Repetitive Head Trauma Induces Chronic Traumatic Encephalopathy by Multiple Mechanisms

Diverse somatic genomic alterations in single neurons in chronic traumatic encephalopathy

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease that is linked to exposure to repetitive head impacts (RHI), yet little is known about its pathogenesis. Applying two single-cell whole-genome sequencing methods to hundreds of neurons from prefrontal cortex of 15 individuals with CTE, and 4 with RHI without CTE, revealed increased somatic single-nucleotide variants in CTE, resembling a pattern previously reported in Alzheimer's disease (AD). Furthermore, we discovered remarkably high burdens of somatic small insertions and deletions in a subset of CTE individuals, resembling a known pattern, ID4, also found in AD. Our results suggest that neurons in CTE experience stereotyped mutational processes shared with AD; the absence of similar changes in RHI neurons without CTE suggests that CTE involves mechanisms beyond RHI alone.

Perivascular glial reactivity is a feature of phosphorylated tau lesions in chronic traumatic encephalopathy

Chronic traumatic encephalopathy (CTE), a neurodegenerative disease associated with repetitive head injuries, is characterised by perivascular hyperphosphorylated tau (p-tau) accumulations within the depths of cortical sulci. Although the majority of CTE literature focuses on p-tau pathology, other pathological features such as glial reactivity, vascular damage, and axonal damage are relatively unexplored. In this study, we aimed to characterise these other pathological features, specifically in CTE p-tau lesion areas, to better understand the microenvironment surrounding the lesion. We utilised multiplex immunohistochemistry to investigate the distribution of 32 different markers of cytoarchitecture and pathology that are relevant to both traumatic brain injury and neurodegeneration. We qualitatively assessed the multiplex images and measured the percentage area of labelling for each marker in the lesion and non-lesion areas of CTE cases. We identified perivascular glial reactivity as a prominent feature of CTE p-tau lesions, largely driven by increases in astrocyte reactivity compared to non-lesion areas. Furthermore, we identified astrocytes labelled for both NAD(P)H quinone dehydrogenase 1 (NQO1) and L-ferritin, indicating that lesion-associated glial reactivity may be a compensatory response to iron-induced oxidative stress. Our findings demonstrate that perivascular inflammation is a consistent feature of the CTE pathognomonic lesion and may contribute to the pathogenesis of brain injury-related neurodegeneration.

Targeting tau in Alzheimer's and beyond: Insights into pathology and therapeutic strategies

Tauopathies encompass a group of approximately 20 neurodegenerative diseases characterized by the accumulation of the microtubule-associated protein tau in brain neurons. The pathogenesis of intracellular neurofibrillary tangles, a hallmark of tauopathies, is initiated by hyperphosphorylated tau protein isoforms that cause neuronal death and lead to diseases like Alzheimer's, Parkinson's disease, frontotemporal dementia, and other complex neurodegenerative diseases. Current applications of tau biomarkers, including imaging, cerebrospinal fluid, and blood-based assays, assist in the evaluation and diagnosis of tauopathies. Emerging research is providing various potential strategies to prevent cellular toxicity caused by tau aggregation such as: 1) suppressing toxic tau aggregation, 2) preventing post-translational modifications of tau, 3) stabilizing microtubules and 4) designing tau-directed immunogens. This review aims to discuss the role of tau in tauopathies along with neuropathological features of the different tauopathies and the new developments in treating tau aggregation with the therapeutics for treating and possibly preventing tauopathies.

Chronic Traumatic Encephalopathy

This article focuses on neuropathologic diagnostic criteria for chronic traumatic encephalopathy (CTE) and consensus research diagnostic criteria for traumatic encephalopathy syndrome (TES). CTE as a tauopathy has a unique pattern for diagnosis and differs from other neurodegenerative diseases. We discuss the history, neuropathology, and mechanism of CTE as well as the preliminary reasearch diagnostic criteria for TES, which is the proposed clinical presentation of suspected CTE.

Neck strength alone does not mitigate adverse associations of soccer heading with cognitive performance in adult amateur players

OBJECTIVES

Soccer heading is adversely associated with neurocognitive performance, but whether greater neck strength or anthropometrics mitigates these outcomes is controversial. Here, we examine the effect of neck strength or anthropometrics on associations of soccer heading with neurocognitive outcomes in a large cohort of adult amateur players.

METHODS

380 adult amateur league soccer players underwent standardized measurement of neck strength (forward flexion, extension, left lateral flexion, right lateral flexion) and head/neck anthropometric measures (head circumference, neck length, neck circumference and neck volume). Participants were assessed for heading (HeadCount) and cognitive performance (Cogstate) on up to 7 visits over a period of two years. Principal components analysis (PCA) was performed on 8 neck strength and anthropometric measures. We used generalized estimating equations to test the moderation effect of each of the three PCs on 8 previously identified adverse associations of 2-week and 12-month heading estimates with cognitive performance (psychomotor speed, immediate verbal recall, verbal episodic memory, attention, working memory) and of unintentional head impacts on moderate to severe central nervous system symptoms.

RESULTS

3 principal components (PC's) account for 80% of the variance in the PCA. In men, PC1 represents head/neck anthropometric measures, PC2 represents neck strength measures, and PC3 represents the flexor/extensor (F/E) ratio. In women, PC1 represents neck strength, PC2 represents anthropometrics, and PC3 represents the F/E ratio. Of the 48 moderation effects tested, only one showed statistical significance after Bonferroni correction, which was not robust to extensive sensitivity analyses.

CONCLUSION

Neither neck strength nor anthropometrics mitigate adverse associations of soccer heading with cognitive performance in adult amateur players.

Cortical circuit principles predict patterns of trauma induced tauopathy in humans

Connections in the cortex of diverse mammalian species are predicted reliably by the Structural Model for direction of pathways and signal processing (reviewed in 1,2). The model is rooted in the universal principle of cortical systematic variation in laminar structure and has been supported widely for connection patterns in animals but has not yet been tested for humans. Here, in postmortem brains of individuals neuropathologically diagnosed with chronic traumatic encephalopathy (CTE) we studied whether the hyperphosphorylated tau (p-tau) pathology parallels connection sequence in time by circuit mechanisms. CTE is a progressive p-tau pathology that begins focally in perivascular sites in sulcal depths of the neocortex (stages I-II) and later involves the medial temporal lobe (MTL) in stages III-IV. We provide novel quantitative evidence that the p-tau pathology in MTL A28 and nearby sites in CTE stage III closely follows the graded laminar patterns seen in homologous cortico-cortical connections in non-human primates. The Structural Model successfully predicted the laminar distribution of the p-tau neurofibrillary tangles and neurites and their density, based on the relative laminar (dis)similarity between the cortical origin (seed) and each connection site. The findings were validated for generalizability by a computational progression model. By contrast, the early focal perivascular pathology in the sulcal depths followed local columnar connectivity rules. These findings support the general applicability of a theoretical model to unravel the direction and progression of p-tau pathology in human neurodegeneration via a cortico-cortical mechanism. Cortical pathways converging on medial MTL help explain the progressive spread of p-tau pathology from focal cortical sites in early CTE to widespread lateral MTL areas and beyond in later disease stages.

Association of Win-Loss Record With Neuropsychiatric Symptoms and Brain Health Among Professional Fighters

OBJECTIVE

Repetitive head impacts in professional fighting commonly lead to head injuries. Increased exposure to repetitive head trauma, measured by the number of professional fights and years of fighting, has been associated with slower processing speed and smaller brain volumes. The impact of win-loss outcomes has been investigated in other sports, with several studies suggesting that individuals on losing teams experience more head injuries. Here, the authors hypothesized that fighters with a worse fight record would exhibit poorer brain health outcomes.

METHODS

The Professional Fighters Brain Health Study examined changes in neuropsychiatric symptoms, regional brain volume, and cognition among professional boxers and mixed martial arts fighters. These data were used to evaluate the relationship between win-loss ratios and brain health outcomes among professional fighters (N=212) by using validated neuropsychiatric symptom and cognitive measures and MRI data.

RESULTS

Retired fighters with a better record demonstrated more impulsiveness (B=0.21, df=48) and slower processing speed (B=-0.42, df=31). More successful fighters did not perform better than fighters with worse records on any neuropsychiatric or cognitive test. Retired fighters with better fight records had smaller brain volumes in the subcortical gray matter, anterior corpus callosum, left and right hippocampi, left and right amygdala, and left thalamus. More successful active fighters had a smaller left amygdala volume.

CONCLUSIONS

These findings suggest that among retired fighters, a better fight record was associated with greater impulsiveness, slower processing speed, and smaller brain volume in certain regions. This study shows that even successful fighters experience adverse effects on brain health.

Chronic Traumatic Encephalopathy in Soccer Players: Review of 14 Cases

OBJECTIVE

Exposure to repetitive sports-related concussions or (sub)concussive head trauma may lead to chronic traumatic encephalopathy (CTE). Which impact (heading or concussion) poses the greatest risk of CTE development in soccer players?

DESIGN

Narrative review.

SETTING

Teaching hospital and University of Applied sciences.

PATIENTS

A literature search (PubMed) was conducted for neuropathologic studies in the period 2005-December 2022, investigating soccer players with dementia and a CTE diagnosis, limited to English language publications. 210 papers were selected for final inclusion, of which 7 papers described 14 soccer players.

ASSESSMENT

Magnetic resonance imaging studies in soccer players show that lifetime estimates of heading numbers are inversely correlated with cortical thickness, grey matter volume, and density of the anterior temporal cortex. Using diffusion tensor imaging-magnetic resonance imaging, higher frequency of headings-particularly with rotational accelerations-are associated with impaired white matter integrity. Serum neurofilament light protein is elevated after heading.

MAIN OUTCOME MEASURES

Chronic traumatic encephalopathy pathology, history of concussion, heading frequency.

RESULTS

In 10 of 14 soccer players, CTE was the primary diagnosis. In 4 cases, other dementia types formed the primary diagnosis and CTE pathology was a concomitant finding. Remarkably, 6 of the 14 cases had no history of concussion, suggesting that frequent heading may be a risk for CTE in patients without symptomatic concussion. Rule changes in heading duels, management of concussion during the game, and limiting the number of high force headers during training are discussed.

CONCLUSIONS

Data suggest that heading frequency and concussions are associated with higher risk of developing CTE in (retired) soccer players. However based on this review of only 14 players, questions persist as to whether or not heading is a risk factor for CTE or long-term cognitive decline.

Risk of impaired school performance in children hospitalized with concussion: a population-based matched cohort study

Aim

To examine the impact of concussion on objective measures of school performance.

Materials & methods

Population-based matched cohort study using linked health and education records of young people aged ≤18 years hospitalized with concussion in New South Wales, Australia, during 2005-2018, and matched comparisons not hospitalized with any injury.

Results

Young people with concussion had higher risk of not achieving the national minimum standards for literacy and numeracy assessments, ranging from 30% for numeracy to 43% for spelling, and not completing high school, ranging from 29% for year 10 to 77% for year 12, compared with matched peers.

Conclusion

Young people hospitalized with concussion have impaired school performance compared with uninjured matched peers.

Sleep/Wake Disorders After Sports Concussion: Risks, Revelations, and Interventions

SUMMARY

Sleep-wake disturbances (SWDs) are among the most prevalent, persistent, and often disregarded sequelae of traumatic brain injury. Identification and treatment of SWDs in patients with traumatic brain injury is important and can complement other efforts to promote maximum functional recovery. SWDs can accentuate other consequences of traumatic brain injury, negatively affect mood, exacerbate pain, heighten irritability, and diminish cognitive abilities and the potential for recovery. The risk for sports injuries increases when athletes are sleep deprived. Sleep deprivation increases risk-taking behaviors, predisposing to injuries. SWDs are an independent risk factor for prolonged recovery after sports-related concussion. SWDs following sports-related concussion have been shown to impede recovery, rehabilitation, and return to preinjury activities.

Examining later-in-life health risks associated with sport-related concussion and repetitive head impacts: a systematic review of case-control and cohort studies

OBJECTIVE

Concern exists about possible problems with later-in-life brain health, such as cognitive impairment, mental health problems and neurological diseases, in former athletes. We examined the future risk for adverse health effects associated with sport-related concussion, or exposure to repetitive head impacts, in former athletes.

DESIGN

Systematic review.

DATA SOURCES

Search of MEDLINE, Embase, Cochrane, CINAHL Plus and SPORTDiscus in October 2019 and updated in March 2022.

ELIGIBILITY CRITERIA

Studies measuring future risk (cohort studies) or approximating that risk (case-control studies).

RESULTS

Ten studies of former amateur athletes and 18 studies of former professional athletes were included. No postmortem neuropathology studies or neuroimaging studies met criteria for inclusion. Depression was examined in five studies in former amateur athletes, none identifying an increased risk. Nine studies examined suicidality or suicide as a manner of death, and none found an association with increased risk. Some studies comparing professional athletes with the general population reported associations between sports participation and dementia or amyotrophic lateral sclerosis (ALS) as a cause of death. Most did not control for potential confounding factors (eg, genetic, demographic, health-related or environmental), were ecological in design and had high risk of bias.

CONCLUSION

Evidence does not support an increased risk of mental health or neurological diseases in former amateur athletes with exposure to repetitive head impacts. Some studies in former professional athletes suggest an increased risk of neurological disorders such as ALS and dementia; these findings need to be confirmed in higher quality studies with better control of confounding factors.

PROSPERO REGISTRATION NUMBER

CRD42022159486.

Longitudinal Changes in Cognitive Functioning and Brain Structure in Professional Boxers and Mixed Martial Artists After They Stop Fighting

BACKGROUND AND OBJECTIVES

This study compares longitudinal changes in cognitive functioning and brain structures in male fighters who transitioned to an inactive fighting status without any further exposure to repetitive head impacts (RHIs) and fighters remaining active with continual exposure to RHIs.

METHODS

Participants were recruited from the Professional Fighters Brain Health Study. At time point (TP)1, all fighters were active, with continual exposure to RHIs. At TP2, fighters were considered "transitioned" if they had no sanctioned professional fights and had not been sparring for the past 2 years. Fighters were considered "active" if they continued to train and compete. All fighters underwent cognitive testing and 3T MRI at both TPs. A subset of our fighters (50%) underwent blood sampling for the characterization of neurofilament light (NfL) levels at both TPs. Linear mixed-effect models were applied to investigate the potentially different longitudinal trajectories (interaction effect between group and time) of cognitive function measures, NfL levels, and regional thickness measures (derived from structural MRI) between transitioned and active fighters.

RESULTS

Forty-five male transitioned fighters (aged 31.69 ± 6.27 years [TP1]; 22 boxers, 22 mixed martial artists, and 1 martial artist) and 45 demographically matched male active fighters (aged 30.24 ± 5.44 years [TP1]; 17 boxers, 27 mixed martial artists, and 1 martial artist) were included in the analyses. Significantly different longitudinal trajectories between transitioned and active fighters were observed in verbal memory (p FDR = 4.73E-04), psychomotor speed (p FDR = 4.73E-04), processing speed (p FDR = 3.90E-02), and NfL levels (p = 0.02). Transitioned fighters demonstrated longitudinally improved cognitive functioning and decreased NfL levels, and active fighters demonstrated declines in cognitive performance and stable NfL levels. Of 68 cortical regions inspected, 54 regions demonstrated a consistently changing trajectory, with thickness measures stabilizing on a group level for transitioned fighters and subtly declining over time for active fighters.

DISCUSSION

After fighters' cessation of RHI exposure, cognitive function and brain thickness measures may stabilize and blood NfL levels may decline. This study could be a starting point to identify potential predictors of individuals who are at a higher risk of RHI-related long-term neurologic conditions.

Neuropathology in chronic traumatic encephalopathy: a systematic review of comparative post-mortem histology literature

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with repetitive head trauma and is characterised by the perivascular accumulation of hyperphosphorylated tau (p-tau) in the depths of cortical sulci. CTE can only be diagnosed postmortem and the cellular mechanisms of disease causation remain to be elucidated. Understanding the full scope of the pathological changes currently identified in CTE is necessary to identify areas requiring further research. This systematic review summarises the current literature on CTE pathology from postmortem human tissue histology studies published until 31 December 2021. Publications were included if they quantitively or qualitatively compared postmortem human tissue pathology in CTE to neuropathologically normal cases or other neurodegenerative diseases such as Alzheimer's disease (AD). Pathological entities investigated included p-tau, beta-amyloid, TDP-43, Lewy bodies, astrogliosis, microgliosis, axonopathy, vascular dysfunction, and cell stress. Of these pathologies, p-tau was the most frequently investigated, with limited reports on other pathological features such as vascular dysfunction, astrogliosis, and microgliosis. Consistent increases in p-tau, TDP-43, microgliosis, axonopathy, and cell stress were reported in CTE cases compared to neuropathologically normal cases. However, there was no clear consensus on how these pathologies compared to AD. The CTE cases used for these studies were predominantly from the VA-BU-CLF brain bank, with American football and boxing as the most frequent sources of repetitive head injury exposure. Overall, this systematic review highlights gaps in the literature and proposes three priorities for future research including: 1. The need for studies of CTE cases with more diverse head injury exposure profiles to understand the consistency of pathology changes between different populations. 2. The need for more studies that compare CTE with normal ageing and AD to further clarify the pathological signature of CTE for diagnostic purposes and to understand the disease process. 3. Further research on non-aggregate pathologies in CTE, such as vascular dysfunction and neuroinflammation. These are some of the least investigated features of CTE pathology despite being implicated in the acute phase response following traumatic head injury.

CCL2 is associated with microglia and macrophage recruitment in chronic traumatic encephalopathy

BACKGROUND

Neuroinflammation has been implicated in the pathogenesis of chronic traumatic encephalopathy (CTE), a progressive neurodegenerative disease association with exposure to repetitive head impacts (RHI) received though playing contact sports such as American football. Past work has implicated early and sustained activation of microglia as a potential driver of tau pathology within the frontal cortex in CTE. However, the RHI induced signals required to recruit microglia to areas of damage and pathology are unknown.

METHODS

Postmortem brain tissue was obtained from 261 individuals across multiple brain banks. Comparisons were made using cases with CTE, cases with Alzheimer's disease (AD), and cases with no neurodegenerative disease and lacked exposure to RHI (controls). Recruitment of Iba1+ cells around the CTE perivascular lesion was compared to non-lesion vessels. TMEM119 staining was used to characterize microglia or macrophage involvement. The potent chemoattractant CCL2 was analyzed using frozen tissue from the dorsolateral frontal cortex (DLFC) and the calcarine cortex. Finally, the amounts of hyperphosphorylated tau (pTau) and Aβ42 were compared to CCL2 levels to examine possible mechanistic pathways.

RESULTS

An increase in Iba1+ cells was found around blood vessels with perivascular tau pathology compared to non-affected vessels in individuals with RHI. TMEM119 staining revealed the majority of the Iba1+ cells were microglia. CCL2 protein levels in the DLFC were found to correlate with greater years of playing American football, the density of Iba1+ cells, the density of CD68+ cells, and increased CTE severity. When comparing across multiple brain regions, CCL2 increases were more pronounced in the DLFC than the calcarine cortex in cases with RHI but not in AD. When examining the individual contribution of pathogenic proteins to CCL2 changes, pTau correlated with CCL2, independent of age at death and Aβ42 in AD and CTE. Although levels of Aβ42 were not correlated with CCL2 in cases with CTE, in males in the AD group, Aβ42 trended toward an inverse relationship with CCL2 suggesting possible gender associations.

CONCLUSION

Overall, CCL2 is implicated in the pathways recruiting microglia and the development of pTau pathology after exposure to RHI, and may represent a future therapeutic target in CTE.