Microenvironmental VEGF concentration, not total dose, determines a threshold between normal and aberrant angiogenesis
Clare R. Ozawa, … , Donald M. McDonald, Helen M. Blau
Clare R. Ozawa, … , Donald M. McDonald, Helen M. Blau
Published February 15, 2004
Citation Information: J Clin Invest. 2004;113(4):516-527. https://doi.org/10.1172/JCI18420.
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Article Cardiology

Microenvironmental VEGF concentration, not total dose, determines a threshold between normal and aberrant angiogenesis

Abstract

Use of long-term constitutive expression of VEGF for therapeutic angiogenesis may be limited by the growth of abnormal blood vessels and hemangiomas. We investigated the relationship between VEGF dosage and the morphology and function of newly formed blood vessels by implanting retrovirally transduced myoblasts that constitutively express VEGF164 into muscles of adult mice. Reducing VEGF dosage by decreasing the total number of VEGF myoblasts implanted did not prevent vascular abnormalities. However, when clonal populations of myoblasts homogeneously expressing different levels of VEGF were implanted, a threshold between normal and aberrant angiogenesis was found. Clonal myoblasts that expressed low to medium levels of VEGF induced growth of stable, pericyte-coated capillaries of uniform size that were not leaky and became VEGF independent, as shown by treatment with the potent VEGF blocker VEGF-TrapR1R2. In contrast, clones that expressed high levels of VEGF induced hemangiomas. Remarkably, when different clonal populations were mixed, even a small proportion of cells with high production of VEGF was sufficient to cause hemangioma growth. These results show for the first time to our knowledge that the key determinant of whether VEGF-induced angiogenesis is normal or aberrant is the microenvironmental amount of growth factor secreted, rather than the overall dose. Long-term continuous delivery of VEGF, when maintained below a threshold microenvironmental level, can lead to normal angiogenesis without other exogenous growth factors.

Authors

Clare R. Ozawa, Andrea Banfi, Nicole L. Glazer, Gavin Thurston, Matthew L. Springer, Peggy E. Kraft, Donald M. McDonald, Helen M. Blau

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Figure 1

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Uncontrolled VEGF production promotes abnormal vascular growth in muscle...
Uncontrolled VEGF production promotes abnormal vascular growth in muscle. (a) Myoblasts expressing both VEGF164 and LacZ or control LacZ myoblasts were implanted into the posterior auricular muscles of mice (crossmarks). (b) X-gal staining of a control ear sectioned along the dashed line in a at 14 days after implantation, showing LacZ myoblasts fused into endogenous myofibers (arrowheads) and clusters of unfused myoblasts or myoblasts fused with each other (arrows; n = 7). (c) Lectin and X-gal staining of control ear bisected in the plane of the cartilage, showing LacZ-positive myofibers at the site of injection at 28 days (arrow; n = 10). (d) Vessels at sites of implanted control myoblasts were normal at all time points (18 hours and 4, 7, 14, 28, and 64 days; n = 10 for each time point). (e) At 7 days after implantation of VEGF myoblasts, vessels leading into the injection site (arrows) became enlarged (n = 9). (f) At 28 days after implantation, aberrant bulbous structures (left arrow) and bundles of capillary-like vessels (right arrow) were present at sites of implanted VEGF myoblasts (n = 10). (g) At day 64, typical large blood-filled growths (hemangiomas) developed in ears implanted with VEGF myoblasts (left). The contralateral control ear was normal (n = 10). (h) H&E staining of an ear containing a hemangioma (top) and of a control ear (bottom). (i) A vessel leading into the injection site (arrow) became abnormal in the immediate vicinity of implanted VEGF myoblasts (from a second VEGF myoblast population, VEGF*; 7 days after implantation). Scale bars: 100 μm (b), 1 mm (c and h), and 50 μm (d–f and i).