Role of Insulin-like growth factor-I (IGF-I) and Kit Ligand (KL) in ovarian function / Papel do fator de crescimento semelhante à Insulina-I (IGF-I) e Kit Ligand (KL) na função ovariana

ABSTRACT

Background: The ovarian function is coordinated by many growth factors and hormones responsible for ensuring the success of follicular and oocyte development. To obtain competent oocytes is necessary to have a perfect interaction between follicular somatic cells and the oocyte, which is potentially regulated by paracrine factors produced in the ovary. Among these factors, we highlight the insulin-like growth factor-I (IGF-I) and Kit ligand (KL). This review summarizes the main aspects of molecular structure of IGF-I and KL and their receptors, the mechanisms of action and expression of these substances, as well as their role on ovarian function.Review The IGF-I is a peptide structurally similar to proinsulin, and is part of IGF-I system. This system comprises two receptors with their respective ligands and six high-affinity IGF binding proteins. Its action is mediated by binding to its specific receptor tyrosine kinase (IGFR-I), that initiates the activation of PI3K and /or MAPK pathway. In ovary, this growth factor was observed in different compartment of follicle (granulosa cells, theca cells and oocyte). IGF-I is the main cell survival factor in the ovary, it protects cell from apoptosis promoted by several agents. Activation of the IGF-I receptor is a particularly important survival-promoting signal during follicular development. The involvement of IGF-I in the early stage...