Extracellular Fibrillar Structure of Latent TGFβ Binding Protein-1: Role in TGFβ-dependent Endothelial-Mesenchymal Transformation during Endocardial Cushion Tissue Formation in Mouse Embryonic Heart

• DOI: 10.1083/jcb.136.1.193
• Publication Date: 2002-07-26T16:47:50Z
• Authors: Yuji Nakajima; Kohei Miyazono; Mitsuyasu Kato; Masao Takase; Toshiyuki Yamagishi; Hiroaki Nakamura
• Keywords: 0301 basic medicine; Mice, Inbred ICR; Myocardium; Intracellular Signaling Peptides and Proteins; Heart; Transfection; Coculture Techniques; Extracellular Matrix; Mesoderm; Mice; 03 medical and health sciences; Latent TGF-beta Binding Proteins; Antibody Specificity; Transforming Growth Factor beta; Culture Techniques; COS Cells; Animals; Humans; Endothelium, Vascular; Fibrinolysin; Carrier Proteins; Endocardium

Transforming growth factor-β (TGFβ) is a dimeric peptide growth factor which regulates cellular differentiation and proliferation during development. Most cells secrete TGFβ as a large latent TGFβ complex containing mature TGFβ, latency associated peptide, and latent TGFβ-binding protein (LTBP)-1. The biological role of LTBP-1 in development remains unclear. Using a polyclonal antiserum specific for LTBP-1 (Ab39) and three-dimensional collagen gel culture assay of embryonic heart, we examined the tissue distribution of LTBP-1 and its functional role during the formation of endocardial cushion tissue in the mouse embryonic heart. Mature TGFβ protein was required at the onset of the endothelial-mesenchymal transformation to initiate endocardial cushion tissue formation. Double antibody staining showed that LTBP-1 colocalized with TGFβ1 as an extracellular fibrillar structure surrounding the endocardial cushion mesenchymal cells. Immunogold electronmicroscopy showed that LTBP-1 localized to 40–100 nm extracellular fibrillar structure and 5–10-nm microfibrils. The anti–LTBP-1 antiserum (Ab39) inhibited the endothelial-mesenchymal transformation in atrio-ventricular endocardial cells cocultured with associated myocardium on a three-dimensional collagen gel lattice. This inhibitory effect was reversed by administration of mature TGFβ proteins in culture. These results suggest that LTBP-1 exists as an extracellular fibrillar structure and plays a role in the storage of TGFβ as a large latent TGFβ complex.