title: Structural and transcriptomic response to antenatal corticosteroids in an Erk3-null mouse model of respiratory distress.
abstract: Neonatal respiratory distress syndrome in preterm infants is a leading cause of neonatal death. Pulmonary insufficiency-related infant mortality rates have improved with antenatal glucocorticoid treatment and neonatal surfactant replacement. However, the mechanism of glucocorticoid-promoted fetal lung maturation is not understood fully, despite decades of clinical use. We previously have shown that genetic deletion of Erk3 in mice results in growth restriction, cyanosis, and early neonatal lethality because of pulmonary immaturity and respiratory distress. Recently, we demonstrated that the addition of postnatal surfactant administration to antenatal dexamethasone treatment resulted in enhanced survival of neonatal Erk3-null mice.
  
  
  
  To better understand the molecular underpinnings of corticosteroid-mediated lung maturation, we used high-throughput transcriptomic and high-resolution morphologic analysis of the murine fetal lung. We sought to examine the alterations in fetal lung structure and function that are associated with neonatal respiratory distress and antenatal glucocorticoid treatment.
  
  
  
  Dexamethasone (0.4 mg/kg) or saline solution was administered to pregnant dams on embryonic days 16.5 and 17.5. Fetal lungs were collected and analyzed by microCT and RNA-seq for differential gene expression and pathway interactions with genotype and treatment. Results from transcriptomic analysis guided further investigation of candidate genes with the use of immunostaining in murine and human fetal lung tissue.
  
  
  
  Erk3(-/-) mice exhibited atelectasis with decreased overall porosity and saccular space relative to wild type, which was ameliorated by glucocorticoid treatment. Of 596 differentially expressed genes (q < 0.05) that were detected by RNA-seq, pathway analysis revealed 36 genes (q < 0.05) interacting with dexamethasone, several with roles in lung development, which included corticotropin-releasing hormone and surfactant protein B. Corticotropin-releasing hormone protein was detected in wild-type and Erk3(-/-) lungs at E14.5, with significantly temporally altered expression through embryonic day 18.5. Antenatal dexamethasone attenuated corticotropin-releasing hormone at embryonic day 18.5 in both wild-type and Erk3(-/-) lungs (0.56-fold and 0.67-fold; P < .001). Wild type mice responded to glucocorticoid administration with increased pulmonary surfactant protein B (P = .003). In contrast, dexamethasone treatment in Erk3(-/-) mice resulted in decreased surfactant protein B (P = .012). In human validation studies, we confirmed that corticotropin-releasing hormone protein is present in the fetal lung at 18 weeks of gestation and increases in expression with progression towards viability (22 weeks of gestation; P < .01).
  
  
  
  Characterization of whole transcriptome gene expression revealed glucocorticoid-mediated regulation of corticotropin-releasing hormone and surfactant protein B via Erk3-independent and -dependent mechanisms, respectively. We demonstrated for the first time the expression and temporal regulation of corticotropin-releasing hormone protein in midtrimester human fetal lung. This unique model allows the effects of corticosteroids on fetal pulmonary morphologic condition to be distinguished from functional gene pathway regulation. These findings implicate Erk3 as a potentially important molecular mediator of antenatal glucocorticoid action in promoting surfactant protein production in the preterm neonatal lung and expanding our understanding of key mechanisms of clinical therapy to improve neonatal survival.
authors.affiliation: Department of Molecular and Cell Biology, Baylor College of Medicine, Houston, TX.
authors.forename: Braden K
authors.initials: BK
authors.lastname: Pew
authors.affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX.
authors.forename: R Alan
authors.initials: RA
authors.lastname: Harris
authors.affiliation: Department of Pathology, University of Texas Medical Branch-Galveston, Galveston, TX.
authors.forename: Elena
authors.initials: E
authors.lastname: Sbrana
authors.affiliation: Department of Pediatrics, Division of Neonatology, Baylor College of Medicine, Houston, TX.
authors.forename: Milenka Cuevas
authors.initials: MC
authors.lastname: Guaman
authors.affiliation: Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Baylor College of Medicine, Houston, TX.
authors.forename: Cynthia
authors.initials: C
authors.lastname: Shope
authors.affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX; Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX.
authors.forename: Rui
authors.initials: R
authors.lastname: Chen
authors.affiliation: Institute de Recherche en Immunologie et Cancérologie, Universite de Montreal, Quebec, Canada.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Meloche
authors.affiliation: Department of Molecular and Cell Biology, Baylor College of Medicine, Houston, TX; Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Baylor College of Medicine, Houston, TX. Electronic address: aagaardt@bcm.tmc.edu.
authors.forename: Kjersti
authors.initials: K
authors.lastname: Aagaard
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D003346:Corticotropin-Releasing Hormone / Q000378:metabolism; D003907:Dexamethasone / Q000008:administration & dosage*; D004195:Disease Models, Animal; D005260:Female; D005938:Glucocorticoids / Q000008:administration & dosage*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D008168:Lung / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D018345:Mice, Knockout; D048053:Mitogen-Activated Protein Kinase 6 / Q000172:deficiency*; D011247:Pregnancy; D037663:Pulmonary Surfactant-Associated Protein D / Q000378:metabolism; D012127:Respiratory Distress Syndrome, Newborn / Q000473:pathology; D055114:X-Ray Microtomography
chemical_list: D005938:Glucocorticoids; D037663:Pulmonary Surfactant-Associated Protein D; D007335:Insulin-Like Growth Factor II; D003907:Dexamethasone; D003346:Corticotropin-Releasing Hormone; C474633:Mapk6 protein, mouse; D048053:Mitogen-Activated Protein Kinase 6
keywords: CRH; ERK3; SFTPB; antenatal glucocorticoid; fetal lung maturation