Cardiomyocyte-specific transforming growth factor β suppression blocks neutrophil infiltration, augments multiple cytoprotective cascades, and reduces early mortality after myocardial infarction

RATIONALE

Wound healing after myocardial infarction involves a highly regulated inflammatory response that is initiated by the appearance of neutrophils to clear out dead cells and matrix debris. Neutrophil infiltration is controlled by multiple secreted factors, including the master regulator transforming growth factor β (TGFβ). Broad inhibition of TGFβ early postinfarction has worsened post-myocardial infarction remodeling; however, this signaling displays potent cell specificity, and targeted suppression particularly in the myocyte could be beneficial.

OBJECTIVE

Our aims were to test the hypothesis that targeted suppression of myocyte TGFβ signaling ameliorates postinfarct remodeling and inflammatory modulation and to identify mechanisms by which this may be achieved.

METHODS AND RESULTS

Mice with TGFβ receptor-coupled signaling genetically suppressed only in cardiac myocytes (conditional TGFβ receptor 1 or 2 knockout) displayed marked declines in neutrophil recruitment and accompanying metalloproteinase 9 activation after infarction and were protected against early-onset mortality due to wall rupture. This is a cell-specific effect, because broader inhibition of TGFβ signaling led to 100% early mortality due to rupture. Rather than by altering fibrosis or reducing the generation of proinflammatory cytokines/chemokines, myocyte-selective TGFβ inhibition augmented the synthesis of a constellation of highly protective cardiokines. These included thrombospondin 4 with associated endoplasmic reticulum stress responses, interleukin-33, follistatin-like 1, and growth and differentiation factor 15, which is an inhibitor of neutrophil integrin activation and tissue migration.

CONCLUSIONS

These data reveal a novel role of myocyte TGFβ signaling as a potent regulator of protective cardiokine and neutrophil-mediated infarct remodeling.

Hyperactive adverse mechanical stress responses in dystrophic heart are coupled to transient receptor potential canonical 6 and blocked by cGMP-protein kinase G modulation

RATIONALE

The heart is exquisitely sensitive to mechanical stimuli to adapt rapidly to physiological demands. In muscle lacking dystrophin, such as Duchenne muscular dystrophy, increased load during contraction triggers pathological responses thought to worsen the disease. The relevant mechanotransducers and therapies to target them remain unclear.

OBJECTIVES

We tested the role of transient receptor potential canonical (TRPC) channels TRPC3 and TRPC6 and their modulation by protein kinase G (PKG) in controlling cardiac systolic mechanosensing and determined their pathophysiological relevance in an experimental model of Duchenne muscular dystrophy.

METHODS AND RESULTS

Contracting isolated papillary muscles and cardiomyocytes from controls and mice genetically lacking either TRPC3 or TRPC6 were subjected to auxotonic load to induce stress-stimulated contractility (SSC, gradual rise in force and intracellular Ca(2+)). Incubation with cGMP (PKG activator) markedly blunted SSC in controls and Trpc3(-/-); whereas in Trpc6(-/-), the resting SSC response was diminished and cGMP had no effect. In Duchenne muscular dystrophy myocytes (mdx/utrophin deficient), the SSC was excessive and arrhythmogenic. Gene deletion or selective drug blockade of TRPC6 or cGMP/PKG activation reversed this phenotype. Chronic phosphodiesterase 5A inhibition also normalized abnormal mechanosensing while blunting progressive chamber hypertrophy in Duchenne muscular dystrophy mice.

CONCLUSIONS

PKG is a potent negative modulator of cardiac systolic mechanosignaling that requires TRPC6 as the target effector. In dystrophic hearts, excess SSC and arrhythmia are coupled to TRPC6 and are ameliorated by its targeted suppression or PKG activation. These results highlight novel therapeutic targets for this disease.

HNO enhances SERCA2a activity and cardiomyocyte function by promoting redox-dependent phospholamban oligomerization

AIMS

Nitroxyl (HNO) interacts with thiols to act as a redox-sensitive modulator of protein function. It enhances sarcoplasmic reticular Ca(2+) uptake and myofilament Ca(2+) sensitivity, improving cardiac contractility. This activity has led to clinical testing of HNO donors for heart failure. Here we tested whether HNO alters the inhibitory interaction between phospholamban (PLN) and the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2a) in a redox-dependent manner, improving Ca(2+) handling in isolated myocytes/hearts.

RESULTS

Ventriculocytes, sarcoplasmic reticulum (SR) vesicles, and whole hearts were isolated from control (wildtype [WT]) or PLN knockout (pln(-/-)) mice. Compared to WT, pln(-/-) myocytes displayed enhanced resting sarcomere shortening, peak Ca(2+) transient, and blunted β-adrenergic responsiveness. HNO stimulated shortening, relaxation, and Ca(2+) transient in WT cardiomyocytes, and evoked positive inotropy/lusitropy in intact hearts. These changes were markedly blunted in pln(-/-) cells/hearts. HNO enhanced SR Ca(2+) uptake in WT but not pln(-/-) SR-vesicles. Spectroscopic studies in insect cell microsomes expressing SERCA2a±PLN showed that HNO increased Ca(2+)-dependent SERCA2a conformational flexibility but only when PLN was present. In cardiomyocytes, HNO achieved this effect by stabilizing PLN in an oligomeric disulfide bond-dependent configuration, decreasing the amount of free inhibitory monomeric PLN available.

INNOVATION

HNO-dependent redox changes in myocyte PLN oligomerization relieve PLN inhibition of SERCA2a.

CONCLUSIONS

PLN plays a central role in HNO-induced enhancement of SERCA2a activity, leading to increased inotropy/lusitropy in intact myocytes and hearts. PLN remains physically associated with SERCA2a; however, less monomeric PLN is available resulting in decreased inhibition of the enzyme. These findings offer new avenues to improve Ca(2+) handling in failing hearts.

Bile acids induce arrhythmias in human atrial myocardium--implications for altered serum bile acid composition in patients with atrial fibrillation

OBJECTIVE

High bile acid serum concentrations have been implicated in cardiac disease, particularly in arrhythmias. Most data originate from in vitro studies and animal models. We tested the hypotheses that (1) high bile acid concentrations are arrhythmogenic in adult human myocardium, (2) serum bile acid concentrations and composition are altered in patients with atrial fibrillation (AF) and (3) the therapeutically used ursodeoxycholic acid has different effects than other potentially toxic bile acids.

METHODS AND RESULTS

Multicellular human atrial preparations ('trabeculae') were exposed to primary bile acids and the incidence of arrhythmic events was assessed. Bile acid concentrations were measured in serum samples from 250 patients and their association with AF and ECG parameters analysed. Additionally, we conducted electrophysiological studies in murine myocytes. Taurocholic acid (TCA) concentration-dependently induced arrhythmias in atrial trabeculae (14/28 at 300 µM TCA, p<0.01) while ursodeoxycholic acid did not. Patients with AF had significantly decreased serum levels of ursodeoxycholic acid conjugates and increased levels of non-ursodeoxycholic bile acids. In isolated myocytes, TCA depolarised the resting membrane potential, enhanced Na(+)/Ca(2+) exchanger (NCX) tail current density and induced afterdepolarisations. Inhibition of NCX prevented arrhythmias in atrial trabeculae.

CONCLUSIONS

High TCA concentrations induce arrhythmias in adult human atria while ursodeoxycholic acid does not. AF is associated with higher serum levels of non-ursodeoxycholic bile acid conjugates and low levels of ursodeoxycholic acid conjugates. These data suggest that higher levels of toxic (arrhythmogenic) and low levels of protective bile acids create a milieu with a decreased arrhythmic threshold and thus may facilitate arrhythmic events.

Abstract 3: Targeted Inhibition Of Transforming Growth Factor Beta In Cardiac Myocytes Prevents Myocardial Rupture After Infarction

Introduction Coronary artery disease is the leading cause of death and myocardial infarction (MI) its most severe manifestation.TGFb is a major switch governing the myocardial response to injury and global inhibition is detrimental following MI. Recently, cell-specific gene manipulation models have enabled investigation of cardiomyocyte (CM) versus non-CM TGFb signaling on maladaptive remodeling. We found CM TGFb to be central to pressure-overload disease. Here, we tested the hypothesis that CM TGFb modifies acute post-MI remodeling, and thus benefits rather than worsens outcome as observed with antibody-based inhibition that primarily targets interstitial/vascular cells.

Methods Mice with cardiac-specific conditional knockdown of TgfbR1 or 2 (aMHC - MCM TgfbR fl/fl) or injection of TGFb-neutralizing antibody were subjected to proximal LAD-ligation and followed by echocardiography and continuous ECG monitoring. Expression and activity of the major matrix metalloproteinases MMP2/MMP9 and TIMP1 were assessed by qRT-PCR, immunoblot, and zymography, respectively. Only mice surviving >24h after surgery (>90%) were included in analyses.

Results LAD ligation decreased fractional shortening on day 1 to 18±2% (61±1% in sham animals) with no differences between genotypes (n≥8). Similarly, echocardiographic parameters of myocardial dimensions and function did not differ at weeks 1 or 3. Early mortality (day 4 - 10) was strikingly lower in knockdown mice as compared to controls (10% vs 48%, p<0.05, n≥10). Remarkably, systemic TGFb inhibition resulted in 100% mortality (n=8) by day 5. The cause of death was established by necropsy and continuous ECG monitoring and was myocardial rupture in all cases. MMP9 expression and gelatinolytic activity was reduced by CM TGFbR knockdown at day 3 after MI, as was TIMP1 expression, while MMP2 expression/activity was not altered.

Conclusion TGFb inhibition exhibits differential effects in wound healing following MI. Where global inhibition is deleterious, CM-targeted knockdown powerfully protects the heart from rupture. This highlights potent cross-talk between the CM TGFb signal and matrix remodeling and the importance of targeted inhibition to benefit cardiac disease.

Sunitinib causes dose-dependent negative functional effects on myocardium and cardiomyocytes

OBJECTIVES

To examine the acute effects of sunitinib on inotropic function, intracellular Ca(2+) transients, myofilament Ca(2+) sensitivity and generation of reactive oxygen species (ROS) in human multicellular myocardium and isolated mouse cardiomyocytes. To search for microRNAs as suitable biomarkers for indicating toxic cardiac effects.

PATIENTS AND METHODS

After exposure to sunitinib (0.1-10 µg/mL) developed force, diastolic tension and kinetic variables were assessed in isolated human myocardium. Changes in myocyte sarcomere length, whole-cell calcium transients, myofilament force-Ca(2+) relationship, and ROS generation were examined in isolated ventricular mouse cardiomyocytes. Microarray and realtime-PCR were used to screen for differentially expressed microRNAs in cultured cardiomyocytes that were exposed for 24 h to sunitinib.

RESULTS

We found that higher concentrations of sunitinib (1 and 10 µg/mL) decreased developed force at 30 minutes 76.9 + 2.8 and 54.5 + 6.3%, compared to 96.1 + 2.6% in controls (P < 0.01). Sunitinib exposure significantly decreased sarcomere shortening and Ca2+ transients. Myofilament Ca(2+) sensitivity was not altered, while ROS levels were significantly increased after exposure to the drug. MicroRNA expression patterns were not altered by sunitinib.

CONCLUSIONS

Sunitinib elicits a dose-dependent negative inotropic effect in myocardium, accompanied by a decline in intracellular Ca(2+) and increased ROS generation. In clinical practice, these cardiotoxic effects should be considered in cases where cardiac concentrations of sunitinib could be increased.

Functional effects of glucose transporters in human ventricular myocardium

AIMS

Insulin-dependent positive inotropic effects (PIE) are partially Ca(2+) independent. This mechanism is potentially glucose dependent. In contrast to most animal species, human myocardium expresses high levels of sodium-glucose-transporter-1 (SGLT-1) mRNA besides the common glucose-transporters-1 and -4 (GLUT1, GLUT4).

METHODS AND RESULTS

We used ventricular myocardium from 61 end-stage failing human hearts (ischaemic cardiomyopathy, ICM and dilated cardiomyopathy, DCM) and 13 non-failing donor hearts. The effect of insulin on isometric twitch force was examined with or without blocking of PI3-kinase, GLUT4-translocation, or SGLT-1. Substrate-dependent (glucose vs. pyruvate vs. palmitoyl-carnitine) effects were tested in atrial myocardium. mRNA expression of glucose transporters was analysed. Insulin increased developed force by 122 + or - 7.4, 121.7 + or - 2.5, and 134.1 + or - 5.7% in non-failing, DCM, and ICM (P < 0.05 vs. DCM), respectively. Positive inotropic effect was partially blunted by inhibition of PI-3-kinase, GLUT4, or SGLT1. Combined inhibition of PI3-kinase and glucose-transport completely abolished PIE. Positive inotropic effect was significantly stronger in glucose-containing solution compared with pyruvate or palmitoyl-carnitine containing. mRNA expression showed only a tendency towards elevated GLUT4-expression in ICM.

CONCLUSIONS

Positive inotropic effect of insulin is pronounced in ICM, but underlying mechanisms are unaltered. The Ca(2+)-independent PIE of insulin is mediated via glucose-transporters. Together with the Ca(2+)-dependent PI-3-kinase mediated pathway, it is responsible for the entire PIE. Substrate-dependency affirms a glucose-dependent part of the PIE.

Case report: Hyperbaric oxygen in the treatment of puff adder (Bitis arietans) bite

INTRODUCTION

The puff adder (Bitis arietans) is a venomous viper mainly found in sub-Saharan Africa. Due to its common occurrence and potent venom, it is considered to be the most dangerous snake in Africa, responsible for most snakebite fatalities there. Puff adder bites outside Africa are rare and involve captive vipers. We present the unusual case of puff adder envenomation in an Austrian man.

CASE REPORT

A 26-year-old Austrian man was bitten by a puff adder that he kept illegally in his home. On admission he showed signs of local and systemic toxicity. He was stabilized with antivenom, intravenous fluids, catecholamines and packed platelets. Hyperbaric oxygenation was begun due to incipient compartment syndrome on the second day and continued until the eleventh day, when the patient had recovered completely and could be discharged.

DISCUSSION

The venom of Bitis arietans can cause serious systemic and local complications. Our patient suffered from both. Systemic signs included hemodynamic as well as hemostaseologic impairment. Local effects included swelling and incipient compartment syndrome. Systemic and local treatment, including hyperbaric oxygenation, effected a full recovery. We suggest that, whenever feasible, hyperbaric oxygenation should be considered as adjunct treatment in snake bites to avert adverse outcomes.

Glucose-transporter-mediated positive inotropic effects in human myocardium of diabetic and nondiabetic patients

Insulin causes inotropic effects via Ca(2+)-dependent and Ca(2+)-independent pathways. The latter one is potentially glucose dependent. We examined inotropic responses and signal transduction of insulin in human atrial myocardium of diabetic and nondiabetic patients to test for the role of glucose transporters. Experiments were performed in isolated atrial myocardium of 88 patients undergoing cardiac surgery and 28 ventricular muscle samples of explanted hearts. Influence of insulin (0.02 micromol/L) on isometric twitch force was examined with and without blocking glucose transporter (GLUT) 4 translocation (latrunculin), sodium-coupled glucose transporter (SGLT) 1 (phlorizin, T-1095A), or PI3-kinase (wortmannin). Experiments were performed in Tyrode solution containing glucose or pyruvate as energetic substrate. Messenger RNA expression of glucose transporters (GLUT1, GLUT4, SGLT1, SGLT2) was analyzed in atrial and ventricular myocardium of both diabetic and nondiabetic patients. Developed force increases after insulin (to 117.8% +/- 2.4% and 115.8% +/- 1.9%) in trabeculae from patients with and without diabetes. Inotropic effect was reduced after displacing glucose with pyruvate as well as after PI3-kinase inhibition (to 103% +/- 2%) or inhibition of glucose transporters GLUT4 (to 105% +/- 2%) and SGLT1 (phlorizin to 106% +/- 2%, T-1095A to 105% +/- 2%), without differences between the 2 groups. In glucose-free pyruvate-containing solution, only inhibition of PI3-kinase but not blocking glucose transporters resulted in further inhibitory effects. Messenger RNA expression did not show significant differences between patients with or without diabetes. Insulin exerts positive inotropic effects in human atrial myocardium. These effects are mediated via a PI3-kinase-sensitive and a glucose-transport-sensitive pathway. Differences in functional effects or messenger RNA expression of glucose transporters were not detectable between patients with and without diabetes.