DHEA Inhibits Leukocyte Recruitment through Regulation of the Integrin Antagonist DEL-1

Abstract

Leukocytes are rapidly recruited to sites of inflammation via interactions with the vascular endothelium. The steroid hormone dehydroepiandrosterone (DHEA) exerts anti-inflammatory properties; however, the underlying mechanisms are poorly understood. In this study, we show that an anti-inflammatory mechanism of DHEA involves the regulation of developmental endothelial locus 1 (DEL-1) expression. DEL-1 is a secreted homeostatic factor that inhibits b2-integrin-dependent leukocyte adhesion, and the subsequent leukocyte recruitment and its expression is downregulated upon inflammation. Similarly, DHEA inhibited leukocyte adhesion to the endothelium in venules of the inflamed mouse cremaster muscle. Importantly, in a model of lung inflammation, DHEA limited neutrophil recruitment in a DEL-1-dependent manner. Mechanistically, DHEA counteracted the inhibitory effect of inflammation on DEL-1 expression. Indeed, whereas TNF reduced DEL-1 expression and secretion in endothelial cells by diminishing C/EBPb binding to the DEL-1 gene promoter, DHEA counteracted the inhibitory effect of TNF via activation of tropomyosin receptor kinase A (TRKA) and downstream PI3K/AKT signaling that restored C/EBPb binding to the DEL-1 promoter. In conclusion, DHEA restrains neutrophil recruitment by reversing inflammation-induced downregulation of DEL-1 expression. Therefore, the anti-inflammatory DHEA/DEL-1 axis could be harnessed therapeutically in the context of inflammatory diseases.

Erythromycin inhibits neutrophilic inflammation and mucosal disease by upregulating DEL-1

“…Additionally, ERM not only reversed the inhibitory effect of IL-17 on C/EBPβ binding to the DEL1 promoter but also elevated C/EBPβ binding over and above its constitutive level (ethanol control treatment) ( Figure 5E). Taken together, ERM not only counteracts the inhibitory effect of IL-17 on the binding activity of C/ EBPβ for the DEL1 promoter, as previously shown for resolvins (20) and DHEA (29), but also can directly enhance the binding of C/EBPβ to the DEL1 promoter.…”

“…We have previously shown that DEL-1 expression is severely reduced under inflammatory conditions (15,20,29). Specifically, both IL-17 and TNF diminish DEL-1 expression by targeting C/EBPβ, although their effects are reversed by the proresolving lipid mediator RvD1 and steroid hormone dehydroepiandrosterone (DHEA) (20,29).…”

“…We have previously shown that DEL-1 expression is severely reduced under inflammatory conditions (15,20,29). Specifically, both IL-17 and TNF diminish DEL-1 expression by targeting C/EBPβ, although their effects are reversed by the proresolving lipid mediator RvD1 and steroid hormone dehydroepiandrosterone (DHEA) (20,29). Although RvD1 and DHEA use different receptors (GPR32 and/or ALX/FPR2 vs. TrkA, respectively), they both activate PI3K/AKT signaling to restore C/EBPβ binding to the DEL1 promoter region, thereby counteracting the inhibitory effect of inflammatory cytokines on DEL-1 production.…”

“…The transcription factor C/EBPβ is involved in the regulation of DEL1 transcription, and its ability to bind to the DEL1 (EDIL3) promoter is inhibited by IL-17 (20). We thus next investigated whether ERM promotes C/EBPβ binding to the DEL1 promoter using a quantitative chromatin immunoprecipitation assay (ChIP-qPCR) (29). Our ChIP assay revealed that ERM, but not JSM or PC, enhanced the binding of C/EBPβ to the DEL1 promoter ( Figure 5D).…”

“…(B and C) HMVECs were transiently transfected with hEDIL3-promoter-Luc reporter plasmid, pretreated for 30 minutes with or without ERM (10 μg/mL), JSM (10 μg/mL), or PC (10 μg/mL), followed by 8-hour stimulation with or without IL-17 ( ERM shares a similar function with RvD1 and DHEA, in that ERM can also reverse inflammation-induced downregulation of DEL-1 transcription in a PI3K/AKT-dependent manner. However, what is unique and novel about ERM is that it can directly upregulate DEL-1 expression even under normal homeostatic (noninflammatory) conditions; RvD1 and DHEA cannot directly induce DEL-1 expression (20,29). Thus, ERM not only counteracts the inhibitory effect of inflammation on the promoter binding activity of C/EBPβ ("reversal effect"), as we showed earlier for RvD1 (20) and DHEA (29), but also can directly enhance the binding of C/EBPβ to the DEL1 promoter.…”