Susceptibility genes in the pathogenesis of murine lupus

Systemic lupus erythematosus (SLE) is the paradigm of a multisystem autoimmune disease in which genetic factors strongly influence susceptibility. Through genome scans and congenic dissection, numerous loci associated with lupus susceptibility have been defined and the complexity of the inheritance of this disease has been revealed. In this review, we provide a brief description of animal models of SLE, both spontaneous models and synthetic models, with an emphasis on the B6 congenic model derived from analyses of the NZM2410 strain. A hypothetical model of disease progression that organizes many of the identified SLE susceptibility loci in three distinct biological pathways that interact to mediate disease pathogenesis is also described. We finally discuss our recent fine mapping analysis, which revealed a cluster of loci that actually comprise the Sle1 locus

Genetic Modifiers of Systemic Lupus Erythematosus in FcγRIIB−/− Mice

FcγRIIB is a potent lupus susceptibility gene as demonstrated by the observation that mice deficient in this molecule develop spontaneous antinuclear antibodies (ANA) and fatal glomerulonephritis when on the C57BL/6 background. To determine the mechanisms underlying the epistasis displayed by this gene we have constructed hybrids between FcγRIIB−/− and the systemic lupus erythematosus (SLE) modifiers yaa and lpr and the susceptibility locus Sle1. Sle1 and B6.RIIB−/− are both physically and functionally coupled; compound heterozygotes of Sle1 and B6.RIIB−/− develop significant disease, while single heterozygotes display no evidence of autoimmunity or disease, indicating that these genes lie on the same genetic pathway resulting in the loss of tolerance to nuclear antigens. However, the generation of ANA in itself is insufficient to account for the severity of autoimmune disease in this model, as demonstrated by analysis of yaa and lpr hybrids. Thus, B6.RIIB−/−/lpr mice are protected from disease progression, despite equivalent titers of ANA. In contrast, B6.RIIB−/−/yaa mice have significantly enhanced disease despite reduced ANA titers. Yaa modifies the specificity and thus the pathogenicity of the B6. RIIB−/− ANA, by converting them to antinucleolar antibodies. In addition to these known modifier pathways, we have discovered two novel, recessive loci contributed by the C57BL/6 genome that are required for the ANA phenotype, further indicating the epistatic properties of this SLE model

Trex1 regulates lysosomal biogenesis and interferon-independent activation of antiviral genes

Innate immune sensing of viral nucleic acids triggers type I interferon (IFN) production, which activates interferon-stimulated genes (ISGs) and directs a multifaceted antiviral response. ISGs can also be activated through IFN-independent pathways, although the precise mechanisms remain elusive. Here we found that the cytosolic exonuclease Trex1 regulates the activation of a subset of ISGs independently of IFN. Both Trex1−/− mouse and TREX1-mutant human cells express high levels of antiviral genes and are refractory to viral infections. The IFN-independent activation of antiviral genes in Trex1−/− cells requires STING, TBK1 and IRF3 and IRF7. We also found that Trex1-deficient cells display expanded lysosomal compartment, altered subcellular localization of the transcription factor EB (TFEB), and reduced mTORC1 activity. Together, our data identify Trex1 as a regulator of lysosomal biogenesis and IFN-independent activation of antiviral genes, and shows dysregulation of lysosomes can elicit innate immune responses

Trex1 regulates lysosomal biogenesis and interferon-independent activation of antiviral genes

Innate immune sensing of viral nucleic acids triggers type I interferon (IFN) production, which activates interferon-stimulated genes (ISGs) and directs a multifaceted antiviral response. ISGs can also be activated through IFN-independent pathways, although the precise mechanisms remain elusive. Here we found that the cytosolic exonuclease Trex1 regulates the activation of a subset of ISGs independently of IFN. Both Trex1−/− mouse and TREX1-mutant human cells express high levels of antiviral genes and are refractory to viral infections. The IFN-independent activation of antiviral genes in Trex1−/− cells requires STING, TBK1 and IRF3 and IRF7. We also found that Trex1-deficient cells display expanded lysosomal compartment, altered subcellular localization of the transcription factor EB (TFEB), and reduced mTORC1 activity. Together, our data identify Trex1 as a regulator of lysosomal biogenesis and IFN-independent activation of antiviral genes, and shows dysregulation of lysosomes can elicit innate immune responses

A Functional Variant in MicroRNA-146a Promoter Modulates Its Expression and Confers Disease Risk for Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease with a strong genetic predisposition, characterized by an upregulated type I interferon pathway. MicroRNAs are important regulators of immune homeostasis, and aberrant microRNA expression has been demonstrated in patients with autoimmune diseases. We recently identified miR-146a as a negative regulator of the interferon pathway and linked the abnormal activation of this pathway to the underexpression of miR-146a in SLE patients. To explore why the expression of miR-146a is reduced in SLE patients, we conducted short parallel sequencing of potentially regulatory regions of miR-146a and identified a novel genetic variant (rs57095329) in the promoter region exhibiting evidence for association with SLE that was replicated independently in 7,182 Asians (Pmeta = 2.74×10−8, odds ratio = 1.29 [1.18–1.40]). The risk-associated G allele was linked to reduced expression of miR-146a in the peripheral blood leukocytes of the controls. Combined functional assays showed that the risk-associated G allele reduced the protein-binding affinity and activity of the promoter compared with those of the promoter containing the protective A allele. Transcription factor Ets-1, encoded by the lupus-susceptibility gene ETS1, identified in recent genome-wide association studies, binds near this variant. The manipulation of Ets-1 levels strongly affected miR-146a promoter activity in vitro; and the knockdown of Ets-1, mimicking its reduced expression in SLE, directly impaired the induction of miR-146a. We also observed additive effects of the risk alleles of miR-146a and ETS1. Our data identified and confirmed an association between a functional promoter variant of miR-146a and SLE. This risk allele had decreased binding to transcription factor Ets-1, contributing to reduced levels of miR-146a in SLE patients

Transancestral mapping and genetic load in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease with marked gender and ethnic disparities. We report a large transancestral association study of SLE using Immunochip genotype data from 27,574 individuals of European (EA), African (AA) and Hispanic Amerindian (HA) ancestry. We identify 58 distinct non-HLA regions in EA, 9 in AA and 16 in HA (B50% of these regions have multiple independent associations); these include 24 novel SLE regions (Po5 10 8), refined association signals in established regions, extended associations to additional ancestries, and a disentangled complex HLA multigenic effect. The risk allele count (genetic load) exhibits an accelerating pattern of SLE risk, leading us to posit a cumulative hit hypothesis for autoimmune disease. Comparing results across the three ancestries identifies both ancestry-dependent and ancestry-independent contributions to SLE risk. Our results are consistent with the unique and complex histories of the populations sampled, and collectively help clarify the genetic architecture and ethnic disparities in SL

Structural and genetic studies of chicken 7S immunoglobulin allotypes

Typescript.Thesis (Ph. D.)--University of Hawaii at Manoa, 1976.Bibliography: leaves 141-150.Microfiche.xv, 150 leaves illSix chicken 7S immunoglobulin (Ig) allotypic specificities were demonstrated with antisera produced in highly inbred chickens. A radioimmunoassay which utilized intact, radiolabeled 7S Ig alloantigens was developed, and was used for the structural and genetic analysis of these specificities. The binding of dinitrophenylated alloantiserum (DAA) with radiolabeled alloantigen was demonstrated by the addition of rabbit anti-dinitrophenyl antiserum followed by precipitation of complexes with sheep anti-rabbit γ-globulin antiserum. Binding inhibition assays with the DAA method detected allotypes on 2 to 5 ng of 7S Ig alloantigen. Structural analyses of the six allotypic specificities were performed by direct binding and binding inhibition analysis with the DAA assay. Specificities CS-1.1 and CS-1.2 were present on papain-produced Fab fragments and isolated 7S Ig heavy (H) chains; but not on light (L) chains, Fc fragments, or 17S Ig. For both specificities H chains reassociated with L chains were three- to five-fold better inhibitors on a weight basis than isolated H chains. Regression coefficients calculated from binding inhibition curves indicated that the avidity of H chains for specific alloantisera was significantly increased following reassociation with L chains, suggesting that the conformation of CS-1.1 and CS-1.2 determinants may depend in part upon Hand L chain interactions. Specificities CS-1.3 and CS-1.4 were detected on isolated 7S Ig H chains; but not on L chains, Fab, Fc, or l7S Ig. In contrast to the results with CS-1.1 and CS-1.2, reassociation of Hand L chains did not significantly increase the inhibitory activity or binding avidity of CS-1.3 and CS-1.4 for specific alloantisera. Specificity CS-1.5 was also present on intact 7S Ig, but absent from Fab, Fc, or 178 Ig. A nonhomologous cross reaction was observed in binding inhibition assays with UCD 2 anti-CS-1.2 alloantiserum. The cross-reacting specificity, designated CS-1.6, was found on 7S Ig and was absent from l7S Ig enriched preparations. These data indicate that at least two regions of the chicken 7S Ig H chain contain genetic variations: (1) specificities CS-1.1 and CS-1.2 are located in the Fd portion of the H chain, perhaps in a region analogous to the CH1 domain of mammalian IgG; and (2) specificities CS-1.3, CS-1.4, and CS-1.5 are located in a region of the H chain which is sensitive to papain digestion. Among F2 progeny, these specificities segregated in a manner statistically indistinguishable from that expected of codominant alleles of a "Mendelian" gene at an autosomal locus. This gene, designated CS-1, occupied a locus which was not closely linked to any of five chicken blood group loci. Combinations of 7S Ig allotypic specificities were inherited as stable phenogroups among the F2 progeny of inbred chicken lines, and direct binding analysis with the DAA assay indicated that the specificities forming phenogroups were present on the same 7S Ig molecules. These results also demonstrated that more than 94% of the serum 7S Ig contained the products of the CS-1 gene. In FI hybrids with the genotype CS-1.1,1.3/1.2, two populations of serum 7S Ig molecules were detected by direct and sequential binding analysis with alloantisera. One population of 7S Ig contained specificities CS-1.1 and CS-1.3, but not CS-1.2; while the second population carried only specificity CS-1.2. Therefore, each population was exclusively the product of one parental allele. Consistent with a genetic regulatory mechanism involving allelic exclusion, no 7S Ig containing allotypes produced by both alleles was detected. A survey of 43 inbred lines derived from four sources in the United States for 7S Ig allotypes revealed considerable genetic polymorphism. A minimum of ten alleles of the CS-1 gene were found as unique combinations of CS-1 specificities. A system of nomenclature for CS-1 alleles was developed and six inbred lines were designated as prototype lines. The remaining four CS-1 alleles occurred only in inbred lines which were polymorphic for 7S Ig allotypic specificities