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

Abstract

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 Ca 2+ 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 Ca 2+ level under the condition of pressure overload was 47% higher and Ca 2+ 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 Ca 2+ overload and dysfunction in type 2 diabetes hearts.

Mitochondria-associated endoplasmic reticulum membrane (MAM): a dark horse for diabetic cardiomyopathy treatment

“…Disruption of Ca 2+ homeostasis in the mitochondria results in Ca 2+ overload, which impairs mitochondrial function. For example, the upregulation of myocardial adenosine monophosphate deaminase (AMPD) promotes MAM formation, triggering mitochondrial Ca 2+ overload and cardiac dysfunction in type 2 diabetes [ 58 ]. However, this study revealed only a linear relationship between AMPD expression and mitochondrial Ca 2+ overload in MAM, without providing insight into the specific mechanism by which AMPD regulates Ca 2+ overload.…”

So close, yet so far away: the relationship between MAM and cardiac disease

“…Intriguingly, before pressure overload, the Ca 2+ retention capacity in MAM-containing crude mitochondria of OLETF was 21% lower than that of LETO. Moreover, in vitro transfection of FLAG-AMPD3 in cells promotes the formation of MAM, resulting in m Ca 2+ overload, mitochondrial dysfunction and impaired mitochondrial respiration ( 37 ).…”