title: Role of mitochondrial fission and fusion in cardiomyocyte contractility.
abstract: BACKGROUND
  Mitochondria constitute 30% of cell volume and are engaged in two dynamic processes called fission and fusion, regulated by Drp-1 (dynamin related protein) and mitofusin 2 (Mfn2). Previously, we showed that Drp-1 inhibition attenuates cardiovascular dysfunction following pressure overload in aortic banding model and myocardial infarction. As dynamic organelles, mitochondria are capable of changing their morphology in response to stress. However, whether such changes can alter their function and in turn cellular function is unknown. Further, a direct role of fission and fusion in cardiomyocyte contractility has not yet been studied. In this study, we hypothesize that disrupted fission and fusion balance by increased Drp-1 and decreased Mfn2 expression in cardiomyocytes affects their contractility through alterations in the calcium and potassium concentrations.
  
  
  METHODS
  To verify this, we used freshly isolated ventricular myocytes from wild type mouse and transfected them with either siRNA to Drp-1 or Mfn2. Myocyte contractility studies were performed by IonOptix using a myopacer. Intracellular calcium and potassium measurements were done using flow cytometry. Immunocytochemistry (ICC) was done to evaluate live cell mitochondria and its membrane potential. Protein expression was done by western blot and immunocytochemistry.
  
  
  RESULTS
  We found that silencing mitochondrial fission increased the myocyte contractility, while fusion inhibition decreased contractility with simultaneous changes in calcium and potassium. Also, we observed that increase in fission prompted decrease in Serca-2a and increase in cytochrome c leakage leading to mitophagy.
  
  
  CONCLUSIONS
  Our results suggested that regulating mitochondrial fission and fusion have direct effects on overall cardiomyocyte contractility and thus function.
authors.affiliation: Department of Physiology and Biophysics, University of Louisville School of Medicine, Louisville, KY 40202, United States. Electronic address: s0givv01@louisville.edu.
authors.forename: S
authors.initials: S
authors.lastname: Givvimani
authors.affiliation: Department of Physiology and Biophysics, University of Louisville School of Medicine, Louisville, KY 40202, United States.
authors.forename: S B
authors.initials: SB
authors.lastname: Pushpakumar
authors.affiliation: Department of Physiology and Biophysics, University of Louisville School of Medicine, Louisville, KY 40202, United States.
authors.forename: N
authors.initials: N
authors.lastname: Metreveli
authors.affiliation: Department of Physiology and Biophysics, University of Louisville School of Medicine, Louisville, KY 40202, United States.
authors.forename: S
authors.initials: S
authors.lastname: Veeranki
authors.affiliation: Department of Physiology and Biophysics, University of Louisville School of Medicine, Louisville, KY 40202, United States.
authors.forename: S
authors.initials: S
authors.lastname: Kundu
authors.affiliation: Department of Physiology and Biophysics, University of Louisville School of Medicine, Louisville, KY 40202, United States.
authors.forename: S C
authors.initials: SC
authors.lastname: Tyagi
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D051379:Mice; D063154:Mitochondrial Dynamics / Q000502:physiology*; D009200:Myocardial Contraction / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000502:physiology*
keywords: Calcium; Cytochrome c; Drp-1; Heart; Mfn2; Mitochondria; Serca-2a
references.citation: Basic Res Cardiol. 2006 May;101(3):204-13
references.pmid: 16369727
references.citation: Life Sci. 2007 May 16;80(23):2154-60
references.pmid: 17499311
references.citation: Cell Calcium. 2008 Jul;44(1):24-35
references.pmid: 18395251
references.citation: Nature. 2008 Dec 4;456(7222):605-10
references.pmid: 19052620
references.citation: J Clin Invest. 2009 May;119(5):1275-85
references.pmid: 19349686
references.citation: J Mol Cell Cardiol. 2009 Jun;46(6):811-20
references.pmid: 19281816
references.citation: Circulation. 2010 May 11;121(18):2012-22
references.pmid: 20421521
references.citation: Biochim Biophys Acta. 2010 Jun-Jul;1797(6-7):913-21
references.pmid: 20347716
references.citation: Circ Res. 2011 Dec 9;109(12):1327-31
references.pmid: 22052916
references.citation: PLoS One. 2012;7(3):e32388
references.pmid: 22479323
references.citation: Eur J Pharmacol. 2012 May 15;683(1-3):1-9
references.pmid: 22374256
references.citation: Antioxid Redox Signal. 2013 Jun 1;18(16):2029-74
references.pmid: 23244576
references.citation: J Am Heart Assoc. 2013 Oct;2(5):e000461
references.pmid: 24103571
references.citation: Mol Cell Proteomics. 2013 Nov;12(11):3094-107
references.pmid: 23882026
references.citation: FASEB J. 2014 Jan;28(1):316-26
references.pmid: 24076965
references.citation: Am J Physiol Heart Circ Physiol. 2014 Apr 15;306(8):H1116-27
references.pmid: 24585779
references.citation: J Clin Invest. 2000 Jul;106(1):55-62
references.pmid: 10880048
references.citation: Circulation. 2001 May 8;103(18):2303-9
references.pmid: 11342481
references.citation: Dev Cell. 2001 Oct;1(4):515-25
references.pmid: 11703942
references.citation: Mol Biol Cell. 2004 Nov;15(11):5001-11
references.pmid: 15356267
references.citation: Am J Pathol. 1972 Jun;67(3):417-40
references.pmid: 5033257
references.citation: Circulation. 1991 Feb;83(2):709-11
references.pmid: 1991389
references.citation: J Physiol. 2005 Aug 15;567(Pt 1):349-58
references.pmid: 15961417
references.citation: Diabetes. 2005 Sep;54(9):2685-93
references.pmid: 16123358
references.citation: J Cell Sci. 2005 Sep 15;118(Pt 18):4141-51
references.pmid: 16118244
references.citation: J Cell Mol Med. 2005 Jul-Sep;9(3):704-13
references.pmid: 16202218