title: Increased mitochondrial nanotunneling activity, induced by calcium imbalance, affects intermitochondrial matrix exchanges.
abstract: Exchanges of matrix contents are essential to the maintenance of mitochondria. Cardiac mitochondrial exchange matrix content in two ways: by direct contact with neighboring mitochondria and over longer distances. The latter mode is supported by thin tubular protrusions, called nanotunnels, that contact other mitochondria at relatively long distances. Here, we report that cardiac myocytes of heterozygous mice carrying a catecholaminergic polymorphic ventricular tachycardia-linked RyR2 mutation (A4860G) show a unique and unusual mitochondrial response: a significantly increased frequency of nanotunnel extensions. The mutation induces Ca2+imbalance by depressing RyR2 channel activity during excitation-contraction coupling, resulting in random bursts of Ca2+release probably due to Ca2+overload in the sarcoplasmic reticulum. We took advantage of the increased nanotunnel frequency in RyR2A4860G+/-cardiomyocytes to investigate and accurately define the ultrastructure of these mitochondrial extensions and to reconstruct the overall 3D distribution of nanotunnels using electron tomography. Additionally, to define the effects of communication via nanotunnels, we evaluated the intermitochondrial exchanges of matrix-targeted soluble fluorescent proteins, mtDsRed and photoactivable mtPA-GFP, in isolated cardiomyocytes by confocal microscopy. A direct comparison between exchanges occurring at short and long distances directly demonstrates that communication via nanotunnels is slower.
authors.affiliation: Department of Cell Developmental Biology, University of Pennsylvania, Philadelphia, PA 19104; manuelalavorato@gmail.com armstroc@mail.med.upenn.edu.
authors.forename: Manuela
authors.initials: M
authors.lastname: Lavorato
authors.affiliation: Division of Cardiology, Children's Hospital of Philadelphia, Philadelphia, PA 19104.
authors.forename: V Ramesh
authors.initials: VR
authors.lastname: Iyer
authors.affiliation: Biomedical Research Core Facility, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Williams
authors.initials: W
authors.lastname: Dewight
authors.affiliation: MitoCare Center Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107.
authors.forename: Ryan R
authors.identifier: 0000-0001-7639-1923
authors.initials: RR
authors.lastname: Cupo
authors.affiliation: MitoCare Center Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107.
authors.forename: Valentina
authors.initials: V
authors.lastname: Debattisti
authors.affiliation: Department of Medicine, Center for Translational Medicine, Thomas Jefferson University, Philadelphia, PA 19107.
authors.forename: Ludovic
authors.initials: L
authors.lastname: Gomez
authors.affiliation: MitoCare Center Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107.
authors.forename: Sergio
authors.initials: S
authors.lastname: De la Fuente
authors.affiliation: Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109.
authors.forename: Yan-Ting
authors.initials: YT
authors.lastname: Zhao
authors.affiliation: Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109.
authors.forename: Héctor H
authors.initials: HH
authors.lastname: Valdivia
authors.affiliation: MitoCare Center Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107.
authors.forename: György
authors.initials: G
authors.lastname: Hajnóczky
authors.affiliation: Department of Cell Developmental Biology, University of Pennsylvania, Philadelphia, PA 19104; manuelalavorato@gmail.com armstroc@mail.med.upenn.edu.
authors.forename: Clara
authors.initials: C
authors.lastname: Franzini-Armstrong
mesh_terms: D000818:Animals; D020013:Calcium Signaling / Q000502:physiology*; D056966:Excitation Contraction Coupling / Q000502:physiology; D051379:Mice; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D008929:Mitochondria, Heart / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D063154:Mitochondrial Dynamics / Q000502:physiology; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D019837:Ryanodine Receptor Calcium Release Channel / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D017180:Tachycardia, Ventricular / Q000235:genetics
chemical_list: D019837:Ryanodine Receptor Calcium Release Channel; C000592748:ryanodine receptor 2. mouse; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases
keywords: CPVT; RyR2; mitochondria; mitochondrial dynamics; nanotunnels