Proceedings of The Physiological Society

Mitochondria: Form and function (London, UK) (2017) Proc Physiol Soc 38, C11

Oral Communications

Type 2 diabetic mitochondria overcome fatty acyl CoA inhibition, but have reduced respiration

M. Kerr1, S. Rohling`1, M. Sousa Fialho1, C. Lopez1, D. Tyler1, L. Heather1

1. Department of physiology, anatomy and genetics, University of Oxford, Oxford, Oxfordshire, United Kingdom.

Introduction: The type 2 diabetic mellitus (T2DM) heart is energetically dysfunctional as seen by a reduced phosphocreatine/adenosine triphosphate (ATP) ratio in humans. The vast majority (95%) of cardiac ATP is generated in the mitochondria through oxidative phosphorylation, making them the most likely candidate for energetic dysfunction. One protein stands out as the key regulatory point in oxidative phosphorylation, with over 70% of control; the adenine nucleotide translocase (ANT). This protein is potently inhibited by fatty acyl CoAs which may link the high fat phenotype and defective energetics of the T2DM heart. We tested whether dysfunctional energetics in the T2DM heart could be traced to altered kinetics around the ANT. Methods: Type 2 diabetes was induced in Wistar rats by feeding of a high fat diet for 7 weeks. Two weeks into this, rats were given a low dose injection of streptozotocin. At 7 weeks, rats were sacrificed under terminal anaesthesia (overdose of isoflurane inhalation). Cardiac subsarcolemmal and interfibrillar mitochondria were isolated from diabetic and control rat hearts. Mitochondrial respiration was measured using a Clark type oxygen electrode. Results: The presence of palmitoyl CoA (P-CoA) competitively inhibited respiration in control mitochondria, shown by a 2.5 fold (136.1±15.7 vs 57.8±8.1) increase in Km in the presence of P-CoA. This was eliminated by uncoupling the mitochondria, demonstrating that inhibition was centred on the phosphorylation apparatus. Diabetic mitochondria were far more resilient to fatty acyl CoA inhibition with no significant increase in Km (82.4±7.3 vs 65.1±6.9). Diabetic mitochondria had a 20% reduction in ADP stimulated respiration compared to controls (110.5±7.8 vs 78.2±5.9) when respired in the absence of fatty acids (on glutamate, pyruvate and malate). There was a very strong correlation (P<0.005) between sensitivity to fatty acyl CoA, and ADP stimulated respiration, indicating that the two phenomena may have the same cause. Despite these phenomena being intrinsically linked by the ANT, there was no change to either ANT1 or 2 expression in diabetic mitochondria (as measured by Western blotting (n=7)). Conclusion: Type 2 diabetic mitochondria showed differential kinetics around the ANT for both P-CoA regulation, and adenine nucleotide transport (as measured by respiratory rates) despite no change to either ANT 1 or 2 expression. Together these data indicate that kinetics around the ANT, the key protein in respiratory control are altered in type 2 diabetes. This provides a potential cause for the dysfunctional energetics observed in the type 2 diabetic heart.

Where applicable, experiments conform with Society ethical requirements