The Ca(2+)-activated cation channel TRPM4 is a negative regulator of angiotensin II-induced cardiac hypertrophy

Functional coupling between Piezo1 and TRPM4 influences the electrical activity of HL-1 atrial myocytes

The transient receptor potential melastatin 4 (TRPM4) channel contributes extensively to cardiac electrical activity, especially cardiomyocyte action potential formation. Mechanical stretch can induce changes in heart rate and rhythm, and the mechanosensitive channel Piezo1 is expressed in many cell types within the myocardium. Our previous study showed that TRPM4 and Piezo1 are closely co-localized in the t-tubules of ventricular cardiomyocytes and contribute to the Ca2+-dependent signalling cascade that underlies hypertrophy in response to mechanical pressure overload. However, there was no direct evidence showing that Piezo1 activation was related to TRPM4 activation in situ. In the present study, we employed the HL-1 mouse atrial myocyte-like cell line as an in vitro model to investigate whether Piezo1-TRPM4 coupling can affect action potential properties. We used the small molecule Piezo1 agonist, Yoda1, as a surrogate for mechanical stretch to activate Piezo1 and detected the action potential changes in HL-1 cells using FluoVolt, a fluorescent voltage sensitive dye. Our results demonstrate that Yoda1-induced activation of Piezo1 changes the action potential frequency in HL-1 cells. This change in action potential frequency is reduced by Piezo1 knockdown using small intefering RNA. Importantly knockdown or pharmacological inhibition of TRPM4 significantly affected the degree to which Yoda1-evoked Piezo1 activation influenced action potential frequency. Thus, the present study provides in vitro evidence of a functional coupling between Piezo1 and TRPM4 in a cardiomyocyte-like cell line. The coupling of a mechanosensitive Ca2+ permeable channel and a Ca2+-activated TRP channel probably represents a ubiquitous model for the role of TRP channels in mechanosensory transduction. KEY POINTS: The transient receptor potential melastatin 4 (TRPM4) and Piezo1 channels have been confirmed to contribute to the Ca2+-dependent signalling cascade that underlies cardiac hypertrophy in response to mechanical pressure overload. However, there was no direct evidence showing that Piezo1 activation was related to TRPM4 activation in situ. We employed the HL-1 mouse atrial myocyte-like cell line as an in vitro model to investigate the effect of Piezo1-TRPM4 coupling on cardiac electrical properties. The results show that both pharmacological and genetic inhibition of TRPM4 significantly affected the degree to which Piezo1 activation influenced action potential frequency in HL-1 cells. Our findings provide in vitro evidence of a functional coupling between Piezo1 and TRPM4 in a cardiomyocyte-like cell line. The coupling of a mechanosensitive Ca2+ permeable channel and a Ca2+-activated TRP channel probably represents a ubiquitous model for the role of TRP channels in mechanosensory transduction in various (patho)physiological processes.

Exploring the role of TRPM4 in calcium-dependent triggered activity and cardiac arrhythmias

Cardiac arrhythmias pose a major threat to a patient's health, yet prove to be often difficult to predict, prevent and treat. A key mechanism in the occurrence of arrhythmias is disturbed Ca2+ homeostasis in cardiac muscle cells. As a Ca2+-activated non-selective cation channel, TRPM4 has been linked to Ca2+-induced arrhythmias, potentially contributing to translating an increase in intracellular Ca2+ concentration into membrane depolarisation and an increase in cellular excitability. Indeed, evidence from genetically modified mice, analysis of mutations in human patients and the identification of a TRPM4 blocking compound that can be applied in vivo further underscore this hypothesis. Here, we provide an overview of these data in the context of our current understanding of Ca2+-dependent arrhythmias.

Polyphenol-mediated sandwich-like coating promotes endothelialization and vascular healing

Drug-eluting stents have become one of the most effective methods to treat cardiovascular diseases. However, this therapeutic strategy may lead to thrombosis, stent restenosis, and intimal hyperplasia and prevent re-endothelialization. In this study, we selected 3-aminophenylboronic acid-modified hyaluronic acid and carboxylate chitosan as polyelectrolyte layers and embedded an epigallocatechin-3-gallate-tanshinone IIA sulfonic sodium (EGCG-TSS) complex to develop a sandwich-like layer-by-layer coating. The introduction of a functional molecular EGCG-TSS complex improved not only the biocompatibility of the coating but also its stability by enriching the interaction between the polyelectrolyte coatings through electrostatic interactions, hydrogen bonding, π-π stacking, and covalent bonding. We further elucidated the effectiveness of sandwich-like coatings in regulating the inflammatory response, smooth muscle cell growth behavior, stent thrombosis and restenosis suppression, and vessel re-endothelialization acceleration via in vivo and in vitro. Conclusively, we demonstrated that sandwich-like coating assisted by an EGCG-TSS complex may be an effective surface modification strategy for cardiovascular therapeutic applications.

New insights into the effect of VMP1 on the treatment of pressure overload-induced pathological cardiac hypertrophy: Involving SERCA-regulated autophagic flux

Pathological cardiac hypertrophy is an adaptive reaction in response to pressure or volume overload. Autophagy is critical for damage caused by pathological cardiac hypertrophy. Vacuole membrane protein 1 (VMP1) is an endoplasmic reticulum (ER) transmembrane protein that is effective in activating autophagy. However, the role of VMP1 in pathological cardiac hypertrophy and its underlying mechanisms remain elusive. This study was designed to explore the potential mechanisms of VMP1 on pressure overload-induced pathological cardiac hypertrophy. In this work, abdominal aorta constriction (AAC) surgery was used to induce pathological cardiac hypertrophy in male C57BL/6 mice. H9C2 cardiomyocytes were treated with phenylephrine stimulation (PE) to induce the hypertrophic response. The in vivo results revealed that mice with AAC surgery caused pathological cardiac hypertrophy as evidenced by improved cardiac function according to multiple echocardiographic parameters. Moreover, elevated VMP1 expression was also observed in mice after AAC surgery. VMP1 knockdown aggravated changes in cardiac structure, cardiac dysfunction, and fibrosis. Meanwhile, VMP1 knockdown suppressed autophagy and endoplasmic reticulum calcium ATPase (SERCA) activity in heart tissues. H9C2 cardiomyocytes with VMP1 overexpression were used to investigate the specific mechanism of VMP1 in pathological cardiac hypertrophy, and VMP1 overexpression increased autophagic flux by upregulating SERCA activity. In conclusion, these findings revealed that VMP1 protected against pressure overload-induced pathological cardiac hypertrophy by inducing SERCA-regulated autophagic flux. Our results provide valuable insights regarding the pathophysiology of pathological cardiac hypertrophy and clues to a novel target for the treatment of pathological cardiac hypertrophy.

Resveratrol prevents Ang II-induced cardiac hypertrophy by inhibition of NF-κB signaling

BACKGROUND

Pathological cardiac hypertrophy is a hallmark of various cardiovascular diseases (CVD) including chronic heart failure (HF) and an important target for the treatment of these diseases. Aberrant activation of Angiotensin II (Ang II)/AT1R signaling pathway is one of the main triggers of cardiac hypertrophy, which further gives rise to excessive inflammation that is mediated by the key transcription factor NF-κB. Resveratrol (REV) is a natural polyphenol with multiple anti-inflammatory and anti-oxidative effects, however the ability of REV in preventing Ang II-induced cardiac hypertrophy in combination with NF-κB signaling activation remains unclear.

METHODS

Murine models of cardiac hypertrophy was conducted via implantation of Ang II osmotic pumps. Primary neonatal rat cardiomyocyte and heart tissues were examined to determine the effect and underlying mechanism of REV in preventing Ang II-induced cardiac hypertrophy.

RESULTS

Administrations of REV significantly prevented Ang II-induced cardiac hypertrophy, as well as robustly attenuated Ang II-induced cardiac fibrosis, and cardiac dysfunction. Furthermore, REV not only directly prevented Ang II/AT1R signal transductions, but also prevented Ang II-induced expressions of pro-inflammatory cytokines and activation of NF-κB signaling pathway.

CONCLUSIONS

Our study provides important new mechanistic insight into the cardioprotective effects of REV in preventing Ang II-induced cardiac hypertrophy via inhibiting adverse NF-κB signaling activation. Our findings further suggest the therapeutic potential of REV as a promising drug for the treatment of cardiac hypertrophy and heart failure.

Knockdown of the TRPM4 channel alters cardiac electrophysiology and hemodynamics in a sex- and age-dependent manner in mice

TRPM4 is a calcium-activated, voltage-modulated, nonselective ion channel widely expressed in various cells and tissues. TRPM4 regulates the influx of sodium ions, thus playing a role in regulating the membrane potential. In the heart, TRPM4 is expressed in both cardiomyocytes and cells of the conductive pathways. Clinical studies have linked TRPM4 mutations to several cardiac disorders. While data from experimental studies have demonstrated TRPM4's functional significance in cardiac physiology, its exact roles in the heart have remained unclear. In this study, we investigated the role of TRPM4 in cardiac physiology in a newly generated Trpm4 knockdown mouse model. Male and female Trpm4 knockdown (Trpm4-/- ) and wild-type mice of different ages (5- to 12- week-old (young) and 24-week-old or more (adult)) were characterized using a multimodal approach, encompassing surface electrocardiograms (ECG), echocardiography recordings, ex vivo ECGs in isolated heart, endocardial mappings, Western blots, and mRNA quantifications. The assessment of cardiac electrophysiology by surface ECGs revealed no significant differences between wild-type and Trpm4-/- young (5- to 12-week-old) mice of either sex. Above 24 weeks of age, adult male Trpm4-/- mice showed reduced heart rate and increased heart rate variability. Echocardiography revealed that only adult male Trpm4-/- mice exhibited slight left ventricular hypertrophic alterations compared to controls, illustrated by alterations of the mitral valve pressure halftime, the mitral valve E/A ratio, the isovolumetric relaxation time, and the mitral valve deceleration. In addition, an assessment of the right ventricular systolic function by scanning the pulmonary valve highlighted an alteration in pulmonary valve peak velocity and pressure in adult male Trpm4-/- mice. Endocardial mapping recordings showed that applying 5 μM of the new TRPM4 inhibitor NBA triggered a third-degree atrioventricular block on 40% of wild-type hearts. These results confirm the key role of TRPM4 in the proper structure and electrical function of the heart. It also reveals differences between male and female animals that have never been reported. In addition, the investigation of the effects of NBA on heart function confirms the role of TRPM4 in atrioventricular conduction.

The Role of TRPM4 in Cardiac Electrophysiology and Arrhythmogenesis

The transient receptor potential melastatin 4 (TRPM4) channel is a non-selective cation channel that activates in response to increased intracellular Ca²⁺ levels but does not allow Ca²⁺ to pass through directly. It plays a crucial role in regulating diverse cellular functions associated with intracellular Ca²⁺ homeostasis/dynamics. TRPM4 is widely expressed in the heart and is involved in various physiological and pathological processes therein. Specifically, it has a significant impact on the electrical activity of cardiomyocytes by depolarizing the membrane, presumably via Na⁺ loading. The TRPM4 channel likely contributes to the development of cardiac arrhythmias associated with specific genetic backgrounds and cardiac remodeling. This short review aims to overview what is known so far about the TRPM4 channel in cardiac electrophysiology and arrhythmogenesis, highlighting its potential as a novel therapeutic target to effectively prevent and treat cardiac arrhythmias.

Multiomics uncover the proinflammatory role of Trpm4 deletion after myocardial infarction in mice

Upon myocardial infarction (MI), ischemia-induced cell death triggers an inflammatory response responsible for removing necrotic material and inducing tissue repair. TRPM4 is a Ca2+-activated ion channel permeable to monovalent cations. Although its role in cardiomyocyte-driven hypertrophy and arrhythmia post-MI has been established, no study has yet investigated its role in the inflammatory process orchestrated by endothelial cells, immune cells, and fibroblasts. This study aims to assess the role of TRPM4 in 1) survival and cardiac function, 2) inflammation, and 3) healing post-MI. We performed ligation of the left coronary artery or sham intervention on 154 Trpm4 WT or KO mice under isoflurane anesthesia. Survival and echocardiographic functions were monitored up to 5 wk. We collected serum during the acute post-MI phase to analyze proteomes and performed single-cell RNA sequencing on nonmyocytic cells of hearts after 24 and 72 h. Lastly, we assessed chronic fibrosis and angiogenesis. We observed no significant differences in survival or cardiac function, even though our proteomics data showed significantly decreased tissue injury markers (i.e., creatine kinase M and VE-cadherin) in KO serum after 12 h. On the other hand, inflammation, characterized by serum amyloid P component in the serum, higher number of recruited granulocytes, inflammatory monocytes, and macrophages, as well as expression of proinflammatory genes, was significantly higher in KO. This correlated with increased chronic cardiac fibrosis and angiogenesis. Since inflammation and fibrosis are closely linked to adverse remodeling, future therapeutic attempts at inhibiting TRPM4 will need to assess these parameters carefully before proceeding with translational studies.NEW & NOTEWORTHY Deletion of Trpm4 increases markers of cardiac and systemic inflammation within the first 24 h after MI, while inducing an earlier fibrotic transition at 72 h and more overall chronic fibrosis and angiogenesis at 5 wk. The descriptive, robust, and methodologically broad approach of this study sheds light on an important caveat that will need to be taken into account in all future therapeutic attempts to inhibit TRPM4 post-MI.

A Novel Role of the TRPM4 Ion Channel in Exocytosis

Under physiological conditions, the widely expressed calcium-activated TRPM4 channel conducts sodium into cells. This sodium influx depolarizes the plasma membrane and reduces the driving force for calcium entry. The aberrant expression or function of TRPM4 has been reported in various diseases, including different types of cancer. TRPM4 is mainly localized in the plasma membrane, but it is also found in intracellular vesicles, which can undergo exocytosis. In this study, we show that calcium-induced exocytosis in the colorectal cancer cell line HCT116 is dependent on TRPM4. In addition, the findings from some studies of prostate cancer cell lines suggest a more general role of TRPM4 in calcium-induced exocytosis in cancer cells. Furthermore, calcium-induced exocytosis depends on TRPM4 ion conductivity. Additionally, an increase in intracellular calcium results in the delivery of TRPM4 to the plasma membrane. This process also depends on TRPM4 ion conductivity. TRPM4-dependent exocytosis and the delivery of TRPM4 to the plasma membrane are mediated by SNARE proteins. Finally, we provide evidence that calcium-induced exocytosis depends on TRPM4 ion conductivity, not within the plasma membrane, but rather in TRPM4-containing vesicles.

Pharmacological Modulation and (Patho)Physiological Roles of TRPM4 Channel-Part 2: TRPM4 in Health and Disease

Transient receptor potential melastatin 4 (TRPM4) is a unique member of the TRPM protein family and, similarly to TRPM5, is Ca²⁺ sensitive and permeable for monovalent but not divalent cations. It is widely expressed in many organs and is involved in several functions; it regulates membrane potential and Ca²⁺ homeostasis in both excitable and non-excitable cells. This part of the review discusses the currently available knowledge about the physiological and pathophysiological roles of TRPM4 in various tissues. These include the physiological functions of TRPM4 in the cells of the Langerhans islets of the pancreas, in various immune functions, in the regulation of vascular tone, in respiratory and other neuronal activities, in chemosensation, and in renal and cardiac physiology. TRPM4 contributes to pathological conditions such as overactive bladder, endothelial dysfunction, various types of malignant diseases and central nervous system conditions including stroke and injuries as well as in cardiac conditions such as arrhythmias, hypertrophy, and ischemia-reperfusion injuries. TRPM4 claims more and more attention and is likely to be the topic of research in the future.

Low-intensity pulsed ultrasound prevents angiotensin II-induced aortic smooth muscle cell phenotypic switch via hampering miR-17-5p and enhancing PPAR-γ

Vascular events can trigger a pathological phenotypic switch in vascular smooth muscle cells (VSMCs), decreasing and disrupting the plasticity and diversity of vascular networks. The development of novel therapeutic approaches is necessary to prevent these changes. We aimed to investigate the effects and associated mechanisms of low-intensity pulsed ultrasound (LIPUS) irradiation on the angiotensin II (AngII)-induced phenotypic switch in VSMCs. In vivo, AngII was infused subcutaneously for 4 weeks to stimulate vascular remodeling in mice, and LIPUS irradiation was applied for 20 min every 2 days for 4 weeks. In vitro, cultured rat aortic VSMCs (RAVSMCs) were pretreated once with LIPUS irradiation for 20 min before 48-h AngII stimulation. Our results showed that LIPUS irradiation prevents AngII-induced vascular remodeling of the whole wall artery without discriminating between adventitia and media in vivo and RAVSMC phenotypic switching in vitro. LIPUS irradiation downregulated miR-17-5p expression and upregulated peroxisome proliferator-activated receptor gamma (PPAR-γ) expression. The PPAR-γ activator rosiglitazone could mimic the favorable effects of LIPUS irradiation on AngII-treated RAVSMCs. In contrast, GW9662 could impede the LIPUS-mediated downregulation of RAVSMC proliferation and inflammation under AngII stimulation conditions in vivo and in vitro. Also, the miR-17-5p agomir has the same effects as GW9662 in vitro. Besides, the inhibitory effects of GW9662 against the anti-remodeling effects of LIPUS irradiation in AngII-induced RAVSMCs could be blocked by pretreatment with the miR-17-5p antagomir. Overall, LIPUS irradiation prevents AngII-induced RAVSMCs phenotypic switching through hampering miR-17-5p and enhancing PPAR-γ, suggesting a new approach for the treatment of vascular disorders.

Electrophysiological Effects of the Transient Receptor Potential Melastatin 4 Channel Inhibitor (4-Chloro-2-(2-chlorophenoxy)acetamido) Benzoic Acid (CBA) in Canine Left Ventricular Cardiomyocytes

Transient receptor potential melastatin 4 (TRPM4) plays an important role in many tissues, including pacemaker and conductive tissues of the heart, but much less is known about its electrophysiological role in ventricular myocytes. Our earlier results showed the lack of selectivity of 9-phenanthrol, so CBA ((4-chloro-2-(2-chlorophenoxy)acetamido) benzoic acid) was chosen as a new, potentially selective inhibitor. Goal: Our aim was to elucidate the effect and selectivity of CBA in canine left ventricular cardiomyocytes and to study the expression of TRPM4 in the canine heart. Experiments were carried out in enzymatically isolated canine left ventricular cardiomyocytes. Ionic currents were recorded with an action potential (AP) voltage-clamp technique in whole-cell configuration at 37 °C. An amount of 10 mM BAPTA was used in the pipette solution to exclude the potential activation of TRPM4 channels. AP was recorded with conventional sharp microelectrodes. CBA was used in 10 µM concentrations. Expression of TRPM4 protein in the heart was studied by Western blot. TRPM4 protein was expressed in the wall of all four chambers of the canine heart as well as in samples prepared from isolated left ventricular cells. CBA induced an approximately 9% reduction in AP duration measured at 75% and 90% of repolarization and decreased the short-term variability of APD₉₀. Moreover, AP amplitude was increased and the maximal rates of phase 0 and 1 were reduced by the drug. In AP clamp measurements, CBA-sensitive current contained a short, early outward and mainly a long, inward current. Transient outward potassium current (I_to) and late sodium current (I_Na,L) were reduced by approximately 20% and 47%, respectively, in the presence of CBA, while L-type calcium and inward rectifier potassium currents were not affected. These effects of CBA were largely reversible upon washout. Based on our results, the CBA induced reduction of phase-1 slope and the slight increase of AP amplitude could have been due to the inhibition of I_to. The tendency for AP shortening can be explained by the inhibition of inward currents seen in AP-clamp recordings during the plateau phase. This inward current reduced by CBA is possibly I_Na,L, therefore, CBA is not entirely selective for TRPM4 channels. As a consequence, similarly to 9-phenanthrol, it cannot be used to test the contribution of TRPM4 channels to cardiac electrophysiology in ventricular cells, or at least caution must be applied.

Theoretical Investigation of the Mechanism by which A Gain-of-Function Mutation of the TRPM4 Channel Causes Conduction Block

In the heart, TRPM4 is most abundantly distributed in the conduction system. Previously, a single mutation, 'E7K', was identified in its distal N-terminus to cause conduction disorder because of enhanced cell-surface expression. It remains, however, unclear how this expression increase leads to conduction failure rather than abnormally enhanced cardiac excitability. To address this issue theoretically, we mathematically formulated the gating kinetics of the E7K-mutant TRPM4 channel by a combined use of voltage jump analysis and ionomycin-perforated cell-attached recording technique and incorporated the resultant rate constants of opening and closing into a human Purkinje fiber single-cell action potential (AP) model (Trovato model) to perform 1D-cable simulations. The results from TRPM4 expressing HEK293 cells showed that as compared with the wild-type, the open state is much preferred in the E7K mutant with increased voltage-and Ca²⁺-sensitivities. These theoretical predictions were confirmed by power spectrum and single channel analyses of expressed wild-type and E7K-mutant TRPM4 channels. In our modified Trovato model, the facilitated opening of the E7K mutant channel markedly prolonged AP duration with concomitant depolarizing shifts of the resting membrane potential in a manner dependent on the channel density (or maximal activity). This was, however, little evident in the wild-type TRPM4 channel. Moreover, 1D-cable simulations with the modified Trovato model revealed that increasing the density of E7K (but not of wild-type) TRPM4 channels progressively reduced AP conduction velocity eventually culminating in complete conduction block. These results clearly suggest the brady-arrhythmogenicity of the E7K mutant channel which likely results from its pathologically enhanced activity.

Ca2+ mishandling in heart failure: Potential targets

Ca²⁺ mishandling is a common feature in several cardiovascular diseases such as heart failure (HF). In many cases, impairment of key players in intracellular Ca²⁺ homeostasis has been identified as the underlying mechanism of cardiac dysfunction and cardiac arrhythmias associated with HF. In this review, we summarize primary novel findings related to Ca²⁺ mishandling in HF progression. HF research has increasingly focused on the identification of new targets and the contribution of their role in Ca²⁺ handling to the progression of the disease. Recent research studies have identified potential targets in three major emerging areas implicated in regulation of Ca²⁺ handling: the innate immune system, bone metabolism factors and post-translational modification of key proteins involved in regulation of Ca²⁺ handling. Here, we describe their possible contributions to the progression of HF.

The Ca2+-activated cation channel TRPM4 is a positive regulator of pressure overload-induced cardiac hypertrophy

Pathological left ventricular hypertrophy (LVH) occurs in response to pressure overload and remains the single most important clinical predictor of cardiac mortality. The molecular pathways in the induction of pressure overload LVH are potential targets for therapeutic intervention. Current treatments aim to remove the pressure overload stimulus for LVH, but do not completely reverse adverse cardiac remodelling. Although numerous molecular signalling steps in the induction of LVH have been identified, the initial step by which mechanical stretch associated with cardiac pressure overload is converted into a chemical signal that initiates hypertrophic signalling remains unresolved. In this study, we show that selective deletion of transient receptor potential melastatin 4 (TRPM4) channels in mouse cardiomyocytes results in an approximately 50% reduction in the LVH induced by transverse aortic constriction. Our results suggest that TRPM4 channel is an important component of the mechanosensory signalling pathway that induces LVH in response to pressure overload and represents a potential novel therapeutic target for the prevention of pathological LVH.

The Calcium Signaling Mechanisms in Arterial Smooth Muscle and Endothelial Cells

The contractile state of resistance arteries and arterioles is a crucial determinant of blood pressure and blood flow. Physiological regulation of arterial contractility requires constant communication between endothelial and smooth muscle cells. Various Ca²⁺ signals and Ca²⁺ -sensitive targets ensure dynamic control of intercellular communications in the vascular wall. The functional effect of a Ca²⁺ signal on arterial contractility depends on the type of Ca²⁺ -sensitive target engaged by that signal. Recent studies using advanced imaging methods have identified the spatiotemporal signatures of individual Ca²⁺ signals that control arterial and arteriolar contractility. Broadly speaking, intracellular Ca²⁺ is increased by ion channels and transporters on the plasma membrane and endoplasmic reticular membrane. Physiological roles for many vascular Ca²⁺ signals have already been confirmed, while further investigation is needed for other Ca²⁺ signals. This article focuses on endothelial and smooth muscle Ca²⁺ signaling mechanisms in resistance arteries and arterioles. We discuss the Ca²⁺ entry pathways at the plasma membrane, Ca²⁺ release signals from the intracellular stores, the functional and physiological relevance of Ca²⁺ signals, and their regulatory mechanisms. Finally, we describe the contribution of abnormal endothelial and smooth muscle Ca²⁺ signals to the pathogenesis of vascular disorders. © 2021 American Physiological Society. Compr Physiol 11:1831-1869, 2021.

TRPM4 Participates in Aldosterone-Salt-Induced Electrical Atrial Remodeling in Mice

Aldosterone plays a major role in atrial structural and electrical remodeling, in particular through Ca2+-transient perturbations and shortening of the action potential. The Ca2+-activated non-selective cation channel Transient Receptor Potential Melastatin 4 (TRPM4) participates in atrial action potential. The aim of our study was to elucidate the interactions between aldosterone and TRPM4 in atrial remodeling and arrhythmias susceptibility. Hyperaldosteronemia, combined with a high salt diet, was induced in mice by subcutaneously implanted osmotic pumps during 4 weeks, delivering aldosterone or physiological serum for control animals. The experiments were conducted in wild type animals (Trpm4+/+) as well as Trpm4 knock-out animals (Trpm4-/-). The atrial diameter measured by echocardiography was higher in Trpm4-/- compared to Trpm4+/+ animals, and hyperaldosteronemia-salt produced a dilatation in both groups. Action potentials duration and triggered arrhythmias were measured using intracellular microelectrodes on the isolated left atrium. Hyperaldosteronemia-salt prolong action potential in Trpm4-/- mice but had no effect on Trpm4+/+ mice. In the control group (no aldosterone-salt treatment), no triggered arrythmias were recorded in Trpm4+/+ mice, but a high level was detected in Trpm4-/- mice. Hyperaldosteronemia-salt enhanced the occurrence of arrhythmias (early as well as delayed-afterdepolarization) in Trpm4+/+ mice but decreased it in Trpm4-/- animals. Atrial connexin43 immunolabelling indicated their disorganization at the intercalated disks and a redistribution at the lateral side induced by hyperaldosteronemia-salt but also by Trpm4 disruption. In addition, hyperaldosteronemia-salt produced pronounced atrial endothelial thickening in both groups. Altogether, our results indicated that hyperaldosteronemia-salt and TRPM4 participate in atrial electrical and structural remodeling. It appears that TRPM4 is involved in aldosterone-induced atrial action potential shortening. In addition, TRPM4 may promote aldosterone-induced atrial arrhythmias, however, the underlying mechanisms remain to be explored.

Upregulation of transient receptor potential melastatin 4 (TRPM4) in ventricular fibroblasts from heart failure patients

The transient receptor potential melastatin 4 (TRPM4) is a Ca2+-activated nonselective monovalent cation channel belonging to the TRP channel superfamily. TRPM4 is widely expressed in various tissues and most abundantly expressed in the heart. TRPM4 plays a critical role in cardiac conduction. Patients carrying a gain-of-function or loss-of-function mutation of TRPM4 display impaired cardiac conduction. Knockout or over-expression of TRPM4 in mice recapitulates conduction defects in patients. Moreover, recent studies have indicated that TRPM4 plays a role in hypertrophy and heart failure. Whereas the role of TRPM4 mediated by cardiac myocytes has been well investigated, little is known about TRPM4 and its role in cardiac fibroblasts. Here we show that in human left ventricular fibroblasts, TRPM4 exhibits typical Ca2+-activation characteristics, linear current-voltage (I-V) relation, and monovalent permeability. TRPM4 currents recorded in fibroblasts from heart failure patients (HF) are more than 2-fold bigger than those from control individuals (CTL). The enhanced functional TRPM4 in HF is not resulted from changed channel properties, as TRPM4 currents from both HF and CTL fibroblasts demonstrate similar sensitivity to intracellular calcium activation and extracellular 9-phenanthrol (9-phen) blockade. Consistent with enhanced TRPM4 activity, the protein level of TRPM4 is about 2-fold higher in HF than that of CTL hearts. Moreover, TRPM4 current in CTL fibroblasts is increased after 24 hours of TGFβ1 treatment, implying that TRPM4 in vivo may be upregulated by fibrogenesis promotor TGFβ1. The upregulated TRPM4 in HF fibroblasts suggests that TRPM4 may play a role in cardiac fibrogenesis under various pathological conditions.

TRPM4 in Cancer-A New Potential Drug Target

Transient receptor potential melastatin 4 (TRPM4) is widely expressed in various organs and associated with cardiovascular and immune diseases. Lately, the interest in studies on TRPM4 in cancer has increased. Thus far, TRPM4 has been investigated in diffuse large B-cell lymphoma, prostate, colorectal, liver, breast, urinary bladder, cervical, and endometrial cancer. In several types of cancer TRPM4 is overexpressed and contributes to cancer hallmark functions such as increased proliferation and migration and cell cycle shift. Hence, TRPM4 is a potential prognostic cancer marker and a promising anticancer drug target candidate. Currently, the underlying mechanism by which TRPM4 contributes to cancer hallmark functions is under investigation. TRPM4 is a Ca²⁺-activated monovalent cation channel, and its ion conductivity can decrease intracellular Ca²⁺ signaling. Furthermore, TRPM4 can interact with different partner proteins. However, the lack of potent and specific TRPM4 inhibitors has delayed the investigations of TRPM4. In this review, we summarize the potential mechanisms of action and discuss new small molecule TRPM4 inhibitors, as well as the TRPM4 antibody, M4P. Additionally, we provide an overview of TRPM4 in human cancer and discuss TRPM4 as a diagnostic marker and anticancer drug target.

TRPM Channels in Human Diseases

The transient receptor potential melastatin (TRPM) subfamily belongs to the TRP cation channels family. Since the first cloning of TRPM1 in 1989, tremendous progress has been made in identifying novel members of the TRPM subfamily and their functions. The TRPM subfamily is composed of eight members consisting of four six-transmembrane domain subunits, resulting in homomeric or heteromeric channels. From a structural point of view, based on the homology sequence of the coiled-coil in the C-terminus, the eight TRPM members are clustered into four groups: TRPM1/M3, M2/M8, M4/M5 and M6/M7. TRPM subfamily members have been involved in several physiological functions. However, they are also linked to diverse pathophysiological human processes. Alterations in the expression and function of TRPM subfamily ion channels might generate several human diseases including cardiovascular and neurodegenerative alterations, organ dysfunction, cancer and many other channelopathies. These effects position them as remarkable putative targets for novel diagnostic strategies, drug design and therapeutic approaches. Here, we review the current knowledge about the main characteristics of all members of the TRPM family, focusing on their actions in human diseases.

TRPM4 non-selective cation channel in human atrial fibroblast growth

Cardiac fibroblasts play an important role in cardiac matrix turnover and are involved in cardiac fibrosis development. Ca²⁺ is a driving belt in this phenomenon. This study evaluates the functional expression and contribution of the Ca²⁺-activated channel TRPM4 in atrial fibroblast phenotype. Molecular and electrophysiological investigations were conducted in human atrial fibroblasts in primary culture and in atrial fibroblasts obtained from wild-type and transgenic mice with disrupted Trpm4 gene (Trpm4^-/-). A typical TRPM4 current was recorded on human cells (equal selectivity for Na⁺ and K⁺, activation by internal Ca²⁺, voltage sensitivity, conductance of 23.2 pS, inhibition by 9-phenanthrol (IC₅₀ = 6.1 × 10^-6 mol L^-1)). Its detection rate was 13% on patches at days 2-4 in culture but raised to 100% on patches at day 28. By the same time, a cell growth was observed. This growth was smaller when cells were maintained in the presence of 9-phenanthrol. Similar cell growth was measured on wild-type mice atrial fibroblasts during culture. However, this growth was minimized on Trpm4^-/- mice fibroblasts compared to control animals. In addition, the expression of alpha smooth muscle actin increased during culture of atrial fibroblasts from wild-type mice. This was not observed in Trpm4^-/- mice fibroblasts. It is concluded that TRPM4 participates in fibroblast growth and could thus be involved in cardiac fibrosis.

New role of TRPM4 channel in the cardiac excitation-contraction coupling in response to physiological and pathological hypertrophy in mouse

The transient receptor potential Melastatin 4 (TRPM4) channel is a calcium-activated non-selective cation channel expressed widely. In the heart, using a knock-out mouse model, the TRPM4 channel has been shown to be involved in multiple processes, including β-adrenergic regulation, cardiac conduction, action potential duration and hypertrophic adaptations. This channel was recently shown to be involved in stress-induced cardiac arrhythmias in a mouse model overexpressing TRPM4 in ventricular cardiomyocytes. However, the link between TRPM4 channel expression in ventricular cardiomyocytes, the hypertrophic response to stress and/or cellular arrhythmias has yet to be elucidated. In this present study, we induced pathological hypertrophy in response to myocardial infarction using a mouse model of Trpm4 gene invalidation, and demonstrate that TRPM4 is essential for survival. We also demonstrate that the TRPM4 is required to activate both the Akt and Calcineurin pathways. Finally, using two hypertrophy models, either a physiological response to endurance training or a pathological response to myocardial infarction, we show that TRPM4 plays a role in regulating transient calcium amplitudes and leads to the development of cellular arrhythmias potentially in cooperation with the Sodium-calcium exchange (NCX). Here, we report two functions of the TRPM4 channel: first its role in adaptive hypertrophy, and second its association with NCX could mediate transient calcium amplitudes which trigger cellular arrhythmias.

Targeting Ca2 + Handling Proteins for the Treatment of Heart Failure and Arrhythmias

Diseases of the heart, such as heart failure and cardiac arrhythmias, are a growing socio-economic burden. Calcium (Ca²⁺) dysregulation is key hallmark of the failing myocardium and has long been touted as a potential therapeutic target in the treatment of a variety of cardiovascular diseases (CVD). In the heart, Ca²⁺ is essential for maintaining normal cardiac function through the generation of the cardiac action potential and its involvement in excitation contraction coupling. As such, the proteins which regulate Ca²⁺ cycling and signaling play a vital role in maintaining Ca²⁺ homeostasis. Changes to the expression levels and function of Ca²⁺-channels, pumps and associated intracellular handling proteins contribute to altered Ca²⁺ homeostasis in CVD. The remodeling of Ca²⁺-handling proteins therefore results in impaired Ca²⁺ cycling, Ca²⁺ leak from the sarcoplasmic reticulum and reduced Ca²⁺ clearance, all of which contributes to increased intracellular Ca²⁺. Currently, approved treatments for targeting Ca²⁺ handling dysfunction in CVD are focused on Ca²⁺ channel blockers. However, whilst Ca²⁺ channel blockers have been successful in the treatment of some arrhythmic disorders, they are not universally prescribed to heart failure patients owing to their ability to depress cardiac function. Despite the progress in CVD treatments, there remains a clear need for novel therapeutic approaches which are able to reverse pathophysiology associated with heart failure and arrhythmias. Given that heart failure and cardiac arrhythmias are closely associated with altered Ca²⁺ homeostasis, this review will address the molecular changes to proteins associated with both Ca²⁺-handling and -signaling; their potential as novel therapeutic targets will be discussed in the context of pre-clinical and, where available, clinical data.

TRPM4 Modulates Right Ventricular Remodeling Under Pressure Load Accompanied With Decreased Expression Level

BACKGROUND

Survival of patients with congenital heart defects including increased right ventricular pressure load (ie, tetralogy of Fallot) or pulmonary hypertension is dependent on the function of the right ventricle (RV). RV remodeling has several effects with progressive transition from compensated status to heart failure. Transient receptor potential melastatin 4 (TRPM4) forms cation channels expressed in myocardium, which was shown to modulate cardiac remodeling in the left ventricle of mice. Aim of this study was to identify the role of TRPM4 for contractile function and remodeling of the RV in a rat model of right ventricular pressure load.

METHODS AND RESULTS

We performed experiments with untreated rats and under monocrotaline (MCT)-induced pressure load comparing wild-type (Trpm4^+/+) and TRPM4-deficient (Trpm4^-/-) rats. RV function was characterized by echocardiography and contractility measurements of isolated papillary muscles. RV hypertrophy was investigated by echocardiography and by determination of hypertrophy indices. Pulmonary arterial remodeling was evaluated by echocardiography and histology. TRPM4 protein expression in RV of human, rat and mouse was detected by Western blot and quantified in rat. TRPM4 proteins were detected in RV myocardium of rat and mouse, which were not detectable in TRPM4-deficient animals. Proteins of the same size were found in RV of a pediatric patient with tetralogy of Fallot. In untreated status, Trpm4^+/+ and Trpm4^-/- rats showed comparable RV contractile function and dimensions. Under pressure load (42 days after MCT injection), RV hypertrophy was significantly increased in Trpm4^-/- rats compared with Trpm4^+/+ controls, whereas MCT-mediated alterations in cardiac contractility and pulmonary arterial remodeling were not affected by TRPM4 inactivation in rats. Finally, TRPM4 protein expression in RV was drastically reduced in MCT-treated rats, whereas left ventricle of the same animals showed no alteration in TRPM4 expression.

CONCLUSIONS

Right ventricular pressure load evoked by MCT treatment in rats leads to a prominent downregulation of TRPM4 protein expression in the RV and complete deletion of TRPM4 expression aggravates right ventricular hypertrophy. Thus, therapeutic modulation of TRPM4 expression and activity might represent a novel approach to target right ventricular remodeling in patients with pulmonary hypertension or otherwise loaded RV.

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.

The oncogenic roles of TRPM ion channels in cancer

Transient receptor potential (TRP) proteins are a diverse family of ion channels present in multiple types of tissues. They function as gatekeepers for responses to sensory stimuli including temperature, vision, taste, and pain through their activities in conducting ion fluxes. The TRPM (melastatin) subfamily consists of eight members (i.e., TRPM1-8), which collectively regulate fluxes of various types of cations such as K⁺ , Na⁺ , Ca²⁺ , and Mg²⁺ . Growing evidence in the past two decades indicates that TRPM ion channels, their isoforms, or long noncoding RNAs encoded within the locus may be oncogenes involved in the regulation of cancer cell growth, proliferation, autophagy, invasion, and epithelial-mesenchymal transition, and their significant association with poor clinical outcomes of cancer patients. In this review, we describe and discuss recent findings implicating TRPM channels in different malignancies, their functions, mechanisms, and signaling pathways involved in cancers, as well as summarizing their normal physiological functions and the availability of ion channel pharmacological inhibitors.

TRP Channels Expression Profile in Human End-Stage Heart Failure

Objectives: Many studies indicate the involvement of transient receptor potential (TRP) channels in the development of heart hypertrophy. However, the data is often conflicted and has originated in animal models. Here, we provide systematic analysis of TRP channels expression in human failing myocardium. Methods and results: Left-ventricular tissue samples were isolated from explanted hearts of NYHA III-IV patients undergoing heart transplants (n = 43). Quantitative real-time PCR was performed to assess the mRNA levels of TRPC, TRPM and TRPV channels. Analysis of functional, clinical and biochemical data was used to confirm an end-stage heart failure diagnosis. Compared to myocardium samples from healthy donor hearts (n = 5), we detected a distinct increase in the expression of TRPC1, TRPC5, TRPM4 and TRPM7, and decreased expression of TRPC4 and TRPV2. These changes were not dependent on gender, clinical or biochemical parameters, nor functional parameters of the heart. We detected, however, a significant correlation of TRPC1 and MEF2c expression. Conclusions: The end-stage heart failure displays distinct expressional changes of TRP channels. Our findings provide a systematic description of TRP channel expression in human heart failure. The results highlight the complex interplay between TRP channels and the need for deeper analysis of early stages of hypertrophy and heart failure development.

AAV9-Mediated Overexpression of TRPM4 Increases the Incidence of Stress-Induced Ventricular Arrhythmias in Mice

Ca²⁺ activated non-selective (CAN) cation channels have been described in cardiomyocytes since the advent of the patch clamp technique. It has been hypothesized that this type of ion channel contributes to the triggering of cardiac arrhythmias. TRPM4 is to date the only molecular candidate for a CAN cation channel in cardiomyocytes. Its significance for arrhythmogenesis in living animals remains, however, unclear. In this study, we have tested whether increased expression of wild-type (WT) TRPM4 augments the risk of arrhythmias in living mice. Overexpression of WT TRPM4 was achieved via tail vein injection of adeno-associated viral vector serotype 9 (AAV9) particles, which have been described to be relatively cardiac specific in mice. Subsequently, we performed ECG-measurements in freely moving mice to determine their in vivo cardiac phenotype. Though cardiac muscle was transduced with TRPM4 viral particles, the majority of viral particles accumulated in the liver. We did not observe any difference in arrhythmic incidents during baseline conditions. Instead, WT mice that overexpress TRPM4 were more vulnerable to develop premature ventricular ectopic beats during exercise-induced β-adrenergic stress. Conduction abnormalities were rare and not more frequent in transduced mice compare to WT mice. Taken together, we provide evidence that overexpression of TRPM4 increases the susceptibility of living mice to stress-induced arrhythmias.

Genome Sequence Analysis Reveals Selection Signatures in Endangered Trypanotolerant West African Muturu Cattle

Like most West African Bos taurus, the shorthorn Muturu is under threat of replacement or crossbreeding with zebu. Their populations are now reduced to a few hundred breeding individuals and they are considered endangered. So far, the genetic variation and genetic basis of the trypanotolerant Muturu environmental adaptation have not been assessed. Here, we present genome-wide candidate positive selection signatures in Muturu following within-population iHS and between population Rsb signatures of selection analysis. We compared the results in Muturu with the ones obtained in N’Dama, a West African longhorn trypanotolerant taurine, and in two European taurine (Holstein and Jersey). The results reveal candidate signatures of selection regions in Muturu including genes linked to the innate (e.g., TRIM10, TRIM15, TRIM40, and TRIM26) and the adaptive (e.g., JSP.1, BOLA-DQA2, BOLA-DQA5, BOLA-DRB3, and BLA-DQB) immune responses. The most significant regions are identified on BTA 23 at the bovine major histocompatibility complex (MHC) (iHS analysis) and on BTA 12 at genes including a heat tolerance gene (INTS6) (Rsb analysis). Other candidate selected regions include genes related to growth traits/stature (e.g., GHR and GHRHR), coat color (e.g., MITF and KIT), feed efficiency (e.g., ZRANB3 and MAP3K5) and reproduction (e.g., RFX2, SRY, LAP3, and GPX5). Genes under common signatures of selection regions with N’Dama, including for adaptive immunity and heat tolerance, suggest shared mechanisms of adaptation to environmental challenges for these two West African taurine cattle. Interestingly, out of the 242,910 SNPs identified within the candidate selected regions in Muturu, 917 are missense SNPs (0.4%), with an unequal distribution across 273 genes. Fifteen genes including RBBP8, NID1, TEX15, LAMA3, TRIM40, and OR12D3 comprise 220 missense variants, each between 11 and 32. Our results, while providing insights into the candidate genes under selection in Muturu, are paving the way to the identification of genes and their polymorphisms linked to the unique tropical adaptive traits of the West Africa taurine, including trypanotolerance.

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.

Unc-51 like autophagy activating kinase 1 accelerates angiotensin II-induced cardiac hypertrophy through promoting oxidative stress regulated by Nrf-2/HO-1 pathway

Unc-51 like autophagy activating kinase 1 (ULK1) is a serine/threonine kinase and the mammalian functional homolog of yeast Atg1, and plays an essential role in regulating various cellular processes. However, whether ULK1 can influence cardiac hypertrophy is unclear. In the study, we investigated the role of ULK1 in the pathogenesis of pathological cardiac hypertrophy and the molecular mechanism. We showed that ULK1 levels were increased in human dilated cardiomyopathic hearts and in mouse hypertrophic hearts. ULK1 knockout conferred resistance to angiotensin II (Ang II) infusion through markedly repressing hypertrophic growth, cardiac function and the deposition of fibrosis. In ULK1 transgenic (TG) mice with ULK1 over-expression, accelerated hypertrophy, reduced cardiac function and promoted fibrosis deposition were observed compared with non-transgenic mice following AngII challenge. In addition, mice lacking ULK1 showed alleviated oxidative stress by improving nuclear erythroid factor 2-related factor 2 (Nrf-2) and heme oxygenase-1 (HO-1) expression, whereas mice with ULK1 over-expression developed an accelerated reactive oxygen species (ROS) production. In vitro, we found that ULK1 knockdown-attenuated oxidative stress, inflammation and fibrosis deposition in AngII-exposed cardiomyocytes were significantly blunted by the inhibition of Nrf-2/HO-1 signaling. However, ULK1 overexpression-accelerated oxidative stress, inflammatory response and fibrosis were markedly ameliorated by the inhibition of ROS production. Our results indicated that ULK1 was a potential therapeutic target in pathological cardiac hypertrophy.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Allicin improves the function of cardiac microvascular endothelial cells by increasing PECAM-1 in rats with cardiac hypertrophy

OBJECTIVE

Cardiac microvascular damage is significantly associated with the development of cardiac hypertrophy (CH). Researchers found that allicin could inhibit CH, but the relationship between cardiac microvessel and the inhibition of allicin on CH has not been reported. We aimed to investigate the effect of allicin on the function of cardiac microvascular endothelial cells (CMECs) in CH rat.

MATERIALS AND METHODS

The hemodynamic parameters were measured by BL-420F biological function experimental system and the indicators of the ventricular structure and function were measured by echocardiographic system. MTT assay was performed to assess the cell viability. Nitrite detection was performed to detect nitric oxide content. The morphology and molecular characteristics were detected by electron micrographs, immunofluorescence, quantitative real-time polymerase chain reaction (qRT-PCR), western blot. Wound healing experiment, analysis of tube formation and shear adaptation were performed to assess CMECs migration ability, angiogenesis and shear-responsiveness respectively.

RESULT

Our findings have identified that microvascular density was decreased by observing the expression of platelet endothelial cell adhesion molecule-1 (PECAM-1) in CH rats. Interestingly, allicin improved the distribution and expression of PECAM-1. Meanwhile, allicin enhanced the migration and angiogenesis ability of CMECs, activated PECAM-1-PI3K-AKT-eNOS signaling pathway, however, the role of allicin was disappear after PECAM-1 was silenced. Allicin decreased the expression of caspase-3 and receptor interacting protein 3 (RIP3), inhibited necroptosis, and increased the levels of Angiopoietin-2 (Ang-2) and platelet-derived growth factor receptor-β (PDGFR-β). Under 10 dyn/cm² condition, allicin advanced the modification ability of CMECs's shear-adaptation by activating PECAM-1.

CONCLUSION

Allicin provided cardioprotection for CH rats by improving the function of CMECs through increasing the expression of PECAM-1.

Functional characterization of TRPM4 variants identified in sudden unexpected natural death

BACKGROUND

The TRPM4 gene encodes the subunit of the Ca²⁺-activated nonselective cation channel, which is enriched in the specialized cardiac conduction system and Purkinje fibers. To date, several putative disease-causing variants in TRPM4 have been reported to be associated with cardiac arrhythmia and progressive conduction disease. Here, we report the functional effects of previously uncharacterized variants of uncertain significance (VUS) that we have found while performing a "genetic autopsy" in individuals who have suffered sudden unexpected death (SUD) in the New York City area.

METHODS AND RESULTS

We have identified thirteen uncommon missense VUS in TRPM4 by testing 95 targeted genes implicated in channelopathy and cardiomyopathy in 330 cases of SUD. In several cases there were co-existing VUS in one or more other genes that were tested. We selected four TRPM4 VUS (C20S, A380V, L595V and I1082S) for functional characterization, since these cases lacked detectable variants in other genes of our testing panel. Two of the cases were infants, one was a child and one an adult. RNA-seq data analysis showed that the longer TRPM4b splice variant is predominantly expressed in adult and fetal human heart. We therefore used site-directed mutagenesis to introduce these variants in a TRPM4b cDNA. HEK293 cells were transfected with the cDNAs and patch clamping was performed to assess the functional consequences of the TRPM4 mutants. The TRPM4 current was recorded in excised patches and was significantly reduced by each of the mutants. The total protein level of TRPM4-C20S was markedly decreased, whereas the A380V and L595V mutants exhibited decreased surface expression. The TRPM4-A380V current rapidly desensitized following patch excision.

CONCLUSIONS

Each of the VUS tested caused a defect in TRPM4 channel function via distinctly different mechanisms, hence, it lays the foundation for further co-segregation family studies and animal studies of the TRPM4 variants.

Role of the TRPM4 Channel in Cardiovascular Physiology and Pathophysiology

The transient receptor potential cation channel subfamily M member 4 (TRPM4) channel influences calcium homeostasis during many physiological activities such as insulin secretion, immune response, respiratory reaction, and cerebral vasoconstriction. This calcium-activated, monovalent, selective cation channel also plays a key role in cardiovascular pathophysiology; for example, a mutation in the TRPM4 channel leads to cardiac conduction disease. Recently, it has been suggested that the TRPM4 channel is also involved in the development of cardiac ischemia-reperfusion injury, which causes myocardial infarction. In the present review, we discuss the physiological function of the TRPM4 channel, and assess its role in cardiovascular pathophysiology.

Transient receptor potential melastatin 4 channel inhibitor 9-phenanthrol inhibits K+ but not Ca2+ currents in canine ventricular myocytes

The role of transient receptor potential melastatin 4 (TRPM4) channels has been frequently tested using their inhibitor 9-phenanthrol in various cardiac preparations; however, the selectivity of the compound is uncertain. Therefore, in the present study, the concentration-dependent effects of 9-phenanthrol on major ionic currents were studied in canine isolated ventricular cells using whole-cell configuration of the patch-clamp technique and 10 mM BAPTA-containing pipette solution to prevent the Ca²⁺-dependent activation of TRPM4 channels. Transient outward (I_to1), rapid delayed rectifier (I_Kr), and inward rectifier (I_K1) K⁺ currents were suppressed by 10 and 30 μM 9-phenanthrol with the blocking potency for I_K1 < I_Kr < I_to1 and partial reversibility. L-type Ca²⁺ current was not affected up to the concentration of 30 μM. In addition, a steady outward current was detected at voltages positive to -40 mV in 9-phenanthrol, which was larger at more positive voltages and larger 9-phenanthrol concentrations. Action potentials were recorded using microelectrodes. Maximal rate of depolarization, phase-1 repolarization, and terminal repolarization were decreased and the plateau potential was depressed by 9-phenanthrol (3-30 μM), congruently with the observed alterations of ionic currents. Significant action potential prolongation was observed by 9-phenanthrol in the majority of the studied cells, but only at 30 μM concentration. In conclusion, 9-phenanthrol is not selective to TRPM4 channels in canine ventricular myocardium; therefore, its application as a TRPM4 blocker can be appropriate only in expression systems but not in native cardiac cells.

Store-Operated Ca2+ Entry as a Prostate Cancer Biomarker - a Riddle with Perspectives

Purpose of Review

Store-operated calcium entry (SOCE) is dysregulated in prostate cancer, contributing to increased cellular migration and proliferation and preventing cancer cell apoptosis. We here summarize findings on gene expression levels and functions of SOCE components, stromal interaction molecules (STIM1 and STIM2), and members of the Orai protein family (Orai1, 2, and 3) in prostate cancer. Moreover, we introduce new research models that promise to provide insights into whether dysregulated SOCE signaling has clinically relevant implications in terms of increasing the migration and invasion of prostate cancer cells.

Recent Findings

Recent reports on Orai1 and Orai3 expression levels and function were in part controversial probably due to the heterogeneous nature of prostate cancer. Lately, in prostate cancer cells, transient receptor melastatin 4 channel was shown to alter SOCE and play a role in migration and proliferation. We specifically highlight new cancer research models: a subpopulation of cells that show tumor initiation and metastatic potential in mice and zebrafish models.

Summary

This review focuses on SOCE component dysregulation in prostate cancer and analyzes several preclinical, cellular, and animal cancer research models.

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.

Transient receptor potential melastatin 4 channel contributes to migration of androgen-insensitive prostate cancer cells

Impaired Ca²⁺ signaling in prostate cancer contributes to several cancer hallmarks, such as enhanced proliferation and migration and a decreased ability to induce apoptosis. Na⁺ influx via transient receptor potential melastatin 4 channel (TRPM4) can reduce store-operated Ca²⁺ entry (SOCE) by decreasing the driving force for Ca²⁺. In patients with prostate cancer, gene expression of TRPM4 is elevated. Recently, TRPM4 was identified as a cancer driver gene in androgen-insensitive prostate cancer.

We investigated TRPM4 protein expression in cancer tissue samples from 20 patients with prostate cancer. We found elevated TRPM4 protein levels in prostatic intraepithelial neoplasia (PIN) and prostate cancer tissue compared to healthy tissue. In primary human prostate epithelial cells (hPEC) from healthy tissue and in the androgen-insensitive prostate cancer cell lines DU145 and PC3, TRPM4 mediated large Na⁺ currents. We demonstrated significantly increased SOCE after siRNA targeting of TRPM4 in hPEC and DU145 cells. In addition, knockdown of TRPM4 reduced migration but not proliferation of DU145 and PC3 cells. Taken together, our data identify TRPM4 as a regulator of SOCE in hPEC and DU145 cells, demonstrate a role for TRPM4 in cancer cell migration and suggest that TRPM4 is a promising potential therapeutic target.

Differential expression of store-operated calcium- and proliferation-related genes in hepatocellular carcinoma cells following TRPC1 ion channel silencing

TRPC1 and store-operated Ca²⁺ (SOC) entry have previously been associated with hepatocellular carcinoma cell proliferation. The aim of the study was to determine genes and processes associated with TRPC1 down-regulation and the resulting increase of SOC entry and decrease in hepatocellular carcinoma cell proliferation. For this purpose, transcriptome analysis was performed to determine differentially expressed genes in TRPC1-silenced Huh7 cells. SOC entry- and proliferation-related genes correlated with TRPC1 down-regulation were also examined. Changes in SOC entry and cell proliferation were monitored in the TRPC1-silenced and parental cells and found to be significantly increased and decreased, respectively, in TRPC1-silenced cells. A total of 71 genes were significantly differentially expressed (40 up- and 31 down-regulated), including four mitogen-activated protein kinase (MAPK) signalling-associated genes. STIM1 levels were significantly up-regulated and negatively correlated with TRPC1 levels. In addition, expression of two cell cycle regulation genes, CDK11A/11B and URGCP, was observed to decrease, whereas ERBB3 and FGFR4, pro-survival genes, increased significantly in TRPC1-silenced cells. In conclusion, these results suggest reciprocal alterations in TRPC1 and STIM1 levels and a role for STIM1 in the regulation of SOC entry in TRPC1-silenced Huh7 cells. In addition to TRPC1, STIM1 may participate in Huh7 cell proliferation by regulating SOC entry. Alterations in MAPK signalling genes may be involved in diminished cell proliferation in TRPC1-silenced Huh7 cells. Similarly, changes in cell cycle regulating genes in TRPC1-silenced cells indicate possible cell cycle arrest along with compensatory up-regulation of ERBB3 growth factor receptor—amongst others—to maintain hepatocellular carcinoma cell proliferation.

"TRP inflammation" relationship in cardiovascular system

Despite considerable advances in the research and treatment, the precise relationship between inflammation and cardiovascular (CV) disease remains incompletely understood. Therefore, understanding the immunoinflammatory processes underlying the initiation, progression, and exacerbation of many cardiovascular diseases is of prime importance. The innate immune system has an ancient origin and is well conserved across species. Its activation occurs in response to pathogens or tissue injury. Recent studies suggest that altered ionic balance, and production of noxious gaseous mediators link to immune and inflammatory responses with altered ion channel expression and function. Among plausible candidates for this are transient receptor potential (TRP) channels that function as polymodal sensors and scaffolding proteins involved in many physiological and pathological processes. In this review, we will first focus on the relevance of TRP channel to both exogenous and endogenous factors related to innate immune response and transcription factors related to sustained inflammatory status. The emerging role of inflammasome to regulate innate immunity and its possible connection to TRP channels will also be discussed. Secondly, we will discuss about the linkage of TRP channels to inflammatory CV diseases, from a viewpoint of inflammation in a general sense which is not restricted to the innate immunity. These knowledge may serve to provide new insights into the pathogenesis of various inflammatory CV diseases and their novel therapeutic strategies.

TRPM4 in cardiac electrical activity

TRPM4 forms a non-selective cation channel activated by internal Ca(2+). Its functional expression was demonstrated in cardiomyocytes of several mammalian species including humans, but the channel is also present in many other tissues. The recent characterization of the TRPM4 inhibitor 9-phenanthrol, and the availability of transgenic mice have helped to clarify the role of TRPM4 in cardiac electrical activity, including diastolic depolarization from the sino-atrial node cells in mouse, rat, and rabbit, as well as action potential duration in mouse cardiomyocytes. In rat and mouse, pharmacological inhibition of TRPM4 prevents cardiac ischaemia-reperfusion injuries and decreases the occurrence of arrhythmias. Several studies have identified TRPM4 mutations in patients with inherited cardiac diseases including conduction blocks and Brugada syndrome. This review identifies TRPM4 as a significant actor in cardiac electrophysiology.