Expression of the transcriptional regulator snail1 in kidney transplants displaying epithelial-to-mesenchymal transition features.

BACKGROUND: The epithelial response to injury is stereotypical and reminiscent of epithelial-to-mesenchymal transitions (EMTs), such as those observed during embryogenesis and tumour metastasis. In the context of solid organ transplantation, EMT-like features are often acquired by epithelial cells and are predictive of graft fibrosis. Here, we studied the possible involvement of several major transcriptional regulators, including snail1, phospho-Smad 2/3 and zeb1, in EMT induction in human renal grafts. METHODS: We used immunohistochemistry to detect the presence of these EMT transcriptional regulators along with that of two validated EMT markers (intra-cytoplasmic translocation of ß-catenin, de novo expression of vimentin), in 103 renal graft biopsy samples taken for routine surveillance or for a clinical indication. RESULTS: We observed the nuclear accumulation of snail1 and phospho-smad2/3 in tubular cells displaying EMT. The level of snail1 was significantly correlated with the scores of EMT markers (ß-catenin: ρ = 0.94, P < 0.0001; vimentin: ρ = 0.93, P < 0.0001) and with deteriorated graft function and proteinuria at the time of biopsy. Furthermore, intense staining for both snail1 and vimentin in tubular cells (≥10% of tubules) was predictive of graft dysfunction 21 months post-biopsy, independently of the other known risk factor for long-term graft dysfunction. In contrast, in both normal and diseased graft, zeb1 expression was detected exclusively in the endothelial cells of glomeruli and peritubular capillaries. CONCLUSION: This study suggests that snail1 is closely related to the fibrogenic, EMT-like response of the tubular epithelium in human renal grafts and predictive of graft function loss.

Early epithelial phenotypic changes predict graft fibrosis.

Chronic allograft nephropathy accounts for the loss of approximately 40% of allografts at 10 yr. Currently, no biomarker is available to detect interstitial fibrosis and tubular atrophy in the renal graft at an early stage, when intervention may be beneficial. Because tubular epithelial cells have been shown to exhibit phenotypic changes suggestive of epithelial-to-mesenchymal transition, we studied whether these changes predict the progression of fibrosis in the allograft. Eighty-three kidney transplant recipients who had undergone a protocol graft biopsy at both 3 and 12 mo after transplantation were enrolled. De novo vimentin expression and translocation of beta-catenin into the cytoplasm of tubular cells were detected on the first biopsy by immunohistochemistry. Patients with expression of these markers in >or=10% of tubules at 3 mo had a higher interstitial fibrosis score at 1 yr and a greater progression of this score between 3 and 12 mo. The intensity of these phenotypic changes positively and significantly correlated with the progression of fibrosis, and multivariate analysis showed that their presence was an independent risk factor for this progression. In addition, the presence of early phenotypic changes was associated with poorer graft function 18 mo after transplantation. In conclusion, early phenotypic changes indicative of epithelial-to-mesenchymal transition predict the progression toward interstitial fibrosis in human renal allografts.

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 ß-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.

Tubular nuclear accumulation of Snail and epithelial phenotypic changes in human myeloma cast nephropathy.

The transcription factor Snail is an important repressor of E-cadherin gene expression. It plays a key role in the induction of epithelial-mesenchymal transition, an essential process important not only in embryonic development and tumor progression but also in organ fibrogenesis. We studied the expression of Snail by immunohistochemistry, along with several epithelial phenotypic changes suggestive of epithelial-mesenchymal transition, in 14 patients with multiple myeloma cast nephropathy. This nephropathy is characterized by a rapid progression toward fibrosis. As controls, we used normal kidneys and kidneys from patients displaying an idiopathic nephrotic syndrome, a syndrome unassociated with renal fibrosis. We discovered that, in all patients with multiple myeloma nephropathy, a drastic accumulation of Snail is seen in the nuclei from tubular epithelial cells showing epithelial phenotypic changes. In contrast, normal and idiopathic nephrotic syndrome kidneys did not exhibit either of these markers. Snail, a major player in the process of epithelial-to-mesenchymal transition, is highly expressed by tubular epithelial cells during multiple myeloma nephropathy. It is, therefore, a potential target to prevent multiple myeloma kidneys from fibrosing. Intranuclear accumulation of Snail is a characteristic in phenotypically altered tubular cells from multiple myeloma kidneys. The epithelial-mesenchymal transition pathway could, therefore, be involved in the rapid renal fibrogenesis observed in this setting.