Estrogen effects on the growth and differentiation of hypothalamic neurons

CAMBIASSO, M.J.

Mar del Plata, 19-22 de Noviembre 2008.

Congreso; LII Reunión Científica de la Sociedad Argentina de Investigación Clínica y Reunión Anual de la Sociedad Argentina de Fisiología; 2008

Estrogen effects on the growth and differentiation of hypothalamic neurons María Julia Cambiasso Instituto de Investigación M y M Ferreyra, INIMEC-CONICET. Friuli 2434 B° Colinas de Vélez Sarsfield,  Córdoba – Argentina E-mail: jcambiasso@immf.uncor.edu Estrogens influence the cellular and synaptic organization of the brain. The neuritogenic effect of estradiol (E2) was first demonstrated in organotypic explants of hypothalamus and subsequently extended to other brain regions, some of them not directly linked to reproduction. Many estrogenic actions are mediated via intracellular estrogen receptors (ERs) that function as ligand-activated transcription factors to regulate the expression of estrogen-responsive genes. Numerous studies also demonstrate that E2 and other estrogenic compounds can rapidly activate a diverse array of intracellular signaling cascades via membrane-initiated mechanisms. Previous studies from our laboratory have demonstrated that the axogenic effect of E2 on male-hypothalamic neurons is dependent on a membrane-initiated mechanism. The application of the nuclear ER antagonists, like tamoxifen or ICI 182,780, did not prevent the axogenic effect of the hormone in vitro; moreover, using a membrane-impermeant E2-albumin construct (E2BSA) the estrogenic effect was preserved (1). In these cultures E2 also induced an increase in the levels of IGF-1R and TrkB (2). Antisense oligonucleotide suppression of TrkB blocked E2-induced axon growth (3)  indicating a convergence of the signaling pathways for E2 and neurotrophins. We also showed that Ca2+ and PKC are necessary for ERK activation as well as axonal outgrowth induced by the hormone in hypothalamic neurons (4); additionally, we showed that E2-induced activation of MEK-ERK does not depend on the nuclear ER but through a membrane-associated receptor. These findings make it imperative to understand the nature of the mER responsible for the activation of ERK signaling in neurons. Using a series of antibodies against classical and non-classical ERs, we found that the expression of ERa, but not ERb or GPR30, is associated with the plasma membrane fraction of hypothalamic tissue at E16. Moreover, our experiments extended these results to hypothalamic neurons in vitro showing that ERa can be detected from the cell exterior as a biotinylated cell-surface protein and is under E2-regulation (5). We have also shown that the ERa agonist, PPT, induced ERK signaling in a dose-dependent manner in times not compatible with genomic actions, supporting the notion of a membrane-initiated phenomenon.  On the other hand, E2-induced ERK activation led to an increase in the phosphorylation of CREB, suggesting the participation of this transcription factor.  In summary, our studies demonstrate that E2, via a membrane ERa induces axonal growth by activating CREB phosphorylation through ERK signaling by a mechanism involving Ca2+ and PKC. Supported by FONCyT and CONICET. References: 1.      Cambiasso MJ, Carrer HF (2001) J Neurosci Res 66:475-481. 2.      Cambiasso MJ, Colombo JA, Carrer HF (2000) Eur J Neurosci 12:2291-2298. 3.      Brito VI, Carrer HF, Cambiasso MJ (2004) Eur J Neurosci 20:331-337. 4.      Gorosito S, Cambiasso MJ (2008) J Neurosci Res 86(1): 145-157. 5.      Gorosito SV,  Lorenzo A, Cambiasso MJ (2008) Neuroscience 154(4):1173-7.