The online version of this article (doi:10.1186/s12974-017-0833-6) contains supplementary material, which is available to authorized users.
Stefanie Albrecht and Ann-Katrin Fleck are co-first authors who equally contributed to this paper.
Luisa Klotz and Tanja Kuhlmann are co-last authors who equally contributed to this paper.
The nuclear receptor farnesoid-X-receptor (FXR; NR1H4) is expressed not only in the liver, gut, kidney and adipose tissue but also in the immune cells. FXR has been shown to confer protection in several animal models of inflammation, including experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). FXR agonists are currently tested in clinical trials for treatment of human metabolic diseases. The beneficial effect of FXR agonists in EAE suggests that FXR might represent a potential target in inflammatory-demyelinating CNS diseases, such as MS. In MS, oligodendrocytes not only undergo cell death but also contribute to remyelination. This repair mechanism is impaired due to a differentiation block of oligodendroglial progenitor cells. Activation of other nuclear receptors that heterodimerize with FXR promote oligodendroglial differentiation. Therefore, we wanted to address the functional relevance of FXR for glial cells, especially for oligodendroglial differentiation.
We isolated primary murine oligodendrocytes from FXR-deficient (FXR Ko) and wild-type (WT) mice and determined the effect of FXR deficiency and activation on oligodendroglial differentiation by analysing markers of oligodendroglial progenitor cells (OPCs) and mature oligodendrocytes (OLs) using qRT-PCR and immunocytochemistry. Additionally, we determined whether FXR activation modulates the pro-inflammatory profile of astrocytes or microglia and whether this may subsequently modulate oligodendroglial differentiation. These in vitro studies were complemented by histological analyses of oligodendrocytes in FXR Ko mice.
FXR is expressed by OPCs and mature oligodendrocytes. However, lack of FXR did not affect oligodendroglial differentiation in vitro or in vivo. Furthermore, activation of FXR using the synthetic agonist GW4064 did not affect oligodendroglial differentiation, remyelination in an ex vivo model or the expression of pro-inflammatory molecules in astrocytes or microglia. Concordantly, no effects of supernatants from macrophages cultured in the presence of GW4064 were observed regarding a possible indirect impact on oligodendroglial differentiation.
Our data suggest that FXR is dispensable for oligodendroglial differentiation and that FXR agonists, such as GW4064, represent a potential therapeutic approach for MS which specifically targets peripheral immune cells including macrophages but not brain-resident cells, such as oligodendrocytes, astrocytes or microglia.
Additional file 1: Figure S1. Cerebellar oligodendroglial differentiation is not affected by direct FXR activation or supernatant of FXR-activated BMMs. Addition of GW4064 during the differentiation of cerebellar oligodendrocytes over 24 and 48 h does not influence Mbp expression levels (a) or the percentages of PDGFRα+ OPCs or MBP+ oligodendrocytes (b, c). Oligodendrocytes of cerebellar origin exhibit no significant difference in their Mbp expression level when incubated with supernatants from BMM cultured either in the presence or absence of GW4064 (d). The percentage of OPCs is unchanged after incubation with BMM-conditioned medium; the percentage of MBP+ oligodendrocytes is reduced independent of additional GW4064 treatment (e, f). Activation of FXR cultures using 10 and 20 μM GW4064 during 14 days of remyelination in cerebellar slice after toxic demyelination does not alter the ratio of MBP+ and NFL+ axonal fibres (g). Remyelinated fibres are exemplarily highlighted (arrows). Note that a high amount of MBP+ debris is still present after 14 days of remyelination (h). In vitro: n = 3, 1way ANOVA with Bonferroni’s correction, 200 cells per condition were evaluated, *p < 0.05; ex vivo: n = 2, 1way ANOVA with Bonferroni`s correction, 6 slices with 3 images each per condition and preparation; all images are representative. (TIF 5564 kb)12974_2017_833_MOESM1_ESM.tif
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- Activation of FXR pathway does not alter glial cell function
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