Podocyte-Derived Vascular Endothelial Growth Factor Mediates the Stimulation of α3(IV) Collagen Production by Transforming Growth Factor-β1 in Mouse Podocytes

Podocyte-Derived Vascular Endothelial Growth Factor Mediates the Stimulation of α3(IV) Collagen Production by Transforming Growth Factor-β1 in Mouse Podocytes Sheldon Chen , Yuki Kasama , Joseph S. Lee , Belinda Jim , Maria Marin and Fuad N. Ziyadeh From the Renal-Electrolyte and Hypertension Division, Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania Address correspondence and reprint requests to Sheldon Chen, MD, 700 Clinical Research Building, 415 Curie Blvd., Philadelphia, Pennsylvania 19104-4218. E-mail: chens{at}mail.med.upenn.edu Abstract Podocyte-derived vascular endothelial growth factor (VEGF) is upregulated in diabetes and may contribute to albuminuria. Although believed to act upon the glomerular endothelium, VEGF may have pronounced effects on the podocyte itself. The functionality of this VEGF autocrine loop was investigated in conditionally immortalized mouse podocytes. Exogenous VEGF 164 increased the production of α3(IV) collagen, an integral component of the glomerular basement membrane (GBM); this effect was completely prevented by SU5416, a pan-VEGF receptor inhibitor. The VEGF inhibitor also partially prevented the stimulation of α3(IV) collagen by transforming growth factor (TGF)-β1, establishing a novel role for endogenous VEGF. However, VEGF did not influence the production of another novel chain of collagen IV, α5(IV) collagen, and SU5416 failed to reverse the known inhibitory effect of TGF-β1 on α5(IV) collagen production. Cultured mouse podocytes possess at least the VEGFR-1 receptor, confirmed by RT-PCR, immunoblotting, and immunocytochemistry. By these techniques, however, VEGFR-2 is absent. VEGF signaling proceeds via autophosphorylation of VEGFR-1 and activation of the phosphatidylinositol 3-kinase (PI3K) pathway. Thus, podocyte-derived VEGF operates in an autocrine loop, likely through VEGFR-1 and PI3K, to stimulate α3(IV) collagen production. The TGF-β1–stimulated endogenous VEGF may have significant implications for podocyte dysfunction in diabetic glomerulopathy, manifesting as GBM thickening and altered macromolecular permeability. DAPI, 4′,6-diamidino-2-phenylindole ELISA, enzyme-linked immunosorbent assay GBM, glomerular basement membrane HRP, horseradish peroxidase P13K, phosphatidylinositol 3-kinase TGF, transforming growth factor VEGF, vascular endothelial growth factor Footnotes Accepted July 23, 2004. Received January 21, 2004. DIABETES