Successful TRPV1 antagonist treatment for cardiac hypertrophy and heart failure in mice

Ca2+ Signaling in Cardiac Fibroblasts: An Emerging Signaling Pathway Driving Fibrotic Remodeling in Cardiac Disorders

Cardiac fibrosis is a scarring event that occurs in the myocardium in response to multiple cardiovascular disorders, such as acute myocardial infarction (AMI), ischemic cardiomyopathy, dilated cardiomyopathy, hypertensive heart disease, inflammatory heart disease, diabetic cardiomyopathy, and aortic stenosis. Fibrotic remodeling is mainly sustained by the differentiation of fibroblasts into myofibroblasts, which synthesize and secrete most of the extracellular matrix (ECM) proteins. An increase in the intracellular Ca2+ concentration ([Ca2+]i) in cardiac fibroblasts is emerging as a critical mediator of the fibrogenic signaling cascade. Herein, we review the mechanisms that may shape intracellular Ca2+ signals involved in fibroblast transdifferentiation into myofibroblasts. We focus our attention on the functional interplay between inositol-1,4,5-trisphosphate (InsP3) receptors (InsP3Rs) and store-operated Ca2+ entry (SOCE). In accordance with this, InsP3Rs and SOCE drive the Ca2+ response elicited by Gq-protein coupled receptors (GqPCRs) that promote fibrotic remodeling. Then, we describe the additional mechanisms that sustain extracellular Ca2+ entry, including receptor-operated Ca2+ entry (ROCE), P2X receptors, Transient Receptor Potential (TRP) channels, and Piezo1 channels. In parallel, we discuss the pharmacological manipulation of the Ca2+ handling machinery as a promising approach to mitigate or reverse fibrotic remodeling in cardiac disorders.

Metabolomics of repetitive myocardial stunning in chronic multivessel coronary artery stenosis: Effect of non-selective and selective β1-receptor blockers

Chronic coronary artery stenosis can lead to regional myocardial dysfunction in the absence of myocardial infarction by repetitive stunning, hibernation or both. The molecular mechanisms underlying repetitive stunning-associated myocardial dysfunction are not clear. We used non-targeted metabolomics to elucidate responses to chronically stunned myocardium in a canine model with and without β-adrenergic blockade treatment. After development of left ventricular systolic dysfunction induced by ameroid constrictors on the coronary arteries, animals were randomized to 3 months of placebo, metoprolol or carvedilol. We compared these two β-blockers with their different β-adrenergic selectivities on myocardial function, perfusion and metabolic pathways involved in tissue undergoing chronic stunning. Control animals underwent sham surgery. Dysfunction in stunned myocardium was associated with reduced fatty acid oxidation and enhanced ketogenic amino acid metabolism, together with alterations in mitochondrial membrane phospholipid composition. These changes were consistent with impaired mitochondrial function and were linked to reduced nitric oxide and peroxisome proliferator-activated receptor signalling, resulting in a decline in adenosine monophosphate-activated protein kinase. Mitochondrial changes were ameliorated by carvedilol more than metoprolol, and improvement was linked to nitric oxide and possibly hydrogen sulphide signalling. In summary, repetitive myocardial stunning commonly seen in chronic multivessel coronary artery disease is associated with adverse metabolic remodelling linked to mitochondrial dysfunction and specific signalling pathways. These changes are reversed by β-blockers, with the non-selective inhibitor having a more favourable impact. This is the first investigation to demonstrate that β-blockade-associated improvement of ventricular function in chronic myocardial stunning is associated with restoration of mitochondrial function. KEY POINTS: The mechanisms responsible for the metabolic changes associated with repetitive myocardial stunning seen in chronic multivessel coronary artery disease have not been fully investigated. In a canine model of repetitive myocardial stunning, we showed that carvedilol, a non-selective β-receptor blocker, ameliorated adverse metabolic remodelling compared to metoprolol, a selective β1-receptor blocker, by improving nitric oxide synthase and adenosine monophosphate protein kinase function, enhancing calcium/calmodulin-dependent protein kinase, probably increasing hydrogen sulphide, and suppressing cyclic-adenosine monophosphate signalling. Mitochondrial fatty acid oxidation alterations were ameliorated by carvedilol to a larger extent than metoprolol; this improvement was linked to nitric oxide and possibly hydrogen sulphide signalling. Both β-blockers improved the cardiac energy imbalance by reducing metabolites in ketogenic amino acid and nucleotide metabolism. These results elucidated why metabolic remodelling with carvedilol is preferable to metoprolol when treating chronic ischaemic left ventricular systolic dysfunction caused by repetitive myocardial stunning.

Therapeutic potential of cannabidiol (CBD) in the treatment of cardiovascular diseases

INTRODUCTION

Cannabidiol (CBD) is the primary non-psychoactive chemical derived from Cannabis Sativa, and its growing popularity is due to its potential therapeutic properties while avoiding the psychotropic effects of other phytocannabinoids, such as tetrahydrocannabinol (THC). Numerous pre-clinical studies in cellular and animal models and human clinical trials have demonstrated a positive impact of CBD on physiological and pathological processes. Recently, the FDA approved its use for the treatment of seizures, and clinical trials to test the efficacy of CBD in myocarditis and pericarditis are ongoing.

AREAS COVERED

We herein reviewed the current literature on the reported effects of CBD in the cardiovascular system, highlighting the physiological effects and the outcomes of using CBD as a therapeutic tool in pathological conditions to address this significant global health concern.

EXPERT OPINION

The comprehensive examination of the literature emphasizes the potential of CBD as a therapeutic option for treating cardiovascular diseases through its anti-inflammatory, vasodilatory, anti-fibrotic, and antioxidant properties in different conditions such as diabetic cardiomyopathy, myocarditis, doxorubicin-induced cardiotoxicity, and ischemia-reperfusion injury.

TRPV1 Channels Are New Players in the Reticulum-Mitochondria Ca2+ Coupling in a Rat Cardiomyoblast Cell Line

The Ca2+ release in microdomains formed by intercompartmental contacts, such as mitochondria-associated endoplasmic reticulum membranes (MAMs), encodes a signal that contributes to Ca2+ homeostasis and cell fate control. However, the composition and function of MAMs remain to be fully defined. Here, we focused on the transient receptor potential vanilloid 1 (TRPV1), a Ca2+-permeable ion channel and a polymodal nociceptor. We found TRPV1 channels in the reticular membrane, including some at MAMs, in a rat cardiomyoblast cell line (SV40-transformed H9c2) by Western blotting, immunostaining, cell fractionation, and proximity ligation assay. We used chemical and genetic probes to perform Ca2+ imaging in four cellular compartments: the endoplasmic reticulum (ER), cytoplasm, mitochondrial matrix, and mitochondrial surface. Our results showed that the ER Ca2+ released through TRPV1 channels is detected at the mitochondrial outer membrane and transferred to the mitochondria. Finally, we observed that prolonged TRPV1 modulation for 30 min alters the intracellular Ca2+ equilibrium and influences the MAM structure or the hypoxia/reoxygenation-induced cell death. Thus, our study provides the first evidence that TRPV1 channels contribute to MAM Ca2+ exchanges.

Intermittent Hypoxic Preconditioning Plays a Cardioprotective Role in Doxorubicin-Induced Cardiomyopathy

Intermittent hypoxic preconditioning (IHP) is a well-established cardioprotective intervention in models of ischemia/reperfusion injury. Nevertheless, the significance of IHP in different cardiac pathologies remains elusive. In order to investigate the role of IHP and its effects on calcium-dependent signalization in HF, we employed a model of cardiomyopathy induced by doxorubicin (Dox), a widely used drug from the class of cardiotoxic antineoplastics, which was i.p. injected to Wistar rats (4 applications of 4 mg/kg/week). IHP-treated group was exposed to IHP for 2 weeks prior to Dox administration. IHP ameliorated Dox-induced reduction in cardiac output. Western blot analysis revealed increased expression of sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA2a) while the expression of hypoxia inducible factor (HIF)-1-α, which is a crucial regulator of hypoxia-inducible genes, was not changed. Animals administered with Dox had further decreased expression of TRPV1 and TRPV4 (transient receptor potential, vanilloid subtype) ion channels along with suppressed Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) activation. In summary, IHP-mediated improvement in cardiac output in the model of Dox-induced cardiomyopathy is likely a result of increased SERCA2a expression which could implicate IHP as a potential protective intervention in Dox cardiomyopathy, however, further analysis of observed effects is still required.

Progress on role of ion channels of cardiac fibroblasts in fibrosis

Cardiac fibrosis is defined as excessive deposition of extracellular matrix (ECM) in pathological conditions. Cardiac fibroblasts (CFs) activated by injury or inflammation differentiate into myofibroblasts (MFs) with secretory and contractile functions. In the fibrotic heart, MFs produce ECM which is composed mainly of collagen and is initially involved in maintaining tissue integrity. However, persistent fibrosis disrupts the coordination of excitatory contractile coupling, leading to systolic and diastolic dysfunction, and ultimately heart failure. Numerous studies have demonstrated that both voltage- and non-voltage-gated ion channels alter intracellular ion levels and cellular activity, contributing to myofibroblast proliferation, contraction, and secretory function. However, an effective treatment strategy for myocardial fibrosis has not been established. Therefore, this review describes the progress made in research related to transient receptor potential (TRP) channels, Piezo1, Ca²⁺ release-activated Ca²⁺ (CRAC) channels, voltage-gated Ca²⁺ channels (VGCCs), sodium channels, and potassium channels in myocardial fibroblasts with the aim of providing new ideas for treating myocardial fibrosis.

Emerging role of transient receptor potential (TRP) ion channels in cardiac fibroblast pathophysiology

Cardiac fibroblasts make up a major proportion of non-excitable cells in the heart and contribute to the cardiac structural integrity and maintenance of the extracellular matrix. During myocardial injury, fibroblasts can be activated to trans-differentiate into myofibroblasts, which secrete extracellular matrix components as part of healing, but may also induce cardiac fibrosis and pathological cardiac structural and electrical remodeling. The mechanisms regulating such cellular processes still require clarification, but the identification of transient receptor potential (TRP) channels in cardiac fibroblasts could provide further insights into the fibroblast-related pathophysiology. TRP proteins belong to a diverse superfamily, with subgroups such as the canonical (TRPC), vanilloid (TRPV), melastatin (TRPM), ankyrin (TRPA), polycystin (TRPP), and mucolipin (TRPML). Several TRP proteins form non-selective channels that are permeable to cations like Na+ and Ca2+ and are activated by various chemical and physical stimuli. This review highlights the role of TRP channels in cardiac fibroblasts and the possible underlying signaling mechanisms. Changes in the expression or activity of TRPs such as TRPCs, TRPVs, TRPMs, and TRPA channels modulate cardiac fibroblasts and myofibroblasts, especially under pathological conditions. Such TRPs contribute to cardiac fibroblast proliferation and differentiation as well as to disease conditions such as cardiac fibrosis, atrial fibrillation, and fibroblast metal toxicity. Thus, TRP channels in fibroblasts represent potential drug targets in cardiac disease.

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.

TRP Channels as Sensors of Aldehyde and Oxidative Stress

The transient receptor potential (TRP) cation channel superfamily comprises more than 50 channels that play crucial roles in physiological processes. TRP channels are responsive to several exogenous and endogenous biomolecules, with aldehydes emerging as a TRP channel trigger contributing to a cellular cascade that can lead to disease pathophysiology. The body is not only exposed to exogenous aldehydes via tobacco products or alcoholic beverages, but also to endogenous aldehydes triggered by lipid peroxidation. In response to lipid peroxidation from inflammation or organ injury, polyunsaturated fatty acids undergo lipid peroxidation to aldehydes, such as 4-hydroxynonenal. Reactive aldehydes activate TRP channels via aldehyde-induced protein adducts, leading to the release of pro-inflammatory mediators driving the pathophysiology caused by cellular injury, including inflammatory pain and organ reperfusion injury. Recent studies have outlined how aldehyde dehydrogenase 2 protects against aldehyde toxicity through the clearance of toxic aldehydes, indicating that targeting the endogenous aldehyde metabolism may represent a novel treatment strategy. An addition approach can involve targeting specific TRP channel regions to limit the triggering of a cellular cascade induced by aldehydes. In this review, we provide a comprehensive summary of aldehydes, TRP channels, and their interactions, as well as their role in pathological conditions and the different therapeutical treatment options.

Chronic ablation of TRPV1-sensitive skeletal muscle afferents attenuates the muscle metaboreflex

Exercise intolerance is a hallmark symptom of cardiovascular disease and likely occurs via enhanced activation of muscle metaboreflex-induced vasoconstriction of the heart and active skeletal muscle which, thereby limits cardiac output and peripheral blood flow. Muscle metaboreflex vasoconstrictor responses occur via activation of metabolite-sensitive afferent fibers located in ischemic active skeletal muscle, some of which express transient receptor potential vanilloid 1 (TRPV1) cation channels. Local cardiac and intrathecal administration of an ultrapotent noncompetitive, dominant negative agonist resiniferatoxin (RTX) can ablate these TRPV1-sensitive afferents. This technique has been used to attenuate cardiac sympathetic afferents and nociceptive pain. We investigated whether intrathecal administration (L4-L6) of RTX (2 µg/kg) could chronically attenuate subsequent muscle metaboreflex responses elicited by reductions in hindlimb blood flow during mild exercise (3.2 km/h) in chronically instrumented conscious canines. RTX significantly attenuated metaboreflex-induced increases in mean arterial pressure (27 ± 5.0 mmHg vs. 6 ± 8.2 mmHg), cardiac output (1.40 ± 0.2 L/min vs. 0.28 ± 0.1 L/min), and stroke work (2.27 ± 0.2 L·mmHg vs. 1.01 ± 0.2 L·mmHg). Effects were maintained until 78 ± 14 days post-RTX at which point the efficacy of RTX injection was tested by intra-arterial administration of capsaicin (20 µg/kg). A significant reduction in the mean arterial pressure response (+45.7 ± 6.5 mmHg pre-RTX vs. +19.7 ± 3.1 mmHg post-RTX) was observed. We conclude that intrathecal administration of RTX can chronically attenuate the muscle metaboreflex and could potentially alleviate enhanced sympatho-activation observed in cardiovascular disease states.

Does Transient Receptor Potential Vanilloid Type 1 Alleviate or Aggravate Pathological Myocardial Hypertrophy?

Transient receptor potential vanilloid type 1 (TRPV1) is a non-selective cation channel, which is involved in the endogenous stress adaptation mechanism for protection of the heart as well as the occurrence and development of some heart diseases. Although the effect of activation of the TRPV1 channel on different types of non-neural cells in the heart remains unclear, most data show that stimulation of sensory nerves expressing TRPV1 or stimulation/overexpression of the TRPV1 channel has a beneficial role in heart disease. Some studies have proven that TRPV1 has an important relationship with pathological myocardial hypertrophy, but the specific mechanism and effect are not clear. In order to help researchers better understand the relationship between TRPV1 and pathological myocardial hypertrophy, this paper aims to summarize the effect of TRPV1 and the related mechanism in the occurrence and development of pathological myocardial hypertrophy from the following three points of view: 1) role of TRPV1 in alleviation of pathological myocardial hypertrophy; 2) role of TRPV1 in aggravation of pathological myocardial hypertrophy; and 3) the point of view of our team of researchers. It is expected that new therapies can provide potential targets for pathological myocardial hypertrophy.

TRPV2 channel as a possible drug target for the treatment of heart failure

Heart transplantation is currently the only viable option available for the treatment of severe heart failure conditions such as dilated cardiomyopathy. Hence, novel drugs for treating such conditions need to be developed urgently. Recent studies suggest that Ca²⁺ overload is involved in the onset and progression of dilated cardiomyopathy, and thus heart failure. The expression and activation of the Ca²⁺ permeable channel, transient receptor potential vanilloid 2 (TRPV2) channel have been found to play an essential role in sustained intracellular Ca²⁺ concentration increase, leading to heart failure. However, since there have been no TRPV2-specific inhibitors available until recently, the effect of TRPV2 inhibition on the pathology has not been clearly elucidated. Recent reports show that inhibiting TRPV2 activity effectively improves cardiac function, suppressing myocardial fibrosis and ameliorating the prognosis in animal models of cardiomyopathy with heart failure. In addition to that, inflammation is reported to be involved in the development of heart failure. Here, we review the recent findings on TRPV2 in cardiomyocytes and immune cells involved in the development of heart failure and discuss the current progress of drug development for the treatment of heart failure via targeting TRPV2.

Transient receptor potential channels in cardiac health and disease

Transient receptor potential (TRP) channels are nonselective cationic channels that are generally Ca²⁺ permeable and have a heterogeneous expression in the heart. In the myocardium, TRP channels participate in several physiological functions, such as modulation of action potential waveform, pacemaking, conduction, inotropy, lusitropy, Ca²⁺ and Mg²⁺ handling, store-operated Ca²⁺ entry, embryonic development, mitochondrial function and adaptive remodelling. Moreover, TRP channels are also involved in various pathological mechanisms, such as arrhythmias, ischaemia-reperfusion injuries, Ca²⁺-handling defects, fibrosis, maladaptive remodelling, inherited cardiopathies and cell death. In this Review, we present the current knowledge of the roles of TRP channels in different cardiac regions (sinus node, atria, ventricles and Purkinje fibres) and cells types (cardiomyocytes and fibroblasts) and discuss their contribution to pathophysiological mechanisms, which will help to identify the best candidates for new therapeutic targets among the cardiac TRP family.

"TRPV1 is a component of the atrial natriuretic signaling complex, and using orally delivered antagonists, presents a valid therapeutic target in the longitudinal reversal and treatment of cardiac hypertrophy and heart failure"

Activation of the atrial natriuretic signaling pathway is intrinsic to the pathological responses associated with a range of cardiovascular diseases that stress the heart, especially those involved in sustained cardiac pressure overload which induces hypertrophy and the pathological remodeling that frequently leads to heart failure. We identify transient receptor potential cation channel, subfamily V, member 1, as a regulated molecular component, and therapeutic target of this signaling system. Data show that TRPV1 is a physical component of the natriuretic peptide A, cGMP, PKG signaling complex, interacting with the Natriuretic Peptide Receptor 1 (NPR1), and upon binding its ligand, Natriuretic Peptide A (NPPA, ANP) TRPV1 activation is subsequently suppressed through production of cGMP and PKG mediated phosphorylation of the TRPV1 channel. Further, inhibition of TRPV1, with orally delivered drugs, suppresses chamber and myocyte hypertrophy, and can longitudinally improve in vivo heart function in mice exposed to chronic pressure overload induced by transverse aortic constriction, reversing pre-established hypertrophy induced by pressure load while restoring chamber function. TRPV1 is a physical and regulated component of the natriuretic peptide signaling system, and TRPV1 inhibition may provide a new treatment strategy for treating, and reversing the loss of function associated with cardiac hypertrophy and heart failure.

Ca2+ Signaling in Cardiac Fibroblasts and Fibrosis-Associated Heart Diseases

Cardiac fibrosis is the excessive deposition of extracellular matrix proteins by cardiac fibroblasts and myofibroblasts, and is a hallmark feature of most heart diseases, including arrhythmia, hypertrophy, and heart failure. This maladaptive process occurs in response to a variety of stimuli, including myocardial injury, inflammation, and mechanical overload. There are multiple signaling pathways and various cell types that influence the fibrogenesis cascade. Fibroblasts and myofibroblasts are central effectors. Although it is clear that Ca2+ signaling plays a vital role in this pathological process, what contributes to Ca2+ signaling in fibroblasts and myofibroblasts is still not wholly understood, chiefly because of the large and diverse number of receptors, transporters, and ion channels that influence intracellular Ca2+ signaling. Intracellular Ca2+ signals are generated by Ca2+ release from intracellular Ca2+ stores and by Ca2+ entry through a multitude of Ca2+-permeable ion channels in the plasma membrane. Over the past decade, the transient receptor potential (TRP) channels have emerged as one of the most important families of ion channels mediating Ca2+ signaling in cardiac fibroblasts. TRP channels are a superfamily of non-voltage-gated, Ca2+-permeable non-selective cation channels. Their ability to respond to various stimulating cues makes TRP channels effective sensors of the many different pathophysiological events that stimulate cardiac fibrogenesis. This review focuses on the mechanisms of Ca2+ signaling in fibroblast differentiation and fibrosis-associated heart diseases and will highlight recent advances in the understanding of the roles that TRP and other Ca2+-permeable channels play in cardiac fibrosis.

TRP Channels: Current Perspectives in the Adverse Cardiac Remodeling

Calcium is an important second messenger required not only for the excitation-contraction coupling of the heart but also critical for the activation of cell signaling pathways involved in the adverse cardiac remodeling and consequently for the heart failure. Sustained neurohumoral activation, pressure-overload, or myocardial injury can cause pathologic hypertrophic growth of the heart followed by interstitial fibrosis. The consequent heart’s structural and molecular adaptation might elevate the risk of developing heart failure and malignant arrhythmia. Compelling evidences have demonstrated that Ca²⁺ entry through TRP channels might play pivotal roles in cardiac function and pathology. TRP proteins are classified into six subfamilies: TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPA (ankyrin), TRPML (mucolipin), and TRPP (polycystin), which are activated by numerous physical and/or chemical stimuli. TRP channels participate to the handling of the intracellular Ca²⁺ concentration in cardiac myocytes and are mediators of different cardiovascular alterations. This review provides an overview of the current knowledge of TRP proteins implication in the pathologic process of some frequent cardiac diseases associated with the adverse cardiac remodeling such as cardiac hypertrophy, fibrosis, and conduction alteration.

Focal selective chemo-ablation of spinal cardiac afferent nerve by resiniferatoxin protects the heart from pressure overload-induced hypertrophy

Resiniferatoxin (RTX), a selective transient receptor potential vanilloid 1 (TRPV1) receptor agonist, can eliminate TRPV1+ primary sensory afferents and blunt cardiac sympathetic afferent reflex for a relatively long period. The present study determined the effects of intrathecal RTX administration on transverse aortic constriction (TAC)-induced cardiac dysfunction and cardiac remodeling in rats. Five days before TAC, RTX (2 μg/10 μl) was injected intrathecally into the T2/T3 interspace of rats. Cardiac sympathetic nerve activities (CSNAs) and cardiac structure and function were determined eight weeks after TAC. Intrathecal RTX administration abolished TRPV1 expression in the dorsal horn and reduced over-activated CSNA in the TAC rat model. Hemodynamic analysis revealed that RTX reduced left ventricular end-diastolic pressure, indicating the improvement of cardiac compliance. Histologic analysis, real-time reverse transcription-polymerase chain reaction, and Western blots showed that RTX prevented TAC-induced cardiac hypertrophy, cardiac fibrosis, and cardiac apoptosis and reduced the expression of apoptotic proteins and myocardial mRNAs. In conclusion, these results demonstrate that focal chemo-ablation of TRPV1+ afferents in the spinal cord protects the heart from pressure overload-induced cardiac remodeling and cardiac dysfunction, which suggest a novel promising therapeutic method for cardiac hypertrophy and diastolic dysfunction.

Muscling in on TRP channels in vascular smooth muscle cells and cardiomyocytes

The human TRP protein family comprises a family of 27 cation channels with diverse permeation and gating properties. The common theme is that they are very important regulators of intracellular Ca²⁺ signaling in diverse cell types, either by providing a Ca²⁺ influx pathway, or by depolarising the membrane potential, which on one hand triggers the activation of voltage-gated Ca²⁺ channels, and on the other limits the driving force for Ca²⁺ entry. Here we focus on the role of these TRP channels in vascular smooth muscle and cardiac striated muscle. We give an overview of highlights from the recent literature, and highlight the important and diverse roles of TRP channels in the pathophysiology of the cardiovascular system. The discovery of the superfamily of Transient Receptor Potential (TRP) channels has significantly enhanced our knowledge of multiple signal transduction mechanisms in cardiac muscle and vascular smooth muscle cells (VSMC). In recent years, multiple studies have provided evidence for the involvement of these channels, not only in the regulation of contraction, but also in cell proliferation and remodeling in pathological conditions. The mammalian family of TRP cation channels is composed by 28 genes which can be divided into 6 subfamilies groups based on sequence similarity: TRPC (Canonical), TRPM (Melastatin), TRPML (Mucolipins), TRPV (Vanilloid), TRPP (Policystin) and TRPA (Ankyrin-rich protein). Functional TRP channels are believed to form four-unit complexes in the plasma, each of them expressed with six transmembrane domain and intracellular N and C termini. Here we review the current knowledge on the expression of TRP channels in both muscle types, and discuss their functional properties and role in physiological and pathophysiological processes.

Mitogen-Activated Protein Kinase and Intracellular Polyamine Signaling Is Involved in TRPV1 Activation-Induced Cardiac Hypertrophy

BACKGROUND

The transient receptor potential vanilloid type 1 (TRPV1) is expressed in the cardiovascular system, and increased TRPV1 expression has been associated with cardiac hypertrophy. Nevertheless, the role of TRPV1 in the pathogenesis of cardiac hypertrophy and the underlying molecular mechanisms remain unclear.

METHODS AND RESULTS

In cultured cardiomyocytes, activation of TRPV1 increased cell size and elevated expression of atrial natriuretic peptide mRNA and intracellular calcium level, which was reversed by TRPV1 antagonist capsazepine. Increased expression of phosphorylated calmodulin-dependent protein kinase IIδ and mitogen-activated protein kinases were found in TRPV1 agonist capsaicin-treated cardiomyocytes. Selective inhibitor of calmodulin-dependent protein kinase IIδ decreased phosphorylation of extracellular signal-regulated kinases and p38. Capsaicin induced an increase in expression of ornithine decarboxylase protein, which is the key enzyme in polyamine biosynthesis in cardiomyocytes. Nevertheless, there was no obvious change of ornithine decarboxylase expression in TRPV1 knockdown cells after capsaicin treatment, and specific inhibitors of calmodulin-dependent protein kinase IIδ or p38 downregulated the capsaicin-induced expression of ornithine decarboxylase. Capsazepine alleviated the increase in cross-sectional area of cardiomyocytes and the ratio of heart weight to body weight and improved cardiac function, including left ventricular internal end-diastolic and -systolic dimensions and ejection fraction and fractional shortening percentages, in mice treated with transverse aorta constriction. Capsazepine also reduced expression of ornithine decarboxylase and cardiac polyamine levels. Transverse aorta constriction induced increases in phosphorylated calmodulin-dependent protein kinase IIδ and extracellular signal-regulated kinases, and p38 and Serca2a were attenuated by capsazepine treatment.

CONCLUSIONS

This study revealed that the mitogen-activated protein kinase signaling pathway and intracellular polyamines are essential for TRPV1 activation-induced cardiac hypertrophy.

Transgenic overexpression of transient receptor potential vanilloid subtype 1 attenuates isoproterenol-induced myocardial fibrosis in mice

Transient receptor potential vanilloid subtype 1 (TRPV1) is a non-selective cation channel with high permeability to Ca2+. Intracellular Ca2+ signaling is an essential regulator of endothelial nitric oxide (NO) synthase (eNOS) that plays a beneficial role in myocardial fibrosis. The aim of the present study was to determine the role of TRPV1 in isoproterenol-induced myocardial fibrosis. Transgenic mice overexpressing TRPV1 were generated on a C57BL/6J genetic background. An animal model of myocardial fibrosis was created by subcutaneously injecting the mice with isoproterenol. We found that the wild-type mice exhibited a significant increase in heart/body weight ratio, left ventricle/body weight ratio, left ventricular end-diastolic pressure (LVEDP), the cardiac fibrotic lesion area and collagen content, as well as a marked decrease in eNOS phosphorylation and NO/cyclic guanosine monophosphate (cGMP) levels at 2 weeks after the administration of isoproterenol (all p<0.01). However, these changes were significantly attenuated in the TRPV1 transgenic mice (p<0.05 or p<0.01). Moreover, the beneficial effects on myocardial fibrosis exerted by the overexpression of TRPV1 were attenuated by the administration of the eNOS inhibitor, Nω-nitro-L-arginine methyl ester (L-NAME) (all p<0.05). Similar anti-fibrotic effects were observed in in vitro experiments with primary cultured cardiac fibroblasts. The findings of our study suggest that TRPV1 overexpression attenuates isoproterenol‑induced myocardial fibrosis.

TRPA1 is functionally co-expressed with TRPV1 in cardiac muscle: Co-localization at z-discs, costameres and intercalated discs

Transient receptor potential channels of the ankyrin subtype-1 (TRPA1) and vanilloid subtype-1 (TRPV1) are structurally related, non-selective cation channels that show a high permeability to calcium. Previous studies indicate that TRP channels play a prominent role in the regulation of cardiovascular dynamics and homeostasis, but also contribute to the pathophysiology of many diseases and disorders within the cardiovascular system. However, no studies to date have identified the functional expression and/or intracellular localization of TRPA1 in primary adult mouse ventricular cardiomyocytes (CMs). Although TRPV1 has been implicated in the regulation of cardiac function, there is a paucity of information regarding functional expression and localization of TRPV1 in adult CMs. Our current studies demonstrate that TRPA1 and TRPV1 ion channels are co-expressed at the protein level in CMs and both channels are expressed throughout the endocardium, myocardium and epicardium. Moreover, immunocytochemical localization demonstrates that both channels predominantly colocalize at the Z-discs, costameres and intercalated discs. Furthermore, specific TRPA1 and TRPV1 agonists elicit dose-dependent, transient rises in intracellular free calcium concentration ([Ca²⁺]_i) that are abolished in CMs obtained from TRPA1^−/− and TRPV1^−/− mice. Similarly, we observed a dose-dependent attenuation of the TRPA1 and TRPV1 agonist-induced increase in [Ca²⁺]_i when WT CMs were pretreated with increasing concentrations of selective TRPA1 or TRPV1 channel antagonists. In summary, these findings demonstrate functional expression and the precise ultrastructural localization of TRPA1 and TRPV1 ion channels in freshly isolated mouse CMs. Crosstalk between TRPA1 and TRPV1 may be important in mediating cellular signaling events in cardiac muscle.

TRPV-1-mediated elimination of residual iPS cells in bioengineered cardiac cell sheet tissues

The development of a suitable strategy for eliminating remaining undifferentiated cells is indispensable for the use of human-induced pluripotent stem (iPS) cell-derived cells in regenerative medicine. Here, we show for the first time that TRPV-1 activation through transient culture at 42 °C in combination with agonists is a simple and useful strategy to eliminate iPS cells from bioengineered cardiac cell sheet tissues. When human iPS cells were cultured at 42 °C, almost all cells disappeared by 48 hours through apoptosis. However, iPS cell-derived cardiomyocytes and fibroblasts maintained transcriptional and protein expression levels, and cardiac cell sheets were fabricated after reducing the temperature. TRPV-1 expression in iPS cells was upregulated at 42 °C, and iPS cell death at 42 °C was TRPV-1-dependent. Furthermore, TRPV-1 activation through thermal or agonist treatment eliminated iPS cells in cardiac tissues for a final concentration of 0.4% iPS cell contamination. These findings suggest that the difference in tolerance to TRPV-1 activation between iPS cells and iPS cell-derived cardiac cells could be exploited to eliminate remaining iPS cells in bioengineered cell sheet tissues, which will further reduce the risk of tumour formation.

Role of TRP channels in the cardiovascular system

The transient receptor potential (TRP) superfamily consists of a large number of nonselective cation channels with variable degree of Ca(2+)-permeability. The 28 mammalian TRP channel proteins can be grouped into six subfamilies: canonical, vanilloid, melastatin, ankyrin, polycystic, and mucolipin TRPs. The majority of these TRP channels are expressed in different cell types including both excitable and nonexcitable cells of the cardiovascular system. Unlike voltage-gated ion channels, TRP channels do not have a typical voltage sensor, but instead can sense a variety of other stimuli including pressure, shear stress, mechanical stretch, oxidative stress, lipid environment alterations, hypertrophic signals, and inflammation products. By integrating multiple stimuli and transducing their activity to downstream cellular signal pathways via Ca(2+) entry and/or membrane depolarization, TRP channels play an essential role in regulating fundamental cell functions such as contraction, relaxation, proliferation, differentiation, and cell death. With the use of targeted deletion and transgenic mouse models, recent studies have revealed that TRP channels are involved in numerous cellular functions and play an important role in the pathophysiology of many diseases in the cardiovascular system. Moreover, several TRP channels are involved in inherited diseases of the cardiovascular system. This review presents an overview of current knowledge concerning the physiological functions of TRP channels in the cardiovascular system and their contributions to cardiovascular diseases. Ultimately, TRP channels may become potential therapeutic targets for cardiovascular diseases.

Transient receptor potential channels as drug targets: from the science of basic research to the art of medicine

The large Trp gene family encodes transient receptor potential (TRP) proteins that form novel cation-selective ion channels. In mammals, 28 Trp channel genes have been identified. TRP proteins exhibit diverse permeation and gating properties and are involved in a plethora of physiologic functions with a strong impact on cellular sensing and signaling pathways. Indeed, mutations in human genes encoding TRP channels, the so-called "TRP channelopathies," are responsible for a number of hereditary diseases that affect the musculoskeletal, cardiovascular, genitourinary, and nervous systems. This review gives an overview of the functional properties of mammalian TRP channels, describes their roles in acquired and hereditary diseases, and discusses their potential as drug targets for therapeutic intervention.

Cardiac sympathetic afferent denervation attenuates cardiac remodeling and improves cardiovascular dysfunction in rats with heart failure

The enhanced cardiac sympathetic afferent reflex (CSAR) contributes to the exaggerated sympathoexcitation in chronic heart failure (CHF). Increased sympathoexcitation is positively related to mortality in patients with CHF. However, the potential beneficial effects of chronic CSAR deletion on cardiac and autonomic function in CHF have not been previously explored. Here, we determined the effects of chronic CSAR deletion on cardiac remodeling and autonomic dysfunction in CHF. To delete the transient receptor potential vanilloid 1 receptor-expressing CSAR afferents selectively, epicardial application of resiniferatoxin (50 μg/mL), an ultrapotent analog of capsaicin, was performed during myocardium infarction surgery in rats. This procedure largely abolished the enhanced CSAR, prevented the exaggerated renal and cardiac sympathetic nerve activity and improved baroreflex sensitivity in CHF rats. Most importantly, we found that epicardial application of resiniferatoxin largely prevented the elevated left ventricle end-diastolic pressure, lung edema, and cardiac hypertrophy, partially reduced left ventricular dimensions in the failing heart, and increased cardiac contractile reserve in response to β-adrenergic receptor stimulation with isoproterenol in CHF rats. Molecular evidence showed that resiniferatoxin attenuated cardiac fibrosis and apoptosis and reduced expression of fibrotic markers and transforming growth factor-β receptor I in CHF rats. Pressure-volume loop analysis showed that resiniferatoxin reduced the end-diastolic pressure volume relationships in CHF rats, indicating improved cardiac compliance. In summary, cardiac sympathetic afferent deletion exhibits protective effects against deleterious cardiac remodeling and autonomic dysfunction in CHF. These data suggest a potential new paradigm and therapeutic potential in the management of CHF.

Cold stress accentuates pressure overload-induced cardiac hypertrophy and contractile dysfunction: role of TRPV1/AMPK-mediated autophagy

Severe cold exposure and pressure overload are both known to prompt oxidative stress and pathological alterations in the heart although the interplay between the two remains elusive. Transient receptor potential vanilloid 1 (TRPV1) is a nonselective cation channel activated in response to a variety of exogenous and endogenous physical and chemical stimuli including heat and capsaicin. The aim of this study was to examine the impact of cold exposure on pressure overload-induced cardiac pathological changes and the mechanism involved. Adult male C57 mice were subjected to abdominal aortic constriction (AAC) prior to exposure to cold temperature (4 °C) for 4 weeks. Cardiac geometry and function, levels of TRPV1, mitochondrial, and autophagy-associated proteins including AMPK, mTOR, LC3B, and P62 were evaluated. Sustained cold stress triggered cardiac hypertrophy, compromised depressed myocardial contractile capacity including lessened fractional shortening, peak shortening, and maximal velocity of shortening/relengthening, enhanced ROS production, and mitochondrial injury, the effects of which were negated by the TRPV1 antagonist SB366791. Western blot analysis revealed upregulated TRPV1 level and AMPK phosphorylation, enhanced ratio of LC3II/LC3I, and downregulated P62 following cold exposure. Cold exposure significantly augmented AAC-induced changes in TRPV1, phosphorylation of AMPK, LC3 isoform switch, and p62, the effects of which were negated by SB366791. In summary, these data suggest that cold exposure accentuates pressure overload-induced cardiac hypertrophy and contractile defect possibly through a TRPV1 and autophagy-dependent mechanism.

The calcium release-activated calcium channel Orai1 represents a crucial component in hypertrophic compensation and the development of dilated cardiomyopathy

As exceptionally calcium selective store-operated channels, Orai channels play a prominent role in cellular calcium signaling. While most studied in the immune system, we are beginning to recognize that Orai1 provides unique calcium signaling pathways in numerous tissue contexts. To assess the involvement of Orai1 in cardiac hypertrophy we used transverse aortic constriction to model pressure overload cardiac hypertrophy and heart failure in Orai1 deficient mice. We demonstrate that Orai1 deficient mice have significantly decreased survival in this pressure overload model. Transthoracic echocardiography reveals that Orai1 deficient mice develop rapid dilated cardiomyopathy, with greater loss of function, and histological and molecular data indicate that this pathology is associated with significant apoptosis, but not major differences in cellular hypertrophy, fibrosis, and some major hypertrophic makers. Orai1 represents a crucial calcium entry mechanism in the compensation of the heart to pressure overload over-load, and the development of dilated cardiomyopathy.