Genomic analysis of response to traumatic brain injury in a mouse model of Alzheimer's disease (APPsw)

Increased Risk of Aging-Related Neurodegenerative Disease after Traumatic Brain Injury

Traumatic brain injury (TBI) survivors frequently suffer from chronically progressive complications, including significantly increased risk of developing aging-related neurodegenerative disease. As advances in neurocritical care increase the number of TBI survivors, the impact and awareness of this problem are growing. The mechanisms by which TBI increases the risk of developing aging-related neurodegenerative disease, however, are not completely understood. As a result, there are no protective treatments for patients. Here, we review the current literature surrounding the epidemiology and potential mechanistic relationships between brain injury and aging-related neurodegenerative disease. In addition to increasing the risk for developing all forms of dementia, the most prominent aging-related neurodegenerative conditions that are accelerated by TBI are amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), Parkinson's disease (PD), and Alzheimer's disease (AD), with ALS and FTD being the least well-established. Mechanistic links between TBI and all forms of dementia that are reviewed include oxidative stress, dysregulated proteostasis, and neuroinflammation. Disease-specific mechanistic links with TBI that are reviewed include TAR DNA binding protein 43 and motor cortex lesions in ALS and FTD; alpha-synuclein, dopaminergic cell death, and synergistic toxin exposure in PD; and brain insulin resistance, amyloid beta pathology, and tau pathology in AD. While compelling mechanistic links have been identified, significantly expanded investigation in the field is needed to develop therapies to protect TBI survivors from the increased risk of aging-related neurodegenerative disease.

Subchronic Pathobiological Response Following Chronic Repetitive Mild Traumatic Brain Injury in an Aged Preclinical Model of Amyloid Pathogenesis

Repetitive mild traumatic brain injury (r-mTBI) is a risk factor for Alzheimer disease (AD). The precise nature of how r-mTBI leads to, or precipitates, AD pathogenesis remains unclear. In this study, we explore subchronic effects of chronic r-mTBI (12-impacts) administered over 1-month in aged-PS1/APP mice and littermate controls. We investigate specific mechanisms that may elucidate the molecular link between AD and r-mTBI, focusing primarily on amyloid and tau pathology, amyloid processing, glial activation states, and associated clearance mechanisms. Herein, we demonstrate r-mTBI in aged PS1/APP mice does not augment, glial activation, amyloid burden, or tau pathology (with exception of pS202-positive Tau) 1 month after exposure to the last-injury. However, we observed a decrease in brain soluble Aβ42 levels without any appreciable change in peripheral soluble Aβ42 levels. This was accompanied by an increase in brain insoluble to soluble Aβ42 ratio in injured PS1/APP mice compared with sham injury. A parallel reduction in phagocytic receptor, triggering receptor expressed on myeloid cells 2, was also observed. This study demonstrates very subtle subchronic effects of r-mTBI on a preexisting amyloid pathology background, which may be on a continuum toward a slow and worsening neurodegenerative outcome compared with sham injury, and therefore, have many implications, especially in the elderly population exposed to TBI.

Systems biology approaches for discovering biomarkers for traumatic brain injury

The rate of traumatic brain injury (TBI) in service members with wartime injuries has risen rapidly in recent years, and complex, variable links have emerged between TBI and long-term neurological disorders. The multifactorial nature of TBI secondary cellular response has confounded attempts to find cellular biomarkers for its diagnosis and prognosis or for guiding therapy for brain injury. One possibility is to apply emerging systems biology strategies to holistically probe and analyze the complex interweaving molecular pathways and networks that mediate the secondary cellular response through computational models that integrate these diverse data sets. Here, we review available systems biology strategies, databases, and tools. In addition, we describe opportunities for applying this methodology to existing TBI data sets to identify new biomarker candidates and gain insights about the underlying molecular mechanisms of TBI response. As an exemplar, we apply network and pathway analysis to a manually compiled list of 32 protein biomarker candidates from the literature, recover known TBI-related mechanisms, and generate hypothetical new biomarker candidates.

Heading in football, long-term cognitive decline and dementia: evidence from screening retired professional footballers

BACKGROUND

Heading impairs cognition in the short and medium-terms; however, little is known about the long-term consequences. This study aimed to investigate the hypothesis that chronic low-level head trauma is associated with persistent cognitive decline.

METHODS

All members of Former Player Associations (FPAs) from four professional football clubs in the UK were contacted to participate in the study. Participants were required to complete a self-assessed test of cognition, the Test Your Memory questionnaire. Further information was collected from respondents in order to analyse the potential effect of a number of variables on cognition.

RESULTS

10 of 92 respondents (10.87%) screened positive for possible mild cognitive impairment (MCI) or dementia. There was no association between low-risk and high-risk playing positions (HR = 0.40, p = 0.456) or length of playing career (HR = 1.051 95% CI 0.879 to 1.257, p = 0.586) and a positive screening result. Age was a risk factor (HR = 1.137 per additional year, 95% CI 1.030 to 1.255, p < 0.05), although this was not significantly different from the population prevalence across age groups.

CONCLUSIONS

These results suggest that once a player ends their playing career, their risk of harm falls in line with the population, suggesting either that changes are reversible or that heading may not be as harmful as commonly thought. Future longitudinal studies of large numbers of professional football players are needed to support the findings from this study.

Role of endoplasmic reticulum (ER) stress in cocaine-induced microglial cell death

While it has been well-documented that drugs of abuse such as cocaine can enhance progression of human immunodeficiency virus (HIV)-associated neuropathological disorders, the underlying mechanisms mediating these effects remain poorly understood. The present study was undertaken to examine the effects of cocaine on microglial viability. Herein we demonstrate that exposure of microglial cell line-BV2 or rat primary microglia to exogenous cocaine resulted in decreased cell viability as determined by MTS and TUNEL assays. Microglial toxicity of cocaine was accompanied by an increase in the expression of cleaved caspase-3 as demonstrated by western blot assays. Furthermore, increased microglial toxicity was also associated with a concomitant increase in the production of intracellular reactive oxygen species, an effect that was ameliorated in cells pretreated with NADPH oxidase inhibitor apocynin, thus emphasizing the role of oxidative stress in this process. A novel finding of this study was the involvement of endoplasmic reticulum (ER) signaling mediators such as PERK, Elf2α, and CHOP, which were up regulated in cells exposed to cocaine. Reciprocally, blocking CHOP expression using siRNA ameliorated cocaine-mediated cell death. In conclusion these findings underscore the importance of ER stress in modulating cocaine induced microglial toxicity. Understanding the link between ER stress, oxidative stress and apoptosis could lead to the development of therapeutic strategies targeting cocaine-mediated microglial death/dysfunction.

Anti-epileptogenesis in rodent post-traumatic epilepsy models

Post-traumatic epilepsy (PTE) accounts for 10-20% of symptomatic epilepsies. The urgency to understand the process of post-traumatic epileptogenesis and search for antiepileptogenic treatments is emphasized by a recent increase in traumatic brain injury (TBI) related to military combat or accidents in the aging population. Recent developments in modeling of PTE in rodents have provided tools for identification of novel drug targets for antiepileptogenesis and biomarkers for predicting the risk of epileptogenesis and treatment efficacy after TBI. Here we review the available data on endophenotypes of humans and rodents with TBI associated with epilepsy. Also, current understanding of the mechanisms and biomarkers for PTE as well as factors associated with preclinical study designs are discussed. Finally, we summarize the attempts to prevent PTE in experimental models.

Nature versus nurture: death of a dogma, and the road ahead

Interaction between the genome and the environment has been widely discussed in the literature, but has the importance ascribed to understanding these interactions been overstated? In this opinion piece, we critically discuss gene-environment interactions and attempt to answer three key questions. First, is it likely that gene-environment interactions actually exist? Second, what is the realistic value of trying to unravel these interactions, both in terms of understanding disease pathogenesis and as a means of ameliorating disease? Finally, and most importantly, do the technologies and methodologies exist to facilitate an unbiased search for gene-environment interactions? Addressing these questions highlights key areas of feasibility that must be considered in this area of research.

Gene-environment interaction research and transgenic mouse models of Alzheimer's disease

The etiology of the sporadic form of Alzheimer's disease (AD) remains largely unknown. Recent evidence has suggested that gene-environment interactions (GxE) may play a crucial role in its development and progression. Whereas various susceptibility loci have been identified, like the apolipoprotein E4 allele, these cannot fully explain the increasing prevalence of AD observed with aging. In addition to such genetic risk factors, various environmental factors have been proposed to alter the risk of developing AD as well as to affect the rate of cognitive decline in AD patients. Nevertheless, aside from the independent effects of genetic and environmental risk factors, their synergistic participation in increasing the risk of developing AD has been sparsely investigated, even though evidence points towards such a direction. Advances in the genetic manipulation of mice, modeling various aspects of the AD pathology, have provided an excellent tool to dissect the effects of genes, environment, and their interactions. In this paper we present several environmental factors implicated in the etiology of AD that have been tested in transgenic animal models of the disease. The focus lies on the concept of GxE and its importance in a multifactorial disease like AD. Additionally, possible mediating mechanisms and future challenges are discussed.

Inflammation in transgenic mouse models of neurodegenerative disorders

Much evidence is available that inflammation contributes to the development of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Our review investigates how well current mouse models reflect this aspect of the pathogenesis. Transgenic models of AD have been available for several years and are the most extensively studied. Modulation of cytokine levels, activation of microglia and, to a lesser extent, activation of the complement system have been reported. Mouse models of PD and HD so far show less evidence for the involvement of inflammation. An increasing number of transgenic mouse strains is being created to model human neurodegenerative diseases. A perfect model should reflect all aspects of a disease. It is important to evaluate continuously the models for their match with the human disease and reevaluate them in light of new findings in human patients. Although none of the transgenic mouse models recapitulates all aspects of the human disorder they represent, all models have provided valuable information on basic molecular pathways. In particular, the mouse models of Alzheimer disease have also led to the development of new therapeutic strategies such as vaccination and modulation of microglial activity.