Tricarboxylic acid cycle-sustained oxidative phosphorylation in isolated myelin vesicles

The Central Nervous System (CNS) function was shown to be fueled exclusively by oxidative phosphorylation (OXPHOS). This is in line with the sensitivity of brain to hypoxia, but less with the scarcity of the mitochondria in CNS. Consistently with the ectopic expression of FoF1-ATP synthase and the electron transfer chain in myelin, we have reported data demonstrating that isolated myelin vesicles (IMV) conduct OXPHOS. It may suggest that myelin sheath could be a site for the whole aerobic degradation of glucose. In this paper, we assayed the functionality of glycolysis and of TCA cycle enzymes in IMV purified from bovine forebrain. We found the presence and activity of all of the glycolytic and TCA cycle enzymes, comparable to those in mitochondria-enriched fractions, in the same experimental conditions. IMV also contain consistent carbonic anhydrase activity. These data suggest that myelin may be a contributor in energy supply for the axon, performing an extra-mitochondrial aerobic OXPHOS. The vision of myelin as the site of aerobic metabolism may shed a new light on many demyelinating pathologies, that cause an a yet unresolved axonal degeneration and whose clinical onset coincides with myelin development completion.