Abstract
Leukodystrophies (LD) are rare inherited disorders that primarily affect the white matter (WM) of the central nervous system. The large heterogeneity of LD results from the diversity of the genetically determined defects that interfere with glial cells functions. Astrocytes have been identified as the primary target of LD with cystic myelin breakdown including those related to mutations in the ubiquitous translation initiation factor eIF2B. EIF2B is involved in global protein synthesis and its regulation under normal and stress conditions. Little is known about how eIF2B mutations have a major effect on WM. We performed a transcriptomic analysis using fibroblasts of 10 eIF2B-mutated patients with a severe phenotype and 10 age matched patients with other types of LD in comparison to control fibroblasts. ANOVA was used to identify genes that were statistically significantly differentially expressed at basal state and after ER-stress. The pattern of differentially expressed genes between basal state and ER-stress did not differ significantly among each of the three conditions. However, 70 genes were specifically differentially expressed in eIF2B-mutated fibroblasts whatever the stress conditions tested compared to controls, 96% being under-expressed. Most of these genes were involved in mRNA regulation and mitochondrial metabolism. The 13 most representative genes, including genes belonging to the Heterogeneous Nuclear Ribonucleoprotein (HNRNP) family, described as regulators of splicing events and stability of mRNA, were dysregulated during the development of eIF2B-mutated brains. HNRNPH1, F and C mRNA were over-expressed in foetus but under-expressed in children and adult brains. The abnormal regulation of HNRNP expression in the brain of eIF2B-mutated patients was concomitant with splicing dysregulation of the main genes involved in glial maturation such as PLP1 for oligodendrocytes and GFAP in astrocytes. These findings demonstrate a developmental deregulation of splicing events in glial cells that is related to abnormal production of HNRNP, in eIF2B-mutated brains.
Highlights
Leukodystrophies (LD) represent a heterogeneous group of rare genetic disorders primarily affecting the white matter (WM) of the central nervous system (CNS)
The demyelinating group of LD includes mainly defects in i) peroxisomal or lysosomal enzymatic activities important for myelin biogenesis and maintenance, or ii) astrocytes functions responsible for progressive cystic myelin breakdown. This last group of vacuolating LD involves mainly genes expressed in astrocytes such as GFAP (Glial Fibrillary Acidic Protein) and MLC1 (Megalencephalic Leukoencephalopathy with subcortical Cysts 1) or genes ubiquitously expressed as the five EIF2B1-5 genes encoding the general translation eukaryotic initiation factor 2B
We described here for the first time genes involved in the mRNA splicing machinery as actors in the abnormal maturation of glial cells observed in the eIF2B-mutated patient brains
Summary
Leukodystrophies (LD) represent a heterogeneous group of rare genetic disorders primarily affecting the white matter (WM) of the central nervous system (CNS). The hypomyelinating group of LD includes diseases due to defects in myelin production or quality. The demyelinating group of LD includes mainly defects in i) peroxisomal or lysosomal enzymatic activities important for myelin biogenesis and maintenance, or ii) astrocytes functions responsible for progressive cystic myelin breakdown. This last group of vacuolating LD involves mainly genes expressed in astrocytes such as GFAP (Glial Fibrillary Acidic Protein) and MLC1 (Megalencephalic Leukoencephalopathy with subcortical Cysts 1) or genes ubiquitously expressed as the five EIF2B1-5 genes encoding the general translation eukaryotic initiation factor 2B (eIF2B)
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