Maintenance of autoantibody production in pristane-induced murine lupus

Animal models of neuropsychiatric systemic lupus erythematosus: deciphering the complexity and guiding therapeutic development

Systemic lupus erythematosus (SLE) poses formidable challenges due to its multifaceted etiology while impacting multiple tissues and organs and displaying diverse clinical manifestations. Genetic and environmental factors contribute to SLE complexity, with relatively limited approved therapeutic options. Murine models offer insights into SLE pathogenesis but do not always replicate the nuances of human disease. This review critically evaluates spontaneous and induced animal models, emphasizing their validity and relevance to neuropsychiatric SLE (NPSLE). While these models undoubtedly contribute to understanding disease pathophysiology, discrepancies persist in mimicking some NPSLE intricacies. The lack of literature addressing this issue impedes therapeutic progress. We underscore the urgent need for refining models that truly reflect NPSLE complexities to enhance translational fidelity. We encourage a comprehensive, creative translational approach for targeted SLE interventions, balancing scientific progress with ethical considerations to eventually improve the management of NPSLE patients. A thorough grasp of these issues informs researchers in designing experiments, interpreting results, and exploring alternatives to advance NPSLE research.

HDAC6 Deletion Decreases Pristane-induced Inflammation

Systemic lupus erythematosus is an autoimmune disease characterized by excessive inflammation and production of pathogenic Abs. Histone deacetylase 6 (HDAC6) is a class IIb histone deacetylase. It has been reported that selective HDAC6 inhibition decreases inflammation in lupus mouse models. In this study, sex- and age-matched wild-type (WT) and HDAC6-/- mice on the C57BL/6 background were administered 0.5 ml of pristane or PBS i.p. at 8-12 wk of age and were euthanized 10 d later. At sacrifice, body weight and spleen weight were measured, sera were collected, and splenocytes and peritoneal cells were harvested for flow cytometry. We found pristane administration increased the spleen weight with no difference between WT and HDAC6-/- mice. Pristane administration promoted the population of CD11b+Ly6C++ inflammatory monocytes and CD11b+Ly6G+ neutrophils. Peritoneal recruitment of these inflammatory monocytes and neutrophils was significantly decreased in HDAC6-/- mice compared with the WT mice. Flow cytometry results showed that the number of CD69+ T and B cells was increased in HDAC6-/- mice. Pristane administration also induced the IFN signature genes as determined by RT-qPCR. Furthermore, IFN signature genes were not affected in HDAC6-/- mice compared with the WT mice. In vitro studies in J774A.1 cells revealed that the selective HDAC6 inhibitor (ACY-738) increased acetylation of NF-κB while increasing Stat1 phosphorylation, which resulted in inducible NO synthase production in LPS/IFN-γ-stimulated cells. Taken together, these results demonstrate that although HDAC6 inhibition may inhibit some inflammatory pathways, others remain unaffected.

A dual-acting DNASE1/DNASE1L3 biologic prevents autoimmunity and death in genetic and induced lupus models

A defining feature of systemic lupus erythematosus (SLE) is loss of tolerance to self-DNA, and deficiency of DNASE1L3, the main enzyme responsible for chromatin degradation in blood, is also associated with SLE. This association can be found in an ultrarare population of pediatric patients with DNASE1L3 deficiency who develop SLE, adult patients with loss-of-function variants of DNASE1L3 who are at a higher risk for SLE, and patients with sporadic SLE who have neutralizing autoantibodies against DNASE1L3. To mitigate the pathogenic effects of inherited and acquired DNASE1L3 deficiencies, we engineered a long-acting enzyme biologic with dual DNASE1/DNASE1L3 activity that is resistant to DNASE1 and DNASE1L3 inhibitors. Notably, we found that the biologic prevented the development of lupus in Dnase1-/-Dnase1L3-/- double-knockout mice and rescued animals from death in pristane-induced lupus. Finally, we confirmed that the human isoform of the enzyme biologic was not recognized by autoantibodies in SLE and efficiently degraded genomic and mitochondrial cell-free DNA, as well as microparticle DNA, in SLE plasma. Our findings suggest that autoimmune diseases characterized by aberrant DNA accumulation, such as SLE, can be effectively treated with a replacement DNASE tailored to bypass pathogenic mechanisms, both genetic and acquired, that restrict DNASE1L3 activity.

Pericardial and mediastinal fat-associated lymphoid clusters are rapidly activated in an alkane-induced model of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease predominated by auto-antibodies that recognise cellular components. Pleural involvement is the most common SLE-related lung disease. Natural antibodies are rapidly secreted by innate-like B cells following perturbation of homeostasis and are important in the early stages of immune activation. The serous cavities are home to large numbers of innate-like B cells present both within serous fluid and resident within fat-associated lymphoid clusters (FALCs). FALCs are important hubs for B-cell activation and local antibody secretion within the body cavities. Patients with SLE can develop anti-phospholipid antibodies and in rare situations develop alveolar haemorrhage. Utilising delivery of the hydrocarbon oil pristane in C57BL/6 mice as a model of SLE we identify a rapid expansion of pleural cavity B cells as early as day 3 after intra-peritoneal pristane delivery. Following pristane delivery, pericardial B1 B cells are proliferative, express the plasma-cell surface marker CD138, and secrete both innate and class-switched antibodies highlighting that this cavity niche may play an unrecognised role in the initiation of lupus pleuritis.

Increase in Double Negative B Lymphocytes in Patients with Systemic Lupus Erythematosus in Remission and Their Correlation with Early Differentiated T Lymphocyte Subpopulations

B and T lymphocytes demonstrate important alterations in patients with systemic lupus erythematous (SLE), with a significant upregulation of double negative (DN) B cells. The aim of this study was to evaluate the correlation of T cell immunity changes with the distinct B-cell-pattern SLE. In the present study, flow cytometry was performed in 30 patients in remission of SLE and 31 healthy controls to detect DN B cells (CD19+IgD-CD27-) and a wide range of T lymphocyte subpopulations based on the presence of CD45RA, CCR7, CD31, CD28, and CD57, defined as naive, memory, and advanced differentiated/senescent T cells. Both B and T lymphocytes were significantly reduced in SLE patients. However, the percentage of DN B cells were increased compared to HC (12.9 (2.3-74.2) vs. 8 (1.7-35), p = 0.04). The distribution of CD4 and CD8 lymphocytes demonstrated a shift to advanced differentiated subsets. The population of DN B cells had a significant positive correlation with most of the early differentiated T lymphocytes, CD4CD31+, CD4CD45RA+CD28+, CD4CD45RA+CD57-, CD4CD45RA-CD57-, CD4CD28+CD57-, CD4CD28+CD57+, CD4 CM, CD8 CD31+, CD8 NAÏVE, CD8CD45RA-CD57-, CD8CD28+CD57-, and CD8CD28+CD57+. Multiple regression analysis revealed CD4CD31+, CD8CD45RA-CD57-, and CD8CD28+CD57- cells as independent parameters contributing to DN B cells, with adjusted R2 = 0.534 and p < 0.0001. The predominance of DN B cells in patients with SLE is closely associated with early differentiated T lymphocyte subsets, indicating a potential causality role of DN B cells in T lymphocyte activation.

Dependence on Autophagy for Autoreactive Memory B Cells in the Development of Pristane-Induced Lupus

The production of autoantibodies by autoreactive B cells plays a major role in the pathogenesis of lupus. Increases in memory B cells have been observed in human lupus patients and autoimmune lpr mice. Autophagy is required for the maintenance of memory B cells against viral infections; however, whether autophagy regulates the persistence of autoantigen-specific memory B cells and the development of lupus remains to be determined. Here we show that memory B cells specific for autoantigens can be detected in autoimmune lpr mice and a pristane-induced lupus mouse model. Interestingly, B cell-specific deletion of Atg7 led to significant loss of autoreactive memory B cells and reduced autoantibody production in pristane-treated mice. Autophagy deficiency also attenuated the development of autoimmune glomerulonephritis and pulmonary inflammation after pristane treatment. Adoptive transfer of wild type autoreactive memory B cells restored autoantibody production in Atg7-deficient recipients. These data suggest that autophagy is important for the persistence of autoreactive memory B cells in mediating autoantibody responses. Our results suggest that autophagy could be targeted to suppress autoreactive memory B cells and ameliorate humoral autoimmunity.

Pristane/Hypoxia (PriHx) Mouse as a Novel Model of Pulmonary Hypertension Reflecting Inflammation and Fibrosis

BACKGROUND

Pulmonary arterial hypertension (PAH), particularly connective tissue disease-associated PAH (CTD-PAH), is a progressive disease and novel therapeutic agents based on the specific molecular pathogenesis are desired. In the pathogenesis of CTD-PAH, inflammation, immune cell abnormality, and fibrosis play important roles. However, the existing mouse pulmonary hypertension (PH) models do not reflect these features enough. The relationship between inflammation and hypoxia is still unclear.

METHODS AND RESULTS

Intraperitoneal administration of pristane, a kind of mineral oil, and exposure to chronic hypoxia were combined, and this model is referred to as pristane/hypoxia (PriHx) mice. Hemodynamic and histological analyses showed that the PriHx mice showed a more severe phenotype of PH than pristane or hypoxia alone. Immunohistological and flow cytometric analyses revealed infiltration of immune cells, including hemosiderin-laden macrophages and activated CD4+helper T lymphocytes in the lungs of PriHx mice. Pristane administration exacerbated lung fibrosis and elevated the expression of fibrosis-related genes. Inflammation-related genes such asIl6andCxcl2were also upregulated in the lungs of PriHx mice, and interleukin (IL)-6 blockade by monoclonal anti-IL-6 receptor antibody MR16-1 ameliorated PH of PriHx mice.

CONCLUSIONS

A PriHx model, a novel mouse model of PH reflecting the pathological features of CTD-PAH, was developed through a combination of pristane administration and exposure to chronic hypoxia.

Connexin43 Is Required for the Effective Activation of Spleen Cells and Immunoglobulin Production

Gap junctions (Gjs), formed by specific protein termed connexins (Cxs), regulate many important cellular processes in cellular immunity. However, little is known about their effects on humoral immunity. Here we tested whether and how Gj protein connexin43 (Cx43) affected antibody production in spleen cells. Detection of IgG in mouse tissues and serum revealed that wild-type (Cx43^+/+) mouse had a significantly higher level of IgG than Cx43 heterozygous (Cx43^+/−) mouse. Consistently, spleen cells from Cx43^+/+ mouse produced more IgG under both basal and lipopolysaccharide (LPS)-stimulated conditions. Further analysis showed that LPS induced a more dramatic activation of ERK and cell proliferation in Cx43^+/+ spleen cells, which was associated with a higher pro-oxidative state, as indicated by the increased NADPH oxidase 2 (NOX2), TXNIP, p38 activation and protein carbonylation. In support of a role of the oxidative state in the control of lymphocyte activation, exposure of spleen cells to exogenous superoxide induced Cx43 expression, p38 activation and IgG production. On the contrary, inhibition of NOX attenuated the effects of LPS. Collectively, our study characterized Cx43 as a novel molecule involved in the control of spleen cell activation and IgG production. Targeting Cx43 could be developed to treat certain antibody-related immune diseases.

Leptin: an unappreciated key player in SLE

Leptin is the forerunner of the adipokine superfamily and plays a key role in regulating energy expenditure and neuroendocrine function. Researches into leptin put emphasize not only on the metabolic role but also its immunoregulatory effect on immune response through immunocyte activation and cytokine secretion. Leptin acts on receptors that are widespread throughout the body and that are expressed across many tissue types. As a consequence, the abnormal expression of leptin has been found to correlate with a number of diseases, including cancers, autoimmune diseases, and cardiovascular diseases. The significance of leptin in the development of autoimmune diseases is becoming increasingly prominent. Systemic lupus erythematosus (SLE) is a severe atypical autoimmune disease that causes damage to multiple organ systems. It is characterised by the following: impaired clearance of apoptotic cells, loss of tolerance to self-antigens, aberrant activation of T cells and B cells, and chronic inflammation. The heightened immunocyte response in SLE means that these physiological systems are particularly vulnerable to regulation by leptin in addition to being of great significance to the research field. Our current review provides insight into the regulatory roles that leptin plays on immune effector cells in SLE.

TLR7 Protein Expression in Mild and Severe Lupus-Prone Models Is Regulated in a Leukocyte, Genetic, and IRAK4 Dependent Manner

The global increase in autoimmunity, together with the emerging autoimmune-related side effects of cancer immunotherapy, have furthered a need for understanding of immune tolerance and activation. Systemic lupus erythematosus (SLE) is the archetypical autoimmune disease, affecting multiple organs, and tissues. Studying SLE creates knowledge relevant not just for autoimmunity, but the immune system in general. Murine models and patient studies have provided increasing evidence for the innate immune toll like receptor-7 (TLR7) in disease initiation and progression. Here, we demonstrated that the kinase activity of the TLR7-downstream signaling molecule, interleukin-1 receptor associated kinase 4 (IRAK4), is essential for mild and severe autoimmune traits of the Sle1 and Sle1-TLR7 transgenic (Sle1Tg7) murine models, respectively. Elimination of IRAK4 signaling prevented all pathological traits associated with murine lupus, including splenomegaly with leukocyte expansion, detectable circulating antinuclear antibodies and glomerulonephritis, in both Sle1 and Sle1Tg7 mice. The expansion of germinal center B cells and increased effector memory T cell phenotypes that are typical of lupus-prone strains, were also prevented with IRAK4 kinase elimination. Analysis of renal leukocyte infiltrates confirmed our earlier findings of an expanded conventional dendritic cell (cDC) within the kidneys of nephritic mice, and this was prevented with IRAK4 kinase elimination. Analysis of TLR7 at the protein level revealed that the expression in immune cells is dependent on the TLR7-transgene itself and/or autoimmune disease factors in a cell-specific manner. Increased TLR7 protein expression in renal macrophages and cDCs correlated with disease parameters such as blood urea nitrogen (BUN) levels and the frequency of leukocytes infiltrating the kidney. These findings suggest that controlling the level of TLR7 or downstream signaling within myeloid populations may prevent chronic inflammation and severe nephritis.

Role of Lgals9 Deficiency in Attenuating Nephritis and Arthritis in BALB/c Mice in a Pristane-Induced Lupus Model

OBJECTIVE

In systemic lupus erythematosus (SLE), an autoimmune disease associated with multiple organ involvement, the development of lupus nephritis determines prognosis, and arthritis impairs quality of life. Galectin 9 (Gal-9, Lgals9) is a β-galactoside-binding lectin that has been used for clinical application in autoimmune diseases, since recombinant Gal-9, as a ligand for T cell immunoglobulin and mucin domain-containing protein 3 (TIM-3), induces apoptosis of activated CD4+TIM-3+ Th1 cells. This study was undertaken to investigate whether deficiency of Lgals9 has beneficial or deleterious effects on lupus in a murine model.

METHODS

Gal-9^+/+ and Gal-9^-/- female BALB/c mice were injected with pristane, and the severity of arthritis, proteinuria, and levels of autoantibody production were assessed at several time points immediately following injection. At 7 months after pristane injection, renal pathologic features, the severity of joint inflammation, and formation of lipogranulomas were evaluated. Subsets of inflammatory cells in the spleen and peritoneal lavage were characterized, and expression levels of cytokines from peritoneal macrophages were analyzed.

RESULTS

Lgals9 deficiency protected against the development of immune complex glomerulonephritis, arthritis, and peritoneal lipogranuloma formation in BALB/c mice in this murine model of pristane-induced lupus. The populations of T cell subsets and B cells in the spleen and peritoneum were not altered by Lgals9 deficiency in pristane-injected BALB/c mice. Furthermore, Lgals9 deficiency protected against pristane-induced lupus without altering the Toll-like receptor 7-type I interferon pathway.

CONCLUSION

Gal-9 is required for the induction and development of lupus nephritis and arthritis in this murine model of SLE. The results of the current investigation provide a potential new strategy in which antagonism of Gal-9 may be beneficial for the treatment of nephritis and arthritis in patients with SLE through targeting of activated macrophages.

Pristane-induced lupus: considerations on this experimental model

Systemic lupus erythematosus (SLE) is a multifactorial, autoimmune inflammatory disease with pleomorphic clinical manifestations involving different organs and tissues. The etiology of this disease has been associated with a dysfunctional response of B and T lymphocytes against environmental stimuli in individuals genetically susceptible to SLE, which determines an immune response against different autoantigens and, consequently, tissue damage. The study of different murine models has provided a better understanding of these autoimmune phenomena. This review primarily focuses on that has been learned from the pristane-induced lupus (PIL) model and how this model can be used to supplement recent advances in understanding the pathogenesis of SLE. We also consider both current and future therapies for this disease. The PubMed, SciELO, and Embase databases were searched for relevant articles published from 1950 to 2016. PIL has been shown to be a useful tool for understanding the multiple mechanisms involved in systemic autoimmunity. In addition, it can be considered an efficient model to evaluate the environmental contributions and interferon signatures present in patients with SLE.

Basophils contribute to pristane-induced Lupus-like nephritis model

Lupus nephritis (LN), one of the most severe outcomes of systemic lupus erythematosus (SLE), is initiated by glomerular deposition of immune-complexes leading to an inflammatory response and kidney failure. Autoantibodies to nuclear antigens and autoreactive B and T cells are central in SLE pathogenesis. Immune mechanisms amplifying this autoantibody production drive flares of the disease. We previously showed that basophils were contributing to LN development in a spontaneous lupus-like mouse model (constitutive Lyn -/- mice) and in SLE subjects through their activation and migration to secondary lymphoid organs (SLOs) where they amplify autoantibody production. In order to study the basophil-specific mechanisms by which these cells contribute to LN development, we needed to validate their involvement in a genetically independent SLE-like mouse model. Pristane, when injected to non-lupus-prone mouse strains, induces a LN-like disease. In this inducible model, basophils were activated and accumulated in SLOs to promote autoantibody production. Basophil depletion by two distinct approaches dampened LN-like disease, demonstrating their contribution to the pristane-induced LN model. These results enable further studies to decipher molecular mechanisms by which basophils contribute to lupus progression.

MicroRNA 155-deficiency leads to decreased autoantibody levels and reduced severity of nephritis and pneumonitis in pristane-induced lupus

Objective

We herein examine the role of endogenous miR155 in the development of systemic manifestations in pristane induced lupus.

Materials and methods

Systemic lupus in miR155-deficient and wild type mice was induced upon injection of pristane and analyzed after 8 months, PBS-injected mice served as controls. Glomerulonephritis and pneumonitis were quantified using the kidney biopsy score and a newly adapted histomorphometric image analysis system; lung tissue was further analyzed by tissue cytometry. Serum levels of anti-dsDNA, anti-histone and anti-chromatin antibodies were measured by ELISA. Frequencies of B cells, activated and regulatory CD4⁺ T cells as well as Th1, Th2, Th17 cells were measured by flow cytometry. RT-qPCR was used to measure expression levels of interferon-signature and T-cell subset related as well as miR155-associated genes.

Results

After induction of lupus, miR155-deficient mice had significant less pulmonary involvement (perivascular inflammatory area in mm2/mm2 lung area 0.00092±0.00015 vs. 0.0027±0.00075, p = 0.0347) and renal disease (glomerular activity score 1.95±0.19 vs 3±0.26, p = 0.0029) compared to wild types. MiR155-deficient mice had significantly lower serum levels of disease-associated auto-antibodies and decreased frequencies of activated CD4⁺CD25⁺ (Foxp3^-) cells. Upon restimulation, CD4⁺ cells showed a less pronounced Th2 and Th17 and a slightly decreased Th1 response in mir155-deficient mice. Pristane-treated wild types showed significantly up-regulated expression of genes related to the INF-signature (MX1, IP10, IRF7, ISG15).

Conclusions

MiR155-deficient mice had less severe organ involvement, lower serum auto-antibody levels, a less prominent T cell response and lower expressions of genes jointly responsible for disease development. Thus, antagonizing miR155 might be a future approach in treating SLE.

Leptin promotes systemic lupus erythematosus by increasing autoantibody production and inhibiting immune regulation

Leptin is an adipocytokine that plays a key role in the modulation of immune responses and the development and maintenance of inflammation. Circulating levels of leptin are elevated in systemic lupus erythematosus (SLE) patients, but it is not clear whether this association can reflect a direct influence of leptin on the propathogenic events that lead to SLE. To investigate this possibility, we compared the extent of susceptibility to SLE and lupus manifestations between leptin-deficient (ob/ob) and H2-matched leptin-sufficient (wild-type, WT) mice that had been treated with the lupus-inducing agent pristane. Leptin deficiency protected ob/ob mice from the development of autoantibodies and renal disease and increased the frequency of immunoregulatory T cells (Tregs) compared with leptin-sufficient WT mice. The role of leptin in the development of SLE was confirmed in the New Zealand Black (NZB) × New Zealand White (NZW)F1 (NZB/W) mouse model of spontaneous SLE, where elevated leptin levels correlated with disease manifestations and the administration of leptin accelerated development of autoantibodies and renal disease. Conversely, leptin antagonism delayed disease progression and increased survival of severely nephritic NZB/W mice. At the cellular level, leptin promoted effector T-cell responses and facilitated the presentation of self-antigens to T cells, whereas it inhibited the activity of regulatory CD4 T cells. The understanding of the role of leptin in modulating autoimmune responses in SLE can open possibilities of leptin-targeted therapeutic intervention in the disease.

Psgl-1 Deficiency is Protective against Stroke in a Murine Model of Lupus

Systemic lupus erythematosus (SLE) is associated with an elevated risk of vascular complications, including premature stroke. Therapies targeting leukocyte recruitment may be beneficial in reducing vascular complications associated with SLE. Lupus was induced in female wild-type (WT) and P-selectin glycoprotein ligand-1 deficient (Psgl-1^−/−) mice with pristane. Stroke was induced following photochemical injury to the middle cerebral artery (MCA). Stroke size was increased in pristane-treated WT mice compared to non-pristane-treated WT controls. However, stroke size was not increased in pristane-treated Psgl-1^−/− mice compared to controls, despite evidence of increased nephritis in Psgl-1^−/− mice. Pristane-treated WT mice showed elevated anti-dsDNA, anti-snRNP, CXCL1, and MCP-1 levels compared to untreated mice; however levels of anti-snRNP, MCP-1, and CXCL1 were reduced in pristane-treated Psgl-1^−/− mice compared to pristane-treated WT mice. Infiltration of neutrophils and macrophages at the cerebral infarction site were reduced in pristane-treated Psgl-1^−/− mice compared to pristane-treated WT mice. In conclusion, the increase in stroke size associated with lupus is prevented by Psgl-1 deficiency while nephritis is exacerbated. Therapies targeting Psgl-1 may be useful in the management of SLE patients at high risk of acute vascular complications although elucidation of downstream pathways will be necessary to identify targets that do not promote nephritis.