Abstract
Members of the transforming growth factor beta (TGF-beta) family of polypeptides have been implicated in morphogenesis and differentiation in numerous tissues, including the lung. In order to further define effects of TGF-beta signaling in lung morphogenesis, a constitutively active form of TGF-beta1 was expressed in respiratory epithelial cells of the fetal mouse lung in vivo. Expression of TGF-beta1 arrested lung morphogenesis in the pseudoglandular stage of development, inhibiting synthesis of differentiation-dependent proteins, SP-B, SP-C, and CCSP, and maintaining embryonic patterns of staining for thyroid transcription factor-1 (TTF-1) and hepatocyte nuclear factor-3beta (HNF-3beta). The pulmonary mesenchyme was thickened and vascular density was increased by TGF-beta1. TGF-beta1 decreased expression of vascular endothelial growth factor-A (VEGF-A) mRNA and protein, and the abundance of Flk-1 mRNA in the lung mesenchyme. Distribution of platelet-endothelial cell adhesion molecule (PECAM)-1, a marker of pulmonary blood vessels, was altered, and ultrastructural studies demonstrated that TGF-beta1 inhibited vascular development in the fetal lung. TGF-beta1 perturbed both epithelial cell differentiation and formation of the pulmonary vasculature, supporting the concept that precise control of signaling via the TGF-beta receptor pathway is critical for normal lung morphogenesis.
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