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Lupus nephritis (LN) is the most severe end-organ pathology in Systemic Lupus Erythematosus (SLE). Research has enhanced our understanding of immune effectors and inflammatory pathways in LN. However, even with the best available therapy, the rate of complete remission for proliferative LN remains below 50%. A deeper understanding of the resistance or susceptibility of renal cells to injury during the progression of SLE is critical for identifying new targets and developing effective long-term therapies. The complex and heterogeneous nature of LN, combined with the limitations of clinical research, make it challenging to investigate the aetiology of this disease directly in patients. Hence, multiple murine models resembling SLE-driven nephritis are utilised to dissect LN's cellular and genetic mechanisms, identify therapeutic targets, and screen novel compounds. This review discusses commonly used spontaneous and inducible mouse models that have provided insights into pathogenic mechanisms and long-term maintenance therapies in LN.

Systemic lupus erythematosus (SLE) and its renal manifestation Lupus nephritis (LN) are characterized by a dysregulated immune system, autoantibodies, and injury to the renal parenchyma. Iron accumulation and ferroptosis in the immune effectors and renal tubules are recently identified pathological features in SLE and LN. Ferroptosis is an iron dependent non-apoptotic form of regulated cell death and ferroptosis inhibitors have improved disease outcomes in murine models of SLE, identifying it as a novel druggable target. In this review, we discuss novel mechanisms by which iron accumulation and ferroptosis perpetuate immune cell mediated pathology in SLE/LN. We highlight intra-renal dysregulation of iron metabolism and ferroptosis as an underlying pathogenic mechanism of renal tubular injury. The basic concepts of iron biology and ferroptosis are also discussed to expose the links between iron, cell metabolism and ferroptosis, that identify intracellular pro-ferroptotic enzymes and their protein conjugates as potential targets to improve SLE/LN outcomes., Competing Interests: Declaration of competing interest The authors have declared that no conflict of interest exists., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Ferroptosis is a druggable, iron-dependent form of cell death that is characterized by lipid peroxidation but has received little attention in lupus nephritis. Kidneys of lupus nephritis patients and mice showed increased lipid peroxidation mainly in the tubular segments and an increase in Acyl-CoA synthetase long-chain family member 4, a pro-ferroptosis enzyme. Nephritic mice had an attenuated expression of SLC7A11, a cystine importer, an impaired glutathione synthesis pathway, and low expression of glutathione peroxidase 4, a ferroptosis inhibitor. Lipidomics of nephritic kidneys confirmed ferroptosis. Using nephrotoxic serum, we induced immune complex glomerulonephritis in congenic mice and demonstrate that impaired iron sequestration within the proximal tubules exacerbates ferroptosis. Lupus nephritis patient serum rendered human proximal tubular cells susceptibility to ferroptosis which was inhibited by Liproxstatin-2, a novel ferroptosis inhibitor. Collectively, our findings identify intra-renal ferroptosis as a pathological feature and contributor to tubular injury in human and murine lupus nephritis., Competing Interests: Declaration of Competing Interest The authors have declared that no conflict of interest exists., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Objective: Sodium-glucose cotransporter-2 inhibitors have been identified profound renal/cardiac protective effects in different diseases. Here, we assessed the safety and efficacy of dapagliflozin among adult patients with systemic lupus erythematosus (SLE)., Methods: We conducted a single-arm, open-label, investigator-initiated phase I/II trial of dapagliflozin in Chinese patients with SLE with/without lupus nephritis (LN). Patients received oral dapagliflozin at a daily dose of 10 mg added to the standard of care for 6 months. The primary end point was the safety profile. The secondary efficacy end points were composite assessments of disease activity., Results: A total of 38 eligible patients were enrolled. Overall, 19 (50%) adverse events (AEs) were recorded, including 8 (21%) AEs leading to drug discontinuation, of which 4 (10.5%) were attributed to dapagliflozin. Two serious AEs (one of major lupus flare and one of fungal pneumonia) were recorded. Lower urinary tract infection was observed in one (2.63%) patient. The secondary end points revealed no improvement of SLE Disease Activity Index scores or proteinuria (among 17 patients with LN); the cumulative lupus flare rate was 18%, and a reduction of ~30% in the prednisone dose was captured. Net changes in body mass index (-0.50 kg/m 2 ), systolic blood pressure (-3.94 mm Hg) and haemoglobin levels (+8.26 g/L) were detected. The overall estimated glomerular filtration rate (eGFR) was stable, and there was an improvement in the eGFR slope among patients with LN with a baseline eGFR <90 mL/min/1.73 m 2 ., Conclusion: Dapagliflozin had an acceptable safety profile in adult patients with SLE. Its possible renal/cardiac protective effects and long-term safety issues in patients with SLE, patients with LN in particular, call for further exploration., Trial Registration Number: ChiCTR1800015030., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY. Published by BMJ.)

CTLA4Ig, a reagent that inhibits CD28 signaling, has shown therapeutic efficacy in mouse models of lupus nephritis (LN) when combined with several other biologics or standard of care drugs. Unfortunately, clinical trials treating LN patients with CTLA4Ig (abatacept) have not met endpoints. Metformin, a drug used to control hyperglycemia that inhibits mitochondrial metabolism, lowered the effective dose of glucocorticoids and prevented major flares when added on to the standard of care treatment of lupus patients with low disease activity. Metformin combined with inhibition of glycolysis by 2-deoxyglucose showed therapeutic efficacy in multiple mouse models of LN. Because CD28 signaling triggers glucose metabolism in T cells, we hypothesized that combining CTLA4Ig treatment with metformin would have the same effect. In this study, we showed that the combination of metformin and CTLA4Ig decreased the development of LN in (NZB × NZW)F1 mice treated at the early stage of disease. This preventive effect was associated with a decreased expansion of CD4 + T cell effector subsets. However, contrary to the combination with 2-deoxyglucose, metformin combined with CTLA4Ig did not alter autoantibody production, suggesting different mechanisms of symptom mitigation. Overall, this study shows therapeutic efficacy of the combination of metformin and CTLA4Ig, two drugs with established safety records, in a preclinical mouse model of LN., (Copyright © 2020 The Authors.)

CSF-1, required for macrophage (Mø) survival, proliferation, and activation, is upregulated in the tubular epithelial cells (TECs) during kidney inflammation. CSF-1 mediates Mø-dependent destruction in lupus-susceptible mice with nephritis and, paradoxically, Mø-dependent renal repair in lupus-resistant mice after transient ischemia/reperfusion injury (I/R). We now report that I/R leads to defective renal repair, nonresolving inflammation, and, in turn, early-onset lupus nephritis in preclinical MRL/MpJ-Faslpr/Fas(lpr) mice (MRL-Fas(lpr) mice). Moreover, defective renal repair is not unique to MRL-Fas(lpr) mice, as flawed healing is a feature of other lupus-susceptible mice (Sle 123) and MRL mice without the Fas(lpr) mutation. Increasing CSF-1 hastens renal healing after I/R in lupus-resistant mice but hinders healing, exacerbates nonresolving inflammation, and triggers more severe early-onset lupus nephritis in MRL-Fas(lpr) mice. Probing further, the time-related balance of M1 "destroyer" Mø shifts toward the M2 "healer" phenotype in lupus-resistant mice after I/R, but M1 Mø continue to dominate in MRL-Fas(lpr) mice. Moreover, hypoxic TECs release mediators, including CSF-1, that are responsible for stimulating the expansion of M1 Mø inherently poised to destroy the kidney in MRL-Fas(lpr) mice. In conclusion, I/R induces CSF-1 in injured TECs that expands aberrant Mø (M1 phenotype), mediating defective renal repair and nonresolving inflammation, and thereby hastens the onset of lupus nephritis.

Objective: Sle2 is a lupus susceptibility locus that has been linked to glomerulonephritis in the NZM2410 mouse. By itself, Sle2 does not induce any autoimmune pathology but results in the accumulation of B-1a cells. This study was designed to assess the contribution of Sle2 to the pathogenesis of autoimmunity., Methods: Sle2 or its subcongenic intervals (Sle2a, Sle2b, and Sle2c1) were bred to Fas-deficient B6.lpr mice. Lymphoid phenotypes, which were focused on T cells, were assessed by flow cytometry, and histopathologic changes were compared between cohorts of B6.Sle2.lpr congenic mice and B6.lpr mice of ages up to 6 months., Results: Sle2 synergized with lpr, resulting in a greatly accelerated lymphadenopathy that largely targeted T cells and mapped to the Sle2c1 locus. This locus has been identified as the main contributor to B-1a cell expansion. Further analyses showed that Sle2c1 expression skewed the differentiation and polarization of Fas-deficient T cells, with a reduction of the CD4+CD25+FoxP3+ regulatory T cell subset and an expansion of the Th17 cells. This was associated with a high number of T cell infiltrates that promoted severe nephritis and dermatitis in the B6.Sle2c1.lpr mice., Conclusion: These results show that Sle2c1 contributes to lupus pathogenesis by affecting T cell differentiation in combination with other susceptibility loci, such as lpr. The significance of the cosegregation of this phenotype and B-1a cell expansion in Sle2c1-expressing mice in relation to the pathogenesis of lupus is discussed., (Copyright © 2011 by the American College of Rheumatology.)

The B6.Sle1.Sle2.Sle3 triple congenic mouse (B6.TC) is a model of lupus coexpressing the three major NZM2410-derived susceptibility loci on a C57BL/6 background. B6.TC mice produce high titers of antinuclear nephrogenic autoantibodies and a highly penetrant glomerulonephritis. Previous studies have shown the Sle1 locus is associated with a reduced number of regulatory T cells (Treg) and that Sle3 results in intrinsic defects of myeloid cells that hyperactivate T cells. In this report, we show that B6.TC dendritic cells (DCs) accumulate in lymphoid organs and present a defective maturation process, in which bone marrow-derived, plasmacytoid, and myeloid DCs express a significantly lower level of CD80, CD86, and MHC class II. B6.TC DCs also induce a higher level of proliferation in CD4(+) T cells than B6 DCs, and B6.TC DCs block the suppressive activity of Treg. B6.TC DCs overproduce IL-6, which is necessary for the blockade of Treg activity, as shown by the effect of anti-IL-6 neutralizing Ab in the suppression assays. The overproduction of IL-6 by DCs and the blockade of Treg activity maps to Sle1, which therefore not only confers a reduced number of Treg but also blocks their ability to regulate autoreactive T cells. Taken together, these results provide a genetic and mechanistic evidence for systemic autoimmunity resulting from an impaired regulatory T cell compartment in both number and function and for Sle1-expressing DCs playing a major role in the latter defect though their production of IL-6.

Systemic lupus erythematosus (SLE) is a prototypic systemic autoimmune disease in which glomerulonephritis represents one of the most severe clinical presentations. Numerous linkage and association studies, as well as the analysis of murine models, have provided ample evidence for a genetic basis for SLE. Genetic susceptibility to SLE results from the combined actions of multiple alleles, each of them conferring a modest incremental risk. SLE susceptibility genes have been identified in 3 major pathways: apoptosis, lymphocyte activation, and clearance of immune complexes and/or apoptotic debris. There also now is evidence that, within SLE patients, renal end-organ targeting also has a genetic basis, which can be divided into 2 branches. There is evidence that susceptibility alleles that are associated with a greater disease severity also are associated with lupus nephritis. There also is evidence for a set of kidney-specific genes that are likely to amplify or to sensitize to the autoimmune pathology.

The role of DNA as the target for pathogenic lupus autoantibodies in systemic lupus erythematosus is equivocal and renal damage may be due to cross-reactivity of lupus Abs with glomerular components. We have previously shown that lupus autoantibodies bind to the laminin component of the extracellular matrix. In the present work, we have analyzed the fine specificity of the interaction of pathogenic murine lupus autoantibodies with this molecule and the effect of inhibiting their binding to laminin during the course of the disease. We have found that pathogenic murine lupus autoantibodies react with a 21-mer peptide located in the globular part of the alpha-chain of laminin. Immunization of young lupus-prone mice with this peptide accelerated renal disease. Analysis of transgenic, congenic, and RAG-1(-/-) mice confirmed the importance of this epitope in the pathogenesis of lupus renal disease. We have synthesized a panel of peptides that cross-react with the anti-laminin Abs and have found that the binding of lupus autoantibodies to the extracellular matrix could be inhibited in vitro by some of these competitive peptides. Treatment of MRL/lpr/lpr mice with these peptides prevented Ab deposition in the kidneys, ameliorated renal disease, and prolonged survival of the peptide-treated mice. We suggest that laminin components can serve as the target for lupus Abs. The interaction with these Ags can explain both the tissue distribution and the immunopathological findings in lupus. Moreover, inhibition of autoantibody binding to the extracellular matrix can lead to suppression of disease.

Lupus pathogenesis in the NZM2410 mouse model results from the expression of multiple interacting susceptibility loci. Sle2 on chromosome 4 was significantly linked to glomerulonephritis in a linkage analysis of a NZM2410 x B6 cross. Yet, Sle2 expression alone on a C57BL/6 background did not result in any clinical manifestation, but in an abnormal B cell development, including the accumulation of B-1a cells in the peritoneal cavity and spleen. Analysis of B6.Sle2 congenic recombinants showed that at least three independent loci, New Zealand White-derived Sle2a and Sle2b, and New Zealand Black-derived Sle2c, contribute to an elevated number of B-1a cells, with Sle2c contribution being the strongest of the three. To determine the contribution of these three Sle2 loci to lupus pathogenesis, we used a mapping by genetic interaction strategy, in which we bred them to B6.Sle1.Sle3 mice. We then compared the phenotypes of these triple congenic mice with that of previously characterized B6.Sle1.Sle2.Sle3, which express the entire Sle2 interval in combination with Sle1 and Sle3. Sle2a and Sle2b, but not Sle2c, contributed significantly to lupus pathogenesis in terms of survival rate, lymphocytic expansion, and kidney pathology. These results show that the Sle2 locus contains several loci affecting B cell development, with only the two NZW-derived loci having the least effect of B-1a cell accumulation significantly contributing to lupus pathogenesis.

Objective: To determine whether overexpression of BAFF can accelerate the development of systemic lupus erythematosus-associated end-organ disease in hosts with an underlying autoimmune diathesis., Methods: We introduced a BAFF transgene (Tg) into autoimmune-prone B6.Sle1 and B6.Nba2 mice and evaluated these mice for serologic autoimmunity and renal pathology., Results: B6.Sle1.BAFF and B6.Nba2.BAFF mice, but not non-Tg littermates, frequently developed severe glomerular pathology by 3 months of age. Age-matched B6.BAFF mice, despite renal Ig deposits and increases in B cells and Ig production similar to those in B6.Sle1.BAFF and B6.Nba2.BAFF mice, did not develop glomerular pathology. In B6.Sle1.BAFF and B6.Nba2.BAFF mice, severity of glomerular disease did not obligately correlate with circulating levels of IgG anti-chromatin and/or anti-double-stranded DNA antibodies or with amounts of these autoantibodies deposited in the kidneys. Even in mice with severe glomerular disease, renal tubulointerstitial infiltrates were very limited, and increased proteinuria was not detected., Conclusion: BAFF-driven effects on glomerular pathology may be mediated, at least in part, by autoantibodies with specificities other than chromatin and/or by autoantibody-independent means. There is an uncoupling of BAFF-driven precocious glomerular pathology from concomitant development of clinically apparent renal disease, strongly suggesting that BAFF overexpression works in concert with other factors to promote overt renal disease.

Sle1 and Sle3 are NZW-derived loci that mediate lupus nephritis on a C57BL/6 background. The absence of severe autoimmunity in NZW suggests that the NZW genome suppresses these genes. (B6.NZMc1[Sle1] x NZW)F1 hybrids develop severe humoral autoimmunity and fatal lupus nephritis, indicating that suppression of Sle1 from NZW is recessive. Linkage analysis identified four epistatic modifiers, Sles1-4, whose cumulative effect accounted for the benign autoimmunity in NZW. The specific suppression of Sle1 but not Sle2 or Sle3 by Sles1 was directly demonstrated via the production and analysis of bicongenic strains. Moreover, Sles1 was sufficient to completely suppress autoimmunity initiated by Sle1 in B6.NZMc1 x NZW hybrids. These results demonstrate the complex epistatic interactions of loci augmenting and suppressing systemic autoimmunity.

Sle1 and Sle3 are 2 loci that confer susceptibility to lupus nephritis in the NZM2410 strain of mice. Our previous work has shown that B6.NZMc1 mice, congenic for Sle1, exhibit loss of tolerance to chromatin but do not develop any pathogenic autoantibodies or disease. B6.NZMc7 mice, congenic for Sle3, exhibit low-grade polyclonal B- and T-cell activation, elevated CD4/CD8 ratios, and mildly penetrant glomerulonephritis. In contrast to these monocongenics, the present study reveals that B6.NZMc1|c7 mice, bicongenic for Sle1 and Sle3, exhibit splenomegaly, significantly expanded populations of activated B and CD4(+) T cells, and a robust, variegated IgG autoantibody response targeting multiple components of chromatin (including double-stranded DNA), intact glomeruli, and basement membrane matrix antigens. As one might predict, these mice, particularly the females, exhibit highly penetrant glomerulonephritis. These findings lend strong support to a two-step epistatic model for the formation of pathogenic, nephrophilic autoantibodies in lupus. Whereas loci such as Sle1 may serve to breach tolerance to chromatin, full-blown pathogenic maturation of the autoantibody response appears to require additional input from other loci (such as Sle3) and gender-based factors.

Advances in genetic mapping have resulted in the identification of multiple lupus susceptibility loci in the NZB/W mouse model. The analysis of congenic strains carrying these loci is now providing functional data on their role in lupus pathogenesis and is paving the way to the identification of the susceptibility genes and their molecular characterization.