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From the Institute of Nephrology, University of Wales College of Medicine, Cardiff, Wales
Increased expression of hyaluronan (HA) has been associated with both acute renal injury and progressive renal disease, although the functional significance of this remains unclear. There is overwhelming evidence that transforming growth factor (TGF)-ß1 is critical to the development of progressive renal disease. Recent studies suggest an interaction between HA and TGF-ß signaling in cancer cell biology. The aim of this study was to examine the potential role of HA as a modulator of TGF-ß1 function in renal proximal tubular epithelial cells (PTC). Under resting conditions, co-localization of the principal receptor for HA, CD44, and both the TGF-ß type I and type II receptors was demonstrated by immunoprecipitation and western analysis and further confirmed by immunocytochemistry and confocal microscopy. Stimulation of PTC with TGF-ß1 led to increased synthesis of both type III and type IV collagen assessed by Western analysis. Addition of HA did not alter collagen synthesis, but abrogated TGF-ß1-mediated increase in type III and type IV collagen. This effect was blocked by the addition of a blocking antibody to CD44 and also by inhibition of MAP kinase kinase (MEK) activity. Furthermore HA decreased TGF-ß1 activation of a luciferase-SMAD responsive construct, and decreased translocation of SMAD4 into the cell nucleus. We have previously demonstrated an anti-migratory effect of TGF-ß1 in a scratch wounding model. As with HA antagonism of TGF-ß1 extracellular matrix generation, HA reduced the anti-migratory effect of TGF-ß1 in a CD44-dependent manner. In contrast to the effect of TGF-ß1 on collagen synthesis, which is SMAD-dependent, the anti-migratory effect of TGF-ß1 in this model is known to be dependent of activation of RhoA. In the presence of HA, TGF-ß1-mediated activation of RhoA was also abrogated in a CD44-dependent manner. The results suggest that co-localization of CD44 and TGF-ß receptors facilitate modulation of both SMAD and non-SMAD-dependent TGF-ß1-mediated events by HA. Our results therefore suggest that alteration of HA synthesis may represent an endogenous mechanism to limit renal injury.
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