INTRACELLULAR SIGNALING PATHWAY OF CARDIAC APOPTOSIS IN THE PREDIABETIC HEART

SOMMESE L; FEDERICO M; ZANUZZI C; PORTIANSKY E; DEDMAN J; KAETZEL M; WEHRENS XH ; MATTIAZZI A; PALOMEQUE J

Baltimore

Congreso; Biophysical Society 59th Annual meeting; 2015

Biophysical Society

Apoptosis is one of the more important steps leading to cardiac dysfunction and heart failure (HF), and this disease occurs more frequently in people with type 2 diabetes than in the general population. However, in impaired glucose tolerance (IGT), which is the major clinical characteristic of the prediabetic state, apoptosis has not been previously evaluated in the heart. Moreover, CaMKII is a well recognized molecule involved in cardiac apoptosis, hypertrophy, Ca2+ mishandling and arrhythmias. Even less known is the connection between CaMKII and IGT. The aim of the present study was to evaluate the presence of cardiac apoptosis in an IGT model and its putative link with CaMKII activity. IGT model was induced by a fructose-rich diet (control, CD; and fructose, FRD; rats or mice). In these animals, echocardiography, biochemical studies, reactive oxygen species (ROS), Ca2+i measurements, mitochondrial swelling and mitochondria membrane potential measurements were performed. FRD rats showed decreased contractility and increased hypertrophy (echocardiography) associated with increased CaMKII (P-CaMKII 191.6±18.3%, P-Thr17 of phospholamban 227.6±28.6%), and ROS (185.4±28.6%) with respect to CD rats (100%). Moreover, the apoptotic ratio Bax/Bcl2 was increased in FRD vs CD rats (273.6±39.7%) as well as TUNEL positive nuclei.. Isolated mitochondria from FRD rats showed significant more swelling (DO 0.34±0.05 CD vs 0.53±0.03 FRD) and enhanced membrane depolarization than CD mitochondria. Moreover, isolated myocytes from FRD rats showed a significant increase in sarcoplasmic reticulum (SR) Ca2+ leak vs CD myocytes. FRD SR-AIP mice (which express the CaMKII autocamtide inhibitory peptide [AIP] selectively at the SR membranes) showed less TUNEL positive nuclei than their matched FRD control mice. In addition, FRD control mice co-treated with fructose and tempol, a membrane permeable ROS scavenger, also showed less apoptosis than the one induced by the treatment with fructose alone. SR Ca2+ leak was also prevented in either FRD SR-AIP mice or CD mice co-treated with tempol. On the other hand, mitochondria swelling could be also prevented in S2814A mice, which ryanodine receptor (RyR2) cannot be phosphorylated by CaMKII. The results would indicate that the signaling apoptotic cascade in IGT hearts involves mitochondria damage by SR Ca2+ leak produced by CaMKII-dependent phosphorylation of RyR2. CaMKII would be activated by both, Ca2+ and ROS.