Human Amniotic Epithelial Cells Promote the Proliferation of Human Corneal Endothelial Cells by Regulating Telomerase Activity via the Wnt/β-catenin Pathway

PURPOSE

Human amniotic epithelial cells (HAECs) have regenerative properties and low immunogenicity, which have enabled their use without immune rejection in regenerative medicine applications, such as wound repair, corneal surgery and burn repair. The aim of this study was to explore the potential role of HAECs in the proliferation of human corneal endothelial cells (HCEnCs) and the possible mechanism of regulation.

METHODS

HAECs and HCEnCs were isolated from donated tissue samples and were cultured; the collected HAEC culture medium (HAEC-Me) was added to the human corneal endothelium medium (CEM) to establish the HAEC-CM system. HCEnCs were cultured in CEM, 20%HAEC-Me, 20% HAEC-CM, 20% HAEC-CM supplemented with a GSK-3β inhibitor TWS119 or CEM supplemented with TWS119. Then, cell proliferation, apoptosis, cell cycle progression, telomerase activity, and Wnt/β-catenin pathway-related protein levels were assessed.

RESULTS

We found that the HCEnCs cultured in the 20% HAEC-CM had increased proliferative capacity, telomerase activity and β-catenin and Tcf4 expression levels, and they had a decrease in the rate of apoptosis and α-SMA expression when they were compared with the HCEnCs cultured in the 20% HAEC-Me. After GSK-3β was inhibited by TWS119, HCEnCs cultured in CEM or 20% HAEC-CM had an increased proliferative capacity, telomerase activity, β-catenin/Tcf4 expression and a decreased α-SMA expression, and they had a decreased apoptotic rate.

CONCLUSIONS

These data indicate that the human amniotic epithelial cells microenvironment can promote the proliferation of human corneal endothelial cells, which may be related to regulating telomerase activity and epithelial-to-mesenchymal transition (EMT) via the Wnt/β-catenin pathway.

Podophyllum hexandrum Fraction (REC-2006) Shows Higher Radioprotective Efficacy in the p53-Carrying Hepatoma Cell Line: A Role of Cell Cycle Regulatory Proteins

The present study was carried out to evaluate the radioprotective efficacy of Podophyllum hexandrum fraction (REC-2006) in hepatoma cell lines having different p53 statuses. Higher radioresistance was observed in the HepG2 (p53++) cell line in comparison to the Hep3B (p53--) cell line, indicating a plausible role of p53 in radioresistance. REC-2006 exhibited nearly twice the survival in p53-expressing HepG2 cells compared with p53-negative Hep3B cells. REC-2006 treatment alone induced p53 expression as compared with untreated controls. However, REC-2006 reduced p53 expression when treated 2 hours before irradiation as compared with the irradiated HepG2 controls, indicating that REC-2006 modulates the expression of p53 to mitigate its apoptotic effect. Induction of p21 in the REC-2006 + radiation treatment group downregulated the expression of cyclin E and CDK2, leading to a delay in the G1 phase of HepG2 cells, which provided time for DNA repair or related processes. However, no significant difference in CDC2 expression in both cell lines suggested that G2 phase arrest might not be the only responsible factor for REC-2006-mediated radioprotection. Significant induction of PCNA and GADD45 expression in HepG2 cells suggested that REC-2006 increased the percentage survival of HepG2 cells by increasing the span of time as well as efficacy for repair processes. In conclusion, REC-2006 modulated the expression of p53 and thereby promoted cell cycle arrest in the G1 phase, encouraging cell proliferation and DNA repair and thus providing significantly higher protection against acute γ-radiation in the HepG2 cell line.

Oncogenes do not Fully Override Cell-intrinsic Traits: Pronounced Impact of the Cellular Programme

Overexpression of p53 tumor suppressor protein in malignant cells induces cell cycle arrest, or alternatively, apoptosis thereby indicating that additional factors may contribute to the p53-mediated outcome. Comparison of the experimental protocols revealed that the construct encoding wild-type (wt) p53 was expressed in cells of different origin. Therefore, we decided to determine whether the intrinsic cellular program of primary cells of the same genetic background could have any effect on the oncogenic potential of mutated c-Ha-RAS and TP53. Primary rat cells (RECs) isolated from rat embryos of different age: at 13.5 gd (y) and 15.5 gd (o), were used for transfection. Immortalized rat cell clones overexpressing temperature-sensitive (ts) p53^135val mutant and transformed cell clones after co-transfection with oncogenic c-Ha-Ras, were generated. The ts p53^135Val mutant, switching between wt and mutant conformation, offers the possibility to study the role of p53 in cell cycle control in a model of malignant transformation in cells with the same genetic background. Surprisingly, the kinetics of cell proliferation at non-permissive temperature and that of cell cycle arrest at 32°C strongly differed between cell clones established from yRECs and oRECs. Furthermore, the kinetics of the re-enter of G₁-arrested cells in the active cell cycle strongly differed between distinct cell clones. Finally, the susceptibility of immortalized and transformed cells to the pharmacological inhibitors of cyclin-dependent kinases (CDKs) considerably differed. Our results clearly show that overexpression of genes such as mutated TP53 and oncogenic c-Ha-RAS is not able to fully override the intrinsic cellular programme.