Microstructural White Matter Abnormalities and Cognitive Impairment After Aneurysmal Subarachnoid Hemorrhage

Therapeutic potential of stem cells in subarachnoid hemorrhage

Aneurysm rupture can result in subarachnoid hemorrhage, a condition with potentially severe consequences, such as disability and death. In the acute stage, early brain injury manifests as intracranial pressure elevation, global cerebral ischemia, acute hydrocephalus, and direct blood-brain contact due to aneurysm rupture. This may subsequently cause delayed cerebral infarction, often with cerebral vasospasm, significantly affecting patient outcomes. Chronic complications such as brain volume loss and chronic hydrocephalus can further impact outcomes. Investigating the mechanisms of subarachnoid hemorrhage-induced brain injury is paramount for identifying effective treatments. Stem cell therapy, with its multipotent differentiation capacity and anti-inflammatory effects, has emerged as a promising approach for treating previously deemed incurable conditions. This review focuses on the potential application of stem cells in subarachnoid hemorrhage pathology and explores their role in neurogenesis and as a therapeutic intervention in preclinical and clinical subarachnoid hemorrhage studies.

Microglia aggravate white matter injury via C3/C3aR pathway after experimental subarachnoid hemorrhage

The activation of glial cells is intimately associated with the pathophysiology of neuroinflammation and white matter injury (WMI) during both acute and chronic phases following subarachnoid hemorrhage (SAH). The complement C3a receptor (C3aR) has a dual role in modulating inflammation and contributes to neurodevelopment, neuroplasticity, and neurodegeneration. However, its impact on WMI in the context of SAH remains unclear. In this study, 175 male C57BL/6J mice underwent SAH through endovascular perforation. Oxyhemoglobin (oxy-Hb) was employed to simulate SAH in vitro. A suite of techniques, including immunohistochemistry, transcriptomic sequencing, and a range of molecular biotechnologies, were utilized to evaluate the activation of the C3-C3aR pathway on microglial polarization and WMI. Results revealed that post-SAH abnormal activation of microglia was accompanied by upregulation of complement C3 and C3aR. The inhibition of C3aR decreased abnormal microglial activation, attenuated neuroinflammation, and ameliorated WMI and cognitive deficits following SAH. RNA-Seq indicated that C3aR inhibition downregulated several immune and inflammatory pathways and mitigated cellular injury by reducing p53-induced death domain protein 1 (Pidd1) and Protein kinase RNA-like ER kinase (Perk) expression, two factors mainly function in sensing and responding to cellular stress and endoplasmic reticulum (ER) stress. The deleterious effects of the C3-C3aR axis in the context of SAH may be related to endoplasmic reticulum (ER) stress-dependent cellular injury and inflammasome formation. Agonists of Perk can exacerbate the cellular injury and neuroinflammation, which was attenuated by C3aR inhibition after SAH. Additionally, intranasal administration of C3a during the subacute phase of SAH was found to decrease astrocyte reactivity and alleviate cognitive deficits post-SAH. This research deepens our understanding of the complex pathophysiology of WMI following SAH and underscores the therapeutic potential of C3a treatment in promoting white matter repair and enhancing functional recovery prognosis. These insights pave the way for future clinical application of C3a-based therapies, promising significant benefits in the treatment of SAH and its related complications.

White matter abnormalities in aneurysmal and angiographically negative subarachnoid hemorrhage: A diffusion kurtosis imaging study

OBJECTIVE

Aneurysmal subarachnoid hemorrhage (aSAH) and angiographically negative subarachnoid hemorrhage (anSAH) cause an abrupt rise in intracranial pressure, resulting in shearing forces, causing damage to the white matter tracts. This study aims to investigate whole-brain white matter abnormalities with diffusion kurtosis imaging (DKI) after both aSAH and anSAH and explores whether these abnormalities are associated with impaired cognitive functioning.

METHODS

Five months post-ictus, 34 patients with aSAH, 24 patients with anSAH and 17 healthy controls (HC) underwent DKI MRI scanning and neuropsychological assessment (measuring verbal memory, psychomotor speed, executive control, and social cognition). Differences in DKI measures (fractional anisotropy, mean diffusivity, axial diffusivity [AD], radial diffusivity, and mean kurtosis) were examined using tract-based spatial statistics. Significant voxel masks were then correlated with neuropsychological scores.

RESULTS

All DKI measures differed significantly between patients with aSAH and HC, but no significant differences were found between patients with anSAH and HC. Although the two SAH groups did not differ significantly on all DKI parameters, effect sizes indicated that the anSAH group might be more similar to HC. Cognitive impairments were found for both SAH groups relative to HC. No significant associations were found between these impairments and white matter abnormalities in the aSAH group, but lower psychomotor speed scores were associated with higher AD values (r = -0.41, p = 0.04) in patients with anSAH.

CONCLUSIONS

Patients with aSAH showed significant white matter diffusion abnormalities, while the anSAH group, despite cognitive deficits, did not. However, there were no significant differences between the SAH groups, and no correlations between DKI metrics and cognitive measures, except for one test on psychomotor speed in the anSAH group. Overall, this study suggests that while anSAH may not be as severe as aSAH, it is still not a benign condition. Further research with larger anSAH cohorts is necessary to gain a more precise understanding of white matter injuries, particularly regarding their prevalence.

Exosomal LncRNA TM7SF3-AU1 Aggravates White Matter Injury via MiR-702-3p/SARM1 Signaling After Subarachnoid Hemorrhage in Rats

Subarachnoid hemorrhage (SAH) is a devastating disease associated with a high mortality and morbidity. Exosomes have been considered as a potential therapeutic target for SAH. However, the effect of exosomes in SAH remains to be elucidated. In this study, we focused on investigating the effect of plasma exosomal lncRNA TM7SF3-AU1 in white matter injury after SAH. The SAH model was established by means of endovascular perforation. Exosomes were extracted from rat plasma samples. The expression of RNAs in the exosomes was detected by the transcriptomic microarray. Differentially expressed circRNA, lncRNA, and mRNA were obtained. The ceRNA network showed that the lncRNA TM7SF3-AU1 and miR-702-3p were closely associated with SARM1. Knocking down TM7SF3-AU1 promoted the expression of miR-702-3p and suppressed the expression of SARM1, and knocking down TM7SF3-AU1 also attenuated white matter injury after SAH. In addition, knocking down TM7SF3-AU1 improved the neurological deficits in locomotion, anxiety, learning, memory, and electrophysiological activity after SAH. Mechanistically, TM7SF3-AU1 was able to absorb miR-702-3p, which directly bind the SARM1 mRNA. Furthermore, the white matter injury attenuated by knockdown of TM7SF3-AU1 was partially reversed by the miR-702-3p antagomir in SAH rats. Taken together, this study showed that TM7SF3-AU1 acts as a sponge for miR-702-3p, reducing the inhibitory effect of miR-702-3p on SARM1, resulting in increased SARM1 expression and thus leading to white matter injury after SAH. Our study provides new insights into exosome-associated white matter injury. It also highlights TM7SF3-AU1 as a potential therapeutic target for white matter injury after SAH.

Single-Cell Transcriptomics Revealed White Matter Repair Following Subarachnoid Hemorrhage

Existing research indicates the potential for white matter injury repair during the subacute phase following subarachnoid hemorrhage (SAH). However, elucidating the role of brain cell subpopulations in the acute and subacute phases of SAH pathogenesis remains challenging due to the cellular heterogeneity of the central nervous system. In this study, single-cell RNA sequencing was conducted on SAH model mice to delineate distinct cell populations. Gene Set Enrichment Analysis was performed to identify involved pathways, and cellular interactions were explored using the CellChat package in R software. Validation of the findings involved a comprehensive approach, including magnetic resonance imaging, immunofluorescence double staining, and Western blot analyses. This study identified ten major brain clusters with cell type-specific gene expression patterns. Notably, we observed infiltration and clonal expansion of reparative microglia in white matter-enriched regions during the subacute stage after SAH. Additionally, microglia-associated pleiotrophin (PTN) was identified as having a role in mediating the regulation of oligodendrocyte precursor cells (OPCs) in SAH model mice, implicating the activation of the mTOR signaling pathway. These findings emphasize the vital role of microglia-OPC interactions might occur via the PTN pathway, potentially contributing to white matter repair during the subacute phase after SAH. Our analysis revealed precise transcriptional changes in the acute and subacute phases after SAH, offering insights into the mechanism of SAH and for the development of drugs that target-specific cell subtypes.

Advanced Diffusion Tensor Imaging in White Matter Injury After Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is recognized as an especially severe stroke variant, notorious for its high mortality and long-term disability rates, in addition to a range of both immediate and enduring neurologic impacts. Over half of the SAH survivors experience varying degrees of neurologic disorders, with many enduring chronic neuropsychiatric conditions. Due to the limitations of traditional imaging techniques in depicting subtle changes within brain tissues posthemorrhage, the accurate detection and diagnosis of white matter (WM) injuries are complicated. Against this backdrop, diffusion tensor imaging (DTI) has emerged as a promising biomarker for structural imaging, renowned for its enhanced sensitivity in identifying axonal damage. This capability positions DTI as an invaluable tool for forming precise and expedient prognoses for SAH survivors. This study synthesizes an assessment of DTI for the diagnosis and prognosis of neurologic dysfunctions in patients with SAH, emphasizing the notable changes observed in DTI metrics and their association with potential pathophysiological processes. Despite challenges associated with scanning technology differences and data processing, DTI demonstrates significant clinical potential for early diagnosis of cognitive impairments following SAH and monitoring therapeutic effects. Future research requires the development of highly standardized imaging paradigms to enhance diagnostic accuracy and devise targeted therapeutic strategies for SAH patients. In sum, DTI technology not only augments our understanding of the impact of SAH but also may offer new avenues for improving patient prognoses.

Rasd1 is involved in white matter injury through neuron-oligodendrocyte communication after subarachnoid hemorrhage

AIMS

Rasd1 has been reported to be correlated with neurotoxicity, metabolism, and rhythm, but its effect in case of subarachnoid hemorrhage (SAH) remained unclear. White matter injury (WMI) and ferroptosis participate in the early brain injury (EBI) after SAH. In this work, we have investigated whether Rasd1 can cause ferroptosis and contribute to SAH-induced WMI.

METHODS

Lentivirus for Rasd1 knockdown/overexpression was administrated by intracerebroventricular (i.c.v) injection at 7 days before SAH induction. SAH grade, brain water content, short- and long-term neurobehavior, Western blot, real-time PCR, ELISA, biochemical estimation, immunofluorescence, diffusion tensor imaging (DTI), and transmission electron microscopy (TEM) were systematically performed. Additionally, genipin, a selective uncoupling protein 2(UCP2) inhibitor, was used in primary neuron and oligodendrocyte co-cultures for further in vitro mechanistic studies.

RESULTS

Rasd1 knockdown has improved the neurobehavior, glia polarization, oxidative stress, neuroinflammation, ferroptosis, and demyelination. Conversely, Rasd1 overexpression aggravated these changes by elevating the levels of reactive oxygen species (ROS), inflammatory cytokines, MDA, free iron, and NCOA4, as well as contributing to the decrease of the levels of UCP2, GPX4, ferritin, and GSH mechanistically. According to the in vitro study, Rasd1 can induce oligodendrocyte ferroptosis through inhibiting UCP2, increasing reactive oxygen species (ROS), and activating NCOA4-mediated ferritinophagy.

CONCLUSIONS

It can be concluded that Rasd1 exerts a modulated role in oligodendrocytes ferroptosis in WMI following SAH.

Inhibition of GPR17/ID2 Axis Improve Remyelination and Cognitive Recovery after SAH by Mediating OPC Differentiation in Rat Model

Myelin sheath injury contributes to cognitive deficits following subarachnoid hemorrhage (SAH). G protein-coupled receptor 17 (GPR17), a membrane receptor, negatively regulates oligodendrocyte precursor cell (OPC) differentiation in both developmental and pathological contexts. Nonetheless, GPR17's role in modulating OPC differentiation, facilitating remyelination post SAH, and its interaction with downstream molecules remain elusive. In a rat SAH model induced by arterial puncture, OPCs expressing GPR17 proliferated prominently by day 14 post-onset, coinciding with compromised myelin sheath integrity and cognitive deficits. Selective Gpr17 knockdown in oligodendrocytes (OLs) via adeno-associated virus (AAV) administration revealed that reduced GPR17 levels promoted OPC differentiation, restored myelin sheath integrity, and improved cognitive deficits by day 14 post-SAH. Moreover, GPR17 knockdown attenuated the elevated expression of the inhibitor of DNA binding 2 (ID2) post-SAH, suggesting a GPR17-ID2 regulatory axis. Bi-directional modulation of ID2 expression in OLs using AAV unveiled that elevated ID2 counteracted the restorative effects of GPR17 knockdown. This resulted in hindered differentiation, exacerbated myelin sheath impairment, and worsened cognitive deficits. These findings highlight the pivotal roles of GPR17 and ID2 in governing OPC differentiation and axonal remyelination post-SAH. This study positions GPR17 as a potential therapeutic target for SAH intervention. The interplay between GPR17 and ID2 introduces a novel avenue for ameliorating cognitive deficits post-SAH.

MCC950 ameliorates cognitive function by reducing white matter microstructure damage in rats after SAH

Neuroinflammation and white matter microstructure damage are important causes of cognitive impairment after subarachnoid hemorrhage (SAH). Nod-like receptor protein 3 (NLRP3) plays an important role in neuroinflammation after SAH and may be a potential therapeutic target for treatment of white matter microstructure injury. In this study, we observed whether MCC950, a specific inhibitor of the NLRP3 inflammasome, exerted a therapeutic effect after SAH. The SAH model was induced by endovascular perforation in SpragueDawley rats. MCC950 was injected intraperitoneally 1 h after SAH at a dose of 10 mg/kg. The results showed that MCC950 significantly attenuated white matter microstructure damage in some brain regions, and behavioral experiments confirmed that MCC950 ameliorated cognitive function in rats after SAH, which may provide a new method for the treatment of cognitive dysfunction in SAH patients.

Utilization of clinical and radiological parameters to predict cognitive prognosis in patients with mild-to-moderate traumatic brain injury

Background

Cognitive impairment is a common sequela following traumatic brain injury (TBI). This study aimed to identify risk factors for cognitive impairment after 3 and 12 months of TBI and to create nomograms to predict them.

Methods

A total of 305 mild-to-moderate TBI patients admitted to the First Affiliated Hospital with Nanjing Medical University from January 2018 to January 2022 were retrospectively recruited. Risk factors for cognitive impairment after 3 and 12 months of TBI were identified by univariable and multivariable logistic regression analyses. Based on these factors, we created two nomograms to predict cognitive impairment after 3 and 12 months of TBI, the discrimination and calibration of which were validated by plotting the receiver operating characteristic (ROC) curve and calibration curve, respectively.

Results

Cognitive impairment was detected in 125/305 and 52/305 mild-to-moderate TBI patients after 3 and 12 months of injury, respectively. Age, the Glasgow Coma Scale (GCS) score, >12 years of education, hyperlipidemia, temporal lobe contusion, traumatic subarachnoid hemorrhage (tSAH), very early rehabilitation (VER), and intensive care unit (ICU) admission were independent risk factors for cognitive impairment after 3 months of mild-to-moderate TBI. Meanwhile, age, GCS score, diabetes mellitus, tSAH, and surgical treatment were independent risk factors for cognitive impairment after 12 months of mild-to-moderate TBI. Two nomograms were created based on the risk factors identified using logistic regression analyses. The areas under the curve (AUCs) of the two nomograms to predict cognitive impairment after 3 and 12 months of mild-to-moderate TBI were 0.852 (95% CI [0.810, 0.895]) and 0.817 (95% CI [0.762, 0.873]), respectively.

Conclusion

Two nomograms are created to predict cognitive impairment after 3 and 12 months of TBI. Age, GCS score, >12 years of education, hyperlipidemia, temporal lobe contusion, tSAH, VER, and ICU admission are independent risk factors for cognitive impairment after 3 months of TBI; meanwhile, age, the GCS scores, diabetes mellitus, tSAH, and surgical treatment are independent risk factors of cognitive impairment after 12 months of TBI. Two nomograms, based on both groups of factors, respectively, show strong discriminative abilities.

White Matter Injury: An Emerging Potential Target for Treatment after Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) refers to vascular brain injury mainly from a ruptured aneurysm, which has a high lifetime risk and imposes a substantial burden on patients, families, and society. Previous studies on SAH mainly focused on neurons in gray matter (GM). However, according to literature reports in recent years, in-depth research on the mechanism of white matter (WM) is of great significance to injury and recovery after SAH. In terms of functional recovery after SAH, all kinds of cells in the central nervous system (CNS) should be protected. In other words, it is necessary to protect not only GM but also WM, not only neurons but also glial cells and axons, and not only for the lesion itself but also for the prevention and treatment of remote damage. Clarifying the mechanism of white matter injury (WMI) and repair after SAH is of great importance. Therefore, this present review systematically summarizes the current research on WMI after SAH, which might provide therapeutic targets for treatment after SAH.

Electroacupuncture promotes remyelination and alleviates cognitive deficit via promoting OPC differentiation in a rat model of subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a devastating cerebral vascular disease which causes neurological deficits including long-term cognitive deficit. Demyelination of white matter is correlated with cognitive deficit in SAH. Electroacupuncture (EA) is a traditional Chinese medical treatment which protects against cognitive deficit in varies of neurological diseases. However, whether EA exerts protective effect on cognitive function in SAH has not been investigated. The underlying mechanism of remyelination regulated by EA remains unclear. This study aimed to investigate the protective effects of EA on cognitive deficit in a rat model of SAH. SAH was induced in SD rats (n = 72) by endovascular perforation. Rats in EA group received EA treatment (10 min per day) under isoflurane anesthesia after SAH. Rats in SAH and sham groups received the same isoflurane anesthesia with no treatment. The mortality rate, neurological score, cognitive function, cerebral blood flow (CBF), and remyelination in sham, SAH and EA groups were assessed at 21 d after SAH.EA treatment alleviated cognitive deficits and myelin injury of rats compared with that in SAH group. Moreover, EA treatment enhanced remyelination in white matter and promoted the differentiation of OPCs after SAH. EA treatment inhibited the expression of Id2 and promoted the expression of SOX10 in oligodendrocyte cells. Additionally, the cerebral blood flow (CBF) of rats was increased by EA compared with that in SAH group. EA treatment exerts protective effect against cognitive deficit in the late phase of SAH. The underlying mechanisms involve promoting oligodendrocyte progenitor cell (OPC) differentiation and remyelination in white matter via regulating the expression of Id2 and SOX10. The improvement of CBF may also account for the protective effect of EA on cognitive function. EA treatment is a potential therapy for the treatment of cognitive deficit after SAH.

Investigating Recovery After Subarachnoid Hemorrhage With the Imaging, Cognition and Outcome of Neuropsychological Functioning After Subarachnoid Hemorrhage (ICONS) Study: Protocol for a Longitudinal, Prospective Cohort Study

Background

A subarachnoid hemorrhage is a hemorrhage in the subarachnoid space that is often caused by the rupture of an aneurysm. Patients who survive a subarachnoid hemorrhage have a high risk of complications and a negative long-term outcome.

Objective

The aim of the Imaging, Cognition and Outcome of Neuropsychological functioning after Subarachnoid hemorrhage (ICONS) study is to investigate whether and to what extent deficits exist in multiple domains after subarachnoid hemorrhage, including cognition, emotion and behavior, and to investigate whether brain damage can be detected in patients with subarachnoid hemorrhage. We aim to determine which early measures of cognition, emotion and behavior, and brain damage in the subacute stage play a role in long-term recovery after subarachnoid hemorrhage. Recovery is defined as functioning at a societal participation level, with a focus on resuming and maintaining work, leisure activities, and social relationships over the long term.

Methods

The ICONS study is an observational, prospective, single-center cohort study. The study includes patients with subarachnoid hemorrhage admitted to the Neurosurgery Unit of the University Medical Centre Groningen in the Netherlands. The inclusion criteria include diagnosis of an aneurysmal subarachnoid hemorrhage or an angiographically negative subarachnoid hemorrhage, sufficient ability in the Dutch language, and age older than 18 years. Patients will undergo neuropsychological assessment and magnetic resonance imaging 6 months after the subarachnoid hemorrhage. Furthermore, patients will be asked to fill in questionnaires on multiple psychosocial measures and undergo a structured interview at 6 months, 1 year, and 2 years after the subarachnoid hemorrhage. The primary outcome measure of the ICONS study is societal participation 1 year after the subarachnoid hemorrhage, measured with the Dutch version of the Impact on Participation and Autonomy questionnaire.

Results

The study was launched in December 2019 and recruitment is expected to continue until June 2023. At the time of the acceptance of this paper, 76 patients and 69 healthy controls have been included. The first results are expected in early 2023.

Conclusions

The ICONS study is the first to collect and combine data after subarachnoid hemorrhage in a variety of domains, including cognition, emotion and behavior, and brain damage. The results will contribute to a more comprehensive understanding of the consequences of both aneurysmal subarachnoid hemorrhage and angiographically negative subarachnoid hemorrhage, which may ultimately optimize timely treatment for this patient group by setting realistic and attainable goals to improve daily functioning.

Trial Registration

Netherlands Trial Register NL7803; https://trialsearch.who.int/Trial2.aspx?TrialID=NL7803

International Registered Report Identifier (IRRID)

DERR1-10.2196/38190

Spontaneous subarachnoid haemorrhage

Subarachnoid haemorrhage (SAH) is the third most common subtype of stroke. Incidence has decreased over past decades, possibly in part related to lifestyle changes such as smoking cessation and management of hypertension. Approximately a quarter of patients with SAH die before hospital admission; overall outcomes are improved in those admitted to hospital, but with elevated risk of long-term neuropsychiatric sequelae such as depression. The disease continues to have a major public health impact as the mean age of onset is in the mid-fifties, leading to many years of reduced quality of life. The clinical presentation varies, but severe, sudden onset of headache is the most common symptom, variably associated with meningismus, transient or prolonged unconsciousness, and focal neurological deficits including cranial nerve palsies and paresis. Diagnosis is made by CT scan of the head possibly followed by lumbar puncture. Aneurysms are commonly the underlying vascular cause of spontaneous SAH and are diagnosed by angiography. Emergent therapeutic interventions are focused on decreasing the risk of rebleeding (ie, preventing hypertension and correcting coagulopathies) and, most crucially, early aneurysm treatment using coil embolisation or clipping. Management of the disease is best delivered in specialised intensive care units and high-volume centres by a multidisciplinary team. Increasingly, early brain injury presenting as global cerebral oedema is recognised as a potential treatment target but, currently, disease management is largely focused on addressing secondary complications such as hydrocephalus, delayed cerebral ischaemia related to microvascular dysfunction and large vessel vasospasm, and medical complications such as stunned myocardium and hospital acquired infections.

Altered functional connectivity within default mode network after rupture of anterior communicating artery aneurysm

Background

Rupture of anterior communicating artery (ACoA) aneurysm often leads to cognitive impairment, especially memory complaints. The medial superior frontal gyrus (SFGmed), a node of the default mode network (DMN), has been extensively revealed to participate in various cognitive processes. However, the functional connectivity (FC) characteristics of SFGmed and its relationship with cognitive performance remain unknown after the rupture of the ACoA aneurysm.

Methods

Resting-state functional MRI (fMRI) and cognitive assessment were acquired in 27 eligible patients and 20 controls. Seed-based FC between unilateral SFGmed and the rest of the brain was calculated separately, and then compared their intensity differences between the two groups. Furthermore, we analyzed the correlation between abnormal FC and cognitive function in patients with ruptured ACoA aneurysm.

Results

Cognitive impairment was confirmed in 51.9% of the patients. Compared with the controls, patients suffering from ruptured ACoA aneurysm exhibited a similar FC decline between each side of SFGmed and predominant nodes within DMN, including the precuneus, angular gyrus, cingulate cortex, left hippocampus, left amygdala, left temporal pole (TPO), and left medial orbitofrontal cortex (mOFC). Besides, significantly decreased FC of left SFGmed and left insula, right middle temporal gyrus (MTG), as well as right mOFC, were also found. In addition, only enhanced insular connectivity with right SFGmed was determined, whereas increased FC of the left SFGmed was not observed. Correlation analyses showed that lower total cognitive performance or stronger subjective memory complaints were related to reduced connectivity in the SFGmed and several cortical regions such as the angular gyrus and middle cingulate cortex (MCC).

Conclusion

Our results suggest that patients with ruptured ACoA aneurysm exist long-term cognitive impairment and intrinsic hypoconnectivity of cognition-related brain regions within DMN. Deactivation of DMN may be a potential neural mechanism leading to cognitive deficits in these patients.

A timeline of oligodendrocyte death and proliferation following experimental subarachnoid hemorrhage

AIMS

White matter (WM) injury is a critical factor associated with worse outcomes following subarachnoid hemorrhage (SAH). However, the detailed pathological changes are not completely understood. This study investigates temporal changes in the corpus callosum (CC), including WM edema and oligodendrocyte death after SAH, and the role of lipocalin-2 (LCN2) in those changes.

METHODS

Subarachnoid hemorrhage was induced in adult wild-type or LCN2 knockout mice via endovascular perforation. Magnetic resonance imaging was performed 4 hours, 1 day, and 8 days after SAH, and T2 hyperintensity changes within the CC were quantified to represent WM edema. Immunofluorescence staining was performed to evaluate oligodendrocyte death and proliferation.

RESULTS

Subarachnoid hemorrhage induced significant CC T2 hyperintensity at 4 hours and 1 day that diminished significantly by 8 days post-procedure. Comparing changes between the 4 hours and 1 day, each individual mouse had an increase in CC T2 hyperintensity volume. Oligodendrocyte death was observed at 4 hours, 1 day, and 8 days after SAH induction, and there was progressive loss of mature oligodendrocytes, while immature oligodendrocytes/oligodendrocyte precursor cells (OPCs) proliferated back to baseline by Day 8 after SAH. Moreover, LCN2 knockout attenuated WM edema and oligodendrocyte death at 24 hours after SAH.

CONCLUSIONS

Subarachnoid hemorrhage leads to T2 hyperintensity change within the CC, which indicates WM edema. Oligodendrocyte death was observed in the CC within 1 day of SAH, with a partial recovery by Day 8. SAH-induced WM injury was alleviated in an LCN2 knockout mouse model.

Midbrain injury in patients with subarachnoid hemorrhage: a diffusion tensor imaging study

We investigated the characteristics of midbrain injuries in patients with spontaneous subarachnoid hemorrhage (SAH) by using diffusion tensor imaging (DTI). Twenty-seven patients with SAH and 25 healthy control subjects were recruited for this study. Fractional anisotropy (FA) and mean diffusivity (MD) data were obtained for four regions of the midbrain (the anterior ventral midbrain, posterior ventral midbrain, tegmentum area, and tectum) in 27 hemispheres that did not show any pathology other than SAH. The mean FA and MD values of the four regions of the midbrain (anterior ventral midbrain, posterior ventral midbrain, tegmentum, and tectum) of the patient group were significantly lower and higher than those of the control group, respectively (p < 0.05). The mean FA values of the patient group were significantly different among the anterior ventral midbrain, posterior ventral midbrain, tegmentum, and tectum regions (ANOVA; F = 3.22, p < 0.05). Post hoc testing showed that the mean FA value of the anterior ventral midbrain was significantly lower than those of the posterior ventral midbrain, tegmentum, and tectum (p < 0.05); in contrast, there were no differences in mean FA values of the posterior ventral midbrain, tegmentum, and tectum (p > 0.05). However, differences were not observed among four regions of the midbrain (anterior ventral midbrain, posterior ventral midbrain, tegmentum, and tectum) in the mean MD values. We detected evidence of neural injury in all four regions of the midbrain of patients with SAH, and the anterior ventral midbrain was the most severely injured among four regions of the midbrain. Our results suggest that a pathophysiological mechanism of these neural injuries might be related to the occurrence of a subarachnoid hematoma.

Loss of monocarboxylate transporter 1 aggravates white matter injury after experimental subarachnoid hemorrhage in rats

Monocarboxylic acid transporter 1 (MCT1) maintains axonal function by transferring lactic acid from oligodendrocytes to axons. Subarachnoid hemorrhage (SAH) induces white matter injury, but the involvement of MCT1 is unclear. In this study, the SAH model of adult male Sprague-Dawley rats was used to explore the role of MCT1 in white matter injury after SAH. At 48 h after SAH, oligodendrocyte MCT1 was significantly reduced, and the exogenous overexpression of MCT1 significantly improved white matter integrity and long-term cognitive function. Motor training after SAH significantly increased the number of ITPR2⁺SOX10⁺ oligodendrocytes and upregulated the level of MCT1, which was positively correlated with the behavioral ability of rats. In addition, miR-29b and miR-124 levels were significantly increased in SAH rats compared with non-SAH rats. Further intervention experiments showed that miR-29b and miR-124 could negatively regulate the level of MCT1. This study confirmed that the loss of MCT1 may be one of the mechanisms of white matter damage after SAH and may be caused by the negative regulation of miR-29b and miR-124. MCT1 may be involved in the neurological improvement of rehabilitation training after SAH.

White Matter Abnormalities in Traumatic Subarachnoid Hemorrhage: A Tract-Based Spatial Statistics Study

Background

The pathophysiology of traumatic subarachnoid hemorrhage and brain injury has not been fully elucidated. In this study, we examined abnormalities of white matter in isolated traumatic subarachnoid hemorrhage patients by applying tract-based spatial statistics.

Material/Methods

For this study, 10 isolated traumatic subarachnoid hemorrhage patients and 10 age- and sex-matched healthy control subjects were recruited. Fractional anisotropy data voxel-wise statistical analyses were conducted through the tract-based spatial statistics as implemented in the FMRIB Software Library. Depending on the intersection between the fractional anisotropy skeleton and the probabilistic white matter atlases of Johns Hopkins University, we calculated mean fractional anisotropy values within the entire tract skeleton and 48 regions of interest.

Results

The fractional anisotropy values for 19 of 48 regions of interest showed significant divergences (P<0.05) between the patient group and control group. The regions showing significant differences included the corpus callosum and its adjacent neural structures, the brainstem and its adjacent neural structures, and the subcortical white matter that passes the long neural tract.

Conclusions

The results demonstrated abnormalities of white matter in traumatic subarachnoid hemorrhage patients, and the abnormality locations are compatible with areas that are vulnerable to diffuse axonal injury. Based on these results, traumatic subarachnoid hemorrhage patients also exhibit diffuse axonal injuries; thus, traumatic subarachnoid hemorrhage could be an indicator of the presence of severe brain injuries associated with acute or excessive mechanical forces.

Secondary White Matter Injury and Therapeutic Targets After Subarachnoid Hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is one of the special stroke subtypes with high mortality and mobility. Although the mortality of SAH has decreased by 50% over the past two decades due to advances in neurosurgery and management of neurocritical care, more than 70% of survivors suffer from varying degrees of neurological deficits and cognitive impairments, leaving a heavy burden on individuals, families, and the society. Recent studies have shown that white matter is vulnerable to SAH, and white matter injuries may be one of the causes of long-term neurological deficits caused by SAH. Attention has recently focused on the pivotal role of white matter injury in the pathophysiological processes after SAH, mainly related to mechanical damage caused by increased intracerebral pressure and the metabolic damage induced by blood degradation and hypoxia. In the present review, we sought to summarize the pathophysiology processes and mechanisms of white matter injury after SAH, with a view to providing new strategies for the prevention and treatment of long-term cognitive dysfunction after SAH.

MiR-706 alleviates white matter injury via downregulating PKCα/MST1/NF-κB pathway after subarachnoid hemorrhage in mice

Increasing numbers of patients with spontaneous subarachnoid hemorrhage(SAH) who recover from surgery and intensive care management still live with cognitive impairment after discharge, indicating the importance of white matter injury at the acute stage of SAH. In the present study, standard endovascular perforation was employed to establish an SAH mouse model, and a microRNA (miRNA) chip was used to analyze the changes in gene expression in white matter tissue after SAH. The data indicate that 17 miRNAs were downregulated, including miR-706, miR-669a-5p, miR-669p-5p, miR-7116-5p and miR-195a-3p, while 13 miRNAs were upregulated, including miR-6907-5p, miR-5135, miR-6982-5p, miR-668-5p, miR-8119. Strikingly, miR-706 was significantly downregulated with the highest fold change. Further experiments confirmed that miR-706 could alleviate white matter injury and improve neurological behavior, at least partially by inhibiting the PKCα/MST1/NF-κB pathway and the release of inflammatory cytokines. These results might provide a deeper understanding of the pathophysiological processes in white matter after SAH, as well as potential therapeutic strategies for the translational research.

Cognitive Impairments and Risk Factors After Ruptured Anterior Communicating Artery Aneurysm Treatment in Low-Grade Patients Without Severe Complications: A Multicenter Retrospective Study

Background: Cognitive impairment is the main factor affecting quality of life in patients with low-grade aneurysmal subarachnoid hemorrhage. Objective: We explored cognitive impairments and risk factors after treatment for ruptured anterior communicating artery (AComA) aneurysms in low-grade (Hunt-Hess grade of 1-3) patients without severe complications. Methods: One-hundred-twenty-six patients with a Hunt-Hess grade of 1-3 who underwent microsurgical clipping or endovascular embolization for ruptured AComA aneurysm treatment at three academic institutions in China from January 2015 to December 2017 were assessed with the modified Telephone Interview for Cognitive Status (TICS-m), the modified Rankin Scale (mRS), and the instrumental activities of daily living (IADL) scale 2 or more years after microsurgical clipping or endovascular coiling. Multiple cox-regression analysis was used to identify variables independently associated with cognitive impairment. Results: Of the total of 126 patients, 115 (91.3%) achieved good clinical outcomes (mRS score 0-2) and 109 (86.5%) had excellent quality of life (IADL score 8). Twenty-eight (22.2%) patients showed cognitive impairments (TICS-m≤27). The multivariate COX regression analysis showed that the female patients and longer duration of loss of consciousness at onset of subarachnoid hemorrhage (SAH) were independently associated with cognitive impairment. Cognitive outcome at the latest follow-up was not significantly different between patients treated after surgical clipping and coiling. Conclusion: About one in five patients showed cognitive impairments after treatment for ruptured AComA aneurysms. Patients who are of the female sex, and who have a longer duration of a loss of consciousness at the onset of SAH may be at risk of cognitive impairment.

Cognitive deficits among patients surviving aneurysmal subarachnoid hemorrhage. A contemporary systematic review

BACKGROUND

Subarachnoid hemorrhage (SAH) is associated with high rates of morbidity, including neurological and cognitive deficits that may be difficult to identify and quantify. This review provides an update on the cognitive deficits that may result from spontaneous aneurysmal SAH (aSAH) and identifies factors that may help predict and manage these deficits at discharge and thereafter.

MATERIALS AND METHODS

We conducted a systematic review of PubMed and Google Scholar to identify studies published between 2010 and 2019 that assessed cognitive deficits at discharge and during follow-up in patients with aSAH. Full-text articles were assessed for information regarding cognitive testing and factors that may be associated with functional outcomes in this population.

RESULTS

We reviewed 65 studies published since 2010 that described the cognitive deficits associated with non-traumatic aSAH. Such deficits may impact functional outcomes, quality of life, and return to work and may result in cognitive impairments, such as memory difficulties, speech problems, and psychiatric disorders.

CONCLUSIONS

Patients with aSAH, even those that appear normal at the time of hospital discharge, may harbor cognitive deficits that are difficult to detect, yet can interfere with daily functioning. Further research is needed to provide additional information and to identify stronger correlations to be used in the identification, treatment, and amelioration of long-term cognitive deficits in aSAH patients, including those who are discharged with good clinical outcomes scores.

White Matter Abnormalities in Spontaneous Subarachnoid Hemorrhage: A Tract-Based Spatial Statistics Study

BACKGROUND AND PURPOSE

We investigated white matter abnormalities in patients with spontaneous subarachnoid hemorrhage following aneurysmal rupture, by using tract-based spatial statistics.

METHODS

Sixteen patients with spontaneous subarachnoid hemorrhage due to aneurysmal rupture and 18 age- and sex-matched healthy control subjects were recruited. Voxel-wise statistical analysis of fractional anisotropy data was performed by using tract-based spatial statistics as implemented in the Functional Magnetic Resonance Imaging of the Brain Software Library. We calculated mean fractional anisotropy values across the tract skeleton and within 48 regions of interest based on the intersections between the fractional anisotropy skeleton and the probabilistic Johns Hopkins University white matter atlases.

RESULTS

Comparing the patient and control groups, the fractional anisotropy values of 44 regions of interest among the 48 regions of interest showed significant differences (P<0.05). However, significant differences were not observed in the remaining 4 regions of interest (both retrolenticular parts of the internal capsule, the right superior longitudinal fasciculus, and the right superior corona radiata; P>0.05).

CONCLUSIONS

By undertaking tract-based spatial statistics analysis, we detected wide-ranging white matter abnormalities in patients with spontaneous subarachnoid hemorrhage. Registration: URL: http://www.e-irb.com/index.jsp. Unique identifier: 2019-06-032.

Demystifying White Matter Injury in the Unconscious Patients with Diffusion Tensor Imaging

Background

Diffusion tensor imaging (DTI) and diffusion tensor tractography (DTT) provide a noninvasive window to study the neural connectivity and reconstruct the tracts. Detection of white matter injury (WMI) by DTT is a recent application being used in stroke, diffuse axonal injury, and neurodegenerative disorders. Fiber tracking in patients with brain hemorrhage can detect loss of fibers and anatomical disruption of the tracts, which can be useful in the prognostication of patient outcome.

Materials and Methods

DTI and fiber tracking was done in four patients admitted at Fujita Health University Banbuntane Hospital, Japan, with decreased consciousness following brain hemorrhage (3 patients with aneurysmal subarachnoid hemorrhage and one patient with bifrontal hemorrhage), and WMI was analyzed. We also reviewed the literature on tractography in patients with brain hemorrhage and its correlation with consciousness.

Results

We found significant frontal WMI in the form of thinning and anatomical disruption in all four cases. The frontal white matter tracts form an important component of the limbic system and ascending reticular activating system and frontal WMI correlated with the poor conscious level and cognitive dysfunction. Structural damage to the fiber tracts demonstrated as thinning, reduction in the volume or absence on tractography with corresponding reduction in the mean fractional anisotropy values in the frontal white matter of the affected side.

Conclusion

DTI can be useful as a critical tool for revealing the anatomical basis for the cognitive dysfunction and unconsciousness and can be possibly used to prognosticate patient recovery. Early detection of WMI by DTI can also help in tailored rehabilitation. The authors believe that DTT could have a crucial role in the future for detecting structural changes which lead to cognitive dysfunction and further studies are needed to arrive at a specific protocol for detecting WMI.

Astrocytic histone deacetylase 2 facilitates delayed depression and memory impairment after subarachnoid hemorrhage by negatively regulating glutamate transporter-1

Background

Delayed cognitive impairment (DCI) after subarachnoid hemorrhage (SAH) is one of the most common sequelae in patients. This study aimed to investigate the characteristics of the course and glutamatergic pathogenesis of DCI after SAH in mice.

Methods

A SAH mouse model of internal carotid puncture was used. Depressive and cognitive behaviors were detected by forced swimming and sucrose preference tests and Morris water maze test, respectively. Microdialysis and high-performance liquid chromatography (HPLC) were used to detect the interstitial glutamate. The expressions of histone deacetylases (HDACs), glutamate transporters, and glutamate receptors were examined. Primary astrocytes magnetically sorted from adult mice were cultured for glutamate uptake assay and protein and mRNA detection. Selective HDAC2 inhibitor and glutamate transporter-1 (GLT-1) inhibitor administered via were intraperitoneal injection to evaluate their effects on DCI in SAH mice.

Results

Depression and memory impairment lasted for more than 12 weeks and peaked at 8 weeks after SAH. Interstitial glutamate accumulation in the hippocampus and impaired glutamate uptake in astrocytes of the SAH mice were found during DCI, which could be explained by there being a significant decrease in GLT-1 expression but not in glutamate and aspartate transporter (GLAST) in hippocampal astrocytes. Meanwhile, the phosphorylation level of excitatory glutamate receptors (GluN2B and GluA1) in the hippocampus was significantly reduced, although there was no significant change in the expression of the receptors. Importantly, the expression of HDAC2 increased most significantly in astrocytes after SAH compared with that of other subtypes of HDACs. Inhibition of HDAC2 markedly rescued the decrease in GLT-1 expression after SAH through transcriptional regulation. Behavioral results showed that a selective HDAC2 inhibitor effectively improved DCI in SAH mice, but this effect could be weakened by GLT-1 inhibition.

Conclusions

In summary, our study suggests that the dysfunction of GLT-1-mediated glutamate uptake in astrocytes may be a key pathological mechanism of DCI after SAH, and that a specific inhibitor of HDAC2 may exert a potential therapy.

Diffusion Tensor Imaging Studies on Spontaneous Subarachnoid Hemorrhage-Related Brain Injury: A Mini-Review

Accurate diagnosis of the presence and severity of neural injury in patients with subarachnoid hemorrhage (SAH) is important in neurorehabilitation because it is essential for establishing appropriate therapeutic strategies and developing a prognosis. Diffusion tensor imaging has a unique advantage in the identification of microstructural white matter abnormalities which are not usually detectable on conventional brain magnetic resonance imaging. In this mini-review article, 12 diffusion tensor imaging studies on SAH-related brain injury were reviewed. These studies have demonstrated SAH-related brain injuries in various neural tracts or structures including the cingulum, fornix, hippocampus, dorsolateral prefrontal region, corticospinal tract, mamillothalamic tract, corticoreticular pathway, ascending reticular activating system, Papez circuit, optic radiation, and subcortical white matter. We believe that these reviewed studies provide information that would be helpful in science-based neurorehabilitation of patients with SAH. Furthermore, the results of these reviewed studies would also be useful for clarification of the pathophysiological mechanisms associated with SAH-related brain injury. However, considering the large number of neural tracts or neural structures in the brain, more research on SAH-related brain injury in other neural tracts or structures should be encouraged.