Glucocorticoids inhibit macrophage differentiation towards a pro-inflammatory phenotype upon wounding without affecting their migration

Glucocorticoid drugs are widely used to treat immune-related diseases, but their use is limited by side effects and by resistance, which especially occurs in macrophage-dominated diseases. In order to improve glucocorticoid therapies, more research is required into the mechanisms of glucocorticoid action. In the present study, we have used a zebrafish model for inflammation to study glucocorticoid effects on the innate immune response. In zebrafish larvae, the migration of neutrophils towards a site of injury is inhibited by the synthetic glucocorticoid beclomethasone, while migration of macrophages is glucocorticoid resistant. RNA sequencing was done on on Fluorescence-Activated Cell Sorting (FACS)-sorted macrophages.The results show that the vast majority of the wounding-induced transcriptional changes in these cells are inhibited by beclomethasone, whereas a small subset is glucocorticoid-insensitive. As a result, beclomethasone decreases the number of macrophages that differentiate towards a pro-inflammatory (M1) phenotype, which we demonstrated using a tnfa:eGFP-F reporter line and analysis of macrophage morphology. We conclude that the glucocorticoid resistance of the wounding-induced macrophage migration is due to the insensitivity of the induction of macrophage-specific chemoattractants to glucocorticoid inhibition, which may explain the relative resistance of macrophage-dominated diseases to glucocorticoid therapy. However, the induction of pro-inflammatory genes in macrophages is strongly attenuated, which inhibits their differentiation to an M1 phenotype. Overall design: After anesthesia with 0.02% aminobenzoic acid ethyl ester (tricaine, Sigma Aldrich), the tails of 3 days post fertilization (dpf) embryos were partially amputated with a 1mm sapphire blade (World Precision Instruments) on 2% agarose-coated Petri dishes under a Leica M165C stereomicroscope (Chatzopoulou et al., 2016). Amputated and non-amputated (control) embryos were pretreated for 2 hours with 25 µM beclomethasone (Sigma Aldrich) or vehicle (0.05% dimethyl sulfoxide (DMSO)) in egg water prior to amputation and received the same treatment after the amputation. Macrophages were sorted from Tg(mpeg1.4:mCherry-F) embryos as previously described (Rougeot et al., 2014; Zakrzewska et al., 2010) at 4 hours post amputation (hpa). The sorted cells were collected in QIAzol lysis reagent (Qiagen) for RNA isolation. Extracted total RNA was amplified using the SMART-seq V4 kit (Clontech) for sequencing. The RNA seq libraries generated with the SMART-seq V4 kit were sequenced using an Illumina HiSeq 2500 instrument according to the manufacturer's instructions with a read length of 50 nucleotides.

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Xie Y, Tolmeijer S, Oskam JM, Tonkens T, Meijer AH, Schaaf MJM