Localization of specific binding sites for125I-TGF-β1 to fenestrated endothelium in bone and anastomosing capillary networks in enamel organ suggests a role for TGF-β1 in angiogenesis
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Previous studies have shown endothelial cells to be a major target for endocrine TGF-β in several soft tissues in the normal growing rat . The potent effect of TGF-β1 on bone formation prompted us to analyze in detail the localization of specific binding sites for endocrine TGF-β in hard tissues. At 2.5 minutes after injection of125I-TGF-β1, specific binding, as demonstrated by quantitative radioautography, was localized to fenestrated endothelium participating in angiogenesis in the vascular invasion region of the growth plate in bone as well as to anatomizing capillary networks in the maturation zone of the enamel organ. At 15 minutes after injection, the bound ligand was internalized into endocytic vesicles of endothelial cells. In bone, quantitation revealed significant differences in receptor density between endothelia undergoing proliferation vs those in a state of elongation and anastomosis with neighboring endothelial cells. In the rat incisor, specific binding of125I-TGF-β1 to endothelium correlated with increased formation of anastomotic capillary networks. These studies identify differential specific binding sites of125I-TGF-β1 in angiogenically active endothelium, providing an important link between TGF-β1, the endothelium, and hard tissue development.
Key wordsEndothelial cells TGF-β Hard tissue Angiogenesis
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