Aberrant cytokine gene expression in the hippocampus in murine systemic lupus erythematosus

Deciphering Mechanisms, Prevention Strategies, Management Plans, Medications, and Research Techniques for Strokes in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune rheumatic condition characterized by an unpredictable course and a wide spectrum of manifestations varying in severity. Individuals with SLE are at an increased risk of cerebrovascular events, particularly strokes. These strokes manifest with a diverse range of symptoms that cannot be solely attributed to conventional risk factors, underscoring their significance among the atypical risk factors in the context of SLE. This complexity complicates the identification of optimal management plans and the selection of medication combinations for individual patients. This susceptibility is further complicated by the nuances of neuropsychiatric SLE, which reveals a diverse array of neurological symptoms, particularly those associated with ischemic and hemorrhagic strokes. Given the broad range of clinical presentations and associated risks linking strokes to SLE, ongoing research and comprehensive care strategies are essential. These efforts are critical for improving patient outcomes by optimizing management strategies and discovering new medications. This review aims to elucidate the pathological connection between SLE and strokes by examining neurological manifestations, risk factors, mechanisms, prediction and prevention strategies, management plans, and available research tools and animal models. It seeks to explore this medical correlation and discover new medication options that can be tailored to individual SLE patients at risk of stroke.

IRAK4 is an immunological checkpoint in neuropsychiatric systemic lupus erythematosus

The search for dementia treatments, including treatments for neuropsychiatric lupus (NPSLE), has not yet uncovered useful therapeutic targets that mitigate underlying inflammation. Currently, NPSLE's limited treatment options are often accompanied by severe toxicity. Blocking toll-like receptor (TLR) and IL-1 receptor signal transduction by inhibiting interleukin-1 receptor-associated kinase 4 (IRAK4) offers a new pathway for intervention. Using a pre-clinical NPSLE model, we compare lupus-like B6.MRL-Faslpr (MRL) mice with B6.MRL-Faslpr-IRAK4 kinase-dead (MRL-IRAK4-KD) mice, which are were less prone to 'general' lupus-like symptoms. We demonstrate that lupus-prone mice with a mutation in the kinase domain of IRAK4 no longer display typical lupus hallmarks such as splenomegaly, inflammation, production of hormones, and anti-double-stranded (ds)DNA antibody. water maze behavioral testing, which measures contextual associative learning, revealed that mice without functional IRAK4 displayed a recovery in memory acquisition deficits. RNA-seq approach revealed that cytokine and hormone signaling converge on the JAK/STAT pathways in the mouse hippocampus. Ultimately, the targets identified in this work may result in broad clinical value that can fill the significant scientific and therapeutic gaps precluding development of cures for dementia.

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.

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.

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.

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.

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.

Lupus brain fog: a biologic perspective on cognitive impairment, depression, and fatigue in systemic lupus erythematosus

Cognitive disturbances, mood disorders and fatigue are common in SLE patients with substantial adverse effects on function and quality of life. Attribution of these clinical findings to immune-mediated disturbances associated with SLE remains difficult and has compromised research efforts in these areas. Improved understanding of the role of the immune system in neurologic processes essential for cognition including synaptic plasticity, long term potentiation and adult neurogenesis suggests multiple potential mechanisms for altered central nervous system function associated with a chronic inflammatory illness such as SLE. This review will focus on the biology of cognition and neuroinflammation in normal circumstances and potential biologic mechanisms for cognitive impairment, depression and fatigue attributable to SLE.

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.

IL-6 regulation of synaptic function in the CNS

A growing body of evidence supports a role for glial-produced neuroimmune factors, including the cytokine IL-6, in CNS physiology and pathology. CNS expression of IL-6 has been documented in the normal CNS at low levels and at elevated levels in several neurodegenerative or psychiatric disease states as well as in CNS infection and injury. The altered CNS function associated with these conditions raises the possibility that IL-6 has neuronal or synaptic actions. Studies in in vitro and in vivo models confirmed this possibility and showed that IL-6 can regulate a number of important neuronal and synaptic functions including synaptic transmission and synaptic plasticity, an important cellular mechanism of memory and learning. Behavioral studies in animal models provided further evidence of an important role for IL-6 as a regulator of CNS pathways that are critical to cognitive function. This review summarizes studies that have lead to our current state of knowledge. In spite of the progress that has been made, there is a need for a greater understanding of the physiological and pathophysiological actions of IL-6 in the CNS, the mechanisms underlying these actions, conditions that induce production of IL-6 in the CNS and therapeutic strategies that could ameliorate or promote IL-6 actions. This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.

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.

Evidence for sustained elevation of IL-6 in the CNS as a key contributor of depressive-like phenotypes

There is compelling clinical literature implicating a role for cytokines in the pathophysiology of major depressive disorder (MDD). Interleukin-6 (IL-6) and interleukin-1β (IL-1β) are pleiotropic inflammatory cytokines that have been reported to be elevated in patients with MDD. The present studies were undertaken to investigate the relationship between IL-6 and IL-1β in animal models of depressive-like behavior. Analysis of brain tissue homogenates in the cortex of rats subjected to chronic stress paradigms revealed elevated levels of IL-6 protein in the absence of elevations in IL-1β. Central administration of recombinant mouse IL-6 produced depressive-like phenotypes in mice, which were not accompanied by IL-1β-induced increases in the brain tissue or IL-1β-related sickness behavior typical of a general central nervous system inflammatory response. Systemic administration of fluoxetine in the presence of centrally administered IL-6 failed to produce the expected antidepressant-like response in mice relative to sham-infused controls. Further, administration of fluoxetine to mice with endogenous overexpression of brain IL-6 (MRL/MpJ-Fas(LPR/LPR) (LPR mice)) failed to produce the expected antidepressant-like effect relative to fluoxetine-treated control mice (MRL/MpJ(+/+)). Interestingly, blockade of IL-6 trans-signaling by coadministration of a gp130/Fc monomer or an anti-mouse IL-6 antibody with IL-6 prevented the IL-6-induced increases in immobility time as well as attenuated IL-6-induced increases of protein in the cortex. Taken together, these data indicate that elevations in IL-6 may have a pathophysiological role underlying depression and more specifically resistance to current classes of antidepressant medications and suggest that modulation of the IL-6 signaling pathway may have therapeutic potential for treatment-resistant depression.

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.

Evaluating fatigue in lupus-prone mice: preliminary assessments

Fatigue is a debilitating condition suffered by many as the result of chronic disease, yet relatively little is known about its biological basis or how to effectively manage its effects. This study sought to evaluate chronic fatigue by using lupus-prone mice and testing them at three different time periods. Lupus-prone mice were chosen because fatigue affects over half of patients with Systemic Lupus Erythematosus. Eleven MLR⁺/(+) (genetic controls) and twelve MLR/MpJ-Fas<lpr>/J (MRL/lpr; lupus-prone) mice were tested three times: once at 12, 16 and 20 weeks of age. All mice were subjected to a variety of behavioral tests including: forced swim, post-swim grooming, running wheel, and sucrose consumption; five of the MLR⁺/(+) and five of the MLR/lpr mice were also tested on a fixed ratio-25 operant conditioning task. MRL/lpr mice showed more peripheral symptoms of lupus than controls, particularly lymphadenopathy and proteinuria. Lupus mice spent more time floating during the forced swim test and traveled less distance in the running wheel at each testing period. There were no differences between groups in post-swim grooming or in number of reinforcers earned in the operant conditioning task indicating the behavioral changes were not likely due simply to muscle weakness or motivation. Correlations between performance in the running wheel, forced swim test and sucrose consumption were conducted and distance traveled in the running wheel was consistently negatively correlated with time spent floating. Based on these data, we conclude that the lupus-prone mice were experiencing chronic fatigue and that running wheel activity and floating during a forced swim test can be used to evaluate fatigue, although these data cannot rule out the possibility that both fatigue and a depressive-like state were mediating these effects.

Memory impairment associated with neurometabolic abnormalities of the hippocampus in patients with non-neuropsychiatric systemic lupus erythematosus

Objective: Memory impairment is common in patients with systemic lupus erythematosus (SLE). This study examined hippocampal volumes and neurometabolic alterations in relation to memory function in SLE patients without a history of neuropsychiatric syndromes (nonNPSLE).

Methods: Subjects included 81 nonNPSLE patients and 34 healthy controls. Volumetric magnetic resonance imaging and magnetic resonance spectroscopy of the right and left hippocampal areas (RH, LH) were performed. Verbal and visual memory tests were administered and a Memory Impairment Index (MII) was derived from standardized tests.

Results: Higher memory impairment (MII) was correlated with lower RH glutamate + glutamine/creatine ( p = 0.009) and lower RH N-acetylaspartic acid/creatine ( p = 0.012) in nonNPSLE patients. A trend for a negative correlation between RH and LH volumes and MII was evident for absolute hippocampal volumes. Lower RH glutamate + glutamine/creatine was also correlated with worse performance in a mean visual memory index ( p = 0.017).

Conclusions: An association between reduced memory and lower N-acetylaspartic acid/creatine in the RH suggests neuronal damage in nonNPSLE patients with very mild and early disease. Alterations in glutamate + glutamine/creatine further indicate early metabolic changes in nonNPSLE are related to memory impairment, a finding that might suggest that memory impairment relates to presynaptic glutamatergic dysfunction in the hippocampus.

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.

Disruption of brain white matter microstructure in primary Sjögren's syndrome: evidence from diffusion tensor imaging

OBJECTIVES

The relationship between cognitive symptoms and underlying neuropathology in primary SS (PSS) is poorly understood. We used high-resolution quantitative brain MRI to identify potential structural correlates of cognitive symptoms.

METHODS

Subjects completed a comprehensive neuropsychometric evaluation. Imaging was performed on a 3 T MRI scanner with T(1) and proton density-weighted, fluid-attenuated inversion recovery (FLAIR) and diffusion tensor imaging (DTI) sequences. We compared MRI group metrics (impaired PSS, not-impaired PSS and controls) and tested for correlations between DTI results and neuropsychological measurements (significance threshold P = 0.05).

RESULTS

Nineteen PSS patients (who met American-European Consensus Group 2002 criteria) and 17 healthy controls completed the cognitive evaluation. MRI scans were performed in six impaired PSS, seven not-impaired PSS and seven controls. No differences were found in regional volumetrics, nor was there a difference in T(2) lesion load between groups. Fractional anisotropy (FA) in the inferior frontal white matter (WM) was lower (P = 0.021) and mean diffusivity higher (P = 0.003) in the impaired PSS relative to the control group. Inferior frontal FA was correlated with cognitive symptoms (P = 0.0064) and with verbal memory (P = 0.0125).

CONCLUSIONS

In this exploratory study, frontal region WM microstructure alterations accompanied cognitive symptoms and were associated with mild cognitive impairment in PSS. While additional study is warranted to assess the specificity and stability of these results, DTI could provide novel insight into the pathological processes accompanying the subtle cognitive dysfunction commonly experienced by PSS patients.

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.

Amelioration of brain pathology and behavioral dysfunction in mice with lupus following treatment with a tolerogenic peptide

OBJECTIVE

Central nervous system (CNS) involvement in systemic lupus erythematosus (SLE) is manifested by neurologic deficits and psychiatric disorders. The aim of this study was to examine SLE-associated CNS pathology in lupus-prone (NZBxNZW)F1 (NZB/NZW) mice, and to evaluate the ameliorating effects of treatment with a tolerogenic peptide, hCDR1 (human first complementarity-determining region), on these manifestations.

METHODS

Histopathologic analyses of brains from lupus-prone NZB/NZW mice treated with vehicle, hCDR1, or a control scrambled peptide were performed. The messenger RNA expression of SLE-associated cytokines and apoptosis-related molecules from the hippocampi was determined. Anxiety-like behavior was assessed by open-field tests and dark/light transfer tests, and memory deficit was assessed using a novel object recognition test.

RESULTS

Infiltration was evident in the hippocampi of the lupus-afflicted mice, and the presence of CD3+ T cells as well as IgG and complement C3 complex deposition was observed. Furthermore, elevated levels of gliosis and loss of neuronal nuclei immunoreactivity were also observed in the hippocampi of the mice with lupus. Treatment with hCDR1 ameliorated the histopathologic changes. Treatment with hCDR1 down-regulated the high expression of interleukin-1beta (IL-1beta), IL-6, IL-10, interferon-gamma, transforming growth factor beta, and the proapoptotic molecule caspase 8 in the hippocampi of the mice with lupus, and up-regulated expression of the antiapoptotic bcl-xL gene. Diseased mice exhibited increased anxiety-like behavior and memory deficit. Treatment with hCDR1 improved these parameters, as assessed by behavior tests.

CONCLUSION

Treatment with hCDR1 ameliorated CNS pathology and improved the tested cognitive and mood-related behavior of the mice with lupus. Thus, hCDR1 is a novel candidate for the treatment of 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.

Prevalence, severity, and predictors of fatigue in subjects with primary Sjögren's syndrome

OBJECTIVE

To investigate the relationship of fatigue severity to other clinical features in primary Sjögren's syndrome (SS) and to identify factors contributing to the physical and mental aspects of fatigue.

METHODS

We identified 94 subjects who met the American-European Consensus Group criteria for the classification of primary SS. Fatigue was assessed with a visual analog scale, the Fatigue Severity Scale (FSS), and the Profile of Fatigue (ProF). Associations with fatigue were compared using multivariate regression.

RESULTS

Abnormal fatigue, defined as an FSS score >or=4, was present in 67% of the subjects. Pain, helplessness, and depression were the strongest predictors of fatigue according to the FSS and the somatic fatigue domain of the ProF (ProF-S), both with and without adjustment for physiologic and serologic characteristics. Depression was associated with higher levels of fatigue; however, the majority of subjects with abnormal fatigue were not depressed. Anti-Ro/SSA-positive subjects were no more likely to report fatigue than seronegative subjects. The regression models explained 62% of the variance in FSS and 78% of the variance in ProF-S scores. Mental fatigue was correlated with depression and helplessness, but the model predicted only 54% of the variance in mental fatigue scores.

CONCLUSION

Psychosocial variables are determinants of fatigue, but only partially account for it. Although fatigue is associated with depression, depression is not the primary cause of fatigue in primary SS. Investigation of the pathophysiologic correlates of physical and mental aspects of fatigue is needed to guide the development of more effective interventions.

Autoantibody-mediated neuroinflammation: pathogenesis of neuropsychiatric systemic lupus erythematosus in the NZM88 murine model

Autoantibodies play an important role in central nervous system manifestations of neuropsychiatric systemic lupus erythematosus (NPSLE). Previous studies have shown that the lupus-prone NZM88 strain has major neural deficits and high titers of serum IgG to brain antigens. ELISA was performed to detect the presence of IgG in different brain regions of NZM88 mice and to compare the levels with NZM2758 mice and control strains (NZW and BALB/c). There was a substantial increase of IgG in the substantia nigra (SN) and hypothalamus (HT) of brains from NZM88 mice compared to control NZW and BALB/c mice, whereas NZM2758 mice had more IgG in the cortex. The increased presence of IgG in the NPSLE-prone NZM88 mouse brain was paralleled by increased TNF-alpha and IL-12 in the SN and HT regions; significantly elevated expression of MHC Class-II was also observed in the SN of NZM88 mice and cortex of NZM2758 mice. A co-culture system of dopaminergic neurons and microglia was used to demonstrate that NZM88 sera modifies dopaminergic cell activity only in the presence of microglia and that TNF-alpha is synthesized and released in this co-culture. This study demonstrates a functional link between the autoantibodies, the activation of microglia, and neuronal function associated dopamine production, which is suggested to be causally related to the predominant NPSLE syndromes.

The potential impact of sickness-motivated behavior on the expression of neuropsychiatric disturbances in systemic lupus erythematosus

Activation of the peripheral immune system is often accompanied by changes in cognition, ingestive behavior, sleep pattern, and sexual drive; collectively referred to as sickness behavior. Mounting evidence suggests that sickness behavior may be a purposeful attempt on the part of an organism to conserve energy and thereby facilitate recuperation. Illnesses characterized by chronic, uncontrolled immune reactivity such as systemic lupus erythematosus are also frequently associated with impaired emotionality and cognition; which, unlike sickness behavior, are conventionally thought to emanate from fixed structural lesions of the brain. Clinical observations, however, indicate that the neuropsychiatric disturbances in lupus may wax and wane in intensity and suggest the hypothesis that sickness-motivated behavior may significantly influence the neuropsychiatric manifestations of systemic lupus erythematosus and, perhaps, those of other autoimmune diseases associated with neuroinflammation. The hypothesis that patients with systemic lupus erythematosus undergo a reorganization of their motivational priorities, which influences cognitive performance and emotional output, may be examined using validated behavior paradigms in autoimmune MRL-MpJ-Tnfrsf6(lpr) (MRL-lpr/lpr) mice that spontaneously develop a lupus-like illness accompanied by disturbances in cognition and emotionality. Confirming that sickness-motivated behavior contributes to the aberrations in cognition and emotionality exhibited by an experimental model of systemic lupus erythematosus might have important therapeutic and prognostic implications by invoking the possibility that similar motivational effects may be influencing cognitive and/or emotional output in patients with neuropsychiatric lupus.

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.

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.

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.

Effects of systemic lupus erythematosus on spatial cognition and cerebral regional metabolic reactivity in BxSB lupus-prone mice

Brain-reactive auto-antibodies appear as key elements in the progressive CNS disturbances associated with systemic lupus erythematosus. The BxSB lupus prone mice are a model of this pathology, in which a gene located on the Y chromosome provokes a sex specific morbidity in males. This study was aimed to establish and characterize the relationships between behavioral disorders, neurological deficiencies and the aged-related immunological perturbations in this murine model. For this purpose, spatial and motor abilities were evaluated in male and female mice at six and 26 weeks of age. The results showed that the older males were greatly altered in their spatial abilities while the young ones and the females, whatever their age, were not. None of the animals had motor skill and motor learning disabilities. These spatial alterations were associated with modifications of basal neuronal activity measured by the cytochrome oxidase histochemical method in several areas directly or indirectly involved in spatial behavior, such as the hippocampus, the amygdala, the parietal and perirhinal cortex. Immunological study allowed us to correlate the behavioral abnormalities to the appearance of antibodies reactivities against cellular and nuclear components.

Proinflammatory cytokine genes are constitutively overexpressed in the heart in experimental systemic lupus erythematosus: a brief communication

The heart is one of a number of organs that may be affected in systemic lupus erythematosus (SLE), a prototypic autoimmune disease. Potential anatomical sites of involvement include the myocardium, pericardium, endocardium, valves, conduction system and blood vessels that subserve the heart. Typically, the severity of cardiovascular disease in lupus correlates with the degree of systemic inflammation, which is mirrored by the level of C-reactive protein (CRP) in the plasma. C-reactive protein, in turn is regulated by proinflammatory cytokines, such as interleukins (ILs) 1beta and 6. These cytokines have been found in functionally and/or structurally damaged areas of the heart and have been implicated in disease pathogenesis. It has been assumed that the source of these putatively pathogenetically relevant cytokines in the compromised heart is infiltrating mononuclear cells. This study tests the hypothesis that cardiomyocytes per se may contribute to proinflammatory cytokine production in the setting of systemic inflammation. Using as the experimental model MRL/MpJ-Tnfrs6(lpr) (MRL-lpr/lpr) mice, which spontaneously manifest an autoimmune syndrome that has clinical features of SLE, we show that ventricular homogenates and ventricular cardiomyocytes constitutively overexpress genes encoding the proinflammatory cytokines IL-1beta, IL-6, IL-10, and gamma interferon. The results suggest the possibility that proinflammatory cytokines emanating from the heart may actually contribute to the high levels of CRP that appear to aid in predicting subsequent cardiac events. Viewed in this setting, CRP becomes a footprint of an ongoing pathogenic process mediated, in part, by the heart muscle itself.

The potential pathogenetic link between peripheral immune activation and the central innate immune response in neuropsychiatric systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown etiology. Neuropsychiatric disturbances unexplained by drugs or by other untoward manifestations of disease are present in up to one-half of SLE patients and have profound economic and social impact. In patients with neuropsychiatric SLE, structural lesions have been identified in the hippocampus and proinflammatory cytokines have been detected in the cerebrospinal fluid. Similarly, murine models of lupus, such as MRL-lpr/lpr mice display behavioral disturbances which map to the hippocampus and exhibit overexpression of proinflammatory cytokine genes in hippocampal homogenates. Neuropsychiatric SLE typically occurs in the presence of serologically and clinically active lupus. In animal models of SLE, such as MRL-lpr/lpr, NZB, BXSB, and [NZB x NZW]F(1), uncontrolled autoreactivity in the periphery is accompanied by behavioral disturbances that are chronic and progressive. These observations suggest the hypothesis that central nervous system disease in SLE is driven by cross-talk between the peripheral immune system and the brain's innate immune system, which results in the inexorable activation of astrocytes, microglia, and/or neurons within the hippocampus. This leads to overproduction of brain cytokines, which induce the synthesis of pro-oxidant molecules, such as eicosanoids and reactive oxygen species, with resultant tissue injury. The cascade becomes self-perpetuating and eventuates in neuronal death, which is followed by impaired cognition. A better understanding of the molecular events that operate in the pathogenesis of neuropsychiatric SLE may provide the basis for a more rational therapeutic approach to this incompletely understood 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.

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.