Activity of pulmonary surfactant protein-D (SP-D) in vivo is dependent on oligomeric structure.
Pulmonary surfactant protein-D (SP-D) is a member of the collectin family of C-type lectins that is synthesized in many tissues including respiratory epithelial cells in the lung. SP-D is assembled predominantly as dodecamers consisting of four homotrimeric subunits each. Association of these subunits is stabilized by interchain disulfide bonds involving two conserved amino-terminal cysteine residues (Cys-15 and Cys-20). Mutant recombinant rat SP-D lacking these residues (RrSP-Dser15/20) is secreted in cell culture as trimeric subunits rather than as dodecamers. In this study, transgenic mice that express this mutant were generated to elucidate the functional importance of SP-D oligomerization in vivo. Expression of RrSP-Dser15/20 failed to correct the pulmonary phospholipid accumulation and emphysema characteristic of SP-D null (mSP-D-/-) mice. Expression of high concentrations of the mutant protein in wild-type mice reduced the abundance of disulfide cross-linked oligomers of endogenous SP-D in the bronchoalveolar lavage fluid and demonstrated a phenotype that partially overlapped with that of the SP-D-/- mice; the animals developed emphysema and foamy macrophages without the associated abnormalities in alveolar phospholipids typical of SP-D-/- mice. Development of foamy macrophages in SP-D-deficient mice is not secondary to the increased abundance of surfactant phospholipids. Disulfide cross-linked SP-D oligomers are required for the regulation of surfactant phospholipid homeostasis and the prevention of emphysema and foamy macrophages in vivo.
Division of Pulmonary Biology, Children's Hospital Medical Center, Cincinnati, Ohio 45229-3039, USA.
L
L
Zhang
M
M
Ikegami
E C
EC
Crouch
T R
TR
Korfhagen
J A
JA
Whitsett
D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D001992:Bronchoalveolar Lavage Fluid; D003545:Cysteine / Q000737:chemistry; D018076:DNA, Complementary / Q000378:metabolism; D019281:Dimerization; D004220:Disulfides; D004305:Dose-Response Relationship, Drug; D004646:Emphysema / Q000235:genetics; D005838:Genotype; D006023:Glycoproteins / Q000378:metabolism* / Q000502:physiology*; D015151:Immunoblotting; D037102:Lectins; D008168:Lung / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D010713:Phosphatidylcholines / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D037663:Pulmonary Surfactant-Associated Protein D; D011663:Pulmonary Surfactants / Q000378:metabolism* / Q000502:physiology*; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012685:Sepharose / Q000378:metabolism
D018076:DNA, Complementary; D004220:Disulfides; D006023:Glycoproteins; D037102:Lectins; D010713:Phosphatidylcholines; D037663:Pulmonary Surfactant-Associated Protein D; D011663:Pulmonary Surfactants; D011994:Recombinant Proteins; D012685:Sepharose; D003545:Cysteine