Abstract
Fibroblast growth factors (FGFs) and their receptors (FGFRs) are involved in demyelinating pathologies including multiple sclerosis (MS). In our recent study, oligodendrocyte‐specific deletion of FGFR1 resulted in a milder disease course, less inflammation, reduced myelin and axon damage in EAE. The objective of this study was to elucidate the role of oligodendroglial FGFR2 in MOG35‐55‐induced EAE. Oligodendrocyte‐specific knockout of FGFR2 (Fgfr2ind −/−) was achieved by application of tamoxifen; EAE was induced using the MOG35‐55 peptide. EAE symptoms were monitored over 62 days. Spinal cord tissue was analysed by histology, immunohistochemistry and western blot. Fgfr2ind −/− mice revealed a milder disease course, less myelin damage and enhanced axonal density. The number of oligodendrocytes was not affected in demyelinated areas. However, protein expression of FGFR2, FGF2 and FGF9 was downregulated in Fgfr2ind −/− mice. FGF/FGFR dependent signalling proteins were differentially regulated; pAkt was upregulated and pERK was downregulated in Fgfr2ind −/− mice. The number of CD3(+) T cells, Mac3(+) cells and B220(+) B cells was less in demyelinated lesions of Fgfr2ind −/− mice. Furthermore, expression of IL‐1β, TNF‐α and CD200 was less in Fgfr2ind −/− mice than controls. Fgfr2ind −/− mice showed an upregulation of PLP and downregulation of the remyelination inhibitors SEMA3A and TGF‐β expression. These data suggest that cell‐specific deletion of FGFR2 in oligodendrocytes has anti‐inflammatory and neuroprotective effects accompanied by changes in FGF/FGFR dependent signalling, inflammatory cytokines and expression of remyelination inhibitors. Thus, FGFRs in oligodendrocytes may represent potential targets for the treatment of inflammatory and demyelinating diseases including MS.
Highlights
Since Fibroblast growth factors (FGFs)/FGFR expression is regulated in multiple sclerosis (MS) and EAE [6,11], we investigated whether cell-specific deletion of FGFR2 alters the expression of FGF and FGFR-related molecules in spinal cord homogenates
We recently showed that brain-derived neurotrophic factor (BDNF) and its receptor TrkB were upregulated by cell-specific deletion of FGFR1 in the chronic phase of EAE [11]
Much of the knowledge on cell-specific function of FGFRs in oligodendrocytes is derived from experimental studies on FGFR1 [11,12], little information is available on the function of FGFR2 in oligodendrocytes
Summary
Animal studies were performed according to the guidelines of FELASA. Animal experiments were approved by the local state authorities of Hesse, Giessen, Germany (GI 20/23-Nr. 31/2008) in accordance with the German animal welfare law and the European legislation for the protection of animals used for scientific purposes. Fgfr2flox/flox mice were crossbred with B6.Cg-Tg(Plp1-cre/ERT)3Pop/J (The Jackson Laboratories, Bar Harbour, ME, USA) to generate inducible oligodendrocyte Fgfr conditional knockout mouse (B6.Cg-Tg(PLP1-cre/ERT)3-Pop:Fgfr2lox/lox). The oligodendrocyte-specific Fgfr knockout (referred to as Fgfr2ind−/−) was induced in 4- to 5-week-old female B6.CgTg(PLP1-cre/ERT)3-Pop:Fgfr2lox/lox mice by daily i.p. injections of tamoxifen (Sigma-Aldrich, Steinheim, Germany; 1 mg of tamoxifen in 100 μl sunflower oil/ethanol) for five consecutive days. B6.Cg-Tg(PLP1-cre/ERT)3-Pop:Fgfr2lox/lox littermate female mice received a sunflower oil/ethanol mixture (no tamoxifen) for five consecutive days at the age of 4 to 5 weeks (referred to as controls). Spinal cord sections were analysed by light microscopy (Olympus BX51, Hamburg, Germany), images were captured using a digital camera (Olympus DP71, Olympus America Inc., Centre Valley PA, USA). CD3(+), B220(+), Mac3(+), Olig2(+) and NogoA(+) cells were counted within spinal cord white matter lesions with an ocular morphometric grid. Values are expressed as mean ±standard error of mean. *indicates p ≤ 0.05, **indicates p ≤ 0.01, ***indicates p ≤ 0.001
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