Epithelial-to-mesenchymal transition in fibrosis: collagen type I expression is highly upregulated after EMT, but does not contribute to collagen deposition

Abstract

The hallmark of fibrosis is an accumulation of fibrillar collagens, especially of collagen type I. There is considerable debate whether in vivo type II epithelial-to-mesenchymal transition (EMT) is involved in organ fibrosis. Lineage tracing experiments by various groups show opposing data concerning the relative contribution of epithelial cells to the pool of myofibroblasts. We hypothesized that EMT-derived cells might directly contribute to collagen deposition. To study this, EMT was induced in human epithelial lung and renal cell lines in vitro by means of TGF-β1 stimulation, and we compared the collagen type I (COL1A1) expression levels of transdifferentiated cells with that of myofibroblasts obtained by TGF-β1 stimulation of human dermal and lung fibroblasts. COL1A1 expression levels of transdifferentiated epithelial cells appeared to be at least one to two orders of magnitude lower than that of myofibroblasts. This was confirmed at immunohistochemical level: in contrast to myofibroblasts, collagen type I deposition by EMT-derived cells was not or hardly detectable. We postulate that, even when type II EMT occurs in vivo, the direct contribution of EMT-derived cells to collagen accumulation is rather limited.

Keywords: ACTA2; BEAS-2B; BSA; CDH1; COL1A1; COL3A1; Collagen deposition; E-cadherin; ECM; EMT; EPCAM; Epithelial cells; Epithelial to mesenchymal transition; FCS; Fibrosis; HDF; HK-2; HLF; Myofibroblasts; NHS; PBS; TAGLN; TGFβ-1; VIM; alpha-actin-2 (alpha smooth muscle actin); bovine serum albumin; ciPTEC; collagen type I; collagen type III; conditionally immortalized human proximal tubule cells; epithelial cell adhesion molecule; epithelial-to-mesenchymal transition; extracellular matrix; fetal calf serum; human dermal fibroblasts; human lung bronchial epithelial cells; human lung fibroblasts; human renal proximal tubule epithelial cells; normal human serum; phosphate buffered saline; qRT-PCR; quantitative Reverse Transcription polymerase chain reaction; transforming growth factor beta 1; transgelin (smooth muscle protein 22-alpha); vimentin.