title: Systemic gene transfer enables optogenetic pacing of mouse hearts.
abstract: OBJECTIVE
  Optogenetic pacing of the heart has been demonstrated in transgenic animals expressing channelrhodopsin-2 (ChR2). However, for the clinical use of optogenetics to treat cardiac arrhythmias, gene transfer to non-transgenic hearts is required. The aim of this study was to describe a reliable method for gene transfer of ChR2 into a sufficient percentage of cardiomyocytes to overcome the electrical sink of all the coupled non-expressing cardiomyocytes during optical pacing of the whole heart in vivo.
  
  
  RESULTS
  Adeno-associated virus (AAV) with cardiac tropism for expression of ChR2 in fusion with mCherry was systemically injected into wild-type mouse hearts. Bright mCherry fluorescence was detected in the whole heart 4-10 weeks later. Single-cell dissociation revealed that on average 58% cardiomyocytes were mCherry-positive. These showed light-induced inward currents, action potentials, and contractions. Pulsed illumination of the left ventricle induced ventricular pacing in vivo in 74% of mice, and higher light intensities were required for reduced pulse duration or size of illumination. Non-responding hearts showed low AAV expression, and the threshold for optical pacing was estimated to be 35-40% ChR2-expressing cardiomyocytes. Optical pacing in vivo was stable over extended periods without negative effects on normal sinus rhythm and ECG parameters after termination of stimulation indicating sufficient cardiac output during pacing.
  
  
  CONCLUSIONS
  Gene transfer generates sufficient ChR2 photocurrent for reliable optogenetic pacing in vivo and lays out the basis for future optogenetic pacemaker and pain-free defibrillation therapies.
authors.affiliation: Institute of Physiology I, Life and Brain Center, University of Bonn, Sigmund-Freud-Str. 25, Bonn 53127, Germany.
authors.forename: Christoph C
authors.initials: CC
authors.lastname: Vogt
authors.affiliation: Institute of Physiology I, Life and Brain Center, University of Bonn, Sigmund-Freud-Str. 25, Bonn 53127, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Bruegmann
authors.affiliation: Institute of Physiology I, Life and Brain Center, University of Bonn, Sigmund-Freud-Str. 25, Bonn 53127, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Malan
authors.affiliation: Institute of Physiology I, Life and Brain Center, University of Bonn, Sigmund-Freud-Str. 25, Bonn 53127, Germany Department of Cardiac Surgery, University of Bonn, Bonn, Germany.
authors.forename: Annika
authors.initials: A
authors.lastname: Ottersbach
authors.affiliation: Department of Cardiac Surgery, University of Bonn, Bonn, Germany.
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Roell
authors.affiliation: Institute of Physiology I, Life and Brain Center, University of Bonn, Sigmund-Freud-Str. 25, Bonn 53127, Germany.
authors.forename: Bernd K
authors.initials: BK
authors.lastname: Fleischmann
authors.affiliation: Institute of Physiology I, Life and Brain Center, University of Bonn, Sigmund-Freud-Str. 25, Bonn 53127, Germany philipp.sasse@uni-bonn.de.
authors.forename: Philipp
authors.initials: P
authors.lastname: Sasse
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000235:genetics / Q000378:metabolism; D000229:Dependovirus / Q000235:genetics*; D005260:Female; D008027:Light; D051379:Mice; D032383:Myocytes, Cardiac / Q000378:metabolism*; D062308:Optogenetics / Q000379:methods; D012243:Rhodopsin / Q000235:genetics
chemical_list: D012243:Rhodopsin
keywords: Adeno-associated virus; Channelrhodopsin; Optogenetic; Pacemaker