TGF-β1 Induces EMT in Bovine Mammary Epithelial Cells Through the TGFβ1/Smad Signaling Pathway

Background/Aims: Transforming growth factor-beta 1 (TGF-beta 1) plays a crucial role in chronic inflammation in various tissues, and is related to inflammation-caused organ fibrogenesis associated with the epithelial-mesenchymal transition (EMT) and the deposition of the extracellular matrix (ECM). However, the effect of TGF-beta 1 on bovine mammary epithelial cells (BMECs) with mastitis, and its mechanism, remain unknown. Methods: We analyzed the level of TGF-beta 1 in inflamed mammary tissues and cells using western blotting. BMECs were treated with TGF-beta 1, and EMT-related gene and protein expression changes were evaluated using quantitative real-time polymerase chain reaction (qPCR), western blotting, and immunofluorescence. We also inhibited the TGF/Smad signaling pathway using a receptor inhibitor, and analyzed EMT-related protein expression by western blotting. In addition, we injected TGF-beta 1 into mice mammary glands to investigate whether it can cause mammary fibrosis in vivo. Results: The TGF-beta 1 level was up-regulated in mammary tissues with mastitis and in inducible inflammatory BMECs. TGF-beta 1 treatment activated the TGF/Smad signaling pathway in BMECs during their transition to the EMT phenotype, as indicated by morphological changes from a cobblestone-like shape to a spindle-like one. TGF-beta 1 treatment also up-regulated the expression of alpha-smooth muscle actin, vimentin, and collagen I, albumin, and down-regulated the expression of E-cadherin both in mRNA level and protein level. Furthermore, TGF-beta 1 enhanced the gene expressions of MMP2, MMP7, and fibronectin in BMECs. TGF-beta 1 injection induced mice mammary infection and fibrosis. Conclusion: These findings suggested that aberrant up-regulation of TGF-beta 1 in bovine mastitic mammary glands might play an important role in bovine mammary fibrosis caused by unresolved inflammation. (C) 2017 The Author(s) Published by S. Karger AG, Basel