Acute white matter injury after experimental subarachnoid hemorrhage: potential role of lipocalin 2

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.

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.

Myelin sheath injury and repairment after subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) can lead to damage to the myelin sheath in white matter. Through classification and analysis of relevant research results, the discussion in this paper provides a deeper understanding of the spatiotemporal change characteristics, pathophysiological mechanisms and treatment strategies of myelin sheath injury after SAH. The research progress for this condition was also systematically reviewed and compared related to myelin sheath in other fields. Serious deficiencies were identified in the research on myelin sheath injury and treatment after SAH. It is necessary to focus on the overall situation and actively explore different treatment methods based on the spatiotemporal changes in the characteristics of the myelin sheath, as well as the initiation, intersection and common action point of the pathophysiological mechanism, to finally achieve accurate treatment. We hope that this article can help researchers in this field to further clarify the challenges and opportunities in the current research on myelin sheath injury and treatment after SAH.

Role of lipocalin 2 in stroke

Stroke is the second leading cause of death worldwide; however, the treatment choices available to neurologists are limited in clinical practice. Lipocalin 2 (LCN2) is a secreted protein, belonging to the lipocalin superfamily, with multiple biological functions in mediating innate immune response, inflammatory response, iron-homeostasis, cell migration and differentiation, energy metabolism, and other processes in the body. LCN2 is expressed at low levels in the brain under normal physiological conditions, but its expression is significantly up-regulated in multiple acute stimulations and chronic pathologies. An up-regulation of LCN2 has been found in the blood/cerebrospinal fluid of patients with ischemic/hemorrhagic stroke, and could serve as a potential biomarker for the prediction of the severity of acute stroke. LCN2 activates reactive astrocytes and microglia, promotes neutrophil infiltration, amplifies post-stroke inflammation, promotes blood-brain barrier disruption, white matter injury, and neuronal death. Moreover, LCN2 is involved in brain injury induced by thrombin and erythrocyte lysates, as well as microvascular thrombosis after hemorrhage. In this paper, we review the role of LCN2 in the pathological processes of ischemic stroke; intracerebral hemorrhage; subarachnoid hemorrhage; and stroke-related brain diseases, such as vascular dementia and post-stroke depression, and their underlying mechanisms. We hope that this review will help elucidate the value of LCN2 as a therapeutic target in stroke.

Lipocalin-2 Is a Key Regulator of Neuroinflammation in Secondary Traumatic and Ischemic Brain Injury

Reactive glial cells are hallmarks of brain injury. However, whether these cells contribute to secondary inflammatory pathology and neurological deficits remains poorly understood. Lipocalin-2 (LCN2) has inflammatory and neurotoxic effects in various disease models; however, its pathogenic role in traumatic brain injury remains unknown. The aim of the present study was to investigate the expression of LCN2 and its role in neuroinflammation following brain injury. LCN2 expression was high in the mouse brain after controlled cortical impact (CCI) and photothrombotic stroke (PTS) injury. Brain levels of LCN2 mRNA and protein were also significantly higher in patients with chronic traumatic encephalopathy (CTE) than in normal subjects. RT-PCR and immunofluorescence analyses revealed that astrocytes were the major cellular source of LCN2 in the injured brain. Lcn2 deficiency or intracisternal injection of an LCN2 neutralizing antibody reduced CCI- and PTS-induced brain lesions, behavioral deficits, and neuroinflammation. Mechanistically, in cultured glial cells, recombinant LCN2 protein enhanced scratch injury-induced proinflammatory cytokine gene expression and inhibited Gdnf gene expression, whereas Lcn2 deficiency exerted opposite effects. Together, our results from CTE patients, rodent brain injury models, and cultured glial cells suggest that LCN2 mediates secondary damage response to traumatic and ischemic brain injury by promoting neuroinflammation and suppressing the expression of neurotropic factors.

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.

The role of lipocalin 2 in brain injury and recovery after ischemic and hemorrhagic stroke

Ischemic and hemorrhagic stroke (including intracerebral hemorrhage, intraventricular hemorrhage, and subarachnoid hemorrhage) is the dominating cause of disability and death worldwide. Neuroinflammation, blood–brain barrier (BBB) disruption, neuronal death are the main pathological progress, which eventually causes brain injury. Increasing evidence indicated that lipocalin 2 (LCN2), a 25k-Da acute phase protein from the lipocalin superfamily, significantly increased immediately after the stroke and played a vital role in these events. Meanwhile, there exists a close relationship between LCN2 levels and the worse clinical outcome of patients with stroke. Further research revealed that LCN2 elimination is associated with reduced immune infiltrates, infarct volume, brain edema, BBB leakage, neuronal death, and neurological deficits. However, some studies revealed that LCN2 might also act as a beneficial factor in ischemic stroke. Nevertheless, the specific mechanism of LCN2 and its primary receptors (24p3R and megalin) involving in brain injury remains unclear. Therefore, it is necessary to investigate the mechanism of LCN2 induced brain damage after stroke. This review focuses on the role of LCN2 and its receptors in brain injury and aiming to find out possible therapeutic targets to reduce brain damage following stroke.

Suberoylanilide hydroxamic acid suppresses axonal damage and neurological dysfunction after subarachnoid hemorrhage via the HDAC1/HSP70/TDP-43 axis

Increased focus has been placed on the role of histone deacetylase inhibitors as crucial players in subarachnoid hemorrhage (SAH) progression. Therefore, this study was designed to expand the understanding of SAH by exploring the downstream mechanism of the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) in SAH. The expression of TDP-43 in patients with SAH and rat models of SAH was measured. Then, western blot analysis, immunofluorescence staining, and transmission electron microscope were used to investigate the in vitro effect of TDP-43 on a neuronal cell model of SAH established by oxyhemoglobin treatment. Immunofluorescence staining and coimmunoprecipitation assays were conducted to explore the relationship among histone deacetylase 1 (HDAC1), heat shock protein 70 (HSP70), and TDP-43. Furthermore, the in vivo effect of HDAC1 on SAH was investigated in rat models of SAH established by endovascular perforation. High expression of TDP-43 in the cerebrospinal fluid of patients with SAH and brain tissues of rat models of SAH was observed, and TDP-43 accumulation in the cytoplasm and the formation of inclusion bodies were responsible for axonal damage, abnormal nuclear membrane morphology, and apoptosis in neurons. TDP-43 degradation was promoted by the HDAC1 inhibitor SAHA via the acetylation of HSP70, alleviating SAH, and this effect was verified in vivo in rat models. In conclusion, SAHA relieved axonal damage and neurological dysfunction after SAH via the HSP70 acetylation-induced degradation of TDP-43, highlighting a novel therapeutic target for SAH.

The blood-brain barrier and the neurovascular unit in subarachnoid hemorrhage: molecular events and potential treatments

The response of the blood-brain barrier (BBB) following a stroke, including subarachnoid hemorrhage (SAH), has been studied extensively. The main components of this reaction are endothelial cells, pericytes, and astrocytes that affect microglia, neurons, and vascular smooth muscle cells. SAH induces alterations in individual BBB cells, leading to brain homeostasis disruption. Recent experiments have uncovered many pathophysiological cascades affecting the BBB following SAH. Targeting some of these pathways is important for restoring brain function following SAH. BBB injury occurs immediately after SAH and has long-lasting consequences, but most changes in the pathophysiological cascades occur in the first few days following SAH. These changes determine the development of early brain injury as well as delayed cerebral ischemia. SAH-induced neuroprotection also plays an important role and weakens the negative impact of SAH. Supporting some of these beneficial cascades while attenuating the major pathophysiological pathways might be decisive in inhibiting the negative impact of bleeding in the subarachnoid space. In this review, we attempt a comprehensive overview of the current knowledge on the molecular and cellular changes in the BBB following SAH and their possible modulation by various drugs and substances.

Astrocytic phagocytosis contributes to demyelination after focal cortical ischemia in mice

Ischemic stroke can cause secondary myelin damage in the white matter distal to the primary injury site. The contribution of astrocytes during secondary demyelination and the underlying mechanisms are unclear. Here, using a mouse of distal middle cerebral artery occlusion, we show that lipocalin-2 (LCN2), enriched in reactive astrocytes, expression increases in nonischemic areas of the corpus callosum upon injury. LCN2-expressing astrocytes acquire a phagocytic phenotype and are able to uptake myelin. Myelin removal is impaired in Lcn2^−/− astrocytes. Inducing re-expression of truncated LCN2(Δ2–20) in astrocytes restores phagocytosis and leads to progressive demyelination in Lcn2^−/− mice. Co-immunoprecipitation experiments show that LCN2 binds to low-density lipoprotein receptor-related protein 1 (LRP1) in astrocytes. Knockdown of Lrp1 reduces LCN2-induced myelin engulfment by astrocytes and reduces demyelination. Altogether, our findings suggest that LCN2/LRP1 regulates astrocyte-mediated myelin phagocytosis in a mouse model of ischemic stroke.

Ischemic stroke can cause secondary demyelination. Whether phagocytic astrocytes can contribute to such demyelination is unclear. Here, the authors show that lipocalin-2 (LCN-2) expression increased in astrocytes upon injury. LCN-2 expressing astrocytes acquire a phagocytic phenotype and contribute to secondary demyelination in a mouse model of ischemic stroke.

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.

Acute T2*-Weighted Magnetic Resonance Imaging Detectable Cerebral Thrombosis in a Rat Model of Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is associated with a high incidence of morbidity and mortality, particularly within the first 72 h after aneurysm rupture. We recently found ultra-early cerebral thrombosis, detectable on T2* magnetic resonance imaging (MRI), in a mouse SAH model at 4 h after onset. The current study examined whether such changes also occur in rat at 24 h after SAH, the vessels involved, whether the degree of thrombosis varied with SAH severity and brain injury, and if it differed between male and female rats. Adult Sprague Dawley rats were subjected to an endovascular perforation SAH model or sham surgery and underwent T2 and T2* MRI 24 h later. Following SAH, increased numbers of T2* hypointense vessels were detected on MRI. The number of such vessels correlated with SAH severity, as assessed by MRI-based grading of bleeding. Histologically, thrombotic vessels were found on hematoxylin and eosin staining, had a single layer of smooth muscle cells on alpha-smooth muscle actin immunostaining, and had laminin 2α/fibrinogen double labeling, suggesting venule thrombosis underlies the T2*-positive vessels on MRI. Capillary thrombosis was also detected which may follow the venous thrombosis. In both male and female rats, the number of T2*-positive thrombotic vessels correlated with T2 lesion volume and neurological function, and the number of such vessels was significantly greater in female rats. In summary, this study identified cerebral venous thrombosis 24 h following SAH in rats that could be detected with T2* MRI imaging and may contribute to SAH-induced brain injury.

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.

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.

Subarachnoid hemorrhage leads to early and persistent functional connectivity and behavioral changes in mice

Aneurysmal subarachnoid hemorrhage (SAH) leads to significant long-term cognitive deficits, which can be associated with alterations in resting state functional connectivity (RSFC). However, modalities such as fMRI-which is commonly used to assess RSFC in humans-have practical limitations in small animals. Therefore, we used non-invasive optical intrinsic signal imaging to determine the effect of SAH on RSFC in mice up to three months after prechiasmatic blood injection. We assessed Morris water maze (MWM), open field test (OFT), Y-maze, and rotarod performance from approximately two weeks to three months after SAH. Compared to sham, we found that SAH reduced motor, retrosplenial, and visual seed-based connectivity indices. These deficits persisted in retrosplenial and visual cortex seeds at three months. Seed-to-seed analysis confirmed early attenuation of correlation coefficients in SAH mice, which persisted in predominantly posterior network connections at later time points. Seed-independent global and interhemispheric indices of connectivity revealed decreased correlations following SAH for at least one month. SAH led to MWM hidden platform and OFT deficits at two weeks, and Y-maze deficits for at least three months, without altering rotarod performance. In conclusion, experimental SAH leads to early and persistent alterations both in hemodynamically derived measures of RSFC and in cognitive performance.

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.

Ultra-Early Cerebral Thrombosis Formation After Experimental Subarachnoid Hemorrhage Detected on T2* Magnetic Resonance Imaging

BACKGROUND AND PURPOSE

The mechanisms of brain damage during ultra-early subarachnoid hemorrhage (SAH) have not been well studied. The current study examined the SAH-induced hyperacute brain damage at 4 hours using magnetic resonance imaging and brain histology in a mouse model.

METHODS

SAH was induced by endovascular perforation in adult mice. First, adult male wild-type mice underwent magnetic resonance imaging T2 and T2* 4 hours after an endovascular perforation or a sham operation and were euthanized to assess brain histology. Second, male and female adult lipocalin-2 knockout mice had SAH. All animals underwent magnetic resonance imaging at 4 hours, and the brains were harvested for brain histology.

RESULTS

T2* hypointensity vessels were observed in the brain 4 hours after SAH in male wild-type mice. The numbers of T2*-positive vessels were significantly higher in SAH brains than in sham-operated mice. Brain histology showed thrombosis and erythrocyte plugs in the T2*-positive cerebral vessels which may be venules. The number of T2*-positive vessels correlated with SAH grade and the presence of T2 lesions. Brain thrombosis was also accompanied by albumin leakage and neuronal injury. LCN2 deficient male mice had lower numbers of T2*-positive vessels after SAH compared with wild-type male mice.

CONCLUSIONS

SAH causes ultra-early brain vessel thrombosis that can be detected by T2* gradient-echo sequence at 4 hours after SAH. LCN2 deficiency decreased the number of T2*-positive vessels.

Role of lipocalin-2 in extracellular peroxiredoxin 2-induced brain swelling, inflammation and neuronal death

Peroxiredoxin-2 (PRX-2) is known to be released from erythrocytes and induce brain damage after intracerebral hemorrhage (ICH); lipocalin-2 (LCN-2) is involved in neuroinflammation following ICH. This study examined the role of LCN-2 in PRX-2 induced brain injury and involved three parts. In the first part, adult male C57BL/6 wild-type (WT), LCN-2 heterozygous (LCN-2 HET), and LCN-2 knockout (LCN-2 KO) mice received either an intracaudate injection of recombinant PRX-2 or saline. In the second part, adult male C57BL/6 WT and male LCN-2 KO mice received recombinant PRX-2 with either recombinant mouse LCN-2 protein or control. In the third part, adult female C57BL/6 WT, LCN-2 HET, and LCN-2 KO mice received recombinant PRX-2. Behavioral tests, and T2- and T2*- weighted magnetic resonance imaging was obtained for all mice. Mice were then euthanized, and their brains used for Western blotting, histology and immunohistochemistry. Intracerebral PRX-2 injections resulted in increased expression of LCN-2 protein. PRX-2-induced brain swelling, neutrophil infiltration, microglia/macrophage activation, neuronal cell death, and neurological deficits were reduced in male LCN-2 HET and LCN-2 KO mice (P < 0.01) compared to WT and were exacerbated by exogenous LCN-2 co-injection. Additionally, intracerebral PRX-2 injections caused brain injury and neurological deficits in female WT mice; effects reduced in female LCN-2 KO mice. In conclusion, intracerebral injection of PRX-2 upregulates LCN-2, and LCN-2 is crucial in the effects of PRX-2 on neutrophil infiltration and microglia/macrophage activation, and ultimately brain damage.

Neutralization of Lipocalin-2 Diminishes Stroke-Reperfusion Injury

Oxidative stress is a key contributor to the pathogenesis of stroke-reperfusion injury. Neuroinflammatory peptides released after ischemic stroke mediate reperfusion injury. Previous studies, including ours, have shown that lipocalin-2 (LCN2) is secreted in response to cerebral ischemia to promote reperfusion injury. Genetic deletion of LCN2 significantly reduces brain injury after stroke, suggesting that LCN2 is a mediator of reperfusion injury and a potential therapeutic target. Immunotherapy has the potential to harness neuroinflammatory responses and provides neuroprotection against stroke. Here we report that LCN2 was induced on the inner surface of cerebral endothelial cells, neutrophils, and astrocytes that gatekeep the blood–brain barrier (BBB) after stroke. LCN2 monoclonal antibody (mAb) specifically targeted LCN2 in vitro and in vivo, attenuating the induction of LCN2 and pro-inflammatory mediators (iNOS, IL-6, CCL2, and CCL9) after stroke. Administration of LCN2 mAb at 4 h after stroke significantly reduced neurological deficits, cerebral infarction, edema, BBB leakage, and infiltration of neutrophils. The binding epitope of LCN2 mAb was mapped to the β3 and β4 strands, which are responsible for maintaining the integrity of LCN2 cup-shaped structure. These data indicate that LCN2 can be pharmacologically targeted using a specific mAb to reduce reperfusion injury after stroke.

Prediction of Motor Recovery in Patients with Basal Ganglia Hemorrhage Using Diffusion Tensor Imaging

Predicting prognosis in patients with basal ganglia hemorrhage is difficult. This study aimed to investigate the usefulness of diffusion tensor imaging in predicting motor outcome after basal ganglia hemorrhage. A total of 12 patients with putaminal hemorrhage were included in the study (aged 50 ± 12 years), 8 patients were male (aged 46 ± 11 years) and 4 were female (aged 59 ± 9 years). We performed diffusion tensor imaging and measured clinical outcome at baseline (pre) and 3 weeks (post1), 3 months (post2), and 6 months (post3) after the initial treatment. In the affected side of the brain, the mean fractional anisotropy (FA) value on pons was significantly higher in the good outcome group than that in the poor outcome group at pre (p = 0.004) and post3 (p = 0.025). Pearson correlation analysis showed that mean FA value at pre significantly correlated with the sum of the Brunnstrom motor recovery stage scores at post3 (R = 0.8, p = 0.002). Change in the FA ratio on diffusion tractography can predict motor recovery after hemorrhagic stroke.

Development of an Early Prediction Model for Subarachnoid Hemorrhage With Genetic and Signaling Pathway Analysis

Subarachnoid hemorrhage (SAH) is devastating disease with high mortality, high disability rate, and poor clinical prognosis. It has drawn great attentions in both basic and clinical medicine. Therefore, it is necessary to explore the therapeutic drugs and effective targets for early prediction of SAH. Firstly, we demonstrate that LCN2 can effectively intervene or treat SAH from the perspective of cell signaling pathway. Next, three potential genes that we explored have been validated by manually reviewed experimental evidences. Finally, we turn out that the SAH early ensemble learning predictive model performs better than the classical LR, SVM, and Naïve-Bayes models.

Apolipoprotein E Deficiency Aggravates Neuronal Injury by Enhancing Neuroinflammation via the JNK/c-Jun Pathway in the Early Phase of Experimental Subarachnoid Hemorrhage in Mice

Neuronal injury is the primary cause of poor outcome after subarachnoid hemorrhage (SAH). The apolipoprotein E (APOE) gene has been suggested to be involved in the prognosis of SAH patients. However, the role of APOE in neuronal injury after SAH has not been well studied. In this study, SAH was induced in APOE-knockout (APOE^−/−) and wild-type (WT) mice to investigate the impact of APOE deficiency on neuronal injury in the early phase of SAH. The experiments of this study were performed in murine SAH models in vivo and primary cultured microglia and neurons in vitro. The SAH model was induced by endovascular perforation in APOE^−/− and APOE WT mice. The mortality rate, weight loss, and neurological deficits were recorded within 72 h after SAH. The neuronal injury was assessed by detecting the neuronal apoptosis and axonal injury. The activation of microglia was assessed by immunofluorescent staining of Iba-1, and clodronate liposomes were used for inhibiting microglial activation. The expression of JNK/c-Jun was evaluated by immunofluorescent staining or western blotting. The expression of TNF-α, IL-1β, and IL-6 was evaluated by ELISA. Primary cultured microglia were treated with hemoglobin (Hb) in vitro for simulating the pathological process of SAH. SP600125, a JNK inhibitor, was used for evaluating the role of JNK in neuroinflammation. Nitrite production was detected for microglial activation, and flow cytometry was performed to detect apoptosis in vitro. The results suggested that SAH induced early neuronal injury and neurological deficits in mice. APOE deficiency resulted in more severe neurological deficits after SAH in mice. The neurological deficits were associated with exacerbation of neuronal injury, including neuronal apoptosis and axonal injury. Moreover, APOE deficiency enhanced microglial activation and related inflammatory injury on neurons. Inhibition of microglia attenuated neuronal injury in mice, whereas inhibition of JNK inhibited microglia-mediated inflammatory response in vitro. Taken together, JNK/c-Jun was involved in the enhancement of microglia-mediated inflammatory injury in APOE^−/− mice. APOE deficiency aggravates neuronal injury which may account for the poor neurological outcomes of APOE^−/− mice. The possible protective role of APOE against EBI via the modulation of inflammatory response indicates its potential treatment for SAH.

Microstructural White Matter Abnormalities and Cognitive Impairment After Aneurysmal Subarachnoid Hemorrhage

Background and Purpose- Aneurysmal subarachnoid hemorrhage (aSAH) may have detrimental effects on white matter microstructure, which may in turn explain the cognitive impairments that occur often after aSAH. We investigated (1) whether the white matter microstructure is altered in patients with aSAH compared with patients with an unruptured intracranial aneurysm and (2) whether these abnormalities are associated with cognitive impairment 3 months after ictus. Methods- Forty-nine patients with aSAH and 22 patients with an unruptured intracranial aneurysm underwent 3T brain magnetic resonance imaging, including a high-resolution diffusion tensor imaging sequence. Patients with aSAH were scanned 2 weeks and 6 months after ictus. Microstructural white matter alterations were quantified by the fractional anisotropy and mean diffusivity (MD). Cognition was evaluated 3 months after ictus. Results- Patients with aSAH had higher white matter MD 2 weeks after ictus than patients with an unruptured intracranial aneurysm (mean difference±SEM, 0.3±0.01×10^-3 mm2/s; P≤0.01), reflecting an abnormal microstructure. After 6 months, the MD had returned to the level of the unruptured intracranial aneurysm group. No between-group differences in fractional anisotropy were found (-0.01±0.01; P=0.16). Higher MD at 2 weeks was associated with cognitive impairment after 3 months (odds ratio per SD increase in MD, 2.6; 95% CI, 1.1-6.7). The association between MD and cognitive impairment was independent of conventional imaging markers of aSAH-related brain injury (ie, cerebral infarction, hydrocephalus, total amount of subarachnoid blood, total brain volume, or white matter hyperintensity severity). Conclusions- Patients with aSAH have temporary white matter abnormalities in the subacute phase that are associated with cognitive impairment at 3 months after ictus.

White matter T2 hyperintensities and blood-brain barrier disruption in the hyperacute stage of subarachnoid hemorrhage in male mice: The role of lipocalin-2

Aims

The current study examined whether white matter injury occurs in the hyperacute (4 hours) phase after subarachnoid hemorrhage (SAH) and the potential role of blood‐brain barrier (BBB) disruption and an acute phase protein, lipocalin 2 (LCN2), in that injury.

Methods

Subarachnoid hemorrhage was induced by endovascular perforation in adult mice. First, wild‐type (WT) mice underwent MRI 4 hours after SAH to detect white matter T2 hyperintensities. Second, changes in LCN2 expression and BBB disruption associated with the MRI findings were examined. Third, SAH‐induced white matter injury at 4 hours was compared in WT and LCN2 knockout (LCN2 KO) mice.

Results

At 4 hours, most animals had uni‐ or bilateral white matter T2 hyperintensities after SAH in WT mice that were associated with BBB disruption and LCN2 upregulation. However, some disruption and LCN2 upregulation was also found in mice with no T2‐hyperintensity lesion. In contrast, there were no white matter T2 hyperintensities in LCN2 KO mice after SAH. LCN2 deficiency also attenuated BBB disruption, myelin damage, and oligodendrocyte loss.

Conclusions

Subarachnoid hemorrhage causes very early BBB disruption and LCN2 expression in white matter that is associated with and may precede T2 hyperintensities. LCN2 deletion attenuates MRI changes and pathological changes in white matter after SAH.

The clinical significance of neutrophil gelatinase-associated lipocalin in ischemic stroke patients with acute kidney injury

BACKGROUND

Acute kidney injury (AKI) has become a common complication of acute ischemic stroke (AIS) and may have a significant impact on the clinical outcomes. Neutrophil gelatinase-associated lipocalin (NGAL), an acute phase protein, has been identified as a novel biomarker for acute kidney impairment. Here, we studied the early expression of NGAL in AIS patients with AKI and its clinic value in predicting and diagnosis of AKI after stroke.

METHODS

A total of 205 subjects diagnosed as first-ever AIS were recruited in this study, including 40 AIS with AKI and 165 AIS without AKI defined using the KDIGO guidelines. The serum and urine levels of NGAL were measured with ELISA. To evaluate the clinic value of NGAL, we also detected creatinine, urea nitrogen and cystatin C and microalbumin (mALB) in serum or urine using chemiluminescence or immunoturbidimetry method, and then the receiver operating characteristic (ROC) curve and correlation was analyzed. The severity of AIS patients was evaluated based on the National Institutes of Health Stroke Scale (NIHSS) score.

RESULTS

The serum and urine NGAL levels were significantly increased in AIS patients with AKI, and line regression analysis indicated that there was a positive correlation between the serum NGAL and creatinine level in AIS patients accompanied AKI. Additionally, the concentration of serum NGAL in AIS patients with AKI increased with the severity of stroke.

CONCLUSION

The increased serum NGAL may be used as a valuable complementary marker for the diagnoses and prediction of AKI in the early stage of AIS patients.

Lipocalin 2 contributes to brain iron dysregulation but does not affect cognition, plaque load, and glial activation in the J20 Alzheimer mouse model

BACKGROUND

Lipocalin 2 (Lcn2) is an acute-phase protein implicated in multiple neurodegenerative conditions. Interestingly, both neuroprotective and neurodegenerative effects have been described for Lcn2. Increased Lcn2 levels were found in human post-mortem Alzheimer (AD) brain tissue, and in vitro studies indicated that Lcn2 aggravates amyloid-β-induced toxicity. However, the role of Lcn2 has not been studied in an in vivo AD model. Therefore, in the current study, the effects of Lcn2 were studied in the J20 mouse model of AD.

METHODS

J20 mice and Lcn2-deficient J20 (J20xLcn2 KO) mice were compared at the behavioral and neuropathological level.

RESULTS

J20xLcn2 KO and J20 mice presented equally strong AD-like behavioral changes, cognitive impairment, plaque load, and glial activation. Interestingly, hippocampal iron accumulation was significantly decreased in J20xLcn2 KO mice as compared to J20 mice.

CONCLUSIONS

Lcn2 contributes to AD-like brain iron dysregulation, and future research should further explore the importance of Lcn2 in AD.

White Matter Injury in Early Brain Injury after Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a major cause of high morbidity, disability, and mortality in the field of neurovascular disease. Most previous SAH studies have focused on improving cerebral blood flow, reducing cerebral vasospasm, reducing neuronal calcium overload, and other treatments. While these studies showed exciting findings in basic science, therapeutic strategies based on the findings have not significantly improved neurological outcomes in patients with SAH. Currently, the only drug proven to effectively reduce the neurological defects of SAH patients is nimodipine. Current advances in imaging technologies in the field of stroke have confirmed that white matter injury (WMI) plays an important role in the prognosis of types of stroke, and suggests that WMI protection is essential for functional recovery and poststroke rehabilitation. However, WMI injury in relation to SAH has remained obscure until recently. An increasing number of studies suggest that the current limitations for SAH treatment are probably linked to overlooked WMI in previous studies that focused only on neurons and gray matter. In this review, we discuss the biology and functions of white matter in the normal brain, and discuss the potential pathophysiology and mechanisms of early brain injury after SAH. Our review demonstrates that WMI encompasses multiple substrates, and, therefore, more than one pharmacological approach is necessary to preserve WMI and prevent neurobehavioral impairment after SAH. Strategies targeting both neuronal injury and WMI may potentially provide a novel future for SAH knowledge and treatment.

Apolipoprotein E Exerts a Whole-Brain Protective Property by Promoting M1? Microglia Quiescence After Experimental Subarachnoid Hemorrhage in Mice

Subarachnoid hemorrhage (SAH) is a neurologically destructive stroke in which early brain injury (EBI) plays a pivotal role in poor patient outcomes. Expanding upon our previous work, multiple techniques and methods were used in this preclinical study to further elucidate the mechanisms underlying the beneficial effects of apolipoprotein E (ApoE) against EBI after SAH in murine apolipoprotein E gene-knockout mice (Apoe^-/-, KO) and wild-type mice (WT) on a C57BL/6J background. We reported that Apoe deficiency resulted in a more extensive EBI at 48 h after SAH in mice demonstrated by MRI scanning and immunohistochemical staining and exhibited more extensive white matter injury and neuronal apoptosis than WT mice. These changes were associated with an increase in NADPH oxidase 2 (NOX2) expression, an important regulator of both oxidative stress and inflammatory cytokines. Furthermore, immunohistochemical analysis revealed that NOX2 was abundantly expressed in activated M1 microglia. The JAK2/STAT3 signaling pathway, an upstream regulator of NOX2, was increased in WT mice and activated to an even greater extent in Apoe^-/- mice; whereas, the JAK2-specific inhibitor, AG490, reduced NOX2 expression, oxidative stress, and inflammation in Apoe-deficient mice. Also, apoE-mimetic peptide COG1410 suppressed the JAK2/STAT3 signaling pathway and significantly reduced M1 microglia activation with subsequent attenuation of oxidative stress and inflammation after SAH. Taken together, apoE and apoE-mimetic peptide have whole-brain protective effects that may reduce EBI after SAH via M1 microglial quiescence through the attenuation of the JAK2/STAT3/NOX2 signaling pathway axis.

Subarachnoid hemorrhage enhances the expression of TDP-43 in the brain of experimental rats and human subjects

The transactive response DNA-binding protein of 43 (TDP-43) may be involved in neurodegenerative disease and in the response to brain injury; however, alterations in the expression of TDP-43 following subarachnoid hemorrhage (SAH) require further investigation. The present study reported a notable elevation in the expression of TDP-43 within the cerebrospinal fluid (CSF) of patients with aneurysmal SAH and increased brain expression of TDP-43 in a rat model of SAH. The TDP-43 protein and a derivative migrated at 43 and 24 kDa, respectively, as observed via the immunoblotting of concentrated CSF samples obtained from patients with SAH; no signal was detected in the CSF from healthy controls. SAH in rats was induced by intravascular suture puncture. The expression levels of TDP-43 in rat cortical lysates following SAH were increased at 0.5 h, peaked at 48 h and remained significantly elevated at 72 h post-injury, compared with sham controls. TDP-43 immunolabeling indication localization within neurons, astrocytes and microglia in the experimental rats. Collectively, the findings of the present study indicated the early involvement of TDP-43 in the brain in response to SAH, and that expression levels of TDP-43 in the CSF may serve as a prognostic biomarker among patients with this condition.

Association of Brain CD163 Expression and Brain Injury/Hydrocephalus Development in a Rat Model of Subarachnoid Hemorrhage

Hemoglobin contributes to brain cell damage and death following subarachnoid hemorrhage (SAH). While CD163, a hemoglobin scavenger receptor, can mediate the clearance of extracellular hemoglobin it has not been well-studied in SAH. In the current study, a filament perforation SAH model was performed in male rats. T2-weighted and T2*-weighted scans were carried out using a 7.0-Tesla MR scanner 24 h after perforation. T2 lesions and hydrocephalus were determined on T2-weighted images. A grading system based on MRI was used to assess SAH severity. The effects of SAH on CD163 were determined by immunohistochemistry staining and Western blots. SAH led to a marked increase in CD163 levels in cortex, white matter and periventricular regions from days 1 to 7. CD163 stained cells were co-localized with neurons, microglia/macrophages, oligodendrocytes and cleaved caspase-3-positive cells, but not astrocytes. Furthermore, CD163 protein levels were increased in rats with higher SAH grades, the presence of T2 lesions on MRI, or hydrocephalus. In conclusion, CD163 expression is markedly upregulated after SAH. It is associated with more severe hemorrhage, as well as MRI T2 lesion and hydrocephalus development.

Taurine supplementation reduces neuroinflammation and protects against white matter injury after intracerebral hemorrhage in rats

Intracerebral hemorrhage (ICH) initiates a neuroinflammatory cascade that contributes to substantial neuronal damage and neurological deterioration. Taurine, an abundant amino acid in the nervous system, is reported to reduce inflammatory injury in various central nervous system diseases, but its role and the possible underlying mechanisms in the pathology following ICH remains unclear. This study was designed to evaluate the effect of taurine supplementation on neurological deficits, acute inflammatory responses and white matter injury in a model of ICH in rats. Adult male Sprague-Dawley (SD) rats subjected to collagenase-induced ICH injury were injected intravenously with different concentrations of taurine or vehicle 10 min after ICH and subsequently daily for 3 days. Behavioral studies, brain water content, and assessments of hemorrhagic lesion volume were quantified at day 1 and day 3 post-ICH. Neuronal damage, peri-hematomal inflammatory responses, and white matter injury were determined at 24 h, meanwhile, the content of hydrogen sulfide (H₂S) along with the expression of cystathionine-β-synthase (CBS) and P2X7 receptor (P2X7R) in peri-hematomal tissues was analyzed to investigate the possible anti-inflammatory mechanism of taurine. Treatment with a high dosage of taurine (50 mg/kg) significantly attenuated functional deficits and reduced brain edema and hemorrhagic lesion volume after ICH. Taurine administration also resulted in significant amelioration of neuronal damage and white matter injury. These changes were associated with marked reductions in neutrophil infiltration, glial activation, and expression levels of inflammatory mediators. Moreover, the anti-inflammatory effect of taurine was accompanied by increased H₂S content, enhanced CBS expression, and less expression of P2X7R. Our study demonstrated that the high dosage of taurine supplementation effectively mitigated the severity of pathological inflammation and white matter injury after ICH, and the mechanism may be related to upregulation of H₂S content and reduced P2X7R expression.

Peli1 Contributions in Microglial Activation, Neuroinflammatory Responses and Neurological Deficits Following Experimental Subarachnoid Hemorrhage

Early brain injury (EBI) following subarachnoid hemorrhage (SAH) is closely associated with neuroinflammation. Microglial activation is an early event that leads to neuroinflammation after SAH. Peli1 is an E3 ubiquitin ligase that mediates the induction of pro-inflammatory cytokines in microglia. Here we report Peli1 contributions in SAH mediated brain pathology. An SAH model was induced by endovascular perforation in adult male C57BL/6J mice. Peli1 was markedly induced in mice brains in a time-dependent manner and was predominantly expressed in CD16/32-positive microglia after SAH. Using genetic approaches, we demonstrated that decreased Peli1 significantly improved neurological deficits, attenuated brain edema, reduced over-expression of pro-inflammatory cytokine IL-6 and modified apoptotic/antiapoptotic biomarkers. In addition, Peli1 downregulation suppressed ERK and JNK phosphorylation levels via the downregulation of cIAP1/2 expression, subsequently reducing inducible nitric oxide synthase (iNOS) expression after SAH. Therefore, these findings demonstrate that Peli1 contributes to microglia-mediated neuroinflammation in EBI by mediating cIAP1/2 activation, thus promoting the activation of MyD88-dependent MAPK pathway after experimental SAH. Our findings also showed that Peli1 could promote the expression of M1 microglia polarization biomarker CD16/32 and iNOS after SAH. Targeting Peli1 exerts neuroprotective effects during EBI after SAH, thus could provide potential option for prevention-therapy in high-risk individuals.

MRI Characterization in the Acute Phase of Experimental Subarachnoid Hemorrhage

A number of mechanisms have been proposed for the early brain injury after subarachnoid hemorrhage (SAH). In this study, we investigated the radiographic characteristics and influence of gender on early brain injury after experimental SAH. SAH was induced by endovascular perforation in male and female rats. Magnetic resonance imaging was performed in a 7.0-T Varian MR scanner at 24 h after SAH. The occurrence and size of T2 lesions, ventricular dilation, and white matter injury (WMI) were determined on T2-weighted images (T2WI). The effects of SAH on heme oxygenase-1 and fibrin/fibrinogen were examined by Western blotting and immunohistochemistry. SAH severity was assessed using a MRI grading system, and neurological function was evaluated according to a modified Garcia's scoring system. T2 hyperintensity areas and enlarged ventricles were observed in T2WI coronal sections 24 h after SAH. The overall incidence of T2 lesions, WMI, and hydrocephalus was 54, 20, and 63%, respectively. Female rats had a higher incidence of T2 hyperintensity lesions and hydrocephalus, as well as larger T2 lesion volumes and higher average ventricular volume. SAH rats graded at 3-4 (our previously validated MRI grading scale) had larger T2 lesion volumes, more hydrocephalus, and worse neurological function compared with those graded at 0-2. In conclusion, T2 lesion, WMI, and hydrocephalus were the most prevalent MRI characteristics 24 h after experimental SAH. The T2 lesion area matched with fibrinogen/fibrin positive staining in the acute phase of SAH. SAH induced more severe brain injury in females compared to males in the acute phase of SAH.

Longitudinal profile of iron accumulation in good-grade subarachnoid hemorrhage

OBJECTIVE

MRI parameters of iron concentration (R2*, transverse relaxation rate), microstructural integrity (mean diffusivity and fractional anisotropy), as well as gray and white matter volumes were analyzed in patients with subarachnoid hemorrhage (SAH) and uncomplicated clinical course to detect the evolution of brain tissue changes 3 weeks and 12 months after ictus.

METHODS

MRI scans of 14 SAH patients (aneurysm of the anterior communicating artery, n = 5; no aneurysm n = 9) were compared with 14 age-matched healthy control subjects. Statistical parametric mapping (SPM) was applied to objectively identify focal changes of MRI parameters throughout the entire brain and to correlate image parameters with neuropsychological measures.

RESULTS

SPM localized significant bilateral increases in R2* signal within the white matter compartment of the temporal and parietal lobe and the cingulate gyrus (P < 0.001) which did not change significantly at 12 months. Significant gray matter volume reduction of the left insula and superior temporal gyrus (P < 0.001), as well as decreases in fractional anisotropy of the cingulate gyrus (P < 0.01) were also evident at 12 months. Significant correlations were found between fractional anisotropy signal alterations adjacent to the left middle and superior frontal gyrus and cognitive parameters of executive dysfunction (P < 0.001).

INTERPRETATION

The study indicates that iron is trapped predominantly throughout large portions of the white matter compartment in SAH patients at 12 months postbleeding. Increased disintegration of fiber tracts colocalizing with iron overload and correlating with lower executive function performance suggests that the white matter compartment is primarily susceptible toward long-term damage in patients with good clinical grade SAH.

Evaluation of a filament perforation model for mouse subarachnoid hemorrhage using 7.0 Tesla MRI

The filament perforation model (FPM) in mice is becoming increasingly popular to elucidate the molecular pathogenesis of neuronal injury after subarachnoid hemorrhage (SAH). We evaluated brain MRI in a mouse FPM. A total of 28 male C57Bl/6J mice were used. Seventeen animals underwent SAH induction by FPM. In two animals, transient middle cerebral artery occlusion (MCAo) was induced. Nine mice served as controls. T1-weighted images (T1WI), T2-weighted images (T2WI), T2(∗)-weighted images (T2*WI) and apparent diffusion coefficient maps were acquired at day 0 and at various time points following SAH (range: day 1-6 after SAH). Cerebral blood flow (CBF) analysis by (14)C-iodoamphetamine ((14)C-IMP) autoradiography was conducted in nine animals. Hemorrhage could be best confirmed using T2*WI. The degree of hemorrhage varied. All animals evaluated for ⩾2days were hydrocephalic, which was best seen on T2WI. T2-hyperintensity of the corpus callosum and external capsule, indicating white matter (WM) injury, was present after SAH. Ventricle and WM injury volumes were statistically significantly higher at day 3 compared to day 0. Territorial ischemia was detectable in MCAo but not in SAH. Markedly hypointense cortical veins were visible in the hyperacute and delayed phase after SAH on T2*WI. The (14)C-IMP analysis indicated decreased CBF after SAH. MRI is feasible and useful in evaluating pathophysiological changes over time. T2*WI seems best for SAH detection and grading. The chronological change of hydrocephalus and WM injury could be analyzed. T2*WI illustrated specific signal changes of cortical veins, possibly caused by increased oxygen extraction fraction due to decreased CBF.

Role of Lipocalin-2 in Thrombin-Induced Brain Injury

BACKGROUND AND PURPOSE

Thrombin and lipocalin-2 (LCN2) contribute to intracerebral hemorrhage-induced brain injury. Thrombin-induced brain damage is partially through a thrombin receptor, protease-activated receptor-1. LCN2 is involved in cellular iron transport and neuroinflammation. This study investigated the role of LCN2 in thrombin-induced brain injury.

METHODS

There were 3 parts in this study. First, male adult C57BL/6 wild-type or LCN2 knockout (LCN2 KO) mice had an intracaudate injection of thrombin (0.4 U) or saline. Second, LCN2 KO mice had an injection of thrombin (0.4 U) with recombinant mouse LCN2 protein (1 μg) into the right caudate. Third, protease-activated receptor-1 KO or wild-type mice had an intracaudate injection of thrombin or saline. All mice had T2-weighted magnetic resonance imaging and behavioral tests. Brains were used for histology, immunohistochemistry, and Western blotting.

RESULTS

Intracerebral thrombin injection caused LCN2 upregulation and brain injury in mice. Thrombin-induced brain swelling, blood-brain barrier disruption, neuronal death, and neurological deficits were markedly less in LCN2 KO mice (P<0.05) and were exacerbated by exogenous LCN2 coinjection. In addition, thrombin injection resulted in less LCN2 expression and brain injury in protease-activated receptor-1 KO mice.

CONCLUSIONS

Thrombin upregulates LCN2 through protease-activated receptor-1 activation and causes brain damage.

Deferoxamine Attenuated the Upregulation of Lipocalin-2 Induced by Traumatic Brain Injury in Rats

Intracranial hemorrhage is one of the most common consequences of traumatic brain injury (TBI). The release of iron from the breakdown of hemoglobin during intracerebral hematoma resolution results in an increase in perihematomal non-heme iron. Lipocalin 2 (LCN-2) is a siderophore-binding protein that mediates transferrin-independent iron transport. This study examined the effects of TBI (lateral fluid percussion) on LCN-2 expression in Sprague-Dawley rats. LCN-2 protein levels were markedly increased in the ipsilateral cortex and hippocampus after TBI, with the highest level at day 1. Most LCN-2-positive cells appeared to be astrocytes. Treatment with an iron chelator, deferoxamine (100 mg/kg, intramuscularly), attenuated the TBI-induced upregulation of LCN-2. In summary, TBI resulted in upregulation of LCN-2 and deferoxamine reduced TBI-induced LCN-2 increase, suggesting LCN-2 may have a role in iron-trafficking after TBI.

Lipocalin 2 and Blood-Brain Barrier Disruption in White Matter after Experimental Subarachnoid Hemorrhage

We reported previously that subarachnoid hemorrhage (SAH) causes acute white matter injury in mice. In this study, we investigated lipocalin 2 (LCN2) mediated blood-brain barrier (BBB) disruption in white matter, which may lead to subsequent injury. SAH was induced by endovascular perforation in wild-type (WT) and LCN2-knockout (LCN2(-/-)) mice. Sham mice underwent the same procedure without perforation. Mice underwent magnetic resonance imaging (MRI) 24 h after SAH to confirm the development of T2-hyperintensity in white matter. Western blotting and immunohistochemistry were performed to elucidate the mechanisms of LCN2-mediated white matter injury and BBB disruption. It was confirmed that LCN2 expression was significantly increased in white matter of WT mice after SAH by Western blotting (versus sham; p < 0.05). Immunohistochemistry showed that LCN2 receptor 24p3R was expressed in oligodendrocytes, astrocytes, endothelial cells, and pericytes in the white matter. In WT mice with SAH, albumin leakage along the white matter was prominently observed and was consistent with T2-hyperintensity on MRI. As with our previous report, LCN2(-/-) mice scarcely developed T2-hyperintensity on MRI or albumin leakage in white matter. Our results suggest that BBB leakage occurs in white matter after SAH and that LCN2 contributes to SAH-induced BBB disruption.

White Matter Injury After Subarachnoid Hemorrhage: Role of Blood-Brain Barrier Disruption and Matrix Metalloproteinase-9

BACKGROUND AND PURPOSE

We recently observed early white matter injury after experimental subarachnoid hemorrhage (SAH), but the underlying mechanisms are uncertain. This study investigated the potential role of matrix metalloproteinase (MMP)-9 in blood-brain barrier (BBB) disruption and consequent white matter injury.

METHODS

SAH was induced by endovascular perforation in adult male mice. The following 3 experiments were devised: (1) mice underwent magnetic resonance imaging at 24 h after SAH and were euthanized to determine BBB disruption and MMP-9 activation in white matter; (2) to investigate the role of MMP-9 in BBB disruption, lesion volumes on magnetic resonance imaging were compared between wild-type (WT) and MMP-9 knockout (MMP-9-/-) mice at 24 h after SAH; (3) WT and MMP-9-/- mice underwent magnetic resonance imaging at 1 and 8 days after SAH to detect time-dependent changes in brain injury. Brains were used to investigate myelin integrity in white matter.

RESULTS

In WT mice with SAH, white matter showed BBB disruption (albumin leakage) and T2 hyperintensity on magnetic resonance imaging. MMP-9 activity was elevated at 24 h after SAH. MMP-9-/- mice had less white matter T2 hyperintensity after SAH than WT mice. At 8 days after SAH, WT mice had decreased myelin integrity and MMP-9-/- mice developed less white matter injury.

CONCLUSIONS

SAH causes BBB disruption and consequent injury in white matter. MMP-9 plays an important role in those pathologies and could be a therapeutic target for SAH-induced white matter injury.

Cerebral vasospasm and corticospinal tract injury induced by a modified rat model of subarachnoid hemorrhage

OBJECTIVE

Double-hemorrhage rat models of subarachnoid hemorrhages (SAH) are most effective at simulating delayed cerebral vasospasms (CVS). The present study modified the models to minimize additional trauma and investigated injury of the corticospinal tract (CST) using diffusion tensor imaging (DTI).

METHODS

On the first day, 0.3ml of autologous arterial blood was collected by puncturing the caudal artery and injected into the cisterna magna via percutaneous puncture; and the operation was repeated on the third day. The diameters of the basilar artery (BA), middle cerebral artery (MCA), and anterior cerebral artery (ACA) were measured by magnetic resonance angiography on days 3, 5, 7, 9, and 11 post-SAH. Meanwhile, on days 3, 7, 11, 15 and 19, DTI was performed to evaluate the injury of the CST at cerebral peduncle (CP) and pyramidal tract (Py) by measuring fractional anisotropy (FA) value.

RESULTS

Blood was deposited mainly in the basal cistern. Diameters of BA, MCA, and ACA were significantly reduced. FA value of the CP was lower in the SAH group than in the control group; but FA value of Py wasn't different between the two groups.

CONCLUSION

This is a minimally-invasive and high performance rat model of SAH. Additionally, the occurrence of CVS is firm and the axons in CP are injured.

Closed head injury in an age-related Alzheimer mouse model leads to an altered neuroinflammatory response and persistent cognitive impairment

Epidemiological studies have associated increased risk of Alzheimer's disease (AD)-related clinical symptoms with a medical history of head injury. Currently, little is known about pathophysiology mechanisms linked to this association. Persistent neuroinflammation is one outcome observed in patients after a single head injury. Neuroinflammation is also present early in relevant brain regions during AD pathology progression. In addition, previous mechanistic studies in animal models link neuroinflammation as a contributor to neuropathology and cognitive impairment in traumatic brain injury (TBI) or AD-related models. Therefore, we explored the potential interplay of neuroinflammatory responses in TBI and AD by analysis of the temporal neuroinflammatory changes after TBI in an AD model, the APP/PS1 knock-in (KI) mouse. Discrete temporal aspects of astrocyte, cytokine, and chemokine responses in the injured KI mice were delayed compared with the injured wild-type mice, with a peak neuroinflammatory response in the injured KI mice occurring at 7 d after injury. The neuroinflammatory responses were more persistent in the injured KI mice, leading to a chronic neuroinflammation. At late time points after injury, KI mice exhibited a significant impairment in radial arm water maze performance compared with sham KI mice or injured wild-type mice. Intervention with a small-molecule experimental therapeutic (MW151) that selectively attenuates proinflammatory cytokine production yielded improved cognitive behavior outcomes, consistent with a link between neuroinflammatory responses and altered risk for AD-associated pathology changes with head injury.

Experimental subarachnoid haemorrhage results in multifocal axonal injury

The great majority of acute brain injury results from trauma or from disorders of the cerebrovasculature, i.e. ischaemic stroke or haemorrhage. These injuries are characterized by an initial insult that triggers a cascade of injurious cellular processes. The nature of these processes in spontaneous intracranial haemorrhage is poorly understood. Subarachnoid haemorrhage, a particularly deadly form of intracranial haemorrhage, shares key pathophysiological features with traumatic brain injury including exposure to a sudden pressure pulse. Here we provide evidence that axonal injury, a signature characteristic of traumatic brain injury, is also a prominent feature of experimental subarachnoid haemorrhage. Using histological markers of membrane disruption and cytoskeletal injury validated in analyses of traumatic brain injury, we show that axonal injury also occurs following subarachnoid haemorrhage in an animal model. Consistent with the higher prevalence of global as opposed to focal deficits after subarachnoid haemorrhage and traumatic brain injury in humans, axonal injury in this model is observed in a multifocal pattern not limited to the immediate vicinity of the ruptured artery. Ultrastructural analysis further reveals characteristic axonal membrane and cytoskeletal changes similar to those associated with traumatic axonal injury. Diffusion tensor imaging, a translational imaging technique previously validated in traumatic axonal injury, from these same specimens demonstrates decrements in anisotropy that correlate with histological axonal injury and functional outcomes. These radiological indicators identify a fibre orientation-dependent gradient of axonal injury consistent with a barotraumatic mechanism. Although traumatic and haemorrhagic acute brain injury are generally considered separately, these data suggest that a signature pathology of traumatic brain injury-axonal injury-is also a functionally significant feature of subarachnoid haemorrhage, raising the prospect of common diagnostic, prognostic, and therapeutic approaches to these conditions.