title: Loss of Krox20 results in aortic valve regurgitation and impaired transcriptional activation of fibrillar collagen genes.
abstract: OBJECTIVE
  Heart valve maturation is achieved by the organization of extracellular matrix (ECM) and the distribution of valvular interstitial cells. However, the factors that regulate matrix components required for valvular structure and function are unknown. Based on the discovery of its specific expression in cardiac valves, we aimed to uncover the role of Krox20 (Egr-2) during valve development and disease.
  
  
  RESULTS
  Using series of mouse genetic tools, we demonstrated that loss of function of Krox20 caused significant hyperplasia of the semilunar valves, while atrioventricular valves appeared normal. This defect was associated with an increase in valvular interstitial cell number and ECM volume. Echo Doppler analysis revealed that adult mutant mice had aortic insufficiency. Defective aortic valves (AoVs) in Krox20(-/-) mice had features of human AoV disease, including excess of proteoglycan deposition and reduction of collagen fibres. Furthermore, examination of diseased human AoVs revealed decreased expression of KROX20. To identify downstream targets of Krox20, we examined expression of fibrillar collagens in the AoV leaflets at different stages in the mouse. We found significant down-regulation of Col1a1, Col1a2, and Col3a1 in the semilunar valves of Krox20 mutant mice. Utilizing in vitro and in vivo experiments, we demonstrated that Col1a1 and Col3a1 are direct targets of Krox20 activation in interstitial cells of the AoV.
  
  
  CONCLUSIONS
  This study identifies a previously unknown function of Krox20 during heart valve development. These results indicate that Krox20-mediated activation of fibrillar Col1a1 and Col3a1 genes is crucial to avoid postnatal degeneration of the AoV leaflets.
authors.affiliation: Aix Marseille Université, GMGF UMR_S910, Faculté de Médecine, 27 Bd Jean Moulin, 13385 Marseille, France Inserm, U910, Faculté de Médecine, 27 Bd Jean Moulin, 13005 Marseille, France.
authors.forename: Gaëlle
authors.initials: G
authors.lastname: Odelin
authors.affiliation: Aix Marseille Université, GMGF UMR_S910, Faculté de Médecine, 27 Bd Jean Moulin, 13385 Marseille, France Inserm, U910, Faculté de Médecine, 27 Bd Jean Moulin, 13005 Marseille, France.
authors.forename: Emilie
authors.initials: E
authors.lastname: Faure
authors.affiliation: Faculté de Médecine, Aix Marseille Université, CNRS, CRMBM UMR7339, Marseille, France.
authors.forename: Frank
authors.initials: F
authors.lastname: Kober
authors.affiliation: Aix Marseille Université, CNRS, IBDM UMR7288, Marseille, France.
authors.forename: Corinne
authors.initials: C
authors.lastname: Maurel-Zaffran
authors.affiliation: Aix Marseille Université, GMGF UMR_S910, Faculté de Médecine, 27 Bd Jean Moulin, 13385 Marseille, France Inserm, U910, Faculté de Médecine, 27 Bd Jean Moulin, 13005 Marseille, France Département de Cardiologie, AP-HM, Hôpital de la Timone, Marseille, France.
authors.forename: Alexis
authors.initials: A
authors.lastname: Théron
authors.affiliation: Inserm, U1024, IBENS, École Normale Supérieure, Paris, France CNRS, UMR8197, IBENS, École Normale Supérieure, Paris, France.
authors.forename: Fanny
authors.initials: F
authors.lastname: Coulpier
authors.affiliation: Faculté de Médecine, Aix Marseille Université, CERIMED, Marseille, France.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Guillet
authors.affiliation: Faculté de Médecine, Aix Marseille Université, CNRS, CRMBM UMR7339, Marseille, France.
authors.forename: Monique
authors.initials: M
authors.lastname: Bernard
authors.affiliation: Aix Marseille Université, GMGF UMR_S910, Faculté de Médecine, 27 Bd Jean Moulin, 13385 Marseille, France Inserm, U910, Faculté de Médecine, 27 Bd Jean Moulin, 13005 Marseille, France Département de Cardiologie, AP-HM, Hôpital de la Timone, Marseille, France.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Avierinos
authors.affiliation: Inserm, U1024, IBENS, École Normale Supérieure, Paris, France CNRS, UMR8197, IBENS, École Normale Supérieure, Paris, France.
authors.forename: Patrick
authors.initials: P
authors.lastname: Charnay
authors.affiliation: Inserm, U1024, IBENS, École Normale Supérieure, Paris, France CNRS, UMR8197, IBENS, École Normale Supérieure, Paris, France.
authors.forename: Piotr
authors.initials: P
authors.lastname: Topilko
authors.affiliation: Aix Marseille Université, GMGF UMR_S910, Faculté de Médecine, 27 Bd Jean Moulin, 13385 Marseille, France Inserm, U910, Faculté de Médecine, 27 Bd Jean Moulin, 13005 Marseille, France stephane.zaffran@univ-amu.fr.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Zaffran
mesh_terms: D000818:Animals; D001021:Aortic Valve / Q000196:embryology* / Q000378:metabolism / Q000473:pathology; D001022:Aortic Valve Insufficiency / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D024042:Collagen Type I / Q000235:genetics / Q000378:metabolism*; D000090602:Collagen Type I, alpha 1 Chain; D051767:Early Growth Response Protein 2 / Q000502:physiology*; D047108:Embryonic Development; D005260:Female; D024022:Fibrillar Collagens / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D006706:Homeostasis; D006801:Humans; D008297:Male; D008648:Mesoderm / Q000378:metabolism; D051379:Mice; D011401:Promoter Regions, Genetic; D015533:Transcriptional Activation
chemical_list: D024042:Collagen Type I; D000090602:Collagen Type I, alpha 1 Chain; D051767:Early Growth Response Protein 2; D024022:Fibrillar Collagens
keywords: Aortic valve disease; Collagens; Extracellular matrix; Heart valve; Krox20; Mouse development