Expression and regulation of possible TGF-b1 local activators in the pituitary gland of wild-type and dopamine D2 receptor knock-out female mice

RECOUVREUX, MARIA VICTORIA; CAMILLETTI, MARIA ANDREA; LAPYCKYJ, LARA; DÍAZ-TORGA, GRACIELA

San Francisco

Congreso; ENDO 2013; 2013

Endocrine Society

Prolactinomas are common benign adenomas that can be usually treated with dopaminergic agonists. However, around a 15% of these tumors are resistant, and there are still not alternative medical therapies. TGF-1 inhibits lactotrope proliferation, partially mediating dopamine inhibitory action. Therefore, we propose that TGF-1 could be a good candidate for developing new therapies against dopamine agonist-resistant-prolactinomas. TGF-1 is secreted in a biological inactive (latent) form and remains associated to the extracellular matrix. TGF-1 activation process is tightly regulated and represents a critical step for its biological function. TGF-1 activators are tissue-specific, and are still unknown in the pituitary gland. We have previously shown that active TGF-1 content (only 8% of total cytokine) was decreased in prolactinomas developed in dopamine D2 receptor knock-out female mice (Drd2-/-) when compared to wt. The aim of this study was to evaluate the expression of potential TGF-1 activators and their regulation by dopamine and estradiol in the pituitary glands of wt and Drd2-/- female mice. The loss of dopaminergic control (Drd2-/- pituitaries) caused a decrease of mRNA expression of many of the activators measured by real time PCR: matrix metalloproteases MMP2 and MT1-MMP, TSP1, and kallikrein 1 (KLK1). MMP2 and MMP9, assessed by zymography, were detected only as inactive zymogens, and were decreased in Drd2-/- pituitaries. No genotype differences were found in integrin 6 expression. Among all activators evaluated, only integrin 8 mRNA levels were markedly increased in Drd2-/- pituitaries. In vivo treatment with estradiol-valerate (E2, 0.1g/kg, 24hs) caused a down-regulation of MMPs and integrins isoforms evaluated in both genotypes. On the contrary, TSP1 expression was largely increased by E2 treatment in both genotypes, while KLK1 expression was induced by E2 only in Drd2-/- pituitaries. These results correlate with our previous observation of a strong increase in active TGF-1 elicited by E2 treatment in Drd2-/- mice, suggesting that TSP1 and/or KLK1 might mediate E2-induced TGF-1 activation in the pituitary. This is the first report regarding TGF-1 local activators in the pituitary gland and their regulation by dopamine and estradiol. Identifying pituitary-specific TGF-1 activation mechanisms is useful for the development of therapeutic tools that could restore active TGF-1 levels locally, without affecting other tissues.