Progestins actions in the lactotroph population: mPR involvement in PRL secretion

CAMILLETTI, MARIA ANDREA; THOMAS, PETER; FARAONI, ERIKA; ABELEDO, ALEJANDRA; FERRARIS, JIMENA; DÍAZ-TORGA, GRACIELA

Steamboats Springs

Conferencia; Growth Hormone/Prolactin Family in Biology and Disease (FASEB SRC); 2017

FASEB

In the pituitary, the role of progesterone (P4) in controlling lactotroph proliferation and prolactin (PRL) secretion remains unclear. It was described that concomitant P4 treatment prevented both the elevation of plasma PRL level and development of prolactinomas in chronically-estrogen treated rats. In contrast, female mice expressing hCGβ with enhanced LH action and high progesterone levels displayed pituitary prolactinomas. We hypothesize that these conflicting results are due to the different hormonal milieu and the progesterone receptor types involved. Two receptor types mediate progestin actions: the nuclear progestin receptors (nPRs) and the membrane progestin receptors (mPRs). The mPRs (α, β, γ, δ, ε) are novel 7-transmembrane-G protein coupled receptors shown to mediate rapid, non-genomic actions in different cell types. On the other hand, TGFβ1 is a known inhibitor of lactotroph function, and we previously demonstrated that pituitary TGFβ1 activity is regulated by dopamine and estradiol. But the involvement of P4 in local TGFβ1 regulation is unknown. In our present work, the relative expression of nPRs and mPRs assayed by qRT-PCR in anterior pituitary glands of Sprague Dawley (SD) female rats showed that nPRs correspond to 86% while mPRs represented the 14%. The relative expression of mPR mRNA was the highest among all the mPRs (41%). mPR expression in lactotrophs was proved by IHQ in rat pituitary sections and flow cytometry assays revealed that approximately 54% of total pituitary cells express mPRα (mPR+), and among them, 65% were lactotrophs (mPRα+, PRL+). In addition, two functional assays were conducted with a selective mPR agonist, 10-ethenyl-19-norporgesterone Org OD 02-0 (OD) to determine mPR involvement in PRL secretion. In an ex vivo experiment, pituitaries from female SD rats were incubated with 100nM OD. After 1h incubation, OD significantly decreased PRL secretion (measured by RIA) (OD vs Ctrl, p=0.006). Concomitantly, stimulation with OD significantly increased the pituitary content of active TGFβ1, (OD vs Ctrl; p=0.009; measured by ELISA). A similar experiment was carried out in vitro using the GH3 somalactotroph cell line. Interestingly, OD (100nM) decreased PRL levels after 30min, 1h and 6h treatment while this effect was not observed with nuclear PR agonist R5020 (10nM). Accordingly, 15min stimulation with OD increased TGFβ1 activation in these cells. Taken together, our results suggest a role for mPRs in progestin actions in the lactotroph population through the inhibition of PRL secretion probably due, at least in part, to the activation of TGF1. This study provides the first evidence of mPRs function in the pituitary gland.