title: Peripheral Blood Mitochondrial DNA as a Biomarker of Cerebral Mitochondrial Dysfunction following Traumatic Brain Injury in a Porcine Model.
abstract: BACKGROUND
  Traumatic brain injury (TBI) has been shown to activate the peripheral innate immune system and systemic inflammatory response, possibly through the central release of damage associated molecular patterns (DAMPs). Our main purpose was to gain an initial understanding of the peripheral mitochondrial response following TBI, and how this response could be utilized to determine cerebral mitochondrial bioenergetics. We hypothesized that TBI would increase peripheral whole blood relative mtDNA copy number, and that these alterations would be associated with cerebral mitochondrial bioenergetics triggered by TBI.
  
  
  METHODS
  Blood samples were obtained before, 6 h after, and 25 h after focal (controlled cortical impact injury: CCI) and diffuse (rapid non-impact rotational injury: RNR) TBI. PCR primers, unique to mtDNA, were identified by aligning segments of nuclear DNA (nDNA) to mtDNA, normalizing values to nuclear 16S rRNA, for a relative mtDNA copy number. Three unique mtDNA regions were selected, and PCR primers were designed within those regions, limited to 25-30 base pairs to further ensure sequence specificity, and measured utilizing qRT-PCR.
  
  
  RESULTS
  Mean relative mtDNA copy numbers increased significantly at 6 and 25 hrs after following both focal and diffuse traumatic brain injury. Specifically, the mean relative mtDNA copy number from three mitochondrial-specific regions pre-injury was 0.84 ± 0.05. At 6 and 25 h after diffuse non-impact TBI, mean mtDNA copy number was significantly higher: 2.07 ± 0.19 (P < 0.0001) and 2.37 ± 0.42 (P < 0.001), respectively. Following focal impact TBI, relative mtDNA copy number was also significantly higher, 1.35 ± 0.12 (P < 0.0001) at 25 hours. Alterations in mitochondrial respiration in the hippocampus and cortex post-TBI correlated with changes in the relative mtDNA copy number measured in peripheral blood.
  
  
  CONCLUSIONS
  Alterations in peripheral blood relative mtDNA copy numbers may be a novel biosignature of cerebral mitochondrial bioenergetics with exciting translational potential for non-invasive diagnostic and interventional studies.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Children's Hospital of Philadelphia, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
authors.forename: Todd J
authors.initials: TJ
authors.lastname: Kilbaugh
authors.affiliation: Center for Mitochondrial and Epigenomic Medicine, Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
authors.forename: Maria
authors.initials: M
authors.lastname: Lvova
authors.affiliation: Mitochondrial Medicine, Department of Clinical Sciences, Lund University, Lund, Sweden.
authors.forename: Michael
authors.initials: M
authors.lastname: Karlsson
authors.affiliation: Center for Mitochondrial and Epigenomic Medicine, Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Center for Mitochondrial and Epigenomic Medicine, Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Leipzig
authors.affiliation: Center for Mitochondrial and Epigenomic Medicine, Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Wallace
authors.affiliation: Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
authors.forename: Susan S
authors.initials: SS
authors.lastname: Margulies
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000097:blood*; D001930:Brain Injuries / Q000150:complications*; D019295:Computational Biology; D017931:DNA Primers / Q000235:genetics; D004272:DNA, Mitochondrial / Q000097:blood* / Q000235:genetics; D004734:Energy Metabolism / Q000502:physiology*; D028361:Mitochondrial Diseases / Q000175:diagnosis* / Q000209:etiology*; D060888:Real-Time Polymerase Chain Reaction; D018709:Statistics, Nonparametric; D013552:Swine
chemical_list: D015415:Biomarkers; D017931:DNA Primers; D004272:DNA, Mitochondrial