Signaling Pathway In Myocytes Research Articles

The cardioprotective effects of hydrogen sulfide by targeting endoplasmic reticulum stress and the Nrf2 signaling pathway: A review.

Cardiac diseases are emerging due to lifestyle, urbanization, and the accelerated aging process. Oxidative stress has been associated with cardiac injury progression through interference with antioxidant strategies and endoplasmic reticulum (ER) function. Hydrogen sulfide (H2 S) is generated endogenously from l-cysteine in various tissues including heart tissue. Pharmacological evaluation of H2 S has suggested a potential role for H2 S against diabetic cardiomyopathy, ischemia/reperfusion injury, myocardial infarction, and cardiotoxicity. Nuclear factor E2-related factor 2 (Nrf2) activity is crucial for cell survival in response to oxidative stress. H2 S up-regulates Nrf2 expression and its related signaling pathway in myocytes. H2 S also suppresses the expression and activity of ER stress-related proteins. H2 S has been reported to improve various cardiac conditions through antioxidant and anti-ER stress-related activities.

Use of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes (hiPSC-CMs) to Monitor Compound Effects on Cardiac Myocyte Signaling Pathways.

There is a need to develop mechanism-based assays to better inform risk of cardiotoxicity. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are rapidly gaining acceptance as a biologically relevant in vitro model for use in drug discovery and cardiotoxicity screens. Utilization of hiPSC-CMs for mechanistic investigations would benefit from confirmation of the expression and activity of cellular pathways that are known to regulate cardiac myocyte viability and function. This unit describes an approach to demonstrate the presence and function of signaling pathways in hiPSC-CMs and the effects of treatments on these pathways. We present a workflow that employs protocols to demonstrate protein expression and functional integrity of signaling pathway(s) of interest and to characterize biological consequences of signaling modulation. These protocols utilize a unique combination of structural, functional, and biochemical endpoints to interrogate compound effects on cardiomyocytes.

Caulerpa lentillifera extract ameliorates insulin resistance and regulates glucose metabolism in C57BL/KsJ-db/db mice via PI3K/AKT signaling pathway in myocytes.

BackgroundGlucose homeostasis is distorted by defects of the PI3K/AKT and AMPK pathways in insulin-sensitive tissues, allowing the accumulation of glucose in the blood. The purpose of this study was to assess the effects and mechanisms by which ethanol extract of Caulerpa lentillifera (CLE) regulates glucose metabolism in C57BL/KsJ-db/db (db/db) mice.MethodsMice were administered CLE (250 or 500 mg/kg BW) or rosiglitazone (RSG, 10 mg/kg BW) for 6 weeks. Then, oral glucose tolerance test (OGTT) and intraperitoneal insulin tolerance test (IPITT) were performed, and blood glucose was measured in db/db mice. Levels of insulin and insulin resistance factors in plasma, glycogen content in the liver, and IRS, PI3K, AKT, and GLUT4 expressions in skeletal muscles were measured in db/db mice. Glucose uptake and insulin signaling molecules were measured in L6 myocytes, using fluorometry and Western blotting.ResultsCLE significantly decreased fasting blood glucose, glucose level in OGTT and IPITT, plasma insulin, homeostatic model assessment-insulin resistant (HOMA-IR), TNF-α, IL-6, FFA, TG and TC levels, and hepatic glycogen content in db/db mice. CLE significantly increased the activation of IRS, AKT, PI3K, and GLUT4, which are the key effector molecules of the PI3K/AKT pathway in L6 myocytes and the skeletal muscles of db/db mice. The enhanced glucose uptake by CLE was abolished by treatment with a PI3K inhibitor (LY294002), but not by an AMPK inhibitor (compound C) in L6 myocytes. CLE regulated glucose uptake and homeostasis via the PI3K/AKT pathway in myocytes and db/db mice, respectively.ConclusionOur results suggest that CLE could be a potential candidate for the prevention of diabetes.

Regulation of Nuclear Factor κB (NF-κB) in the Nucleus of Cardiomyocytes by G Protein-coupled Receptor Kinase 5 (GRK5)

G protein-coupled receptor kinase 5 GRK5 plays a key role in regulating cardiac signaling and its expression is increased in heart failure. GRK5 activity in the nucleus of myocytes has been shown to be detrimental in the setting of pressure-overload hypertrophy. The ubiquitous nuclear transcription factor κB (NF-κB) is involved in the regulation of numerous genes in various tissues, and activation of NF-κB has been shown to be associated with heart disease. Herein, we investigated whether GRK5 can specifically regulate the NF-κB signaling pathway in myocytes. We found that overexpression of GRK5 increased the levels of NF-κB -p50 and p65 in vitro and in vivo, whereas loss of GRK5 resulted in lower cardiac NF-κB levels. Furthermore, increased GRK5 expression induced the phosphorylation status of p65, increased the activity of a NF-κB reporter, and increased NF-κB DNA binding activity in cultured neonatal rat ventricular myocytes. Importantly, siRNA against GRK5 presented with the opposite results in neonatal rat ventricular myocytes as p65 and p50 were decreased, and there was a loss of NF-κB DNA binding activity. The influence of GRK5 on NF-κB expression and activity was dependent on its nuclear localization as overexpression of a mutant GRK5 that cannot enter the nucleus was devoid of NF-κB activation or DNA binding. Our study demonstrates that a novel pathological consequence of GRK5 up-regulation in the injured and failing heart is the induction of NF-κB expression and activity.

Macrophage MicroRNA-155 Promotes Cardiac Hypertrophy and Failure

Cardiac hypertrophy and subsequent heart failure triggered by chronic hypertension represent major challenges for cardiovascular research. Beyond neurohormonal and myocyte signaling pathways, growing evidence suggests inflammatory signaling pathways as therapeutically targetable contributors to this process. We recently reported that microRNA-155 is a key mediator of cardiac inflammation and injury in infectious myocarditis. Here, we investigated the impact of microRNA-155 manipulation in hypertensive heart disease. Genetic loss or pharmacological inhibition of the leukocyte-expressed microRNA-155 in mice markedly reduced cardiac inflammation, hypertrophy, and dysfunction on pressure overload. These alterations were macrophage dependent because in vivo cardiomyocyte-specific microRNA-155 manipulation did not affect cardiac hypertrophy or dysfunction, whereas bone marrow transplantation from wild-type mice into microRNA-155 knockout animals rescued the hypertrophic response of the cardiomyocytes and vice versa. In vitro, media from microRNA-155 knockout macrophages blocked the hypertrophic growth of stimulated cardiomyocytes, confirming that macrophages influence myocyte growth in a microRNA-155-dependent paracrine manner. These effects were at least partly mediated by the direct microRNA-155 target suppressor of cytokine signaling 1 (Socs1) because Socs1 knockdown in microRNA-155 knockout macrophages largely restored their hypertrophy-stimulating potency. Our findings reveal that microRNA-155 expression in macrophages promotes cardiac inflammation, hypertrophy, and failure in response to pressure overload. These data support the causative significance of inflammatory signaling in hypertrophic heart disease and demonstrate the feasibility of therapeutic microRNA targeting of inflammation in heart failure.

Controlling Parasympathetic Regulation of Heart Rate: A Gatekeeper Role for RGS Proteins in the Sinoatrial Node

Neurotransmitters released from sympathetic and parasympathetic nerve terminals in the sinoatrial node (SAN) exert their effects via G-protein-coupled receptors. Integration of these different G-protein signals within pacemaker cells of the SAN is critical for proper regulation of heart rate and function. For example, excessive parasympathetic signaling can be associated with sinus node dysfunction (SND) and supraventricular arrhythmias. Our previous work has shown that one member of the regulator of G-protein signaling (RGS) protein family, RGS4, is highly and selectively expressed in pacemaker cells of the SAN. Consistent with its role as an inhibitor of parasympathetic signaling, RGS4-knockout mice have reduced basal heart rates and enhanced negative chronotropic responses to parasympathetic agonists. Moreover, RGS4 appears to be an important part of SA nodal myocyte signaling pathways that mediate G-protein-coupled inwardly rectifying potassium channel (GIRK) channel activation/deactivation and desensitization. Since RGS4 acts immediately downstream of M2 muscarinic receptors, it is tempting to speculate that RGS4 functions as a master regulator of parasympathetic signaling upstream of GIRKs, HCNs, and L-type Ca2+ channels in the SAN. Thus, loss of RGS4 function may lead to increased susceptibility to conditions associated with increased parasympathetic signaling, including bradyarrhythmia, SND, and atrial fibrillation.

Communication Signals Between Cardiac Fibroblasts and Cardiac Myocytes

Interspersed between cardiac myocytes, cardiac fibroblasts serve mainly as a structural support during ventricular wall thickening from embryogenesis until adulthood. Cardiac fibroblasts, however, may also serve as a source of mitogens, extracellular matrix proteins, cytokines, and growth factors that could affect the phenotype of the cardiac myocyte. The crosstalk between cardiac fibroblasts and myocytes is important during cardiac development and remodeling in response to injury. The cell-to-cell communication involves paracrine signals (cytokines and growth factors), direct interactions (connexins and cadherins) as well as indirect interactions (integrin signaling through the extracellular matrix). In this review, known cardiac fibroblast-cardiac myocyte signaling pathways are briefly examined and their effect on the heart during disease progression is discussed. Furthermore, speculations are made regarding the possibility that vascular endothelial growth factor B can serve as an important signaling molecule between cardiac fibroblasts and cardiac myocytes and could promote cardiac function in compromised hearts.

The Giant Protein Titin as an Integrator of Myocyte Signaling Pathways

The giant muscle protein titin, the "backbone" of the sarcomere, harbors a complex molecular spring whose stiffness is variably tuned in health and disease. Titin is increasingly recognized as a crucial integrator of diverse myocyte signaling pathways. The titin-associated signalosome includes hotspots of protein-protein interactions important for the regulation of protein quality-control mechanisms, hypertrophic gene activation, and mechanosensing.

Inducible Nitric Oxide Synthase Attenuates Adrenergic Signaling in Alcohol Fed Rats

Chronic, excessive alcohol consumption is associated with myocardial dysfunction in humans. The molecular mechanisms and cellular signaling pathways contributing to this cardiac dysfunction remain largely unknown. This study examined the effects of chronic alcohol consumption on myocardial function and cardiac myocyte signaling pathways. Adult male rats were fed a commercially prepared diet containing either ethanol (13 g/kg/d) or isocaloric control diet for 1 month. In vivo hemodynamics were measured in awake rats after inserting a catheter tip in the left ventricle under general anesthesia. Ventricular dysfunction was evidenced in awake, alcohol-fed rats by increased left ventricular end diastolic pressure, decreased systolic developed left ventricular pressure, and decreases in both positive and negative dp/dt compared with controls. Cardiac myocytes isolated from alcohol-fed rats also demonstrated an attenuated response to the beta-adrenergic agonist, isoproterenol, compared to controls. This response was significantly reversed by the nitric oxide synthase (NOS) inhibitor, N-monomethyl-L-arginine (L-NMMA). Western analyses confirmed inducible nitric oxide synthase (iNOS) protein synthesis in cardiac myocytes isolated from alcohol fed rats. It is therefore concluded that chronic alcohol ingestion results in iNOS-mediated attenuation of adrenergic signaling and depression in both systolic and diastolic function in rats.