Life After Mild Traumatic Brain Injury: Widespread Structural Brain Changes Associated With Psychological Distress Revealed With Multimodal Magnetic Resonance Imaging

Background

Traumatic brain injury (TBI) can alter brain structure and lead to onset of persistent neuropsychological symptoms. This study investigates the relationship between brain injury and psychological distress after mild TBI using multimodal magnetic resonance imaging.

Methods

A total of 89 patients with mild TBI from the TRACK-TBI (Transforming Research and Clinical Knowledge in Traumatic Brain Injury) pilot study were included. Subscales of the Brief Symptoms Inventory 18 for depression, anxiety, and somatization were used as outcome measures of psychological distress approximately 6 months after the traumatic event. Glasgow Coma Scale scores were used to evaluate recovery. Magnetic resonance imaging data were acquired within 2 weeks after injury. Perivascular spaces (PVSs) were segmented using an enhanced PVS segmentation method, and the volume fraction was calculated for the whole brain and white matter regions. Cortical thickness and gray matter structures volumes were calculated in FreeSurfer; diffusion imaging indices and multifiber tracts were extracted using the Quantitative Imaging Toolkit. The analysis was performed considering age, sex, intracranial volume, educational attainment, and improvement level upon discharge as covariates.

Results

PVS fractions in the posterior cingulate, fusiform, and postcentral areas were found to be associated with somatization symptoms. Depression, anxiety, and somatization symptoms were associated with the cortical thickness of the frontal-opercularis and occipital pole, putamen and amygdala volumes, and corticospinal tract and superior thalamic radiation. Analyses were also performed on the two hemispheres separately to explore lateralization.

Conclusions

This study shows how PVS, cortical, and microstructural changes can predict the onset of depression, anxiety, and somatization symptoms in patients with mild TBI.

Optical molecular imaging and theranostics in neurological diseases based on aggregation-induced emission luminogens

Optical molecular imaging and image-guided theranostics benefit from special and specific imaging agents, for which aggregation-induced emission luminogens (AIEgens) have been regarded as good candidates in many biomedical applications. They display a large Stokes shift, high quantum yield, good biocompatibility, and resistance to photobleaching. Neurological diseases are becoming a substantial burden on individuals and society that affect over 50 million people worldwide. It is urgently needed to explore in more detail the brain structure and function, learn more about pathological processes of neurological diseases, and develop more efficient approaches for theranostics. Many AIEgens have been successfully designed, synthesized, and further applied for molecular imaging and image-guided theranostics in neurological diseases such as cerebrovascular disease, neurodegenerative disease, and brain tumor, which help us understand more about the pathophysiological state of brain through noninvasive optical imaging approaches. Herein, we focus on representative AIEgens investigated on brain vasculature imaging and theranostics in neurological diseases including cerebrovascular disease, neurodegenerative disease, and brain tumor. Considering different imaging modalities and various therapeutic functions, AIEgens have great potential to broaden neurological research and meet urgent needs in clinical practice. It will be inspiring to develop more practical and versatile AIEgens as molecular imaging agents for preclinical and clinical use on neurological diseases.

Protein S-sulfhydration: Unraveling the prospective of hydrogen sulfide in the brain, vasculature and neurological manifestations

Hydrogen sulfide (H₂S) and hydrogen polysulfides (H₂S_n) are essential regulatory signaling molecules generated by the entire body, including the central nervous system. Researchers have focused on the classical H₂S signaling from the past several decades, whereas the last decade has shown the emergence of H₂S-induced protein S-sulfhydration signaling as a potential therapeutic approach. Cysteine S-persulfidation is a critical paradigm of post-translational modification in the process of H₂S signaling. Additionally, studies have shown the cross-relationship between S-sulfhydration and other cysteine-induced post-translational modifications, namely nitrosylation and carbonylation. In the central nervous system, S-sulfhydration is involved in the cytoprotection through various signaling pathways, viz. inflammatory response, oxidative stress, endoplasmic reticulum stress, atherosclerosis, thrombosis, and angiogenesis. Further, studies have demonstrated H₂S-induced S-sulfhydration in regulating different biological processes, such as mitochondrial integrity, calcium homeostasis, blood-brain permeability, cerebral blood flow, and long-term potentiation. Thus, protein S-sulfhydration becomes a crucial regulatory molecule in cerebrovascular and neurodegenerative diseases. Herein, we first described the generation of intracellular H₂S followed by the application of H₂S in the regulation of cerebral blood flow and blood-brain permeability. Further, we described the involvement of S-sulfhydration in different biological and cellular functions, such as inflammatory response, mitochondrial integrity, calcium imbalance, and oxidative stress. Moreover, we highlighted the importance of S-sulfhydration in cerebrovascular and neurodegenerative diseases.

VBNet: An end-to-end 3D neural network for vessel bifurcation point detection in mesoscopic brain images

BACKGROUND AND OBJECTIVE

Accurate detection of vessel bifurcation points from mesoscopic whole-brain images plays an important role in reconstructing cerebrovascular networks and understanding the pathogenesis of brain diseases. Existing detection methods are either less accurate or inefficient. In this paper, we propose VBNet, an end-to-end, one-stage neural network to detect vessel bifurcation points in 3D images.

METHODS

Firstly, we designed a 3D convolutional neural network (CNN), which input a 3D image and output the coordinates of bifurcation points in this image. The network contains a two-scale architecture to detect large bifurcation points and small bifurcation points, respectively, which takes into account the accuracy and efficiency of detection. Then, to solve the problem of low accuracy caused by the imbalance between the numbers of large bifurcations and small bifurcations, we designed a weighted loss function based on the radius distribution of blood vessels. Finally, we extended the method to detect bifurcation points in large-scale volumes.

RESULTS

The proposed method was tested on two mouse cerebral vascular datasets and a synthetic dataset. In the synthetic dataset, the F₁-score of the proposed method reached 96.37%. In two real datasets, the F₁-score was 92.35% and 86.18%, respectively. The detection effect of the proposed method reached the state-of-the-art level.

CONCLUSIONS

We proposed a novel method for detecting vessel bifurcation points in 3D images. It can be used to precisely locate vessel bifurcations from various cerebrovascular images. This method can be further used to reconstruct and analyze vascular networks, and also for researchers to design detection methods for other targets in 3D biomedical images.

Brain pericyte activation occurs early in Huntington's disease

Microvascular changes have recently been described for several neurodegenerative disorders, including Huntington's disease (HD). HD is characterized by a progressive neuronal cell loss due to a mutation in the Huntingtin gene. However, the temporal and spatial microvascular alterations in HD remain unclear. Also, knowledge on the implication of pericytes in HD pathology is still sparse and existing findings are contradictory. Here we examine alterations in brain pericytes in the R6/2 mouse model of HD and in human post mortem HD brain sections. To specifically track activated pericytes, we crossbred R6/2 mice with transgenic mice expressing the Green fluorescent protein gene under the Regulator of G-protein signaling 5 (Rgs5) promoter. We demonstrate an increase in activated pericytes in the R6/2 brain and in post mortem HD brain tissue. Importantly, pericyte changes are already detected before striatal neuronal cell loss, weight loss or behavioural deficits occur in R6/2 mice. This is associated with vascular alterations, whereby striatal changes precede cortical changes. Our findings suggest that pericyte activation may be one of the initial steps contributing to the observed vascular modifications in HD. Thus, pericytes may constitute an important target to address early microvascular changes contributing to disease progression in HD.

Single-Cell mRNA Sequencing of the Mouse Brain Vasculature

In this chapter, we describe a method for analyzing the vasculature of the mouse brain using single-cell transcriptomics. More specifically, we focus on the use of fluorescence-activated cell sorting (FACS) for selection of the cells of interest and sorting of these cells in a 384-well format, allowing for enrichment for the cells being studied. Furthermore, we outline the Smart-Seq2 single-cell library construction method for transforming single-cell mRNA into Illumina sequencing compatible libraries. As single-cell sequencing is still a costly technology, we take special care to describe strategies to include many quality control steps. Finally, we touch upon techniques to convert the sequencing data into a meaningful biological readout. The methods reported in this chapter can be expanded toward other tissues and will prove useful also for the study of different cell types beyond adult brain vasculature.

Understanding the neurovascular unit at multiple scales: Advantages and limitations of multi-photon and functional ultrasound imaging

Developing efficient brain imaging technologies by combining a high spatiotemporal resolution and a large penetration depth is a key step for better understanding the neurovascular interface that emerges as a main pathway to neurodegeneration in many pathologies such as dementia. This review focuses on the advances in two complementary techniques: multi-photon laser scanning microscopy (MPLSM) and functional ultrasound imaging (fUSi). MPLSM has become the gold standard for in vivo imaging of cellular dynamics and morphology, together with cerebral blood flow. fUSi is an innovative imaging modality based on Doppler ultrasound, capable of recording vascular brain activity over large scales (i.e., tens of cubic millimeters) at unprecedented spatial and temporal resolution for such volumes (up to 10μm pixel size at 10kHz). By merging these two technologies, researchers may have access to a more detailed view of the various processes taking place at the neurovascular interface. MPLSM and fUSi are also good candidates for addressing the major challenge of real-time delivery, monitoring, and in vivo evaluation of drugs in neuronal tissue.

Brain damage resulting from postnatal hypoxic-ischemic brain injury is reduced in C57BL/6J mice as compared to C57BL/6N mice

Perinatal hypoxia is a critical complication during delivery and is mostly studied in animal models of postnatal hypoxic-ischemic brain injury. We here studied the effects of postnatal hypoxic-ischemic brain injury in two different sub-strains of C57BL/6 mice, i.e. C57BL/6J and C57BL/6N mice. These two sub-strains show different metabolic properties, for instance an impaired glucose tolerance in C57BL/6J mice. Genetically, this was linked to differences in their nicotinamide nucleotide transhydrogenase (Nnt) genes: In C57BL/6J mice, exons 7-11 of the Nnt gene are deleted, resulting in the absence of functional Nnt protein. The mitochondrial Nnt-protein is one of several enzymes that catalyses the generation of NADPH, which in turn is important for the elimination of reactive oxygen species (ROS). As ROS is thought to contribute to the pathophysiology of hypoxia-ischemia, the lack of Nnt might indirectly increase ROS levels and therefore result in increased brain damage. We therefore hypothesize that lesion score and lesion size will increase in C57BL/6J mice as compared to C57BL/6N mice. Surprisingly, the results showed exactly the opposite: C57BL/6J mice showed a decrease in lesion score and size, associated with a reduced number of apoptotic cells and activated microglia. In contrast, the number of cells with ROS-induced DNA modifications (detected by 8OHdG) was higher in C57BL/6J than C57BL/6N mice. In conclusion, C57BL/6J mice showed reduced ischemic consequences after postnatal hypoxic-ischemic brain injury compared to C57BL/6N mice, with the exception of the amount of ROS-induced DNA-damage. These differences might relate to the lack of Nnt, but also to a modified metabolic setting (cardiovascular parameters, oxygen and glucose metabolism, immune function) in C57BL/6J mice.

Immunoadsorption of Agonistic Autoantibodies Against α1-Adrenergic Receptors in Patients With Mild to Moderate Dementia

Dementia has been shown to be associated with agonistic autoantibodies. The deleterious action of autoantibodies on the α1-adrenergic receptor for brain vasculature has been demonstrated in animal studies. In the current study, 169 patients with dementia were screened for the presence of agonistic autoantibodies. 47% of patients suffering from mild to moderate Alzheimer's disease and/or vascular dementia carried these autoantibodies. Eight patients positive for autoantibodies underwent immunoadsorption. Patients treated on four consecutive days were subsequently negative for autoantibodies and displayed stabilization of cognitive and mental condition during 12-18 months' follow-up. In patients treated for 2-3 days, autoantibodies were reduced by only 78%. They suffered a rebound of autoantibodies during follow-up, benefited from immunoadsorption too, but their mental parameters worsened. We provide first data on the clinical relevance of agonistic autoantibodies in dementia and show that immunoadsorption is safe and efficient in removing autoantibodies with overall benefits for patients.

Reck enables cerebrovascular development by promoting canonical Wnt signaling

The cerebral vasculature provides the massive blood supply that the brain needs to grow and survive. By acquiring distinctive cellular and molecular characteristics it becomes the blood-brain barrier (BBB), a selectively permeable and protective interface between the brain and the peripheral circulation that maintains the extracellular milieu permissive for neuronal activity. Accordingly, there is great interest in uncovering the mechanisms that modulate the formation and differentiation of the brain vasculature. By performing a forward genetic screen in zebrafish we isolated no food for thought (nft (y72)), a recessive late-lethal mutant that lacks most of the intracerebral central arteries (CtAs), but not other brain blood vessels. We found that the cerebral vascularization deficit of nft (y72) mutants is caused by an inactivating lesion in reversion-inducing cysteine-rich protein with Kazal motifs [reck; also known as suppressor of tumorigenicity 15 protein (ST15)], which encodes a membrane-anchored tumor suppressor glycoprotein. Our findings highlight Reck as a novel and pivotal modulator of the canonical Wnt signaling pathway that acts in endothelial cells to enable intracerebral vascularization and proper expression of molecular markers associated with BBB formation. Additional studies with cultured endothelial cells suggest that, in other contexts, Reck impacts vascular biology via the vascular endothelial growth factor (VEGF) cascade. Together, our findings have broad implications for both vascular and cancer biology.

Cerebrovascular and mitochondrial abnormalities in Alzheimer's disease: a brief overview

Multiple lines of evidence suggest that vascular alterations contribute to Alzheimer's disease (AD) pathogenesis. It is also well established that mitochondrial abnormalities occur early in course of AD. Here, we give an overview of the vascular and mitochondrial abnormalities occurring in AD, including mitochondrial alterations in vascular endothelial cells within the brain, which is emerging as a common feature that bridges cerebral vasculature and mitochondrial metabolism.

A perfusion procedure for imaging of the mouse cerebral vasculature by X-ray micro-CT

BACKGROUND

Micro-CT is a novel X-ray imaging modality which can provide 3D high resolution images of the vascular network filled with contrast agent. The cerebrovascular system is a complex anatomical structure that can be imaged with contrast enhanced micro-CT. However, the morphology of the cerebrovasculature and many circulatory anastomosis in the brain result in high variations in the extent of contrast agent filling in the blood vessels and as a result, the vasculature of different subjects appear differently in the acquired images. Specifically, the posterior circulation is not consistently perfused with the contrast agent in many brain specimens and thus, many major vessels that perfuse blood to the midbrain and hindbrain are not visible in the micro-CT images acquired from these samples.

NEW METHOD

In this paper, we present a modified surgical procedure of cerebral vasculature perfusion through the left ventricle with Microfil contrast agent, in order to achieve a more uniform perfusion of blood vessels throughout the brain and as a result, more consistent images of the cerebrovasculature. Our method consists of filling the posterior cerebral circulation with contrast agent, followed by the perfusion of the whole cerebrovasculature.

RESULTS

Our histological results show that over 90% of the vessels in the entire brain, including the cerebellum, were filled with contrast agent.

COMPARISON WITH EXISTING METHOD

Our results show that the new technique of sample perfusion decreases the variability of the posterior circulation in the cerebellum in micro-CT images by 6.9%.

CONCLUSIONS

This new technique of sample preparation improves the quality of cerebrovascular images.

Automated subtraction CT angiography for visualization of the whole brain vasculature: a feasibility study

RATIONALE AND OBJECTIVES

To develop an automated computed tomography angiography (CTA) imaging protocol that allows visualization of the whole brain vasculature and evaluate the clinical usefulness of the technique for delineation of intracranial vessels in patients with cerebrovascular disorders.

MATERIALS AND METHODS

We prospectively included 100 patients who underwent automated subtraction CTA for suspected cerebrovascular disorders. The nonenhanced and contrast enhanced scans were obtained with the same table feeding speed. The x-ray tube start angles of the two scans were matched to enable accurate registration and subtraction of the CTA datasets. Subtracted CTA datasets were reformatted as three-dimensional volume rendering and maximum intensity projection images for further review. Two independent readers assessed the quality of subtraction and delineation of intracranial vessels. The visibility of ophthalmic arteries was also assessed.

RESULTS

Subtraction was successful in all patients. The image quality of bone removal was rated excellent in 95 patients, with no or minimal bone remnants. Incomplete bone removal was observed in five patients because of severe motions between the scans. In 97 of 100 patients, arterial segments at the circle of Willis could be clearly visualized. Excellent delineation of bilateral ophthalmic arteries was possible in 81 of 100 patients.

CONCLUSIONS

The whole brain vasculature would be clearly visualized by using the optimized automated CTA protocol. Our automated, single-source, dual-energy subtraction CTA protocol is a fully automated subtraction method that is capable of delineating major intracranial vessels as well as very small arteries.