Abstract
Surfactant protein D (SP-D) is a member of the collectin family of innate defense proteins. Members of this family share four distinct structural domains: an N-terminal cross-linking domain, a collagenous domain, a neck region, and a carbohydrate recognition domain. In this study, the function of the collagenous domain was evaluated by expressing a SP-D collagen deletion mutant protein (rSftpdCDM) in wild type and SP-D null mice (Sftpd(-/-)). rSftpdCDM formed disulfide-linked trimers that further oligomerized into higher order structures. The mutant protein effectively bound carbohydrate and aggregated bacteria in vitro. Whereas rSftpdCDM did not disrupt pulmonary morphology or surfactant phospholipid levels in wild type mice, the mutant protein failed to rescue the emphysema or enlarged foamy macrophages that are characteristic of Sftpd(-/-) mice. Moreover, rSftpdCDM partitioned with small aggregate surfactant in a manner similar to SP-D, but rSftpdCDM did not correct the abnormal surfactant ultrastructure or phospholipid levels observed in Sftpd(-/-) mice. In contrast, rSftpdCDM completely corrected viral clearance and the abnormal inflammatory response that occurs following pulmonary influenza A challenge in Sftpd(-/-) mice. Our findings indicate that the collagen domain of SP-D is not required for assembly of disulfide-stabilized oligomers or the innate immune response to viral pathogens. The collagen domain of SP-D is required for the regulation of pulmonary macrophage activation, airspace remodeling, and surfactant lipid homeostasis.
Highlights
Surfactant protein D (SP-D)2 is a member of the collectin family of C-type lectins
Whereas expression of the fulllength rat Sftpd gene fully rescues the SftpdϪ/Ϫ mouse phenotype, expression of a fusion protein that included the N-terminal and collagen domains of surfactant protein A (SP-A) fused to the neck and carbohydrate recognition domain (CRD) of SP-D was not sufficient to correct the emphysema or lipid accumulations characteristic of SftpdϪ/Ϫ mice, indicating that the collagenous and N-terminal domains of SP-D are essential for these functions [22]
To further investigate the function of the SP-D structural domains, we genetically introduced into wild type and SftpdϪ/Ϫ mice lungs an SP-D collagen deletion mutant protein that formed multimers via an increase the amount of starting material for protein purification, rSftpdCDM was purified from rSftpdCDMTgϩ/SftptdϪ/Ϫ/ GmcsfϪ/Ϫ mice
Summary
Surfactant protein D (SP-D)2 is a member of the collectin family of C-type lectins. Members of this family include surfactant protein A (SP-A), SP-D, mannose-binding protein, conglu-. Used to assess MMP-9 and MMP-2 activity in media containing Correction of Influenza A Infection by rSftpdCDM—Previous alveolar macrophages from wild type, SftpdϪ/Ϫ, and in vitro studies demonstrated that SP-D binds IAV and rSftpdCDMTgϩ/SftpdϪ/Ϫ mice (Fig. 6).
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