Epithelial mesenchymal transition of epithelial cells induced by TGF-β signaling in lymphedema

Abstract

Abstract TGF-β driven fibrosis of the skin is a key pathologic feature of secondary lymphedema. However, the cellular mechanisms that regulate this process remain unknown. Epithelial mesenchymal transition (EMT) is a mechanism by which TGF-β induces fibrosis in other skin diseases. This process is characterized by loss of epithelial cell markers and polarity and increased migratory capacity and invasiveness. Therefore, the purpose of this study was to determine if EMT of skin keratinocytes is activated in lymphedema and if this process is mediated by TGF-β. Using clinical lymphedema biopsy specimens and mouse models of lymphedema, we found that lymphedema results in fibrosis in the papillary dermis and a greater number of rete ridges in the basal layer of epithelium. Keratinocytes in the basal layer of lymphedematous skin express EMT markers (vimentin, fsp1, itgb4, slug, mmp9, twist) and fail to express epithelial markers (keratin14, E-cadherin). Interestingly, we found psamd3 expression in these EMT-like epithelial cells with accumulated TGF-β in papillary dermis by immunohistochemistry. Inhibition of TGF-β signaling markedly decreased EMT and prevented development of fibrosis in a mouse model. To determine if EMT of epithelial cells is induced by lymphedema fluid in skin, we treated keratinocytes with lymph fluid obtained from patients with lymphedema and analyzed in cultures with or without TGF-β inhibitors. We found that keratinocytes cultured with arm fluid only rapidly underwent EMT. In contrast, inhibition of TGF-β signaling prevented this response. Taken together, our findings show for the first time that EMT is activated by TGF-β signaling in lymphedema and that this process plays an important role in the pathology of this disease. Supported by grants from NIH (R01HL111130).