Estrogen receptor beta-selective agonists stimulate calcium oscillations in human and mouse embryonic stem cell-derived neurons

Abstract

Estrogens are used extensively to treat hot flashes in menopausal women. Some of the beneficial effects of estrogens in hormone therapy on the brain might be due to nongenomic effects in neurons such as the rapid stimulation of calcium oscillations. Most studies have examined the nongenomic effects of estrogen receptors (ER) in primary neurons or brain slices from the rodent brain. However, these cells can not be maintained continuously in culture because neurons are post-mitotic. Neurons derived from embryonic stem cells could be a potential continuous, cell-based model to study nongenomic actions of estrogens in neurons if they are responsive to estrogens after differentiation. In this study ER-subtype specific estrogens were used to examine the role of ERalpha and ERbeta on calcium oscillations in neurons derived from human (hES) and mouse embryonic stem cells. Unlike the undifferentiated hES cells the differentiated cells expressed neuronal markers, ERbeta, but not ERalpha. The non-selective ER agonist 17beta-estradiol (E(2)) rapidly increased [Ca2+]i oscillations and synchronizations within a few minutes. No change in calcium oscillations was observed with the selective ERalpha agonist 4,4',4''-(4-Propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT). In contrast, the selective ERbeta agonists, 2,3-bis(4-Hydroxyphenyl)-propionitrile (DPN), MF101, and 2-(3-fluoro-4-hydroxyphenyl)-7-vinyl-1,3 benzoxazol-5-ol (ERB-041; WAY-202041) stimulated calcium oscillations similar to E(2). The ERbeta agonists also increased calcium oscillations and phosphorylated PKC, AKT and ERK1/2 in neurons derived from mouse ES cells, which was inhibited by nifedipine demonstrating that ERbeta activates L-type voltage gated calcium channels to regulate neuronal activity. Our results demonstrate that ERbeta signaling regulates nongenomic pathways in neurons derived from ES cells, and suggest that these cells might be useful to study the nongenomic mechanisms of estrogenic compounds.

Figure 1. Immunofluorescent staining of neurons from human ES cells with neuronal markers.

The cells were stained positively with mature neuronal markers, such as Map2 (green), TujIII (red), Tau (red) and Syp (red) at day 30–36. The homogeneity of culture was shown by 4′,6-diamidino-2-phenylindole (DAPI, blue) and Map2 double-staining. The cells exhibited both GABAergic and glutamatergic properties as shown by glutamic acid decarboxylase (Gad65, red), GABA (green) and vesicular glutamate transporter (VGlut, red) immunofluorescence. The left two lanes are staining of neurons from the H9 cell line, and the right two lanes are staining of neurons from the H7 cell line as labeled. Scale bar: 200 µm for Map2 in row 1, and 63 µm for the rest.

Figure 2. Neurons from the H9 cell line are excitable by ion channel regulators at day 30–36.

(A) Tracings of [Ca2+]i changes in response to KCl (56 mM), VTD (50 µM) and TTX (1 µM) in representative cells. “*” indicates Pulsar recognized [Ca2+]i peaks. Changes after treatment (gray bars) in the frequency of [Ca2+]i oscillations (B) and amplitudes of [Ca2+]i peaks (C) compared to basal activity (black bars, normalized to 1). The number of cells analyzed for KCl, VTD, TTX and Control were 180, 175, 104 and 98, respectively, from 2 or 3 independent experiments. ** p<0.01 compared to control.

Figure 3. Neurons from the H7 cell line are excitable by ion channel regulators at day 30–36.

(A) Tracings of [Ca2+]i changes in response to KCl (56 mM), VTD (50 µM) and TTX (1 µM) in representative cells. “*” indicates Pulsar recognized [Ca2+]i peaks. Changes after treatment (gray bars) in the frequency of [Ca2+]i oscillations (B) and amplitudes of [Ca2+]i peaks (C) compared to basal activity (black bars, normalized to 1). The number of cells analyzed for KCl, VTD, TTX and Control were 164, 189, 172 and 153, respectively from 2 or 3 independent experiments. ** p<0.01 compared to control.

Figure 4. Neurons from the human ES cell lines express endogenous ERβ.

(A) Immunoprecipitation and western blot analysis with anti-ERα of H9- and H7-neurons. No endogenous ERα expression was revealed in both neurons (left two lanes). Exogenous ERα (pointed by arrows) was introduced by infection with 10 MOI of Ad-ERα (right two lanes). The blots have been rearranged from the same gel. (B) Immunoprecipitation and western blot analysis with anti-ERβ of H9- (left panel) and H7-neurons (right panel). The usual size ERβ (denoted by →) and a slightly bigger ERβ isoform (denoted by →) were detected in both H9- and H7-neurons. Immunoprecipitation with IgG from the same amount of cell lysates was used as negative control.

Figure 5. ERβ-selective ligands increase [Ca2+]i oscillations in H9-neurons.

Changes in the frequency of [Ca2+]i oscillations (A) and amplitudes of [Ca2+]i peaks (B) after treatment with E₂ (10 nM), ERB-041 (1 µM), DPN (1 µM), MF101 (125 µg/ml), PPT (1 µM), PPT plus Ad-ERα (PPT+ERα) and Control. The data after treatment (gray bars) are expressed relative to those before treatment (basal, black bars), which are normalized to 1. The number of cells analyzed for the above groups were 143, 221, 260, 188, 134, 179 and 98, respectively from 2 or 3 independent experiments. ** p<0.01, H9-neurons treated by different drugs are compared to control.

Figure 6. Neurons from mouse ES cells express endogenous ERα and ERβ.

(A) Real-time PCR analysis of ERα and ERβ mRNAs in neurons relative to undifferentiated mES cells (assigned to 1). The data shown are the average of ten independent cultures. Immunoprecipitation and western blot analysis of ERα (B) and ERβ (C) (pointed by arrows) in neurons (Neuron) and undifferentiated ES14 cells (ESC).

Figure 7. E₂-mediated increase of [Ca2+]i oscillations occurs through L-type Ca2+ channels.

Neurons from mES cells were pretreated for 15 min with different Ca2+ channel inhibitors: nifedipine (Nif, 10 µM), ω-conotoxin GVIA (CgTx, 1 µM), ω-agatoxin IVA (AgTx, 200 nM) before exposed to 10 nM E₂. Alternatively, the cells were treated directly with the above inhibitors, E₂ and membrane-impermeable E₂-BSA (10 nM). Changes after drug treatment (gray bars) in the frequency of [Ca2+]i oscillations (A) and amplitudes of [Ca2+]i peaks (B) compared to basal levels (black bars, normalized to 1). The number of cells for Nif, Nif+E₂, AgTx, AgTx+E₂, CgTx, CgTx+E₂, E₂-BSA, E₂ and Ctrl are 233, 213, 163, 170, 165, 156, 139, 113 and 99, respectively, from 5, 4, 3, 3, 3, 3, 3, 3, and 2 independent experiments. ** p<0.01, * p<0.05 in comparison to non-treatment control.

Figure 8. AKAP150 knockdown decreases [Ca2+]i oscillations induced by E₂.

(A) RNA levels of AKAP150 in neurons from mES cells at 48 h postinfection with adenovirus delivering siRNA to AKAP150 (Ad-si-AKAP) and luciferase (Ad-si-Luc). The data shown are normalized to AKAP150 levels of uninfected cells (assigned to 1), and are the average of three independent experiments. (B) Immunofluorescent staining of AKAP150 (green) in mES-neurons at 48 h postinfection with 20 MOI Ad-si-AKAP or Ad-si-Luc. Scale bar represents 63 µm. Changes in the frequency (C) and amplitudes (D) of [Ca2+]i peaks after E₂ (10 nM) treatment in neurons from mES cells at 48 h postinfection with 10 MOI of Ad-si-AKAP, Ad-si-Luc and uninfected control (Ctrl). The data after treatment (gray bars) are expressed relative to basal levels (black bars, normalized to 1). The numbers of cells analyzed for the above groups are 366, 286, 320, respectively, from 6 or 7 independent experiments. **p<0.01, Ad-si-AKAP cells are compared to Ad-si-Luc cells.

Figure 9. E₂ rapidly activates multiple signaling transduction events in neurons from mES cells.

The cells were treated with E₂ (10 nM), lysed at the indicated time points and subjected to SDS-PAGE. Western blotting was performed with phospho-specific antibodies against PKCα/β-P (A), AKT-P (B), c-RAF-P (C), ERK1/2-P (D) and CREB-P (E), or with corresponding phospho-independent antibodies against total PKC (PKC- ζ), AKT, c-RAF, ERK1/2 and CREB as loading controls. A representative immunoblot is shown for each signaling pathway. Densitometric analysis is plotted in columns below the blots. Levels of E₂-induced activation were calculated as fold-increase in comparison to time point zero (normalized to 1). The results shown are the average ± SD of three independent experiments done in three independent cultures. NS: non-specific band of c-RAF-P or c-RAF. ** p<0.01, * p<0.05, all time points after E₂ exposure were compared to time point zero.

Figure 10. ERβ-selective ligands activate AKT, ERK1/2 and CREB signaling in neurons from mES cells.

The cells were treated with E₂ (10 nM), ERB-041 (1 µM), DPN (1 µM), MF101 (125 µg/ml), and PPT (1 µM) for 30 min, lysed and analyzed by western blotting using phospho-specific AKT (A), ERK1/2 (B) and CREB (C). Total AKT, ERK1/2 and CREB blots were used as loading controls. Blots from a representative experiment were shown. Bands were quantified as fold-increase compared to untreated control (assigned to 1). The average ± SD of 3 or 4 independent experiments were plotted in columns. **p<0.01, * p<0.05, all treatment groups were compared with non-treatment control.