In prediabetic hearts, SR-Ca2+ leak, mitochondria Ca2+ overload, and SR-mitochondria miscommunication culminate in apoptosis

PORTIANSKY, ENRIQUE L.; MATTIAZZI, ALICIA; LOPEZ, SOFIA; VILLA ABRILLE, CELESTE; FEDERICO, MARILÉN; ZAVALA, MAITE; PALOMEQUE, JULIETA

Beijing

Congreso; 2019 XXIII ISHR WORLD CONGRESS; 2019

In pre-diabetic hearts, SR Ca2+ leak, mitochondria Ca2+ overload, and SR-mitochondria miscommunication culminate in apoptosis Federico M, Lopez S, Zabala M, Villa Abrille MC, Mattiazzi A, Palomeque J.Pre-diabetic hearts presents Ca2+ mishandling, Ca2+-calmodulin kinase II (CaMKII) hyperactivity, mitochondria dysfunction, enhanced proximity between sarcoplasmic reticulum (SR)-mitochondria and apoptosis. The SR-mitochondrion interplay is pivotal in patho-physiological situations. Among the proteins that are involved in these microdomains, mitofusin 2 (Mfn-2), glucose regulated protein (GRP75) and voltage-dependent anion channel (VDAC) could be involved in the miscommunication between organelles. We hypothesize that in pre-diabetic hearts SR Ca2+ leak is due to increased Ryanodine receptors 2 (RyR2) activity via CaMKII-dependent pathway. Moreover, the increased expression level of the mentioned proteins affects the SR-mitochondria interplay. We measured spontaneous Ca2+ release events (SCaRE), 3H-Ryanodine ([3H]Ry) binding assay, mitochondria Ca2+ retention capacity (CRC) and morphology, and Mfn2, GRP75 and VDAC expression in pre-diabetic model induced by high fructose diet (FRD) in WT, AC3I (which express a CaMKII inhibitor at heart level), and in S2814D mice hearts [which have the CaMKII phosphorylation site (Ser2814) mutated to Asp, behaving as constitutive pseudo-phosphorylation].In isolated myocytes, confocal images showed significantly increase in SCaRE in WT FRD with respect to WT CD, while AC3I FRD and CD did not showed difference. [3H]Ry binding assay revealed that WT FRD presented higher Bmax (ftmol/mg protein, 40.8±2.1) than WT CD (29.9±4.1) and AC3I FRD (23.7±4.4). Moreover, in S2814D CD, Bmax was similar (46.32±4.69) to WT FRD. In isolated mitochondria, CRC decreased in WT FRD with respect to WT CD (2.78±0.39 vs 4.26±0.73). Transmission Electron Microscopy photographs showed that mitochondria area (1.15±0.02 vs 1.03±0.01) and diameter (1.16±0.004 vs 1.11±0.004) were decrease in WT FRD whereas feret diameter (1.26±0.01 vs 1.17±0.0045) and roundness (1.36±0.004 vs 1.26±0.001) was closer to 1 than WT CD. A clear disarrangement in WT FRD tissue was evident with respect to WT CD. These parameters were not different in AC3I CD or FRD. Surprisingly, no difference were found in neither Mfn-2, GRP75 nor VDAC expression in any line mice or condition. We conclude that CaMKII would be involved in SR Ca2+ leak in FRD due to increased RyR2 activity and in the changes in mitochondria morphology. SR-mitochondria proximity would favor the decreased CRC. However, Mfn-2, GRP75 and VDAC whole heart expression were not dependent on FRD or CaMKII activity.