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.
Zhang
L
L
Division of Pulmonary Biology, Children's Hospital Medical Center, Cincinnati, Ohio 45229-3039, USA.
Ikegami
M
M
Crouch
E C
EC
Korfhagen
T R
TR
Whitsett
J A
JA
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