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theses

Alcohol exposure during gestation increases breast cancer risk in offspring. While the mechanisms that underlie this effect are not fully understood, serum estradiol (E2) is increased in these animals during proestrus, suggesting a role for the estrogen axis. To test this hypothesis, it was necessary to develop a stress-free method of hormone administration that could be used in long-term studies of carcinogen exposure to ovariectomized (OVX) rats. Rats were OVX on post-natal day (PND) 40 then treated with daily peroral E2 with or without P4 by adding hormones to peanut butter. On PND 50 rats were injected with nitrosomethylurea (NMU) to induce mammary tumor development. After 26 weeks, there was no difference in tumor incidence suggesting that E2 alone at a normal physiological level can result in tumor development. These results indicate that this may be a useful method to examine the mechanisms of steroid action in mammary tumorigenesis. In addition to changes in circulating E2, local estrogen signaling may be altered in the mammary gland in response to alcohol in utero. To explore this possibility as well as obtain a global view of changes that occur in the mammary gland transcriptome, pregnant Sprague-Dawley rats were treated with alcohol or a control diet during pregnancy. Serum analysis demonstrated an increase in circulating E2 in alcohol-exposed dams during gestation suggesting that alcohol in utero may act as an endocrine disruptor during early development. Mammary glands from PND 2, 10, and 20 offspring were analyzed by RNASeq to look for changes in the estrogen axis. Initial analysis with cummeRbund using a low read depth of 25 million reads demonstrated limited differences between alcohol-exposed rats and controls at PND 2 and PND 10. An analysis of additional samples at PND 20 using qRTPCR suggested that heterogeneity of the gland may prevent differences from being observed using the approach taken here. Further analyses of changes in the transcriptome from PND 2 to 10 suggested an increase in stromal cells over time that was corroborated by changes in mammary gland morphology. Comparisons were made with triple negative breast cancer (TNBC), a disease characterized by hormone independent growth similar to this period of mammary gland development. These results suggest that this may be a useful model to study TNBC. Future studies using greater read depth or a larger sample size may uncover differences between alcohol-exposed offspring and controls that were not seen with the present analysis.

ETD_7160

Ph.D.

Includes bibliographical references

by Hillary Stires

doi:10.7282/T32809SH

ETD doctoral

The author owns the copyright to this work.