Background: The development of effective treatments for multiple sclerosis (MS), and in particular its progressive forms, is hampered by the lack of etiologically relevant cellular and animal models of human disease. Models that recapitulate the biological and pathological processes leading to the onset and progression of MS in patients are likely to afford better translational efficacy. Following the discovery of the NR1H3 p.Arg415Gln pathogenic mutation for progressive MS in two Canadian families, we developed a knock-in mouse model harboring a homologous mutation in the endogenous gene to provide a more physiologically relevant model of human MS.
Methods: Gene expression was evaluated in constitutive heterozygote (which recapitulates the human disease genotype) and homozygote Nr1h3 p.Arg413Gln knock-in mice on a C57BL/6 background, and compared to wild-type littermates. AmpliSeq Transcriptome Mouse Gene Expression kits analyzed on an Ion Proton sequencer were used to generate the gene expression profiles of spleen, liver, brain and spinal cord tissue from three-month-old male and female mice. Differential expression between genotypes was assessed with DESeq2, and Gene Ontologies pathways enrichment analysis performed with DAVID v6.8. Benjamini-Hochberg false discovery rate (FDR) correction for multiple testing was applied.
Results: Transcriptome analysis of spleen tissue from Nr1h3 p.Arg413Gln mice revealed 23 significantly dysregulated genes (FDR<0.05) with greater than a two-fold change in expression. These include CD5 antigen-like (Cd5l), complement component 6 (C6), procollagen C-endopeptidase enhancer 2 (Pcolce2), interleukin 22 receptor, alpha 2 (Il22ra2), and T cell immunoglobulin and mucin domain containing 4 (Timd4). Gene Ontology enrichment analysis support upregulation of cell cycle pathways and downregulation of immune system response in splenic cells. The liver transcriptome identified 27 significantly dysregulated genes with greater than a two-fold change in expression compared to wild-type littermates. Cd5l, Timd4, C-C motif chemokine receptor 3 (Ccr3), ADAM metallopeptidase domain 11 (Adam11) and macrophage expressed 1 (Mpeg1) were amongst those most significantly dysregulated. Enrichment analysis supported altered immune function with upregulation of sterol and steroid metabolic processes and downregulation of fatty acid biosynthesis and inflammatory and immune system responses. Although brain and spinal cord transcriptome profiles identified several genes significantly dysregulated in Nr1h3 mice compared to wild-type littermates (FDR<0.05), none presented greater than two-fold changes in gene expression.
Discussion: The analysis of the Nr1h3 p.Arg413Gln mouse model of MS suggests that the predominance of a pro-inflammatory over a healing or reparative phenotype, combined with deficiencies in myelination and remyelination, are the biological mechanisms implicated in the onset of MS and the development of a more severe progressive disease course observed in patients with NR1H3 mutations. Association of NR1H3 common variants with MS risk indicates that the disruption of these biological and immunological processes is not only informative for familial forms of disease but MS patients at large. Differences in transcriptome profiles underline the value of this model for the development and validation of novel therapeutic strategies and ultimately treatments with the potential to delay or even halt the onset of progressive MS and to ameliorate the severity of clinical symptoms.
Characterization of microglial transcriptomes in the brain and spinal cord of mice in early and late experimental autoimmune encephalomyelitis using a RiboTag strategy