Activation-induced deaminase heterozygous MRL/lpr mice are delayed in the production of high-affinity pathogenic antibodies and in the development of lupus nephritis

Laboratory of Molecular Genetics, D3-01 National Institute of Environmental Health Sciences/National Institutes of Health, Research Triangle Park, NC 27709, USA.
Immunology (Impact Factor: 3.8). 07/2008; 126(1):102-13. DOI: 10.1111/j.1365-2567.2008.02882.x
Source: PubMed


We previously reported that activation-induced deaminase (AID) heterozygous MRL/lpr mice have substantially lower levels of serum anti-dsDNA autoantibodies than AID wild-type littermates. Given the known functions of AID, here we examined whether this decrease in pathogenic autoantibodies in the heterozygotes was the result of a defect in class switch recombination, somatic hypermutation, or both. We report significant impairment of switch recombination to most isotypes except immunoglobulin G3 (IgG3) in vitro. However, serum levels of IgG were similar to AID wild-type levels even in very young mice. Mutation accumulation in the B cells from Peyer's patches also revealed reduced somatic hypermutation in the heterozygotes. Unlike the switch defect, the hypermutation defect probably resulted in an in vivo effect because the serum IgG antibodies from the heterozygotes were of strikingly lower affinity to dsDNA than serum IgG antibodies from wild-type littermates. This suggests that the somatic hypermutation defect resulted in impaired affinity maturation of autoantibodies in these mice and explains the low levels of specific anti-dsDNA antibodies in the heterozygotes. This correlated with a delay in the development of kidney damage. These results imply that AID levels impact the class switch recombination and somatic hypermutation mechanisms and directly implicate affinity maturation of autoantibodies in autoimmunity.

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    • "In heterozygous Aicda þ/2 MRL/Fas lpr/lpr mice, reduced AID expression resulted in a reduction in the production of high-affinity anti-dsDNA IgG, moderately diminished kidney pathology, temporary decrease in nephritis, and increased survival rates [43] [44]. The delayed and reduced symptoms observed in heterozygous Aicda þ/2 MRL/Fas lpr/lpr mice suggest that discrete levels of AID expression, and not solely its presence or absence, are important in lupus pathogenesis [43]. Malignancies are associated with systemic lupus and are a significant cause of death in SLE patients [45 – 53]. "
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    ABSTRACT: Immunoglobulin gene somatic hypermutation (SHM) and class switch DNA recombination (CSR) play important roles in the generation of autoantibodies in systemic lupus erythematosus. Systemic lupus is characterized by the production of an array of pathogenic high-affinity mutated and class-switched, mainly IgG, antibodies to a variety of self-antigens, including nuclear components, such as dsDNA, histones, and chromatin. We previously found that MRL/Fas(lpr/lpr) mice, which develop a systemic autoimmune syndrome sharing many features with human lupus, display greatly upregulated CSR, particularly to IgG2a, in B cells of the spleen, lymph nodes, and Peyer's patches. In MRL/Fas(lpr/lpr) mice, the significant upregulation of CSR is associated with increased expression of activation-induced cytidine deaminase (AID), which is critical for CSR and SHM. We also found that HoxC4 directly activates the promoter of the AID gene to induce AID expression, CSR and SHM. Here, we show that in both lupus patients and lupus-prone MRL/Fas(lpr/lpr) mice, the expression of HoxC4 and AID is significantly upregulated. To further analyze the role of HoxC4 in lupus, we generated HoxC4(-/-) MRL/Fas(lpr/lpr) mice. In these mice, HoxC4-deficiency resulted in reduced AID expression, impaired CSR, and decreased serum anti-dsDNA IgG, particularly IgG2a, autoantibodies, which were associated with a reduction in IgG deposition in kidney glomeruli. In addition, consistent with our previous findings in MRL/Fas(lpr/lpr) mice that upregulated AID expression is associated with extensive DNA lesions, comprising deletions and insertions in the IgH locus, we found that c-Myc to IgH (c-Myc/IgH) translocations occur frequently in B cells of MRL/Fas(lpr/lpr) mice. The frequency of such translocations was significantly reduced in HoxC4(-/-) MRL/Fas(lpr/lpr) mice. These findings suggest that in lupus B cells, upregulation of HoxC4 plays a major role in dysregulation of AID expression, thereby increasing CSR and autoantibody production and promoting c-Myc/IgH translocations.
    Full-text · Article · May 2011 · Autoimmunity
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    • "inAID-deficientMRL/fas lpr/lprmice,inwhichcirculat- inganti-dsDNAIgGsarebarelydetectable[36]. Accordingly,inAicda þ/2MRL/fas lpr/lprmice,a25– 40%reductionofAicdaexpressionleadstosignificantly reducedhigh-affinityanti-dsDNAIgGs[77],further suggestingthatahighlevelofAIDexpressioniscritical forthegenerationofpathogenicautoantibodies. OurfindingsimplythatthedysregulationofSHM andCSRinlupusBcellsismediatedbyasignificantly increasedAIDexpressionand,possibly,anenhanced recruitmentofTLSpolymerasestoV(D)JandS regionDNA,respectively.Thisissupportedbyour demonstrationthatsomaticmutationsinlupusBcells preferentiallytargetedtheWGCWAIDhotspotand weremainlydG!dAanddC!dTtransitions. "
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    ABSTRACT: Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of an array of pathogenic autoantibodies, including high-affinity anti-dsDNA IgG antibodies. These autoantibodies are mutated and class-switched, mainly to IgG, indicating that immunoglobulin (Ig) gene somatic hypermutation (SHM) and class switch DNA recombination (CSR) are important in their generation. Lupus-prone MRL/fas(lpr/lpr) mice develop a systemic autoimmune syndrome that shares many features with human SLE. We found that Ig genes were heavily mutated in MRL/fas(lpr/lpr) mice and contained long stretches of DNA deletions and insertions. The spectrum of mutations in MRL/fas(lpr/lpr) B cells was significantly altered, including increased dG/dC transitions, increased targeting of the RGYW/WRCY mutational hotspot and the WGCW AID-targeting hotspot. We also showed that MRL/fas(lpr/lpr) greatly upregulated CSR, particularly to IgG2a and IgA in B cells of the spleen, lymph nodes and Peyer's patches. In MRL/fas(lpr/lpr) mice, the significant upregulation of SHM and CSR was associated with increased expression of activation-induced cytidine deaminase (AID), which mediates DNA lesion, the first step in SHM and CSR, and translesion DNA synthesis (TLS) polymerase (pol) theta, pol eta and pol zeta, which are involved in DNA synthesis/repair process associated with SHM and, possibly, CSR. Thus, in lupus-prone MRL/fas(lpr/lpr) mice, SHM and CSR are upregulated, as a result of enhanced AID expression and, therefore, DNA lesions, and dysregulated DNA repair factors, including TLS polymerases, which are involved in the repair process of AID-mediated DNA lesions.
    Full-text · Article · Mar 2009 · Autoimmunity
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    • "urde gezeigt , dass AID im Prinzip Genom - weit wirken kann ( Wang et al . , 2004 ) . Eine Verbindung zwischen dem AID Transkriptionslevel und dem Ausmaß der pathologischen Aktivität von AID wurde bei Studien mit AID - heterozygoten Mäusen mit reduziertem AID - mRNA und – Proteinlevel entdeckt , ( McBride et al . , 2008 ; Takizawa et al . , 2008 ; Jiang et al . , 2009 ) . Im Hintergrund des Klassenwechsels zeigten die AID + / - Lymphozyten eine beeinträchtigte Switch - Rekombination und eine Verminderung in der Frequenz der Mutationen und chromosomalen Brüche . Außerdem zeigte sich , dass die Kreuzung von AID defizienten Mäusen mit verschiedenen GC - und Post - GC - Lymphom - Maus - Modellen dazu füh"
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    ABSTRACT: In this Ph. D. Thesis it was possible to get new insight about the variety of genomic lesions in B-NHLs and gain new knowledge about the mechanisms of deregulated NF-kB signaling in B-NHLs and cHL. The absence of inactivating mutations in TNFAIP3, indicates that, in contrast to other lymphomas, this gene was not involved in the constitutive activation of the NF-kB pathway in CLL. The supposition that TNFAIP3 is the target of the rare 6q deletion in some CLL-cases was therefore disproved. TRAF3 was inactivated by a deletion only once in a cHL cell line, but it was not affected by inactivating mutations or deletions in all other analyzed cell lines and in seven primary cHL-cases. This demonstrates that TRAF3 inactivation does not account normally for the constitutive NF-kB-expression in HRS-cells, but seems to be an uncommon event. In this work, two MYC-LDI-PCR approaches were established and used to amplify in one out of 13 B-NHL-cases a translocation with SOCS1 as a to date unknown translocation partner of MYC-translocations. Because SOCS1 is a known tumor suppressor, a translocation juxtaposing SOCS1 to the MYC-oncogene is of great interest. The mechanism affecting both translocated genes remains to be identified. The partly new established igH-LDI-PCR approaches in this work were successfully used to amplify and sequence the translocation partner of seven out of 28 DLBCLs with IgH-associated translocations. In four of these cases the translocation partners were so far not described in translocations involving the IgH-locus in DLBCLs. In the majority of the cases the translocation disrupted the coding sequence of the partner gene. It remains to clarify, if the translocations inactivate an unknown tumor suppressor or deregulate a distant unknown oncogene. In one of the cases IRF4 was identified as target oncogene of the translocation; this finding led to the characterization of a novel subtype of GCB-DLBCL. The results presented here show that DLBCL is more heterogeneous as previously expected and the identification of PVRL2 as translocation partner shows another example of translocations affecting the same breakpoint in B- and T-cell lymphomas.
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