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Marin Gantner, kevin eade, Edith Aguilar, Mitchell Prins, Alec Johnson, Martin Friedlander; Mitochondrial activity in the retina relies on glycolysis independent of substrate availability. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3013.
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© ARVO (1962-2015); The Authors (2016-present)
The neural retina has some of the highest biosynthetic and ATP demands in the body. To meet these demands the retina uses a large glycolytic flux as well as high levels of mitochondrial oxidative phosphorylation. The retina is unique in that blocking glycolysis impairs mitochondrial function even when adequate substrates are provided. We are therefore investigating the mechanisms underlying the reliance of mitochondrial function on glycolysis.
To assess glycolytic and mitochondrial activity we monitored the extracellular acidification and oxygen consumption rates in ex vivo mouse retinas, as well as human stem cell derived eye cups using a Seahorse Flux Analyzer. To inhibit different stages of glycolysis, the retina was treated with either 2-deoxyglucose (2DG), a competitive inhibitor of hexokinase, or iodoacetate, an inhibitor of glyceraldehyde 3-phosphate dehydrogenase (GAPDH). To determine which cell types have a similar response, primary Müller glia, retinal pigment epithelium (RPE) and cells derived from mature human eye cups were tested in a similar manner.
Even in the presence of mitochondrial substrates, pyruvate and glutamine, the oxidative capacity of the retina decreases rapidly when exposed to 2DG. This phenomenon is observed both in the ex vivo mouse retina as well as the human eye cups. Treatment with iodoacetate also reduced oxidative phosphorylation, but to a lesser extent than 2DG. Treatment of primary Müller glia and RPE with 2DG does not impair mitochondrial activity. However, cells derived from the human eye cups maintain partial sensitivity to both 2DG and iodoacetate.
The retina has a unique reliance on glucose. In the absence of glycolysis, oxygen consumption in the mitochondria is blocked even when supplied the downstream product of glycolysis (pyruvate). Given that inhibition of GAPDH has a similar (albeit lesser) effect, indicates that it is not glucose signaling alone, but the flux through glycolysis that is responsible for influencing mitochondrial activity. Unlike primary Müller glia and RPE, human eye cups show a similar sensitivity, as do cells derived from the eye cups. These data indicate 1) that human eye cups are a relevant model to study metabolism in the retina and 2) that the phenomenon is not dependent on the tissue being intact or on metabolic dependency between cell types.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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