Human pulmonary acinar aplasia: reduction of transforming growth factor-beta ligands and receptors

Pulmonary hypoplasia has been found in the human neonatal autopsy population and has been attributed to an alteration in epithelial-mesenchymal interactions during development of the lung. Pulmonary acinar aplasia is a very rare and severe form of pulmonary hypoplasia. The transforming growth factor-betas (TGF-beta) are multifunctional regulatory peptides that are secreted by a variety of normal and malignant cells and are expressed in developing organs including the lung; their tissue distribution patterns have possible significance for signaling roles in many epithelial-mesenchymal interactions. Here, we report our examination of TGF-beta in the lungs of a term female infant diagnosed with pulmonary acinar aplasia whose autopsy revealed extremely hypoplastic lungs with complete absence of alveolar ducts and alveoli. Immunohistochemical and in situ hybridization analyses were used to localize and measure the proteins and mRNA, respectively, for TGF-beta1, TGF-beta2, TGF-beta3, and TGF-beta type I and type II receptors (TGF-beta RI and RII) in formalin-fixed and paraffin-embedded sections of these hypoplastic lungs and normal lungs. Immunostaining for TGF-beta1, TGF-beta2, and TGF-beta RI and RII was significantly lower in the bronchial epithelium and muscle of the hypoplastic lungs than in normal lungs, whereas no difference was detected in staining for other proteins including Clara cell 10-kD protein, adrenomedullin, hepatocyte growth factor/scatter factor, and hepatocyte growth factor receptor/Met in the hypoplastic and normal lungs or in the liver and kidneys of this infant compared with normal liver and kidney. In addition, in situ hybridization showed that TGF-beta1 and TGF-beta RI transcripts were considerably reduced in the bronchial epithelium of the hypoplastic lung compared with normal lung. These results show that there is a selective reduction of TGF-beta in pulmonary acinar aplasia and suggest that the signaling action of TGF-beta in epithelial-mesenchymal interactions in the lungs of this developmental condition may be compromised.