title: Increased expression of adenosine triphosphate-sensitive K+ channels in mitral dysfunction: mechanically stimulated transcription and hypoxia-induced protein stability?
abstract: OBJECTIVE
  The aim of this study was to test whether adenosine triphosphate-sensitive K(+) (KATP) channel expression relates to mechanical and hypoxic stress within the left human heart.
  
  
  BACKGROUND
  The KATP channels play a vital role in preserving the metabolic integrity of the stressed heart. However, the mechanisms that govern the expression of their subunits (e.g., potassium inward rectifier [Kir] 6.2) in adult pathologies are mostly unknown.
  
  
  METHODS
  We collected biopsies from the 4 cardiac chambers and 50 clinical parameters from 30 surgical patients with severe mitral dysfunction. Proteins and messenger ribonucleic acids (mRNAs) of KATP pore subunits and mRNAs of their known transcriptional regulators (forkhead box [FOX] F2, FOXO1, FOXO3, and hypoxia inducible factor [HIF]-1α) were measured respectively by Western blotting, immunohistochemistry, and quantitative real-time polymerase chain reaction, and submitted to statistical analysis.
  
  
  RESULTS
  In all heart chambers, Kir6.2 mRNA correlated with HIF-1α mRNA. Neither Kir6.1 nor Kir6.2 proteins positively correlated with their respective mRNAs. The HIF-1α mRNA related in the left ventricle to aortic pressure, in the left atrium to left atrial pressure, and in all heart chambers to a decreased Kir6.2 protein/mRNA ratio. Interestingly, in the left heart, Kir6.2 protein and its immunohistochemical detection in myocytes were maximal at low venous PO(2). In the left ventricle, the Kir6.2 protein/mRNA ratio was also significantly higher at low venous PO(2), suggesting that tissue hypoxia might stabilize the Kir6.2 protein.
  
  
  CONCLUSIONS
  Results suggest that post-transcriptional events determine Kir6.2 protein expression in the left ventricle of patients with severe mitral dysfunction and low venous PO(2). Mechanical stress mainly affects transcription of HIF-1α and Kir6.2. This study implies that new therapies could aim at the proteasome for stabilizing the left ventricular Kir6.2 protein.
authors: Department of Neuroscience, University of Geneva, Centre Médical Universitaire, Geneva, Switzerland.
authors: Véronique
authors: V
authors: Raeis-Dauvé
authors: Pierre
authors: P
authors: Philip-Couderc
authors: Giuseppe
authors: G
authors: Faggian
authors: Maddalena
authors: M
authors: Tessari
authors: Angela
authors: A
authors: Roatti
authors: Aldo D
authors: AD
authors: Milano
authors: Marie-Luce
authors: ML
authors: Bochaton-Piallat
authors: Alex J
authors: AJ
authors: Baertschi
mesh_terms: D000368:Aged; D000818:Animals; D001784:Blood Gas Analysis; D001794:Blood Pressure; D004452:Echocardiography; D005260:Female; D005786:Gene Expression Regulation; D006352:Heart Ventricles / Q000378:metabolism; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D054086:KATP Channels / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008875:Middle Aged; D008944:Mitral Valve Insufficiency / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D010100:Oxygen / Q000502:physiology; D010313:Partial Pressure; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism*; D055550:Protein Stability; D012333:RNA, Messenger / Q000378:metabolism; D013314:Stress, Mechanical; D000099161:Kcnj11 Channel
chemical_list: D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D054086:KATP Channels; D010100:Oxygen; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger; D000099161:Kcnj11 Channel; C497442:HIF1A protein, human