Cortistatin is a cyclic-neuropeptide produced by brain cortex and immune cells that shows potent anti-inflammatory activity. In this article, we investigated the effect of cortistatin in two models of experimental autoimmune encephalomyelitis (EAE) that mirror chronic and relapsing-remitting multiple sclerosis. A short-term systemic treatment with cortistatin reduced clinical severity and incidence of EAE, the appearance of inflammatory infiltrates in spinal cord, and the subsequent demyelination and axonal damage. This effect was associated with a reduction of the two deleterious components of the disease, namely, the autoimmune and inflammatory response. Cortistatin decreased the presence/activation of encephalitogenic Th1 and Th17 cells in periphery and nervous system, and downregulated various inflammatory mediators, whereas it increased the number of regulatory T cells with suppressive effects on the encephalitogenic response. Moreover, cortistatin regulated glial activity and favored an active program of neuroprotection/regeneration. We further used cortistatin-deficient mice to investigate the role of endogenous cortistatin in the control of immune responses. Surprisingly, cortistatin-deficient mice were partially resistant to EAE and other inflammatory disorders, despite showing competent inflammatory/autoreactive responses. This unexpected phenotype was associated with elevated circulating glucocorticoids and an anxiety-like behavior. Our findings provide a powerful rationale for the assessment of the efficacy of cortistatin as a novel multimodal therapeutic approach to treat multiple sclerosis and identify cortistatin as a key endogenous component of neuroimmune system.

Activated microglia play a central role in the course of neurodegenerative diseases as they secrete cytotoxic substances which lead to neuronal cell death. Understanding the mechanisms that drive activation of microglia is essential to reverse this phenotype and to protect from neurodegeneration. With some exceptions, evidence indicates that changes in cell morphology from a star shape to a round and flat shape accompany the process of activation in microglia. In this study, we investigated the effect of adipose-tissue-derived mesenchymal stem cells (ASCs), which exert important anti-inflammatory actions, in microglia morphology. Microglia exposed to ASCs or their secreted factors (conditioned medium) underwent a cell shape change into a ramifying morphology in basal and inflammatory conditions, similar to that observed in microglia found in healthy brain. Colony-stimulating factor-1 secreted by ASCs played a critical role in the induction of this phenotype. Importantly, ASCs reversed the activated round phenotype induced in microglia by bacterial endotoxins. The ramifying morphology of microglia induced by ASCs was associated with a decrease of the proinflammatory cytokines tumor necrosis factor-α and interleukin-6, an increase in phagocytic activity, and the upregulation of neurotrophic factors and of Arginase-1, a marker for M2-like regulatory microglia. In addition, activation of the phosphoinositide-3-kinase/Akt pathway and the RhoGTPases Rac1 and Cdc42 played a major role in the acquisition of this phenotype. Therefore, these RhoGTPases emerge as key players in the ramification of microglia by anti-inflammatory agents like ASCs, being fundamental to maintain the tissue-surveying, central nervous system supporting state of microglia in healthy conditions.

Anti-N-methyl-d-aspartate receptor (NMDAR) encephalitis is an immune-mediated disease characterized by a complex neuropsychiatric syndrome in association with an antibody-mediated decrease of NMDAR. About 85% of patients respond to immunotherapy (and removal of an associated tumour if it applies), but it often takes several months or more than 1 year for patients to recover. There are no complementary treatments, beyond immunotherapy, to accelerate this recovery. Previous studies showed that SGE-301, a synthetic analogue of 24(S)-hydroxycholesterol, which is a potent and selective positive allosteric modulator of NMDAR, reverted the memory deficit caused by phencyclidine (a non-competitive antagonist of NMDAR), and prevented the NMDAR dysfunction caused by patients’ NMDAR antibodies in cultured neurons. An advantage of SGE-301 is that it is optimized for systemic delivery such that plasma and brain exposures are sufficient to modulate NMDAR activity. Here, we used SGE-301 to confirm that in cultured neurons it prevented the antibody-mediated reduction of receptors, and then we applied it to a previously reported mouse model of passive cerebroventricular transfer of patient’s CSF antibodies. Four groups were established: mice receiving continuous (14-day) infusion of patients’ or controls’ CSF, treated with daily subcutaneous administration of SGE-301 or vehicle (no drug). The effects on memory were examined with the novel object location test at different time points, and the effects on synaptic levels of NMDAR (assessed with confocal microscopy) and plasticity (long-term potentiation) were examined in the hippocampus on Day 18, which in this model corresponds to the last day of maximal clinical and synaptic alterations. As expected, mice infused with patient’s CSF antibodies, but not those infused with controls’ CSF, and treated with vehicle developed severe memory deficit without locomotor alteration, accompanied by a decrease of NMDAR clusters and impairment of long-term potentiation. All antibody-mediated pathogenic effects (memory, synaptic NMDAR, long-term potentiation) were prevented in the animals treated with SGE-301, despite this compound not antagonizing antibody binding. Additional investigations on the potential mechanisms related to these SGE-301 effects showed that (i) in cultured neurons SGE-301 prolonged the decay time of NMDAR-dependent spontaneous excitatory postsynaptic currents suggesting a prolonged open time of the channel; and (ii) it significantly decreased, without fully preventing, the internalization of antibody-bound receptors suggesting that additional, yet unclear mechanisms, contribute in keeping unchanged the surface NMDAR density. Overall, these findings suggest that SGE-301, or similar NMDAR modulators, could potentially serve as complementary treatment for anti-NMDAR encephalitis and deserve future investigations.

ObjectiveTo determine whether maternofetal transfer of NMDA receptor (NMDAR) antibodies has pathogenic effects on the fetus and offspring, we developed a model of placental transfer of antibodies.MethodsPregnant C57BL/6J mice were administered via tail vein patients' or controls' immunoglobulin G (IgG) on days 14–16 of gestation, when the placenta is able to transport IgG and the immature fetal blood-brain barrier is less restrictive to IgG crossing. Immunohistochemical and DiOlistic (gene gun delivery of fluorescent dye) staining, confocal microscopy, standardized developmental and behavioral tasks, and hippocampal long-term potentiation were used to determine the antibody effects.ResultsIn brains of fetuses, patients' IgG, but not controls' IgG, bound to NMDAR, causing a decrease in NMDAR clusters and cortical plate thickness. No increase in neonatal mortality was observed, but offspring exposed in utero to patients' IgG had reduced levels of cell-surface and synaptic NMDAR, increased dendritic arborization, decreased density of mature (mushroom-shaped) spines, microglial activation, and thinning of brain cortical layers II–IV with cellular compaction. These animals also had a delay in innate reflexes and eye opening and during follow-up showed depressive-like behavior, deficits in nest building, poor motor coordination, and impaired social-spatial memory and hippocampal plasticity. Remarkably, all these paradigms progressively improved (becoming similar to those of controls) during follow-up until adulthood.ConclusionsIn this model, placental transfer of patients' NMDAR antibodies caused severe but reversible synaptic and neurodevelopmental alterations. Reversible antibody effects may contribute to the infrequent and limited number of complications described in children of patients who develop anti-NMDAR encephalitis during pregnancy.