Differential Quantitative Proteomics of Human Microvascular Endothelial Cells 1 by iTRAQ Reveals Palladin to be a New Biomarker During TGF-?1 Induced Endothelial Mesenchymal Transition

The study uses global quantitative proteomics to investigate the molecular mechanisms behind the induction of endothelial-mesenchymal transition (EndMT) by transforming growth factor–β (TGF-β). Orbitrap Velos mass spectrometers and iTRAQ – a labeling-based analysis were used to perform a global and quantitative comparison of two proteomes of Human Microvascular Endothelial Cells-1 (HMEC-1) treated or not treated by TGF-β1. iTRAQ analysis identified 43 differentially-expressed proteins in the early stages of EndMT induced by TGF-β1. From 5522 identified proteins, 26 were downregulated and 17 were upregulated, including proteins such as palladin, POTE I, torsin A and nucleoporin (NDC1). Further analysis of palladin revealed its increased mRNA and protein expression in response to TGF-β and Snail transcription factor. Our findings demonstrate that the newly- identified proteins may be involved in early stages of biological processes leading to EndMT.Biological Significance: Endothelial to mesenchymal transition is a possible source of myofibroblasts, which play a crucial role in the pathogenesis of fibrosis. EndMT participate in tissue fibrotic processes in various organs. TGF-β family growth factors are involved in the initiation of EndMT. The intracellular cascades activated by TGF-β that result in the remarkable phenotypic change of endothelial cells to mesenchymal cells have not been entirely elucidated. The downstream signaling pathway initiated by TGF-β resulted in a strong upregulation of the Snail1 transcriptional repressor. Our proteomics data demonstrated that TGF-β -induced EndMT leads to alterations in protein profiles, more specifically, the upregulation of palladin. This upregulation is mediated by Snail transcription factor and GSK-3 β signaling kinase. Our results also suggest that palladin could be considered a new biomarker in the early stages of cellular transdifferentiation, eventually leading to endothelial-mesenchymal transition.