Hypoxic conditions stimulate the production of angiogenin and vascular endothelial growth factor by human renal proximal tubular epithelial cells in culture.
BACKGROUND
Chronic low oxygen in the tubulointerstitial area is a crucial cause of renal degradation and tubulointerstitial damage. Previous reports have suggested that the maintenance of renal blood flow plays a role in the suppression of progressive renal damage. Neovascularization is important for the maintenance of blood flow. We studied the production of angiogenic factors by culturing renal proximal tubular epithelial cells (PTEC) under hypoxic conditions.


METHODS
Cultured PTEC were exposed to normal and low-oxygen conditions. The levels of angiogenin (ANG) and vascular endothelial growth factor (VEGF) in the cell supernatants were measured by enzyme-linked immunosorbent assay. The messenger RNAs (mRNAs) of ANG and VEGF in the PTEC were examined by real-time reverse transcriptase polymerase chain reaction (real-time RT-PCR). The presence of ANG, VEGF and hypoxia-inducible factor-1 (HIF-1) was studied by immunofluorescence techniques. The effect of cobalt chloride (CoCl(2)), which is an HIF-1 inducer, on the production of ANG and VEGF was also examined in order to elucidate the contribution of the HIF-1 pathway to the production of these cytokines.


RESULTS
ANG and VEGF were demonstrated to exist in the cell supernatants, and ANG and VEGF mRNAs were detected in the PTEC. Hypoxic conditions stimulated the secretion of ANG (2.5-fold vs normoxia, P<0.001) and VEGF (3.2-fold vs normoxia, P<0.001) by PTEC. Hypoxic conditions increased the mRNA expression of ANG for 6 h (1.38-fold vs normoxia, P<0.05) and VEGF for 24 h (2.04-fold vs normoxia, P<0.01). Hypoxic conditions also enhanced ANG, VEGF and HIF-1 protein expression in PTEC. The CoCl(2) increased the secretion of ANG (5.2-fold vs control, P<0.0001) and VEGF (2.3-fold vs control, P<0.0001) by PTEC.


CONCLUSIONS
Under hypoxic conditions, the ANG and VEGF secreted by PTEC may modulate angiogenesis and vascular remodeling in the renal interstitium via an increase in the production of HIF-1.
The Second Department of Internal Medicine, Hirosaki University School of Medicine, Hirosaki, 036-8562 Aomori, Japan.
Masayuki
M
Nakamura
Hideaki
H
Yamabe
Hiroshi
H
Osawa
Norio
N
Nakamura
Michiko
M
Shimada
Ryuichiro
R
Kumasaka
Reiichi
R
Murakami
Takeshi
T
Fujita
Tomohiro
T
Osanai
Ken
K
Okumura
D015687:Cell Hypoxia / Q000502:physiology*; D002460:Cell Line; D004847:Epithelial Cells / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D051793:Hypoxia-Inducible Factor 1 / Q000032:analysis / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000166:cytology* / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D012259:Ribonuclease, Pancreatic / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics
D051793:Hypoxia-Inducible Factor 1; D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A; C046366:angiogenin; D012259:Ribonuclease, Pancreatic