Abstract
Oligodendrocytes (OLs) generate lipid-rich myelin membranes that wrap axons to enable efficient transmission of electrical impulses. Using a RIT1 knockout mouse model and in situ high-resolution matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) coupled with MS-based lipidomic analysis to determine the contribution of RIT1 to lipid homeostasis. Here, we report that RIT1 loss is associated with altered lipid levels in the central nervous system (CNS), including myelin-associated lipids within the corpus callosum (CC). Perturbed lipid metabolism was correlated with reduced numbers of OLs, but increased numbers of GFAP+ glia, in the CC, but not in grey matter. This was accompanied by reduced myelin protein expression and axonal conduction deficits. Behavioral analyses revealed significant changes in voluntary locomotor activity and anxiety-like behavior in RIT1KO mice. Together, these data reveal an unexpected role for RIT1 in the regulation of cerebral lipid metabolism, which coincide with altered white matter tract oligodendrocyte levels, reduced axonal conduction velocity, and behavioral abnormalities in the CNS.
| Original language | English |
|---|---|
| Article number | e20384 |
| Journal | Heliyon |
| Volume | 9 |
| Issue number | 10 |
| DOIs | |
| State | Published - Oct 2023 |
Bibliographical note
Publisher Copyright:© 2023
Funding
We would like to Mrs. Dana Napier for performing immunohistochemical-staining on tissue slices at the Markey Cancer Center. This work was supported by National Institutes of Health ( NIH ) grants R01 NS102196, R56NS124707 and Kentucky Spinal Cord and Head Injury Trust grant 16-1 awarded to Douglas A. Andres, NIH grant R01 MH125903 to Weikang Cai, NIH grant R01 AG033649 to Olivier Thibault, NIH grants R35 NS116824 and P01 NS097197 to Matthew S. Gentry, Hilaree N. Frazier was supported by NIH / NIA training grant T32AG057461, and Lyndsay E. A. Young was support by NIH / NCI F99CA2664165. This research was also supported by funding from the University of Kentucky Markey Cancer Center and the NIH-funded Biospecimen Procurement & Translational Pathology Shared Resource Facility of the University of Kentucky Markey Cancer Center P30 CA177558. The mammalian brain is highly enriched in heterogeneous lipids, where they play important roles as structural and signaling molecules. Lipids contribute to the structural integrity of cell and organelle membranes, control cellular signaling pathways, and regulate gene expression, neurogenesis, and neural communication [55,56]. The use of quantitative mass spectrometry-based lipidomic analysis first suggested widespread CNS lipid alterations in RIT1KO mice. These results were further buttressed by state-of-the-art MALDI-MSI analysis, permitting high-resolution spatial resolution of a more limited set of lipid species, and together demonstrate that RIT1 loss results in complex alterations in the abundance and spatial distribution of a diverse array of lipid species within the mouse brain. Notable changes included a significant reduction in glycosphingolipids (GSLs) and sulfated galactocerebrosides, sulfatides, which are major lipid components of myelin [44] within the corpus callosum, suggesting that impaired lipid biosynthesis resulting from RIT1 deletion may compromise myelin integrity. Indeed, LFB staining was significantly reduced in the CNS of RIT1KO mice, including a quantitative reduction in staining within the corpus callosum, further supporting a role for RIT1 signaling in maintaining myelin levels and myelinated axons within the corpus callosum (Fig. 3D). However, alterations in lipid levels within the brain of RIT1KO mice have implications beyond myelination. Transcriptional differences in lipid metabolic genes have been noted between quiescent and activated NSCs [39,57], with fatty acid oxidation being required for NSC proliferation [58,59], and lipid metabolic defects serving to disrupt NSC proliferation [40]. Interesting, the MALDI-MSI data suggests that fatty acid levels in the hippocampus of RIT1KO mice are reduced (Fig. 1B; see m/z 255, 279, and 281). Additional studies are needed to determine whether modulation of CNS lipids contributes to RIT1KO-dependent regulation of hippocampal neurogenesis following contusive brain injury, exercise stimulus, and/or IGF-1 signaling [34,37,38].We would like to Mrs. Dana Napier for performing immunohistochemical-staining on tissue slices at the Markey Cancer Center. This work was supported by National Institutes of Health (NIH) grants R01 NS102196, R56NS124707 and Kentucky Spinal Cord and Head Injury Trust grant 16-1 awarded to Douglas A. Andres, NIH grant R01 MH125903 to Weikang Cai, NIH grant R01 AG033649 to Olivier Thibault, NIH grants R35 NS116824 and P01 NS097197 to Matthew S. Gentry, Hilaree N. Frazier was supported by NIH/NIA training grant T32AG057461, and Lyndsay E. A. Young was support by NIH/NCI F99CA2664165. This research was also supported by funding from the University of Kentucky Markey Cancer Center and the NIH-funded Biospecimen Procurement & Translational Pathology Shared Resource Facility of the University of Kentucky Markey Cancer Center P30 CA177558.
| Funders | Funder number |
|---|---|
| National Institutes of Health (NIH) | P30 CA177558, R01 NS102196, R56NS124707 |
| National Institutes of Health (NIH) | |
| National Institute on Aging | T32AG057461 |
| National Institute on Aging | |
| National Childhood Cancer Registry – National Cancer Institute | F99CA2664165 |
| National Childhood Cancer Registry – National Cancer Institute | |
| Kentucky Spinal Cord and Head Injury Research Trust | R01 AG033649, R35 NS116824, R01 MH125903, P01 NS097197, 16-1 |
| Kentucky Spinal Cord and Head Injury Research Trust | |
| University of Kentucky Markey Cancer Center | |
| National Society of Collegiate Scholars | 39,57, 58,59, 34,37,38 |
| National Society of Collegiate Scholars |
Keywords
- Endothelin-1
- Lipidomics
- MALDI-MSI
- Myelin
- Myelination
- Oligodendrocyte progenitor cell
- Ras
- Rit GTPase
ASJC Scopus subject areas
- General