The influence of tubular phenotypic changes on the development of diffuse interstitial fibrosis in renal allografts.

It has been reported that myofibroblasts are the major cells in the development of interstitial fibrosis (IF) and, therefore, chronic dysfunction in renal allografts. Our aim was two fold: first, to understand the key markers controlling tubular and glomerular epithelial-to-mesenchymal transition (EMT); second, to show the role of tubular EMT on the development of interstitial fibrosis (IF) and the role of glomerular EMT on the development of proteinuria and, therefore, graft survival. For this purpose we evaluated the vinculin- and paxillin-containing adhesion complexes and α-smooth muscle actin (α-SMA) expression on tubular cells and glomerular podocytes in first year renal allograft biopsy specimens of 74 patients. We established the proteinuric state at the time of the biopsy of all patients. Follow-up biopsy specimens of all patients were evaluated for the development of diffuse IF (≥50% of the biopsy specimen). Among 74 patients, 21 showed grade 1 and 9 showed grade 2 tubular EMT. Only 25/74 cases showed glomerular EMT. The incidence of the development of diffuse IF at 18 and 24 months after the initial biopsy and the graft loss at 5 years were higher among subjects with tubules and glomerular podocytes showing EMT (P<.001 for all). The development of IF and graft loss was significantly earlier in cases with grade 2 compared with grade 1 or no tubular EMT (P<.001 for all). The proteinuric state at the time of the biopsy showed a significant positive correlation with the glomerular EMT (P<.001). In conclusion, our results showed that renal tubular cells and glomerular podocytes can undergo epithelial-to-mesenchymal differentiation. The transformed cells with reorganized cytoskeletal features have an important role in renal allograft survival by inducing the development of diffuse IF and proteinuria.