Dual effect of cardiac FKBP12.6 overexpression on excitation-contraction coupling and the incidence of ventricular arrhythmia depending on its expression level.

FKBP12.6, a binding protein to the immunosuppressant FK506, which also binds the ryanodine receptor (RyR2) in the heart, has been proposed to regulate RyR2 function and to have antiarrhythmic properties. However, the level of FKBP12.6 expression in normal hearts remains elusive and some controversies still persist regarding its effects, both in basal conditions and during ß-adrenergic stimulation. We quantified FKBP12.6 in the left ventricles (LV) of WT (wild-type) mice and in two novel transgenic models expressing distinct levels of FKBP12.6, using a custom-made specific anti-FKBP12.6 antibody and a recombinant protein. FKBP12.6 level in WT LV was very low (0.16 ± 0.02 nmol/g of LV), indicating that <15% RyR2 monomers are bound to the protein. Mice with 14.1 ± 0.2 nmol of FKBP12.6 per g of LV (TG1) had mild cardiac hypertrophy and normal function and were protected against epinephrine/caffeine-evoked arrhythmias. The ventricular myocytes showed higher [Ca2+]i transient amplitudes than WT myocytes and normal SR-Ca2+ load, while fewer myocytes showed Ca2+ sparks. TG1 cardiomyocytes responded to 50 nM Isoproterenol increasing these [Ca2+]i parameters and producing RyR2-Ser2808 phosphorylation. Mice with more than twice the TG1 FKBP12.6 value (TG2) showed marked cardiac hypertrophy with calcineurin activation and more arrhythmias than WT mice during ß-adrenergic stimulation, challenging the protective potential of high FKBP12.6. RyR2R420Q CPVT mice overexpressing FKBP12.6 showed fewer proarrhythmic events and decreased incidence and duration of stress-induced bidirectional ventricular tachycardia. Our study, therefore, quantifies for the first time endogenous FKBP12.6 in the mouse heart, questioning its physiological relevance, at least at rest due its low level. By contrast, our work demonstrates that with caution FKBP12.6 remains an interesting target for the development of new antiarrhythmic therapies.

Cardiac Overexpression of PDE4B Blunts ß-Adrenergic Response and Maladaptive Remodeling in Heart Failure.

BACKGROUND: The cyclic AMP (adenosine monophosphate; cAMP)-hydrolyzing protein PDE4B (phosphodiesterase 4B) is a key negative regulator of cardiac ß-adrenergic receptor stimulation. PDE4B deficiency leads to abnormal Ca2+ handling and PDE4B is decreased in pressure overload hypertrophy, suggesting that increasing PDE4B in the heart is beneficial in heart failure. METHODS: We measured PDE4B expression in human cardiac tissues and developed 2 transgenic mouse lines with cardiomyocyte-specific overexpression of PDE4B and an adeno-associated virus serotype 9 encoding PDE4B. Myocardial structure and function were evaluated by echocardiography, ECG, and in Langendorff-perfused hearts. Also, cAMP and PKA (cAMP dependent protein kinase) activity were monitored by Förster resonance energy transfer, L-type Ca2+ current by whole-cell patch-clamp, and cardiomyocyte shortening and Ca2+ transients with an Ionoptix system. Heart failure was induced by 2 weeks infusion of isoproterenol or transverse aortic constriction. Cardiac remodeling was evaluated by serial echocardiography, morphometric analysis, and histology. RESULTS: PDE4B protein was decreased in human failing hearts. The first PDE4B-transgenic mouse line (TG15) had a ≈15-fold increase in cardiac cAMP-PDE activity and a ≈30% decrease in cAMP content and fractional shortening associated with a mild cardiac hypertrophy that resorbed with age. Basal ex vivo myocardial function was unchanged, but ß-adrenergic receptor stimulation of cardiac inotropy, cAMP, PKA, L-type Ca2+ current, Ca2+ transients, and cell contraction were blunted. Endurance capacity and life expectancy were normal. Moreover, these mice were protected from systolic dysfunction, hypertrophy, lung congestion, and fibrosis induced by chronic isoproterenol treatment. In the second PDE4B-transgenic mouse line (TG50), markedly higher PDE4B overexpression, resulting in a ≈50-fold increase in cardiac cAMP-PDE activity caused a ≈50% decrease in fractional shortening, hypertrophy, dilatation, and premature death. In contrast, mice injected with adeno-associated virus serotype 9 encoding PDE4B (1012 viral particles/mouse) had a ≈50% increase in cardiac cAMP-PDE activity, which did not modify basal cardiac function but efficiently prevented systolic dysfunction, apoptosis, and fibrosis, while attenuating hypertrophy induced by chronic isoproterenol infusion. Similarly, adeno-associated virus serotype 9 encoding PDE4B slowed contractile deterioration, attenuated hypertrophy and lung congestion, and prevented apoptosis and fibrotic remodeling in transverse aortic constriction. CONCLUSIONS: Our results indicate that a moderate increase in PDE4B is cardioprotective and suggest that cardiac gene therapy with PDE4B might constitute a new promising approach to treat heart failure.

Orai1 Channel Inhibition Preserves Left Ventricular Systolic Function and Normal Ca2+ Handling After Pressure Overload.

BACKGROUND: Orai1 is a critical ion channel subunit, best recognized as a mediator of store-operated Ca2+ entry (SOCE) in nonexcitable cells. SOCE has recently emerged as a key contributor of cardiac hypertrophy and heart failure but the relevance of Orai1 is still unclear. METHODS: To test the role of these Orai1 channels in the cardiac pathophysiology, a transgenic mouse was generated with cardiomyocyte-specific expression of an ion pore-disruptive Orai1R91W mutant (C-dnO1). Synthetic chemistry and channel screening strategies were used to develop 4-(2,5-dimethoxyphenyl)-N-[(pyridin-4-yl)methyl]aniline (hereafter referred to as JPIII), a small-molecule Orai1 channel inhibitor suitable for in vivo delivery. RESULTS: Adult mice subjected to transverse aortic constriction (TAC) developed cardiac hypertrophy and reduced ventricular function associated with increased Orai1 expression and Orai1-dependent SOCE (assessed by Mn2+ influx). C-dnO1 mice displayed normal cardiac electromechanical function and cellular excitation-contraction coupling despite reduced Orai1-dependent SOCE. Five weeks after TAC, C-dnO1 mice were protected from systolic dysfunction (assessed by preserved left ventricular fractional shortening and ejection fraction) even if increased cardiac mass and prohypertrophic markers induction were observed. This is correlated with a protection from TAC-induced cellular Ca2+ signaling alterations (increased SOCE, decreased [Ca2+]i transients amplitude and decay rate, lower SR Ca2+ load and depressed cellular contractility) and SERCA2a downregulation in ventricular cardiomyocytes from C-dnO1 mice, associated with blunted Pyk2 signaling. There was also less fibrosis in heart sections from C-dnO1 mice after TAC. Moreover, 3 weeks treatment with JPIII following 5 weeks of TAC confirmed the translational relevance of an Orai1 inhibition strategy during hypertrophic insult. CONCLUSIONS: The findings suggest a key role of cardiac Orai1 channels and the potential for Orai1 channel inhibitors as inotropic therapies for maintaining contractility reserve after hypertrophic stress.

Microtubule cytoskeleton regulates Connexin 43 localization and cardiac conduction in cardiomyopathy caused by mutation in A-type lamins gene.

Mutations in the lamin A/C gene (LMNA) cause an autosomal dominant inherited form of dilated cardiomyopathy associated with cardiac conduction disease (hereafter referred to as LMNA cardiomyopathy). Compared with other forms of dilated cardiomyopathy, mutations in LMNA are responsible for a more aggressive clinical course owing to a high rate of malignant ventricular arrhythmias. Gap junctions are intercellular channels that allow direct communication between neighboring cells, which are involved in electrical impulse propagation and coordinated contraction of the heart. For gap junctions to properly control electrical synchronization in the heart, connexin-based hemichannels must be correctly targeted to intercalated discs, Cx43 being the major connexin in the working myocytes. We here showed an altered distribution of Cx43 in a mouse model of LMNA cardiomyopathy. However, little is known on the molecular mechanisms of Cx43 remodeling in pathological context. We now show that microtubule cytoskeleton alteration and decreased acetylation of α-tubulin lead to remodeling of Cx43 in LMNA cardiomyopathy, which alters the correct communication between cardiomyocytes, ultimately leading to electrical conduction disturbances. Preventing or reversing this process could offer a strategy to repair damaged heart. Stabilization of microtubule cytoskeleton using Paclitaxel improved intraventricular conduction defects. These results indicate that microtubule cytoskeleton contributes to the pathogenesis of LMNA cardiomyopathy and that drugs stabilizing the microtubule may be beneficial for patients.

Specific Activation of the Alternative Cardiac Promoter of Cacna1c by the Mineralocorticoid Receptor.

RATIONALE: The MR (mineralocorticoid receptor) antagonists belong to the current therapeutic armamentarium for the management of cardiovascular diseases, but the mechanisms conferring their beneficial effects are poorly understood. Part of the cardiovascular effects of MR is because of the regulation of L-type Cav1.2 Ca2+ channel expression, which is generated by tissue-specific alternative promoters as a long cardiac or short vascular N-terminal transcripts. OBJECTIVE: To analyze the molecular mechanisms by which aldosterone, through MR, modulates Cav1.2 expression and function in a tissue-specific manner. METHODS AND RESULTS: In primary cultures of neonatal rat ventricular myocytes, aldosterone exposure for 24 hours increased in a concentration-dependent manner long cardiac Cav1.2 N-terminal transcripts expression at both mRNA and protein levels, correlating with enhanced concentration-, time-, and MR-dependent P1-promoter activity. In silico analysis and mutagenesis identified MR interaction with both specific activating and repressing DNA-binding elements on the P1-promoter. The relevance of this regulation is confirmed both ex and in vivo in transgenic mice harboring the luciferase reporter gene under the control of the cardiac P1-promoter. Moreover, we show that this cis-regulatory mechanism is not limited to the heart. Indeed, in smooth muscle cells from different vascular beds, in which the short vascular Cav1.2 N-terminal transcripts is normally the major isoform, we found that MR signaling activates long cardiac Cav1.2 N-terminal transcripts expression through P1-promoter activation, leading to vascular contractile dysfunction. These results were further corroborated in hypertensive aldosterone/salt rodent models, showing notably a positive correlation between blood pressure and cardiac P1-promoter activity in aorta. This new vascular long cardiac Cav1.2 N-terminal transcripts molecular signature reduced sensitivity to the Ca2+ channel blocker, nifedipine, in aldosterone-treated vessels. CONCLUSIONS: Our results reveal that MR acts as a transcription factor to translate aldosterone signal into specific cardiac P1-promoter activation that might influence the therapeutic outcome of cardiovascular diseases.

Synergic PDE3 and PDE4 control intracellular cAMP and cardiac excitation-contraction coupling in a porcine model.

AIMS: Cyclic AMP phosphodiesterases (PDEs) are important modulators of the cardiac response to ß-adrenergic receptor (ß-AR) stimulation. PDE3 is classically considered as the major cardiac PDE in large mammals and human, while PDE4 is preponderant in rodents. However, it remains unclear whether PDE4 also plays a functional role in large mammals. Our purpose was to understand the role of PDE4 in cAMP hydrolysis and excitation-contraction coupling (ECC) in the pig heart, a relevant pre-clinical model. METHODS AND RESULTS: Real-time cAMP variations were measured in isolated adult pig right ventricular myocytes (APVMs) using a Förster resonance energy transfer (FRET) biosensor. ECC was investigated in APVMs loaded with Fura-2 and paced at 1 Hz allowing simultaneous measurement of intracellular Ca2+ and sarcomere shortening. The expression of the different PDE4 subfamilies was assessed by Western blot in pig right ventricles and APVMs. Similarly to PDE3 inhibition with cilostamide (Cil), PDE4 inhibition with Ro 20-1724 (Ro) increased cAMP levels and inotropy under basal conditions. PDE4 inhibition enhanced the effects of the non-selective ß-AR agonist isoprenaline (Iso) and the effects of Cil, and increased spontaneous diastolic Ca2+ waves (SCWs) in these conditions. PDE3A, PDE4A, PDE4B and PDE4D subfamilies are expressed in pig ventricles. In APVMs isolated from a porcine model of repaired tetralogy of Fallot which leads to right ventricular failure, PDE4 inhibition also exerts inotropic and pro-arrhythmic effects. CONCLUSIONS: Our results show that PDE4 controls ECC in APVMs and suggest that PDE4 inhibitors exert inotropic and pro-arrhythmic effects upon PDE3 inhibition or ß-AR stimulation in our pre-clinical model. Thus, PDE4 inhibitors should be used with caution in clinics as they may lead to arrhythmogenic events upon stress.

Two-pore channels (TPCs) acts as a hub for excitation-contraction coupling, metabolism and cardiac hypertrophy signalling.

Ca2+ signaling is essential for cardiac contractility and excitability in heart function and remodeling. Intriguingly, little is known about the role of a new family of ion channels, the endo-lysosomal non-selective cation "two-pore channel" (TPCs) in heart function. Here we have used double TPC knock-out mice for the 1 and 2 isoforms of TPCs (Tpcn1/2-/-) and evaluated their cardiac function. Doppler-echocardiography unveils altered left ventricular (LV) systolic function associated with a LV relaxation impairment. In cardiomyocytes isolated from Tpcn1/2-/- mice, we observed a reduction in the contractile function with a decrease in the sarcoplasmic reticulum Ca2+ content and a reduced expression of various key proteins regulating Ca2+ stores, such as calsequestrin. We also found that two main regulators of the energy metabolism, AMP-activated protein kinase and mTOR, were down regulated. We found an increase in the expression of TPC1 and TPC2 in a model of transverse aortic constriction (TAC) mice and in chronically isoproterenol infused WT mice. In this last model, adaptive cardiac hypertrophy was reduced by Tpcn1/2 deletion. Here, we propose a central role for TPCs and lysosomes that could act as a hub integrating information from the excitation-contraction coupling mechanisms, cellular energy metabolism and hypertrophy signaling.

Phosphodiesterases type 2, 3 and 4 promote vascular tone in mesenteric arteries from rats with heart failure.

Phosphodiesterases (PDE) type 3 and 4 promote vasoconstriction by hydrolysing cAMP. In experimental heart failure (HF), PDE3 makes PDE4 redundant in aorta, but it is not known if this occurs in resistance vessels, such as mesenteric artery. As PDE2 is increased in the failing myocardium, its possible role in the vasculature also needs to be addressed. Here, the function of PDE2, PDE3 and PDE4 in rat mesenteric arteries was characterized in experimental HF. Mesenteric arteries were isolated from rats sacrificed 22 weeks after surgical stenosis of the ascending aorta (HF), or Sham surgery. PDE inhibitors were used to probe isoenzyme contributions in enzymatic and isometric tension assays. PDE2 and PDE4 activities, but not PDE3 activity, facilitate contraction produced by the thromboxane analogue U46619 in Sham arteries, while in HF all three isoenzymes contribute to this response. NO synthase inhibition by L-NAME abolished the action of the PDE2 inhibitor. L-NAME eliminated the contribution of PDE4 in HF, but unmasked a contribution for PDE3 in Sham. PDE3 and PDE4 activities attenuated relaxant response to ß-adrenergic stimulation in Sham and HF. PDE2 did not participate in cAMP or cGMP-mediated relaxant responses. PDE3 and PDE4 cAMP-hydrolysing activities were smaller in HF mesenteric arteries, while PDE2 activity was scarce in both groups. Endothelial cells and arterial myocytes displayed PDE2 immunolabelling. We highlight that, by contrast with previous observations in aorta, PDE4 participates equally as PDE3 in contracting mesenteric artery in HF. PDE2 activity emerges as a promoter of contractile response that is preserved in HF.

EPAC1 inhibition protects the heart from doxorubicin-induced toxicity.

Anthracyclines, such as doxorubicin (Dox), are widely used chemotherapeutic agents for the treatment of solid tumors and hematologic malignancies. However, they frequently induce cardiotoxicity leading to dilated cardiomyopathy and heart failure. This study sought to investigate the role of the exchange protein directly activated by cAMP (EPAC) in Dox-induced cardiotoxicity and the potential cardioprotective effects of EPAC inhibition. We show that Dox induces DNA damage and cardiomyocyte cell death with apoptotic features. Dox also led to an increase in both cAMP concentration and EPAC1 activity. The pharmacological inhibition of EPAC1 (with CE3F4) but not EPAC2 alleviated the whole Dox-induced pattern of alterations. When administered in vivo, Dox-treated WT mice developed a dilated cardiomyopathy which was totally prevented in EPAC1 knock-out (KO) mice. Moreover, EPAC1 inhibition potentiated Dox-induced cell death in several human cancer cell lines. Thus, EPAC1 inhibition appears as a potential therapeutic strategy to limit Dox-induced cardiomyopathy without interfering with its antitumoral activity.

CD38-NADase is a new major contributor to Duchenne muscular dystrophic phenotype.

Duchenne muscular dystrophy (DMD) is characterized by progressive muscle degeneration. Two important deleterious features are a Ca2+ dysregulation linked to Ca2+ influxes associated with ryanodine receptor hyperactivation, and a muscular nicotinamide adenine dinucleotide (NAD+ ) deficit. Here, we identified that deletion in mdx mice of CD38, a NAD+ glycohydrolase-producing modulators of Ca2+ signaling, led to a fully restored heart function and structure, with skeletal muscle performance improvements, associated with a reduction in inflammation and senescence markers. Muscle NAD+ levels were also fully restored, while the levels of the two main products of CD38, nicotinamide and ADP-ribose, were reduced, in heart, diaphragm, and limb. In cardiomyocytes from mdx/CD38-/- mice, the pathological spontaneous Ca2+ activity was reduced, as well as in myotubes from DMD patients treated with isatuximab (SARCLISA® ) a monoclonal anti-CD38 antibody. Finally, treatment of mdx and utrophin-dystrophin-deficient (mdx/utr-/- ) mice with CD38 inhibitors resulted in improved skeletal muscle performances. Thus, we demonstrate that CD38 actively contributes to DMD physiopathology. We propose that a selective anti-CD38 therapeutic intervention could be highly relevant to develop for DMD patients.

Decreased expression and activity of cAMP phosphodiesterases in cardiac hypertrophy and its impact on beta-adrenergic cAMP signals.

RATIONALE: Multiple cyclic nucleotide phosphodiesterases (PDEs) degrade cAMP in cardiomyocytes but the role of PDEs in controlling cAMP signaling during pathological cardiac hypertrophy is poorly defined. OBJECTIVE: Evaluate the beta-adrenergic regulation of cardiac contractility and characterize the changes in cardiomyocyte cAMP signals and cAMP-PDE expression and activity following cardiac hypertrophy. METHODS AND RESULTS: Cardiac hypertrophy was induced in rats by thoracic aortic banding over a time period of 5 weeks and was confirmed by anatomic measurements and echocardiography. Ex vivo myocardial function was evaluated in Langendorff-perfused hearts. Engineered cyclic nucleotide-gated (CNG) channels were expressed in single cardiomyocytes to monitor subsarcolemmal cAMP using whole-cell patch-clamp recordings of the associated CNG current (I(CNG)). PDE variant activity and protein level were determined in purified cardiomyocytes. Aortic stenosis rats exhibited a 67% increase in heart weight compared to sham-operated animals. The inotropic response to maximal beta-adrenergic stimulation was reduced by approximately 54% in isolated hypertrophied hearts, along with a approximately 32% decrease in subsarcolemmal cAMP levels in hypertrophied myocytes. Total cAMP hydrolytic activity as well as PDE3 and PDE4 activities were reduced in hypertrophied myocytes, because of a reduction of PDE3A, PDE4A, and PDE4B, whereas PDE4D was unchanged. Regulation of beta-adrenergic cAMP signals by PDEs was blunted in hypertrophied myocytes, as demonstrated by the diminished effects of IBMX (100 micromol/L) and of both the PDE3 inhibitor cilostamide (1 micromol/L) and the PDE4 inhibitor Ro 201724 (10 micromol/L). CONCLUSIONS: Beta-adrenergic desensitization is accompanied by a reduction in cAMP-PDE and an altered modulation of beta-adrenergic cAMP signals in cardiac hypertrophy.

Activation of sarcolipin expression and altered calcium cycling in LMNA cardiomyopathy.

Cardiomyopathy caused by A-type lamins gene (LMNA) mutations (LMNA cardiomyopathy) is associated with dysfunction of the heart, often leading to heart failure. LMNA cardiomyopathy is highly penetrant with bad prognosis with no specific therapy available. Searching for alternative ways to halt the progression of LMNA cardiomyopathy, we studied the role of calcium homeostasis in the evolution of this disease. We showed that sarcolipin, an inhibitor of the sarco/endoplasmic reticulum (SR) Ca2+ ATPase (SERCA) was abnormally elevated in the ventricular cardiomyocytes of mutated mice compared with wild type mice, leading to an alteration of calcium handling. This occurs early in the progression of the disease, when the left ventricular function was not altered. We further demonstrated that down regulation of sarcolipin using adeno-associated virus (AAV) 9-mediated RNA interference delays cardiac dysfunction in mouse model of LMNA cardiomyopathy. These results showed a novel role for sarcolipin on calcium homeostasis in heart and open perspectives for future therapeutic interventions to LMNA cardiomyopathy.

Contribution of BKCa channels to vascular tone regulation by PDE3 and PDE4 is lost in heart failure.

Aims: Regulation of vascular tone by 3',5'-cyclic adenosine monophosphate (cAMP) involves many effectors including the large conductance, Ca2+-activated, K+ (BKCa) channels. In arteries, cAMP is mainly hydrolyzed by type 3 and 4 phosphodiesterases (PDE3, PDE4). Here, we examined the specific contribution of BKCa channels to tone regulation by these PDEs in rat coronary arteries, and how this is altered in heart failure (HF). Methods and results: Concomitant application of PDE3 (cilostamide) and PDE4 (Ro-20-1724) inhibitors increased BKCa unitary channel activity in isolated myocytes from rat coronary arteries. Myography was conducted in isolated, U46619-contracted coronary arteries. Cilostamide (Cil) or Ro-20-1724 induced a vasorelaxation that was greatly reduced by iberiotoxin (IBTX), a BKCa channel blocker. Ro-20-1724 and Cil potentiated the relaxation induced by the ß-adrenergic agonist isoprenaline (ISO) or the adenylyl cyclase activator L-858051 (L85). IBTX abolished the effect of PDE inhibitors on ISO but did not on L85. In coronary arteries from rats with HF induced by aortic stenosis, contractility and response to acetylcholine were dramatically reduced compared with arteries from sham rats, but relaxation to PDE inhibitors was retained. Interestingly, however, IBTX had no effect on Ro-20-1724- and Cil-induced vasorelaxations in HF. Expression of the BKCa channel α-subunit, of a 98 kDa PDE3A and of a 80 kDa PDE4D were lower in HF compared with sham coronary arteries, while that of a 70 kDa PDE4B was increased. Proximity ligation assays demonstrated that PDE3 and PDE4 were localized in the vicinity of the channel. Conclusion: BKCa channels mediate the relaxation of coronary artery induced by PDE3 and PDE4 inhibition. This is achieved by co-localization of both PDEs with BKCa channels, enabling tight control of cAMP available for channel opening. Contribution of the channel is prominent at rest and on ß-adrenergic stimulation. This coupling is lost in HF.

A specific pattern of phosphodiesterases controls the cAMP signals generated by different Gs-coupled receptors in adult rat ventricular myocytes.

Compartmentation of cAMP is thought to generate the specificity of Gs-coupled receptor action in cardiac myocytes, with phosphodiesterases (PDEs) playing a major role in this process by preventing cAMP diffusion. We tested this hypothesis in adult rat ventricular myocytes by characterizing PDEs involved in the regulation of cAMP signals and L-type Ca2+ current (I(Ca,L)) on stimulation with beta1-adrenergic receptors (beta1-ARs), beta2-ARs, glucagon receptors (Glu-Rs) and prostaglandin E1 receptors (PGE1-Rs). All receptors but PGE1-R increased total cAMP, and inhibition of PDEs with 3-isobutyl-1-methylxanthine strongly potentiated these responses. When monitored in single cells by high-affinity cyclic nucleotide-gated (CNG) channels, stimulation of beta1-AR and Glu-R increased cAMP, whereas beta2-AR and PGE1-R had no detectable effect. Selective inhibition of PDE3 by cilostamide and PDE4 by Ro 20-1724 potentiated beta1-AR cAMP signals, whereas Glu-R cAMP was augmented only by PD4 inhibition. PGE1-R and beta2-AR generated substantial cAMP increases only when PDE3 and PDE4 were blocked. For all receptors except PGE1-R, the measurements of I(Ca,L) closely matched the ones obtained with CNG channels. Indeed, PDE3 and PDE4 controlled beta1-AR and beta2-AR regulation of I(Ca,L), whereas only PDE4 controlled Glu-R regulation of I(Ca,L) thus demonstrating that receptor-PDE coupling has functional implications downstream of cAMP. PGE1 had no effect on I(Ca,L) even after blockade of PDE3 or PDE4, suggesting that other mechanisms prevent cAMP produced by PGE1 to diffuse to L-type Ca2+ channels. These results identify specific functional coupling of individual PDE families to Gs-coupled receptors as a major mechanism enabling cardiac cells to generate heterogeneous cAMP signals in response to different hormones.

PDE4 and mAKAPß are nodal organizers of ß2-ARs nuclear PKA signalling in cardiac myocytes.

Aims: ß1- and ß2-adrenergic receptors (ß-ARs) produce different acute contractile effects on the heart partly because they impact on different cytosolic pools of cAMP-dependent protein kinase (PKA). They also exert different effects on gene expression but the underlying mechanisms remain unknown. The aim of this study was to understand the mechanisms by which ß1- and ß2-ARs regulate nuclear PKA activity in cardiomyocytes. Methods and results: We used cytoplasmic and nuclear targeted biosensors to examine cAMP signals and PKA activity in adult rat ventricular myocytes upon selective ß1- or ß2-ARs stimulation. Both ß1- and ß2-AR stimulation increased cAMP and activated PKA in the cytoplasm. Although the two receptors also increased cAMP in the nucleus, only ß1-ARs increased nuclear PKA activity and up-regulated the PKA target gene and pro-apoptotic factor, inducible cAMP early repressor (ICER). Inhibition of phosphodiesterase (PDE)4, but not Gi, PDE3, GRK2 nor caveolae disruption disclosed nuclear PKA activation and ICER induction by ß2-ARs. Both nuclear and cytoplasmic PKI prevented nuclear PKA activation and ICER induction by ß1-ARs, indicating that PKA activation outside the nucleus is required for subsequent nuclear PKA activation and ICER mRNA expression. Cytoplasmic PKI also blocked ICER induction by ß2-AR stimulation (with concomitant PDE4 inhibition). However, in this case nuclear PKI decreased ICER up-regulation by only 30%, indicating that other mechanisms are involved. Down-regulation of mAKAPß partially inhibited nuclear PKA activation upon ß1-AR stimulation, and drastically decreased nuclear PKA activation upon ß2-AR stimulation in the presence of PDE4 inhibition. Conclusions: ß1- and ß2-ARs differentially regulate nuclear PKA activity and ICER expression in cardiomyocytes. PDE4 insulates a mAKAPß-targeted PKA pool at the nuclear envelope that prevents nuclear PKA activation upon ß2-AR stimulation.

Standard and Strain Measurements by Echocardiography Detect Early Overloaded Right Ventricular Dysfunction: Validation against Hemodynamic and Myocyte Contractility Changes in a Large Animal Model.

BACKGROUND: Early detection of right ventricular (RV) failure is required to improve the management of patients with congenital heart diseases. The aim of this study was to validate echocardiography for the early detection of overloaded RV dysfunction, compared with hemodynamic and myocyte contractility assessment. METHODS: Using a porcine model reproducing repaired tetralogy of Fallot, RV function was evaluated over 4 months using standard echocardiography and speckle-tracking compared with hemodynamic parameters (conductance catheter). Sarcomere shortening and calcium transients were recorded in RV isolated myocytes. Contractile reserve (ΔEmax) was assessed by ß-adrenergic stimulation in vivo (dobutamine 5 µg/kg) and ex vivo (isoproterenol 100 nM). RESULTS: Six operated animals were compared with four age- and sex-matched controls. In the operated group, hemodynamic RV efficient ejection fraction was significantly decreased (29.7% [26.2%-34%] vs 42.9% [40.7%-48.6%], P < .01), and inotropic responses to dobutamine were attenuated (ΔEmax was 51% vs 193%, P < .05). Echocardiographic measurements of fraction of area change, tricuspid annular plane systolic excursion, tricuspid annular peak systolic velocity (S') and RV free wall longitudinal systolic strain and strain rate were significantly decreased. Strain rate, S', and tricuspid annular plane systolic excursion were correlated with ΔEmax (r = 0.75, r = 0.78, and r = 0.65, respectively, P < .05). These alterations were associated in RV isolated myocytes with the decrease of sarcomere shortening in response to isoproterenol and perturbations of calcium homeostasis assessed by the increase of spontaneous calcium waves. CONCLUSIONS: In this porcine model, both standard and strain echocardiographic parameters detected early impairments of RV function and cardiac reserve, which were associated with cardiomyocyte excitation-contraction coupling alterations.

Calmodulin kinase II inhibition limits the pro-arrhythmic Ca2+ waves induced by cAMP-phosphodiesterase inhibitors.

AIMS: A major concern of using phosphodiesterase (PDE) inhibitors in heart failure is their potential to increase mortality by inducing arrhythmias. By diminishing cyclic adenosine monophosphate (cAMP) hydrolysis, they promote protein kinase A (PKA) activity under ß-adrenergic receptor (ß-AR) stimulation, hence enhancing Ca(2+) cycling and contraction. Yet, cAMP also activates CaMKII via PKA or the exchange protein Epac, but it remains unknown whether these pathways are involved in the pro-arrhythmic effect of PDE inhibitors. METHODS AND RESULTS: Excitation-contraction coupling was investigated in isolated adult rat ventricular myocytes loaded with Fura-2 and paced at 1 Hz allowing coincident measurement of intracellular Ca(2+) and sarcomere shortening. The PDE4 inhibitor Ro 20-1724 (Ro) promoted the inotropic effects of the non-selective ß-AR agonist isoprenaline (Iso) and also spontaneous diastolic Ca(2+) waves (SCWs). PDE4 inhibition potentiated RyR2 and PLB phosphorylation at specific PKA and CaMKII sites increasing sarcoplasmic reticulum (SR) Ca(2+) load and SR Ca(2+) leak measured in a 0Na(+)/0Ca(2+) solution ± tetracaine. PKA inhibition suppressed all the effects of Iso ± Ro, whereas CaMKII inhibition prevented SR Ca(2+) leak and diminished SCW incidence without affecting the inotropic effects of Ro. Inhibition of Epac2 but not Epac1 diminished the occurrence of SCWs. PDE3 inhibition with cilostamide induced an SR Ca(2+) leak, which was also blocked by CaMKII inhibition. CONCLUSION: Our results show that PDE inhibitors exert inotropic effects via PKA but lead to SCWs via both PKA and CaMKII activation partly via Epac2, suggesting the potential use of CaMKII inhibitors as adjuncts to PDE inhibition to limit their pro-arrhythmic effects.

Reconciling depressed Ca2+ sparks occurrence with enhanced RyR2 activity in failing mice cardiomyocytes.

Abnormalities in cardiomyocyte Ca2+ handling contribute to impaired contractile function in heart failure (HF). Experiments on single ryanodine receptors (RyRs) incorporated into lipid bilayers have indicated that RyRs from failing hearts are more active than those from healthy hearts. Here, we analyzed spontaneous Ca2+ sparks (brief, localized increased in [Ca2+]i) to evaluate RyR cluster activity in situ in a mouse post-myocardial infarction (PMI) model of HF. The cardiac ejection fraction of PMI mice was reduced to ∼30% of that of sham-operated (sham) mice, and their cardiomyocytes were hypertrophied. The [Ca2+]i transient amplitude and sarcoplasmic reticulum (SR) Ca2+ load were decreased in intact PMI cardiomyocytes compared with those from sham mice, and spontaneous Ca2+ sparks were less frequent, whereas the fractional release and the frequency of Ca2+ waves were both increased, suggesting higher RyR activity. In permeabilized cardiomyocytes, in which the internal solution can be controlled, Ca2+ sparks were more frequent in PMI cells (under conditions of similar SR Ca2+ load), confirming the enhanced RyR activity. However, in intact cells from PMI mice, the Ca2+ sparks frequency normalized by the SR Ca2+ load in that cell were reduced compared with those in sham mice, indicating that the cytosolic environment in intact cells contributes to the decrease in Ca2+ spark frequency. Indeed, using an internal "failing solution" with less ATP (as found in HF), we observed a dramatic decrease in Ca2+ spark frequency in permeabilized PMI and sham myocytes. In conclusion, our data show that, even if isolated RyR channels show more activity in HF, concomitant alterations in intracellular media composition and SR Ca2+ load may mask these effects at the Ca2+ spark level in intact cells. Nonetheless, in this scenario, the probability of arrhythmogenic Ca2+ waves is enhanced, and they play a potential role in the increase in arrhythmia events in HF patients.

Sexual dimorphism of doxorubicin-mediated cardiotoxicity: potential role of energy metabolism remodeling.

BACKGROUND: Cardiovascular diseases are the major cause of mortality among both men and women with a lower incidence in women before menopause. The clinical use of doxorubicin, widely used as an antineoplastic agent, is markedly hampered by severe cardiotoxicity. Even if there is a significant sex difference in incidence of cardiovascular disease at the adult stage, it is not known whether a difference in doxorubicin-related cardiotoxicity between men and women also exists. The objective of this work was to explore the cardiac side effects of doxorubicin in adult rats and decipher whether signaling pathways involved in cardiac toxicity differ between sexes. METHODS AND RESULTS: After 7 weeks of doxorubicin (2 mg/kg per week), males developed major signs of cardiomyopathy with cardiac atrophy, reduced left ventricular ejection fraction and 50% mortality. In contrast, no female died and their left ventricular ejection fraction was only moderately affected. Surprisingly, neither global oxidation levels nor the antioxidant response nor the apoptosis signaling pathways were altered by doxorubicin. However, the level of total adenosine monophosphate-activated protein kinase was severely decreased only in males. Moreover, markers of mitochondrial biogenesis and cardiolipin content were strongly reduced only in males. To analyze the onset of the pathology, maximal oxygen consumption rate of left ventricular permeabilized fibers after 4 weeks of treatment was reduced only in doxorubicin-treated males. CONCLUSIONS: Altogether, these results clearly evidence sex differences in doxorubicin toxicity. Cardiac mitochondrial dysfunction and adenosine monophosphate-activated protein kinase seem as critical sites of sex differences in cardiotoxicity as evidenced by significant statistical interactions between sex and treatment effects.

Control of cytoplasmic and nuclear protein kinase A by phosphodiesterases and phosphatases in cardiac myocytes.

AIMS: The cAMP-dependent protein kinase (PKA) mediates ß-adrenoceptor (ß-AR) regulation of cardiac contraction and gene expression. Whereas PKA activity is well characterized in various subcellular compartments of adult cardiomyocytes, its regulation in the nucleus remains largely unknown. The aim of the present study was to compare the modalities of PKA regulation in the cytoplasm and nucleus of cardiomyocytes. METHODS AND RESULTS: Cytoplasmic and nuclear cAMP and PKA activity were measured with targeted fluorescence resonance energy transfer probes in adult rat ventricular myocytes. ß-AR stimulation with isoprenaline (Iso) led to fast cAMP elevation in both compartments, whereas PKA activity was fast in the cytoplasm but markedly slower in the nucleus. Iso was also more potent and efficient in activating cytoplasmic than nuclear PKA. Similar slow kinetics of nuclear PKA activation was observed upon adenylyl cyclase activation with L-858051 or phosphodiesterase (PDE) inhibition with 3-isobutyl-1-methylxantine. Consistently, pulse stimulation with Iso (15 s) maximally induced PKA and myosin-binding protein C phosphorylation in the cytoplasm, but marginally activated PKA and cAMP response element-binding protein phosphorylation in the nucleus. Inhibition of PDE4 or ablation of the Pde4d gene in mice prolonged cytoplasmic PKA activation and enhanced nuclear PKA responses. In the cytoplasm, phosphatase 1 (PP1) and 2A (PP2A) contributed to the termination of PKA responses, whereas only PP1 played a role in the nucleus. CONCLUSION: Our study reveals a differential integration of cytoplasmic and nuclear PKA responses to ß-AR stimulation in cardiac myocytes. This may have important implications in the physiological and pathological hypertrophic response to ß-AR stimulation.