title: Effect of nicotinamide mononucleotide on brain mitochondrial respiratory deficits in an Alzheimer's disease-relevant murine model.
abstract: BACKGROUND
  Mitochondrial dysfunction is a hallmark of neurodegenerative diseases including Alzheimer's disease (AD), with morphological and functional abnormalities limiting the electron transport chain and ATP production. A contributing factor of mitochondrial abnormalities is loss of nicotinamide adenine dinucleotide (NAD), an important cofactor in multiple metabolic reactions. Depletion of mitochondrial and consequently cellular NAD(H) levels by activated NAD glycohydrolases then culminates in bioenergetic failure and cell death. De Novo NAD(+) synthesis from tryptophan requires a multi-step enzymatic reaction. Thus, an alternative strategy to maintain cellular NAD(+) levels is to administer NAD(+) precursors facilitating generation via a salvage pathway. We administered nicotinamide mononucleotide (NMN), an NAD(+) precursor to APP(swe)/PS1(ΔE9) double transgenic (AD-Tg) mice to assess amelioration of mitochondrial respiratory deficits. In addition to mitochondrial respiratory function, we examined levels of full-length mutant APP, NAD(+)-dependent substrates (SIRT1 and CD38) in homogenates and fission/fusion proteins (DRP1, OPA1 and MFN2) in mitochondria isolated from brain. To examine changes in mitochondrial morphology, bigenic mice possessing a fluorescent protein targeted to neuronal mitochondria (CaMK2a-mito/eYFP), were administered NMN.
  
  
  METHODS
  Mitochondrial oxygen consumption rates were examined in N2A neuroblastoma cells and non-synaptic brain mitochondria isolated from mice (3 months). Western blotting was utilized to assess APP, SIRT1, CD38, DRP1, OPA1 and MFN2 in brain of transgenic and non-transgenic mice (3-12 months). Mitochondrial morphology was assessed with confocal microscopy. One-way or two-way analysis of variance (ANOVA) and post-hoc Holm-Sidak method were used for statistical analyses of data. Student t-test was used for direct comparison of two groups.
  
  
  RESULTS
  We now demonstrate that mitochondrial respiratory function was restored in NMN-treated AD-Tg mice. Levels of SIRT1 and CD38 change with age and NMN treatment. Furthermore, we found a shift in dynamics from fission to fusion proteins in the NMN-treated mice.
  
  
  CONCLUSIONS
  This is the first study to directly examine amelioration of NAD(+) catabolism and changes in mitochondrial morphological dynamics in brain utilizing the immediate precursor NMN as a potential therapeutic compound. This might lead to well-defined physiologic abnormalities that can serve an important role in the validation of promising agents such as NMN that target NAD(+) catabolism preserving mitochondrial function.
authors.affiliation: Research Service, VAMHCS, 10 North Greene Street, Baltimore, MD, 21201, USA. Aaron.Long@va.gov.|Department of Neurology, University of Maryland, School of Medicine, Baltimore, MD, 21201, USA. Aaron.Long@va.gov.
authors.forename: Aaron N
authors.initials: AN
authors.lastname: Long
authors.affiliation: Research Service, VAMHCS, 10 North Greene Street, Baltimore, MD, 21201, USA. kowens@anes.umm.edu.
authors.forename: Katrina
authors.initials: K
authors.lastname: Owens
authors.affiliation: Program in Neuroscience and Cognitive Sciences, University of Maryland, College Park, MD, 20742, USA. aschlapp@umd.edu.|Present address: Department of Neurotrauma, Henry M. Jackson Foundation, Naval Medical Research Center, Silver Spring, MD, 20910, USA. aschlapp@umd.edu.
authors.forename: Anna E
authors.initials: AE
authors.lastname: Schlappal
authors.affiliation: Research Service, VAMHCS, 10 North Greene Street, Baltimore, MD, 21201, USA. tkristian@anes.umm.edu.|Department of Anesthesiology, Center for Shock, Trauma and Anesthesiology Research, School of Medicine, Baltimore, MD, 21201, USA. tkristian@anes.umm.edu.
authors.forename: Tibor
authors.initials: T
authors.lastname: Kristian
authors.affiliation: Department of Neurology, University of Maryland, School of Medicine, Baltimore, MD, 21201, USA. Paul.Fishman@va.gov.|Neurology Service, VAMHCS, Baltimore, MD, 21201, USA. Paul.Fishman@va.gov.
authors.forename: Paul S
authors.initials: PS
authors.lastname: Fishman
authors.affiliation: Research Service, VAMHCS, 10 North Greene Street, Baltimore, MD, 21201, USA. rschuh@som.umaryland.edu.|Department of Neurology, University of Maryland, School of Medicine, Baltimore, MD, 21201, USA. rschuh@som.umaryland.edu.
authors.forename: Rosemary A
authors.initials: RA
authors.lastname: Schuh
mesh_terms: D000544:Alzheimer Disease / Q000188:drug therapy* / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism / Q000473:pathology*; D005260:Female; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008928:Mitochondria / Q000473:pathology*; D009243:NAD / Q000378:metabolism; D019636:Neurodegenerative Diseases / Q000503:physiopathology; D009537:Nicotinamide Mononucleotide / Q000494:pharmacology*; D010101:Oxygen Consumption / Q000502:physiology
chemical_list: D009243:NAD; D009537:Nicotinamide Mononucleotide