Dose-dependent benefits of iron-magnetic nanoparticle-coated human umbilical-derived mesenchymal stem cell treatment in rat intracranial hemorrhage model.

BACKGROUND: This study tested whether two doses of human umbilical-derived mesenchymal stem cells (hUC-MSCs) were superior to one dose for protecting the brain against intracranial hemorrhage (ICH) induced by intracranial injection collagenase and the capacity of ironic-magnetic-nanoparticles (Ir-MNa) coated hUC-MSCs tracked by MRI. METHODS AND RESULTS: Adult male SD rats (n = 40) were equally categorized into group 1 (sham-operated-control), group 2 (ICH), group 3 [ICH + Ir-MNa-coated hUC-MSCs/1.2 × 106 cells with an extracorporeal magnet over rat head (eCMag)/administered by left internal carotid artery (LICA) at post-3 h ICH], and group 4 (ICH + Ir-MNa-coated hUC-MSCs/1.2 × 106 cells with an eCMag/administered post-3 h ICH by LICA and 24 h by IV) and euthanized by day 28. The result showed that by day 28 after ICH induction the neurological function was severely impaired in group 2 than in group 1 that was significantly improved in group 3 and further significantly improved in group 4, whereas ICH volume exhibited an opposite pattern of neurological impairment among the groups (all p < 0.0001). Brain MRI demonstrated that by 4 h after ICH, Ir-MNa-coated hUC-MSCs were abundantly identified in ischemic area in group 4. The protein expressions of inflammatory (TNF-α/MMP-9/IL-1ß/iNOS)/oxidative-stress (NOX-1/NOX-2/oxidized protein)/apoptotic (caspase-3/mitochondrial Bax/PARP)/fibrotic (Smad3/TGF-ß)/mitochondrial-damaged (cytosolic-cytochrome-C) biomarkers displayed an identical pattern of neurological impairment among the groups (all p < 0.0001). The cellular expressions of inflammation (CD68+/CD11b+)/brain edema (AQP4+) biomarkers exhibited an identical pattern, whereas the neuronal-myelin (Doublecortin+/NeuN/nestin) biomarkers displayed an opposite pattern of neurological impairment (all p < 0.0001). CONCLUSION: Two doses of hUC-MSCs were superior to just one dose for protecting the brain against ICH-induced damage and Ir-MNa-coated hUC-MSCs offered a well adopted method for tracking hUC-MSCs homing into the brain.

Hemin-Induced Death Models Hemorrhagic Stroke and Is a Variant of Classical Neuronal Ferroptosis.

Ferroptosis is a caspase-independent, iron-dependent form of regulated necrosis extant in traumatic brain injury, Huntington disease, and hemorrhagic stroke. It can be activated by cystine deprivation leading to glutathione depletion, the insufficiency of the antioxidant glutathione peroxidase-4, and the hemolysis products hemoglobin and hemin. A cardinal feature of ferroptosis is extracellular signal-regulated kinase (ERK)1/2 activation culminating in its translocation to the nucleus. We have previously confirmed that the mitogen-activated protein (MAP) kinase kinase (MEK) inhibitor U0126 inhibits persistent ERK1/2 phosphorylation and ferroptosis. Here, we show that hemin exposure, a model of secondary injury in brain hemorrhage and ferroptosis, activated ERK1/2 in mouse neurons. Accordingly, MEK inhibitor U0126 protected against hemin-induced ferroptosis. Unexpectedly, U0126 prevented hemin-induced ferroptosis independent of its ability to inhibit ERK1/2 signaling. In contrast to classical ferroptosis in neurons or cancer cells, chemically diverse inhibitors of MEK did not block hemin-induced ferroptosis, nor did the forced expression of the ERK-selective MAP kinase phosphatase (MKP)3. We conclude that hemin or hemoglobin-induced ferroptosis, unlike glutathione depletion, is ERK1/2-independent. Together with recent studies, our findings suggest the existence of a novel subtype of neuronal ferroptosis relevant to bleeding in the brain that is 5-lipoxygenase-dependent, ERK-independent, and transcription-independent. Remarkably, our unbiased phosphoproteome analysis revealed dramatic differences in phosphorylation induced by two ferroptosis subtypes. As U0126 also reduced cell death and improved functional recovery after hemorrhagic stroke in male mice, our analysis also provides a template on which to build a search for U0126's effects in a variant of neuronal ferroptosis.SIGNIFICANCE STATEMENT Ferroptosis is an iron-dependent mechanism of regulated necrosis that has been linked to hemorrhagic stroke. Common features of ferroptotic death induced by diverse stimuli are the depletion of the antioxidant glutathione, production of lipoxygenase-dependent reactive lipids, sensitivity to iron chelation, and persistent activation of extracellular signal-regulated kinase (ERK) signaling. Unlike classical ferroptosis induced in neurons or cancer cells, here we show that ferroptosis induced by hemin is ERK-independent. Paradoxically, the canonical MAP kinase kinase (MEK) inhibitor U0126 blocks brain hemorrhage-induced death. Altogether, these data suggest that a variant of ferroptosis is unleashed in hemorrhagic stroke. We present the first, unbiased phosphoproteomic analysis of ferroptosis as a template on which to understand distinct paths to cell death that meet the definition of ferroptosis.

MED1/BDNF/TrkB pathway is involved in thalamic hemorrhage-induced pain and depression by regulating microglia.

Central post-stroke pain (CPSP) and associated depression remain poorly understood and pharmacological treatments are unsatisfactory. Recently, microglia activation was suggested to be involved in CPSP pathophysiology. The goal of this study was to investigate the effectiveness of a co-ultramicronized combination of N-palmitoylethanolamide and luteolin (PEALut) in a mouse model of thalamic hemorrhage (TH)-induced CPSP. TH was established through the collagenase-IV injection in thalamic ventral-posterolateral-nucleus. PEALut effects in CPSP-associated behaviors were evaluated during a 28-days observation period. We found that repeated administrations of co-ultra PEALut significantly reduced mechanical hypersensitivity after TH, as compared to vehicle, by reducing the early microglial activation in the perilesional site. Moreover, PEALut prevented the development of depressive-like behavior (21 days post-TH). These effects were associated with the restoration of synaptic plasticity in LEC-DG pathway and monoamines levels found impaired in TH mice. Hippocampal MED1 and TrkB expressions were significantly increased in TH compared to sham mice 21 days post-TH, whereas BDNF levels were decreased. PEALut restored MED1/TrkB/BDNF expression in mice. Remarkably, we found significant overexpression of MED1 in the human autoptic brain specimens after stroke, indicating a translational potential of our findings. These results pave the way for better-investigating depression in TH- induced CPSP, together with the involvement of MED1/TrkB/BDNF pathway, proposing PEALut as an adjuvant treatment.

Succinylation profiles of brain injury after intracerebral hemorrhage.

Protein posttranslational modifications (PTMs) regulate the biological processes of human diseases by genetic code expansion and cellular pathophysiology regulation; however, system-wide changes in PTM levels in the intracerebral hemorrhage (ICH) brain remain poorly understood. Succinylation refers to a major PTM during the regulation of multiple biological processes. In this study, according to the methods of quantitative succinyllysine proteomics based on high-resolution mass spectrometry, we investigated ICH-associated brain protein succinyllysine modifications and obtained 3,680 succinylated sites and quantified around 3,530 sites. Among them, 25 succinyllysine sites on 23 proteins were upregulated (hypersuccinylated), whereas 13 succinyllysine sites on 12 proteins were downregulated (hyposuccinylated) following ICH. The cell component enrichment analysis of these succinylproteins with significant changes showed that 58.3% of the hyposuccinylated proteins were observed in the mitochondria, while the hyper-succinylproteins located in mitochondria decreased in the percentage to about 35% in ICH brains with a concomitant increase in the percentage of cytoplasm to 30.4%. Further bioinformatic analysis showed that the succinylproteins were mostly mitochondria and synapse-related subcellular located and involved in many pathophysiological processes, like metabolism, synapse working, and ferroptosis. Moreover, the integrative analysis of our succinylproteomics data and previously published transcriptome data showed that the mRNAs matched by most differentially succinylated proteins were especially highly expressed in neurons, endothelial cells, and astrocytes. Our study uncovers some succinylation-affected processes and pathways in response to ICH brains and gives us novel insights into understanding pathophysiological processes of brain injury caused by ICH.

Androgen receptor contributes to microglial/macrophage activation in rats with intracranial hemorrhage by mediating the JMJD3/Botch/Notch1 axis.

Intracerebral hemorrhage (ICH) is a leading medical problem and has no effective treatment approach up until now. The transcription factor androgen receptor (AR) has been indicated in the cerebrovascular function recently. However, its participation in ICH remains unclear. The present study aims to expound the regulation of AR in microglia/macrophage phenotypes and the secondary brain injury in a rat model with ICH, and to discuss the involved pathway. Following the induction of ICH in rats, we found that ICH led to increased mNSS score, enhanced microglial activity, and promoted levels of inflammatory factors and apoptosis of brain cells. Using microarray analysis, AR was found to be significantly overexpressed in ICH rat brain tissues. AR repressed the transcription of Jumonji d3 (JMJD3, histone 3 demethylase). JMJD3 inhibited the methylation of Botch and promoted the activity of Notch1. JMJD3 hampered microglial activity and ameliorated secondary brain injury in rats, whereas upregulation of AR or downregulation of Botch reversed the protective effects of JMJD3. In conclusion, we found that AR promoted microglial activation and secondary brain injury via transcriptionally repressing JMJD3 and mediating the subsequent Botch/Notch1 pathway, which may provide novel insights into therapeutic options for the treatment of ICH.

Review of treatment and therapeutic targets in brain arteriovenous malformation.

Brain arteriovenous malformations (bAVM) are an important cause of intracranial hemorrhage (ICH), especially in younger patients. The pathogenesis of bAVM are largely unknown. Current understanding of bAVM etiology is based on studying genetic syndromes, animal models, and surgically resected specimens from patients. The identification of activating somatic mutations in the Kirsten rat sarcoma viral oncogene homologue (KRAS) gene and other mitogen-activated protein kinase (MAPK) pathway genes has opened up new avenues for bAVM study, leading to a paradigm shift to search for somatic, de novo mutations in sporadic bAVMs instead of focusing on inherited genetic mutations. Through the development of new models and understanding of pathways involved in maintaining normal vascular structure and functions, promising therapeutic targets have been identified and safety and efficacy studies are underway in animal models and in patients. The goal of this paper is to provide a thorough review or current diagnostic and treatment tools, known genes and key pathways involved in bAVM pathogenesis to summarize current treatment options and potential therapeutic targets uncovered by recent discoveries.

MiR-18a Aggravates Intracranial Hemorrhage by Regulating RUNX1-Occludin/ZO-1 Axis to Increase BBB Permeability.

OBJECTIVES: To study the molecular mechanisms of miR-18a aggravating intracranial hemorrhage (ICH) by increasing the blood-brain barrier (BBB) permeability. METHODS: Brain microvascular endothelial cells (BMVECs) and astrocytes were isolated, identified, and co-cultured to establish in vitro BBB model. BMVECs co-cultured with astrocytes were stimulated with or without thrombase and then transfected with miR-18a mimic and/or si-RUNX1. The trans-endothelial electric resistance (TEER) and FlNa flux were measured, respectively. The potential interaction between RUNX1 and miR-18a was also detected. Additionally, SD rats were injected with fresh autologous non-anticoagulant blood into the brain basal ganglia to establish ICH model. After administration with miR-18a, sh-miR-18a, miR-18a+RUNX1, sh-miR-18a+sh-RUNX1, respectively, BBB permeability was assessed. RESULTS: After overexpressing miR-18a, the expression levels of RUNX1, Occludin and ZO-1 were decreased, but the Evan's blue contents and brain water contents were significantly increased in ICH rats. Additionally, rat neurological function was impaired, accompanying with an increase of TEER and fluorescein sodium flux. MiR-18a was a direct target of RUNX1 and it could bind to the promoters of RUNX1 to inhibit the expression of Occuldin and ZO-1. Consistently, these phenomena could also be observed in the corresponding cell model. Conversely, miR-18a knockdown or RUNX1 overexpression just presented an improvement effect on ICH. CONCLUSIONS: MiR-18a plays a critical role during ICH because it targets to RUNX1 to inhibit the expression of tight junction proteins (Occludin and ZO-1) and then disrupt BBB permeability. MiR-18a might be a probable therapeutic target for ICH diseases.

Divergent Functions of Tissue-Resident and Blood-Derived Macrophages in the Hemorrhagic Brain.

Background and Purpose: Brain tissue-resident microglia and monocyte-derived macrophages (MDMs) are innate immune cells that contribute to the inflammatory response, phagocytosis of debris, and tissue repair after injury. We have previously reported that both microglia and MDMs transition from proinflammatory to reparative phenotypes over days after an intracerebral hemorrhage (ICH). However, their individual functional properties in the brain remain largely unknown. Here we characterized the differences between microglia and MDMs and further elucidate their distinct activation states and functional contributions to the pathophysiology and recovery after ICH. Methods: Autologous blood injection was used to model ICH in mice. Longitudinal transcriptomic analyses on isolated microglia and MDMs from mice at days 1, 3, 7 and 10 after ICH and naive controls identified core transcriptional programs that distinguish these cells. Imaging flow cytometry and in vivo phagocytosis assays were used to study phagocytic ability of microglia and MDMs. Antigen presentation was evaluated by ovalbumin-OTII CD4 T-cell proliferation assays with bone marrow­derived macrophages and primary microglia cultures. Results: MDMs had higher phagocytic activity and higher erythrophagocytosis in the ICH brain. Differential gene expression revealed distinct transcriptional signatures in the MDMs and microglia after ICH. MDMs had higher expression of MHCII (major histocompatibility complex class II) genes than microglia at all time points and greater ability to induce antigen-specific T-cell proliferation. Conclusions: The different ontogeny of microglia and MDMs lead to divergent responses and functions in the inflamed brain as these 2 cell populations differ in phagocytic functions and antigen-presenting capabilities in the brain after ICH.

Potential therapeutic effects of Nrf2 activators on intracranial hemorrhage.

Intracranial hemorrhage (ICH) is a devastating disease which induces high mortality and poor outcomes including severe neurological dysfunctions. ICH pathology is divided into two types: primary brain injury (PBI) and secondary brain injury (SBI). Although there are numerous preclinical studies documenting neuroprotective agents in experimental ICH models, no effective drugs have been developed for clinical use due to complicated ICH pathology. Oxidative and inflammatory stresses play central roles in the onset and progression of brain injury after ICH, especially SBI. Nrf2 is a crucial transcription factor in the anti-oxidative stress defense system. Under normal conditions, Nrf2 is tightly regulated by the Keap1. Under ICH pathological conditions, such as overproduction of reactive oxygen species (ROS), Nrf2 is translocated into the nucleus where it up-regulates the expression of several anti-oxidative phase II enzymes such as heme oxygenase-1 (HO-1). Recently, many reports have suggested the therapeutic potential of Nrf2 activators (including natural or synthesized compounds) for treating neurodegenerative diseases. Moreover, several Nrf2 activators attenuate ischemic stroke-induced brain injury in several animal models. This review summarizes the efficacy of several Nrf2 activators in ICH animal models. In the future, Nrf2 activators might be approved for the treatment of ICH patients.

Neuroinflammation in hemorrhagic transformation after tissue plasminogen activator thrombolysis: Potential mechanisms, targets, therapeutic drugs and biomarkers.

Hemorrhagic transformation (HT) is a common and serious complication following ischemic stroke, especially after tissue plasminogen activator (t-PA) thrombolysis, which is associated with increased mortality and disability. Due to the unknown mechanisms and targets of HT, there are no effective therapeutic drugs to decrease the incidence of HT. In recent years, many studies have found that neuroinflammation is closely related to the occurrence and development of HT after t-PA thrombolysis, including glial cell activation in the brain, peripheral inflammatory cell infiltration and the release of inflammatory factors, involving inflammation-related targets such as NF-κB, MAPK, HMGB1, TLR4 and NLRP3. Some drugs with anti-inflammatory activity have been shown to protect the BBB and reduce the risk of HT in preclinical experiments and clinical trials, including minocycline, fingolimod, tacrolimus, statins and some natural products. In addition, the changes in MMP-9, VAP-1, NLR, sICAM-1 and other inflammatory factors are closely related to the occurrence of HT, which may be potential biomarkers for the diagnosis and prognosis of HT. In this review, we summarize the potential inflammation-related mechanisms, targets, therapeutic drugs, and biomarkers associated with HT after t-PA thrombolysis and discuss the relationship between neuroinflammation and HT, which provides a reference for research on the mechanisms, prevention and treatment drugs, diagnosis and prognosis of HT.

The CTSC-RAB38 Fusion Transcript Is Associated With the Risk of Hemorrhage in Brain Arteriovenous Malformations.

Brain arteriovenous malformations (bAVMs) are congenital anomalies of blood vessels that cause intracranial hemorrhage in children and young adults. Chromosomal rearrangements and fusion genes play an important role in tumor pathogenesis, though the role of fusion genes in bAVM pathophysiological processes is unclear. The aim of this study was to identify fusion transcripts in bAVMs and analyze their effects. To identify fusion transcripts associated with bAVM, RNA sequencing was performed on 73 samples, including 66 bAVM and 7 normal cerebrovascular samples, followed by STAR-Fusion analysis. Reverse transcription polymerase chain reaction and Sanger sequencing were applied to verify fusion transcripts. Functional pathway analysis was performed to identify potential effects of different fusion types. A total of 21 fusion transcripts were detected. Cathepsin C (CTSC)-Ras-Related Protein Rab-38 (RAB38) was the most common fusion and was detected in 10 of 66 (15%) bAVM samples. In CTSC-RAB38 fusion-positive samples, CTSC and RAB38 expression was significantly increased and activated immune/inflammatory signaling. Clinically, CTSC-RAB38 fusion bAVM cases had a higher hemorrhage rate than non-CTSC-RAB38 bAVM cases (p < 0.05). Our study identified recurrent CTSC-RAB38 fusion transcripts in bAVMs, which may be associated with bAVM hemorrhage by promoting immune/inflammatory signaling.

Rh-relaxin-2 attenuates degranulation of mast cells by inhibiting NF-κB through PI3K-AKT/TNFAIP3 pathway in an experimental germinal matrix hemorrhage rat model.

BACKGROUND: Mast cells play an important role in early immune reactions in the brain by degranulation and the consequent inflammatory response. Our aim of the study is to investigate the effects of rh-relaxin-2 on mast cells and the underlying mechanisms in a germinal matrix hemorrhage (GMH) rat model. METHODS: One hundred seventy-three P7 rat pups were subjected to GMH by an intraparenchymal injection of bacterial collagenase. Clodronate liposome was administered through intracerebroventricular (i.c.v.) injections 24 h prior to GMH to inhibit microglia. Rh-relaxin-2 was administered intraperitoneally at 1 h and 13 h after GMH. Small interfering RNA of RXFP1 and PI3K inhibitor LY294002 were given by i.c.v. injection. Post-GMH evaluation included neurobehavioral function, Western blot analysis, immunofluorescence, Nissl staining, and toluidine blue staining. RESULTS: Our results demonstrated that endogenous relaxin-2 was downregulated and that RXFP1 level peaked on the first day after GMH. Administration of rh-relaxin-2 improved neurological functions, attenuated degranulation of mast cells and neuroinflammation, and ameliorated post-hemorrhagic hydrocephalus (PHH) after GMH. These effects were associated with RXFP1 activation, increased expression of PI3K, phosphorylated AKT and TNFAIP3, and decreased levels of phosphorylated NF-κB, tryptase, chymase, IL-6, and TNF-α. However, knockdown of RXFP1 and PI3K inhibition abolished the protective effects of rh-relaxin-2. CONCLUSIONS: Our findings showed that rh-relaxin-2 attenuated degranulation of mast cells and neuroinflammation, improved neurological outcomes, and ameliorated hydrocephalus after GMH through RXFP1/PI3K-AKT/TNFAIP3/NF-κB signaling pathway.

Characterization of tissue and functional deficits in a clinically translational pig model of acute ischemic stroke.

The acute stroke phase is a critical time frame used to evaluate stroke severity, therapeutic options, and prognosis while also serving as a major tool for the development of diagnostics. To further understand stroke pathophysiology and to enhance the development of treatments, our group developed a translational pig ischemic stroke model. In this study, the evolution of acute ischemic tissue damage, immune responses, and functional deficits were further characterized. Stroke was induced by middle cerebral artery occlusion in Landrace pigs. At 24 h post-stroke, magnetic resonance imaging revealed a decrease in ipsilateral diffusivity, an increase in hemispheric swelling resulting in notable midline shift, and intracerebral hemorrhage. Stroke negatively impacted white matter integrity with decreased fractional anisotropy values in the internal capsule. Like patients, pigs showed a reduction in circulating lymphocytes and a surge in neutrophils and band cells. Functional responses corresponded with structural changes through reductions in open field exploration and impairments in spatiotemporal gait parameters. Characterization of acute ischemic stroke in pigs provided important insights into tissue and functional-level assessments that could be used to identify potential biomarkers and improve preclinical testing of novel therapeutics.

Meningeal Lymphatic Pathway of Brain Clearing From the Blood After Haemorrhagic Injuries.

This seems to be the time to gain new knowledge about the meningeal lymphatic system and a deeper understanding of its anatomy and physiology. Although it is known that the meningeal lymphatics present in the layers of the brain, limited information is available about the role of this system in brain function. Here, for the first time we clearly demonstrate that the meningeal lymphatic pathway is involved in brain clearing from the blood after intracranial hemorrhage associated with hypoxia and forms a connective bridge between interstitial, cerebral spinal fluid and peripheral lymphatics. We also show that the development of methods to stimulate meningeal lymph flow after hemorrhagic evidence in the brain might be a neuroprotective strategy for effective recovery of the brain after a cerebrovascular catastrophe.

Crotalus atrox disintegrin reduces hemorrhagic transformation by attenuating matrix metalloproteinase-9 activity after middle cerebral artery occlusion in hyperglycemic male rats.

Hemorrhagic transformation after ischemic stroke is an independent predictor for poor outcome and is characterized by blood vessel rupture leading to brain edema. To date, no therapies for preventing hemorrhagic transformation exist. Disintegrins from the venom of Crotalus atrox have targets within the coagulation cascade, including receptors on platelets. We hypothesized that disintegrins from C. atrox venom can attenuate hemorrhagic transformation by preventing activation of matrix metalloproteinase after middle cerebral artery occlusion (MCAO) in hyperglycemic rats. We subjected 48 male Sprague-Dawley rats weighing 240-260 g to MCAO and hyperglycemia to induce hemorrhagic transformation of the infarction. At reperfusion, we administered either saline (vehicle), whole C. atrox venom (two doses were used), or fractionated C. atrox venom (HPLC Fraction 2). Rats were euthanized 24 hr post-ictus for measurement of infarction and hemoglobin volume. Reversed-phase HPLC was performed to fractionate the whole venom and peaks were combined to form Fraction 2, which contained the disintegrin Crotatroxin. Fraction 2 protected against hemorrhagic transformation after MCAO, and attenuated activation of matrix metalloproteinase-9. Administering matrix metalloproteinase antagonists prevented the protection by Fraction 2. The results of this study indicate that disintegrins found in C. atrox venom may have therapeutic potential for reducing hemorrhagic transformation after ischemic stroke. Moreover, the RP-HPLC fractions retained sufficient protein activity to suggest that gentler and less efficient orthogonal chromatographic methods may be unnecessary to isolate proteins and explore their function.

Posthemorrhagic hydrocephalus development after germinal matrix hemorrhage: Established mechanisms and proposed pathways.

In addition to being the leading cause of morbidity and mortality in premature infants, germinal matrix hemorrhage (GMH) is also the leading cause of acquired infantile hydrocephalus. The pathophysiology of posthemorrhagic hydrocephalus (PHH) development after GMH is complex and vaguely understood, although evidence suggests fibrosis and gliosis in the periventricular and subarachnoid spaces disrupts normal cerebrospinal fluid (CSF) dynamics. Theories explaining general hydrocephalus etiology have substantially evolved from the original bulk flow theory developed by Dr. Dandy over a century ago. Current clinical and experimental evidence supports a new hydrodynamic theory for hydrocephalus development involving redistribution of vascular pulsations and disruption of Starling forces in the brain microcirculation. In this review, we discuss CSF flow dynamics, history and development of theoretical hydrocephalus pathophysiology, and GMH epidemiology and etiology as it relates to PHH development. We highlight known mechanisms and propose new avenues that will further elucidate GMH pathophysiology, specifically related to hydrocephalus.

A comprehensive review of therapeutic targets that induce microglia/macrophage-mediated hematoma resolution after germinal matrix hemorrhage.

Currently, there is no effective treatment for germinal matrix hemorrhage and intraventricular hemorrhage (GMH-IVH), a common and often fatal stroke subtype in premature infants. Secondary brain injury after GMH-IVH is known to involve blood clots that contribute to inflammation and neurological deficits. Furthermore, the subsequent blood clots disrupt normal cerebrospinal fluid circulation and absorption after GMH-IVH, contributing to posthemorrhagic hydrocephalus (PHH). Clinically, GMH-IVH severity is graded on a I to IV scale: Grade I is confined to the germinal matrix, grade II includes intraventricular hemorrhage, grade III includes intraventricular hemorrhage with extension into dilated ventricles, and grade IV includes intraventricular hemorrhage with extension into dilated ventricles as well as parenchymal hemorrhaging. GMH-IVH hematoma volume is the best prognostic indicator, where patients with higher grades have worsened outcomes. Various preclinical studies have shown that rapid hematoma resolution quickly ameliorates inflammation and improves neurological outcomes. Current experimental evidence identifies alternatively activated microglia as playing a pivotal role in hematoma clearance. In this review, we discuss the pathophysiology of GMH-IVH in the development of PHH, microglia/macrophage's role in the neonatal CNS, and established/potential therapeutic targets that enhance M2 microglia/macrophage phagocytosis of blood clots after GMH-IVH.

Recent Advances in Basic Research for Brain Arteriovenous Malformation.

Arteriovenous malformations (AVMs) are abnormal connections of vessels that shunt blood directly from arteries into veins. Rupture of brain AVMs (bAVMs) can cause life-threatening intracranial bleeding. Even though the majority of bAVM cases are sporadic without a family history, some cases are familial. Most of the familial cases of bAVMs are associated with a genetic disorder called hereditary hemorrhagic telangiectasia (HHT). The mechanism of bAVM formation is not fully understood. The most important advances in bAVM basic science research is the identification of somatic mutations of genes in RAS-MAPK pathways. However, the mechanisms by which mutations of these genes lead to AVM formation are largely unknown. In this review, we summarized the latest advance in bAVM studies and discussed some pathways that play important roles in bAVM pathogenesis. We also discussed the therapeutic implications of these pathways.