Intersubunit disulfide bridge is not required for the protective role of SP-B against lung inflammation.
Surfactant protein B (SP-B) is known to promote surfactant phospholipid film formation and reduce surface tension. Native SP-B is a homodimer in which subunit association is stabilized via covalent linkage through cysteine 48. We hypothesized that loss of the intersubunit bridge would alter SP-B function and lead to increased inflammation in response to challenge by hyperoxia or endotoxin. Transgenic mice in which SP-B cysteine 48 was mutated to serine were generated and crossed into the SP-B(-/-) background. Wild-type mice and transgenic mice carrying a single copy (SP-Bmon(+)) or two copies (SP-Bmon(++)) of the transgene were exposed to 95% O2 for 3 days or intratracheally injected with 10 microg of endotoxin. Interleukin-1beta, major intrinsic protein 2, and interleukin-6 in lung homogenates after 3 days of hyperoxia were significantly higher (P < 0.001) in SP-Bmon(+) mice than SP-Bmon(++) or wild-type mice. At 16 h after endotoxin injection, cytokines in lung tissues were higher in SP-Bmon(+) mice compared with wild-type mice (P < 0.05). Consistent with prolonged recovery in SP-Bmon(+) mice, the percentage of apoptotic cells in alveolar lavage was significantly lower in SP-Bmon(+) mice than in SP-Bmon(++) and wild-type mice. Overall, increased inflammation in SP-Bmon(+) mice was corrected to a large extent by increased gene dosage, indicating that formation of the intersubunit disulfide bridge is not critical for SP-B function.
Ikegami
Machiko
M
Division of Pulmonary Biology, Cincinnati Children's Hospital, Cincinnati, Ohio 45229-3039, USA. machiko.ikegami@chmcc.org
Takabatake
Noriaki
N
Weaver
Timothy E
TE
D000818:Animals; D017209:Apoptosis / Q000276:immunology; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry / Q000166:cytology / Q000276:immunology; D016207:Cytokines / Q000032:analysis; D004220:Disulfides / Q000737:chemistry*; D004731:Endotoxins / Q000494:pharmacology; D018496:Hyperoxia / Q000276:immunology; D051379:Mice; D008822:Mice, Transgenic; D016296:Mutagenesis / Q000502:physiology; D011014:Pneumonia / Q000276:immunology*; D011312:Pressure; D017434:Protein Structure, Tertiary; D011650:Pulmonary Alveoli / Q000166:cytology / Q000276:immunology; D037701:Pulmonary Surfactant-Associated Protein B / Q000737:chemistry / Q000235:genetics* / Q000276:immunology*; D013329:Structure-Activity Relationship
D016207:Cytokines; D004220:Disulfides; D004731:Endotoxins; D037701:Pulmonary Surfactant-Associated Protein B