Human neutrophils are a key target of glucocorticoids

Abstract Neutrophils play central roles in immunity and inflammation. Glucocorticoids (GCs) are the cornerstone of anti-inflammatory and immunosuppressive therapy. While GCs trigger an acute rise in circulating neutrophils, little is known about the mechanisms by which GCs modulate neutrophil biology. We studied the response of 9 primary human cells to in vitro treatment with GCs. Surprisingly, neutrophils were transcriptionally the most responsive cell type, and they express proportionally the most glucocorticoid receptor (GR) transcripts. Long-read RNA-seq revealed 42 full-length GR transcript isoforms in neutrophils, twice as many as had been reported previously in all other cell types. At the protein level, neutrophils also have a unique and diverse set of GR isoforms. In contrast to the widely accepted model of GR signaling, in which GR binds GC molecules in the cytoplasm and then translocates to the nucleus, GR localization in neutrophils is almost exclusively nuclear, even in the absence of GC treatment. To validate our findings in vivo, we then performed a study of healthy volunteers, with blood collected before and serially after GC infusion. We generated a pathway-level map of the human neutrophil transcriptome at baseline and in response to GCs. The in vivo transcriptional response of human neutrophils to GCs was as strong as that observed in vitro, with a predominance of upregulation. Among the most strongly induced genes are several that are either not expressed, or expressed at very low levels, in human neutrophils at baseline. Some of the proteins encoded by these genes may have putative effects on neutrophil function, including SAMSN1 and ZBTB16. These findings indicate that human neutrophils are a key target for GC action.