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Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease primarily affecting motor neurons in the central nervous system. Although most cases of ALS are sporadic, about 5-10% of cases are familial (FALS) with approximately 20% of FALS caused by mutations in the Cu/Zn superoxide dismutase (SOD1) gene. We have reported that hSOD1-G93A transgenic mice modeling this disease show a more severe phenotype when the transgene is bred on a pure SJL background and a milder phenotype when bred on a pure B6 background and that these phenotype differences link to a region on mouse Chromosome 17.To examine whether other models of motor neuron degeneration are affected by genetic background, we bred the mutant human dynactin p150Glued (G59S-hDCTN1) transgene onto inbred SJL and B6 congenic lines. This model is based on an autosomal dominant lower motor neuron disease in humans linked to a mutation in the p150Glued subunit of the dynactin complex. As seen in hSOD1-G93A mice, we observed a more severe phenotype with earlier disease onset (p<0.001) and decreased survival (p<0.00001) when the G59S-hDCTN1 transgene was bred onto the SJL background and delayed onset (p<0.0001) with increased survival (p<0.00001) when bred onto the B6 background. Furthermore, B6 mice with an SJL derived chromosome 17 interval previously shown to delay disease onset in hSOD1-G93A mice also showed delays onset in G59S-hDCTN1 mice suggesting that at least some genetic modifiers are shared. We have shown that genetic background influences phenotype in G59S-hDCTN1 mice, in part through a region of chromosome 17 similar to the G93-hSOD1 ALS mouse model. These results support the presence of genetic modifiers in both these models some of which may be shared. Identification of these modifiers will highlight intracellular pathways involved in motor neuron disease and provide new therapeutic targets that may be applicable to motor neuron degeneration.

Multiple sclerosis (MS) is a debilitating chronic inflammatory disease of the nervous system that affects approximately 2.3 million individuals worldwide, with higher prevalence in females, and a strong genetic component. While over 200 MS susceptibility loci have been identified in GWAS, the underlying mechanisms whereby they contribute to disease susceptibility remains ill-defined. Forward genetics approaches using conventional laboratory mouse strains are useful in identifying and functionally dissecting genes controlling disease-relevant phenotypes, but are hindered by the limited genetic diversity represented in such strains. To address this, we have combined the powerful chromosome substitution (consomic) strain approach with the genetic diversity of a wild-derived inbred mouse strain. Using experimental allergic encephalomyelitis (EAE), a mouse model of MS, we evaluated genetic control of disease course among a panel of 26 consomic strains of mice inheriting chromosomes from the wild-derived PWD strain on the C57BL/6J background, which models the genetic diversity seen in human populations. Nineteen linkages on 18 chromosomes were found to harbor loci controlling EAE. Of these 19 linkages, six were male-specific, four were female-specific, and nine were non-sex-specific, consistent with a differential genetic control of disease course between males and females. An MS-GWAS candidate-driven bioinformatic analysis using orthologous genes linked to EAE course identified sex-specific and non-sex-specific gene networks underlying disease pathogenesis. An analysis of sex hormone regulation of genes within these networks identified several key molecules, prominently including the MAP kinase family, known hormone-dependent regulators of sex differences in EAE course. Importantly, our results provide the framework by which consomic mouse strains with overall genome-wide genetic diversity, approximating that seen in humans, can be used as a rapid and powerful tool for modeling the genetic architecture of MS. Moreover, our data represent the first step towards mechanistic dissection of genetic control of sexual dimorphism in CNS autoimmunity.

Genetic mapping is a primary tool of genetics in model organisms; however, many quantitative trait loci (QTL) contain tens or hundreds of positional candidate genes. Prioritizing these genes for validation is often ad hoc and biased by previous findings. Here we present a technique for prioritizing positional candidates based on computationally inferred gene function. Our method uses machine learning with functional genomic networks, whose links encode functional associations among genes, to identify network-based signatures of functional association to a trait of interest. We demonstrate the method by functionally ranking positional candidates in a large locus on mouse Chr 6 (45.9 Mb to 127.8 Mb) associated with histamine hypersensitivity (Histh). Histh is characterized by systemic vascular leakage and edema in response to histamine challenge, which can lead to multiple organ failure and death. Although Histh risk is strongly influenced by genetics, little is known about its underlying molecular or genetic causes, due to genetic and physiological complexity of the trait. To dissect this complexity, we ranked genes in the Histh locus by predicting functional association with multiple Histh-related processes. We integrated these predictions with new single nucleotide polymorphism (SNP) association data derived from a survey of 23 inbred mouse strains and congenic mapping data. The top-ranked genes included Cxcl12, Ret, Cacna1c, and Cntn3, all of which had strong functional associations and were proximal to SNPs segregating with Histh. These results demonstrate the power of network-based computational methods to nominate highly plausible quantitative trait genes even in challenging cases involving large QTL and extreme trait complexity.

Disruption of the blood-brain barrier (BBB) underlies the development of experimental autoimmune encephalomyelitis (EAE) and multiple sclerosis. Environmental factors, such as Bordetella pertussis, are thought to sensitize central endothelium to biogenic amines like histamine, thereby leading to increased BBB permeability. B. pertussis-induced histamine sensitization (Bphs) is a monogenic intermediate phenotype of EAE controlled by histamine H₁ receptor (Hrh1/H₁R). Here, we transgenically overexpressed H₁R in endothelial cells of Hrh1-KO (H₁RKO) mice to test the role of endothelial H₁R directly in Bphs and EAE. Unexpectedly, transgenic H₁RKO mice expressing endothelial H₁R under control of the von Willebrand factor promoter (H₁RKO-vWFH¹R Tg) were Bphs-resistant. Moreover, H₁RKO-vWFH¹R Tg mice exhibited decreased BBB permeability and enhanced protection from EAE compared with H₁RKO mice. Thus, contrary to prevailing assumptions, our results show that endothelial H₁R expression reduces BBB permeability, suggesting that endothelial H₁R signaling may be important in the maintenance of cerebrovascular integrity.

Histamine (HA), a biogenic amine with a broad spectrum of activities in both physiological and pathological settings, plays a key regulatory role in experimental allergic encephalomyelitis, the autoimmune model of multiple sclerosis. HA exerts its effect through four G protein-coupled receptors designated HA receptor H₁, H₂, H₃, and H₄. We report here that, compared with wild-type animals, mice with a disrupted HA H₃ receptor (H3RKO), the expression of which is normally confined to cells of the nervous system, develop more severe disease and neuroinflammation. We show that this effect is associated with dysregulation of blood-brain barrier permeability and increased expression of MIP-2, IP-10, and CXCR3 by peripheral T cells. Our data suggest that pharmacological targeting of the H₃R may be useful in preventing the development and formation of new lesions in multiple sclerosis, thereby significantly limiting the progression of the disease.

Histamine plays pivotal role in normal physiology and dysregulated production of histamine or signaling through histamine receptors (HRH) can promote pathology. Previously, we showed that Bordetella pertussis or pertussis toxin can induce histamine sensitization in laboratory inbred mice and is genetically controlled by Hrh1 /HRH1. HRH1 allotypes differ at three amino acid residues with P 263 -V 313 -L 331 and L 263 -M 313 -S 331 , imparting sensitization and resistance respectively. Unexpectedly, we found several wild-derived inbred strains that carry the resistant HRH1 allotype (L 263 -M 313 -S 331 ) but exhibit histamine sensitization. This suggests the existence of a locus modifying pertussis-dependent histamine sensitization. Congenic mapping identified the location of this modifier locus on mouse chromosome 6 within a functional linkage disequilibrium domain encoding multiple loci controlling sensitization to histamine. We utilized interval-specific single-nucleotide polymorphism (SNP) based association testing across laboratory and wild-derived inbred mouse strains and functional prioritization analyses to identify candidate genes for this modifier locus. Atg7, Plxnd1, Tmcc1, Mkrn2, Il17re, Pparg, Lhfpl4, Vgll4, Rho and Syn2 are candidate genes within this modifier locus, which we named Bphse , enhancer of Bordetella pertussis induced histamine sensitization. Taken together, these results identify, using the evolutionarily significant diversity of wild-derived inbred mice, additional genetic mechanisms controlling histamine sensitization. Mice with the histamine sensitization resistant alleles are still susceptible to histamine shock, with a locus on chromosome 6 associated with histamine sensitization reported.

Histamine H3 receptor (Hrh3/H3R) is primarily expressed by neurons in the central nervous system (CNS) where it functions as a presynaptic inhibitory autoreceptor and heteroreceptor. Previously, we identified an H3R-mediated central component in susceptibility to experimental allergic encephalomyelitis (EAE), the principal autoimmune model of multiple sclerosis (MS), related to neurogenic control of blood brain barrier permeability and peripheral T cell effector responses. Furthermore, we identified Hrh3 as a positional candidate for the EAE susceptibility locus Eae8. Here, we characterize Hrh3 polymorphisms between EAE-susceptible and resistant SJL and B10.S mice, respectively, and show that Hrh3 isoform expression in the CNS is differentially regulated by acute peripheral inflammatory stimuli in an allele-specific fashion. Next, we show that Hrh3 is not expressed in any subpopulations of the immune compartment, and that secondary lymphoid tissue is anatomically poised to be regulated by central H3R signaling. Accordingly, using transcriptome analysis, we show that, inflammatory stimuli elicit unique transcriptional profiles in the lymph nodes of H3RKO mice compared to WT mice, which is indicative of negative regulation of peripheral immune responses by central H3R signaling. These results further support a functional link between the neurogenic control of T cell responses and susceptibility to CNS autoimmune disease coincident with acute and/or chronic peripheral inflammation. Pharmacological targeting of H3R may therefore be useful in preventing the development and formation of new lesions in MS, thereby limiting disease progression.

Experimental allergic encephalomyelitis (EAE), an autoimmune model of multiple sclerosis, is a complex disease influenced by genetic, intrinsic, and environmental factors. In this study, we questioned whether parent-of-origin effects influence EAE, using reciprocal F₂ intercross progeny generated between EAE-susceptible SJL/J (S) and EAE-resistant B10.S/SgMcdJ (B) mice. EAE susceptibility and severity were found to be different in female BS x BS intercross mice as compared with females from the three other birth crosses (BS x SB, SB x SB, and SB x BS), and in fact, both traits in female mice resembled those of their male siblings. This masculinization is associated with transmission of the SJL/J Y chromosome and an increased male-to-female sex ratio. Related studies using progeny of C57BL/6J Y-chromosome substitution strains demonstrate that the Y chromosome again influences EAE in both male and female mice, and that the disease course in females resembles that of their male littermates. Importantly, these data provide experimental evidence supporting the existence of a Y-chromosome polymorphism capable of modifying autoimmune disease susceptibility in both males and females.

Virus-Induced Autoimmune Diabetes in the LEW.1WR1 Rat Requires Iddm14 and a Genetic Locus Proximal to the Major Histocompatibility Complex Elizabeth P. Blankenhorn 1 , Laura Cort 1 , Dale L. Greiner 2 , Dennis L. Guberski 3 and John P. Mordes 2 1 Department of Microbiology and Immunology, Center for Immunogenetics and Inflammatory Diseases, Drexel University College of Medicine, Philadelphia, Pennsylvania; 2 Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts; 3 Biomedical Research Models, Worcester, Massachusetts. Corresponding author: Elizabeth P. Blankenhorn, eblanken{at}drexelmed.edu . Abstract OBJECTIVE To identify genes that confer susceptibility to autoimmune diabetes following viral infection in the LEW.1WR1 rat. RESEARCH DESIGN AND METHODS About 2% of LEW.1WR1 rats develop spontaneous autoimmune diabetes. Immunological perturbants including viral infection increase both the frequency and tempo of diabetes onset. To identify diabetes susceptibility genes (LEW.1WR1 × WF), F2 rats were infected with Kilham rat virus following brief pretreatment with polyinosinic:polycytidylic acid. This treatment induces diabetes in 100% of parental LEW.1WR1 rats and 0% of parental WF rats. Linkage to diabetes was analyzed by genome-wide scanning. RESULTS Among 182 F2 rats, 57 (31%) developed autoimmune diabetes after a mean latency of 16 days. All diabetic animals and ∼20% of nondiabetic animals exhibited pancreatic insulitis. Genome-wide scanning revealed a requirement for the Iddm14 locus, long known to be required for diabetes in the BB rat. In addition, a new locus near the RT1 major histocompatibility complex (MHC) was found to be a major determinant of disease susceptibility. Interestingly, one gene linked to autoimmune diabetes in mouse and human, UBD , lies within this region. CONCLUSIONS The Iddm14 diabetes locus in the rat is a powerful determinant of disease penetrance in the LEW.1WR1 rat following viral infection. In addition, a locus near the MHC ( Iddm37 ) conditions diabetes susceptibility in these animals. Other, as-yet-unidentified genes are required to convert latent susceptibility to overt diabetes. These data provide insight into the polygenic nature of autoimmune diabetes in the rat and the interplay of genetic and environmental factors underlying disease expression. Footnotes The contents of this publication are solely the responsibility of the authors and do not necessarily represent the official views of the National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Received March 17, 2009. Accepted August 26, 2009. © 2009 American Diabetes Association

Polymorphisms in genes in the human leukocyte antigen (HLA) class II region comprise the most important inherited risk factors for many autoimmune diseases, including type 1 diabetes (T1D) and celiac disease (CD): both diseases are positively associated with the HLA-DR3 haplotype ( DRB1*03:01-DQA1*05:01-DQB1*02:01 ). Studies of two different populations have recently documented that T1D susceptibility in HLA-DR3 homozygous individuals is stratified by a haplotype consisting of three single nucleotide polymorphisms (‘tri-SNP’) in intron 1 of the HLA-DRA gene. In this study, we use a large cohort from the longitudinal ‘The Environmental Determinants of Diabetes in the Young’ (TEDDY) study to further refine the tri-SNP association with T1D and with autoantibody-defined T1D endotypes. We found that the tri-SNP association is primarily in subjects whose first-appearing T1D autoantibody is to insulin. In addition, we discovered that the tri-SNP is also associated with CD, and that the particular tri-SNP haplotype (‘101’) that is negatively associated with T1D risk is positively associated with risk for CD. The opposite effect of the tri-SNP haplotype on two DR3-associated diseases can enhance and refine current models of disease prediction based on genetic risk. Finally, we investigated possible functional differences between the individuals carrying high and low-risk tri-SNP haplotypes and found that differences in complement system genes C4A and C4B may underlie the observed divergence in disease risk.