulus increased in degenerative NP tissues. Stiff ECM activated the Piezo1 channel and increased intracellular Ca2+ levels. Moreover, the activation of Piezo1 increased intracellular reactive oxygen species (ROS) levels and the expression of GRP78 and CHOP, which contribute to oxidative stress and endoplasmic reticulum (ER) stress. Furthermore, stiff ECM aggravated oxidative stress-induced senescence and apoptosis in human NP cells. Piezo1 inhibition alleviated oxidative stress-induced senescence and apoptosis, caused by the increase in ECM stiffness. Finally, Piezo1 silencing ameliorated IDD in an in vivo rat model and decreased the elasticity modulus of rat NP tissues. In conclusion, we identified the mechanosensitive ion channel Piezo1 in human NP cells as a mechanical transduction mediator for stiff ECM stimulation. Our results provide novel insights into the mechanism of mechanical transduction in NP cells, with potential for treating IDD.

Bioinformatics analysis of miRNA and mRNA expression profiles to reveal the key miRNAs and genes in osteoarthritis

Background

Osteoarthritis (OA) is a chronic degenerative joint disease and the most frequent type of arthritis. This study aimed to identify the key miRNAs and genes associated with OA progression.

Methods

The GSE105027 (microRNA [miRNA/miR] expression profile; 12 OA samples and 12 normal samples) and GSE48556 (messenger RNA [mRNA] expression profile; 106 OA samples and 33 normal samples) datasets were selected from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) and miRNAs (DEMs) were analyzed using the limma and ROCR packages in R, respectively. The target genes that negatively correlated with the DEMs were predicted, followed by functional enrichment analysis and construction of the miRNA-gene and miRNA-transcription factor (TF)-gene regulatory networks. Additionally, key miRNAs and genes were screened, and their expression levels were verified by real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR).

Results

A total of 1696 DEGs (739 upregulated and 957 downregulated) and 108 DEMs (56 upregulated and 52 downregulated) were identified in the OA samples. Furthermore, 56 target genes that negatively correlated with the DEMs were predicted and found to be enriched in three functional terms (e.g., positive regulation of intracellular protein transport) and three pathways (e.g., human cytomegalovirus infection). In addition, three key miRNAs (miR-98-5p, miR-7-5p, and miR-182-5p) and six key genes (murine double minute 2, MDM2; glycogen synthase kinase 3-beta, GSK3B; transmembrane P24-trafficking protein 10, TMED10; DDB1 and CUL4-associated factor 12, DCAF12; caspase 3, CASP3; and ring finger protein 44, RNF44) were screened, among which the miR-7-5p → TMED10/DCAF12, miR-98-5p → CASP3/RNF44, and miR-182-5p → GSK3B pairs were observed in the regulatory network. Moreover, the expression levels of TMED10, miR-7-5p, CASP3, miR-98-5p, GSK3B, and miR-182-5p showed a negative correlation with qRT-PCR verification.

Conclusion

MiR-98-5p, miR-7-5p, miR-182-5p, MDM2, GSK3B, TMED10, DCAF12, CASP3, and RNF44 may play critical roles in OA progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-021-02201-2.

Inhibitory Effects of Isobavachalcone on Tau Protein Aggregation, Tau Phosphorylation, and Oligomeric Tau-Induced Apoptosis

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases without any effective medicine treatments. The neurofibrillary tangles containing hyperphosphorylated tau protein are one important pathological characteristic. Thus, one practicable strategy for AD drug design is to discover compounds that could inhibit tau protein aggregation and/or phosphorylation. In this study, isobavachalcone, a natural plant-derived compound, has been shown to inhibit tau protein aggregation and disaggregate tau fibrils in vitro by directly interacting with tau protein at amino acids I278, V309, etc. It is able to reduce tau phosphorylation at four disease-related sites in vivo by regulating the critical kinase and protein phosphatase, GSK3β and PP2A. The compound also exhibits protection against tau oligomers-induced apoptosis through the mitochondria and ER mediated apoptotic pathways. In summary, isobavachalcone is a promising candidate for further evaluation as a potential preventive and therapeutic medicine for AD.

Role of mitochondria in mediating chondrocyte response to mechanical stimuli

As the most common form of arthritis, osteoarthritis (OA) has become a major cause of severe joint pain, physical disability, and quality of life impairment in the affected population. To date, precise pathogenesis of OA has not been fully clarified, which leads to significant obstacles in developing efficacious treatments such as failures in finding disease-modifying OA drugs (DMOADs) in the last decades. Given that diarthrodial joints primarily display the weight-bearing and movement-supporting function, it is not surprising that mechanical stress represents one of the major risk factors for OA. However, the inner connection between mechanical stress and OA onset/progression has yet to be explored. Mitochondrion, a widespread organelle involved in complex biological regulation processes such as adenosine triphosphate (ATP) synthesis and cellular metabolism, is believed to have a controlling role in the survival and function implement of chondrocytes, the singular cell type within cartilage. Mitochondrial dysfunction has also been observed in osteoarthritic chondrocytes. In this review, we systemically summarize mitochondrial alterations in chondrocytes during OA progression and discuss our recent progress in understanding the potential role of mitochondria in mediating mechanical stress-associated osteoarthritic alterations of chondrocytes. In particular, we propose the potential signaling pathways that may regulate this process, which provide new views and therapeutic targets for the prevention and treatment of mechanical stress-associated OA.

Piezo1 activates the NLRP3 inflammasome in nucleus pulposus cell-mediated by Ca2+/NF-κB pathway

Studying and understanding the mechanism of inflammation in nucleus pulposus is the key to understand and prevent intervertebral disc degeneration. We propose a model of mechanical sensitive ion channel Piezo1 mediated inflammation of nucleus pulposus cells. Piezo1 can up-regulate the level of interleukin-1β (IL-1β) in nucleus pulposus cells once it is activated. It is suggested that Piezo1 may mediate inflammation by activating Nod-like receptor protein 3 (NLRP3) inflammasome to accelerate the production and maturation of IL-1β. The primary objective of this study was to explore whether Piezo1 activates NLRP3 inflammasome in nucleus pulposus cells. Piezo1 sensitization was induced by mechanical stretch following which we analyzed the priming and assembly of NLRP3 inflammasome and also studied if the downstream Ca²⁺/NF-κB pathway mediated this activation in nucleus pulposus cells. The expression of Piezo1 and NLRP3 inflammasome increased in a time-dependent manner upon mechanical stretch. Piezo1 activation promoted NLRP3 inflammasome assembly, which was demonstrated by the upregulation of caspase-1 activation and IL-1β production. Transfection of Piezo1-siRNA reversed this process. The inhibition of Ca²⁺/NF-κB pathway reduced Piezo1-dependent activation of NLRP3 inflammasome. Thus, we propose that activation of NLRP3 inflammasome in nucleus pulposus cells mediated by Piezo1 through the Ca²⁺/NF-κB pathway is a novel pathogenesis for the progress of intervertebral disc degeneration. As per our knowledge this is the first study which has provided evidence linking Piezo1-mediated inflammation in nucleus pulposus cells with the production of NLRP3 inflammasome.

Ablation of PKM2 ameliorated ER stress-induced apoptosis and associated inflammation response in IL-1β-treated chondrocytes via blocking Rspo2-mediated Wnt/β-catenin signaling

Endoplasmic reticulum (ER) stress and the related apoptosis and inflammation damage play key roles in osteoarthritis development. The aim of the present work was to investigate the exact role and potential underlying mechanism of pyruvate kinase M2 (PKM2) in rat chondrocytes exposed to interleukin-Iβ (IL-1β). We observed that IL-1β stimulation resulted in an apparent enhancement in PKM2 expression. Additionally, loss of PKM2 evidently ascended cell viability in response to IL-1β exposure. Simultaneously, elimination of PKM2 manifestly repressed IL-1β-stimulated chondrocyte apoptosis, concomitant with attenuated in the proapoptotic protein markers Bax and cleaved caspase-3, and elevated the antiapoptotic protein Bcl-2. In the meanwhile, knockdown of PKM2 ameliorated ER stress in IL-1β-treated chondrocytes, as evidenced by reduced expression of the ER stress-associated proteins GRP78, CHOP, and cleaved caspase-12. Furthermore, PKM2 silencing protected chondrocytes against IL-1β-triggered inflammatory response, as reflected by the downregulated release of proinflammatory mediators, including tumor necrosis factor-α, IL-6, inducible nitric oxide synthase, cyclooxygenase-2, and prostaglandin E2, as well as decreased nitric oxide generation. More important, abrogating PKM2 expression caused a marked decline in Rspo2 expression, and subsequently blocked Wnt/β-catenin signaling. Mechanistically, the Wnt/β-catenin signaling activator Licl effectively impeded the beneficial effects of PKM2 ablation on IL-1β-stimulated apoptosis and inflammatory response. These findings collectively implicated that PKM2 inhibition protected against ER stress-mediated cell apoptosis and inflammatory injury in rat chondrocytes stimulated with IL-1β by inactivating Rspo2-mediated Wnt/β-catenin pathway, and may represented a novel therapeutic target for osteoarthritis.

The PERK Pathway Plays a Neuroprotective Role During the Early Phase of Secondary Brain Injury Induced by Experimental Intracerebral Hemorrhage

The protein kinase RNA-like endoplasmic reticulum kinase (PERK) pathway, which is a branch of the unfolded protein response, participates in a range of pathophysiological processes of neurological diseases. However, few studies have investigated the role of the PERK in intracerebral hemorrhage (ICH). The present study evaluated the role of the PERK pathway during the early phase of ICH-induced secondary brain injury (SBI) and its potential mechanisms. An autologous whole blood ICH model was established in rats, and cultured primary cortical neurons were treated with oxyhemoglobin to mimic ICH in vitro. We found that levels of phosphorylated alpha subunit of eukaryotic translation initiation factor 2 (p-eIF2α) and activating transcription factor 4 (ATF4) increased significantly and peaked at 12 h during the early phase of the ICH. To further elucidate the role of the PERK pathway, we assessed the effects of the PERK inhibitor, GSK2606414, and the eIF2α dephosphorylation antagonist, salubrinal, at 12 h after ICH both in vivo and in vitro. Inhibition of PERK with GSK2606414 suppressed the protein levels of p-eIF2α and ATF4, resulting in increase of transcriptional activator CCAAT/enhancer-binding protein homologous protein (CHOP) and caspase-12, which promoted apoptosis and reduced neuronal survival. Treatment with salubrinal yielded opposite results, which suggested that activation of the PERK pathway could promote neuronal survival and reduce apoptosis. In conclusion, the present study has demonstrated the neuroprotective effects of the PERK pathway during the early phase of ICH-induced SBI. These findings highlight the potential value of PERK pathway as a therapeutic target for ICH.

Excessive mechanical stress induces chondrocyte apoptosis through TRPV4 in an anterior cruciate ligament-transected rat osteoarthritis model

AIMS

Chondrocyte apoptosis is the most common pathological feature of cartilage in osteoarthritis (OA). Excessive mechanical stress can induce chondrocyte apoptosis and destroy cartilage tissue. Transient receptor potential channel vanilloid 4 (TRPV4) is a mechanosensitive ion channel that mediates chondrocyte response to mechanical stress. Here, we investigated the potential role of TRPV4 in chondrocyte apoptosis induced by excessive mechanical stress.

MAIN METHODS

Using a rat OA anterior cruciate-ligament transection (ALCT) model, we detected immunolocalization of calmodulin protein and mRNA and protein levels of TRPV4, calmodulin, and cleaved caspase-8 in articular cartilage. Primary chondrocytes were isolated and cultured in vitro, and Fluo-4AM staining was used to assess intracellular Ca²⁺ levels in order to evaluate TRPV4-mediated Ca²⁺ influx. Flow cytometry and western blot were performed to detect apoptosis and apoptosis-related protein levels in chondrocytes, respectively.

KEY FINDINGS

TRPV4 was upregulated in ALCT-induced OA articular cartilage, and we found that administration of a TRPV4 inhibitor attenuated cartilage degeneration. Additionally, TRPV4 specifically mediated extracellular Ca²⁺ influx, leading to chondrocyte apoptosis in vitro, which was inhibited by transfection of TRPV4 small-interfering RNA or administration of a TRPV4 inhibitor. Moreover, increased Ca²⁺ influx triggered apoptosis by upregulating FAS-associated protein with death domain and cleaved caspase-3, -6, -7, and -8 levels, with these effects abolished by TRPV4 knockdown or TRPV4 inhibition.

SIGNIFICANCE

These results indicated that TRPV4 was upregulated in OA articular cartilage, and that excessive mechanical stress might induce chondrocyte apoptosis via TRPV4-mediated Ca²⁺ influx, suggesting TRPV4 as a potential drug target in OA.

Taurine alleviates endoplasmic reticulum stress in the chondrocytes from patients with osteoarthritis

Osteoarthritis (OA), characterized by pain and stiffness, swelling, deformity and dysfunction of joints, affects large numbers of population. The purpose of this study was to discover the effects of taurine in human OA chondrocytes and explore the underlying mechanisms. 46 patients with different grades of OA were recruited. Of these patients, 24 underwent total knee replacement and cartilages were harvested. The mRNA expressions of type II collagen (Collagen II) and endoplasmic reticulum (ER) stress markers (GRP78, GADD153 and Caspase-12) in cartilages were quantified by qRT-PCR. Cell viability and apoptosis of patient-derived chondrocytes were assessed by the CCK-8 assay and flow cytometry assay, respectively. Meanwhile, protein levels of Collagen II and ER stress markers both in cartilages and chondrocytes were evaluated by Western blot. The mRNA and protein levels of Collagen II decreased as OA progressed, while the expressions of ER stress markers increased dramatically. H₂O₂ induced ER stress in chondrocytes, as shown by the significant increase in the expression of ER stress markers, inhibited chondrocyte viability and Collagen II synthesis, promoted apoptosis. However, taurine treatment inhibited these above phenomena. These results indicated that taurine exhibited anti-OA effect by alleviating H₂O₂ induced ER stress and subsequently inhibiting chondrocyte apoptosis.

Study on the mechanism of excessive apoptosis of nucleus pulposus cells induced by shRNA-Piezo1 under abnormal mechanical stretch stress

OBJECTIVE

The aim of the study was to explore the mechanism of excessive apoptosis of nucleus pulposus cells induced by short hairpin RNA (shRNA) Piezo type mechanosensitive ion channel component 1 (Piezo1) under abnormal mechanical stretch stress.

METHODS

In vitro mechanical stretch stress model of nucleus pulposus cells in vitro was established, in which the expression of Piezo1 was interfered by transfection of shRNA-Piezo1 interfering vector. Both messenger RNA and protein level of Piezo1 were measured by reverse-transcription polymerase chain reaction and Western blot analysis, respectively. Cytoplasmic Ca²⁺ was detected by Fluo3-AM kit, and changes of mitochondrial membrane potential in cells were detected using Cell Meter Assay kit. Finally, the apoptosis was evaluated with annexin V-fluorescein isothiocyanate kit.

RESULTS

The highest transfection efficiency of lentivirus titer was 1 × 10 TU/mL and the nucleus pulposus cells were transfected with plural multiplicity of infection = 50. Homo-3201 sequence exhibited the most effective silencing effect and was used in subsequent experiments as the default sequence of shRNA-Piezo1. The calcium content in the cytoplasm of the tension stress group increased significantly compared with that in the blank control group ( q = 3.773; P < 0.05). The level of cytosolic calcium in shRNA-interference group was significantly lower than that in stretch stress group ( q = 5.159; P < 0.05). Stretch stress treatment resulted in an elevated ratio of mitochondrial membrane potential turnover as opposed to blank control group ( q = 4.332; P < 0.05), while shRNA-interference group showed smaller ratio of mitochondrial membrane potential turnover than that in stretch stress group ( q = 4.974; P < 0.05). Similar results were also observed in apoptosis rate analysis ( q = 3.175; P < 0.05).

CONCLUSION

ShRNA-Piezo1 can protect cells by reducing the level of intracellular Ca²⁺ and the change of mitochondrial membrane potential.

Fasudil inhibits actin polymerization and collagen synthesis and induces apoptosis in human urethral scar fibroblasts via the Rho/ROCK pathway

Purpose

To examine the effects and mechanism of action of fasudil on cytoskeletal polymerization, collagen synthesis, and apoptosis in fibroblasts derived from human urethral scar tissue.

Materials and methods

Fibroblasts treated with or without transforming growth factor β1 (TGF-β1, 10 ng/mL) were incubated with fasudil (12.5, 25, 50 μmol/L) for 24 hours. Quantitative real-time polymerase chain reaction and Western blotting were used to determine the expression of Arp2, Arp3, WASP, and WAVE2. Collagen I and III protein levels were also evaluated by Western blotting. The filamentous actin cytoskeleton was examined by immunofluorescence and epifluorescence microscopy. An Annexin V-FITC/PI staining assay was used to investigate apoptosis.

Results

TGF-β1-dependent induction of actin polymerization and collagen synthesis and promotion of apoptosis were dose dependent. When compared with untreated controls, fasudil significantly decreased the expression of Arp2, Arp3, WASP, WAVE2, Collagen I, and Collagen III in cells treated with or without TGF-β1. Fasudil also promoted apoptosis in cells, irrespective of TGF-β1 treatment.

Conclusion

Irrespective of TGF-β1 activation status, fasudil suppressed actin polymerization and collagen synthesis and induced apoptosis in human urethral scar fibroblasts via the Rho/ROCK signaling pathway.

PIEZO1 Channel Is a Potential Regulator of Synovial Sarcoma Cell-Viability

Detection of mechanical stress is essential for diverse biological functions including touch, audition, and maintenance of vascular myogenic tone. PIEZO1, a mechano-sensing cation channel, is widely expressed in neuronal and non-neuronal cells and is expected to be involved in important biological functions. Here, we examined the possibility that PIEZO1 is involved in the regulation of synovial sarcoma cell-viability. Application of a PIEZO1 agonist Yoda1 effectively induced Ca²⁺ response and cation channel currents in PIEZO1-expressing HEK (HEK-Piezo1) cells and synovial sarcoma SW982 (SW982) cells. Mechanical stress, as well as Yoda1, induced the activity of an identical channel of conductance with 21.6 pS in HEK-Piezo1 cells. In contrast, Yoda1 up to 10 μM had no effects on membrane currents in HEK cells without transfecting PIEZO1. A knockdown of PIEZO1 with siRNA in SW982 cells abolished Yoda1-induced Ca²⁺ response and significantly reduced cell cell-viability. Because PIEZO1 is highly expressed in SW982 cells and its knockdown affects cell-viability, this gene is a potential target against synovial sarcoma.

Mechanoelectrical transduction in chondrocytes

Cartilage tissue lines the joints of mammals, helping to lubricate joint movement and distribute mechanical loads. This tissue is comprised of isolated cells known as chondrocytes which are embedded in an extracellular matrix. Chondrocytes produce and maintain the cartilage by sensing and responding to changing mechanical loads. Mechanosensitive ion channels have been implicated in chondrocyte mechanotransduction and recent studies have shown that both PIEZO1 and TRPV4 can be activated by mechanical stimuli in these cells. The 2 channels mediate separate but overlapping mechanoelectrical transduction pathways, PIEZO1 in response to stretch and substrate deflections and TRPV4 in response to substrate deflections alone. These distinct pathways of mechanoelectrical transduction suggest a mechanism by which chondrocytes can distinguish between different stimuli that arise in their complex mechanical environment.

The Function of the Novel Mechanical Activated Ion Channel Piezo1 in the Human Osteosarcoma Cells

Background

The Piezo1 protein ion channel is a novel mechanical activated ion channel which is related to mechanical signal transduction. However, the function of the mechanically activated ion channel Piezo1 had not been explored. In this study, we explored the function of the Piezo1 ion channel in human osteosarcoma (OS) cells related to apoptosis, invasion, and the cell proliferation.

Material/Methods

Reverse transcription polymerase chain reaction (RT-PCR) and western-blotting were used to detect the expression of the Piezo1 protein. CCK-8, Transwell experiments and AV-PI were used to detected cell proliferation, cell invasion and cell apoptosis.

Results

The Piezo1 protein ion channel was highly expressed in human OS cells. The Piezo1-shRNA inhibited the expression of the Piezo1. We explored whether LV3-PIEZO1-homo-3201 could act as Piezo1-shRNA, which could then be an inhibitor of Piezo1. The expression of Piezo1 in the 2-hour stretch group were slightly higher than the 0-hour stretch group, and the difference was not statistically significant (n=3, p>0.05, one-way ANOVA). The apoptotic gene such as the Bax, BAD, caspase-3, and caspase-9 had the same characteristics as the Piezo1 expression under the stretch force. We also explored the invasion of Piezo1 in vivo using nude mice, and found that Piezo1-shRNA could inhibit the invasion of the OS cells.

Conclusions

The Piezo1 protein may be a novel, potential therapeutic target for OS.