Age-Dependent Alterations in the Interactions of NF-κB and N-myc with GLT-1/EAAT2 Promoter in the Pericontusional Cortex of Mice Subjected to Traumatic Brain Injury

Metabolic dysfunction contributes to mood disorders after traumatic brain injury

Traumatic brain injury (TBI) presents significant risks concerning mortality and morbidity. Individuals who suffer from TBI may exhibit mood disorders, including anxiety and depression. Both preclinical and clinical research have established correlations between TBI and disturbances in the metabolism of amino acids, lipids, iron, zinc, and copper, which are implicated in the emergence of mood disorders post-TBI. The purpose of this review is to elucidate the impact of metabolic dysfunction on mood disorders following TBI and to explore potential strategies for mitigating anxiety and depression symptoms. We researched the PubMed and Web of Science databases to delineate the mechanisms by which metabolic dysfunction contributes to mood disorders in the context of TBI. Particular emphasis was placed on the roles of glutamate, kynurenine, lipids, iron, zinc, and copper metabolism. Metabolic dysfunction is linked to mood disorders post-TBI through multiple pathways, encompassing the glutamatergic system, the kynurenine pathway, endocannabinoids, iron deposition, iron-related ferroptosis, zinc deficiency, and copper dysregulation. Furthermore, this review addresses the influence of metabolic dysfunction on mood disorders in the elderly demographic following TBI. Targeting metabolic dysfunction for therapeutic intervention appears promising in alleviating symptoms of anxiety and depression that arise after TBI. While further investigation is warranted to delineate the underlying pathophysiologic mechanisms of mood disorders post-TBI, current evidence underscores the potential contribution of metabolic dysfunction to these conditions. Therefore, rectifying metabolic dysfunction represents a viable and strategic approach to addressing mood disorders following TBI.

Differential binding of CREB and REST/NRSF to NMDAR1 promoter is associated with the sex-selective cognitive deficit following postnatal PBDE-209 exposure in mice

Neonatal exposure to decabromodiphenyl ether (PBDE-209), a widely used flame retardant, affects cognitive performances in the later stage of life in a sex-dependent manner. PBDE-209 interferes with glutamatergic signaling and N-methyl-D-aspartate receptor (NMDAR) subunits with unresolved regulatory mechanisms. This study exposed male and female mice pups through postnatal day (PND) 3-10 to PBDE-209 (oral dose: 0, 6, or 20 mg/kg body weight). The frontal cortex and hippocampus, collected from neonate (PND 11) and young (PND 60) mice, were analyzed for cAMP response element-binding protein (CREB) and RE1-silencing transcription factor/ Neuron-restrictive silencer factor (REST/NRSF) binding to NMDAR1 promoter and expression of NMDAR1 gene by electrophoretic mobility shift assay and semi-quantitative RT-PCR respectively. Behavioral changes were assessed using spontaneous alternation behavior and novel object recognition tests in young mice. In neonates, the binding of CREB was increased, while REST/NRSF was decreased significantly to their cognate NMDAR1 promoter sequences at the high dose of PBDE-209 in both the sexes. This reciprocal pattern of CREB and REST/NRSF interactions correlates with the up-regulation of NMDAR1 expression. Young males followed a similar pattern of CREB and REST/NRSF binding and NMDAR1 expression as in neonates. Surprisingly, young females did not show any alteration when compared to age-matched controls. Also, we found that only young males showed working and recognition memory deficits. These results indicate that early exposure to PBDE-209 interferes with CREB- and REST/NRSF-dependent regulation of the NMDAR1 gene in an acute setting. However, long-term effects persist only in young males that could be associated with cognitive impairment.

The contribution of the meningeal immune interface to neuroinflammation in traumatic brain injury

Traumatic brain injury (TBI) is a major cause of disability and mortality worldwide, particularly among the elderly, yet our mechanistic understanding of what renders the post-traumatic brain vulnerable to poor outcomes, and susceptible to neurological disease, is incomplete. It is well established that dysregulated and sustained immune responses elicit negative consequences after TBI; however, our understanding of the neuroimmune interface that facilitates crosstalk between central and peripheral immune reservoirs is in its infancy. The meninges serve as the interface between the brain and the immune system, facilitating important bi-directional roles in both healthy and disease settings. It has been previously shown that disruption of this system exacerbates neuroinflammation in age-related neurodegenerative disorders such as Alzheimer's disease; however, we have an incomplete understanding of how the meningeal compartment influences immune responses after TBI. In this manuscript, we will offer a detailed overview of the holistic nature of neuroinflammatory responses in TBI, including hallmark features observed across clinical and animal models. We will highlight the structure and function of the meningeal lymphatic system, including its role in immuno-surveillance and immune responses within the meninges and the brain. We will provide a comprehensive update on our current knowledge of meningeal-derived responses across the spectrum of TBI, and identify new avenues for neuroimmune modulation within the neurotrauma field.

Age at Injury as a Modifier of Preclinical TBI Behavioral, Neuropathological, and Inflammatory Outcomes

Traumatic brain injury (TBI) is a leading cause of injury-related death and disability. In high-income countries, TBI is most prevalent among the older population (≥65 years), commonly caused by falls. Though age at injury is associated with increased risk of mortality and poor outcome, the underlying mechanisms are unclear. Studies in animal models may yield insights into the intersection of TBI with age. Here we review recent studies in animal models where TBI induced in aged animals is associated with exacerbated behavioral deficits (e.g., mortality, thigmotaxis, and cognitive deficits), neuropathology (microgliosis and astrogliosis), neuroinflammation (e.g., cytokines and iNOS), microglial alterations (e.g., more cellular vesicles and adopting a damage-associated microglia gene signature), and cell signaling and pathway changes (e.g., complement, phagocytosis, autophagy, trophic factor signaling). As relatively few preclinical studies focus on aged animals, more research is needed to fully understand the pathophysiology of TBI in the aged population. Particularly, we recommend that (1) more aged animals should be used, (2) closed-head TBI models should be considered, and (3) animal models of comorbidity or polytrauma should be considered.

Cognition and Behavior in the Aging Brain Following TBI: Surveying the Preclinical Evidence

Elderly individuals (65 years and older) represent the fastest-growing demographic of new clinical traumatic brain injury (TBI) cases, yet there is a paucity of preclinical research in aged animals. The limited preclinical work available aligns with the clinical literature in that there appear to be significant differences in pathophysiology, recovery potential, and response to medications between animals at different points across the age spectrum. The aim of this review is to discuss the limited studies and highlight critical age-related differences in affective, cognitive, and neurobehavioral deficits, to discuss factors that influence functional outcomes, and to identify targets for future research. The consensus is that aged rodents face challenges related to dysregulated inflammation, reduced neuroplasticity, and age-related cellular changes, which hinder their recovery after TBI. The most successful intervention studies in animal models to date, of the limited array available, have explored interventions targeting inflammatory downregulation. Current standards of neuropsychopharmacology for post-TBI neurocognitive recovery have not been investigated in a significant capacity. In addition, currently available animal models do not sufficiently account for important age-related comorbidities, dual insults, or differences in TBI mechanism of injury in elderly individuals. TBI in the aged population is more likely to lead to additional neurodegenerative diseases that further complicate recovery. The findings underscore the need for tailored therapeutic interventions to improve outcomes in both adult and elderly populations.

Single Versus Repetitive Traumatic Brain Injury: Current Knowledge on the Chronic Outcomes, Neuropathology and the Role of TDP-43 Proteinopathy

Traumatic brain injury (TBI) is one of the most important causes of death and disability in adults and thus an important public health problem. Following TBI, secondary pathophysiological processes develop over time and condition the development of different neurodegenerative entities. Previous studies suggest that neurobehavioral changes occurring after a single TBI are the basis for the development of Alzheimer's disease, while repetitive TBI is considered to be a contributing factor for chronic traumatic encephalopathy development. However, pathophysiological processes that determine the evolvement of a particular chronic entity are still unclear. Human post-mortem studies have found combinations of amyloid, tau, Lewi bodies, and TAR DNA-binding protein 43 (TDP-43) pathologies after both single and repetitive TBI. This review focuses on the pathological changes of TDP-43 after single and repetitive brain traumas. Numerous studies have shown that TDP-43 proteinopathy noticeably occurs after repetitive head trauma. A relatively small number of available preclinical research on single brain injury are not in complete agreement with the results from the human samples, which makes it difficult to draw specific conclusions. Also, as TBI is considered a heterogeneous type of injury, different experimental trauma models and injury intensities may cause differences in the cascade of secondary injury, which should be considered in future studies. Experimental and post-mortem studies of TDP-43 pathobiology should be carried out, preferably in the same laboratories, to determine its involvement in the development of neurodegenerative conditions after one and repetitive TBI, especially in the context of the development of new therapeutic options.

Traumatic Brain Injury and Secondary Neurodegenerative Disease

Traumatic brain injury (TBI) is a devastating event with severe long-term complications. TBI and its sequelae are one of the leading causes of death and disability in those under 50 years old. The full extent of secondary brain injury is still being intensely investigated; however, it is now clear that neurotrauma can incite chronic neurodegenerative processes. Chronic traumatic encephalopathy, Parkinson's disease, and many other neurodegenerative syndromes have all been associated with a history of traumatic brain injury. The complex nature of these pathologies can make clinical assessment, diagnosis, and treatment challenging. The goal of this review is to provide a concise appraisal of the literature with focus on emerging strategies to improve clinical outcomes. First, we review the pathways involved in the pathogenesis of neurotrauma-related neurodegeneration and discuss the clinical implications of this rapidly evolving field. Next, because clinical evaluation and neuroimaging are essential to the diagnosis and management of neurodegenerative diseases, we analyze the clinical investigations that are transforming these areas of research. Finally, we briefly review some of the preclinical therapies that have shown the most promise in improving outcomes after neurotrauma.

MicroRNA-101a-3p mimic ameliorates spinal cord ischemia/reperfusion injury

miR-101a-3p is expressed in a variety of organs and tissues and plays a regulatory role in many diseases, but its role in spinal cord ischemia/reperfusion injury remains unclear. In this study, we established a rat model of spinal cord ischemia/reperfusion injury by clamping the aortic arch for 14 minutes followed by reperfusion for 24 hours. Results showed that miR-101a-3p expression in L4–L6 spinal cord was greatly decreased, whereas MYCN expression was greatly increased. Dual-luciferase reporter assay results showed that miR-101a-3p targeted MYCN. MYCN immunoreactivity, which was primarily colocalized with neurons in L4–L6 spinal tissue, greatly increased after spinal cord ischemia/reperfusion injury. However, intrathecal injection of an miR-101a-3p mimic within 24 hours before injury decreased MYCN, p53, caspase-9 and interleukin-1β expression, reduced p53 immunoreactivity, reduced the number of MYCN/NeuN-positive cells and the number of necrotic cells in L4–L6 spinal tissue, and increased Tarlov scores. These findings suggest that the miR-101a-3p mimic improved spinal ischemia/reperfusion injury-induced nerve cell apoptosis and inflammation by inhibiting MYCN and the p53 signaling pathway. Therefore, miR-101a-3p mimic therapy may be a potential treatment option for spinal ischemia/reperfusion injury.

Traumatic Brain Injury: Mechanisms of Glial Response

Traumatic brain injury (TBI) is a heterogeneous disorder that involves brain damage due to external forces. TBI is the main factor of death and morbidity in young males with a high incidence worldwide. TBI causes central nervous system (CNS) damage under a variety of mechanisms, including synaptic dysfunction, protein aggregation, mitochondrial dysfunction, oxidative stress, and neuroinflammation. Glial cells comprise most cells in CNS, which are mediators in the brain’s response to TBI. In the CNS are present astrocytes, microglia, oligodendrocytes, and polydendrocytes (NG2 cells). Astrocytes play critical roles in brain’s ion and water homeostasis, energy metabolism, blood-brain barrier, and immune response. In response to TBI, astrocytes change their morphology and protein expression. Microglia are the primary immune cells in the CNS with phagocytic activity. After TBI, microglia also change their morphology and release both pro and anti-inflammatory mediators. Oligodendrocytes are the myelin producers of the CNS, promoting axonal support. TBI causes oligodendrocyte apoptosis, demyelination, and axonal transport disruption. There are also various interactions between these glial cells and neurons in response to TBI that contribute to the pathophysiology of TBI. In this review, we summarize several glial hallmarks relevant for understanding the brain injury and neuronal damage under TBI conditions.

Neuroprotective effects of FK866 against traumatic brain injury: Involvement of p38/ERK pathway

OBJECTIVE

FK866 is an inhibitor of nicotinamide phosphoribosyltransferase (NAMPT), which exhibits neuroprotective effects in ischemic brain injury. However, in traumatic brain injury (TBI), the role and mechanism of FK866 remain unclear. The present research was aimed to investigate whether FK866 could attenuate TBI and clarified the underlying mechanisms.

METHODS

A controlled cortical impact model was established, and FK866 at a dose of 5 mg/kg was administered intraperitoneally at 1 h and 6 h, then twice per day post-TBI until sacrifice. Brain water content, Evans blue dye extravasation, modified neurological severity scores (mNSS), Morris water maze test, enzyme-linked immunosorbent assay (ELISA), immunofluorescence staining, and western blot were performed.

RESULTS

The results demonstrated that FK866 significantly mitigated the brain edema, blood-brain barrier (BBB) disruption, and ameliorated the neurological function post-TBI. Moreover, FK866 decreased the number of Iba-1-positive cells, GFAP-positive astrocytes, and AQP4-positive cells. FK866 reduced the protein levels of proinflammatory cytokines and inhibited NF-κB from translocation to the nucleus. FK866 upregulated the expression of Bcl-2, diminished the expression of Bax and caspase 3, and the number of apoptotic cells. Moreover, p38 MAPK and ERK activation were significantly inhibited by FK866.

INTERPRETATION

FK866 attenuated TBI-induced neuroinflammation and apoptosis, at least in part, through p38/ERK MAPKs signaling pathway.

Models of Traumatic Brain Injury in Aged Animals: A Clinical Perspective

Traumatic brain injury (TBI) is a major cause of morbidity and mortality in the United States, with advanced age being one of the major predictors of poor prognosis. To replicate the mechanisms and multifaceted complexities of human TBI and develop prospective therapeutic treatments, various TBI animal models have been developed. These models have been essential in furthering our understanding of the pathophysiology and biochemical effects on brain mechanisms following TBI. Despite these advances, translating preclinical results to clinical application, particularly in elderly individuals, continues to be challenging. This review aims to provide a clinical perspective, identifying relevant variables currently not replicated in TBI animal models, to potentially improve translation to clinical practice, especially as it applies to elderly populations. As background for this clinical perspective, we reviewed articles indexed on PubMed from 1970 to 2019 that used aged animal models for studying TBI. These studies examined end points relevant for clinical translation, such as neurocognitive effects, sensorimotor behavior, physiological mechanisms, and efficacy of neuroprotective therapies. However, compared with the higher incidence of TBI in older individuals, animal studies on the basic science of aging and TBI remain remarkably scarce. Moreover, a fundamental disconnect remains between experiments in animal models of TBI and successful translation of findings for treating the older TBI population. In this article, we aim to provide a clinical perspective on the unique attributes of TBI in older individuals and a critical appraisal of the research to date on TBI in aged animal models as well as recommendations for future studies.

A Systematic Review of Closed Head Injury Models of Mild Traumatic Brain Injury in Mice and Rats

Mild TBI (mTBI) is a significant health concern. Animal models of mTBI are essential for understanding mechanisms, and pathological outcomes, as well as to test therapeutic interventions. A variety of closed head models of mTBI that incorporate different aspects (i.e., biomechanics) of the mTBI have been reported. The aim of the current review was to compile a comprehensive list of the closed head mTBI rodent models, along with the common data elements, and outcomes, with the goal to summarize the current state of the field. Publications were identified from a search of PubMed and Web of Science and screened for eligibility following PRISMA guidelines. Articles were included that were closed head injuries in which the authors classified the injury as mild in rats or mice. Injury model and animal-specific common data elements, as well as behavioral and histological outcomes, were collected and compiled from a total of 402 articles. Our results outline the wide variety of methods used to model mTBI. We also discovered that female rodents and both young and aged animals are under-represented in experimental mTBI studies. Our findings will aid in providing context comparing the injury models and provide a starting point for the selection of the most appropriate model of mTBI to address a specific hypothesis. We believe this review will be a useful starting place for determining what has been done and what knowledge is missing in the field to reduce the burden of mTBI.

Age at injury and genotype modify acute inflammatory and neurofilament-light responses to mild CHIMERA traumatic brain injury in wild-type and APP/PS1 mice

Peak incidence of traumatic brain injury (TBI) occurs in both young and old individuals, and older age at injury is associated with worse outcome and poorer recovery. Moderate-severe TBI is a reported risk factor for dementia, including Alzheimer's disease (AD), but whether mild TBI (mTBI) alters AD pathogenesis is not clear. To delineate how age at injury and predisposition to amyloid formation affect the acute response to mTBI, we used the Closed Head Impact Model of Engineered Rotational Acceleration (CHIMERA) model of TBI to induce two mild injuries in wild-type (WT) and APP/PS1 mice at either 6 or 13months of age and assessed behavioural, histological and biochemical changes up to 14days post-injury. Age at injury did not alter acute behavioural responses to mTBI, including measures of neurological status, motor performance, spatial memory, fear, or anxiety, in either strain. Young APP/PS1 mice showed a subtle and transient increase in diffuse Aβ deposits after injury, whereas old APP/PS1 mice showed decreased amyloid deposits, without significant alterations in total soluble or insoluble Aβ levels at either age. Age at injury and genotype showed complex responses with respect to microglial and cytokine outcomes, where post-injury neuroinflammation is increased in old WT mice but attenuated in old APP/PS1 mice. Intriguingly, silver staining confirmed axonal damage in both strains and ages, yet only young WT and APP/PS1 mice showed neurofilament-positive axonal swellings after mTBI, as this response was almost entirely attenuated in old mice. Plasma neurofilament-light levels were significantly elevated after injury only in young APP/PS1 mice. This study suggests that mild TBI has minimal effects on Aβ metabolism, but that age and genotype can each modify acute outcomes related to white matter injury.

Nuclear Factor-Kappa B and Alzheimer Disease, Unifying Genetic and Environmental Risk Factors from Cell to Humans

Alzheimer's disease (AD) is the most common form of dementia, an eversible, progressive disease that causes problems with memory, thinking, language, planning, and behavior. There are a number of risk factors associated with developing AD but the exact cause remains unknown. The predominant theory is that excessive build-up of amyloid protein leads to cell death, brain atrophy, and cognitive and functional decline. However, the amyloid hypothesis has not led to a single successful treatment. The recent failure of Solanezumab, a monoclonal antibody to amyloid, in a large phase III trial was emblematic of the repeated failure of anti-amyloid therapeutics. New disease targets are urgently needed. The innate immune system is increasingly being implicated in the pathology of number of chronic diseases. This focused review will summarize the role of transcription factor nuclear factor-kappa B (NF-κB), a key regulator of innate immunity, in the major genetic and environmental risk factors in cellular, invertebrate and vertebrate models of AD. The paper will also explore the relationship between NF-κB and emerging environmental risk factors in an attempt to assess the potential for this transcription factor to be targeted for disease prevention.

Neurometabolic indicators of mitochondrial dysfunction in repetitive mild traumatic brain injury

Mild traumatic brain injury (mTBI) is a significant national health concern and there is growing evidence that repetitive mTBI (rmTBI) can cause long-term change in brain structure and function. The mitochondrion has been suggested to be involved in the mechanism of TBI. There are noninvasive methods of determining mitochondrial dysfunction through biomarkers and spectroscopy. Mitochondrial dysfunction has been implicated in a variety of neurological consequences secondary to rmTBI through activation of caspases and calpains. The purpose of this review is to examine the mechanism of mitochondrial dysfunction in rmTBI and its downstream effects on neuronal cell death, axonal injury and blood–brain barrier compromise.

The role of aquaporin-4 in synaptic plasticity, memory and disease

Since the discovery of aquaporins, it has become clear that the various mammalian aquaporins play critical physiological roles in water and ion balance in multiple tissues. Aquaporin-4 (AQP4), the principal aquaporin expressed in the central nervous system (CNS, brain and spinal cord), has been shown to mediate CNS water homeostasis. In this review, we summarize new and exciting studies indicating that AQP4 also plays critical and unanticipated roles in synaptic plasticity and memory formation. Next, we consider the role of AQP4 in Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), multiple sclerosis (MS), neuromyelitis optica (NMO), epilepsy, traumatic brain injury (TBI), and stroke. Each of these conditions involves changes in AQP4 expression and/or distribution that may be functionally relevant to disease physiology. Insofar as AQP4 is exclusively expressed on astrocytes, these data provide new evidence of "astrocytopathy" in the etiology of diverse neurological diseases.

Traumatic brain injury: a risk factor for neurodegenerative diseases

Traumatic brain injury (TBI), a major global health and socioeconomic problem, is now established as a chronic disease process with a broad spectrum of pathophysiological symptoms followed by long-term disabilities. It triggers multiple and multidirectional biochemical events that lead to neurodegeneration and cognitive impairment. Recent studies have presented strong evidence that patients with TBI history have a tendency to develop proteinopathy, which is the pathophysiological feature of neurodegenerative disorders such as Alzheimer disease (AD), chronic traumatic encephalopathy (CTE), and amyotrophic lateral sclerosis (ALS). This review mainly focuses on mechanisms related to AD, CTE, and ALS that are induced after TBI and their relevance to the advancement of these neurodegenerative diseases. This review encompasses acute effects and chronic neurodegenerative consequences after TBI for a better understanding of TBI-induced neuronal death and to design therapies that will effectively treat patients in the primary or secondary progressive stages.

Older Age Results in Differential Gene Expression after Mild Traumatic Brain Injury and Is Linked to Imaging Differences at Acute Follow-up

Older age consistently relates to a lesser ability to fully recover from a traumatic brain injury (TBI); however, there is limited data to explicate the nature of age-related risks. This study was undertaken to determine the relationship of age on gene-activity following a TBI, and how this biomarker relates to changes in neuroimaging findings. A young group (between the ages of 19 and 35 years), and an old group (between the ages of 60 and 89 years) were compared on global gene-activity within 48 h following a TBI, and then at follow-up within 1-week. At each time-point, gene expression profiles, and imaging findings from both magnetic resonance imaging (MRI) and computed tomography were obtained and compared. The young group was found to have greater gene expression of inflammatory regulatory genes at 48 h and 1-week in genes such as basic leucine zipper transcription factor 2 (BACH2), leucine-rich repeat neuronal 3 (LRRN3), and lymphoid enhancer-binding factor 1 (LEF1) compared to the old group. In the old group, there was increased activity in genes within S100 family, including calcium binding protein P (S100P) and S100 calcium binding protein A8 (S100A8), which previous studies have linked to poor recovery from TBI. The old group also had reduced activity of the noggin (NOG) gene, which is a member of the transforming growth factor-β superfamily and is linked to neurorecovery and neuroregeneration compared to the young group. We link these gene expression findings that were validated to neuroimaging, reporting that in the old group with a MRI finding of TBI-related damage, there was a lesser likelihood to then have a negative MRI finding at follow-up compared to the young group. Together, these data indicate that age impacts gene activity following a TBI, and suggest that this differential activity related to immune regulation and neurorecovery contributes to a lesser likelihood of neuronal recovery in older patients as indicated through neuroimaging.