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

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 VEGF₁₆₄ 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.