Physiological and pathophysiological role of transient receptor potential canonical channels in cardiac myocytes

TRPC5 channel participates in myocardial injury in chronic intermittent hypoxia

OBJECTIVE

The purpose of this study is to develop an animal model of Chronic Intermittent Hypoxia (CIH) and investigate the role of the TRPC5 channel in cardiac damage in OSAHS rats.

METHODS

Twelve male Sprague Dawley rats were randomly divided into the CIH group and the Normoxic Control (NC) group. Changes in structure, function, and pathology of heart tissue were observed through echocardiography, transmission electron microscopy, HE-staining, and TUNEL staining.

RESULTS

The Interventricular Septum thickness at diastole (IVSd) and End-Diastolic Volume (EDV) of rats in the CIH group significantly increased, whereas the LV ejection fraction and LV fraction shortening significantly decreased. TEM showed that the myofilaments in the CIH group were loosely arranged, the sarcomere length varied, the cell matrix dissolved, the mitochondrial cristae were partly flocculent, the mitochondrial outer membrane dissolved and disappeared, and some mitochondria were swollen and vacuolated. The histopathological examination showed that the cardiomyocytes in the CIH group were swollen with granular degeneration, some of the myocardial fibers were broken and disorganized, and most of the nuclei were vacuolar and hypochromic.

CONCLUSION

CIH promoted oxidative stress, the influx of Ca2+, and the activation of the CaN/NFATc signaling pathway, which led to pathological changes in the morphology and ultrastructure of cardiomyocytes, the increase of myocardial apoptosis, and the decrease of myocardial contractility. These changes may be associated with the upregulation of TRPC5.

TRPC1 channels underlie stretch-modulated sarcoplasmic reticulum calcium leak in cardiomyocytes

Transient receptor potential canonical 1 (TRPC1) channels are Ca2+-permeable ion channels expressed in cardiomyocytes. An involvement of TRPC1 channels in cardiac diseases is widely established. However, the physiological role of TRPC1 channels and the mechanisms through which they contribute to disease development are still under investigation. Our prior work suggested that TRPC1 forms Ca2+ leak channels located in the sarcoplasmic reticulum (SR) membrane. Prior studies suggested that TRPC1 channels in the cell membrane are mechanosensitive, but this was not yet investigated in cardiomyocytes or for SR localized TRPC1 channels. We applied adenoviral transfection to overexpress or suppress TRPC1 expression in neonatal rat ventricular myocytes (NRVMs). Transfections were evaluated with RT-qPCR, western blot, and fluorescent imaging. Single-molecule localization microscopy revealed high colocalization of exogenously expressed TRPC1 and the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA2). To test our hypothesis that TRPC1 channels contribute to mechanosensitive Ca2+ SR leak, we directly measured SR Ca2+ concentration ([Ca2+]SR) using adenoviral transfection with a novel ratiometric genetically encoded SR-targeting Ca2+ sensor. We performed fluorescence imaging to quantitatively assess [Ca2+]SR and leak through TRPC1 channels of NRVMs cultured on stretchable silicone membranes. [Ca2+]SR was increased in cells with suppressed TRPC1 expression vs. control and Transient receptor potential canonical 1-overexpressing cells. We also detected a significant reduction in [Ca2+]SR in cells with Transient receptor potential canonical 1 overexpression when 10% uniaxial stretch was applied. These findings indicate that TRPC1 channels underlie the mechanosensitive modulation of [Ca2+]SR. Our findings are critical for understanding the physiological role of TRPC1 channels and support the development of pharmacological therapies for cardiac diseases.

Dapagliflozin reduces the vulnerability of rats with pulmonary arterial hypertension-induced right heart failure to ventricular arrhythmia by restoring calcium handling

Background

Malignant ventricular arrhythmia (VA) is a major contributor to sudden cardiac death (SCD) in patients with pulmonary arterial hypertension (PAH)-induced right heart failure (RHF). Recently, dapagliflozin (DAPA), a sodium/glucose cotransporter-2 inhibitor (SGLT2i), has been found to exhibit cardioprotective effects in patients with left ventricular systolic dysfunction. In this study, we examined the effects of DAPA on VA vulnerability in a rat model of PAH-induced RHF.

Methods

Rats randomly received monocrotaline (MCT, 60 mg/kg) or vehicle via a single intraperitoneal injection. A day later, MCT-injected rats were randomly treated with placebo, low-dose DAPA (1 mg/kg/day), or high-dose (3 mg/kg/day) DAPA orally for 35 days. Echocardiographic analysis, haemodynamic experiments, and histological assessments were subsequently performed to confirm the presence of PAH-induced RHF. Right ventricle (RV) expression of calcium (Ca²⁺) handling proteins were detected via Western blotting. RV expression of connexin 43 (Cx43) was determined via immunohistochemical staining. An optical mapping study was performed to assess the electrophysiological characteristics in isolated hearts. Cellular Ca²⁺ imaging from RV cardiomyocytes (RVCMs) was recorded using Fura-2 AM or Fluo-4 AM.

Results

High-dose DAPA treatment attenuated RV structural remodelling, improved RV function, alleviated Cx43 remodelling, increased the conduction velocity, restored the expression of key Ca²⁺ handling proteins, increased the threshold for Ca²⁺ and action potential duration (APD) alternans, decreased susceptibility to spatially discordant APD alternans and spontaneous Ca²⁺ events, promoted cellular Ca²⁺ handling, and reduced VA vulnerability in PAH-induced RHF rats. Low-dose DAPA treatment also showed antiarrhythmic effects in hearts with PAH-induced RHF, although with a lower level of efficacy.

Conclusion

DAPA administration reduced VA vulnerability in rats with PAH-induced RHF by improving RVCM Ca²⁺ handling.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-022-01614-5.

Effects of Sarcolemmal Background Ca2+ Entry and Sarcoplasmic Ca2+ Leak Currents on Electrophysiology and Ca2+ Transients in Human Ventricular Cardiomyocytes: A Computational Comparison

The intricate regulation of the compartmental Ca²⁺ concentrations in cardiomyocytes is critical for electrophysiology, excitation-contraction coupling, and other signaling pathways. Research into the complex signaling pathways is motivated by cardiac pathologies including arrhythmia and maladaptive myocyte remodeling, which result from Ca²⁺ dysregulation. Of interest to this investigation are two types of Ca²⁺ currents in cardiomyocytes: 1) background Ca²⁺ entry, i.e., Ca²⁺ transport across the sarcolemma from the extracellular space into the cytosol, and 2) Ca²⁺ leak from the sarcoplasmic reticulum (SR) across the SR membrane into the cytosol. Candidates for the ion channels underlying background Ca²⁺ entry and SR Ca²⁺ leak channels include members of the mechano-modulated transient receptor potential (TRP) family. We used a mathematical model of a human ventricular myocyte to analyze the individual contributions of background Ca²⁺ entry and SR Ca²⁺ leak to the modulation of Ca²⁺ transients and SR Ca²⁺ load at rest and during action potentials. Background Ca²⁺ entry exhibited a positive relationship with both [Ca²⁺]_i and [Ca²⁺]_SR. Modulating SR Ca²⁺ leak had opposite effects of background Ca²⁺ entry. Effects of SR Ca²⁺ leak on Ca²⁺ were particularly pronounced at lower pacing frequency. In contrast to the pronounced effects of background and leak Ca²⁺ currents on Ca²⁺ concentrations, the effects on cellular electrophysiology were marginal. Our studies provide quantitative insights into the differential modulation of compartmental Ca²⁺ concentrations by the background and leak Ca²⁺ currents. Furthermore, our studies support the hypothesis that TRP channels play a role in strain-modulation of cardiac contractility. In summary, our investigations shed light on the physiological effects of the background and leak Ca²⁺ currents and their contribution to the development of disease caused by Ca²⁺ dysregulation.

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.

Mechanisms and significance of Ca2+ entry through TRPC channels

The transient receptor potential (TRP) superfamily of plasma membrane cation channels has been recognized as a signaling hub in highly diverse settings of human physiopathology. In the past three decades of TRP research, attention was focused mainly on the channels Ca2+ signaling function, albeit additional cellular functions, aside of providing a Ca2+ entry pathway, have been identified. Our understanding of Ca2+ signaling by TRP proteins has recently been advanced by a gain in high-resolution structure information on these pore complexes, and by the development of novel tools to investigate their role in spatiotemporal Ca2+ handling. This review summarizes recent discoveries as well as remaining, unresolved aspects of the canonical subfamily of transient receptor potential channels (TRPC) research. We aim at a concise overview on current mechanistic concepts of Ca2+ entry through- and Ca2+ signaling by TRPC channels.

Transcriptional signatures regulated by TRPC1/C4-mediated Background Ca2+ entry after pressure-overload induced cardiac remodelling

AIMS

After summarizing current concepts for the role of TRPC cation channels in cardiac cells and in processes triggered by mechanical stimuli arising e.g. during pressure overload, we analysed the role of TRPC1 and TRPC4 for background Ca²⁺ entry (BGCE) and for cardiac pressure overload induced transcriptional remodelling.

METHODS AND RESULTS

Mn²⁺-quench analysis in cardiomyocytes from several Trpc-deficient mice revealed that both TRPC1 and TRPC4 are required for BGCE. Electrically-evoked cell shortening of cardiomyocytes from TRPC1/C4-DKO mice was reduced, whereas parameters of cardiac contractility and relaxation assessed in vivo were unaltered. As pathological cardiac remodelling in mice depends on their genetic background, and the development of cardiac remodelling was found to be reduced in TRPC1/C4-DKO mice on a mixed genetic background, we studied TRPC1/C4-DKO mice on a C57BL6/N genetic background. Cardiac hypertrophy was reduced in those mice after chronic isoproterenol infusion (-51.4%) or after one week of transverse aortic constriction (TAC; -73.0%). This last manoeuvre was preceded by changes in the pressure overload induced transcriptional program as analysed by RNA sequencing. Genes encoding specific collagens, the Mef2 target myomaxin and the gene encoding the mechanosensitive channel Piezo2 were up-regulated after TAC in wild type but not in TRPC1/C4-DKO hearts.

CONCLUSIONS

Deletion of the TRPC1 and TRPC4 channel proteins protects against development of pathological cardiac hypertrophy independently of the genetic background. To determine if the TRPC1/C4-dependent changes in the pressure overload induced alterations in the transcriptional program causally contribute to cardio-protection needs to be elaborated in future studies.

TRPCs: Influential Mediators in Skeletal Muscle

Ca²⁺ itself or Ca²⁺-dependent signaling pathways play fundamental roles in various cellular processes from cell growth to death. The most representative example can be found in skeletal muscle cells where a well-timed and adequate supply of Ca²⁺ is required for coordinated Ca²⁺-dependent skeletal muscle functions, such as the interactions of contractile proteins during contraction. Intracellular Ca²⁺ movements between the cytosol and sarcoplasmic reticulum (SR) are strictly regulated to maintain the appropriate Ca²⁺ supply in skeletal muscle cells. Added to intracellular Ca²⁺ movements, the contribution of extracellular Ca²⁺ entry to skeletal muscle functions and its significance have been continuously studied since the early 1990s. Here, studies on the roles of channel proteins that mediate extracellular Ca²⁺ entry into skeletal muscle cells using skeletal myoblasts, myotubes, fibers, tissue, or skeletal muscle-originated cell lines are reviewed with special attention to the proposed functions of transient receptor potential canonical proteins (TRPCs) as store-operated Ca²⁺ entry (SOCE) channels under normal conditions and the potential abnormal properties of TRPCs in muscle diseases such as Duchenne muscular dystrophy (DMD).

Modulation of Calcium Transients in Cardiomyocytes by Transient Receptor Potential Canonical 6 Channels

Transient receptor potential canonical 6 (TRPC6) channels are non-selective cation channels that are thought to underlie mechano-modulation of calcium signaling in cardiomyocytes. TRPC6 channels are involved in development of cardiac hypertrophy and related calcineurin-nuclear factor of activated T cells (NFAT) signaling. However, the exact location and roles of TRPC6 channels remain ill-defined in cardiomyocytes. We used an expression system based on neonatal rat ventricular myocytes (NRVMs) to investigate the location of TRPC6 channels and their role in calcium signaling. NRVMs isolated from 1- to 2-day-old animals were cultured and infected with an adenoviral vector to express enhanced-green fluorescent protein (eGFP) or TRPC6-eGFP. After 3 days, NRVMs were fixed, immunolabeled, and imaged with confocal and super-resolution microscopy to determine TRPC6 localization. Cytosolic calcium transients at 0.5 and 1 Hz pacing rates were recorded in NRVMs using indo-1, a ratio-metric calcium dye. Confocal and super-resolution microscopy suggested that TRPC6-eGFP localized to the sarcolemma. NRVMs infected with TRPC6-eGFP exhibited higher diastolic and systolic cytosolic calcium concentration as well as increased sarcoplasmic reticulum (SR) calcium load compared to eGFP infected cells. We applied a computer model comprising sarcolemmal TRPC6 current to explain our experimental findings. Altogether, our studies indicate that TRPC6 channels play a role in sarcolemmal and intracellular calcium signaling in cardiomyocytes. Our findings support the hypothesis that upregulation or activation of TRPC6 channels, e.g., in disease, leads to sustained elevation of the cytosolic calcium concentration, which is thought to activate calcineurin-NFAT signaling and cardiac hypertrophic remodeling. Also, our findings support the hypothesis that mechanosensitivity of TRPC6 channels modulates cytosolic calcium transients and SR calcium load.

Location and function of transient receptor potential canonical channel 1 in ventricular myocytes

Transient receptor potential canonical 1 (TRPC1) protein is abundantly expressed in cardiomyocytes. While TRPC1 is supposed to be critically involved in cardiac hypertrophy, its physiological role in cardiomyocytes is poorly understood. We investigated the subcellular location of TRPC1 and its contribution to Ca²⁺ signaling in mammalian ventricular myocytes. Immunolabeling, three-dimensional scanning confocal microscopy and quantitative colocalization analysis revealed an abundant intracellular location of TRPC1 in neonatal rat ventricular myocytes (NRVMs) and adult rabbit ventricular myocytes. TRPC1 was colocalized with intracellular proteins including sarco/endoplasmic reticulum Ca²⁺ ATPase 2 in the sarcoplasmic reticulum (SR). Colocalization with wheat germ agglutinin, which labels the glycocalyx and thus marks the sarcolemma including the transverse tubular system, was low. Super-resolution and immunoelectron microscopy supported the intracellular location of TRPC1. We investigated Ca²⁺ signaling in NRVMs after adenoviral TRPC1 overexpression or silencing. In NRVMs bathed in Na⁺ and Ca²⁺ free solution, TRPC1 overexpression and silencing was associated with a decreased and increased SR Ca²⁺ content, respectively. In isolated rabbit cardiomyocytes bathed in Na⁺ and Ca²⁺ free solution, we found an increased decay of the cytosolic Ca²⁺ concentration [Ca²⁺]_i and increased SR Ca²⁺ content in the presence of the TRPC channel blocker SKF-96365. In a computational model of rabbit ventricular myocytes at physiological pacing rates, Ca²⁺ leak through SR TRPC channels increased the systolic and diastolic [Ca²⁺]_i with only minor effects on the action potential and SR Ca²⁺ content. Our studies suggest that TRPC1 channels are localized in the SR, and not present in the sarcolemma of ventricular myocytes. The studies provide evidence for a role of TRPC1 as a contributor to SR Ca²⁺ leak in cardiomyocytes, which was previously explained by ryanodine receptors only. We propose that the findings will guide us to an understanding of TRPC1 channels as modulators of [Ca²⁺]_i and contractility in cardiomyocytes.

TRPC Channels: Dysregulation and Ca2+ Mishandling in Ischemic Heart Disease

Transient receptor potential canonical (TRPC) channels are ubiquitously expressed in excitable and non-excitable cardiac cells where they sense and respond to a wide variety of physical and chemical stimuli. As other TRP channels, TRPC channels may form homo or heterotetrameric ion channels, and they can associate with other membrane receptors and ion channels to regulate intracellular calcium concentration. Dysfunctions of TRPC channels are involved in many types of cardiovascular diseases. Significant increase in the expression of different TRPC isoforms was observed in different animal models of heart infarcts and in vitro experimental models of ischemia and reperfusion. TRPC channel-mediated increase of the intracellular Ca²⁺ concentration seems to be required for the activation of the signaling pathway that plays minor roles in the healthy heart, but they are more relevant for cardiac responses to ischemia, such as the activation of different factors of transcription and cardiac hypertrophy, fibrosis, and angiogenesis. In this review, we highlight the current knowledge regarding TRPC implication in different cellular processes related to ischemia and reperfusion and to heart infarction.

Specific Upregulation of TRPC1 and TRPC5 Channels by Mineralocorticoid Pathway in Adult Rat Ventricular Cardiomyocytes

Whereas cardiac TRPC (transient receptor potential canonical) channels and the associated store-operated Ca²⁺ entry (SOCE) are abnormally elevated during cardiac hypertrophy and heart failure, the mechanism of this upregulation is not fully elucidated but might be related to the activation of the mineralocorticoid pathway. Using a combination of biochemical, Ca²⁺ imaging, and electrophysiological techniques, we determined the effect of 24-h aldosterone treatment on the TRPCs/Orai-dependent SOCE in adult rat ventricular cardiomyocytes (ARVMs). The 24-h aldosterone treatment (from 100 nM to 1 µM) enhanced depletion-induced Ca²⁺ entry in ARVMs, as assessed by a faster reduction of Fura-2 fluorescence decay upon the addition of Mn²⁺ and increased Fluo-4/AM fluorescence following Ca²⁺ store depletion. These effects were prevented by co-treatment with a specific mineralocorticoid receptor (MR) antagonist, RU-28318, and they are associated with the enhanced depletion-induced N-[4-[3,5-Bis(trifluoromethyl)-1H-pyrazol-1-yl]phenyl]-4-methyl-1,2,3-thiadiazole-5-carboxamide (BTP2)-sensitive macroscopic current recorded by patch-clamp experiments. Molecular screening by qRT-PCR and Western blot showed a specific upregulation of TRPC1, TRPC5, and STIM1 expression at the messenger RNA (mRNA) and protein levels upon 24-h aldosterone treatment of ARVMs, corroborated by immunostaining. Our study provides evidence that the mineralocorticoid pathway specifically promotes TRPC1/TRPC5-mediated SOCE in adult rat cardiomyocytes.