R-Ras1 and R-Ras2 Expression in Anatomical Regions and Cell Types of the Central Nervous System.

Since the optic nerve is one of the most myelinated tracts in the central nervous system (CNS), many myelin diseases affect the visual system. In this sense, our laboratory has recently reported that the GTPases R-Ras1 and R-Ras2 are essential for oligodendrocyte survival and maturation. Hypomyelination produced by the absence of one or both proteins triggers axonal degeneration and loss of visual and motor function. However, little is known about R-Ras specificity and other possible roles that they could play in the CNS. In this work, we describe how a lack of R-Ras1 and/or R-Ras2 could not be compensated by increased expression of the closely related R-Ras3 or classical Ras. We further studied R-Ras1 and R-Ras2 expression within different CNS anatomical regions, finding that both were more abundant in less-myelinated regions, suggesting their expression in non-oligodendroglial cells. Finally, using confocal immunostaining colocalization, we report for the first time that R-Ras2 is specifically expressed in neurons. Neither microglia nor astrocytes expressed R-Ras1 or R-Ras2. These results open a new avenue for the study of neuronal R-Ras2's contribution to the process of myelination.

R-Ras1 and R-Ras2 Are Essential for Oligodendrocyte Differentiation and Survival for Correct Myelination in the Central Nervous System.

Rapid and effective neural transmission of information requires correct axonal myelination. Modifications in myelination alter axonal capacity to transmit electric impulses and enable pathological conditions. In the CNS, oligodendrocytes (OLs) myelinate axons, a complex process involving various cellular interactions. However, we know little about the mechanisms that orchestrate correct myelination. Here, we demonstrate that OLs express R-Ras1 and R-Ras2. Using female and male mutant mice to delete these proteins, we found that activation of the PI3K/Akt and Erk1/2-MAPK pathways was weaker in mice lacking one or both of these GTPases, suggesting that both proteins coordinate the activity of these two pathways. Loss of R-Ras1 and/or R-Ras2 diminishes the number of OLs in major myelinated CNS tracts and increases the proportion of immature OLs. In R-Ras1-/- and R-Ras2-/--null mice, OLs show aberrant morphologies and fail to differentiate correctly into myelin-forming phenotypes. The smaller OL population and abnormal OL maturation induce severe hypomyelination, with shorter nodes of Ranvier in R-Ras1-/- and/or R-Ras2-/- mice. These defects explain the slower conduction velocity of myelinated axons that we observed in the absence of R-Ras1 and R-Ras2. Together, these results suggest that R-Ras1 and R-Ras2 are upstream elements that regulate the survival and differentiation of progenitors into OLs through the PI3K/Akt and Erk1/2-MAPK pathways for proper myelination.SIGNIFICANCE STATEMENT In this study, we show that R-Ras1 and R-Ras2 play essential roles in regulating myelination in vivo and control fundamental aspects of oligodendrocyte (OL) survival and differentiation through synergistic activation of PI3K/Akt and Erk1/2-MAPK signaling. Mice lacking R-Ras1 and/or R-Ras2 show a diminished OL population with a higher proportion of immature OLs, explaining the observed hypomyelination in main CNS tracts. In vivo electrophysiology recordings demonstrate a slower conduction velocity of nerve impulses in the absence of R-Ras1 and R-Ras2. Therefore, R-Ras1 and R-Ras2 are essential for proper axonal myelination and accurate neural transmission.

Target and untargeted GC-MS based metabolomic study of mouse optic nerve and its potential in the study of neurological visual diseases.

The optic nerve is made of highly specialized neurons and the energetic supply to their axons is crucial due to their great demand. The energy comes basically through the oxidative phosphorylation in the mitochondria, supported by glial cells metabolism. Mitochondrial dysfunction is a shared feature encountered within the optic neuropathies, including Leber's Hereditary Optic Neuropathy, Leigh's Syndrome, or Kjer's syndrome. In an effort to investigate the metabolic alterations produced within the optic nerve in a mutant mouse model of Neurological Visual Disease (NVD), a rapid, robust, and efficient one-single phase extraction methodology has been developed and validated for the GC-MS platform. Once the method was successfully validated for lactic acid and pyruvic acid as markers of an adequate optic nerve function, the protocol was applied to unveil the metabolomic signature of the wild-type mouse optic nerve. Along the chromatographic profile of the optic nerve, 94 peaks were identified and, to our knowledge, for the first time. Afterwards, a targeted metabolomics analysis was performed to quantify lactic acid and pyruvic acid in the NDV mice group (n = 8) and its corresponding wild-type (n = 8). Finally, an untargeted metabolomic study was carried out and univariate and multivariate data analyses showed 34 compounds modified in the optic nerve of the mouse with NVD mutation. Then, the metabolic reaction network of the identified metabolites highlighted alterations in the catabolism of proteins, TCA cycle, and urea cycle, reflecting a mitochondrial energetic dysfunction. Taken together, this metabolomic study has proven to be suited for the study of optic neuropathies.