IGF-I induces vascular endothelial growth factor in human mesangial cells via a Src-dependent mechanism.
BACKGROUND
Both insulin-like growth factor-I (IGF-I) and vascular endothelial growth factor (VEGF) have been implicated in the pathogenesis of early renal dysfunction in diabetes. We investigated whether IGF-I affects VEGF gene expression and protein secretion in human mesangial cells. Furthermore, we studied the intracellular signaling pathway involved and the interaction of IGF-I with mechanical stretch, a known VEGF inducer.


METHODS
Human mesangial cells were exposed to IGF-I in the presence and in the absence of (1) anti-IGF-I type I receptor antibody (alpha IR3) (1 microg/mL), a monoclonal antibody blocking the IGF-I type I receptor; (2) wortmannin (600 nmol/L), a phosphatidylinositol 3-kinase (PI3K) inhibitor; (3) 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), a specific Src inhibitor (10 micromol/L); and (4) cyclic stretch (approximately 10% elongation).


RESULTS
IGF-I induced a dose-dependent increase in VEGF protein levels (10(-11) mol/L, 5%; 10(-10) mol/L, 14%; 10(-9) mol/L, 46%; 10(-8) mol/L, 66%; 10(-7) mol/L, 68%; P < 0.001). IGF-I-induced VEGF production rose by 6 hours with a peak at 12 hours, and declined by 24 hours (52%, 72%, and 34%, respectively; P < 0.01 at 12 hours). A corresponding 50% increase in VEGF mRNA levels was seen at 6 hours (P < 0.01). IGF-I-induced VEGF protein secretion was not affected by the addition of wortmannin (IGF-I, 76% vs. IGF-I + wortmannin, 79% increase over control; P = NS), but was abolished by alpha IR3 (IGF-I, 69% vs. IGF-I +alpha IR3, 0%; P < 0.001) and significantly reduced by PP2 (IGF-I, 50% vs. IGF-I + PP2, 14%; P < 0.01). Simultaneous exposure of human mesangial cells to both IGF-I and stretch failed to further increase VEGF production (IGF-I, 1.49 +/- 0.05; stretch, 1.76 +/- 0.05; and IGF-I + stretch, 1.83 +/- 0.11).


CONCLUSIONS
IGF-I induces VEGF gene expression and protein secretion in human mesangial cells via a Src-dependent mechanism.
Gruden
Gabriella
G
Department of Diabetes and Endocrinology, GKT School of Medicine, King's College London, London, England, United Kingdom. ggruden@hotmail.com
Araf
Shawanna
S
Zonca
Silvia
S
Burt
Davina
D
Thomas
Stephen
S
Gnudi
Luigi
L
Viberti
Giancarlo
G
D002478:Cells, Cultured; D015870:Gene Expression / Q000187:drug effects; D005920:Glomerular Mesangium / Q000166:cytology / Q000502:physiology*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013314:Stress, Mechanical; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics* / Q000378:metabolism; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
C412373:AG 1879; D011743:Pyrimidines; D042461:Vascular Endothelial Growth Factor A; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D017526:Receptor, IGF Type 1; D019061:src-Family Kinases