Orexins/hypocretins increase the promoter activity of selective steroidogenic enzymes

Orexins (hypocretins) regulate multiple physiological functions, including central regulation of energy homeostasis and sleep–wake behavior but also peripheral hormonal actions. Recent data suggest specific effects of orexins at adrenal glands. To further assess the mechanism by which orexins regulate steroidogenesis we analyzed the effect of orexin A and B on the transcriptional activity of the luciferase reporter gene driven by the human steroid 21-hydroxylase (CYP21), 3β-hydroxysteroid dehydrogenase (HSD3B2), 11β-hydroxylase (CYP11B1), and aldosterone synthase (CYP11B2) gene promoter regions. After transient transfection of the reporter gene constructs into human NCI H295R cells, treatment with orexin A and B for 6 and 12 h increased the promoter activity of the CYP11B2, HSD3B2 and, to a lesser extend, CYP21 genes. The activity of the CYP11B1 was increased by both orexins after 3 h of treatment. Compared to the effects of forskolin or angiotensin II, however, the effect of orexins on the transcriptional activity of the steroidogenic enzyme genes was moderate. Our results suggest that orexins increase the expression of steroidogenic enzymes at the transcriptional level and that orexins play a role in the long term regulation of adrenal steroid production.

Research highlights
► The increased promoter activities of CYP21, HSD3B2, CYP11B1, and CYP11B2 genes in human NCI-H295R-cells after orexin A and orexin B treatment demonstrate the regulation of these genes at the transcriptional level by orexins.
► In contrast, orexin has no effect on CYP21, HSD3B2, CYP11B1, and CYP11B2 mRNA stability.
► These results substantiate a role of orexins in adrenal gland regulation of steroid synthesis.