BDNF polymorphism predicts general intelligence after penetrating traumatic brain injury

Studying the social mind: An updated summary of findings from the Vietnam Head Injury Study

Lesion mapping studies allow us to evaluate the potential causal contribution of specific brain areas to human cognition and complement other cognitive neuroscience methods, as several authors have recently pointed out. Here, we present an updated summary of the findings from the Vietnam Head Injury Study (VHIS) focusing on the studies conducted over the last decade, that examined the social mind and its intricate neural and cognitive underpinnings. The VHIS is a prospective, long-term follow-up study of Vietnam veterans with penetrating traumatic brain injury (pTBI) and healthy controls (HC). The scope of the work is to present the studies from the latest phases (3 and 4) of the VHIS, 70 studies since 2011, when the Raymont et al. paper was published (Raymont et al., 2011). These studies have contributed to our understanding of human social cognition, including political and religious beliefs, theory of mind, but also executive functions, intelligence, and personality. This work finally discusses the usefulness of lesion mapping as an approach to understanding the functions of the human brain from basic science and clinical perspectives.

Interleukin-1 Receptor Antagonist as Therapy for Traumatic Brain Injury

Traumatic brain injury is a common type of acquired brain injury of varying severity carrying potentially deleterious consequences for the afflicted individuals, families, and society. Following the initial, traumatically induced insult, cellular injury processes ensue. These are believed to be amenable to treatment. Among such injuries, neuroinflammation has gained interest and has become a specific focus for both experimental and clinical researchers. Neuroinflammation is elicited almost immediately following trauma, and extend for a long time, possibly for years, after the primary injury. In the acute phase, the inflammatory response is characterized by innate mechanisms such as the activation of microglia which among else mediates cytokine production. Among the earliest cytokines to emerge are the interleukin- (IL-) 1 family members, comprising, for example, the agonist IL-1β and its competitive antagonist, IL-1 receptor antagonist (IL-1ra). Because of its early emergence following trauma and its increased concentrations also after human TBI, IL-1 has been hypothesized to be a tractable treatment target following TBI. Ample experimental data supports this, and demonstrates restored neurological behavior, diminished lesion zones, and an attenuated inflammatory response following IL-1 modulation either through IL-1 knock-out experiments, IL-1β inhibition, or IL-1ra treatment. Of these, IL-1ra treatment is likely the most physiological. In addition, recombinant human IL-1ra (anakinra) is already approved for utilization across a few rheumatologic disorders. As of today, one randomized clinical controlled trial has utilized IL-1ra inhibition as an intervention and demonstrated its safety. Further clinical trials powered for patient outcome are needed in order to demonstrate efficacy. In this review, we summarize IL-1 biology in relation to acute neuroinflammatory processes following TBI with a particular focus on current evidence for IL-1ra treatment both in the experimental and clinical context.

COMT Val158Met and BDNF Val66Met Single-Nucleotide Polymorphisms Are Not Associated With Emotional Distress One Year After Moderate-Severe Traumatic Brain Injury

Emotional distress is a common, but poorly addressed, feature of moderate-severe traumatic brain injury (TBI). Previously identified sociodemographic, psychological, and injury-related factors account for only a small proportion of the variability in emotional distress post-TBI. Genetic factors may help to further understand emotional distress in this population. The catechol-O-methyltransferase (COMT) Val158 and brain-derived neurotrophic factor (BDNF) 66Met single-nucleotide polymorphisms (SNPs) have been identified as possible contributory factors to outcomes after TBI. We investigated whether the COMT Val158 and BDNF 66Met SNPs were associated with emotional distress 1 year after moderate-severe TBI, and whether these associations were moderated by age, sex, and TBI severity (as measured by the duration of post-traumatic amnesia [PTA]). Moderate-severe TBI survivors (COMT, n = 391; BDNF, n = 311) provided saliva samples after admission to a TBI rehabilitation hospital. At a follow-up interview ∼1 year after injury, participants completed a self-report measure of emotional distress (Hospital Anxiety and Depression Scale; HADS). Multiple linear regression models were constructed for each SNP to predict total scores on the HADS. Neither COMT Val158 nor BDNF 66Met carriage status (carrier vs. non-carrier) significantly predicted emotional distress (COMT, p = 0.49; BDNF, p = 0.66). Interactions of SNP × age (COMT, p = 0.90; BDNF, p = 0.93), SNP × sex (COMT, p = 0.09; BDNF, p = 0.60), SNP × injury severity (COMT, p = 0.53; BDNF, p = 0.87), and SNP × sex × age (COMT, p = 0.08; BDNF, p = 0.76) were also non-significant. Our null findings suggest that COMT Val158 and BDNF 66Met SNPs do not aid the prediction of emotional distress 1 year after moderate-severe TBI, neither in isolation nor in interaction with age, sex and injury severity. The reporting of null findings such as ours is important to avoid publication bias and prompt researchers to consider the challenges of single-gene candidate studies in understanding post-TBI outcomes. Analyses in larger samples that incorporate multiple genetic factors and their relevant moderating factors may provide a greater understanding of the role of genetics in post-TBI emotional distress.

Association Between Chronic Tinnitus and Brain-Derived Neurotrophic Factor Antisense RNA Polymorphisms Linked to the Val66Met Polymorphism in BDNF

Tinnitus is the sound heard in the ear or head of a person in the absence of external stimuli. Its etiopathogenesis is still not fully understood and the etiological causes responsible for tinnitus are quite variable. Brain-derived neurotrophic factor (BDNF) is one of the key neurotrophic factors in the growth, differentiation, and survival of neurons and in the developing auditory pathway, including the inner ear sensory epithelium. The regulation of BDNF gene is known to be managed by BDNF antisense (BDNF-AS) gene. BDNF-AS is located downstream of the BDNF gene and transcribes a long non-coding RNA. Inhibition of BDNF-AS upregulates BDNF mRNA, which increases protein levels and stimulates neuronal development and differentiation. Thus, BDNF and BDNF-AS both may play roles in the auditory pathway. Polymorphisms in both genes may have impact on hearing performance. A link was suggested between tinnitus and BDNF Val66Met polymorphism. However, there is no study questioning the relationship of tinnitus with BDNF-AS polymorphisms linked with BDNF Val66Met polymorphism. Therefore, this study aimed to scrutinize the role of BDNF-AS polymorphisms showing linkage with the BDNF Val66Met polymorphism in the course of tinnitus pathophysiology. Six BDNF-AS polymorphisms were analyzed on the tinnitus patients (n=85) and the control subjects (n=60) by Fluidigm Real-Time PCR using the Fluidigm Biomark microfluidic platform. When BDNF-AS polymorphisms were compared between the groups in terms of genotype and gender distribution, statistically significant differences were detected in rs925946, rs1519480, and rs10767658, polymorphisms (p<0.05). When the polymorphisms were compared by the duration of tinnitus, significant differences were found in rs925946, rs1488830, rs1519480, and rs10767658 polymorphisms (p<0.05). According to genetic inheritance model analysis, 2.33 and 1.53-fold risks were found for the rs10767658 polymorphism in the recessive and the additive models, respectively. For the rs1519480 polymorphism, a 2.25 fold risk was observed in the additive model. For the rs925946 polymorphism, 2.44 fold protective effect in dominant model, and 0.62 fold risk was found in the additive model. In conclusion, four of the polymorphisms in BDNF-AS gene (rs955946, rs1488830, rs1519480, and rs10767658) are potential gene loci that may play a role in the auditory pathway and affect auditory performance.

Looking for factors affecting functioning in euthymic patients with bipolar I disorder: the importance of cognitive complaints and BDNF's Val66Met polymorphism

INTRODUCTION

Functioning in Bipolar Disorder (BD) is affected in a substantial proportion of patients. The impact of demographic, clinical, cognitive, and genetic factors on functioning has been shown individually; however, as a complex phenomenon, a global approach to identify the most relevant as well as possible interactions is needed.

METHODS

102 patients with type I BD in euthymia were invited for evaluation of demographic, clinical, and cognitive characteristics as well as genotype for Val66Met polymorphism of BDNF gene to determine those associated with poor functioning according to the FAST scale cut-off score. Clinical evaluation included assessment of residual affective symptoms and anxiety. Cognitive evaluation included the COBRA scale, verbal memory, and executive functions testing.

RESULTS

Residual depressive symptoms, anxiety, cognitive complaints and being a Met carrier were more frequent in the poor functioning group and were entered in a logistic regression model. Being a Met carrier (OR=4.46, CI=1.19-16.67) and cognitive complaints (OR=1.29, CI= 1.13-1.46) were the most important predictors of poor functioning in type I BD.

LIMITATIONS

Cross-sectional study, with select population limiting generalizability of findings.

CONCLUSIONS

A better understanding of underlying factors affecting cognition, including the possible involvement of BDNF Val66Met polymorphism, its systematic evaluation and a continued search for targeted treatment, along with recognition and attention of residual affective and anxious symptoms might improve psychosocial outcomes such as functioning in this population.

Pharmacogenetics of Addiction Therapy

Drug addiction is a serious relapsing disease that has high costs to society and to the individual addicts. Treatment of these addictions is still in its nascency, with only a few examples of successful therapies. Therapeutic response depends upon genetic, biological, social, and environmental components. A role for genetic makeup in the response to treatment has been shown for several addiction pharmacotherapies with response to treatment based on individual genetic makeup. In this chapter, we will discuss the role of genetics in pharmacotherapies, specifically for cocaine, alcohol, and opioid dependences. The continued elucidation of the role of genetics should aid in the development of new treatments and increase the efficacy of existing treatments.

Moderators of gene-outcome associations following traumatic brain injury

The field of genomics is the principal avenue in the ongoing development of precision/personalised medicine for a variety of health conditions. However, relating genes to outcomes is notoriously complex, especially when considering that other variables can change, or moderate, gene-outcome associations. Here, we comprehensively discuss moderation of gene-outcome associations in the context of traumatic brain injury (TBI), a common, chronically debilitating, and costly neurological condition that is under complex polygenic influence. We focus our narrative review on single nucleotide polymorphisms (SNPs) of three of the most studied genes (apolipoprotein E, brain-derived neurotrophic factor, and catechol-O-methyltransferase) and on three demographic variables believed to moderate associations between these SNPs and TBI outcomes (age, biological sex, and ethnicity). We speculate on the mechanisms which may underlie these moderating effects, drawing widely from biomolecular and behavioural research (n = 175 scientific reports) within the TBI population (n = 72) and other neurological, healthy, ageing, and psychiatric populations (n = 103). We conclude with methodological recommendations for improved exploration of moderators in future genetics research in TBI and other populations.

The Role of BDNF in Experimental and Clinical Traumatic Brain Injury

Traumatic brain injury is one of the leading causes of mortality and morbidity in the world with no current pharmacological treatment. The role of BDNF in neural repair and regeneration is well established and has also been the focus of TBI research. Here, we review experimental animal models assessing BDNF expression following injury as well as clinical studies in humans including the role of BDNF polymorphism in TBI. There is a large heterogeneity in experimental setups and hence the results with different regional and temporal changes in BDNF expression. Several studies have also assessed different interventions to affect the BDNF expression following injury. Clinical studies highlight the importance of BDNF polymorphism in the outcome and indicate a protective role of BDNF polymorphism following injury. Considering the possibility of affecting the BDNF pathway with available substances, we discuss future studies using transgenic mice as well as iPSC in order to understand the underlying mechanism of BDNF polymorphism in TBI and develop a possible pharmacological treatment.

Neurotrophins Time Point Intervention after Traumatic Brain Injury: From Zebrafish to Human

Traumatic brain injury (TBI) remains the leading cause of long-term disability, which annually involves millions of individuals. Several studies on mammals reported that neurotrophins could play a significant role in both protection and recovery of function following neurodegenerative diseases such as stroke and TBI. This protective role of neurotrophins after an event of TBI has also been reported in the zebrafish model. Nevertheless, reparative mechanisms in mammalian brain are limited, and newly formed neurons do not survive for a long time. In contrast, the brain of adult fish has high regenerative properties after brain injury. The evident differences in regenerative properties between mammalian and fish brain have been ascribed to remarkable different adult neurogenesis processes. However, it is not clear if the specific role and time point contribution of each neurotrophin and receptor after TBI is conserved during vertebrate evolution. Therefore, in this review, I reported the specific role and time point of intervention for each neurotrophic factor and receptor after an event of TBI in zebrafish and mammals.

The genetic basis of inter-individual variation in recovery from traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of death among young people, and is increasingly prevalent in the aging population. Survivors of TBI face a spectrum of outcomes from short-term non-incapacitating injuries to long-lasting serious and deteriorating sequelae. TBI is a highly complex condition to treat; many variables can account for the observed heterogeneity in patient outcome. The limited success of neuroprotection strategies in the clinic has led to a new emphasis on neurorestorative approaches. In TBI, it is well recognized clinically that patients with similar lesions, age, and health status often display differences in recovery of function after injury. Despite this heterogeneity of outcomes in TBI, restorative treatment has remained generic. There is now a new emphasis on developing a personalized medicine approach in TBI, and this will require an improved understanding of how genetics impacts on long-term outcomes. Studies in animal model systems indicate clearly that the genetic background plays a role in determining the extent of recovery following an insult. A candidate gene approach in human studies has led to the identification of factors that can influence recovery. Here we review studies of the genetic basis for individual differences in functional recovery in the CNS in animals and man. The application of in vitro modeling with human cells and organoid cultures, along with whole-organism studies, will help to identify genes and networks that account for individual variation in recovery from brain injury, and will point the way towards the development of new therapeutic approaches.

Edaravone attenuates neuronal apoptosis in hippocampus of rat traumatic brain injury model via activation of BDNF/TrkB signaling pathway

INTRODUCTION

The purpose of our study was to explore the effects of edaravone on rats with traumatic brain injury (TBI) and investigate the underlying mechanism.

MATERIAL AND METHODS

All rats were separated randomly into 3 groups as follows: sham group (n = 25), TBI group (n = 25), TBI + edaravone group (n = 25). Edaravone was administered intraperitoneally (i.p.) at a dose of 3 mg/kg at 30 min, 12 h, and 24 h after TBI. The neurological impairment and spatial cognitive function were assessed by the neurologic severity score (NSS) and Morris water maze (MWM), respectively. Western blot and reverse transcription polymerase chain reaction (RT-PCR) were used to determine the expression levels of caspase-3, B-cell lymphoma-2 (Bcl-2), Bcl-2 associated X protein (Bax), brain-derived neurotrophic factor (BDNF) and tyrosine kinase receptor B (TrkB). Transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay as well as flow cytometry assay was used to determine the apoptosis rate of cells.

RESULTS

Edaravone administration significantly attenuated neurological impairment induced by TBI and promoted cognitive function outcome. The expression of BDNF and TrkB was elevated with treatment of edaravone, which was increased after TBI. The expression of apoptosis related proteins such as caspase-3 and Bax-2 was decreased while that of Bcl-2 was enhanced with edaravone administration following TBI. In addition, edaravone treatment reduced TBI-induced cell apoptosis in the hippocampus.

CONCLUSIONS

Our study showed that administration with edaravone was able to inhibit neuronal apoptosis in the hippocampus in a rat TBI model. The neuroprotective function of edaravone may relate to modulation of the BDNF/TrkB signaling pathway.

Blast-Related Mild TBI Alters Anxiety-Like Behavior and Transcriptional Signatures in the Rat Amygdala

The short and long-term neurological and psychological consequences of traumatic brain injury (TBI), and especially mild TBI (mTBI) are of immense interest to the Veteran community. mTBI is a common and detrimental result of combat exposure and results in various deleterious outcomes, including mood and anxiety disorders, cognitive deficits, and post-traumatic stress disorder (PTSD). In the current study, we aimed to further define the behavioral and molecular effects of blast-related mTBI using a well-established (3 × 75 kPa, one per day on three consecutive days) repeated blast overpressure (rBOP) model in rats. We exposed adult male rats to the rBOP procedure and conducted behavioral tests for anxiety and fear conditioning at 1-1.5 months (sub-acute) or 12-13 months (chronic) following blast exposure. We also used next-generation sequencing to measure transcriptome-wide gene expression in the amygdala of sham and blast-exposed animals at the sub-acute and chronic time points. Results showed that blast-exposed animals exhibited an anxiety-like phenotype at the sub-acute timepoint but this phenotype was diminished by the chronic time point. Conversely, gene expression analysis at both sub-acute and chronic timepoints demonstrated a large treatment by timepoint interaction such that the most differentially expressed genes were present in the blast-exposed animals at the chronic time point, which also corresponded to a Bdnf-centric gene network. Overall, the current study identified changes in the amygdalar transcriptome and anxiety-related phenotypic outcomes dependent on both blast exposure and aging, which may play a role in the long-term pathological consequences of mTBI.

Genetic Background Influences Acute Response to TBI in Kindling-Susceptible, Kindling-Resistant, and Outbred Rats

We hypothesized that the acute response to traumatic brain injury (TBI) shares mechanisms with brain plasticity in the kindling model. Utilizing two unique, complementary strains of inbred rats, selected to be either susceptible or resistant to seizure-induced plasticity evoked by kindling of the perforant path, we examined acute electrophysiological alterations and differences in brain-derived neurotrophic factor (BDNF) protein concentrations after a moderate-to-severe brain injury. At baseline, limited strain-dependent differences in acute electrophysiological activity were found, and no differences in BDNF. Following injury, pronounced strain-dependent differences in electrophysiologic activity were noted at 0.5 min. However, the divergence is transient, with diminished differences at 5 min after injury and no differences at 10 and 15 min after injury. Strain-specific differences in BDNF protein concentration were noted 4 h after injury. A simple risk score model generated by machine learning and based solely on post-injury electrophysiologic activity at the 0.5-min timepoint distinguished perforant path kindling susceptible (PPKS) rats from non-plasticity-susceptible strains. The findings demonstrate that genetic background which affects brain circuit plasticity also affects acute response to TBI. An improved understanding of the effect of genetic background on the cellular, molecular, and circuit plasticity mechanisms activated in response to TBI and their timecourse is key in developing much-needed novel therapeutic approaches.

BDNF Val66Met Genetic Polymorphism Results in Poor Recovery Following Repeated Mild Traumatic Brain Injury in a Mouse Model and Treatment With AAV-BDNF Improves Outcomes

Clinicians have long noticed that some Traumatic Brain Injury (TBI) patients have worse symptoms and take a longer time to recover than others, for reasons unexplained by known factors. Identifying what makes some individuals more susceptible is critical to understanding the underlying mechanisms through which TBI causes deleterious effects. We have sought to determine the effect of a single nucleotide polymorphism (SNP) in Brain-derived neurotrophic factor (BDNF) at amino acid 66 (rs6265) on recovery after TBI. There is controversy from human studies as to whether the BDNF Val66Val or Val66Met allele is the risk factor for worse outcomes after brain trauma. We therefore investigated cellular and behavioral outcomes in genetically engineered mice following repeated mild TBI (rmTBI) using a lateral fluid percussion (LFP) injury model. We found that relative to injured Val66Val carriers, injured Val66Met carriers had a larger inflammation volume and increased levels of neurodegeneration, apoptosis, p-tau, activated microglia, and gliosis in the cortex and/or hippocampus at 1 and/or 21 days post-injury (DPI). We therefore concluded that the Val66Met genetic polymorphism is a risk factor for poor outcomes after rmTBI. In order to determine the mechanism for these differences, we investigated levels of the apoptotic-inducing pro BDNF and survival-inducing mature BDNF isoforms and found that Met carriers had less total BDNF in the cortex and a higher pro/mature ratio of BDNF in the hippocampus. We then developed a personalized approach to treating genetically susceptible individuals by overexpressing wildtype BDNF in injured Val66Met mice using an AAV-BDNF virus. This intervention improved cellular, motor, and cognitive behavior outcomes at 21 DPI and increased levels of mature BDNF and phosphorylation of mature BDNF's receptor trkB. This study lays the groundwork for further investigation into the genetics that play a role in the extent of injury after rmTBI and highlights how personalized therapeutics may be targeted for recovery in susceptible individuals.

The Influence of the Val66Met Polymorphism of Brain-Derived Neurotrophic Factor on Neurological Function after Traumatic Brain Injury

Functional outcomes after traumatic brain injury (TBI) vary widely across patients with apparently similar injuries. This variability hinders prognosis, therapy, and clinical innovation. Recently, single nucleotide polymorphism (SNPs) that influence outcome after TBI have been identified. These discoveries create opportunities to personalize therapy and stratify clinical trials. Both of these changes would propel clinical innovation in the field. This review focuses on one of most well-characterized of these SNPs, the Val66Met SNP in the brain-derived neurotrophic factor (BDNF) gene. This SNP influences neurological function in healthy subjects as well as TBI patients and patients with similar acute insults to the central nervous system. A host of other patient-specific factors including ethnicity, age, gender, injury severity, and post-injury time point modulate this influence. These interactions confound efforts to define a simple relationship between this SNP and TBI outcomes. The opportunities and challenges associated with personalizing TBI therapy around this SNP and other similar SNPs are discussed in light of these results.

Genetic Influences on Patient-Oriented Outcomes in Traumatic Brain Injury: A Living Systematic Review of Non-Apolipoprotein E Single-Nucleotide Polymorphisms

There is a growing literature on the impact of genetic variation on outcome in traumatic brain injury (TBI). Whereas a substantial proportion of these publications have focused on the apolipoprotein E (APOE) gene, several have explored the influence of other polymorphisms. We undertook a systematic review of the impact of single-nucleotide polymorphisms (SNPs) in non–apolipoprotein E (non-APOE) genes associated with patient outcomes in adult TBI). We searched EMBASE, MEDLINE, CINAHL, and gray literature from inception to the beginning of August 2017 for studies of genetic variance in relation to patient outcomes in adult TBI. Sixty-eight articles were deemed eligible for inclusion into the systematic review. The SNPs described were in the following categories: neurotransmitter (NT) in 23, cytokine in nine, brain-derived neurotrophic factor (BDNF) in 12, mitochondrial genes in three, and miscellaneous SNPs in 21. All studies were based on small patient cohorts and suffered from potential bias. A range of SNPs associated with genes coding for monoamine NTs, BDNF, cytokines, and mitochondrial proteins have been reported to be associated with variation in global, neuropsychiatric, and behavioral outcomes. An analysis of the tissue, cellular, and subcellular location of the genes that harbored the SNPs studied showed that they could be clustered into blood–brain barrier associated, neuroprotective/regulatory, and neuropsychiatric/degenerative groups. Several small studies report that various NT, cytokine, and BDNF-related SNPs are associated with variations in global outcome at 6–12 months post-TBI. The association of these SNPs with neuropsychiatric and behavioral outcomes is less clear. A definitive assessment of role and effect size of genetic variation in these genes on outcome remains uncertain, but could be clarified by an adequately powered genome-wide association study with appropriate recording of outcomes.

The Val66Met BDNF Polymorphism and Peripheral Nerve Injury: Enhanced Regeneration in Mouse Met-Carriers Is Not Further Improved With Activity-Dependent Treatment

Activity-dependent treatments to enhance peripheral nerve regeneration after injury have shown great promise, and clinical trials implementing them have begun. Success of these treatments requires activity-dependent release of brain-derived neurotrophic factor (BDNF). A single nucleotide polymorphism (SNP) in the bdnf gene known as Val66Met, which is found in nearly one third of the human population, results in defective activity-dependent BDNF secretion and could impact the effectiveness of these therapies. Here, we used a mouse model of this SNP to test the efficacy of treadmill exercise in enhancing axon regeneration in animals both heterozygous (V/M) and homozygous (M/M) for the SNP. Axon regeneration was studied 4 weeks after complete transection and repair of the sciatic nerve in both male and female animals, using both electrophysiological and histological outcome measures. Regeneration was enhanced significantly without treatment in V/M mice, compared with wild type (V/V) controls. Unlike V/V mice, treatment of both V/M and M/M mice with treadmill exercise did not result in enhanced regeneration. These results were recapitulated in vitro using dissociated neurons containing the light-sensitive cation channel, channelrhodopsin. Three days after plating, neurites of neurons from V/M and M/M mice were longer than those of V/V neurons. In neurons from V/V mice, but not those from V/M or M/M animals, longer neurites were found after optogenetic stimulation. Taken together, Met-carriers possess an intrinsically greater capacity to regenerate axons in peripheral nerves, but this cannot be enhanced further by activity-dependent treatments.

Effects of Neurotrophic Factors in Glial Cells in the Central Nervous System: Expression and Properties in Neurodegeneration and Injury

Astrocytes, oligodendrocytes, and microglia are abundant cell types found in the central nervous system and have been shown to play crucial roles in regulating both normal and disease states. An increasing amount of evidence points to the critical importance of glia in mediating neurodegeneration in Alzheimer’s and Parkinson’s diseases (AD, PD), and in ischemic stroke, where microglia are involved in initial tissue clearance, and astrocytes in the subsequent formation of a glial scar. The importance of these cells for neuronal survival has previously been studied in co-culture experiments and the search for neurotrophic factors (NTFs) initiated after finding that the addition of conditioned media from astrocyte cultures could support the survival of primary neurons in vitro. This led to the discovery of the potent dopamine neurotrophic factor, glial cell line-derived neurotrophic factor (GDNF). In this review, we focus on the relationship between glia and NTFs including neurotrophins, GDNF-family ligands, CNTF family, and CDNF/MANF-family proteins. We describe their expression in astrocytes, oligodendrocytes and their precursors (NG2-positive cells, OPCs), and microglia during development and in the adult brain. Furthermore, we review existing data on the glial phenotypes of NTF knockout mice and follow NTF expression patterns and their effects on glia in disease models such as AD, PD, stroke, and retinal degeneration.

In silico analysis of the V66M variant of human BDNF in psychiatric disorders: An approach to precision medicine

Brain-derived neurotrophic factor (BDNF) plays an important role in neurogenesis and synapse formation. The V66M is the most prevalent BDNF mutation in humans and impairs the function and distribution of BDNF. This mutation is related to several psychiatric disorders. The pro-region of BDNF, particularly position 66 and its adjacent residues, are determinant for the intracellular sorting and activity-dependent secretion of BDNF. However, it has not yet been fully elucidated. The present study aims to analyze the effects of the V66M mutation on BDNF structure and function. Here, we applied nine algorithms, including SIFT and PolyPhen-2, for functional and stability prediction of the V66M mutation. The complete theoretical model of BNDF was generated by Rosetta and validated by PROCHECK, RAMPAGE, ProSa, QMEAN and Verify-3D algorithms. Structural alignment was performed using TM-align. Phylogenetic analysis was performed using the ConSurf server. Molecular dynamics (MD) simulations were performed and analyzed using the GROMACS 2018.2 package. The V66M mutation was predicted as deleterious by PolyPhen-2 and SIFT in addition to being predicted as destabilizing by I-Mutant. According to SNPeffect, the V66M mutation does not affect protein aggregation, amyloid propensity, and chaperone binding. The complete theoretical structure of BDNF proved to be a reliable model. Phylogenetic analysis indicated that the V66M mutation of BDNF occurs at a non-conserved position of the protein. MD analyses indicated that the V66M mutation does not affect the BDNF flexibility and surface-to-volume ratio, but affects the BDNF essential motions, hydrogen-bonding and secondary structure particularly at its pre and pro-domain, which are crucial for its activity and distribution. Thus, considering that these parameters are determinant for protein interactions and, consequently, protein function; the alterations observed throughout the MD analyses may be related to the functional impairment of BDNF upon V66M mutation, as well as its involvement in psychiatric disorders.

The Role of BDNF in Peripheral Nerve Regeneration: Activity-Dependent Treatments and Val66Met

Despite the ability of peripheral nerves to spontaneously regenerate after injury, recovery is generally very poor. The neurotrophins have emerged as an important modulator of axon regeneration, particularly brain derived neurotrophic factor (BDNF). BDNF regulation and signaling, as well as its role in activity-dependent treatments including electrical stimulation, exercise, and optogenetic stimulation are discussed here. The importance of a single nucleotide polymorphism in the BDNF gene, Val66Met, which is present in 30% of the human population and may hinder the efficacy of these treatments in enhancing regeneration after injury is considered. Preliminary data are presented on the effectiveness of one such activity-dependent treatment, electrical stimulation, in enhancing axon regeneration in mice expressing the met allele of the Val66Met polymorphism.

Differences in brain-derived neurotrophic factor gene polymorphisms between acute ischemic stroke patients and healthy controls in the Han population of southwest China

Single-nucleotide polymorphisms in the brain-derived neurotrophic factor gene may affect the secretion and function of brain-derived neurotrophic factor, thereby affecting the occurrence, severity and prognosis of ischemic stroke. This case-control study included 778 patients (475 males and 303 females, mean age of 64.0 ± 12.6 years) in the acute phase of ischemic stroke and 865 control subjects (438 males and 427 females, mean age of 51.7 ± 14.7 years) from the Department of Neurology, West China Hospital, Sichuan University, China between September 2011 and December 2014. The patients’ severities of neurological deficits in the acute phase were assessed using the National Institutes of Health Stroke Scale immediately after admission to hospital. The ischemic stroke patients were divided into different subtypes according to the Trial of Org 10172 in Acute Stroke Treatment classification. Early prognosis was evaluated using the Modified Rankin Scale when the patients were discharged. Genomic DNA was extracted from peripheral blood of participants. Genotyping of rs7124442 and rs6265 was performed using Kompetitive Allele Specific polymerase chain reaction genotyping technology. Our results demonstrated that patients who carried the C allele of the rs7124442 locus had a lower risk of poor prognosis than the T allele carriers (odds ratio [OR] = 0.67; 95% confidence interval [CI]: 0.45–1.00; P = 0.048). The patients with the CC or TC genotype also exhibited lower risk than TT carriers (OR = 0.65; 95% CI: 0.42–1.00; P = 0.049). The AA genotype at the rs6265 locus was associated with the occurrence of ischemic stroke in patients with large-artery atherosclerosis (OR = 0.58; 95% CI: 0.37–0.90; P = 0.015). We found that the C allele (CC and TC genotypes) at the rs7124442 locus may be protective for the prognosis of ischemic stroke. The AA genotype at the rs6265 locus is likely a protective factor against the occurrence of ischemic stroke in patients with large-artery atherosclerosis. The study protocol was approved by the Ethics Committee of West China Hospital of Sichuan University, China (approval ID number 2008[4]) on July 25, 2008.

Intelligence across the seventh decade in patients with brain injuries acquired in young adulthood

In this longitudinal study, we examined intelligence in a group of Vietnam veterans in their 60 s who suffered combat-related penetrating traumatic brain injuries (pTBI) in their 20 s (n = 120), as well as matched veterans with no brain damage (n = 33). Intelligence was evaluated using the Armed Forces Qualification Test (AFQT) administered before the injury occurred and then again at three points in time over the following 45 years. We tested for potential predictors and correlates of late midlife intelligence score, as well as the recent change in score over the seventh decade. The pTBI group had lower intelligence scores than the control group when currently evaluated. Pre-injury intelligence and the presence of a pTBI were the most consistent predictors of current intelligence scores. While exacerbated intellectual decline occurs following a young-adulthood pTBI and affects everyday life, no evidence for late midlife accelerated cognitive decline or dementia was found.

Protein biomarkers of epileptogenicity after traumatic brain injury

Traumatic brain injury (TBI) is a major risk factor for acquired epilepsy. Post-traumatic epilepsy (PTE) develops over time in up to 50% of patients with severe TBI. PTE is mostly unresponsive to traditional anti-seizure treatments suggesting distinct, injury-induced pathomechanisms in the development of this condition. Moderate and severe TBIs cause significant tissue damage, bleeding, neuron and glia death, as well as axonal, vascular, and metabolic abnormalities. These changes trigger a complex biological response aimed at curtailing the physical damage and restoring homeostasis and functionality. Although a positive correlation exists between the type and severity of TBI and PTE, there is only an incomplete understanding of the time-dependent sequelae of TBI pathobiologies and their role in epileptogenesis. Determining the temporal profile of protein biomarkers in the blood (serum or plasma) and cerebrospinal fluid (CSF) can help to identify pathobiologies underlying the development of PTE, high-risk individuals, and disease modifying therapies. Here we review the pathobiological sequelae of TBI in the context of blood- and CSF-based protein biomarkers, their potential role in epileptogenesis, and discuss future directions aimed at improving the diagnosis and treatment of PTE.

The p75 neurotrophin receptor regulates cranial irradiation-induced hippocampus-dependent cognitive dysfunction

Cognitive deficits, characterized by progressive problems with hippocampus-dependent learning, memory and spatial processing, are the most serious complication of cranial irradiation. However, the underlying mechanisms remain obscure. The p75 neurotrophin receptor (p75^NTR) is involved in a diverse arrays of cellular responses, including neurite outgrowth, neurogenesis, and negative regulation of spine density, which are associated with various neurological disorders. In this study, male Sprague-Dawley (SD) rats received 10 Gy cranial irradiation. Then, we evaluated the expression of p75^NTR in the hippocampus after cranial irradiation and explored its potential role in radiation-induced synaptic dysfunction and memory deficits. We found that the expression of p75^NTR was significantly increased in the irradiated rat hippocampus. Knockdown of p75^NTR by intrahippocampal infusion of AAV8-shp75 ameliorated dendritic spine abnormalities, and restored synapse-related protein levels, thus preventing memory deficits, likely through normalization the phosphor-AKT activity. Moreover, viral-mediated overexpression of p75^NTR in the normal hippocampus reproduced learning and memory deficits. Overall, this study demonstrates that p75^NTR is an important mediator of irradiation-induced cognitive deficits by regulating dendritic development and synapse structure.

Transcranial Ultrasound Stimulation Improves Long-Term Functional Outcomes and Protects Against Brain Damage in Traumatic Brain Injury

The purpose of this study was to assess the long-term treatment efficacy of low-intensity pulsed ultrasound (LIPUS) on functional outcomes, brain edema, and the possible involvement of reactions in mice following traumatic brain injury (TBI). Mice subjected to controlled cortical impact injury received LIPUS treatment daily for a period of 4 weeks. The effects of LIPUS on edema were detected by MR imaging in the mouse brain at 148 days following TBI. Long-term functional outcomes of LIPUS stimulation were evaluated by behavioral analyses. One-way or two-way analysis of variance and Student's t test were used for statistical analyses, with a significant level of .05. Up to post-injury day 148, treatment with LIPUS significantly improved functional outcomes (all p < 0.05). LIPUS also significantly attenuated brain edema and neuronal death at day 148 after TBI (all p < 0.05). Furthermore, LIPUS reduced MMP9 activity, neutrophil infiltration, and microglial activation at day 1 or day 4 following TBI (all p < 0.05). Meanwhile, LIPUS increased the Bcl-2/Bax ratio and enhanced the phosphorylation of Bad and FOXO-1 at day 1 or day 4 following TBI (all p < 0.05). Almost 5 months of follow-up showed that the treatment efficacy of post-injury LIPUS stimulation on reduced brain edema and improved functional outcomes persisted over time after TBI. The neuroprotective effects of LIPUS are associated with a reduction of early inflammatory events and inhibition of apoptotic progression.

Transcranial ultrasound stimulation promotes brain-derived neurotrophic factor and reduces apoptosis in a mouse model of traumatic brain injury

BACKGROUND

The protein expressions of brain-derived neurotrophic factor (BDNF) can be elevated by transcranial ultrasound stimulation in the rat brain.

OBJECTIVE

The purpose of this study was to investigate the effects and underlying mechanisms of BDNF enhancement by low-intensity pulsed ultrasound (LIPUS) on traumatic brain injury (TBI).

METHODS

Mice subjected to controlled cortical impact injury were treated with LIPUS in the injured region daily for a period of 4 days. Western blot analysis and immunohistochemistry were performed to assess the effects of LIPUS.

RESULTS

The results showed that the LIPUS treatment significantly promoted the neurotrophic factors BDNF and vascular endothelial growth factor (VEGF) at day 4 after TBI. Meanwhile, LIPUS also enhanced the phosphorylation of Tropomyosin-related kinase B (TrkB), Akt, and cAMP-response element binding protein (CREB). Furthermore, treatment with LIPUS significantly decreased the level of cleaved caspase-3. The reduction of apoptotic process was inhibited by the anti-BDNF antibody.

CONCLUSIONS

In short, post-injury LIPUS treatment increased BDNF protein levels and inhibited the progression of apoptosis following TBI. The neuroprotective effects of LIPUS may be associated with enhancements of the protein levels of neurotrophic factors, at least partially via the TrkB/Akt-CREB signaling pathway.

Systematic Review of Genetic Risk Factors for Sustaining a Mild Traumatic Brain Injury

This systematic review examined the association between genetics and risk for sustaining a traumatic brain injury. We retrieved articles published in English from 1980 to July 2016 obtained from the online databases PubMed, PsycINFO®, MEDLINE®, Embase, and Web of Science. In total 5903 articles were identified, 77 underwent full-text screening, and 6 were included in this review. Five studies examined the risk of concussion associated with apolipoprotein E alleles (APOE-ɛ2, ɛ3,ɛ4), and polymorphisms of the APOE promoter (rs405509), brain derived neurotrophic factor (BDNF, rs6265), and dopamine receptor D2 (DRD2, rs1800497) were each considered in two studies. Microtubule associated protein tau (TAU exon 6 polymorphisms His47Tyr [rs2258689] and Ser53Pro [rs10445337]), and neurofilament heavy (NEHF, rs165602) genotypic variants, were the focus of single studies. No study showed an increased risk associated solely with the presence of the APOE-ɛ4 allele, nor were there any significant findings for the NEFH, TAU, or DRD2 genotypic variants. Two studies examined the APOE promoter -219G/T polymorphism in athletes, and both found an association with concussion. Both BDNF studies also found a significant association with concussion incidence; United States soldiers with the Met/Met genotype were more likely to report a history of concussion prior to deployment and to sustain a concussion during deployment. We conclude that the APOE promoter -219G/T polymorphism and the BDNF Met/Met genotype might confer risk for sustaining a TBI. Based on research to date, the APOE-ɛ4 allele does not appear to influence risk. More research is needed to determine if these findings replicate.

Neurotrauma: The Crosstalk between Neurotrophins and Inflammation in the Acutely Injured Brain

Traumatic brain injury (TBI) is a major cause of morbidity and mortality among young individuals worldwide. Understanding the pathophysiology of neurotrauma is crucial for the development of more effective therapeutic strategies. After the trauma occurs, immediate neurologic damage is produced by the traumatic forces; this primary injury triggers a secondary wave of biochemical cascades together with metabolic and cellular changes, called secondary neural injury. In the scenario of the acutely injured brain, the ongoing secondary injury results in ischemia and edema culminating in an uncontrollable increase in intracranial pressure. These areas of secondary injury progression, or areas of “traumatic penumbra”, represent crucial targets for therapeutic interventions. Neurotrophins are a class of signaling molecules that promote survival and/or maintenance of neurons. They also stimulate axonal growth, synaptic plasticity, and neurotransmitter synthesis and release. Therefore, this review focuses on the role of neurotrophins in the acute post-injury response. Here, we discuss possible endogenous neuroprotective mechanisms of neurotrophins in the prevailing environment surrounding the injured areas, and highlight the crosstalk between neurotrophins and inflammation with focus on neurovascular unit cells, particularly pericytes. The perspective is that neurotrophins may represent promising targets for research on neuroprotective and neurorestorative processes in the short-term following TBI.

Applying Systems Biology Methodology To Identify Genetic Factors Possibly Associated with Recovery after Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the leading causes of morbidity and mortality worldwide. It is linked with a number of medical, neurological, cognitive, and behavioral sequelae. The influence of genetic factors on the biology and related recovery after TBI is poorly understood. Studies that seek to elucidate the impact of genetic influences on neurorecovery after TBI will lead to better individualization of prognosis and inform development of novel treatments, which are considerably lacking. Current genetic studies related to TBI have focused on specific candidate genes. The objectives of this study were to use a system biology-based approach to identify biologic processes over-represented with genetic variants previously implicated in clinical outcomes after TBI and identify unique genes potentially related to recovery after TBI. After performing a systematic review to identify genes in the literature associated with clinical outcomes, we used the genes identified to perform a systems biology-based integrative computational analysis to ascertain the interactions between molecular components and to develop models for regulation and function of genes involved in TBI recovery. The analysis identified over-representation of genetic variants primarily in two biologic processes: response to injury (cell proliferation, cell death, inflammatory response, and cellular metabolism) and neurocognitive and behavioral reserve (brain development, cognition, and behavior). Overall, this study demonstrates the use of a systems biology-based approach to identify unique/novel genes or sets of genes important to the recovery process. Findings from this systems biology-based approach provide additional insight into the potential impact of genetic variants on the underlying complex biological processes important to TBI recovery and may inform the development of empirical genetic-related studies for TBI. Future studies that combine systems biology methodology and genomic, proteomic, and epigenetic approaches are needed in TBI.

BDNF Variants May Modulate Long-Term Visual Memory Performance in a Healthy Cohort

Brain-derived neurotrophic factor (BDNF) is involved in numerous cognitive functions including learning and memory. BDNF plays an important role in synaptic plasticity in humans and rats with BDNF shown to be essential for the formation of long-term memories. We previously identified a significant association between the BDNF Val66Met polymorphism (rs6265) and long-term visual memory (p-value = 0.003) in a small cohort (n = 181) comprised of healthy individuals who had been phenotyped for various aspects of memory function. In this study, we have extended the cohort to 597 individuals and examined multiple genetic variants across both the BDNF and BDNF-AS genes for association with visual memory performance as assessed by the Wechsler Memory Scale—Fourth Edition subtests Visual Reproduction I and II (VR I and II). VR I assesses immediate visual memory, whereas VR II assesses long-term visual memory. Genetic association analyses were performed for 34 single nucleotide polymorphisms genotyped on Illumina OmniExpress BeadChip arrays with the immediate and long-term visual memory phenotypes. While none of the BDNF and BDNF-AS variants were shown to be significant for immediate visual memory, we found 10 variants (including the Val66Met polymorphism (p-value = 0.006)) that were nominally associated, and three variants (two variants in BDNF and one variant in the BDNF-AS locus) that were significantly associated with long-term visual memory. Our data therefore suggests a potential role for BDNF, and its anti-sense transcript BDNF-AS, in long-term visual memory performance.

Pathological vascular and inflammatory biomarkers of acute- and chronic-phase traumatic brain injury

Given the demand for developing objective methods for characterizing traumatic brain injury (TBI), research dedicated to evaluating putative biomarkers has burgeoned over the past decade. Since it is critical to elucidate the underlying pathological processes that underlie the higher diverse outcomes that follow neurotrauma, considerable efforts have been aimed at identifying biomarkers of both the acute- and chronic-phase TBI. Such information is not only critical for helping to elucidate the pathological changes that lead to poor long-term outcomes following TBI but it may also assist in the identification of possible prevention and interventions for individuals who sustain head trauma. In the current review, we discuss the potential role of vascular dysfunction and chronic inflammation in both acute- and chronic-phase TBI, and we also highlight existing studies that have investigated inflammation biomarkers associated with poorer injury outcome.

Post-concussion symptoms and chronic pain after mild traumatic brain injury are modulated by multiple locus effect in the BDNF gene through the expression of antisense: A pilot prospective control study

Background: Mild traumatic brain injury (mTBI) often results in post-concussion symptoms, chronic pain, and sleepiness. Genetic factors are thought to play an important role in poor prognosis.

Aims: The aims of this study are to (1) document the prevalence of pain and post-concussion symptoms in mTBI patients in acute and chronic phases (2) determine whether candidate genes predispose to post-concussive symptoms and pain.

Methods: Posttraumatic symptoms, evaluated using the Rivermead Post-Concussion Symptoms Questionnaire, and pain were assessed in 94 mTBI patients in the acute phase as well as in 22 healthy controls. Assessment was repeated in 36 patients after one year who agreed to participate in the follow-up visit. Gene polymorphisms and expression were assessed in mTBI patients and healthy controls.

Results: In the acute phase, mTBI patients with pain (69%) presented more psychological symptoms and sleepiness and were less able to return to work than those without pain. At one year, 19% of mTBI patients had persistent pain and psychological distress. Two haplotypes (H2 and H3) in the brain-derived neurotrophic factor (BDNF) gene were shown to be respectively deleterious and protective against post-concussion symptoms and pain in both acute and chronic phases. Protective haplotype H3 was associated with a decreased expression of the anti-sense of BDNF (BDNF-AS). Deleterious haplotype H2 predicted the development of chronic pain at one year, whereas H3 was protective.

Conclusions: This pilot study suggests a protective mechanism of a multilocus effect in BDNF, through BDNF-AS, against post-concussion symptoms and pain in the acute phase and possibly chronic pain at one year post-mTBI. The role of antisense RNA should be validated in larger cohorts.

Missense Mutation of Brain Derived Neurotrophic Factor (BDNF) Alters Neurocognitive Performance in Patients with Mild Traumatic Brain Injury: A Longitudinal Study

The predictability of neurocognitive outcomes in patients with traumatic brain injury is not straightforward. The extent and nature of recovery in patients with mild traumatic brain injury (mTBI) are usually heterogeneous and not substantially explained by the commonly known demographic and injury-related prognostic factors despite having sustained similar injuries or injury severity. Hence, this study evaluated the effects and association of the Brain Derived Neurotrophic Factor (BDNF) missense mutations in relation to neurocognitive performance among patients with mTBI. 48 patients with mTBI were prospectively recruited and MRI scans of the brain were performed within an average 10.1 (SD 4.2) hours post trauma with assessment of their neuropsychological performance post full Glasgow Coma Scale (GCS) recovery. Neurocognitive assessments were repeated again at 6 months follow-up. The paired t-test, Cohen's d effect size and repeated measure ANOVA were performed to delineate statistically significant differences between the groups [wildtype G allele (Val homozygotes) vs. minor A allele (Met carriers)] and their neuropsychological performance across the time point (T1 = baseline/ admission vs. T2 = 6th month follow-up). Minor A allele carriers in this study generally performed more poorly on neuropsychological testing in comparison wildtype G allele group at both time points. Significant mean differences were observed among the wildtype group in the domains of memory (M = -11.44, SD = 10.0, p = .01, d = 1.22), executive function (M = -11.56, SD = 11.7, p = .02, d = 1.05) and overall performance (M = -6.89 SD = 5.3, p = .00, d = 1.39), while the minor A allele carriers showed significant mean differences in the domains of attention (M = -11.0, SD = 13.1, p = .00, d = .86) and overall cognitive performance (M = -5.25, SD = 8.1, p = .01, d = .66).The minor A allele carriers in comparison to the wildtype G allele group, showed considerably lower scores at admission and remained impaired in most domains across the timepoints, although delayed signs of recovery were noted to be significant in the domains attention and overall cognition. In conclusion, the current study has demonstrated the role of the BDNF rs6265 Val66Met polymorphism in influencing specific neurocognitive outcomes in patients with mTBI. Findings were more detrimentally profound among Met allele carriers.

The role of biomarkers and MEG-based imaging markers in the diagnosis of post-traumatic stress disorder and blast-induced mild traumatic brain injury

BACKGROUND

Pervasive use of improvised explosive devices (IEDs), rocket-propelled grenades, and land mines in the recent conflicts in Iraq and Afghanistan has brought traumatic brain injury (TBI) and its impact on health outcomes into public awareness. Blast injuries have been deemed signature wounds of these wars. War-related TBI is not new, having become prevalent during WWI and remaining medically relevant in WWII and beyond. Medicine's past attempts to accurately diagnose and disentangle the pathophysiology of war-related TBI parallels current lines of inquiry and highlights limitations in methodology and attribution of symptom etiology, be it organic, psychological, or behavioral. New approaches and biomarkers are needed.

PRECLINICAL

Serological biomarkers and biomarkers of injury obtained with imaging techniques represent cornerstones in the translation between experimental data and clinical observations. Experimental models for blast related TBI and PTSD can generate critical data on injury threshold, for example for white matter injury from acceleration. Carefully verified and validated models can be evaluated with gene expression arrays and proteomics to identify new candidates for serological biomarkers. Such models can also be analyzed with diffusion MRI and microscopy in order to identify criteria for detection of diffuse white matter injuries, such as DAI (diffuse axonal injury). The experimental models can also be analyzed with focus on injury outcome in brain stem regions, such as locus coeruleus or nucleus raphe magnus that can be involved in response to anxiety changes.

CLINICAL

Mild (and some moderate) TBI can be difficult to diagnose because the injuries are often not detectable on conventional MRI or CT. There is accumulating evidence that injured brain tissues in TBI patients generate abnormal low-frequency magnetic activity (ALFMA, peaked at 1-4Hz) that can be measured and localized by magnetoencephalography (MEG). MEG imaging detects TBI abnormalities at the rates of 87% for the mild TBI, group (blast-induced plus non-blast causes) and 100% for the moderate group. Among the mild TBI patients, the rates of abnormalities are 96% and 77% for the blast and non-blast TBI groups, respectively. There is emerging evidence based on fMRI and MEG studies showing hyper-activity in the amygdala and hypo-activity in pre-frontal cortex in individuals with PTSD. MEG signal may serve as a sensitive imaging marker for mTBI, distinguishable from abnormalities generated in association with PTSD. More work is needed to fully describe physiological mechanisms of post-concussive symptoms.

Impact of traumatic brain injury on sleep structure, electrocorticographic activity and transcriptome in mice

Traumatic brain injury (TBI), including mild TBI (mTBI), is importantly associated with vigilance and sleep complaints. Because sleep is required for learning, plasticity and recovery, we here evaluated the bidirectional relationship between mTBI and sleep with two specific objectives: (1) Test that mTBI rapidly impairs sleep-wake architecture and the dynamics of the electrophysiological marker of sleep homeostasis (i.e., non-rapid eye movement sleep delta (1-4Hz) activity); (2) evaluate the impact of sleep loss following mTBI on the expression of plasticity markers that have been linked to sleep homeostasis and on genome-wide gene expression. A closed-head injury model was used to perform a 48h electrocorticographic (ECoG) recording in mice submitted to mTBI or Sham surgery. mTBI was found to immediately decrease the capacity to sustain long bouts of wakefulness as well as the amplitude of the time course of ECoG delta activity during wakefulness. Significant changes in ECoG spectral activity during wakefulness, non-rapid eye movement and rapid eye movement sleep were observed mainly on the second recorded day. A second experiment was performed to measure gene expression in the cerebral cortex and hippocampus after a mTBI followed either by two consecutive days of 6h sleep deprivation (SD) or of undisturbed behavior (quantitative PCR and next-generation sequencing). mTBI modified the expression of genes involved in immunity, inflammation and glial function (e.g., chemokines, glial markers) and SD changed that of genes linked to circadian rhythms, synaptic activity/neuronal plasticity, neuroprotection and cell death and survival. SD appeared to affect gene expression in the cerebral cortex more importantly after mTBI than Sham surgery including that of the astrocytic marker Gfap, which was proposed as a marker of clinical outcome after TBI. Interestingly, SD impacted the hippocampal expression of the plasticity elements Arc and EfnA3 only after mTBI. Overall, our findings reveal alterations in spectral signature across all vigilance states in the first days after mTBI, and show that sleep loss post-mTBI reprograms the transcriptome in a brain area-specific manner and in a way that could be deleterious to brain recovery.

Neurotransmitter Systems in a Mild Blast Traumatic Brain Injury Model: Catecholamines and Serotonin

Exposure to improvised explosive devices can result in a unique form of traumatic brain injury--blast-induced traumatic brain injury (bTBI). At the mild end of the spectrum (mild bTBI [mbTBI]), there are cognitive and mood disturbances. Similar symptoms have been observed in post-traumatic stress disorder caused by exposure to extreme psychological stress without physical injury. A role of the monoaminergic system in mood regulation and stress is well established but its involvement in mbTBI is not well understood. To address this gap, we used a rodent model of mbTBI and detected a decrease in immobility behavior in the forced swim test at 1 d post-exposure, coupled with an increase in climbing behavior, but not after 14 d or later, possibly indicating a transient increase in anxiety-like behavior. Using in situ hybridization, we found elevated messenger ribonucleic acid levels of both tyrosine hydroxylase and tryptophan hydroxylase 2 in the locus coeruleus and the dorsal raphe nucleus, respectively, as early as 2 h post-exposure. High-performance liquid chromatography analysis 1 d post-exposure primarily showed elevated noradrenaline levels in several forebrain regions. Taken together, we report that exposure to mild blast results in transient changes in both anxiety-like behavior and brain region-specific molecular changes, implicating the monoaminergic system in the pathobiology of mbTBI.

The neuropathology of traumatic brain injury

Traumatic brain injury, a leading cause of mortality and morbidity, is divided into three grades of severity: mild, moderate, and severe, based on the Glasgow Coma Scale, the loss of consciousness, and the development of post-traumatic amnesia. Although mild traumatic brain injury, including concussion and subconcussion, is by far the most common, it is also the most difficult to diagnose and the least well understood. Proper recognition, management, and treatment of acute concussion and mild traumatic brain injury are the fundamentals of an emerging clinical discipline. It is also becoming increasingly clear that some mild traumatic brain injuries have persistent, and sometimes progressive, long-term debilitating effects. Evidence indicates that a single traumatic brain injury can precipitate or accelerate multiple age-related neurodegenerations, increase the risk of developing Alzheimer's disease, Parkinson's disease, and motor neuron disease, and that repetitive mild traumatic brain injuries can provoke the development of a tauopathy, chronic traumatic encephalopathy. Clinically, chronic traumatic encephalopathy is associated with behavioral changes, executive dysfunction, memory loss, and cognitive impairments that begin insidiously and progress slowly over decades. Pathologically, chronic traumatic encephalopathy produces atrophy of the frontal and temporal lobes, thalamus, and hypothalamus, septal abnormalities, and abnormal deposits of hyperphosphorylated tau (τ) as neurofibrillary tangles and disordered neurites throughout the brain. The incidence and prevalence of chronic traumatic encephalopathy and the genetic risk factors critical to its development are currently unknown. Chronic traumatic encephalopathy frequently occurs as a sole diagnosis, but may be associated with other neurodegenerative disorders, including Alzheimer's disease, Lewy body disease, and motor neuron disease. Currently, chronic traumatic encephalopathy can be diagnosed only at autopsy; however, promising efforts to develop imaging, spinal fluid, and peripheral blood biomarkers are underway to diagnose and monitor the course of disease in living subjects.

Variation in the BDNF gene interacts with age to predict mortality in a prospective, longitudinal cohort with severe TBI

BACKGROUND

Mortality predictions following traumatic brain injury (TBI), and our understanding of TBI pathology, may be improved by including genetic risk in addition to traditional prognostic variables. One promising target is the gene coding for brain-derived neurotrophic factor (BDNF), a ubiquitous neurotrophin important for neuronal survival and neurogenesis.

OBJECTIVE

We hypothesized the addition of BDNF genetic variation would improve mortality prediction models and that BDNF Met-carriers (rs6265) and C-carriers (rs7124442) would have the highest mortality rates post-TBI.

METHODS

This study examined BDNF functional single nucleotide polymorphisms rs6265 (val66met) and rs7124442 (T>C) in relation to mortality in a prospective, longitudinal cohort with severe TBI. We examined 315 individuals receiving care for a closed head injury within the University of Pittsburgh Medical Center, aged 16 to 74 years. Mortality was examined acutely (0-7 days postinjury) and postacutely (8-365 days postinjury). A gene risk score (GRS) was developed to examine both BDNF loci. Cox proportional hazards models were used to calculate hazard ratios for survivability post-TBI while controlling for covariates.

RESULTS

BDNF GRS was significantly associated with acute mortality, regardless of age. Interestingly, subjects in the hypothesized no-risk allele group had the lowest survival probability. Postacutely, BDNF-GRS interacted with age such that younger participants in the no-risk group had the highest survival probability, while older participants in the hypothesized no-risk group had the lowest probability of survival.

CONCLUSIONS

These data suggest complex relationships between BDNF and TBI mortality that interact with age to influence survival predictions beyond clinical variables alone. Evidence supporting dynamic, temporal balances of pro-survival/pro-apoptotic target receptors may explain injury and age-related gene associations.

Melatonin reduced microglial activation and alleviated neuroinflammation induced neuron degeneration in experimental traumatic brain injury: Possible involvement of mTOR pathway

This study was designed to detect the modulation manner of melatonin on microglial activation and explore herein possible involvement of mammalian target of rapamycin (mTOR) pathway following traumatic brain injury (TBI). ICR mice were divided into four groups: sham group, TBI group, TBI+sal group and TBI+Melatonin group. A weight-drop model was employed to cause TBI. Neurological severity score (NSS) tests were performed to measure behavioral outcomes. Nissl staining was conducted to observe the neuronal degeneration and wet-to-dry weight ratio indicated brain water content. Immunofluorescence was designed to investigate microglial activation. Enzyme-linked immunosorbent assay (ELISA) was employed to evaluate proinflammatory cytokine levels (interleukin-beta (IL-1β), tumor necrosis factor-alpha (TNF-α)). Western blotting was engaged to analyze the protein content of mammalian target of rapamycin (mTOR), p70 ribosomal S6 kinase (p70S6K) and S6 ribosomal protein (S6RP). Melatonin administration was associated with markedly restrained microglial activation, decreased release of proinflammatory cytokines and increased the number of surviving neurons at the site of peri-contusion. Meanwhile, melatonin administration resulted in dephosphorylated mTOR pathway. In conclusion, this study presents a new insight into the mechanisms responsible for the anti-neuroinflammation of melatonin, with possible involvement of mTOR pathway.

Preservation of general intelligence following traumatic brain injury: contributions of the Met66 brain-derived neurotrophic factor

Brain-derived neurotrophic factor (BDNF) promotes survival and synaptic plasticity in the human brain. The Val66Met polymorphism of the BDNF gene interferes with intracellular trafficking, packaging, and regulated secretion of this neurotrophin. The human prefrontal cortex (PFC) shows lifelong neuroplastic adaption implicating the Val66Met BDNF polymorphism in the recovery of higher-order executive functions after traumatic brain injury (TBI). In this study, we examined the effect of this BDNF polymorphism on the preservation of general intelligence following TBI. We genotyped a sample of male Vietnam combat veterans (n = 156) consisting of a frontal lobe lesion group with focal penetrating head injuries for the Val66Met BDNF polymorphism. Val/Met did not differ from Val/Val genotypes in general cognitive ability before TBI. However, we found substantial average differences between these groups in general intelligence (≈ half a standard deviation or 8 IQ points), verbal comprehension (6 IQ points), perceptual organization (6 IQ points), working memory (8 IQ points), and processing speed (8 IQ points) after TBI. These results support the conclusion that Val/Met genotypes preserve general cognitive functioning, whereas Val/Val genotypes are largely susceptible to TBI.

Pharmacogenetics of addiction therapy

Drug addiction is a serious relapsing disease that has high costs to society and to the individual addicts. Treatment of these addictions is still in its nascency, with only a few examples of successful therapies. Therapeutic response depends upon genetic, biological, social, and environmental components. A role for genetic makeup in the response to treatment has been shown for several addiction pharmacotherapies. For several addiction pharmacotherapies, response to treatment varies based on individual genetic makeup. In this chapter, we discuss the role of genetics in pharmacotherapies, specifically for cocaine, alcohol, and opioid dependences. The elucidation of the role of genetics should aid in the development of new treatments and increase the efficacy of existing treatments.

Alteration in BDNF and its receptors, full-length and truncated TrkB and p75(NTR) following penetrating traumatic brain injury

The evidence that BDNF is involved in neuroprotection, neuronal repair and recovery after traumatic brain injury (TBI) is substantial. We have previously shown that the polymorphism of the human BDNF gene predicts cognitive recovery and outcome following penetrating TBI. The distribution of expression of BDNF and its receptors after penetrating TBI has not been investigated. In this study we examined the expression of these genes in a rat model of penetrating TBI. The injury is produced by a controlled penetration of a 2mm thick needle-shaped object, which is accelerated with a pellet from an air gun. We used in situ hybridization and investigated the mRNA expression of BDNF and its receptors: the full-length and the truncated TrkB and p75(NTR), from 1 day to 8 weeks following penetrating TBI. In addition, the protein level of BDNF in frontal cortex and hippocampus was measured by reverse phase protein microarray (RPPM). The mRNA expression of BDNF and its receptors decreased in the hippocampus in the border zone ipsilateral to the injury while there was an increase in mRNA expression at the contralateral side. The increase in BDNF mRNA expression in the hippocampus was sustained for 2 weeks following injury, with the highest expression noted in the CA3 cell layer. Furthermore, the protein analysis by RPPM showed increased levels of BDNF in the frontal cortex and the hippocampus up to 2 weeks after TBI. At 8 weeks following injury there was an intense labeling of the truncated TrkB receptor and the p75(NTR) in the area surrounding the cavity. Our study is the first report on the expression of BDNF and its receptors following penetrating TBI and suggests that their expression is altered long after the acute phase of injury. Further studies are needed to investigate if the late expressions of these receptors are beneficial or deleterious. In either case it indicates the possibility to influence the recovery after brain injury during the chronic phase and the development of treatments that may improve the outcome of TBI patients.

Association study between BDNF gene variants and Mexican patients with obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a psychiatric disorder whose etiology is not yet known. We investigate the role of three variants of the BDNF gene (rs6265, rs1519480 and rs7124442) by single SNP and haplotype analysis in OCD Mexican patients using a case-control and family-based association design. BDNF gene variants were genotyped in 283 control subjects, 232 OCD patients and first degree relatives of 111 OCD subjects. Single SNP analysis in case-control study showed an association between rs6265 and OCD with a high frequency of Val/Val genotype and Val allele (p=0.0001 and p=0.0001, respectively). Also, genotype and allele analysis of rs1519480 showed significant differences (p=0.0001, p=0.0001; respectively) between OCD and control groups. Haplotype analysis showed a high frequency of A-T (rs6265-rs1519480) in OCD patients compared with the control group (OR=2.06 [1.18-3.59], p=0.0093) and a low frequency of haplotype A-C in the OCD patients (OR=0.04 [0.01-0.16], p=0.000002). The family-based association study showed no significant differences in the transmission of any variant. Our study replicated the association between BDNF Val66Met gene polymorphism and OCD. Also, we found a significant association of rs1519480 in OCD patients compared with a control group, region that has never been analyzed in OCD. In conclusion, our findings suggest that BDNF gene could be related to the development of OCD.

Distinct roles for somatically and dendritically synthesized brain-derived neurotrophic factor in morphogenesis of dendritic spines

Dendritic spines undergo the processes of formation, maturation, and pruning during development. Molecular mechanisms controlling spine maturation and pruning remain largely unknown. The gene for brain-derived neurotrophic factor (BDNF) produces two pools of mRNA, with either a short or long 3' untranslated region (3' UTR). Our previous results show that short 3' UTR Bdnf mRNA is restricted to cell bodies, whereas long 3' UTR Bdnf mRNA is also trafficked to dendrites for local translation. Mutant mice lacking long 3' UTR Bdnf mRNA display normal spines at 3 weeks of age, but thinner and denser spines in adults compared to wild-type littermates. These observations suggest that BDNF translated from long 3' UTR Bdnf mRNA, likely in dendrites, is required for spine maturation and pruning. In this study, using rat hippocampal neuronal cultures, we found that knocking down long 3' UTR Bdnf mRNA blocked spine head enlargement and spine elimination, whereas overexpressing long 3' UTR Bdnf mRNA had the opposite effect. The effect of long 3' UTR Bdnf mRNA on spine head enlargement and spine elimination was diminished by a human single-nucleotide polymorphism (SNP, rs712442) in its 3' UTR that inhibited dendritic localization of Bdnf mRNA. Furthermore, we found that overexpression of either Bdnf mRNA increased spine density at earlier time points. Spine morphological alterations were associated with corresponding changes in density, size, and function of synapses. These results indicate that somatically synthesized BDNF promotes spine formation, whereas dendritically synthesized BDNF is a key regulator of spine head growth and spine pruning.

Age-modulated association between prefrontal NAA and the BDNF gene

Brain-derived neurotrophic factor (BDNF) has been implicated in the pathophysiology of psychiatric and neurological disorders and in the mechanisms of antidepressant pharmacotherapy. Psychiatric and neurological conditions have also been associated with reduced brain levels of N-acetyl-aspartate (NAA), which has been used as a putative marker of neural integrity. However, few studies have explored the relationship between BDNF polymorphisms and NAA levels directly. Here, we present data from a single-voxel proton magnetic resonance spectroscopy study of 64 individuals and explore the relationship between BDNF polymorphisms and prefrontal NAA level. Our results indicate an association between a single nucleotide polymorphism (SNP) within BDNF, known as rs1519480, and reduced NAA level (p = 0.023). NAA levels were further predicted by age and Asian ancestry. There was a significant rs1519480 × age interaction on NAA level (p = 0.031). Specifically, the effect of rs1519480 on NAA level became significant at age ⩾34.17 yr. NAA level decreased with advancing age for genotype TT (p = 0.001) but not for genotype CT (p = 0.82) or CC (p = 0.34). Additional in silico analysis of 142 post-mortem brain samples revealed an association between the same SNP and reduced BDNF mRNA expression in the prefrontal cortex. The rs1519480 SNP influences BDNF mRNA expression and has an impact on prefrontal NAA level over time. This genetic mechanism may contribute to inter-individual variation in cognitive performance seen during normal ageing, as well as contributing to the risk for developing psychiatric and neurological conditions.

Microglia activation as a biomarker for traumatic brain injury

Traumatic brain injury (TBI) has become the signature wound of wars in Afghanistan and Iraq. Injury may result from a mechanical force, a rapid acceleration-deceleration movement, or a blast wave. A cascade of secondary cell death events ensues after the initial injury. In particular, multiple inflammatory responses accompany TBI. A series of inflammatory cytokines and chemokines spreads to normal brain areas juxtaposed to the core impacted tissue. Among the repertoire of immune cells involved, microglia is a key player in propagating inflammation to tissues neighboring the core site of injury. Neuroprotective drug trials in TBI have failed, likely due to their sole focus on abrogating neuronal cell death and ignoring the microglia response despite these inflammatory cells’ detrimental effects on the brain. Another relevant point to consider is the veracity of results of animal experiments due to deficiencies in experimental design, such as incomplete or inadequate method description, data misinterpretation, and reporting may introduce bias and give false-positive results. Thus, scientific publications should follow strict guidelines that include randomization, blinding, sample-size estimation, and accurate handling of all data (Landis et al., 2012). A prolonged state of inflammation after brain injury may linger for years and predispose patients to develop other neurological disorders, such as Alzheimer’s disease. TBI patients display progressive and long-lasting impairments in their physical, cognitive, behavioral, and social performance. Here, we discuss inflammatory mechanisms that accompany TBI in an effort to increase our understanding of the dynamic pathological condition as the disease evolves over time and begin to translate these findings for defining new and existing inflammation-based biomarkers and treatments for TBI.