Induction of Aberrant Vascular Growth,But Not of Normal Angiogenesis,by Cell-Based Expression of Different Doses of Human and Mouse VEGF Is Species-Dependent

Abstract

Therapeutic angiogenesis by vascular endothelial growth factor (VEGF) gene delivery is an attractive approach to treat ischemia. VEGF remains localized around each producing cell in vivo, and overexpression of mouse VEGF₁₆₄ (mVEGF₁₆₄) induces normal or aberrant angiogenesis, depending strictly on its dose in the microenvironment in vivo. However, the dose-dependent effects of the clinically relevant factor, human VEGF₁₆₅ (hVEGF₁₆₅), are unknown. Here we exploited a highly controlled gene delivery platform, based on clonal populations of transduced myoblasts overexpressing specific VEGF levels, to rigorously compare the in vivo dose-dependent effects of hVEGF₁₆₅ and mVEGF₁₆₄ in skeletal muscle of severe combined immune deficient (SCID) mice. While low levels of both factors efficiently induced similar amounts of normal angiogenesis, only high levels of mVEGF₁₆₄ caused widespread angioma-like structures, whereas equivalent or even higher levels of hVEGF₁₆₅ induced exclusively normal and mature capillaries. Expression levels were confirmed both in vitro and in vivo by enzyme-linked immunosorbent assay (ELISA) and quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR). However, in vitro experiments showed that hVEGF₁₆₅ was significantly more effective in activating VEGF receptor signaling in human endothelial cells than mVEGF₁₆₄, while the opposite was true in murine endothelial cells. In conclusion, we found that, even though hVEGF is similarly efficient to the syngenic mVEGF in inducing angiogenesis at lower doses in a widely adopted and convenient mouse preclinical model, species-dependent differences in the relative activation of the respective receptors may specifically mask the toxic effects of high doses of the human factor.

Mujagic and colleagues evaluate dose-dependent effects of cell-based overexpression of human or mouse vascular endothelial growth factor (hVEGF, mVEGF) in human and mouse endothelial cell cultures as well as in the skeletal muscle of immunocompromised mice. At low levels, both factors similarly induced normal angiogenesis in vivo, whereas at high levels, mVEGF resulted in widespread angiomalike structures. In vitro, hVEGF was significantly more effective in activating VEGF receptor signaling in human cells than mVEGF, with the opposite effect observed in murine cultures.