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theses

Breast cancer is the most common cancer in women worldwide and in 2019 it is estimated that approximately 41,000 women will die from the disease. There are a variety of factors that increase risk for breast cancer one of which is alcohol consumption. However, the mechanism that underlies this increased risk is unknown. The mammary gland is a dynamic organ composed of a multiple cell types including adipose cells, fibroblasts, immune cells, and epithelial cells. The epithelial cells can be categorized into luminal and basal epithelial cells, whose composition is maintained and controlled by a pool of mammary stem cells. Mammary stem cells are quiescent and long lived, and therefore have the potential to accumulate mutations and transform into breast cancer stem cells. Breast cancer stem cells have the potential to maintain a tumor and may not be irradiated by conventional therapies, leading to relapse. Therefore, understanding what regulates the overall mammary epithelial cell hierarchy is key to improving breast cancer treatments. The goal of this project was to determine whether alcohol consumption alters the mammary epithelial cell composition to favor a tumorigenic state, whether alcohol consumption affects tumor latency, and whether alcohol alters the mammary tumor epithelial cell composition.
The MMTV-Wnt1 mouse model is a useful model for studying the role of mammary stem cells in breast cancer, as the tumors that develop in this model arise from a stem or stem-like cell, and downstream targets of the Wnt signaling cascade have been found to be upregulated in breast cancer. To investigate the effect of alcohol on mammary epithelial cell composition and tumorigenesis, 7- week old MMTV-Wnt1 female mice were given a 20% alcohol solution in place of drinking water sweetened with 0.2% saccharin. Control animals were given a 0.12% saccharin solution for the entire duration of the study. Animals were weighed once per week and were sacrificed after either 8 weeks to analyze the preneoplastic mammary gland or after the first tumor had reached 1.5cm in diameter. Animals in the alcohol group gained more weight compared to the controls, and this difference in weight gain was due to an increase in overall caloric intake due to alcohol consumption. Mammary epithelial cells were isolated and analyzed by flow cytometry and plated for mammosphere/tumorsphere assays. Mammary glands from the alcohol group exhibited an increase in the luminal progenitor population, but a decrease in mammosphere forming efficiency. Alcohol consumption decreased tumor latency in animals that presented with tumors by 43 weeks of age, however, alcohol consumption did not effect on the tumor epithelial cell composition nor the tumorsphere forming efficiency. Alcohol consumption decreased the expression of the epithelial-mesenchymal transition (EMT) factors Snail and Twist in the mammary gland mRNA, and the proliferation marker Ki67. It also decreased expression of Snail in mRNA from the mammary tumor. Alcohol did not affect estrogen receptor positivity in the mammary tumors, suggesting an estrogen-independent mechanism in this model.
In conclusion, alcohol consumption in adulthood altered the mammary epithelial cell composition by increasing the number of luminal progenitor cells, which have been implicated as tumor initiating cells in basal like breast tumors. Alcohol consumption also decreased mammosphere forming efficiency, suggesting a decrease in the stem cell population. Analysis of gene expression further suggested that alcohol decreased the stem cell population in the mammary gland due to a decrease in Snail and Twist expression. It is also possible that alcohol affected the mammary epithelial cell composition by increasing body weight and altering composition, which has also been identified as a risk factor for breast cancer risk.

ETD_10075

M.S.

Includes bibliographical references

doi:10.7282/t3-f46z-6662

ETD graduate

The author owns the copyright to this work.