Date of Award

5-2011

Degree Type

Thesis

Degree Name

Master of Science

Major

Life Sciences

Major Professor

Brynn H. Voy

Committee Members

Arnold Saxton, Naima Moustaid-Moussa

Abstract

While diet and sedentary lifestyle remain important factors in the development of obesity, recent findings have shown the possible involvement of environmental obesogens, chemicals that can disrupt homeostatic energy balance and increase adiposity. Bisphenol A (BPA) is a compound used in the manufacturing of plastics as a hardening agent and is ubiquitous in the environment due to its widespread use. BPA has been shown to be an endocrine disruptor through its ability to mimic estrogen, which is now known to play important roles in adipose tissue growth and metabolism. In fact, a small but compelling number of studies have shown that mice exposed to BPA in utero or postnatally are fatter as adults.
We hypothesized that BPA exposure exerts effects on adipose tissue, promoting adipogenesis and inflammation, and altering energy homeostasis in a manner that promotes obesity. We tested our hypothesis using both in vitro and in vivo models. First, we found that low concentrations of BPA increased the expression of the inflammatory genes, Il-6 and Tnfa, approximately 1.5-3.0 fold in mouse adipose tissue explants. We also found a 3-fold increase in the expression of the lipogenic gene, Fasn. BPA also altered the adipose tissue metabolism, increasing the levels of a number of glycolytic and TCA cycle metabolites, suggesting that BPA may disrupt energy homeostasis. We also found that BPA exposure increased proliferation of mesenchymal stem cells approximately 1.2-fold, which are potential adipocyte
precursors. The study was expanded using two different strains of mice, C57BL/6 and DBA/2J, chronically exposing them to BPA through drinking water for six weeks. A moderate concentration of BPA increased the perigonadal fat pad mass in males. This increase in adiposity was associated with adipocyte hypertrophy and decreased serum adiponectin levels. There were also changes in the expression of some genes with BPA treatment, including a 1.4-fold increase in Leptin and decreases in some Cytochrome P450 genes; however the genes differentially expressed were different between the two strains. Our results suggest that childhood exposure to low doses of BPA, in lieu of any developmental exposure, may contribute to childhood obesity.

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