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Traumatic brain injury in the presence of Aβ pathology affects neuronal survival, glial activation and autophagy.

ABSTRACT: Traumatic brain injury (TBI) presents a widespread health problem in the elderly population. In addition to the acute injury, epidemiological studies have observed an increased probability and earlier onset of dementias in the elderly following TBI. However, the underlying mechanisms of the connection between TBI and Alzheimer's disease in the aged brain and potential exacerbating factors is still evolving. The aim of this study was to investigate cellular injury-induced processes in the presence of amyloid β (Aβ) pathology. For this purpose, a co-culture system of cortical stem-cell derived astrocytes, neurons and oligodendrocytes were exposed to Aβ₄₂ protofibrils prior to a mechanically induced scratch injury. Cellular responses, including neurodegeneration, glial activation and autophagy was assessed by immunoblotting, immunocytochemistry, ELISA and transmission electron microscopy. Our results demonstrate that the combined burden of Aβ exposure and experimental TBI causes a decline in the number of neurons, the differential expression of the key astrocytic markers glial fibrillary acidic protein and S100 calcium-binding protein beta, mitochondrial alterations and prevents the upregulation of autophagy. Our study provides valuable information about the impact of TBI sustained in the presence of Aβ deposits and helps to advance the understanding of geriatric TBI on the cellular level.

SUBMITTER: Streubel-Gallasch L

PROVIDER: S-EPMC8626479 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:[18F]AV-1451 (aka 18F-Flortaucipir, [18F]T807) was developed for positron-emission tomography (PET) imaging of paired helical filaments of hyperphosphorylated tau, which are of interest in a range of neuropathologies, including traumatic brain injury (TBI). Magnetic resonance imaging (MRI) techniques like diffusion tensor imaging (DTI) and resting state functional connectivity assess structural and functional characteristics of the brain, complementing the molecular information that can be obtained by PET. The goal herein was to explore the utility of such multi-modal imaging in a case series based on a population of TBI subjects. This study probes the interrelationship between tau deposition, white matter integrity, and gray matter functional connectivity across the spectrum of TBI. Nineteen subjects (11 controls, five former contact sports athletes, one automotive accident, and two with military-related injury) underwent [18F]AV-1451 PET and magnetic resonance scanning procedures. [18F]AV-1451 distribution volume ratio (DVR) was estimated using the Logan method and the cerebellum as a reference region. Diffusion tractography images and fractional anisotropy (FA) images were generated using diffusion toolkit and FSL. Resting-state functional MRI (fMRI) analysis was based on a graph theory metric, namely weighted degree centrality. TBI subjects showed greater heterogeneity in [18F]AV-1451 DVR when compared with control subjects. In a subset of TBI subjects, areas with high [18F]AV-1451 binding corresponded with increased FA and diminished white matter tract density in DTI. Functional MRI results exhibited an increase in functional connectivity, particularly among local connections, in the areas where tau aggregates were more prevalent. In a case series of a diverse group of TBI subjects, brain regions with elevated tau burden exhibited increased functional connectivity as well as decreased white matter integrity. These findings portray molecular, microstructural, and functional corollaries of TBI that spatially coincide and can be measured in the living human brain using noninvasive neuroimaging techniques.

Project description:Chronic traumatic encephalopathy (CTE) is a neurodegenerative tauopathy characterized by accumulation of hyperphosphorylated tau (p-tau) in perivascular aggregates in neurons and glia at the depths of neocortical sulci and progresses to diffuse neocortical, allocortical and brainstem structures. The strongest risk factor is exposure to repetitive head impacts acquired most commonly through contact sports and military service. Given that CTE can only be definitively diagnosed after death, a better understanding of the cellular and molecular changes in CTE brains may lead to identification of mechanisms that could be used for novel biomarkers, monitoring progression or therapeutic development. Disruption of alternative pre-mRNA splicing of tau mRNA plays a pathogenic role in tauopathy, with multiple characteristic patterns of isoform accumulation varying among tauopathies. Limited data are available on CTE, particularly at early stages. Using biochemical and histological approaches, we performed a detailed characterization of tau isoform signatures in post-mortem human brain tissue from individuals with a range of CTE stages (n = 99). In immunoblot analyses, severity was associated with decreased total monomeric tau and increased total oligomeric tau. Immunoblot with isoform-specific antisera revealed that oligomeric tau with three and four microtubule binding domain repeats (3R and 4R) also increased with CTE severity. Similarly, immunohistochemical studies revealed p-tau accumulation consisting of both 3R and 4R in perivascular lesions. When the ratio of 4R:3R was analyzed, there was mixed expression throughout CTE stages, although 4R predominated in early CTE stages (I-II), a 3R shift was observed in later stages (III-IV). While neurons were found to contain both 3R and 4R, astrocytes only contained 4R. These 4R-positive cells were exclusively neuronal at early stages. Overall, these findings demonstrate that CTE is a mixed 4R/3R tauopathy. Furthermore, histologic analysis reveals a progressive shift in tau isoforms that correlates with CTE stage and extent of neuronal pathology.

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Traumatic brain injury in the presence of Aβ pathology affects neuronal survival, glial activation and autophagy.

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