Effect of blue light on extramitochondrial oxidative metabolism in rod outer segments

Purpose: The effect of short wavelength blue light was studied on the ectopic oxidative phosphorylation (OXPHOS) that has been described in retinal rod outer segments (OS) [1]. Blue light can damage retinal tissue [2] and photoreceptors causing significant production of reactive oxygen intermediates (ROI) in the OS [3]. On the other hand OXPHOS is considered the major source of ROI. Methods: Both the expression and the activity of the OXPHOS proteins in blue light-treated (BL) as well as in control mice were investigated by luminometry, oximetry, electron transmission microscopy and in situ histochemistry on retinal sections. ATP production and oxygen consumption were evaluated in OS purified from BL or control retinas. Results: In BL OS, oxygen consumption in the presence of NADH and fumarate decreased by 50 and 57% respectively with respect to control OS. In the presence of succinate respiratory rates were similar to those observed in control OS. Moreover BL OS synthesized a negligible amount of ATP in the presence of NADH, succinate or fumarate. No differences were noticed in respiratory chain complex I and ATP synthase expression by TEM. Preliminary histochemical results of in situ respiratory chain activity show a correlation with the general decrease in OS function. Conclusions: Data suggest that blue light-induced oxidative stress observed in OS may be due to impairment of extramitochondrial OXPHOS. Data can shed light on the importance of antioxidant treatment to prevent rod degeneration. 1 D. Calzia, S. Barabino, P. Bianchini, G. Garbarino, M. Oneto, F. Caicci, A. Diaspro, C. Tacchetti, L. Manni, S. Candiani, S. Ravera, A. Morelli, C. Enrico Traverso and I. Panfoli, "New findings in ATP supply in rod outer segments: insights for retinopathies," (2013) Biology of the cell 105(8), 345-358. 2. A. Wenzel, C. Grimm, M. Samardzija and C. E. Reme, "Molecular mechanisms of light-induced photoreceptor apoptosis and neuroprotection for retinal degeneration,(2005) " Progress in retinal and eye research 24(2), 275-306. 3. C. Roehlecke, U. Schumann, M. Ader, C. Brunssen, S. Bramke, H. Morawietz and R. H. Funk, "Stress reaction in outer segments of photoreceptors after blue light irradiation," (2013) PLoS One 8(9), e71570.