Hypoxia up-regulates angiopoietin-2, a Tie-2 ligand, in mouse mesangial cells.
BACKGROUND
Angiopoietins are secreted factors modulating endothelial survival and morphogenesis. Our previous studies demonstrated angiopoietin-2 (Ang-2) promoter activity in vivo in maturing kidney vascular smooth muscle and mesangial cells, with Tie-2 expressed by adjacent endothelia, including glomerular capillaries.


METHODS
In this study we investigated Ang-2 expression in immortalized mouse mesangial cell lines and studied the response to hypoxia.


RESULTS
Using reverse transcription-polymerase chain reaction, Ang-2 and Ang-3 mRNA were detected but Ang-1 and Tie-2 transcripts were absent. As assessed by Northern and slot blotting, 8 to 24 hours hypoxia (3% O(2)) significantly increased Ang-2 mRNA levels versus normoxic (21% O(2)) cells and the rate of Ang-2 mRNA degradation was similar in both conditions, consistent with increased transcription. Hypoxia also increased immunoreactive Ang-2 in cell lysates. Hypoxic stimulation of Ang-2 mRNA was significantly reduced by inhibitors of tyrosine kinase (genistein) and protein kinase C (GF109203X), but not by a mitogen-activated protein kinase 1 inhibitor (PD98059). Furthermore, hypoxia coincidentally up-regulated levels of vascular endothelial growth factor (VEGF) mRNA in these cells. Finally, in vivo, immunoreactive Ang-2 was observed in the cores of immature glomeruli of neonatal mice, but immunostaining in this location was absent in four-week postnatal mice.


CONCLUSIONS
This is the first demonstration that isolated mesangial cells express Ang-2 mRNA and protein and up-regulate Ang-2 in response to hypoxia. We speculate that hypoxia-induced, mesangial-derived Ang-2 and VEGF may have synergistic paracrine roles in the growth of glomerular endothelia during normal development and diseases.
Yuan
H T
HT
Nephro-Urology Unit, Institute of Child Health, University College London, London, England, United Kingdom. h.yuan@ich.ucl.ac.uk
Yang
S P
SP
Woolf
A S
AS
D042702:Angiopoietin-2; D000818:Animals; D002461:Cell Line, Transformed; D016228:Endothelial Growth Factors / Q000235:genetics; D005920:Glomerular Mesangium / Q000166:cytology / Q000378:metabolism* / Q000473:pathology; D000860:Hypoxia / Q000378:metabolism*; D008024:Ligands; D008222:Lymphokines / Q000235:genetics; D051379:Mice; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D042787:Receptor, TIE-2; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors
D042702:Angiopoietin-2; D016228:Endothelial Growth Factors; D008024:Ligands; D008222:Lymphokines; D011506:Proteins; D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D020794:Receptor Protein-Tyrosine Kinases; D042787:Receptor, TIE-2