title: Mitochondrial fusion is essential for organelle function and cardiac homeostasis.
abstract: BACKGROUND
  Mitochondria constitute 30% of myocardial mass. Mitochondrial fusion and fission appear essential for health of most tissues. Mitochondrial fission occurs in neonatal cardiomycyte and is implicated in cardiomyocyte death. Mitochondrial fusion has not been observed in postmitotic myocytes of adult hearts, and its occurrence and function in this context are controversial.
  
  
  OBJECTIVE
  Determine the consequences on organelle and organ function of disrupting cardiomyocyte mitochondrial fusion in vivo.
  
  
  RESULTS
  The murine mfn1 and mfn2 genes, encoding mitofusins (Mfn) 1 and 2 that mediate mitochondrial tethering and outer mitochondrial membrane fusion, were interrupted by Cre-mediated excision of essential exons in neonatal (Nkx2.5-Cre) and adult (MYH6 modified estrogen receptor-Cre-modified estrogen receptor plus tamoxifen or Raloxifene) hearts. Embryonic combined Mfn1/Mfn2 ablation was lethal after e9.5. Conditional combined Mfn1/Mfn2 ablation in adult hearts induced mitochondrial fragmentation, cardiomyocyte and mitochondrial respiratory dysfunction, and rapidly progressive and lethal dilated cardiomyopathy. Before heart failure developed, cardiomyocyte shortening and calcium cycling were unaffected by absence of Mfn1 and Mfn2. Based on the time course over which fusion-defective mitochondrial size decreases, a mitochondrial fusion/fission cycle in adult mouse hearts occurs approximately every 16 days.
  
  
  CONCLUSIONS
  Mitochondrial fusion in adult cardiac myocytes is necessary to maintain normal mitochondrial morphology and is essential for normal cardiac respiratory and contractile function. Interruption of mitochondrial fusion causes lethal cardiac failure at a time corresponding to 3 or 4 cycles of unopposed mitochondrial fission.
authors: Center for Pharmacogenomics, Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA. gdorn@dom.wustl.edu
authors: Yun
authors: Y
authors: Chen
authors: Yingqiu
authors: Y
authors: Liu
authors: Gerald W
authors: GW
authors: Dorn
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D017353:Gene Deletion; D006321:Heart / Q000196:embryology / Q000502:physiology*; D006706:Homeostasis / Q000502:physiology*; D008561:Membrane Fusion / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D008929:Mitochondria, Heart / Q000502:physiology*; D051336:Mitochondrial Membranes / Q000502:physiology*; D023421:Models, Animal; D009200:Myocardial Contraction / Q000502:physiology; D032383:Myocytes, Cardiac / Q000502:physiology
chemical_list: D020558:GTP Phosphohydrolases; C488750:Mfn1 protein, mouse; C488751:Mfn2 protein, mouse; D002118:Calcium