Figure 4.

Functional roles of orexin A in the activities of CRH and BMP−4 in corticotrope cells. OX2R rather than OX1R was predominantly expressed in corticotrope AtT20 cells. Orexin A upregulated CRHR1 expression and CRH−induced POMC transcription. Orexin A also suppressed BMP−4−induced Smad1/5/9 phosphorylation and Id−1 transcription by upregulating inhibitory Smad6 and Smad7. Thus, orexin A has an enhancing effect on POMC expression by upregulating CRH signaling and downregulating BMP−Smad action, which is possibly involved in the control of stress responses and their resilience.