Proceedings of The Physiological Society

Mitochondria: Form and function (London, UK) (2017) Proc Physiol Soc 38, C06

Oral Communications

Krebs cycle intermediates drive abnormal metabolic signalling in response to hypoxia in the diabetic heart

M. Dodd1, M. Sousa Fialho1, C. Montes Aparicio1, M. Kerr1, K. Timm1, J. Griffin2, D. Tyler1, L. Heather1

1. University of Oxford, Oxford, United Kingdom. 2. University of Cambridge, Cambridge, United Kingdom.

M. Dodd1, MdaL. Sousa Fialho1, C. Montes Aparicio1, M. Kerr1, K. Timm1, J. Griffin2, D. Tyler1, Lisa Heather1 1 Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, United Kingdom. 2 Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom. Hypoxia-inducible factor 1α (HIF1α) is activated following myocardial infarction, and is critical for cell survival in hypoxia. In cancer, changes in Krebs cycle intermediates have also been shown to modify HIF1α stabilisation. We have previously shown that type 2 diabetic hearts have decreased tolerance of hypoxia. We questioned whether abnormal metabolism could prevent HIF1α activation in diabetes, and whether Krebs cycle intermediates were mediating this maladaptation. Methods: Type 2 diabetes was generated in male Wistar rats by 6 weeks of high fat feeding in combination with a low dose intraperitoneal injection of streptozotocin (25mg/kg) after 2 weeks. Rats were terminally anaesthetized using an intraperitoneal injection of sodium pentobarbital (150 mg/kg bodyweight, Euthatal). Insulin resistance was also modelled in cell culture, using HL1-cardiomyocytes cultured with glucose, lipids and insulin. Results: Type 2 diabetic hearts have decreased HIF1α protein accumulation following myocardial ischemia, which correlated negatively with plasma fatty acid concentrations and positively with myocardial succinate concentrations. In insulin-resistant cardiomyocytes, HIF signalling and downstream metabolic adaptation was suppressed in response to hypoxia. Impaired HIF1α stabilisation was due to increased degradation of the protein in hypoxia, as inhibition of the proteasome or inhibition of the regulatory HIF hydroxylases was able to increase HIF1α. Increased HIF1α degradation in diabetes was due to abnormal metabolism. We have found that long chain fatty acids prevented HIF1α accumulation in a concentration-dependent manner, which could be reversed by blocking fatty acid uptake. Succinate promotes HIF stabilisation by inhibiting the HIF hydroxylases, however, we have found that fatty acids suppressed succinate accumulation during hypoxia. Supplementing succinate concentrations in cells overrides the fatty acid-mediated inhibition of HIF1α, in a concentration-dependent manner. Finally, pharmacologically inhibiting the HIF hydroxylases promoted HIF1α accumulation and improved cardiac function following ischemia-reperfusion in diabetic rats. In conclusion, elevated fatty acids in type 2 diabetes prevent HIF1α accumulation by decreasing succinate concentrations in hypoxia.

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