Hypothesis of an Energetic Function for Myelin

Abstract

Nervous system is a great oxygen consumer, but the site of oxygen absorption has remained elusive. Four proteomic studies have shown that the respiratory complexes I to V may be expressed in isolated myelin. Myelin is an outgrowth of glial cells, surrounding many axons in multiple spires both in peripheral and central nervous system. Recent quantitative analyses strongly support the daring hypothesis that myelin is functional in aerobic ATP production, to supply the neuron with chemical energy. A vision of myelin sheath as a structure devoted to the oxygen absorbance for glucose combustion in nervous system thank to its enormous surface, would be also supported by an impressive series of characteristics and properties of myelin that do not presently find an explanation, all of which are herein examined.

A Novel Hypothesis About Mechanisms Affecting Conduction Velocity of Central Myelinated Fibers

“…Thus, it is apparent that a crucial element of maintained axonal conduction velocity is the energy charge of the axon, and that gap junctions normally favor the maintenance of a normal energy charge. These findings strongly support, even if they still do not demonstrate, a novel hypothesis on the interaction between oligodendrocytes and the axons they wrap that some of us recently proposed [16]. Specifically, we hypothesize that the oligodendrocytes serve as energy suppliers to the axons, synthesizing ATP and transferring it to the axons they wrap through gap junctions.…”

“…Moreover, we explored the possibility that oligodendrocyte support of the axon involves energy metabolism. The latter hypothesis has been recently proposed by some of us [16] and stems among else (1) from previous research by some of us [22,23] showing that the myelin sheath is capable of aerobic metabolism and ATP synthesis and (2) from the consideration that damage to the oligodendrocytes not only slows down conduction velocity, but also causes a morphological degeneration of the axons they wrap [6]. The latter finding strongly suggests that myelin provides some form of metabolic support to the axons, the nature of which has not been elucidated yet.…”

“…Given the above mentioned considerations, this finding prompted us to hypothesize that the glial-axonal interaction may involve the transfer of ATP from the myelin sheath to the axon [16]. In the crayfish, myelin accounts for an astounding 30-100% of the oxygen consumption of the axon-glial sheath unit [9].…”

“…Moreover, it seeks to find preliminary data on whether or not the trophic support of myelin may involve transfer of ATP from oligodendrocytes to axons, as recently hypothesized by some of us [16].…”

Diffusion Tensor Imaging Mapping of Brain White Matter Pathology in Mitochondrial Optic Neuropathies

“…35 Most interesting, recent studies propose that myelin itself has an autonomous respiratory activity, thus linking white matter integrity to defective oxidative phosphorylation. 36 An interesting and strong correlation was found between diffusivity parameters and age for patients with OPA1-DOA, but not for those with LHON or healthy controls, suggesting a diseasespecific association. The absence of a correlation with "apparent" disease duration (.05 Ͻ P Ͻ .07 in the same areas) and the difficulty of accurately defining the onset of this insidious disease in clinical practice suggest that OPA1-DOA may be a congenital disease.…”