title: Cardiac-targeted NADPH oxidase 4 in the adaptive cardiac remodelling of the murine heart.
abstract: BACKGROUND
  The mechanisms that determine whether the heart adapts to overload stress, or fails, are poorly understood. NADPH oxidase (NOX) proteins produce reactive oxygen species (ROS) involved in redox signalling, and our recent studies have found that an increase in Nox4 during pressure overload protects the heart against failure. We aimed to identify novel Nox4-driven cardioprotective mechanisms that promote adaptive cardiac remodelling.
  
  
  METHODS
  We first undertook a proteomic comparison of heart tissue from cardiac-targeted Nox4-overexpressing mice and controls. The Nox4 cardiac metabolome was then investigated by (1)H nuclear magnetic resonance (NMR) spectroscopy. Effects on cardiac metabolism were assessed by ex-vivo working heart perfusions and isolated mitochondrial respiration studies. Ex-vivo cardiac energetics were assessed by (31)P NMR. Alterations to cardiac fatty acid oxidation were explored in primary cardiomyocytes (extracellular flux analysis).
  
  
  RESULTS
  Cardiac-targeted Nox4 overexpression profoundly remodelled the cardiac proteome in an isoform-specific manner, both in the unstressed and stressed heart. Glycolysis and fatty acid oxidation were identified as the most enriched pathways that were altered by Nox4. Metabolomic analysis showed a 2·2 times increase in acetylcarnitine concentrations (p=0·002). Ex-vivo heart perfusions demonstrated a profound increase in palmitate oxidation relative to wild-type hearts (3·6 times increase, p=0·01), with opposite findings observed in primary cardiomyocytes with a knockdown of Nox4. A preference for fatty acid oxidation in Nox4 hearts correlated with a better energetic state (phosphocreatine:ATP ratio) when subjected to increasing doses of isoprenaline stress under baseline and pressure-overload.
  
  
  CONCLUSIONS
  In this study we identified a novel role for Nox4 in the regulation of cardiac fatty acid oxidation. Cardiomyocyte-targeted Nox4 hearts preferentially oxidised fatty acids for energy provision, improving myocardial energetics under stress. Enhancing fatty acid oxidation might have an adaptive role in the setting of pressure-overload hypertrophy. These data provide novel insights into ROS-dependent metabolic programming.
  
  
  BACKGROUND
  UK Medical Research Council, British Heart Foundation.
authors: Cardiovascular Division, King's College London, London, UK. Electronic address: adam.a.nabeebaccus@kcl.ac.uk.
authors: Adam
authors: A
authors: Nabeebaccus
authors: Cardiovascular Research Group, Department of Medical Biology, University of Tromsø, Tromsø, Norway.
authors: Anne
authors: A
authors: Hafstad
authors: Cardiovascular Division, King's College London, London, UK.
authors: Tom
authors: T
authors: Eykyn
authors: Cardiovascular Division, King's College London, London, UK.
authors: Xiaoke
authors: X
authors: Yin
authors: Cardiovascular Division, King's College London, London, UK.
authors: Alison
authors: A
authors: Brewer
authors: Cardiovascular Division, King's College London, London, UK.
authors: Min
authors: M
authors: Zhang
authors: Cardiovascular Division, King's College London, London, UK.
authors: Manuel
authors: M
authors: Mayr
authors: Cardiovascular Division, King's College London, London, UK.
authors: Ajay
authors: A
authors: Shah