title: Chronic hypoxia down-regulates tight junction protein ZO-2 expression in children with cyanotic congenital heart defect.
abstract: OBJECTIVE
  Tight junction protein zonula occludens protein 2 (ZO-2) is a member of the membrane-associated guanylate kinases protein family known to be expressed at tight junctions of epithelial and endothelial cells and at adherens junctions (AJs) in cardiomyocytes. Little is known about ZO-2 expression and function in the human heart. Here, we examined the hypothesis that chronic hypoxia down-regulates ZO-2 expression in human myocardium and cultured rat cardiomyocytes.
  
  
  RESULTS
  Patients with a diagnosis of cyanotic (n= 10) or acyanotic (n= 10) Tetralogy of Fallot undergoing surgical repair were used to examine ZO-2 messenger RNA and protein expression by real time-PCR, immunohistochemistry, and western blotting. A model of cultured rat cardiomyocytes was used to measure ZO-2 and AJ proteins levels in response to hypoxia and to investigate ZO-2 cellular localization. We showed that ZO-2 is expressed in myocardial tissue in acyanotic and cyanotic children with congenital heart defects. ZO-2 was specifically down-regulated in cyanotic myocardium at both the messenger RNA and protein levels when compared with acyanotic patients. This specific down-regulation can be mimicked in cultured rat cardiomyocytes by treating them with hypoxic conditions confirming that ZO-2 gene down-regulation is specifically due to cyanosis. Furthermore, in addition to its cytoplasmic expression, ZO-2 showed nuclear expression in cultured rat cardiomyocytes suggesting potential role in transcription regulation.
  
  
  CONCLUSIONS
  Hypoxia down-regulates ZO-2 expression in both cyanotic patient's myocardium and cultured rat cardiomyocytes. This down-regulation suggest an involvement of ZO-2 in cardiac remodelling of AJs in cyanotic children and may explain the greater susceptibility of cyanotic patients to corrective heart surgery.
authors.affiliation: Bristol Heart Institute, School of Clinical Sciences University of Bristol Bristol UK.
authors.forename: Emma L
authors.initials: EL
authors.lastname: Jenkins
authors.affiliation: Bristol Heart Institute, School of Clinical Sciences University of Bristol Bristol UK.
authors.forename: Massimo
authors.initials: M
authors.lastname: Caputo
authors.affiliation: Bristol Heart Institute, School of Clinical Sciences University of Bristol Bristol UK.
authors.forename: Gianni D
authors.initials: GD
authors.lastname: Angelini
authors.affiliation: Bristol Heart Institute, School of Clinical Sciences University of Bristol Bristol UK.
authors.forename: Mohamed T
authors.initials: MT
authors.lastname: Ghorbel
keywords: Cardiomyocyte; Congenital heart defects; Cyanosis; Hypoxia; ZO‐2