Reduced reticulum-mitochondria Ca2+ transfer is an early and reversible trigger of mitochondrial dysfunctions in diabetic cardiomyopathy

Abstract

Type 2 diabetic cardiomyopathy features Ca²⁺ signaling abnormalities, notably an altered mitochondrial Ca²⁺ handling. We here aimed to study if it might be due to a dysregulation of either the whole Ca²⁺ homeostasis, the reticulum-mitochondrial Ca²⁺ coupling, and/or the mitochondrial Ca²⁺ entry through the uniporter. Following a 16-week high-fat high-sucrose diet (HFHSD), mice developed cardiac insulin resistance, fibrosis, hypertrophy, lipid accumulation, and diastolic dysfunction when compared to standard diet. Ultrastructural and proteomic analyses of cardiac reticulum-mitochondria interface revealed tighter interactions not compatible with Ca²⁺ transport in HFHSD cardiomyocytes. Intramyocardial adenoviral injections of Ca²⁺ sensors were performed to measure Ca²⁺ fluxes in freshly isolated adult cardiomyocytes and to analyze the direct effects of in vivo type 2 diabetes on cardiomyocyte function. HFHSD resulted in a decreased IP3R-VDAC interaction and a reduced IP3-stimulated Ca²⁺ transfer to mitochondria, with no changes in reticular Ca²⁺ level, cytosolic Ca²⁺ transients, and mitochondrial Ca²⁺ uniporter function. Disruption of organelle Ca²⁺ exchange was associated with decreased mitochondrial bioenergetics and reduced cell contraction, which was rescued by an adenovirus-mediated expression of a reticulum-mitochondria linker. An 8-week diet reversal was able to restore cardiac insulin signaling, Ca²⁺ transfer, and cardiac function in HFHSD mice. Therefore, our study demonstrates that the reticulum-mitochondria Ca²⁺ miscoupling may play an early and reversible role in the development of diabetic cardiomyopathy by disrupting primarily the mitochondrial bioenergetics. A diet reversal, by counteracting the MAM-induced mitochondrial Ca²⁺ dysfunction, might contribute to restore normal cardiac function and prevent the exacerbation of diabetic cardiomyopathy.

Keywords: Ca2+ flux; Diabetic cardiomyopathy; Metabolic syndrome disease; Mitochondria-associated membranes MAM; Protein database; Proteomic analysis of cardiac MAM proteome.