Shawn Grant

Cincinnati Children's Hospital Medical Center, Cincinnati, OH, United States

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Publications (4)17.01 Total impact

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    ABSTRACT: A number of transcriptional pathways regulating fetal lung development are active during repair of the injured lung. We hypothesized that C/EBPalpha, a transcription factor critical for lung maturation, plays a role in protection of the alveolar epithelium following hyperoxic injury of the mature lung. Transgenic Cebpalpha(Delta/Delta) mice, in which Cebpalpha was conditionally deleted from Clara cells and type II cells after birth, were developed. While no pulmonary abnormalities were observed in the Cebpalpha(Delta/Delta) mice (7-8 wk old) under normal conditions, the mice were highly susceptible to hyperoxia. Cebpalpha(Delta/Delta) mice died within 4 days of exposure to 95% oxygen in association with severe lung inflammation, altered maturation of surfactant protein B and C, decreased surfactant lipid secretion, and abnormal lung mechanics at a time when all control mice survived. mRNA microarray analysis of isolated type II cells at 0, 2, and 24 h of hyperoxia demonstrated the reduced expression of number of genes regulating surfactant lipid and protein homeostasis, including Srebf, Scap, Lpcat1, Abca3, Sftpb, and Napsa. Genes influencing cell signaling or immune responses were induced in the lungs of Cebpalpha(Delta/Delta) mice. C/EBPalpha was required for the regulation of genes associated with surfactant lipid homeostasis, surfactant protein biosynthesis, processing and transport, defense response to stress, and cell redox homeostasis during exposure to hyperoxia. While C/EBPalpha did not play a critical role in postnatal pulmonary function under normal conditions, C/EBPalpha mediated protection of the lung during acute lung injury induced by hyperoxia.
    AJP Lung Cellular and Molecular Physiology 06/2009; 297(2):L286-98. · 3.52 Impact Factor
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    ABSTRACT: Surfactant protein (SP)-D plays an important role in host defense and pulmonary surfactant homeostasis. In SP-D-deficient (Sftpd(-/-)) mice, the abnormal large surfactant forms seen at the ultrastructural level are taken up inefficiently by type II cells, resulting in an over threefold increase in the surfactant pool size. The mechanisms by which SP-D influences surfactant ultrastructure are unknown. We hypothesized that SP-D binds to surfactant immediately after being secreted and influences surfactant ultrastructure conversion. In newborn and adult sheep lungs, immunogold-labeled SP-D was associated with both lamellated membranous lipid structures of newly secreted surfactant and with small aggregate surfactant but not with tubular myelin. Since SP-D preferentially binds to phosphatidylinositol (PI) in vitro, the postnatal changes in PI were assessed. PI content in the bronchoalveolar lavage fluid increased after birth and peaked at 2-5 days of age, a time of rapid conversion of surfactant forms that is associated with the peak of surfactant lipid pool size. SP-D selectively interacted with PI-rich liposomes in vitro, causing their lysis. Similarly, the abnormal surfactant ultrastructure in Sftpd(-/-) mice was corrected by the addition of SP-D or melittin, and both peptides caused lysis of lipid vesicles. The normal conversion of surfactant ultrastructure requires SP-D that preferentially interacts with PI-rich, newly secreted surfactant, causing lysis of surfactant lipid membranes, converting the lipid forms into smaller surfactant lamellated structures that are critical for surfactant uptake by type II cells and normal surfactant homeostasis. SP-D regulates the dramatic decreases in the surfactant pool size that occurs in the newborn period.
    Journal of Applied Physiology 04/2009; 106(5):1545-52. · 3.48 Impact Factor
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    ABSTRACT: Alveolar capillaries are located in close proximity to the alveolar epithelium and beneath the surfactant film. We hypothesized that the shape of alveolar capillaries and accompanying oxygenation are influenced by surfactant surface tension in the alveolus. To prove our hypothesis, surfactant surface tension was regulated by conditional expression of surfactant protein (SP)-B in Sftpb(-/-) mice, thereby inhibiting surface tension-lowering properties of surfactant in vivo within 24 hours after depletion of Sftpb. Minimum surface tension of isolated surfactant was increased and oxygen saturation was significantly reduced after 2 days of SP-B deficiency in association with deformation of alveolar capillaries. Intravascularly injected 3.2-mum-diameter microbeads through jugular vein were retained within narrowed pulmonary capillaries after reduction of SP-B. Ultrastructure studies demonstrated that the capillary protrusion typical of the normal alveolar-capillary unit was reduced in size, consistent with altered pulmonary blood flow. Pulmonary hypertension and intrapulmonary shunting are commonly associated with surfactant deficiency and dysfunction in neonates and adults with respiratory distress syndromes. Increased surfactant surface tension caused by reduction in SP-B induced narrowing of alveolar capillaries and oxygen desaturation, demonstrating an important role of surface tension-lowering properties of surfactant in the regulation of pulmonary vascular perfusion.
    American Journal of Respiratory Cell and Molecular Biology 03/2009; 41(4):433-9. · 4.15 Impact Factor
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    ABSTRACT: Acute lung injury is a common cause of morbidity and mortality following pulmonary or systemic infections. Surfactant protein-D is a member of the collectin family of proteins, which play important roles in innate host defense of the lung. In this study, the effect of exogenous recombinant human SP-D (rhSP-D) on protection of the adult mouse lung from lipopolysaccharide (LPS)-induced and lipoteichoic acid (LTA)-induced injury was assessed. The effect of rhSP-D on LPS-induced and LTA-induced lung inflammation and injury was assessed with and without exogenous pulmonary surfactant in Sftpd+/+ and Sftpd-/- mice. A total of 204 mice (6 mice per group) were used for the present study. Sftpd-/- mice were more susceptible to intratracheal LPS than were Sftpd+/+ mice. rhSP-D decreased neutrophilic infiltrates induced by LPS and LTA in the lungs of both Sftpd+/+ and Sftpd-/- mice. The addition of exogenous pulmonary surfactant to rhSP-D further decreased LPS-induced and LTA-induced pulmonary inflammation in Sftpd-/- and Sftpd+/+ mice. Intratracheal rhSP-D inhibited inflammation induced by intratracheal LPS and LTA instillation in the lung. The antiinflammatory effects of rhSP-D were enhanced by the addition of pulmonary surfactant, providing a potential therapy for the treatment of lung inflammation.
    Chest 12/2007; 132(5):1447-54. · 5.85 Impact Factor