Estrogen-induced retinal endothelial cell proliferation: possible involvement of pigment epithelium-derived factor and phosphoinositide 3-kinase/mitogen-activated protein kinase pathways.

Purpose: Diabetic retinopathy is a leading cause of blindness due to a progressive damage of the retina by neovascularization and other related ocular complications. However, the molecular mechanism underlying the development of diabetic retinopathy is not well understood. An increase in estrogen levels during puberty is associated with an accelerated development of diabetic retinopathy. Previously, we have introduced 17β-estradiol (E2) to rhesus retinal capillary endothelial cells (RhRECs) in culture and observed a dose- and time-dependent increase in the number of viable cells. The purpose of this present study was to investigate the molecular signaling pathway associated with this estrogen-induced proliferation of RhRECs.

Methods: Estrogen receptor (ER) ER(α) and ER(β) mRNA expression, and protein synthesis were measured at 0, 3, 6, and 12 h using nested polymerase chain reaction and Western blots. Phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathway inhibitors were introduced into culture media to study their effects on E2-induced cell proliferation and pigment epithelium-derived factor (PEDF) synthesis. The levels of PEDF in the conditioned media were measured by enzyme-linked immunosorbent assay.

Results: Exogenous E2 induced a significant increase in the expression of ER(β) along with an increase in the number of viable RhRECs. Cotreatment of E2 with PI3K and MAPK inhibitors significantly reduced the E2-induced effect on cell proliferation and PEDF production in a dose-dependent manner.

Conclusion: Results from the present study suggest that an E2-induced increase in the proliferation of RhRECs may be mediated by the action of ER(β.) Both PI3K and MAPK signaling pathways are involved in this E2-induced cell proliferation, which may follow changes in PEDF levels controlled by these pathways. Further studies will provide additional details on the interaction between these pathways to control changes in PEDF levels and cell proliferation.