Obese individuals with breast cancer have a poorer prognosis and higher risk of metastatic disease vs. non-obese patients. Adipose tissue in obese individuals is characterized by an enhanced macrophage infiltration, creating a microenvironment that favors tumor progression. Here, we demonstrate a role for adipocyte-macrophage interactions in the regulation of angiogenesis. Co-culture of THP-1 macrophages with human breast adipocytes led to increased expression of the pro-angiogenic growth factor, vascular endothelial growth factor A (VEGFA). Several adipocyte-derived proteins including leptin, insulin, IL-6, and TNF-α were each capable of increasing VEGFA expression in THP-1 macrophages, identifying these as possible mediators of the changes that were observed with co-culture. Furthermore, analysis of THP-1 culture media by antibody array revealed that THP-1 secrete several other pro-angiogenic signals in response to adipocyte co-culture, including interleukin 8 (IL-8), matrix metalloproteinase 9 (MMP9), pentraxin 3 (PTX3), and serpin E1 (plasminogen activator inhibitor 1, PAI1) after co-culture with human adipocytes. We used an in vitro endothelial tube formation assay with human vascular endothelial cells to evaluate the effects of THP-1 culture media on angiogenesis. Here, culture media from THP-1 cells previously exposed to human adipocytes stimulated endothelial tube formation more significantly than THP-1 cells cultured alone. In summary, we find that adipocyte co-culture stimulates the expression of pro-angiogenic mediators in macrophages and has pro-angiogenic effects in vitro, thus representing a possible mechanism for the enhanced risk of breast cancer progression in obese individuals.

Obese individuals with breast cancer have a poorer prognosis and higher risk of metastatic disease vs. non-obese patients. Prior research has largely focused on defining the interactions between adipocytes and tumor cells, but other cell types may also play a role. Adipose tissue in obese individuals is characterized by a significant infiltration of macrophages. We have therefore investigated the adipocyte-macrophage interaction as a possible mechanism whereby obesity promotes breast cancer metastasis. We performed co-culture with both human and murine cells to determine whether adipocytes influence the expression of metastasis-promoting signals in macrophages. For the human system we co-cultured primary breast adipocytes with THP-1 macrophages. For the murine system we co-cultured 3T3-L1 differentiated adipocytes with J774.1 macrophages. We then assayed the mRNA levels and protein expression of metastasis-promoting genes. In both systems we found that co-culture with adipocytes increased the expression of Vascular Endothelial Growth Factor A (VEGF-A) in macrophages. In examining a potential mechanism, we also show that media collected from cultured adipocytes (adipocyte-conditioned media) activates the transcription factor Egr-1 in macrophages. Since Egr-1 is a known regulator of VEGF-A expression, this is a potential mechanism whereby VEGF-A transcription is up-regulated. Treatment of human macrophages with Interleukin-6, Leptin and Insulin induced VEGF-A levels to a similar degree as co-culture, identifying these as adipocyte-derived signals that can possibly mediate this effect. In summary we have found that the interaction between adipocytes and macrophages leads to the up-regulation of the pro-angiogenic signal VEGF-A in macrophages. Therefore this represents a potential mechanism whereby obesity could promote breast cancer metastasis. Citation Format: Connelly L, Yadav N, Barcikowski A, Imaizumi Y, Jacobs A. Obesity and breast cancer: The adipocyte-macrophage interaction as a mediator of metastasis [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-03-13.