title: Neutrophil elastase mediates acute pathogenesis and is a determinant of long-term behavioral recovery after traumatic injury to the immature brain.
abstract: While neutrophil elastase (NE), released by activated neutrophils, is a key mediator of secondary pathogenesis in adult models of brain ischemia and spinal cord injury, no studies to date have examined this protease in the context of the injured immature brain, where there is notable vulnerability resulting from inadequate antioxidant reserves and prolonged exposure to infiltrating neutrophils. We thus reasoned that NE may be a key determinant of secondary pathogenesis, and as such, adversely influence long-term neurological recovery. To address this hypothesis, wild-type (WT) and NE knockout (KO) mice were subjected to a controlled cortical impact at post-natal day 21, approximating a toddler-aged child. To determine if NE is required for neutrophil infiltration into the injured brain, and whether this protease contributes to vasogenic edema, we quantified neutrophil numbers and measured water content in the brains of each of these genotypes. While leukocyte trafficking was indistinguishable between genotypes, vasogenic edema was markedly attenuated in the NE KO. To determine if early pathogenesis is dependent on NE, indices of cell death (TUNEL and activated caspase-3) were quantified across genotypes. NE KO mice showed a reduction in these markers of cell death in the injured hippocampus, which corresponded to greater preservation of neuronal integrity as well as reduced expression of heme oxygenase-1, a marker of oxidative stress. WT mice, treated with a competitive inhibitor of NE at 2, 6 and 12h post-injury, likewise showed a reduction in cell death and oxidative stress compared to vehicle-treated controls. We next examined the long-term behavioral and structural consequences of NE deficiency. NE KO mice showed an improvement in long-term spatial memory retention and amelioration of injury-induced hyperactivity. However, volumetric and stereological analyses found comparable tissue loss in the injured cortex and hippocampus independent of genotype. Further, WT mice treated acutely with the NE inhibitor showed no long-term behavioral or structural improvements. Together, these findings validate the central role of NE in both acute pathogenesis and chronic functional recovery, and support future exploration of the therapeutic window, taking into account the prolonged period of neutrophil trafficking into the injured immature brain.
authors.affiliation: Department of Neurological Surgery, University of California San Francisco, San Francisco, CA 94143, USA; Department of Medicine (Royal Melbourne Hospital), University of Melbourne, Parkville, VIC 3000, Australia. Electronic address: Bridgette.Semple@ucsf.edu.
authors.forename: Bridgette D
authors.initials: BD
authors.lastname: Semple
authors.affiliation: Department of Neurological Surgery, University of California San Francisco, San Francisco, CA 94143, USA. Electronic address: Alpa.Mahuvakar@ucsf.edu.
authors.forename: Alpa
authors.initials: A
authors.lastname: Trivedi
authors.affiliation: Department of Neurological Surgery, University of California San Francisco, San Francisco, CA 94143, USA. Electronic address: Kayleen.Gimlin@ucsf.edu.
authors.forename: Kayleen
authors.initials: K
authors.lastname: Gimlin
authors.affiliation: Department of Neurological Surgery, University of California San Francisco, San Francisco, CA 94143, USA; Department of Physical Therapy and Rehabilitation Sciences, University of California San Francisco, San Francisco, CA 94143, USA. Electronic address: Linda.Noble@ucsf.edu.
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Noble-Haeusslein
mesh_terms: D000208:Acute Disease; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development / Q000473:pathology; D001929:Brain Edema / Q000201:enzymology / Q000473:pathology; D001930:Brain Injuries / Q000201:enzymology* / Q000473:pathology / Q000523:psychology; D053148:Caspase 3 / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D004195:Disease Models, Animal; D051547:Heme Oxygenase-1 / Q000378:metabolism; D019272:Leukocyte Elastase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008297:Male; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology; D009504:Neutrophils / Q000201:enzymology*; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology; D011480:Protease Inhibitors / Q000494:pharmacology; D020127:Recovery of Function / Q000187:drug effects / Q000502:physiology*; D065852:Spatial Memory / Q000187:drug effects / Q000502:physiology
chemical_list: D008565:Membrane Proteins; D011480:Protease Inhibitors; D051547:Heme Oxygenase-1; C496542:Hmox1 protein, mouse; D019272:Leukocyte Elastase; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020780:Matrix Metalloproteinase 9; C501830:Mmp9 protein, mouse
keywords: Traumatic brain injury; behavior; cell death; neutrophil elastase; pathology; pediatric