National Institute of Neurological Disorders and Stroke Consensus Diagnostic Criteria for Traumatic Encephalopathy Syndrome

Chronic Traumatic Encephalopathy as a Preventable Environmental Disease

In this Perspective we explore the evolution of our understanding of chronic traumatic encephalopathy (CTE) and its relationship with repetitive head injury. As with many neurodegenerative conditions, there is an imperfect correspondence between neuropathology and clinical phenotype, but unlike other neurodegenerative diseases, CTE has a discrete and easily modifiable risk factor: exposure to repetitive head injury. Consequently, evaluation of the evidence regarding exposure to repetitive head injury and CTE risk should be undertaken using public or occupational health frameworks of medical knowledge. The current debate over the existence of CTE as a disease of concern is fuelled in part by immediate medico-legal considerations, and the involvement of high-profile athletes, with inevitable media interest. Moving beyond this debate has significant potential to address and reduce disease impact in the near future, and provide novel insights into mechanisms underlying abnormal protein accumulation in CTE and other neurodegenerative diseases.

Chronic Traumatic Encephalopathy in the Brains of Military Personnel

BACKGROUND

Persistent neuropsychiatric sequelae may develop in military personnel who are exposed to combat; such sequelae have been attributed in some cases to chronic traumatic encephalopathy (CTE). Only limited data regarding CTE in the brains of military service members are available.

METHODS

We performed neuropathological examinations for the presence of CTE in 225 consecutive brains from a brain bank dedicated to the study of deceased service members. In addition, we reviewed information obtained retrospectively regarding the decedents' histories of blast exposure, contact sports, other types of traumatic brain injury (TBI), and neuropsychiatric disorders.

RESULTS

Neuropathological findings of CTE were present in 10 of the 225 brains (4.4%) we examined; half the CTE cases had only a single pathognomonic lesion. Of the 45 brains from decedents who had a history of blast exposure, 3 had CTE, as compared with 7 of 180 brains from those without a history of blast exposure (relative risk, 1.71; 95% confidence interval [CI], 0.46 to 6.37); 3 of 21 brains from decedents with TBI from an injury during military service caused by the head striking a physical object without associated blast exposure (military impact TBI) had CTE, as compared with 7 of 204 without this exposure (relative risk, 4.16; 95% CI, 1.16 to 14.91). All brains with CTE were from decedents who had participated in contact sports; 10 of 60 contact-sports participants had CTE, as compared with 0 of 165 who had not participated in contact sports (point estimate of relative risk not computable; 95% CI, 6.16 to infinity). CTE was present in 8 of 44 brains from decedents with non-sports-related TBI in civilian life, as compared with 2 of 181 brains from those without such exposure in civilian life (relative risk, 16.45; 95% CI, 3.62 to 74.79).

CONCLUSIONS

Evidence of CTE was infrequently found in a series of brains from military personnel and was usually reflected by minimal neuropathologic changes. Risk ratios for CTE were numerically higher among decedents who had contact-sports exposure and other exposures to TBI in civilian life than among those who had blast exposure or other military TBI, but the small number of CTE cases and wide confidence intervals preclude causal conclusions. (Funded by the Department of Defense-Uniformed Services University Brain Tissue Repository and Neuropathology Program and the Henry M. Jackson Foundation for the Advancement of Military Medicine.).

MicroRNA Alterations in Chronic Traumatic Encephalopathy and Amyotrophic Lateral Sclerosis

Repetitive head impacts (RHI) and traumatic brain injuries are risk factors for the neurodegenerative diseases chronic traumatic encephalopathy (CTE) and amyotrophic lateral sclerosis (ALS). ALS and CTE are distinct disorders, yet in some instances, share pathology, affect similar brain regions, and occur together. The pathways involved and biomarkers for diagnosis of both diseases are largely unknown. MicroRNAs (miRNAs) involved in gene regulation may be altered in neurodegeneration and be useful as stable biomarkers. Thus, we set out to determine associations between miRNA levels and disease state within the prefrontal cortex in a group of brain donors with CTE, ALS, CTE + ALS and controls. Of 47 miRNAs previously implicated in neurological disease and tested here, 28 (60%) were significantly different between pathology groups. Of these, 21 (75%) were upregulated in both ALS and CTE, including miRNAs involved in inflammatory, apoptotic, and cell growth/differentiation pathways. The most significant change occurred in miR-10b, which was significantly increased in ALS, but not CTE or CTE + ALS. Overall, we found patterns of miRNA expression that are common and unique to CTE and ALS and that suggest shared and distinct mechanisms of pathogenesis.

Remote blast-related mild traumatic brain injury is associated with differential expression of exosomal microRNAs identified in neurodegenerative and immunological processes

BACKGROUND

Blast traumatic brain injury (TBI) and subconcussive blast exposure have been associated, pathologically, with chronic traumatic encephalopathy (CTE) and, clinically, with cognitive and affective symptoms, but the underlying pathomechanisms of these associations are not well understood. We hypothesized that exosomal microRNA (miRNA) expression, and their relation to neurobehavioral outcomes among Veterans with blunt or blast mild TBI (mTBI) may provide insight into possible mechanisms for these associations and therapeutic targets.

METHODS

This is a subanalysis of a larger Chronic Effects of Neurotrauma Consortium Biomarker Discovery Project. Participants (n = 152) were divided into three groups: Controls (n = 35); Blunt mTBI only (n = 54); and Blast/blast+blunt mTBI (n = 63). Postconcussive and post-traumatic stress symptoms were evaluated using the NSI and PCL-5, respectively. Exosomal levels of 798 miRNA expression were measured.

RESULTS

In the blast mTBI group, 23 differentially regulated miRNAs were observed compared to the blunt mTBI group and 23 compared to controls. From the pathway analysis, significantly dysregulated miRNAs in the blast exposure group correlated with inflammatory, neurodegenerative, and androgen receptor pathways.

DISCUSSION

Our findings suggest that chronic neurobehavioral symptoms after blast TBI may pathomechanistically relate to dysregulated cellular pathways involved with neurodegeneration, inflammation, and central hormonal regulation.

A Pilot Study of Whole-Blood Transcriptomic Analysis to Identify Genes Associated with Repetitive Low-Level Blast Exposure in Career Breachers

Repetitive low-level blast exposure is one of the major occupational health concerns among US military service members and law enforcement. This study seeks to identify gene expression using microRNA and RNA sequencing in whole-blood samples from experienced breachers and unexposed controls. We performed experimental RNA sequencing using Illumina’s HiSeq 2500 Sequencing System, and microRNA analysis using NanoString Technology nCounter miRNA expression panel in whole-blood total RNA samples from 15 experienced breachers and 14 age-, sex-, and race-matched unexposed controls. We identified 10 significantly dysregulated genes between experienced breachers and unexposed controls, with FDR corrected <0.05: One upregulated gene, LINC00996 (long intergenic non-protein coding RNA 996); and nine downregulated genes, IGLV3-16 (immunoglobulin lambda variable 3-16), CD200 (CD200 molecule), LILRB5 (leukocyte immunoglobulin-like receptor B5), ZNF667-AS1 (ZNF667 antisense RNA 1), LMOD1 (leiomodin 1), CNTNAP2 (contactin-associated protein 2), EVPL (envoplakin), DPF3 (double PHD fingers 3), and IGHV4-34 (immunoglobulin heavy variable 4-34). The dysregulated gene expressions reported here have been associated with chronic inflammation and immune response, suggesting that these pathways may relate to the risk of lasting neurological symptoms following high exposures to blast over a career.

Longitudinal trajectory of depression symptom severity and the influence of concussion history and physical function over a 19-year period among former National Football League (NFL) players: an NFL-LONG Study

OBJECTIVE

This study investigated the longitudinal course of depressive symptom severity over 19 years in former American football players and the influence of concussion history, contact sport participation and physical function on observed trajectories.

METHODS

Former American football players completed a general health questionnaire involving demographic information, medical/psychiatric history, concussion/football history and validated measures of depression and physical function at three time points (2001, 2010 and 2019). Parallel process latent growth curve modelling tested associations between concussion history, years of football participation, and overall and change in physical function on the overall level and trajectory of depressive symptoms.

RESULTS

Among the 333 participants (mean(SD) age, 48.95 (9.37) at enrolment), there was a statistically significant, but small increase in depressive symptom severity from 2001 (48.34 (7.75)) to 2019 (49.77 (9.52)), slope=0.079 (SE=0.11), p=0.007. Those with greater concussion history endorsed greater overall depressive symptom severity, B=1.38 (SE=0.33), p<0.001. Concussion history, B<0.001 (SE=0.02), p=0.997 and years of participation, B<0.001 (SE=0.01), p=0.980, were not associated with rate of change (slope factor) over 19 years. Greater decline in physical function, B=-0.71 (SE=0.16), p<0.001, was predictive of a faster growth rate (ie, steeper increase) of depression symptom endorsement over time.

CONCLUSIONS

Concussion history, not years of participation, was associated with greater depressive symptom severity. Neither factor was predictive of changes over a 19-year period. Decline in physical function was a significant predictor of a steeper trajectory of increased depressive symptoms, independent of concussion effects. This represents one viable target for preventative intervention to mitigate long-term neuropsychiatric difficulties associated with concussion across subsequent decades of life.

Mental Health Consequences of Traumatic Brain Injury

Traumatic brain injury (TBI) is associated with a host of psychiatric and neurobehavioral problems. As mortality rates have declined for severe TBI, attention has turned to the cognitive, affective, and behavioral sequelae of injuries across the severity spectrum, which are often more disabling than residual physical effects. Moderate and severe TBI can cause personality changes including impulsivity, severe irritability, affective instability, and apathy. Mild TBI, once considered a largely benign phenomenon, is now known to be associated with a range of affective symptoms, with suicidality, and with worsening or new onset of several psychiatric disorders including posttraumatic stress disorder and major depressive disorder. Repetitive head impacts, often in athletic contexts, are now believed to be associated with a number of emotional and behavioral sequelae. The nature and etiology of mental health manifestations of TBI (including a combination of brain dysfunction and psychological trauma and interrelationships between cognitive, affective, and physical symptoms) are complex and have been a focus of recent epidemiological and mechanistic studies. This paper will review the epidemiology of psychiatric and neurobehavioral problems after TBI in military, civilian, and athletic contexts.

High School Football and Risk for Depression and Suicidality in Adulthood: Findings From a National Longitudinal Study

BACKGROUND

There is growing public concern regarding the potential long-term effects of playing football on brain health, specifically that playing football before and during high school might cause damage to the brain that manifests years or decades later as depression or suicidality. This study examined if playing high school football was associated with increased lifetime risk for depression, suicidality over the past year, or depressed mood in the past week in men aged between their middle 30 s to early 40 s.

METHODS

Publicly available data from the National Longitudinal Study of Adolescent to Adult Health were analyzed. This longitudinal, prospective cohort study sampled nationally representative U.S. youth starting in 1994-1995 (Wave I) and most recently in 2016-2018 (Wave V). A total of 3,147 boys participated in Wave I (median age = 15), of whom 1,805 were re-assessed during Wave V (median age = 38).

RESULTS

Of the 1,762 men included in the study, 307 (17.4%) men reported being diagnosed with depression and 275 (15.6%) reported being diagnosed with an anxiety disorder or panic disorder at some point in their life. When comparing men who played high school football to those who did not, there were no differences in the proportions of the sample who had a lifetime diagnosis of depression, lifetime diagnosis of anxiety/panic disorders, suicidal ideation in the past year, psychological counseling in the past year, or current depressed mood. However, men who received psychological counseling and/or experienced suicidal ideation during adolescence were significantly more likely to report a lifetime history of depression, suicidal ideation in the past year, and current depressed mood.

CONCLUSION

Individuals who reported playing football during adolescence did not have an increased risk of depression or suicidal ideation when they were in their middle 30 s to early 40 s, but mental health problems during adolescence were associated with an increased risk for psychological health difficulties more than 20 years later.

Sports-Related Dystonia

Background

Task-specific dystonia (TSD) is a form of focal dystonia that occurs in the context of the performance of selective, highly skilled, often repetitive, motor activity. TSD may be apparent during certain tasks such as writing, playing musical instruments, or other activities requiring fine motor control, but may also occur during certain sports, and maybe detrimental to professional athletes' careers. Therefore, sports physicians and movement disorder neurologists need to be aware of the presentation and phenomenology of sports-related dystonia (SRD), the topic of this review.

Methods

A broad PubMed search using a wide range of keywords and combinations was done in October 2021 to identify suitable articles for this review.

Results

Most of the publications are on yips in golfers and on runners' dystonia. Other sports in which SRD has been reported are ice skating, tennis, table tennis, pistol shooting, petanque, baseball, and billiards.

Discussion

Yips, which may affect up to half of the golfers and rarely athletes in other sports (e.g., baseball, cricket, basketball, speed skating, gymnastics) seems to be a multi-factorial form of TSD that is particularly troublesome in highly skilled professional golfers. Runners' dystonia, affecting the foot, leg, and hip (in decreasing order), may evolve into more generalized and less specific dystonia. The pathophysiologic mechanisms of SRD are not well understood. Botulinum toxin has been reported to alleviate dystonia in golfers', runners', and other forms of SRD. Future studies should utilize neurophysiologic, imaging, and other techniques to elucidate mechanisms of this underrecognized group of movement disorders.

Association Between Antemortem FLAIR White Matter Hyperintensities and Neuropathology in Brain Donors Exposed to Repetitive Head Impacts

BACKGROUND AND OBJECTIVES

Late neuropathologies of repetitive head impacts from contact sports can include chronic traumatic encephalopathy (CTE) and white matter degeneration. White matter hyperintensities (WMH) on fluid-attenuated inversion recovery (FLAIR) MRI scans are often viewed as microvascular disease from vascular risk, but might have unique underlying pathologies and risk factors in the setting of repetitive head impacts. We investigated the neuropathologic correlates of antemortem WMH in brain donors exposed to repetitive head impacts. The association between WMH and repetitive head impact exposure and informant-reported cognitive and daily function were tested.

METHODS

This imaging-pathologic correlation study included symptomatic male decedents exposed to repetitive head impacts. Donors had antemortem FLAIR scans from medical records and were without evidence of CNS neoplasm, large vessel infarcts, hemorrhage, or encephalomalacia. WMH were quantified using log-transformed values for total lesion volume (TLV), calculated using the lesion prediction algorithm from the Lesion Segmentation Toolbox. Neuropathologic assessments included semiquantitative ratings of white matter rarefaction, cerebrovascular disease, hyperphosphorylated tau (p-tau) severity (CTE stage, dorsolateral frontal cortex), and β-amyloid (Aβ). Among football players, years of play was a proxy for repetitive head impact exposure. Retrospective informant-reported cognitive and daily function were assessed using the Cognitive Difficulties Scale (CDS) and Functional Activities Questionnaire (FAQ). Regression models controlled for demographics, diabetes, hypertension, and MRI resolution. Statistical significance was defined as p ≤ 0.05.

RESULTS

The sample included 75 donors: 67 football players and 8 nonfootball contact sport athletes or military veterans. Dementia was the most common MRI indication (64%). Fifty-three (70.7%) had CTE at autopsy. Log TLV was associated with white matter rarefaction (odds ratio [OR] 2.32, 95% confidence interval [CI] 1.03, 5.24; p = 0.04), arteriolosclerosis (OR 2.38, 95% CI 1.02, 5.52; p = 0.04), CTE stage (OR 2.58, 95% CI 1.17, 5.71; p = 0.02), and dorsolateral frontal p-tau severity (OR 3.03, 95% CI 1.32, 6.97; p = 0.01). There was no association with Aβ. More years of football play was associated with log TLV (unstandardized β 0.04, 95% CI 0.01, 0.06; p = 0.01). Greater log TLV correlated with higher FAQ (unstandardized β 4.94, 95% CI 0.42, 8.57; p = 0.03) and CDS scores (unstandardized β 15.35, 95% CI -0.27, 30.97; p = 0.05).

DISCUSSION

WMH might capture long-term white matter pathologies from repetitive head impacts, including those from white matter rarefaction and p-tau, in addition to microvascular disease. Prospective imaging-pathologic correlation studies are needed.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence of associations between FLAIR white matter hyperintensities and neuropathologic changes (white matter rarefaction, arteriolosclerosis, p-tau accumulation), years of American football play, and reported cognitive symptoms in symptomatic brain donors exposed to repetitive head impacts.

Neuropathology of Alzheimer's Disease

The key pathological hallmarks-extracellular plaques and intracellular neurofibrillary tangles (NFT)-described by Alois Alzheimer in his seminal 1907 article are still central to the postmortem diagnosis of Alzheimer's disease (AD), but major advances in our understanding of the underlying pathophysiology as well as significant progress in clinical diagnosis and therapy have changed the perspective and importance of neuropathologic evaluation of the brain. The notion that the pathological processes underlying AD already start decades before symptoms are apparent in patients has brought a major change reflected in the current neuropathological classification of AD neuropathological changes (ADNC). The predictable progression of beta-amyloid (Aβ) plaque pathology from neocortex, over limbic structures, diencephalon, and basal ganglia, to brainstem and cerebellum is captured in phases described by Thal and colleagues. The progression of NFT pathology from the transentorhinal region to the limbic system and ultimately the neocortex is described in stages proposed by Braak and colleagues. The density of neuritic plaque pathology is determined by criteria defined by the Consortium to establish a registry for Alzheimer's diseases (CERAD). While these changes neuropathologically define AD, it becomes more and more apparent that the majority of patients present with a multitude of additional pathological changes which are possible contributing factors to the clinical presentation and disease progression. The impact of co-existing Lewy body pathology has been well studied, but the importance of more recently described pathologies including limbic-predominant age-related TDP-43 encephalopathy (LATE), chronic traumatic encephalopathy (CTE), and aging-related tau astrogliopathy (ARTAG) still needs to be evaluated in large cohort studies. In addition, it is apparent that vascular pathology plays an important role in the AD patient population, but a lack of standardized reporting criteria has hampered progress in elucidating the importance of these changes for clinical presentation and disease progression. More recently a key role was ascribed to the immune response to pathological protein aggregates, and it will be important to analyze these changes systematically to better understand the temporal and spatial distribution of the immune response in AD and elucidate their importance for the disease process. Advances in digital pathology and technologies such as single cell sequencing and digital spatial profiling have opened novel avenues for improvement of neuropathological diagnosis and advancing our understanding of underlying molecular processes. Finally, major strides in biomarker-based diagnosis of AD and recent advances in targeted therapeutic approaches may have shifted the perspective but also highlight the continuous importance of postmortem analysis of the brain in neurodegenerative diseases.

Quantifying and Examining Reserve in Symptomatic Former National Football League Players

BACKGROUND

Repetitive head impacts (RHI) from contact sports have been associated with cognitive and neuropsychiatric disorders. However, not all individuals exposed to RHI develop such disorders. This may be explained by the reserve hypothesis. It remains unclear if the reserve hypothesis accounts for the heterogenous symptom presentation in RHI-exposed individuals. Moreover, optimal measurement of reserve in this population is unclear and likely unique from non-athlete populations.

OBJECTIVE

We examined the association between metrics of reserve and cognitive and neuropsychiatric functioning in 89 symptomatic former National Football League players.

METHODS

Individual-level proxies (e.g., education) defined reserve. We additionally quantified reserve as remaining residual variance in 1) episodic memory and 2) executive functioning performance, after accounting for demographics and brain pathology. Associations between reserve metrics and cognitive and neuropsychiatric functioning were examined.

RESULTS

Higher reading ability was associated with better attention/information processing (β=0.25; 95% CI, 0.05-0.46), episodic memory (β=0.27; 95% CI, 0.06-0.48), semantic and phonemic fluency (β=0.24; 95% CI, 0.02-0.46; β=0.38; 95% CI, 0.17-0.59), and behavioral regulation (β=-0.26; 95% CI, -0.48, -0.03) performance. There were no effects for other individual-level proxies. Residual episodic memory variance was associated with better attention/information processing (β=0.45; 95% CI, 0.25, 0.65), executive functioning (β=0.36; 95% CI, 0.15, 0.57), and semantic fluency (β=0.38; 95% CI, 0.17, 0.59) performance. Residual executive functioning variance was associated with better attention/information processing (β=0.44; 95% CI, 0.24, 0.64) and episodic memory (β=0.37; 95% CI, 0.16, 0.58) performance.

CONCLUSION

Traditional reserve proxies (e.g., years of education, occupational attainment) have limitations and may be unsuitable for use in elite athlete samples. Alternative approaches of reserve quantification may prove more suitable for this population.

Case report: Lingering post-concussive symptoms in a pediatric patient with presumed Ehlers-Danlos syndrome

BACKGROUND

Connective tissue disorders such as Ehlers-Danlos Syndrome (EDS) can affect collagen and elastin content and structure, including weakening of tissues and vasculature, thus contributing to multiple systemic manifestations. Prior research has successfully focused on peripheral life-threatening manifestations resulting in increased life expectancy, yet clinical observations have warranted investigation of neurological vulnerability, where little is known. Compromised brain tissues and cerebrovasculature could leave these patients vulnerable to mild traumatic brain injury (TBI), with increased severity and duration of post-concussive symptoms and delayed recovery. Clinical reports in adults indicate that higher severity of symptoms after a mild TBI, such as a concussion, can unmask connective tissues disorders leading toward diagnosis. This clinical case report is an example of a pediatric patient with presumed Ehlers-Danlos syndrome who demonstrates increased vulnerability to mild TBI/concussion.

PATIENT

A pediatric female patient presents with unexplained lingering post-concussive symptoms, including trouble sleeping, nausea, frontal headaches, dizziness, visual changes, fatigue, and left-sided weakness more than 6 months post-mild concussion. Patient history of hypermobility, joint derangement, soft tissue mobility, and bruising suggests a potential diagnosis of Ehlers-Danlos syndrome, which may explain symptom severity and length of recovery.

DISCUSSION

This case is the first documented instance of increased vulnerability to TBI in a pediatric patient with presumed Ehlers-Danlos syndrome. It highlights the need for awareness and prevention of injury in this vulnerable patient population, suggests more targeted therapeutic intervention for recovery, and demonstrates the need for preclinical research evaluating the influence of genetic mutations associated with connective tissue disorders on the central nervous system.

Structural MRI profiles and tau correlates of atrophy in autopsy-confirmed CTE

BACKGROUND

Chronic traumatic encephalopathy (CTE), a neurodegenerative tauopathy, cannot currently be diagnosed during life. Atrophy patterns on magnetic resonance imaging could be an effective in vivo biomarker of CTE, but have not been characterized. Mechanisms of neurodegeneration in CTE are unknown. Here, we characterized macrostructural magnetic resonance imaging features of brain donors with autopsy-confirmed CTE. The association between hyperphosphorylated tau (p-tau) and atrophy on magnetic resonance imaging was examined.

METHODS

Magnetic resonance imaging scans were obtained by medical record requests for 55 deceased symptomatic men with autopsy-confirmed CTE and 31 men (n = 11 deceased) with normal cognition at the time of the scan, all >60 years Three neuroradiologists visually rated regional atrophy and microvascular disease (0 [none]-4 [severe]), microbleeds, and cavum septum pellucidum presence. Neuropathologists rated tau severity and atrophy at autopsy using semi-quantitative scales.

RESULTS

Compared to unimpaired males, donors with CTE (45/55=stage III/IV) had greater atrophy of the orbital-frontal (mean diff.=1.29), dorsolateral frontal (mean diff.=1.31), superior frontal (mean diff.=1.05), anterior temporal (mean diff.=1.57), and medial temporal lobes (mean diff.=1.60), and larger lateral (mean diff.=1.72) and third (mean diff.=0.80) ventricles, controlling for age at scan (ps<0.05). There were no effects for posterior atrophy or microvascular disease. Donors with CTE had increased odds of a cavum septum pellucidum (OR = 6.7, p < 0.05). Among donors with CTE, greater tau severity across 14 regions corresponded to greater atrophy on magnetic resonance imaging (beta = 0.68, p < 0.01).

CONCLUSIONS

These findings support frontal-temporal atrophy as a magnetic resonance imaging finding of CTE and show p-tau accumulation is associated with atrophy in CTE.

Tau seeding in chronic traumatic encephalopathy parallels disease severity

Chronic traumatic encephalopathy (CTE), a neurodegenerative tauopathy, is associated with behavioral, mood and cognitive impairment, including dementia. Tauopathies are neurodegenerative diseases whose neuropathological phenotypes are characterized by distinct histopathologic features of tau pathology, which progressively deposit throughout the brain. In certain tauopathies, especially Alzheimer's disease (AD), tau deposition appears to follow brain network connections. Experimental evidence suggests that the progression of tau pathology in humans, mouse and cell models could be explained by tau seeds that adopt distinct conformations and serve as templates for their own amplification to mediate transcellular propagation of pathology. Tau seeds are efficiently detected by the induction of aggregation in cell-based "biosensors" that express tau repeat domain (RD) with a disease-associated mutation (P301S) fused to complementary fluorescent protein tags (cyan and yellow fluorescent protein). Biosensors enable quantification of tau seeding in fixed and fresh-frozen brain tissue. Phospho-tau deposition in CTE follows progressive stages (I-IV), but the relationship of seeding to this deposition is unclear. We have used an established biosensor assay to independently quantify tau seeding as compared to AT8 phospho-tau histopathology in thin sections of fixed tissues of 11 brain regions from 27 patients with CTE, 5 with other tauopathies, and 5 negative controls. In contrast to prior studies of AD, we detected tau seeding late in the course of CTE (predominantly stages III and IV). It was less anatomically prevalent than AT8-positive inclusions, which were relatively widespread. We especially observed seeding in the limbic system (amygdala, thalamus, basal ganglia), which may explain the dominant cognitive and behavior impairments that characterize CTE.

Alzheimer's Disease-Related Dementias Summit 2019: National research priorities for the investigation of traumatic brain injury as a risk factor for Alzheimer's Disease and Related Dementias

TBI is a risk factor for later life dementia. Clinical and preclinical studies have elucidated multiple mechanisms through which TBI may influence or exacerbate multiple pathological processes underlying Alzheimer's Disease and Alzheimer's Disease Related Dementias (AD/ADRD). The National Institutes of Health hosts triennial ADRD Summits to inform a national research agenda, and the 2019 ADRD Summit was the first to highlight 'TBI and AD/ADRD Risk' as an emerging topic in the field. A multidisciplinary committee of TBI researchers with relevant expertise reviewed extant literature, identified research gaps and opportunities, and proposed draft research recommendations at the 2019 ADRD Summit. These research recommendations, further refined after broad stakeholder input at the Summit, cover four overall areas: (1) Encourage crosstalk and interdisciplinary collaboration between TBI and dementia researchers, (2) Establish infrastructure to study TBI as a risk factor for AD/ADRD, (3) Promote basic and clinical research examining the development and progression of TBI AD/ADRD neuropathologies and associated clinical symptoms, and (4) Characterize the clinical phenotype of progressive dementia associated with TBI and develop non-invasive diagnostic approaches. These recommendations recognize a need to strengthen communication and build frameworks to connect the complexity of TBI with rapidly evolving AD/ADRD research. Recommendations acknowledge TBI as a clinically and pathologically heterogeneous disease whose associations with AD/ADRDs remain incompletely understood. The recommendations highlight the scientific advantage of investigating AD/ADRD in the context of a known TBI exposure, the study of which can directly inform on disease mechanisms and treatment targets for AD/ADRDs with shared common pathways.

Developing methods to detect and diagnose chronic traumatic encephalopathy during life: rationale, design, and methodology for the DIAGNOSE CTE Research Project

BACKGROUND

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease that has been neuropathologically diagnosed in brain donors exposed to repetitive head impacts, including boxers and American football, soccer, ice hockey, and rugby players. CTE cannot yet be diagnosed during life. In December 2015, the National Institute of Neurological Disorders and Stroke awarded a seven-year grant (U01NS093334) to fund the "Diagnostics, Imaging, and Genetics Network for the Objective Study and Evaluation of Chronic Traumatic Encephalopathy (DIAGNOSE CTE) Research Project." The objectives of this multicenter project are to: develop in vivo fluid and neuroimaging biomarkers for CTE; characterize its clinical presentation; refine and validate clinical research diagnostic criteria (i.e., traumatic encephalopathy syndrome [TES]); examine repetitive head impact exposure, genetic, and other risk factors; and provide shared resources of anonymized data and biological samples to the research community. In this paper, we provide a detailed overview of the rationale, design, and methods for the DIAGNOSE CTE Research Project.

METHODS

The targeted sample and sample size was 240 male participants, ages 45-74, including 120 former professional football players, 60 former collegiate football players, and 60 asymptomatic participants without a history of head trauma or participation in organized contact sports. Participants were evaluated at one of four U.S. sites and underwent the following baseline procedures: neurological and neuropsychological examinations; tau and amyloid positron emission tomography; magnetic resonance imaging and spectroscopy; lumbar puncture; blood and saliva collection; and standardized self-report measures of neuropsychiatric, cognitive, and daily functioning. Study partners completed similar informant-report measures. Follow-up evaluations were intended to be in-person and at 3 years post-baseline. Multidisciplinary diagnostic consensus conferences are held, and the reliability and validity of TES diagnostic criteria are examined.

RESULTS

Participant enrollment and all baseline evaluations were completed in February 2020. Three-year follow-up evaluations began in October 2019. However, in-person evaluation ceased with the COVID-19 pandemic, and resumed as remote, 4-year follow-up evaluations (including telephone-, online-, and videoconference-based cognitive, neuropsychiatric, and neurologic examinations, as well as in-home blood draw) in February 2021.

CONCLUSIONS

Findings from the DIAGNOSE CTE Research Project should facilitate detection and diagnosis of CTE during life, and thereby accelerate research on risk factors, mechanisms, epidemiology, treatment, and prevention of CTE.

TRIAL REGISTRATION

NCT02798185.

Oxidative Stress Signaling in Blast TBI-Induced Tau Phosphorylation

Traumatic brain injury caused by blast is associated with long-term neuropathological changes including tau phosphorylation and pathology. In this study, we aimed to determine changes in initial tau phosphorylation after exposure to a single mild blast and the potential contribution of oxidative stress response pathways. C57BL/6 mice were exposed to a single blast overpressure (BOP) generated by a compressed gas-driven shock tube that recapitulates battlefield-relevant open-field BOP, and cortical tissues were harvested at different time points up to 24 h after blast for Western blot analysis. We found that BOP caused elevated tau phosphorylation at Ser202/Thr205 detected by the AT8 antibody at 1 h post-blast followed by tau phosphorylation at additional sites (Ser262 and Ser396/Ser404 detected by PHF1 antibody) and conformational changes detected by Alz50 antibody. BOP also induced acute oxidative damage at 1 h post-blast and gradually declined overtime. Interestingly, Extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) were acutely activated in a similar temporal pattern as the rise and fall in oxidative stress after blast, with p38 showing a similar trend. However, glycogen synthase kinase-3 β (GSK3β) was inhibited at 1 h and remained inhibited for 24 h post blast. These results suggested that mitogen-activated protein kinases (MAPKs) but not GSK3β are likely involved in mediating the effects of oxidative stress on the initial increase of tau phosphorylation following a single mild blast.