We demonstrate a physiological role for tumstatin, a cleavage fragment of the alpha3 chain of type IV collagen (Col IValpha3), which is present in the circulation. Mice with a genetic deletion of Col IValpha3 show accelerated tumor growth associated with enhanced pathological angiogenesis, while angiogenesis associated with development and tissue repair are unaffected. Supplementing Col IValpha3-deficient mice with recombinant tumstatin to a normal physiological concentration abolishes the increased rate of tumor growth. The suppressive effects of tumstatin require alphaVbeta3 integrin expressed on pathological, but not on physiological, angiogenic blood vessels. Mice deficient in matrix metalloproteinase-9, which cleaves tumstatin efficiently from Col IValpha3, have decreased circulating tumstatin and accelerated growth of tumor. These results indicate that MMP-generated fragments of basement membrane collagen can have endogenous function as integrin-mediated suppressors of pathologic angiogenesis and tumor growth.

There are about 2.5 million glomeruli in the kidneys each consisting of a barrel of glomerular basement membrane surrounded by glomerular endothelial cells on the inside and glomerular epithelial cells with established foot processes (podocytes) on the outside. Defects in this filtration apparatus lead to glomerular vascular leak or proteinuria. The role of vascular endothelial growth factor (VEGF) in the regulation of glomerular vascular permeability is still unclear. Recent studies indicate that patients receiving anti-VEGF antibody therapy may have an increased incidence of proteinuria. In a different setting, pregnancies complicated by preeclampsia are associated with elevated soluble VEGF receptor 1 protein (sFlt-1), endothelial cell dysfunction and proteinuria. These studies suggest that neutralization of physiologic levels of VEGF, a key endothelial survival factor, may lead to proteinuria. In the present study, we evaluated the potential of anti-VEGF neutralizing antibodies and sFlt-1 in the induction of proteinuria. Our studies demonstrate that anti-VEGF antibodies and sFlt-1 cause rapid glomerular endothelial cell detachment and hypertrophy, in association with down-regulation of nephrin, a key epithelial protein in the glomerular filtration apparatus. These studies suggest that down-regulation or neutralization of circulating VEGF may play an important role in the induction of proteinuria in various kidney diseases, some forms of cancer therapy and also in women with preeclampsia.

Despite intense investigation, mechanisms that facilitate the emergence of the pre-eclampsia phenotype in women are still unknown. Placental hypoxia, hypertension, proteinuria and oedema are the principal clinical features of this disease. It is speculated that hypoxia-driven disruption of the angiogenic balance involving vascular endothelial growth factor (VEGF)/placenta-derived growth factor (PLGF) and soluble Fms-like tyrosine kinase-1 (sFLT-1, the soluble form of VEGF receptor 1) might contribute to some of the maternal symptoms of pre-eclampsia. However, pre-eclampsia does not develop in all women with high sFLT-1 or low PLGF levels, and it also occurs in some women with low sFLT-1 and high PLGF levels. Moreover, recent experiments strongly suggest that several soluble factors affecting the vasculature are probably elevated because of placental hypoxia in the pre-eclamptic women, indicating that upstream molecular defect(s) may contribute to pre-eclampsia. Here we show that pregnant mice deficient in catechol-O-methyltransferase (COMT) show a pre-eclampsia-like phenotype resulting from an absence of 2-methoxyoestradiol (2-ME), a natural metabolite of oestradiol that is elevated during the third trimester of normal human pregnancy. 2-ME ameliorates all pre-eclampsia-like features without toxicity in the Comt(-/-) pregnant mice and suppresses placental hypoxia, hypoxia-inducible factor-1alpha expression and sFLT-1 elevation. The levels of COMT and 2-ME are significantly lower in women with severe pre-eclampsia. Our studies identify a genetic mouse model for pre-eclampsia and suggest that 2-ME may have utility as a plasma and urine diagnostic marker for this disease, and may also serve as a therapeutic supplement to prevent or treat this disorder.