Loss of caveolin-1 alters extracellular matrix protein expression and ductal architecture in murine mammary glands

The extracellular matrix (ECM) is abnormal in breast tumors and has been reported to contribute to breast tumor progression. One factor, which may drive ongoing matrix synthesis in breast tumors, is the loss of stromal caveolin-1 (cav-1), a scaffolding protein of caveolae, which has been linked to breast tumor aggressiveness. To determine whether loss of cav-1 results in the abnormal expression of matrix proteins, mammary glands from cav- 1-/- and cav- 1 +/+ mice were investigated for differences in expression of several ECM proteins. In addition, the presence of myofibroblasts, changes in the vessel density, and differences in duct number and size were assessed in the mammary glands of both animal models. Using immunohistochemistry, expression of fibronectin, tenascin-C, collagens and αSMA were significantly increased in the mammary glands of cav-1-/- mice. Second harmonic generation revealed more organized collagen fibers in cav-1 -/- glands and supported immunohistochemical analyses of increased collagen abundance in the glands of cav-1 -/- mice. Analysis of the ductal structure demonstrated a significant increase in the number of proliferating ducts in addition to significant increases in the duct circumference and area in cav-1 -/- glands compared to cav- 1 +/+ glands. Differences in microvessel density weren’t apparent between the animal models. In summary, we found that the loss of cav-1 resulted in increased ECM and α-SMA protein expression in murine mammary glands. Furthermore, we found that an abnormal ductal architecture accompanied the loss of cav-1. These data support a role for cav-1 in maintaining mammary gland structure.

细胞外基质（extracellular matrix, ECM）在乳腺肿瘤中存在异常，且已有研究证实其可推动乳腺肿瘤的进展。可能驱动乳腺肿瘤中基质持续合成的一个关键因素，是间质窖蛋白-1（stromal caveolin-1, cav-1）的缺失——该蛋白是细胞质膜微囊（caveolae）的支架蛋白，既往研究已将其与乳腺肿瘤侵袭性关联起来。为明确cav-1缺失是否会引发基质蛋白的异常表达，研究人员对cav-1基因敲除（cav-1-/-）与野生型（cav-1+/+）小鼠的乳腺组织展开分析，检测多种ECM蛋白的表达差异。此外，还对两种小鼠模型的乳腺组织中的肌成纤维细胞分布、血管密度变化以及导管数量与大小的差异进行了评估。通过免疫组织化学检测发现，cav-1-/-小鼠的乳腺组织中，纤连蛋白、肌腱蛋白-C、胶原蛋白以及α平滑肌肌动蛋白（αSMA）的表达水平显著升高。二次谐波成像结果显示，cav-1-/-小鼠的乳腺组织内胶原纤维排列更为规整，这一结果佐证了免疫组化分析中该组小鼠乳腺胶原蛋白丰度上升的结论。对导管结构的分析表明，与cav-1+/+小鼠相比，cav-1-/-小鼠的增殖性导管数量显著增加，同时导管的周长与面积也均出现明显增大。两种动物模型的微血管密度未观察到显著差异。综上，本研究证实cav-1缺失会导致小鼠乳腺组织中ECM及α-SMA蛋白表达上调。此外，cav-1缺失还会伴随导管结构的异常。上述数据支持cav-1在维持乳腺组织结构完整性中发挥作用的结论。