Inflammatory biomarkers for neurobehavioral dysregulation in former American football players: findings from the DIAGNOSE CTE Research Project.

BACKGROUND: Traumatic encephalopathy syndrome (TES) is defined as the clinical manifestation of the neuropathological entity chronic traumatic encephalopathy (CTE). A core feature of TES is neurobehavioral dysregulation (NBD), a neuropsychiatric syndrome in repetitive head impact (RHI)-exposed individuals, characterized by a poor regulation of emotions/behavior. To discover biological correlates for NBD, we investigated the association between biomarkers of inflammation (interleukin (IL)-1ß, IL-6, IL-8, IL-10, C-reactive protein (CRP), tumor necrosis factor (TNF)-α) in cerebrospinal fluid (CSF) and NBD symptoms in former American football players and unexposed individuals. METHODS: Our cohort consisted of former American football players, with (n = 104) or without (n = 76) NBD diagnosis, as well as asymptomatic unexposed individuals (n = 55) from the DIAGNOSE CTE Research Project. Specific measures for NBD were derived (i.e., explosivity, emotional dyscontrol, impulsivity, affective lability, and a total NBD score) from a factor analysis of multiple self-report neuropsychiatric measures. Analyses of covariance tested differences in biomarker concentrations between the three groups. Within former football players, multivariable linear regression models assessed relationships among log-transformed inflammatory biomarkers, proxies for RHI exposure (total years of football, cumulative head impact index), and NBD factor scores, adjusted for relevant confounding variables. Sensitivity analyses tested (1) differences in age subgroups (< 60, ≥ 60 years); (2) whether associations could be identified with plasma inflammatory biomarkers; (3) associations between neurodegeneration and NBD, using plasma neurofilament light (NfL) chain protein; and (4) associations between biomarkers and cognitive performance to explore broader clinical symptoms related to TES. RESULTS: CSF IL-6 was higher in former American football players with NBD diagnosis compared to players without NBD. Furthermore, elevated levels of CSF IL-6 were significantly associated with higher emotional dyscontrol, affective lability, impulsivity, and total NBD scores. In older football players, plasma NfL was associated with higher emotional dyscontrol and impulsivity, but also with worse executive function and processing speed. Proxies for RHI exposure were not significantly associated with biomarker concentrations. CONCLUSION: Specific NBD symptoms in former American football players may result from multiple factors, including neuroinflammation and neurodegeneration. Future studies need to unravel the exact link between NBD and RHI exposure, including the role of other pathophysiological pathways.

Chronic traumatic encephalopathy (CTE): criteria for neuropathological diagnosis and relationship to repetitive head impacts.

Over the last 17 years, there has been a remarkable increase in scientific research concerning chronic traumatic encephalopathy (CTE). Since the publication of NINDS-NIBIB criteria for the neuropathological diagnosis of CTE in 2016, and diagnostic refinements in 2021, hundreds of contact sport athletes and others have been diagnosed at postmortem examination with CTE. CTE has been reported in amateur and professional athletes, including a bull rider, boxers, wrestlers, and American, Canadian, and Australian rules football, rugby union, rugby league, soccer, and ice hockey players. The pathology of CTE is unique, characterized by a pathognomonic lesion consisting of a perivascular accumulation of neuronal phosphorylated tau (p-tau) variably alongside astrocytic aggregates at the depths of the cortical sulci, and a distinctive molecular structural configuration of p-tau fibrils that is unlike the changes observed with aging, Alzheimer's disease, or any other tauopathy. Computational 3-D and finite element models predict the perivascular and sulcal location of p-tau pathology as these brain regions undergo the greatest mechanical deformation during head impact injury. Presently, CTE can be definitively diagnosed only by postmortem neuropathological examination; the corresponding clinical condition is known as traumatic encephalopathy syndrome (TES). Over 97% of CTE cases published have been reported in individuals with known exposure to repetitive head impacts (RHI), including concussions and nonconcussive impacts, most often experienced through participation in contact sports. While some suggest there is uncertainty whether a causal relationship exists between RHI and CTE, the preponderance of the evidence suggests a high likelihood of a causal relationship, a conclusion that is strengthened by the absence of any evidence for plausible alternative hypotheses. There is a robust dose-response relationship between CTE and years of American football play, a relationship that remains consistent even when rigorously accounting for selection bias. Furthermore, a recent study suggests that selection bias underestimates the observed risk. Here, we present the advances in the neuropathological diagnosis of CTE culminating with the development of the NINDS-NIBIB criteria, the multiple international studies that have used these criteria to report CTE in hundreds of contact sports players and others, and the evidence for a robust dose-response relationship between RHI and CTE.

Repetitive head impacts and chronic traumatic encephalopathy are associated with TDP-43 inclusions and hippocampal sclerosis.

Hippocampal sclerosis (HS) is associated with advanced age as well as transactive response DNA-binding protein with 43 kDa (TDP-43) deposits. Both hippocampal sclerosis and TDP-43 proteinopathy have also been described in chronic traumatic encephalopathy (CTE), a neurodegenerative disease linked to exposure to repetitive head impacts (RHI). However, the prevalence of HS in CTE, the pattern of TDP-43 pathology, and associations of HS and TDP-43 with RHI are unknown. A group of participants with a history of RHI and CTE at autopsy (n = 401) as well as a group with HS-aging without CTE (n = 33) was examined to determine the prevalence of HS and TDP-43 inclusions in CTE and to compare the clinical and pathological features of HS and TDP-43 inclusions in CTE to HS-aging. In CTE, HS was present in 23.4%, and TDP-43 inclusions were present in 43.3% of participants. HS in CTE occurred at a relatively young age (mean 77.0 years) and was associated with a greater number of years of RHI than CTE without HS adjusting for age (p = 0.029). In CTE, TDP-43 inclusions occurred frequently in the frontal cortex and occurred both with and without limbic TDP-43. Additionally, structural equation modeling demonstrated that RHI exposure years were associated with hippocampal TDP-43 inclusions (p < 0.001) through increased CTE stage (p < 0.001). Overall, RHI and the development of CTE pathology may contribute to TDP-43 deposition and hippocampal sclerosis.

Associations between near end-of-life flortaucipir PET and postmortem CTE-related tau neuropathology in six former American football players.

PURPOSE: Flourine-18-flortaucipir tau positron emission tomography (PET) was developed for the detection for Alzheimer's disease. Human imaging studies have begun to investigate its use in chronic traumatic encephalopathy (CTE). Flortaucipir-PET to autopsy correlation studies in CTE are needed for diagnostic validation. We examined the association between end-of-life flortaucipir PET and postmortem neuropathological measurements of CTE-related tau in six former American football players. METHODS: Three former National Football League players and three former college football players who were part of the DIAGNOSE CTE Research Project died and agreed to have their brains donated. The six players had flortaucipir (tau) and florbetapir (amyloid) PET prior to death. All brains from the deceased participants were neuropathologically evaluated for the presence of CTE. On average, the participants were 59.0 (SD = 9.32) years of age at time of PET. PET scans were acquired 20.33 (SD = 13.08) months before their death. Using Spearman correlation analyses, we compared flortaucipir standard uptake value ratios (SUVRs) to digital slide-based AT8 phosphorylated tau (p-tau) density in a priori selected composite cortical, composite limbic, and thalamic regions-of-interest (ROIs). RESULTS: Four brain donors had autopsy-confirmed CTE, all with high stage disease (n = 3 stage III, n = 1 stage IV). Three of these four met criteria for the clinical syndrome of CTE, known as traumatic encephalopathy syndrome (TES). Two did not have CTE at autopsy and one of these met criteria for TES. Concomitant pathology was only present in one of the non-CTE cases (Lewy body) and one of the CTE cases (motor neuron disease). There was a strong association between flortaucipir SUVRs and p-tau density in the composite cortical (ρ = 0.71) and limbic (ρ = 0.77) ROIs. Although there was a strong association in the thalamic ROI (ρ = 0.83), this is a region with known off-target binding. SUVRs were modest and CTE and non-CTE cases had overlapping SUVRs and discordant p-tau density for some regions. CONCLUSIONS: Flortaucipir-PET could be useful for detecting high stage CTE neuropathology, but specificity to CTE p-tau is uncertain. Off-target flortaucipir binding in the hippocampus and thalamus complicates interpretation of these associations. In vivo biomarkers that can detect the specific p-tau of CTE across the disease continuum are needed.

Neuroimmune proteins can differentiate between tauopathies.

BACKGROUND: Tauopathies are a group of neurodegenerative diseases where there is pathologic accumulation of hyperphosphorylated tau protein (ptau). The most common tauopathy is Alzheimer's disease (AD), but chronic traumatic encephalopathy (CTE), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and argyrophilic grain disease (AGD) are significant health risks as well. Currently, it is unclear what specific molecular factors might drive each distinct disease and represent therapeutic targets. Additionally, there is a lack of biomarkers that can differentiate each disease in life. Recent work has suggested that neuroinflammatory changes might be specific among distinct diseases and offers a novel resource for mechanistic targets and biomarker candidates. METHODS: To better examine each tauopathy, a 71 immune-related protein multiplex ELISA panel was utilized to analyze anterior cingulate grey matter from 127 individuals neuropathologically diagnosed with AD, CTE, PSP, CBD, and AGD. A partial least square regression analysis was carried out to perform unbiased clustering and identify proteins that are distinctly correlated with each tauopathy correcting for age and gender. Receiver operator characteristic and binary logistic regression analyses were then used to examine the ability of each candidate protein to distinguish diseases. Validation in postmortem cerebrospinal fluid (CSF) from 15 AD and 14 CTE cases was performed to determine if candidate proteins could act as possible novel biomarkers. RESULTS: Five clusters of immune proteins were identified and compared to each tauopathy to determine if clusters were specific to distinct disease. Each cluster was found to correlate with either CTE, AD, PSP, CBD, or AGD. When examining which proteins were the strongest driver of each cluster, it was observed the most distinctive protein for CTE was CCL21, AD was FLT3L, and PSP was IL13. Individual proteins that were specific to CBD and AGD were not observed. CCL21 was observed to be elevated in CTE CSF compared to AD cases (p = 0.02), further validating the use as possible biomarkers. Sub-analyses for male only cases confirmed the results were not skewed by gender differences. CONCLUSIONS: Overall, these results highlight that different neuroinflammatory responses might underlie unique mechanisms in related neurodegenerative pathologies. Additionally, the use of distinct neuroinflammatory signatures could help differentiate between tauopathies and act as novel biomarker candidate to increase specificity for in-life diagnoses.

Dysregulated coordination of MAPT exon 2 and exon 10 splicing underlies different tau pathologies in PSP and AD.

Understanding regulation of MAPT splicing is important to the etiology of many nerurodegenerative diseases, including Alzheimer disease (AD) and progressive supranuclear palsy (PSP), in which different tau isoforms accumulate in pathologic inclusions. MAPT, the gene encoding the tau protein, undergoes complex alternative pre-mRNA splicing to generate six isoforms. Tauopathies can be categorized by the presence of tau aggregates containing either 3 (3R) or 4 (4R) microtubule-binding domain repeats (determined by inclusion/exclusion of exon 10), but the role of the N-terminal domain of the protein, determined by inclusion/exclusion of exons 2 and 3 has been less well studied. Using a correlational screen in human brain tissue, we observed coordination of MAPT exons 2 and 10 splicing. Expressions of exon 2 splicing regulators and subsequently exon 2 inclusion are differentially disrupted in PSP and AD brain, resulting in the accumulation of 1N4R isoforms in PSP and 0N isoforms in AD temporal cortex. Furthermore, we identified different N-terminal isoforms of tau present in neurofibrillary tangles, dystrophic neurites and tufted astrocytes, indicating a role for differential N-terminal splicing in the development of disparate tau neuropathologies. We conclude that N-terminal splicing and combinatorial regulation with exon 10 inclusion/exclusion is likely to be important to our understanding of tauopathies.

Genome-wide association study and functional validation implicates JADE1 in tauopathy.

Primary age-related tauopathy (PART) is a neurodegenerative pathology with features distinct from but also overlapping with Alzheimer disease (AD). While both exhibit Alzheimer-type temporal lobe neurofibrillary degeneration alongside amnestic cognitive impairment, PART develops independently of amyloid-ß (Aß) plaques. The pathogenesis of PART is not known, but evidence suggests an association with genes that promote tau pathology and others that protect from Aß toxicity. Here, we performed a genetic association study in an autopsy cohort of individuals with PART (n = 647) using Braak neurofibrillary tangle stage as a quantitative trait. We found some significant associations with candidate loci associated with AD (SLC24A4, MS4A6A, HS3ST1) and progressive supranuclear palsy (MAPT and EIF2AK3). Genome-wide association analysis revealed a novel significant association with a single nucleotide polymorphism on chromosome 4 (rs56405341) in a locus containing three genes, including JADE1 which was significantly upregulated in tangle-bearing neurons by single-soma RNA-seq. Immunohistochemical studies using antisera targeting JADE1 protein revealed localization within tau aggregates in autopsy brains with four microtubule-binding domain repeats (4R) isoforms and mixed 3R/4R, but not with 3R exclusively. Co-immunoprecipitation in post-mortem human PART brain tissue revealed a specific binding of JADE1 protein to four repeat tau lacking N-terminal inserts (0N4R). Finally, knockdown of the Drosophila JADE1 homolog rhinoceros (rno) enhanced tau-induced toxicity and apoptosis in vivo in a humanized 0N4R mutant tau knock-in model, as quantified by rough eye phenotype and terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) in the fly brain. Together, these findings indicate that PART has a genetic architecture that partially overlaps with AD and other tauopathies and suggests a novel role for JADE1 as a modifier of neurofibrillary degeneration.

Tau phosphorylation sites serine202 and serine396 are differently altered in chronic traumatic encephalopathy and Alzheimer's disease.

INTRODUCTION: Chronic traumatic encephalopathy (CTE) is a neurodegenerative tauopathy associated with repetitive head impacts (RHI) typically sustained by contact sport athletes. Post-translation modifications to tau in CTE have not been well delineated or compared to Alzheimer's disease (AD). METHODS: We measured phosphorylated tau epitopes within dorsolateral frontal cortex from post mortem brains with neither CTE nor AD (n = 108), CTE (n = 109), AD (n = 223), and both CTE and AD (n = 33). RESULTS: Levels of hyperphosphorylated tau (p-tau)202 , p-tau231 , and p-tau396 were significantly increased in CTE. Total years of RHI exposure was significantly associated with increased p-tau202 levels (P = .001), but not p-tau396 . Instead, p-tau396 was most closely related to amyloid beta (Aß)1-42 levels (P < .001). The p-tau202 :p-tau396 ratio was significantly increased in early and late CTE compared to AD. DISCUSSION: In frontal cortex, p-tau202 is the most upregulated p-tau species in CTE, while p-tau396 is most increased in AD. p-tau202 and p-tau396 measurements may aid in developing biomarkers for disease.

Duration of American Football Play and Chronic Traumatic Encephalopathy.

OBJECTIVE: Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with exposure to contact and collision sports, including American football. We hypothesized a dose-response relationship between duration of football played and CTE risk and severity. METHODS: In a convenience sample of 266 deceased American football players from the Veterans Affairs-Boston University-Concussion Legacy Foundation and Framingham Heart Study Brain Banks, we estimated the association of years of football played with CTE pathological status and severity. We evaluated the ability of years played to classify CTE status using receiver operating characteristic curve analysis. Simulation analyses quantified conditions that might lead to selection bias. RESULTS: In total, 223 of 266 participants met neuropathological diagnostic criteria for CTE. More years of football played were associated with having CTE (odds ratio [OR] = 1.30 per year played, 95% confidence interval [CI] = 1.19-1.41; p = 3.8 × 10-9 ) and with CTE severity (severe vs mild; OR = 1.14 per year played, 95% CI = 1.07-1.22; p = 3.1 × 10-4 ). Participants with CTE were 1/10th as likely to have played <4.5 years (negative likelihood ratio [LR] = 0.102, 95% CI = 0.100-0.105) and were 10 times as likely to have played >14.5 years (positive LR = 10.2, 95% CI = 9.8-10.7) compared with participants without CTE. Sensitivity and specificity were maximized at 11 years played. Simulation demonstrated that years played remained adversely associated with CTE status when years played and CTE status were both related to brain bank selection across widely ranging scenarios. INTERPRETATION: The odds of CTE double every 2.6 years of football played. After accounting for brain bank selection, the magnitude of the relationship between years played and CTE status remained consistent. ANN NEUROL 2020;87:116-131.

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.

Validity of the 2014 traumatic encephalopathy syndrome criteria for CTE pathology.

INTRODUCTION: Validity of the 2014 traumatic encephalopathy syndrome (TES) criteria, proposed to diagnose chronic traumatic encephalopathy (CTE) in life, has not been assessed. METHODS: A total of 336 consecutive brain donors exposed to repetitive head impacts from contact sports, military service, and/or physical violence were included. Blinded to clinical information, neuropathologists applied National Institute on Neurological Disorders and Stroke/National Institute of Biomedical Imaging and Bioengineering CTE criteria. Blinded to neuropathological information, clinicians interviewed informants and reviewed medical records. An expert panel adjudicated TES diagnoses. RESULTS: A total of 309 donors were diagnosed with TES; 244 donors had CTE pathology. TES criteria demonstrated sensitivity and specificity of 0.97 and 0.21, respectively. Cognitive (odds ratio [OR] = 3.6; 95% confidence interval [CI]: 1.2-5.1), but not mood/behavior or motor symptoms, were significantly associated with CTE pathology. Having Alzheimer's disease (AD) pathology was significantly associated with reduced TES accuracy (OR = 0.27; 95% CI: 0.12-0.59). DISCUSSION: TES criteria provided good evidence to rule out, but limited evidence to rule in, CTE pathology. Requiring cognitive symptoms in revised criteria and using AD biomarkers may improve CTE pathology prediction.

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 Aß42 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 Aß42 in AD and CTE. Although levels of Aß42 were not correlated with CCL2 in cases with CTE, in males in the AD group, Aß42 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.

Characterizing tau deposition in chronic traumatic encephalopathy (CTE): utility of the McKee CTE staging scheme.

Chronic traumatic encephalopathy (CTE) is a tauopathy associated with repetitive head impacts (RHI) that has been neuropathologically diagnosed in American football players and other contact sport athletes. In 2013, McKee and colleagues proposed a staging scheme for characterizing the severity of the hyperphosphorylated tau (p-tau) pathology, the McKee CTE staging scheme. The staging scheme defined four pathological stages of CTE, stages I(mild)-IV(severe), based on the density and regional deposition of p-tau. The objective of this study was to test the utility of the McKee CTE staging scheme, and provide a detailed examination of the regional distribution of p-tau in CTE. We examined the relationship between the McKee CTE staging scheme and semi-quantitative and quantitative assessments of regional p-tau pathology, age at death, dementia, and years of American football play among 366 male brain donors neuropathologically diagnosed with CTE (mean age 61.86, SD 18.90). Spearman's rho correlations showed that higher CTE stage was associated with higher scores on all semi-quantitative and quantitative assessments of p-tau severity and density (p's < 0.001). The severity and distribution of CTE p-tau followed an age-dependent progression: older age was associated with increased odds for having a higher CTE stage (p < 0.001). CTE stage was independently associated with increased odds for dementia (p < 0.001). K-medoids cluster analysis of the semi-quantitative scales of p-tau across 14 regions identified 5 clusters of p-tau that conformed to increasing CTE stage (stage IV had 2 slightly different clusters), age at death, dementia, and years of American football play. There was a predilection for p-tau pathology in five regions: dorsolateral frontal cortex (DLF), superior temporal cortex, entorhinal cortex, amygdala, and locus coeruleus (LC), with CTE in the youngest brain donors and lowest CTE stage restricted to DLF and LC. These findings support the usefulness of the McKee CTE staging scheme and demonstrate the regional distribution of p-tau in CTE.

Association of probable REM sleep behavior disorder with pathology and years of contact sports play in chronic traumatic encephalopathy.

Probable rapid eye movement (REM) sleep behavior disorder (pRBD) is a synucleinopathy-associated parasomnia in which loss of REM sleep muscle atonia results in motor behavior during REM sleep, including dream enactment. Traumatic brain injury is independently associated with increased risk of pRBD and Lewy body disease, and both pRBD and Lewy body disease are often observed in chronic traumatic encephalopathy (CTE). However, the frequency and pathological substrate of pRBD in CTE have not been formally studied and remain unknown. Of the total sample of 247 men, age at death of 63.1 ± 18.8 years (mean ± SD), 80 [32%] were determined by informant report to have symptoms of pRBD. These participants had played more years of contact sports (18.3 ± 11.4) than those without pRBD (15.1 ± 6.5; P = 0.02) and had an increased frequency of Lewy body disease (26/80 [33%] vs 28/167 [17%], P = 0.005). Of the 80 participants with pRBD, 54 [68%] did not have Lewy body disease; these participants were more likely to have neurofibrillary tangles and pretangles in the dorsal and median raphe (41 of 49 [84%] non-LBD participants with pRBD symptoms vs 90 of 136 [66%] non-LBD participants without pRBD symptoms, P = 0.02), brainstem nuclei with sleep regulatory function. Binary logistic regression modeling in the total study sample showed that pRBD in CTE was associated with dorsal and median raphe nuclei neurofibrillary tangles (OR = 3.96, 95% CI [1.43, 10.96], P = 0.008), Lewy body pathology (OR = 2.36, 95% CI [1.18, 4.72], P = 0.02), and years of contact sports participation (OR = 1.04, 95% CI [1.00, 1.08], P = 0.04). Overall, pRBD in CTE is associated with increased years of contact sports participation and may be attributable to Lewy body and brainstem tau pathologies.

Repetitive Head Trauma Induces Chronic Traumatic Encephalopathy by Multiple Mechanisms.

Exposure to repetitive neurotrauma increases lifetime risk for developing progressive cognitive deficits, neurobehavioral abnormalities, and chronic traumatic encephalopathy (CTE). CTE is a tau protein neurodegenerative disease first identified in boxers and recently described in athletes participating in other contact sports (notably American football, ice hockey, rugby, and wrestling) and in military veterans with blast exposure. Currently, CTE can only be diagnosed by neuropathological examination of the brain after death. The defining diagnostic lesion of CTE consists of patchy perivascular accumulations of hyperphosphorylated tau protein that localize in the sulcal depths of the cerebral cortex. Neuronal abnormalities, axonopathy, neurovascular dysfunction, and neuroinflammation are triggered by repetitive head impacts (RHIs) and likely act as catalysts for CTE pathogenesis and progression. However, the specific mechanisms that link RHI to CTE are unknown. This review will explore two important areas of CTE pathobiology. First, we will review what is known about the biomechanical properties of RHI that initiate CTE-related pathologies. Second, we will provide an overview of key features of CTE neuropathology and how these contribute to abnormal tau hyperphosphorylation, accumulation, and spread.

Contact sport participation and chronic traumatic encephalopathy are associated with altered severity and distribution of cerebral amyloid angiopathy.

Cerebral amyloid angiopathy (CAA) consists of beta-amyloid deposition in the walls of the cerebrovasculature and is commonly associated with Alzheimer's disease (AD). However, the association of CAA with repetitive head impacts (RHI) and with chronic traumatic encephalopathy (CTE) is unknown. We evaluated the relationship between RHI from contact sport participation, CTE, and CAA within a group of deceased contact sport athletes (n = 357), a community-based cohort (n = 209), and an AD cohort from Boston University AD Center (n = 241). Unsupervised hierarchal cluster analysis demonstrated a unique cluster (n = 11) with increased CAA in the leptomeningeal vessels compared to the intracortical vessels (p < 0.001) comprised of participants with significantly greater frequencies of CTE (7/11) and history of RHI. Overall, participants with CTE (n = 251) had more prevalent (p < 0.001) and severe (p = 0.010) CAA within the frontal leptomeningeal vessels compared to intracortical vessels. Compared to those with AD, participants with CTE had more severe CAA in frontal than parietal lobes (p < 0.001) and more severe CAA in leptomeningeal than intracortical vessels (p = 0.002). The overall frequency of CAA in participants with CTE was low, and there was no significant association between contact sport participation and the presence of CAA. However, in those with CAA, a history of contact sports was associated with increased CAA severity in the frontal leptomeningeal vessels (OR = 4.01, 95% CI 2.52-6.38, p < 0.001) adjusting for AD, APOE ε4 status, and age. Participants with CAA had increased levels of sulcal tau pathology and decreased levels of the synaptic marker PSD-95 (p's < 0.05), and CAA was a predictor of dementia (OR = 1.75, 95% CI 1.02-2.99, p = 0.043) adjusting for age, sex, and comorbid pathology. Overall, contact sport participation and CTE were associated with more severe frontal and leptomeningeal CAA, and CAA was independently associated with worse pathological and clinical outcomes.

Arginase 1+ microglia reduce Aß plaque deposition during IL-1ß-dependent neuroinflammation.

BACKGROUND: Neuroinflammation has long been considered a driver of Alzheimer's disease progression. However, experiments developed to explore the interaction between neuroinflammation and Alzheimer's disease (AD) pathology showed a surprising reduction in amyloid beta (Aß) plaque deposition. We sought to understand this unexpected outcome by examining microglia phenotypes during chronic neuroinflammation. METHODS: Using an adeno-associated virus vector carrying hIL-1ß cDNA, inflammation was induced in one hippocampus of 8-month-old amyloid precursor protein (APP)/PS1 mice for 4 weeks, while the other hemisphere received control injections. Bone marrow chimeras and staining analysis were used to identify the origins and types of immune cells present during sustained inflammation. Arginase 1 (Arg1) and inducible nitric oxide synthase (iNOS) immunoreactivity were used as markers of alternatively activated and classically activated cells, respectively, and changes in cellular uptake of Aß by Arg1+ or iNOS+ microglia was demonstrated by confocal microscopy. To determine if an anti-inflammatory phenotype was present during neuroinflammation, RNA was extracted on flow-sorted microglia and rt-PCR was performed. Interleukin-4 injection was used to induce alternatively activated cells, whereas a minipump and intrahippocampal cannula was used to deliver an interleukin (IL)-4Rα antibody to block the induction of Arg1+ cells in the setting of sustained IL-1ß expression. RESULTS: We observed a robust upregulation of centrally derived Arg1+ microglia present only in the inflamed hemisphere. Furthermore, in the inflamed hemisphere, greater numbers of Arg1+ microglia contained Aß when compared to iNOS+ microglia. RNA isolated from flow-sorted microglia from the inflamed hemisphere demonstrated elevation of mRNA species consistent with alternative activation as well as neuroprotective genes such as BDNF and IGF1. To explore if Arg1+ microglia mediated plaque reduction, we induced Arg1+ microglia with IL-4 and observed significant plaque clearance. Moreover, when we reduced Arg1+ microglia induction in the context of neuroinflammation using an anti-IL-4Rα antibody delivered via intrahippocampal cannula, we observed a clear correlation between numbers of Arg1+ microglia and plaque reduction. CONCLUSIONS: Together, these findings suggest that Arg1+ microglia are involved in Aß plaque reduction during sustained, IL-1ß-dependent neuroinflammation, opening up possible new avenues for immunomodulatory therapy of AD.

Neuroinflammation and M2 microglia: the good, the bad, and the inflamed.

The concept of multiple macrophage activation states is not new. However, extending this idea to resident tissue macrophages, like microglia, has gained increased interest in recent years. Unfortunately, the research on peripheral macrophage polarization does not necessarily translate accurately to their central nervous system (CNS) counterparts. Even though pro- and anti-inflammatory cytokines can polarize microglia to distinct activation states, the specific functions of these states is still an area of intense debate. This review examines the multiple possible activation states microglia can be polarized to. This is followed by a detailed description of microglial polarization and the functional relevance of this process in both acute and chronic CNS disease models described in the literature. Particular attention is given to utilizing M2 microglial polarization as a potential therapeutic option in treating diseases.

Repetitive head impacts induce neuronal loss and neuroinflammation in young athletes.

Repetitive head impacts (RHI) sustained from contact sports are the largest risk factor for chronic traumatic encephalopathy (CTE). Currently, CTE can only be diagnosed after death and the multicellular cascade of events that trigger initial hyperphosphorylated tau (p-tau) deposition remain unclear. Further, the symptoms endorsed by young individuals with early disease are not fully explained by the extent of p-tau deposition, severely hampering development of therapeutic interventions. Here, we show that RHI exposure associates with a multicellular response in young individuals (<51 years old) prior to the onset of CTE p-tau pathology that correlates with number of years of RHI exposure. Leveraging single nucleus RNA sequencing of tissue from 8 control, 9 RHI-exposed, and 11 low stage CTE individuals, we identify SPP1+ inflammatory microglia, angiogenic and inflamed endothelial cell profiles, reactive astrocytes, and altered synaptic gene expression in excitatory and inhibitory neurons in all individuals with exposure to RHI. Surprisingly, we also observe a significant loss of cortical sulcus layer 2/3 neurons in contact sport athletes compared to controls independent of p-tau pathology. These results provide robust evidence that multiple years of RHI exposure is sufficient to induce lasting cellular alterations that may underlie p-tau deposition and help explain the early clinical symptoms observed in young former contact sport athletes. Furthermore, these data identify specific cellular responses to repetitive head impacts that may direct future identification of diagnostic and therapeutic strategies for CTE.

Substantia Nigra Pathology, Contact Sports Play, and Parkinsonism in Chronic Traumatic Encephalopathy.

Importance: Parkinsonism is associated with traumatic brain injury and chronic traumatic encephalopathy (CTE), a neurodegenerative disease associated with repetitive head impact (RHI) exposure, but the neuropathologic substrates that underlie parkinsonism in individuals with CTE are yet to be defined. Objective: To evaluate the frequency of parkinsonism in individuals with CTE and the association of RHI and neuropathologic substrates with parkinsonism in these individuals. Design, Setting, and Participants: This cross-sectional study included brain donors with neuropathologically diagnosed CTE without other significant neurodegenerative disease and with information on parkinsonism from the Understanding Neurologic Injury and Traumatic Encephalopathy brain bank between July 2015 and May 2022. Exposure: Years of contact sports participation as a proxy for RHI. Main Outcomes and Measures: The main outcomes were frequency of parkinsonism in individuals with CTE and associations between (1) RHI with substantia nigra (SN) Lewy bodies (LBs) and neurofibrillary tangles (NFTs); (2) LBs, NFTs, and arteriolosclerosis with SN neuronal loss; and (3) SN neuronal loss, LBs, NFTs, and arteriolosclerosis with parkinsonism, tested by age-adjusted logistic regressions. Results: Of 481 male brain donors with neuropathologically diagnosed CTE, parkinsonism occurred frequently in individuals with CTE (119 [24.7%]; 362 [75.3%] did not have parkinsonism). Participants with parkinsonism had a higher mean (SD) age at death (71.5 [13.0] years) than participants without parkinsonism (54.1 [19.3] years) (P < .001) and higher rates of dementia (104 [87.4%] vs 105 [29.0%]), visual hallucinations (45 [37.8%] vs 51 [14.1%]), and probable rapid eye movement sleep behavior disorder (52 [43.7%] vs 58 [16.0%]) (P < .001 for all). Participants with parkinsonism had a more severe CTE stage (eg, stage IV: 35 [29.4%] vs 39 [10.8%]) and nigral pathology than those without parkinsonism (NFTs: 50 of 117 [42.7%] vs 103 of 344 [29.9%]; P = .01; neuronal loss: 61 of 117 [52.1%] vs 59 of 344 [17.1%]; P < .001; and LBs: 28 of 116 [24.1%] vs 20 of 342 [5.8%]; P < .001). Years of contact sports participation were associated with SN NFTs (adjusted odds ratio [AOR], 1.04; 95% CI, 1.00-1.07; P = .03) and neuronal loss (AOR, 1.05; 95% CI, 1.01-1.08; P = .02). Nigral neuronal loss (AOR, 2.61; 95% CI, 1.52-4.47; P < .001) and LBs (AOR, 2.29; 95% CI, 1.15-4.57; P = .02) were associated with parkinsonism. However, SN neuronal loss was associated with SN LBs (AOR, 4.48; 95% CI, 2.25-8.92; P < .001), SN NFTs (AOR, 2.51; 95% CI, 1.52-4.15; P < .001), and arteriolosclerosis (AOR, 2.27; 95% CI, 1.33-3.85; P = .002). In American football players, regression analysis demonstrated that SN NFTs and neuronal loss mediated the association between years of play and parkinsonism in the context of CTE (ß, 0.012; 95% CI, 0.001-0.038). Conclusions and Relevance: In this cross-sectional study of contact sports athletes with CTE, years of contact sports participation were associated with SN tau pathology and neuronal loss, and these pathologies were associated with parkinsonism. Repetitive head impacts may incite neuropathologic processes that lead to symptoms of parkinsonism in individuals with CTE.