Long-term goals of this research are to understand how hyperinsulinemia negatively impacts fertility, with a focus on oocyte chromatin segregation and subsequent embryonic developmental competence. Type II diabetes and obesity in women have increased to epidemic proportions. Due to present day lifestyles, insulin resistance has become more prevalent in reproductive age women. Ethnic groups, such as African Americans, Native Americans, Asians and Mexican Americans, are even more affected by these pathologies. Insulin resistance alone, or in association with PCOS, is associated with increased miscarriages, reduced fecundity and increased incidence of infertility. This reduced reproductive efficiency can not be explained by endocrinopathies alone. In animals and in vitro model systems, elevated insulin during oocyte growth negatively impacts oocyte developmental competence, defined as ability of oocytes to support embryo development to the blastocyst stage. This effect of insulin is exacerbated by FSH exposure, yet the mechanism is unknown. Insulin's terminal signaling enzyme is glycogen synthase kinase-3 (GSK-3). Glycogen synthase kinase-3 is an enzyme with many roles; including regulation of glycogen metabolism, apoptosis, cell fate, and spindle dynamics. At a cellular level insulin, acting at its receptor and through a cascade of enzymes, ultimately inhibits GSK-3 activity. Oocytes contain GSK-3, and inhibition of oocyte GSK-3 activity causes abnormal meiotic chromatin segregation. Thus, our overall hypothesis is that FSH increases oocyte responsiveness to insulin, and prolonged elevated insulin negatively impacts fertility by inhibition of oocyte GSK-3, leading to chromatin segregation aberrations and embryos with elevated incidence of aneuploidy and reduced ability to establish a normal pregnancy.
Two specific aims are proposed to address this hypothesis: (1) Test the hypothesis that prolonged elevated FSH exacerbates insulin-induced compromise of oocyte developmental competence by increasing oocyte responsiveness to insulin at the receptor and/or signal transduction level. (2) Test the hypothesis that prolonged elevated insulin results in reduced intra-oocyte GSK-3 activity, abnormal chromatin condensation and/or spindle formation, and disruption of normal chromatin segregation. The well-established mouse oocyte granulosa cell complex system, combined with molecular, genetic, and cell biology approaches will be used in Specific Aims 1 and 2. These studies will provide novel information on mechanisms involved in regulating oocyte normalcy and embryo developmental competence and pregnancy success when insulin-resistance, obesity, diabetes, and/or PCOS compromise women's health and fertility. ? ?
