Excess deposition of collagen in mammary glands of tamoxifen-treated Holstein heifers is associated with impaired mammary growth

• Published in: Domestic animal endocrinology Vol. 65; pp. 49 - 55
• Main Authors: Tucker, H.L.M., Holdridge, J., Parsons, C.L.M., Akers, R.M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.10.2018
• Subjects: Animals; Cattle; Collagen - analysis; Collagen - metabolism; ECM; Estrogen; Estrogen Antagonists - administration & dosage; Estrogen Receptor alpha - analysis; Estrogen Receptor alpha - antagonists & inhibitors; Female; Mammary; Mammary Glands, Animal - chemistry; Mammary Glands, Animal - drug effects; Mammary Glands, Animal - growth & development; Placebos; Random Allocation; Stroma; Tamoxifen; Tamoxifen - administration & dosage; Stroma; Tamoxifen; Mammary; ECM; Estrogen
• ISSN: 0739-7240; 1879-0054
• DOI: 10.1016/j.domaniend.2018.05.006

It is established that the ovary and estrogen are essential to bovine mammary development with the onset of puberty. Recent studies have shown that ovariectomy in the very early prepubertal period, well before onset of puberty, also dramatically impairs mammary growth. Similarly, prepubertal heifers treated with the antiestrogen tamoxifen (TAM) also exhibit markedly impaired mammary growth in correspondence with reduced estrogen receptor α (ESR1) expression. Our objective was to evaluate the effect of TAM on the mammary stroma and specifically to determine if the reported decrease in mammary development was related to changes in TAM-induced alterations in the stroma surrounding the mammary parenchyma. Briefly, 16 Holstein heifers calves were randomly assigned to one of 2 treatment groups: TAM-injected or control. Calves were administered TAM (0.3 mg kg1 d1) or placebo from 28 to 120 d of age. At day 120, calves were euthanized and udders removed. Mammary tissue from near the boundary between the parenchyma and surrounding mammary fat pad was collected for histology and morphometric analysis, expression of selected extracellular matrix–related genes, and quantitation of stromal collagen deposition by study of Sirius Red-stained tissue sections imaged with polarized light. Compared with tissue from control heifers, TAM heifers frequently exhibited areas with abundant fibroblasts and mesenchymal cells especially within the intralobular stroma, as well as less complex ductal structures. Among the array of extracellular matrix–related genes tested, only a small difference (P < 0.05) in expression of laminin was found between treatments. The relative tissue area occupied by stromal tissue was not impacted by treatment. However, the deposition of collagen within the stromal tissue was more than doubled (P < 0.0001) in TAM-treated heifers. These data suggest that blocking ESR1 expression with TAM allows for excessive collagen deposition in the stroma surrounding the developing epithelial structures and that this interferes with both the degree of overall mammary parenchymal development, as well as the pattern of normal ductal morphogenesis. •The significance of estrogen and progesterone in control of bovine mammary development generally has been extensively studied and well understood but the impact of the ovary and presumably ovarian-derived estrogen before puberty is not well defined.•Previous work shows that TAM, a well-known antiestrogen, markedly reduced mammary gland development and expression of ESR1, which emphasizes the importance of ESR1 in regulation of bovine mammary development well before the onset of puberty.•The goal of this study was to evaluate the impact of altered ESR1 expression on development of stroma within the developing mammary gland, an area of research largely unstudied in the bovine mammary gland.•We used Sirius red staining coupled with polarized light imaging to discover that the impairment in ESR1 expression within the epithelium was associated with a marked increase in the deposition of collagen within the intralobular and interlobular stroma of the developing bovine mammary gland.