Hildert Bronkhorst, Thomas Schrauwen, Erin Faught & Marcel Schaaf (Leiden University, Institute of Biology)

Glucocorticoids (GCs) are widely prescribed anti-inflammatory drugs, but their therapeutic use is limited by diverse side effects. Due to the ubiquitous expression of the glucocorticoid receptor (GR), GCs act on virtually all cell types. While the molecular mechanisms of GR activation have been studied extensively, its cell-specific effects remain incompletely understood. Here, we applied single-cell RNA sequencing to characterize the transcriptional landscape of zebrafish tail fin tissues upon 6 h of treatment with the GC dexamethasone under both basal and inflammatory conditions, induced by tail fin wounding. We profiled almost 100,000 cells across four experimental conditions and identified all known cell populations, including epithelial, mesenchymal, muscle, neuronal, and immune cells. The transcriptional response to wounding was most prominent in a cluster of epidermal glucagon a-positive cells. Besides high expression levels of inflammatory markers, those cells showed a cell proliferation signature, indicating a shift from acute inflammation to a pro-healing state. Dexamethasone attenuated most of the wounding-induced pathways, and exerted additional tissue-specific effects, where epidermal and mesenchymal cells showed a greater transcriptional response than neuronal and vascular cells. Together, our data provide a comprehensive single-cell expression atlas of GC action during acute inflammation and early stages of regeneration processes, offering more insight in cell type-specific GC sensitivity in vivo. Our data was applied in a screen of novel glucocorticoids that could induce cell-specific GR activation.