Heparin-binding epidermal growth factor-like growth factor in experimental models of membranous and minimal change nephropathy

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a recently described member of the epidermal growth factor (EGF) family. It binds to heparan sulfate proteoglycans via a cationic domain and is a potent mitogen for epithelial cells, fibroblasts and vascular smooth muscle cells. In the present study we have attempted to identify changes in quantity and distribution of HB-EGF in two models of acute glomerular epithelial cell injury, using Western blotting, immunohistochemistry and in situ hybridization. Prior to disease induction, Western blots showed some expression of HB-EGF protein within glomeruli. Within the first three days in the acute puromycin aminonucleoside (PAN) and passive Heymann nephritis (PHN) models, immunohistochemistry and in situ hybridization demonstrated an up- regulation of HB-EGF mRNA and protein in glomerular epithelial cells (GEC). In both cases, increased protein and mRNA was found prior to the onset of proteinuria and continued until day 21 post-induction, the last time point studied. Early in the course of the models, HB-EGF was localized to the cytoplasm of glomerular epithelial cells. At day 21, however, HB-EGF protein was distributed in a nodular pattern within GEC and along the glomerular basement membrane (GBM) in both models, suggesting that the secreted form might bind to the membrane. The increase in HB-EGF protein within glomeruli was confirmed by Western blots of glomerular membrane protein which, however, demonstrated a single 29 kDa species, consistent with the transmembrane form. These data are not consistent with binding of the secreted form of HB-EGF to the GBM. The transmembrane form of HB-EGF is able to signal in a juxtracrine fashion, so increased expression of HB-EGF mRNA and protein by GEC might contribute to the genesis of proteinuria through the initiation of abortive GEC mitogenesis.