The timing of lung maturation is controlled precisely by complex genetic and cellular programs. Lung immaturity following preterm birth frequently results in Respiratory Distress Syndrome (RDS) and Broncho-Pulmonary Dysplasia (BPD), which are leading causes of mortality and morbidity in preterm infants. Mechanisms synchronizing gestational length and lung maturation remain to be elucidated. In this study, we designed a genome-wide mRNA expression time-course study from E15.5 to Postnatal Day 0 (PN0) using lung RNAs from C57BL/6J (B6) and A/J mice that differ in gestational length by ∼30 hr (B6
Rationale: Airway mucous cell metaplasia and chronic inflammation are pathophysiological features that influence morbidity and mortality associated with asthma and other chronic pulmonary disorders. Elucidation of the molecular mechanisms regulating mucous metaplasia and hypersecretion provides the scientific basis for diagnostic and therapeutic opportunities to improve the care of chronic pulmonary diseases.
Objectives: To determine the role of the airway epithelial–specific transcription factor NK2 homeobox 1 (NKX2-1, also known as thyroid transcription factor-1 [TTF-1]) in mucous cell metaplasia and lung inflammation.
Methods: Expression of NKX2-1 in airway epithelial cells from patients with asthma was analyzed. NKX2-1+/− gene targeted or transgenic mice expressing NKX2-1 in conducting airway epithelial cells were sensitized to the aeroallergen ovalbumin. In vitro studies were used to identify mechanisms by which NKX2-1 regulates mucous cell metaplasia and inflammation.
Measurements and Main Results: NKX2-1 was suppressed in airway epithelial cells from patients with asthma. Reduced expression of NKX2-1 in heterozygous NKX2-1+/− gene targeted mice increased mucous metaplasia in the small airways after pulmonary sensitization to ovalbumin. Conversely, mucous cell metaplasia induced by aeroallergen was inhibited by expression of NKX2-1 in the respiratory epithelium in vivo. Genome-wide mRNA analysis of lung tissue from ovalbumin-treated mice demonstrated that NKX2-1 inhibited mRNAs associated with mucous metaplasia and Th2-regulated inflammation, including Spdef, Ccl17, and Il13. In vitro, NKX2-1 inhibited SPDEF, a critical regulator of airway mucous cell metaplasia, and the Th2 chemokine CCL26.
Conclusions: The present data demonstrate a novel function for NKX2-1 in a gene network regulating mucous cell metaplasia and allergic inflammation in the respiratory epithelium.
asthma; goblet cell; respiratory epithelium; NK2 homeobox 1
Recent advances in cellular, molecular, and developmental biology have revolutionized our concepts regarding the process of organogenesis that have important implications for our understanding of both lung formation and pulmonary disease pathogenesis. Pulmonary investigators have long debated whether developmental processes are recapitulated during normal repair of the lung or in the setting of chronic pulmonary diseases. Although the cellular events involved in lung morphogenesis and those causing pulmonary disease are likely to include processes that are distinct, there is increasing evidence that the pathogenesis of many lung disorders involves the same genetic machinery that regulates cell growth, specification, and differentiation during normal lung development.
lung; morphogenesis; transcription; respiratory
The fetus is thought to play a central role in the onset of labor. Pulmonary surfactant protein (SP)-A, secreted by the maturing fetal lung, has been implicated in the mechanisms initiating parturition in mice. The present study was conducted to determine whether amniotic fluid concentrations of SP-A and SP-B change during human parturition.
Amniotic fluid SP-A and SP-B concentrations were measured with sensitive and specific ELISA in the following groups of pregnant women: 1) mid-trimester of pregnancy between 15th and 18th weeks of gestation (n=29); 2) term pregnancy not in labor (n=28); and 3) term pregnancy in spontaneous labor (n=26). Non-parametric statistics were used for analysis.
SP-A was detected in all amniotic fluid samples. SP-B was detected in 24.1% (7/29) of mid-trimester samples and in all samples at term. The median amniotic fluid concentration of SP-A and SP-B were significantly higher in women at term than in women in the mid-trimester (SP-A term no labor: median 5.6 μg/ml, range 2.2–15.2 μg/ml vs. mid-trimester: median 1.64 μg/ml, range 0.1–4.7 μg/ml; and SP-B term no labor: median 0.54 μg/ml, range 0.17–1.99 μg/ml vs. mid-trimester: median 0 μg/ml, range 0–0.35 μg/ml; both p<0.001). The median amniotic fluid SP-A concentration in women at term in labor was significantly lower than that in women at term not in labor (term in labor: median 2.7 μg/ml, range 1.2–10.1 μg/ml vs. term no labor: median 5.6 μg/ml, range 2.2–15.2 μg/ml; p<0.001). There was no significant difference in the median amniotic fluid SP-B concentrations between women in labor and those not in labor (term in labor: median 0.47 μg/ml range 0.04–1.32 μg/ml vs. term no labor: median 0.54 μg/ml range 0.17–1.99 μg/ml; p=0.2).
The amniotic fluid concentration of surfactant protein-A decreases in spontaneous human parturition at term.
Surfactant protein; SP-A; SP-B; amniotic fluid; term; labor; parturition
Members of the Krüppel-like family of transcription factors regulate diverse developmental processes in various organs. Previously, we have demonstrated the role of Klf4 in the mouse ocular surface. Herein, we determined the role of the structurally related Klf5, using Klf5-conditional null (Klf5CN) mice derived by mating Klf5-LoxP and Le-Cre mice. Klf5 mRNA was detected as early as embryonic day 12 (E12) in the cornea, conjunctiva and eyelids, wherein its expression increased during development. Though the embryonic eye morphogenesis was unaltered in the Klf5CN mice, postnatal maturation was defective, resulting in smaller eyes with swollen eyelids that failed to separate properly. Klf5CN palpebral epidermis was hyperplastic with 7-9 layers of keratinocytes, compared with 2-3 in the wild type (WT). Klf5CN eyelid hair follicles and sebaceous glands were significantly enlarged, and the meibomian glands malformed. Klf5CN lacrimal glands displayed increased vasculature and large number of infiltrating cells. Klf5CN corneas were translucent, thicker with defective epithelial basement membrane and hypercellular stroma. Klf5CN conjunctiva lacked goblet cells, demonstrating that Klf5 is required for conjunctival goblet cell development. The number of Ki67-positive mitotic cells was more than doubled, consistent with the increased number of Klf5CN ocular surface epithelial cells. Co-ablation of Klf4 and Klf5 resulted in a more severe ocular surface phenotype compared with Klf4CN or Klf5CN, demonstrating that Klf4 and Klf5 share few if any, redundant functions. Thus, Klf5CN mice provide a useful model for investigating ocular surface pathologies involving meibomian gland dysfunction, blepharitis, corneal or conjunctival defects.
Klf5; cornea; conjunctiva; meibomian glands; lacrimal glands; eyelids; goblet cells
Endometrial cancer (EMC) is the most common gynecological malignancy. The etiology and the cell types that are conducive to EMC are not completely understood, provoking further studies. Our objective was to determine whether deletion of Pten specifically in the uterine stroma and myometrium induces cancer or manifests different phenotypes.
PtenAmhr2(d/d) mice with conditional deletion of Pten in the mouse uterine stroma and myometrium, but not in the epithelium, were generated by mating floxed Pten mice and anti-Mullerian hormone type 2 receptor (Amhr2)-Cre mice. The phenotypes were compared between Ptenf/f and PtenAmhr2(d/d) uteri.
We show that conditional deletion of Pten in the mouse uterine stroma and myometrium, but not in the epithelium, fails to generate EMC even at the age of 5 months. Surprisingly Pten deletion by Amhr2-Cre transformed a large number of myometrial cells into adipocytes with lipid accumulation, possibly a result of increased levels of SREBP1 and PPARγ which regulate adipose differentiation.
These results provide evidence that deletion of Pten specifically in the stroma and myometrium does not result in EMC in female mice examined up to 5 months of age but alters the myocytes to adipocytes and mimics histologic similarities with lipoleiomyomas in humans, raising the possibility of using this mouse model to further explore the cause of the disease.
Sox2, a transcription factor critical for the maintenance of embryonic stem cells and induction of pluripotent stem cells, is expressed exclusively in the conducting airway epithelium of the lung, where it is required for differentiation of nonciliated, goblet, and ciliated cells. To determine the role of Sox2 in respiratory epithelial cells, Sox2 was selectively and conditionally expressed in nonciliated airway epithelial cells and in alveolar type II cells in the adult mouse. Sox2 induced epithelial cell proliferation within 3 days of expression. Epithelial cell proliferation was associated with increased Ki-67 and cyclin D1 staining. Expression of cell cycle genes, including FoxM1, Ccna2 (Cyclin A2), Ccnb2 (Cyclin B2), and Ccnd1 (Cyclin D1), was increased. Consistent with a role in cell proliferation, Sox2 activated the transcription of FoxM1 in vitro. In alveoli, Sox2 caused hyperplasia and ectopic differentiation of epithelial cells to those with morphologic and molecular characteristics of conducting airway epithelium. Sox2 induced the expression of conducting airway epithelial specific genes, including Scgb1a1, Foxj1, Tubb3, and Cyp2f2. Although prolonged expression of Sox2 caused cell proliferation and epithelial hyperplasia, Sox2 did not induce pulmonary tumors. Sox2 induces proliferation of respiratory epithelial cells and, subsequently, partially reprograms alveolar epithelial cells into cells with characteristics of the conducting airways.
lung; transcription; progenitor cell; differentiation; tumorigenesis
In April 2010, a NIH workshop was convened to discuss the current state of understanding of lung cell plasticity, including the responses of epithelial cells to injury, with the objectives of summarizing what is known, what the field needs to know, and how to get there. The proximal stimulus for this workshop is the body of recent evidence suggesting that plasticity is a prominent but incompletely characterized property of lung epithelial cells, and that a focus on understanding this aspect of epithelial cell biology in particular, may be an important window into disease pathobiology and pathogenesis. In addition to their many vital functions in maintaining tissue homeostasis, epithelial cells have emerged as both a central target of disease initiation and an active contributor to disease progression, making a workshop to investigate the role of cell plasticity in lung injury and repair timely. The workshop was organized around four major themes: lung epithelial cell plasticity, signaling control of plasticity, fibroblast plasticity and crosstalk, and translation to human disease. Although this breakdown was recognized to be somewhat artificial, it was felt that this approach would promote cross-fertilization among groups that ordinarily do not communicate and lend itself to the generation of new approaches. The summary reports of individual group discussions below are followed by consensus priorities and recommendations of the workshop participants.
epithelial-mesenchymal transition (EMT); idiopathic pulmonary fibrosis; cell lineage
Rationale: The respiratory epithelium has a remarkable capacity to respond to acute injury. In contrast, repeated epithelial injury is often associated with abnormal repair, inflammation, and fibrosis. There is increasing evidence that nonciliated epithelial cells play important roles in the repair of the bronchiolar epithelium after acute injury. Cellular processes underlying the repair and remodeling of the lung after chronic epithelial injury are poorly understood.
Objectives: To identify cell processes mediating epithelial regeneration and remodeling after acute and chronic Clara cell depletion.
Methods: A transgenic mouse model was generated to conditionally express diphtheria toxin A to ablate Clara cells in the adult lung. Epithelial regeneration and peribronchiolar fibrosis were assessed after acute and chronic Clara cell depletion.
Measurements and Main Results: Acute Clara cell ablation caused squamous metaplasia of ciliated cells and induced proliferation of residual progenitor cells. Ciliated cells in the bronchioles and pro–surfactant protein C–expressing cells in the bronchiolar alveolar duct junctions did not proliferate. Epithelial cell proliferation occurred at multiple sites along the airways and was not selectively associated with regions around neuroepithelial bodies. Chronic Clara cell depletion resulted in ineffective repair and caused peribronchiolar fibrosis.
Conclusions: Colocalization of proliferation and cell type–specific markers demonstrate that Clara cells are critical airway progenitor cells. Continuous depletion of Clara cells resulted in persistent squamous metaplasia, lack of normal reepithelialization, and peribronchiolar fibrosis. Induction of proliferation in subepithelial fibroblasts supports the concept that chronic epithelial depletion caused peribronchiolar fibrosis.
chronic obstructive pulmonary disease; bronchiolitis obliterans syndrome; squamous metaplasia; diphtheria toxin; progenitor cells
Asthma is a major public health burden worldwide. Studies from our group and others have demonstrated that SERPINB3 and B4 are induced in asthmatics; however their mechanistic role in asthma has yet to be determined.
To evaluate the role of Serpin3a, the murine homolog of human SERPINB3 and B4, in asthma.
We studied wild type Balb/c and Serpinb3a null mice in house dust mite or IL-13 induced asthma models and evaluated airway hyperresponsiveness, inflammation, and goblet cell hyperplasia.
Airway hyperresponsiveness and goblet cell hyperplasia were markedly attenuated in the Serpinb3a null mice compared to the wild type mice following allergen challenge, with minimal effects on inflammation. Expression of SPDEF, a transcription factor that mediates goblet cell hyperplasia, was decreased in the absence of Serpinb3a. IL-13 treated Serpinb3a null mice showed attenuated AHR, inflammation, and mucus production.
Excessive mucus production and mucus plugging are key pathologic features of asthma, yet the mechanisms responsible for mucus production are not well understood. Our data reveal a novel non-redundant role for Serpinb3a in mediating mucus production through regulation of SPDEF expression. This pathway may be used to effectively target mucus hypersecretion.
goblet cells; SPDEF; IL-13; hyperplasia
The many challenges associated with lung transplantation provide a strong rationale for the development of cell- and tissue-based therapies for patients with respiratory failure caused by the loss of lung tissue that is associated with chronic pulmonary disease, injury, or resection. In this issue of the JCI, Chapman et al. take an important step forward in the development of regenerative medicine for the treatment of lung disease by identifying a novel integrin α6β4–expressing alveolar epithelial cell that serves as a multipotent progenitor during repair of the severely injured lung.
CD8+ T-cell-mediated pulmonary immunopathology in respiratory virus infection is mediated in large part by antigen-specific TNF-α expression by antiviral effector T cells, which results in epithelial chemokine expression and inflammatory infiltration of the lung. To further define the signaling events leading to lung epithelial chemokine production in response to CD8+ T-cell antigen recognition, we expressed the adenoviral 14.7K protein, a putative inhibitor of TNF-α signaling, in the distal lung epithelium, and analyzed the functional consequences. Distal airway epithelial expression of 14.7K resulted in a significant reduction in lung injury resulting from severe influenza pneumonia. In vitro analysis demonstrated a significant reduction in the expression of an important mediator of injury, CCL2, in response to CD8+ T-cell recognition, or to TNF-α. The inhibitory effect of 14.7K on CCL2 expression resulted from attenuation of NF-κB activity, which was independent of Iκ-Bα degradation or nuclear translocation of the p65 subunit. Furthermore, epithelial 14.7K expression inhibited serine phosphorylation of Akt, GSK-3β, and the p65 subunit of NF-κB, as well as recruitment of NF-κB for DNA binding in vivo. These results provide insight into the mechanism of 14.7K inhibition of NF-κB activity, as well as further elucidate the mechanisms involved in the induction of T-cell-mediated immunopathology in respiratory virus infection.
Foxm1 is a member of the Forkhead Box (Fox) family of transcription factors. Foxm1 (previously called Foxm1b, HFH-11B, Trident, Win, or MPP2) is expressed in multiple cell types and plays important roles in cellular proliferation, differentiation and tumorigenesis. Genetic deletion of Foxm1 from mouse respiratory epithelium during initial stages of lung development inhibits lung maturation and causes respiratory failure after birth. However, the role of Foxm1 during postnatal lung morphogenesis remains unknown. In the present study, Foxm1 expression was detected in epithelial cells of conducting and peripheral airways and changing dynamically with lung maturation. To discern the biological role of Foxm1 in the prenatal and postnatal lung, a novel transgenic mouse line that expresses a constitutively active form of FoxM1 (FoxM1 N-terminal deletion mutant or FoxM1-ΔN) under the control of lung epithelial-specific SPC promoter was produced. Expression of the FoxM1-ΔN transgene during embryogenesis caused epithelial hyperplasia, inhibited lung sacculation and expression of the type II epithelial marker, pro-SPC. Expression of FoxM1-ΔN mutant during the postnatal period did not influence alveologenesis but caused focal airway hyperplasia and increased proliferation of Clara cells. Likewise, expression of FoxM1-ΔN mutant in conducting airways with Scgb1a1 promoter was sufficient to induce Clara cell hyperplasia. Furthermore, FoxM1-ΔN cooperated with activated K-Ras to induce lung tumor growth in vivo. Increased activity of Foxm1 altered lung sacculation, induced proliferation in the respiratory epithelium and accelerated lung tumor growth, indicating that precise regulation of Foxm1 is critical for normal lung morphogenesis and development of lung cancer.
Rationale: We identified a 6-year-old girl with pulmonary alveolar proteinosis (PAP), impaired granulocyte-macrophage colony–stimulating factor (GM-CSF) receptor function, and increased GM-CSF.
Objectives: Increased serum GM-CSF may be useful to identify individuals with PAP caused by GM-CSF receptor dysfunction.
Methods: We screened 187 patients referred to us for measurement of GM-CSF autoantibodies to diagnose autoimmune PAP. Five were children with PAP and increased serum GM-CSF but without GM-CSF autoantibodies or any disease causing secondary PAP; all were studied with family members, subsequently identified patients, and controls.
Measurement and Main Results: Eight children (seven female, one male) were identified with PAP caused by recessive CSF2RA mutations. Six presented with progressive dyspnea of insidious onset at 4.8 ± 1.6 years and two were asymptomatic at ages 5 and 8 years. Radiologic and histopathologic manifestations were similar to those of autoimmune PAP. Molecular analysis demonstrated that GM-CSF signaling was absent in six and severely reduced in two patients. The GM-CSF receptor β chain was detected in all patients, whereas the α chain was absent in six and abnormal in two, paralleling the GM-CSF signaling defects. Genetic analysis revealed multiple distinct CSF2RA abnormalities, including missense, duplication, frameshift, and nonsense mutations; exon and gene deletion; and cryptic alternative splicing. All symptomatic patients responded well to whole-lung lavage therapy.
Conclusions: CSF2RA mutations cause a genetic form of PAP presenting as insidious, progressive dyspnea in children that can be diagnosed by a combination of characteristic radiologic findings and blood tests and treated successfully by whole-lung lavage.
GM-CSF receptor; genetic disease; surfactant; alveolar macrophage; whole lung lavage
Among all mammals, fetal growth and organ maturation must be precisely synchronized with gestational length to optimize survival at birth. Lack of pulmonary maturation is the major cause of infant mortality in preterm birth. Whether fetal or maternal genotypes influence the close relationship between the length of gestation and lung function at birth is unknown. Structural and biochemical indicators of pulmonary maturity were measured in two mouse strains whose gestational length differed by one day. Shorter gestation in C57BL/6J mice was associated with advanced morphological and biochemical pulmonary development and better perinatal survival when compared to A/J pups born prematurely. After ovarian transplantation, A/J pups were born early in C57BL/6J dams and survived after birth, consistent with maternal control gestational length. Expression of genes critical for perinatal lung function was assessed in A/J pups born after ovarian transfer. A subset of mRNAs important for perinatal respiratory adaptation was selectively induced in the A/J pups born after ovarian transfer. mRNAs precociously induced after ovarian transfer indicated an important role for the transcription factors C/EBPα and CREB in maternally induced lung maturation. We conclude that fetal lung maturation is determined by both fetal and maternal genotypes. Ovarian transfer experiments demonstrated that maternal genotype determines the timing of birth and can influence fetal lung growth and maturation to ensure perinatal survival.
To investigate the expression of pancreatic microRNAs (miRNAs) during the period of perinatal beta-cell expansion and maturation in rats, determine the localization of these miRNAs and perform a pathway analysis with predicted target mRNAs expressed in perinatal pancreas.
Research Design and Methods
RNA was extracted from whole pancreas at embryonic day 20 (E20), on the day of birth (P0) and two days after birth (P2) and hybridized to miRNA microarrays. Differentially expressed miRNAs were verified by northern blotting and their pancreatic localization determined by in situ hybridization. Pathway analysis was done using regulated sets of mRNAs predicted as targets of the miRNAs. Possible target genes were tested using reporter-gene analysis in INS-1E cells.
Nine miRNAs were differentially expressed perinatally, seven were confirmed to be regulated at the level of the mature miRNA. The localization studies showed endocrine localization of six of these miRNAs (miR-21, -23a, -29a, -125b-5p, -376b-3p and -451), and all were expressed in exocrine cells at one time point at least. Pathways involving metabolic processes, terpenoid and sterol metabolism were selectively affected by concomitant regulation by miRNAs and mRNAs, and Srebf1 was validated as a target of miR-21.
The findings suggest that miRNAs are involved in the functional maturation of pancreatic exocrine and endocrine tissue following birth. Pathway analysis of target genes identify changes in sterol metabolism around birth as being selectively affected by differential miRNA expression during this period.
The ER chaperone GRP78/BiP is a homolog of the Hsp70 family of heat shock proteins, yet GRP78/BiP is not induced by heat shock but instead by ER stress. However, previous studies had not considered more physiologically relevant temperature elevation associated with febrile hyperthermia. In this report we examine the response of GRP78/BiP and other components of the ER stress pathway in cells exposed to 40°C.
AD293 cells were exposed to 43°C heat shock to confirm inhibition of the ER stress response genes. Five mammalian cell types, including AD293 cells, were then exposed to 40°C hyperthermia for various time periods and induction of the ER stress pathway was assessed.
The inhibition of the ER stress pathway by heat shock (43°C) was confirmed. In contrast cells subjected to more mild temperature elevation (40°C) showed either a partial or full ER stress pathway induction as determined by downstream targets of the three arms of the ER stress pathway as well as a heat shock response. Cells deficient for Perk or Gcn2 exhibit great sensitivity to ER stress induction by hyperthermia.
The ER stress pathway is induced partially or fully as a consequence of hyperthermia in parallel with induction of Hsp70. These findings suggest that the ER and cytoplasm of cells contain parallel pathways to coordinately regulate adaptation to febrile hyperthermia associated with disease or infection.
Thyroid transcription factor-1 (TTF-1) deficiency syndrome is characterized by neurologic, thyroidal, and pulmonary dysfunction. Children usually have mild-to-severe respiratory symptoms and occasionally die of respiratory failure. Herein, we describe an infant with a constitutional 14q12–21.3 haploid deletion encompassing the TTF-1 gene locus who had cerebral dysgenesis, thyroidal dysfunction, and respiratory insufficiency. The clinical course was notable for mild hyaline membrane disease, continuous ventilatory support, and symmetrically distributed pulmonary cysts by imaging. He developed pneumonia and respiratory failure and died at 8 months. Pathologically, the lungs had grossly visible emphysematous changes with “cysts” up to 2 mm in diameter. The airway generations and radial alveolar count were diminished. In addition to acute bacterial pneumonia, there was focally alveolar septal fibrosis, pneumocyte hypertrophy, and clusters of airspace macrophages. Ultrastructurally, type II pneumocytes had numerous lamellar bodies, and alveolar spaces contained fragments of type II pneumocytes and extruded lamellar bodies. Although immunoreactivity for surfactant protein SP-A and ABCA3 was diminished, that for SP-B and proSP-C was robust, although irregularly distributed, corresponding to the distribution of type II pneumocytes. Immunoreactivity for TTF-1 protein was readily detected. In summation, we document abnormal airway and alveolar morphogenesis and altered expression of surfactant-associated proteins, which may explain the respiratory difficulties encountered in TTF-1 haploinsufficiency. These findings are consistent with experimental evidence documenting the important role of TTF-1 in pulmonary morphogenesis and surfactant metabolism.
alveolar growth abnormality; cerebral dysgenesis; thyroid transcription factor-1; bronchopulmonary dysplasia; surfactant protein
Pulmonary fibrosis complicates a number of disease processes and leads to substantial morbidity and mortality. Idiopathic pulmonary fibrosis (IPF) is perhaps the most pernicious and enigmatic form of the greater problem of lung fibrogenesis with a median survival of three years from diagnosis in affected patients. In this review, we will focus on the pathology of IPF as a model of pulmonary fibrotic processes, review possible cellular mechanisms, review current treatment approaches and review two transgenic mouse models of lung fibrosis to provide insight into processes that cause lung fibrosis. We will also summarize the potential utility of signaling pathway inhibitors as a future treatment in pulmonary fibrosis. Finally, we will present data demonstrating a minimal contribution of epithelial-mesenchymal transition in the development of fibrotic lesions in the transforming growth factor-alpha transgenic model of lung fibrosis.
epithelial mesenchymal transition; epidermal growth factor receptor; transforming growth factor alpha
Rationale: Granulocyte/macrophage colony–stimulating factor (GM-CSF) autoantibodies (GMAb) are strongly associated with idiopathic pulmonary alveolar proteinosis (PAP) and are believed to be important in its pathogenesis. However, levels of GMAb do not correlate with disease severity and GMAb are also present at low levels in healthy individuals.
Objectives: Our primary objective was to determine whether human GMAb would reproduce PAP in healthy primates. A secondary objective was to determine the concentration of GMAb resulting in loss of GM-CSF signaling in vivo (i.e., critical threshold).
Methods: Nonhuman primates (Macaca fascicularis) were injected with highly purified, PAP patient-derived GMAb in dose-ranging (2.2–50 mg) single and multiple administration studies, and after blocking antihuman immunoglobulin immune responses, in chronic administration studies maintaining serum levels greater than 40 μg/ml for up to 11 months.
Measurements and Main Results: GMAb blocked GM-CSF signaling causing (1) a milky-appearing bronchoalveolar lavage fluid containing increased surfactant lipids and proteins; (2) enlarged, foamy, surfactant-filled alveolar macrophages with reduced PU.1 and PPARγ mRNA, and reduced tumor necrosis factor-α secretion; (3) pulmonary leukocytosis; (4) increased serum surfactant protein-D; and (5) impaired neutrophil functions. GM-CSF signaling varied inversely with GMAb concentration below a critical threshold of 5 μg/ml, which was similar in lungs and blood and to the value observed in patients with PAP.
Conclusions: GMAb reproduced the molecular, cellular, and histopathologic features of PAP in healthy primates, demonstrating that GMAb directly cause PAP. These results have implications for therapy of PAP and help define the therapeutic window for potential use of GMAb to treat other disorders.
alveolar macrophages; surfactant homeostasis; autoimmunity; neutrophils; anti–granulocyte/macrophage colony–stimulating factor therapy
Rationale: Premature newborns frequently require manual ventilation for resuscitation during which lung injury occurs. Although surfactant protein (SP)-D regulates pulmonary inflammation, SP-D levels are low in the preterm lung. Commercial surfactants for treatment of respiratory distress syndrome do not contain SP-D.
Objectives: To determine whether addition of recombinant human SP-D (rhSP-D) to commercial surfactant influences lung inflammation in ventilated premature newborn lambs.
Methods: Prematurely delivered lambs (130 d gestation age) were resuscitated with 100% O2 and peak inspiratory pressure 40 cm H2O for 20 minutes and then treated with Survanta or Survanta containing rhSP-D. Ventilation was then changed to regulate tidal volume at 8 to 9 ml/kg. At 5 hours of age lambs were killed for sample collection.
Measurements and Main Results: Sequential blood gas and tidal volume were similar in lambs treated with or without rhSP-D, indicating that lung immaturity and ventilatory stress used to support premature lambs were comparable between the two groups. Ventilation caused pulmonary inflammation in lambs treated with surfactant alone. In contrast, surfactant containing rhSP-D decreased neutrophil numbers in bronchoalveolar lavage fluid and decreased neutrophil elastase activity in lung tissue. IL-8 mRNA and IL-8 protein were significantly decreased in the +rhSP-D group lamb lungs, to 20% of those in controls. The addition of rhSP-D also rendered Survanta more resistant to plasma protein inhibition of surfactant function.
Conclusions: Treatment with rhSP-D–containing surfactant inhibited lung inflammation and enhanced the resistance of surfactant to inhibition, supporting its potential usefulness for prevention of lung injury in the preterm newborn.
respiratory distress syndrome; surfactant treatment; IL-8; newborn resuscitation; lung injury