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Integrated Stress Response Inhibitor Reverses Sex-Dependent Behavioral and Cell-Specific Deficits after Mild Repetitive Head Trauma.

ABSTRACT: Mild repetitive traumatic brain injury (rTBI) induces chronic behavioral and cognitive alterations and increases the risk for dementia. Currently, there are no therapeutic strategies to prevent or mitigate chronic deficits associated with rTBI. Previously we developed an animal model of rTBI that recapitulates the cognitive and behavioral deficits observed in humans. We now report that rTBI results in an increase in risk-taking behavior in male but not female mice. This behavioral phenotype is associated with chronic activation of the integrated stress response and cell-specific synaptic alterations in the type A subtype of layer V pyramidal neurons in the medial prefrontal cortex. Strikingly, by briefly treating animals weeks after injury with ISRIB, a selective inhibitor of the integrated stress response (ISR), we (1) relieve ISR activation, (2) reverse the increased risk-taking behavioral phenotype and maintain this reversal, and (3) restore cell-specific synaptic function in the affected mice. Our results indicate that targeting the ISR even at late time points after injury can permanently reverse behavioral changes. As such, pharmacological inhibition of the ISR emerges as a promising avenue to combat rTBI-induced behavioral dysfunction.

SUBMITTER: Krukowski K

PROVIDER: S-EPMC7249463 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Clinical studies examining the interaction between traumatic brain injury (TBI) and stress-related disorders (e.g., post-traumatic stress disorder) are often complicated by methodological constraints, such as heterogeneity in injury type and severity, time post-trauma, and predisposing risk factors. Developing relevant animal models whereby many variables can be efficiently controlled is thus essential to understanding this elusive relationship. Here, we use our repeated unpredictable stress (RUS) paradigm, in combination with our established mouse model of repetitive mild TBI (r-mTBI), to assess the impact of repeated exposures to these paradigms on behavioral and neurobiological measures. C57BL/6J male mice were exposed to RUS and r-mTBI at 3 and 6 months of age followed by batteries of behavioral testing. Mice were euthanized 10 days and 3 months post-exposure, with brain and plasma samples collected for molecular profiling. The RUS paradigm involved exposure to a predator odor (trimethylthiazoline; TMT) while under restraint, daily unstable social housing, five inescapable footshocks on separate days, and chronic social isolation. Animals receiving r-mTBI ( × 5) and stress were exposed to a single closed-head injury 1 h after each footshock. Stress-alone mice showed significant weight loss, recall of traumatic memories, and anxiety-like and passive stress-coping behavior when compared with control mice. However, in stress+r-mTBI animals, the changes in cued fear memory, anxiety, and stress-coping tests were diminished, possibly due to TBI-induced hyperactivity. We also report complex brain molecular and neuropathological findings. Stress and r-mTBI, either individually or comorbidly, were associated with a chronic reduction in dendritic spine GluN2A/GluN2B ratio in the hippocampus. While stress augmented the r-mTBI-dependent astrogliosis in the corpus callosum, it mitigated r-mTBI-induced increases in hippocampal pro-brain-derived neurotrophic factor. We anticipate that our model will be a good platform to untangle the complex comorbid pathophysiology in stress disorders and r-mTBI.

Project description:Background and scope of reviewVarying severities and frequencies of head trauma may result in dynamic acute and chronic pathophysiologic responses in the brain. Heightened attention to long-term effects of head trauma, particularly repetitive head trauma, has sparked recent efforts to identify neuroimaging biomarkers of underlying disease processes. Imaging modalities like structural magnetic resonance imaging (MRI) and positron emission tomography (PET) are the most clinically applicable given their use in neurodegenerative disease diagnosis and differentiation. In recent years, researchers have targeted repetitive head trauma cohorts in hopes of identifying in vivo biomarkers for underlying biologic changes that might ultimately improve diagnosis of chronic traumatic encephalopathy (CTE) in living persons. These populations most often include collision sport athletes (e.g., American football, boxing) and military veterans with repetitive low-level blast exposure. We provide a clinically-oriented review of neuroimaging data from repetitive head trauma cohorts based on structural MRI, FDG-PET, Aβ-PET, and tau-PET. We supplement the review with two patient reports of neuropathology-confirmed, clinically impaired adults with prior repetitive head trauma who underwent structural MRI, FDG-PET, Aβ-PET, and tau-PET in addition to comprehensive clinical examinations before death.Review conclusionsGroup-level comparisons to controls without known head trauma have revealed inconsistent regional volume differences, with possible propensity for medial temporal, limbic, and subcortical (thalamus, corpus callosum) structures. Greater frequency and severity (i.e., length) of cavum septum pellucidum (CSP) is observed in repetitive head trauma cohorts compared to unexposed controls. It remains unclear whether CSP predicts a particular neurodegenerative process, but CSP presence should increase suspicion that clinical impairment is at least partly attributable to the individual's head trauma exposure (regardless of underlying disease). PET imaging similarly has not revealed a prototypical metabolic or molecular pattern associated with repetitive head trauma or predictive of CTE based on the most widely studied radiotracers. Given the range of clinical syndromes and neurodegenerative pathologies observed in a subset of adults with prior repetitive head trauma, structural MRI and PET imaging may still be useful for differential diagnosis (e.g., assessing suspected Alzheimer's disease).

Project description:Background and objectives: In patients who receive antiplatelet therapy (APT), the bleeding risk profile after mild head trauma (MHT) still needs clarification. Some studies have demonstrated an association with bleeding risk, whereas others have not. We studied the population of our level II emergency department (ED) trauma center to determine the risk of bleeding in patients receiving APT and whether bleeding results not from antiplatelet agents but rather from age. We assessed the bleeding risk, the incidence of intracranial hemorrhage (ICH) that necessitated hospitalization for observation, the need for cranial neurosurgery, the severity of the patient's condition at discharge, and the frequency of ED revisits for head trauma in patients receiving APT. Materials and Methods: This retrospective single-center study included 483 patients receiving APT who were in the ED for MHT in 2019. The control group consisted of 1443 patients in the ED with MHT over the same period who were not receiving APT or anticoagulant therapy. Our ED diagnostic therapeutic protocol mandates both triage and the medical examination to identify patients with MHT who are taking any anticoagulant or APT. Results: APT was not significantly associated with bleeding risk (p > 0.05); as a risk factor, age was significantly associated with the risk of bleeding, even after adjustment for therapy. Patients receiving APT had a greater need of surgery (1.2% vs. 0.4%; p < 0.0001) and a higher rate of hospitalization (52.9% vs. 37.4%; p < 0.0001), and their clinical condition was more severe (evaluated according to the exit code value on a one-dimensional quantitative five-point numerical scale) at the time of discharge (p = 0.013). The frequency of ED revisits due to head trauma did not differ between the two groups. Conclusions: The risk of bleeding in patients receiving APT who had MHT was no higher than that in the control group. However, the clinical condition of patients receiving APT, including hospital admission for ICH monitoring and cranial neurosurgical interventions, was more severe.

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Integrated Stress Response Inhibitor Reverses Sex-Dependent Behavioral and Cell-Specific Deficits after Mild Repetitive Head Trauma.

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