The collagen-like region of surfactant protein A (SP-A) is required for correction of surfactant structural and functional defects in the SP-A null mouse.
Pulmonary surfactant isolated from gene-targeted surfactant protein A null mice (SP-A(-/-)) is deficient in the surfactant aggregate tubular myelin and has surface tension-lowering activity that is easily inhibited by serum proteins in vitro. To further elucidate the role of SP-A and its collagen-like region in surfactant function, we used the human SP-C promoter to drive expression of rat SP-A (rSPA) or SP-A containing a deletion of the collagen-like domain (DeltaG8-P80) in the Clara cells and alveolar type II cells of SP-A(-/-) mice. The level of the SP-A in the alveolar wash of the SP-A(-/-,rSP-A) and SP-A(-/-,DeltaG8-P80) mice was 6.1-and 1.3-fold higher, respectively, than in the wild type controls. Tissue levels of saturated phosphatidylcholine were slightly reduced in the SP-A(-/-,rSP-A) mice compared with SP-A(-/-) littermates. Tubular myelin was present in the large surfactant aggregates isolated from the SP-A(-/-,rSP-A) lines but not in the SP-A(-/-,DeltaG8-P80) mice or SP-A(-/-) controls. The equilibrium and minimum surface tensions of surfactant from the SP-A(-/-,rSP-A) mice were similar to SP-A(-/-) controls, but both were markedly elevated in the SP-A(-/-,DeltaG8-P80) mice. There was no defect in the surface tension-lowering activity of surfactant from SP-A(+/+,DeltaG8-P80) mice, indicating that the inhibitory effect of DeltaG8-P80 on surface activity can be overcome by wild type levels of mouse SP-A. The surface activity of surfactant isolated from the SP-A(-/-,rSP-A) but not the SP-A(-/-,DeltaG8-P80) mice was more resistant than SP-A(-/-) littermate control animals to inhibition by serum proteins in vitro. Pressure volume relationships of lungs from the SP-A(-/-), SP-A(-/-,rSP-A), and SP-A(-/-,DeltaG8-P80) lines were very similar. These data indicate that expression of SP-A in the pulmonary epithelium of SP-A(-/-) animals restores tubular myelin formation and resistance of isolated surfactant to protein inhibition by a mechanism that is dependent on the collagen-like region.
Ikegami
M
M
Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Cincinnati School of Medicine, Cincinnati, Ohio 45229-3039, USA.
Elhalwagi
B M
BM
Palaniyar
N
N
Dienger
K
K
Korfhagen
T
T
Whitsett
J A
JA
McCormack
F X
FX
D000818:Animals; D015139:Blotting, Southern; D003094:Collagen / Q000737:chemistry*; D017353:Gene Deletion; D006801:Humans; D015151:Immunoblotting; D008168:Lung / Q000166:cytology* / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008854:Microscopy, Electron; D009186:Myelin Sheath / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D011510:Proteolipids / Q000737:chemistry* / Q000235:genetics* / Q000502:physiology; D011650:Pulmonary Alveoli / Q000378:metabolism; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000737:chemistry* / Q000235:genetics* / Q000502:physiology; D051381:Rats; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry* / Q000378:metabolism; D013997:Time Factors; D019076:Transgenes
D010713:Phosphatidylcholines; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D013501:Surface-Active Agents; D003094:Collagen