Quantitative Imaging of Electron Transfer Flavoprotein Autofluorescence Reveals Lipid Partitioning Dynamics in Pancreatic Islets

Abstract

Pancreatic islet beta-cells are sensitive to plasma nutrients in the body. Excess levels of glucose and fatty acids lead to glucolipotoxicity, resulting in declined beta-cell function and survival - a major component of type 2 diabetes mellitus (T2DM). Despite significant knowledge of glucose-stimulated insulin secretion, the effect of fatty acids remains uncertain. Here we show a novel way to measure a response from fatty acids in ex vivo pancreatic islets using quantitative autofluorescence imaging of a Complex II flavin, electron transfer flavoprotein (ETF). Together with two-photon imaging of NAD(P)H and our previously reported lipoamide dehydrogenase (LipDH) autofluorescence, we found that the electron transport chain is nutrient supply-driven and dominated by Complex I rather than Complex II. These data are consistent with beta-cells being predominantly glucose responsive. Furthermore, we found an oxidized ETF redox response in the presence of excess glucose-stimulation, suggesting a shift in lipid partitioning from fatty acid oxidization to synthesis above 10 mM glucose. Our results demonstrate that ETF autofluorescence can in part be used as readout of islet response to fat. Overall, we anticipate our ETF imaging platform to be a starting point for more sophisticated biological studies that will explore mechanisms of mitochondrial dysfunction in T2DM.