The origin and fate of renal interstitial myofibroblasts (MFs), the effector cells of renal fibrosis, are still debated. Experimental evidence suggests that renal MFs derive from tubular epithelial cells throughout the epithelial-mesenchymal transition (EMT) process. Primary human tubular epithelial cells (HUTECs) were cultured for 4 and 6 days on plastic or type I collagen-coated plates with 1, 5, 10 and 50 ng/ml of transforming growth factor beta1 (TGFbeta1). The EMT process was monitored by morphology and immunophenotyping for alphaSMA, cytokeratin 8-18, E-cadherin, vimentin and collagen III. Quantitative comparative RT/PCR and real-time PCR were used to evaluate the expression of collagen III and IV, fibronectin, tenascin, MMP-2, CTGF, E-cadherin and cadherin 11 genes, as well as those of the Smad signalling pathway. TGFbeta1 was found capable of reactivating the mesenchymal programme switched off during tubulogenesis, but it induced no de novo expression of alphaSMA gene or myofibroblast phenotype. We demonstrate that the EMT process is conditioned by the extracellular matrix and characterized by TGFbeta1-driven Smad3 downregulation. Our study results suggest that TGFbeta1 could function as a classic embryonal inducer, initiating a cascade of de-differentiating events that might be further controlled by other factors in the cellular environment.

Regulation of mesangial matrix deposition is a dynamic phenomenon involving synthetic and degradative processes. The latter involve a number of matrix metalloproteinases (MMP) and tissue inhibitors of matrix metalloproteinases (TIMP). Experimental studies suggest that mesangial matrix degradation is inhibited in diabetic nephropathy, and that this phenomenon has a pathogenic role. The expression of genes for MMP2 and TIMP2 in human diabetic nephropathy was investigated. Reverse transcription polymerase chain reaction was carried out in microdissected glomeruli and tubulo-interstitium obtained from kidney biopsies. We studied 16 NIDDM patients, 5 patients with glomerulonephritis or chronic kidney transplant rejection, and 5 normal control subjects. Albumin excretion rate and renal histology for NIDDM patients were available. Contrary to TIMP2 which was expressed both in tubulo-interstitium and glomeruli in almost all renal biopsies, MMP2 gene down-regulation was observed in glomeruli from all NIDDM patients, irrespective of the albumin excretion rate, and of renal histology. In contrast, this gene was expressed in biopsies from other subjects (chi(2) = 20.6; p = 0.000). In conclusion, this study demonstrates that: 1) in glomeruli of NIDDM patients the MMP2 gene is down-regulated; 2) in biopsies of NIDDM patients the MMP2/TIMP2 pattern is peculiar for NIDDM; 3) the MMP2 gene down-regulation is observed in all NIDDM patients, irrespective of the level of albuminuria and of renal histology. MMP2 gene down-regulation seems to be a molecular epiphenomenon of diabetes, rather than a marker of diabetic nephropathy.

The therapeutic potential of adult stem cells in the treatment of chronic degenerative diseases has becoming increasingly evident over the last few years. Significant attention is currently being paid to the development of novel treatments for acute and chronic kidney diseases too. To date, promising sources of stem cells for renal therapies include adult bone marrow stem cells and the kidney precursors present in the early embryo. Both cells have clearly demonstrated their ability to differentiate into the kidney's specialized structures. Adult renal stem cells have yet to be identified, but the papilla is where the stem cell niche is probably located. Now we need to isolate and characterize the fraction of papillary cells that constitute the putative renal stem cells. Our growing understanding of the cellular and molecular mechanisms behind kidney regeneration and repair processes -together with a knowledge of the embryonic origin of renal cells -should induce us, however, to bear in mind that in the kidney, as in other mesenchymal tissues, the need for a real stem cell compartment might be less important than the phenotypic flexibility of tubular cells. Thus, by displaying their plasticity during kidney maintenance and repair, terminally differentiated cells may well function as multipotent stem cells despite being at a later stage of maturation than adult stem cells. One of the major tasks of Regenerative Medicine will be to disclose the molecular mechanisms underlying renal tubular plasticity and to exploit its biological and therapeutic potential.

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Diabetic nephropathy is one of the leading causes of renal failure in Western countries, where diabetic patients account for nearly half of all patients on haemodialysis. Progressive expansion of the mesangial matrix, and thickening of the glomerular and tubular basement membranes without signs of major cell proliferation are hallmarks of human and experimental diabetic nephropathy. These lesions eventually lead to glomerular fibrosis, a central pathological feature in many human acute and chronic kidney diseases, which progressively destroys the renal filtration unit, and may finally cause renal failure. Indeed, structure function relationship studies have shown that mesangial matrix expansion is strongly related to the clinical manifestation of diabetic nephropathy.