Doctor of Philosophy
Dr. Dwayne Jackson
Chronic stress is associated with elevated levels of sympathetic neurotransmitter release and immunosuppression. A growing body of evidence suggests that stress-related factors may contribute to the initiation, development and progression of breast cancer. Neuropeptide Y (NPY) has recently been determined as such a factor, however few investigations have addressed the functional effects of NPY on breast cells and tumors. Thus, the overall objective of this thesis was to elucidate the mechanisms by which NPY may contribute to the disease. Using the 4T1 murine breast cancer model, we began by first characterizing NPY receptor expression in cancer cells and tumors. Y1R, Y2R and Y5R’s were expressed in 4T1 cells and tumors. In vitro assays were then conducted to determine the effects of NPY receptor activation on 4T1 cell proliferation and migration. NPY treatment of 4T1 cells stimulated Y5R mediated increases in proliferation, whereas, NPY increased chemotaxis through Y2R and Y5R activation. We then tested whether NPY could function as an angiogenic factor by augmenting expression and secretion of the pro-angiogenic factor VEGF from breast cancer cells. We found that NPY functioned as a paracrine system within 4T1 and MDA-MB-231 cancer cells to promote angiogenesis, signaling to increase expression and release of VEGF through Y5R activation. These findings served as a motivation for our final study where we sought to develop an in vivo model in which the components of NPY system (i.e., nerves, ligands and receptors) could be functionally studied. We first demonstrated sympathetic neural innervation and NPY expression in 4T1 tumors. Secondly, when tumor sympathetic neural innervation was attenuated (via chemical sympathectomy), we observed a significant decrease in tumor growth and vascular development. Furthermore, we observed that treatment with a Y5R antagonist significantly attenuated tumor growth. Finally, we established a protocol for intravital microscopy imaging of tumoral vasculature. Overall, this dissertation provides: 1) evidence that NPY elicits proliferative, migratory and angiogenic effects on breast cancer cells, 2) an in vivo model for functional studies examining the role of sympathetic nerves, neurotransmitters, cancer cells and blood vessels, and 3) highlights the Y5R as a potential therapeutic target.
Medeiros, Philip J., "The Impact of the Neuropeptide Y System on the Progression of Breast Cancer" (2012). Electronic Thesis and Dissertation Repository. 1065.