Ontogeny of Rapid Estrogen-Mediated Extracellular Signal-Regulated Kinase Signaling in the Rat Cerebellar Cortex: Potent Nongenomic Agonist and Endocrine Disrupting Activity of the Xenoestrogen Bisphenol A

Abstract

In addition to regulating estrogen receptor-dependent gene expression, 17beta-estradiol (E(2)) can directly influence intracellular signaling. In primary cultured cerebellar neurons, E(2) was previously shown to regulate growth and oncotic cell death via rapid stimulation of ERK1/2 signaling. Here we show that ERK1/2 signaling in the cerebellum of neonatal and mature rats was rapidly responsive to E(2) and during development to the environmental estrogen bisphenol A (BPA). In vivo dose-response analysis for each estrogenic compound was performed by brief (6-min) intracerebellar injection, followed by rapid fixation and phosphorylation-state-specific immunohistochemistry to quantitatively characterize changes in activated ERK1/2 (pERK) immunopositive cell numbers. Beginning on postnatal d 8, E(2) significantly influenced the number of pERK-positive cells in a cell-specific manner that was dependent on concentration and age but not sex. In cerebellar granule cells on postnatal d 10, E(2) or BPA increased pERK-positive cell numbers at low doses (10(-12) to 10(-10) M) and at higher (10(-7) to 10(-6) M) concentrations. Intermediate concentrations of either estrogenic compound did not modify basal ERK signaling. Rapid E(2)-induced increases in pERK immunoreactivity were specific to the ERK1/2 pathway as demonstrated by coinjection of the mitogen-activated, ERK-activating kinase (MEK)1/2 inhibitor U0126. Coadministration of BPA (10(-12) to 10(-10) M) with 10(-10) M E(2) dose-dependently inhibited rapid E(2)-induced ERK1/2 activation in developing cerebellar neurons. The ability of BPA to act as a highly potent E(2) mimetic and to also disrupt the rapid actions of E(2) at very low concentrations during cerebellar development highlights the potential low-dose impact of xenoestrogens on the developing brain.

Expression of Concern: Laccase treatment impairs bisphenol A‐induced cancer cell proliferation affecting estrogen receptor α‐dependent rapid signals

“…Therefore, it is reasonable to suggest that BPA, similarly to E2, binds to ERa and produces changes in these rapid signals. Few data address the ability of BPA to mediate nongenomic estrogenic actions (see [25][26][27][28][29][30][31] and, as far we know, no information focuses on the involvement of these pathways in the proliferative effect of BPA.…”

Chapel Hill bisphenol A expert panel consensus statement: Integration of mechanisms, effects in animals and potential to impact human health at current levels of exposure

“…BPA also results in changes in tissue enzymes and hormone receptors, and interacts with other hormone-response systems, such as the androgen and thyroid hormone receptor signaling systems. While BPA was initially considered to be a "weak" estrogen based on a lower affinity for estrogen receptor alpha relative to estradiol [18], research shows that BPA is equipotent with estradiol in its ability to activate responses via recently discovered estrogen receptors associated with the cell membrane [19][20][21][22]. It is through these receptors that BPA stimulates rapid physiological responses at low picogram per ml (parts per trillion) concentrations.…”

Rapid signaling mechanisms of estrogens in the developing cerebellum

“…These estradiol-mediated signaling events are of major importance during development and function of the brain McEwen, 2002;Wong et al, 2003;Woolley, 1999;Zsarnovszky et al, 2005). Specific examples of rapid signaling actions include estradiol rapidly activating non-NMDA glutamate receptors in hippocampal neurons through a G-protein coupled and protein kinase A (PKA) dependent mechanism.…”

“…temporal considerations and the impacts of steroid binding proteins on bioactive concentrations of steroid). To decrease uncontrolled variables associated with systemic exposures, an in vivo model system where the cerebellum of anesthetized neonatal and adult rats was directly exposed to known concentrations of estrogens by intracerebellar infusion was developed (Zsarnovszky et al, 2005). Using that approach, the rapid impact of estradiol on active ERK-IR in the cerebellum was pharmacologically characterized.…”

“…In this regard, we have been able to separate the physiological actions of rapid estradiol-induced ERK-signaling from longer duration estradioleffects and found that rapid ERK-signaling and slower acting ER-mediated actions differentially regulate neuronal cell death, mitosis, and neuroprotection (Wong et al, 2003). Using in vitro and in vivo models our studies have also characterized new estrogen-initiated signaling pathways, and found that endocrine disrupting chemicals such as bisphenol A (BPA) can paradoxically act as extremely potent estrogen mimetics and as inhibitors of 17β-estradiol activity Zsarnovszky et al, 2005).…”