This proposal seeks to continue funding of HL-63329 to determine the mechanisms by which surfactant protein D (SPD) regulates surfactant phospholipid homeostasis. SP-D is a 43 kd member of the collectin family of polypeptides that is expressed in bronchiolar and alveolar epithelial cells of the vertebrate lung. While SP-D plays an important rote in the mediation of innate host defenses against viral, bacterial and fungal pathogens, our findings in SP-D gene targeted mice demonstrated that SP-D played a critical role in the generation of 1) normal surfactant pool sizes, 2) the structure of tubular myelin and other alveolar lipids, 3) macrophage activation, oxidant and metalloproteinase production, and 4) maintenance of normal alveolar structure during development. Our preliminary data strongly support a model in which SP-D regulates surfactant metabolism, catabolism, and/or recycling by type II epithelial cells in the lung. The present aims are therefore designed to discern the mechanisms by which SP-D regulates surfactant homeostasis.
The specific aims are designed to test two alternative hypothesis: 1) that SP-D contributes to the generation of unique surfactant forms whose uptake catabolism and routing degradation are perturbed leading to the accumulation of surfactant phospholipids in the airspaces and in type II ceils, and 2) the alternative and/or overlapping hypothesis that SP-D interacts directly with type II epithelial cells to alter surfactant homeostasis.
In Specific Aim 1 we will determine the effects of SP-D on surfactant structure in experiments in which SP-D is restored in vivo and in vitro. Effects of the presence or absence of SP-D on ultrastructure, large aggregate/small aggregate ratios and uptake or catabolism of surfactant particles and surfactant-coated beads by type II cells will be assessed. SP-D(-/-) mice in which SP-D is conditionally expressed in the lung will be utilized.
In Aim 2, the structure and function of chimeric mutant SP-D molecules will be assessed. SP-D and mutant SP-D molecules will be produced in vitro and in vivo. SP-D/SP-A mutant proteins will be reconstituted with surfactant phospholipids to discern the precise structural domains mediating the effects of SP-D on surfactant structure and its metabolism/catabolism in vitro. Function of site-specific SP-D mutant proteins will be tested in SP-D (-/-) mice in which the mutant SP-D proteins are expressed. Finally, in Specific Aim 3 we will utilize microarray analyses of lung and isolated type II cells from SP-D (-/-) mice to define the genomic responses to altered lipid pool sizes in the presence and absence of SP-D. SP-D plays a critical role in surfactant homeostasis and in defense of the lung. Elucidation of the critical roles of SP-D on surfactant homeostasis and host defense will enhance our understanding of the pathogenesis of a number of acute and chronic lung disorders including cystic fibrosis, acute bacterial infection and ARDS. The intended studies will provide fundamental insights into the role of SP-D in the protection of the lung, as well as into the basic mechanisms determining surfactant homeostasis.
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| McCurnin, Donald; Seidner, Steven; Chang, Ling-Yi et al. (2008) Ibuprofen-induced patent ductus arteriosus closure: physiologic, histologic, and biochemical effects on the premature lung. Pediatrics 121:945-56 |
| Senft, Albert P; Korfhagen, Thomas R; Whitsett, Jeffrey A et al. (2007) Surfactant protein D regulates the cell surface expression of alveolar macrophage beta(2)-integrins. Am J Physiol Lung Cell Mol Physiol 292:L469-75 |
| Ikegami, Machiko; Scoville, Elizabeth A; Grant, Shawn et al. (2007) Surfactant protein-D and surfactant inhibit endotoxin-induced pulmonary inflammation. Chest 132:1447-54 |
| Maeda, Yutaka; Hunter, Thomas C; Loudy, David E et al. (2006) PARP-2 interacts with TTF-1 and regulates expression of surfactant protein-B. J Biol Chem 281:9600-6 |
| Martis, Prithy C; Whitsett, Jeffrey A; Xu, Yan et al. (2006) C/EBPalpha is required for lung maturation at birth. Development 133:1155-64 |
| Ikegami, Machiko; Carter, Karen; Bishop, Kimberly et al. (2006) Intratracheal recombinant surfactant protein d prevents endotoxin shock in the newborn preterm lamb. Am J Respir Crit Care Med 173:1342-7 |
| Ikegami, Machiko (2006) Surfactant catabolism. Respirology 11 Suppl:S24-7 |
| Zhang, Liqian; Ikegami, Machiko; Korfhagen, Thomas R et al. (2006) Neither SP-A nor NH2-terminal domains of SP-A can substitute for SP-D in regulation of alveolar homeostasis. Am J Physiol Lung Cell Mol Physiol 291:L181-90 |
| Kingma, Paul S; Zhang, Liqian; Ikegami, Machiko et al. (2006) Correction of pulmonary abnormalities in Sftpd-/- mice requires the collagenous domain of surfactant protein D. J Biol Chem 281:24496-505 |
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