Abstract LB-009: Collagen regulation in postpartum mammary gland involution, a novel breast cancer prevention target

Abstract

Abstract Collagen is the most abundant extracellular protein in breast tissue and plays a critical role in breast cancer progression. Intravital imaging shows collagen fibers as “highways” for tumor cell invasion, and collagen fibers arranged perpendicular to the tumor border (radial alignment) independently predict breast cancer metastasis. To understand the role of collagen in breast cancer, we argue it is necessary to understand collagen biology in the normal breast. While collagen production has been well studied in the context of wound healing, little is known about its regulation in normal breast physiology. Here we utilize a murine, weaning-induced mammary gland involution model, which is characterized by robust collagen deposition and remodeling, to investigate collagen regulation in the normal mammary gland. During mammary gland involution, we find increased collagen-I, -III, and -V gene expression and high levels of lysyl-oxidase (LOX), a major collagen cross-linker. By SHG analysis, we find collagen fibers around mammary ducts in the involuting gland are more tightly organized than nulliparous gland, with “hot spots” of radial alignment. Collagen is predominantly produced by fibroblasts and we identified mammary fibroblasts as PDGFRα+. Using flow cytometry-based cell sorting and gene expression analysis, PDGFRα+ fibroblasts isolated from the involuting mammary gland have increased gene expression of collagen-I,-III, and LOX. Further, there is ∼2 fold increase in number of PDGFRα+ cells/mg weight of tissue in the involuting gland, suggesting that fibroblasts may be recruited and activated during involution. Increased production of collagen by fibroblasts and radial alignment of collagen are consistent with a tumor promotional microenvironment during mammary gland involution. In fact, our lab has demonstrated pro-tumorigenic attributes of involution in rodent models of postpartum breast cancer, which can be mitigated by non-steroidal anti-inflammatory drug (NSAID) treatment. To investigate the impact of NSAID treatment on collagen during involution, we isolated fibroblasts from mammary glands of animals undergoing involution in the presence and absence of NSAID intervention. Mammary fibroblasts flow sorted from NSAID treated hosts display reduced collagen I, TGFβ1, and MMP-3 gene expression by 30∼60% compared to involution-fibroblasts isolated from untreated mice. Taken together, these data demonstrate that fibroblasts are responsive to COX-2 inhibition and suggest a novel mechanism of NSAIDs action that may be mediated through suppression of collagen deposition. Collagen and breast cancer are inseparable topics, as collagen abundance, architecture and tension impact breast cancer risk and prognosis. Weaning induced mammary gland involution provides a unique physiological window to study collagen regulation. Studying the mechanism of how NSAIDs regulate collagen may provide insight into the use of NSAIDs as a preventative and therapeutic intervention in breast cancer. Citation Format: Qiuchen Guo, Pepper J. Schedin. Collagen regulation in postpartum mammary gland involution, a novel breast cancer prevention target. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-009. doi:10.1158/1538-7445.AM2015-LB-009