Adenosine monophosphate deaminase in the endoplasmic reticulum–mitochondria interface promotes mitochondrial Ca²⁺ overload in type 2 diabetes rat hearts

<jats:title>Abstract</jats:title><jats:sec><jats:title>Aims/Introduction</jats:title><jats:p>We previously showed that upregulation of myocardial adenosine monophosphate deaminase (AMPD) is associated with pressure overload‐induced diastolic dysfunction in type 2 diabetes hearts. Here, we examined involvement of AMPD localized in the endoplasmic reticulum–mitochondria interface in mitochondrial Ca<jats:sup>2+</jats:sup> overload and its pathological significance.</jats:p></jats:sec><jats:sec><jats:title>Materials and Methods</jats:title><jats:p>We used type 2 diabetes Otsuka Long–Evans Tokushima Fatty rats (OLETF) and non‐diabetes Long–Evans Tokushima Otsuka Fatty rats (LETO) as well as AMPD3‐overexpressing H9c2 cells and human embryonic kidney 293 cells.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>OLETF, but not LETO, showed diastolic dysfunction under the condition of phenylephrine‐induced pressure overload. The levels of 90‐kDa AMPD3 in outer mitochondrial membranes/endoplasmic reticulum and mitochondria‐associated endoplasmic reticulum membrane (MAM) fractions were significantly higher in OLETF than in LETO. The area of the MAM quantified by electron microscopic analysis was 57% larger, mitochondrial Ca<jats:sup>2+</jats:sup> level under the condition of pressure overload was 47% higher and Ca<jats:sup>2+</jats:sup> retention capacity in MAM‐containing crude mitochondria isolated before the pressure overloading was 21% lower in OLETF than in LETO (all <jats:italic>P</jats:italic>‐values <0.05). Transfection of FLAG‐AMPD3 in cells resulted in significant enlargement of the MAM area, and impairment in pyruvate/malate‐driven adenosine triphosphate‐stimulated and uncoupler‐stimulated mitochondrial respiration compared with those in control cells.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>The findings suggest that 90‐kDa AMPD3 localized in the endoplasmic reticulum–mitochondria interface promotes formation of the MAM, inducing mitochondrial Ca<jats:sup>2+</jats:sup> overload and dysfunction in type 2 diabetes hearts.</jats:p></jats:sec>