Department of Dairy Science, Virginia Tech, Blacksburg, VA 24061, USA.
Department of Dairy Science, Virginia Tech, Blacksburg, VA 24061, USA.
Domest Anim Endocrinol. 2018 Oct;65:49-55. doi: 10.1016/j.domaniend.2018.05.006. Epub 2018 May 18.
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 kg d) 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.
研究表明，卵巢和雌激素对牛乳腺的发育至关重要，青春期的开始与之密切相关。最近的研究表明，在青春期开始之前的早期，即非常早的初情期对牛进行卵巢切除术，也会严重损害乳腺的生长。同样，用抗雌激素他莫昔芬（TAM）处理的初情前期小母牛，其乳腺生长也明显受损，与雌激素受体α（ESR1）表达减少相对应。我们的目的是评估 TAM 对乳腺基质的影响，特别是确定报告的乳腺发育减少是否与 TAM 诱导的乳腺实质周围基质变化有关。简而言之，16 头荷斯坦小母牛犊随机分为 2 个处理组之一：TAM 注射或对照。从 28 日龄到 120 日龄，小牛每天接受 TAM（0.3 mg/kg/d）或安慰剂治疗。在 120 日龄时，小牛被安乐死并取出乳房。在乳腺实质和周围乳腺脂肪垫的边界附近采集乳腺组织，用于组织学和形态计量分析、选择的细胞外基质相关基因的表达以及研究天狼星红染色组织切片的偏光图像定量分析基质胶原沉积。与对照小母牛的组织相比，TAM 小母牛的组织中经常出现大量成纤维细胞和间充质细胞，尤其是小叶内基质中，以及更简单的导管结构。在所测试的细胞外基质相关基因中，只有层粘连蛋白的表达在处理之间存在微小差异（P < 0.05）。处理对基质组织的相对组织面积没有影响。然而，在 TAM 处理的小母牛中，基质组织内胶原的沉积增加了一倍以上（P < 0.0001）。这些数据表明，用 TAM 阻断 ESR1 表达允许在发育中的上皮结构周围的基质中过度沉积胶原，这不仅干扰了整个乳腺实质的发育程度，还干扰了正常导管形态发生的模式。
