The TRPV4-TAZ mechanotransduction signaling axis in matrix stiffness- and TGFβ1-induced epithelial-mesenchymal transition

Trpv4-mediated mechanotransduction regulates the differentiation of valvular interstitial cells to myofibroblasts: implications for aortic valve stenosis

As aortic valve stenosis (AVS) progresses, the valve tissue also stiffens. This increase in tissue stiffness causes the valvular interstitial cells (VICs) to transform into myofibroblasts in response. VIC-to-myofibroblast differentiation is critically involved in the development of AVS. Herein, we investigated the role of mechanosensitive Ca2+-permeant transient receptor potential vanilloid 4 (Trpv4) channels in matrix stiffness- and transforming growth factor β1 (TGFβ1)-induced VIC-myofibroblast activation. We confirmed Trpv4 functionality in primary mouse wild-type VICs compared with Trpv4 null VICs using live Ca2+ influx detection during application of its selective agonist and antagonist. Using physiologically relevant hydrogels of varying stiffness that respectively mimic healthy or diseased aortic valve tissue stiffness, we found that genetic ablation of Trpv4 blocked matrix stiffness- and TGFβ1-induced VIC-myofibroblast activation as determined by changes in morphology, alterations of expression of α-smooth muscle actin, and modulations of F-actin generation. Our results showed that N-terminal residues 30-130 in Trpv4 were crucial for cellular force generation and VIC-myofibroblast activation, while deletion of residues 1-30 had no noticeable negative effect on these processes. Collectively, these data suggest a differential regulatory role for Trpv4 in stiffness/TGFβ1-induced VIC-myofibroblast activation. Our data further showed that Trpv4 regulates stiffness/TGFβ1-induced PI3K-AKT activity that is required for VIC-myofibroblast differentiation and cellular force generation, suggesting a mechanism by which Trpv4 activity regulates VIC-myofibroblast activation. Altogether, these data identify a novel role for Trpv4 mechanotransduction in regulating VIC-myofibroblast activation, implicating Trpv4 as a potential therapeutic target to slow and/or reverse AVS development.NEW & NOTEWORTHY Aortic valve stenosis (AVS) progression involves stiffened valve tissue, driving valvular interstitial cells (VICs) to transform into myofibroblasts. This study highlights the role of Trpv4 channels in VIC activation triggered by matrix stiffness and TGFß1. Using hydrogels mimicking healthy and diseased valves, researchers found that Trpv4 regulates cellular force generation and differentiation via PI3K-AKT activity. These findings identify Trpv4 as a potential therapeutic target to slow or reverse AVS progression.

The role of TRP channels in lung fibrosis: Mechanisms and therapeutic potential

Idiopathic pulmonary fibrosis (IPF) is a severe lung disease affecting around 5 million people globally, with a median survival of 3-4 years. Characterized by excessive scarring of lung tissue, IPF results from the accumulation of myofibroblasts that deposit extracellular matrix (ECM), causing fibrosis. Current treatments, pirfenidone and nintedanib, slow the disease but do not stop its progression. IPF pathogenesis involves repeated alveolar injury, leading to pro-fibrotic mediators like TGFβ1, which trigger fibroblast-to-myofibroblast transitions and ECM deposition. Recent research suggests that transient receptor potential (TRP) channels, such as TRPV4, TRPC6, and TRPA1, play a key role in regulating calcium signalling and mechanical stress, crucial in myofibroblast activation. Targeting TRP channels may disrupt fibrosis and offer new therapeutic strategies. Preclinical studies indicate that inhibiting TRP channels could reduce fibrosis, warranting further trials to explore their efficacy and safety in treating IPF and related fibrotic conditions.

Matrix stiffness regulates NPC invasiveness by modulating a mechanoresponsive TRPV4-Nox4-IL-8 signaling axis

Matrix stiffness is a critical determinant of tumorigenesis and cancer progression. Transient receptor potential vanilloid 4 (TRPV4), a mechanosensitive calcium channel, regulates angiogenesis and stromal stiffness in various tumors. However, it is unclear whether matrix stiffness regulates the invasiveness of nasopharyngeal carcinoma (NPC) cells through TRPV4. In this study, we found that increased matrix stiffness of NPC tissues correlated with advanced tumor stages. Furthermore, simulation of high matrix stiffness in vitro upregulated TRPV4, and increased the migration, invasion, and epithelial mesenchymal transition (EMT) of NPC cells. Knockdown or pharmacological inhibition of TRPV4 significantly suppressed the calcium influx in NPC cells, and inhibited their invasiveness and EMT under high-stiffness conditions. Mechanistically, TRPV4 modulated the invasiveness of NPC cells in response to matrix stiffness via the NOX4/IL-8 axis. Notably, TRPV4 and IL-8 levels were significantly increased in the high-stiffness NPC tissues, and showed a positive correlation. Taken together, matrix stiffness promotes the malignant progression of NPC cells through the activation of the TRPV4/NOX4/IL-8 axis, which could be explored further as a potential target for NPC therapy.

Recent advances on the structure and the function relationships of the TRPV4 ion channel

The members of the superfamily of Transient Receptor Potential (TRP) ion channels are physiologically important molecules that have been studied for many years and are still being intensively researched. Among the vanilloid TRP subfamily, the TRPV4 ion channel is an interesting protein due to its involvement in several essential physiological processes and in the development of various diseases. As in other proteins, changes in its function that lead to the development of pathological states, have been closely associated with modification of its regulation by different molecules, but also by the appearance of mutations which affect the structure and gating of the channel. In the last few years, some structures for the TRPV4 channel have been solved. Due to the importance of this protein in physiology, here we discuss the recent progress in determining the structure of the TRPV4 channel, which has been achieved in three species of animals (Xenopus tropicalis, Mus musculus, and Homo sapiens), highlighting conserved features as well as key differences among them and emphasizing the binding sites for some ligands that play crucial roles in its regulation.

YAP/TAZ Signalling Controls Epidermal Keratinocyte Fate

The paralogues Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) control cell proliferation and cell fate determination from embryogenesis to ageing. In the skin epidermis, these proteins are involved in both homeostatic cell renewal and injury-induced regeneration and also drive carcinogenesis and other pathologies. YAP and TAZ are usually considered downstream of the Hippo pathway. However, they are the central integrating link for the signalling microenvironment since they are involved in the interplay with signalling cascades induced by growth factors, cytokines, and physical parameters of the extracellular matrix. In this review, we summarise the evidence on how YAP and TAZ are activated in epidermal keratinocytes; how YAP/TAZ-mediated signalling cooperates with other signalling molecules at the plasma membrane, cytoplasmic, and nuclear levels; and how YAP/TAZ ultimately controls transcription programmes, defining epidermal cell fate.

TRPV4-mediated Mechanotransduction Regulates the Differentiation of Valvular Interstitial Cells to Myofibroblasts: Implications for Aortic Stenosis

As aortic valve stenosis (AVS) progresses, the valve tissue also stiffens. This increase in tissue stiffness causes the valvular interstitial cells (VICs) to transform into myofibroblasts in response. VIC-to-myofibroblast differentiation is critically involved in the development of AVS. Herein, we investigated the role of mechanosensitive Ca2+-permeant transient receptor potential vanilloid 4 (Trpv4) channels in matrix stiffness- and transforming growth factor β1 (TGFβ1)-induced VIC-myofibroblast activation. We confirmed Trpv4 functionality in primary mouse wild-type VICs compared to Trpv4 null VICs using live Ca2+ influx detection during application of its selective agonist and antagonist. Using physiologically relevant hydrogels of varying stiffness that respectively mimic healthy or diseased aortic valve tissue stiffness, we found that genetic ablation of Trpv4 blocked matrix stiffness- and TGFβ1-induced VIC-myofibroblast activation as determined by changes in morphology, alterations of expression of α-smooth muscle actin, and modulations of F-actin generation. Our results showed that N-terminal residues 30-130 in Trpv4 were crucial for cellular force generation and VIC-myofibroblast activation, while deletion of residues 1-30 had no noticeable negative effect on these processes. Collectively, these data suggest a differential regulatory role for Trpv4 in stiffness/TGFβ1-induced VIC-myofibroblast activation. Our data further showed that Trpv4 regulates stiffness/TGFβ1-induced PI3K-AKT activity that is required for VIC-myofibroblast differentiation and cellular force generation, suggesting a mechanism by which Trpv4 activity regulates VIC-myofibroblast activation. Altogether, these data identify a novel role for Trpv4 mechanotransduction in regulating VIC-myofibroblast activation, implicating Trpv4 as a potential therapeutic target to slow and/or reverse AVS development.

TRPV4-A Multifunctional Cellular Sensor Protein with Therapeutic Potential

Transient receptor potential vanilloid (TRPV) channel proteins belong to the superfamily of TRP proteins that form cationic channels in the animal cell membranes. These proteins have various subtype-specific functions, serving, for example, as sensors for pain, pressure, pH, and mechanical extracellular stimuli. The sensing of extracellular cues by TRPV4 triggers Ca2+-influx through the channel, subsequently coordinating numerous intracellular signaling cascades in a spatio-temporal manner. As TRPV channels play such a wide role in various cellular and physiological functions, loss or impaired TRPV protein activity naturally contributes to many pathophysiological processes. This review concentrates on the known functions of TRPV4 sensor proteins and their potential as a therapeutic target.

Impact of TRP Channels on Extracellular Matrix Remodeling: Focus on TRPV4 and Collagen

Disturbed remodeling of the extracellular matrix (ECM) is frequently observed in several high-prevalence pathologies that include fibrotic diseases of organs such as the heart, lung, periodontium, liver, and the stiffening of the ECM surrounding invasive cancers. In many of these lesions, matrix remodeling mediated by fibroblasts is dysregulated, in part by alterations to the regulatory and effector systems that synthesize and degrade collagen, and by alterations to the functions of the integrin-based adhesions that normally mediate mechanical remodeling of collagen fibrils. Cell-matrix adhesions containing collagen-binding integrins are enriched with regulatory and effector systems that initiate localized remodeling of pericellular collagen fibrils to maintain ECM homeostasis. A large cadre of regulatory molecules is enriched in cell-matrix adhesions that affect ECM remodeling through synthesis, degradation, and contraction of collagen fibrils. One of these regulatory molecules is Transient Receptor Potential Vanilloid-type 4 (TRPV4), a mechanically sensitive, Ca2+-permeable plasma membrane channel that regulates collagen remodeling. The gating of Ca2+ across the plasma membrane by TRPV4 and the consequent generation of intracellular Ca2+ signals affect several processes that determine the structural and mechanical properties of collagen-rich ECM. These processes include the synthesis of new collagen fibrils, tractional remodeling by contractile forces, and collagenolysis. While the specific mechanisms by which TRPV4 contributes to matrix remodeling are not well-defined, it is known that TRPV4 is activated by mechanical forces transmitted through collagen adhesion receptors. Here, we consider how TRPV4 expression and function contribute to physiological and pathological collagen remodeling and are associated with collagen adhesions. Over the long-term, an improved understanding of how TRPV4 regulates collagen remodeling could pave the way for new approaches to manage fibrotic lesions.

Mechanosensitive TRPV4 channel guides maturation and organization of the bilayered mammary epithelium

Biophysical cues from the cell microenvironment are detected by mechanosensitive components at the cell surface. Such machineries convert physical information into biochemical signaling cascades within cells, subsequently leading to various cellular responses in a stimulus-dependent manner. At the surface of extracellular environment and cell cytoplasm exist several ion channel families that are activated by mechanical signals to direct intracellular events. One of such channel is formed by transient receptor potential cation channel subfamily V member, TRPV4 that is known to act as a mechanosensor in wide variaty of tissues and control ion-influx in a spatio-temporal way. Here we report that TRPV4 is prominently expressed in the stem/progenitor cell populations of the mammary epithelium and seems important for the lineage-specific differentiation, consequently affecting mechanical features of the mature mammary epithelium. This was evident by the lack of several markers for mature myoepithelial and luminal epithelial cells in TRPV4-depleted cell lines. Interestingly, TRPV4 expression is controlled in a tension-dependent manner and it also impacts differentation process dependently on the stiffness of the microenvironment. Furthermore, such cells in a 3D compartment were disabled to maintain normal mammosphere structures and displayed abnormal lumen formation, size of the structures and disrupted cellular junctions. Mechanosensitive TRPV4 channel therefore act as critical player in the homeostasis of normal mammary epithelium through sensing the physical environment and guiding accordingly differentiation and structural organization of the bilayered mammary epithelium.

Micro-Vessels-Like 3D Scaffolds for Studying the Proton Radiobiology of Glioblastoma-Endothelial Cells Co-Culture Models

Glioblastoma (GBM) is a devastating cancer of the brain with an extremely poor prognosis. While X-ray radiotherapy and chemotherapy remain the current standard, proton beam therapy is an appealing alternative as protons can damage cancer cells while sparing the surrounding healthy tissue. However, the effects of protons on in vitro GBM models at the cellular level, especially when co-cultured with endothelial cells, the building blocks of brain micro-vessels, are still unexplored. In this work, novel 3D-engineered scaffolds inspired by the geometry of brain microvasculature are designed, where GBM cells cluster and proliferate. The architectures are fabricated by two-photon polymerization (2PP), pre-cultured with endothelial cells (HUVECs), and then cultured with a human GBM cell line (U251). The micro-vessel structures enable GBM in vivo-like morphologies, and the results show a higher DNA double-strand breakage in GBM monoculture samples when compared to the U251/HUVECs co-culture, with cells in 2D featuring a larger number of DNA damage foci when compared to cells in 3D. The discrepancy in terms of proton radiation response indicates a difference in the radioresistance of the GBM cells mediated by the presence of HUVECs and the possible induction of stemness features that contribute to radioresistance and improved DNA repair.

Ca2+ signaling and the Hippo pathway: Intersections in cellular regulation

The Hippo signaling pathway is a master regulator of organ size and tissue homeostasis. Hippo integrates a broad range of cellular signals to regulate numerous processes, such as cell proliferation, differentiation, migration and mechanosensation. Ca2+ is a fundamental second messenger that modulates signaling cascades involved in diverse cellular functions, some of which are also regulated by the Hippo pathway. Studies published over the last five years indicate that Ca2+ can influence core Hippo pathway components. Nevertheless, comprehensive understanding of the crosstalk between Ca2+ signaling and the Hippo pathway, and possible mechanisms through which Ca2+ regulates Hippo, remain to be elucidated. In this review, we summarize the multiple intersections between Ca2+ and the Hippo pathway and address the biological consequences.

Matrix stiffness induces epithelial-to-mesenchymal transition via Piezo1-regulated calcium flux in prostate cancer cells

Cells utilize calcium channels as one of the main signaling mechanisms to sense changes in the extracellular space and convert these changes to intracellular signals. Calcium regulates several key signaling networks, such as the induction of EMT. The current study expands on the understanding of how EMT is controlled via the mechanosensitive calcium channel Piezo1 in cancerous cells, which senses changes in the extracellular matrix stiffness. We model the biophysical environment of healthy and cancerous prostate tissue using polyacrylamide gels of different stiffnesses. Significant increases in calcium steady-state concentration, vimentin expression, and aspect ratio, and decreases in E-cadherin expression were observed by increasing matrix stiffness and also after treatment with Yoda1, a chemical agonist of Piezo1. Overall, this study concludes that Piezo1-regulated calcium flux plays a role in prostate cancer cell metastatic potential by sensing changes in ECM stiffness and modulating EMT markers.

LGR5 promotes invasion and migration by regulating YAP activity in hypopharyngeal squamous cell carcinoma cells under inflammatory condition

High leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) expression caused by an inflammatory condition was reported to promote tumor proliferation and the epithelial-mesenchymal transition (EMT) in various malignant tumors, but those effects have not been studied in hypopharyngeal squamous cell carcinoma (HSCC) and the molecular mechanism remains unclear. This study was aimed to determine whether YAP/TAZ is involved in the regulation of LGR5 expression in the inflammatory condition. Human hypopharyngeal carcinoma FaDu cells were stimulated with inflammatory medium. The cell invasion ability were evaluated through wound healing assay and transwell invasion assay. The expression levels of EMT-related proteins, LGR5, and p-YAP were detected by real time PCR, western blotting, and immunofluorescence. The results showed that LGR5 expression and the EMT process were significantly enhanced under inflammatory condition. The expression of EMT-related proteins was up-regulated, while that of p-YAP was decreased. After inhibiting the high LGR5 expression with short interfering RNA, the expression of EMT-related proteins was also down-regulated, while that of p-YAP was significantly increased. The use of verteporfin (VP), an inhibitor of YAP activity that promotes YAP phosphorylation, did not affect LGR5 expression. In conclusion, we suggest that the inflammatory condition leads to high LGR5 expression, which up-regulating the expression of EMT-related proteins by inhibiting the YAP phosphorylation.

The interplay between physical cues and mechanosensitive ion channels in cancer metastasis

Physical cues have emerged as critical influencers of cell function during physiological processes, like development and organogenesis, and throughout pathological abnormalities, including cancer progression and fibrosis. While ion channels have been implicated in maintaining cellular homeostasis, their cell surface localization often places them among the first few molecules to sense external cues. Mechanosensitive ion channels (MICs) are especially important transducers of physical stimuli into biochemical signals. In this review, we describe how physical cues in the tumor microenvironment are sensed by MICs and contribute to cancer metastasis. First, we highlight mechanical perturbations, by both solid and fluid surroundings typically found in the tumor microenvironment and during critical stages of cancer cell dissemination from the primary tumor. Next, we describe how Piezo1/2 and transient receptor potential (TRP) channels respond to these physical cues to regulate cancer cell behavior during different stages of metastasis. We conclude by proposing alternative mechanisms of MIC activation that work in tandem with cytoskeletal components and other ion channels to bestow cells with the capacity to sense, respond and navigate through the surrounding microenvironment. Collectively, this review provides a perspective for devising treatment strategies against cancer by targeting MICs that sense aberrant physical characteristics during metastasis, the most lethal aspect of cancer.

Calcium influx through TRPV4 channels involve in hyperosmotic stress-induced epithelial-mesenchymal transition in tubular epithelial cells

The epithelial-mesenchymal transition (EMT) is a biological process that occurs in the pathogenesis of kidney diseases in which injured tubular epithelial cells transform into myofibroblasts. We previously showed that mannitol-mediated hyperosmotic stress induces EMT of tubular epithelial cells. Although Ca²⁺ signaling is essential for the induction of EMT in tubular epithelial cells, the role of specific calcium channels is unknown. In this study, we assessed the transient receptor potential vanilloid 4 (TRPV4)-mediated Ca²⁺ influx in the hyperosmolarity-induced EMT. The Fluo-4 assay was used to examine the effect of hyperosmotic stress on the intracellular Ca²⁺ level of normal rat kidney (NRK)-52E cells. Expression of a mesenchymal marker α-smooth muscle actin (α-SMA) and an epithelial marker E-cadherin was also observed by fluorescence microscopy. The hyperosmotic stress caused a transient increase in intracellular Ca²⁺ concentration as well as a decrease in E-cadherin and an increase in α-SMA expressions in tubular epithelial cells, indicating the induction of EMT. A TRPV4 channel antagonist inhibited hyperosmotic stress-induced Ca²⁺ influx and the EMT, whereas, a TRPV4 channel agonist increased Ca²⁺ influx and EMT induction in tubular epithelial cells without the hyperosmotic stress. These findings suggest that Ca²⁺ influx through TRPV4 channels contributes to the hyperosmotic stress-induced EMT of tubular epithelial cells.

[Effects of transient receptor potential vanilloid type 4-specific activator on human vascular endothelial cell functions and blood supply of rat perforator flap and its mechanism]

Objective: To analyze the effects of transient receptor potential vanilloid type 4 (TRPV4) activation on the function and endothelial-to-mesenchymal transition (EndMT) of human umbilical vein endothelial cells (HUVECs), as well as to explore the effects of TRPV4 activation on blood perfusion and survival of rat perforator flap and the mechanism. Methods: The experimental research methods were used. The 3rd to 6th passages of HUVECs were used for experiments and divided into 0.5 μmol/L 4α-phorbol 12, 13-didecanoate (4αPDD) group, 1.0 μmol/L 4αPDD group, 3.0 μmol/L 4αPDD group, 10.0 μmol/L 4αPDD group, and phosphate buffer solution (PBS) group, which were cultivated in corresponding final molarity of 4αPDD and PBS, respectively. The cell proliferation activity at 6 and 12 h of culture was detected using cell counting kit-8 (CCK-8). Another batch of cells was acquired and divided into PBS group, 1 μmol/L 4αPDD group, and 3 μmol/L 4αPDD group, which were treated similarly as described before and then detected for cell proliferation activity at 6, 12, 24, and 48 h of culture. The residual scratch area of cells at post scratch hour (PSH) 12, 24, and 48 was detected by scratch test, and the percentage of the residual scratch area was calculated. The number of migrated cells at 24 and 48 h of culture was detected by Transwell experiment. The tube-formation assay was used to measure the number of tubular structures at 4 and 8 h of culture. The protein expressions of E-cadherin, N-cadherin, Slug, and Snail at 24 h of culture were detected by Western blotting. All the sample numbers in each group at each time point in vitro experiments were 3. A total of 36 male Sprague-Dawley rats aged 8 to 10 weeks were divided into delayed flap group, 4αPDD group, and normal saline group according to the random number table, with 12 rats in each group, and iliolumbar artery perforator flap models on the back were constructed. The flap surgical delay procedure was only performed in the rats in delayed flap group one week before the flap transfer surgery. Neither rats in 4αPDD group nor normal saline group had flap surgical delay; instead, they were intraperitoneally injected with 4αPDD and an equivalent mass of normal saline, respectively, at 10 min before, 24 h after, and 48 h after the surgery. The general state of flap was observed on post surgery day (PSD) 0 (immediately), 1, 4, and 7. The flap survival rates were assessed on PSD 7. The flap blood perfusion was detected by laser speckle contrast imaging technique on PSD 1, 4, and 7. The microvascular density in the flap's choke vessel zone was detected by immunohistochemical staining. All the sample numbers in each group at each time point in vivo experiments were 12. Data were statistically analyzed with analysis of variance for factorial design, analysis of variance for repeated measurement, one-way analysis of variance, least significant difference t test, and Bonferroni correction. Results: At 6 and 12 h of culture, there were no statistically significant differences in cell proliferation activity in the overall comparison among PBS group, 0.5 μmol/L 4αPDD group, 1.0 μmol/L 4αPDD group, 3.0 μmol/L 4αPDD group, and 10.0 μmol/L 4αPDD group (P>0.05). At 6, 12, 24, and 48 h of culture, there were no statistically significant differences in cell proliferation activity in the overall comparison among PBS group, 1 μmol/L 4αPDD group, and 3 μmol/L 4αPDD group (P>0.05). At PSH 12, the percentages of the residual scratch area of cells in 1 μmol/L 4αPDD group and 3 μmol/L 4αPDD group were close to that in PBS group (P>0.05). At PSH 24 and 48, compared with those in PBS group, the percentages of the residual scratch area of cells in 3 μmol/L 4αPDD group were significantly decreased (with t values of 2.83 and 2.79, respectively, P<0.05), while the percentages of the residual scratch area of cells in 1 μmol/L 4αPDD group showed no significant differences (P>0.05). At 24 h of culture, the number of migrated cells in 1 μmol/L 4αPDD group and 3 μmol/L 4αPDD group were close to that in PBS group (P>0.05). At 48 h of culture, the number of migrated cells in 1 μmol/L 4αPDD group and 3 μmol/L 4αPDD groups were significantly greater than that in PBS group (with t values of 6.20 and 9.59, respectively, P<0.01). At 4 h of culture, the numbers of tubular structures of cells in 1 μmol/L 4αPDD group and 3 μmol/L 4αPDD group were significantly greater than that in PBS group (with t values of 4.68 and 4.95, respectively, P<0.05 or <0.01). At 8 h of culture, the numbers of tubular structures of cells in 1 μmol/L 4αPDD and 3 μmol/L 4αPDD groups were similar to that in PBS group (P>0.05). At 24 h of culture, compared with those in PBS group, the protein expression level of E-cadherin of cells in 3 μmol/L 4αPDD group was significantly decreased (t=5.13, P<0.01), whereas there was no statistically significant difference in the protein expression level of E-cadherin of cells in 1 μmol/L 4αPDD group (P>0.05); the protein expression level of N-cadherin of cells in 3 μmol/L 4αPDD group was significantly increased (t=4.93, P<0.01), whereas there was no statistically significant difference in the protein expression level of N-cadherin of cells in 1 μmol/L 4αPDD group (P>0.05); the protein expression levels of Slug of cells in 1 μmol/L 4αPDD group and 3 μmol/L 4αPDD group were significantly increased (with t values of 3.85 and 6.52, respectively, P<0.05 or P<0.01); and the protein expression level of Snail of cells in 3 μmol/L 4αPDD group was significantly increased (t=4.08, P<0.05), whereas there was no statistically significant difference in the protein expression level of Snail of cells in 1 μmol/L 4αPDD group (P>0.05). There were no statistically significant differences in the protein expression levels of E-cadherin, N-cadherin, Slug, or Snail of cells between 1 μmol/L 4αPDD group and 3 μmol/L 4αPDD group (P>0.05). The general condition of flaps of rats in the three groups was good on PSD 0. On PSD 1, the flaps of rats in the three groups were basically similar, with bruising and swelling at the distal end. On PSD 4, the swelling of flaps of rats in the three groups subsided, and the distal end turned dark brown and necrosis occurred, with the area of necrosis in flaps of rats in normal saline group being larger than the areas in 4αPDD group and delayed flap group. On PSD 7, the necrotic areas of flaps of rats in the 3 groups were fairly stable, with the area of necrosis at the distal end of flap of rats in delayed flap group being the smallest. On PSD 7, the flap survival rates of rats in 4αPDD group ((80±13)%) and delayed flap group ((87±9)%) were similar (P>0.05), and both were significantly higher than (70±11)% in normal saline group (with t values of 2.24 and 3.65, respectively, P<0.05 or P<0.01). On PSD 1, the overall blood perfusion signals of rats in the 3 groups were basically the same, and the blood perfusion signals in the choke vessel zone were relatively strong, with a certain degree of underperfusion at the distal end. On PSD 4, the boundary between the surviving and necrotic areas of flaps of rats in the 3 groups became evident, and the blood perfusion signals in the choke vessel zone were improved, with the normal saline group's distal hypoperfused area of flap being larger than the areas in delayed flap group and 4αPDD group. On PSD 7, the blood perfusion signals of overall flap of rats had generally stabilized in the 3 groups, with the intensity of blood perfusion signal in the choke vessel zone and overall flap of rats in delayed flap group and 4αPDD group being significantly greater than that in normal saline group. On PSD 7, the microvascular density in the choke vessel zone of flap of rats in 4αPDD group and delayed flap group were similar (P>0.05), and both were significantly higher than that in normal saline group (with t values of 4.11 and 5.38, respectively, P<0.01). Conclusions: After activation, TRPV4 may promote the migration and tubular formation of human vascular endothelial cells via the EndMT pathway, leading to the enhanced blood perfusion of perforator flap and microvascular density in the choke vessel zone, and therefore increase the flap survival rate.

Evaluation of Proton-Induced DNA Damage in 3D-Engineered Glioblastoma Microenvironments

Glioblastoma (GBM) is a devastating cancer of the brain with an extremely poor prognosis. For this reason, besides clinical and preclinical studies, novel in vitro models for the assessment of cancer response to drugs and radiation are being developed. In such context, three-dimensional (3D)-engineered cellular microenvironments, compared to unrealistic two-dimensional (2D) monolayer cell culture, provide a model closer to the in vivo configuration. Concerning cancer treatment, while X-ray radiotherapy and chemotherapy remain the current standard, proton beam therapy is an appealing alternative as protons can be efficiently targeted to destroy cancer cells while sparing the surrounding healthy tissue. However, despite the treatment's compelling biological and medical rationale, little is known about the effects of protons on GBM at the cellular level. In this work, we designed novel 3D-engineered scaffolds inspired by the geometry of brain blood vessels, which cover a vital role in the colonization mechanisms of GBM cells. The architectures were fabricated by two-photon polymerization (2PP), cultured with U-251 GBM cells and integrated for the first time in the context of proton radiation experiments to assess their response to treatment. We employed Gamma H2A.X as a fluorescent biomarker to identify the DNA damage induced in the cells by proton beams. The results show a higher DNA double-strand breakage in 2D cell monolayers as compared to cells cultured in 3D. The discrepancy in terms of proton radiation response could indicate a difference in the radioresistance of the GBM cells or in the rate of repair kinetics between 2D cell monolayers and 3D cell networks. Thus, these biomimetic-engineered 3D scaffolds pave the way for the realization of a benchmark tool that can be used to routinely assess the effects of proton therapy on 3D GBM cell networks and other types of cancer cells.

Role of mechanosensitive channels/receptors in atherosclerosis

Mechanical forces are critical physical cues that can affect numerous cellular processes regulating the development, tissue maintenance, and functionality of cells. The contribution of mechanical forces is especially crucial in the vascular system where it is required for embryogenesis and for maintenance of physiological function in vascular cells including aortic endothelial cells, resident macrophages, and smooth muscle cells. Emerging evidence has also identified a role of these mechanical cues in pathological conditions of the vascular system such as atherosclerosis and associated diseases like hypertension. Of the different mechanotransducers, mechanosensitive ion channels/receptors are gaining prominence due to their involvement in numerous physiological and pathological conditions. However, only a handful of potential mechanosensory ion channels/receptors have been shown to be involved in atherosclerosis, and their precise role in disease development and progression remains poorly understood. Here, we provide a comprehensive account of recent studies investigating the role of mechanosensitive ion channels/receptors in atherosclerosis. We discuss the different groups of mechanosensitive proteins and their specific roles in inflammation, endothelial dysfunction, macrophage foam cell formation, and lesion development, which are crucial for the development and progression of atherosclerosis. Results of the studies discussed here will help in developing an understanding of the current state of mechanobiology in vascular diseases, specifically in atherosclerosis, which may be important for the development of innovative and targeted therapeutics for this disease.

Hydrogel cultures reveal Transient Receptor Potential Vanilloid 4 regulation of myofibroblast activation and proliferation in valvular interstitial cells

As aortic valve stenosis develops, valve tissue becomes stiffer. In response to this change in environmental mechanical stiffness, valvular interstitial cells (VICs) activate into myofibroblasts. We aimed to investigate the role of mechanosensitive calcium channel Transient Receptor Potential Vanilloid type 4 (TRPV4) in stiffness induced myofibroblast activation. We verified TRPV4 functionality in VICs using live calcium imaging during application of small molecule modulators of TRPV4 activity. We designed hydrogel biomaterials that mimic mechanical features of healthy or diseased valve tissue microenvironments, respectively, to investigate the role of TRPV4 in myofibroblast activation and proliferation. Our results show that TRPV4 regulates VIC proliferation in a microenvironment stiffness-independent manner. While there was a trend toward inhibiting myofibroblast activation on soft microenvironments during TRPV4 inhibition, we observed near complete deactivation of myofibroblasts on stiff microenvironments. We further identified Yes-activated protein (YAP) as a downstream target for TRPV4 activity on stiff microenvironments. Mechanosensitive TRPV4 channels regulate VIC myofibroblast activation, whereas proliferation regulation is independent of the microenvironmental stiffness. Collectively, the data suggests differential regulation of stiffness-induced proliferation and myofibroblast activation. Our data further suggest a regulatory role for TRPV4 regarding YAP nuclear localization. TRPV4 is an important regulator for VIC myofibroblast activation, which is linked to the initiation of valve fibrosis. Although more validation studies are necessary, we suggest TRPV4 as a promising pharmaceutical target to slow aortic valve stenosis progression.

Emergent Temporal Signaling in Human Trabecular Meshwork Cells: Role of TRPV4-TRPM4 Interactions

Trabecular meshwork (TM) cells are phagocytic cells that employ mechanotransduction to actively regulate intraocular pressure. Similar to macrophages, they express scavenger receptors and participate in antigen presentation within the immunosuppressive milieu of the anterior eye. Changes in pressure deform and compress the TM, altering their control of aqueous humor outflow but it is not known whether transducer activation shapes temporal signaling. The present study combines electrophysiology, histochemistry and functional imaging with gene silencing and heterologous expression to gain insight into Ca²⁺ signaling downstream from TRPV4 (Transient Receptor Potential Vanilloid 4), a stretch-activated polymodal cation channel. Human TM cells respond to the TRPV4 agonist GSK1016790A with fluctuations in intracellular Ca²⁺ concentration ([Ca²⁺]_i) and an increase in [Na⁺]_i. [Ca²⁺]_i oscillations coincided with monovalent cation current that was suppressed by BAPTA, Ruthenium Red and the TRPM4 (Transient Receptor Potential Melastatin 4) channel inhibitor 9-phenanthrol. TM cells expressed TRPM4 mRNA, protein at the expected 130-150 kDa and showed punctate TRPM4 immunoreactivity at the membrane surface. Genetic silencing of TRPM4 antagonized TRPV4-evoked oscillatory signaling whereas TRPV4 and TRPM4 co-expression in HEK-293 cells reconstituted the oscillations. Membrane potential recordings suggested that TRPM4-dependent oscillations require release of Ca²⁺ from internal stores. 9-phenanthrol did not affect the outflow facility in mouse eyes and eyes from animals lacking TRPM4 had normal intraocular pressure. Collectively, our results show that TRPV4 activity initiates dynamic calcium signaling in TM cells by stimulating TRPM4 channels and intracellular Ca²⁺ release. It is possible that TRPV4-TRPM4 interactions downstream from the tensile and compressive impact of intraocular pressure contribute to homeostatic regulation and pathological remodeling within the conventional outflow pathway.

Mechanosensing by TRPV4 mediates stiffness-induced foreign body response and giant cell formation

Implantation of biomaterials or devices into soft tissue often leads to the development of the foreign body response (FBR), an inflammatory condition that can cause implant failure, tissue injury, and death of the patient. Macrophages accumulate and fuse to generate destructive foreign body giant cells (FBGCs) at the tissue-implant interface, leading to the development of fibrous scar tissue around the implant that is generated by myofibroblasts. We previously showed that the FBR in vivo and FBGC formation in vitro require transient receptor potential vanilloid 4 (TRPV4), a mechanosensitive ion channel. Here, we report that TRPV4 was required specifically for the FBR induced by implant stiffness independently of biochemical cues and for intracellular stiffening that promotes FBGC formation in vitro. TRPV4 deficiency reduced collagen deposition and the accumulation of macrophages, FBGCs, and myofibroblasts at stiff, but not soft, implants in vivo and inhibited macrophage-induced differentiation of wild-type fibroblasts into myofibroblasts in vitro. Atomic force microscopy demonstrated that TRPV4 was required for implant-adjacent tissue stiffening in vivo and for cytoskeletal remodeling and intracellular stiffening induced by fusogenic cytokines in vitro. Together, these data suggest a mechanism whereby a reciprocal functional interaction between TRPV4 and substrate stiffness leads to cytoskeletal remodeling and cellular force generation to promote FBGC formation during the FBR.

Transient Receptor Potential Channels in the Epithelial-to-Mesenchymal Transition

The epithelial-to-mesenchymal transition (EMT) is a strictly regulated process that is indispensable for normal development, but it can result in fibrosis and cancer progression. It encompasses a complete alteration of the cellular transcriptomic profile, promoting the expression of genes involved in cellular migration, invasion and proliferation. Extracellular signaling factors driving the EMT process require secondary messengers to convey their effects to their targets. Due to its remarkable properties, calcium represents an ideal candidate to translate molecular messages from receptor to effector. Therefore, calcium-permeable ion channels that facilitate the influx of extracellular calcium into the cytosol can exert major influences on cellular phenotype. Transient receptor potential (TRP) channels represent a superfamily of non-selective cation channels that decode physical and chemical stimuli into cellular behavior. Their role as cellular sensors renders them interesting proteins to study in the context of phenotypic transitions, such as EMT. In this review, we elaborate on the current knowledge regarding TRP channel expression and activity in cellular phenotype and EMT.

TRPV Protein Family-From Mechanosensing to Cancer Invasion

Biophysical cues from the cellular microenvironment are detected by mechanosensitive machineries that translate physical signals into biochemical signaling cascades. At the crossroads of extracellular space and cell interior are located several ion channel families, including TRP family proteins, that are triggered by mechanical stimuli and drive intracellular signaling pathways through spatio-temporally controlled Ca2+-influx. Mechanosensitive Ca2+-channels, therefore, act as critical components in the rapid transmission of physical signals into biologically compatible information to impact crucial processes during development, morphogenesis and regeneration. Given the mechanosensitive nature of many of the TRP family channels, they must also respond to the biophysical changes along the development of several pathophysiological conditions and have also been linked to cancer progression. In this review, we will focus on the TRPV, vanilloid family of TRP proteins, and their connection to cancer progression through their mechanosensitive nature.

Identification and functional analysis of a biflavone as a novel inhibitor of transient receptor potential vanilloid 4-dependent atherogenic processes

Atherosclerosis, a chronic inflammatory disease of large arteries, is the major contributor to the growing burden of cardiovascular disease-related mortality and morbidity. During early atherogenesis, as a result of inflammation and endothelial dysfunction, monocytes transmigrate into the aortic intimal areas, and differentiate into lipid-laden foam cells, a critical process in atherosclerosis. Numerous natural compounds such as flavonoids and polyphenols are known to have anti-inflammatory and anti-atherogenic properties. Herein, using a fluorometric imaging plate reader-supported Ca2+ influx assay, we report semi high-throughput screening-based identification of ginkgetin, a biflavone, as a novel inhibitor of transient receptor potential vanilloid 4 (TRPV4)-dependent proatherogenic and inflammatory processes in macrophages. We found that ginkgetin (1) blocks TRPV4-elicited Ca2+ influx into macrophages, (2) inhibits oxidized low-density lipoprotein (oxLDL)-induced foam cell formation by suppressing the uptake but not the binding of oxLDL in macrophages, and (3) attenuates oxLDL-induced phosphorylation of JNK2, expression of TRPV4 proteins, and induction of inflammatory mRNAs. Considered all together, the results of this study show that ginkgetin inhibits proatherogenic/inflammatory macrophage function in a TRPV4-dependent manner, thus strengthening the rationale for the use of natural compounds for developing therapeutic and/or chemopreventive molecules.

Mechanotransduction via a TRPV4-Rac1 signaling axis plays a role in multinucleated giant cell formation

Multinucleated giant cells are formed by the fusion of macrophages and are a characteristic feature in numerous pathophysiological conditions including the foreign body response (FBR). Foreign body giant cells (FBGCs) are inflammatory and destructive multinucleated macrophages and may cause damage and/or rejection of implants. However, while these features of FBGCs are well established, the molecular mechanisms underlying their formation remain elusive. Improved understanding of the molecular mechanisms underlying the formation of FBGCs may permit the development of novel implants that eliminate or reduce the FBR. Our previous study showed that transient receptor potential vanilloid 4 (TRPV4), a mechanosensitive ion channel/receptor, is required for FBGC formation and FBR to biomaterials. Here, we have determined that (a) TRPV4 is directly involved in fusogenic cytokine (interleukin-4 plus granulocyte macrophage-colony stimulating factor)-induced activation of Rac1, in bone marrow-derived macrophages; (b) TRPV4 directly interacts with Rac1, and their interaction is further augmented in the presence of fusogenic cytokines; (c) TRPV4-dependent activation of Rac1 is essential for the augmentation of intracellular stiffness and regulation of cytoskeletal remodeling; and (d) TRPV4-Rac1 signaling axis is critical in fusogenic cytokine-induced FBGC formation. Together, these data suggest a novel mechanism whereby a functional interaction between TRPV4 and Rac1 leads to cytoskeletal remodeling and intracellular stiffness generation to modulate FBGC formation.

TRPV4 Plays a Role in Matrix Stiffness-Induced Macrophage Polarization

Phenotypic polarization of macrophages is deemed essential in innate immunity and various pathophysiological conditions. We have now determined key aspects of the molecular mechanism by which mechanical cues regulate macrophage polarization. We show that Transient Receptor Potential Vanilloid 4 (TRPV4), a mechanosensitive ion channel, mediates substrate stiffness-induced macrophage polarization. Using atomic force microscopy, we showed that genetic ablation of TRPV4 function abrogated fibrosis-induced matrix stiffness generation in skin tissues. We have determined that stiffer skin tissue promotes the M1 macrophage subtype in a TRPV4-dependent manner; soft tissue does not. These findings were further validated by our in vitro results which showed that stiff matrix (50 kPa) alone increased expression of macrophage M1 markers in a TRPV4-dependent manner, and this response was further augmented by the addition of soluble factors; neither of which occurred with soft matrix (1 kPa). A direct requirement for TRPV4 in M1 macrophage polarization spectrum in response to increased stiffness was evident from results of gain-of-function assays, where reintroduction of TRPV4 significantly upregulated the expression of M1 markers in TRPV4 KO macrophages. Together, these data provide new insights regarding the role of TRPV4 in matrix stiffness-induced macrophage polarization spectrum that may be explored in tissue engineering and regenerative medicine and targeted therapeutics.

Engineering Three-Dimensional Tumor Models to Study Glioma Cancer Stem Cells and Tumor Microenvironment

Glioblastoma (GBM) is the most common and devastating primary brain tumor, leading to a uniform fatality after diagnosis. A major difficulty in eradicating GBM is the presence of microscopic residual infiltrating disease remaining after multimodality treatment. Glioma cancer stem cells (CSCs) have been pinpointed as the treatment-resistant tumor component that seeds ultimate tumor progression. Despite the key role of CSCs, the ideal preclinical model to study the genetic and epigenetic landmarks driving their malignant behavior while simulating an accurate interaction with the tumor microenvironment (TME) is still missing. The introduction of three-dimensional (3D) tumor platforms, such as organoids and 3D bioprinting, has allowed for a better representation of the pathophysiologic interactions between glioma CSCs and the TME. Thus, these technologies have enabled a more detailed study of glioma biology, tumor angiogenesis, treatment resistance, and even performing high-throughput screening assays of drug susceptibility. First, we will review the foundation of glioma biology and biomechanics of the TME, and then the most up-to-date insights about the applicability of these new tools in malignant glioma research.

Role of TRPV4 in matrix stiffness-induced expression of EMT-specific LncRNA

Long non-coding RNAs (LncRNAs) are long (> 200 bases), non-coding, single-stranded RNAs that have emerged as major regulators of gene expression, cell differentiation, development, and oncogenesis. In view of the fact that matrix stiffness plays a role in cellular functions associated with these processes, it is important to ask what role matrix stiffness plays in regulating expression of LncRNAs. In this report, we show that (i) matrix stiffness causes differential expression of epithelial-mesenchymal transition (EMT)-related LncRNAs and mRNAs in primary mouse normal epidermal keratinocytes, (ii) differential expression of EMT-related LncRNAs and mRNAs occurs in response to combined stimulation of transforming growth factor β1 and matrix stiffness, and (iii) transient receptor potential (TRP) channel of the vanilloid subfamily, TRPV4, a matrix stiffness-sensitive ion channel, plays a role in differential expression of EMT-related LncRNAs and mRNAs in response to combined stimulation by TGFβ1 and matrix stiffness. These data identify TRPV4 as a candidate plasma membrane mechanosensor that transmits matrix-sensing signals essential to LncRNA expression. Our results also show that we have established and validated an assay system capable of discovering novel LncRNAs and mRNAs sensitive to matrix stiffening.

Dysfunctional Mechanotransduction through the YAP/TAZ/Hippo Pathway as a Feature of Chronic Disease

In order to ascertain their external environment, cells and tissues have the capability to sense and process a variety of stresses, including stretching and compression forces. These mechanical forces, as experienced by cells and tissues, are then converted into biochemical signals within the cell, leading to a number of cellular mechanisms being activated, including proliferation, differentiation and migration. If the conversion of mechanical cues into biochemical signals is perturbed in any way, then this can be potentially implicated in chronic disease development and processes such as neurological disorders, cancer and obesity. This review will focus on how the interplay between mechanotransduction, cellular structure, metabolism and signalling cascades led by the Hippo-YAP/TAZ axis can lead to a number of chronic diseases and suggest how we can target various pathways in order to design therapeutic targets for these debilitating diseases and conditions.

Emodin Retarded Renal Fibrosis Through Regulating HGF and TGFβ-Smad Signaling Pathway

BACKGROUND

Renal fibrosis is a frequently occurring type of chronic kidney disease that can cause end-stage renal disease. It has been verified that emodin or HGF can inhibit the development of renal fibrosis. However, the antifibrotic effect of emodin in combination with HGF remains unclear.

METHODS

Cell viability was detected with CCK8. Gene and protein expression in HK2 cells was detected by qRT-PCR and Western blot, respectively. Moreover, a unilateral ureteral obstruction-induced mouse model of renal fibrosis was established for investigating the antifibrotic effect of emodin in combination with HGF in vivo.

RESULTS

HGF notably increased the expression of collagen II in TGFβ-treated HK2 cells. In addition, HGF-induced increase in collagen II expression was further enhanced by emodin. In contrast, fibronectin, αSMA and Smad2 expression in TGFβ-stimulated HK2 cells was significantly inhibited by HGF and further decreased by combination treatment (emodin plus HGF). Moreover, we found that combination treatment exhibited better antifibrotic effects compared with emodin or HGF in vivo.

CONCLUSION

These data demonstrated that emodin plus HGF exhibited better antifibrotic effects compared with emodin or HGF. As such, emodin in combination with HGF may serve as a new possibilty for treatment of renal fibrosis.