β-Adrenergic induced SR Ca 2+ leak is mediated by an Epac-NOS pathway

Abstract

Cardiac β-adrenergic receptors (β-AR) and Ca2+-Calmodulin dependent protein kinase (CaMKII) regulate both physiological and pathophysiological Ca2+ signaling. Elevated diastolic Ca2+ leak from the sarcoplasmic reticulum (SR) contributes to contractile dysfunction in heart failure and to arrhythmogenesis. β-AR activation is known to increase SR Ca2+ leak via CaMKII-dependent phosphorylation of the ryanodine receptor. Two independent and reportedly parallel pathways have been implicated in this β-AR-CaMKII cascade, one involving exchange protein directly activated by cAMP (Epac2) and another involving nitric oxide synthase 1 (NOS1). Here we tested whether Epac and NOS function in a single series pathway to increase β-AR induced and CaMKII-dependent SR Ca2+ leak. Leak was measured as both Ca2+ spark frequency and tetracaine-induced shifts in SR Ca2+, in mouse and rabbit ventricular myocytes. Direct Epac activation by 8-CPT (8-(4-chlorophenylthio)-2′-O-methyl-cAMP) mimicked β-AR-induced SR Ca2+ leak, and both were blocked by NOS inhibition. The same was true for myocyte CaMKII activation (assessed via a FRET-based reporter) and ryanodine receptor phosphorylation. Inhibitor and phosphorylation studies also implicated phosphoinositide 3-kinase (PI3K) and protein kinase B (Akt) downstream of Epac and above NOS activation in this pathway. We conclude that these two independently characterized parallel pathways function mainly via a single series arrangement (β-AR-cAMP-Epac-PI3K-Akt-NOS1-CaMKII) to mediate increased SR Ca2+ leak. Thus, for β-AR activation the cAMP-PKA branch effects inotropy and lusitropy (by effects on Ca2+ current and SR Ca2+-ATPase), this cAMP-Epac-NOS pathway increases pathological diastolic SR Ca2+leak. This pathway distinction may allow novel SR Ca2+ leak therapeutic targeting in treatment of arrhythmias in heart failure that spare the inotropic and lusitropic effects of the PKA branch.

S-nitrosylation of connexin43 hemichannels elicits cardiac stress–induced arrhythmias in Duchenne muscular dystrophy mice

“…Recent studies indicate that β-adrenergic signaling promotes NO production in cardiomyocytes (29,(56)(57)(58). In addition to the canonical pathway of NO-induced protein kinase G activation, NO also induces direct posttranslational modification of thiol groups in specific cysteine residues on various proteins via S-nitrosylation (59).…”

miR-139-5p inhibits isoproterenol-induced cardiac hypertrophy by targetting c-Jun

“…The β-AR signaling pathway, which is classically activated by catecholamines, is one of the well-known pathways in the induction of cardiac hypertrophy [ 12 , 13 ]. The activation of β-AR regulates cardiac excitation–contraction and leads to the increase in heart rate and cardiomyocyte contractility [ 21–23 ]. The hyperactivation of β-AR results in cardiac hypertrophy, fibrosis, senescence, inflammation, and cardiomyocyte apoptosis and necrosis [ 24–29 ].…”

Arrhythmogenic Mechanisms in Heart Failure: Linking β-Adrenergic Stimulation, Stretch, and Calcium

“…A second pathway, independent of cAMP, involves PI3K and Akt as upstream activators of nNOS inducing CaMKII activation via nitrosylation ( Curran et al, 2014 ). A recent study suggested that the Epac and nNOS pathway are interdependent and function largely in series ( Pereira et al, 2017 ).…”