title: Alterations in mammalian target of rapamycin signaling pathways after traumatic brain injury.
abstract: In response to traumatic brain injury (TBI), neurons initiate neuroplastic processes through the activation of intracellular signaling pathways. However, the molecular mechanisms underlying neuroplasticity after TBI are poorly understood. To study this, we utilized the fluid-percussion brain injury (FPI) model to investigate alterations in the mammalian target of rapamycin (mTOR) signaling pathways in response to TBI. Mammalian target of rapamycin stimulates mRNA translation through phosphorylation of eukaryotic initiation factor 4E binding protein-1 (4E-BP1), p70 ribosomal S6 kinase (p70S6K), and ribosomal protein S6 (rpS6). These pathways coordinate cell growth and neuroplasticity via dendritic protein synthesis. Rats received sham surgery or moderate parasagittal FPI on the right side of the parietal cortex, followed by 15 mins, 30 mins, 4 h, 24 h, or 72 h of recovery. Using Western blot analysis, we found that mTOR, p70S6K, rpS6, and 4E-BP1 phosphorylation levels were significantly increased in the ipsilateral parietal cortex and hippocampus from 30 mins to 24 h after TBI, whereas total protein levels were unchanged. Using confocal microscopy to localize these changes, we found that rpS6 phosphorylation was increased in the parietal cortex and all subregions of the hippocampus. In accordance with these results, eIF4E, a key, rate-limiting mRNA translation factor, was also phosphorylated by mitogen-activated protein kinase-interacting kinase 1 (Mnk1) 15 mins after TBI. Together, these results suggest that changes in mRNA translation may be one mechanism that neurons use to respond to trauma and may contribute to the neuroplastic changes observed after TBI.
authors.affiliation: The Neurochemistry Laboratory of Brain Injury, Department of Neurology, University of Miami Miller School of Medicine, Miami, Florida 33136, USA.
authors.forename: Shaoyi
authors.initials: S
authors.lastname: Chen
authors.forename: Coleen M
authors.initials: CM
authors.lastname: Atkins
authors.forename: Chunli L
authors.initials: CL
authors.lastname: Liu
authors.forename: Ofelia F
authors.initials: OF
authors.lastname: Alonso
authors.forename: W Dalton
authors.initials: WD
authors.lastname: Dietrich
authors.forename: Bingren R
authors.initials: BR
authors.lastname: Hu
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001930:Brain Injuries / Q000503:physiopathology*; D002352:Carrier Proteins / Q000378:metabolism; D003712:Dendrites / Q000473:pathology* / Q000648:ultrastructure; D006624:Hippocampus / Q000473:pathology* / Q000648:ultrastructure; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D018613:Microscopy, Confocal; D009473:Neuronal Plasticity / Q000502:physiology*; D010750:Phosphoproteins / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D019893:Ribosomal Protein S6 Kinases / Q000096:biosynthesis / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology*; D013347:Subcellular Fractions / Q000378:metabolism; D013569:Synapses / Q000473:pathology*; D058570:TOR Serine-Threonine Kinases
chemical_list: D002352:Carrier Proteins; C499526:Eif4ebp1 protein, rat; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger; D011494:Protein Kinases; C546845:mTOR protein, rat; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases