title: Role of CaMKII and ROS in rapid pacing-induced apoptosis.
abstract: Tachycardia promotes cell death and cardiac remodeling, leading to congestive heart failure. However, the underlying mechanism of 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, Ca(2+) and reactive oxygen species (ROS). However, whether these molecules mediate 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 8Hz for 1hr. RP at 5 and 8Hz decreased myocyte viability by 58±3% and 75±6% (n=24), respectively, compared to cells maintained at 0.5Hz, 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 Ca(2+) 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 Ca(2+) release, and ruthenium red used to prevent Ca(2+) entry into the mitochondria prevented RP-induced cell death, whereas PI3K inhibition with Wortmannin 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 Ca(2+) release and mitochondrial Ca(2+) 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.
authors.affiliation: Centro de Investigaciones Cardiovasculares, Conicet La Plata, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata 1900, Argentina.
authors.forename: Marisa
authors.initials: M
authors.lastname: Sepúlveda
authors.forename: Luis A
authors.initials: LA
authors.lastname: Gonano
authors.forename: Tom G
authors.initials: TG
authors.lastname: Back
authors.forename: S R Wayne
authors.initials: SR
authors.lastname: Chen
authors.forename: Martin
authors.initials: M
authors.lastname: Vila Petroff
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism*; D016923:Cell Death; D002470:Cell Survival; D051379:Mice; D008822:Mice, Transgenic; D032383:Myocytes, Cardiac / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013610:Tachycardia / Q000378:metabolism*; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D017382:Reactive Oxygen Species; D000077191:Wortmannin
keywords: Apoptosis; CaMKII; Calcium; Heart failure; ROS; Tachycardia