Oxydative Metabolism in Optic Nerve Myelin: New Perspectives in Hereditary Optic Neuropathies.

Myelin from both central and peripheral nervous system was shown to express functional FoF1-ATP synthase and respiratory chain complexes that conduct an aerobic metabolism, to supportthe axonal energy demand. Along this view, it has been proposed that the trophic action of myelin that has been recognized to cause degeneration of chronically demyelinated is a major and not replaceable energetic role. Optic nerve displays great metabolic demand. Its demyelisation is implicated in Leber’s hereditary optic neuropathy (LHON), one of the most frequent hereditary optic neuropathies caused by mutations in respiratory Complex I. The specific damage of retinal ganglion cells (RGC) in LHON has not been clarified yet. In this work, by biochemical analyses, we show that myelin isolated from bovine optic nerve, conducts an extra-mitochondrial oxidative phosphorylation, displaying active respiratory complexes I to IV, as well as oxygen consumption and ATP synthesis activity, sensitive to specific inhibitors. Immunohystochemical microscopy shows that myelin basic protein and respiratory complex I colocalize in optic nerve sections. Data support the notion that mutations of Complex I would impair oxidative phosphorylation, not only in neuronal mitochondria, but also in myelin of the optic nerve. This may shed new light on some optic neuropathies.