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

Paeoniflorin modulates AGEs/RAGE/P38MAPK/ERK/mTOR autophagy pathway to improve cognitive dysfunction in MRL/lpr mice

OBJECTIVE

The objective of this study was to investigate the therapeutic effects of paeoniflorin (PA) on cognitive impairment and to elucidate its potential mechanisms in MRL/lpr mice, a model of systemic lupus erythematosus-associated cognitive dysfunction.

METHOD

Cognitive performance and behavioral responses were assessed using a comprehensive battery of tests, including the Morris water maze, the Novel object recognition test, and the Y maze. Neuropathological changes in the hippocampal regions were visualized through Nissl, HE and Immunohistochemistry staining. Protein expression levels of receptor for advanced glycation end-products (RAGE) and LC3B were quantified by immunofluorescence, while the ultrastructure of autophagic organelles was examined using transmission electron microscopy (TEM). Inflammatory cytokines, namely tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), and interleukin-6 (IL-6) were quantified in both serum and hippocampal homogenates by enzyme-linked immunosorbent assay (ELISA). The hippocampal expression of advanced glycation end-products (AGEs), RAGE, p62, Beclin-1, and key proteins involved in the mitogen-activated protein kinase (MAPK) pathways, including p38MAPK, ERK, and mTOR were analyzed by Western blotting.

RESULT

Paeoniflorin ameliorates cognitive dysfunction, neuronal damage, pro-inflammatory cytokine production in MRL/lpr mice. Paeoniflorin suppresses RAGE and autophagy levels and P38 MAPK/ERK/mTOR signaling pathway activation in the hippocampus of MRL/lpr mice.

CONCLUSION

Paeoniflorin may exert its neuroprotective effects by modulating the AGEs/RAGE/P38MAPK/ERK/mTOR autophagy signaling pathway.

Depression-like behavior is associated with changes in the meningeal lymphatic vasculature and meningeal B cells in a murine lupus model

Meningeal lymphatic vasculature (mLV) comprises a network of vessels responsible for draining immune cells and fluid from the central nervous system (CNS) into the deep cervical lymph nodes. While changes in mLV function have been implicated in several neurodegenerative disorders, its role in autoimmune diseases is less clear. Systemic lupus erythematosus (SLE) is an autoimmune disease affecting multiple organs. When SLE affects the CNS, it is known as neuropsychiatric lupus (NPSLE), although the status of mLV during NPSLE has not been yet evaluated. Here, by using the lupus FcγRIIb-/- murine model, we found that this model develops NPSLE along with increased mLV coverage and function at 4 mo of age. Altered B cell developmental stages were evident in this lupus mouse model. In fact, increased B cell clusters in the meninges of FcγRIIb-/- mice were also observed. These findings suggest that mLV morphology and function are increased in FcγRIIb-/- mice together with changes in the meningeal B cell population that could have an impact on NPSLE symptoms.

Association of miR-21 gene polymorphisms with cognitive function in patients with systemic lupus erythematosus

OBJECTIVES

The genetic variant rs13137 of miR-21 is associated with susceptibility in many diseases. However, the association with cognitive dysfunction (CD) in Chinese patients with systemic lupus erythematosus (SLE) remains unclear.

MATERIALS AND METHODS

Two hundred and thirty SLE patients (Non-CD) and 230 SLE-related CD patients (CD) were recruited. MiR-21 level was calculated by qRT-PCR. The ROC curve was established to evaluate the diagnosibility. The independent risk factors were identified by multivariate logistic regression analysis.

RESULTS

The miR-21 in CD group was obviously increased. Compared to AA carriers, the miR-21 level in carriers of rs13137 AT/TT in CD group were significantly lower than those in Non-CD group. The AUC was 0.9023 with sensitivity of 78.70% and specificity of 90.87%. Comparison of genotype and allele frequencies indicated that SLE patients carrying rs13137 AT/TT genotype had low risk of CD. Multivariate logistic regression analysis showed that the rs13137 polymorphism, education years, and MoCA score were correlated with CD risk.

CONCLUSION

The miR-21 rs13137 polymorphism was correlated with CD risk in the Chinese population. MiR-21 in rs13137 AT/TT carriers was significantly lower than that of AA genotype and the AT/TT genotype was correlated with low CD risk in SLE patients.

Single-cell RNA-seq reveals disease-specific CD8+ T cell clonal expansion and a high frequency of transcriptionally distinct double-negative T cells in diabetic NOD mice

T cells primarily drive the autoimmune destruction of pancreatic beta cells in Type 1 diabetes (T1D). However, the profound yet uncharacterized diversity of the T cell populations in vivo has hindered obtaining a clear picture of the T cell changes that occur longitudinally during T1D onset. This study aimed to identify T cell clonal expansion and distinct transcriptomic signatures associated with T1D progression in Non-Obese Diabetic (NOD) mice. Here we profiled the transcriptome and T cell receptor (TCR) repertoire of T cells at single-cell resolution from longitudinally collected peripheral blood and pancreatic islets of NOD mice using single-cell RNA sequencing technology. We detected disease dependent development of infiltrating CD8 + T cells with altered cytotoxic and inflammatory effector states. In addition, we discovered a high frequency of transcriptionally distinct double negative (DN) T cells that fluctuate throughout T1D pathogenesis. This study identifies potential disease relevant TCR sequences and potential disease biomarkers that can be further characterized through future research.

Alpha-Ketoglutarate Alleviates Systemic Lupus Erythematosus-Associated Periodontitis in a Novel Murine Model

AIM

To establish a reproducible experimental animal model for systemic lupus erythematosus (SLE)-associated periodontitis (PD), investigate the effects of SLE on PD and assess the therapeutic potential of alpha-ketoglutarate (αKG) for SLE-PD treatment.

MATERIALS AND METHODS

An SLE-PD murine model was established via ligature-induced PD in MRL-lpr strain, with MRL/MpJ strain as a non-SLE control. The periodontal state was assessed using micro-CT, real-time PCR, histology, immunofluorescence and flow cytometry assays. αKG levels were analysed, and a thermoresponsive gel was designed as a periodontal dimethyl (DM)-αKG delivery system. αKG levels were analysed in gingival crevicular fluid (GCF) of PD patients with or without SLE.

RESULTS

SLE significantly increased the periodontal inflammation and bone resorption in the SLE-PD model. αKG levels in GCF were lower in PD patients with SLE than in PD patients without SLE. Decreased αKG levels in the gingiva and macrophage M1/M2 imbalance were observed in SLE-PD mice. However, DM-αKG thermoresponsive gel effectively alleviated the periodontal inflammation, bone resorption and macrophage M1/M2 imbalance in SLE-PD mice.

CONCLUSIONS

Our study established, for the first time, a novel SLE-PD murine model and revealed that SLE increases the severity of PD in vivo. Our findings highlight the therapeutic potential of αKG for SLE-associated PD.

Dysregulated Intestinal Host-Microbe Interactions in Systemic Lupus Erythematosus: Insights from Patients and Mouse Models

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by chronic inflammation that affects multiple organs, with its prevalence varying by ethnicity. Intestinal dysbiosis has been observed in both SLE patients and murine models. Additionally, intestinal barrier impairment is thought to contribute to the ability of pathobionts to evade and breach immune defenses, resulting in antigen cross-reactivity, microbial translocation, subsequent immune activation, and, ultimately, multiple organ failure. Since the detailed mechanisms underlying these processes are difficult to examine using human samples, murine models are crucial. Various SLE murine models, including genetically modified spontaneous and inducible murine models, offer insights into pathobionts and how they dysregulate systemic immune systems. Furthermore, since microbial metabolites modulate systemic immune responses, bacteria and their metabolites can be targeted for treatment. Based on human and mouse research insights, this review examines how lupus pathobionts trigger intestinal and systemic immune dysregulation. Therapeutic approaches, such as fecal microbiota transplantation and dietary adjustments, show potential as cost-effective and safe methods for preventing and treating SLE. Understanding the complex interactions between the microbiota, host factors, and immune dysregulation is essential for developing novel, personalized therapies to tackle this multifaceted disease.

Blood-CSF barrier clearance of ABC transporter substrates is suppressed by interleukin-6 in lupus choroid plexus spheroids

BACKGROUND

The choroid plexus (CP) has been recently implicated in the pathogenesis of the neuropsychiatric manifestations of systemic lupus erythematosus (NPSLE). Lupus patients demonstrate increased serum and cerebrospinal fluid (CSF) concentrations of interleukin-6 (IL-6), which can disrupt vital blood-CSF barrier (B-CSFB) functions performed by the CP. However, difficulty accessing this tissue has largely precluded dynamic imaging or evaluation of CP barrier function in vivo.

METHODS

In this study, explant CP spheroids which replicate the functional and structural properties of the B-CSFB were generated from 12 + week old female MRL/lpr (IL-6 wildtype; IL-6 WT) lupus mice, IL-6 knockout (IL-6 KO) MRL/lpr mice, and congenic control MRL/mpj mice. CP spheroids derived from IL-6 WT MRL/lpr mice were found to synthesize and secrete IL-6, similar to the CP in vivo, whereas the IL-6 KO spheroids did not produce IL-6. Accumulation of different fluorescent tracers within the central CSF-like fluid vacuole of spheroids, modeling brain ventricles, was measured to probe transcellular permeability, paracellular diffusion, and clearance functions of the CP.

RESULTS

As shown by blocking the IL-6 receptor in IL-6 WT spheroids or comparing them to IL-6 KO spheroids, IL-6 signaling decreased spheroid clearance of methotrexate, a chemotherapeutic drug employed in the therapy of lupus, and lucifer yellow. This suppression occurred without altering CP epithelial morphology and ultrastructure. Methotrexate and lucifer yellow efflux can occur through ATP-binding cassette (ABC) transporters, including BCRP and MRP1. Cytoplasmic accumulation of the ABC-specific dye fluorescein diacetate was also increased by IL-6. Pharmacologic inhibition of either BCRP or MRP1 in IL-6 KO spheroids was sufficient to recreate the clearance deficits observed in IL-6 WT spheroids. Moreover, CP expression of BCRP was significantly lower in IL-6 WT mice.

CONCLUSIONS

In this study, we establish, validate, and apply a CP spheroid model to the study of B-CSFB function in lupus. Our results show that IL-6, a key cytokine increased in NPSLE, can potentially suppress the CP-specific function and expression of BCRP and MRP1. Therefore, IL-6 could affect the CSF clearance of inflammatory substrates (e.g., leukotrienes), the accumulation of which would incite neurotoxicity and promote progression of NPSLE.

Changes in Gut Microbiota According to Disease Severity in a Lupus Mouse Model

Systemic lupus erythematosus (SLE) is a multifaceted autoimmune disease driven by immune dysregulation. This study investigated the relationship between gut microbiota and lupus severity using the MRL/lpr lupus mouse model. Mice were grouped based on total immunoglobulin (Ig)G, IgG2a levels, and urine albumin-to-creatinine ratio (ACR), allowing for the comparison of gut microbiota profiles across different disease severities. Interestingly, severe lupus mice exhibited significant reductions in Ruminiclostridium cellulolyticum, Lactobacillus johnsonii, and Kineothrix alysoides, while Clostridium saudiense, Pseudoflavonifractor phocaeensis, and Intestinimonas butyriciproducens were enriched. These microbial shifts correlated with elevated IgG, IgG2a, and ACR levels, indicating that changes in the gut microbiome may directly influence key immunological markers associated with lupus severity. The depletion of beneficial species and the enrichment of potentially pathogenic bacteria appear to contribute to immune activation and disease progression. This study suggests that gut microbiota dysbiosis plays a critical role in exacerbating lupus by modulating immune responses, reinforcing the link between microbial composition and lupus pathogenesis. Our findings provide the first evidence identifying these distinct gut microbial species as potential contributors to lupus severity, highlighting their role as key factors in disease progression.

The role of vitamin D: a promising pathway to combat neuropsychiatric lupus disorders

To evaluate neuropsychiatric manifestations in the pristane-induced lupus (PIL) model, as well as to evaluate immunoregulatory effects of vitamin D (vit-D) in the brain of mice with PIL. Eighty female BALB/c mice were divided into six groups with 90 (3 months) and 180 (6 months) days of experimentation: CO3, CO6 (controls), PIL3, PIL6 (pristane-induced lupus), VD3 and VD6 (PIL supplemented with 1,25-dihydroxyvitamin D). Forced-swim, elevated plus maze and Barnes maze were the behavioral tests performed. Expression of pVDR was assessed by immunofluorescence. Brain IgM and IgG deposits were evaluated by double staining fluorescence. Serum IL-6 and IFN-α1 were quantified by ELISA. AUC-ROC curve was also performed for immunoglobulins. PIL and VD showed depressive-like behavior in the forced-swim test and anxious-like behavior in the elevated plus maze test. PIL also presented cognitive and memory impairment in the Barnes maze test. Additionally, PIL and VD presented higher levels of serum IFN-α1, but not IL-6. Mice supplemented with vit-D had reduced IgM and IgG deposits and increased pVDR expression in the brain after 180 days. The AUC-ROC curve demonstrated high sensitivity and specificity for IgM and IgG in the brain. We observed neuropsychiatric manifestations in this model of systemic lupus erythematosus (SLE), strongly corroborating to PIL model being suitable as a neuropsychiatric lupus (NPSLE) model. Vit-D was able to reduce immunoglobulin deposits in the brain and influenced the levels of serum IL-6 in the animals assessed. Also, it improved memory, but it had no effect on depressive and anxious-like behavior.

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

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

Lithium Ions as Modulators of Complex Biological Processes: The Conundrum of Multiple Targets, Responsiveness and Non-Responsiveness, and the Potential to Prevent or Correct Dysregulation of Systems during Aging and in Disease

Lithium is one of the lightest elements on Earth and it has been in the environment since the formation of the galaxy. While a common element, it has not been found to be an essential element in biological processes, ranging from single cell organisms to Homo sapiens. Instead, at an early stage of evolution, organisms committed to a range of elements such as sodium, potassium, calcium, magnesium, zinc, and iron to serve essential functions. Such ions serve critical functions in ion channels, as co-factors in enzymes, as a cofactor in oxygen transport, in DNA replication, as a storage molecule in bone and liver, and in a variety of other roles in biological processes. While seemingly excluded from a major essential role in such processes, lithium ions appear to be able to modulate a variety of biological processes and "correct" deviation from normal activity, as a deficiency of lithium can have biological consequences. Lithium salts are found in low levels in many foods and water supplies, but the effectiveness of Li salts to affect biological systems came to recent prominence with the work of Cade, who reported that administrating Li salts calmed guinea pigs and was subsequently effective at relatively high doses to "normalize" a subset of patients with bipolar disorders. Because of its ability to modulate many biological pathways and processes (e.g., cyclic AMP, GSK-3beta, inositol metabolism, NaK ATPases, neuro processes and centers, immune-related events, respectively) both in vitro and in vivo and during development and adult life, Li salts have become both a useful tool to better understand the molecular regulation of such processes and to also provide insights into altered biological processes in vivo during aging and in disease states. While the range of targets for lithium action supports its possible role as a modulator of biological dysregulation, it presents a conundrum for researchers attempting to elucidate its specific primary target in different tissues in vivo. This review will discuss aspects of the state of knowledge regarding some of the systems that can be influenced, focusing on those involving neural and autoimmunity as examples, some of the mechanisms involved, examples of how Li salts can be used to study model systems, as well as suggesting areas where the use of Li salts could lead to additional insights into both disease mechanisms and natural processes at the molecular and cell levels. In addition, caveats regarding lithium doses used, the strengths and weaknesses of rodent models, the background genetics of the strain of mice or rats employed, and the sex of the animals or the cells used, are discussed. Low-dose lithium may have excellent potential, alone or in combination with other interventions to prevent or alleviate aging-associated conditions and disease progression.

Ectopic CD4+ T cells in choroid plexus mediate neuropsychiatric lupus symptoms in mice via interferon-γ induced microglia activation

Neuropsychiatric systemic lupus erythematosus (NPSLE) is a disabling and potentially life-threatening complication of SLE. This study aims to investigate whether ectopic CD4+ T cells in the choroid plexus mediate NPSLE in mice. Intracerebroventricular (ICV) injection of anti-CD4 antibody effectively depleted CP-resident CD4+ T cells and alleviated NPSLE-like symptoms in MRL/lpr mice. Following ICV injection, the majority of isolated lupus CD4+ T cells from donor MRL/lpr mice predominantly stayed in the CP for at least 28 days in recipient C57BL/6 mice, while nearly all isolated CD4+ T cells from MRL/MpJ mice disappeared within 7 days. ICV injection of lupus CD4+ T cells resulted in NPSLE-like symptoms, including impaired behavioral performances, increased microglial activation, and abnormal microstructure changes. Flow cytometry analysis revealed that the majority of isolated lupus CD4+ T cells were positive for IFN-γ. Neutralizing intracerebral IFN-γ alleviated NPSLE-like symptoms in MRL/lpr mice. Moreover, ICV injection of anti-IFN-γ antibody or microglial depletion by PLX3397 benefited most NPSLE-like symptoms in lupus CD4+ T-treated mice, while ICV injection of IFN-γ mimicked most NPSLE-like symptoms. In conclusion, CP-resident lupus CD4+ T cells contribute to NPSLE-like symptoms in mice via Interferon-γ induced microglia activation. Depleting CP-resident lupus CD4+ T cells, interferon-γ, or activated microglia may be potential therapeutic targets for NPSLE.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Microglia orchestrate synaptic and neuronal stripping: Implication in neuropsychiatric lupus

Systemic lupus erythematosus (SLE), a multifactorial autoimmune disease, can affect the brain and cause neuropsychiatric dysfunction, also named neuropsychiatric lupus (NPSLE). Microglial activation is observed in NPSLE patients. However, the mechanisms regulating microglia-mediated neurotoxicity in NPSLE remain elusive. Here, we showed that M1-like proinflammatory cytokine levels were increased in the cerebrospinal fluid (CSF) of SLE patients, especially those with neuropsychiatric symptoms. We also demonstrated that MRL/lpr lupus mice developed anxiety-like behaviours and cognitive deficits in the early and active phases of lupus, respectively. An increase in microglial number was associated with upregulation of proinflammatory cytokines in the MRL/lpr mouse brain. RNA sequencing revealed that genes associated with phagocytosis and M1 polarization were upregulated in microglia from lupus mice. Functionally, activated microglia induced synaptic stripping in vivo and promoted neuronal death in vitro. Finally, tofacitinib ameliorated neuropsychiatric disorders in MRL/lpr mice, as evidenced by reductions in microglial number and synaptic/neuronal loss and alleviation of behavioural abnormalities. Thus, our results indicated that classically activated (M1) microglia play a crucial role in NPSLE pathogenesis. Minocycline and tofacitinib were found to alleviate NPSLE by inhibiting micrglial activation, providing a promising therapeutic strategy.

ω-3 polyunsaturated fatty acid alleviates systemic lupus erythematosus by suppressing autoimmunity in a murine model

Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune inflammatory disease that damages multiple organs by the production of autoantibodies. Numerous research studies have demonstrated the anti-inflammatory effects of ω-3 polyunsaturated fatty acids (PUFAs). A diet rich in ω-3 PUFAs reduces chronic inflammatory and autoimmune conditions. Herein, we investigated the protective effect of ω-3 PUFAs against autoimmune injury in SLE. In a TMPD-induced mouse model of SLE, supplementation with eicosapentaenoic acid (EPA)-rich (97%) fish oil was found to alleviate systemic autoimmune phenotypes such as ascites, lipogranulomas and serum dsDNA levels. In addition, EPA also significantly improved renal manifestations, reducing proteinuria, glomerulonephritis, and immune complex deposition. Mechanistically, ω-3 PUFAs were shown to modulate the differentiation of B lymphocyte subsets of primary splenic lymphocytes in the spontaneous murine lupus model MRL/MpJ-Faslpr in vitro, specifically that both EPA and DHA suppressed the number of total B cells, B1B2 cells and plasma cells. Concurrently, they were also found to promote the secretion of the anti-inflammatory cytokine IL10, mainly produced by Breg and Treg cells. Thus, nutritional supplementation with ω-3 PUFAs can regulate B cell's differentiation and anti-inflammatory function and strongly prevent autoimmune responses and lupus nephritis. The diets balance between ω-6 and ω-3 PUFAs intake may represent a promising treatment strategy to prevent or delay the onset of SLE.

Microglia activation in the presence of intact blood-brain barrier and disruption of hippocampal neurogenesis via IL-6 and IL-18 mediate early diffuse neuropsychiatric lupus

INTRODUCTION

Inflammatory mediators are detected in the cerebrospinal fluid of systemic lupus erythematosus patients with central nervous system involvement (NPSLE), yet the underlying cellular and molecular mechanisms leading to neuropsychiatric disease remain elusive.

METHODS

We performed a comprehensive phenotyping of NZB/W-F1 lupus-prone mice including tests for depression, anxiety and cognition. Immunofluorescence, flow cytometry, RNA-sequencing, qPCR, cytokine quantification and blood-brain barrier (BBB) permeability assays were applied in hippocampal tissue obtained in both prenephritic (3-month-old) and nephritic (6-month-old) lupus mice and matched control strains. Healthy adult hippocampal neural stem cells (hiNSCs) were exposed ex vivo to exogenous inflammatory cytokines to assess their effects on proliferation and apoptosis.

RESULTS

At the prenephritic stage, BBB is intact yet mice exhibit hippocampus-related behavioural deficits recapitulating the human diffuse neuropsychiatric disease. This phenotype is accounted by disrupted hippocampal neurogenesis with hiNSCs exhibiting increased proliferation combined with decreased differentiation and increased apoptosis in combination with microglia activation and increased secretion of proinflammatory cytokines and chemokines. Among these cytokines, IL-6 and IL-18 directly induce apoptosis of adult hiNSCs ex vivo. During the nephritic stage, BBB becomes disrupted which facilitates immune components of peripheral blood, particularly B-cells, to penetrate into the hippocampus further augmenting inflammation with locally increased levels of IL-6, IL-12, IL-18 and IL-23. Of note, an interferon gene signature was observed only at nephritic-stage.

CONCLUSION

An intact BBB with microglial activation disrupting the formation of new neurons within the hippocampus represent early events in NPSLE. Disturbances of the BBB and interferon signature are evident later in the course of the disease.

Mouse models, antibodies, and neuroimaging: Current knowledge and future perspectives in neuropsychiatric systemic lupus erythematosus (NPSLE)

As a chronic autoimmune disease systemic lupus erythematosus (SLE) can also affect the central and the peripheral nervous system causing symptoms which are summed up as neuropsychiatric systemic lupus erythematosus (NPSLE). These symptoms are heterogenous including cognitive impairment, seizures, and fatigue, leading to morbidity or even mortality. At present, little is known about the pathophysiological processes involved in NPSLE. This review focuses on the current knowledge of the pathogenesis of NPSLE gained from the investigation of animal models, autoantibodies, and neuroimaging techniques. The antibodies investigated the most are anti-ribosomal P protein antibodies (Anti-rib P) and anti-N-Methyl-D-Aspartic Acid Receptor 2 antibodies (Anti-NR2), which represent a subpopulation of anti-dsDNA autoantibodies. Experimental data demonstrates that Anti-rib P and Anti-NR2 cause different neurological pathologies when applied intravenously (i.v.), intrathecally or intracerebrally in mice. Moreover, the investigation of lupus-prone mice, such as the MRL/MpJ-Faslpr/lpr strain (MRL/lpr) and the New Zealand black/New Zealand white mice (NZB × NZW F1) showed that circulating systemic antibodies cause different neuropsychiatric symptoms compared to intrathecally produced antibodies. Furthermore, neuroimaging techniques including magnetic resonance imaging (MRI) and positron emission tomography (PET) are commonly used tools to investigate structural and functional abnormalities in NPSLE patients. Current research suggests that the pathogenesis of NPSLE is heterogenous, complex and not yet fully understood. However, it demonstrates that further investigation is needed to develop individual therapy in NPSLE.

Inhibitor of NF-κB Kinase Subunit ε Contributes to Neuropsychiatric Manifestations in Lupus-Prone Mice Through Microglial Activation

OBJECTIVE

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by multiorgan dysfunction. Neuropsychiatric SLE (NPSLE) occurs in 30-40% of lupus patients and is the most severe presentation of SLE, frequently resulting in limitation of daily life. Recent studies have shown that microglia, tissue-resident macrophages in the central nervous system, are involved in the pathogenesis of NPSLE. This study was undertaken to explore new therapeutic targets for NPSLE focusing on microglia.

METHODS

RNA sequencing of microglia in MRL/lpr, lupus-prone mice, as well as that of microglia cultured in vitro with cytokines were performed. A candidate gene, which could be a therapeutic target for NPSLE, was identified, and its role in microglial activation and phagocytosis was investigated using specific inhibitors and small interfering RNA. The effect of intracerebroventricular administration of the inhibitor on the behavioral abnormalities of MRL/lpr was also evaluated.

RESULTS

Transcriptome analysis revealed the up-regulation of Ikbke, which encodes the inhibitor of NF-κB kinase subunit ɛ (IKBKε) in both microglia from MRL/lpr mice and cytokine-stimulated microglia in vitro. Intracerebroventricular administration of an IKBKε inhibitor ameliorated cognitive function and suppressed microglial activation in MRL/lpr mice. Mechanistically, IKBKε inhibition reduced glycolysis, which dampened microglial activation and phagocytosis.

CONCLUSION

These findings suggest that IKBKε plays a vital role in the pathogenesis of NPSLE via microglial activation, and it could serve as a therapeutic target for NPSLE.

Small molecule compound K-7174 attenuates neuropsychiatric manifestations in lupus-prone mice

The neuropsychiatric manifestations of systemic lupus erythematosus (NPSLE) present significant morbidity and mortality due to frequent non-response or adverse effects of the current clinical drugs. The disruption of the blood-brain barrier (BBB) contributes to inflammatory NPSLE disease progression. K-7174, a highly piperazine-derived compound, inhibits leukocyte adhesion and inflammatory factor expression. The present study aimed to comprehensively assess the treatment effect of neurobehavioral deficits in MRL/lpr mice, a validated neuropsychiatric lupus model. The intraperitoneal injection of K-7174 alleviated lupus-like symptoms and improved cognitive dysfunction in MRL/lpr mice. Also, it significantly attenuated neuronal degeneration and decreased serum albumin deposition in the hippocampus. Furthermore, K-7174 acted directly on the brain microvascular endothelial bEnd.3 cells and reduced the BBB permeability, manifested by inhibiting the activation of brain microvascular endothelial cells and increasing the expression of tight junctions (TJs). Notably, in vitro experiments showed that K-7174 alleviates the decreased ZO1 and Occludin expression in bEnd.3 cells caused by lactate increase, improving cell permeability via the MCT4/NKAP/CREB signaling pathway. These findings suggested that K-7174 mediates the attenuation of NPSLE in MRL/lpr mice, indicating a promising therapeutic strategy for NPSLE.

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.

Microstructural Changes in the Corpus Callosum in Systemic Lupus Erythematous

Central nervous system (CNS) involvement in childhood-onset systemic lupus erythematosus (cSLE) occurs in more than 50% of patients. Structural magnetic resonance imaging (MRI) has identified global cerebral atrophy, as well as the involvement of the corpus callosum and hippocampus, which is associated with cognitive impairment. In this cross-sectional study we included 71 cSLE (mean age 24.7 years (SD 4.6) patients and a disease duration of 11.8 years (SD 4.8) and two control groups: (1) 49 adult-onset SLE (aSLE) patients (mean age of 33.2 (SD 3.7) with a similar disease duration and (2) 58 healthy control patients (mean age of 29.9 years (DP 4.1)) of a similar age. All of the individuals were evaluated on the day of the MRI scan (Phillips 3T scanner). We reviewed medical charts to obtain the clinical and immunological features and treatment history of the SLE patients. Segmentation of the corpus callosum was performed through an automated segmentation method. Patients with cSLE had a similar mid-sagittal area of the corpus callosum in comparison to the aSLE patients. When compared to the control groups, cSLE and aSLE had a significant reduction in the mid-sagittal area in the posterior region of the corpus callosum. We observed significantly lower FA values and significantly higher MD, RD, and AD values in the total area of the corpus callosum and in the parcels B, C, D, and E in cSLE patients when compared to the aSLE patients. Low complement, the presence of anticardiolipin antibodies, and cognitive impairment were associated with microstructural changes. In conclusion, we observed greater microstructural changes in the corpus callosum in adults with cSLE when compared to those with aSLE. Longitudinal studies are necessary to follow these changes, however they may explain the worse cognitive function and disability observed in adults with cSLE when compared to aSLE.

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.

Choroid Plexus-Infiltrating T Cells as Drivers of Murine Neuropsychiatric Lupus

OBJECTIVE

T cells are critical in the pathogenesis of systemic lupus erythematosus (SLE) in that they secrete inflammatory cytokines, help autoantibody production, and form autoreactive memory T cells. Although the contribution of T cells to several forms of organ-mediated damage in SLE has been previously demonstrated, the role of T cells in neuropsychiatric SLE (NPSLE), which involves diffuse central nervous system manifestations and is observed in 20-40% of SLE patients, is not known. Therefore, we conducted this study to evaluate how behavioral deficits are altered after depletion or transfer of T cells, to directly assess the role of T cells in NPSLE.

METHODS

MRL/lpr mice, an NPSLE mouse model, were either systemically depleted of CD4+ T cells or intracerebroventricularly injected with choroid plexus (CP)-infiltrating T cells and subsequently evaluated for alterations in neuropsychiatric manifestations. Our study end points included evaluation of systemic disease and assessment of central nervous system changes.

RESULTS

Systemic depletion of CD4+ T cells ameliorated systemic disease and cognitive deficits. Intracerebroventricular injection of CP-infiltrating T cells exacerbated depressive-like behavior and worsened cognition in recipient mice compared with mice who received injection of splenic lupus T cells or phosphate buffered saline. Moreover, we observed enhanced activation in CP-infiltrating T cells when cocultured with brain lysate-pulsed dendritic cells in comparison to the activation levels observed in cocultures with splenic T cells.

CONCLUSION

T cells, and more specifically CP-infiltrating antigen-specific T cells, contributed to the pathogenesis of NPSLE in mice, indicating that, in the development of more targeted treatments for NPSLE, modulation of T cells may represent a potential therapeutic strategy.

Strategies of Targeting Inflammasome in the Treatment of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by multiple organ dysfunction resulting from the production of multiple autoantibodies and adaptive immune system abnormalities involving T and B lymphocytes. In recent years, inflammasomes have been recognized as an important component of innate immunity and have attracted increasing attention because of their pathogenic role in SLE. In short, inflammasomes regulate the abnormal differentiation of immune cells, modulate pathogenic autoantibodies, and participate in organ damage. However, due to the clinical heterogeneity of SLE, the pathogenic roles of inflammasomes are variable, and thus, the efficacy of inflammasome-targeting therapies is uncertain. To provide a foundation for the development of such therapeutic strategies, in this paper, we review the role of different inflammasomes in the pathogenesis of SLE and their correlation with clinical phenotypes and propose some corresponding treatment strategies.

The correlation between proteoglycan 2 and neuropsychiatric systemic lupus erythematosus

The proposed pathogenesis of neuropsychiatric systemic lupus erythematosus (NPSLE) mainly includes ischemia and neuroinflammation mechanisms. Protein encoded by Proteoglycan 2 (PRG2) mRNA is involved in the immune process related to eosinophils, also being found in the placenta and peripheral blood of pregnant women. We evaluated the correlation between PRG2 and NPSLE for the first time and found that PRG2 protein is overexpressed in the serum of patients with NPSLE and correlated with the SLE disease activity index (SLEDAI) subset scores of psychosis. Moreover, we investigated the correlation between hippocampal PRG2 level and hippocampally dependent learning and memory ability in MRL/lpr mice, and discovered that the number of PRG2⁺GFAP⁺ astrocytes in the cortex and hypothalamus and the number of PRG2⁺IBA-1⁺ microglia in the hippocampus and cortex significantly increased in the MRL/lpr mice. These data provided a reference for the follow-up exploration of the role of PRG2 in SLE or other diseases.

Animal models of systemic lupus erythematosus and their applications in drug discovery

INTRODUCTION

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease with substantial phenotypic heterogeneity. Currently, our understanding of the pathogenesis is still limited, and as a result, specific and efficacious therapies are lacking. Various mouse models have been established to serve as powerful tools that will promote a better understanding of the disease and the ability to test novel drugs before clinical application.

AREAS COVERED

The authors review the existing mouse models of SLE in terms of pathogenesis and manifestations, as well as their applications in drug discovery and development. The areas of focus include promising novel therapeutics that could benefit patients in the future and the contribution of mouse models used in preclinical studies.

EXPERT OPINION

Given the diversity of SLE mouse models with different characteristics, researchers must select a suitable model based on the mechanism involved. The use of multiple models is needed for drug testing studies to evaluate drug efficacy on different genetic backgrounds and other mechanisms to provide a reference for clinical trials.

Application of Animal Models in Interpreting Dry Eye Disease

Different pathophysiologic mechanisms are involved in the initiation, development, and outcome of dry eye disease (DED). Animal models have proven valuable and efficient in establishing ocular surface microenvironments that mimic humans, thus enabling better understanding of the pathogenesis. Several dry eye animal models, including lacrimal secretion insufficiency, evaporation, neuronal dysfunction, and environmental stress models, are related to different etiological factors. Other models may be categorized as having a multifactorial DED. In addition, there are variations in the methodological classification, including surgical lacrimal gland removal, drug-induced models, irradiation impairment, autoimmune antibody-induced models, and transgenic animals. The aforementioned models may manifest varying degrees of severity or specific pathophysiological mechanisms that contribute to the complexity of DED. This review aimed to summarize various dry eye animal models and evaluate their respective characteristics to improve our understanding of the underlying mechanism and identify therapeutic prospects for clinical purposes.

Neuronal NR4A1 deficiency drives complement-coordinated synaptic stripping by microglia in a mouse model of lupus

Neuropsychiatric lupus (NPSLE) is a frequent manifestation of systemic lupus erythematosus (SLE) that occurs in 40–90% of SLE patients; however, the underlying mechanisms remain elusive, causing a severe lack of therapeutic targets for this condition. Here, we show that complement-coordinated elimination of synapses participated in NPSLE in MRL/lpr mice, a lupus-prone murine model. We demonstrated that lupus mice developed increased anxiety-like behaviors and persistent phagocytic microglial reactivation before overt peripheral lupus pathology. In the lupus brain, C1q was increased and localized at synaptic terminals, causing the apposition of phagocytic microglia and ensuing synaptic engulfment. We further determined that neuronal Nr4a1 signaling was essential for attracting C1q synaptic deposition and subsequent microglia-mediated synaptic elimination. Minocycline-mediated deactivation of microglia, antibody blockade of C1q, or neuronal restoration of Nr4a1 protected lupus mice from synapse loss and NP manifestations. Our findings revealed an active role of neurons in coordinating microglia-mediated synaptic loss and highlighted neuronal Nr4a1 and C1q as critical components amenable to therapeutic intervention in NPSLE.

Aptamer-based screen of Neuropsychiatric Lupus cerebrospinal fluid reveals potential biomarkers that overlap with the choroid plexus transcriptome

OBJECTIVES

As no gold-standard diagnostic test exists for neuropsychiatric systemic lupus erythematosus (NPSLE), we executed a broad screen of NPSLE cerebrospinal fluid (CSF) using an aptamer-based platform.

METHODS

CSF were obtained from NPSLE patients and subjected to proteomic assay using the aptamer-based screen. Potential biomarkers were identified and validated in independent NPSLE cohorts in comparison with other neurological diseases.

RESULTS

40 proteins out of 1129 screened were elevated in NPSLE CSF. By ELISA validation, CSF Angiostatin, α2-Macroglobulin, DAN, Fibronectin, HCC-1, IgM, Lipocalin 2, M-CSF and SERPING1 were significantly elevated in a predominantly Caucasian NPSLE cohort (n=24), compared to patients with other neurological diseases (n=54), with CSF IgM (AUC=0.95) and M-CSF (AUC=0.91) being the most discriminatory. In a second, Hong Kong NPSLE cohort, CSF IgM (AUC=0.78) and Lipocalin-2 (AUC=0.85) were the most discriminatory. Several CSF proteins exhibited high diagnostic specificity for NPSLE in both cohorts. Elevated CSF C3 was associated with acute confusional state. Eleven molecules elevated in NPSLE CSF exhibited concordant elevation in the choroid plexus, suggesting shared origins.

CONCLUSIONS

CSF Lipocalin-2, M-CSF, IgM and complement C3 emerge as promising CSF biomarkers of NPSLE with diagnostic potential.

Therapeutic Potential of Anti-Interferon α Vaccination on SjS-Related Features in the MRL/lpr Autoimmune Mouse Model

Sjögren’s syndrome (SjS) is a frequent systemic autoimmune disease responsible for a major decrease in patients’ quality of life, potentially leading to life-threatening conditions while facing an unmet therapeutic need. Hence, we assessed the immunogenicity, efficacy, and tolerance of IFN-Kinoid (IFN-K), an anti-IFNα vaccination strategy, in a well-known mouse model of systemic autoimmunity with SjS-like features: MRL/MpJ-Faslpr/lpr (MRL/lpr) mice. Two cohorts (with ISA51 or SWE01 as adjuvants) of 26 female MRL/lpr were divided in parallel groups, “controls” (not treated, PBS and Keyhole Limpet Hemocyanin [KLH] groups) or “IFN-K” and followed up for 122 days. Eight-week-old mice received intra-muscular injections (days 0, 7, 28, 56 and 84) of PBS, KLH or IFN-K, emulsified in the appropriate adjuvant, and blood samples were serially collected. At sacrifice, surviving mice were euthanized and their organs were harvested for histopathological analysis (focus score in salivary/lacrimal glands) and IFN signature evaluation. SjS-like features were monitored. IFN-K induced a disease-modifying polyclonal anti-IFNα antibody response in all treated mice with high IFNα neutralization capacities, type 1 IFN signature’s reduction and disease features’ (ocular and oral sicca syndrome, neuropathy, focus score, glandular production of BAFF) improvement, as reflected by the decrease in Murine Sjögren’s Syndrome Disease Activity Index (MuSSDAI) modelled on EULAR Sjögren’s Syndrome Disease Activity Index (ESSDAI). No adverse effects were observed. We herein report on the strong efficacy of an innovative anti-IFNα vaccination strategy in a mouse model of SjS, paving the way for further clinical development (a phase IIb trial has just been completed in systemic lupus erythematosus with promising results).

Pyruvate kinase isoform M2 impairs cognition in systemic lupus erythematosus by promoting microglial synaptic pruning via the β-catenin signaling pathway

BACKGROUND

Neuropsychiatric systemic lupus erythematosus (NPSLE) is a severe complication, which involves pathological damage to the brain and cognitive function. However, its exact mechanism of action still remains unclear. In this study, we explored the role of microglia in the cognitive dysfunction of NPSLE mice. We also analyzed and compared the metabolites in the hippocampal tissues of the lupus model and control mice.

METHODS

MRL/MpJ-Fas^lpr (MRL/lpr) female mice were used as the NPSLE mouse model. Metabolomics was used to assess hippocampal glycolysis levels. Glucose, lactic acid, IL-6, and IL-1β of the hippocampus were detected by ELISA. Based on the glycolysis pathway, we found that pyruvate kinase isoform M2 (PKM2) in the hippocampus was significantly increased. Thus, the expression of PKM2 was detected by qRT-PCR and Western blotting, and the localization of PKM2 in microglia (IBA-1⁺) or neurons (NeuN⁺) was assessed by immunofluorescence staining. Flow cytometry was used to detect the number and phenotype of microglia; the changes in microglial phagocytosis and the β-catenin signaling pathway were detected in BV2 cells overexpressing PKM2. For in vivo experiments, MRL/lpr mice were treated with AAV9-shPKM2. After 2 months, Morris water maze and conditional fear tests were applied to investigate the cognitive ability of mice; H&E and immunofluorescence staining were used to evaluate brain damage; flow cytometry was used to detect the phenotype and function of microglia; neuronal synapse damage was monitored by qRT-PCR, Western blotting, and immunofluorescence staining.

RESULTS

Glycolysis was elevated in the hippocampus of MRL/lpr lupus mice, accompanied by increased glucose consumption and lactate production. Furthermore, the activation of PKM2 in hippocampal microglia was observed in lupus mice. Cell experiments showed that PKM2 facilitated microglial activation and over-activated microglial phagocytosis via the β-catenin signaling pathway. In vivo, AAV9-shPKM2-treated mice showed decreased microglial activation and reduced neuronal synapses loss by blocking the β-catenin signaling pathway. Furthermore, the cognitive impairment and brain damage of MRL/lpr mice were significantly relieved after microglial PKM2 inhibition.

CONCLUSION

These data indicate that microglial PKM2 have potential to become a novel therapeutic target for treating lupus encephalopathy.

Hippocampal microglia CD40 mediates NPSLE cognitive dysfunction in mice

Neuropsychiatric systemic lupus erythematosus (NPSLE) is the most serious and complicated clinical manifestation of lupus erythematosus. Cognitive dysfunction is the most common symptom of NPSLE. A variety of potential mechanisms or mediators related to the pathogenesis of NPSLE cognitive dysfunction have been proposed. However, the involvement of microglia CD40 has not been reported yet. This study aimed to investigate whether hippocampal microglia CD40 of MRL/MpJ-Fas^lpr (MRL/lpr) mice was involved in NPSLE cognitive dysfunction. This study found, using quantitative polymerase chain reaction, western blotting and immunohistochemistry, that hippocampal CD40 was aberrantly overexpressed in the MRL/lpr lupus mice. It also determined using flow cytometry and immunofluorescence that the aberrantly overexpressed CD40 was mainly derived from hippocampal microglia. The adeno-associated virus was used to inhibit microglia CD40 expression, and the brain damage and cognitive dysfunction of MRL/lpr mice improved. Also, imiquimod (IMQ)-induced lupus mice had the same NPSLE cognitive dysfunction, brain damage, and overexpressed hippocampal microglia CD40 as MRL/lpr mice. Therefore, IMQ-induced lupus mouse was proposed as one of the mouse models for studying NPSLE cognitive dysfunction for the first time in this study. The findings indicated that hippocampal microglia CD40 was involved in the development of NPSLE cognitive dysfunction, thus providing a novel research direction for the study of the pathogenesis of NPSLE.

Cognitive Impairment in SLE: Mechanisms and Therapeutic Approaches

A wide range of patients with systemic lupus erythematosus (SLE) suffer from cognitive dysfunction (CD) which severely impacts their quality of life. However, CD remains underdiagnosed and poorly understood. Here, we discuss current findings in patients and in animal models. Strong evidence suggests that CD pathogenesis involves known mechanisms of tissue injury in SLE. These mechanisms recruit brain resident cells, in particular microglia, into the pathological process. While systemic immune activation is critical to central nervous system injury, the current focus of therapy is the microglial cell and not the systemic immune perturbation. Further studies are critical to examine additional potential therapeutic targets and more specific treatments based on the cause and progress of the disease.

A novel mouse model for checkpoint inhibitor-induced adverse events

Immune checkpoint inhibitors have demonstrated significant efficacy in the treatment of a variety of cancers, however their therapeutic potential is limited by abstruse immune related adverse events. Currently, no robust animal model exists of checkpoint inhibitor-induced adverse events. Establishing such a model will improve our mechanistic understanding of this process, which in turn will inform design of improved therapies. We developed a mouse model to determine inflammatory toxicities in response to dual checkpoint blockade in the presence of syngeneic tumors. Mice from susceptible genetic backgrounds received intraperitoneal injections of anti-mouse PD-1 and CTLA-4 antibodies. The mice were monitored for weight loss and histologic evidence of inflammation. Blood was collected for basic metabolic panels and titers of anti-nuclear antibodies. In parallel, mice were also treated with prednisolone, which is commonly used to treat immune related adverse events among cancer patients. Among all the genetic backgrounds, B6/lpr mice treated with anti-CTLA-4 and anti-PD-1 antibodies developed more substantial hepatitis, pancreatitis, colitis, and pneumonitis characterized by organ infiltration of immune cells. Mice that developed tissue infiltration demonstrated high serum levels of glucose and high titers of anti-nuclear antibodies. Finally, while administration of prednisolone prevented the development of the inflammatory adverse events, it also abrogated the protective anti-tumor effect of the checkout inhibitors. Genetic background and treatment modalities jointly modified the inflammatory adverse events in tumor bearing mice, suggesting a complex mechanism for checkpoint inhibitor-related inflammation. Future studies will assess additional genetic susceptibility factors and will examine possible contributions from the administration of other anti-inflammatory drugs.

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.

The T Cell Receptor Repertoire in Neuropsychiatric Systemic Lupus Erythematosus

Objective: In systemic lupus erythematosus (SLE), widespread T cell infiltration into target organs contributes to inflammation and organ damage. Autoreactive T cells become aberrantly activated in this disease due to dysfunctional T cell receptor signaling that lowers the activation threshold. Characterizing the T cell repertoire can provide further insight into the specific homing and proliferation of these T cells into lupus target organs. In the spontaneous lupus model, MRL/lpr, the TCR repertoire has not been fully elucidated, especially for T cells infiltrating the brain. Our aim was to investigate and compare the TCR repertoire between MRL/lpr mice and its congenic controls, MRL/MpJ, and within MRL/lpr tissues. Methods: Spleen, salivary gland, and brain choroid plexus were isolated from female MRL/lpr mice and MRL/MpJ mice. The TCRβ CDR3 region was analyzed by multiplex PCRs and sequencing. Results: Significant differences were seen not only between the MRL/lpr and MRL/MpJ spleens, but also between MRL/lpr tissues. The TCR repertoire in MRL/lpr choroid plexus tissues had significantly increased clonality and sequence homology compared to MRL/lpr spleen and salivary gland. The consensus sequence, CASSQDWGGYEQYFF, was identified in the MRL/lpr choroid plexus repertoire. Conclusions: The TCR repertoire in lupus prone mice is not uniform between target organs, and suggests that T cells are specifically recruited into the choroid plexus of MRL/lpr mice. Further studies are needed to determine the antigen specificities for these infiltrating T cells in target organs of lupus mice, and their possible contribution to the pathogenesis of neuropsychiatric disease and other lupus manifestations.

Using the Mouse to Model Human Diseases: Cognitive Impairment in Systemic Lupus Erythematosus

In this 2020 Dunlop-Dottridge Lecture, the authors discuss cognitive impairment (CI), one of the most prevalent neuropsychiatric syndromes in systemic lupus erythematosus (SLE). Patients often report CI as the most bothersome disease-related manifestation, with a great effect on their quality of life. Nevertheless, studies focusing on CI remain scarce and no effective targeted therapy has been identified. We herein present murine models of CI in SLE with insights into the pathogenesis of this condition as well as the role of the renin angiotensin system in microglial activation. We will discuss the role of neuroimaging as a useful objective assessment tool, describing our experience in previous and ongoing clinical trials of CI in patients with SLE.

Complex epigenetic patterns in cerebellum generated after developmental exposure to trichloroethylene and/or high fat diet in autoimmune-prone mice

Trichloroethylene (TCE) is an environmental contaminant associated with immune-mediated inflammatory disorders and neurotoxicity. Based on known negative effects of developmental overnutrition on neurodevelopment, we hypothesized that developmental exposure to high fat diet (HFD) consisting of 40% kcal fat would enhance neurotoxicity of low-level (6 μg per kg per day) TCE exposure in offspring over either stressor alone. Male offspring were evaluated at ∼6 weeks of age after exposure beginning 4 weeks preconception in the dams until weaning. TCE, whether used as a single exposure or together with HFD, appeared to be more robust than HFD alone in altering one-carbon metabolites involved in glutathione redox homeostasis and methylation capacity. In contrast, opposing effects of expression of key enzymes related to DNA methylation related to HFD and TCE exposure were observed. The mice generated unique patterns of anti-brain antibodies detected by western blotting attributable to both TCE and HFD. Taken together, developmental exposure to TCE and/or HFD appear to act in complex ways to alter brain biomarkers in offspring.

Unique primed status of microglia under the systemic autoimmune condition of lupus-prone mice

BACKGROUND

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of various autoantibodies. This disease causes disabling neuropsychiatric symptoms even in the absence of apparent inflammation in the central nervous system (CNS), but the mechanisms involved remain unknown. Innate immune-mediated inflammation has attracted attention as a pathogenic mechanism in neuropsychiatric diseases.

METHODS

We investigated the CNS of lupus-prone mice focusing on innate immunity. Three strains of lupus-prone mice, FcγRIIB^-/-Yaa, an F1 hybrid of NZB and NZW (NZB/NZW) mice, and MRL/Fas^lpr (MRL/lpr) mice were used to analyze CNS immunopathology.

RESULTS

Flow cytometry analysis demonstrated the numbers of brain CD45⁺ cells were increased compared with controls in lupus-prone mice. Upregulation of MHC class I and PDCA1 was observed in microglia and CD11b⁺ myeloid cells of lupus-prone mice, indicating they were activated in response to interferons (IFN). Microglial gene expression analysis of FcγRIIB^-/-Yaa mice revealed the upregulation of IFN-responsive genes and inflammation-related genes including Axl, Clec7a, and Itgax, which were previously reported in neurodegenerative conditions and primed conditions. Upregulated chemokine gene expressions including Ccl5 and Cxcl10 were concurrent with increased numbers of T cells and monocytes, especially Ly6C^lo monocytes in the CNS. Upregulation of Axl, Clec7a, Itgax, Ccl5, and Cxcl10 was also observed in NZB/NZW mice, indicating common lupus pathology. The primed status of microglia in FcγRIIB^-/-Yaa mice was also demonstrated by morphological changes such as enlarged cell bodies with hypertrophic processes, and hyperreactivity to lipopolysaccharide. Immunohistochemistry of FcγRIIB^-/-Yaa mice indicated reactive responses of astrocytes and vascular endothelium. Behavioral studies of FcγRIIB^-/-Yaa mice revealed depressive-like behavior and heat hyperalgesia in the forced swim test and the tail-flick test, respectively.

CONCLUSIONS

Our data indicated that microglia in lupus exhibit a unique primed phenotype characterized by the upregulated expressions of neurodegeneration-related genes and IFN-responsive genes. Interaction with peripheral cells and brain resident cells was presumed to orchestrate neuroinflammation. Targeting innate immune cells, such as microglia and monocytes, may be a promising therapeutic approach for neuropsychiatric SLE.

Analysis of brain metabolites by gas chromatography-mass spectrometry reveals the risk-benefit concerns of prednisone in MRL/lpr lupus mice

OBJECTIVE

Neuropsychiatric systemic lupus erythematosus (NPSLE) is a common cause of disability in systemic lupus erythematosus (SLE). This study aims to investigate the metabolic changes in the hypothalamus and frontal cortex in lupus-prone MRL/lpr mice.

METHODS

Metabolic changes were analyzed using gas chromatography-mass spectrometry (GC-MS).

RESULTS

According to the principal component analysis (PCA), the metabolic profiles were different between the frontal cortex and hypothalamus, but they were comparable between MRL/lpr and MRL/MpJ mice (16 weeks of age). By OPLS-DA, eight cortical and six hypothalamic differential metabolites were identified in MRL/lpr as compared to MRL/MpJ mice. Among these differential metabolites, we found a decrease of N-acetyl-L-aspartate (NAA, a potential marker of neuronal integrity), an increase of pyruvate and a decrease of glutamate in the frontal cortex but not in the hypothalamus. Prednisone treatment (3 mg/kg from 8 weeks of age) relieved the decrease of NAA but further increased the accumulation of pyruvate in the frontal cortex, additionally affected eight enriched pathways in the hypothalamus, and led to significant imbalances between the excitation and inhibition in both the frontal cortex and hypothalamus.

CONCLUSION

These results suggest that the frontal cortex may be more preferentially affected than the hypothalamus in SLE. Prednisone disrupted rather than relieved metabolic abnormalities in the brain, especially in the hypothalamus, indicating that the risk-benefit balance of prednisone for SLE or NPSLE remains to be further evaluated.

Cognitive Dysfunction in Systemic Lupus Erythematosus: A Case for Initiating Trials

Cognitive dysfunction (CD) is an insidious and underdiagnosed manifestation of systemic lupus erythematosus (SLE) that has a considerable impact on quality of life, which can be devastating. Given the inconsistencies in the modes of assessment and the difficulties in attribution to SLE, the reported prevalence of CD ranges from 5% to 80%. Although clinical studies of SLE-related CD have been hampered by heterogeneous subject populations and a lack of sensitive and standardized cognitive tests or other validated objective biomarkers for CD, there are, nonetheless, strong data from mouse models and from the clinical arena that show CD is related to known disease mechanisms. Several cytokines, inflammatory molecules, and antibodies have been associated with CD. Proposed mechanisms for antibody- and cytokine-mediated neuronal injury include the abrogation of blood-brain barrier integrity with direct access of soluble molecules in the circulation to the brain and ensuing neurotoxicity and microglial activation. No treatments for SLE-mediated CD exist, but potential candidates include agents that inhibit microglial activation, such as angiotensin-converting enzyme inhibitors, or that protect blood-brain barrier integrity, such as C5a receptor blockers. Structural and functional neuroimaging data have shown a range of regional abnormalities in metabolism and white matter microstructural integrity in SLE patients that correlate with CD and could in the future become diagnostic tools and outcome measures in clinical trials aimed at preserving cognitive function in SLE.

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.

Tertiary lymphoid structures in the choroid plexus in neuropsychiatric lupus

The central nervous system manifestations of systemic lupus erythematosus (SLE) remain poorly understood. Given the well-defined role of autoantibodies in other lupus manifestations, extensive work has gone into the identification of neuropathic autoantibodies. However, attempts to translate these findings to patients with SLE have yielded mixed results. We used the MRL/MpJ-Faslpr/lpr mouse, a well-established, spontaneous model of SLE, to establish the immune effectors responsible for brain disease. Transcriptomic analysis of the MRL/MpJ-Faslpr/lpr choroid plexus revealed an expression signature driving tertiary lymphoid structure formation, including chemokines related to stromal reorganization and lymphocyte compartmentalization. Additionally, transcriptional profiles indicated various stages of lymphocyte activation and germinal center formation. The extensive choroid plexus infiltrate present in MRL/MpJ-Faslpr/lpr mice with overt neurobehavioral deficits included locally proliferating B and T cells, intercellular interactions between lymphocytes and antigen-presenting cells, as well as evidence for in situ somatic hypermutation and class switch recombination. Furthermore, the choroid plexus was a site for trafficking lymphocytes into the brain. Finally, histological evaluation in human lupus patients with neuropsychiatric manifestations revealed increased leukocyte migration through the choroid plexus. These studies identify a potential new pathway underlying neuropsychiatric lupus and support tertiary lymphoid structure formation in the choroid plexus as a novel mechanism of brain-immune interfacing.

Limited preventive effect of prednisone on neuropsychiatric symptoms in murine systemic lupus erythematosus

OBJECTIVE

To investigate whether glucocorticoids, the hallmark medication for systemic lupus erythematosus (SLE), could prevent the development of neuropsychiatric SLE (NPSLE).

METHODS

The protective effects of prednisone on NPSLE were tested using the open field, object recognition/placement, forced swim, tail suspension, and sucrose preference tests in MRL/lpr mice. Auto-antibody titres and the weight of lymph nodes were also measured.

RESULTS

MRL/lpr mice exhibited mild depression at the age of 8 weeks before progressing with spatial cognitive impairment and severe depression-like behaviour at the age of 16 weeks. Treating MRL/lpr mice with prednisone (5 mg/kg) from the age of 8 weeks decreased anti-cardiolipin and anti-N-methyl-D-aspartate (NMDA) receptor antibody titres in the brain, reduced the weight of lymph nodes, and prolonged the floating latency in the forced swim test. However, prednisone (3 or 5 mg/kg) had no preventive effect on the development of spatial cognitive impairment and other depression-like behaviours in MRL/lpr mice. The dose of prednisone had a positive correlation with the floating latency in the forced swim test, while it offered no effects on all other behavioural tests.

CONCLUSION

Our results provide evidence that early treatment with prednisone had a limited effect on the development of neuropsychiatric symptoms in MRL/lpr mice. Further work is needed in other models beyond NPSLE in MRL/lpr mice before any definitive conclusions are made on the efficacy of prednisone in human NPSLE.

Diminished responses to monoaminergic antidepressants but not ketamine in a mouse model for neuropsychiatric lupus

BACKGROUND

A significant proportion of patients suffering from major depression fail to remit following treatment and develop treatment-resistant depression. Developing novel treatments requires animal models with good predictive validity. MRL/lpr mice, an established model of systemic lupus erythematosus, show depression-like behavior.

AIMS

We evaluated responses to classical antidepressants, and associated immunological and biochemical changes in MRL/lpr mice.

METHODS AND RESULTS

MRL/lpr mice showed increased immobility in the forced swim test, decreased wheel running and sucrose preference when compared with the controls, MRL/MpJ mice. In MRL/lpr mice, acute fluoxetine (30 mg/kg, intraperitoneally (i.p.)), imipramine (10 mg/kg, i.p.) or duloxetine (10 mg/kg, i.p.) did not decrease the immobility time in the Forced Swim Test. Interestingly, acute administration of combinations of olanzapine (0.03 mg/kg, subcutaneously)+fluoxetine (30 mg/kg, i.p.) or bupropion (10 mg/kg, i.p.)+fluoxetine (30 mg/kg, i.p.) retained efficacy. A single dose of ketamine but not three weeks of imipramine (10 mg/kg, i.p.) or escitalopram (5 mg/kg, i.p.) treatment in MRL/lpr mice restored sucrose preference. Further, we evaluated inflammatory, immune-mediated and neuronal mechanisms. In MRL/lpr mice, there was an increase in autoantibodies' titers, [3H]PK11195 binding and immune complex deposition. There was a significant infiltration of the brain by macrophages, neutrophils and T-lymphocytes. p11 mRNA expression was decreased in the prefrontal cortex. Further, there was an increase in the 5-HT_2aR expression, plasma corticosterone and indoleamine 2,3-dioxygenase activity.

CONCLUSION

In summary, the MRL/lpr mice could be a useful model for Treatment Resistant Depression associated with immune dysfunction with potential to expedite antidepressant drug discovery.

Laboratory and Neuroimaging Biomarkers in Neuropsychiatric Systemic Lupus Erythematosus: Where Do We Stand, Where To Go?

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by multi-systemic involvement. Nervous system involvement in SLE leads to a series of uncommon and heterogeneous neuropsychiatric (NP) manifestations. Current knowledge on the underlying pathogenic processes and their subsequent pathophysiological changes leading to NP-SLE manifestations is incomplete. Several putative laboratory biomarkers have been proposed as contributors to the genesis of SLE-related nervous system damage. Alongside the laboratory biomarkers, several neuroimaging tools have shown to reflect the nature of tissue microstructural damage associated with SLE, and thus were suggested to contribute to the understanding of the pathophysiological changes and subsequently help in clinical decision making. However, the number of useful biomarkers in NP-SLE in clinical practice is disconcertingly modest. In some cases it is not clear whether the biomarker is truly involved in pathogenesis, or the result of non-specific pathophysiological changes in the nervous system (e.g., neuroinflammation) or whether it is the consequence of a concomitant underlying abnormality related to SLE activity. In order to improve the diagnosis of NP-SLE and provide a better targeted care to these patients, there is still a need to develop and validate a range of biomarkers that reliably capture the different aspects of disease heterogeneity. This article critically reviews the current state of knowledge on laboratory and neuroimaging biomarkers in NP-SLE, discusses the factors that need to be addressed to make these biomarkers suitable for clinical application, and suggests potential future research paths to address important unmet needs in the NP-SLE field.

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.