Tumor Necrosis Factor-Like Weak Inducer of Apoptosis Activates Type I Interferon Signals in Lupus Nephritis.

Type I interferon (IFN) plays a central role in pathogenesis of systemic lupus erythematosus (SLE); tumor necrosis factor-like weak inducer of apoptosis (TWEAK) has been associated with a pathogenic role in lupus nephritis (LN). Thus we investigated whether TWEAK could induce the activation of type I IFN pathway in LN. We examined this in patient-derived peripheral blood mononuclear cells (PBMCs) as well as MRL/lpr mice, a murine LN model. Relative to the control cohorts, MRL/lpr mice showed severe histological changes, high index levels of renal damage, and elevated expression of type I IFN-inducible genes. After shRNA suppression of TWEAK, we observed that renal damage was significantly attenuated and expression of type I IFN-inducible genes was reduced in MRL/lpr mice. In parallel, siRNA of TWEAK also significantly reduced the expression of type I IFN-inducible genes in PBMCs relative to control transfections. In PBMCs, TWEAK stimulation also led to expression of type I IFN-inducible genes. Our results illustrate a novel regulatory role of TWEAK, in which its activity positively regulates type I IFN pathway in LN based on preclinical models. Our findings suggest TWEAK could act as a critical target in preventing renal damage in patients with LN.

B cell-derived IL-10 does not regulate spontaneous systemic autoimmunity in MRL.Fas(lpr) mice.

B cells contribute to the pathogenesis of chronic autoimmune disorders, like systemic lupus erythematosus (SLE), via multiple effector functions. However, B cells are also implicated in regulating SLE and other autoimmune syndromes via release of IL-10. B cells secreting IL-10 were termed "Bregs" and were proposed as a separate subset of cells, a concept that remains controversial. The balance between pro- and anti-inflammatory effects could determine the success of B cell-targeted therapies for autoimmune disorders; therefore, it is pivotal to understand the significance of B cell-secreted IL-10 in spontaneous autoimmunity. By lineage-specific deletion of Il10 from B cells, we demonstrated that B cell-derived IL-10 is ineffective in suppressing the spontaneous activation of self-reactive B and T cells during lupus. Correspondingly, severity of organ disease and survival rates in mice harboring Il10-deficient B cells are unaltered. Genetic marking of cells that transcribe Il10 illustrated that the pool of IL-10-competent cells is dominated by CD4 T cells and macrophages. IL-10-competent cells of the B lineage are rare in vivo and, among them, short-lived plasmablasts have the highest frequency, suggesting an activation-driven, rather than lineage-driven, phenotype. Putative Breg phenotypic subsets, such as CD1d(hi)CD5(+) and CD21(hi)CD23(hi) B cells, are not enriched in Il10 transcription. These genetic studies demonstrated that, in a spontaneous model of murine lupus, IL-10-dependent B cell regulation does not restrain disease and, thus, the pathogenic effects of B cells are not detectably counterbalanced by their IL-10-dependent regulatory functions.

Quantitative trait locus analysis of ovarian cysts derived from rete ovarii in MRL/MpJ mice.

MRL/MpJ (MRL) is a model mouse for autoimmune diseases such as dermatitis, vasculitis, arthritis, and glomerulonephritis. In addition to these immune-associated disorders, we found that older MRL mice develop ovarian cysts originating from the rete ovarii, which is lined by ciliated or nonciliated epithelium and considered remnants of mesonephric tubules. Ovarian cysts, which are reported to have several sources, are associated with female infertility, but information regarding the genetic etiology of ovarian cysts originating from the rete ovarii is rare. In this study, to elucidate the genetic background of development of ovarian cysts, we performed quantitative trait locus (QTL) analysis using 120 microsatellite markers, which cover the whole genome of murine chromosomes, and 213 backcross progenies between female MRL and male C57BL/6N mice. The quantitative trait measured was the circumferences of rete ovarii or ovarian cysts. As a result, suggestive linkages were detected on Chrs 3, 4, 6, and 11, but significant linkages were located on Chr 14 by interval mapping. We thereby designated the 27.5-cM region of Chr 14 "MRL Rete Ovarian Cysts (mroc)." The peak regions of Chrs 4 and 14 in particular showed a close additive interaction (p < 0.00001). From these results we concluded that multiple loci on Chrs 3, 4, 6, 11, and 14 interact to result in development of ovarian cysts in MRL mice.

Analysis of factors decreasing testis weight in MRL mice.

MRL/MpJ (MRL) mouse testes have several unique characteristics, including the appearance of oocytes, the occurrence of metaphase-specific apoptosis of meiotic spermatocytes, and the presence of heat-shock-resistant spermatocytes. In the present study we used chromosomal mapping to determine the genomic background associated with small testis size in MRL mice. We prepared and analyzed C57BL/6-based congenic mice carrying MRL mouse loci. Quantitative trait loci (QTL) analysis revealed susceptibility loci for small testis size at 100 cM on chromosome (Chr) 1 and at around 80 cM on Chr 2. Analysis with B6.MRLc1 and B6.MRLc2 congenic mice and double-congenic mice confirmed the QTL data and showed that low testis weight in MRL mice was caused by germ cell apoptosis. Through histological examinations we found that B6.MRLc1 and B6.MRLc2 mice showed stage-specific apoptosis in their testes, the former at metaphase stage XII and the later at pachytene stage IV. Metaphase-specific apoptosis of spermatocytes occurs due to mutation of the exonuclease 1 (Exo1) gene located at 100 cM on Chr 1. Thus, the mutation of the Exo1 gene is also responsible for low testis weight caused by metaphase-specific apoptosis. In conclusion, testis weight is reduced in MRL mice due to apoptosis of germ cells caused by mutations in loci on Chrs 1 and 2.

Retained features of embryonic metabolism in the adult MRL mouse.

The MRL mouse is an inbred laboratory strain that was derived by selective breeding in 1960 from the rapidly growing LG/J (Large) strain. MRL mice grow to nearly twice the size of other commonly used mouse strains, display uncommonly robust healing and regeneration properties, and express later onset autoimmune traits similar to Systemic Lupus Erythematosis. The regeneration trait (heal) in the MRL mouse maps to 14-20 quantitative trait loci and the autoimmune traits map to 5-8 loci. In this paper we report the metabolic and biochemical features that characterize the adult MRL mouse and distinguish it from C57BL/6 control animals. We found that adult MRL mice have retained a number of features of embryonic metabolism that are normally lost during development in other strains. These include an emphasis on aerobic glycolytic energy metabolism, increased glutamate oxidation, and a reduced capacity for fatty acid oxidation. MRL tissues, including the heart, liver, and regenerating ear hole margins, showed considerable mitochondrial genetic and physiologic reserve, decreased mitochondrial transmembrane potential (DeltaPsi(m)), decreased reactive oxygen species (ROS), and decreased oxidative phosphorylation, yet increased mitochondrial DNA and protein content. The discovery of embryonic metabolic features led us to look for cells that express markers of embryonic stem cells. We found that the adult MRL mouse has retained populations of cells that express the stem cell markers Nanog, Islet-1, and Sox2. These are present in the heart at baseline and highly induced after myocardial injury. The retention of embryonic features of metabolism in adulthood is rare in mammals. The MRL mouse provides a unique experimental window into the relationship between metabolism, stem cell biology, and regeneration.

Mast cell hyperplasia in the skin of Dsg4-deficient hypotrichosis mice, which are long-living mutants of lupus-prone mice.

Desmosomal cadherins are essential cell adhesion molecules expressed in the epidermis. We identified a mutation of a cadherin superfamily member, namely, desmoglein 4 (Dsg4), in early onset of death (EOD)( hage ) mice with hypotrichosis. The mutation was induced by the insertion of an early transposon II-beta into intron 8 of Dsg4. Mast cell hyperplasia was observed in the skin of EOD( hage ) mice. The abnormally expanded population of lpr T cells, i.e., CD4(-)CD8(-)B220(+)Thy1.2(+) alphabetaT cells, in the splenocytes of EOD mice was reduced in EOD( hage ) mice. Therefore, it was suspected that the long-living mutant EOD( hage ) mice were selected from lupus-prone EOD mice because of their immunological immaturity. These findings clearly indicate that Dsg4 is an important molecule for the formation of hair follicles and hypothesize that unorganized hyperplastic hair follicles in anagen due to the Dsg4 mutation provide niches for mast cell precursors in the skin.

A genetic locus controlling aging-sensitive regression of B lymphopoiesis in an autoimmune-prone MRL/lpr strain of mice.

Aging readily affects immune system under the influence of environmental and/or intrinsic factors while accelerating the development of various immune disorders including autoimmune diseases. Little is known about molecular and cellular mechanisms connecting between immune senescence and development of autoimmune diseases. Here, we first show strain-specific and aging-sensitive onset of B-cell abnormality in a lupus-prone MRL/Mp.Fas(lpr) (MRL/lpr) strain of mice. This abnormality was characterized by the regression of B lymphopoiesis in the bone marrow of this strain. We next examined the association between the B-cell regression and onset of autoimmune diseases in aged (MRL/lpr x C3H/He.Fas(lpr)) F2 mice, in which pathologic phenotypes, such as glomerulonephritis, vasculitis, sialoadenitis and arthritis, variously developed. We also searched whole genome to identify genetic loci linked to the B-cell regression by using the same F2 mice. The B-cell regression manifested in the spleen of F2 mice was retrospectively evaluated by reverse transcriptase-based PCR quantification. The results demonstrated that the onset of autoimmune diseases in the F2 mice was not associated with the aging-sensitive B-cell regression. The genetic study identified a significant locus responsible for the B-cell regression in the vicinity of D5Mit233 (29 cM). This is first evidence for the presence of a genetic locus that affects B lymphopoiesis in an aging-sensitive manner.

Mouse chromosome 9 quantitative trait loci for soft tissue regeneration: congenic analysis and fine mapping.

Development of gene therapies for wound healing will depend on the identification of the genes involved in wound healing and tissue regeneration. Previous quantitative trait loci (QTL) studies in mice using the ear punch model have shown that major QTL exist on chromosome (Chr) 9 for soft tissue regeneration. In this study, we have developed a congenic line that contains the Chr 9 QTL chromosomal region from super healer MRL/MpJ in the genomic background of poor-healing SJL/J. The phenotypic effect of this QTL was confirmed in male mice, where the congenic line has shown significant healing improvement over SJL. Fine mapping of the Chr 9 QTL region with 23 markers at an average distance of 4.2 Mb using a total of 1,564 MRL/MpJ x SJL/J F(2) mice revealed the presence of at least three QTL peaks, implying that three separate loci may contribute to the phenotypic effect of this QTL. Based on the 2-LOD intervals, the total QTL region was confined to a combined length of no more than 28.2 Mb. Application of a Bayesian shrinkage estimation indicated that a major locus was located in a region of just 1.3 Mb.

The characteristics of hematopoietic stem cells from autoimmune-prone mice and the role of neural cell adhesion molecules in abnormal proliferation of these cells in MRL/lpr mice.

BACKGROUND AND OBJECTIVES: Using various animal models for autoimmune diseases, we have previously shown that such diseases are stem cell disorders.1 In order to understand how autoimmune diseases develop, we investigated the distinct qualitative differences between hematopoietic stem cells (HSC) from normal and autoimmune-prone mice. DESIGN AND METHODS: We studied the major histocompatibility complex (MHC) restriction between HSC and stromal cells in vitro and in vivo. We also examined the ability of HSC to adhere to a stromal cell line and, using flow cytometry, analyzed the expression of various adhesion molecules in HSC before and after the onset of autoimmune disease. In addition, the effect of antibodies to anti-adhesion molecules on the proliferation of HSC was investigated. RESULTS: The abnormal HSC of MRL/lpr mice showed no MHC restriction (or preference) with stromal cells either in vitro or in vivo, although there was MHC restriction between normal HSC and stromal cells, as we previously reported.2,3 The abnormal HSC of MRL/lpr mice exhibited enhanced adhesion to stromal cells in vitro and expressed a higher amount of adhesion molecules such as neural cell adhesion molecule (NCAM). Interestingly, the proliferation of HSC in MRL/lpr mice was significantly suppressed by anti-NCAM monoclonaal antibodies. INTERPRETATION AND CONCLUSIONS: Abnormal HSC of MRL/lpr mice are more resilient than normal HSC. Furthermore, among various adhesion molecules, only NCAM shows increased expression on HSC of MRL/lpr mice after the onset of autoimmune diseases, and these molecules contribute to the enhanced proliferation capacity of abnormal HSC in MRL/lpr mice. The present findings suggest that there are intrinsic qualitative differences between HSC from normal and autoimmune-prone MRL/lpr mice.

Nephritogenic anti-DNA antibodies regulate gene expression in MRL/lpr mouse glomerular mesangial cells.

OBJECTIVE: Lupus-associated IgG anti-double-stranded DNA antibodies are thought to be pathogenic in the kidney due to cross-reaction with glomerular antigens, leading subsequently to immune complex formation in situ and complement activation. We undertook this study to determine if pathogenic anti-DNA antibodies may also contribute to renal damage by directly influencing mesangial gene expression. METHODS: Complementary DNA microarray gene profiling was performed in primary mesangial cells (derived from lupus-prone MRL/lpr mice) treated with pathogenic, noncomplexed anti-DNA antibodies. Significant gene up-regulation induced by anti-DNA antibodies as determined by microarray analysis was further investigated by real-time polymerase chain reaction and methods to detect the relevant proteins. Induction of proinflammatory genes by pathogenic antibodies was confirmed by comparing gene expression in glomeruli of old versus young MRL/lpr mice, and by antibody injection in vivo. RESULTS: Pathogenic, but not nonpathogenic, antibodies significantly induced a number of transcripts, including CXCL1/KC, LCN2, iNOS, CX3CL1/fractalkine, SERPINA3G, and IkappaBalpha ("marker genes"). Blocking of Fcgamma receptors or using Fcgamma chain-knockout mesangial cells had no effect on the gene regulation effect of the pathogenic antibody R4A, indicating a non-Fc-dependent mechanism. The glomerular expression of these marker genes increased over time with the development of glomerular antibody deposition and active nephritis in MRL/lpr mice. Moreover, injection of R4A into SCID mice in vivo significantly up-regulated glomerular marker gene expression. CONCLUSION: These findings indicate that the renal pathogenicity of anti-DNA antibodies may be attributed in part to their ability to directly modulate gene expression in kidney mesangial cells through both Fc-dependent and non-Fc-dependent mechanisms.

A critical evaluation of the effect of population size and phenotypic measurement on QTL detection and localization using a large F2 murine mapping population

Population size and phenotypic measurement are two key factors determining the detection power of quantitative trait loci (QTL) mapping. We evaluated how these two controllable factors quantitatively affect the detection of QTL and their localization using a large F2 murine mapping population and found that three main points emerged from this study. One finding was that the sensitivity of QTL detection significantly decreased as the population size decreased. The decrease in the percentage logarithm of the odd score (LOD score, which is a statistical measure of the likelihood of two loci being lied near each other on a chromosome) can be estimated using the formula 1 - n/N, where n is the smaller and N the larger population size. This empirical formula has several practical implications in QTL mapping. We also found that a population size of 300 seems to be a threshold for the detection of QTL and their localization, which challenges the small population sizes commonly-used in published studies, in excess of 60 percent of which cite population sizes <300. In addition, it seems that the precision of phenotypic measurement has a limited capacity to affect detection power, which means that quantitative traits that cannot be measured precisely can also be used in QTL mapping for the detection of major QTL.

Membranous glomerulonephritis development with Th2-type immune deviations in MRL/lpr mice deficient for IL-27 receptor (WSX-1).

MRL/lpr mice develop spontaneous glomerulonephritis that is essentially identical with diffuse proliferative glomerulonephritis (World Health Organization class IV) in human lupus nephritis. Lupus nephritis is one of the most serious complications of systemic lupus erythematosus. Diffuse proliferative glomerulonephritis is associated with autoimmune responses dominated by Th1 cells producing high levels of IFN-gamma. The initial mounting of Th1 responses depends on the function of the WSX-1 gene, which encodes a subunit of the IL-27R with homology to IL-12R. In mice deficient for the WSX-1 gene, proper Th1 differentiation was impaired and abnormal Th2 skewing was observed during infection with some intracellular pathogens. Disruption of the WSX-1 gene dramatically changed the pathophysiology of glomerulonephritis developing in MRL/lpr mice. WSX-1-/- MRL/lpr mice developed disease resembling human membranous glomerulonephritis (World Health Organization class V) with a predominance of IgG1 in glomerular deposits, accompanied by increased IgG1 and IgE in the sera. T cells in WSX-1-/- MRL/lpr mice displayed significantly reduced IFN-gamma production along with elevated IL-4 expression. Loss of WSX-1 thus favors Th2-type autoimmune responses, suggesting that the Th1/Th2 balance may be a pivotal determinant of human lupus nephritis development.

MRL/Mp CD4+,CD25- T cells show reduced sensitivity to suppression by CD4+,CD25+ regulatory T cells in vitro: a novel defect of T cell regulation in systemic lupus erythematosus.

OBJECTIVE: To investigate the hypothesis that loss of suppression mediated by peripheral CD4+,CD25+ regulatory T cells is a hallmark of systemic lupus erythematosus (SLE). METHODS: Mice of the MRL/Mp strain were studied as a polygenic model of SLE. Following immunomagnetic selection, peripheral lymphoid CD25+ and CD25- CD4+ T cells were cultured independently or together in the presence of anti-CD3/CD28 monoclonal antibody-coated beads. Proliferation was assessed by measuring the incorporation of tritiated thymidine. RESULTS: While MRL/Mp CD4+,CD25+ regulatory T cells showed only subtle abnormalities of regulatory function in vitro, syngeneic CD4+,CD25- T cells showed significantly reduced sensitivity to suppression, as determined by crossover experiments in which MRL/Mp CD4+,CD25- T cells were cultured with H-2-matched CBA/Ca CD4+,CD25+ regulatory T cells in the presence of a polyclonal stimulus. CONCLUSION: Our findings highlight a novel defect of peripheral tolerance in SLE. Identification of this defect could open new opportunities for therapeutic intervention.

Altered CNS response to injury in the MRL/MpJ mouse.

The MRL/MpJ mouse has a greatly enhanced healing response and an absence of scarring compared with other mouse strains. Following lesions to the CNS mammals show a scarring response known as reactive gliosis, and this CNS scar tissue blocks regeneration of cut axons. We have therefore compared reactive gliosis in the MRL/MpJ mouse and the Swiss Webster mouse, which exhibits normal scarring in the periphery. The lesion model was a stab lesion to the cortex, in which reactive gliosis has previously been quantified. Axon regeneration was examined following a cut lesion to the dopaminergic projection from the substantia nigra to the striatum used in previous regeneration experiments. In the MRL/MpJ following the lesion compared with Swiss Webster mice there was greater cell loss around the lesion followed by greater and more widespread and more prolonged cellular proliferation. Early after the lesion there was a greater loss of glial fibrillary acidic protein (GFAP)-positive astrocytes around the injury site in the MRL/MpJ, and an enhancement and prolongation of the microglial inflammatory response. This was accompanied by greater and more widespread blood-brain barrier leakage following injury. RNA levels for the matrix metalloproteinases (MMP)-2 and MMP-9 as well as for the thrombin receptors PAR-1 and PAR-4 were also greater at the MRL/MpJ injury site. All of these differences were transient and by 14 days post-injury there were no differences observed between MRL/MpJ and control mice. No axonal regeneration was observed following axotomy to the nigrostriatal pathway of the MRL/MpJ or the Swiss Webster mice at any time point.

Spallanzani's mouse: a model of restoration and regeneration.

The ability to regenerate is thought to be a lost phenotype in mammals, though there are certainly sporadic examples of mammalian regeneration. Our laboratory has identified a strain of mouse, the MRL mouse, which has a unique capacity to heal complex tissue in an epimorphic fashion, i.e., to restore a damaged limb or organ to its normal structure and function. Initial studies using through-and-through ear punches showed rapid full closure of the ear holes with cartilage growth, new hair follicles, and normal tissue architecture reminiscent of regeneration seen in amphibians as opposed to the scarring usually seen in mammals. Since the ear hole closure phenotype is a quantitative trait, this has been used to show-through extensive breeding and backcrossing--that the trait is heritable. Such analysis reveals that there is a complex genetic basis for this trait with multiple loci. One of the major phenotypes of the MRL mouse is a potent remodeling response with the absence or a reduced level of scarring. MRL healing is associated with the upregulation of the metalloproteinases MMP-2 and MMP-9 and the downregulation of their inhibitors TIMP-2 and TIMP-3, both present in inflammatory cells such as neutrophils and macrophages. This model has more recently been extended to the heart. In this case, a cryoinjury to the right ventricle leads to near complete scarless healing in the MRL mouse whereas scarring is seen in the control mouse. In the MRL heart, bromodeoxyuridine uptake by cardiomyocytes filling the wound site can be seen 60 days after injury. This does not occur in the control mouse. Function in the MRL heart, as measured by echocardiography, returns to normal.

A new mutation, ataxia and male sterility (ams), of autoimmune-prone MRL/lpr mouse is not linked to lpr gene but associated with reduction of spleen size and alteration of lymphocyte subpopulations.

We describe changes in the immune system of the newly established mutant line, ataxia and male sterility (AMS) mouse, and that the putative ams mutation is independent of lpr but seemed to affect lymphoproliferation in its mother strain, MRL/lpr. The mean weights of the spleen and lymph nodes of ams-lpr double-homozygous mouse were reduced compared with lpr single-homozygous mouse. Comparison between ams single-homozygous and control mice revealed 45-50% reduction of the spleen weight in the former for which reduction of the number of nucleated cells contributed greatly. In the lymphocyte/monocyte fraction of the spleen, there were significant changes in the proportion of lymphocyte subpopulations, with a reduction of B cells, an increase in CD4 and CD8 T cells, and a decrease in the CD4 : CD8 ratio. In vitro response of splenocytes to concanavalin A showed inconspicuous dose- and time-dependent responses in ams homozygous spleen, suggesting functional alteration of the immunological response. Our results indicate that ams mutation affects the immune system in addition to its two other major effects on the central nervous system and male reproductive system.

Genetic basis of tissue specificity of vasculitis in MRL/lpr mice.

OBJECTIVE: To clarify the mode of inheritance of the tissue distribution of vasculitis in MRL/Mp-lpr/lpr (MRL/lpr) lupus-prone mice and to identify the susceptibility loci. METHODS: Vasculitis in individual MRL/lpr, C3H/HeJ-lpr/lpr (C3H/lpr), (MRL/lpr x C3H/lpr)F(1), and (MRL/lpr x C3H/lpr)F(2) intercross mice was analyzed by histopathologic grading of main branches of the aorta and of medium-sized arteries in the lower limbs. Genomic DNA samples from F(2) intercross mice were examined by simple sequence-length polymorphism analysis, and the polymorphic microsatellite markers highly associated with vasculitis in each tissue were determined as vasculitis susceptibility loci. RESULTS: A susceptibility locus with significant linkage to vasculitis of main branches of the aorta was mapped on chromosome 4 at D4Mit213 (map position 13.3cM) selectively in males, while vasculitis of medium-sized arteries in the lower limbs was mapped to different chromosomes: at D8Mit31 on chromosome 8 (map position 33.0) selectively in females and at D5Mit36 on chromosome 5 (map position 65.0). All of these were different from the previously defined loci governing susceptibility to vasculitis involving the kidneys. CONCLUSION: Systemic vasculitis in MRL/lpr mice is genetically controlled with cumulative effects of multiple gene loci, each of which has tissue specificity.

A possible mouse model for spontaneous cholangitis: serological and histological characteristics of MRL/lpr mice.

AIMS: MRL/Mp-lpr/lpr (MRL/lpr) mice spontaneously develop lymphadenopathy, hypergammaglobulinaemia, serum auto-antibodies, and a generalised auto-immune disease including glomerulonephritis and arthritis, and have been used as a model for the study of systemic lupus erythematosus. Recently, MRL/lpr mice were also reported as a potentially suitable animal model of primary biliary cirrhosis (PBC). The aim of this study was to determine the suitability of MRL/Mp-lpr/lpr (MRL/lpr) mice as an experimental auto-immune-mediated cholangitis model for PBC. METHODS: We investigated the serum hepatobiliary enzymes, histopathological findings, and the target antigen of antimitochondrial antibodies (AMA) in MRL/lpr mice. RESULTS: Serum levels of total bilirubin and hepatobiliary enzymes including alanine aminotransferase (ALT), leucine aminopeptidase (LAP), and gamma-glutamyl transpeptidase (G-GTP) in older-aged (over 20 weeks old) MRL/lpr or MRL/Mp-+/+ (MRL/+) mice were not significantly higher than those in younger (8-12 weeks old) MRL/lpr, MRL/+, or older-aged control mice (C3H/HeJ and BALB/C mice). Histopathologically, 24 of 47 (51%) older-aged MRL/lpr mice showed evidence of cholangitis, compared with two of 20 (10%) younger MRL/lpr mice. Especially, epithelioid granuloma and/or bile duct loss were seen in 11 out of 47 (23%) older-aged MRL/lpr mice, whereas such findings were seen in only one of 20 (5%) younger MRL/lpr mice. None of the MRL/+, C3H/HeJ, and BALB/C mice developed cholangitis. The target antigens of AMA were not pyruvate dehydrogenase complex but 2-oxoglutarate dehydrogenase complex and/or branched-chain oxo-acid dehydrogenase complex as confirmed by immunoblotting. There was no significant correlation between the presence of AMA and severity of histological lesions in older-aged MRL/lpr mice, and there were no significant differences in these biochemical data, the proportion of mice with portal inflammation, cholangitis and AMA between male and female MRL/lpr mice. CONCLUSION: Although several clinical features were incompatible with PBC, the serological and histopathological features of MRL/lpr mice indicate that these mice can be used as an experimental immune-mediated cholangitis model for PBC.

Arthritis in MRL/lpr mice is under the control of multiple gene loci with an allelic combination derived from the original inbred strains.

OBJECTIVE: To clarify the mode of inheritance and the genome origins of arthritis in a lupus-prone strain of mice, MRL/MpJ, bearing a Fas deletion mutant gene, lpr (MRL/lpr). METHODS: Using non-lupus-prone strains of mice, C3H/HeJ-lpr/lpr (C3H/lpr), (MRL/lpr x C3H/lpr)F(1) intercross and MRL/lpr x (MRL/lpr x C3H/lpr)F(1) backcross mice were prepared. Arthritis in individual mice was analyzed by histopathologic grading, and the genomic DNA of the backcross mice was examined by simple sequence-length polymorphism analysis to determine the polymorphic microsatellite markers highly associated with arthritis. RESULTS: Arthritis-susceptibility loci with significant linkage were mapped between D15Mit111 and D15Mit18 (map position 17.8-18.7 cM) on chromosome 15 and between D19Mit112 and D19Mit72 (map position 43.0-55.0) on chromosome 19 (logarithm of odds scores 3.5 and 4.3, respectively). Three other loci, one mapped to each of chromosomes 1, 2, and 7, showed suggestive linkage. Loci homozygous for MRL alleles on chromosomes 1 and 19 enhanced arthritis in both sexes, whereas other loci on chromosomes 2 and 15 selectively affected males. A locus homozygous for MRL alleles on chromosome 7 inhibited arthritis in both sexes. Three of these loci were found to originate from an LG/J strain and 1 from an AKR/J strain. Some combinations of these loci showed an additive effect in a hierarchical manner on the development of arthritis. CONCLUSION: Arthritis in MRL/lpr mice is a complex pathologic manifestation resulting from the cumulative effect of multiple gene loci with an allelic combination derived from the original inbred strains.

Identification of wound healing/regeneration quantitative trait loci (QTL) at multiple time points that explain seventy percent of variance in (MRL/MpJ and SJL/J) mice F2 population.

Studies on genetic mechanisms of wound healing in mammals are very few, although injury is a leading cause of the global burden of disease. In this study, we performed a high-density, genome-wide scan using 633 (MRL/MPJ x SJL/J) F(2) intercross at multiple time points (days 15, 21, and 25) to identify quantitative trait loci (QTL) involved in wound healing/regeneration. The hypothesis of the study was that QTL and unique epistatic interactions are involved at each time point to promote wound healing/regeneration. Ten QTL were identified from chromosomes 1, 4, 6, 7, 9, and 13. Of the 10 QTL, eight from chromosomes 1, 4, 6, and 9 were novel as compared to QTL identified in the study. The 10 QTL altogether explained 70% of variance in F(2) mice. The same QTL were identified at each time point, with simple linear correlation between days 15, 21, and 25, showing very high significant relationships (R >0.92, P <0.0001). Unique epistatic interactions were identified at each time point except those from chromosomes 4, 6, 9, and 13 that were found at all three time points, showing that some loci are involved at all the three time points of wound healing (days 15, 21, and 25). Therefore, loci-to-loci interactions may play a major role in wound healing. Information from these studies may help in the identification of genes that could be involved in wound healing/regeneration.