Understanding how events at the molecular and cellular scales contribute to tissue form and function is key to uncovering the mechanisms driving animal development, physiology and disease. ...Elucidating these mechanisms has been enhanced through the study of model organisms and the use of sophisticated genetic, biochemical and imaging tools. Here, we present an accessible method for non-invasive imaging of
at high resolution using micro-computed tomography (µ-CT). We show how rapid processing of intact animals, at any developmental stage, provides precise quantitative assessment of tissue size and morphology, and permits analysis of inter-organ relationships. We then use µ-CT imaging to study growth defects in the
brain through the characterization of
(
) and
(
), orthologs of the two most commonly mutated genes in human microcephaly patients. Our work demonstrates the power of combining µ-CT with traditional genetic, cellular and developmental biology tools available in model organisms to address novel biological mechanisms that control animal development and disease.
Due to their viscoelastic nature, white matter axons are susceptible to damage by high strain rates produced during traumatic brain injury (TBI). Indeed, diffuse axonal injury (DAI) is one of the ...most common features of TBI, characterized by the hallmark pathological profiles of axonal bulbs at disconnected terminal ends of axons and periodic swellings along axons, known as “varicosities.” Although transport interruption underlies axonal bulb formation, it is unclear how varicosities arise, with multiple sites accumulating transported materials along one axon. Recently, axonal microtubules have been found to physically break during dynamic stretch injury of cortical axons in vitro. Here, the same in vitro model was used in parallel with histopathological analyses of human brains acquired acutely following TBI to examine the potential role of mechanical microtubule damage in varicosity formation post-trauma. Transmission electron microscopy (TEM) following in vitro stretch injury revealed periodic breaks of individual microtubules along axons that regionally corresponded with undulations in axon morphology. However, typically less than a third of microtubules were broken in any region of an axon. Within hours, these sites of microtubule breaks evolved into periodic swellings. This suggests axonal transport may be halted along one broken microtubule, yet can proceed through the same region via other intact microtubules. Similar axonal undulations and varicosities were observed following TBI in humans, suggesting primary microtubule failure may also be a feature of DAI. These data indicate a novel mechanism of mechanical microtubule damage leading to partial transport interruption and varicosity formation in traumatic axonal injury.
► Diffuse axonal injury results in transport interruption observed as varicosities along axons. ► Using a model of axonal stretch injury the mechanism of axonal varicosity formation was examined. ► Individual microtubule breakage results in partial transport interruption and varicose swelling. ► Similar varicosities found in humans indicate primary microtubule failure may be a feature of DAI.
Biomarkers for diffuse axonal injury could have utilities for the acute diagnosis and clinical care of concussion, including those related to sports. The calpain-derived αII-spectrin N-terminal ...fragment (SNTF) accumulates in axons after traumatic injury and increases in human blood after mild traumatic brain injury (mTBI) in relation to white matter abnormalities and persistent cognitive dysfunction. However, SNTF has never been evaluated as a biomarker for sports-related concussion. Here, we conducted longitudinal analysis of serum SNTF in professional ice hockey players, 28 of whom had a concussion, along with 45 players evaluated during the preseason, 17 of whom were also tested after a concussion-free training game. Compared with preseason levels, serum SNTF increased at 1 h after concussion and remained significantly elevated from 12 h to 6 days, before declining to preseason baseline. In contrast, serum SNTF levels were unchanged after training. In 8 players, postconcussion symptoms resolved within a few days, and in these cases serum SNTF levels were at baseline. On the other hand, for the 20 players withheld from play for 6 days or longer, serum SNTF levels rose from 1 h to 6 days postconcussion, and at 12-36 h differed significantly from the less-severe concussions (p=0.004). Serum SNTF exhibited diagnostic accuracy for concussion, especially so with delayed return to play (area under the curve=0.87). Multi-variate analyses of serum SNTF and tau improved the diagnostic accuracy, the relationship with the delay in return to play, and the temporal window beyond tau alone. These results provide evidence that blood SNTF, a biomarker for axonal injury after mTBI, may be useful for diagnosis and prognosis of sports-related concussion, as well as for guiding neurobiologically informed decisions on return to play.
See Sastre et al. (doi:10.1093/brain/awy225) for a scientific commentary on this article.
Traumatic brain injury (TBI) is a risk factor for subsequent neurodegenerative disease. Zanier et al. report ...that single severe TBI induces tau pathology in humans and mice. Studies in the latter provide evidence that this pathology is self-propagating and can be transmitted between animals, causing brain dysfunction like a prion.
Abstract
Traumatic brain injury is a risk factor for subsequent neurodegenerative disease, including chronic traumatic encephalopathy, a tauopathy mostly associated with repetitive concussion and blast, but not well recognized as a consequence of severe traumatic brain injury. Here we show that a single severe brain trauma is associated with the emergence of widespread hyperphosphorylated tau pathology in a proportion of humans surviving late after injury. In parallel experimental studies, in a model of severe traumatic brain injury in wild-type mice, we found progressive and widespread tau pathology, replicating the findings in humans. Brain homogenates from these mice, when inoculated into the hippocampus and overlying cerebral cortex of naïve mice, induced widespread tau pathology, synaptic loss, and persistent memory deficits. These data provide evidence that experimental brain trauma induces a self-propagating tau pathology, which can be transmitted between mice, and call for future studies aimed at investigating the potential transmissibility of trauma associated tau pathology in humans.
Despite the large number of promising neuroprotective agents identified in experimental traumatic brain injury (TBI) studies, none has yet shown meaningful improvements in long-term outcome in ...clinical trials. To develop recommendations and guidelines for pre-clinical testing of pharmacological or biological therapies for TBI, the Moody Project for Translational Traumatic Brain Injury Research hosted a symposium attended by investigators with extensive experience in pre-clinical TBI testing. The symposium participants discussed issues related to pre-clinical TBI testing including experimental models, therapy and outcome selection, study design, data analysis, and dissemination. Consensus recommendations included the creation of a manual of standard operating procedures with sufficiently detailed descriptions of modeling and outcome measurement procedures to permit replication. The importance of the selection of clinically relevant outcome variables, especially related to behavior testing, was noted. Considering the heterogeneous nature of human TBI, evidence of therapeutic efficacy in multiple, diverse (e.g., diffuse vs. focused) rodent models and a species with a gyrencephalic brain prior to clinical testing was encouraged. Basing drug doses, times, and routes of administration on pharmacokinetic and pharmacodynamic data in the test species was recommended. Symposium participants agreed that the publication of negative results would reduce costly and unnecessary duplication of unsuccessful experiments. Although some of the recommendations are more relevant to multi-center, multi-investigator collaborations, most are applicable to pre-clinical therapy testing in general. The goal of these consensus guidelines is to increase the likelihood that therapies that improve outcomes in pre-clinical studies will also improve outcomes in TBI patients.
Traumatic brain injury (TBI) is a risk factor for dementia. Mixed neurodegenerative pathologies have been described in late survivors of TBI, but the mechanisms driving post-TBI neurodegeneration ...remain elusive. Increasingly, blood-brain barrier (BBB) disruption has been recognized in a range of neurologic disorders including dementias, but little is known of the consequences of TBI on the BBB. Autopsy cases of single moderate or severe TBI from the Glasgow TBI Archive (n = 70) were selected to include a range from acute (10 hours–13 days) to long-term (1–47 years) survival, together with age-matched uninjured controls (n = 21). Multiple brain regions were examined using immunohistochemistry for the BBB integrity markers fibrinogen and immunoglobulin G. After TBI, 40% of patients dying in the acute phase and 47% of those surviving a year or more from injury showed multifocal, abnormal, perivascular, and parenchymal fibrinogen and immunoglobulin G immunostaining localized to the gray matter, with preferential distribution toward the crests of gyri and deep neocortical layers. In contrast, when present, controls showed only limited localized immunostaining. These preliminary data demonstrate evidence of widespread BBB disruption in a proportion of TBI patients emerging in the acute phase and, intriguingly, persisting in a high proportion of late survivors.
ABSTRACTTraumatic brain injury (TBI) is a risk factor for dementia. Mixed neurodegenerative pathologies have been described in late survivors of TBI, but the mechanisms driving post-TBI ...neurodegeneration remain elusive. Increasingly, blood-brain barrier (BBB) disruption has been recognized in a range of neurologic disorders including dementias, but little is known of the consequences of TBI on the BBB. Autopsy cases of single moderate or severe TBI from the Glasgow TBI Archive (n = 70) were selected to include a range from acute (10 hours–13 days) to long-term (1–47 years) survival, together with age-matched uninjured controls (n = 21). Multiple brain regions were examined using immunohistochemistry for the BBB integrity markers fibrinogen and immunoglobulin G. After TBI, 40% of patients dying in the acute phase and 47% of those surviving a year or more from injury showed multifocal, abnormal, perivascular, and parenchymal fibrinogen and immunoglobulin G immunostaining localized to the gray matter, with preferential distribution toward the crests of gyri and deep neocortical layers. In contrast, when present, controls showed only limited localized immunostaining. These preliminary data demonstrate evidence of widespread BBB disruption in a proportion of TBI patients emerging in the acute phase and, intriguingly, persisting in a high proportion of late survivors.
Blood biomarkers have been explored for their potential to provide objective measures in the assessment of traumatic brain injury (TBI). However, it is not clear which biomarkers are best for ...diagnosis and prognosis in different severities of TBI. Here, we compare existing studies on the discriminative abilities of serum biomarkers for four commonly studied clinical situations: detecting concussion, predicting intracranial damage after mild TBI (mTBI), predicting delayed recovery after mTBI, and predicting adverse outcome after severe TBI (sTBI). We conducted a literature search of publications on biomarkers in TBI published up until July 2018. Operating characteristics were pooled for each biomarker for comparison. For detecting concussion, 4 biomarker panels and creatine kinase B type had excellent discriminative ability. For detecting intracranial injury and the need for a head CT scan after mTBI, 2 biomarker panels, and hyperphosphorylated tau had excellent operating characteristics. For predicting delayed recovery after mTBI, top candidates included calpain-derived αII-spectrin N-terminal fragment, tau A, neurofilament light, and ghrelin. For predicting adverse outcome following sTBI, no biomarker had excellent performance, but several had good performance, including markers of coagulation and inflammation, structural proteins in the brain, and proteins involved in homeostasis. The highest-performing biomarkers in each of these categories may provide insight into the pathophysiologies underlying mild and severe TBI. With further study, these biomarkers have the potential to be used alongside clinical and radiological data to improve TBI diagnostics, prognostics, and evidence-based medical management.
A single traumatic brain injury is associated with an increased risk of dementia and, in a proportion of patients surviving a year or more from injury, the development of hallmark Alzheimer's ...disease-like pathologies. However, the pathological processes linking traumatic brain injury and neurodegenerative disease remain poorly understood. Growing evidence supports a role for neuroinflammation in the development of Alzheimer's disease. In contrast, little is known about the neuroinflammatory response to brain injury and, in particular, its temporal dynamics and any potential role in neurodegeneration. Cases of traumatic brain injury with survivals ranging from 10 h to 47 years post injury (n = 52) and age-matched, uninjured control subjects (n = 44) were selected from the Glasgow Traumatic Brain Injury archive. From these, sections of the corpus callosum and adjacent parasaggital cortex were examined for microglial density and morphology, and for indices of white matter pathology and integrity. With survival of ≥3 months from injury, cases with traumatic brain injury frequently displayed extensive, densely packed, reactive microglia (CR3/43- and/or CD68-immunoreactive), a pathology not seen in control subjects or acutely injured cases. Of particular note, these reactive microglia were present in 28% of cases with survival of >1 year and up to 18 years post-trauma. In cases displaying this inflammatory pathology, evidence of ongoing white matter degradation could also be observed. Moreover, there was a 25% reduction in the corpus callosum thickness with survival >1 year post-injury. These data present striking evidence of persistent inflammation and ongoing white matter degeneration for many years after just a single traumatic brain injury in humans. Future studies to determine whether inflammation occurs in response to or, conversely, promotes white matter degeneration will be important. These findings may provide parallels for studying neurodegenerative disease, with traumatic brain injury patients serving as a model for longitudinal investigations, in particular with a view to identifying potential therapeutic interventions.
Little is known about which components of the axonal cytoskeleton might break during rapid mechanical deformation, such as occurs in traumatic brain injury. Here, we micropatterned neuronal cell ...cultures on silicone membranes to induce dynamic stretch exclusively of axon fascicles. After stretch, undulating distortions formed along the axons that gradually relaxed back to a straight orientation, demonstrating a delayed elastic response. Subsequently, swellings developed, leading to degeneration of almost all axons by 24 h. Stabilizing the microtubules with taxol maintained the undulating geometry after injury but greatly reduced axon degeneration. Conversely, destabilizing microtubules with nocodazole prevented undulations but greatly increased the rate of axon loss. Ultrastructural analyses of axons postinjury revealed immediate breakage and buckling of microtubules in axon undulations and progressive loss of microtubules. Collectively, these data suggest that dynamic stretch of axons induces direct mechanical failure at specific points along microtubules. This microtubule disorganization impedes normal relaxation of the axons, resulting in undulations. However, this physical damage also triggers progressive disassembly of the microtubules around the breakage points. While the disintegration of microtubules allows delayed recovery of the "normal" straight axon morphology, it comes at a great cost by interrupting axonal transport, leading to axonal swelling and degeneration.--Tang-Schomer, M. D., Patel, A. R,, Baas, P. W., Smith, D. H. Mechanical breaking of microtubules in axons during dynamic stretch injury underlies delayed elasticity, microtubule disassembly, and axon degeneration.
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