Role of CaMKII and ROS in rapid pacing-induced apoptosis

SEPÚLVEDA MARISA; GONANO LUIS; TOMG. BACK; S.R.WAYNE CHEN; VILA PETROFF MARTÍN

JOURNAL OF MOLECULAR AND CELLULAR CARDIOLOGY

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2013 p. 135 - 145

0022-2828

Tachycardia promotes cell death and cardiac remodeling, leading to congestive heart failure.However, the underlyingmechanismof tachycardia- or rapid pacing (RP)-induced cell death remains unknown.Myocyte loss by apoptosis is recognized as a critical factor in the progression to heart failure and simulation of tachycardia by RP has been shown to increase the intracellular levels of at least two potentially proapoptotic molecules, Ca2+ and reactive oxygen species (ROS). However,whether thesemoleculesmediate tachycardia- or RP-induced cell death has yet to be determined. The aim of this study was to examine the subcellular mechanisms underlying RP-induced apoptosis. For this purpose rat ventricular myocytes were maintained quiescent or paced at 0.5, 5 and 8 Hz for 1 hr. RP at 5 and 8 Hz decreased myocyte viability by 58 ± 3% and 75 ± 6% (n = 24), respectively, compared to cells maintained at 0.5 Hz, and increased caspase-3 activity and Bax/Bcl-2 ratio, indicative of apoptosis. RP-induced cell death and apoptosis were prevented when pacing protocols were conducted in the presence of either the ROS scavenger,MPG, or nifedipine to reduce Ca2+ entry or the CaMKII inhibitors, KN93 and AIP. Consistently, myocytes from transgenic mice expressing a CaMKII inhibitory peptide (AC3-I) were protected against RP-induced cell death. Interestingly, tetracaine and carvedilol used to reduce ryanodine receptor (RyR) diastolic Ca2+ release, and ruthenium red used to prevent Ca2+ entry into the mitochondria prevented RP-induced cell death, whereas PI3K inhibition withWortmannin exacerbated pacing-induced cell mortality. We conclude that CaMKII activation and ROS production are involved in RP-induced apoptosis. Particularly, our results suggest that CaMKII-dependent posttranslational modifications of the cardiac ryanodine receptor (RyR) leading to enhanced diastolic Ca2+ release and mitochondrial Ca2+ overload could be the underlying mechanism involved. We further show that RP simultaneously activates a protective cascade involving PI3K/AKT signaling which is however, insufficient to completely suppress apoptosis.