Autocrine and paracrine functions of vascular endothelial growth factor (VEGF) in renal tubular epithelial cells.
BACKGROUND
VEGF secreted by organ parenchymal cells controls vascularization by recruiting endothelial cells and supporting their proliferation. In the developing kidney VEGF-expressing epithelial cells also express VEGF receptors. We showed that VEGF stimulates tubulogenesis in addition to promoting vascularization in metanephric explants. Since explants are grown in serum-free media and are not perfused, we hypothesized that VEGF secreted by renal epithelia may induce their proliferation in an autocrine manner and chemoattract endothelial cells.


METHODS
To test these hypotheses, we analyzed VEGF-mediated responses in vitro using several renal epithelial cell lines [immortalized rat proximal tubular cells (IRPT), transformed mouse proximal tubular cells (tsMPT), and normal rat kidney cells (NRK-52E)] expressing VEGF receptors (VEGFR).


RESULTS
We demonstrated that VEGFR-2 phosphorylates upon human recombinant VEGF (rhVEGF) exposure, indicating that VEGFR-2 is the signaling receptor. All three cell lines secreted VEGF into the media as indicated by enzyme-linked immunosorbent assay (ELISA) and Western blotting. We showed that these tubular epithelial cells chemoattract endothelial cells when cocultured in vitro and that the chemoattraction is abolished by anti-VEGF neutralizing antibody. rhVEGF (10 ng/mL) induced a mitogenic effect similar to 10% fetal bovine serum (FBS) as assessed by H(3)-thymidine incorporation and elicited 30% decrease in apoptosis as determined by annexin V-fluorescein isothiocyanate (FITC) staining.


CONCLUSIONS
These in vitro studies indicate that (1) tubular epithelial cells chemoattract endothelial cells in a paracrine fashion by secreting VEGF, and (2) VEGF stimulates proliferation and promotes survival of renal epithelial cells in an autocrine manner via VEGFR-2. Taken together, our results suggest that VEGF supports the growth of renal epithelia in addition to mediating kidney vascularization.
Villegas
Guillermo
G
Department of Pediatrics, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Lange-Sperandio
Bäerbel
B
Tufro
Alda
A
D000818:Animals; D017209:Apoptosis; D049109:Cell Proliferation; D002470:Cell Survival; D004847:Epithelial Cells / Q000502:physiology; D007684:Kidney Tubules / Q000166:cytology* / Q000502:physiology; D051379:Mice; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D015398:Signal Transduction; D042461:Vascular Endothelial Growth Factor A / Q000502:physiology*; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000032:analysis
D011518:Proto-Oncogene Proteins; D042461:Vascular Endothelial Growth Factor A; D040301:Vascular Endothelial Growth Factor Receptor-2; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt