Neuroimmunopathology in a murine model of neuropsychiatric lupus

Pristane induced lupus mice as a model for neuropsychiatric lupus (NPSLE)

BACKGROUND

The pristane-induced lupus (PIL) model is a useful tool for studying environmental-related systemic lupus erythematosus (SLE). However, neuropsychiatric manifestations in this model have not been investigated in detail. Because neuropsychiatric lupus (NPSLE) is an important complication of SLE, we investigated the neuropsychiatric symptoms in the PIL mouse model to evaluate its suitability for NPSLE studies.

RESULTS

PIL mice showed olfactory dysfunction accompanied by an anxiety- and depression-like phenotype at month 2 or 4 after pristane injection. The levels of cytokines (IL-1β, IFN-α, IFN-β, IL-10, IFN-γ, IL-6, TNF-α and IL-17A) and chemokines (CCL2 and CXCL10) in the brain and blood-brain barrier (BBB) permeability increased significantly from week 2 or month 1, and persisted throughout the observed course of the disease. Notably, IgG deposition in the choroid plexus and lateral ventricle wall were observed at month 1 and both astrocytes and microglia were activated. Persistent activation of astrocytes was detected throughout the observed course of the disease, while microglial activation diminished dramatically at month 4. Lipofuscin deposition, a sign of neuronal damage, was detected in cortical and hippocampal neurons from month 4 to 8.

CONCLUSION

PIL mice exhibit a series of characteristic behavioral deficits and pathological changes in the brain, and therefore might be suitable for investigating disease pathogenesis and for evaluating potential therapeutic targets for environmental-related NPSLE.

Lipidomics Changes in a Murine Model of Neuropsychiatric Lupus

Purpose

Neuropsychiatric lupus (NPSLE) is one of the important manifestations of systemic lupus erythematosus. Previous studies mainly focused on the disruption of the blood-brain barrier and the production of brain-reactive autoantibodies, However, there is no comprehensive lipidomic analysis in NPSLE. Therefore, this research evaluated the lipidomic analysis in the hippocampus and liver of NPSLE mice with mood disorders, to explore the influence of the liver-brain axis on this disease.

Methods

MRL/lpr mice and MRL/mpj mice were respectively used as NPSLE and control groups. Behavioral tests and systemic disease characteristics of mice were assessed at the age of 18 weeks. Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS) was used for lipid metabolite determination. Multivariate statistical analysis was used to identify lipid metabolites that were differentially expressed in two groups.

Results

Our results showed that 355 and 405 lipid metabolites were differentially expressed between the NPSLE and control groups in the hippocampus and liver. According to the pathway enrichment analysis, several pathways were affected, and the glycerophospholipid metabolism pathway was most relevant to the mouse's depressive behavior.

Conclusion

Based on UPLC-MS/MS, the results provide evidence for how the liver-brain axis affects NPSLE and improve the understanding of NPSLE pathogenesis.

(NZW × BXSB) F1 male mice: An unusual, severe and fatal mouse model of lupus erythematosus

Background

Systemic lupus erythematosus (SLE) is a chronic autoimmune/inflammatory disease. The heterogeneity and complexity of clinical presentation has made it challenging to study or treat this syndrome. The (NZW×BXSB) F1 lupus-prone male mouse model of this disease is potentially useful to study mechanism and treatment modalities, but there is a lack of information about this model’s characterization and disease progression. Therefore, the aim was to examine this lupus model’s physical/clinical disease presentation and its immunological status.

Materials and methods

Clinical and physical status were observed in 8- and 16-week-old male and female (± 1 week) (NZW/LacJ x BXSB/MpJ) F1 mice (n = 8 per group). Young males (8 ± 1 week) without disease and female (16 ± 1 week) mice served as controls. Physical changes, quantitative values of autoantibodies, and blood cell parameters were determined. Necropsy and post-mortem histopathology were also performed.

Results

With aging (≥ 12 weeks), significant increases in severe abdominal distension/swelling, inability to walk, paleness of paws and significant weight increase were observed compared to controls (p < 0.05). The necropsy examination showed abdominal distension associated with serous effusion and histological examination identified severe edema and multi-organ abnormalities (spleen, lymph nodes, and kidney). Significant increases in anti-double-stranded DNA antibody (anti-dsDNA) was seen in old/sick compared to female (p = 0.0002) or young male (p = 0.0036) mice. Old mice developed immune thrombocytopenia compared to female (p = 0.0056) and young male (p = 0.0007) mice. Anti-platelet was detectable in old, sick mice. The mortality rate increased with aging; more than 35% of male mice died during this study between the ages of 13-18 weeks.

Conclusion

We found that the (NZW/LacJ x BXSB/MpJ) F1 male mice spontaneously exhibit, over varying lengths of time, extremely severe and fatal clinical disease symptoms. This model may be too severe to be helpful in investigating SLE and testing potential treatment modalities.

TWEAKing the Hippocampus: The Effects of TWEAK on the Genomic Fabric of the Hippocampus in a Neuropsychiatric Lupus Mouse Model

Neuropsychiatric manifestations of systemic lupus erythematosus (SLE), specifically cognitive dysfunction and mood disorders, are widely prevalent in SLE patients, and yet poorly understood. TNF-like weak inducer of apoptosis (TWEAK) has previously been implicated in the pathogenesis of neuropsychiatric lupus (NPSLE), and we have recently shown its effects on the transcriptome of the cortex of the lupus-prone mice model MRL/lpr. As the hippocampus is thought to be an important focus of NPSLE processes, we explored the TWEAK-induced transcriptional changes that occur in the hippocampus, and isolated several genes (Dnajc28, Syne2, transthyretin) and pathways (PI3K-AKT, as well as chemokine-signaling and neurotransmission pathways) that are most differentially affected by TWEAK activation. While the functional roles of these genes and pathways within NPSLE need to be further investigated, an interesting link between neuroinflammation and neurodegeneration appears to emerge, which may prove to be a promising novel direction in NPSLE research.

Exercise alleviates symptoms of CNS lupus

Systemic lupus erythematosus (lupus) is a global health problem where 20-80% patients display cognitive problems and central nervous system (CNS) dysfunction. Early diagnosis and treatment of lupus remains a clinical challenge. Exercise improves experimental lupus nephritis. However, the effects of exercise in CNS lupus remains unknown. This study investigates the effects of controlled exercise (CE) that consisted of treadmill walking (5 m/min for 10 min everyday) on experimental CNS lupus using the well-established mouse model, MRL/lpr mice. The MRL/lpr mice were subjected to CE from 8 weeks (preclinical) to 16 weeks (disease). Multiplex gene expression analysis revealed significant upregulation of genes involved in neurite growth, proliferation and synaptic plasticity, and a decrease in inflammatory genes including complement proteins, NFkB, chemokines and cytokines in exercised mice compared to the unmanipulated, age-matched controls. The loss of blood-brain barrier integrity, astrogliosis and edema seen in MRL/lpr mice were reduced with exercise. Exercised mice performed better in behavioral assessments such as open field, nesting, and tail suspension test. For the first time our results show that a supervised, well-regulated and controlled exercise regimen alleviates CNS lupus and could potentially serve as an intervention strategy to improve the quality of life. Exercise could also serve as an adjunct therapy for lupus and other neuroinflammatory diseases, thereby reducing the need for the current therapies with toxic side effects. The validity of the findings and a safe exercise regimen needs to be established by additional studies in patients.

Remodeling of Neurotransmission, Chemokine, and PI3K-AKT Signaling Genomic Fabrics in Neuropsychiatric Systemic Lupus Erythematosus

Cognitive dysfunction and mood changes are prevalent and especially taxing issues for patients with systemic lupus erythematosus (SLE). Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) and its cognate receptor Fn14 have been shown to play an important role in neurocognitive dysfunction in murine lupus. We profiled and compared gene expression in the cortices of MRL/+, MRL/lpr (that manifest lupus-like phenotype) and MRL/lpr-Fn14 knockout (Fn14ko) adult female mice to determine the transcriptomic impact of TWEAK/Fn14 on cortical gene expression in lupus. We found that the TWEAK/Fn14 pathway strongly affects the expression level, variability and coordination of the genomic fabrics responsible for neurotransmission and chemokine signaling. Dysregulation of the Phosphoinositide 3-kinase (PI3K)-AKT pathway in the MRL/lpr lupus strain compared with the MRL/+ control and Fn14ko mice was particularly prominent and, therefore, promising as a potential therapeutic target, although the complexity of the transcriptomic fabric highlights important considerations in in vivo experimental models.

Lupus animal models and neuropsychiatric implications

Systemic lupus erythematosus (SLE) that involves neurological complications is known as neuropsychiatric systemic lupus erythematosus (NPSLE). Research in humans is difficult due to the disease's great heterogeneity. Animal models are a resource for new discoveries. In this review, we examine experimental models of lupus that present neuropsychiatric manifestations. Spontaneous animal models such as NZB/W F1 and MRL/lpr are commonly used in NPSLE research; these models present few SLE symptoms compared to induced animal models, such as pristane-induced lupus (PIL). The PIL model is known to present eight of the main clinical and laboratory manifestations of SLE described by the American College of Rheumatology. Many cytokines associated with NPSLE are expressed in the PIL model, such as IL-6, TNF-α, and IFN. However, to date, NPSLE manifestations have been poorly studied in the PIL model. In this review article, we discuss whether the PIL model can mimic neuropsychiatric manifestations of SLE. Key Points • PIL model have a strong interferon signature. • Animals with PIL express learning and memory deficit.

Neuropsychiatric lupus: new mechanistic insights and future treatment directions

Patients with systemic lupus erythematosus (SLE) frequently show symptoms of central nervous system (CNS) involvement, termed neuropsychiatric SLE (NPSLE). The CNS manifestations of SLE are diverse and have a broad spectrum of severity and prognostic implications. Patients with NPSLE typically present with nonspecific symptoms, such as headache and cognitive impairment, but might also experience devastating features, such as memory loss, seizures and stroke. Some features of NPSLE, in particular those related to coagulopathy, have been characterized and an evidence-based treatment algorithm is available. The cognitive and affective manifestations of NPSLE, however, remain poorly understood. Various immune effectors have been evaluated as contributors to its pathogenesis, including brain-reactive autoantibodies, cytokines and cell-mediated inflammation. Additional brain-intrinsic elements (such as resident microglia, the blood-brain barrier and other neurovascular interfaces) are important facilitators of NPSLE. As yet, however, no unifying model has been found to underlie the pathogenesis of NPSLE, suggesting that this disease has multiple contributors and perhaps several distinct aetiologies. This heterogeneity presents a challenge for clinicians who have traditionally relied on empirical judgement in choosing treatment modalities for patients with NPSLE. Improved understanding of this manifestation of SLE might yield further options for managing this disease.

Anti-IFNAR treatment does not reverse neuropsychiatric disease in MRL/lpr lupus mice

OBJECTIVE

Many systemic lupus erythematosus patients display a type I interferon (IFN) signature, and IFNα levels positively correlate with disease severity. Previous studies blocking the type I IFN pathway systemically in lupus models showed some beneficial effects. However, its effects on neuropsychiatric manifestations have yet to be carefully assessed, even though IFNα has been associated with induction of depression. Our aim was to investigate whether disrupting the type I IFN pathway would attenuate the development of murine neuropsychiatric lupus.

METHODS

Female MRL/lpr mice were administered an antitype I IFN receptor (IFNAR) antibody or a control antibody intraperitoneally three times weekly for 12 weeks starting at age 4-5 weeks. Behavior was assessed during and at the end of the treatment schedule.

RESULTS

No significant differences were seen between the anti-IFNAR- and control-treated mice when assessing for depression-like behavior or cognitive dysfunction, although anti-IFNAR antibody-treated mice displayed significant decreases in levels of IFN-stimulated genes. Anti-IFNAR treatment also did not significantly improve brain histology, cellular infiltration, or blood-brain barrier integrity.

CONCLUSIONS

Surprisingly, our results showed no improvement in neuropsychiatric disease and suggest that the role of IFNAR signaling in the pathogenesis of neuropsychiatric lupus continues to need to be carefully assessed.

Association between schizophrenia and an autoimmune bullous skin disease-pemphigus: a population-based large-scale study

AIMS

Immunological hypotheses have become increasingly prominent suggesting that autoimmunity may be involved in the pathogenesis of schizophrenia. Schizophrenia was found to be associated with a wide range of autoimmune diseases. However, the association between pemphigus and schizophrenia has not been established yet. We aimed to estimate the association between pemphigus and schizophrenia using a large-scale real-life computerised database.

METHODS

This study was conducted as a cross-sectional study utilising the database of Clalit Health Services. The proportion of schizophrenia was compared between patients diagnosed with pemphigus and age-, gender- and ethnicity-matched control subjects. Univariate analysis was performed using χ2 and Student's t-test and a multivariate analysis was performed using a logistic regression model.

RESULTS

A total of 1985 pemphigus patients and 9874 controls were included in the study. The prevalence of schizophrenia was greater in patients with pemphigus as compared to the control group (2.0% v. 1.3%, respectively; p = 0.019). In a multivariate analysis, pemphigus was significantly associated with schizophrenia (OR, 1.5; 95% CI, 1.1-2.2). The association was more prominent among females, patients older than 60 years, and Jews.

CONCLUSIONS

Pemphigus is significantly associated with schizophrenia. Physicians treating patients with pemphigus should be aware of this possible association. Patients with pemphigus should be carefully assessed for comorbid schizophrenia and be treated appropriately.

Bipolar Disorder Associated with Another Autoimmune Disease-Pemphigus: A Population-based Study

OBJECTIVES

Recent evidence suggests a notable role for inflammation and immune dysregulation in the neuroprogression of bipolar disorders (BD). Several autoimmune comorbidities have been reported in association with BD. However, the epidemiological relationship between pemphigus and BD has not yet been elucidated. We aimed to estimate the association between pemphigus and BD using a large-scale, real-life computerized database.

METHODS

Data for this study were retrieved from the database of the Clalit Health Services, the largest, state-mandated, health service organization in Israel. This study was designed as a cross-sectional study. The proportion of patients with BD was compared between patients diagnosed with pemphigus and age-, sex-, and ethnicity-matched control subjects. A logistic regression model was performed to estimate how pemphigus and other covariates contributed as risk factors for BD.

RESULTS

A total of 1,985 pemphigus cases and 9,874 controls were included in the study. The prevalence of BD was greater in cases with pemphigus than in controls (1.0% v. 0.5%, respectively; P = 0.023). This coexistence was more prominent among patients of Jewish ethnicity. After controlling for confounders, such as age, sex, ethnicity, socioeconomic status, drug abuse, alcohol abuse, smoking, healthcare utilization, and comorbidities, pemphigus demonstrated a substantial independent association with BD (OR, 1.7; 95% CI, 1.0 to 2.9).

CONCLUSIONS

Pemphigus is significantly associated with BD. Patients with pemphigus should be assessed for comorbid BD. Experimental research is needed to better recognize the biological mechanisms underlying this observation.

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.

Conjugated linoleic acid prevents age-dependent neurodegeneration in a mouse model of neuropsychiatric lupus via the activation of an adaptive response

Oxidative stress is a key mediator of autoimmune/neurodegenerative disorders. The antioxidant/anti-inflammatory effect of a synthetic conjugated linoleic acid (CLA) mixture in MRL/MpJ-Fas lpr mice (MRL/lpr), an animal model of neuropsychiatric lupus, was previously associated with the improvement of nuclear factor-E2-related factor 2 (Nrf2) defenses in the spleen and liver. However, little is known about the neuroprotective ability of a CLA mixture. This study investigated the age-dependent progression of oxidative stress and the hyperactivation of redox-sensitive compensatory pathways (macroautophagy, Nrf2) in old/diseased MRL/lpr mice brains and examines the effect produced by dietary CLA supplementation. Disrupted redox homeostasis was evidenced in the blood, liver, and brain of 21- to 22-week-old MRL/lpr (Old) mice compared with 8- to 10-week-old MRL/lpr (Young) animals. This alteration was associated with significant hyperactivation of compensatory mechanisms (macroautophagy, Nrf2, and astrocyte activation) in the brains of Old mice. Five-week daily supplementation with CLA (650 mg/kg-1 body weight) of 16-week-old (CLA+Old) mice diminished all the pathological hallmarks at a level comparable to Young mice or healthy controls (BALB/c). Such data demonstrated that MRL/lpr mice can serve as a valuable model for the evaluation of the effectiveness of neuroprotective drugs. Notably, the preventive effect provided by CLA supplementation against age-associated neuronal damage and hyperactivation of compensatory mechanisms suggests that the activation of an adaptive response is at least in part accountable for its neuroprotective ability.

Chronic peripheral inflammation, hippocampal neurogenesis, and behavior

Adult hippocampal neurogenesis is involved in memory and learning, and disrupted neurogenesis is implicated in cognitive impairment and mood disorders, including anxiety and depression. Some long-term peripheral illnesses and metabolic disorders, as well as normal aging, create a state of chronic peripheral inflammation. These conditions are associated with behavioral disturbances linked to disrupted adult hippocampal neurogenesis, such as cognitive impairment, deficits in learning and memory, and depression and anxiety. Pro-inflammatory cytokines released in the periphery are involved in peripheral immune system-to-brain communication by activating resident microglia in the brain. Activated microglia reduce neurogenesis by suppressing neuronal stem cell proliferation, increasing apoptosis of neuronal progenitor cells, and decreasing survival of newly developing neurons and their integration into existing neuronal circuits. In this review, we summarize evolving evidence that the state of chronic peripheral inflammation reduces adult hippocampal neurogenesis, which, in turn, produces the behavioral disturbances observed in chronic inflammatory disorders. As there are no data available on neurogenesis in humans with chronic peripheral inflammatory disease, we focus on animal models and, in parallel, consider the evidence of cognitive disturbance and mood disorders in human patients.

Neuropsychiatric systemic lupus erythematosus persists despite attenuation of systemic disease in MRL/lpr mice

Background

Systemic lupus erythematosus (SLE) is a prototypical autoimmune disease marked by both B and T cell hyperactivity which commonly affects the joints, skin, kidneys, and brain. Neuropsychiatric disease affects about 40 % of SLE patients, most frequently manifesting as depression, memory deficits, and general cognitive decline. One important and yet unresolved question is whether neuropsychiatric SLE (NPSLE) is a complication of systemic autoimmunity or whether it is primarily driven by brain-intrinsic factors.

Methods

To dissect the relative contributions of the central nervous system from those of the hematopoietic compartment, we generated bone marrow chimeras between healthy control (MRL/+) and lupus-prone MRL/Tnfrsf6^lpr/lpr mice (MRL/+ → MRL/lpr), as well as control chimeras. After bone marrow reconstitution, mice underwent extensive behavioral testing, analysis of brain tissue, and histological assessment.

Results

Despite transfer of healthy MRL/+ bone marrow and marked attenuation of systemic disease, we found that MRL/+ → MRL/lpr mice had a behavioral phenotype consisting of depressive-like behavior and visuospatial memory deficits, comparable to MRL/lpr → MRL/lpr control transplanted mice and the behavioral profile previously established in MRL/lpr mice. Moreover, MRL/+ → MRL/lpr chimeric mice displayed increased brain RANTES expression, neurodegeneration, and cellular infiltration in the choroid plexus, as well as blood brain barrier disruption, all in the absence of significant systemic autoimmunity.

Conclusions

Chimeric MRL/+ → MRL/lpr mice displayed no attenuation of the behavioral phenotype found in MRL/lpr mice, despite normalized serum autoantibodies and conserved renal function. Therefore, neuropsychiatric disease in the MRL/lpr lupus-prone strain of mice can occur absent any major contributions from systemic autoimmunity.

Significantly reduced lymphadenopathy, salivary gland infiltrates and proteinuria in MRL-lpr/lpr mice treated with ultrasoluble curcumin/turmeric: increased survival with curcumin treatment

Objectives

Commercial curcumin (CU), derived from food spice turmeric (TU), has been widely studied as a potential therapeutic for a variety of oncological and inflammatory conditions. Lack of solubility/bioavailability has hindered curcumin's therapeutic efficacy in human diseases. We have solubilised curcumin in water applying heat/pressure, obtaining up to 35-fold increase in solubility (ultrasoluble curcumin (UsC)). We hypothesised that UsC or ultrasoluble turmeric (UsT) will ameliorate systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS)-like disease in MRL-lpr/lpr mice.

Methods

Eighteen female MRL-lpr/lpr (6 weeks old) and 18 female MRL-MpJ mice (6 weeks old) were used. Female MRL-lpr/lpr mice develop lupus-like disease at the 10th week and die at an average age of 17 weeks. MRL-MpJ mice develop lupus-like disease around 47 weeks and typically die at 73 weeks. Six mice of each strain received autoclaved water only (lpr-water or MpJ-water group), UsC (lpr-CU or MpJ-CU group) or UsT (lpr-TU or MpJ-TU group) in the water bottle.

Results

UsC or UsT ameliorates SLE in the MRL-lpr/lpr mice by significantly reducing lymphoproliferation, proteinuria, lesions (tail) and autoantibodies. lpr-CU group had a 20% survival advantage over lpr-water group. However, lpr-TU group lived an average of 16 days shorter than lpr-water group due to complications unrelated to lupus-like illness. CU/TU treatment inhibited lymphadenopathy significantly compared with lpr-water group (p=0.03 and p=0.02, respectively) by induction of apoptosis. Average lymph node weights were 2606±1147, 742±331 and 385±68 mg, respectively, for lpr-water, lpr-CU and lpr-TU mice. Transferase dUTP nick end labelling assay showed that lymphocytes in lymph nodes of lpr-CU and lpr-TU mice underwent apoptosis. Significantly reduced cellular infiltration of the salivary glands in the lpr-TU group compared with the lpr-water group, and a trend towards reduced kidney damage was observed in the lpr-CU and lpr-TU groups.

Conclusions

These studies show that UsC/UsT could prove useful as a therapeutic intervention in SLE/SS.

The Role of Infections and Autoimmune Diseases for Schizophrenia and Depression: Findings from Large-Scale Epidemiological Studies

An immunologic component to schizophrenia and depression has been increasingly recognized, which has led to extensive research into the associations with infections and autoimmune diseases. Large-scale nationwide epidemiological studies have displayed an increased prevalence of both autoimmune diseases and infections among persons with schizophrenia and depression. Autoimmune diseases, and especially the number of infections requiring hospitalization, increase the risk of schizophrenia and depression in a dose–response relationship. Infections are a common exposure and a broad spectrum of infections are associated with schizophrenia and depression. Particularly the autoimmune diseases with a potential presence of brain-reactive antibodies were associated with psychiatric disorders. However, the associations seem to be bidirectional, since the risk of autoimmune diseases and infections is also increased after diagnosis with schizophrenia and depression. The risk of autoimmune diseases was particularly increased in individuals with prior hospital contacts for infections.

It has been suggested that inflammation and autoimmunity could be involved in the etiology and pathogenesis of some patients with symptoms of schizophrenia and depression. The psychiatric symptoms can be directly triggered by immune components, such as brain-reactive antibodies and cytokines, or infections reaching the central nervous system (CNS), or be secondary to systemic inflammation indirectly affecting the brain. However, the associations could also be caused by shared genetic factors, other environmental factors, or common etiological components. Nonetheless, autoimmune diseases and infections should be considered by clinicians in the treatment of individuals with psychiatric symptoms, since treatment would probably improve the psychiatric symptoms, quality of life, and the survival of the individuals.

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.

The epidemiologic evidence linking autoimmune diseases and psychosis

This review summarizes the epidemiologic evidence linking autoimmune diseases and psychosis. The associations between autoimmune diseases and psychosis have been studied for more than a half century, but research has intensified within the last decades, since psychosis has been associated with genetic markers of the immune system and with excess autoreactivity and other immune alterations. A range of psychiatric disorders, including psychosis, have been observed to occur more frequently in some autoimmune diseases, such as systemic lupus erythematosus and multiple sclerosis. Many autoimmune diseases involve multiple organs and general dysfunction of the immune system, which could affect the brain and induce psychiatric symptoms. Most studies have been cross-sectional, observing an increased prevalence of a broad number of autoimmune diseases in people with psychotic disorders. Furthermore, there is some evidence of associations of psychosis with a family history of autoimmune disorders and vice versa. Additionally, several autoimmune diseases, individually and in aggregate, have been identified as raising the risk for psychotic disorders in longitudinal studies. The associations have been suspected to be caused by inflammation or brain-reactive antibodies associated with the autoimmune diseases. However, the associations could also be caused by shared genetic factors or common etiologic components such as infections. Infections can induce the development of autoimmune diseases and autoantibodies, possibly affecting the brain. Autoimmune diseases and brain-reactive antibodies should be considered by clinicians in the treatment of individuals with psychotic symptoms, and even if the association is not causal, treatment would probably still improve quality of life and survival.

Altered neuroendocrine status at the onset of CNS lupus-like disease

Neuropsychiatric (NP) manifestations and brain atrophy are common, etiologically unexplained complications of the systemic autoimmune disease lupus erythematosus (SLE). Similar to patients with NP SLE, behavioral deficits and neurodegeneration occur in aged, lupus-prone MRL/lpr mice. In order to gain a better understanding of the time course and nature of CNS involvement, we compare the neuro-immuno-endocrine profiles of two lupus-prone MRL/lpr stocks, which differ in disease onset and severity. Mice from stock 485 (characterized by early lupus-like manifestations) display blunted responsiveness to palatable solutions and impaired nocturnal activity as early as 7 weeks of age. They also have increased IgG in cerebrospinal fluid (CSF) before high serum autoantibody levels and splenomegaly are detected. Moreover, when compared to age-matched 6825 controls, 485 mice exhibit elevated serum corticosterone, enlarged left adrenal gland, and enhanced haematoxylin/eosin staining in the hypothalamic paraventricular nucleus. Swimming speed and novel object exploration become impaired only when more severe peripheral manifestations are documented in 17 week-old 485 mice. The obtained results suggest that performance deficits during the prodromal phase of NP SLE-like disease are associated with autoantibodies in CSF and asymmetric activation of the hypothalamus-pituitary-adrenal axis. Subsequent deterioration in behavioral performance evolves alongside systemic autoimmunity and inflammation. Although a leaky blood-CSF barrier is a possible explanation, one may hypothesize that, similar to neonatal lupus, maternal antibodies to brain antigens cross blood-placental barrier during embryogenesis and induce early endocrine and behavioral deficits in offspring.

Neuropsychiatric disease in murine lupus is dependent on the TWEAK/Fn14 pathway

Given the early onset of neuropsychiatric disease and the potential response to immunosuppressive therapy, neuropsychiatric disease is considered a primary disease manifestation in systemic lupus erythematosus (SLE). However, the pathogenesis is not fully understood and optimal treatment has yet to be determined. TWEAK is a TNF family ligand that mediates pleotropic effects through its receptor Fn14, including the stimulation of inflammatory cytokine production by astrocytes, endothelial cells, and other non-hematopeotic cell types, and induction of neuronal death. Furthermore, TWEAK-inducible mediators are implicated in neuropsychiatric lupus. Thus, we hypothesized that the TWEAK/Fn14 pathway may be involved in the pathogenesis of neuropsychiatric SLE. We generated MRL-lpr/lpr (MRL/lpr) mice deficient for Fn14, the sole known signaling receptor for TWEAK. Neuropsychiatric disease was compared in age- and gender-matched MRL/lpr Fn14 wild type (WT) and knockout (KO) mice, using a comprehensive battery of neurobehavioral tests. We found that MRL/lpr Fn14WT mice displayed profound depression-like behavior as seen by increased immobility in a forced swim test and loss of preference for sweetened fluids, which were significantly ameliorated in Fn14KO mice. Similarly, MRL/lpr Fn14WT mice had impaired cognition, and this was significantly improved in Fn14KO mice. To determine the mechanism by which Fn14 deficiency ameliorates neuropsychiatric disease, we assessed the serum levels of autoantibodies and local expression of cytokines in the cortex and hippocampus of lupus mice. No significant differences were found in the serum levels of antibodies to nuclear antigens, or autoantibodies specifically associated with neuropsychiatric disease, between MRL/lpr Fn14WT and KO mice. However, MRL/lpr Fn14KO mice had significantly decreased brain expression of RANTES, C3, and other proinflammatory mediators. Furthermore, MRL/lpr Fn14KO mice displayed improved blood brain barrier integrity. In conclusion, several central manifestations of neuropsychiatric lupus, including depression-like behavior and altered cognition, are normalized in MRL/lpr mice lacking Fn14. Our results are the first to indicate a role for the TWEAK/Fn14 pathway in the pathogenesis of neuropsychiatric lupus, and suggest this ligand-receptor pair as a potential therapeutic target for a common and dangerous disease manifestation.

Metabolic changes and DNA hypomethylation in cerebellum are associated with behavioral alterations in mice exposed to trichloroethylene postnatally

Previous studies demonstrated that low-level postnatal and early life exposure to the environmental contaminant, trichloroethylene (TCE), in the drinking water of MRL+/+ mice altered glutathione redox homeostasis and increased biomarkers of oxidative stress indicating a more oxidized state. Plasma metabolites along the interrelated transmethylation pathway were also altered indicating impaired methylation capacity. Here we extend these findings to further characterize the impact of TCE exposure in mice exposed to water only or two doses of TCE in the drinking water (0, 2, and 28mg/kg/day) postnatally from birth until 6weeks of age on redox homeostasis and biomarkers of oxidative stress in the cerebellum. In addition, pathway intermediates involved in methyl metabolism and global DNA methylation patterns were examined in cerebellar tissue. Because the cerebellum is functionally important for coordinating motor activity, including exploratory and social approach behaviors, these parameters were evaluated in the present study. Mice exposed to 28mg/kg/day TCE exhibited increased locomotor activity over time as compared with control mice. In the novel object exploration test, these mice were more likely to enter the zone with the novel object as compared to control mice. Similar results were obtained in a second test when an unfamiliar mouse was introduced into the testing arena. The results show for the first time that postnatal exposure to TCE causes key metabolic changes in the cerebellum that may contribute to global DNA methylation deficits and behavioral alterations in TCE-exposed mice.

Autoimmune diseases and infections as risk factors for schizophrenia

Immunological hypotheses have become increasingly prominent when studying the etiology of schizophrenia. Autoimmune diseases, and especially the number of infections requiring hospitalization, have been identified as significant risk factors for schizophrenia in a dose-response relationship, which seem compatible with an immunological hypothesis for subgroups of patients with schizophrenia. Inflammation and infections may affect the brain through many different pathways that are not necessarily mutually exclusive and can possibly increase the risk of schizophrenia in vulnerable individuals. However, the findings could also be an epiphenomenon and not causal, due to, for instance, common genetic vulnerability, which could be supported by the observations of an increased prevalence of autoimmune diseases and infections in parents of patients with schizophrenia. Nevertheless, autoimmune diseases and infections should be considered in the treatment of individuals with schizophrenia symptoms, and further research is needed of the immune system's possible contributing pathogenic factors in the etiology of schizophrenia.

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.

Postnatal exposure to trichloroethylene alters glutathione redox homeostasis, methylation potential, and neurotrophin expression in the mouse hippocampus

Previous studies have shown that continuous exposure throughout gestation until the juvenile period to environmentally relevant doses of trichloroethylene (TCE) in the drinking water of MRL+/+ mice promoted adverse behavior associated with glutathione depletion in the cerebellum indicating increased sensitivity to oxidative stress. The purpose of this study was to extend our findings and further characterize the impact of TCE exposure on redox homeostasis and biomarkers of oxidative stress in the hippocampus, a brain region prone to oxidative stress. Instead of a continuous exposure, the mice were exposed to water only or two environmentally relevant doses of TCE in the drinking water postnatally from birth until 6 weeks of age. Biomarkers of plasma metabolites in the transsulfuration pathway and the transmethylation pathway of the methionine cycle were also examined. Gene expression of neurotrophins was examined to investigate a possible relationship between oxidative stress, redox imbalance and neurotrophic factor expression with TCE exposure. Our results show that hippocampi isolated from male mice exposed to TCE showed altered glutathione redox homeostasis indicating a more oxidized state. Also observed was a significant, dose dependent increase in glutathione precursors. Plasma from the TCE treated mice showed alterations in metabolites in the transsulfuration and transmethylation pathways indicating redox imbalance and altered methylation capacity. 3-Nitrotyrosine, a biomarker of protein oxidative stress, was also significantly higher in plasma and hippocampus of TCE-exposed mice compared to controls. In contrast, expression of key neurotrophic factors in the hippocampus (BDNF, NGF, and NT-3) was significantly reduced compared to controls. Our results demonstrate that low-level postnatal and early life TCE exposure modulates neurotrophin gene expression in the mouse hippocampus and may provide a mechanism for TCE-mediated neurotoxicity.

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 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.

Electroconvulsive therapy for catatonia in neuropsychiatric systemic lupus erythematosus

Neuropsychiatric systemic lupus erythematosus encompasses neurological syndromes of the central, peripheral, and autonomic nervous system and a variety of psychiatric syndromes. Neuropsychiatric systemic lupus erythematosus presenting as catatonia is uncommon, and treatment of this condition is not well defined. Here we describe a case of neuropsychiatric systemic lupus erythematosus with catatonia and our treatment approach focusing on electroconvulsive therapy in conjunction with cyclophosphamide. We also discuss the pathophysiological underpinnings of the condition and the basis for treatment.

Reduced adult neurogenesis and altered emotional behaviors in autoimmune-prone B-cell activating factor transgenic mice

BACKGROUND

It has been postulated that brain inflammatory processes associated with autoimmune diseases may be causative factors in emotional disorders. Accordingly, we examined emotional behaviors in autoimmune-prone cytokine B-cell-activating factor (BAFF) transgenic mice, a model of systemic lupus erythematosus, rheumatoid arthritis, and Sjögren's syndrome.

METHODS

Male BAFF transgenic mice were examined on a series of standard laboratory assays of emotionality. Mice were also tested for brain inflammation, stress-induced c-Fos expression, hippocampal progenitor cell proliferation, and hippocampal neurogenesis-dependent and neurogenesis-independent long-term potentiation (LTP).

RESULTS

Our study revealed that older BAFF transgenic mice exhibit an anxiety-like phenotype associated with brain inflammation. Furthermore, anxious mice display an abnormal neuronal activation within the limbic system in response to mild anxiogenic stimuli. Proliferation of newly formed neurons in the subgranular zone of adult hippocampus was significantly decreased in anxious BAFF transgenic mice that also showed impaired neurogenesis-dependent and neurogenesis-independent dentate gyrus LTP.

CONCLUSIONS

Our results suggest that anxiety associated with autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, and Sjögren's syndrome can be linked to brain inflammation, impaired neurogenesis, and hippocampal plasticity. BAFF transgenic mice can be used in future studies to test compounds of therapeutic value for the treatment of mood disorders associated with autoimmune diseases.

Intrathecal antibodies and brain damage in autoimmune MRL mice

Neuropsychiatric (NP) manifestations and brain pathology are poorly understood and potentially fatal concomitants of systemic lupus erythematosus (SLE). For many years, autoantibodies to brain tissue (i.e., brain-reactive antibodies, BRA) were proposed as a key factor in pathogenesis of CNS manifestations. Recent evidence suggests that intrathecal BRA, rather than serum autoantibodies, are a better predictor of disturbed brain morphology and function. We presently test this hypothesis by examining the relationship among BRA in cerebrospinal fluid (CSF), behavioral deficits, and brain pathology in a well-established animal model of CNS lupus. We showed earlier that significant diversity in disease manifestations within genetically homogenous MRL-lpr mice allows for constructive and informative correlational analysis. Therefore, levels of CSF antibodies were presently correlated with behavioral, neuropathological and immune measures in a cohort of diseased MRL-lpr males (N=40). ELISA, Western Blotting, standardized behavioral battery, digital planimetry, HE staining, and immunohistochemistry were employed in overall data collection. The IgG antibodies from CSF were binding to different regions of brain parenchyma, with dentate gyrus, amygdale, and subventricular zones showing enhanced immunoreactivity. High levels of CSF antibodies correlated with increased immobility in the forced-swim test and density of HE(+) cells in the paraventricular nucleus. Peripheral measures of autoimmunity were associated with other deficits in behavior and neuropathology. This correlation pattern suggests that etiology of brain damage in lupus-prone mice is multifactorial. Intrathecal BRA may be important in altering motivated responses and activity of major neuroendocrine axes at the onset of SLE-like disease.

C5a alters blood-brain barrier integrity in experimental lupus

The blood-brain barrier (BBB) is a crucial anatomic location in the brain. Its dysfunction complicates many neurodegenerative diseases, from acute conditions, such as sepsis, to chronic diseases, such as systemic lupus erythematosus (SLE). Several studies suggest an altered BBB in lupus, but the underlying mechanism remains unknown. In the current study, we observed a definite loss of BBB integrity in MRL/MpJ-Tnfrsf6(lpr) (MRL/lpr) lupus mice by IgG infiltration into brain parenchyma. In line with this result, we examined the role of complement activation, a key event in this setting, in maintenance of BBB integrity. Complement activation generates C5a, a molecule with multiple functions. Because the expression of the C5a receptor (C5aR) is significantly increased in brain endothelial cells treated with lupus serum, the study focused on the role of C5a signaling through its G-protein-coupled receptor C5aR in brain endothelial cells, in a lupus setting. Reactive oxygen species production increased significantly in endothelial cells, in both primary cells and the bEnd3 cell line treated with lupus serum from MRL/lpr mice, compared with those treated with control serum from MRL(+/+) mice. In addition, increased permeability monitored by changes in transendothelial electrical resistance, cytoskeletal remodeling caused by actin fiber rearrangement, and increased iNOS mRNA expression were observed in bEnd3 cells. These disruptive effects were alleviated by pretreating cells with a C5a receptor antagonist (C5aRant) or a C5a antibody. Furthermore, the structural integrity of the vasculature in MRL/lpr brain was maintained by C5aR inhibition. These results demonstrate the regulation of BBB integrity by the complement system in a neuroinflammatory setting. For the first time, a novel role of C5a in the maintenance of BBB integrity is identified and the potential of C5a/C5aR blockade highlighted as a promising therapeutic strategy in SLE and other neurodegenerative diseases.

Efficiency of the DNA repair and polymorphisms of the XRCC1, XRCC3 and XRCC4 DNA repair genes in systemic lupus erythematosus

Impaired DNA repair efficiency in systemic lupus erythematosus (SLE) patients has been reported in some studies, mainly regarding the repair of oxidative damage, but little is known about repair kinetics towards primarily single-stranded DNA breaks. In the present study, we aimed to investigate: (a) the efficiency of SLE peripheral blood leucocytes in repairing DNA damage induced by ionizing radiation and (b) the association of DNA repair gene (XRCC1 Arg399Gln, XRCC3 Thr241Met and XRCC4 Ile401Thr) polymorphisms in SLE patients, considering the whole group, or stratified sub-groups according to clinical and laboratory features. A total of 163 SLE patients and 125 healthy controls were studied. The kinetics of DNA strand break repair was evaluated by the comet assay, and genotyping for DNA repair genes was performed by PCR-RFLP. Compared with controls, SLE leucocytes exhibited decreased efficiency of DNA repair evaluated at 30 min following irradiation. A significant association with DNA repair gene polymorphisms was not observed for the whole group of SLE patients; however, the XRCC1Arg399Gln polymorphism was associated with the presence of anti-dsDNA antibody. The concomitance of two DNA repair polymorphic sites was associated with the presence of neuropsychiatric manifestations and antiphospholipid antibody syndrome. Taken together, these results indicated that SLE leucocytes repair less efficiently the radiation-induced DNA damage, and DNA repair polymorphic sites may predispose to the development of particular clinical and laboratory features.

Purine receptor antagonist modulates serology and affective behaviors in lupus-prone mice: evidence of autoimmune-induced pain?

Neurologic and psychiatric (NP) manifestations are severe complications of systemic lupus erythematosus (SLE). As commonly seen in patients, spontaneous disease onset in the MRL/MpJ-Fas(lpr)/J (MRL-lpr) mouse model of NP-SLE is accompanied by increased autoantibodies, pro-inflammatory cytokines and behavioral dysfunction which precede neuroinflammation and structural brain lesions. The role of purinergic receptors in the regulation of immunity and behavior remains largely unexplored in the field of neuropsychiatry. To examine the possibility that purinoception is involved in the development of affective behaviors, the P2X purinoceptor antagonist, suramin, was administered to lupus-prone mice from 5 to 14 weeks of age. In addition to food and water measures, novel object and sucrose preference tests were performed to assess neophobic anxiety- and anhedonic-like behaviors. Enzyme-linked immunosorbant assays for anti-nuclear antibodies (ANA) and pro-inflammatory cytokines were employed in immunopathological analyses. Changes in dendritic morphology in the hippocampal CA1 region were examined by a Golgi impregnation method. Suramin significantly lowered serum ANA and prevented behavioral deficits, but did not prevent neuronal atrophy in MRL-lpr animals. In a new batch of asymptomatic mice, systemic administration of corticosterone was found to induce aberrations in CA1 dendrites, comparable to the "stress" of chronic disease. The precise mechanism(s) through which purine receptor inhibition exerted beneficial effects is not known. The present data supports the hypothesis that activation of the peripheral immune system induces nociceptive-related behavioral symptomatology which is attenuated by the analgesic effects of suramin. Hypercortisolemia may also initiate neuronal damage, and metabolic perturbations may underlie neuro-immuno-endocrine imbalances in MRL-lpr mice.