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Rapid neuroinflammatory response localized to injured neurons after diffuse traumatic brain injury in swine.

ABSTRACT: Despite increasing appreciation of the critical role that neuroinflammatory pathways play in brain injury and neurodegeneration, little is known about acute microglial reactivity following diffuse traumatic brain injury (TBI) - the most common clinical presentation that includes all concussions. Therefore, we investigated acute microglial reactivity using a porcine model of closed-head rotational velocity/acceleration-induced TBI that closely mimics the biomechanical etiology of inertial TBI in humans. We observed rapid microglial reactivity within 15min of both mild and severe TBI. Strikingly, microglial activation was restrained to regions proximal to individual injured neurons - as denoted by trauma-induced plasma membrane disruption - which served as epicenters of acute reactivity. Single-cell quantitative analysis showed that in areas free of traumatically permeabilized neurons, microglial density and morphology were similar between sham or following mild or severe TBI. However, microglia density increased and morphology shifted to become more reactive in proximity to injured neurons. Microglial reactivity around injured neurons was exacerbated following repetitive TBI, suggesting further amplification of acute neuroinflammatory responses. These results indicate that neuronal trauma rapidly activates microglia in a highly localized manner, and suggest that activated microglia may rapidly influence neuronal stability and/or pathophysiology after diffuse TBI.

SUBMITTER: Wofford KL

PROVIDER: S-EPMC5529036 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Rapid neuroinflammatory response localized to injured neurons after diffuse traumatic brain injury in swine.

Wofford Kathryn L KL Harris James P JP Browne Kevin D KD Brown Daniel P DP Grovola Michael R MR Mietus Constance J CJ Wolf John A JA Duda John E JE Putt Mary E ME Spiller Kara L KL Cullen D Kacy DK

Experimental neurology 20170109

Despite increasing appreciation of the critical role that neuroinflammatory pathways play in brain injury and neurodegeneration, little is known about acute microglial reactivity following diffuse traumatic brain injury (TBI) - the most common clinical presentation that includes all concussions. Therefore, we investigated acute microglial reactivity using a porcine model of closed-head rotational velocity/acceleration-induced TBI that closely mimics the biomechanical etiology of inertial TBI in ...[more]

PMID: 28081963

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Project description:BackgroundNo agents that are specifically neuroprotective are currently approved to emergently treat patients with traumatic brain injury (TBI). The histone deacetylase inhibitor, high-dose valproic acid (VPA) has been shown to have cytoprotective potential in models of combined TBI and hemorrhagic shock, but it has not been tested in an isolated TBI model. We hypothesized that VPA, administered after isolated TBI, will penetrate the injured brain, attenuate the lesion size, and activate prosurvival pathways.MethodsYorkshire swine were subjected to severe TBI by cortical impact. One hour later, animals were randomized to VPA treatment (150 mg/kg delivered intravenously for 1 hour; n = 4) or control (saline vehicle; n = 4) groups. Seven hours after injury, animals were sacrificed, and brain lesion size was measured. Mass spectrometry imaging was used to visualize and quantitate brain tissue distribution of VPA. Sequential serum samples were assayed for key biomarkers and subjected to proteomic and pathway analysis.ResultsBrain lesion size was 50% smaller (p = 0.01) in the VPA-treated animals (3,837 ± 948 mm) compared with the controls (1,900 ± 614 mm). Endothelial regions had eightfold higher VPA concentrations than perivascular regions by mass spectrometry imaging, and it readily penetrated the injured brain tissues. Serum glial fibrillary acid protein was significantly lower in the VPA-treated compared with the control animals (p < 0.05). More than 500 proteins were differentially expressed in the brain, and pathway analysis revealed that VPA affected critical modulators of TBI response including calcium signaling pathways, mitochondria metabolism, and biosynthetic machinery.ConclusionValproic acid penetrates injured brain tissues and exerts neuroprotective and prosurvival effects that resulted in a significant reduction in brain lesion size after isolated TBI. Levels of serum biomarkers reflect these changes, which could be useful for monitoring the response of TBI patients during clinical studies.

Project description:BackgroundTraumatic brain injury (TBI) is a major risk factor for the development of multiple neurodegenerative diseases, including Alzheimer's disease (AD) and numerous recent reports document the development of dementia after TBI. Age is a significant factor in both the risk of and the incidence of acquired brain injury. TBI-induced inflammatory response is associated with activation of brain resident microglia and accumulation of infiltrating monocytes, which plays a pivotal role in chronic neurodegeneration and loss of neurological function after TBI. Despite the extensive clinical evidence implicating neuroinflammation with the TBI-related sequelae, the specific role of these different myeloid cells and the influence of age on TBI-initiated innate immune response remain unknown and poorly studied.MethodsWe used gene profiling and pathway analysis to define the effect of age on inflammatory response at the time of injury. The recruitment of peripheral CCR2(+) macrophages was delineated using the CX3CR1 (GFP/+) CCR2 (RFP/+) reporter mouse. These responses were examined in the context of CCR2/5 antagonism using cenicriviroc.ResultsUnsupervised gene clustering and pathway analysis revealed that age predisposes exacerbated inflammatory response related to the recruitment and activation of peripheral monocytes to the injured brain. Using a unique reporter animal model able to discriminate resident versus peripherally derived myeloid cells, we demonstrate that in the aged brain, there is an increased accumulation of peripherally derived CCR2(+) macrophages after TBI compared to young animals. Exaggerated recruitment of this population of cells was associated with an augmented inflammatory response in the aged TBI animals. Targeting this cellular response with cenicriviroc, a dual CCR2/5 antagonist, significantly ameliorated injury-induced sequelae in the aged TBI animals.ConclusionsImportantly, these findings demonstrate that peripheral monocytes play a non-redundant and contributing role to the etiology of trauma-induced inflammatory sequelae in the aged brain.

Project description:BACKGROUND:Diffuse traumatic brain injury (TBI) is known to lead to microstructural changes within both white and grey matter detected in vivo with diffusion tensor imaging (DTI). Numerous studies have shown alterations in fractional anisotropy (FA) and mean diffusivity (MD) within prominent white matter tracts, but few have linked these to changes within the grey matter with confirmation via histological assessment. This is especially important as alterations in the grey matter may be predictive of long-term functional deficits. METHODS:A total of 33 male Sprague Dawley rats underwent severe closed-head TBI. Eight animals underwent tensor-based morphometry (TBM) and DTI at baseline (pre-TBI), 24 hours (24 h), 7, 14, and 30 days post-TBI. Immunohistochemical analysis for the detection of ionised calcium-binding adaptor molecule 1 (IBA1) to assess microglia number and percentage of activated cells, ?-amyloid precursor protein (APP) as a marker of axonal injury, and myelin basic protein (MBP) to investigate myelination was performed at each time-point. RESULTS:DTI showed significant alterations in FA and RD in numerous white matter tracts including the corpus callosum, internal and external capsule, and optic tract and in the grey-matter in the cortex, thalamus, and hippocampus, with the most significant effects observed at 14 D post-TBI. TBM confirmed volumetric changes within the hippocampus and thalamus. Changes in DTI were in line with significant axonal injury noted at 24 h post-injury via immunohistochemical analysis of APP, with widespread microglial activation seen within prominent white matter tracts and the grey matter, which persisted to 30 D within the hippocampus and thalamus. Microstructural alterations in MBP+ve fibres were also noted within the hippocampus and thalamus, as well as the cortex. CONCLUSION:This study confirms the widespread effects of diffuse TBI on white matter tracts which could be detected via DTI and extends these findings to key grey matter regions, with a comprehensive investigation of the whole brain. In particular, the hippocampus and thalamus appear to be vulnerable to ongoing pathology post-TBI, with DTI able to detect these alterations supporting the clinical utility in evaluating these regions post-TBI.

Project description:BackgroundNeuroinflammation following traumatic brain injury (TBI) has been shown to be associated with secondary injury development; however, how systemic inflammatory mediators affect this is not fully understood. The aim of this study was to see how systemic inflammation affects markers of neuroinflammation, if this inflammatory response had a temporal correlation between compartments and how different compartments differ in cytokine composition.MethodsTBI patients recruited to a previous randomised controlled trial studying the effects of the drug anakinra (Kineret®), a human recombinant interleukin-1 receptor antagonist (rhIL1ra), were used (n = 10 treatment arm, n = 10 control arm). Cytokine concentrations were measured in arterial and jugular venous samples twice a day, as well as in microdialysis-extracted brain extracellular fluid (ECF) following pooling every 6 h. C-reactive protein level (CRP), white blood cell count (WBC), temperature and confirmed systemic clinical infection were used as systemic markers of inflammation. Principal component analyses, linear mixed-effect models, cross-correlations and multiple factor analyses were used.ResultsJugular and arterial blood held similar cytokine information content, but brain-ECF was markedly different. No clear arterial to jugular gradient could be seen. No substantial delayed temporal associations between blood and brain compartments were detected. The development of a systemic clinical infection resulted in a significant decrease of IL1-ra, G-CSF, PDGF-ABBB, MIP-1b and RANTES (p < 0.05, respectively) in brain-ECF, even if adjusting for injury severity and demographic factors, while an increase in several cytokines could be seen in arterial blood.ConclusionsSystemic inflammation, and infection in particular, alters cytokine levels with different patterns seen in brain and in blood. Cerebral inflammatory monitoring provides independent information from arterial and jugular samples, which both demonstrate similar information content. These findings could present potential new treatment options in severe TBI patients, but novel prospective trials are warranted to confirm these associations.

Dataset Information

Rapid neuroinflammatory response localized to injured neurons after diffuse traumatic brain injury in swine.

Publications

Rapid neuroinflammatory response localized to injured neurons after diffuse traumatic brain injury in swine.

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