The role of pulmonary collectin N-terminal domains in surfactant structure, function, and homeostasis in vivo.
The N-terminal domains of the lung collectins, surfactant proteins A (SP-A) and D (SP-D), are critical for surfactant phospholipid interactions and surfactant homeostasis, respectively. To further assess the importance of lung collectin N-terminal domains in surfactant structure and function, a chimeric SP-D/SP-A (D/A) gene was constructed by substituting nucleotides encoding amino acids Asn(1)-Ala(7) of rat SP-A with the corresponding N-terminal sequences from rat SP-D, Ala(1)-Asn(25). Recombinant D/A migrated as a 35-kDa band on reducing SDS-PAGE and as a ladder of disulfide-linked multimers under nonreducing conditions. The recombinant D/A bound and aggregated phosphatidylcholine containing vesicles as effectively as rat SP-A. Mice in which endogenous pulmonary collectins were replaced with D/A were developed by human SP-C promoter-driven overexpression of the D/A gene in SP-A(-/-) and SP-D(-/-) animals. Analysis of lavage fluid from SP-A(-/-,D/A) mice revealed that glycosylated, oligomeric D/A was secreted into the air spaces at levels that were comparable with the authentic collectins and that the N-terminal interchange converted SP-A from a "bouquet" to a cruciform configuration. Transmission electron microscopy of surfactant from the SP-A(-/-,D/A) mice revealed atypical tubular myelin containing central "target-like" electron density. Surfactant isolated from SP-A(-/-,D/A) mice exhibited elevated surface tension both in the presence and absence of plasma inhibitors, but whole lung compliance of the SP-A(-/-,D/A) animals was not different from the SP-A(-/-) littermates. Lung-specific overexpression of D/A in the SPD(-/-) mouse resulted in hetero-oligomer formation with mouse SP-A and did not correct the air space dilation or phospholipidosis that occurs in the absence of SP-D. These studies indicate that the N terminus of SP-D 1) can functionally replace the N terminus of SP-A for lipid aggregation and tubular myelin formation, but not for surface tension lowering properties of SP-A, and 2) is not sufficient to reverse the structural and metabolic pulmonary defects in the SP-D(-/-) mouse.
Palaniyar
Nades
N
Division of Pulmonary/Critical Care Medicine, Department of Medicine, Children's Hospital Research Foundation, University of Cincinnati School of Medicine, Cincinnati, OH 45267-0564, USA.
Zhang
Liquian
L
Kuzmenko
Alexander
A
Ikegami
Machiko
M
Wan
Sijue
S
Wu
Huixing
H
Korfhagen
Thomas R
TR
Whitsett
Jeffrey A
JA
McCormack
Francis X
FX
D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry* / Q000502:physiology*; D002460:Cell Line; D002850:Chromatography, Gel; D037222:Collectins; D018076:DNA, Complementary / Q000378:metabolism; D004220:Disulfides / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006023:Glycoproteins / Q000737:chemistry*; D006801:Humans; D015151:Immunoblotting; D007313:Insecta; D050356:Lipid Metabolism; D008168:Lung / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D008854:Microscopy, Electron; D008957:Models, Genetic; D009186:Myelin Sheath / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011510:Proteolipids / Q000737:chemistry*; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000737:chemistry*; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D013501:Surface-Active Agents / Q000737:chemistry*; D013997:Time Factors
D002352:Carrier Proteins; D037222:Collectins; D018076:DNA, Complementary; D004220:Disulfides; D006023:Glycoproteins; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D011994:Recombinant Proteins; D013501:Surface-Active Agents