Metformin does not prevent the alteration of reticulum-mitochondria Ca2+ coupling and the progression towards early diabetic cardiomyopathy with HFpEF in a diet-induced mouse model of T2D

Abstract

Diabetic cardiomyopathy, as a major complication of type 2 diabetes (T2D), shows a rising prevalence nowadays. Reticulum-mitochondria Ca2+ uncoupling was recently reported as an early but reversible trigger of cardiac dysfunction using a diet-induced murine model of DCM with heart failure and preserved ejection fraction (HFpEF). Metformin is the first-line treatment prescribed to treat T2D patients, with known protective effects against myocardial infarction. We here aimed to determine if metformin could hinder the alteration of the reticulum-mitochondria Ca2+ coupling and the cardiac dysfunction induced by a high-fat high-sucrose diet (HFHSD) in mice. Mice were either fed a HFHSD or a standard diet for 16 weeks. During the last 6 weeks of diet, HFHSD mice received a daily oral gavage with either metformin or vehicle. Reticulum-mitochondria Ca2+ coupling was assessed: 1) structrally by proximity ligation assay between IP3R and VDAC; and 2) functionally by Ca2+ imaging of the mitochondrial Ca2+ sensor, 4mtD3cpv, expressed by intramyocardial adenoviral injection. Echocardiography was perfomed on lightly anesthetized animals to assess systolic function and hypertrophy. Metformin rescued the glucose tolerance and insulinemia in HFHSD mice, but partially for the cardiac insulin resistance. However, in the HFHSD cardiomyocyte, metformin did not preclude the reduction of the proximity between IP3R and VDAC, and of the histamine-driven reticulum-mitochondria Ca2+ transfer through the IP3R-VDAC complex. Echocardiography also revealed no prevention of HFHSD-induced cardiac hypertrophy and strain rate reduction. Our data report that 6 weeks of metformin treatment did not preserve the reticulum-mitochondria Ca2+ coupling in the diabetic heart and did not prevent the progression towards early DCM with HFpEF.