Autocrine and paracrine functions of vascular endothelial growth factor (VEGF) in renal tubular epithelial cells

Kidney Int. 2005 Feb;67(2):449-57. doi: 10.1111/j.1523-1755.2005.67101.x.

Abstract

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.

Conclusion: 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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Apoptosis
  • Cell Proliferation
  • Cell Survival
  • Epithelial Cells / physiology
  • Kidney Tubules / cytology*
  • Kidney Tubules / physiology
  • Mice
  • Protein-Serine-Threonine Kinases / physiology
  • Proto-Oncogene Proteins / physiology
  • Proto-Oncogene Proteins c-akt
  • Rats
  • Signal Transduction
  • Vascular Endothelial Growth Factor A / physiology*
  • Vascular Endothelial Growth Factor Receptor-2 / analysis

Substances

  • Proto-Oncogene Proteins
  • Vascular Endothelial Growth Factor A
  • Vascular Endothelial Growth Factor Receptor-2
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt