Genetic analysis of experimentally induced lupus in mice

Abnormal Morphology of Distal Tubular Epithelial Cells Is Regulated by Genetic Factors Derived from Mouse Chromosome 12

The distal tubule (DT) helps regulate blood pressure and electrolytes. We describe a novel, autosomal recessive, morphofunctional DT abnormality in inbred mice evident as columnar alternations and age-related cystic changes. This abnormality developed in both sexes of DBA/2Cr. Similar phenotypes were observed in A/J, C3H/He, DBA/1J, and FVB/N strains, but not in AKR/N, BALB/c, or C57BL/6N strains. In DBA/2Cr, abnormal DT localized to straight and convoluted segments and showed IL-36α DT injury marker expression. However, DT epithelial proliferation, examined by bromodeoxyuridine incorporation, was not remarkably altered with the progression of abnormality. Abnormal DT epithelial cells in DBA/2Cr displayed elongated primary cilia, loose intercellular adhesions, and numerous vesicles with altered localization of CD9, Na⁺/K⁺ATPase, and E-cadherin, indicating altered cell function, adhesion, and polarity. DBA/2Cr-type D12Mit182-D12Mit83 was identified as a candidate locus designated DBA/2 renal cyst (drecy). Within drecy, the gene regulated by estrogen in breast cancer protein (Greb1) transcript variant 2 was significantly up-regulated in DBA/2Cr kidney versus C57BL/6N. Greb1 localized to DT cytoplasm in C57BL/6 and to cytoplasm and nucleus in DBA/2Cr. Greb1-overexpressing M-1 kidney cells showed an altered epithelial-mesenchyme phenotype. B6.D2-(D12Mit182-D12Mit83) congenic mice carrying drecy did not show DT abnormalities, whereas DBA/2Cr × B6.D2-(D12Mit182-D12Mit83) mice did. Identification of this novel DT abnormality regulated by a DBA/2Cr mouse chromosome 12-derived locus and additional genetic factors improve the understanding of DT pathogenesis.

Effects of prolonged treatment with memantine in the MRL model of CNS lupus

OBJECTIVES

Neuropsychiatric manifestations and brain atrophy of unknown etiology are common and severe complications of systemic lupus erythematosus (SLE). An autoantibody that binds to N-methyl-D-aspartate (NMDA) receptor NR2 has been proposed as a key factor in the etiology of central nervous system (CNS) SLE. This hypothesis was supported by evidence suggesting memantine (MEM), an uncompetitive NMDA receptor antagonist, prevents behavioral dysfunction and brain pathology in healthy mice immunized with a peptide similar to an epitope on the NR2 receptor. Given that SLE is a chronic condition, we presently examine the effects of MEM in MRL/lpr mice, which develop behavioral deficits alongside SLE-like disease.

METHODS

A broad behavioral battery and 7-Tesla MRI were used to examine whether prolonged treatment with MEM (~25 mg/kg b.w. in drinking water) prevents CNS involvement in this spontaneous model of SLE.

RESULTS

Although MEM increased novel object exploration in MRL/lpr mice, it did not show other beneficial, substrain-specific effects. Conversely, MEM was detrimental to spontaneous activity in control MRL +/+ mice and had a negative effect on body mass gain. Similarly, MRI revealed comparable increases in the volume of periventricular structures in MEM-treated groups.

CONCLUSIONS

Sustained exposure to MEM affects body growth, brain morphology, and behavior primarily by pharmacological, and not autoimmunity-dependant mechanisms. Substrain-specific improvement in exploratory behavior of MEM-treated MRL/lpr mice may indicate that the NMDA system is merely a constituent of a complex pathogenenic cascade. However, it was evident that chronic administration of MEM is unable to completely prevent the development of a CNS SLE-like syndrome.

Altered gene expression in mice with lupus treated with edratide, a peptide that ameliorates the disease manifestations

OBJECTIVE

To identify genes that are differently expressed in (NZB x NZW)F(1) mice with established lupus compared with healthy controls, and to determine how gene expression is affected by treatment with hCDR1 (Edratide), a peptide synthesized on the basis of the sequence of the first complementarity-determining region (CDR1) of an autoantibody.

METHODS

RNA was extracted from spleen cells of young, disease-free mice and of older mice with systemic lupus erythematosus (SLE) that were treated with hCDR1 or with vehicle alone. Gene expression was assessed using the DNA microarray technique and verified by real-time reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

In mice with SLE, numerous genes showed increased or decreased expression relative to that in the disease-free controls. Treatment with hCDR1 restored the expression of many of these genes to control levels. Real-time RT-PCR verified that in diseased mice RNA transcripts of Tnfsf4, Il5ra, Zbtb20, and Nid1 were up-regulated, while transcripts of Tfpi and S100a8 were down-regulated, and confirmed the effects of hCDR1 on the expression of those genes. Kidney immunostaining demonstrated that the up-regulated expression of OX40 ligand, which is a protein product of the gene tumor necrosis factor (ligand) superfamily member 4, in diseased mice was reduced by hCDR1.

CONCLUSION

Expression of numerous genes in mice with SLE differs from that in young, disease-free control mice. Treatment with hCDR1 restores the expression of 22% of these genes to levels similar to those in controls. Thus, one of the mechanisms by which hCDR1 exerts its beneficial effects on the clinical symptoms of SLE is through regulation of gene expression.

Chimerism in systemic lupus erythematosus—three hypotheses

Systemic lupus erythematosus (SLE) is an immune-mediated disease characterized by the presence of autoantibodies and a wide array of clinical symptoms. Despite intensive research, the aetiology of SLE is still unknown and is probably multifactorial. Both genetic and environmental factors have been associated with SLE, but these factors alone are insufficient to explain the onset of SLE. Recently, it has been suggested that chimerism plays a role in the pathogenesis of autoimmune diseases, including SLE. Chimerism indicates the presence of cells from one individual in another individual. In an experimental mouse model, the injection of chimeric cells induces a lupus-like disease. In addition, chimerism is found more often in kidneys of women with SLE than in healthy controls. There are several mechanisms by which chimeric cells could be involved in the pathogenesis of SLE. In this review, three hypotheses on the role of chimerism in SLE are discussed. The first two hypotheses describe the possibilities that chimeric cells induce either a graft-vs-host reaction in the host (comparable with reactions seen after bone marrow transplantation) or a host-vs-graft reaction (comparable with reactions seen after solid organ transplantation). The third hypothesis discusses the possible beneficial role chimeric cells may play in repair mechanisms due to their stem cell-like properties. This review provides insights into the mechanisms by which chimerism may be involved in SLE and proposes several lines of inquiry to further investigate chimerism in SLE.

Production of a novel class of polyreactive pathogenic autoantibodies in BXD2 mice causes glomerulonephritis and arthritis

OBJECTIVE

The BXD2 mouse strain spontaneously develops glomerulonephritis and erosive arthritis. The goal of this study was to identify the antigenic target proteins and epitopes and to unravel the mechanisms by which the related conditions arise in BXD2 mice.

METHODS

Individual hybridomas isolated from the spleen of a 10-month-old BXD2 mouse were injected intraperitoneally into nonautoimmune mice for evaluation of pathogenicity of each autoantibody. Autoantigens were immunoprecipitated with the pathogenic autoantibody L3A4. Autoantigens were identified using enzyme-linked immunosorbent assay, Western blotting, 2-dimensional gel electrophoresis, and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MS) and tandem MS. Antigenic epitopes were determined using a high-throughput epitope mapping method.

RESULTS

The production of autoantibodies in BXD2 mice occurred in an orderly progression, with peak levels of autoantibodies to nitrotyrosine (NT)-modified enolase, Ro, alpha-actin, and heat-shock proteins (HSPs) preceding peak levels of antihistone, anti-DNA, and rheumatoid factor. Two monoclonal autoantibodies, L3A4 and T56G10, were identified that could induce immune complexes, renal disease, and/or arthritis. Both L3A4 and T56G10 were polyreactive, and each reacted with separate sets of autoantigens. The antigenic targets of L3A4 consisted of NT-modified enolase, ATP5b, alpha-actin, and Hsp70 family proteins including Hspa5 and Hsp74. The antigenic epitopes of NT-modified enolase and Hspa5 exhibited sequence homology and cross-reactivity, suggesting that epitope spreading may occur through a molecular mimicry mechanism.

CONCLUSION

The polyreactivity of autoantibodies that target a novel class of autoantigens may enable these autoantibodies to induce erosive arthritis or glomerulonephritis either by direct pathogenic mechanisms or indirectly via Fc or immune complex deposition.

Synovial fibroblasts promote osteoclast formation by RANKL in a novel model of spontaneous erosive arthritis

OBJECTIVE

Erosion of cartilage and bone is a hallmark of rheumatoid arthritis (RA). This study was undertaken to explore the roles of hyperproliferating synovial fibroblasts and macrophages in abnormal osteoclast formation, using the recently described BXD2 mouse model of RA.

METHODS

Cell distribution in the joints was analyzed by immunohistochemistry, using tartrate-resistant acid phosphatase (TRAP) staining to identify osteoclasts. To identify the defective cells in BXD2 mice, mouse synovial fibroblasts (MSFs) were cultured with bone marrow-derived macrophages. Osteoclast formation was assayed by TRAP staining and bone resorption pit assay, and the cytokine profiles of the MSFs and macrophages were determined by quantitative real-time polymerase chain reaction and enzyme-linked immunosorbent assay.

RESULTS

In BXD2 mice, TRAP-positive osteoclasts were found at sites of active bone erosion, in close proximity to hyperproliferating synovial fibroblasts. On coculture, MSFs from BXD2 mice, but not C57BL/6 mice, produced high levels of RANKL messenger RNA, induced macrophages to form osteoclasts, and actively eroded bone slices, through a mechanism(s) that could be blocked by pretreatment with osteoprotegerin. Although macrophages from BXD2 mice expressed higher basal levels of tumor necrosis factor alpha (TNFalpha), interleukin-1beta (IL-1beta), and IL-6 than those from C57BL/6 mice, abnormal osteoclast formation was not due to enhanced sensitivity of the BXD2 mouse macrophages to RANKL. TNFalpha, produced by both BXD2 MSFs and BXD2 mouse macrophages, had a strong stimulatory effect on RANKL expression.

CONCLUSION

BXD2 MSFs produce RANKL and induce the development of osteoclasts from macrophages. The enhanced production of RANKL is possibly due to autocrine stimulation, together with paracrine stimulation by factors produced by macrophages.

Genetic segregation of spontaneous erosive arthritis and generalized autoimmune disease in the BXD2 recombinant inbred strain of mice

The BXD2 strain of mice is one of approximately 80 BXD recombinant inbred (RI) mouse strains derived from an intercross between C57BL/6J (B6) and DBA/2J (D2) strains. We have discovered that adult BXD2 mice spontaneously develop generalized autoimmune disease, including glomerulonephritis (GN), increased serum titres of rheumatoid factor (RF) and anti-DNA antibody, and a spontaneous erosive arthritis characterized by mononuclear cell infiltration, synovial hyperplasia, and bone and cartilage erosion. The features of lupus and arthritis developed by the BXD2 mice segregate in F2 mice generated by crossing BXD2 mice with the parental B6 and D2 strains. Genetic linkage analysis of the serum levels of anti-DNA and RF by using the BXD RI strains shows that the serum titers of anti-DNA and RF were influenced by a genetic locus on mouse chromosome (Chr) 2 near the marker D2Mit412 (78 cm, 163 Mb) and on Chr 4 near D4Mit146 (53.6 cm, 109 Mb), respectively. Both loci are close to the B-cell hyperactivity, lupus or GN susceptibility loci that have been identified previously. The results of our study suggest that the BXD2 strain of mice is a novel model for complex autoimmune disease that will be useful in identifying the mechanisms critical for the immunopathogenesis and genetic segregation of lupus and erosive arthritis.

BXD recombinant inbred mice represent a novel T cell-mediated immune response tumor model

To develop a better animal model for studying the effects of the host environment in neoplasia, we injected various genetically well-characterized H-2(d) RI strains of BXD mice with syngeneic breast cancer cells (TS/A) and monitored the growth of tumors over time. There was a marked difference in the growth of the implanted breast cancer cells among the 14 BXD RI strains, with 4 patterns of tumor development being observed: in type I, the implanted tumor cells grew rapidly in the first 2 weeks, necrosis of the tumors was observed and metastases to the intestinal lymph nodes and pancreas was observed, causing death; in type II, the implanted tumor cells grew slowly and attained a size after day 50 that required killing the animal, with tumor necrosis being rare and metastases absent; in type III, the implanted tumor cells grew initially but underwent a slow decline after 4 weeks; and in type IV, the implanted tumor cells failed to develop. Apoptosis of the implanted tumor cells was responsible for the regression of tumor nodules. The T-cell immune response minimized tumor development in types III and IV since T-cell depletion of the BXD RI mice resulted in aggressively growing tumors in these strains.

Genetic dissection of age-related changes of immune function in mice

Understanding of the genetic basis of normal and abnormal development of the immune response is an enormous undertaking. The immune response, at the most minimal level, involves interactions of antigen presenting cells (APCs), T and B cells. Each of these cells produce cell surface and soluble factors (cytokines) that affect both autocrine and paracrine functions. A second level of complexity needs to consider the development of the macrophage/monocyte lineage as well as the production of the common lymphoid precursor which undergoes distinct maturation steps in the thymus and periphery to form mature T cells as well as in BM (BM) and lymphoid organs to form mature B cells. A third level of complexity involves the immune response to infectious agents including viruses and also the response to tumour antigens. In addition, there are imbalances that predispose to decreased responses (immunodeficiencies) or increased responses (autoimmunity). A fourth level of complexity involves attempts to understand the differences in the immune response that occurs at a very young age, in adults, and at a very old age. This review will focus on the use of C57BL/6 J X DBA/2 J (BXD) recombinant inbred (RI) strains of mice to map genetic loci associated with the production of lymphoid precursors in the BM, development of T cells in the thymus, and T-cell responses to stimulation in the peripheral lymphoid organs in adult and in aged mice. Strategies to improve the power and precision in which complex traits such as the age-related immune response can be mapped is limited with the current set of 35 strains of BXD mice. Strategies to increase these strains by generating recombinant intercross (RIX) strains of mice are being developed to enable this large set of lines to detect quantitative trait loci (QTLs) with a much higher consistency and statistical power. More importantly, the resolution with which these QTLs can be mapped would be greatly improved and, in many cases, adequate to carry out direct identification of candidate genes. It is likely that, given the complexity of the immune system development, the number of cells involved in an immune response, and especially the changes in the immune system with ageing, mapping hundreds of genes will be required to fully understand age-related changes in the immune response. This review outlines ongoing and future strategies that will enable the mapping and identification of these genes.

Progression from acute to chronic disease in a murine parent-into-F1 model of graft-versus-host disease

The parent-into-immunocompetent-F(1) model of graft-vs-host disease (GVHD) induces immune dysregulation, resulting in acute or chronic GVHD. The disease outcome is thought to be determined by the number of parental anti-F(1) CTL precursor cells present in the inoculum. Injection of C57BL/6 (B6) splenocytes into (B6 x DBA/2)F(1) (B6D2F(1)) mice (acute model) leads to extensive parental cell engraftment and early death, whereas injection of DBA/2 cells (chronic model) results in little parental cell engraftment and a lupus-like disease. This study demonstrated that injection of BALB/c splenocytes into (BALB/c x B6)F(1) (CB6F(1)) mice resulted in little engraftment of parental lymphocytes and the development of lupus as expected. Injection of B6 splenocytes into CB6F(1) initiated an initial burst of parental cell engraftment similar to that of B6 into B6D2F(1). However, the acute disease resolved, and the CB6F(1) mice went on to develop chronic GVHD with detectable Abs to ssDNA, dsDNA, and extractable nuclear Ags. Limiting dilution CTL assays determined that B6 splenocytes have CTL precursor frequencies of 1/1000 against both CB6F(1) and B6D2F(1), whereas DBA/2 and BALB/c splenocytes have a CTL precursor frequency of 1/20,000 for their respective F(1)s. The Th cell precursor frequency for B6 anti-DBA/2 was 3-fold higher than that for B6 anti-BALB/c determined by limiting dilution proliferation assays. These results indicate the importance of adequate allospecific helper as well as effector T cells for the induction and maintenance of acute GVHD in this model, and presents an unexpected model in which initial acute GVHD is replaced by the chronic form of disease.

Genetic factors influencing the development of chronic graft-versus-host disease in a murine model

Graft-versus-host disease (GVHD) is a major complication of bone marrow transplantation that can occur in either acute or chronic forms. Much of the long-term pathology seen in chronic GVHD is a result of autoantibody production. In the DBA/2-->B6D2F1 murine model of chronic GVHD, anti-ssDNA autoantibodies can be detected by 14 days post cell transfer. These autoantibodies are not observed in B6D2F1 recipients of cells from C57BL/6 or B10.D2 donors, which develop acute rather than chronic GVHD. Therefore, in this model, donor genetic factors predispose to the development of chronic GVHD in recipients. We performed a genetic analysis aimed at mapping donor loci that influence the magnitude of early autoantibody production in B6D2F1 recipients of cells from DBA/2 donor mice. Linkage analysis suggested an influence of two loci: a locus on chromosome 11 linked to D11Mit278 and a locus on chromosome 4 linked to D4Mit226. The locus on chromosome 11 also appeared to influence the development of renal pathology associated with chronic GVHD.

A locus closely linked to Mtv7 on mouse chromosome 1 influences development of acute versus chronic graft-versus-host disease in a murine model

The relationship between acute and chronic graft-versus-host disease (GVHD) is not well understood. A murine model of acute and chronic GVHD is the B6D2F1 parent-->F1 model in which transfer of C57BL/6 parental strain lymphoid cells to B6D2F1 recipients results in development of Th1-mediated acute GVHD, whereas transfer of DBA/2 parental strain lymphoid cells to B6D2F1 recipients results in development of Th2-mediated chronic GVHD. Numerous studies have investigated the reason for the differential development of acute versus chronic GVHD in this model but have as yet failed to identify the factor that determines which type of T helper cell will predominate and thereby which type of GVHD will develop. In this report, we demonstrate, using congenic strains of mice, that a locus in the vicinity of the Mtv7 locus on Chromosome 1 of the mouse significantly influences development of acute versus chronic GVHD in the B6D2F1 model.