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Inhibition of Phosphatidylinositol 3-Kinase Amplifies TEGDMA-induced Apoptosis in Primary Human Pulp Cells

G. Spagnuolo1, K. Galler2, G. Schmalz2, C. Cosentino3, S. Rengo1, and H. Schweikl2,*

1 Department of Oral and Maxillo-Facial Sciences and
3 Department of Cellular and Molecular Biology and Pathology, University of Naples "Federico II", via S. Pansini 5, 80131-Naples, Italy; and
2 Department of Operative Dentistry and Periodontology, University of Regensburg, D-93042 Regensburg, Germany;



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Figure 1. The effect of TEGDMA on the induction of apoptosis and necrosis in human primary pulp cells. Cell cultures were incubated with annexin V-FITC (apoptotic cells) and PI (necrotic cells) and analyzed by flow cytometry. The representative dual-parameter fluorescence histograms were derived from cell cultures exposed to various TEGDMA concentrations for 24 hrs. The numbers indicate the percentages of the viable (annexin V-; PI-) cell population (lower left quadrant), the apoptotic (annexin V+) cell population (lower right quadrant), and the necrotic cell populations in the upper right (annexin V+; PI+) and the upper left quadrants (annexin V-; PI +) in one typical experiment.

 


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Figure 2. Dose-dependent induction of apoptosis and necrosis in human pulp cells. Cell cultures were treated with various concentrations of TEGDMA in duplicate for 24 hrs. The percentages of apoptotic ({circ}) and necrotic ({square}) cell populations were analyzed by flow cytometry. Values (means ± SD) from 6 independent experiments are presented (n = 6); * indicates significant (p ≤ 0.05), and ** indicates highly significant (p ≤ 0.01) differences from untreated control cultures (Mann-Whitney U-test).

 


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Figure 3. Time-dependent induction of apoptosis by TEGDMA. Primary human pulp cell cultures were continuously exposed to 1 mmol/L TEGDMA for 6, 12, and 24 hrs. The percentages of the apoptotic cell population in untreated controls ({circ}) and TEGDMA-treated cultures (•) were analyzed by flow cytometry. Values (means ± SD) from 3 independent experiments in duplicate are presented (n = 3); * indicates a significant (p ≤ 0.05) difference from untreated control cultures (Mann-Whitney U-test).

 


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Figure 4. The effects of the inhibition of MAPK/ERK and PI3K pathways in human pulp cells. (a) Total extracts derived from human primary pulp cells treated with 1 mmol/L TEGDMA or 3 mmol/L TEGDMA for 15 min were separated on 10% SDS-PAGE, and immunoblotted with anti-P-Akt (ser 473) or anti-P-ERK 1/2. The amounts of total protein present in the extracts were determined by immunoblotting with anti-Akt, anti-tubulin, and anti-ERK 2. Experiments were performed 3 times, and a representative result is shown. (b) The ratio between P-Akt and total Akt in pulp cells after treatment with TEGDMA determined by densitometry. Asterisk indicates significant differences from untreated cell cultures (n = 3). (c) Induction of apoptosis and necrosis in human pulp cells. Cells were pre-treated with 50 µmol/L LY294002 and 40 µmol/L PD98056 for 30 min, and then further exposed to 1 mmol/L TEGDMA for 24 hrs. Apoptotic (annexin V+) and necrotic (PI+) cell populations were analyzed by flow cytometry as described. Viability of a cell population is expressed as the difference between the total cell population and the populations which stained with annexin V-FITC and PI. Values (means ± SD) from at least 4 independent experiments in duplicate are presented (n = 4); * indicates significant (p ≤ 0.05), and ** indicates highly significant (p ≤ 0.01) differences from untreated control cultures (Mann-Whitney U-test). (d) Inhibition of Akt phosphorylation in human pulp cells. The cells were treated with 40 mmol/L LY294002 for 30 min, and then exposed to 1 mmol/L TEGDMA for 15 min. Cell lysates were separated on SDS-PAGE and blotted with anti-P-Akt or total Akt antibodies.

 





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