Department of Animal Science, Michigan State University, East Lansing 48824-1225, USA.
J Dairy Sci. 2010 Jun;93(6):2433-43. doi: 10.3168/jds.2009-2764.
During the dry period between successive lactations, the mammary gland of dairy cows undergoes extensive remodeling that is marked by phases of involution and mammogenesis. Changes in the mammary epithelium during the dry period have been well characterized; however, few studies have examined the changes that occur in stromal tissue. The objective of this study was to characterize changes that occur in mammary stroma during the dry period. Mammary biopsies were taken from 9 multigravid Holstein cows in late lactation, at 1 wk after dry-off, 3 wk before expected calving date, and 1 wk before expected calving date. Tissue was fixed in formalin, embedded in paraffin, and cut into 5-mum sections. Sections were stained with hematoxylin and eosin or with immunohistochemistry for expression of smooth muscle alpha actin (SMA), fibronectin, stromelysin-1 (MMP-3), transforming growth factor-beta1 (TGF-beta1), and TGF-beta receptor 2 (TGF-betaR2). Images of tissues were captured with light microscopy, and imaging software was used to measure intralobular stromal area, number of activated fibroblasts, as identified by expression of SMA, and percentage of intralobular stromal area expressing fibronectin, MMP3, TGF-beta1, and TGF-betaR2. Analyses of variance were conducted and statistical differences were based on the least squares means of biopsy stage. Number of activated fibroblasts was greater at 1 wk dry than at 1 wk before calving (2,720 vs. 1,800 cells/mm(2)), percentage intralobular stromal area was greater at 1 wk dry (32%) and 3 wk before calving (37%) than at 1 wk before calving (25%), and TGF-beta1 expression decreased 15% from late lactation to the dry period. The percentages of stromal area expressing fibronectin, MMP-3, and TGF-betaR2 and the percentage of myofibroblasts were not different across biopsy stages. These results support the concept that stromal expression of transforming growth factor-beta1 and fibroblast proliferation may be important for remodeling during the dry period.
在连续泌乳期之间的干奶期，奶牛的乳腺经历广泛的重塑，其特征是退化和乳腺发生阶段。干奶期乳腺上皮的变化已经得到很好的描述；然而，很少有研究检查间质组织中发生的变化。本研究的目的是描述干奶期乳腺间质发生的变化。从 9 头泌乳后期的多胎荷斯坦奶牛中采集乳腺活检，在干奶后 1 周、预计产犊日期前 3 周和预计产犊日期前 1 周。组织用福尔马林固定，石蜡包埋，切成 5μm 切片。用苏木精和伊红或免疫组化染色，检测平滑肌α肌动蛋白（SMA）、纤维连接蛋白、基质金属蛋白酶-1（MMP-3）、转化生长因子-β1（TGF-β1）和 TGF-β 受体 2（TGF-βR2）的表达。用光镜捕获组织图像，并使用成像软件测量小叶内间质面积、表达 SMA 的活化成纤维细胞数量以及表达纤维连接蛋白、MMP3、TGF-β1 和 TGF-βR2 的小叶内间质面积百分比。进行方差分析，基于活检阶段的最小二乘均值进行统计差异。与产犊前 1 周相比，干奶后 1 周的活化成纤维细胞数量更多（2720 对 1800 个细胞/mm2），干奶后 1 周（32%）和产犊前 3 周（37%）的小叶内间质面积百分比高于产犊前 1 周（25%），TGF-β1 的表达从泌乳后期到干奶期下降了 15%。纤维连接蛋白、MMP-3 和 TGF-βR2 的基质面积百分比和肌成纤维细胞的百分比在不同的活检阶段没有差异。这些结果支持这样的概念，即转化生长因子-β1 的间质表达和成纤维细胞增殖可能是干奶期重塑的重要因素。
