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

Aims/introduction: 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 Ca²⁺ overload and its pathological significance.

Materials and methods: 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.

Results: 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 Ca²⁺ level under the condition of pressure overload was 47% higher and Ca²⁺ retention capacity in MAM-containing crude mitochondria isolated before the pressure overloading was 21% lower in OLETF than in LETO (all P-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.

Conclusions: The findings suggest that 90-kDa AMPD3 localized in the endoplasmic reticulum-mitochondria interface promotes formation of the MAM, inducing mitochondrial Ca²⁺ overload and dysfunction in type 2 diabetes hearts.