Eae19, a new locus on rat chromosome 15 regulating experimental autoimmune encephalomyelitis

Abstract

Multiple sclerosis (MS) and its animal model, myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (MOG-EAE), share a complex genetic predisposition with contributions from the major histocompatibility complex class II genes and many other genes. Linkage mapping in F(2) crosses between the susceptible DA rat strain and the resistant ACI or BN rat strains in various models of autoimmune neuroinflammation have repeatedly displayed suggestive linkage to a region on rat chromosome 15. A direct study of this region was undertaken in congenic strains by transferring resistant ACI alleles to the susceptible DA background. Phenotypic analysis demonstrated lower maximal and cumulative EAE scores in the DA.ACI-D15Rat6-D15Rat71 (C15), DA.ACI-D15Rat6-D15Rat48, D15Rat126-D15Rat71 (C15R3b), and DA.ACI-D15Rat23-D15rat71 (C15R4) strains compared to the parental DA rat strain. Linkage analysis was then performed in a (DA x PVG.AV1)F(7) advanced intercross line, resulting in a LOD score of 4.7 for the maximal EAE score phenotype at the peak marker D15Rat71 and a confidence interval of 13 Mb, overlapping with the congenic fragment defined by the C15R3b and the C15R4 strains. Thus, a new MOG-EAE locus with the designation Eae19 is identified on rat chromosome 15. There are 32 confirmed or predicted genes in the confidence interval, including immune-responsive gene 1 and neuronal ceroid lipofuscinose gene 5. Definition of loci such as Eae19 enables the characterization of genetically regulated, evolutionary conserved disease pathways in complex neuroinflammatory diseases.

Figure 1.—

A schematic of the distal part of rat chromosome 15, aligned with the intervals defined in the congenic strains. The full-length congenic strain DA.ACI–D15Rat6-D15Rat71 (C15) and the recombinant congenic strains DA.ACI–D15rat 6-D15rat13 (C15R1), DA.ACI–D15Rat6-D15Rat48 (C15R3a), DA.ACI–D15Rat6-D15rat48, D15Rat126-D15Rat71 (C15R3b), and DA.ACI–D15Rat23-D15rat71 (C15R4) are depicted. The thin vertical line represents rat chromosome 15 along with microsatellite markers placed according to positions in megabases derived from the rat genome sequence (http://www.nsembl.org/Rattus_norvegicus/). Markers not mapped to assembly in the current Ensembl database are marked “n.m.” and positioned according to the SHRSP × BN version 7 linkage map (http://rgd.mcw.edu/). The thick black vertical lines represent different ACI rat intervals transferred to the DA rat background and the dashed lines represent the interval within which recombination has occurred. The open vertical line represents DA rat background genes.

Figure 2.—

Combined analysis of the clinical MOG-EAE phenotypes in six separate experiments encompassing the DA (n = 72), C15 (n = 49), C15R1 (n = 23), C15R3a (n = 9), C15R3b (n = 14), and C15R4 (n = 17) strains. Maximum EAE score, cumulative EAE score, and onset day were tested with the Wilcoxon two-sample test after normalization; *P < 0.05, **P < 0.01, and ***P < 0.001. Pairwise comparisons were made with the congenic strains and the DA strain. Mean values and SEM for disease onset day after immunization were calculated only for affected rats.

Figure 3.—

The clinical course of rMOG (aa 1–125)-induced EAE in selected strains and experiments. (a) Experiment 3: a mild disease course in DA rats (n = 11) and almost complete protection in C15 rats (n = 8). (b) Experiment 5: a severe disease in DA rats (n = 16) and reduced disease severity in C15R3b (n = 5) and C15R4 (n = 9) rats.

Figure 4.—

Log-likelihood plot of Eae19, identified in the (DA × PVG.AV1)F₇ AIL. Eae19 displayed significant linkage to all clinical EAE phenotypes: EAE incidence and day of onset and maximum and cumulative EAE scores. The markers in the region are listed on the x-axis (R, D15Rat; M, D15Mgh; G, D15Got. Eae19 is 13 Mb and contains 32 confirmed or predicted genes according to the rat physical map retrieved from http://www.ensembl.org