title: Critical Role of Coaptive Strain in Aortic Valve Leaflet Homeostasis: Use of a Novel Flow Culture Bioreactor to Explore Heart Valve Mechanobiology.
abstract: Aortic valve (AV) disease presents critical situations requiring surgery in over 2% of the US population and is increasingly the reason for cardiac surgery. Throughout the AV cycle, mechanical forces of multiple types and varying intensities are exerted on valve leaflets. The mechanisms whereby forces regulate leaflet homeostasis are incompletely understood. We used a novel flow bioreactor culture to investigate alteration of AV opening or closure on leaflet genes.
  
  
  
  Culture of rat AV was conducted in a flow bioreactor for 7 days at 37°C under conditions approximating the normal stroke volume. Three force condition groups were compared: Cycling (n=8); always open (Open; n=3); or always closed (Closed; n=5). From each culture, AV leaflets were pooled by force condition and RNA expression evaluated using microarrays. Hierarchical clustering of 16 transcriptome data sets from the 3 groups revealed only 2 patterns of gene expression: Cycling and Closed groups clustered together, whereas Open AV were different (P<0.05). Sustained AV opening induced marked changes in expression (202 transcripts >2-fold; P<0.05), whereas Closed AV exhibited similar expression pattern as Cycling (no transcripts >2-fold; P<0.05). Comparison with human sclerotic and calcific AV transcriptomes demonstrated high concordance of >40 Open group genes with progression toward disease.
  
  
  
  Failure of AV to close initiates an extensive response characterized by expression changes common to progression to calcific aortic valve disease. AV coaptation, whether phasic or chronic, preserved phenotypic gene expression. These results demonstrate, for the first time, that coaptation of valve leaflets is a fundamentally important biomechanical cue driving homeostasis.
authors.affiliation: Pediatric Cardiac Surgery Division, Department of Cardiothoracic Surgery, Stanford University School of Medicine, Falk Cardiovascular Research Center, Stanford, CA.
authors.forename: Katsuhide
authors.initials: K
authors.lastname: Maeda
authors.affiliation: Pediatric Cardiac Surgery Division, Department of Cardiothoracic Surgery, Stanford University School of Medicine, Falk Cardiovascular Research Center, Stanford, CA.
authors.forename: Xiaoyuan
authors.initials: X
authors.lastname: Ma
authors.affiliation: Pediatric Cardiac Surgery Division, Department of Cardiothoracic Surgery, Stanford University School of Medicine, Falk Cardiovascular Research Center, Stanford, CA.
authors.forename: Fariba
authors.initials: F
authors.lastname: Chalajour
authors.affiliation: Pediatric Cardiac Surgery Division, Department of Cardiothoracic Surgery, Stanford University School of Medicine, Falk Cardiovascular Research Center, Stanford, CA.
authors.forename: Frank L
authors.initials: FL
authors.lastname: Hanley
authors.affiliation: Pediatric Cardiac Surgery Division, Department of Cardiothoracic Surgery, Stanford University School of Medicine, Falk Cardiovascular Research Center, Stanford, CA riemerk@stanford.edu.
authors.forename: R Kirk
authors.initials: RK
authors.lastname: Riemer
mesh_terms: D000818:Animals; D001021:Aortic Valve / Q000502:physiology*; D055592:Biophysical Phenomena; D002478:Cells, Cultured; D004195:Disease Models, Animal; D015536:Down-Regulation / Q000235:genetics; D005260:Female; D005786:Gene Expression Regulation; D006349:Heart Valve Diseases / Q000235:genetics*; D006706:Homeostasis / Q000235:genetics*; D046228:Microarray Analysis; D008955:Models, Cardiovascular; D017207:Rats, Sprague-Dawley; D013314:Stress, Mechanical; D013312:Stress, Physiological / Q000502:physiology; D015854:Up-Regulation / Q000235:genetics
keywords: animal model of human disease; gene expression/regulation; mechanical stretch; valve dynamics