TRPM7 regulates angiotensin II-induced sinoatrial node fibrosis in sick sinus syndrome rats by mediating Smad signaling

Comprehensive analyses of m6A RNA methylation patterns and related immune microenvironment in idiopathic pulmonary arterial hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is a life-threatening disease with a poor prognosis and high heritability, characterized by elevated pulmonary vascular resistance (PVR) and pulmonary artery pressure. N6-methyladenosine (m6A) RNA modification influences many RNA metabolism pathways. However, the position of m6A methylation regulators in IPAH remains unknown. Therefore, the study aims to disclose the function m6A regulators exert in the pathological mechanisms of IPAH and the immune microenvironment involved. The GSE117261 dataset was downloaded from the Gene Expression Omnibus (GEO) to screen the differentially expressed genes (DEGs) between normal and IPAH samples. Functional and pathway enrichment analyses of DEGs were then conducted by Gene ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG). We also identified the differentially-expressed m6A (DEm6A) regulators between normal and IPAH samples. Key m6A regulators related to the prediction of IPAH were selected using the random forest model. The results showed that FMR1, RBM15, HNRNPA2B1 and IGFBP3 were upregulated in IPAH. In contrast, LRPPRC was downregulated. The single sample gene set enrichment analysis (ssGSEA) method was then adopted to estimate the immune microenvironment in distinct m6A clusters and m6A phenotype-related genes (PRGs) clusters, respectively. Furthermore, we calculated the m6A score via principal component analysis (PCA), and the Sankey diagram was selected to present the correlation among the m6A clusters, m6A PRGs clusters and m6A score. Finally, quantitative RT-PCR and Western blotting were used to validate the key genes in human pulmonary artery smooth muscle cells (HPASMCs) treated by human platelet-derived growth factor-BB (PDGF-BB). The relative mRNA and protein expression levels of FMR1 were significantly elevated, however, the relative mRNA and protein expression levels of LRPPRC were downregulated. Besides, the relative mRNA level of HNRNPA2B1 was increased. Generally, this bioinformatics analysis might provoke more insights into diagnosing and treating IPAH.

Roles and mechanisms of natural drugs on sinus node dysfunction

Sinus node dysfunction is a common arrhythmia disorder with a high incidence and significant social and economic burden. Currently, there are no effective drugs for treating chronic sinus node dysfunction. The disease is associated with ion channel disturbances caused by aging, fibrosis, inflammation, oxidative stress, and autonomic dysfunction. Natural active substances and Chinese herbal medicines have been widely used and extensively studied in the medical community for the treatment of arrhythmias. Multiple studies have demonstrated that various active ingredients and Chinese herbal medicines, such as astragaloside IV, quercetin, and ginsenosides, exhibit antioxidant effects, reduce fibrosis, and maintain ion channel stability, providing promising drugs for treating sinus node dysfunction. This article summarizes the research progress on natural active ingredients and Chinese herbal formulas that regulate sick sinoatrial node function, providing valuable references for the treatment of sinus node dysfunction.

Sinus node dysfunction and atrial fibrillation-Relationships, clinical phenotypes, new mechanisms, and treatment approaches

Although the anatomical basis of the pathogenesis of sinus node dysfunction (SND) and atrial fibrillation (AF) is located primarily in the left and right atria, increasing evidence suggests a strong correlation between SND and AF, in terms of both clinical presentation and formation mechanisms. However, the exact mechanisms underlying this association are unclear. The relationship between SND and AF may not be causal, but is likely to involve common factors and mechanisms, including ion channel remodeling, gap junction abnormalities, structural remodeling, genetic mutations, neuromodulation abnormalities, the effects of adenosine on cardiomyocytes, oxidative stress, and viral infections. Ion channel remodeling manifests primarily as alterations in the "funny" current (I_f) and Ca²⁺ clock associated with cardiomyocyte autoregulation, and gap junction abnormalities are manifested primarily as decreased expression of connexins (Cxs) mediating electrical impulse propagation in cardiomyocytes. Structural remodeling refers primarily to fibrosis and cardiac amyloidosis (CA). Some genetic mutations can also cause arrhythmias, such as SCN5A, HCN4, EMD, and PITX2. The intrinsic cardiac autonomic nervous system (ICANS), a regulator of the heart's physiological functions, triggers arrhythmias.In addition, we discuss arrhythmias caused by viral infections, notably Coronavirus Disease 2019 (COVID-19). Similarly to upstream treatments for atrial cardiomyopathy such as alleviating CA, ganglionated plexus (GP) ablation acts on the common mechanisms between SND and AF, thus achieving a dual therapeutic effect.

Detection of TRPM6 and TRPM7 Proteins in Normal and Diseased Cardiac Atrial Tissue and Isolated Cardiomyocytes

Magnesium-sensitive transient receptor potential melastatin (TRPM) ion channels, TRPM6 and TRPM7, are present in several organs, but their roles in the heart remain unclear. Therefore, here, we studied the expression patterns of TRPM6 and TRPM7 in normal and diseased myocardium. Cardiac atrial tissue and cardiomyocytes were obtained from healthy pigs and undiseased human hearts as well as from hearts of patients with ischemic heart disease (IHD) or atrial fibrillation (AF). Immunofluorescence and ELISA were used to detect TRP proteins. TRPM6 and TRPM7 immunofluorescence signals, localized at/near the cell surface or intracellularly, were detected in pig and human atrial tissues. The TRP channel modulators carvacrol (CAR, 100 µM) or 2-aminoethoxydiphenyl borate (2-APB, 500 µM) decreased the TRPM7 signal, but enhanced that of TRPM6. At a higher concentration (2 mM), 2-APB enhanced the signals of both proteins. TRPM6 and TRPM7 immunofluorescence signals and protein concentrations were increased in atrial cells and tissues from IHD or AF patients. TRPM6 and TRPM7 proteins were both detected in cardiac atrial tissue, with relatively similar subcellular localization, but distinctive drug sensitivity profiles. Their upregulated expression in IHD and AF suggests a possible role of the channels in cardiac atrial disease.

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.

Neural crest mechanosensors: Seeing old proteins in a new light

Mechanical forces exerted on neural crest cells control their collective migration and differentiation. This perspective discusses our current understanding of neural crest mechanotransduction during cell migration and differentiation. Additionally, we describe proteins that have mechanosensitive functions in other systems, such as mechanosensitive G-protein-coupled receptors, mechanosensitive ion channels, cell-cell adhesion, and cell-matrix-interacting proteins, and highlight that these same proteins have in the past been studied in neural crest development from a purely signaling point of view. We propose that future studies elucidate the mechanosensitive functions these receptors may play in neural crest development and integrate this with their known molecular role.

The zinc transporter ZIP12 regulates monocrotaline-induced proliferation and migration of pulmonary arterial smooth muscle cells via the AKT/ERK signaling pathways

Background

The zinc transporter ZIP12 is a membrane-spanning protein that transports zinc ions into the cytoplasm from the extracellular space. Recent studies demonstrated that upregulation of ZIP12 is involved in elevation of cytosolic free zinc and excessive proliferation of pulmonary arterial smooth muscle cells (PASMCs) induced by hypoxia. However, the expression of ZIP12 and its role in pulmonary arterial hypertension (PAH) induced by monocrotaline (MCT) in rats have not been evaluated previously. The aim of this study was to investigate the effect of ZIP12 on the proliferation and migration of PASMCs and its underlying mechanisms in MCT-induced PAH.

Methods

A PAH rat model was generated by intraperitoneal injection of 20 mg/kg MCT twice at one-week intervals. PASMCs were isolated from the pulmonary arteries of rats with MCT-induced PAH or control rats. The expression of ZIP12 and related molecules was detected in the lung tissues and cells. A ZIP12 knockdown lentivirus and an overexpressing lentivirus were constructed and transfected into PASMCs derived from PAH and control rats, respectively. EdU assays, wound healing assays and Western blotting were carried out to explore the function of ZIP12 in PASMCs.

Results

Increased ZIP12 expression was observed in PASMCs derived from MCT-induced PAH rats. The proliferation and migration of PASMCs from PAH rats were significantly increased compared with those from control rats. These results were corroborated by Western blot analysis of PCNA and cyclin D1. All these effects were significantly reversed by silencing ZIP12. Comparatively, ZIP12 overexpression resulted in the opposite effects as shown in PASMCs from control rats. Furthermore, selective inhibition of AKT phosphorylation by LY294002 abolished the effect of ZIP12 overexpression on enhancing cell proliferation and migration and partially suppressed the increase in ERK1/2 phosphorylation induced by ZIP12 overexpression. However, inhibition of ERK activity by U0126 resulted in partial reversal of this effect and did not influence an increase in AKT phosphorylation induced by ZIP12 overexpression.

Conclusions

ZIP12 is involved in MCT-induced pulmonary vascular remodeling and enhances the proliferation and migration of PASMCs. The mechanism of these effects was partially mediated by enhancing the AKT/ERK signaling pathways.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-022-01905-3.

Potential Protective Role of TRPM7 and Involvement of PKC/ERK Pathway in Blue Light-Induced Apoptosis in Retinal Pigment Epithelium Cells in Vitro

PURPOSE

Blue light triggers apoptosis of retinal pigment epithelium (RPE) cells and causes retinal damage. The aim of this study was to elucidate the protective role of transient receptor potential melastatin 7 (TRPM7) in photodamaged RPE cells.

METHODS

RPE cells were isolated from Sprague-Dawley (SD) rats and exposed to varying intensities of blue light (500-5000 lux) in vitro. Cell proliferation and metabolic activity were respectively assessed by bromodeoxyuridine (BrdU) incorporation and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assays. Real-time polymerase chain reaction (RT-PCR) and western blotting were used to analyze the TRPM7, protein kinase C (PKC), extracellular signal-regulated kinase (ERK) and Bcl2-associated x/B-cell lymphoma 2 (Bax/Bcl-2) messenger RNA (mRNA) and protein expression levels. The cells were transfected with TRPM7 small interfering RNA (siRNA) or transduced with TRPM7-overexpressing lentiviruses and cultured with or without the pigment epithelium-derived factor (PEDF).

RESULTS

Blue light inhibited the proliferation and metabolic activity of RPE cells in an intensity-dependent manner when compared to nonirradiated controls (P < 0.05). Compared to the control, photodamaged RPE cells showed decreased levels of TRPM7, PKC, ERK, and Bax, and an increase in Bcl-2 levels (P < 0.01). Forced expression of TRPM7 partially rescued the proliferative capacity of RPE cells (P < 0.01) and restored the levels of TRPM7, PKC, ERK, and Bax (P < 0.01), whereas TRPM7 knockdown had the opposite effects (P < 0.01). TRPM7 and PEDF synergistically alleviated the damaging effects of blue light.

CONCLUSIONS

Blue light triggers apoptosis of RPE cells, and its deleterious effects can be partially attenuated by the synergistic action of TRPM7 and PEDF via the PKC/ERK signaling pathway.

Inherited and Acquired Rhythm Disturbances in Sick Sinus Syndrome, Brugada Syndrome, and Atrial Fibrillation: Lessons from Preclinical Modeling

Rhythm disturbances are life-threatening cardiovascular diseases, accounting for many deaths annually worldwide. Abnormal electrical activity might arise in a structurally normal heart in response to specific triggers or as a consequence of cardiac tissue alterations, in both cases with catastrophic consequences on heart global functioning. Preclinical modeling by recapitulating human pathophysiology of rhythm disturbances is fundamental to increase the comprehension of these diseases and propose effective strategies for their prevention, diagnosis, and clinical management. In silico, in vivo, and in vitro models found variable application to dissect many congenital and acquired rhythm disturbances. In the copious list of rhythm disturbances, diseases of the conduction system, as sick sinus syndrome, Brugada syndrome, and atrial fibrillation, have found extensive preclinical modeling. In addition, the electrical remodeling as a result of other cardiovascular diseases has also been investigated in models of hypertrophic cardiomyopathy, cardiac fibrosis, as well as arrhythmias induced by other non-cardiac pathologies, stress, and drug cardiotoxicity. This review aims to offer a critical overview on the effective ability of in silico bioinformatic tools, in vivo animal studies, in vitro models to provide insights on human heart rhythm pathophysiology in case of sick sinus syndrome, Brugada syndrome, and atrial fibrillation and advance their safe and successful translation into the cardiology arena.

An Insight on Multicentric Signaling of Angiotensin II in Cardiovascular system: A Recent Update

The multifaceted nature of the renin-angiotensin system (RAS) makes it versatile due to its involvement in pathogenesis of the cardiovascular disease. Angiotensin II (Ang II), a multifaceted member of RAS family is known to have various potential effects. The knowledge of this peptide has immensely ameliorated after meticulous research for decades. Several studies have evidenced angiotensin I receptor (AT1 R) to mediate the majority Ang II-regulated functions in the system. Functional crosstalk between AT1 R mediated signal transduction cascades and other signaling pathways has been recognized. The review will provide an up-to-date information and recent discoveries involved in Ang II receptor signal transduction and their functional significance in the cardiovascular system for potential translation in therapeutics. Moreover, the review also focuses on the role of stem cell-based therapies in the cardiovascular system.

Clinical review of sick sinus syndrome and atrial fibrillation

Sick sinus syndrome (SSS) is a set of diseases with abnormal cardiac pacing, which manifests as diverse cardiac arrhythmias, especially bradycardia. The clinical presentation is inconspicuous in the early stage, but with the progression of this disease, patients may present with symptoms and signs of end-organ hypoperfusion. As a common result in the natural history of the disease, SSS coexisting with atrial fibrillation (AF) forms the basis of bradycardia-tachycardia syndrome. Age-related interstitial fibrosis is considered to be the common pathophysiological mechanism between SSS and AF. The combination of these diseases will adversely affect the condition of patients and the efficiency of subsequent treatment. Although the exact mechanism is not clear to date, the extensive structural and electrical remodeling of the atrium are considered to be the important mechanism for the occurrence of AF in patients with SSS. Pacemaker implantation is the first-line treatment for symptomatic patients with SSS and documented bradycardia history. In view of the adverse effects of AF on the treatment of SSS, researchers have focused on evaluating different pacing modes and algorithms to reduce the risk of AF during pacing. Catheter ablation may also be used as an alternative second-line therapy for some patients with SSS and AF.

Role of TRPM7 in cardiac fibrosis: A potential therapeutic target (Review)

Cardiac fibrosis is a hallmark of cardiac remodeling associated with nearly all forms of heart disease. Clinically, no effective therapeutic drugs aim to inhibit cardiac fibrosis, owing to the complex etiological heterogeneity and pathogenesis of this disease. A two-in-one protein structure, a ubiquitous expression profile and unique biophysical characteristics enable the involvement of transient receptor potential melastatin-subfamily member 7 (TRPM7) in the pathogenesis and development of fibrosis-related cardiac diseases, such as heart failure (HF), cardiomyopathies, arrhythmia and hyperaldosteronism. In response to a variety of stimuli, multiple bioactive molecules can activate TRPM7 and related signaling pathways, leading to fibroblast proliferation, differentiation and extracellular matrix production in cardiac fibroblasts. TRPM7-mediated Ca²⁺ signaling and TGF-β1 signaling pathways are critical for the formation of fibrosis. Accumulating evidence has demonstrated that TRPM7 is a potential pharmacological target for halting the development of fibrotic cardiac diseases. Reliable drug-like molecules for further development of high-affinity in vivo drugs targeting TRPM7 are urgently needed. The present review discusses the widespread and significant role of TRPM7 in cardiac fibrosis and focuses on its potential as a therapeutic target for alleviating heart fibrogenesis.

Epidermal growth factor signaling through transient receptor potential melastatin 7 cation channel regulates vascular smooth muscle cell function

OBJECTIVE

Transient receptor potential (TRP) melastatin 7 (TRPM7) cation channel, a dual-function ion channel/protein kinase, regulates vascular smooth muscle cell (VSMC) Mg2+ homeostasis and mitogenic signaling. Mechanisms regulating vascular growth effects of TRPM7 are unclear, but epidermal growth factor (EGF) may be important because it is a magnesiotropic hormone involved in cellular Mg2+ regulation and VSMC proliferation. Here we sought to determine whether TRPM7 is a downstream target of EGF in VSMCs and if EGF receptor (EGFR) through TRPM7 influences VSMC function. Approach and results: Studies were performed in primary culture VSMCs from rats and humans and vascular tissue from mice deficient in TRPM7 (TRPM7+/Δkinase and TRPM7R/R). EGF increased expression and phosphorylation of TRPM7 and stimulated Mg2+ influx in VSMCs, responses that were attenuated by gefitinib (EGFR inhibitor) and NS8593 (TRPM7 inhibitor). Co-immunoprecipitation (IP) studies, proximity ligation assay (PLA) and live-cell imaging demonstrated interaction of EGFR and TRPM7, which was enhanced by EGF. PP2 (c-Src inhibitor) decreased EGF-induced TRPM7 activation and prevented EGFR-TRPM7 association. EGF-stimulated migration and proliferation of VSMCs were inhibited by gefitinib, PP2, NS8593 and PD98059 (ERK1/2 inhibitor). Phosphorylation of EGFR and ERK1/2 was reduced in VSMCs from TRPM7+/Δkinase mice, which exhibited reduced aortic wall thickness and decreased expression of PCNA and Notch 3, findings recapitulated in TRPM7R/R mice.

CONCLUSIONS

We show that EGFR directly interacts with TRPM7 through c-Src-dependent processes. Functionally these phenomena regulate [Mg2+]i homeostasis, ERK1/2 signaling and VSMC function. Our findings define a novel signaling cascade linking EGF/EGFR and TRPM7, important in vascular homeostasis.

TRPM7 Upregulate the Activity of SMAD1 through PLC Signaling Way to Promote Osteogenesis of hBMSCs

TRPM7 is a member of the transient receptor potential cation channel (TRP channel) subfamily M and possesses both an ion channel domain and a functional serine/threonine α-kinase domain. It has been proven to play an essential role in the osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs). However, the signaling pathway and molecular mechanism for TRPM7 in regulating osteogenic differentiation remain largely unknown. In this study, the potential role and mechanism of TRPM7 in the osteogenic differentiation of hBMSCs were investigated. The results showed that the expression of TRPM7 mRNA and protein increased, as did the osteogenic induction time. Upregulation or inhibition of TRPM7 could promote or inhibit the osteogenic differentiation of hBMSCs for 14 days. It was also found that the upregulation or inhibition of TRPM7 promoted or inhibited the activity of PLC and SMAD1, respectively, during osteogenic differentiation. PLC could promote osteogenic differentiation by upregulating the activity of SMAD1. However, inhibition of PLC alone could reduce the activity of SMAD1 but not inhibit completely the activation of SMAD1. Therefore, we inferred that it is an important signaling pathway for TRPM7 to upregulate the activity of SMAD1 through PLC and thereby promote the osteogenic differentiation of hBMSCs, but it is not a singular pathway. TRPM7 may also regulate the activation of SMAD1 through other ways, except for PLC, during osteogenic differentiation of hBMSCs.

Molecular Signatures of Sinus Node Dysfunction Induce Structural Remodeling in the Right Atrial Tissue

The sinus node (SN) is located at the apex of the cardiac conduction system, and SN dysfunction (SND)-characterized by electrical remodeling-is generally attributed to idiopathic fibrosis or ischemic injuries in the SN. SND is associated with increased risk of cardiovascular disorders, including syncope, heart failure, and atrial arrhythmias, particularly atrial fibrillation. One of the histological SND hallmarks is degenerative atrial remodeling that is associated with conduction abnormalities and increased right atrial refractoriness. Although SND is frequently accompanied by increased fibrosis in the right atrium (RA), its molecular basis still remains elusive. Therefore, we investigated whether SND can induce significant molecular changes that account for the structural remodeling of RA. Towards this, we employed a rabbit model of experimental SND, and then compared the genome-wide RNA expression profiles in RA between SND-induced rabbits and sham-operated controls to identify the differentially expressed transcripts. The accompanying gene enrichment analysis revealed extensive pro-fibrotic changes within 7 days after the SN ablation, including activation of transforming growth factor-β (TGF-β) signaling and alterations in the levels of extracellular matrix components and their regulators. Importantly, our findings suggest that periostin, a matricellular factor that regulates the development of cardiac tissue, might play a key role in mediating TGF-β-signaling-induced aberrant atrial remodeling. In conclusion, the present study provides valuable information regarding the molecular signatures underlying SND-induced atrial remodeling, and indicates that periostin can be potentially used in the diagnosis of fibroproliferative cardiac dysfunctions.

RNA sequencing analysis of monocrotaline-induced PAH reveals dysregulated chemokine and neuroactive ligand receptor pathways

Pulmonary arterial hypertension (PAH) is a serious disease characterized by elevated pulmonary artery pressure, inflammatory cell infiltration and pulmonary vascular remodeling. However, little is known about the pathogenic mechanisms underlying the disease onset and progression. RNA sequencing (RNA-seq) was used to identify the transcriptional profiling in control and rats injected with monocrotaline (MCT) for 1, 2, 3 and 4 weeks. A total of 23200 transcripts and 280, 1342, 908 and 3155 differentially expressed genes (DEGs) were identified at the end of week 1, 2, 3 and 4, of which Svop was the common top 10 DEGs over the course of PAH progression. Functional enrichment analysis of DEGs showed inflammatory/immune response occurred in the early stage of PAH development. KEGG pathway enrichment analysis of DEGs showed that cytokine-cytokine receptor interaction and neuroactive ligand-receptor interaction were in the initiation and progression of PAH. Further analysis revealed impaired expression of cholinergic receptors, adrenergic receptors including alpha1, beta1 and beta2 receptor, and dysregulated expression of γ-aminobutyric acid receptors. In summary, the dysregulated inflammation/immunity and neuroactive ligand receptor signaling pathways may be involved in the onset and progression of PAH.

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.

Quantitative proteomics and single-nucleus transcriptomics of the sinus node elucidates the foundation of cardiac pacemaking

The sinus node is a collection of highly specialised cells constituting the heart’s pacemaker. The molecular underpinnings of its pacemaking abilities are debated. Using high-resolution mass spectrometry, we here quantify >7,000 proteins from sinus node and neighbouring atrial muscle. Abundances of 575 proteins differ between the two tissues. By performing single-nucleus RNA sequencing of sinus node biopsies, we attribute measured protein abundances to specific cell types. The data reveal significant differences in ion channels responsible for the membrane clock, but not in Ca²⁺ clock proteins, suggesting that the membrane clock underpins pacemaking. Consistently, incorporation of ion channel expression differences into a biophysically-detailed atrial action potential model result in pacemaking and a sinus node-like action potential. Combining our quantitative proteomics data with computational modeling, we estimate ion channel copy numbers for sinus node myocytes. Our findings provide detailed insights into the unique molecular make-up of the cardiac pacemaker.

The sinus node generates rhythmic heartbeat but the molecular basis of pacemaking is still under debate. Here, the authors combine quantitative proteomics and single-nucleus transcriptomics to characterize the molecular composition of the sinus node and provide insights into the underpinnings of pacemaking.

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.

Sinoatrial node remodels in chronic sleep-restricted rats

Chronic Sleep Restriction (CSR) is known as a risk factor for cardiovascular diseases. However, the structural changes of Sinoatrial (SA) node cells have received less attention. This study aimed to evaluate the effects of CSR on SA node in an animal model using stereological methods. Adult male Sprague-Dawley rats were randomly divided into CSR, grid-floor, and control groups. The CSR procedure was designed such a way that the animals had a full cycle of sleep (6 hours) per day, while they were unable to have a Rapid Eye Movement (REM) sleep during the remaining 18 hours. This was induced by a multiplatform box containing water. The grid-floor animals were placed in the same multiplatform box with a grid-floor covering to prevent falling in water. After 21 days, the right atria were dissected out. Then, the location of the SA node was determined and evaluated by stereological techniques. The total volume of the SA node, the total volume of the main node cells, the volume of the connective tissue, and mean volume of the node cells were respectively enlarged by 60%, 47%, 68%, and 51% in the CSR animals compared to the grid-floor rats (p < 0.05). However, no significant changes were detected in these parameters in the control and grid-floor animals. The population of the main node cells remained constant in all animal groups. In addition, the three-dimensional reconstruction of the SA node in the CSR group showed a hypertrophied appearance. In conclusion, CSR induced hypertrophic changes in the rats' SA node structures without alteration in the number of main node cells.

Development of a Rat Model of Sick Sinus Syndrome Using Pinpoint Press Permeation

Objective

Sick sinus syndrome (SSS) is one of the most common causes of cardiac impairment necessitating pacemaker implantation. However, studies of SSS pathogenesis are neither comprehensive nor conclusive due to limited success in achieving a stable rat SSS model. Here, we modified pinpoint press permeation to establish a stable rat SSS model.

Methods

We randomly assigned 138 male Sprague-Dawley rats into three groups: normal control (n = 8), sham (n = 10), and SSS (n = 120). Postoperatively, the SSS group was further divided into SSSA (n = 40), SSSB (n = 40), and SSSC (n = 40), based on reduction in heart rates by 20–30%, 31–40%, and 41–50%, respectively. We also assessed histomorphological characteristics and hyperpolarization-activated cyclic nucleotide-gated cation channel 4 (HCN4) expression in the sinoatrial node (SAN) at 1, 2, 3, and 4 weeks after surgery.

Results

Mortality was statistically higher in SSSC compared to SSSA and SSSB (7.5% versus 90.0% and 87.5%; P < 0.05). Heart rate in SSSA was gradually restored to preoperative levels by week 4 after surgery. In contrast, heart rate in SSSB was stable at 2–3 weeks after surgery. However, we observed that the tissues and cells in SAN were severely injured and also found a time-dependent increase in collagen content and atrium myocardium in SSSB. HCN4 expression was significantly reduced at all 4 time points in SSSB, with statistically significant differences among the groups (P < 0.01).

Conclusion

We successfully developed a rat SSS model that was sustainable for up to 4 weeks.

TRP channels in cardiac and intestinal fibrosis

It is now widely accepted that advanced fibrosis underlies many chronic inflammatory disorders and is the main cause of morbidity and mortality of the modern world. The pathogenic mechanism of advanced fibrosis involves diverse and intricate interplays between numerous extracellular and intracellular signaling molecules, among which the non-trivial roles of a stress-responsive Ca²⁺/Na⁺-permeable cation channel superfamily, the transient receptor potential (TRP) protein, are receiving growing attention. Available evidence suggests that several TRP channels such as TRPC3, TRPC6, TRPV1, TRPV3, TRPV4, TRPA1, TRPM6 and TRPM7 may play central roles in the progression and/or prevention of fibroproliferative disorders in vital visceral organs such as lung, heart, liver, kidney, and bowel as well as brain, blood vessels and skin, and may contribute to both acute and chronic inflammatory processes involved therein. This short paper overviews the current knowledge accumulated in this rapidly growing field, with particular focus on cardiac and intestinal fibrosis, which are tightly associated with the pathogenesis of atrial fibrillation and inflammatory bowel diseases such as Crohn's disease.

Pulmonary arterial hypertension induced by a novel method: Twice-intraperitoneal injection of monocrotaline

Pulmonary arterial hypertension (PAH) in humans manifests as a chronic process. However, PAH induced by high-dose monocrotaline (MCT) in animals occurs as a subacute process. To establish a chronic PAH model, rats were randomly divided into three groups, control (ctrl), single injection (SI), and twice injection (TI) groups. Rats in the SI group received a single intraperitoneal injection of 40 mg/kg MCT on day 0. Rats in the TI group received twice injections of 20 mg/kg MCT on days 0 and 7. Survival percentage, characteristic changes of pulmonary arterial variables, and right ventricular features were evaluated. Thirty-five days after the first MCT injection, survival percentage in TI group was higher than that in the SI group. The mean pulmonary arterial pressure (mPAP), right ventricular hypertrophy index (RVHI), pulmonary vascular remodeling, serum tumor necrosis factor α (TNFα), and interleukin-6 (IL-6) were higher either in SI or in TI 28 and 35 days after the first MCT injection. The rats in the SI and TI groups exhibited higher right ventricle end diastolic diameter (RVEDD) and lower adjusted pulmonary artery acceleration time (PAAT/HR), tricuspid annular plane systolic excursion (TAPSE), cardiac output (CO) and right ventricle fractional shortening (RVFS) when compared with controls. However, mPAP, RVHI, TAPSE, PAAT/HR, CO, TNFα, and IL-6 were lower and RVEDD were higher in the TI group than in the SI group. Pulmonary macrophage infiltration and right ventricle (RV) fibrosis were lower in TI than SI groups. The cardiomyocyte cross-sectional area and the beta myosin heavy chain (MYH7) mRNA level of RV were lower in TI than SI, whereas alpha myosin heavy chain (MYH6) was increased. These results show that two intraperitoneal injections of 20 mg/kg MCT with seven days interval could induce a model similar to chronic PAH with increased survival percentage in rats. Impact statement We demonstrated previously that a single intraperitoneal injection of 40 mg/kg MCT produced a subacute, not chronic, PAH model in rats, and the short survival periods of these rats did not represent adequately the chronic PAH seen in humans. To overcome this limitation, in this study, the single dose of 40 mg/kg MCT was divided into twice injections of 20 mg/kg with an interval of seven days. This modified administration of MCT produced an animal model much more similar to chronic PAH with prolonged survival and characteristic changes of structures and function in pulmonary arteries and right ventricles.