Regulation Of Cardiac Function Research Articles

Association of attenuated leptin signaling pathways with impaired cardiac function under prolonged high-altitude hypoxia

Cardiovascular function and adipose metabolism were markedly influenced under high altitudes. However, the interplay between adipokines and heart under hypoxia remains to be elucidated. We aim to explore alterations of adipokines and underlying mechanisms in regulating cardiac function under high altitudes. We investigated the cardiopulmonary function and five adipokines in Antarctic expeditioners at Kunlun Station (4,087 m) for 20 days and established rats exposed to hypobaric hypoxia (5,000 m), simulating Kunlun Station. Antarctic expeditioners exhibited elevated heart rate, blood pressure, systemic vascular resistance, and decreased cardiac pumping function. Plasma creatine phosphokinase-MB (CK-MB) and platelet-endothelial cell adhesion molecule-1 (sPecam-1) increased, and leptin, resistin, and lipocalin-2 decreased. Plasma leptin significantly correlated with altered cardiac function indicators. Additionally, hypoxic rats manifested impaired left ventricular systolic and diastolic function, elevated plasma CK-MB and sPecam-1, and decreased plasma leptin. Chronic hypoxia for 14 days led to increased myocyte hypertrophy, fibrosis, apoptosis, and mitochondrial dysfunction, coupled with reduced protein levels of leptin signaling pathways in myocardial tissues. Cardiac transcriptome analysis revealed leptin was associated with downregulated genes involved in rhythm, Na+/K+ transport, and cell skeleton. In conclusion, chronic hypoxia significantly reduced leptin signaling pathways in cardiac tissues along with significant pathological changes, thus highlighting the pivotal role of leptin in regulation of cardiac function under high altitudes.

Intrinsic cardiac neurons as the consulate general of the brain in the heart: A review

Contrary to the prevailing understanding about one-way communication from brain to heart, recent research has unveiled a two-way communication pathway between these two organs, featuring the delivery of signals from the cardiac afferents to the brain. While the medulla oblongata is known to send autonomic signals for cardiac function regulation, 80% of the vagal afferents send signals to the brain for cardiac regulation. The vagus nerve receives these signals from the intrinsic cardiac neurons, often referred to as “the little brain of the heart.” Intrinsic cardiac neurons are neuronal structures with the same biochemical profile as neurons, communicating with the vagus nerve through acetylcholine and expresses markers of neuronal function such as tyrosine hydroxylase and others. Intrinsic cardiac neurons also influence the autonomic system, which can be studied through heart-rate variability measures. Heart rate variability (HRV) is altered in many types of cardiac disorders and is a well-known measure for studying short- and long-term disease-related variations in cardiac function. Some psychiatric disorders such as post-traumatic stress disorder, schizophrenia, and major depression also exhibited alterations in HRV. HRV is related to heartbeat-evoked potentials (HEPs) and electrical potentials in the brain that are influenced by the heart. HEPs are altered in disease states and can be impacted by environmental factors. This paper reviews the existing literature concerning intrinsic cardiac neurons and their possible role in heart-brain communication.

Impact on the Transcriptome of Proton Beam Irradiation Targeted at Healthy Cardiac Tissue of Mice.

Proton beam therapy is considered a step forward with respect to electromagnetic radiation, thanks to the reduction in the dose delivered. Among unwanted effects to healthy tissue, cardiovascular complications are a known long-term radiotherapy complication. The transcriptional response of cardiac tissue from xenografted BALB/c nude mice obtained at 3 and 10 days after proton irradiation covering both the tumor region and the underlying healthy tissue was analyzed as a function of dose and time. Three doses were used: 2 Gy, 6 Gy, and 9 Gy. The intermediate dose had caused the greatest impact at 3 days after irradiation: at 2 Gy, 219 genes were differently expressed, many of them represented by zinc finger proteins; at 6 Gy, there were 1109, with a predominance of genes involved in energy metabolism and responses to stimuli; and at 9 Gy, there were 105, mainly represented by zinc finger proteins and molecules involved in the regulation of cardiac function. After 10 days, no significant effects were detected, suggesting that cellular repair mechanisms had defused the potential alterations in gene expression. The nonlinear dose-response curve indicates a need to update the models built on photons to improve accuracy in health risk prediction. Our data also suggest a possible role for zinc finger protein genes as markers of proton therapy efficacy.

Manipulation of Glutamatergic Neuronal Activity in the Primary Motor Cortex Regulates Cardiac Function in Normal and Myocardial Infarction Mice.

Cardiac function is under neural regulation; however, brain regions in the cerebral cortex responsible for regulating cardiac function remain elusive. In this study, retrograde trans-synaptic viral tracing is used from the heart to identify a specific population of the excitatory neurons in the primary motor cortex (M1) that influences cardiac function in mice. Optogenetic activation of M1 glutamatergic neurons increases heart rate, ejection fraction, and blood pressure. By contrast, inhibition of M1 glutamatergic neurons decreased cardiac function and blood pressure as well as tyrosine hydroxylase (TH) expression in the heart. Using viral tracing and optogenetics, the median raphe nucleus (MnR) is identified as one of the key relay brain regions in the circuit from M1 that affect cardiac function. Then, a mouse model of cardiac injury is established caused by myocardial infarction (MI), in which optogenetic activation of M1 glutamatergic neurons impaired cardiac function in MI mice. Moreover, ablation of M1 neurons decreased the levels of norepinephrine and cardiac TH expression, and enhanced cardiac function in MI mice. These findings establish that the M1 neurons involved in the regulation of cardiac function and blood pressure. They also help the understanding of the neural mechanisms underlying cardiovascular regulation.

Effects of gas signaling molecule SO2 in cardiac functions of hyperthyroid rats.

Sulfur dioxide (SO2), a novel endogenous gas signaling molecule, is involved in the regulation of cardiac function. Exerting a key role in progression of hyperthyroidism-induced cardiomyopathy (HTC), myocardial fibrosis is mainly caused by myocardial apoptosis, leading to poor treatment outcomes and prognoses. This study aimed to investigate the effect of SO2 on the hyperthyroidism-induced myocardial fibrosis and the underlying regulatory mechanisms. Elisa, Masson staining, Western-Blot, transmission electron microscope, and immunofluorescence were employed to evaluate the myocardial interstitial collagen deposition, endoplasmic reticulum stress (ERS), apoptosis, changes in endogenous SO2, and Hippo pathways from in vitro and in vivo experiments. The study results indicated that the hyperthyroidism-induced myocardial fibrosis was accompanied by decreased cardiac function, and down-regulated ERS, apoptosis, and endogenous SO2-producing enzyme aspartate aminotransferase (AAT)1/2 in cardiac myocytes. In contrast, exogenous SO2 donors improved cardiac function, reduced myocardial interstitial collagen deposition, up-regulated AAT1/2, antagonized ERS and apoptosis, and inhibited excessive activation of Hippo pathway in hyperthyroid rats. In conclusion, the results herein suggested that SO2 inhibited the overactivation of the Hippo pathway, antagonized ERS and apoptosis, and alleviated myocardial fibrosis in hyperthyroid rats. Therefore, this study was expected to identify intervention targets and new strategies for prevention and treatment of HTC.

Role of the Mast Cell–Neuron Tandem in Cardiac Function Regulation in Cardiovascular Pathologies

Role of the Mast Cell–Neuron Tandem in Cardiac Function Regulation in Cardiovascular Pathologies

Downregulation of the CD151 protects the cardiac function by the crosstalk between the endothelial cells and cardiomyocytes via exosomes.

Heart failure (HF) is the last stage in the progression of various cardiovascular diseases. Although it is documented that CD151 contributes to regulate the myocardial infarction, the function of CD151 on HF and involved mechanisms are still unclear. In the present study, we found that the recombinant adeno-associated virus (rAAV)-mediated endothelial cell-specific knockdown of CD151-transfected mice improved transverse aortic constriction (TAC)-induced cardiac function, attenuated myocardial hypertrophy and fibrosis, and increased coronary perfusion, whereas overexpression of the CD151 protein aggravated cardiac dysfunction and showed the opposite effects. In vitro, the cardiomyocytes hypertrophy induced by PE were significantly improved, while the proliferation and migration of cardiac fibroblasts (CFs) were significantly reduced, when co-cultured with the CD151-silenced endothelial cells (ECs). To further explore the mechanisms, the exosomes from the CD151-silenced ECs were taken by cardiomyocyte (CMs) and CFs, verified the intercellular communication. And the protective effects of CD151-silenced ECs were inhibited when exosome inhibitor (GW4869) was added. Additionally, a quantitative proteomics method was used to identify potential proteins in CD151-silenced EC exosomes. We found that the suppression of CD151 could regulate the PPAR signaling pathway via exosomes. Our observations suggest that the downregulation of CD151 is an important positive regulator of cardiac function of heart failure, which can regulate exosome-stored proteins to play a role in the cellular interaction on the CMs and CFs. Modulating the exosome levels of ECs by reducing CD151 expression may offer novel therapeutic strategies and targets for HF treatment.

Further investigations on the influence of protein phosphatases on the signaling of muscarinic receptors in the atria of mouse hearts.

The vagal regulation of cardiac function involves acetylcholine (ACh) receptor activation followed by negative chronotropic and negative as well as positive inotropic effects. The resulting signaling pathways may include Gi/o protein-coupled reduction in adenylyl cyclase (AC) activity, direct Gi/o protein-coupled activation of ACh-activated potassium current (IKACh), inhibition of L-type calcium ion channels, and/or the activation of protein phosphatases. Here, we studied the role of the protein phosphatases 1 (PP1) and 2A (PP2A) for muscarinic receptor signaling in isolated atrial preparations of transgenic mice with cardiomyocyte-specific overexpression of either the catalytic subunit of PP2A (PP2A-TG) or the inhibitor-2 (I2) of PP1 (I2-TG) or in double transgenic mice overexpressing both PP2A and I2 (DT). In mouse left atrial preparations, carbachol (CCh), cumulatively applied (1nM-10µM), exerted at low concentrations a negative inotropic effect followed by a positive inotropic effect at higher concentrations. This biphasic effect was noted with CCh alone as well as when CCh was added after β-adrenergic pre-stimulation with isoprenaline (1µM). Whereas the response to stimulation of β-adrenoceptors or adenosine receptors (used as controls) was changed in PP2A-TG, the response to CCh was unaffected in atrial preparations from all transgenic models studied here. Therefore, the present data tentatively indicate that neither PP2A nor PP1, but possibly other protein phosphatases, is involved in the muscarinic receptor-induced inotropic and chronotropic effects in the mouse heart.

Cardioprotective O-GlcNAc signaling is elevated in murine female hearts via enhanced O-GlcNAc transferase activity

The post-translational modification of intracellular proteins by O-linked β-N-acetylglucosamine (O-GlcNAc) has emerged as a critical regulator of cardiac function. Enhanced O-GlcNAcylation activates cytoprotective pathways in cardiac models of ischemia reperfusion (I/R) injury; however, the mechanisms underpinning O-GlcNAc-cycling in response to I/R injury have not been comprehensively assessed. The cycling of O-GlcNAc is regulated by the collective efforts of two enzymes: O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), which catalyze the addition and hydrolysis of O-GlcNAc respectively. It has previously been shown that baseline heart physiology and pathophysiology are impacted by sex. Here, we hypothesized that sex differences in molecular signaling may target protein O-GlcNAcylation both basally and in ischemic hearts. To address this question, we subjected male and female wild type murine hearts to ex vivo ischemia or ischemia-reperfusion injury. We assessed hearts for protein O-GlcNAcylation, abundance of OGT, OGA, and glutamine:fructose-6-phosphate aminotransferase (GFAT2), activity of OGT and OGA, and UDP-GlcNAc levels. Our data demonstrate elevated O-GlcNAcylation in female hearts both basally and during ischemia. We show OGT activity was enhanced in female hearts in all treatments, suggesting a mechanism for these observations. Furthermore, we found ischemia led to reduced O-GlcNAcylation and OGT specific activity. Our findings provide a foundation for understanding molecular mechanisms that regulate O-GlcNAcylation in the heart and highlight the importance of sex as a significant factor when assessing key regulatory events that control O-GlcNAc-cycling. These data suggest the intriguing possibility that elevated O-GlcNAcylation in females contributes to reduced ischemic susceptibility.

Abstract 17081: Targeted Proteomics Identifies Circulating Biomarkers Associated With Biological Sex in Dilated Cardiomyopathy

Background: The pathophysiology underlying sex specific differences in dilated cardiomyopathy (DCM) is incompletely understood. Targeted proteomic discovery enables quantification of low abundance circulating proteins to elucidate mechanisms of disease. Hypothesis: Female sex is associated with a distinct biomarker profile that confers insights into DCM pathogenesis. Aim: Evaluate the biomarker profile associated with biological sex in dilated cardiomyopathy. Methods: Cross sectional analysis of 490 patients with dilated cardiomyopathy confirmed by cardiovascular magnetic resonance imaging. Targeted proteomic analysis was performed with proximity extension assays to determine sex differential expression of 276 proteins associated with inflammation or cardiovascular disease. Expression was compared between males and females. Results: A third of patients were female (n=160, 33%). After adjusting for false discovery, 10 proteins were significantly upregulated and 8 were significantly downregulated in female compared to male patients (A Inflammatory panel, B Cardiovascular panel). These were grouped into 3 clusters (C), enriched for cytokine pathways (red), regulators of cardiac function (green), and markers of fat metabolism (blue). Of the sex differentially expressed proteins, GDF2 (regulates angiogenesis), protein BOC (augments cardiac tissue repair) and CD5 (linked to inflammation) were top determinants of biological sex after adjusting for age, renal function, body mass, and cardiac function (D). Conclusion: Sex specific proteomic signatures provide new insights into the pathophysiology underlying sex differences in DCM. Figure: Volcano plots showing log2 fold change in protein expression in inflammatory (A) and cardiovascular (B) proteins. Blue = lower and red = higher levels in females. Protein interactions shown in C. Top predictive feature of sex is body surface area, followed by biomarkers GDF2 and Protein BOC, shown in D.

RBPMS regulates cardiomyocyte contraction and cardiac function through RNA alternative splicing.

RNA binding proteins play essential roles in mediating RNA splicing and are key post-transcriptional regulators in the heart. Our recent study demonstrated that RBPMS (RNA binding protein with multiple splicing) is crucial for cardiac development through modulating mRNA splicing, but little is known about its functions in the adult heart. In this study, we aim to characterize the post-natal cardiac function of Rbpms and its mechanism of action. We generated a cardiac-specific knockout mouse line and found that cardiac-specific loss of Rbpms caused severe cardiomyocyte contractile defects, leading to dilated cardiomyopathy and early lethality in adult mice. We showed by proximity-dependent biotin identification assay and mass spectrometry that RBPMS associates with spliceosome factors and other RNA binding proteins, such as RBM20, that are important in cardiac function. We performed paired-end RNA sequencing and RT-PCR and found that RBPMS regulates mRNA alternative splicing of genes associated with sarcomere structure and function, such as Ttn, Pdlim5, and Nexn, generating new protein isoforms. Using a minigene splicing reporter assay, we determined that RBPMS regulates target gene splicing through recognizing tandem intronic CAC motifs. We also showed that RBPMS knockdown in human induced pluripotent stem cell-derived cardiomyocytes impaired cardiomyocyte contraction. This study identifies RBPMS as an important regulator of cardiomyocyte contraction and cardiac function by modulating sarcomeric gene alternative splicing.

Brain Regulation of Cardiac Function during Hypoglycemia.

Hypoglycemia occurs frequently in people with type 1 and type 2 diabetes. Hypoglycemia activates the counter-regulatory response. Besides peripheral glucose sensors located in the pancreas, mouth, gastrointestinal tract, portal vein, and carotid body, many brain regions also contain glucose-sensing neurons that detect this fall in glucose. The autonomic nervous system innervates the heart, and during hypoglycemia, can cause many changes. Clinical and animal studies have revealed changes in electrocardiograms during hypoglycemia. Cardiac repolarization defects (QTc prolongation) occur during moderate levels of hypoglycemia. When hypoglycemia is severe, it can be fatal. Cardiac arrhythmias are thought to be the major mediator of sudden death due to severe hypoglycemia. Both the sympathetic and parasympathetic nervous systems of the brain have been implicated in regulating these arrhythmias. Besides cardiac arrhythmias, hypoglycemia can have profound changes in the heart and most of these changes are exacerbated in the setting of diabetes. A better understanding of how the brain regulates cardiac changes during hypoglycemia will allow for better therapeutic intervention to prevent cardiovascular death associated with hypoglycemia in people with diabetes. The aim of this paper is to provide a narrative review of what is known in the field regarding how the brain regulates the heart during hypoglycemia.

Myeloid cell-specific deletion of epidermal growth factor receptor aggravates acute cardiac injury.

Myeloid cells, including macrophages, play important roles as first responders to cardiac injury and stress. Epidermal growth factor receptor (EGFR) has been identified as a mediator of macrophage responsiveness to select diseases, though its impact on cardiac function or remodeling following acute ischemic injury is unknown. We aimed to define the role of myeloid cell-specific EGFR in the regulation of cardiac function and remodeling following acute myocardial infarction (MI)-induced injury. Floxed EGFR mice were bred with homozygous LysM-Cre (LMC) transgenic mice to yield myeloid-specific EGFR knockout (mKO) mice. Via echocardiography, immunohistochemistry, RNA sequencing and flow cytometry, the impact of myeloid cell-specific EGFR deletion on cardiac structure and function was assessed at baseline and following injury. Compared with LMC controls, myeloid cell-specific EGFR deletion led to an increase in cardiomyocyte hypertrophy at baseline. Bulk RNASeq analysis of isolated cardiac Cd11b+ myeloid cells revealed substantial changes in mKO cell transcripts at baseline, particularly in relation to predicted decreases in neovascularization. In response to myocardial infarction, mKO mice experienced a hastened decline in cardiac function with isolated cardiac Cd11b+ myeloid cells expressing decreased levels of the pro-reparative mediators Vegfa and Il10, which coincided with enhanced cardiac hypertrophy and decreased capillary density. Overall, loss of EGFR qualitatively alters cardiac resident macrophages that promotes a low level of basal stress and a more rapid decrease in cardiac function along with worsened repair following acute ischemic injury.

Features of Application of the Optimized Physical Rehabilitation Program in Patients with Coronary Heart Disease

Multisymptomatic coronary heart disease (CHD) remains a leading problem in cardiology. A person’s ability to perform physical work determines their quality of life, especially in patients with existing symptoms of damage to the cardiovascular system. The most advanced approach in the physical rehabilitation of patients with CHD is the use of ergometric testing indicators.
 The aim. To study the influence of the developed method of cycling training on the indicators of cardiopulmonary exercise (CPX) in patients with CHD.
 Materials and methods. We examined 65 men with CHD, I-II functional class stable angina pectoris, mean age 44.6 ± 1.39 years (from 32 to 60 years). The diagnosis was made on the basis of clinical findings, electrocardiography and laboratory examination according to the generally accepted criteria of the European Society of Cardiology.
 Results. The treatment results were evaluated two weeks after the completion of the physical rehabilitation program. Qualitative assessment was performed by using the CPX test with the recording of cardiac bioelectric potentials from 12 leads. The criteria for discontinuation of the test were generally accepted provisions based on WHO recommendations.
 While developing a physical rehabilitation program and predicting the timing of a functional recovery, several factors have to be taken into account that significantly affect the patient’s motor activity and determine the pace and outcome of the rehabilitation process as a whole. Long-term, regular physical activity in patients with CHD with limited coronary reserve have an impact on the mechanisms of cardiac function regulation, synchronization and optimization of the activity of the muscular, cardiovascular and respiratory systems. Systematic training sessions reduce the volume of drug therapy and can improve the patients’ quality of life.
 Conclusions. The use of the proposed individualized uniform interval cycling training combined with the intake of citrulline malate leads to a significant improvement in the achieved load capacity, heart rate, duration of work, total volume of completed work, inotropic reserve index, optimization of coronary blood circulation and improvement of bioenergy metabolism in the myocardium.

C-type natriuretic peptide induces inotropic and lusitropic effects in human 3D-engineered cardiac tissue: Implications for the regulation of cardiac function in humans.

The role of C-type natriuretic peptide (CNP) in the regulation of cardiac function in humans remains to be established as previous investigations have been confined to animal model systems. Here, we used well-characterized engineered cardiac tissues (ECTs) generated from human stem cell-derived cardiomyocytes and fibroblasts to study the acute effects of CNP on contractility. Application of CNP elicited a positive inotropic response as evidenced by increases in maximum twitch amplitude, maximum contraction slope and maximum calcium amplitude. This inotropic response was accompanied by a positive lusitropic response as demonstrated by reductions in time from peak contraction to 90% of relaxation and time from peak calcium transient to 90% of decay that paralleled increases in maximum contraction decay slope and maximum calcium decay slope. To establish translatability, CNP-induced changes in contractility were also assessed in rat ex vivo (isolated heart) and in vivo models. Here, the effects on force kinetics observed in ECTs mirrored those observed in both the ex vivo and in vivo model systems, whereas the increase in maximal force generation with CNP application was only detected in ECTs. In conclusion, CNP induces a positive inotropic and lusitropic response in ECTs, thus supporting an important role for CNP in the regulation of human cardiac function. The high degree of translatability between ECTs, ex vivo and in vivo models further supports a regulatory role for CNP and expands the current understanding of the translational value of human ECTs. NEW FINDINGS: What is the central question of this study? What are the acute responses to C-type natriuretic peptide (CNP) in human-engineered cardiac tissues (ECTs) on cardiac function and how well do they translate to matched concentrations in animal ex vivo and in vivo models? What is the main finding and its importance? Acute stimulation of ECTs with CNP induced positive lusitropic and inotropic effects on cardiac contractility, which closely reflected the changes observed in rat ex vivo and in vivo cardiac models. These findings support an important role for CNP in the regulation of human cardiac function and highlight the translational value of ECTs.

Unpacking the multimodal, multi-scale data of the fast and slow lanes of the cardiac vagus through computational modelling.

What is the topic of this review? The vagus nerve is a crucial regulator of cardiovascular homeostasis, and its activity is linked to heart health. Vagal activity originates from two brainstem nuclei: the nucleus ambiguus (fast lane) and the dorsal motor nucleus of the vagus (slow lane), nicknamed for the time scales that they require to transmit signals. What advances does it highlight? Computational models are powerful tools for organizing multi-scale, multimodal data on the fast and slow lanes in a physiologically meaningful way. A strategy is laid out for how these models can guide experiments aimed at harnessing the cardiovascular health benefits of differential activation of the fast and slow lanes. The vagus nerve is a key mediator of brain-heart signaling, and its activity is necessary for cardiovascular health. Vagal outflow stems from the nucleus ambiguus, responsible primarily for fast, beat-to-beat regulation of heart rate and rhythm, and the dorsal motor nucleus of the vagus, responsible primarily for slow regulation of ventricular contractility. Due to the high-dimensional and multimodal nature of the anatomical, molecular and physiological data on neural regulation of cardiac function, data-derived mechanistic insights have proven elusive. Elucidating insights has been complicated further by the broad distribution of the data across heart, brain and peripheral nervous system circuits. Here we lay out an integrative framework based on computational modelling for combining these disparate and multi-scale data on the two vagal control lanes of the cardiovascular system. Newly available molecular-scale data, particularly single-cell transcriptomic analyses, have augmented our understanding of the heterogeneous neuronal states underlying vagally mediated fast and slow regulation of cardiac physiology. Cellular-scale computational models built from these data sets represent building blocks that can be combined using anatomical and neural circuit connectivity, neuronal electrophysiology, and organ/organismal-scale physiology data to create multi-system, multi-scale models that enable in silico exploration of the fast versus slow lane vagal stimulation. The insights from the computational modelling and analyses will guide new experimental questions on the mechanisms regulating the fast and slow lanes of the cardiac vagus toward exploiting targeted vagal neuromodulatory activity to promote cardiovascular health.

Investigation into miRNA profile in patient groups with and without ST elevation

Abstract Objectives Because acute myocardial infarction (AMI) may occur suddenly and cannot be predicted, it is critical to identify early diagnosis markers. In recent years, in addition to the developing diagnostic methods, other markers that may be related to the diagnosis of AMI are miRNA molecules. The specificity of miRNAs involved in the pathogenesis of atherosclerosis and regulation of cardiac functions has been shown. The present study aimed to investigate the changes in miRNA expression levels in MI patients with ST-elevation (STEMI) and without ST elevation (NSTEMI). Methods In this study, 25 patients with STEMI, 25 with NSTEMI, and 20 healthy participants were included. Expression analysis of miRNAs isolated from the plasma of individuals was performed using high-throughput real-time PCR. Results Compared with the control group, miR-221-3p and miR-30d-5p were downregulated, while miR-25-3p, miR-92a-3p, miR-34a-5p and miR-150 upregulated in the patient group with NSTEMI; miR-221-3p, miR-25-3p, miR-30d-5p and miR-92a-3p were downregulated while miR-208a-3p was upregulated in patients with STEMI (p>0.05). Conclusions In conclusion, miRNAs may be an early biomarker for diagnosing AMI; however, further and larger studies are needed.

Cardiac RGS Proteins in Human Heart Failure and Atrial Fibrillation: Focus on RGS4.

The regulator of G protein signaling (RGS) proteins are crucial for the termination of G protein signals elicited by G protein-coupled receptors (GPCRs). This superfamily of cell membrane receptors, by far the largest and most versatile in mammals, including humans, play pivotal roles in the regulation of cardiac function and homeostasis. Perturbations in both the activation and termination of their G protein-mediated signaling underlie numerous heart pathologies, including heart failure (HF) and atrial fibrillation (AFib). Therefore, RGS proteins play important roles in the pathophysiology of these two devasting cardiac diseases, and several of them could be targeted therapeutically. Although close to 40 human RGS proteins have been identified, each RGS protein seems to interact only with a specific set of G protein subunits and GPCR types/subtypes in any given tissue or cell type. Numerous in vitro and in vivo studies in animal models, and also in diseased human heart tissue obtained from transplantations or tissue banks, have provided substantial evidence of the roles various cardiomyocyte RGS proteins play in cardiac normal homeostasis as well as pathophysiology. One RGS protein in particular, RGS4, has been reported in what are now decades-old studies to be selectively upregulated in human HF. It has also been implicated in protection against AFib via knockout mice studies. This review summarizes the current understanding of the functional roles of cardiac RGS proteins and their implications for the treatment of HF and AFib, with a specific focus on RGS4 for the aforementioned reasons but also because it can be targeted successfully with small organic molecule inhibitors.

Acute PKA modulation of the cardiac sodium current is mediated by 14-3-3.

Nav1.5 is an essential component of the cardiac action potential. Dysregulation of Nav1.5 contributes to cardiac arrhythmias and Nav1.5 mutations have been linked to lethal congenital cardiac diseases. However, myriad aspects of Nav1.5 function and regulation, mainly as it relates to associated regulatory proteins, remain to be elucidated. PKA or β-adrenergic stimulation is a regulator of cardiac function, and could modulate Nav1.5 function under both healthy and diseased conditions. 14-3-3 is a Nav1.5 interacting protein. Mass spectrometry studies revealed proximity between Nav1.5 PKA phosphorylation sites and the 14-3-3 binding site. Importantly, the 14-3-3 binding site on Nav1.5 was suggested to be phosphorylated by PKA. This led us to hypothesize that PKA could acutely modulate Nav1.5 through 14-3-3. We studied acute modulation by PKA of Nav1.5 using high-throughput automated patch clamping. Our data showed that acute PKA modifications could significantly change the sodium current. Interestingly, inhibition of 14-3-3 abolished the acute PKA effects. Serine 460 is part of the putative 14-3-3 binding motif and mutating Serine 460 to alanine (S460A) behaves like 14-3-3 inhibition and uncouples sodium currents. We therefore tested the effect of PKA modulation on Nav1.5-S460A and found that similarly to 14-3-3 inhibition, PKA had no effect on Nav1.5-S460A currents. To confirm the specific involvement of S460 and 14-3-3 in PKA modulation of Nav1.5, we mutated other phosphorylation sites found in the DI-DII linker. We found that except for S460A, all the other phospho-inhibiting mutations responded to PKA modulation. Our study demonstrated that PKA or β-adrenergic stimulation can acutely modulate Nav1.5 through protein 14-3-3 and Nav1.5-S460 appears to be central to this modulation. We conclude that 14-3-3 does not only regulate the Nav1.5 function and coupling, but also plays a key role in the PKA modulation.

BIN1 is essential for β-adrenergic regulation of cardiac function.

The number and activity of voltage gated L-type CaV1.2 Ca2+ channels in the sarcolemma of cardiomyocytes tunes the magnitude of Ca2+-induced Ca2+ release and subsequent contraction. Previous studies from our group revealed that β-adrenergic receptor stimulation in mouse ventricular myocytes triggers mobilization of CaV1.2 channels from early and recycling endosomal reservoirs to augment sarcolemmal expression and clustering and enhancing excitation-contraction coupling. In the heart, the membrane curvature-mediating protein bridging integrator 1 (BIN1) mediates t-tubule micro-folding, and targeted delivery of CaV1.2 channels to t-tubules via anchored microtubules. BIN1 deficits are associated with heart failure. In neurons, BIN1 is known to play an essential role in tubulation of endosomes to permit cargo exit and recycling. We used myocytes isolated from cardiac-specific BIN1 knockout mice, to test the hypothesis that expressional deficits in BIN1 impairs isoproterenol-stimulated endosomal recycling of CaV1.2, reducing the ability to respond to acute stress. Super-resolution Airyscan imaging of immunostained ventricular myocytes revealed that CaV1.2 pools on early and recycling endosomes are mobilized to the sarcolemma to bolster channel expression in response to β-adrenergic stimulation with isoproterenol in WT but not BIN1-/- cells. Moreover, single molecule localization microscopy revealed that isoproterenol-stimulated CaV1.2 upregulation and super-clustering at the t-tubule sarcolemma occurs in wild-type myocytes but is reduced in BIN1+/- and absent in BIN1-/- myocytes. To assess the functional implications on β-adrenergic regulation of CaV1.2 and excitation-contraction coupling, we performed voltage-clamp electrophysiological recordings of whole-cell Ca2+ currents and measured Ca2+transients from paced myocytes finding impaired responses to isoproterenol in BIN1 knockout cells versus wild-type controls. Based on these data, we propose that tight regulation of BIN1 expression is required to support β-adrenergic receptor stimulated CaV1.2 channel trafficking and recycling to increase Ca2+ influx and inotropy in times of acute stress.