MAP Kinase Pathway is Involved in IGF-1-Stimulated Proliferation of Human Retinal Pigment Epithelial Cells (hRPE)

Abstract

Purpose: To investigate the mitogenic activity of insulin-like growth factor-1 (IGF-1) on the proliferation of human retinal pigment epithelial cells (hRPE) and to elucidate the role of vascular endothelial growth factor (VEGF) and MAP kinase (MAPK) in the IGF-1 signaling cascade.

Methods: Human RPE specimens were obtained from postmortem non-pathological eyes and cultured in vitro through several passages. Cellular proliferation in the presence of increasing concentrations of IGF-1 and IGF-1 + PD98059 (a known MAPK inhibitor) was measured by [³H]thymidine incorporation; trypan blue exclusion studies (T) verified cell viability. Under the same experimental conditions, synthesis of VEGF was measured utilizing [¹⁴C]methionine immunoprecipitation and immunocytochemical methods as well as Western blot analysis.

Results: IGF-1 stimulated hRPE proliferation, as demonstrated by [³H]thymidine incorporation. There was also an IGF-1-induced increase in VEGF synthesis as measured quantitatively by [¹⁴C]methionine-VEGF immunoprecipitation. This was qualitatively confirmed by immunocytochemistry and Western blotting. PD98059 suppressed both IGF-1-induced cell proliferation as well as IGF-1-stimulated VEGF production.

Conclusions: These studies suggest that IGF-1 is a mitogen for hRPE cells and also stimulates production of the angiogenic factor, VEGF. Additionally, PD98059 inhibits the production of VEGF, suggesting that the MAP kinase pathway is involved in IGF-1-mediated angiogenesis.

KEYWORDS:

• hRPE
• VEGF
• IGF-1
• MAPK
• Proliferative retinopathy

ACKNOWLEDGMENTS

This study was supported by the Skillman Foundation, Research to Prevent Blindness, and Core Center for Vision Research EY007003. Thanks to Chris Yang, Jennifer Willins, Shadmani Kushi, and Stephen Atkins for their assistance.

Declaration of interest: The author of this paper have no commercial relationships or financial interests to disclose.