title: Cell cycle inhibition reduces inflammatory responses, neuronal loss, and cognitive deficits induced by hypobaria exposure following traumatic brain injury.
abstract: Traumatic brain injury (TBI) patients in military settings can be exposed to prolonged periods of hypobaria (HB) during aeromedical evacuation. Hypobaric exposure, even with supplemental oxygen to prevent hypoxia, worsens outcome after experimental TBI, in part by increasing neuroinflammation. Cell cycle activation (CCA) after TBI has been implicated as a mechanism contributing to both post-traumatic cell death and neuroinflammation. Here, we examined whether hypobaric exposure in rats subjected to TBI increases CCA and microglial activation in the brain, as compared to TBI alone, and to evaluate the ability of a cyclin-dependent kinase (CDK) inhibitor (CR8) to reduce such changes and improve behavioral outcomes.
  
  
  
  Adult male Sprague Dawley rats were subjected to fluid percussion-induced injury, and HB exposure was performed at 6 h after TBI. Western blot and immunohistochemistry (IHC) were used to assess cell cycle-related protein expression and inflammation at 1 and 30 days after injury. CR8 was administered intraperitoneally at 3 h post-injury; chronic functional recovery and histological changes were assessed.
  
  
  
  Post-traumatic hypobaric exposure increased upregulation of cell cycle-related proteins (cyclin D1, proliferating cell nuclear antigen, and CDK4) and microglial/macrophage activation in the ipsilateral cortex at day 1 post-injury as compared to TBI alone. Increased immunoreactivity of cell cycle proteins, as well as numbers of Iba-1+and GFAP+cells in both the ipsilateral cortex and hippocampus were found at day 30 post-injury. TBI/HB significantly increased the numbers of NADPH oxidase 2 (gp91phox) enzyme-expressing cells that were co-localized with Iba-1+. Each of these changes was significantly reduced by the administration of CR8. Unbiased stereological assessment showed significantly decreased numbers of microglia displaying the highly activated phenotype in the ipsilateral cortex of TBI/HB/CR8 rats compared with TBI/HB/Veh rats. Moreover, treatment with this CDK inhibitor also significantly improved spatial and retention memory and reduced lesion volume and hippocampal neuronal cell loss.
  
  
  
  HB exposure following TBI increases CCA, neuroinflammation, and associated neuronal cell loss. These changes and post-traumatic cognitive deficits are reduced by CDK inhibition; such drugs may therefore serve to protect TBI patients requiring aeromedical evacuation.
authors.affiliation: Department of Anesthesiology and Center for Shock, Trauma and Anesthesiology Research (STAR), University of Maryland School of Medicine, Baltimore, MD, 21201, USA.|Research Division Pharmacology Branch, United States Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, Aberdeen, MD, 21010, USA.
authors.forename: Jacob W
authors.initials: JW
authors.lastname: Skovira
authors.affiliation: Department of Anesthesiology and Center for Shock, Trauma and Anesthesiology Research (STAR), University of Maryland School of Medicine, Baltimore, MD, 21201, USA. jwu@anes.umm.edu.
authors.forename: Junfang
authors.identifier: 0000-0003-3338-7291
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Anesthesiology and Center for Shock, Trauma and Anesthesiology Research (STAR), University of Maryland School of Medicine, Baltimore, MD, 21201, USA.
authors.forename: Jessica J
authors.initials: JJ
authors.lastname: Matyas
authors.affiliation: Department of Anesthesiology and Center for Shock, Trauma and Anesthesiology Research (STAR), University of Maryland School of Medicine, Baltimore, MD, 21201, USA.
authors.forename: Alok
authors.initials: A
authors.lastname: Kumar
authors.affiliation: Department of Anesthesiology and Center for Shock, Trauma and Anesthesiology Research (STAR), University of Maryland School of Medicine, Baltimore, MD, 21201, USA.
authors.forename: Marie
authors.initials: M
authors.lastname: Hanscom
authors.affiliation: Department of Anesthesiology and Center for Shock, Trauma and Anesthesiology Research (STAR), University of Maryland School of Medicine, Baltimore, MD, 21201, USA.
authors.forename: Shruti V
authors.initials: SV
authors.lastname: Kabadi
authors.affiliation: Program in Trauma, Center for the Sustainment of Trauma and Readiness Skills (C-STARS), University of Maryland School of Medicine, Baltimore, MD, 21201, USA.
authors.forename: Raymond
authors.initials: R
authors.lastname: Fang
authors.affiliation: Department of Anesthesiology and Center for Shock, Trauma and Anesthesiology Research (STAR), University of Maryland School of Medicine, Baltimore, MD, 21201, USA. afaden@anes.umm.edu.
authors.forename: Alan I
authors.initials: AI
authors.lastname: Faden
mesh_terms: D000818:Animals; D001274:Atmospheric Pressure; D001921:Brain / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D000070642:Brain Injuries, Traumatic / Q000188:drug therapy / Q000276:immunology / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D003072:Cognition Disorders / Q000188:drug therapy / Q000276:immunology / Q000378:metabolism*; D007249:Inflammation / Q000188:drug therapy / Q000276:immunology / Q000378:metabolism; D018836:Inflammation Mediators / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D011687:Purines / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: C532131:CR8 compound; D018836:Inflammation Mediators; D011687:Purines; D011725:Pyridines
keywords: Aeromedical evacuation; Hypobaria; Inflammation; Neuronal cell death; Traumatic brain injury