IN VITRO EFFECTS OF LIPOPOLYSACCHARIDE ON LACTOTROPH CELLS ARE MEDIATED IN PART BY TOLL-LIKE RECEPTOR 4: MODULATOR ROLE OF ESTRADIOL

RODRIGO FANTON E. T.; GUTIÉRREZ S.; PETITI J.P.; SOSA L.; PALMERI C.; QUINTAR A.; TORRES A.I.; DE PAUL A.L,

Rio de Janeiro

Congreso; 13 International Congress of Endocrinology; 2008

INTERNATIONAL SOCIETY OF ENDOCRINOLOGY

Bacterial lipopolysaccharide (LPS) increases the levels of circulating cytokines modulating the release of pituitary hormones. Moreover, LPS is also able to induce local production of cytokines within the gland. Our objective was to analyse the effects of LPS on PRL secretion and lactotroph proliferation from hyperplastic pituitary and evaluate the role of estrogen. Male rats were subcutaneously implanted with silastic capsules filled with 10mg of 17b-estradiol (E2) for 60 days. Then, anterior pituitaries were cultured and treated as follows: LPS (100ng or 2ug/ml) for 6 and 24 h, E2 (100 nM) for 4 and 24 h, Interaction LPS+E2 for 24h (I), and Sensitization by preincubation with E2 for 4h, followed by a treatment with LPS (100ng/ml) for 24h (S). Lactotroph cell proliferation was assessed by dual-immunocytochemical detection of BrdU/PRL and the PRL secretion was measured by RIA. The molecules TLR4 and NF-kB, involved in LPS action pathways, were determined by western blot and by using immunocytochemistry at both optic and electron microscopy level. Both doses of LPS doubled the lactotroph cell population after 6h as well as 24h of stimulus (ANOVA-Fisher p<0.001); whereas E2 increase 60% (vs. control). In I model, the raise in the mitogenic activity was 130% and in S model, E2 partially decreased the PRL cell proliferation induced by LPS (60% vs. control, p<0.001). PRL levels were not modified by E2 for 24h. LPS alone or co-incubate with E2 decreased significantly the PRL release. TLR4 expression increased after LPS treatment and its presence was mainly detected in the cytoplasm of lactotroph and corticotroph cells. Nuclear fractions showed a higher expression of NF-kB after LPS treatment and in I model (p< 0.05 vs control), indicating NFkB translocation to the nucleus in these conditions. After E2 treatment, no changes in NF-kB expression were seen, while in S model, a high expression of NF-kB was detected in cytosolic extracts. Lactotrophs from hyperplastic pituitaries respond directly to LPS through TLR4-NF-kB to elicit cell proliferation and inhibit PRL secretion.We propose that estrogen could act as a modulator of LPS-induced lactotroph cell proliferation.