5152 The interplay of FOXO1 and NR3C1 in the development and function of pituitary somatotropes

Abstract Disclosure: P. Das: None. D.A. Jabal: None. D.A. Sunny: None. B.S. Ellsworth: None. Our research focuses on the role of glucocorticoid (GC) in regulating the maturation of pituitary somatotropes. We previously demonstrated that deletion of the forkhead transcription factor, FOXO1, affects the development of somatotropes both in vivo and in vitro. Our studies reveal that treating pregnant mice with the synthetic glucocorticoid, dexamethasone leads to premature somatotrope maturation. Interestingly, we have observed that the ability of GC to promote Gh1 expression is compromised in the absence of FOXO1 in a somatotrope-like cell line. This finding leads to further investigation into the GC receptor, NR3C1, and its developmental role in the pituitary gland. In mouse embryos, we detect NR3C1-positive cells localized primarily in the nucleus, initially in small numbers at embryonic day (e)12.5 and becoming more abundant by e14.5. At e14.5 there is a subset of cells where NR3C1 co-localizes with POU1F1, a marker of pre-somatotropes, suggesting the importance of NR3C1 in the formation of the somatotrope lineage. In dexamethasone-treated animals, we observe an increase in NR3C1-positive cells. However, no significant change was noted in POU1F1 expression. Significantly, the premature somatotropes identified are NR3C1 and POU1F1-positive, suggesting the pituitary cells expressing both POU1F1 and NR3C1 at e14.5 are likely differentiating into somatotropes when exposed to GC. Normally, by e16.5, GH-positive cells begin to appear in mice. Double immunostaining reveals that some of these cells also express NR3C1. Further supporting this finding, the deletion of Nr3c1 results in a decreased number of GH-positive cells at e16.5. Altogether these findings demonstrate that NR3C1 and FOXO1 are key factors regulating somatotrope maturation. Presentation: 6/2/2024