Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, C071

Oral Communications

Hyperglycaemia adversely affects mitochondrial function in pancreatic islets

E. Haythorne1, A. I. Tarasov2, F. M. Ashcroft1

1. Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom. 2. OCDEM, University of Oxford, Oxford, United Kingdom.

Glucose metabolism is essential for glucose-stimulated insulin secretion from pancreatic β-cells. Metabolically generated ATP causes KATP channel closure, membrane depolarisation and calcium influx, which stimulates exocytosis. There is accumulating evidence to suggest that β-cell mitochondrial metabolism is impaired in type 2 diabetes mellitus (T2DM), and contributes to the reduced insulin secretion. As hyperglycaemia is common to all forms of diabetes, we aimed to determine if hyperglycaemia adversely affects mitochondrial function and thereby ATP production in pancreatic islets. In human patients and animal models of T2DM, hyperglycaemia often occurs in conjunction with elevated levels of circulating lipids, making it difficult to distinguish between the deleterious effects of glucose and lipids. We therefore used the βV59M mouse model in which hyperglycaemia is not accompanied by dyslipidaemia. In these mice, tamoxifen-inducible expression of a constitutively open KATP channel specifically in pancreatic β-cells inhibits insulin secretion and rapidly elevates blood glucose (>20 mmol/l). Diabetes was induced at 12 weeks of age and islets isolated 2 weeks later. Non-diabetic littermates were used as controls. Cellular Oxygen Consumption Rate (OCR) was monitored in real-time using the XF-24 extracellular flux analyser (Seahorse Bioscience, Inc.). Imaging the kinetics of ATP in β-cells was performed on a zoom microscope AxioZoom.V16 (Carl Zeiss) and utilised fluorescent sensor for Mg2+ (Mg-Green, ThermoFisher) as a surrogate for ATP. In comparison to islets from control mice, islets from diabetic mice showed a significant reduction in the % increase in OCR when ambient glucose was raised from 2 to 20 mmol/l (diabetic = 48.44±8.98 vs. control = 91.29±7.26% increase in OCR, p<0.005; n=9-12, 6 animals/genotype). Sequential addition of the ATP-synthase inhibitor oligomycin produced significantly less inhibition of OCR in islets from diabetic mice compared to control, indicating hyperglycaemia reduces the activity of ATP-synthase (diabetic = 88.72±6.43 vs control = 123.05±5.59% decrease in OCR, p<0.05; n=5-7, 3 animals/genotype). Subsequent addition of rotenone and antimycin A, which inhibit complex 1 and 3 of the electron transport chain respectively, supressed OCR to the same degree in both diabetic and control islets, indicating no difference in the level of mitochondrial leak. ATP increase in response to 20 mmol/l glucose was reduced in hyperglycaemic islets by 56±6%. Our results demonstrate that hyperglycaemia leads to impaired mitochondrial respiration and ATP production in pancreatic islets. Mitochondrial metabolism is essential for the stimulation of insulin secretion by glucose and therefore hyperglycaemia-induced mitochondrial dysfunction is likely to contribute to β-cell failure in T2DM. It remains to be determined if the deleterious effects of hyperglycaemia are limited to β-cells or if they occur in all islet cell types.

Where applicable, experiments conform with Society ethical requirements