title: Absence of physiological Ca2+transients is an initial trigger for mitochondrial dysfunction in skeletal muscle following denervation.
abstract: Motor neurons control muscle contraction by initiating action potentials in muscle. Denervation of muscle from motor neurons leads to muscle atrophy, which is linked to mitochondrial dysfunction. It is known that denervation promotes mitochondrial reactive oxygen species (ROS) production in muscle, whereas the initial cause of mitochondrial ROS production in denervated muscle remains elusive. Since denervation isolates muscle from motor neurons and deprives it from any electric stimulation, no action potentials are initiated, and therefore, no physiological Ca2+transients are generated inside denervated muscle fibers. We tested whether loss of physiological Ca2+transients is an initial cause leading to mitochondrial dysfunction in denervated skeletal muscle.
  
  
  
  A transgenic mouse model expressing a mitochondrial targeted biosensor (mt-cpYFP) allowed a real-time measurement of the ROS-related mitochondrial metabolic function following denervation, termed "mitoflash." Using live cell imaging, electrophysiological, pharmacological, and biochemical studies, we examined a potential molecular mechanism that initiates ROS-related mitochondrial dysfunction following denervation.
  
  
  
  We found that muscle fibers showed a fourfold increase in mitoflash activity 24 h after denervation. The denervation-induced mitoflash activity was likely associated with an increased activity of mitochondrial permeability transition pore (mPTP), as the mitoflash activity was attenuated by application of cyclosporine A. Electrical stimulation rapidly reduced mitoflash activity in both sham and denervated muscle fibers. We further demonstrated that the Ca2+level inside mitochondria follows the time course of the cytosolic Ca2+transient and that inhibition of mitochondrial Ca2+uptake by Ru360 blocks the effect of electric stimulation on mitoflash activity.
  
  
  
  The loss of cytosolic Ca2+transients due to denervation results in the downstream absence of mitochondrial Ca2+uptake. Our studies suggest that this could be an initial trigger for enhanced mPTP-related mitochondrial ROS generation in skeletal muscle.
authors.affiliation: Rush University School of Medicine, Chicago, IL, USA.
authors.forename: Chehade
authors.initials: C
authors.lastname: Karam
authors.affiliation: Rush University School of Medicine, Chicago, IL, USA.|Kansas City University of Medicine and Bioscience, 1750 Independence Ave, Kansas City, MO, 64106, USA.
authors.forename: Jianxun
authors.initials: J
authors.lastname: Yi
authors.affiliation: Rush University School of Medicine, Chicago, IL, USA.|Kansas City University of Medicine and Bioscience, 1750 Independence Ave, Kansas City, MO, 64106, USA.
authors.forename: Yajuan
authors.initials: Y
authors.lastname: Xiao
authors.affiliation: Kansas City University of Medicine and Bioscience, 1750 Independence Ave, Kansas City, MO, 64106, USA.
authors.forename: Kamal
authors.initials: K
authors.lastname: Dhakal
authors.affiliation: Rush University School of Medicine, Chicago, IL, USA.|Kansas City University of Medicine and Bioscience, 1750 Independence Ave, Kansas City, MO, 64106, USA.
authors.forename: Lin
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Kansas City University of Medicine and Bioscience, 1750 Independence Ave, Kansas City, MO, 64106, USA.
authors.forename: Xuejun
authors.initials: X
authors.lastname: Li
authors.affiliation: Rush University School of Medicine, Chicago, IL, USA.
authors.forename: Carlo
authors.initials: C
authors.lastname: Manno
authors.affiliation: Institute of Molecular Medicine, Peking University, Beijing, China.
authors.forename: Jiejia
authors.initials: J
authors.lastname: Xu
authors.affiliation: Institute of Molecular Medicine, Peking University, Beijing, China.
authors.forename: Kaitao
authors.initials: K
authors.lastname: Li
authors.affiliation: Institute of Molecular Medicine, Peking University, Beijing, China.
authors.forename: Heping
authors.initials: H
authors.lastname: Cheng
authors.affiliation: Wexner Medical Center, The Ohio State University, 460 West 12th Avenue, Columbus, OH, USA. jianjie.ma@osumc.edu.
authors.forename: Jianjie
authors.initials: J
authors.lastname: Ma
authors.affiliation: Rush University School of Medicine, Chicago, IL, USA. jzhou@kcumb.edu.|Kansas City University of Medicine and Bioscience, 1750 Independence Ave, Kansas City, MO, 64106, USA. jzhou@kcumb.edu.
authors.forename: Jingsong
authors.identifier: 0000-0002-5684-7177
authors.initials: J
authors.lastname: Zhou
mesh_terms: D000200:Action Potentials; D000818:Animals; D020013:Calcium Signaling; D056966:Excitation Contraction Coupling; D051379:Mice; D008931:Mitochondria, Muscle / Q000378:metabolism*; D009121:Muscle Denervation; D018482:Muscle, Skeletal / Q000294:innervation* / Q000378:metabolism / Q000502:physiology; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D017382:Reactive Oxygen Species
keywords: Calcium imaging; Calcium intracellular release; Calcium signaling; Denervation; E-C coupling; Mitochondria