Spatial lipidomics reveals altered lipid profiles in TMEM63A mutant rats with hypomyelination

Hypomyelinating leukodystrophies (HLDs) are genetic disorders characterized by deficient myelination. While TMEM63A variants are associated with HLD19, the specific lipid alterations in affected brain regions remain to be fully characterized. This study aimed to investigate the spatial distribution of lipid changes in a Tmem63a mutant rat model of hypomyelination. A homozygous Tmem63a c.500G > A p.(G167E) knock-in rat model (Tmem63a^G167E/G167E) was established. Brain sections from Tmem63a^G167E/G167E and Tmem63a^WT rats (n = 3/group) were analyzed using MALDI-MSI for lipid profiling across nine distinct brain regions. Myelin structure was characterized by transmission electron microscopy (TEM) and g-ratio quantification. Statistical analyses included Mann-Whitney U tests for g-ratio distributions and ROC analysis for feature screening. Out of 702 analyzed features, 124 were differentially expressed. Lipids constituted the most altered class (43 features), including 22 glycerophospholipid, 9 fatty acid, 5 sphingolipid, 5 sterol lipid, and 2 prenol lipid species. These alterations were predominantly observed in white matter-rich regions and gray-white matter junctions. TEM revealed thinner and less dense myelin sheaths in Tmem63a^G167E/G167E rats, with a reduced proportion of optimal g-ratios. This study provides a comprehensive spatial lipidomic characterization in a Tmem63a mutant rat model, revealing significant lipid alterations associated with hypomyelination. These findings offer new insights into the pathology of hypomyelination and highlight specific lipid species for future investigation.