The Role of Oxidative Phosphorylation in Müller Glia Functions and Survival

Purpose The importance of mitochondria to the energy production of Müller glia (MG), the main glial cells of the retina, is controversial. Previous studies showed MG are mainly glycolytic. Others challenge this view because MG are deficient in key glycolytic enzymes. Our goal is to potentially settle this debate by destabilizing the electron transport chain in MG mitochondria and assessing how retinal metabolism may be impacted. Methods MG that lack oxidative phosphorylation in vivo through destabilization of Complex IV were generated using GLASTCreERT2::Cox10fl/fl transgenic mice. Mice received daily tamoxifen injections for 5 consecutive days beginning at P30. Confirmation of recombination of the floxed Cox10 locus and enzyme activity was performed using PCR analysis of genomic DNA isolated from the retina and sequential cytochrome c oxidase (COX)/succinate dehydrogenase (SDH) histochemistry, respectively. Cell lysates from primary Müller cells were used for western blotting and total protein analysis. Full-field electroretinography (ERG) was performed to assess MG function from transgenic and wild-type mice in vivo. Scotopic ERGs were recorded (OcuScience® HMsERG, Xenotec Inc., Henderson, NV) in response to six light flash intensities ranging from −3 to 1 log cd x s/m2 on a dark background. Each stimulus was presented in a series of three. Data were analyzed with GraphPad Prism and ERG b-wave amplitudes were compared using a paired two-tailed Student’s t-test. The b-wave amplitude was measured from the trough of the a-wave to the peak of the b-wave. Results A 465bp DNA fragment amplified from genomic DNA of mutant mice, with no corresponding fragment from control, confirmed Cox10 locus recombination. Total protein analysis, with normalization to the mitochondrial protein VDAC1, showed lower levels of cytochrome c oxidase protein from mutant mice compared to controls. Scotopic ERG b-wave was not significantly different between mutant and wild-type age-controlled mice at all light intensities. No overt retinal abnormalities were observed in GLASTCreERT2::Cox10fl/fl transgenic mice. Conclusion Our results show that cre recombinase induction in GLASTCreERT2::Cox10fl/fl successfully inhibits cytochrome c oxidase activity in MG from adult mice. Our in vivo experiments suggest that oxidative phosphorylation is not necessary for Müller glia energy metabolism under physiological conditions.