Abstract 1096: Investigating the role of the adipocyte-macrophage interaction in breast cancer metastasis
Authors: Yadav Nalini V.S. , Jacobs Aaron T. , Connelly Linda 
Published: May 2015

Abstract
Obesity is linked with a higher incidence of hormone-receptor positive breast cancer in post-menopausal women. Obesity is also associated with a worse outcome after the diagnosis of breast cancer, including greater tumor burden and higher grade tumors. Although several theories exist to explain these relationships, the proposed mechanisms are still being investigated.
Obesity and the resulting expansion of adipose tissue is associated with aberrant cytokine production and a chronic inflammatory state, characterized by the recruitment of macrophages. Macrophages have been shown elsewhere to promote breast cancer progression. Therefore, we hypothesize that the interaction between adipocytes and macrophages promotes metastasis of breast cancer. Our data suggest that oxidized lipids released from adipocytes may have a role in mediating this interaction.
We used a co-culture system to determine whether adipocytes could promote a pro-tumor phenotype in the macrophages. THP-1 macrophages were co-cultured with primary human visceral adipocytes using a Transwell system for 8 hours, then macrophage mRNA was analyzed for changes in transcription of markers for increased metastatic potential. Vascular Endothelial Growth Factor A (VEGF-A) mRNA levels were significantly increased in macrophages after exposure to adipocytes in comparison to control macrophages that were cultured alone. Co-culture experiments were repeated using human breast adipocytes to more directly model the conditions in the breast microenvironment. Again VEGF-A mRNA levels were significantly increased in macrophages after co-culture with adipocytes. Obesity is associated with stressed and necrotic adipose tissue in the breast. Therefore, to mimic obesity related dysfunction and cell death, we treated breast adipocytes with Tumor Necrosis Factor-alpha and Interleukin 6 prior to co-culturing with macrophages. The cytokine treatment enhanced the effects of adipocyte co-culture on macrophage VEGF-A mRNA levels. The increased inflammation and adipocyte dysfunction seen in obesity has been proposed to favor the generation of biologically active oxidized lipid mediators such as 4-hydroxynonenal (4-HNE). We therefore treated THP-1 macrophages with 4-HNE as a model oxidized lipid, hypothesizing that 4-HNE may convey some of the effects on macrophage gene expression seen in co-culture. We found that transcription of VEGF-D and platelet derived growth factor (PGF), both members of the VEGF family of cytokines, were significantly enhanced in 4-HNE-treated THP-1 cells.
Together, our data show that the interaction of adipocytes and macrophages in obese breast tissue can stimulate pro-angiogenic macrophage signaling. This is a novel mechanism whereby the obese microenvironment can promote breast cancer metastasis.
Citation Format: Nalini V.S. Yadav, Aaron T. Jacobs, Linda Connelly. Investigating the role of the adipocyte-macrophage interaction in breast cancer metastasis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1096. doi:10.1158/1538-7445.AM2014-1096