Traumatic brain injury as a risk factor for Alzheimer's disease: current knowledge and future directions

Exploring Heparan Sulfate Proteoglycans as Mediators of Human Mesenchymal Stem Cell Neurogenesis

Alzheimer's disease (AD) and traumatic brain injury (TBI) are major public health issues worldwide, with over 38 million people living with AD and approximately 48 million people (27-69 million) experiencing TBI annually. Neurodegenerative conditions are characterised by the accumulation of neurotoxic amyloid beta (Aβ) and microtubule-associated protein Tau (Tau) with current treatments focused on managing symptoms rather than addressing the underlying cause. Heparan sulfate proteoglycans (HSPGs) are a diverse family of macromolecules that interact with various proteins and ligands and promote neurogenesis, a process where new neural cells are formed from stem cells. The syndecan (SDC) and glypican (GPC) HSPGs have been implicated in AD pathogenesis, acting as drivers of disease, as well as potential therapeutic targets. Human mesenchymal stem cells (hMSCs) provide an attractive therapeutic option for studying and potentially treating neurodegenerative diseases due to their relative ease of isolation and subsequent extensive in vitro expansive potential. Understanding how HSPGs regulate protein aggregation, a key feature of neurodegenerative disorders, is essential to unravelling the underlying disease processes of AD and TBI, as well as any link between these two neurological disorders. Further research may validate HSPG, specifically SDCs or GPCs, use as neurodegenerative disease targets, either via driving hMSC stem cell therapy or direct targeting.

Improving quantitative susceptibility mapping for the identification of traumatic brain injury neurodegeneration at the individual level

BACKGROUND

Emerging evidence suggests that traumatic brain injury (TBI) is a major risk factor for developing neurodegenerative disease later in life. Quantitative susceptibility mapping (QSM) has been used by an increasing number of studies in investigations of pathophysiological changes in TBI. However, generating artefact-free quantitative susceptibility maps in brains with large focal lesions, as in the case of moderate-to-severe TBI (ms-TBI), is particularly challenging. To address this issue, we utilized a novel two-pass masking technique and reconstruction procedure (two-pass QSM) to generate quantitative susceptibility maps (QSMxT; Stewart et al., 2022, Magn Reson Med.) in combination with the recently developed virtual brain grafting (VBG) procedure for brain repair (Radwan et al., 2021, NeuroImage) to improve automated delineation of brain areas. We used QSMxT and VBG to generate personalised QSM profiles of individual patients with reference to a sample of healthy controls.

METHODS

Chronic ms-TBI patients (N = 8) and healthy controls (N = 12) underwent (multi-echo) GRE, and anatomical MRI (MPRAGE) on a 3T Siemens PRISMA scanner. We reconstructed the magnetic susceptibility maps using two-pass QSM from QSMxT. We then extracted values of magnetic susceptibility in grey matter (GM) regions (following brain repair via VBG) across the whole brain and determined if they deviate from a reference healthy control group [Z-score < -3.43 or > 3.43, relative to the control mean], with the aim of obtaining personalised QSM profiles.

RESULTS

Using two-pass QSM, we achieved susceptibility maps with a substantial increase in quality and reduction in artefacts irrespective of the presence of large focal lesions, compared to single-pass QSM. In addition, VBG minimised the loss of GM regions and exclusion of patients due to failures in the region delineation step. Our findings revealed deviations in magnetic susceptibility measures from the HC group that differed across individual TBI patients. These changes included both increases and decreases in magnetic susceptibility values in multiple GM regions across the brain.

CONCLUSIONS

We illustrate how to obtain magnetic susceptibility values at the individual level and to build personalised QSM profiles in ms-TBI patients. Our approach opens the door for QSM investigations in more severely injured patients. Such profiles are also critical to overcome the inherent heterogeneity of clinical populations, such as ms-TBI, and to characterize the underlying mechanisms of neurodegeneration at the individual level more precisely. Moreover, this new personalised QSM profiling could in the future assist clinicians in assessing recovery and formulating a neuroscience-guided integrative rehabilitation program tailored to individual TBI patients.

Comparing Brain and Blood Lipidome Changes following Single and Repetitive Mild Traumatic Brain Injury in Rats

Traumatic brain injury (TBI) is a major health concern in the United States and globally, contributing to disability and long-term neurological problems. Lipid dysregulation after TBI is underexplored, and a better understanding of lipid turnover and degradation could point to novel biomarker candidates and therapeutic targets. Here, we investigated overlapping lipidome changes in the brain and blood using a data-driven discovery approach to understand lipid alterations in the brain and serum compartments acutely following mild TBI (mTBI) and the potential efflux of brain lipids to peripheral blood. The cortices and sera from male and female Sprague-Dawley rats were analyzed via ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS) in both positive and negative ion modes following single and repetitive closed head impacts. The overlapping lipids in the data sets were identified with an in-house data dictionary for investigating lipid class changes. MS-based lipid profiling revealed overall increased changes in the serum compartment, while the brain lipids primarily showed decreased changes. Interestingly, there were prominent alterations in the sphingolipid class in the brain and blood compartments after single and repetitive injury, which may suggest efflux of brain sphingolipids into the blood after TBI. Genetic algorithms were used for predictive panel selection to classify injured and control samples with high sensitivity and specificity. These overlapping lipid panels primarily mapped to the glycerophospholipid metabolism pathway with Benjamini-Hochberg adjusted q-values less than 0.05. Collectively, these results detail overlapping lipidome changes following mTBI in the brain and blood compartments, increasing our understanding of TBI-related lipid dysregulation while identifying novel biomarker candidates.

The Role of Insulin-like Growth Factor I in Mechanisms of Resilience and Vulnerability to Sporadic Alzheimer's Disease

Despite decades of intense research, disease-modifying therapeutic approaches for Alzheimer's disease (AD) are still very much needed. Apart from the extensively analyzed tau and amyloid pathological cascades, two promising avenues of research that may eventually identify new druggable targets for AD are based on a better understanding of the mechanisms of resilience and vulnerability to this condition. We argue that insulin-like growth factor I (IGF-I) activity in the brain provides a common substrate for the mechanisms of resilience and vulnerability to AD. We postulate that preserved brain IGF-I activity contributes to resilience to AD pathology as this growth factor intervenes in all the major pathological cascades considered to be involved in AD, including metabolic impairment, altered proteostasis, and inflammation, to name the three that are considered to be the most important ones. Conversely, disturbed IGF-I activity is found in many AD risk factors, such as old age, type 2 diabetes, imbalanced diet, sedentary life, sociality, stroke, stress, and low education, whereas the Apolipoprotein (Apo) E4 genotype and traumatic brain injury may also be influenced by brain IGF-I activity. Accordingly, IGF-I activity should be taken into consideration when analyzing these processes, while its preservation will predictably help prevent the progress of AD pathology. Thus, we need to define IGF-I activity in all these conditions and develop a means to preserve it. However, defining brain IGF-I activity cannot be solely based on humoral or tissue levels of this neurotrophic factor, and new functionally based assessments need to be developed.

Identification of Factors in Moderate-Severe TBI Related to a Functional Decline in Cognition Decades After Injury

OBJECTIVE

To investigate whether a functional decline in cognitive activities decades after moderate-to-severe traumatic brain injury (m-sTBI) might relate to injury features and/or lifetime health factors, some of which may emerge as consequences of the injury.

DESIGN

Secondary analysis of the TBI Model Systems National Database, a prospective, multi-center, longitudinal study of patients with m-sTBI.

SETTING

TBI Model Systems Centers.

PARTICIPANTS

Included were 732 participants rated on the cognitive subscale of the Functional Independence Measure (FIM Cognitive), a metric for everyday cognitive skills, across 3 time points out to 20 years (visits at 2-, 10-, and 20-year follow-ups; N=732).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURE(S)

FIM Cognitive Scale. Injury characteristics such as timing and features pertaining to severity and health-related factors (eg, alcohol use, socioeconomic status) were examined to discriminate stable from declining participants on the FIM Cognitive Scale using logistic regression.

RESULTS

At 20 years post-injury, there was a low base rate of FIM Cognitive decline (11%, n=78), with most being stable or having meaningful improvement (89%, n=654). Older age at injury, longer duration of post-traumatic amnesia, and presence of repetitive seizures were significant predictors of FIM Cognitive decline in the final model (area under the curve=0.75), while multiple health-related factors that can represent independent co-morbidities or possible consequences of injury were not.

CONCLUSION(S)

The strongest contributors to reported functional decline in cognitive activities later-in-life were related to acute characteristics of m-sTBI and experiencing post-traumatic seizures. Future studies are needed integrating functional with performance-based cognitive assessments to affirm conclusions and identify the timeline and trajectory of cognitive decline.

Amyloid PET across the cognitive spectrum in former professional and college American football players: findings from the DIAGNOSE CTE Research Project

BACKGROUND

Exposure to repetitive head impacts (RHI) in American football players can lead to cognitive impairment and dementia due to neurodegenerative disease, particularly chronic traumatic encephalopathy (CTE). The pathognomonic lesion of CTE consists of perivascular aggregates of hyper-phosphorylated tau in neurons at the depths of cortical sulci. However, it is unclear whether exposure to RHI accelerates amyloid-β (Aβ) plaque formation and increases the risk for Alzheimer's disease (AD). Although the Aβ neuritic plaques characteristic of AD are observed in a minority of later-stage CTE cases, diffuse plaques are more common. This study examined whether former professional and college American football players, including those with cognitive impairment and dementia, have elevated neuritic Aβ plaque density, as measured by florbetapir PET. Regardless of cognitive and functional status, elevated levels of florbetapir uptake were not expected.

METHODS

We examined 237 men ages 45-74, including 119 former professional (PRO) and 60 former college (COL) football players, with and without cognitive impairment and dementia, and 58 same-age men without a history of contact sports or TBI (unexposed; UE) and who denied cognitive or behavioral symptoms at telephone screening. Former players were categorized into four diagnostic groups: normal cognition, subjective memory impairment, mild cognitive impairment, and dementia. Positive florbetapir PET was defined by cortical-cerebellar average SUVR of ≥ 1.10. Multivariable linear regression and analysis of covariance (ANCOVA) compared florbetapir average SUVR across diagnostic and exposure groups. Multivariable logistic regression compared florbetapir positivity. Race, education, age, and APOE4 were covariates.

RESULTS

There were no diagnostic group differences either in florbetapir average SUVR or the proportion of elevated florbetapir uptake. Average SUVR means also did not differ between exposure groups: PRO-COL (p = 0.94, 95% C.I. = [- 0.033, 0.025]), PRO-UE (p = 0.40, 95% C.I. = [- 0.010, 0.029]), COL-UE (p = 0.36, 95% CI = [0.0004, 0.039]). Florbetapir was not significantly associated with years of football exposure, cognition, or daily functioning.

CONCLUSIONS

Cognitive impairment in former American football players is not associated with PET imaging of neuritic Aβ plaque deposition. These findings are inconsistent with a neuropathological diagnosis of AD in individuals with substantial RHI exposure and have both clinical and medico-legal implications.

TRIAL REGISTRATION

NCT02798185.

DNA Methylation-Mediated Mfn2 Gene Regulation in the Brain: A Role in Brain Trauma-Induced Mitochondrial Dysfunction and Memory Deficits

Repeated mild traumatic brain injuries (rMTBI) affect mitochondrial homeostasis in the brain. However, mechanisms of long-lasting neurobehavioral effects of rMTBI are largely unknown. Mitofusin 2 (Mfn2) is a critical component of tethering complexes in mitochondria-associated membranes (MAMs) and thereby plays a pivotal role in mitochondrial functions. Herein, we investigated the implications of DNA methylation in the Mfn2 gene regulation, and its consequences on mitochondrial dysfunction in the hippocampus after rMTBI. rMTBI dramatically reduced the mitochondrial mass, which was concomitant with decrease in Mfn2 mRNA and protein levels. DNA hypermethylation at the Mfn2 gene promoter was observed post 30 days of rMTBI. The treatment of 5-Azacytidine, a pan DNA methyltransferase inhibitor, normalized DNA methylation levels at Mfn2 promoter, which further resulted into restoration of Mfn2 function. The normalization of Mfn2 function was well correlated with recovery in memory deficits in rMTBI-exposed rats. Since, glutamate excitotoxicity serves as a primary insult after TBI, we employed in vitro model of glutamate excitotoxicity in human neuronal cell line SH-SY5Y to investigate the causal epigenetic mechanisms of Mfn2 gene regulation. The glutamate excitotoxicity reduced Mfn2 levels via DNA hypermethylation at Mfn2 promoter. Loss of Mfn2 caused significant surge in cellular and mitochondrial ROS levels with lowered mitochondrial membrane potential in cultured SH-SY5Y cells. Like rMTBI, these consequences of glutamate excitotoxicity were also prevented by 5-AzaC pre-treatment. Therefore, DNA methylation serves as a vital epigenetic mechanism involved in Mfn2 expression in the brain; and this Mfn2 gene regulation may play a pivotal role in rMTBI-induced persistent cognitive deficits. Closed head weight drop injury method was employed to induce repeated mild traumatic brain (rMTBI) in jury in adult, male Wistar rats. rMTBI causes hyper DNA methylation at the Mfn2 promoter and lowers the Mfn2 expression triggering mitochondrial dysfunction. However, the treatment of 5-azacytidine normalizes DNA methylation at the Mfn2 promoter and restores mitochondrial function.

Spinal cord injury induced exacerbation of Alzheimer's disease like pathophysiology is reduced by topical application of nanowired cerebrolysin with monoclonal antibodies to amyloid beta peptide, p-tau and tumor necrosis factor alpha

Hallmark of Alzheimer's disease include amyloid beta peptide and phosphorylated tau deposition in brain that could be aggravated following traumatic of concussive head injury. However, amyloid beta peptide or p-tau in spinal cord following injury is not well known. In this investigation we measured amyloid beta peptide and p-tau together with tumor necrosis factor-alpha (TNF-α) in spinal cord and brain following 48 h after spinal cord injury in relation to the blood-spinal cord and blood-brain barrier, edema formation, blood flow changes and cell injury in perifocal regions of the spinal cord and brain areas. A focal spinal cord injury was inflicted over the right dorsal horn of the T10-11 segment (4 mm long and 2 mm deep) and amyloid beta peptide and p-tau was measured in perifocal rostral (T9) and caudal (T12) spinal cord segments as well as in the brain areas. Our observations showed a significant increase in amyloid beta peptide in the T9 and T12 segments as well as in remote areas of brain and spinal cord after 24 and 48 h injury. This is associated with breakdown of the blood-spinal cord (BSCB) and brain barriers (BBB), edema formation, reduction in blood flow and cell injury. After 48 h of spinal cord injury elevation of amyloid beta peptide, phosphorylated tau (p-tau) and tumor necrosis factor-alpha (TNF-α) was seen in T9 and T12 segments of spinal cord in cerebral cortex, hippocampus and brain stem regions associated with microglial activation as seen by upregulation of Iba1 and CD86. Repeated nanowired delivery of cerebrolysin topically over the traumatized segment repeatedly together with monoclonal antibodies (mAb) to amyloid beta peptide (AβP), p-tau and TNF-α significantly attenuated amyloid beta peptide, p-tau deposition and reduces Iba1, CD68 and TNF-α levels in the brain and spinal cord along with blockade of BBB and BSCB, reduction in blood flow, edema formation and cell injury. These observations are the first to show that spinal cord injury induces Alzheimer's disease like symptoms in the CNS, not reported earlier.

Traumatic brain injury-associated epigenetic changes and the risk for neurodegenerative diseases

Epidemiological studies have shown that traumatic brain injury (TBI) increases the risk for developing neurodegenerative diseases (NDs). However, molecular mechanisms that underlie this risk are largely unidentified. TBI triggers widespread epigenetic modifications. Similarly, NDs such as Alzheimer's or Parkinson's are associated with numerous epigenetic changes. Although epigenetic changes can persist after TBI, it is unresolved if these modifications increase the risk of later ND development and/or dementia. We briefly review TBI-related epigenetic changes, and point out putative feedback loops that might contribute to long-term persistence of some modifications. We then focus on evidence suggesting persistent TBI-associated epigenetic changes may contribute to pathological processes (e.g., neuroinflammation) which may facilitate the development of specific NDs - Alzheimer's disease, Parkinson's disease, or chronic traumatic encephalopathy. Finally, we discuss possible directions for TBI therapies that may help prevent or delay development of NDs.

Meningeal lymphatics and their role in CNS disorder treatment: moving past misconceptions

The central nervous system (CNS) was previously thought to lack lymphatics and shielded from the free diffusion of molecular and cellular components by the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCB). However, recent findings have redefined the roles played by meningeal lymphatic vessels in the recruitment and drainage of lymphocytes from the periphery into the brain and the potentiation of an immune response. Emerging knowledge surrounding the importance of meningeal lymphatics has the potential to transform the treatment of CNS disorders. This review details the most recent understanding of the CNS-lymphatic network and its immunologic implications in both the healthy and diseased brain. Moreover, the review provides in-depth coverage of several exciting avenues for future therapeutic treatments that involve the meningeal lymphatic system. These therapeutic avenues will have potential implications in many treatment paradigms in the coming years.

The multifactorial nature of healthy brain ageing: Brain changes, functional decline and protective factors

As the global population faces a progressive shift towards a higher median age, understanding the mechanisms underlying healthy brain ageing has become of paramount importance for the preservation of cognitive abilities. The first part of the present review aims to provide a comprehensive look at the anatomical changes the healthy brain endures with advanced age, while also summarizing up to date findings on modifiable risk factors to support a healthy ageing process. Subsequently, we describe the typical cognitive profile displayed by healthy older adults, conceptualizing the well-established age-related decline as an impairment of four main cognitive factors and relating them to their neural substrate previously described; different cognitive trajectories displayed by typical Alzheimer's Disease patients and successful agers with a high cognitive reserve are discussed. Finally, potential effective interventions and protective strategies to promote cognitive reserve and defer cognitive decline are reviewed and proposed.

Overexpression of GPX4 attenuates cognitive dysfunction through inhibiting hippocampus ferroptosis and neuroinflammation after traumatic brain injury

Ferroptosis is a newly discovered form of regulated cell death that is triggered primarily by lipid peroxidation. A growing body of evidence has implicated ferroptosis in the pathophysiology of traumatic brain injury (TBI). However, none of these studies focused its role on TBI-induced hippocampal injury. Here, we demonstrated that the distinct ferroptotic signature was detected in the injured hippocampus at the early stage of TBI. Besides, a prominent pro-ferroptosis environment was detected in the ipsilateral hippocampus after TBI, including elevated levels of arachidonic acid (AA), ACLS4, and ALXO15, and deficiency of GPX4. Subsequently, we used AAV-mediated Gpx4 overexpression to counteract ferroptosis in the hippocampus, and found that TBI-induced cognitive deficits were significantly alleviated after Gpx4 overexpression. Biochemical results also confirmed that TBI-induced hippocampal ferroptosis and synaptic damage were partially reversed by Gpx4 overexpression. In addition, Gpx4 overexpression inhibited TBI-induced neuroinflammation and peripheral macrophage infiltration. Interestingly, the results of transwell migration assay showed that ferroptotic neurons increased CCL2 expression and promoted iBMDM cell migration. However, this effect was inhibited by CCL2 antagonist, RS102895. These data suggested that inhibition of ferroptosis may be as a potential strategy to ameliorate TBI-induced cognitive deficits through blockade of hippocampal ferroptosis and neuroinflammation.

Inhibiting degradation of 2-arachidonoylglycerol as a therapeutic strategy for neurodegenerative diseases

Endocannabinoids are endogenous lipid signaling mediators that participate in a variety of physiological and pathological processes. 2-Arachidonoylglycerol (2-AG) is the most abundant endocannabinoid and is a full agonist of G-protein-coupled cannabinoid receptors (CB1R and CB2R), which are targets of Δ⁹-tetrahydrocannabinol (Δ⁹-THC), the main psychoactive ingredient in cannabis. While 2-AG has been well recognized as a retrograde messenger modulating synaptic transmission and plasticity at both inhibitory GABAergic and excitatory glutamatergic synapses in the brain, growing evidence suggests that 2-AG also functions as an endogenous terminator of neuroinflammation in response to harmful insults, thus maintaining brain homeostasis. Monoacylglycerol lipase (MAGL) is the key enzyme that degrades 2-AG in the brain. The immediate metabolite of 2-AG is arachidonic acid (AA), a precursor of prostaglandins (PGs) and leukotrienes. Several lines of evidence indicate that pharmacological or genetic inactivation of MAGL, which boosts 2-AG levels and reduces its hydrolytic metabolites, resolves neuroinflammation, mitigates neuropathology, and improves synaptic and cognitive functions in animal models of neurodegenerative diseases, including Alzheimer's disease (AD), multiple sclerosis (MS), Parkinson's disease (PD), and traumatic brain injury (TBI)-induced neurodegenerative disease. Thus, it has been proposed that MAGL is a potential therapeutic target for treatment of neurodegenerative diseases. As the main enzyme hydrolyzing 2-AG, several MAGL inhibitors have been identified and developed. However, our understanding of the mechanisms by which inactivation of MAGL produces neuroprotective effects in neurodegenerative diseases remains limited. A recent finding that inhibition of 2-AG metabolism in astrocytes, but not in neurons, protects the brain from TBI-induced neuropathology might shed some light on this unsolved issue. This review provides an overview of MAGL as a potential therapeutic target for neurodegenerative diseases and discusses possible mechanisms underlying the neuroprotective effects of restraining degradation of 2-AG in the brain.

White matter hyperintensities in former American football players

INTRODUCTION

The presentation, risk factors, and etiologies of white matter hyperintensities (WMH) in people exposed to repetitive head impacts are unknown. We examined the burden and distribution of WMH, and their association with years of play, age of first exposure, and clinical function in former American football players.

METHODS

A total of 149 former football players and 53 asymptomatic unexposed participants (all men, 45-74 years) completed fluid-attenuated inversion recovery magnetic resonance imaging, neuropsychological testing, and self-report neuropsychiatric measures. Lesion Segmentation Toolbox estimated WMH. Analyses were performed in the total sample and stratified by age 60.

RESULTS

In older but not younger participants, former football players had greater total, frontal, temporal, and parietal log-WMH compared to asymptomatic unexposed men. In older but not younger former football players, greater log-WMH was associated with younger age of first exposure to football and worse executive function.

DISCUSSION

In older former football players, WMH may have unique presentations, risk factors, and etiologies.

HIGHLIGHTS

Older but not younger former football players had greater total, frontal, temporal, and parietal lobe white matter hyperintensities (WMH) compared to same-age asymptomatic unexposed men. Younger age of first exposure to football was associated with greater WMH in older but not younger former American football players. In former football players, greater WMH was associated with worse executive function and verbal memory.

The Effects of Galactic Cosmic Rays on the Central Nervous System: From Negative to Unexpectedly Positive Effects That Astronauts May Encounter

Galactic cosmic rays (GCR) pose a serious threat to astronauts’ health during deep space missions. The possible functional alterations of the central nervous system (CNS) under GCR exposure can be critical for mission success. Despite the obvious negative effects of ionizing radiation, a number of neutral or even positive effects of GCR irradiation on CNS functions were revealed in ground-based experiments with rodents and primates. This review is focused on the GCR exposure effects on emotional state and cognition, emphasizing positive effects and their potential mechanisms. We integrate these data with GCR effects on adult neurogenesis and pathological protein aggregation, forming a complete picture. We conclude that GCR exposure causes multidirectional effects on cognition, which may be associated with emotional state alterations. However, the irradiation in space-related doses either has no effect or has performance enhancing effects in solving high-level cognition tasks and tasks with a high level of motivation. We suppose the model of neurotransmission changes after irradiation, although the molecular mechanisms of this phenomenon are not fully understood.

Cdk5 mediates rotational force-induced brain injury

Millions of traumatic brain injuries (TBIs) occur annually. TBIs commonly result from falls, traffic accidents, and sports-related injuries, all of which involve rotational acceleration/deceleration of the brain. During these injuries, the brain endures a multitude of primary insults including compression of brain tissue, damaged vasculature, and diffuse axonal injury. All of these deleterious effects can contribute to secondary brain ischemia, cellular death, and neuroinflammation that progress for weeks, months, and lifetime after injury. While the linear effects of head trauma have been extensively modeled, less is known about how rotational injuries mediate neuronal damage following injury. Here, we developed a new model of repetitive rotational head trauma in rodents and demonstrated acute and prolonged pathological, behavioral, and electrophysiological effects of rotational TBI (rTBI). We identify aberrant Cyclin-dependent kinase 5 (Cdk5) activity as a principal mediator of rTBI. We utilized Cdk5-enriched phosphoproteomics to uncover potential downstream mediators of rTBI and show pharmacological inhibition of Cdk5 reduces the cognitive and pathological consequences of injury. These studies contribute meaningfully to our understanding of the mechanisms of rTBI and how they may be effectively treated.

Polynitroxylated PEGylated hemoglobin protects pig brain neocortical gray and white matter after traumatic brain injury and hemorrhagic shock

Polynitroxylated PEGylated hemoglobin (PNPH, aka SanFlow) possesses superoxide dismutase/catalase mimetic activities that may directly protect the brain from oxidative stress. Stabilization of PNPH with bound carbon monoxide prevents methemoglobin formation during storage and permits it to serve as an anti-inflammatory carbon monoxide donor. We determined whether small volume transfusion of hyperoncotic PNPH is neuroprotective in a porcine model of traumatic brain injury (TBI) with and without accompanying hemorrhagic shock (HS). TBI was produced by controlled cortical impact over the frontal lobe of anesthetized juvenile pigs. Hemorrhagic shock was induced starting 5 min after TBI by 30 ml/kg blood withdrawal. At 120 min after TBI, pigs were resuscitated with 60 ml/kg lactated Ringer's (LR) or 10 or 20 ml/kg PNPH. Mean arterial pressure recovered to approximately 100 mmHg in all groups. A significant amount of PNPH was retained in the plasma over the first day of recovery. At 4 days of recovery in the LR-resuscitated group, the volume of frontal lobe subcortical white matter ipsilateral to the injury was 26.2 ± 7.6% smaller than homotypic contralateral volume, whereas this white matter loss was only 8.6 ± 12.0% with 20-ml/kg PNPH resuscitation. Amyloid precursor protein punctate accumulation, a marker of axonopathy, increased in ipsilateral subcortical white matter by 132 ± 71% after LR resuscitation, whereas the changes after 10 ml/kg (36 ± 41%) and 20 ml/kg (26 ± 15%) PNPH resuscitation were not significantly different from controls. The number of cortical neuron long dendrites enriched in microtubules (length >50 microns) decreased in neocortex by 41 ± 24% after LR resuscitation but was not significantly changed after PNPH resuscitation. The perilesion microglia density increased by 45 ± 24% after LR resuscitation but was unchanged after 20 ml/kg PNPH resuscitation (4 ± 18%). Furthermore, the number with an activated morphology was attenuated by 30 ± 10%. In TBI pigs without HS followed 2 h later by infusion of 10 ml/kg LR or PNPH, PNPH remained neuroprotective. These results in a gyrencephalic brain show that resuscitation from TBI + HS with PNPH protects neocortical gray matter, including dendritic microstructure, and white matter axons and myelin. This neuroprotective effect persists with TBI alone, indicating brain-targeting benefits independent of blood pressure restoration.

Inhibition of Caspase 3 and Caspase 9 Mediated Apoptosis: A Multimodal Therapeutic Target in Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the significant causes of death and morbidity, and it is hence a focus of translational research. Apoptosis plays an essential part in the pathophysiology of TBI, and its inhibition may help overcome TBI's negative consequences and improve functional recovery. Although physiological neuronal death is necessary for appropriate embryologic development and adult cell turnover, it can also drive neurodegeneration. Caspases are principal mediators of cell death due to apoptosis and are critical for the required cleavage of intracellular proteins of cells committed to die. Caspase-3 is the major executioner Caspase of apoptosis and is regulated by a range of cellular components during physiological and pathological conditions. Activation of Caspase-3 causes proteolyzation of DNA repair proteins, cytoskeletal proteins, and the inhibitor of Caspase-activated DNase (ICAD) during programmed cell death, resulting in morphological alterations and DNA damage that define apoptosis. Caspase-9 is an additional crucial part of the intrinsic pathway, activated in response to several stimuli. Caspases can be altered post-translationally or by modulatory elements interacting with the zymogenic or active form of a Caspase, preventing their activation. The necessity of Caspase-9 and -3 in diverse apoptotic situations suggests that mammalian cells have at least four distinct apoptotic pathways. Continued investigation of these processes is anticipated to disclose new Caspase regulatory mechanisms with consequences far beyond apoptotic cell death control. The present review discusses various Caspase-dependent apoptotic pathways and the treatment strategies to inhibit the Caspases potentially.

Association of Traumatic Brain Injury with Late Life Neuropathological Outcomes in a Community-Based Cohort

BACKGROUND

Prior studies into the association of head trauma with neuropathology have been limited by incomplete lifetime neurotrauma exposure characterization.

OBJECTIVE

To investigate the neuropathological sequelae of traumatic brain injury (TBI) in an autopsy sample using three sources of TBI ascertainment, weighting findings to reflect associations in the larger, community-based cohort.

METHODS

Self-reported head trauma with loss of consciousness (LOC) exposure was collected in biennial clinic visits from 780 older adults from the Adult Changes in Thought study who later died and donated their brain for research. Self-report data were supplemented with medical record abstraction, and, for 244 people, structured interviews on lifetime head trauma. Neuropathology outcomes included Braak stage, CERAD neuritic plaque density, Lewy body distribution, vascular pathology, hippocampal sclerosis, and cerebral/cortical atrophy. Exposures were TBI with or without LOC. Modified Poisson regressions adjusting for age, sex, education, and APOE ɛ4 genotype were weighted back to the full cohort of 5,546 participants.

RESULTS

TBI with LOC was associated with the presence of cerebral cortical atrophy (Relative Risk 1.22, 95% CI 1.02, 1.42). None of the other outcomes was associated with TBI with or without LOC.

CONCLUSION

TBI with LOC was associated with increased risk of cerebral cortical atrophy. Despite our enhanced TBI ascertainment, we found no association with the Alzheimer's disease-related neuropathologic outcomes among people who survived to at least age 65 without dementia. This suggests the pathophysiological processes underlying post-traumatic neurodegeneration are distinct from the hallmark pathologies of Alzheimer's disease.

Risk Factors for Alzheimer Disease Development After Traumatic Brain Injury: A Preliminary Study

Traumatic brain injury (TBI) is increasingly recognized as a major risk factor for developing neurocognitive disorders, though this association remains controversial. Determination of risk factors for post-traumatic neurodegeneration in patients with TBI is critical given the high incidence of TBI. We hypothesized that cardiovascular and metabolic comorbidities, in addition to TBI severity, are associated with the risk of post-traumatic development of Alzheimer disease dementia (ADD). A case-controlled retrospective study was conducted using medical records and medical insurance data of 5642 patients with TBI admitted to a tertiary trauma center over a 12-year period, to assess risk factors of developing ADD after TBI. Logistic regression shows that presence of post-traumatic amnesia ( P= 0.03) and chronic vascular lesions ( P= 0.04) are significantly associated with development of ADD after TBI. This innovative preliminary study is the first to explore risk factors for post-traumatic ADD. Further association studies are essential to optimize care following TBI.

APOE in the bullseye of neurodegenerative diseases: impact of the APOE genotype in Alzheimer’s disease pathology and brain diseases

ApoE is the major lipid and cholesterol carrier in the CNS. There are three major human polymorphisms, apoE2, apoE3, and apoE4, and the genetic expression of APOE4 is one of the most influential risk factors for the development of late-onset Alzheimer's disease (AD). Neuroinflammation has become the third hallmark of AD, together with Amyloid-β plaques and neurofibrillary tangles of hyperphosphorylated aggregated tau protein. This review aims to broadly and extensively describe the differential aspects concerning apoE. Starting from the evolution of apoE to how APOE's single-nucleotide polymorphisms affect its structure, function, and involvement during health and disease. This review reflects on how APOE's polymorphisms impact critical aspects of AD pathology, such as the neuroinflammatory response, particularly the effect of APOE on astrocytic and microglial function and microglial dynamics, synaptic function, amyloid-β load, tau pathology, autophagy, and cell–cell communication. We discuss influential factors affecting AD pathology combined with the APOE genotype, such as sex, age, diet, physical exercise, current therapies and clinical trials in the AD field. The impact of the APOE genotype in other neurodegenerative diseases characterized by overt inflammation, e.g., alpha- synucleinopathies and Parkinson's disease, traumatic brain injury, stroke, amyotrophic lateral sclerosis, and multiple sclerosis, is also addressed. Therefore, this review gathers the most relevant findings related to the APOE genotype up to date and its implications on AD and CNS pathologies to provide a deeper understanding of the knowledge in the APOE field.

TDP-43 drives synaptic and cognitive deterioration following traumatic brain injury

Traumatic brain injury (TBI) has been recognized as an important risk factor for Alzheimer's disease (AD). However, the molecular mechanisms by which TBI contributes to developing AD remain unclear. Here, we provide evidence that aberrant production of TDP-43 is a key factor in promoting AD neuropathology and synaptic and cognitive deterioration in mouse models of mild closed head injury (CHI). We observed that a single mild CHI is sufficient to exacerbate AD neuropathology and accelerate synaptic and cognitive deterioration in APP transgenic mice but repeated mild CHI are required to induce neuropathological changes and impairments in synaptic plasticity, spatial learning, and memory retention in wild-type animals. Importantly, these changes in animals exposed to a single or repeated mild CHI are alleviated by silencing of TDP-43 but reverted by rescue of the TDP-43 knockdown. Moreover, overexpression of TDP-43 in the hippocampus aggravates AD neuropathology and provokes cognitive impairment in APP transgenic mice, mimicking single mild CHI-induced changes. We further discovered that neuroinflammation triggered by TBI promotes NF-κB-mediated transcription and expression of TDP-43, which in turn stimulates tau phosphorylation and Aβ formation. Our findings suggest that excessive production of TDP-43 plays an important role in exacerbating AD neuropathology and in driving synaptic and cognitive declines following TBI.

Intravenous infusion of the exosomes derived from human umbilical cord mesenchymal stem cells enhance neurological recovery after traumatic brain injury via suppressing the NF-κB pathway

Traumatic brain injury (TBI) is a predominant cause of death and permanent disability globally. In recent years, much emphasis has been laid on treatments for TBI. Increasing evidence suggests that human umbilical cord mesenchymal stem cells (HUCMSCs) can improve neurological repair after TBI. However, the clinical use of HUCMSCs transplantation in TBI has been limited by immunological rejection, ethical issues, and the risk of tumorigenicity. Many studies have shown that HUCMSCs-derived exosomes may be an alternative approach for HUCMSCs transplantation. We hypothesized that exosomes derived from HUCMSCs could inhibit apoptosis after TBI, reduce neuroinflammation, and promote neurogenesis. A rat model of TBI was established to investigate the efficiency of neurological recovery with exosome therapy. We found that exosomes derived from HUCMSCs significantly ameliorated sensorimotor function and spatial learning in rats after TBI. Moreover, HUCMSCs-derived exosomes significantly reduced proinflammatory cytokine expression by suppressing the NF-κB signaling pathway. Furthermore, we found that HUCMSC-derived exosomes inhibited neuronal apoptosis, reduced inflammation, and promoted neuron regeneration in the injured cortex of rats after TBI. These results indicate that HUCMSCs-derived exosomes may be a promising therapeutic strategy for TBI.

The Emergence of Model Systems to Investigate the Link Between Traumatic Brain Injury and Alzheimer’s Disease

Numerous epidemiological studies have demonstrated that individuals who have sustained a traumatic brain injury (TBI) have an elevated risk for developing Alzheimer’s disease and Alzheimer’s-related dementias (AD/ADRD). Despite these connections, the underlying mechanisms by which TBI induces AD-related pathology, neuronal dysfunction, and cognitive decline have yet to be elucidated. In this review, we will discuss the various in vivo and in vitro models that are being employed to provide more definite mechanistic relationships between TBI-induced mechanical injury and AD-related phenotypes. In particular, we will highlight the strengths and weaknesses of each of these model systems as it relates to advancing the understanding of the mechanisms that lead to TBI-induced AD onset and progression as well as providing platforms to evaluate potential therapies. Finally, we will discuss how emerging methods including the use of human induced pluripotent stem cell (hiPSC)-derived cultures and genome engineering technologies can be employed to generate better models of TBI-induced AD.

Lipidome Alterations following Mild Traumatic Brain Injury in the Rat

Traumatic brain injury (TBI) poses a major health challenge, with tens of millions of new cases reported globally every year. Brain damage resulting from TBI can vary significantly due to factors including injury severity, injury mechanism and exposure to repeated injury events. Therefore, there is need for robust blood biomarkers. Serum from Sprague Dawley rats was collected at several timepoints within 24 h of mild single or repeat closed head impacts. Serum samples were analyzed via ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MS) in positive and negative ion modes. Known lipid species were identified through matching to in-house tandem MS databases. Lipid biomarkers have a unique potential to serve as objective molecular measures of injury response as they may be liberated to circulation more readily than larger protein markers. Machine learning and feature selection approaches were used to construct lipid panels capable of distinguishing serum from injured and uninjured rats. The best multivariate lipid panels had over 90% cross-validated sensitivity, selectivity, and accuracy. These mapped onto sphingolipid signaling, autophagy, necroptosis and glycerophospholipid metabolism pathways, with Benjamini adjusted p-values less than 0.05. The novel lipid biomarker candidates identified provide insight into the metabolic pathways altered within 24 h of mild TBI.

A Levee to the Flood: Pre-injury Neuroinflammation and Immune Stress Influence Traumatic Brain Injury Outcome

Increasing evidence demonstrates that aging influences the brain's response to traumatic brain injury (TBI), setting the stage for neurodegenerative pathology like Alzheimer's disease (AD). This topic is often dominated by discussions of post-injury aging and inflammation, which can diminish the consideration of those same factors before TBI. In fact, pre-TBI aging and inflammation may be just as critical in mediating outcomes. For example, elderly individuals suffer from the highest rates of TBI of all severities. Additionally, pre-injury immune challenges or stressors may alter pathology and outcome independent of age. The inflammatory response to TBI is malleable and influenced by previous, coincident, and subsequent immune insults. Therefore, pre-existing conditions that elicit or include an inflammatory response could substantially influence the brain's ability to respond to traumatic injury and ultimately affect chronic outcome. The purpose of this review is to detail how age-related cellular and molecular changes, as well as genetic risk variants for AD affect the neuroinflammatory response to TBI. First, we will review the sources and pathology of neuroinflammation following TBI. Then, we will highlight the significance of age-related, endogenous sources of inflammation, including changes in cytokine expression, reactive oxygen species processing, and mitochondrial function. Heightened focus is placed on the mitochondria as an integral link between inflammation and various genetic risk factors for AD. Together, this review will compile current clinical and experimental research to highlight how pre-existing inflammatory changes associated with infection and stress, aging, and genetic risk factors can alter response to TBI.

Epigenetics of Neurotrauma

Epigenetic changes have been linked to a host of disease states. Besides the physiological function of epigenetic changes in regulating cellular function, recent data indicates that key changes in epigenetic activity also play an important pathophysiologic role following neurotrauma specifically. Such manifestations occur through the activation or silencing of different genes. Histone methylation has emerged as a critical component of this process and can be selectively modulated after injury. Pre-clinical studies have resulted in key discoveries regarding specific methylation sites of interest. This focused review highlights some of these early findings and their relationship to clinical outcomes. These findings suggest areas of future investigation and discovery in the quest to develop ideal biomarkers and methods to utilize them in developing therapeutic interventions.

Melatonin as a Potential Regulator of Oxidative Stress, and Neuroinflammation: Mechanisms and Implications for the Management of Brain Injury-Induced Neurodegeneration

This review covers the preclinical and clinical literature supporting the role of melatonin in the management of brain injury-induced oxidative stress, neuroinflammation, and neurodegeneration, and reviews the past and current therapeutic strategies. Traumatic brain injury (TBI) is a neurodegenerative condition, unpredictably and potentially progressing into chronic neurodegeneration, with permanent cognitive, neurologic, and motor dysfunction, having no standard therapies. Due to its complex and multi-faceted nature, the TBI has highly heterogeneous pathophysiology, characterized by the highest mortality and disability worldwide. Mounting evidence suggests that the TBI induces oxidative and nitrosative stress, which is involved in the progression of chronic and acute neurodegenerative diseases. Defenses against such conditions are mostly dependent on the usage of antioxidant compounds, the majority of whom are ingested as nutraceuticals or as dietary supplements. A large amount of literature is available regarding the efficacy of antioxidant compounds to counteract the TBI-associated damage in animal and cellular models of the TBI and several clinical studies. Collectively, the studies have suggested that TBI induces oxidative stress, by suppressing the endogenous antioxidant system, such as nuclear factor erythroid 2–related factor-2 (Nrf-2) increasing the lipid peroxidation and elevation of oxidative damage. Moreover, elevated oxidative stress may induce neuroinflammation by activating the microglial cells, releasing and activating the inflammatory cytokines and inflammatory mediators, and energy dyshomeostasis. Thus, melatonin has shown regulatory effects against the TBI-induced autophagic dysfunction, regulation of mitogen-activated protein kinases, such as ERK, activation of the NLRP-3 inflammasome, and release of the inflammatory cytokines. The collective findings strongly suggest that melatonin may regulate TBI-induced neurodegeneration, although further studies should be conducted to better facilitate future therapeutic windows.

Endocannabinoid Metabolism and Traumatic Brain Injury

Traumatic brain injury (TBI) represents a major cause of morbidity and disability and is a risk factor for developing neurodegenerative diseases, including Alzheimer’s disease (AD). However, no effective therapies are currently available for TBI-induced AD-like disease. Endocannabinoids are endogenous lipid mediators involved in a variety of physiological and pathological processes. The compound 2-arachidonoylglycerol (2-AG) is the most abundant endocannabinoid with profound anti-inflammatory and neuroprotective properties. This molecule is predominantly metabolized by monoacylglycerol lipase (MAGL), a key enzyme degrading about 85% of 2-AG in the brain. Studies using animal models of inflammation, AD, and TBI provide evidence that inactivation of MAGL, which augments 2-AG signaling and reduces its metabolites, exerts neuroprotective effects, suggesting that MAGL is a promising therapeutic target for neurodegenerative diseases. In this short review, we provide an overview of the inhibition of 2-AG metabolism for the alleviation of neuropathology and the improvement of synaptic and cognitive functions after TBI.

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.

Penetrating Ballistic Brain Injury Produces Acute Alterations in Sleep and Circadian-Related Genes in the Rodent Cortex: A Preliminary Study

Traumatic brain injury (TBI) affects millions of Americans each year, with extremely high prevalence in the Veteran community, and sleep disturbance is one of the most commonly reported symptoms. Reduction in the quality and amount of sleep can negatively impact recovery and result in a wide range of behavioral and physiological symptoms, such as impaired cognition, mood and anxiety disorders, and cardiovascular effects. Thus, to improve long-term patient outcomes and develop novel treatments, it is essential to understand the molecular mechanisms involved in sleep disturbance following TBI. In this effort, we performed transcriptional profiling in an established rodent model of penetrating ballistic brain injury (PBBI) in conjunction with continuous sleep/wake EEG/EMG recording of the first 24 h after injury. Rats subjected to PBBI showed profound differences in sleep architecture. Injured animals spent significantly more time in slow wave sleep and less time in REM sleep compared to sham control animals. To identify PBBI-related transcriptional differences, we then performed transcriptome-wide gene expression profiling at 24 h post-injury, which identified a vast array of immune- related genes differentially expressed in the injured cortex as well as sleep-related genes. Further, transcriptional changes associated with total time spent in various sleep stages were identified. Such molecular changes may underlie the pathology and symptoms that emerge following TBI, including neurodegeneration, sleep disturbance, and mood disorders.

The potential role of Piper guineense (black pepper) in managing geriatric brain aging: a review

Brain aging is one of the unavoidable aspects of geriatric life. As one ages, changes such as the shrinking of certain parts (particularly the frontal cortex, which is vital to learning and other complex mental activities) of the brain may occur. Consequently, communications between neurons are less effective, and blood flow to the brain could also decrease. Efforts made at the biological level for repair become inadequate, leading to the accumulation of β-amyloid peptide in the brain faster than its probable degradation mechanism, resulting in cognitive malfunction. Subsequent clinical usage of drugs in battling related brain-aging ailments has been associated with several undesirable side effects. However, recent research has investigated the potential use of natural compounds from food in combating such occurrences. This review provides information about the use of Piper guineense (black pepper) as a possible agent in managing brain aging because of its implications for practical brain function. P. guineense contains an alkaloid (piperine) reported to be an antioxidant, anti-depressant, and central nervous system stimulant. This alkaloid and other related compounds are neuroprotective agents that reduce lipid oxidation and inhibit tangles in the brain tissues.

The Clinical and Neuropathological Features of Sporadic (Late-Onset) and Genetic Forms of Alzheimer's Disease

The purpose of this review is to compare and highlight the clinical and pathological aspects of genetic versus acquired Alzheimer's disease: Down syndrome-associated Alzheimer's disease in (DSAD) and Autosomal Dominant Alzheimer's disease (ADAD) are compared with the late-onset form of the disease (LOAD). DSAD and ADAD present in a younger population and are more likely to manifest with non-amnestic (such as dysexecutive function features) in the prodromal phase or neurological features (such as seizures and paralysis) especially in ADAD. The very large variety of mutations associated with ADAD explains the wider range of phenotypes. In the LOAD, age-associated comorbidities explain many of the phenotypic differences.

Aging with Traumatic Brain Injury: Deleterious Effects of Injury Chronicity Are Most Pronounced in Later Life

Understanding the effects of age on longitudinal traumatic brain injury (TBI) outcomes requires attention to both chronic and evolving TBI effects and age-related changes in health and function. The present study examines the independent and interactive effects of aging and chronicity on functional outcomes after TBI. We leveraged a well-defined cohort of individuals who sustained a moderate/severe TBI and received acute inpatient rehabilitation at specialized centers with high follow up rate as part of their involvement in the TBI Model Systems longitudinal study. We selected individuals at one of two levels of TBI chronicity (either 2 or 10 years post-injury) and used an exact matching procedure to obtain balanced chronicity groups based on age and other characteristics (N = 1993). We found that both older age and greater injury chronicity were related to greater disability, reduced functional independence, and less community participation. There was a significant age by chronicity interaction, indicating that the adverse effects of greater time post-injury were most pronounced among survivors who were age 75 or older. The inflection point at roughly 75 years of age was corroborated by post hoc analyses, dividing the sample by age at 75 years and examining the interaction between age group and chronicity. These findings point to a need for provision of rehabilitation services in the chronic injury period, particularly for those who are over 75 years old. Future work should investigate the underlying mechanisms of this interaction towards the goal of developing interventions and models of care to promote healthy aging with TBI.

Lipocalin 2 as a link between ageing, risk factor conditions and age-related brain diseases

Chronic (neuro)inflammation plays an important role in many age-related central nervous system (CNS) diseases, including Alzheimer's disease, Parkinson's disease and vascular dementia. Inflammation also characterizes many conditions that form a risk factor for these CNS disorders, such as physical inactivity, obesity and cardiovascular disease. Lipocalin 2 (Lcn2) is an inflammatory protein shown to be involved in different age-related CNS diseases, as well as risk factor conditions thereof. Lcn2 expression is increased in the periphery and the brain in different age-related CNS diseases and also their risk factor conditions. Experimental studies indicate that Lcn2 contributes to various neuropathophysiological processes of age-related CNS diseases, including exacerbated neuroinflammation, cell death and iron dysregulation, which may negatively impact cognitive function. We hypothesize that increased Lcn2 levels as a result of age-related risk factor conditions may sensitize the brain and increase the risk to develop age-related CNS diseases. In this review we first provide a comprehensive overview of the known functions of Lcn2, and its effects in the CNS. Subsequently, this review explores Lcn2 as a potential (neuro)inflammatory link between different risk factor conditions and the development of age-related CNS disorders. Altogether, evidence convincingly indicates Lcn2 as a key constituent in ageing and age-related brain diseases.

The Impact of Age and Severity on Dementia After Traumatic Brain Injury: A Comparison Study

BACKGROUND

Growing evidence associates traumatic brain injury (TBI) with increased risk of dementia, but few studies have evaluated associations in patients younger than 55 yr using non-TBI orthopedic trauma (NTOT) patients as controls to investigate the influence of age and TBI severity, and to identify predictors of dementia after trauma.

OBJECTIVE

To investigate the relationship between TBI and dementia in an institutional group.

METHODS

Retrospective cohort study (2000-2018) of TBI patients aged 45 to 100 yr vs NTOT controls. Primary outcome was dementia after TBI (followed ≤10 yr). Cox proportional hazards models were used to assess risk of dementia; logistic regression models assessed predictors of dementia.

RESULTS

Among 24 846 patients, TBI patients developed dementia (7.5% vs 4.6%) at a younger age (78.6 vs 82.7 yr) and demonstrated higher 10-yr mortality than controls (27% vs 14%; P < .001). Mild TBI patients had higher incidence of dementia (9%) than moderate/severe TBI (5.4%), with lower 10-yr mortality (20% vs 31%; P < .001). Risk of dementia was significant in all mild TBI age groups, even 45 to 54 yr (hazard ratio 4.1, 95% CI 2.7-7.8). A total of 10-yr cumulative incidence was higher in mild TBI (14.4%) than moderate/severe TBI (11.3%) and controls (6.8%) (P < .001). Predictors of dementia include TBI, sex, age, hypertension, hyperlipidemia, stroke, depression, anxiety, and Injury Severity Score.

CONCLUSION

Mild and moderate/severe TBI patients experienced higher incidence of dementia, even in the youngest group (45-54 yr old), than NTOT controls. All TBI patients, especially middle-aged adults with minor injury who are more likely to be overlooked, should be monitored for dementia.

Alzheimer's disease neuropathology is exacerbated following traumatic brain injury. Neuroprotection by co-administration of nanowired mesenchymal stem cells and cerebrolysin with monoclonal antibodies to amyloid beta peptide

Military personnel are prone to traumatic brain injury (TBI) that is one of the risk factors in developing Alzheimer's disease (AD) at a later stage. TBI induces breakdown of the blood-brain barrier (BBB) to serum proteins into the brain and leads to extravasation of plasma amyloid beta peptide (ΑβP) into the brain fluid compartments causing AD brain pathology. Thus, there is a need to expand our knowledge on the role of TBI in AD. In addition, exploration of the novel roles of nanomedicine in AD and TBI for neuroprotection is the need of the hour. Since stem cells and neurotrophic factors play important roles in TBI and in AD, it is likely that nanodelivery of these agents exert superior neuroprotection in TBI induced exacerbation of AD brain pathology. In this review, these aspects are examined in details based on our own investigations in the light of current scientific literature in the field. Our observations show that TBI exacerbates AD brain pathology and TiO₂ nanowired delivery of mesenchymal stem cells together with cerebrolysin-a balanced composition of several neurotrophic factors and active peptide fragments, and monoclonal antibodies to amyloid beta protein thwarted the development of neuropathology following TBI in AD, not reported earlier.

Brain Injury and Later-Life Cognitive Impairment and Neuropathology: The Honolulu-Asia Aging Study

BACKGROUND

Findings are inconsistent regarding the role of traumatic head injury in the subsequent development of neurologic outcomes.

OBJECTIVE

Examine the relationship between head injury and later cognitive impairment.

METHODS

A sample of 3,123 Japanese-American men was assessed for history of head injury and evaluated for cognitive impairment using the Cognitive Abilities Screening Instrument (CASI). For a subsample of 676 respondents, neuropathologic results from those with and without head injury were compared.

RESULTS

Although the crude model showed an association between history of head injury and later severe cognitive impairment, the relationship lost significance in the adjusted model (OR = 1.320, CI: 0.90-1.93), regardless of time between injury and impairment. Similar to cognitive impairment, hippocampal sclerosis was observed significantly more in the brains of respondents with a history of head injury in the crude model, but the relationship weakened in the adjusted model (OR = 1.462, CI: 0.68-3.12). After adjustment, decedents with a head injury demonstrated marginally higher brain weight (OR = 1.003, CI: 1.00-1.01).

CONCLUSION

We did not find a relationship between head injury and subsequent cognitive decline in this cohort. The neuropathology results also displayed no strong association between history of head injury and specific brain lesions and characteristics. These results support other findings in prospective cohorts. However, they could be influenced by the demographic make-up of the sample (male Japanese-Americans) or by the observation that the majority reported only a single head injury.

Exploiting formyl peptide receptor 2 to promote microglial resolution: a new approach to Alzheimer's disease treatment

Alzheimer's disease and dementia are among the most significant current healthcare challenges given the rapidly growing elderly population, and the almost total lack of effective therapeutic interventions. Alzheimer's disease pathology has long been considered in terms of accumulation of amyloid beta and hyperphosphorylated tau, but the importance of neuroinflammation in driving disease has taken greater precedence over the last 15-20 years. Inflammatory activation of the primary brain immune cells, the microglia, has been implicated in Alzheimer's pathogenesis through genetic, preclinical, imaging and postmortem human studies, and strategies to regulate microglial activity may hold great promise for disease modification. Neuroinflammation is necessary for defence of the brain against pathogen invasion or damage but is normally self-limiting due to the engagement of endogenous pro-resolving circuitry that terminates inflammatory activity, a process that appears to fail in Alzheimer's disease. Here, we discuss the potential for a major regulator and promoter of resolution, the receptor FPR2, to restrain pro-inflammatory microglial activity, and propose that it may serve as a valuable target for therapeutic investigation in Alzheimer's disease.

Toward a global and reproducible science for brain imaging in neurotrauma: the ENIGMA adult moderate/severe traumatic brain injury working group

The global burden of mortality and morbidity caused by traumatic brain injury (TBI) is significant, and the heterogeneity of TBI patients and the relatively small sample sizes of most current neuroimaging studies is a major challenge for scientific advances and clinical translation. The ENIGMA (Enhancing NeuroImaging Genetics through Meta-Analysis) Adult moderate/severe TBI (AMS-TBI) working group aims to be a driving force for new discoveries in AMS-TBI by providing researchers world-wide with an effective framework and platform for large-scale cross-border collaboration and data sharing. Based on the principles of transparency, rigor, reproducibility and collaboration, we will facilitate the development and dissemination of multiscale and big data analysis pipelines for harmonized analyses in AMS-TBI using structural and functional neuroimaging in combination with non-imaging biomarkers, genetics, as well as clinical and behavioral measures. Ultimately, we will offer investigators an unprecedented opportunity to test important hypotheses about recovery and morbidity in AMS-TBI by taking advantage of our robust methods for large-scale neuroimaging data analysis. In this consensus statement we outline the working group's short-term, intermediate, and long-term goals.

Glucose metabolism: A link between traumatic brain injury and Alzheimer's disease

Traumatic brain injury (TBI), a growing public health problem, is a leading cause of death and disability worldwide, although its prevention measures and clinical cares are substantially improved. Increasing evidence shows that TBI may increase the risk of mood disorders and neurodegenerative diseases, including Alzheimer's disease (AD). However, the complex relationship between TBI and AD remains elusive. Metabolic dysfunction has been the common pathology in both TBI and AD. On the one hand, TBI perturbs the glucose metabolism of the brain, and causes energy crisis and subsequent hyperglycolysis. On the other hand, glucose deprivation promotes amyloidogenesis via β-site APP cleaving enzyme-1 dependent mechanism, and triggers tau pathology and synaptic function. Recent findings suggest that TBI might facilitate Alzheimer's pathogenesis by altering metabolism, which provides clues to metabolic link between TBI and AD. In this review, we will explore how TBI-induced metabolic changes contribute to the development of AD.

Immune Regulation of Adult Neurogenic Niches in Health and Disease

Microglia regulate neuronal development during embryogenesis, postnatal development, and in specialized microenvironments of the adult brain. Recent evidence demonstrates that in adulthood, microglia secrete factors which modulate adult hippocampal neurogenesis by inhibiting cell proliferation and survival both in vitro and in vivo, maintaining a balance between cell division and cell death in neurogenic niches. These resident immune cells also shape the nervous system by actively pruning synapses during critical periods of learning and engulfing excess neurons. In neurodegenerative diseases, aberrant microglial activity can impede the proper formation and prevent the development of appropriate functional properties of adult born granule cells. Ablating microglia has been presented as a promising therapeutic approach to alleviate the brain of maladaptive immune response. Here, we review key mechanisms through which the immune system actively shapes neurogenic niches throughout the lifespan of the mammalian brain in both health and disease. We discuss how interactions between immune cells and developing neurons may be leveraged for pharmacological intervention and as a means to preserve adult neurogenesis.

Traumatic brain injury alters neuropsychiatric symptomatology in all-cause dementia

INTRODUCTION

Traumatic brain injury (TBI) may alter the course of neuropsychiatric symptom (NPS) onset during dementia development. The connection among TBI, NPS, and dementia progression is of increasing interest to researchers and clinicians.

METHODS

Incidence of NPS was examined in participants with normal cognition who progressed to all-cause dementia based on whether TBI history was present (n = 130) or absent (n = 849). Survival analyses were used to examine NPS incidence across 7.6 ± 3.0 years of follow-up.

RESULTS

Participants with TBI history had increased prevalence and incidence of apathy (44.7% vs 29.9%, P = .0062; HR_adj. = 1.708, P = .0018) and motor disturbances (17.2% vs 9.5%, P = .0458; HR_adj. = 2.023, P = .0168), controlling for demographics and type of dementia diagnosis. Earlier anxiety onset was associated with TBI (692 days prior to dementia diagnosis vs 161 days, P = .0265).

DISCUSSION

History of TBI is associated with increased risk for and earlier onset of NPS in the trajectory of dementia development.

Concussive head injury exacerbates neuropathology of sleep deprivation: Superior neuroprotection by co-administration of TiO2-nanowired cerebrolysin, alpha-melanocyte-stimulating hormone, and mesenchymal stem cells

Sleep deprivation (SD) is common in military personnel engaged in combat operations leading to brain dysfunction. Military personnel during acute or chronic SD often prone to traumatic brain injury (TBI) indicating the possibility of further exacerbating brain pathology. Several lines of evidence suggest that in both TBI and SD alpha-melanocyte-stimulating hormone (α-MSH) and brain-derived neurotrophic factor (BDNF) levels decreases in plasma and brain. Thus, a possibility exists that exogenous supplement of α-MSH and/or BDNF induces neuroprotection in SD compounded with TBI. In addition, mesenchymal stem cells (MSCs) are very portent in inducing neuroprotection in TBI. We examined the effects of concussive head injury (CHI) in SD on brain pathology. Furthermore, possible neuroprotective effects of α-MSH, MSCs and neurotrophic factors treatment were explored in a rat model of SD and CHI. Rats subjected to 48h SD with CHI exhibited higher leakage of BBB to Evans blue and radioiodine compared to identical SD or CHI alone. Brain pathology was also exacerbated in SD with CHI group as compared to SD or CHI alone together with a significant reduction in α-MSH and BDNF levels in plasma and brain and enhanced level of tumor necrosis factor-alpha (TNF-α). Exogenous administration of α-MSH (250μg/kg) together with MSCs (1×10⁶) and cerebrolysin (a balanced composition of several neurotrophic factors and active peptide fragments) (5mL/kg) significantly induced neuroprotection in SD with CHI. Interestingly, TiO₂ nanowired delivery of α-MSH (100μg), MSCs, and cerebrolysin (2.5mL/kg) induced enhanced neuroprotection with higher levels of α-MSH and BDNF and decreased the TNF-α in SD with CHI. These observations are the first to show that TiO₂ nanowired administration of α-MSH, MSCs and cerebrolysin induces superior neuroprotection following SD in CHI, not reported earlier. The clinical significance of our findings in light of the current literature is discussed.

Tumour necrosis factor induces increased production of extracellular amyloid-β- and α-synuclein-containing aggregates by human Alzheimer's disease neurons

In addition to increased aberrant protein aggregation, inflammation has been proposed as a key element in the pathogenesis and progression of Alzheimer’s disease. How inflammation interacts with other disease pathways and how protein aggregation increases during disease are not clear. We used single-molecule imaging approaches and membrane permeabilization assays to determine the effect of chronic exposure to tumour necrosis factor, a master proinflammatory cytokine, on protein aggregation in human-induced pluripotent stem cell-derived neurons harbouring monogenic Alzheimer’s disease mutations. We report that exposure of Alzheimer’s disease neurons, but not control neurons, to tumour necrosis factor induces substantial production of extracellular protein aggregates. Aggregates from Alzheimer’s disease neurons are composed of amyloid-β and α-synuclein and induce significant permeabilization of lipid membranes in an assay of pathogenicity. These findings provide support for a causal relationship between two crucial processes in Alzheimer’s disease pathogenesis and suggest that targeting inflammation, particularly tumour necrosis factor, may have beneficial downstream effects on ameliorating aberrant protein aggregation and accumulation.

Prevention and Treatment of Alzheimer's Disease: Biological Mechanisms of Exercise

Alzheimer's disease (AD) is the most common form of dementia. With an aging population and no disease modifying treatments available, AD is quickly becoming a global pandemic. A substantial body of research indicates that lifestyle behaviors contribute to the development of AD, and that it may be worthwhile to approach AD like other chronic diseases such as cardiovascular disease, in which prevention is paramount. Exercise is an important lifestyle behavior that may influence the course and pathology of AD, but the biological mechanisms underpinning these effects remain unclear. This review focuses on how exercise can modify four possible mechanisms which are involved with the pathology of AD: oxidative stress, inflammation, peripheral organ and metabolic health, and direct interaction with AD pathology. Exercise is just one of many lifestyle behaviors that may assist in preventing AD, but understanding the systemic and neurobiological mechanisms by which exercise affects AD could help guide the development of novel pharmaceutical agents and non-pharmacological personalized lifestyle interventions for at-risk populations.

Chronic Traumatic Encephalopathy and Neuropathological Comorbidities

With age, the presence of multiple neuropathologies in a single individual becomes increasingly common. Given that traumatic brain injury and the repetitive head impacts (RHIs) that occur in contact sports have been associated with the development of many neurodegenerative diseases, including chronic traumatic encephalopathy (CTE), Alzheimer's disease, Lewy body disease, and amyotrophic lateral sclerosis, it is becoming critical to understand the relationship and interactions between these pathologies. In fact, comorbid pathology is common in CTE and likely influenced by both age and the severity and type of exposure to RHI as well as underlying genetic predisposition. Here, we review the major comorbid pathologies seen with CTE and in former contact sports athletes and discuss what is known about the associations between RHI, age, and the development of neuropathologies. In addition, we examine the distinction between CTE and age-related pathology including primary age-related tauopathy and age-related tau astrogliopathy.