Expression of neuropilin-1 by human glomerular epithelial cells in vitro and in vivo

Vascular endothelial growth factor (VEGF) is a potent promoter of endotheli al mitogenesis and of endothelial permeability. Within the kidney it is syn thesized primarily in the visceral glomerular epithelial cells (vGECs), how ever, the role of VEGF in the glomerulus remains unknown, as does the targe t cell upon which it acts. Although the target cells may be those of the gl omerular endothelium, there are micro-anatomical reasons why this might not be the case. This, therefore, led us to consider the possibility that glom erular VEGF may bind to the vGECs themselves. Since it has been shown that vGECs do not express the main tyrosine kinase VEGF receptors, we chose to s tudy vGEC expression of the more recently described VEGF isoform-specific r eceptors, the neuropilins. The expression of mRNAs for neuropilin-1, neurop ilin-2 and soluble neuropilin was studied in whole kidney, sieved glomeruli and cultured podocytes by reverse transcription-PCR, and neuropilin-1 mRNA expression in isolated single glomeruli was analysed by nested reverse tra nscription-PCR. The expression of neuropilin-1 protein was investigated in cultured vGECs by Western blotting and immunocytochemistry, and in normal k idney sections by immunohistochemistry. Neuropilin-1 mRNA was detected in w hole kidney, single and sieved glomeruli and cultured vGECs. Neuropilin-1 p rotein was detected in cultured vGECs and in vGECs in normal kidney section s by immunohistochemistry. Thus the present study suggests that vGECs may h ave the potential to bind the VEGF that they secrete. Functional studies wi ll be required to address the potential significance of this finding in ter ms of an autocrine loop or VEGF sequestration.