Altered receptor binding densities in experimental antiphospholipid syndrome despite only moderately enhanced autoantibody levels and absence of behavioral features

[Mental disorders and cognitive impairment in patients with antiphospholipid syndrome]

Mental disorders (mainly anxiety and depressive disorders) and cognitive impairment are often found in patients with antiphospholipid syndrome (APS), but their prevalence, structure, and mechanisms of occurrence are not well researched. The review provides literature data on the frequency, spectrum and possible causes of mental disorders and cognitive impairment in patients with APS, the pathogenetic mechanisms of these disorders (in particular, the important role of antiphospholipid antibodies, stress factors, chronic inflammation), the relationship between APS, mental disorders and as well as cognitive impairment is examined. Special attention is paid to the influence of mental disorders and cognitive impairment on patients adherence to treatment, their quality of life, as well as the particularities of psychopharmacotherapy of mental disorders in patients with APS. The aim of the review is to actualize the interdisciplinary problem of mental disorders and cognitive impairment in patients with APS and the need to introduce a partnership model of care.

Serotonin: A Potent Immune Cell Modulator in Autoimmune Diseases

Serotonin, also known as 5-hydroxytryptamine (5-HT) is a signaling mediator that regulates emotion, behavior, and cognition. Previous studies have focused more on the roles of 5-HT in the central nervous system (CNS). However, 5-HT also shares a strong relationship with the pathological cases of tumor, inflammation, and pathogen infection. 5-HT participates in tumor cell migration, metastatic dissemination, and angiogenesis. In addition, 5-HT affects immune regulation via different 5-HT receptors (5-HTRs) expressed immune cells, including both innate and adaptive immune system. Recently, drugs targeting at 5-HT signaling were tested to be beneficial in mouse models and clinical trials of multiple sclerosis (MS) and inflammatory bowel disease (IBD). Thus, it is reasonable to assume that 5-HT participates in the pathogenesis of autoimmune diseases. However, the underlying mechanism by 5-HT modulates the development of autoimmune diseases has not been fully understood. Based on our previous studies and pertinent literature, we provide circumstantial evidence for an essential role of 5-HT, especially the regulation of 5-HT on immune cells in the pathogenesis of autoimmune diseases, which may provide a new point cut for the treatment of autoimmune diseases.

Decreased hippocampal cell proliferation in mice with experimental antiphospholipid syndrome

The antiphospholipid syndrome (APS) is an autoimmune disease characterized by the presence of antiphospholipid antibodies, which may trigger vascular thrombosis with consecutive infarcts. However, cognitive dysfunctions representing one of the most commonest neuropsychiatric symptoms are frequently present despite the absence of any ischemic brain lesions. Data on the structural and functional basis of the neuropsychiatric symptoms are sparse. To examine the effect of APS on hippocampal neurogenesis and on white matter, we induced experimental APS (eAPS) in adult female Balb/C mice by immunization with β2-glycoprotein 1. To investigate cell proliferation in the dentate gyrus granular cell layer (DG GCL), eAPS and control mice (n = 5, each) were injected with 5-bromo-2'-deoxyuridine (BrdU) once a day for 10 subsequent days. Sixteen weeks after immunization, eAPS resulted in a significant reduction of BrdU-positive cells in the DG GCL compared to control animals. However, double staining with doublecortin and NeuN revealed a largely preserved neurogenesis. Ultrastructural analysis of corpus callosum (CC) axons in eAPS (n = 6) and control mice (n = 7) revealed no significant changes in CC axon diameter or g-ratio. In conclusion, decreased cellular proliferation in the hippocampus of eAPS mice indicates a limited regenerative potential and may represent one neuropathological substrate of cognitive changes in APS while evidence for alterations of white matter integrity is lacking.

Cross-reactivity between annexin A2 and Beta-2-glycoprotein I in animal models of antiphospholipid syndrome

Antiphospholipid syndrome (APS) affects coagulation and the brain by autoimmune mechanisms. The major antigen in APS is beta-2-glycoprotein I (β2-GPI) is known to complex with annexin A2 (ANXA2), and antibodies to ANXA2 have been described in APS. We measured these antibodies in mice with experimental APS (eAPS) induced by immunization with β2-GPI. Sera of these mice reacted significantly with recombinant ANXA2 by enzyme-linked immunosorbent assay (ELISA) and the eAPS mice had significantly high levels of immunoglobulin G (IgG) in the brain by immunoblot assays compared to adjuvant immunized controls. Immunoprecipitation performed by mixing eAPS brain tissue with protein-G beads resulted in identification of two autoantigens unique to the eAPS group, one of which was ANXA2. In order to study more directly and methodically the specific role of anti-ANXA2 antibodies in APS, we immunized mice with β2-GPI which contained no ANXA2 or with ANXA2 and measured antibodies to these proteins. Levels of antibodies to ANXA2 measured by ELISA were 0.72 ± 0.007 arbitrary units (a.u), 0.24 ± 0.03 and 0.02 ± 0.01 a.u for sera from ANXA2, β2-GPI and control mice, respectively (p < 0.0001 and p = 0.037 for the comparison of the ANXA2 and β2-GPI groups to the controls). Purified IgG from β2-GPI sera did not show cross-binding with ANXA2. Antibodies to β2-GPI and phospholipids were found in the β2-GPI immunized group only. The present study suggests an immune response to the β2-GPI-ANXA2 complex in eAPS and provides a novel ANXA2 immunization model which will serve to study the role of ANXA2 antibodies in of APS.

Neuronal Growth and Behavioral Alterations in Mice Deficient for the Psychiatric Disease-Associated Negr1 Gene

Neuronal growth regulator 1 (NEGR1), a member of the immunoglobulin superfamily cell adhesion molecule subgroup IgLON, has been implicated in neuronal growth and connectivity. In addition, genetic variants in or near the NEGR1 locus have been associated with obesity and more recently with learning difficulties, intellectual disability and psychiatric disorders. However, experimental evidence is lacking to support a possible link between NEGR1, neuronal growth and behavioral abnormalities. Initial expression analysis of NEGR1 mRNA in C57Bl/6 wildtype (WT) mice by in situ hybridization demonstrated marked expression in the entorhinal cortex (EC) and dentate granule cells. In co-cultures of cortical neurons and NSC-34 cells overexpressing NEGR1, neurite growth of cortical neurons was enhanced and distal axons occupied an increased area of cells overexpressing NEGR1. Conversely, in organotypic slice co-cultures, Negr1-knockout (KO) hippocampus was less permissive for axons grown from EC of β-actin-enhanced green fluorescent protein (EGFP) mice compared to WT hippocampus. Neuroanatomical analysis revealed abnormalities of EC axons in the hippocampal dentate gyrus (DG) of Negr1-KO mice including increased numbers of axonal projections to the hilus. Neurotransmitter receptor ligand binding densities, a proxy of functional neurotransmitter receptor abundance, did not show differences in the DG of Negr1-KO mice but altered ligand binding densities to NMDA receptor and muscarinic acetylcholine receptors M1 and M2 were found in CA1 and CA3. Activity behavior, anxiety-like behavior and sensorimotor gating were not different between genotypes. However, Negr1-KO mice exhibited impaired social behavior compared to WT littermates. Moreover, Negr1-KO mice showed reversal learning deficits in the Morris water maze and increased susceptibility to pentylenetetrazol (PTZ)-induced seizures. Thus, our results from neuronal growth assays, neuroanatomical analyses and behavioral assessments provide first evidence that deficiency of the psychiatric disease-associated Negr1 gene may affect neuronal growth and behavior. These findings might be relevant to further evaluate the role of NEGR1 in cognitive and psychiatric disorders.

Rheumatic diseases and autoimmune vascular dementia

Vascular dementia (VD) comes second after Alzheimer's disease (AD) as a cause of impaired cognition. VD is not a specific nosological entity, but rather a syndrome encompassing a number of diseases caused by impaired supply of blood to the brain. Systemic autoimmune disorders such as systemic lupus erythematosus, rheumatoid arthritis, vasculitis and antiphospholipid syndrome (APS) can be associated with dementia. VD is often related to the presence of traditional cardiovascular risk factors, but it may also be associated with a host of disorders affecting the brain blood vessels, neuronal cells, or both. It is important to entertain in the differential diagnosis of VD, to recognize and to cure them accurately in order to preserve life's quality of our patients.

Mice with experimental antiphospholipid syndrome display hippocampal dysfunction and a reduction of dendritic complexity in hippocampal CA1 neurones

AIMS

The antiphospholipid syndrome (APS) is an autoimmune disease characterized by high titres of auto-antibodies (aPL) leading to thrombosis and consequent infarcts. However, many affected patients develop neurological symptoms in the absence of stroke. Similarly, in a mouse model of this disease (eAPS), animals consistently develop behavioural abnormalities despite lack of ischemic brain injury. Therefore, the present study was designed to identify structural alterations of hippocampal neurones underlying the neurological symptoms in eAPS.

METHODS

Adult female Balb/C mice were subjected to either induction of eAPS by immunization with β2-Glycoprotein 1 or to a control group. After sixteen weeks animals underwent behavioural and cognitive testing using Staircase test (experiment 1 and 2) and Y-maze alternation test (experiment 1) and were tested for serum aPL levels (both experiments). Animals of experiment 1 (n = 7/group) were used for hippocampal neurone analysis using Golgi-Cox staining. Animals of experiment 2 (n = 7/group) were used to analyse molecular markers of total dendritic integrity (MAP2), presynaptic plasticity (synaptobrevin 2/VAMP2) and dendritic spines (synaptopodin) using immunohistochemistry.

RESULTS

eAPS mice developed increased aPL titres and presented with abnormal behaviour and impaired short term memory. Further, they revealed a reduction of dendritic complexity of hippocampal CA1 neurones as reflected by decreased dendritic length, arborization and spine density, respectively. Additional decrease of the spine-associated protein expression of Synaptopodin points to dendritic spines as major targets in the pathological process.

CONCLUSION

Reduction of hippocampal dendritic complexity may represent the structural basis for the behavioural and cognitive abnormalities of eAPS mice.