Altered stability of pulmonary surfactant in SP-C-deficient mice

The surfactant protein C (SP-C) gene encodes an extremely hydrophobic, 4-kD a peptide produced by alveolar epithelial cells in the lung. To discern the role of SP-C in lung function, SP-C-deficient (-/-) mice were produced. Th e SP-C (-/-) mice were viable at birth and grew normally to adulthood witho ut apparent pulmonary abnormalities, SP-C mRNA was not detected in the lung s of SP-C(-/-) mice, nor was mature SP-C protein detected by Western blot o f alveolar lavage from SP-C (-/-) mice. The levels of the other surfactant proteins (A, B, D) in alveolar ravage were comparable to those in wild-type mice. Surfactant pool sizes, surfactant synthesis, and lung morphology wer e similar in SP-C (-/-) and SP-C (+/+) mice. Lamellar bodies were present i n SP-C (-/-) type II cells, and tubular myelin was present in the alveolar lumen. Lung mechanics studies demonstrated abnormalities in lung hysteresiv ity (a term used to reflect the mechanical coupling between energy dissipat ive forces and tissue-elastic properties) at low, positive-end, expiratory pressures. The stability of captive bubbles with surfactant from the SP-C ( -/-) mice was decreased significantly, indicating that SP-C plays a role in the stabilization of surfactant at low lung volumes, a condition that may accompany respiratory distress syndrome in infants and adults.