title: Reversible Disruption of Neuronal Mitochondria by Ischemic and Traumatic Injury Revealed by Quantitative Two-Photon Imaging in the Neocortex of Anesthetized Mice.
abstract: Mitochondria play a variety of functional roles in cortical neurons, from metabolic support and neuroprotection to the release of cytokines that trigger apoptosis. In dendrites, mitochondrial structure is closely linked to their function, and fragmentation (fission) of the normally elongated mitochondria indicates loss of their function under pathological conditions, such as stroke and brain trauma. Using in vivo two-photon microscopy in mouse brain, we quantified mitochondrial fragmentation in a full spectrum of cortical injuries, ranging from severe to mild. Severe global ischemic injury was induced by bilateral common carotid artery occlusion, whereas severe focal stroke injury was induced by Rose Bengal photosensitization. The moderate and mild traumatic injury was inflicted by focal laser lesion and by mild photo-damage, respectively. Dendritic and mitochondrial structural changes were tracked longitudinally using transgenic mice expressing fluorescent proteins localized either in cytosol or in mitochondrial matrix. In response to severe injury, mitochondrial fragmentation developed in parallel with dendritic damage signified by dendritic beading. Reconstruction from serial section electron microscopy confirmed mitochondrial fragmentation. Unlike dendritic beading, fragmentation spread beyond the injury core in focal stroke and focal laser lesion models. In moderate and mild injury, mitochondrial fragmentation was reversible with full recovery of structural integrity after 1-2 weeks. The transient fragmentation observed in the mild photo-damage model was associated with changes in dendritic spine density without any signs of dendritic damage. Our findings indicate that alterations in neuronal mitochondria structure are very sensitive to the tissue damage and can be reversible in ischemic and traumatic injuries.
  
  
  
  During ischemic stroke or brain trauma, mitochondria can either protect neurons by supplying ATP and adsorbing excessive Ca2+, or kill neurons by releasing proapoptotic factors. Mitochondrial function is tightly linked to their morphology: healthy mitochondria are thin and long; dysfunctional mitochondria are thick (swollen) and short (fragmented). To date, fragmentation of mitochondria was studied either in dissociated cultured neurons or in brain slices, but not in the intact living brain. Using real-time in vivo two-photon microscopy, we quantified mitochondrial fragmentation during acute pathological conditions that mimic severe, moderate, and mild brain injury. We demonstrated that alterations in neuronal mitochondria structural integrity can be reversible in traumatic and ischemic injuries, highlighting mitochondria as a potential target for therapeutic interventions.
authors.affiliation: Neuroscience Center, University of Helsinki, Helsinki, Finland FI-00014.
authors.forename: Mikhail
authors.identifier: 0000-0002-5447-8881
authors.initials: M
authors.lastname: Kislin
authors.affiliation: Brain and Behavior Discovery Institute and.
authors.forename: Jeremy
authors.identifier: 0000-0001-7303-6010
authors.initials: J
authors.lastname: Sword
authors.affiliation: Department of Neurosurgery, Medical College of Georgia at Augusta University, Augusta, Georgia 30912.
authors.forename: Ioulia V
authors.initials: IV
authors.lastname: Fomitcheva
authors.affiliation: Brain and Behavior Discovery Institute and.
authors.forename: Deborah
authors.initials: D
authors.lastname: Croom
authors.affiliation: Neuroscience Center, University of Helsinki, Helsinki, Finland FI-00014.|Neurotar Ltd, Helsinki, Finland FI-00790.
authors.forename: Evgeny
authors.initials: E
authors.lastname: Pryazhnikov
authors.affiliation: Laboratory of Biosystem Dynamics, Department of Signal Processing, Tampere University of Technology, Tampere, Finland FI-33101, and.
authors.forename: Eero
authors.initials: E
authors.lastname: Lihavainen
authors.affiliation: Neurotar Ltd, Helsinki, Finland FI-00790.
authors.forename: Dmytro
authors.initials: D
authors.lastname: Toptunov
authors.affiliation: Neuroscience Center, University of Helsinki, Helsinki, Finland FI-00014.
authors.forename: Heikki
authors.identifier: 0000-0001-7809-9811
authors.initials: H
authors.lastname: Rauvala
authors.affiliation: Laboratory of Biosystem Dynamics, Department of Signal Processing, Tampere University of Technology, Tampere, Finland FI-33101, and.
authors.forename: Andre S
authors.identifier: 0000-0002-7255-5211
authors.initials: AS
authors.lastname: Ribeiro
authors.affiliation: Neuroscience Center, University of Helsinki, Helsinki, Finland FI-00014, leonard.khirug@helsinki.fi skirov13@gmail.com.|Neurotar Ltd, Helsinki, Finland FI-00790.
authors.forename: Leonard
authors.initials: L
authors.lastname: Khiroug
authors.affiliation: Brain and Behavior Discovery Institute and leonard.khirug@helsinki.fi skirov13@gmail.com.|Department of Neurosurgery, Medical College of Georgia at Augusta University, Augusta, Georgia 30912.
authors.forename: Sergei A
authors.identifier: 0000-0003-0105-0694
authors.initials: SA
authors.lastname: Kirov
mesh_terms: D000758:Anesthesia / Q000379:methods; D000818:Animals; D001930:Brain Injuries / Q000000981:diagnostic imaging* / Q000378:metabolism; D002545:Brain Ischemia / Q000000981:diagnostic imaging* / Q000378:metabolism; D003712:Dendrites / Q000378:metabolism / Q000473:pathology; D005260:Female; D005456:Fluorescent Dyes / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods; D008928:Mitochondria / Q000378:metabolism / Q000473:pathology*; D019579:Neocortex / Q000000981:diagnostic imaging* / Q000378:metabolism; D009474:Neurons / Q000378:metabolism / Q000473:pathology*
chemical_list: D005456:Fluorescent Dyes
keywords: brain trauma; dendrite; mitochondria; stroke; structural dynamics; two-photon in vivo imaging