Mammary collagen is under reproductive control with implications for breast cancer

• Published in: Matrix biology 2022-01, Vol.105, p.104-126
• Main Authors: Guo, Qiuchen, Sun, Duanchen, Barrett, Alexander S., Jindal, Sonali, Pennock, Nathan D., Conklin, Matthew W., Xia, Zheng, Mitchell, Elizabeth, Samatham, Ravikant, Mirza, Naomi, Jacques, Steven, Weinmann, Sheila, Borges, Virginia F., Hansen, Kirk C., Schedin, Pepper J.
• Format: Article
• Language: English
• Subjects: Animals; Breast - metabolism; Breast cancer; Breast Neoplasms - genetics; Breast Neoplasms - metabolism; Breastfeeding & lactation; Collagen; Collagen - genetics; Collagen - metabolism; Cross-linking; Epithelium; Etiology; Female; Gene expression; Gene regulation; Humans; Lactation; Lactation - physiology; Lysyl oxidase; Mammary gland; Mammary Glands, Animal - metabolism; Mammographic density; Mass spectroscopy; Postpartum breast cancer; Pregnancy; Rats; Weaning; Womens health
• ISSN: 0945-053X; 1569-1802
• DOI: 10.1016/j.matbio.2021.10.006

•Mammary collagen gene expression, composition, and structure vary by reproductive state.•Peak collagen deposition occurs after weaning, during mammary gland involution.•Involution-collagen shares similarities with tumor-associated collagen.•Cases of postpartum breast cancer show elevated tumor-associated collagen gene signatures, implicating involution. Mammographically-detected breast density impacts breast cancer risk and progression, and fibrillar collagen is a key component of breast density. However, physiologic factors influencing collagen production in the breast are poorly understood. In female rats, we analyzed gene expression of the most abundantly expressed mammary collagens and collagen-associated proteins across a pregnancy, lactation, and weaning cycle. We identified a triphasic pattern of collagen gene regulation and evidence for reproductive state-dependent composition. An initial phase of collagen deposition occurred during pregnancy, followed by an active phase of collagen suppression during lactation. The third phase of collagen regulation occurred during weaning-induced mammary gland involution, which was characterized by increased collagen deposition. Concomitant changes in collagen protein abundance were confirmed by Masson's trichrome staining, second harmonic generation (SHG) imaging, and mass spectrometry. We observed similar reproductive-state dependent collagen patterns in human breast tissue obtained from premenopausal women. SHG analysis also revealed structural variation in collagen across a reproductive cycle, with higher packing density and more collagen fibers arranged perpendicular to the mammary epithelium in the involuting rat mammary gland compared to nulliparous and lactating glands. Involution was also characterized by high expression of the collagen cross-linking enzyme lysyl oxidase, which was associated with increased levels of cross-linked collagen. Breast cancer relevance is suggested, as we found that breast cancer diagnosed in recently postpartum women displayed gene expression signatures consistent with increased collagen deposition and crosslinking compared to breast cancers diagnosed in age-matched nulliparous women. Using publicly available data sets, we found this involution-like, collagen gene signature correlated with poor progression-free survival in breast cancer patients overall and in younger women. In sum, these findings of physiologic collagen regulation in the normal mammary gland may provide ins