Activation of transient receptor potential vanilloid 4 is involved in pressure overload-induced cardiac hypertrophy

TRPV4 inhibition suppresses myocardial ischemia-reperfusion arrhythmia of mice by alleviating calcium handling abnormalities

BACKGROUND

Transient receptor potential vanilloid 4 (TRPV4), a calcium (Ca2+) permeable channel, is upregulated during myocardial ischemia-reperfusion (IR). Although TRPV4 inhibition has cardioprotective effects, its impact on arrhythmogenesis remains unclear.

OBJECTIVE

This study aimed to evaluate the antiarrhythmic effects of TRPV4 inhibition, using the TRPV4 antagonist GSK2193874 (GSK219) and TRPV4 knockout (TRPV4-/-) mice, after IR.

METHODS

Surface electrocardiogram and optical mapping recordings were performed during 15 minutes of global ischemia and 10 minutes of reperfusion in Langendorff perfused mouse hearts. Ca2+ sparks were detected by confocal microscopy, and protein expression was analyzed by Western blot.

RESULTS

GSK219 or TRPV4 deletion significantly decreased the incidence and duration of ventricular tachycardia during reperfusion. TRPV4 inhibition shortened Ca2+ transient (CaT) recovery, suppressed CaT alternans, and decreased Ca2+ leak without affecting IR-induced prolongation of action potential duration (APD) and APD alternations. Activation of TRPV4 by GSK101790A (GSK101) increased arrhythmia susceptibility and Ca2+ leak. Moreover, GSK101 prolonged CaT recovery and promoted CaT alternans, which were greatly avoided by pretreatment with Ca2+/calmodulin-dependent protein kinase II (CaMKII) inhibitor. Interestingly, IR or GSK101 markedly increased the phosphorylation of CaMKII, ryanodine receptors, and phospholamban, which was significantly blocked by TRPV4 inhibition.

CONCLUSION

TRPV4 inhibition exerts antiarrhythmic effects after IR by modulating CaMKII-dependent Ca2+ handling abnormalities, reducing CaT alternans and Ca2+ leak, without affecting APD.

TRPV4 Promotes Vascular Calcification by Directly Associating With and Activating β-Catenin

BACKGROUND

Vascular calcification contributes to increased cardiovascular morbidity and mortality in patients with chronic kidney disease, diabetes, and atherosclerosis. Currently, there are no effective therapeutic strategies to prevent or reverse vascular calcification. TRPV4 (transient receptor potential channel V4), a key Ca2+-permeable channel, plays an important role in various diseases. However, the role and mechanism of TRPV4 in vascular calcification have not yet been elucidated.

METHODS

The effects of TRPV4 on vascular calcification were explored in vitro and in vivo. TRPV4 interactome assessment and molecular docking were performed to investigate the mechanism and specific therapeutic strategy for vascular calcification.

RESULTS

TRPV4 was substantially upregulated in high inorganic phosphate-induced calcified vascular smooth muscle cells (SMCs) and calcified aortas from cholecalciferol (vitamin D3)-overloaded mice. TRPV4 overexpression increased the expression of the osteochondrogenic markers Runx2 (runt-related transcription factor 2), Msx2 (Msh homeobox 2), and Sox9 (SRY-box transcription factor 9) and exacerbated high inorganic phosphate-induced vascular SMC calcification in a Ca2+ influx-dependent manner. In contrast, TRPV4 deficiency or inactivation significantly inhibited vascular SMC calcification under high inorganic phosphate conditions. Moreover, compared with that in control littermates, SMC-specific TRPV4 deficiency in mice alleviated vitamin D3-induced and 5/6 nephrectomy-induced vascular calcification. Mechanistically, TRPV4 interacted with β-catenin and activated β-catenin/TCF (T-cell factor) transcriptional activity via Ca2+/ASK1 (apoptosis signal regulating kinase 1)/p38 signaling. β-Catenin knockdown abolished the effects of TRPV4 overexpression on vascular SMC calcification. TRPV4/β-catenin interaction is pivotal for maintaining TRPV4/Ca2+-induced ASK1/p38/β-catenin activation. Hesperidin, a natural product found in citrus fruits, effectively disrupted TRPV4/β-catenin interaction, thereby inhibiting ASK1/p38/β-catenin activity and preventing vascular calcification.

CONCLUSIONS

Our study identified TRPV4 as a new pathogenic factor for vascular calcification that directly associates with and activates β-catenin. Blocking the TRPV4/β-catenin interaction through hesperidin suppressed the progression of vascular calcification and may be an effective precision strategy to address vascular calcification.

Semaglutide attenuates myocardial ischemia-reperfusion injury by inhibiting ferroptosis of cardiomyocytes via activation of PKC-S100A9 axis

Objective

The incidence of ischemic cardiomyopathy increases annually worldwide, and it is the leading cause of mortality in China. Although interventional diagnostic and therapeutic techniques can promptly open the culprit vessels, myocardial ischemia-reperfusion injury (MIRI), resulting from restored blood flow, is often inevitable. Semaglutide (Sem), a novel GLP-1 analogue, is primarily utilized in managing Type 2 diabetes mellitus (T2DM). Recent research indicates that semaglutide may reduce the risk of major adverse cardiovascular events. Therefore, the purpose of this study is to explore whether semaglutide can ameliorate MIRI and explore its potential mechanism.

Methods and results

: A mouse model of myocardial ischemia-reperfusion (I/R) was created by ligating the left anterior descending coronary artery (LAD) first for 45 min and then reperfusing the heart for 24 h. Assessment of cardiac function and fibrosis were conducted through small animal ultrasound and Masson's staining. It was observed that semaglutide enhanced cardiac function recovery and diminished fibrosis in the I/R model. In vivo experiments, semaglutide proved to mitigate oxidative stress and inhibit ferroptosis in cardiomyocytes. RNA sequencing showed that S100 calcium binding protein A9 (S100A9) was the target gene of semaglutide to protect against MIRI. In vitro, experiments showed that semaglutide decreased the expression of S100A9 by activating the Protein Kinase C(PKC) pathway, thus inhibiting ferroptosis in cardiomyocytes.

Conclusion

Semaglutide can reduce I/R-induced myocardial injury by inhibiting the ferroptosis of cardiomyocytes. In the mechanism, semaglutide mainly reduce the expression of S100A9 via the activation of PKC signaling pathway. Therefore, semaglutide is considered as a potential treatment option for MIRI.

Mast Cells Contribute to Pressure Overload-Induced Myocardial Hypertrophy by Upregulating TRPV4 via Histamine: Role of Ca2+/ CnA/NFATc3 Signaling Pathway

OBJECTIVE

To investigate whether cardiac mast cells (MCs) participate in pressure overload-induced myocardial hypertrophy through the regulation of transient receptor potential vanilloid 4 (TRPV4).

METHODS

Pressure overload-induced myocardial hypertrophy was induced via abdominal aortic constriction (AAC). Myocardial hypertrophy was evaluated by measuring the heart weight index (HW/BW), lung weight index (LW/BW), ratio of heart weight to tibia length (HW/TL), ratio of lung weight to tibia length (LW/TL), and cross-sectional area of myocardial cells. qRT-PCR was used to detect the mRNA expression of TRPV4. Western blotting was used to detect the protein expression of TRPV4, mast cell tryptase, myosin heavy chain beta (β-MHC), calcineurin A (CnA), and nuclear factor of activated T-cell c3 (NFATc3). ELISA was used to measure the levels of brain natriuretic peptide (BNP) and histamine. Fluo4 AM was used to detect the calcium signal in H9c2 myocardial cells.

RESULTS

Compared with those of the sham rats, the myocardial mast cells, tryptase, HW/BW, LW/BW, HW/TL, and LW/TL, the cross-sectional area of the myocardial cells, and the expression of β-MHC, TRPV4, CnA, and NFATc3 in the myocardial tissue and the serum BNP of the AAC-treated rats increased significantly, whereas the MC stabilizer cromolyn sodium (CS) reversed these indicators. In H9c2 cardiomyocytes, treatment with histamine and the TRPV4 agonist GSK1016790A upregulated the expression of TRPV4, β-MHC, BNP, CnA and NFATc3 and increased calcium ion influx, whereas these effects were inhibited by the H2 receptor inhibitor famotidine and the TRPV4 inhibitor HC067047.

CONCLUSION

Cardiac MCs participate in pressure overload-induced myocardial hypertrophy through the upregulation of TRPV4 via its mediator histamine, and the Ca2+/CnA/NFATc3 signaling pathway is involved in this process.

CaMK II in Cardiovascular Diseases, Especially CaMK II-δ: Friends or Enemies

Cardiovascular diseases (CVDs) tend to affect the young population and are associated with a significant economic burden and psychological distress to the society and families. The physiological and pathological processes underlying CVDs are complex. Ca2+/calmodulin-dependent kinase II (CaMK II), a protein kinase, has multiple biological functions. It participates in multiple pathological processes and plays a central role in the development of CVDs. Based on this, this paper analyzes the structural characteristics and distribution of CaMK II, the mechanism of action of CaMK II, and the relationship between CaMK II and CVDs, including ion channels, ischemia-reperfusion injury, arrhythmias, myocardial hypertrophy, cardiotoxicity, hypertension, and dilated cardiomyopathy. Given the different regulatory mechanisms of different isoforms of CaMK II, the clinical use of specific targeted inhibitors or novel compounds should be evaluated in future research to provide new directions.

Maintaining calcium homeostasis as a strategy to alleviate nephrotoxicity caused by evodiamine

Evodiamine (EVO), the main active alkaloid in Evodia rutaecarpa, was shown to exert various pharmacological activities, especially anti-tumor. Currently, it is considered a potential anti-cancer drug due to its excellent anti-tumor activity, which unfortunately has adverse reactions, such as the risk of liver and kidney injury, when Evodia rutaecarpa containing EVO is used clinically. In the present study, we aim to clarify the potential toxic target organs and toxicity mechanism of EVO, an active monomer in Evodia rutaecarpa, and to develop mitigation strategies for its toxicity mechanism. Transcriptome analysis and related experiments showed that the PI3K/Akt pathway induced by calcium overload was an important step in EVO-induced apoptosis of renal cells. Specifically, intracellular calcium ions were increased, and mitochondrial calcium ions were decreased. In addition, EVO-induced calcium overload was associated with TRPV1 receptor activation. In vivo TRPV1 antagonist and calcium chelator effects were observed to significantly reduce body weight loss and renal damage in mice due to EVO toxicity. The potential nephrotoxicity of EVO was further confirmed by an in vivo test. In conclusion, TRPV1-mediated calcium overload-induced apoptosis is one of the mechanisms contributing to the nephrotoxicity of EVO due to its toxicity, whereas maintaining body calcium homeostasis is an effective measure to reduce toxicity. These studies suggest that the clinical use of EVO-containing herbal medicines should pay due attention to the changes in renal function of patients as well as the off-target effects of the drugs.

Fibroblast and myofibroblast activation in normal tissue repair and fibrosis

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

TRPV4 mediates IL-1-induced Ca2+ signaling, ERK activation and MMP expression

Ca2+ permeation through TRPV4 in fibroblasts is associated with pathological matrix degradation. In human gingival fibroblasts, IL-1β binding to its signaling receptor (IL-1R1) induces activation of extracellular regulated kinase (ERK) and MMP1 expression, processes that require Ca2+ flux across the plasma membrane. It is not known how IL-1R1, which does not conduct Ca2+, generates Ca2+ signals in response to IL-1. We examined whether TRPV4 mediates the Ca2+ fluxes required for ERK signaling in IL-1 stimulated gingival fibroblasts. TRPV4 was immunostained in fibroblasts of human gingival connective tissue and in focal adhesions of cultured mouse gingival fibroblasts. Human gingival fibroblasts treated with IL-1β showed no change of TRPV4 expression but there was increased MMP1 expression. In mouse, gingival fibroblasts expressing TRPV4, IL-1 strongly increased [Ca2+]i. Pre-incubation of cells with IL-1 Receptor Antagonist blocked Ca2+ entry induced by IL-1 or the TRPV4 agonist GSK101. Knockout of TRPV4 or expression of a non-Ca2+-conducting TRPV4 pore-mutant or pre-incubation with the TRPV4 inhibitor RN1734, blocked IL-1-induced Ca2+ transients and expression of the mouse interstitial collagenase, MMP13. Treatment of mouse gingival fibroblasts with GSK101 phenocopied Ca2+ and ERK responses induced by IL-1; these responses were absent in TRPV4-null cells or cells expressing a non-conducting TRPV4 pore-mutant. Immunostained IL-1R1 localized with TRPV4 in adhesions within cell extensions. While TRPV4 immunoprecipitates analyzed by mass spectrometry showed no association with IL-1R1, TRPV4 associated with Src-related proteins and Src co-immunoprecipitated with TRPV4. Src inhibition reduced IL-1-induced Ca2+ responses. The functional linkage of TRPV4 with IL-1R1 expands its repertoire of innate immune signaling processes by mediating IL-1-driven Ca2+ responses that drive matrix remodeling in fibroblasts. Thus, inhibiting TRPV4 activity may provide a new pharmacological approach for blunting matrix degradation in inflammatory diseases.

Trilobatin attenuates cerebral ischaemia/reperfusion-induced blood-brain barrier dysfunction by targeting matrix metalloproteinase 9: The legend of a food additive

BACKGROUND AND PURPOSE

Blood-brain barrier (BBB) breakdown is one of the crucial pathological changes of cerebral ischaemia-reperfusion (I/R) injury. Trilobatin (TLB), a naturally occurring food additive, exerts neuroprotective effects against cerebral I/R injury as demonstrated in our previous study. This study was designed to investigate the effect of TLB on BBB disruption after cerebral I/R injury.

EXPERIMENTAL APPROACH

Rats with focal cerebral ischaemia caused by transient middle cerebral artery occlusion were studied along with brain microvascular endothelial cells and human astrocytes to mimic BBB injury caused by oxygen and glucose deprivation/reoxygenation (OGD/R).

KEY RESULTS

The results showed that TLB effectively maintained BBB integrity and inhibited neuronal loss following cerebral I/R challenge. Furthermore, TLB increased tight junction proteins including ZO-1, Occludin and Claudin 5, and decreased the levels of apolipoprotein E (APOE) 4, cyclophilin A (CypA) and phosphorylated nuclear factor kappa B (NF-κB), thereby reducing proinflammatory cytokines. TLB also decreased the Bax/Bcl-2 ratio and cleaved-caspase 3 levels along with a reduced number of apoptotic neurons. Molecular docking and transcriptomics predicted MMP9 as a prominent gene evoked by TLB treatment. The protective effects of TLB on cerebral I/R-induced BBB breakdown was largely abolished by overexpression of MMP9, and the beneficial effects of TLB on OGD/R-induced loss of BBB integrity in human brain microvascular endothelial cells and astrocyte co-cultures was markedly reinforced by knockdown of MMP9.

CONCLUSIONS AND IMPLICATIONS

Our findings reveal a novel property of TLB: preventing BBB disruption following cerebral I/R via targeting MMP9 and inhibiting APOE4/CypA/NF-κB axis.

Role of mechanically-sensitive cation channels Piezo1 and TRPV4 in trabecular meshwork cell mechanotransduction

Glaucoma is one of the leading causes of irreversible blindness in developed countries, and intraocular pressure (IOP) is primary and only treatable risk factor, suggesting that to a significant extent, glaucoma is a disease of IOP disorder and pathological mechanotransduction. IOP-lowering ways are limited to decreaseing aqueous humour (AH) production or increasing the uveoscleral outflow pathway. Still, therapeutic approaches have been lacking to control IOP by enhancing the trabecular meshwork (TM) pathway. Trabecular meshwork cells (TMCs) have endothelial and myofibroblast properties and are responsible for the renewal of the extracellular matrix (ECM). Mechanosensitive cation channels, including Piezo1 and TRPV4, are abundantly expressed in primary TMCs and trigger mechanostress-dependent ECM and cytoskeletal remodelling. However, prolonged mechanical stimulation severely affects cellular biosynthesis through TMC mechanotransduction, including signaling, gene expression, ECM remodelling, and cytoskeletal structural changes, involving outflow facilities and elevating IOP. As for the functional coupling relationship between Piezo1 and TRPV4 channels, inspired by VECs and osteoblasts, we hypothesized that Piezo1 may also act upstream of TRPV4 in glaucomatous TM tissue, mediating the activation of TRPV4 via Ca2+ inflow or Ca2+ binding to phospholipase A2(PLA2), and thus be involved in increasing TM outflow resistance and elevated IOP. Therefore, this review aims to help identify new potential targets for IOP stabilization in ocular hypertension and primary open-angle glaucoma by understanding the mechanical transduction mechanisms associated with the development of glaucoma and may provide ideas into novel treatments for preventing the progression of glaucoma by targeting mechanotransduction.

TRPV4 blockade alleviates endoplasmic reticulum stress mediated apoptosis in hypoxia-induced cardiomyocyte injury

BACKGROUND

Hypoxia-induced myocardial injury remains to be a huge health issue worldwide. Transient receptor potential vanilloid 4 (TRPV4) is a high-flux Ca2+ channel that is involved in numerous cardiovascular diseases. However, the role of TRPV4 in myocardial hypoxic injury remains unclear. Accordingly, this study aimed to investigate the antiapoptotic activity of TRPV4 inhibition and elucidate the underlying mechanisms in myocardial hypoxic injury.

METHODS

The ability of TRPV4 to modulate the endoplasmic reticulum stress (ERS) and apoptosis was assessed in vitro through the administration of the TRPV4 antagonist HC-067047 or the agonist GSK1016790A. Additionally, intracellular Ca2+ concentration was measured by Fluo-4 AM.

RESULTS

TRPV4 expression was significantly upregulated in hypoxic H9c2 cells compared with that in normoxic cardiomyocytes, accompanied with increased intracellular Ca2+ levels. Conversely, TRPV4 inhibition alleviated ERS in hypoxic H9c2 cells and prevented apoptosis, whereas TRPV4 agonist exacerbated such events. Furthermore, H9c2 cell apoptosis was attenuated with the administration of 4-PBA, an ERS inhibitor.

CONCLUSION

TRPV4 inhibition alleviates hypoxia-induced H9c2 cell apoptosis by mitigating ERS.

The Multifaceted Functions of TRPV4 and Calcium Oscillations in Tissue Repair

The transient receptor potential vanilloid 4 (TRPV4) specifically functions as a mechanosensitive ion channel and is responsible for conveying changes in physical stimuli such as mechanical stress, osmotic pressure, and temperature. TRPV4 enables the entry of cation ions, particularly calcium ions, into the cell. Activation of TRPV4 channels initiates calcium oscillations, which trigger intracellular signaling pathways involved in a plethora of cellular processes, including tissue repair. Widely expressed throughout the body, TRPV4 can be activated by a wide array of physicochemical stimuli, thus contributing to sensory and physiological functions in multiple organs. This review focuses on how TRPV4 senses environmental cues and thereby initiates and maintains calcium oscillations, critical for responses to organ injury, tissue repair, and fibrosis. We provide a summary of TRPV4-induced calcium oscillations in distinct organ systems, along with the upstream and downstream signaling pathways involved. In addition, we delineate current animal and disease models supporting TRPV4 research and shed light on potential therapeutic targets for modulating TRPV4-induced calcium oscillation to promote tissue repair while reducing tissue fibrosis.

Ubiquitin-specific protease 38 promotes inflammatory atrial fibrillation induced by pressure overload

AIMS

Atrial structural and electrical remodelling is a major reason for the initiation and perpetuation of atrial fibrillation (AF). Ubiquitin-specific protease 38 (USP38) is a deubiquitinating enzyme, but its function in the heart remains unknown. The aim of this study was to investigate the effect of USP38 in pressure overload-induced AF.

METHODS AND RESULTS

Cardiac-specific knockout USP38 and cardiac-specific transgenic USP38 mice and their corresponding control mice were used in this study. After 4 weeks with or without aortic banding (AB) surgery, atrial echocardiography, atrial histology, electrophysiological study, and molecular analysis were assessed. Ubiquitin-specific protease 38 knockout mice showed a remarkable improvement in vulnerability to AF, atrial weight and diameter, atrial fibrosis, and calcium-handling protein expression after AB surgery. Conversely, USP38 overexpression further increased susceptibility to AF by exacerbating atrial structural and electrical remodelling. Mechanistically, USP38 interacted with and deubiquitinated nuclear factor-kappa B (NF-κB), and USP38 overexpression increased the level of p-NF-κB in vivo and in vitro, accompanied by the upregulation of NOD-like receptor protein 3 (NLRP3) and inflammatory cytokines, suggesting that USP38 contributes to adverse effects by driving NF-κB/NLRP3-mediated inflammatory responses.

CONCLUSION

Overall, our study indicates that USP38 promotes pressure overload-induced AF through targeting NF-κB/NLRP3-mediated inflammatory responses.

C/EBPβ isoform-specific regulation of podocyte pyroptosis in lupus nephritis-induced renal injury

As an essential factor in the prognosis of systemic lupus erythematosus (SLE), lupus nephritis (LN) can accelerate the rate at which patients with SLE can transition to chronic kidney disease or even end-stage renal disease. Podocytes now appear to be a possible direct target in LN in addition to being prone to collateral damage from glomerular capillary lesions induces by immune complexes and inflammatory processes. The NLRP3 inflammasome is regulated by CCAAT/enhancer-binding protein β (C/EBPβ), which is involved in the pathogenesis of SLE. However, the role and mechanism of C/EBPβ in LN remain unclear. In this investigation, glomerular podocytes treated with LN serum and MRL/lpr mice were employed as in vivo and in vitro models of LN, respectively. In vivo, the expression of C/EBPβ isoforms was detected in kidney specimens of humans and mice with LN. Then we assessed the effect of C/EBPβ inhibition on renal structure and function by injecting RNAi adeno-associated virus of C/EBPβ shRNA into MRL/lpr mice. In vitro, glomerular podocytes were treated with LN serum and C/EBPβ siRNA to explore the role of C/EBPβ in the activation of the AIM2 inflammasome and podocyte injury. C/EBPβ-LAP and C/EBPβ-LIP were significantly overexpressed in kidney tissue samples from LN patients and mice, and C/EBPβ inhibition significantly alleviated renal function damage and ameliorated renal structural deficiencies. Inflammatory pathways downstream from the AIM2 inflammasome could be suppressed by C/EBPβ knockdown. Furthermore, the upregulation of C/EBPβ-LAP could activate the AIM2 inflammasome and podocyte pyroptosis by binding to the promoters of AIM2 and CASPASE1 to enhance their expression, and the knockdown of AIM2 or (and) caspase-1 reversed the effects of C/EBPβ-LAP overexpression. Interestingly, C/EBPβ-LIP overexpression could transcriptionally inhibit IRAG and promote Ca2+ release-mediated activation of the AIM2 inflammasome. This finding suggests that C/EBPβ is not only involved in the regulation of the expression of key proteins of the AIM2 inflammasome but also affects the polymerization of key proteins of the AIM2 inflammasome through the regulation of Ca2+ release. In conclusion, this study provides a new idea for studying the regulatory mechanism of C/EBPβ and provides a theoretical basis for the early diagnosis and treatment of LN in the future. © 2023 The Pathological Society of Great Britain and Ireland.

Deletion of Endothelial TRPV4 Protects Heart From Pressure Overload-Induced Hypertrophy

BACKGROUND

Left ventricular hypertrophy is a bipolar response, starting as an adaptive response to the hemodynamic challenge, but over time develops maladaptive pathology partly due to microvascular rarefaction and impaired coronary angiogenesis. Despite the profound influence on cardiac function, the mechanotransduction mechanisms that regulate coronary angiogenesis, leading to heart failure, are not well known.

METHODS

We subjected endothelial-specific knockout mice of mechanically activated ion channel, TRPV4 (transient receptor potential cation channel subfamily V member 4; TRPV4ECKO) to pressure overload via transverse aortic constriction and examined cardiac function, cardiomyocyte hypertrophy, cardiac fibrosis, and apoptosis. Further, we measured microvascular density and underlying TRPV4 mechanotransduction mechanisms using human microvascular endothelial cells, extracellular matrix gels of varying stiffness, unbiased RNA sequencing, small interfering RNA, Western blot, quantitative-PCR, and confocal immunofluorescence techniques.

RESULTS

We demonstrate that endothelial-specific deletion of TRPV4 preserved cardiac function, cardiomyocyte structure, and reduced cardiac fibrosis compared with TRPV4lox/lox mice, 28 days post-transverse aortic constriction. Interestingly, comprehensive RNA sequencing analysis revealed an upregulation of proangiogenic factors (VEGFα [vascular endothelial growth factor α], NOS3 [nitric oxide synthase 3], and FGF2 [fibroblast growth factor 2]) with concomitant increase in microvascular density in TRPV4ECKO hearts after transverse aortic constriction compared with TRPV4lox/lox. Further, an increased expression of VEGFR2 (vascular endothelial growth factor receptor 2) and activation of the YAP (yes-associated protein) pathway were observed in TRPV4ECKO hearts. Mechanistically, we found that downregulation of TRPV4 in endothelial cells induced matrix stiffness-dependent activation of YAP and VEGFR2 via the Rho/Rho kinase/large tumor suppressor kinase pathway.

CONCLUSIONS

Our results suggest that endothelial TRPV4 acts as a mechanical break for coronary angiogenesis, and uncoupling endothelial TRPV4 mechanotransduction attenuates pathological cardiac hypertrophy by enhancing coronary angiogenesis.

Novel approaches to target fibroblast mechanotransduction in fibroproliferative diseases

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

Pathophysiological Roles of the TRPV4 Channel in the Heart

The transient receptor potential vanilloid 4 (TRPV4) channel is a non-selective cation channel that is mostly permeable to calcium (Ca²⁺), which participates in intracellular Ca²⁺ handling in cardiac cells. It is widely expressed through the body and is activated by a large spectrum of physicochemical stimuli, conferring it a role in a variety of sensorial and physiological functions. Within the cardiovascular system, TRPV4 expression is reported in cardiomyocytes, endothelial cells (ECs) and smooth muscle cells (SMCs), where it modulates mitochondrial activity, Ca²⁺ homeostasis, cardiomyocytes electrical activity and contractility, cardiac embryonic development and fibroblast proliferation, as well as vascular permeability, dilatation and constriction. On the other hand, TRPV4 channels participate in several cardiac pathological processes such as the development of cardiac fibrosis, hypertrophy, ischemia-reperfusion injuries, heart failure, myocardial infarction and arrhythmia. In this manuscript, we provide an overview of TRPV4 channel implications in cardiac physiology and discuss the potential of the TRPV4 channel as a therapeutic target against cardiovascular diseases.