Regulation of Angiogenesis by CD36/TSP‐1 Signaling In Rat Mesentery Provides Evidence for the Functional Significance of a CD36‐ Capillary Sprout‐Specific Endothelial Phenotype

Abstract

We have recently identified a capillary sprout specific endothelial phenotype that is identified by the marked downregulation of CD36 and prevalent when neovascularization is stimulated by mechanical irritation of rat mesenteric connective tissue. Because CD36 is a receptor for thrombospondin-1 (TSP-1), an anti-angiogenic factor, the expression of this CD36-phenotype may have functional significance. To test this hypothesis, either exogenous TSP-1 (5 ug/ml), neutralizing monoclonal antibodies (mAbs) to TSP-1 (20 g/ml) or to CD36 (20 ug/ml), were directly applied to rat mesentery during surgical exteriorization of the tissue. Three days after surgery, mesenteries were whole mounted and fluorescently immunolabeled for CD31. Angiogenesis was quantified by measuring the percent area of mesenteric tissue that was vascularized and the length of CD31+ microvessel per unit tissue area (vessel length density). TSP-1 treatment resulted in a 35% decrease in vascularized area and a 30% decrease in vessel length density when compared to saline controls. Conversely, blocking endogenous TSP-1/CD36 signaling with mAbs resulted in a 25% increase in vascularized area over non-specific IgG isotype controls. We conclude that TSP-1/CD36 signaling has a significant role in regulating the extent of neovascularization in this model of angiogenesis. These results are consistent with the hypothesis that the downregulation of CD36 by capillary sprout endothelial cells limits the anti-angiogenic activity of endogenous TSP-1 in vivo. Supported by NIH HL66307.