Genetic Complementation in Female (BXSB × NZW)F2 Mice

Increased development of T-bet+CD11c+ B cells predisposes to lupus in females: Analysis in BXD2 mouse and genetic crosses

Cardinal features of lupus include elevated B cell activation and autoantibody production with a female sex preponderance. We quantified interactions of sex and genetic variation on the development of autoimmune B-cell phenotypes and autoantibodies in the BXD2 murine model of lupus using a cohort of backcrossed progeny (BXD2 x C57BL/6J) x BXD2. Sex was the key factor leading to increased total IgG, IgG2b, and autoantibodies. The percentage of T-bet+CD11c+ IgD+ activated naive B cells (aNAV) was higher in females and was associated with increased T-bet+CD11c+ IgD- age-related B cells, Fas+GL7+ germinal center B cells, Cxcr5-Icos+ peripheral T-helper cells, and Cxcr5+Icos+ follicular T-helper cells. IFN-β was elevated in females. Variation in aNAV cells was mapped to Chr 7 in a locus that shows significant interactions between the female sex and heterozygous B/D variant. Our results suggest that activation of naive B cells forms the basis for the female-predominant development of autoantibodies in lupus-susceptible BXD2 mice.

Genetic dissection of the ity3 locus identifies a role for ncf2 co-expression modules and suggests selp as a candidate gene underlying the ity3.2 locus

Typhoid fever and salmonellosis, which are caused by Salmonella typhi and typhimurium, respectively, are responsible for significant morbidity and mortality in both developed and developing countries. We model typhoid fever using mice infected with Salmonella typhimurium, which results in a systemic disease, whereby the outcome of infection is variable in different inbred strains of mice. This model recapitulates several clinical aspects of the human disease and allows the study of the host response to Salmonella typhimurium infection in vivo. Previous work in our laboratory has identified three loci (Ity, Ity2, and Ity3) in the wild-derived MOLF/Ei mice influencing survival after infection with Salmonella typhimurium. Fine mapping of the Ity3 locus indicated that two sub-loci contribute collectively to the susceptibility of B6.MOLF-Ity/Ity3 congenic mice to Salmonella infection. In the current paper, we provided further evidence supporting a role for Ncf2 (neutrophil cytosolic factor 2 a subunit of NADPH oxidase) as the gene underlying the Ity3.1 sub-locus. Gene expression profiling indicated that the Ity3.1 sub-locus defined a global gene expression signature with networks articulated around Ncf2. Furthermore, based on differential expression and complementation analysis using Selp (selectin-P) knock-out mice, Selp was identified as a strong candidate gene for the Ity3.2 sub-locus.

Forward genetic approaches to understanding complex behaviors

Assigning function to genes has long been a focus of biomedical research.Even with complete knowledge of the genomic sequences of humans, mice and other experimental organisms, there is still much to be learned about gene function and control. Ablation or overexpression of single genes using knockout or transgenic technologies has provided functional annotation for many genes, but these technologies do not capture the extensive genetic variation present in existing experimental mouse populations. Researchers have only recently begun to truly appreciate naturally occurring genetic variation resulting from single nucleotide substitutions,insertions, deletions, copy number variation, epigenetic changes (DNA methylation,histone modifications, etc.) and gene expression differences and how this variation contributes to complex phenotypes. In this chapter, we will discuss the benefits and limitations of different forward genetic approaches that capture the genetic variation present in inbred mouse strains and present the utility of these approaches for mapping QTL that influence complex behavioral phenotypes.

Genetic basis of murine lupus nephritis

Systemic lupus erythematosus is a generalized autoimmune disease affecting multiple end-organs including the kidneys. Glomerulonephritis is a leading cause of death in lupus, both in patients and murine models that develop disease spontaneously. Genetic mapping studies have uncovered several genetic intervals that confer susceptibility to nephritis both in human beings and in mice. This review surveys the genomic positions of these nephritis susceptibility loci in murine lupus. Currently we know very little about the molecular identities of the culprit genes within these mapped loci and whether these genetic elements contribute to nephritis directly in a renal-intrinsic fashion or indirectly by augmenting the formation of pathogenic autoantibodies. The next decade is likely to witness a significant broadening of our understanding of how different genes and molecules might facilitate end-organ damage in lupus.

Genetic Dissection of Vasculitis, Myeloperoxidase-Specific Antineutrophil Cytoplasmic Autoantibody Production, and Related Traits in Spontaneous Crescentic Glomerulonephritis-Forming/Kinjoh Mice

The spontaneous crescentic glomerulonephritis-forming/Kinjoh (SCG/Kj) mouse is a model of human crescentic glomerulonephritis and vasculitis associated with the production of the myeloperoxidase (MPO)-specific antineutrophil cytoplasmic autoantibody (MPO-ANCA). Although the disease is mediated initially by mutation of the Fas gene (lpr), SCG/Kj mice also have non-Fas predisposing genetic factors. To define these factors, genome-wide quantitative trait locus (QTL) mapping was performed on female (B(6)x SCG/Kj) F(2) intercross mice. Fourteen non-Fas QTLs were identified. QTLs of glomerulonephritis were located on chromosomes 1, 10, 13, 16, and 17, vasculitis on chromosomes 1 and 17, splenomegaly on chromosome 1, hypergammaglobulinemia on chromosomes 1, 2, 4, 6, 7, 11, 13, and 17, antinuclear Ab on chromosomes 1, 8, 10, and 12, and MPO-ANCA production on chromosomes 1 and 10. Significant QTLs derived from SCG/Kj on chromosomes 1, 2, 7, and 13 were designated Scg-1 to Scg-5, respectively, and those derived from B(6) on chromosomes 4, 6, 17, and 10 were designated Sxb-1 to Sxb-4, respectively. Two loci linked to MPO-ANCA production on chromosomes 1 and 10 were designated Man-1 and Man-2 (for MPO-ANCA), respectively. Although both Scg-1 and Scg-2 were on chromosome 1 and shared several functions, it was of interest that aberrant MPO-ANCA production was exclusively controlled by Man-1, the centromeric half region of the Scg-2 chromosomal segment. We also examined the epistatic effects between the lpr mutation and non-Fas susceptibility genes. QTLs are discussed in relation to previously described loci, with emphasis on their candidate genes.

Polymorphism of the mouse gene for the interleukin 10 receptor alpha chain (Il10ra) and its association with the autoimmune phenotype

Several studies suggest that interleukin (IL)-10 pathway is involved in murine lupus, while no linkage of IL-10 gene polymorphism to disease susceptibility has been reported in studies with lupus-prone mice. Since IL-10 functions through the specific IL-10 receptor alpha (IL-10RA) chain and the IL-10RA gene (Il10ra) is linked to the susceptibility loci of atopic dermatitis and Crohn's disease identified using mouse models, we supposed that IL-10RA might be involved in murine lupus. By flow cytometry analysis, we found that NZW mice, one of the parental strains of lupus-prone (NZBxNZW) F1 mice, express extremely low levels of IL-10RA compared with NZB mice, the other parental strain, and the healthy BALB/c and C57BL/6 mice. Sequence analyses of Il10ra cDNA of NZW mice showed multiple nucleotide mutations compared with that of NZB and C57BL/6 strains, some of which would result in amino acid substitutions in the IL-10RA protein. Lupus-prone MRL mice shared the same polymorphism with NZW. Analyses using (NZBxNZW) F1xNZB backcross mice showed that high serum levels of IgG antichromatin antibodies were regulated by a combinatorial effect of the NZW Il10ra allele and a heterozygous genotype for Tnfa microsatellite locus. Our data suggest that the polymorphic NZW-type Il10ra may be involved in the pathologic production of antichromatin antibodies and, if so, may contribute in part to the development of systemic lupus erythematosus as one susceptibility allele.

Genetic Dissection of Systemic Lupus Erythematosus Pathogenesis: Partial Functional Complementation betweenSle1andSle3/5Demonstrates Requirement for Intracellular Coexpression for Full Phenotypic Expression of Lupus

Sle1 on chromosome 1 and Sle3/5 on chromosome 7 are two of the most critical lupus susceptibility loci of the New Zealand Black/White-derived NZM2410 mouse strain. In contrast to C57BL/6 mice congenic for either Sle1 (B6.Sle1) or Sle3/5 (B6.Sle3/5), strains that express only a modest lupus-related phenotype, the bicongenic B6.Sle1.Sle3/5 strain has a robust phenotype, suggesting a critical role for epistatic interactions in lupus pathogenesis. Mixed chimera experiments indicated that the two loci are functionally expressed by different cell populations and predicted that phenotypic expression of the phenotypic features of the B6.Sle1.Sle3/5 strain could be fully reproduced with a combination of B6.Sle1 and B6.Sle3/5 bone marrow. Contrary to our expectations, there was only a partial functional complementation in these mixed chimeras. Spleen enlargement, CD4:CD8 ratio elevation, and epitope spreading of autoantibodies were fully developed in B6+B6.Sle1.Sle3/5 but not in B6.Sle1+B6.Sle3/5 mixed chimeras. This study is the first to present evidence that the pathways mediated by two critical lupus susceptibility loci derived from the New Zealand White strain must be integrated intracellularly for epistatic interactions to occur. Our mixed chimera approach continues to provide novel insights into the functional genetic pathways underlying this important murine model of systemic autoimmunity.

Implication of allelic polymorphism of osteopontin in the development of lupus nephritis in MRL/lpr mice

Potentially, autoimmune diseases develop from a combination of multiple genes with allelic polymorphisms. An MRL/Mp-Fas(lpr) (/) (lpr) (MRL/lpr) strain of mice develops autoimmune diseases, including lupus nephritis, but another lpr strain, C3H/HeJ-Fas(lpr) (/) (lpr) (C3H/lpr) does not. This indicates that MRL polymorphic genes are involved in the development of the diseases. By quantitative trait loci (QTL) analysis using 527 of the (MRL/lpr x C3H/lpr)F(2) mice, we identified a novel locus for susceptibility to lupus nephritis at map position D5Mit115 on chromosome 5, the same alias of the osteopontin (Opn) gene (LOD score =4.0), susceptible in the MRL allele. In functional analyses of the MRL and C3H Opn alleles using synthetic osteopontin (OPN) made with a new method "cell-free system" with wheat germ ribosomes, the MRL-OPN induced higher expression and production of immunoglobulins as well as cytokines including TNF-alpha, IL-1beta and IFN-gamma in splenocytes and/or macrophages than that of the C3H allele. These findings suggest that allelic polymorphism of OPN causes the functional differences in antibody production and macrophage activation between MRL and C3H strains, possibly involved in the development of lupus nephritis.

Accelerating effect of an MRL gene locus on the severity and onset of arthropathy in DBA/1 mice

OBJECTIVE

To analyze the influence of the genetic background of an arthritis-prone strain of mice, MRL, on the spontaneous development of arthropathy in DBA/1 mice, which histopathologically resembles enthesopathy in humans, and to clarify the strain-specific gene loci and their interactions that confer susceptibility to arthropathy.

METHODS

MRL, DBA/1, (MRL x DBA/1)F(1), and (MRL x DBA/1)F(2) intercross mice were prepared, and the severity and onset of arthropathy of the ankle joints in individual mice were quantified (0-3 and 0-5 scale, respectively). A genome-wide scan of 271 male F(2) intercross mice with polymorphic microsatellite markers was performed.

RESULTS

Only male DBA/1, (MRL x DBA/1)F(1), and (MRL x DBA/1)F(2) mice developed arthropathy. The macroscopic and histopathologic findings of arthropathy in the F(2) mice were similar to those in the parental DBA/1 mice, but the onset was significantly earlier. In the quantitative trait locus analysis of male F(2) mice, 1 susceptibility locus for both the severity and early onset of the disease in the region of an MRL allele, Amd1, was located at marker D10Mit259 (map position 40.0 cM), which was common to 1 of the sialadenitis susceptibility loci in MRL mice, Asm1. Another susceptibility locus for the severity and early onset of arthropathy in the region of a DBA allele, Amd2, was located at D3Mit46 (29.5 cM). These loci manifested an additive effect on the development of arthropathy.

CONCLUSION

Arthropathy in DBA/1 mice is under the control of an allelic combination of gene loci, one of which is common to the locus for sialadenitis in MRL/MpJ-lpr/lpr mice.

Multiple loci are linked with anti-red blood cell antibody production in NZB mice -- comparison with other phenotypes implies complex modes of action

The New Zealand Black (NZB) mouse strain is a model of autoimmune haemolytic anaemia (AHA) and systemic lupus erythematosus (SLE), characterized by the production of anti-red blood cell (RBC) antibodies and anti-nuclear antibodies (ANA), respectively. A linkage analysis was carried out in an (NZB x BALB/c) F(2) cross in order to identify loci involved in the production of both anti-RBC IgM and IgG antibodies. These regions of linkage were compared with linkage data to ANA from the same cohort and other linkage analyses involving New Zealand mice. Four previously described NZB loci linked to anti-RBC antibodies were confirmed, and eight novel loci linked to this trait were also mapped: five of which were of NZB origin, and three derived from the non-autoimmune BALB/c background. A comparison between loci linked with anti-RBC antibodies and ANA demonstrated many that co-localize, suggesting the presence of genes that result in the general breaking of tolerance to self-antigen. Furthermore, the observation that some loci were associated only with the anti-RBC response suggests an antigen specific mechanism in addition to a general breaking of tolerance. A locus linked with anti-RBC antibodies and ANA on distal chromosome 7 in this cohort is orthologous to one on the q arm of human chromosome 11, a region linked to AHA and ANA in human SLE.

Dissection of BXSB lupus phenotype using mice congenic for chromosome 1 demonstrates that separate intervals direct different aspects of disease

To dissect the individual effects of the four non-MHC, autosomal loci (Bxs1 to Bxs4) that contribute to SLE susceptibility in BXSB mice, we generated congenic lines from chromosome 1 on a C57BL/10.Y(BXSB) (B10.Yaa) background for the intervals (values in megabases (Mb)) Bxs1 (46.3-89.2 Mb), Bxs1/4 (20.0-65.9 Mb), Bxs1/2 (64.4-159.0 Mb), and Bxs2/3 (105.4-189.0 Mb). Glomerulonephritis, qualitatively similar to that seen in the parental BXSB strain, developed in three of these congenic strains. Early onset, severe disease was observed in B10.Yaa.BXSB-Bxs2/3 congenic mice and caused 50% mortality by 12 mo. In B10.Yaa.BXSB-Bxs1/4 mice disease progressed more slowly, resulting in 13% mortality at 12 mo. The progression of renal disease in both of these strains was correlated with the level of anti-dsDNA Abs. B10.Yaa.BXSB-Bxs1 mice, despite their genetic similarity to B10.Yaa.BXSB-Bxs1/4 mice, developed a low-grade glomerulonephritis in the absence of anti-dsDNA Abs. Thus, Bxs4 directed an increase in titer and spectrum of autoantibodies, whereas Bxs1 promoted the development of nephritis. The Bxs2 interval was linked to the production of anti-dsDNA Abs without concomitant glomerulonephritis. In contrast, the Bxs3 interval was sufficient to generate classic lupus nephritis in a nonautoimmune-prone strain. Immune phenotype differed between controls and congenics with a significant increase in B220(+) cells in BXSB and B10.Yaa.BXSB-Bxs2/3, and an increase in CD4 to CD8 ratio in both BXSB and B10.Yaa.BXSB-Bxs1/4. Disease in the Bxs3 mice was delayed in comparison to the BXSB parental strain, emphasizing the necessity for multiple interactions in the production of the full BXSB phenotype.