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Obesity-Associated Alterations in Inflammation, Epigenetics, and Mammary Tumor Growth Persist in Formerly Obese Mice.

ABSTRACT: Using a murine model of basal-like breast cancer, we tested the hypothesis that chronic obesity, an established breast cancer risk and progression factor in women, induces mammary gland epigenetic reprogramming and increases mammary tumor growth. Moreover, we assessed whether the obesity-induced epigenetic and protumor effects are reversed by weight normalization. Ovariectomized female C57BL/6 mice were fed a control diet or diet-induced obesity (DIO) regimen for 17 weeks, resulting in a normal weight or obese phenotype, respectively. Mice on the DIO regimen were then randomized to continue the DIO diet or were switched to the control diet, resulting in formerly obese (FOb) mice with weights comparable with control mice. At week 24, all mice were orthotopically injected with MMTV-Wnt-1 mouse mammary tumor cells. Mean tumor volume, serum IL6 levels, expression of proinflammatory genes in the mammary fat pad, and mammary DNA methylation profiles were similar in DIO and FOb mice and higher than in controls. Many of the genes found to have obesity-associated hypermethylation in mice were also found to be hypermethylated in the normal breast tissue of obese versus nonobese human subjects, and nearly all of these concordant genes remained hypermethylated after significant weight loss in the FOb mice. Our findings suggest that weight normalization may not be sufficient to reverse the effects of chronic obesity on epigenetic reprogramming and inflammatory signals in the microenvironment that are associated with breast cancer progression. Cancer Prev Res; 9(5); 339-48. ©2016 AACR.

SUBMITTER: Rossi EL

PROVIDER: S-EPMC4854773 | biostudies-literature | 2016 May

REPOSITORIES: biostudies-literature

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Obesity-Associated Alterations in Inflammation, Epigenetics, and Mammary Tumor Growth Persist in Formerly Obese Mice.

Rossi Emily L EL de Angel Rebecca E RE Bowers Laura W LW Khatib Subreen A SA Smith Laura A LA Van Buren Eric E Bhardwaj Priya P Giri Dilip D Estecio Marcos R MR Troester Melissa A MA Hair Brionna Y BY Kirk Erin L EL Gong Ting T Shen Jianjun J Dannenberg Andrew J AJ Hursting Stephen D SD

Cancer prevention research (Philadelphia, Pa.) 20160211 5

Using a murine model of basal-like breast cancer, we tested the hypothesis that chronic obesity, an established breast cancer risk and progression factor in women, induces mammary gland epigenetic reprogramming and increases mammary tumor growth. Moreover, we assessed whether the obesity-induced epigenetic and protumor effects are reversed by weight normalization. Ovariectomized female C57BL/6 mice were fed a control diet or diet-induced obesity (DIO) regimen for 17 weeks, resulting in a normal ...[more]

PMID: 26869351

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Project description:BackgroundObesity is a risk factor for breast cancer, and women with obesity that develop breast cancer have a worsened prognosis. Within the mammary gland, obesity causes chronic, macrophage-driven inflammation and adipose tissue fibrosis. Weight loss is a recommended intervention to resolve obesity, but the impact of weight loss on the mammary gland microenvironment and in tumors has not been well identified.MethodsTo examine the effects of weight loss following obesity, mice were fed a high-fat diet for 16 weeks to induce obesity, then switched to a low-fat diet for 6 weeks. We examined changes in immune cells, including fibrocytes, which are myeloid lineage cells that have attributes of both macrophages and myofibroblasts, and collagen deposition within the mammary glands of non-tumor-bearing mice and within the tumors of mice that were transplanted with estrogen receptor alpha positive TC2 tumor cells.ResultsIn formerly obese mice, we observed reduced numbers of crown-like structures and fibrocytes in mammary glands, while collagen deposition was not resolved with weight loss. Following transplant of TC2 tumor cells into the mammary glands of lean, obese, and formerly obese mice, diminished collagen deposition and cancer-associated fibroblasts were observed in tumors from formerly obese mice compared to obese mice. Within tumors of obese mice, increased myeloid-derived suppressor cells and diminished CD8+ T cells were identified, while the microenvironment of tumors of formerly obese mice were more similar to tumors from lean mice. When TC2 tumor cells were mixed with CD11b+CD34+ myeloid progenitor cells, which are the cells of origin for fibrocytes, and transplanted into mammary glands of lean and obese mice, collagen deposition within the tumors of both lean and obese was significantly greater than when tumor cells were mixed with CD11b+CD34- monocytes or total CD45+ immune cells.ConclusionsOverall, these studies demonstrate that weight loss resolved some of the microenvironmental conditions within the mammary gland that may contribute to tumor progression. Additionally, fibrocytes may contribute to early collagen deposition in mammary tumors of obese mice leading to the growth of desmoplastic tumors.

Project description:PurposeExposure to the polyphenolic plant lignan secoisolariciresinol diglucoside (SDG) and its metabolite enterolactone (ENL) has been associated with reduced breast cancer progression, particularly for estrogen receptor alpha (ER?)-negative disease, and decreased preclinical mammary tumor growth. However, while preclinical studies have established that SDG and ENL affect measures of progression in models of triple-negative breast cancer (TNBC, a subset of ER?-negative disease), the molecular mechanisms underlying these effects remain unclear.MethodsC57BL/6 mice were fed a control diet (control, 10% kcal from fat) or control diet?+?SDG (SDG, 100 mg/kg diet) for 8 weeks, then orthotopically injected with syngeneic E0771 mammary tumor cells (a model of TNBC); tumor growth was monitored for 3 weeks. The role of reduced NF-?B signaling in SDG's anti-tumor effects was explored in vitro via treatment with the bioactive SDG metabolite ENL. In addition to the murine E0771 cells, the in vitro studies utilized MDA-MB-231 and MCF-7 cells, two human cell lines which model the triple-negative and luminal A breast cancer subtypes, respectively.ResultsSDG supplementation in the mice significantly reduced tumor volume and expression of phospho-p65 and NF-?B target genes (P?<?0.05). Markers of macrophage infiltration were decreased in the distal-to-tumor mammary fat pad of mice supplemented with SDG relative to control mice (P?<?0.05). In vitro, ENL treatment inhibited viability, survival, and NF-?B activity and target gene expression in E0771, MDA-MB-231, and MCF-7 cells (P?<?0.05). Overexpression of Rela attenuated ENL's inhibition of E0771 cell viability and survival.ConclusionsSDG reduces tumor growth in the E0771 model of TNBC, likely via a mechanism involving inhibition of NF-?B activity. SDG could serve as a practical and effective adjuvant treatment to reduce recurrence, but greater understanding of its effects is needed to inform the development of more targeted recommendations for its use.

Project description:Obesity enhances breast cancer risk in postmenopausal women and premenopausal women with genetic or familial risk factors. We have shown previously that within breast tissue, obesity increases macrophage-driven inflammation and promotes expansion of luminal epithelial cell populations that are hypothesized to be the cells of origin for the most common subtypes of breast cancer. However, it is not clear how these changes within the microenvironment of the breast alter cancer risk and tumor growth. Using a high-fat diet to induce obesity, we examined preneoplastic changes associated with epithelial cell-specific loss of Trp53. Obesity significantly enhanced the incidence of tumors of diverse histotypes and increased stromal cells within the tumor microenvironment. Obesity also promoted the growth of preneoplastic lesions containing elevated numbers of luminal epithelial progenitor cells, which were surrounded by macrophages. To understand how macrophage-driven inflammation due to obesity enhances tumor formation, mice were treated with IgG or anti-F4/80 antibodies to deplete macrophages during preneoplastic growth. Unexpectedly, depletion of macrophages in obese mice enhanced mammary epithelial cell stem/progenitor activity, elevated expression of estrogen receptor alpha, and increased DNA damage in cells. Together, these results suggest that in obesity, macrophages reduce epithelial cells with DNA damage, which may limit the progression of preneoplastic breast lesions, and uncovers complex macrophage function within the evolving tumor microenvironment. Understanding how obesity alters the function of macrophages during tumor formation may lead to chemoprevention options for at-risk obese women. SIGNIFICANCE: Understanding how obesity impacts early tumor growth and response to macrophage-targeted therapies may improve therapeutics for obese patients with breast cancer and identify patient populations that would benefit from macrophage-targeted therapies.

Dataset Information

Obesity-Associated Alterations in Inflammation, Epigenetics, and Mammary Tumor Growth Persist in Formerly Obese Mice.

Publications

Obesity-Associated Alterations in Inflammation, Epigenetics, and Mammary Tumor Growth Persist in Formerly Obese Mice.

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