Insulin-like growth factor-1 regulates VEGF expression in primary human uterine epithelial cells

Abstract

Objective: Angiogenesis, the formation of new blood vessels from preexisting endothelial cells, is important for the normal functioning of many organs and tissues, including the female reproductive tract. In addition, the process of angiogenesis is understood to play a requisite role in the growth and metastasis of tumor cells. Vascular endothelial growth factor (VEGF) is a mitogen for endothelial cells, necessary for the normal process of angiogenesis during events such as cyclic endometrial regeneration, corpus luteum formation and normal wound healing. In addition, VEGF has been implicated in the growth of many tumors. Therefore, the dysregulation of the VEGF signaling pathway may play a role in the development and/or progression of cancers and other pathologies of the female reproductive tract that require vascularization. Previous studies of uterine cells have shown that VEGF expression can be regulated by the ovarian steroid hormones estradiol (E) and progesterone (P). Other studies from our laboratory and others have shown that uterine insulin-like growth factor-1 (IGF-1) expression is increased by estrogens and that IGF-1 alone can stimulate many of the same uterine events as E. Because IGF-1 is also implicated in the growth of many cancers, the experiments herein were designed to determine whether IGF-1 also stimulates VEGF expression in uterine cells. Design: Tissue culture based research Materials and Methods: Primary human uterine epithelial cells were isolated from endometrial tissue, cultured on collagen-coated tissue culture dishes, and treated with either vehicle or IGF-1. Conditioned medium was then assayed for VEGF content, and cells were examined for the expression of VEGF mRNA. To investigate the mechanism through which IGF-1 stimulates an increase in VEGF expression by primary uterine epithelial cells, inhibitors to the phosphatidylinositol 3-kinase (PI3-K) and MAP kinase (MAPK) signaling pathways were used to investigate the signaling pathway responsible for IGF-1 stimulation of VEGF in uterine cells. Results: In a time-dependent manner, IGF-1 increased the level of VEGF secreted by the primary uterine epithelial cells. Furthermore, IGF-1 stimulated an increase in the levels of VEGF mRNA expressed by the cells. Inhibition of PI3-K signaling, but not MAPK signaling, decreased the amount of VEGF secreted by the uterine cells in response to IGF-1, indicating that PI3-K may be the primary pathway through which IGF-1 regulates VEGF expression in uterine cells. Conclusion: Taken together, these results demonstrate that IGF-1 can increase VEGF production by primary uterine epithelial cells in a PI3-K dependent manner. Elevated IGF-1 levels, in addition to or in response to, elevated E levels may contribute to the vascularization and, thus, growth of endometrial pathologies.