PROJECT ABSTRACT Obesity rates are rising worldwide. Obesity is a significant risk factor for development of breast cancer, and obese breast cancer patients have a worse prognosis. Breast tumors from obese patients have increased desmoplasia, with significantly more smooth muscle actin (SMA) positive cells, a marker for myofibroblasts, within tumors. Obesity induces a state of chronic, macrophage-driven inflammation. It is not understood how inflammation within the obese breast contributes to adipose tissue fibrosis and tumor desmoplasia. In obesity, myeloid progenitor cells are significantly increased within bone marrow. Fibrocytes, a myeloid lineage cell type with characteristics of both macrophages and myofibroblasts, are derived from myeloid progenitor cells and are increased in chronic inflammatory and fibrotic diseases. The long-term goal is to understand how the systemic inflammatory conditions of obesity contribute to fibrotic tumors. The rationale is that tumor fibrosis is associated with more aggressive tumors, and understanding this inflammatory microenvironment will lead to discoveries of much needed therapeutic targets for obese cancer patients. The overall objective of this proposal is to identify how obesity increases fibrocytes to enhance collagen deposition within tumors, and how weight loss intervention reverses these effects of obesity. The central hypothesis is that obesity reversibly increases myeloid progenitor cells and fibrocytes within the bone marrow and mammary gland, respectively, leading to an increase in collagen deposition within tumors. This hypothesis will be tested in three specific aims: 1) To identify how obesity-induced fibrocytes contribute to mammary tumor stroma; 2) To elucidate how obesity-induced fibrocytes enhance fibrosis during tumor growth; 3) To examine how weight loss decreases fibrocytes within the normal mammary gland and mammary tumors, resulting in reduced fibrosis. A diet-induced mouse model of obesity and trp53-/- mammary tumor cell xenografts will be utilized to test these aims. Myeloid progenitor cells and monocytes/ macrophages in bone marrow and mammary tumors will be quantified from lean, obese, and weight loss mice using FACS and flow cytometry. Colony formation from FACS isolated cells will be used to quantify mammary tumor fibrocytes. Adoptive transfer using FACS isolated GFP-expressing bone marrow cells from obese mice will be used to examine cell populations responsible for tumor fibrosis. Picrosirius red staining multiplexed with immunofluorescence will be used to examine collagen deposition in mammary tumors and localize fibrocytes. This approach is innovative because fibrocytes have not been studied in obesity, and the mechanisms underlying obesity-induced tumor desmoplasia are not well understood. Identifying how obesity regulates fibrocytes and tumor fibrosis is important to develop novel therapies to treat the more aggressive tumors observed in obese cancer patients. Beyond new...