Experimental Investigations of Monomethyl and Dimethyl Fumarate in an Astrocyte-Microglia Co-Culture Model of Inflammation.

INTRODUCTION: Multiple sclerosis (MS) is the most common chronic inflammatory, demyelinating disease of the central nervous system. Dimethyl fumarate (DMF) and monomethyl fumarate (MMF) belong to the disease-modifying drugs in treatment of MS. There is evidence that astrocytes and microglia are involved in MS pathology, but few studies are available about MMF and DMF effects on astrocytes and microglia. The aim of this study was to investigate the effects of MMF and DMF on microglial activation and morphology as well as potential effects on glial viability, Cx43, and AQP4 expressions in different set-ups of an in vitro astrocyte-microglia co-culture model of inflammation. METHODS: Primary rat glial co-cultures of astrocytes containing 5% (M5, mimicking "physiological" conditions) or 30% (M30, mimicking "pathological, inflammatory" conditions) of microglia were treated with different concentrations of MMF (0.1, 0.5, and 2 µg/mL) or DMF (1.5, 5, and 15 µM) for 24 h. Viability, proliferation, and cytotoxicity of glial cells were examined using MTT assay. Immunocytochemistry was performed to analyze the microglial phenotypes. Connexin 43 (Cx43) and aquaporin 4 (AQP4) expressions were quantified by immunoblot analysis. RESULTS: Treatment with different concentrations of MMF or DMF for 24 h did not change the glial cell viability in M5 and M30 co-cultures. Microglial phenotypes were not altered by DMF under physiological M5 conditions, but treatment with higher concentration of DMF (15 µM) induced microglial activation under inflammatory M30 conditions. Incubation with different concentrations of MMF had no effects on microglial phenotypes. The Cx43 expression in M5 and M30 co-cultures was not changed significantly by immunoblot analysis after incubation with different concentrations of DMF or MMF for 24 h. The AQP4 expression was significantly increased in M5 co-cultures after incubation with 5 µm DMF. Under the other conditions, AQP4 expression was not affected by DMF or MMF. DISCUSSION: In different set-ups of the astrocyte-microglia co-culture model of inflammation, MMF has not shown significant effects. DMF had only limited effects on microglia phenotypes and AQP4 expression. In summary, mechanisms of action of fumarates probably do not involve direct effects on microglia phenotypes as well as Cx43 and AQP4 expression.

Fumaric Acids Directly Influence Gene Expression of Neuroprotective Factors in Rodent Microglia.

Dimethylfumarate (DMF) has been approved the for treatment of relapsing-remitting multiple sclerosis. The mode of action of DMF and its assumed active primary metabolite monomethylfumarate (MMF) is still not fully understood, notably for brain resident cells. Therefore we investigated potential direct effects of DMF and MMF on microglia and indirect effects on oligodendrocytes. Primary rat microglia were differentiated into M1-like, M2-like and M0 phenotypes and treated in vitro with DMF or MMF. The gene expression of pro-inflammatory and anti-inflammatory factors such as growth factors (IGF-1), interleukins (IL-10, IL-1ß), chemokines (CCl3, CXCL-10) as well as cytokines (TGF-1ß, TNFα), iNOS, and the mannose receptor (MRC1) was examined by determining their transcription level with qPCR, and on the protein level by ELISA and FACS analysis. Furthermore, microglia function was determined by phagocytosis assays and indirect effects on oligodendroglial proliferation and differentiation. DMF treatment of M0 and M1-like polarized microglia demonstrated an upregulation of gene expression for IGF-1 and MRC1, but not on the protein level. While the phagocytic activity remained unchanged, DMF and MMF treated microglia supernatants led to an enhanced proliferation of oligodendrocyte precursor cells (OPC). These results suggest that DMF has anti-inflammatory effects on microglia which may result in enhanced proliferation of OPC.

Delayed Demyelination and Impaired Remyelination in Aged Mice in the Cuprizone Model.

To unravel the failure of remyelination in multiple sclerosis (MS) and to test promising remyelinating treatments, suitable animal models like the well-established cuprizone model are required. However, this model is only standardized in young mice. This does not represent the typical age of MS patients. Furthermore, remyelination is very fast in young mice, hindering the examination of effects of remyelination-promoting agents. Thus, there is the need for a better animal model to study remyelination. We therefore aimed to establish the cuprizone model in aged mice. 6-month-old C57BL6 mice were fed with different concentrations of cuprizone (0.2-0.6%) for 5-6.5 weeks. De- and remyelination in the medial and lateral parts of the corpus callosum were analyzed by immunohistochemistry. Feeding aged mice 0.4% cuprizone for 6.5 weeks resulted in the best and most reliable administration scheme with virtually complete demyelination of the corpus callosum. This was accompanied by a strong accumulation of microglia and near absolute loss of mature oligodendrocytes. Subsequent remyelination was initially robust but remained incomplete. The remyelination process in mature adult mice better represents the age of MS patients and offers a better model for the examination of regenerative therapies.

Investigation of Neuregulin-1 and Glial Cell-Derived Neurotrophic Factor in Rodent Astrocytes and Microglia.

Growth factors play a crucial role during de- and remyelination of the central nervous system (CNS) due to their neurotrophic functions. We have previously shown that the growth factors neuregulin-1 (Nrg-1) and glial cell-derived neurotrophic factor (Gdnf) are upregulated during the first 2 weeks after induction of toxic demyelination in the CNS. Nevertheless, the factors responsible for Nrg-1/Gdnf upregulation and their effects on glia cells are unknown. We investigated the effect on Nrg-1 and Gdnf expressions after stimulation of primary mouse microglia or astrocytes with various pro- and anti-inflammatory factors. Additionally, primary cells were incubated with NRG-1 and/or GDNF followed by determining the gene expression level of their receptors, chemokines, and other growth factors. We demonstrate that inflammatory stimuli have a distinct impact on the expression of Gdnf, Nrg-1, and their receptors in astrocytes and microglia. In microglia, LPS or simultaneous treatment with IFNγ plus TNFα led to downregulation of Nrg-1, whereas LPS treatment slightly increased Nrg-1 expression in astrocytes. Furthermore, Gdnf was slightly upregulated after TFG-ß treatment in microglia, while Gdnf was significantly upregulated after LPS treatment in astrocytes. In contrast, treatment with GDNF or/and NRG-1 did not alter any measured gene expression in microglia or astrocytes. Taken together, our in vitro studies show that Nrg-1, Gdnf, and their receptors are differently regulated in astrocytes and microglia upon inflammatory stimuli. The lack of response of astrocytes and microglia to NRG-1 and GDNF suggests that both factors exert their effects directly on neurons.

Correction to: Investigation of Neuregulin-1 and Glial Cell-Derived Neurotrophic Factor in Rodent Astrocytes and Microglia.

The original version of this article unfortunately contained mistakes in the author group and affiliation sections. Author Markus H. Schwab's name was incorrectly presented as "H. Markus Schwab" and his affiliations were incorrectly assigned as "1 and 3" instead of "2 and 3".

Investigation of Cuprizone Inactivation by Temperature.

Animal models, such as cuprizone (bis-cyclohexanone oxaldihydrazone) feeding, are helpful to study experimental demyelination and remyelination in the context of diseases like multiple sclerosis. Cuprizone is a copper chelator, which when supplemented to the normal food of C57BL/6J mice in a concentration of 0.2% leads to oligodendroglial loss, subsequent microglia and astrocyte activation, resulting in demyelination. Termination of the cuprizone diet results in remyelination, promoted by newly formed mature oligodendrocytes. The exact mode of cuprizone's action is not well understood, and information about its inactivation and cleavage are still not available. The knowledge of these processes could lead to a better understanding of cuprizone's mode of action, as well as a safer handling of this toxin. We therefore performed experiments with the aim to inactivate cuprizone by thermal heating, since it was suggested in the past that cuprizone is heat sensitive. C57BL/6J mice were fed for 4 weeks with 0.2% cuprizone, either thermally pretreated (60, 80, 105, 121 °C) or not heated. In addition, primary rat oligodendrocytes, as a known selective toxic target of cuprizone, were incubated with 350 µM cuprizone solutions, which were either thermally pretreated or not. Our results demonstrate that none of the tested thermal pretreatment conditions could abrogate or restrict the toxic and demyelinating effects of cuprizone, neither in vitro nor in vivo. In conclusion, the current study rebuts the hypothesis of cuprizone as a heat-sensitive compound, as well as the assumption that heat exposure is a reason for an insufficient demyelination of cuprizone-containing pellets.

Low dose fumaric acid esters are effective in a mouse model of spontaneous chronic encephalomyelitis.

In this study we examined the role of fumaric acid esters (FAE) in a spontaneous and chronic animal model, the opticospinal EAE (OSE). Preventive treatment of dimethylfumarate (DMF) promotes onset of disease in animals treated with high dose DMF. This group also exhibited a significantly exacerbated disease course in a therapeutic treatment as compared to the low dose DMF approach, where less demyelination, macrophage infiltration, and increased Nrf2 expression in the spinal cord were observed. We conclude that low dose DMF treatment is effective in the therapy of the spontaneous opticospinal EAE model and mediates neuroprotective effects via the oxidative stress response pathway.

A pivotal role of nonmuscle myosin II during microglial activation.

Microglia are resident macrophages in the central nervous system (CNS) and the primary cells that contribute to CNS inflammation in many pathological conditions. Upon any signs of brain damage, microglia become activated and undergo tremendous cellular reorganization to adopt appropriate phenotypes. They migrate to lesion areas, accumulate, phagocytose cells or cellular debris, and produce a large array of inflammatory mediators like cytokines, chemokines, reactive oxygen species, and other mediators. To cope with the extreme cellular rearrangements during activation, microglia have to be highly dynamic. One major component of the cytoskeleton in nonmuscle cells is nonmuscle myosin II (NM II). This study was aimed to examine the functional role of NM II in resting and activated microglia. Using immunohistochemistry, we demonstrate strong expression of NM II isoform B (NM IIB) in microglia during cuprizone-induced demyelination as well as in cultured microglia. Treatment with the NM II inhibitor blebbistatin prevented the morphological shaping of microglial cells, led to functional deficits during chemokine-directed migration and phagocytosis, induced NM IIB redistribution, and affected actin microfilament patterning. In addition, inhibition of NM II led to an attenuated release of nitric oxide (NO), while TNFα secretion was not altered. In conclusion, we propose a pivotal role of NM II in cytoskeleton organization during microglial activation. This is of great importance to understand the mechanisms of microglial action in inflammatory CNS diseases.