Anti-histone antibodies in the serum of autoimmune MRL and NZB/NZW1 F1 mice

Constitutive knockout of interleukin-6 ameliorates memory deficits and entorhinal astrocytosis in the MRL/lpr mouse model of neuropsychiatric lupus

BACKGROUND

Neuropsychiatric lupus (NPSLE) describes the cognitive, memory, and affective emotional burdens faced by many lupus patients. While NPSLE's pathogenesis has not been fully elucidated, clinical imaging studies and cerebrospinal fluid (CSF) findings, namely elevated interleukin-6 (IL-6) levels, point to ongoing neuroinflammation in affected patients. Not only linked to systemic autoimmunity, IL-6 can also activate neurotoxic glial cells the brain. A prior pre-clinical study demonstrated that IL-6 can acutely induce a loss of sucrose preference; the present study sought to assess the necessity of chronic IL-6 exposure in the NPSLE-like disease of MRL/lpr lupus mice.

METHODS

We quantified 1308 proteins in individual serum or pooled CSF samples from MRL/lpr and control MRL/mpj mice using protein microarrays. Serum IL-6 levels were plotted against characteristic NPSLE neurobehavioral deficits. Next, IL-6 knockout MRL/lpr (IL-6 KO; n = 15) and IL-6 wildtype MRL/lpr mice (IL-6 WT; n = 15) underwent behavioral testing, focusing on murine correlates of learning and memory deficits, depression, and anxiety. Using qPCR, we quantified the expression of inflammatory genes in the cortex and hippocampus of MRL/lpr IL-6 KO and WT mice. Immunofluorescent staining was performed to quantify numbers of microglia (Iba1 +) and astrocytes (GFAP +) in multiple cortical regions, the hippocampus, and the amygdala.

RESULTS

MRL/lpr CSF analyses revealed increases in IL-17, MCP-1, TNF-α, and IL-6 (a priori p-value < 0.1). Serum levels of IL-6 correlated with learning and memory performance (R2 = 0.58; p = 0.03), but not motivated behavior, in MRL/lpr mice. Compared to MRL/lpr IL-6 WT, IL-6 KO mice exhibited improved novelty preference on object placement (45.4% vs 60.2%, p < 0.0001) and object recognition (48.9% vs 67.9%, p = 0.002) but equivalent performance in tests for anxiety-like disease and depression-like behavior. IL-6 KO mice displayed decreased cortical expression of aif1 (microglia; p = 0.049) and gfap (astrocytes; p = 0.044). Correspondingly, IL-6 KO mice exhibited decreased density of GFAP + cells compared to IL-6 WT in the entorhinal cortex (89 vs 148 cells/mm2, p = 0.037), an area vital to memory.

CONCLUSIONS

The inflammatory composition of MRL/lpr CSF resembles that of human NPSLE patients. Increased in the CNS, IL-6 is necessary to the development of learning and memory deficits in the MRL/lpr model of NPSLE. Furthermore, the stimulation of entorhinal astrocytosis appears to be a key mechanism by which IL-6 promotes these behavioral deficits.

Autoimmune and neuropsychiatric phenotypes in a Mecp2 transgenic mouse model on C57BL/6 background

Introduction

Systemic Lupus Erythematosus (SLE) impacts the central nervous system (CNS), leading to severe neurological and psychiatric manifestations known as neuropsychiatric lupus (NPSLE). The complexity and heterogeneity of clinical presentations of NPSLE impede direct investigation of disease etiology in patients. The limitations of existing mouse models developed for NPSLE obstruct a comprehensive understanding of this disease. Hence, the identification of a robust mouse model of NPSLE is desirable.

Methods

C57BL/6 mice transgenic for human MeCP2 (B6.Mecp2Tg1) were phenotyped, including autoantibody profiling through antigen array, analysis of cellularity and activation of splenic immune cells through flow cytometry, and measurement of proteinuria. Behavioral tests were conducted to explore their neuropsychiatric functions. Immunofluorescence analyses were used to reveal altered neurogenesis and brain inflammation. Various signaling molecules implicated in lupus pathogenesis were examined using western blotting.

Results

B6.Mecp2Tg1 exhibits elevated proteinuria and an overall increase in autoantibodies, particularly in female B6.Mecp2Tg1 mice. An increase in CD3+CD4+ T cells in the transgenic mice was observed, along with activated germinal center cells and activated CD11b+F4/80+ macrophages. Moreover, the transgenic mice displayed reduced locomotor activity, heightened anxiety and depression, and impaired short-term memory. Immunofluorescence analysis revealed IgG deposition and immune cell infiltration in the kidneys and brains of transgenic mice, as well as altered neurogenesis, activated microglia, and compromised blood-brain barrier (BBB). Additionally, protein levels of various key signaling molecules were found to be differentially modulated upon MeCP2 overexpression, including GFAP, BDNF, Albumin, NCoR1, mTOR, and NLRP3.

Discussion

Collectively, this work demonstrates that B6.Mecp2Tg1 mice exhibit lupus-like phenotypes as well as robust CNS dysfunctions, suggesting its utility as a new animal model for NPSLE.

The MRL/lpr mouse strain as a model for neuropsychiatric systemic lupus erythematosus

To date, CNS disease and neuropsychiatric symptoms of systemic lupus erythematosus (NP-SLE) have been understudied compared to end-organ failure and peripheral pathology. In this review, we focus on a specific mouse model of lupus and the ways in which this model reflects some of the most common manifestations and potential mechanisms of human NP-SLE. The mouse MRL lymphoproliferation strain (a.k.a. MRL/lpr) spontaneously develops the hallmark serological markers and peripheral pathologies typifying lupus in addition to displaying the cognitive and affective dysfunction characteristic of NP-SLE, which may be among the earliest symptoms of lupus. We suggest that although NP-SLE may share common mechanisms with peripheral organ pathology in lupus, especially in the latter stages of the disease, the immunologically privileged nature of the CNS indicates that early manifestations of particularly mood disorders maybe derived from some unique mechanisms. These include altered cytokine profiles that can activate astrocytes, microglia, and alter neuronal function before dysregulation of the blood-brain barrier and development of clinical autoantibody titres.

Effects of estrogen receptor subtype-selective agonists on autoimmune disease in lupus-prone NZB/NZW F1 mouse model

The specific roles of estrogen receptor (ER) subtypes alpha and beta in mediating estrogen's influences on lupus autoimmunity are unknown. Herein we found that ovariectomized NZB/NZW F1 mice treated with propyl pyrazole triol (ERalpha-selective agonist) had significantly shorter survival, earlier development of albuminuria, higher serum concentrations of total IgG and prolactin, increased serum levels of anti-DNA IgG3, IgG2a and IgG2b and decreased anti-DNA IgG1 level compared to vehicle controls. In contrast, diarylpropionitrile (ERbeta-selective agonist) administration significantly decreased serum anti-DNA IgG2b level but did not significantly affect serum levels of other anti-DNA IgG subclasses, serum total IgG or prolactin concentration, mortality or the occurrence of albuminuria. These findings suggest that ERalpha activation plays the predominant and immunostimulatory role in estrogen-mediated modulation of lupus while ERbeta activation appears to have a slightly immunosuppressive effect on this disease. ERalpha activation coincidentally increased serum prolactin concentrations and may accelerate lupus disease activity also through this mechanism.

Spotlight on the role of hormonal factors in the emergence of autoreactive B-lymphocytes

Pathogenic autoimmunity requires a combination of inherited and acquired factors. In as much as hormones influence the sexual dimorphism of the immune system, it is possible that they can initiate or accelerate an autoimmune process, and contribute to gender-biased autoimmune disorders. Not only natural hormones, but also endocrine disruptors, such as environmental estrogens, may act in conjunction with other factors to override immune tolerance to self-antigens. In lupus, murine and human studies demonstrate that female sex hormones are implicated in disease pathogenesis. In the B cell compartment, both prolactin and estrogen are immunomodulators that affect maturation, selection and antibody secretion. Their impact may be based on their capacity to allow autoreactive B cells to escape the normal mechanisms of tolerance and to accumulate in sufficient numbers to cause clinically apparent disease. Both hormones lead to the survival and activation of autoreactive B cells, but they skew B cell maturation towards different directions, with prolactin inducing T cell-dependent autoreactive follicular B cells and estrogen eliciting T cell-independent autoreactive marginal zone B cells. Differential modulation of the cytokine milieu by hormones may also affect the development and activation of specific mature B cell subsets. This novel insight suggests that targeted manipulation of these pathways may represent a promising avenue in the treatment of lupus and other gender-biased autoimmune diseases.

The effect of the phytoestrogen coumestrol on the NZB/W F1 murine model of systemic lupus

Coumestrol is a naturally occurring plant estrogen. As estrogen influences cellular and humoral immunity, and has known effects on murine models of lupus, we investigated the effect of coumestrol on disease expression in the NZB/W F1 mouse. Female NZB/W F1 mice were fed a "standard" rodent diet including soy proteins, a non-soy diet, or a non-soy diet with 0.01% coumestrol. Outcome measures included survival, autoantibody expression, immunoglobulin levels, proteinuria, renal histology and B cell immunohistochemistry, and renal mRNA expression. At 24 weeks, the treatment group had decreased prevalence of autoantibodies detected by immunofluorescence and less splenomegaly. At 39 weeks, the prevalence of autoantibodies was similar but the treatment group had less proteinuria. Overall, there was little effect of treatment on renal mRNA levels as assessed by gene array analysis, but functional ontology mapping revealed that genes encoding proteins involved in the immune response were most often affected. These results suggest that treatment with coumestrol may ameliorate some aspects of disease progression in this model of systemic autoimmunity.

Deficiency of 5-Lipoxygenase Abolishes Sex-Related Survival Differences in MRL-lpr/lpr Mice

Leukotrienes, the 5-lipoxygenase (5LO) products of arachidonic acid metabolism, have many proinflammatory actions that have been implicated in the pathogenesis of a variety of inflammatory diseases. To investigate the role of LTs in autoimmune disease, we generated an MRL-lpr/lpr mouse line with a targeted disruption of the 5lo gene. MRL-lpr/lpr mice spontaneously develop autoimmune disease that has many features resembling human systemic lupus erythematosus, including sex-related survival differences; female MRL-lpr/lpr mice experience significant early mortality compared with males. Unexpectedly, we found that mortality was accelerated in male 5LO-deficient MRL-lpr/lpr mice compared with male wild-type MRL-lpr/lpr animals. In contrast, the 5lo mutation had no effect on survival in females. Mortality was also accelerated in male MRL-lpr/lpr mice that were treated chronically with a pharmacological inhibitor of LT synthesis. Furthermore, LT-dependent inflammatory responses are enhanced in male MRL-lpr/lpr mice compared with females, and the 5lo mutation has greater impact on these responses in males. Because immune complex-mediated glomerulonephritis is the major cause of death in MRL-lpr/lpr mice and has been related to arachidonic acid metabolites, we also assessed kidney function and histopathology. In male MRL-lpr/lpr mice, renal plasma flow was significantly reduced in the 5lo−/− compared with the 5lo+/+ group, although there were no differences in the severity of renal histopathology, lymphoid hyperplasia, or arthritis between the groups. These findings suggest that the presence of a functional 5lo gene confers a survival advantage on male MRL-lpr/lpr mice and that, when 5LO function is inhibited, either genetically or pharmacologically, this advantage is abolished.

Analysis of a nucleic-acid-binding antibody fragment: Construction and characterization of heavy-chain complementarity-determining region switch variants

The display of antibody (AB) fragments (Fab) on the surface of filamentous bacteriophage (phage) and selection of phage that interact with a particular antigen (Ag) has enabled the isolation of Fab that bind nucleic acids. Nucleic acid (NA) binding Ab occur in vivo in connective tissue disease patients and certain inbred strains of mice and are thought to be pathogenic. Although there is ample data concerning the amino acid (aa) sequence of murine monoclonal Ab (mAb) reactive with DNA, significantly less is known about how autoAb interact with NA. The complementarity-determining regions (CDR) contained in the Fab contribute to most Ag binding, especially through heavy (H)-chain CDR 3. We have examined the role of individual H-chain CDR of a previously isolated recombinant single-stranded DNA-binding Fab (DNA-1) in nucleic acid interaction using a combination of H-chain CDR switching and solution-binding experiments. The three H-chain CDR of DNA-1 Fab were independently switched with the H-chain CDR of a Fab (D5) with very similar sequence and framework (FR) that binds DNA poorly in order to create all possible H-chain CDR combinations. The chimeric Fab genes were bacterially expressed, and their products were purified and analyzed. Results indicated that the H-chain CDR 3 of DNA-1 Fab, in the context of the remainder of the H-chain of D5 Fab, restored binding to oligo(dT)15 to 60% of DNA-1 levels, whereas H-chain CDR 1 and 3 of DNA-1 with CDR 2 of D5 Fab restored binding to 100% A combination of H-chain CDR 2 and 3 of DNA-1 Fab with H-chain CDR 1 of D5, unexpectedly resulted in the ability of the chimeric Fab to bind RNA preferentially over DNA. These studies demonstrate the importance of both H-chain CDR 1 and 3 in DNA recognition and further suggest that the specificity of the type of NA recognized by a particular Fab can be drastically altered by exchanging CDR.

Isolation and characterization of nucleic acid-binding antibody fragments from autoimmune mice-derived bacteriophage display libraries

The display of antibody fragments (Fab) on the surface of filamentous bacteriophage and selection of phage that bind to a particular antigen has enabled the isolation of Fab with numerous specificities, including haptens, proteins and viral particles. We have examined the possibility of isolating nucleic acid-binding Fab by constructing a combinatorial library of phage displaying Fab derived from autoimmune (MRL/lpr) mice. Autoimmune mice were chosen because they contain antibodies (Ab) reactive against nuclear components, including DNA, RNA and protein complexes. The library was panned against single-stranded (ss) calf thymus (CT) DNA and the selected Fabs were analyzed further. Characterization of the nucleic acid-binding phage led to the identification of two kinds of Fab with quite different properties. One Fab bound with high affinity a variety of ssDNA molecules, as well as several model RNA substrates. This Fab has been affinity purified to greater than 95% and competition studies revealed a marked preference for binding to poly(dT). The second Fab showed a reduced binding to RNA ligands and a restricted number of ssDNA molecules. Analysis of the deduced amino acid (aa) sequences of the Fab variable (V) regions revealed that the heavy (H) chain V region from the strong nucleic acid-binding Fab was derived from a VH gene that is used recurrently in autoantibodies. This VH domain was most similar to an anti-ssDNA autoimmune monoclonal antibody (mAb) suggesting that antigen-binding specificities present in an autoimmune repertoire may be directly accessed by this approach.(ABSTRACT TRUNCATED AT 250 WORDS)