J. C. Clark

Role of Sonic hedgehog in Patterning of Tracheal- Bronchial Cartilage and the Peripheral Lung

Sonic hedgehog (Shh) was conditionally deleted in respiratory epithelial cells of the embryonic lung in vivo. Deletion of Shh before embryonic day (E) 13.5 resulted in respiratory failure at birth. While lobulation was not perturbed, the lungs were hypoplastic, with reduced branching of peripheral lung tubules, evident from E13.5. Smooth muscle and endothelial cells were absent or reduced, the latter in relationship to the loss of peripheral lung parenchyma. Tracheal–bronchial ring abnormalities occurred when Shh was deleted between E8.5 and E12.5. Deletion of Shh later in gestation (after E13.5) caused mild abrogation of peripheral branching morphogenesis but did not disrupt tracheal‐bronchial development. Defects in branching morphogenesis and vascularization seen in Shh null mutant (Shh‐/‐) mice were substantially corrected when SHH was ectopically expressed in the respiratory epithelium; however, peripheral expression of SHH failed to correct cartilage abnormalities in the trachea and bronchi, indicating a spatial requirement for SHH expression near sites of cartilage formation. Expression of SHH by the respiratory epithelium plays an important role in the patterning of tracheal–bronchial mesenchyme required for formation of cartilage rings in conducting airways. SHH regulates branching morphogenesis and influences differentiation of the peripheral lung mesenchyme required for formation of bronchial and vascular smooth muscle. Developmental Dynamics 231:57–71, 2004.

Pulmonary dysfunction in neonatal SP-B-deficient mice

Pulmonary function was assessed in newborn wild-type and homozygous and heterozygous surfactant protein B (SP-B)-deficient mice after birth. SP-B +/+ and SP-B+/- mice became well oxygenated and survived postnatally. Although lung compliance was decreased slightly in the SP-B+/- mice, lung volumes and compliances were decreased markedly in homozygous SP-B-/- mice. They died rapidly after birth, failing to inflate their lungs or oxygenate. SP-B proprotein was absent in the SP-B-/- mice and was reduced in the SP-B+/- mice, as assessed by Western analysis. Surfactant protein A, surfactant proprotein C, surfactant protein D, and surfactant phospholipid content in lungs from SP-B+/- and SP-B-/- mice were not altered. Lung saturated phosphatidylcholine and precursor incorporation into saturated phosphatidylcholine were not influenced by SP-B genotype. Intratracheal administration of perfluorocarbon resulted in lung expansion, oxygenation, and prolonged survival of SP-B-/- mice and in reduced lung compliance in SP-B+/+ and SP-B+/- mice. Lack of SP-B caused respiratory failure at birth, and decreased SP-B protein was associated with reduced lung compliance. These findings demonstrate the critical role of SP-B in perinatal adaptation to air breathing.Pulmonary function was assessed in newborn wild-type and homozygous and heterozygous surfactant protein B (SP-B)-deficient mice after birth. SP-B+/+ and SP-B+/- mice became well oxygenated and survived postnatally. Although lung compliance was decreased slightly in the SP-B+/- mice, lung volumes and compliances were decreased markedly in homozygous SP-B-/- mice. They died rapidly after birth, failing to inflate their lungs or oxygenate. SP-B proprotein was absent in the SP-B-/- mice and was reduced in the SP-B+/- mice, as assessed by Western analysis. Surfactant protein A, surfactant proprotein C, surfactant protein D, and surfactant phospholipid content in lungs from SP-B+/- and SP-B-/- mice were not altered. Lung saturated phosphatidylcholine and precursor incorporation into saturated phosphatidylcholine were not influenced by SP-B genotype. Intratracheal administration of perfluorocarbon resulted in lung expansion, oxygenation, and prolonged survival of SP-B-/- mice and in reduced lung compliance in SP-B+/+ and SP-B+/- mice. Lack of SP-B caused respiratory failure at birth, and decreased SP-B protein was associated with reduced lung compliance. These findings demonstrate the critical role of SP-B in perinatal adaptation to air breathing.

Transcriptional Adaptation to Cystic Fibrosis Transmembrane Conductance Regulator Deficiency

Cystic fibrosis, the most commonly inherited lethal pulmonary disorder in Caucasians, is caused by mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR). To identify genomic responses to the presence or absence of CFTR in pulmonary tissues in vivo, microarray analyses of lung mRNAs were performed on whole lung tissue from mice lacking (CFTR(−)) or expressing mouse CFTR (CFTR(+)). Whereas the histology of lungs from CFTR(−) and CFTR(+) mice was indistinguishable, statistically significant increases in the relative abundance of 29 and decreases in 25 RNAs were identified by RNA microarray analysis. Of RNAs whose expression was consistently altered by the absence of CFTR, functional classes of genes influencing gene transcription, inflammation, intracellular trafficking, signal transduction, and ion transport were identified. RNAs encoding the transcription factor CCAAT enhancer-binding protein (CEBP) δ and interleukin (IL) 1β, both known to regulate CFTR expression, were induced, perhaps indicating adaptation to the lack of CFTR. RNAs mediating lung inflammation including calgranulin-S100 family members, IL-1β and IL-4, were increased. Likewise, expression of several membrane transport proteins that interact directly with CFTR were increased, suggesting that CFTR-protein complexes initiate genomic responses. Absence of CFTR influenced the expression of genes modulating diverse pulmonary cell functions that may ameliorate or contribute to the pathogenesis of CF.