Characterization of multiple signaling pathways of insulin in the regulation of vascular endothelial growth factor expression in vascular cells and angiogenesis.
The effects of insulin on vascular endothelial growth factor (VEGF) expression in cultured vascular cells and in angiogenesis were characterized. Insulin increased VEGF mRNA levels in mouse aortic smooth muscle cells from 10(-9) to 10(-7) m with an initial peak of 3.7-fold increases at 1 h and a second peak of 2.8-fold after 12 h. The first peak of VEGF expression was inhibited by LY294002, an inhibitor of phosphatidylinositol (PI) 3-kinase, and by the overexpression of dominant negative forms of p85 subunit of PI 3-kinase or Akt. Inhibitors of MEK kinase, PD98059, or overexpression of dominant negative forms of Ras was ineffective. In contrast, the chronic effect of insulin on VEGF expression was partially inhibited by both LY294002 or PD98059 as well as by the overexpression of dominant negatives of PI 3-kinase or Ras. The importance of PI 3-kinase-Akt pathway on VEGF expression was confirmed in mouse aortic smooth muscle cells isolated from insulin receptor substrate -1 knockout (IRS-1-/-) mice that showed parallel reductions of 46-49% in insulin-stimulated VEGF expression and PI 3-kinase-Akt activation. Insulin-induced activation of PI 3-kinase-Akt on hypoxia-induced VEGF expression and neovascularization was reduced by 40% in the retina of neonatal hypoxia model using IRS-1-/- mice. Thus, unlike other cells, insulin can regulate VEGF expression by both IRS-1/PI 3-kinase-Akt cascade and Ras-MAPK pathways in aortic smooth muscle cells. The in vivo results provide direct evidence that insulin can modulate hypoxia-induced angiogenesis via reduction in VEGF expression in vivo.
Jiang
Zhen Y
ZY
Research Division, Joslin Diabetes Center, Harvard Medical School, Boston, Massachusetts 02215, USA.
He
Zhiheng
Z
King
Benjamin L
BL
Kuroki
Tatsuya
T
Opland
Darren M
DM
Suzuma
Kiyoshi
K
Suzuma
Izumi
I
Ueki
Kohjiro
K
Kulkarni
Rohit N
RN
Kahn
C Ronald
CR
King
George L
GL
D000818:Animals; D002460:Cell Line; D016228:Endothelial Growth Factors / Q000235:genetics*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000502:physiology*; D007328:Insulin / Q000378:metabolism* / Q000502:physiology; D055504:Insulin Receptor Substrate Proteins; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics*; D008222:Lymphokines / Q000235:genetics*; D051379:Mice; D018919:Neovascularization, Physiologic; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins / Q000235:genetics / Q000502:physiology; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D012171:Retinal Vessels / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors
D016228:Endothelial Growth Factors; D004791:Enzyme Inhibitors; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D036341:Intercellular Signaling Peptides and Proteins; C526295:Irs1 protein, mouse; D008222:Lymphokines; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins; D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors