Multiple sclerosis (MS) is an inflammatory disease characterized by myelin loss and neuronal dysfunction. Despite the aggregation observed in some families, pathogenic mutations have remained elusive. In this study we describe the identification of NR1H3 p.Arg415Gln in seven MS patients from two multi-incident families presenting severe and progressive disease, with an average age at onset of 34 years. Additionally, association analysis of common variants in NR1H3 identified rs2279238 conferring a 1.35-fold increased risk of developing progressive MS. The p.Arg415Gln position is highly conserved in orthologs and paralogs, and disrupts NR1H3 heterodimerization and transcriptional activation of target genes. Protein expression analysis revealed that mutant NR1H3 (LXRA) alters gene expression profiles, suggesting a disruption in transcriptional regulation as one of the mechanisms underlying MS pathogenesis. Our study indicates that pharmacological activation of LXRA or its targets may lead to effective treatments for the highly debilitating and currently untreatable progressive phase of MS.

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Protein kinase D (PKD), also called protein kinase C (PKC)μ, is a serine-threonine kinase that is involved in diverse areas of cellular function such as lymphocyte signaling, oxidative stress, and protein secretion. After identifying a putative PKD phosphorylation site in the Toll/IL-1R domain of TLR5, we explored the role of this kinase in the interaction between human TLR5 and enteroaggregative Escherichia coli flagellin in human epithelial cell lines. We report several lines of evidence that implicate PKD in TLR5 signaling. First, PKD phosphorylated the TLR5-derived target peptide in vitro, and phosphorylation of the putative target serine 805 in HEK 293T cell-derived TLR5 was identified by mass spectrometry. Furthermore, mutation of serine 805 to alanine abrogated responses of transfected HEK 293T cells to flagellin. Second, TLR5 interacted with PKD in coimmunoprecipitation experiments, and this association was rapidly enhanced by flagellin treatment. Third, pharmacologic inhibition of PKC or PKD with Gö6976 resulted in reduced expression and secretion of IL-8 and prevented the flagellin-induced activation of p38 MAPK, but treatment with the PKC inhibitor Gö6983 had no significant effects on these phenotypes. Finally, involvement of PKD in the p38-mediated IL-8 response to flagellin was confirmed by small hairpin RNA-mediated gene silencing. Together, these results suggest that phosphorylation of TLR5 by PKD may be one of the proximal elements in the cellular response to flagellin, and that this event contributes to p38 MAPK activation and production of inflammatory cytokines in epithelial cells.

Genetic variants in the purinergic receptors P2RX4 and P2RX7 have been shown to affect susceptibility to multiple sclerosis (MS). In this study we set out to evaluate whether rare coding variants of major effect could also be identified in these purinergic receptors. Sequencing analysis of P2RX4 and P2RX7 in 193 MS patients and 100 controls led to the identification of a rare three variant haplotype (P2RX7 rs140915863:C>T (p.T205M), P2RX7 rs201921967:A>G (p.N361S) and P2RX4 rs765866317:G>A (p.G135S)) segregating with disease in a multi-incident family with six family members diagnosed with MS (LOD=3.07). Functional analysis of this haplotype in HEK293 cells revealed impaired P2X7 surface expression (p<0.01), resulting in over 95% inhibition of ATP-induced pore function (p<0.001) and a marked reduction in phagocytic ability (p<0.05). In addition, transfected cells showed 40% increased peak ATP-induced inward current (p<0.01), and a greater Ca 2+ response to the P2X4 135S variant compared to wild type (p<0.0001). Our study nominates rare genetic variants in P2RX4 and P2RX7 as major genetic contributors to disease, further supporting a role for these purinergic receptors in MS and suggesting the disruption of transmembrane cation channels leading to impairment of phagocytosis as the pathological mechanisms of disease.

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system characterized by myelin loss and neuronal dysfunction. Although the majority of patients do not present familial aggregation, Mendelian forms have been described. We performed whole-exome sequencing analysis in 132 patients from 34 multi-incident families, which nominated likely pathogenic variants for MS in 12 genes of the innate immune system that regulate the transcription and activation of inflammatory mediators. Rare missense or nonsense variants were identified in genes of the fibrinolysis and complement pathways ( PLAU , MASP1 , C2 ), inflammasome assembly ( NLRP12 ), Wnt signaling ( UBR2 , CTNNA3 , NFATC2 , RNF213 ), nuclear receptor complexes ( NCOA3 ), and cation channels and exchangers ( KCNG4 , SLC24A6 , SLC8B1 ). These genes suggest a disruption of interconnected immunological and pro-inflammatory pathways as the initial event in the pathophysiology of familial MS, and provide the molecular and biological rationale for the chronic inflammation, demyelination and neurodegeneration observed in MS patients.