title: Synaptic mitochondria: a brain mitochondria cluster with a specific proteome.
abstract: The synapse is a particularly important compartment of neurons. To reveal its molecular characteristics we isolated whole brain synaptic (sMito) and non-synaptic mitochondria (nsMito) from the mouse brain with purity validated by electron microscopy and fluorescence activated cell analysis and sorting. Two-dimensional differential gel electrophoresis and mass spectrometry based proteomics revealed 22 proteins with significantly higher and 34 proteins with significantly lower levels in sMito compared to nsMito. Expression differences in some oxidative stress related proteins, such as superoxide dismutase [Mn] (Sod2) and complement component 1Q subcomponent-binding protein (C1qbp), as well as some tricarboxylic acid cycle proteins, including isocitrate dehydrogenase subunit alpha (Idh3a) and ATP-forming β subunit of succinyl-CoA ligase (SuclA2), were verified by Western blot, the latter two also by immunohistochemistry. The data suggest altered tricarboxylic acid metabolism in energy supply of synapse while the marked differences in Sod2 and C1qbp support high sensitivity of synapses to oxidative stress. Further functional clustering demonstrated that proteins with higher synaptic levels are involved in synaptic transmission, lactate and glutathione metabolism. In contrast, mitochondrial proteins associated with glucose, lipid, ketone metabolism, signal transduction, morphogenesis, protein synthesis and transcription were enriched in nsMito. Altogether, the results suggest a specifically tuned composition of synaptic mitochondria.
  
  
  CONCLUSIONS
  Neurons communicate with each other through synapse, a compartment metabolically isolated from the cell body. Mitochondria are concentrated in presynaptic terminals by active transport to provide energy supply for information transfer. Mitochondrial composition in the synapse may be different than in the cell body as some examples have demonstrated altered mitochondrial composition with cell type and cellular function in the muscle, heart and liver. Therefore, we posed the question whether protein composition of synaptic mitochondria reflects its specific functions. The determined protein difference pattern was in accordance with known functional specialties of high demand synaptic mitochondria. The data also suggest specifically tuned metabolic fluxes for energy production by means of interaction with glial cells surrounding the synapse. These findings provide possible mechanisms for dynamically adapting synaptic mitochondrial output to actual demand. In turn, an increased vulnerability of synaptic mitochondria to oxidative stress is implied by the data. This is important from theoretical but potentially also from therapeutic aspects. Mitochondria are known to be affected in some neurodegenerative and psychiatric disorders, and proteins with elevated level in synaptic mitochondria, e.g. C1qbp represent targets for future drug development, by which synaptic and non-synaptic mitochondria can be differentially affected.
authors.affiliation: MTA-ELTE NAP Laboratory of Molecular and Systems Neurobiology, Institute of Biology, Hungarian Academy of Sciences and Eötvös Loránd University, Budapest H-1117, Hungary; Laboratory of Proteomics, Institute of Biology, Eötvös Loránd University, Budapest H-1117, Hungary.
authors.forename: Katalin
authors.initials: K
authors.lastname: Völgyi
authors.affiliation: Laboratory of Proteomics, Institute of Biology, Eötvös Loránd University, Budapest H-1117, Hungary; MTA-TTK NAP MS Neuroproteomics Research Group, Hungarian Academy of Sciences, Budapest H-1117, Hungary.
authors.forename: Péter
authors.initials: P
authors.lastname: Gulyássy
authors.affiliation: Laboratory of Proteomics, Institute of Biology, Eötvös Loránd University, Budapest H-1117, Hungary.
authors.forename: Krisztina
authors.initials: K
authors.lastname: Háden
authors.affiliation: Department of Anatomy, Cell and Developmental Biology, Eötvös Loránd University, H-1117 Budapest, Hungary.
authors.forename: Viktor
authors.initials: V
authors.lastname: Kis
authors.affiliation: Laboratory of Proteomics, Institute of Biology, Eötvös Loránd University, Budapest H-1117, Hungary.
authors.forename: Kata
authors.initials: K
authors.lastname: Badics
authors.affiliation: Laboratory of Proteomics, Institute of Biology, Eötvös Loránd University, Budapest H-1117, Hungary; Department of Physiology and Neurobiology, Eötvös Loránd University, Budapest H-1117, Hungary.
authors.forename: Katalin Adrienna
authors.initials: KA
authors.lastname: Kékesi
authors.affiliation: Laboratory of Proteomics, Institute of Biology, Eötvös Loránd University, Budapest H-1117, Hungary.
authors.forename: Attila
authors.initials: A
authors.lastname: Simor
authors.affiliation: Laboratory of Proteomics, Institute of Biology, Eötvös Loránd University, Budapest H-1117, Hungary.
authors.forename: Balázs
authors.initials: B
authors.lastname: Györffy
authors.affiliation: Department of Immunology, Eötvös Loránd University, Budapest H-1117, Hungary; Faculty of Science Research and Instrument Core Facility (ELTE FS-RICF), Eötvös Loránd University, Budapest H-1117, Hungary.
authors.forename: Eszter Angéla
authors.initials: EA
authors.lastname: Tóth
authors.affiliation: Department of Pediatrics, Medical University of Vienna, Vienna A-1090, Austria.
authors.forename: Gert
authors.initials: G
authors.lastname: Lubec
authors.affiliation: Laboratory of Proteomics, Institute of Biology, Eötvös Loránd University, Budapest H-1117, Hungary; MTA-TTK NAP MS Neuroproteomics Research Group, Hungarian Academy of Sciences, Budapest H-1117, Hungary.
authors.forename: Gábor
authors.initials: G
authors.lastname: Juhász
authors.affiliation: MTA-ELTE NAP Laboratory of Molecular and Systems Neurobiology, Institute of Biology, Hungarian Academy of Sciences and Eötvös Loránd University, Budapest H-1117, Hungary. Electronic address: dobolyia@caesar.elte.hu.
authors.forename: Arpád
authors.initials: A
authors.lastname: Dobolyi
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000648:ultrastructure*; D051379:Mice; D008807:Mice, Inbred BALB C; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D013569:Synapses / Q000378:metabolism* / Q000648:ultrastructure*
chemical_list: D024101:Mitochondrial Proteins; D009419:Nerve Tissue Proteins
keywords: Brain metabolism; Citric acid cycle; Functional clustering; Mass spectrometry; Synaptic mitochondria; Two-dimensional differential gel electrophoresis