Receptors (mPRs) in the Pituitary. Novel Role of Mprα in the Function of Lactotroph Population

ABELEDO-MACHADO, ALEJANDRA; PISERA, DANIEL; FARAONI, ERIKA; FERRARIS JIMENA; CAMILLETI, MARIA ANDREA; DALLOTTO MORENO, TOMAS; DIAZ-TORGA, GRACIELA

Congreso; ENDO 2017; 2017

Progesterone (P4) function in controlling lactotroph proliferation and prolactin secretion is controversial. The direction and extent of P4 actions depends on the endogenous hormonal milieu and the receptor involved. There are two receptor types for mediating progestin actions: membrane progestin receptors (mPRs) and nuclear progestin receptors (nPRs). The mPRs are novel 7-TM-G protein coupled receptors which have recently been shown to mediate a variety of rapid, non-genomic progesterone functions in different cell types including gametes, cancer cells and ovarian follicle cells. The functions of these receptors in the pituitary, however, have not been reported to date. Our main objective is to study the involvement of mPRs in pituitary physiology and pathology. We have previously demonstrated the mPRs expression in rat pituitaries, and their regulation by estrogens and progesterone. In the present study, we have characterized the relative expression of nPRs and mPRs, measured by qRT-PCR, in the pituitary gland of female Sprague Dawley (SD) rats in Diestrus (Di). Results: mPRs represented 14,3% of total P4 receptors, while 85,7% corresponded to nPRs (PR-A: 62.4% and PR-B 23,3%). Ovariectomy (OVX, 15 days after surgery) increased pituitary mPRs relative expression (up to 37% mPRs) and PR-A increased up to 93% at expense of a drastic reduction in PR-B expression (6,9%). Among mPRs, (α, β, γ, δ, ε) mPRα was the most abundant in the pituitary gland (40,8% in Di and 48,4% in OVX rats), followed by mPRβ (28,9% in Di) and mPRε (18,9% in Di). On this basis, immunofluorescence studies and flow citometry analysis were conducted for the characterization of mPRα in lactotroph population. About 54% of the pituitary cells were found to be mPRα+; among them 65% were lactotrophs (mPRα+ PRL+). In addition, an ex vivo assay was conducted to determine mPR involvement in PRL secretion. Pituitaries from female SD rats were collected in supplemented medium and then stimulated for 1 hour with mPRα specific ligand ORG OD 02-0 (100nM), P4 (100nM) in serum-free medium (control). Interestingly, 1 hour exposure to OD 02-0 decreased PRL levels measured by RIA compared to control group (486,8±27,8 ng/ml OD vs 736,4±65,5 ng/ml control, p=0,006). TGFβ1 is a known inhibitor of lactotroph proliferation and PRL secretion. mPRα stimulation significantly increased pituitary active TGFβ1 content (measured by ELISA; OD 56,74 ± 8,12 pg/mg protein vs Control 29±0,84, p=0,009). On the other hand, P4 treatment did not modified TGFβ1 activity. Collectively, these results demonstrate: (i) mPRs are expressed in rat pituitary gland being mPRα the most abundant. (ii) Among pituitary cells, mPRα is mainly expressed in lactotrophs. (iii) We described for the first time a possible role for pituitary mPRs: P4 acting through mPRα reduced PRL secretion, and our results suggest the involvement of local TGFβ1 mediating this action.