Abrogation of betaglycan attenuates TGF- β-mediated inhibition of embryonic murine lung branching morphogenesis in culture

Abstract

Although betaglycan (TGF- β type III receptor) is known to enhance TGF- β ligand binding to its type II receptor in murine lung epithelial cell lines, the biological significance of this phenomenon in the process of lung organogenesis is not understood. Betaglycan gene expression was detected in embryonic murine lungs undergoing branching morphogenesis in ex vivo culture. Antisense betaglycan oligodeoxynucleotides (ODN) resulted in up to 56% stimulation of lung branching morphogenesis in culture, while betaglycan mRNA and protein expression levels were suppressed by 90 and 82%, respectively. Following abrogation of betaglycan expression with antisense oligodeoxynucleotide, embryonic lungs were relatively insensitive to TGF- β: TGF- β2 (0.5 ng/ml) and TGF- β1 (20 ng/ml), respectively, down-regulated lung morphogenesis by 38 and 34% in control cultures, whereas TGF- β-induced inhibition was attenuated to 13 and 26% respectively, in the presence of betaglycan antisense oligodeoxynucleotides. TGF- β neutralizing antibodies also prevented TGF- β-mediated inhibition of lung branching in culture, supporting the speculation that autocrine/paracrine TGF- β signaling is minimal in the absence of betaglycan. Betaglycan was immunolocalized mainly to the epithelial cells in developing airways, a spatial distribution which overlaps with that of TGF- β type II receptor. Furthermore, abrogation of endogenous betaglycan gene expression prevented the characteristic down-regulation of cyclin A and surfactant protein C (SP-C) mRNAs by exogenous TGF- β ligands. These results show that betaglycan expression is essential for optimal TGF- β signaling during embryonic lung development. We therefore conclude that the abrogation of endogenous betaglycan attenuates endogenous autocrine and/or paracrine TGF- β-mediated negative regulation of lung organogenesis.