Rnd3 is necessary for the correct oligodendrocyte differentiation and myelination in the central nervous system

Abstract

Rho small GTPases are proteins with key roles in the development of the central nervous system. Rnd proteins are a subfamily of Rho GTPases characterized by their constitutive activity. Rnd3/RhoE is a member of this subfamily ubiquitously expressed in the CNS, whose specific functions during brain development are still not well defined. Since other Rho proteins have been linked to the myelination process, we study here the expression and function of Rnd3 in oligodendrocyte development. We have found that Rnd3 is expressed in a subset of oligodendrocyte precursor cells and of mature oligodendrocytes both in vivo and in vitro. We have analyzed the role of Rnd3 in myelination using mice lacking Rnd3 expression (Rnd3 gt/gt mice), showing that these mice exhibit hypomyelination in the brain and a reduction in the number of mature and total oligodendrocytes in the corpus callosum and striatum. The mutants display a decreased expression of several myelin proteins and a reduction in the number of myelinated axons. In addition, myelinated axons exhibit thinner myelin sheaths. In vitro experiments using Rnd3 gt/gt mutant mice showed that the differentiation of the precursor cells is altered in the absence of Rnd3 expression, suggesting that Rnd3 is directly required for the differentiation of oligodendrocytes and, in consequence, for the correct myelination of the CNS. This work shows Rnd3 as a new protein involved in oligodendrocyte maturation, opening new avenues to further study the function of Rnd3 in the development of the central nervous system and its possible involvement in demyelinating diseases.

Rnd3 Expression is Necessary to Maintain Mitochondrial Homeostasis but Dispensable for Autophagy

“…Our previous results demonstrated that Rnd3 deficient mice show alterations both in the structure and the function of the CNS (Mocholi et al, 2011;Ballester-Lurbe et al, 2015;Kaur et al, 2020;Madrigal et al, 2021;Marfull-Oromi et al, 2021). To determine if there were defects also at the subcellular level, we analyzed brain sections at the subventricular zone (SVZ) by electron microscopy (Figure 1A), where we had previously described several alterations (Ballester-Lurbe et al, 2015).…”

“…We have previously described that mice lacking Rnd3 expression show defects in the development of the CNS ( Mocholi et al, 2011 ; Ballester-Lurbe et al, 2015 ; Kaur et al, 2020 ; Madrigal et al, 2021 ). We now describe some subcellular phenotypes, such as increased content of lipid droplets and accumulation of mitochondria with irregular morphology, that might be compatible with defects in autophagy or mitophagy, as those described in neurodegenerative diseases like Alzheimer’s, Parkinson’s, Huntington’s diseases and amyotrophic lateral sclerosis ( Xu et al, 2021 ).…”

“…Brains from 15 days old wildtype and Rnd3 gt/gt mice (P15) were removed from the braincase after cervical dislocation and fixed overnight in 2% paraformaldehyde/2.5% glutaraldehyde, as previously described ( Madrigal et al, 2021 ). Ultra-thin (0.07 μm) sections corresponding to the subventricular zone (SVZ) were obtained for the corresponding ultrastructural analysis.…”

Investigating the Protective Effects of a Citrus Flavonoid on the Retardation Morphogenesis of the Oligodendroglia-like Cell Line by Rnd2 Knockdown

“…It is therefore presumed that Rnd proteins promote myelination. Research groups, including our own, report that Rnd2 and Rnd3 are involved in the regulation of myelination, at least in part [ 25 , 50 ]. Despite the increased expression of Rnd2 protein [ 25 ], it is unclear whether Rnd3 and Rnd1 are upregulated as brain development proceeds [ 50 ].…”

“…Research groups, including our own, report that Rnd2 and Rnd3 are involved in the regulation of myelination, at least in part [ 25 , 50 ]. Despite the increased expression of Rnd2 protein [ 25 ], it is unclear whether Rnd3 and Rnd1 are upregulated as brain development proceeds [ 50 ]. It is thought that the activities of Rnd3 and probably Rnd1, acting cooperatively with those of Rnd2, are needed to trigger myelination.…”