Apoptosis in pre-diabetic heart is associated with increased sarcoplasmic reticulum (SR) Ca2+ leak, SR-mitochondria interplay and altered Mfn-2 and GRP75 expression

LOPEZ SOFIA; MATTIAZZI, A; FEDERICO M; ZAVALA MAITE; PALOMEQUE J; NUOZZI G; VILLA ABRILLE CELESTE

Mar del Plata

Congreso; Reunión Anual de la Asociación de Fisiología; 2018

SAFIS

Apoptosis in pre-diabetic heart is associated with increased sarcoplasmic reticulum (SR) Ca2+ leak, SR-mitochondria interplay and altered Mfn-2 and GRP75 expressionFederico M, Nuozzi G, Lopez S, Zabala M, Villa Abrille MC, Mattiazzi A, Palomeque J.We have previously reported that pre-diabetic heart presents Ca2+ mishandling, increased reactive oxygen species and CaMKII activity, swelling and depolarized mitochondria, enhanced proximity between sarcoplasmic reticulum (SR)-mitochondria and apoptosis. The communication (interplay) between SR and mitochondrion through Ca2+ ions is pivotal in either physiological or pathological situations. Several proteins are involved in this relationship and Ca2+ trafficking, like mitofusin 2 (Mfn-2), glucose regulated protein (GRP75) and voltage-dependent anion channel (VDAC). We proposed that in pre-diabetic mice hearts SR Ca2+ leak and the level of expression of these proteins affect the relationship SR-mitochondria, favoring Ca2+ trafficking and apoptosis as part of a CaMKII-dependent pathway.3H-Ryanodine (3HRy) binding assay and Mfn2, GRP75 and VDAC expression were measured in a pre-diabetic model induced by high fructose diet in WT, AC3I mice (which express a CaMKII inhibitor at heart level), and in S2814D knock-in mice hearts (which have the CaMKII phosphorylation site, Ser2814, mutated to Asp, mimicking a maximal and continuous phosphorylation of this site).3HRy binding assay revealed that WT pre-diabetic mice hearts had higher Vmax, in ftmol/mg protein, 47.9±5.3, than control, 33.6±4.2 and pre-diabetic AC3I mice, 32.2±5.9. Moreover, the Vmax in pre-diabetic S2814D knock-in mice hearts did not differ (65.8±9.8) from pre-diabetic WT mice. Mfn2 expression was significantly increased in pre-diabetic mice, either WT (53.6±12.4%) or AC3I (91.1±21.9%). GRP75 increased in WT pre-diabetic mice (38.3±9.7%), whereas this effect was prevented in pre-diabetic AC3I mice. In contrast, VDAC expression was similar in all conditions and mice lines.These results allow us to conclude that the increased SR Ca2+ leak is consequence of CaMKII activation and GRP75 and Mfn2 increased expression would be favoring SR-mitochondria proximity and Ca2+ traffic.