Animal Science Department

 

Date of this Version

12-2010

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science Major: Animal Science Under the Supervision of Professor Jennifer R. Wood Lincoln, Nebraska December, 2010 Copyright 2010 Elizabeth Mack

Abstract

It has become increasingly clear that female obesity is associated with a myriad of adverse side effects including abnormal female reproduction due, in part, to amenorrhea and anovulatory infertility. The lethal yellow (LY) mouse possesses a deletion mutation which results in ectopic expression of agouti and adult-onset obesity. Furthermore, LY mice exhibit premature loss of fertility, which has been associated with progressive obesity making the LY mouse line an excellent model to study the effects of obesity-dependent factors on ovarian function. In the current study blood serum and granulosa cells were obtained from LY (Ay/a) and age-matched B6 controls (C57BL/6J) to identify changes in metabolic hormone profiles and gene expression, respectively. As expected, LY females exhibited higher circulating levels of insulin and leptin compared to age-matched B6 controls. For the first time, we identified a significant increase in circulating insulin like-growth factor-1 (IGF-1) levels in the LY compared to B6 at 6 weeks of age. Despite these differences in circulating hormone levels, there was little evidence that gene expression is altered in age-matched granulosa cells from LY and B6 females. However, age-dependent changes in the expression of several genes involved in follicular growth in both LY and B6 females were detected. Given that IGF-1 exhibited increased levels in LY compared to B6 mice at 6 weeks of age, the objective of our in vitro study was to determine the role of IGF-1 on granulosa cell gene expression. To this end, short-term granulosa cell cultures were treated with cAMP (the second messenger of both FSH and LH signaling), IGF-1, or a combination of both. IGF-1 had an additive effect on cAMP-dependent regulation of a subset of genes involved in follicular growth, bi-directional communication, steroidogenesis, and ovulation. Western blot analyses provided evidence that the additive effect of IGF-1 on cAMP regulation of gene expression is mediated by stimulation of Akt phosphorylation. Thus, the cooperative effect of IGF-1 on FSH- and LH-dependent signaling may enhance the expression of genes which are crucial for optimal follicular growth and ovulation. Furthermore, these collective data provide a plausible mechanism for age and obesity-dependent anovulatory infertility.

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