Hippocampal damage in mouse and human forms of systemic autoimmune disease

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

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

Immunity and acquired alterations in cognition and emotion: lessons from SLE

Classic immunologic teaching describes the brain as an immunologically privileged site. Studies of neuroimmunology have focused for many years almost exclusively on multiple sclerosis, a disease in which inflammatory cells actually infiltrate brain tissue, and the rodent model of this disease, experimental allergic encephalitis. Over the past decade, however, increasingly, brain-reactive antibodies have been demonstrated in the serum of patients with numerous neurological diseases. The contribution these antibodies make to neuronal dysfunction has, in general, not been determined. Here, we describe recent studies showing that serum antibodies to the N-methyl-D-aspartate receptor occur frequently in patients with systemic lupus erythematosus and can cause alterations in cognition and behavior following a breach in the blood-brain barrier.

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.

Proclivity to self-injurious behavior in MRL-lpr mice: implications for autoimmunity-induced damage in the dopaminergic system

Systemic lupus erythematosus is frequently accompanied by psychiatric manifestations of unknown origin. Although damage of central neurons had been documented, little is known about neurotransmitter systems affected by the autoimmune/inflammatory process. Recent studies on lupus-prone MRL-lpr mice point to imbalanced dopamine function and neurodegeneration in dopamine-rich brain regions. We follow up on anecdotal observations of singly housed mice developing chest wounds. Compulsive grooming and/or skin biting accounted for open lesions, lending itself to the operational term 'self-injurious behavior' (SIB). Low incidence of spontaneous SIB increased significantly after repeated injections of dopamine-2/3 receptor (D2/D3R) agonist quinpirole (QNP). To further probe the dopaminergic circuitry and examine whether SIB is associated with development of lupus-like disease, we compared behavioral responses among cohorts that differed in the immune status. Two-week treatment with QNP (intraperitoneal, 0.5 mg kg(-1) body weight per day) induced SIB in 60% of diseased MRL-lpr mice, and exacerbated their splenomegaly. Although increased grooming and stereotypy were observed in less symptomatic MRL+/+ controls, only one mouse (10%) developed SIB. Similarly, SIB was not seen in young, asymptomatic groups despite dissimilar ambulatory responses to QNP. In situ hybridization revealed treatment-independent upregulation of D2R mRNA in substantia nigra of diseased MRL-lpr mice. The above results suggest that development of systemic autoimmunity alters sensitivity of the dopaminergic system and renders MRL-lpr mice prone to SIB. Although pathogenic factors were not examined, we hypothesize that immune and endocrine mechanisms jointly contribute to early neuronal damage, which underlies behavioral deficiency in the adulthood.

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.

Ibuprofen fails to prevent brain pathology in a model of neuropsychiatric lupus

OBJECTIVE

Neurologic and psychiatric manifestations are severe complications of systemic lupus erythematosus (SLE). As commonly seen in patients, spontaneous development of lupus-like disease in MRL-lpr mice is accompanied by brain atrophy and behavioral dysfunction. We examined inflammatory and ultrastructural aspects of central nervous system (CNS) involvement using a nonselective cyclooxygenase-2 (COX-2) inhibitor and measuring effects on behavior, microglial activation, and neuronal morphology.

METHODS

Ibuprofen (IBU) was provided in a rodent chow (375 ppm) for animals 5-19 weeks of age. Exploration of a novel environment and performance in the forced swim test assessed effects on behavior. Immunohistochemistry, fluoro-Jade B (FJB) staining, and flow cytometry were employed in neuropathological analysis. Transmission electron microscopy was used to examine ultrastructural morphology of cortical, hippocampal, hypothalamic, nigral, and cerebellar cells.

RESULTS

Chronic IBU treatment failed to normalize immune status, behavior, and brain mass in lupus-prone MRL-lpr mice. It also did not reduce density of CD3+ lymphocytes in the choroid plexus, or FJB+ neurons in the hypothalamus. Activated F4/80+ microglia increased with age, but IBU treatment was not effective in reducing their numbers. Although numerous dark cells were seen in functionally critical brain regions (e.g., paraventricular nucleus and subgranular zone), ultrastructural morphologies of classical apoptosis or necrosis were not detected.

CONCLUSION

The COX-dependent pathway does not seem to be critical in the etiology of CNS disease in this model of neuropsychiatric lupus. Reduced brain mass, increased microglial activation, and condensation of cytoplasm point to a metabolic perturbation (e.g., excitotoxic damage) that compromises function and survival of central neurons during lupus-like disease.

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.

Molecular mimicry: anti-DNA antibodies bind microbial and nonnucleic acid self-antigens

Although cells of the innate immune response have a variety of pattern recognition receptors that are triggered by blood classes of markers, a critical feature of the adaptive immune response is antigenic specificity. Yet it is becoming increasingly clear that the specificity of lymphocyte receptors admits of some laxity. Cross-reactivity may, in fact, be necessary for lymphocyte survival as antigen receptor signaling maintains cellular viability in the absence of antigen activation. Studies of molecular mimicry have revealed many instances in which antibodies to microbial antigens bind also to self-antigens; in some cases, this cross-reactivity has pathogenic potential. In this chapter, we describe cross-reactivity between two self-antigens, DNA and NMDA receptors, and how antibodies with specificity for DNA in patients with splenic lupus may cause central nervous system damage by virtue of binding also to neuronal receptors. This example serves as a reminder that cross-reactivity may exist among self-antigens as well as between foreign and self-antigens.

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.

Impaired response to amphetamine and neuronal degeneration in the nucleus accumbens of autoimmune MRL-lpr mice

Spontaneous development of lupus-like disease in MRL-lpr mice is accompanied by a constellation of behavioral deficits, including blunted responsiveness to sucrose. Although autoimmunity-induced damage of limbic areas is proposed to underlie this deficit, the systemic nature of the disease precludes inference of a causal relationship between CNS damage and functional loss. Based on the stimulatory effects of d-amphetamine sulfate (AMPH) on sucrose intake, the present study pharmacologically probes the functional status of central dopaminergic circuits involved in control of behavioral reward. The response rates were compared between diseased MRL-lpr mice and congenic MRL +/+ controls tested in the sucrose preference paradigm. Neuronal loss was assessed by Fluoro Jade B (FJB) staining of nucleus accumbens and the CA2/CA3 region. While control mice significantly increased intake of sucrose solutions 60 min after administration of AMPH (i.p., 0.5 mg/kg), the intake in drugged MRL-lpr mice was comparable to those given saline injection. Increased FJB staining was detected in the nucleus accumbens and hippocampus of diseased mice, and AMPH treatment neither altered this nor other measures of organ pathology. The results obtained are consistent with previously observed changes in the mesolimbic dopamine system of MRL-lpr mice and suggest that the lesion in the nucleus accumbens and deficits in dopamine release underlie impaired responsiveness to palatable stimulation during the progress of systemic autoimmune disease. As such, they point to a neurotransmitter-specific regional brain damage which may account for depressive behaviors in neuropsychiatric lupus erythematosus.