Transient receptor potential vanilloid 4 channel participates in mouse ventricular electrical activity

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 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.

TRPV4 Channels Promote Pathological, but Not Physiological, Cardiac Remodeling through the Activation of Calcineurin/NFAT and TRPC6

TRPV4 channels, which respond to mechanical activation by permeating Ca2+ into the cell, may play a pivotal role in cardiac remodeling during cardiac overload. Our study aimed to investigate TRPV4 involvement in pathological and physiological remodeling through Ca2+-dependent signaling. TRPV4 expression was assessed in heart failure (HF) models, induced by isoproterenol infusion or transverse aortic constriction, and in exercise-induced adaptive remodeling models. The impact of genetic TRPV4 inhibition on HF was studied by echocardiography, histology, gene and protein analysis, arrhythmia inducibility, Ca2+ dynamics, calcineurin (CN) activity, and NFAT nuclear translocation. TRPV4 expression exclusively increased in HF models, strongly correlating with fibrosis. Isoproterenol-administered transgenic TRPV4-/- mice did not exhibit HF features. Cardiac fibroblasts (CFb) from TRPV4+/+ animals, compared to TRPV4-/-, displayed significant TRPV4 overexpression, elevated Ca2+ influx, and enhanced CN/NFATc3 pathway activation. TRPC6 expression paralleled that of TRPV4 in all models, with no increase in TRPV4-/- mice. In cultured CFb, the activation of TRPV4 by GSK1016790A increased TRPC6 expression, which led to enhanced CN/NFATc3 activation through synergistic action of both channels. In conclusion, TRPV4 channels contribute to pathological remodeling by promoting fibrosis and inducing TRPC6 upregulation through the activation of Ca2+-dependent CN/NFATc3 signaling. These results pose TRPV4 as a primary mediator of the pathological response.

Modulating TRPV4 Channel Activity in Pro-Inflammatory Macrophages within the 3D Tissue Analog

Investigating macrophage plasticity emerges as a promising strategy for promoting tissue regeneration and can be exploited by regulating the transient receptor potential vanilloid 4 (TRPV4) channel. The TRPV4 channel responds to various stimuli including mechanical, chemical, and selective pharmacological compounds. It is well documented that treating cells such as epithelial cells and fibroblasts with a TRPV4 agonist enhances the Ca2+ influx to the cells, which leads to secretion of pro-inflammatory cytokines, while a TRPV4 antagonist reduces both Ca2+ influx and pro-inflammatory cytokine secretion. In this work, we investigated the effect of selective TRPV4 modulator compounds on U937-differentiated macrophages encapsulated within three-dimensional (3D) matrices. Despite offering a more physiologically relevant model than 2D cultures, pharmacological treatment of macrophages within 3D collagen matrices is largely overlooked in the literature. In this study, pro-inflammatory macrophages were treated with an agonist, 500 nM of GSK1016790A (TRPV4(+)), and an antagonist, 10 mM of RN-1734 (TRPV4(-)), to elucidate the modulation of the TRPV4 channel at both cellular and extracellular levels. To evaluate macrophage phenotypic alterations within 3D collagen matrices following TRPV4 modulator treatment, we employed structural techniques (SEM, Masson's trichrome, and collagen hybridizing peptide (CHP) staining), quantitative morphological measures for phenotypic assessment, and genotypic methods such as quantitative real-time PCR (qRT-PCR) and immunohistochemistry (IHC). Our data reveal that pharmacological modulation of the macrophage TRPV4 channel alters the cytoskeletal structure of macrophages and influences the 3D structure encapsulating them. Moreover, we proved that treating macrophages with a TRPV4 agonist and antagonist enhances the expression of pro- and anti-inflammatory genes, respectively, leading to the upregulation of surface markers CD80 and CD206. In the TRPV4(-) group, the CD206 gene and CD206 surface marker were significantly upregulated by 9- and 2.5-fold, respectively, compared to the control group. These findings demonstrate that TRPV4 modulation can be utilized to shift macrophage phenotype within the 3D matrix toward a desired state. This is an innovative approach to addressing inflammation in musculoskeletal tissues.

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.

Guidelines for assessment of cardiac electrophysiology and arrhythmias in small animals

Cardiac arrhythmias are a major cause of morbidity and mortality worldwide. Although recent advances in cell-based models, including human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM), are contributing to our understanding of electrophysiology and arrhythmia mechanisms, preclinical animal studies of cardiovascular disease remain a mainstay. Over the past several decades, animal models of cardiovascular disease have advanced our understanding of pathological remodeling, arrhythmia mechanisms, and drug effects and have led to major improvements in pacing and defibrillation therapies. There exist a variety of methodological approaches for the assessment of cardiac electrophysiology and a plethora of parameters may be assessed with each approach. This guidelines article will provide an overview of the strengths and limitations of several common techniques used to assess electrophysiology and arrhythmia mechanisms at the whole animal, whole heart, and tissue level with a focus on small animal models. We also define key electrophysiological parameters that should be assessed, along with their physiological underpinnings, and the best methods with which to assess these parameters.

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

Previous studies, including our own, have demonstrated that transient receptor potential vanilloid 4 (TRPV4) is expressed in hearts and implicated in cardiac remodeling and dysfunction. However, the effects of TRPV4 on pressure overload-induced cardiac hypertrophy remain unclear. In this study, we found that TRPV4 expression was significantly increased in mouse hypertrophic hearts, human failing hearts, and neurohormone-induced hypertrophic cardiomyocytes. Deletion of TRPV4 attenuated transverse aortic constriction (TAC)-induced cardiac hypertrophy, cardiac dysfunction, fibrosis, inflammation, and the activation of NFκB - NOD - like receptor pyrin domain-containing protein 3 (NLRP3) in mice. Furthermore, the TRPV4 antagonist GSK2193874 (GSK3874) inhibited cardiac remodeling and dysfunction induced by TAC. In vitro, pretreatment with GSK3874 reduced the neurohormone-induced cardiomyocyte hypertrophy and intracellular Ca2+ concentration elevation. The specific TRPV4 agonist GSK1016790A (GSK790A) triggered Ca2+ influx and evoked the phosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaMKII). But these effects were abolished by removing extracellular Ca2+ or GSK3874. More importantly, TAC or neurohormone stimulation-induced CaMKII phosphorylation was significantly blocked by TRPV4 inhibition. Finally, we show that CaMKII inhibition significantly prevented the phosphorylation of NFκB induced by GSK790A. Our results suggest that TRPV4 activation contributes to pressure overload-induced cardiac hypertrophy and dysfunction. This effect is associated with upregulated Ca2+/CaMKII mediated activation of NFκB-NLRP3. Thus, TRPV4 may represent a potential therapeutic drug target for cardiac hypertrophy and dysfunction after pressure overload.

Role of Known Transient Receptor Potential Vanilloid Channels in Modulating Cardiac Mechanobiology

The transient receptor potential (TRP) channels have been described in almost every mammalian cell type. Several members of the Vanilloid (TRPV) subtype have been found to play important roles in modulating cardiac structure and function through Ca²⁺ handling in response to systemic and local mechanobiological cues. In this review, we will consider the most studied TRPV channels in the cardiovascular field; transient receptor potential vanilloid 1 as a modulator of cardiac hypertrophy; transient receptor potential vanilloid 2 as a structural and functional protein; transient receptor potential vanilloid 3 in the development of hypertrophy and myocardial fibrosis; and transient receptor potential vanilloid 4 in its roles modulating the fibrotic and functional responses of the heart to pressure overload. Lastly, we will also review the potential overlapping roles of these channels with other TRP proteins as well as the advances in translational and clinical arenas associated with TRPV channels.

TRPV4 Mechanotransduction in Fibrosis

Fibrosis is an irreversible, debilitating condition marked by the excessive production of extracellular matrix and tissue scarring that eventually results in organ failure and disease. Differentiation of fibroblasts to hypersecretory myofibroblasts is the key event in fibrosis. Although both soluble and mechanical factors are implicated in fibroblast differentiation, much of the focus is on TGF-β signaling, but to date, there are no specific drugs available for the treatment of fibrosis. In this review, we describe the role for TRPV4 mechanotransduction in cardiac and lung fibrosis, and we propose TRPV4 as an alternative therapeutic target for fibrosis.

Activation of transient receptor potential vanilloid 4 exacerbates myocardial ischemia-reperfusion injury via JNK-CaMKII phosphorylation pathway in isolated mice hearts

Previous studies, including our own, have demonstrated that transient receptor potential vanilloid 4 (TRPV4) is involved in myocardial ischemia-reperfusion (IR) injury, yet its underlying molecular mechanism remains unclear. In this study, we isolated mice hearts for a Langendorff perfusion test and used HL-1 myocytes for in vitro assessments. We first confirmed that TRPV4 agonist (GSK101) enhanced myocardial IR injury, as demonstrated by the reduced recovery of cardiac function, larger myocardial infarct size, and more apoptotic cells. We also found that GSK101 could further increase the phosphorylation of JNK and CaMKII in isolated hearts during IR. Notably, GSK101 dose-dependently evoked the phosphorylation of JNK and CaMKII in isolated normal hearts. All above GSK101-induced effects could be significantly blocked by the pharmacological inhibition or genetic ablation of TRPV4. More importantly, JNK inhibition (with SP600125) or CaMKII inhibition (with KN93 or in transgenic AC3-I mice) could prevent GSK101-induced myocardial injury during IR. In HL-1 myocytes, GSK101 triggered Ca²⁺ influx and evoked the phosphorylation of JNK and CaMKII but these effects were abolished by removing extracellular Ca²⁺ or in the presence of a TRPV4 antagonist. Finally, we showed that in HL-1 myocytes and isolated hearts during IR, JNK inhibition significantly inhibited the phosphorylation of CaMKII induced by GSK101 but CaMKII inhibition had no effect on JNK activation induced by GSK101. Our data suggest that TRPV4 activation exacerbates myocardial IR injury via the JNK-CaMKII phosphorylation pathway.

Modulation of the Cardiac Myocyte Action Potential by the Magnesium-Sensitive TRPM6 and TRPM7-like Current

The cardiac Mg²⁺-sensitive, TRPM6, and TRPM7-like channels remain undefined, especially with the uncertainty regarding TRPM6 expression in cardiomyocytes. Additionally, their contribution to the cardiac action potential (AP) profile is unclear. Immunofluorescence assays showed the expression of the TRPM6 and TRPM7 proteins in isolated pig atrial and ventricular cardiomyocytes, of which the expression was modulated by incubation in extracellular divalent cation-free conditions. In patch clamp studies of cells dialyzed with solutions containing zero intracellular Mg²⁺ concentration ([Mg²⁺]_i) to activate the Mg²⁺-sensitive channels, raising extracellular [Mg²⁺] ([Mg²⁺]_o) from the 0.9-mM baseline to 7.2 mM prolonged the AP duration (APD). In contrast, no such effect was observed in cells dialyzed with physiological [Mg²⁺]_i. Under voltage clamp, in cells dialyzed with zero [Mg²⁺]_i, depolarizing ramps induced an outward-rectifying current, which was suppressed by raising [Mg²⁺]_o and was absent in cells dialyzed with physiological [Mg²⁺]_i. In cells dialyzed with physiological [Mg²⁺]_i, raising [Mg²⁺]_o decreased the L-type Ca²⁺ current and the total delayed-rectifier current but had no effect on the APD. These results suggest a co-expression of the TRPM6 and TRPM7 proteins in cardiomyocytes, which are therefore the molecular candidates for the native cardiac Mg²⁺-sensitive channels, and also suggest that the cardiac Mg²⁺-sensitive current shortens the APD, with potential implications in arrhythmogenesis.

Calcium and Heart Failure: How Did We Get Here and Where Are We Going?

The occurrence and prevalence of heart failure remain high in the United States as well as globally. One person dies every 30 s from heart disease. Recognizing the importance of heart failure, clinicians and scientists have sought better therapeutic strategies and even cures for end-stage heart failure. This exploration has resulted in many failed clinical trials testing novel classes of pharmaceutical drugs and even gene therapy. As a result, along the way, there have been paradigm shifts toward and away from differing therapeutic approaches. The continued prevalence of death from heart failure, however, clearly demonstrates that the heart is not simply a pump and instead forces us to consider the complexity of simplicity in the pathophysiology of heart failure and reinforces the need to discover new therapeutic approaches.