Early events in angiogenesis: cloning an alpha-prolyl 4-hydroxylase-like gene

A critical analysis of current in vitro and in vivo angiogenesis assays

The study of angiogenesis has grown exponentially over the past 40 years with the recognition that angiogenesis is essential for numerous pathologies and, more recently, with the advent of successful drugs to inhibit angiogenesis in tumours. The main problem with angiogenesis research remains the choice of appropriate assays to evaluate the efficacy of potential new drugs and to identify potential targets within the angiogenic process. This selection is made more complex by the recognition that heterogeneity occurs, not only within the endothelial cells themselves, but also within the specific microenvironment to be studied. Thus, it is essential to choose the assay conditions and cell types that most closely resemble the angiogenic disease being studied. This is especially important when aiming to translate data from in vitro to in vivo and from preclinical to the clinic. Here we critically review and highlight recent advances in the principle assays in common use including those for endothelial cell proliferation, migration, differentiation and co-culture with fibroblasts and mural cells in vitro, vessel outgrowth from organ cultures and in vivo assays such as chick chorioallantoic membrane (CAM), zebrafish, sponge implantation, corneal, dorsal air sac, chamber and tumour angiogenesis models. Finally, we briefly discuss the direction likely to be taken in future studies, which include the use of increasingly sophisticated imaging analysis systems for data acquisition.

Subtractive hybridization--genetic takeaways and the search for meaning

Gene expression profiling relies on mRNA extraction from defined cell systems, which in the case of pathological processes necessarily results in the use of small quantities of tissues, sometimes as little as a few cells. This obviates the use of many systems of gene expression profiling and is best carried out using cDNA amplified by poly(A) reverse transcription polymerase chain reaction, which is capable of generating material representative of all the expressed genes in samples as small as one cell. Analysis of this material using subtractive hybridization compares the genes expressed at different stages of a biological/pathological process allowing identification of the all the genes upregulated during the process. The identification of the genes present is not dependent on their prior description or on the choice of genes used in a screen and as such the method is ideal for identifying novel genes or unsuspected genes. We have used the method to identify genes involved in normal osteoblastic differentiation and in Paget's disease of bone and it has been widely used to study normal differentiation and pathological processes in a number of systems. The method, its applications and its relationship with the other methods of gene expression profiling are reviewed.

Ges, A human GTPase of the Rad/Gem/Kir family, promotes endothelial cell sprouting and cytoskeleton reorganization

Rad, Gem/Kir, and mRem (RGK) represent a unique GTPase family with largely unknown functions (Reynet, C., and C.R. Kahn. 1993. Science. 262:1441-1444; Cohen, L., R. Mohr, Y. Chen, M. Huang, R. Kato, D. Dorin, F. Tamanoi, A. Goga, D. Afar, N. Rosenberg, and O. Witte. Proc. Natl. Acad. Sci. USA. 1994. 91:12448-12452; Maguire, J., T. Santoro, P. Jensen, U. Siebenlist, J. Yewdell, and K. Kelly. 1994. Science. 265:241-244; Finlin, B.S., and D.A. Andres. 1997. J. Biol. Chem. 272:21982-21988). We report that Ges (GTPase regulating endothelial cell sprouting), a human RGK protein expressed in the endothelium, functions as a potent morphogenic switch in endothelial cells (ECs). Ges function is sufficient to substitute for angiogenic growth factor/extracellular matrix (ECM) signals in promoting EC sprouting, since overexpression of Ges in ECs cultured on glass leads to the development of long cytoplasmic extensions and reorganization of the actin cytoskeleton. Ges function is also necessary for Matrigel-induced EC sprouting, since this event is blocked by its dominant negative mutant, Ges(T94N), predicted to prevent the activation of endogenous Ges through sequestration of its guanine nucleotide exchange factor. Thus, Ges appears to be a key transducer linking extracellular signals to cytoskeleton/morphology changes in ECs.

Inhibition of neovascularization and tumor growth, and facilitation of wound repair, by halofuginone, an inhibitor of collagen type I synthesis

Halofuginone, an inhibitor of collagen alpha1(I) gene expression was used for the treatment of subcutaneously implanted C6 glioma tumors. Halofuginone had no effect on the growth of C6 glioma spheroids in vitro, and these spheroids showed no collagen alpha1(I) expression and no collagen synthesis. However, a significant attenuation of tumor growth was observed in vivo, for spheroids implanted in CD-1 nude mice which were treated by oral or intraperitoneal (4 microg every 48 hours) administration of halofuginone. In these mice, treatment was associated with a dose-dependent reduction in collagen alpha1(I) expression and dose- and time-dependent inhibition of angiogenesis, as measured by MRI. Moreover, halofuginone treatment was associated with improved re-epithelialization of the chronic wounds that are associated with this experimental model. Oral administration of halofuginone was effective also in intervention in tumor growth, and here, too, the treatment was associated with reduced angiogenic activity and vessel regression. These results demonstrate the important role of collagen type I in tumor angiogenesis and tumor growth and implicate its role in chronic wounds. Inhibition of the expression of collagen type I provides an attractive new target for cancer therapy.