The role of exchange protein directly activated by cAMP (EPAC) in cardiac remodeling

Cardiac arrhythmias remain a leading cause of mortality for patients afflicted by cardiac diseases, such as heart failure (HF). Sudden cardiac death is implicated in ~50% of deaths in HF, and remodeling of ion channels further leads to lethal arrhythmias. Neurohormonal activation plays a significant role in cardiac remodeling and progression of the disease. In this thesis, I investigated the role of exchange protein directly activated by cAMP (Epac) in cardiac remodeling.HF is associated with an increase in adrenergic drive, with plasma norepinephrine concentrations predictive of mortality outcomes. Reduction in the slowly activating delayed-rectifier potassium current (IKs) is commonly observed in HF-related remodeling and plays a role in arrhythmogenesis. I sought to identify the underlying mechanisms of IKs downregulation via sustained β-adrenergic stimulation. Using an in vitro guinea pig model, I identified a signaling pathway that proceeded through β1-adrenergic receptors and involved the activation of Epac1 protein. Epac1 increased intracellular calcium activation of the calcineurin/nuclear factor of activated T cell (NFAT) pathway to transcriptionally down-regulate the expression of KCNE1 subunits of IKs. Adenovirus-mediated knockdown of Epac1 in vitro demonstrated the central role of Epac 1 in regulating IKs in guinea pigs.In vivo administration of isoproterenol and a specific Epac activator significantly increased action potential duration, indicating repolarization abnormalities, while IKs, L-type calcium current (ICaL), and inward rectifier current (IK1) were significantly decreased. The signaling pathway identified in our in vivo study will assist in devising more effective approaches to prevent arrhythmias.HF is associated with fibrotic remodeling that creates a substrate for atrial fibrillation (AF). Fibroblasts regulate extracellular matrix (ECM) production and excess ECM deposition leads to fibrosis. Fibrosis is more prominent in the atrium and atrial fibroblasts are more responsive to fibrotic stimuli. I sought to determine the role of Epac in the fibrotic response. Epac1 expression was decreased in an experimental model of tachypacing-induced HF with AF. Incubation of atrial fibroblasts with a specific Epac activator decreased collagen mRNA expression. Profibrotic stimuli such as norepinephrine and TGFβ1 decreased Epac1 expression in atrial fibroblasts. Sustained β-adrenergic stimulation modulated collagen expression through activation of Epac1 via β2-adrenergic receptors. These findings demonstrated the different roles of Epac in cardiomyocytes versus fibroblasts in cardiac remodeling in the heart.Les arythmies cardiaques demeurent la principale cause de mortalité pour de nombreuses maladies cardiaques notamment l'insuffisance cardiaque (IC). La mort subite cardiaque est impliquée dans environ 50% des décès.Le remodelage ionique arythmogène provoque une altération des canaux ioniques qui participe de façon significative à l'apparition d'une arythmie fatale. L'activation neuro-hormonale joue aussi un rôle important dans le remodelage cardiaque et de la progression des maladies cardiovasculaires. Dans cette thèse de doctorat, nous avons étudié le rôle des protéines Epac dans le remodelage cardiaque au niveau du cœur.L'IC est associée à une activation du système nerveux sympathique et conséquemment à une stimulation adrénergique. Le taux de noradrénaline plasmatique est un excellent index pronostique, indépendant de la fraction d'éjection. La réduction du courant potassique cardiaque à rectification retardée (IKs) est couramment observé dans le remodelage liés à l'IC et joue un rôle dans l'arythmogénèse. Ainsi, l'objectif de ce projet était d'identifier les mécanismes sous-jacents impliqués dans la diminution d'IKs via la stimulation β-adrénergique soutenue. Les résultats obtenus avec un modèle in vitro ont révélé une voie de signalisation qui implique l'activation des récepteurs β1-adrénergiques et une protéine clé: l'Epac 1. L'Epac 1 augment l'activation du calcium intracellulaire de la voie calcineurine/NFAT pour réguler négativement l'expression de sous-unités KCNE1 d'IKs. In vitro, l'abolition de l'expression de l'Epac 1 par les adénovirus a démontré le rôle primordial d'Epac 1 dans la régulation d'IKs chez les cobayes. In vivo, l'administration de l'isoprotérénol et un activateur spécifique d'Epac ont considérablement augmenté la durée du potentielle d'action, indiquant des anomalies au niveau de la repolarization, tandis que l'IKs, le courant calcique de type L (ICaL) et le courant potassique à rectification entrante (IK1) ont diminué de façon significative. Les voies de signalisations identifiées dans cette étude aideront à élaborer des approches plus efficaces pour prévenir les troubles de rythmes cardiaques.L'IC est aussi associée à un remodelage fibrotique qui crée un substrat pour la fibrillation auriculaire (FA). Les fibroblastes cardiaques régulent la production et le dépôt de la matrice extracellulaire (MEC) et l'excès conduit à une fibrose. La fibrose est plus important dans les oreillettes et les fibroblastes auriculaires sont plus sensibles aux stimuli fibrotiques. Nous avons donc essayé de déterminer le rôle d'Epac dans la réponse fibrotique. L'expression d'Epac 1 est diminuée dans un modèle expérimental d'IC avec FA induit par une tachystimulation. L'incubation avec un activateur spécifique d'Epac diminue l'expression d'ARNm du collagène. De plus, les stimuli profibrotiques telles que la noradrénaline et le TGFβ1 diminuent l'expression d'Epac1 dans les fibroblastes auriculaires. La stimulation soutenue du système adrénergique module l'expression du collagène par l'activation de l'Epac1 via les récepteurs β2-adrénergiques. Ces résultats démontrent les différents rôles d'Epac dans les cardiomyocytes versus les fibroblastes dans le remodelage cardiaque

Exchange protein directly activated by cAMP mediates slow delayed-rectifier current remodeling by sustained β-adrenergic activation in guinea pig hearts

Prolonged β1-adrenoceptor stimulation suppresses IKs by downregulating KCNE1 mRNA and protein via Epac-mediated Ca(2+)/calcineurin/NFAT signaling. These results provide new insights into the molecular basis of K(+) channel remodeling under sustained adrenergic stimulation

Role of Small-Conductance Calcium-Activated Potassium Channels in Atrial Electrophysiology and Fibrillation in the Dog

BACKGROUND: Recent evidence points to functional Ca²⁺-dependent K⁺ (SK) channels in the heart that may govern atrial fibrillation (AF) risk, but the underlying mechanisms are unclear. This study addressed the role of SK channels in atrial repolarization and AF persistence in a canine AF model. METHODS AND RESULTS: Electrophysiological variables were assessed in dogs subjected to atrial remodeling by 7-day atrial tachypacing (AT-P), as well as controls. Ionic currents and single-channel properties were measured in isolated canine atrial cardiomyocytes by patch clamp. NS8593, a putative selective SK blocker, suppressed SK current with an IC₅₀ of ≈5 μmol/L, without affecting Na⁺, Ca²⁺, or other K⁺ currents. Whole-cell SK current sensitive to NS8593 was significantly larger in pulmonary vein (PV) versus left atrial (LA) cells, without a difference in SK single-channel open probability (P(o)), whereas AT-P enhanced both whole-cell SK currents and single-channel P(o). SK-current block increased action potential duration in both PV and LA cells after AT-P; but only in PV cells in absence of AT-P. SK2 expression was more abundant at both mRNA and protein levels for PV versus LA in control dogs, in both control and AT-P; AT-P upregulated only SK1 at the protein level. Intravenous administration of NS8593 (5 mg/kg) significantly prolonged atrial refractoriness and reduced AF duration without affecting the Wenckebach cycle length, left ventricular refractoriness, or blood pressure. CONCLUSIONS: SK currents play a role in canine atrial repolarization, are larger in PVs than LA, are enhanced by atrial-tachycardia remodeling, and appear to participate in promoting AF maintenance. These results are relevant to the potential mechanisms underlying the association between SK single-nucleotide polymorphisms and AF and suggest SK blockers as potentially interesting anti-AF drugs

Management of Renin-Angiotensin-Aldosterone System blockade in patients admitted to hospital with confirmed coronavirus disease (COVID-19) infection (The McGill RAAS-COVID- 19): A structured summary of a study protocol for a randomized controlled trial

International audienceObjectives: The aim of the RAAS-COVID-19 randomized control trial is to evaluate whether an upfront strategy of temporary discontinuation of renin angiotensin aldosterone system (RAAS) inhibition versus continuation of RAAS inhibition among patients admitted with established COVID-19 infection has an impact on short term clinical and biomarker outcomes. We hypothesize that continuation of RAAS inhibition will be superior to temporary discontinuation with regards to the primary endpoint of a global rank sum score. The global rank sum score has been successfully used in previous cardiovascular clinical trials.Trial design: This is an open label parallel two arm (1,1 ratio) randomized control superiority trial of approximately 40 COVID-19 patients who are on chronic RAAS inhibitor therapy

A Randomized Controlled Trial of Renin-Angiotensin-Aldosterone System Inhibitor Management in Patients Admitted in Hospital with COVID-19

International audienceBackground: Renin-angiotensin aldosterone system inhibitors (RAASi) are commonly used among patients hospitalized with a severe acute respiratory syndrome coronavirus 2 infection (COVID-19). We evaluated whether continuation versus discontinuation of RAASi were associated with short term clinical or biochemical outcomes. Methods: The RAAS-COVID-19 trial was a randomized, open label study in adult patients previously treated with RAASi who are hospitalized with COVID-19 (NCT04508985). Participants were randomized 1:1 to discontinue or continue RAASi. The primary outcome was a global rank score calculated from baseline to day 7 (or discharge) incorporating clinical events and biomarker changes. Global rank scores were compared between groups using the Wilcoxon test statistic and the negative binomial test (using incident rate ratio [IRR]) and the intention-totreat principle. Results: Overall, 46 participants were enrolled; 21 participants were randomized to discontinue RAASi and 25 to continue. Patients' mean age was 71.5 years and 43.5% were female. Discontinuation of RAASi, versus continuation, resulted in a non-statistically different mean global rank score (discontinuation 6 [standard deviation [SD] 6.3] vs continuation 3.8 (SD 2.5); p= 0.60). The negative binomial analysis identified that discontinuation increased the risk of adverse outcomes (IRR 1.67 [95% CI 1.06 to 2.62]; p=0.027); RAASi discontinuation increased brain natriuretic peptide (BNP) levels (% change from baseline: +16.7% vs.-27.5%; p= 0.024) and the incidence of acute heart failure (33% vs. 4.2%, p=0.016). Conclusion: RAASi continuation in participants hospitalized with COVID-19 appears safe; discontinuation increased BNP levels and may increase risk of acute heart failure; where possible, RAASi should be continued