Collagen architecture in pregnancy-induced protection from breast cancer

Abstract

SummaryThe reduction in breast cancer risk attributed to early-age pregnancy is mediated in part by changes in the mammary epithelium. Here, we address the role of the mammary stroma in this protection. Utilizing tumor cells capable of transitioning from indolent to proliferative or invasive states, we demonstrate that mammary extracellular matrix (ECM) from parous rats (parous matrix) decreases tumor growth and impedes cellular phenotypes associated with tumor cell invasion compared with that observed using nulliparous matrix. Proteomic analysis identifies an increased abundance of collagen I in parous matrix, an observation extended to breast tissue of parous women. Given the pro-tumorigenic attributes of fibrillar collagen, these results were unexpected. Second-harmonic generation imaging and atomic force microscopy revealed that the abundant collagen observed in the mammary glands of parous rats is less linearized and associated with a decrease in stromal stiffness, implicating collagen organization and stiffness in parity-induced protection. Using 3D cell culture models, we demonstrate that linearized (fibrillar) collagen I induces cellular phenotypes consistent with an invasive behavior in mammary tumor cells and alters the subcellular distribution of b1 integrin. Conversely, high-density non-fibrillar collagen I induces tumor-suppressive attributes, including increases in junctional E-cadherin in tumor cells, upregulation of genes encoding components of cell-cell junctions, and downregulation of mesenchymal-specific and metalloproteinase-encoding genes. These data show that collagen organization, rather than density alone, is a key contributor to the invasive phenotype. Furthermore, our data show that parity alters the composition and organization of mammary ECM, particularly fibrillar collagen, in a manner consistent with tumor suppression.

Mammary gland development: cell fate specification, stem cells and the microenvironment

“…These collagen I fibers appear to be oriented prior to mammary branching morphogenesis, indicating that epithelial architecture might be pre-patterned in the stroma of the pubertal mammary gland. Such structural components, which support tissue architecture, are often overlooked as regulators of morphogenesis, but we now understand that correct tissue architecture and stiffness of the ECM are essential components of normal development, differentiation and function within the mammary gland (Bissell et al, 1982;Maller et al, 2013;Schedin and Keely, 2011). Future studies of the stroma in mammary gland development would undoubtedly provide additional clues into the role of stroma in breast cancer initiation and progression.…”

The extracellular matrix in breast cancer predicts prognosis through composition, splicing, and crosslinking

“…The diverse microarchitectures of fibrillar collagen and the range of resulting biomechanics can result in very different microenvironments despite equivalent levels of collagen [83][84][85], which potentially explains the weak clinical link between collagen I and prognosis in older studies [86,87]. It remains difficult to decouple the effects of fiber diameter, pore size and biomechanics, but it appears that all three act on cells (reviewed in [88]).…”

“…In contrast, softer collagen I rich matrices appear to reduce breast cancer risk and progression. Parity appears to increase collagen I deposition, but in an unorganized, uncrosslinked form, resulting in softer ECM and reduced risk of breast cancers [83]. Collagen III disrupts formation of dense, organized collagen I networks, resulting in softer ECM [94].…”

A Portal Vein Injection Model to Study Liver Metastasis of Breast Cancer

“…These mammary tumor lines were selected based on their characterized behavior in mammary fat pad models and include the highly aggressive and metastatic 4T1 cell line, the less aggressive metastatic D2A1 line, and the low/non-metastatic D2.OR line 37,61,73,74 . 2,000 and 10,000 cells per injection were tested with no notable differences in the time to development of overt metastasis with these low cell concentrations.…”