Opposite Regulation of Homer Signal at the NMJ Postsynaptic Micro Domain between Slow- and Fast-Twitch Muscles in an Experimentally Induced Autoimmune Myasthenia Gravis (EAMG) Mouse Model.

Accelerated postsynaptic remodelling and disturbance of neuromuscular transmission are common features of autoimmune neurodegenerative diseases. Homer protein isoform expression, crosslinking activity and neuromuscular subcellular localisation are studied in mouse hind limb muscles of an experimentally induced autoimmune model of Myasthenia Gravis (EAMG) and correlated to motor end plate integrity. Soleus (SOL), extensor digitorum longus (EDL) and gastrocnemius (GAS) skeletal muscles are investigated. nAChR membrane clusters were studied to monitor neuromuscular junction (NMJ) integrity. Fibre-type cross-sectional area (CSA) analysis is carried out in order to determine the extent of muscle atrophy. Our findings clearly showed that crosslinking activity of Homer long forms (Homer 1b/c and Homer2a/b) are decreased in slow-twitch and increased in fast-twitch muscle of EAMG whereas the short form of Homer that disrupts Homer crosslinking (Homer1a) is upregulated in slow-twitch muscle only. Densitometry analysis showed a 125% increase in Homer protein expression in EDL, and a 45% decrease in SOL of EAMG mice. In contrast, nAChR fluorescence pixel intensity decreased in endplates of EAMG mice, more distinct in type-I dominant SOL muscle. Morphometric CSA of EAMG vs. control (CTR) revealed a significant reduction in EDL but not in GAS and SOL. Taken together, these results indicate that postsynaptic Homer signalling is impaired in slow-twitch SOL muscle from EAMG mice and provide compelling evidence suggesting a functional coupling between Homer and nAChR, underscoring the key role of Homer in skeletal muscle neurophysiology.

Selective depletion of plasma cells in vivo based on the specificity of their secreted antibodies.

Antibody-mediated diseases affect more than 10% of the human population. For most, no cure is available, particularly when the pathogenic antibodies are secreted by long-lived plasma cells resistant to conventional immunosuppressive therapies. Current therapeutic approaches target not only the plasma cells that secrete pathogenic antibodies, but also those providing protective antibodies. Here, in a murine model bearing long-lived plasma cells secreting anti-OVA and -chicken gamma globulin (CGG) antibodies, we describe the first-time use of an antigen-antibody (OVA/anti-CD138 antibody) conjugate for in vivo labeling and selective ablation of plasma cells that secrete antibodies specific for the antigen OVA. The selective depletion also led to a stable reduction of the corresponding serum anti-OVA antibody levels. In contrast, CGG-specific plasma cells and circulating anti-CGG antibody levels remained unchanged. The method described here should enable the development of unique causative treatment strategies for established antibody-mediated diseases sparing humoral immunity.

S1P receptor antagonists fingolimod and siponimod do not improve the outcome of experimental autoimmune myasthenia gravis mice after disease onset.

Myasthenia gravis (MG) is an autoimmune disease characterized by muscle weakness and fatigue in the presence of circulating antibodies against components of the neuromuscular junction. Most patients have a good prognosis, but some are refractory to standard-of-care immunosuppressive treatment and suffer from recurrent myasthenic crises. Functional sphingosine-1-phosphate (S1P) antagonists like fingolimod and siponimod (BAF312) are successfully used for the treatment of multiple sclerosis, and fingolimod was shown to prevent the development of myasthenic symptoms in experimental autoimmune myasthenia gravis (EAMG), the standard model of MG. Here, we investigated whether fingolimod or siponimod improves outcome in EAMG mice when administered after disease onset, modeling the clinical setting in human MG. Both S1P antagonists inhibited lymphocyte egress, resulting in peripheral lymphopenia. After stimulation, there were differences in T-cell responses, but no change in either antibody titers or total or antigen-specific plasma cell populations after treatment. Most importantly, disease incidence and severity were not influenced by fingolimod or siponimod therapy. Although fingolimod and siponimod did lead to subtle changes in T-cell responses, they had no significant effect on antibody titers and disease severity. In conclusion, our data show no evidence of a therapeutic potential for S1P receptor antagonists in MG treatment.

IL-17-producing CD4(+) T cells contribute to the loss of B-cell tolerance in experimental autoimmune myasthenia gravis.

The role of Th17 cells in the pathogenesis of autoantibody-mediated diseases is unclear. Here, we assessed the contribution of Th17 cells to the pathogenesis of experimental autoimmune myasthenia gravis (EAMG), which is induced by repetitive immunizations with Torpedo californica acetylcholine receptor (tAChR). We show that a significant fraction of tAChR-specific CD4(+) T cells is producing IL-17. IL-17(ko) mice developed fewer or no EAMG symptoms, although the frequencies of tAChR-specific CD4(+) T cells secreting IL-2, IFN-γ, or IL-21, and the percentage of FoxP3(+) Treg cells were similar to WT mice. Even though the total anti-tAChR antibody levels were equal, the complement fixating IgG2b subtype was reduced in IL-17(ko) as compared to WT mice. Most importantly, pathogenic anti-murine AChR antibodies were significantly lower in IL-17(ko) mice. Furthermore, we confirmed the role of Th17 cells in EAMG pathogenesis by the reconstitution of TCR ß/δ(ko) mice with WT or IL-17(ko) CD4(+) T cells. In conclusion, we show that the level of IgG2b and the loss of B-cell tolerance, which results in pathogenic anti-murine AChR-specific antibodies, are dependent on IL-17 production by CD4(+) T cells. Thus, we describe here for the first time how Th17 cells are involved in the induction of classical antibody-mediated autoimmunity.

Minocycline rescues decrease in neurogenesis, increase in microglia cytokines and deficits in sensorimotor gating in an animal model of schizophrenia.

Adult neurogenesis in the hippocampus is impaired in schizophrenic patients and in an animal model of schizophrenia. Amongst a plethora of regulators, the immune system has been shown repeatedly to strongly modulate neurogenesis under physiological and pathological conditions. It is well accepted, that schizophrenic patients have an aberrant peripheral immune status, which is also reflected in the animal model. The microglia as the intrinsic immune competent cells of the brain have recently come into focus as possible therapeutic targets in schizophrenia. We here used a maternal immune stimulation rodent model of schizophrenia in which polyinosinic-polycytidilic acid (Poly I:C) was injected into pregnant rats to mimic an anti-viral immune response. We identified microglia IL-1ß and TNF-α increase constituting the factors correlating best with decreases in net-neurogenesis and impairment in pre-pulse inhibition of a startle response in the Poly I:C model. Treatment with the antibiotic minocycline (3mg/kg/day) normalized microglial cytokine production in the hippocampus and rescued neurogenesis and behavior. We could also show that enhanced microglial TNF-α and IL-1ß production in the hippocampus was accompanied by a decrease in the pro-proliferative TNFR2 receptor expression on neuronal progenitor cells, which could be attenuated by minocycline. These findings strongly support the idea to use anti-inflammatory drugs to target microglia activation as an adjunctive therapy in schizophrenic patients.

Glioma-associated microglia/macrophages display an expression profile different from M1 and M2 polarization and highly express Gpnmb and Spp1.

Malignant glioma belong to the most aggressive neoplasms in humans with no successful treatment available. Patients suffering from glioblastoma multiforme (GBM), the highest-grade glioma, have an average survival time of only around one year after diagnosis. Both microglia and peripheral macrophages/monocytes accumulate within and around glioma, but fail to exert effective anti-tumor activity and even support tumor growth. Here we use microarray analysis to compare the expression profiles of glioma-associated microglia/macrophages and naive control cells. Samples were generated from CD11b+ MACS-isolated cells from naïve and GL261-implanted C57BL/6 mouse brains. Around 1000 genes were more than 2-fold up- or downregulated in glioma-associated microglia/macrophages when compared to control cells. A comparison with published data sets of M1, M2a,b,c-polarized macrophages revealed a gene expression pattern that has only partial overlap with any of the M1 or M2 gene expression patterns. Samples for the qRT-PCR validation of selected M1 and M2a,b,c-specific genes were generated from two different glioma mouse models and isolated by flow cytometry to distinguish between resident microglia and invading macrophages. We confirmed in both models the unique glioma-associated microglia/macrophage phenotype including a mixture of M1 and M2a,b,c-specific genes. To validate the expression of these genes in human we MACS-isolated CD11b+ microglia/macrophages from GBM, lower grade brain tumors and control specimens. Apart from the M1/M2 gene analysis, we demonstrate that the expression of Gpnmb and Spp1 is highly upregulated in both murine and human glioma-associated microglia/macrophages. High expression of these genes has been associated with poor prognosis in human GBM, as indicated by patient survival data linked to gene expression data. We also show that microglia/macrophages are the predominant source of these transcripts in murine and human GBM. Our findings provide new potential targets for future anti-glioma therapy.