Estradiol has a rapid proapoptotic action in anterior pituitary cells

ZÁRATE SANDRA; JAITA GABRIELA; ZALDIVAR VERóNICA; RADL DANIELA; EIJO GUADALUPE; PISERA DANIEL; SEILICOVICH ADRIANA

Toronto

Congreso; 89th Annual Meeting of the Endocrine Society; 2007

For many years, estrogen was thought to exert its action exclusively through binding to nuclear receptors and the subsequent transactivation of target genes. However, some rapid actions of this hormone cannot be explained by this mechanism, and membrane initiated steroid signaling has been proposed recently. It involves the activation of signal transduction pathways whose effects are cell-context specific and lead to estrogen regulation of different cell functions such as differentiation, proliferation or death. We have previously shown that estradiol modulates apoptosis of anterior pituitary (AP) cells not only by sensitizing them to proapoptotic stimuli but also by a direct proapoptotic action on somatotrophs in vitro. In the present study we investigated the involvement of membrane initiated steroid signaling in the proapoptotic action of estrogen in AP cells. To achieve this aim, we used 17â-estradiol (E2), E2 bound to bovine seroalbumin (E2-BSA, a membrane impermeable form of E2) and the nongenotropic signaling activator estren (4-estren-3alpha,17beta-diol). Cultured AP cells from ovariectomized Wistar rats were incubated either with E2 (10-9M) or E2-BSA (10-9M) for 120 min and apoptosis was analized by FACS with Annexin-V/propidium iodide (PI) staining. Both E2 and E2-BSA increased the percentage of apoptotic cells (C 14.7±1.6 %, E2 32.0±1.5 %, E2-BSA 28.7±1.9 % p<0.01, ANOVA). Also, both steroids induced an increase in the percentage of TUNEL positive AP cells (C 1.1 %,  E2 2.4 %, E2-BSA 2.9 % p<0.001, Chi square) and somatotrophs, identified by immunocytochemistry (C 3.6 %,  E2 9.4 %, E2-BSA 13.8 % p<0.01, Chi square). Then, we studied the effects of estren in the apoptosis of AP cells by incubation with this synthetic steroid (10-7M) for 30, 60 and 240 min and evaluated apoptosis by FACS. Estren induced apoptosis as early as at 60 min of incubation (30 min, C 4.1±0.5 %, estren 4.8±1.1 %; 60 min, C 7.9±0.4 %, estren 11.9±1.2 % p<0.01; 240 min, C 10.8±0.9 %, estren 17.5±2.4 % p<0.05, ANOVA). Also, incubation with estren for 120 min increased the percentage of TUNEL positive AP cells (C 0.9 %, estren 6.0 % p<0.01, Chi square) and somatotrophs (C 1.7 %, estren 10.4 % p<0.05,  Chi square). Taken together, these results show that E2 has a rapid proapoptotic action on AP cells and suggest the involvement of extranuclear initiated estrogen signaling in pituitary cell apoptosis. These events could be associated to the regulation of cell renewal in this gland.