Increased TUNEL staining in brains of autoimmune Fas-deficient mice

The MRL Model: A Valuable Tool in Studies of Autoimmunity-Brain Interactions

The link between systemic autoimmunity, brain pathology, and aberrant behavior is still largely unexplored field of biomedical science. Accumulating evidence points to causal relationships between immune factors, neurodegeneration, and neuropsychiatric manifestations. By documenting autoimmunity-associated neuronal degeneration and cytotoxicity of the cerebrospinal fluid from disease-affected subjects, the murine MRL model has shown high validity in revealing principal pathogenic circuits. In addition, unlike any other autoimmune strain, MRL mice produce antibodies commonly found in patients suffering from lupus and other autoimmune disorders. This review highlights the importance of the MRL model as a useful preparation for understanding the links between the immune system and brain function.

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.

From Systemic Inflammation to Neuroinflammation: The Case of Neurolupus

It took decades to arrive at the general consensus dismissing the notion that the immune system is independent of the central nervous system. In the case of uncontrolled systemic inflammation, the relationship between the two systems is thrown off balance and results in cognitive and emotional impairment. It is specifically true for autoimmune pathologies where the central nervous system is affected as a result of systemic inflammation. Along with boosting circulating cytokine levels, systemic inflammation can lead to aberrant brain-resident immune cell activation, leakage of the blood⁻brain barrier, and the production of circulating antibodies that cross-react with brain antigens. One of the most disabling autoimmune pathologies known to have an effect on the central nervous system secondary to the systemic disease is systemic lupus erythematosus. Its neuropsychiatric expression has been extensively studied in lupus-like disease murine models that develop an autoimmunity-associated behavioral syndrome. These models are very useful for studying how the peripheral immune system and systemic inflammation can influence brain functions. In this review, we summarize the experimental data reported on murine models developing autoimmune diseases and systemic inflammation, and we explore the underlying mechanisms explaining how systemic inflammation can result in behavioral deficits, with a special focus on in vivo neuroimaging techniques.

Mechanisms of neuropsychiatric lupus: The relative roles of the blood-cerebrospinal fluid barrier versus blood-brain barrier

The pathogenesis of neuropsychiatric lupus (NPSLE) is believed to include the entry of circulating neuropathic antibodies to the brain via a pathologically permeable blood-brain barrier (BBB). Nevertheless, direct evidence of BBB pathology or mechanisms underlying BBB dysfunction is missing. Here, we examined BBB integrity in an established NPSLE mouse model (MRL/fas^lpr/lpr). Surprisingly, challenging the barrier with various exogenous tracers demonstrated insignificant changes in BBB permeability. Furthermore, electron microscopy showed no ultrastructure changes supporting hyper-permeability. However, we found that abnormal function of the blood-cerebrospinal fluid barrier (BCSFB) in the choroid plexus underlies brain exposure to neuropathic antibodies. Considerable intrathecal lymphocyte infiltration likely occurs through the BCSFB, accompanied by epithelial hyper-permeability to antibodies. Our results challenge the commonly held view of BBB disruption in NPSLE, supporting a shift in focus to BCSFB dysfunction as a causative factor in the disease.

The MRL Model: A Valuable Tool in Studies of Autoimmunity-Brain Interactions

The link between systemic autoimmunity, brain pathology, and aberrant behavior is still a largely unexplored field of biomedical science. Accumulating evidence points to causal relationships between immune factors, neurodegeneration, and neuropsychiatric manifestations. By documenting autoimmunity-associated neuronal degeneration and cytotoxicity of the cerebrospinal fluid from disease-affected subjects, the murine MRL model had shown high validity in revealing principal pathogenic circuits. In addition, unlike any other autoimmune strain, MRL mice produce antibodies commonly found in patients suffering from lupus and other autoimmune disorders. This review highlights importance of the MRL model as a useful preparation in understanding the links between immune system and brain function.

TNF-like weak inducer of apoptosis promotes blood brain barrier disruption and increases neuronal cell death in MRL/lpr mice

Neuropsychiatric disease is one of the most common manifestations of human systemic lupus erythematosus, but the mechanisms remain poorly understood. In human brain microvascular endothelial cells in vitro, TNF-like weak inducer of apoptosis (TWEAK) decreases tight junction ZO-1 expression and increases the permeability of monolayer cell cultures. Furthermore, knockout (KO) of the TWEAK receptor, Fn14, in the MRL/lpr lupus mouse strain markedly attenuates neuropsychiatric disease, as demonstrated by significant reductions in depressive-like behavior and improved cognitive function. The purpose of the present study was to determine the mechanisms by which TWEAK signaling is instrumental in the pathogenesis of neuropsychiatric lupus (NPSLE). Evaluating brain sections of MRL/lpr Fn14WT and Fn14KO mice, we found that Fn14KO mice displayed significantly decreased cellular infiltrates in the choroid plexus. To evaluate the integrity of the blood brain barrier (BBB) in MRL/lpr mice, Western blot for fibronectin, qPCR for iNOS, and immunohistochemical staining for VCAM-1/ICAM-1 were performed. We found preserved BBB permeability in MRL/lpr Fn14KO mice, attributable to reduced brain expression of VCAM-1/ICAM-1 and iNOS. Additionally, administration of Fc-TWEAK intravenously directly increased the leakage of a tracer (dextran-FITC) into brain tissue. Furthermore, MRL/lpr Fn14KO mice displayed reduced antibody (IgG) and complement (C3, C6, and C4a) deposition in the brain. Finally, we found that MRL/lpr Fn14KO mice manifested reduced neuron degeneration and hippocampal gliosis. Our studies indicate that TWEAK/Fn14 interactions play an important role in the pathogenesis of NPSLE by increasing the accumulation of inflammatory cells in the choroid plexus, disrupting BBB integrity, and increasing neuronal damage, suggesting a novel target for therapy in this disease.

Neuropsychiatric systemic lupus erythematosus and cognitive dysfunction: the MRL-lpr mouse strain as a model

Mouse models of autoimmunity, such as (NZB×NZW)F1, MRL/MpJ-Fas(lpr) (MRL-lpr) and BXSB mice, spontaneously develop systemic lupus erythematosus (SLE)-like syndromes with heterogeneity and complexity that characterize human SLE. Despite their inherent limitations, such models have highly contributed to our current understanding of the pathogenesis of SLE as they provide powerful tools to approach the human disease at the genetic, cellular, molecular and environmental levels. They also allow novel treatment strategies to be evaluated in a complex integrated system, a favorable context knowing that very few murine models that adequately mimic human autoimmune diseases exist. As we move forward with more efficient medications to treat lupus patients, certain forms of the disease that requires to be better understood at the mechanistic level emerge. This is the case of neuropsychiatric (NP) events that affect 50-60% at SLE onset or within the first year after SLE diagnosis. Intense research performed at deciphering NP features in lupus mouse models has been undertaken. It is central to develop the first lead molecules aimed at specifically treating NPSLE. Here we discuss how mouse models, and most particularly MRL-lpr female mice, can be used for studying the pathogenesis of NPSLE in an animal setting, what are the NP symptoms that develop, and how they compare with human SLE, and, with a critical view, what are the neurobehavioral tests that are pertinent for evaluating the degree of altered functions and the progresses resulting from potentially active therapeutics.

Systemic autoimmunity in TAM triple knockout mice causes inflammatory brain damage and cell death

The Tyro3, Axl and Mertk (TAM) triply knockout (TKO) mice exhibit systemic autoimmune diseases, with characteristics of increased proinflammatory cytokine production, autoantibody deposition and autoreactive lymphocyte infiltration into a variety of tissues. Here we show that TKO mice produce high level of serum TNF-α and specific autoantibodies deposited onto brain blood vessels. The brain-blood barrier (BBB) in mutant brains exhibited increased permeability for Evans blue and fluorescent-dextran, suggesting a breakdown of the BBB in the mutant brains. Impaired BBB integrity facilitated autoreactive T cells infiltrating into all regions of the mutant brains. Brain autoimmune disorder caused accumulation of the ubiquitin-reactive aggregates in the mutant hippocampus, and early formation of autofluorescent lipofuscins in the neurons throughout the entire brains. Chronic neuroinflammation caused damage of the hippocampal mossy fibers and neuronal apoptotic death. This study shows that chronic systemic inflammation and autoimmune disorders in the TKO mice cause neuronal damage and death.

Discovery and antitumor activities of constituents from Cyrtomium fortumei (J.) Smith rhizomes

Background

Cyrtomium fortumei (J.) Smith is an important Chinese herbal medicine because of its biological functions. However, systematic and comprehensive studies on the phytochemicals from Cyrtomium fortumei (J.) Smith and their bioactivity are limited.

Results

Using the bioassay-guided technique, the ethyl acetate and n-BuOH extracts of the rhizomes of Cyrtomium fortumei (J.) Smith were shown to exhibit good antitumor activities, consequently leading to the isolation of 23 compounds. All compounds were isolated from the plant for the first time. The inhibitory activities of these compounds were investigated on tumor cells MGC-803, PC3, and A375 in vitro by MTT (thiazolyl blue tetrazolium bromide) assay, and the results showed that pimpinellin (3) had potent cytotoxic activities against the three cell lines, with the IC₅₀ values of 14.4 ± 0.3 μM, 20.4 ± 0.5 μM, and 29.2 ± 0.6 μM, respectively. The mechanism of the antitumor action indicated that pimpinellin inhibited the growth of MGC-803 cells via the induction of tumor cell apoptosis, with apoptosis ratio of 27.44% after 72 h of treatment at 20 μM.

Conclusions

This study suggests that most of the compounds from the roots of Cyrtomium fortumei (J.) Smith could inhibit the growth of human carcinoma cells. Moreover, pimpinellin inhibited the growth of tumor cells via the induction of tumor cell apoptosis.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Altered olfactory function in the MRL model of CNS lupus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disorder that damages several bodily systems, including the CNS. Brain atrophy and diverse neuropsychiatric manifestations are common and serious complications of SLE. Recently, it has been reported that many patients with CNS involvement also present with olfactory deficits of unknown etiology. Similar to CNS SLE, spontaneous development of lupus-like disease in MRL/lpr mice is accompanied by neurodegeneration in periventricular regions and a constellation of behavioral deficits dependent on olfaction. To test the possibility that olfactory dysfunction also occurs in autoimmune mice, we presently examine odor-guided behaviors using a battery of paradigms. Indeed, lupus-prone males spent less time exploring unfamiliar conspecifics and demonstrated age-dependant performance deficits when exposed to low concentrations of attractant and repellant odors. The emergence of olfactory changes was associated with a skewed distribution of DCX(+) cells in the proximal portion of the rostral migratory stream (RMS). The present results are consistent with the hypothesis that the onset of a SLE-like condition affects periventricular regions, including the RMS, as evidenced by disrupted migration of neuronal precursor cells toward the olfactory bulb. If so, ensuing hyposmia and/or olfactory memory deficit may contribute to altered performance in other behavioral tasks and reflect a prodrome of brain damage induced by chronic autoimmune disease.

The MRL model: an invaluable tool in studies of autoimmunity-brain interactions

The link between systemic autoimmunity, brain pathology, and aberrant behavior is still largely unexplored field of biomedical science. Accumulating evidence points to causal relationships between immune factors, neurodegeneration, and neuropsychiatric manifestations. By documenting autoimmunity-associated neuronal degeneration and cytotoxicity of the cerebrospinal fluid from disease-affected subjects, the murine MRL model had shown high validity in revealing principal pathogenic circuits. In addition, unlike any other autoimmune strain, MRL mice produce antibodies commonly found in patients suffering from lupus and other autoimmune disorders. This review highlights importance of the MRL model as an indispensible preparation in understanding the links between immune system and brain function.

The role of tumor necrosis factor receptor superfamily members in mammalian brain development, function and homeostasis

Tumor necrosis factor receptor superfamily (TNFRSF) members were initially identified as immunological mediators, and are still commonly perceived as immunological molecules. However, our understanding of the diversity of TNFRSF members' roles in mammalian physiology has grown significantly since the first discovery of TNFRp55 (TNFRSF1) in 1975. In particular, the last decade has provided evidence for important roles in brain development, function and the emergent field of neuronal homeostasis. Recent evidence suggests that TNFRSF members are expressed in an overlapping regulated pattern during neuronal development, participating in the regulation of neuronal expansion, growth, differentiation and regional pattern development. This review examines evidence for non-immunological roles of TNFRSF members in brain development, function and maintenance under normal physiological conditions. In addition, several aspects of brain function during inflammation will also be described, when illuminating and relevant to the non-immunological role of TNFRSF members. Finally, key questions in the field will be outlined.

Inhibition of C5a receptor alleviates experimental CNS lupus

To investigate the role of C5a generated on complement activation in brain, the lupus model, MRL/lpr mice were treated with C5a receptor(R) antagonist (ant). Neutrophil infiltration, ICAM, TNF-alpha and iNOS mRNA expression, neuronal apoptosis and the expression of p-JNK, pSTAT1 and p-Erk were reduced and p-Akt increased on C5aR inhibition in MRL/lpr brains. MRL/lpr serum caused increased apoptosis in neurons showing that lupus had a direct effect on these cells. C5aRant pretreatment prevented the lupus serum induced loss of neuronal cells. Our findings demonstrate for the first time that C5a/C5aR signaling plays an important role in the pathogenesis of CNS lupus.

Circulating brain-reactive autoantibodies and behavioral deficits in the MRL model of CNS lupus

Brain-reactive autoantibodies (BRAA) are hypothesized to play a role in the neuropsychiatric manifestations that accompany systemic lupus erythematosus (SLE). The present study tests the proposed relation between circulating BRAA and behavioral deficits in lupus-prone MRL/lpr mice. Two age-matched cohorts born at different times were used to test the relationship in the context of altered disease severity. Significant correlations between autoimmunity and behavior were detected in both cohorts. These results are the first to report correlations between behavior and autoantibodies to integral membrane proteins of brain, supporting the hypothesis that BRAA contribute to the behavioral dysfunction seen in lupus.

C3aR inhibition reduces neurodegeneration in experimental lupus

Complement activation is an important aspect of systemic lupus erythematosus. In this study we investigated the role of C3a/C3a receptor (R) signaling in brains of the lupus model, MRL/lpr mice, by treating the mice with C3aR antagonist (a) from 13 to 19 weeks of age. C3aR mRNA (0.2 +/- 0.027 versus 0.56 +/- 0.19) and protein (0.16 +/- 0.09 versus 0.63 +/- 0.19) expression was increased in MRL/lpr brains compared with MRL+/+ controls. Apoptosis, a key feature in lupus brain, was significantly reduced by C3aRa treatment, as assessed by DNA laddering, TUNEL staining and caspase3 activity (48% of MRL/lpr mice). mRNA expression of proinflammatory molecules that cause apoptosis, TNFalpha (0.33 +/- 0.07 versus 0.15 +/- 0.1), MIP2 (3.8 +/- 1.3 versus 1.7 +/- 0.6), and INFgamma (4.8 +/- 1.0 versus 2.07 +/- 1.28) are reduced in MRL/lpr brains with C3aRa treatment. In line with these results, Western blotting demonstrates the significant increase in phosphorylation of survival molecules Akt and Erk, decrease in PTEN and reduced iNOS expression. INFgamma receptor (R) and AMPA-GluR1 co-localized, and concomitant with reduced INFgammaR expression, AMPAGluR1 expression was also decreased by C3aR antagonist. All of these variables that modulate neuronal excitability and regulate synaptic plasticity are C3aR dependent in the MRL/lpr brains and suggest a potential therapeutic role for C3aR inhibition in CNS lupus.

Disturbed distribution of proliferative brain cells during lupus-like disease

Brain atrophy and neuronal degeneration of unknown etiology are frequent and severe concomitants of the systemic autoimmune disease lupus erythematosus (SLE). Using the murine MRL/lpr model, we examined populations of proliferative brain cells during the development of SLE-like disease and brain atrophy. The disease onset was associated with reduced expression of Ki67 and BrdU proliferation markers in the dorsal part of the rostral migratory stream, enhanced Fluoro Jade C staining in the subgranular zone of the dentate gyrus, and paradoxical increase in density of Ki67(+)/BrdU(-) cells in the paraventricular nucleus. Protuberances containing clusters of BrdU(+) cells were frequent along the lateral ventricles and in some cases were bridging ventricular walls. Cells infiltrating the choroid plexus were Ki67(+)/BrdU(+), suggesting proliferative leukocytosis in this cerebrospinal fluid-producing organ. The above results further support the hypothesis that systemic autoimmune disease induces complex CNS pathology, including impaired neurogenesis in the hippocampus. Moreover, changes in the paraventricular nucleus implicate a metabolic dysfunction in the hypothalamus-pituitary-adrenal axis, which may account for altered hormonal status and psychiatric manifestations in SLE.

Absence of functional alternative complement pathway alleviates lupus cerebritis

The complement inhibitor, Crry, which blocks both the classical and alternative pathways, alleviates CNS disease in the lupus model, MRL/MpJ-Tnfrsf6lpr (MRL/lpr) mice. To understand the role of the alternative pathway, we studied mice deficient in a key alternative pathway protein, complement factor B (fB). Immune deposits (IgG and C3) were reduced in the brains of MRL/lpr fB-deficient (fB-/-MRL/lpr) compared to fB-sufficient (MRL/lpr) mice, indicating reduced complement activation. Reduced neutrophil infiltration (22% of MRL/lpr mice) and apoptosis (caspase-3 activity was reduced to 33% of MRL/lpr mice) in these mice indicates that the absence of the alternative pathway was neuroprotective. Furthermore, expression of phospho (p)-Akt (0.16+/-0.02 vs. 0.35+/-0.13, p<0.03) was increased, while expression of p-PTEN (0.40+/-0.06 vs. 0.11+/-0.07, p<0.05) was decreased in fB-/-MRL/lpr mice compared to their MRL/lpr counterparts. The expression of fibronectin, laminin and collagen IV was significantly decreased in fB-/-MRL/lpr mice compared to MRL/lpr mice, indicating that in the lupus setting, tissue integrity was maintained in the absence of the alternative pathway. Absence of fB reduced behavioral alterations in MRL/lpr mice. Our results suggest that in lupus, the alternative pathway may be the key mechanism through which complement activation occurs in brain, and therefore it might serve as a therapeutic target for lupus cerebritis.

Neuroimmunopathology in a murine model of neuropsychiatric lupus

Animal models are extremely useful tools in defining pathogenesis and treatment of human disease. For many years researchers believed that structural damage to the brain of neuropsychiatric (NP) patients lead to abnormal mental function, but this possibility was not extensively explored until recently. Imaging studies of NP-systemic lupus erythematosus (SLE) support the notion that brain cell death accounts for the emergence of neurologic and psychiatric symptoms, and evidence suggests that it is an autoimmunity-induced brain disorder characterized by profound metabolic alterations and progressive neuronal loss. While there are a number of murine models of SLE, this article reviews recent literature on the immunological connections to neurodegeneration and behavioral dysfunction in the Fas-deficient MRL model of NP-SLE. Probable links between spontaneous peripheral immune activation, the subsequent central autoimmune/inflammatory responses in MRL/MpJ-Tnfrsf6(lpr) (MRL-lpr) mice and the sequential mode of events leading to Fas-independent neurodegenerative autoimmune-induced encephalitis will be reviewed. The role of hormones, alternative mechanisms of cell death, the impact of central dopaminergic degeneration on behavior, and germinal layer lesions on developmental/regenerative capacity of MRL-lpr brains will also be explored. This model can provide direction for future therapeutic interventions in patients with this complex neuroimmunological syndrome.

Autoreactive MZ and B-1 B-cell activation by Faslpr is coincident with an increased frequency of apoptotic lymphocytes and a defect in macrophage clearance

Murine autoreactive anti-Smith (Sm) B cells are negatively regulated by anergy and developmental arrest, but are also positively selected into the marginal zone (MZ) and B-1 B-cell populations. Despite positive selection, anti-Sm production occurs only in autoimmune-prone mice. To investigate autoreactive B-cell activation, an anti-Sm transgene was combined with the lpr mutation, a mutation of the proapoptotic gene Fas (Fas(lpr)), on both autoimmune (MRL) and nonautoimmune backgrounds. Fas(lpr) induces a progressive and autoantigen-specific loss of anti-Sm MZ and B-1 B cells in young adult Fas(lpr) and MRL/Fas(lpr) mice that does not require that Fas(lpr) be B-cell intrinsic. This loss is accompanied by a bypass of the early pre-plasma cell (PC) tolerance checkpoint. Although the MRL bkg does not lead to a progressive loss of anti-Sm MZ or B-1 B cells, it induces a robust bypass of the early pre-PC tolerance checkpoint. Fas(lpr) mice have a high frequency of apoptotic lymphocytes in secondary lymphoid tissues and a macrophage defect in apoptotic cell phagocytosis. Since Sm is exposed on the surface of apoptotic cells, we propose that anti-Sm MZ and B-1 B-cell activation is the result of a Fas(lpr)-induced defect in apoptotic cell clearance.

Systemic lupus erythematosus and the brain: what mice are telling us

Neuropsychiatric symptoms occur in systemic lupus erythematosus (SLE), a complex, autoimmune disease of unknown origin. Although several pathogenic mechanisms have been suggested to play a significant role in the etiology of the disease, the exact underlying mechanisms still remain elusive. Several inbred strains of mice are used as models to study SLE, which exhibit a diversity of central nervous system (CNS) manifestations similar to that observed in patients. This review will attempt to give a brief overview of the CNS alterations observed in these models, including biochemical, structural and behavioral changes.

Relationship between serum NR2a antibodies and cognitive dysfunction in systemic lupus erythematosus

OBJECTIVE

To assess the association between serum NR2a antibodies and cognitive dysfunction in systemic lupus erythematosus (SLE).

METHODS

The study population consisted of English-speaking adults who met American College of Rheumatology (ACR) criteria for SLE and had at least 1 serum sample stored in the Hospital for Special Surgery Autoimmune Registry and Repository. Demographic and clinical information was obtained, and patients completed the neuropsychological test battery recommended by the ACR, the Center for Epidemiologic Studies Depression Scale, and the Spielberger State-Trait Anxiety Inventory. Cognitive impairment was defined as scores >1.5 SD below the mean of age-matched published normative data on at least 2 neuropsychological tests. Sera were tested for NR2a antibodies by enzyme-linked immunosorbent assay. Performance on neuropsychological tests was compared between NR2a-positive and NR2a-negative patients.

RESULTS

Of the 93 patients, 24 (25.8%) were positive for NR2a antibodies. Of the 48 patients who were cognitively impaired based on test results, 31% were positive for NR2a antibodies, compared with 20% of those who were not cognitively impaired (P = 0.24). Among antibody-positive patients, the mean +/- SD number of neuropsychological tests with abnormal results was 2.3 +/- 2.2, compared with 2.0 +/- 1.8 in the antibody-negative group (P = 0.59). Similar nonsignificant differences were found when impairment was defined using a more stringent definition (i.e., test scores >2.0 SD below the mean) and using a neuropsychologist's clinical ratings. No association was detected between NR2a antibody positivity and depressive symptoms (P = 0.73) or anxiety (P = 0.42).

CONCLUSION

No significant association was found between NR2a antibody positivity and cognitive dysfunction, depressive symptoms, or anxiety. These results indicate that the presence of these antibodies alone does not have a direct effect on cognitive functioning or any other neuropsychiatric manifestation of SLE.

Distribution and prevalence of leukocyte phenotypes in brains of lupus-prone mice

Autoantibody-mediated compromise of central neurotransmission is a pathogenic mechanism proposed in etiology of neuropsychiatric lupus (NP-SLE). Recent experimental data support the hypothesis that intrathecally-synthesized antibodies play a key role in brain damage and behavioral dysfunction. However, autoantibody-producing plasma cells have not yet been detected in brain tissue. We presently use contemporary immunohistochemical markers and flow cytometry to assess distribution and prevalence of plasma cells and other phenotypes, which infiltrate brains of lupus-prone MRL-lpr mice. The functional status of infiltrates was confirmed by in situ hybridization for TNF-alpha mRNA. Consistent with the notion of breached blood-CSF and blood-brain barriers, CD3+ T-cells (approximately 20% of the mononuclear cell infiltrate) were plentiful in choroid plexuses and commonly seen around blood vessels. The CD138+ plasma cells were restricted to the choroid plexus and stria medullaris of diseased MRL-lpr mice. Although accounting for less than 1% of the total cell infiltrate, CD19+IgM+ B-cells increased with age in brains of MRL-lpr mice. Severe mononuclear cell infiltration was accompanied by splenomegaly and retarded brain growth. The results obtained support the hypothesis of progressive neurodegeneration as a consequence of leukocyte infiltration and intrathecal autoantibody synthesis. Further characterization of neuroactive antibodies and their targets may contribute to a better understanding of brain atrophy and behavioral dysfunction in the MRL model, and potentially in NP-SLE.

Complement-dependent apoptosis and inflammatory gene changes in murine lupus cerebritis

The role of complement activation in the brains of MRL/lpr lupus mice was determined using the potent C3 convertase inhibitor, CR1-related y (Crry), administered both as an overexpressing Crry transgene and as Crry-Ig. Prominent deposition of complement proteins C3 and C9 in brains of MRL/lpr mice was indicative of complement activation and was significantly reduced by Crry. Apoptosis was determined in brain using different independent measures of apoptosis, including TUNEL staining, DNA laddering, and caspase-3 activity, all of which were markedly increased in lupus mice and could be blocked by inhibiting complement with Crry. Complement activation releases inflammatory mediators that can induce apoptosis. The mRNA for potentially proinflammatory proteins such as TNFR1, inducible NO synthase, and ICAM-1 were up-regulated in brains of lupus mice. Crry prevented the increased expression of these inflammatory molecules, indicating that the changes were complement dependent. Furthermore, microarray analysis revealed complement-dependent up-regulation of glutamate receptor (AMPA-GluR) expression in lupus brains, which was also validated for AMPA-GluR1 mRNA and protein. Our results clearly demonstrate that apoptosis is a prominent feature in lupus brains. Complement activation products either directly and/or indirectly through TNFR1, ICAM-1, inducible NO synthase, and AMPA-GluR, all of which were altered in MRL/lpr mouse brains, have the potential to induce such apoptosis. These findings present the exciting possibility that complement inhibition is a therapeutic option for lupus cerebritis.

Proliferating brain cells are a target of neurotoxic CSF in systemic autoimmune disease

Brain atrophy, neurologic and psychiatric (NP) manifestations are common complications in the systemic autoimmune disease, lupus erythematosus (SLE). Here we show that the cerebrospinal fluid (CSF) from autoimmune MRL-lpr mice and a deceased NP-SLE patient reduce the viability of brain cells which proliferate in vitro. This detrimental effect was accompanied by periventricular neurodegeneration in the brains of autoimmune mice and profound in vivo neurotoxicity when their CSF was administered to the CNS of a rat. Multiple ionic responses with microfluorometry and protein peaks on electropherograms suggest more than one mechanism of cellular demise. Similar to the CSF from diseased MRL-lpr mice, the CSF from a deceased SLE patient with a history of psychosis, memory impairment, and seizures, reduced viability of the C17.2 neural stem cell line. Proposed mechanisms of cytotoxicity involve binding of intrathecally synthesized IgG autoantibodies to target(s) common to different mammalian species and neuronal populations. More importantly, these results indicate that the viability of proliferative neural cells can be compromised in systemic autoimmune disease. Antibody-mediated lesions of germinal layers may impair the regenerative capacity of the brain in NP-SLE and possibly, brain development and function in some forms of CNS disorders in which autoimmune phenomena have been documented.

Behavioral heterogeneity in an animal model of neuropsychiatric lupus

BACKGROUND

Various psychiatric manifestations of unknown etiology are common in systemic autoimmune disease lupus erythematosus (SLE). Profound heterogeneity at clinical and neuropathological levels suggests distinct subpopulations of SLE patients and multiple mechanisms in the pathogenesis of aberrant behavior. Using inbred mice prone to SLE-like condition, we presently examine whether subpopulations of diseased mice can be identified on the basis of their behavioral performance.

METHODS

Hierarchical cluster analysis was used to classify 105 MRL-lpr males into clusters. Multivariate analysis of variance (MANOVA) and discriminant function analysis were used to detect overall differences and identify discriminative variables.

RESULTS

Cluster 1 was characterized by blunted responsiveness to palatable stimulation, as well as increased spleen mass and serum levels of interleukin-1. Cluster 2 comprised of animals with reduced ambulation speed and enlarged spleen. Mice from cluster 3 showed profound dilatation of brain ventricles, reduced brain mass, impaired nutrition and performance in task reflective of emotional reactivity.

CONCLUSIONS

Present results suggest that systemic autoimmunity compromises brain function via non-Mendelian mechanisms. Although neuroactive cytokines may impair reward systems, brain atrophy seems to underlie deficits in ingestive behavior and emotional reactivity. This study supports the hypothesis that multiple neuroimmunological pathways are involved in the etiology of aberrant behavior during SLE-like disease.

Hippocampal damage in mouse and human forms of systemic autoimmune disease

Systemic lupus erythematosus (SLE) is frequently accompanied by neuropsychiatric (NP) and cognitive deficits of unknown etiology. By using autoimmune MRL-lpr mice as an animal model of NP-SLE, we examine the relationship between autoimmunity, hippocampal damage, and behavioral dysfunction. Fluoro Jade B (FJB) staining and anti-ubiquitin (anti-Ub) immunocytochemistry were used to assess neuronal damage in young (asymptomatic) and aged (diseased) mice, while spontaneous alternation behavior (SAB) was used to estimate the severity of hippocampal dysfunction. The causal relationship between autoimmunity and neuropathology was tested by prolonged administration of the immunosuppressive drug cyclophosphamide (CY). In comparison to congenic MRL +/+ controls, SAB acquisition rates and performance in the "reversal" trial were impaired in diseased MRL-lpr mice, suggesting limited use of the spatial learning strategy. FJB-positive neurons and anti-Ub particles were frequent in the CA3 region. Conversely, CY treatment attenuated the SAB deficit and overall FJB staining. Similarly to mouse brain, the hippocampus from a patient who died from NP-SLE showed reduced neuronal density in the CA3 region and dentate gyrus, as well as increased FJB positivity in these regions. Gliosis and neuronal loss were observed in the gray matter, and T lymphocytes and stromal calcifications were common in the choroid plexus. Taken together, these results suggest that systemic autoimmunity induces significant hippocampal damage, which may underlie affective and cognitive deficits in NP-SLE.

Autoimmune-induced damage of the midbrain dopaminergic system in lupus-prone mice

Spontaneous development of lupus-like disease is accompanied by impaired dopamine catabolism and degenerating axon terminals in the mesencephalon of MRL-lpr mice. We presently examine the hypothesis that systemic autoimmunity affects the central dopaminergic system in behaviorally impaired animals. The functional damage of the nigrostriatal pathway was assessed from rotational behavior after a single injection of the D1/D2-receptor agonist apomorphine. Neurodegeneration in the midbrain was estimated by Fluoro Jade B (FJB) staining. The causal role of autoimmunity was tested by comparing asymptomatic and diseased MRL-lpr mice, and by employing the immunosuppressive drug cyclophosphamide. Damage of dopaminergic neurons was assessed by tyrosine-hydroxylase (TH) staining of the midbrain. Apomorphine induced significant asymmetry in limb use, which lead to increased circling in the diseased MRL-lpr group. While FJB-positive somas were not seen in the striatum, increased staining in the substantia nigra (SN) and ventral tegmental area (VTA) were detected in behaviorally impaired MRL-lpr mice, but not in age-matched controls. Reduced brain mass and increased levels of TNF-alpha in their cerebrospinal fluid (CSF) suggested cerebral atrophy and inflammation. In addition, CSF was neurotoxic to a dopaminergic progenitor cell line. Immunosuppression attenuated CSF cytotoxicity, TNF-alpha levels, and midbrain neurodegeneration. Supportive of the notion that dying neurons were dopaminergic, the SN of autoimmune mice showed approximately a 35% reduction in the number of TH-positive cells. A three-fold increase in serum brain-reactive antibodies accompanied this loss. Although the source of toxic mediator(s) remains unknown, present results are consistent with the hypothesis that autoimmunity-induced destruction of mesonigral and mesolimbic dopaminergic pathways contributes to the etiology of aberrant behavior in an animal model of neuropsychiatric lupus.

B and T cells in the brains of autoimmune mice

Systemic lupus erythematosus (SLE) is an autoimmune disorder that can involve the central nervous system (CNS). Recently, we reported the presence of autoantibodies bound to the brain tissue of murine models of lupus; MRL/lpr and BXSB. We postulated that the source of these autoantibodies was in part due to in situ production, caused by the entry of B and T cells. Frozen brain sections of MRL/lpr and BXSB at 1 and 4 months of age were stained for CD3 (T cells) and CD19 (B cells) markers using an immunofluorescent antibody binding assay. Confocal fluorescence microscopy showed both CD3(+) and CD19(+) cells at 4 months of age only in MRL/lpr mice. There were no lymphocytes seen in the other autoimmune model, BXSB. Results suggest a difference in the mechanisms by which autoantibodies access the brain in these two autoimmune models of lupus.

Neurodegeneration in autoimmune MRL-lpr mice as revealed by Fluoro Jade B staining

As in many humans suffering from lupus erythematosus, the development of systemic autoimmunity and inflammation in Fas-deficient MRL-lpr mice is accompanied by CNS dysfunction of unknown etiology. Experimental studies revealed infiltration of lymphoid cells into the choroid plexus, reduced neuronal complexity, retarded brain growth, and enlargement of cerebral ventricles. Moreover, an increased presence of cells with nicked-DNA (TUNEL+ cells) in the periventricular areas suggested accelerated apoptosis in brain cells of MRL-lpr mice. However, direct evidence that the dying cells were neurons was lacking. For this purpose, we presently use Fluoro-Jade B (FJB), a novel fluorescent dye which has high affinity for dying neurons (both apoptotic and necrotic). As expected, in comparison to the control groups, the brains of diseased, 5-month-old MRL-lpr mice showed increased numbers of FJB-positive (+) cells in cortical and periventricular regions. The FJB+ cells were significantly more numerous than TUNEL+ cells, and only approximately 7% co-localized with TUNEL. Immunostaining for CD4 and CD8 markers did not correlate with the number of FJB+ cells, suggesting that T-lymphocyte infiltration into the brain tissue is not a reliable predictor of neuronal demise. Conversely, indices of systemic autoimmunity (splenomegaly and high serum anti-nuclear antibody levels) were associated with increased FJB+ cell numbers in brains of autoimmune MRL-lpr mice, supporting the causal link between autoimmunity and neurodegeneration. Taken together, the above results suggest that factors other than T-cell infiltration and cell death mechanisms other than Fas-mediated apoptosis dominate neuronal degeneration in lupus-prone MRL-lpr mice.

Relationship between the development of autoimmunity and sensorimotor gating in MRL-lpr mice with reduced IL-2 production

MRL-lpr mice develop systemic lupus-like autoimmune disease associated with changes in emotional reactivity and spatial learning and memory. Although the major immunological deficit in MRL-lpr mice is uncontrolled lymphoproliferation associated with a Fas gene mutation, these mice have a marked deficit in interleukin-2 (IL-2) production which, when treated, can prevent the development of autoimmune disease. Moreover, both MRL-lpr and IL-2 knockout mice manifest alterations in hippocampal cytoarchitecture and cognitive behavior. We found previously that IL-2 knockout mice have alterations in prepulse inhibition (PPI), a measure of sensorimotor gating. Thus, the present study sought to test the hypothesis that that PPI would be altered in MRL-lpr mice. Compared to MRL(+/+) control mice, MRL-lpr mice exhibited different patterns of PPI during development. Whereas 7 and 12-week MRL-lpr mice with evidence of autoimmune disease (the onset and early stages, respectively) showed increased PPI, 5 week predisease MRL-lpr mice did not. MRL-lpr mice also exhibited increased acoustic startle reactivity that was independent of autoimmune disease. These behavioral changes were not associated with increased brain expression of the proinflammatory cytokines genes, IL-1alpha and IL-6, CD3, or c-myc-associated apoptosis.

Altered neurotransmission in brains of autoimmune mice: pharmacological and neurochemical evidence

Depressive-like behavior is the most profound manifestation of autoimmunity-associated behavioral syndrome in lupus-prone MRL-lpr mice. This led to the hypothesis that chronic autoimmunity and inflammation alter the activity of central serotonergic and dopaminergic systems. Three drugs with a selective mode of action were used to probe the functional status of these two systems in vivo. The behavioral effects of single and repeated intraperitoneal (i.p.) injections of sertraline, quinpirole (QNP) and risperidone were measured in the forced swim and brief sucrose preference tests. In comparison to MRL +/+ controls, autoimmune MRL-lpr mice did not show a reduction in sucrose intake after the administration of sertraline. Acute injection of quinpirole increased floating more in the MRL-lpr than in the control group, while intermittent administration induced self-injurious behavior in both groups. Acute injection of risperidone significantly increased floating in MRL-lpr mice, while repeated administration abolished the difference between the substrains in sucrose intake. These discrepancies in responsiveness implied that the central neurotransmitter activity is dissimilar in the two MRL substrains. This notion was confirmed in a cohort of untreated MRL-lpr and MRL +/+ mice by comparing their neurotransmitter/metabolite levels in several brain regions. In particular, MRL-lpr brains showed increased dopamine (DA) levels in the paraventricular nucleus (PVN) and median eminence (ME), decreased concentrations of serotonin in the PVN and enhanced levels in the hippocampus, as well as decreased norepinephrine (NE) levels in the prefrontal cortex. Behavioral deficits correlated with the changes in PVN and median eminence. These results are consistent with the hypothesis that imbalanced neurotransmitter regulation of the hypothalamus-pituitary axis plays an important role in the etiology of behavioral dysfunction induced by systemic autoimmune disease.

Comparison of neuronal density and subfield sizes in the hippocampus of CD95L-deficient (gld), CD95-deficient (lpr) and nondeficient mice

During brain development, the majority of neurons undergo programmed cell death. It is now clear that caspases are involved in this process of selective induction of neuronal apoptosis, yet the signals for this caspase activation remain undefined. As an upstream activator of these enzymes, the death receptor CD95 (Fas, APO1) was recently shown on neurons in the cornu ammonis (CA)2 and CA3 hippocampal subfields of early postnatal mice and rats. In vitro, cortical neuroblast cells are susceptible to CD95 ligand (CD95L, FasL, APO-1 L)-induced apoptosis. It was therefore suggested that the CD95/CD95L system is involved in neuronal apoptosis during hippocampal development. We therefore performed a blinded study comparing field size and neuronal density in the hippocampi of p20 CD95-deficient (lpr), CD95L-deficient (gld) and C57 mice. Whereas field sizes did not differ significantly between these strains, paired Mann-Whitney analyses revealed an increased number of neurons in the CA2 regions of CD95-deficient mice (P = 0.008), and minor, yet at 1% nonsignificant, differences between gld, lpr and C57 strains in the CA1 and CA3 regions. However, joint comparison of the three strains using the Kruskal-Wallis test rendered all differences insignificant. We conclude that the CD95/CD95L system is either not involved, or can be replaced by alternate mechanisms in the control of neuronal populations during hippocampal development.

Neurotoxic properties of cerebrospinal fluid from behaviorally impaired autoimmune mice

The chronic, lupus-like autoimmune disease in MRL-lpr mice is associated with leucocyte infiltration into the choroid plexus, brain cell death, and deficits in motivated behavior. The presence of lymphoid cells in the ventricular lumen and the increased number of TUNEL-positive cells in periventricular areas led to the hypothesis that immune cells enter into the cerebrospinal fluid (CSF) and induce primary neuronal damage in regions bordering the cerebral ventricles. Using an in vitro approach, we presently examine the possibility that CSF from autoimmune mice is neurotoxic and/or gliotoxic. The CSF and serum from diseased MRL-lpr mice, less symptomatic MRL +/+ controls, and healthy Swiss/Webster mice (non-autoimmune controls) were frozen until their effects on the viability of pyramidal neurons and astrocytes were assessed in a two-color fluorescence assay. Significant reduction in neuronal viability (in some cases as low as 67%) was observed in the co-cultures of hippocampal neurons and astrocytes incubated for 24 h with CSF from autoimmune MRL-lpr mice. The viability of astrocytes did not differ among the groups, and the CSF from autoimmune mice appeared more toxic than the serum. The behavior of MRL-lpr mice differed significantly from the control groups, as indicated by impaired exploration, reduced intake of palatable food, and excessive immobility in the forced swim test. The present results suggest that CSF from the behaviorally impaired lupus-prone mice is neurotoxic and are consistent with the hypothesis that neuroactive metabolites are produced intrathecally in neuropsychiatric lupus erythematosus.

Immunosuppression prevents neuronal atrophy in lupus-prone mice: evidence for brain damage induced by autoimmune disease?

An early onset of systemic, lupus-like disease in MRL-lpr mice is accompanied by deterioration in their behavioral performance and atrophy of pyramidal neurons in the parietal cortex and the hippocampal CA1 area. Using the immunosuppressive drug cyclophosphamide (CY) to attenuate the disease, we have tested the hypothesis that the autoimmune/inflammatory process is responsible for changes in brain morphology. A modified Golgi impregnation method revealed that, in comparison to saline-treated controls, immunosuppressive treatment with CY (100 mg/kg/week i.p. over 8 weeks) increased dendritic branching and spine numerical density in the CA1 region of MRL-lpr mice and MRL +/+ mice, which develop less severe manifestations of the disease. More interestingly, CY selectively prevented the atrophy and aberrant morphology of pyramidal neurons in the parietal cortex of MRL-lpr mice. The neuropathological measures (in particular reduced dendritic spine density) significantly correlated with increased serum levels of antinuclear antibodies and splenomegaly. The present results support the hypothesis that chronic autoimmune disease induces functionally important changes in neuronal morphology, and provide an empirical basis for understanding the behavioral dysfunction in systemic lupus erythematosus and autoimmune phenomena reported in some forms of mental illness.