Epithelial phenotypic changes are associated with a tubular active fibrogenic process in human renal grafts

Some recently published works contest the epithelial origin of myofibroblasts, which are the major extracellular matrix producers. However, our previous studies showed that, in tubular cells, some phenotypic changes reminiscent of epithelial-to-mesenchymal transition constitute an interesting early marker that predicts the progression of fibrosis in renal grafts. We hypothesized that activated epithelial cells could directly contribute to fibrogenesis, although they remain within the tubules. Using immunohistochemistry, we studied the association between epithelial phenotypic changes (de novo expression of vimentin and intracellular translocation of β-catenin) and the production of profibrotic molecules (connective tissue growth factor, HSP47, and laminin), in tubular epithelial cells from 93 renal grafts biopsied of 77 patients. We observed the de novo production of connective tissue growth factor, HSP47, and laminin in the tubular epithelial cells displaying epithelial phenotypic changes. The score of vimentin was significantly correlated with those of connective tissue growth factor (r = 0.785, P < .0001), HSP47 (r = 0.887, P < .0001), and laminin (r = 0.836, P < .0001). The level of tubular expression of mesenchymal cell markers and profibrogenic molecules, but not graft histologic lesions according to Banff acute or chronic scores, was correlated with graft dysfunction and proteinuria at the time of biopsy (r = -0.611, P < .0001 for vimentin with estimated glomerular filtration rate) (r = 0.42, P = .0006 for vimentin with proteinuria). Our results demonstrate that the epithelial phenotypic switch is associated with an active fibrogenic process in tubular epithelial cells and with graft injury indicators. Perpetuation of this tissue injury-repair response may drive fibrogenesis in renal grafts. This "repair response" represents an interesting marker for renal graft surveillance.