Carbon monoxide controls microglial erythrophagocytosis by regulating CD36 surface expression to reduce the severity of hemorrhagic injury

Exploring medical gas therapy in hemorrhagic stroke treatment: A narrative review

Hemorrhagic stroke (HS) is a neurological disorder caused by the rupture of cerebral blood vessels, resulting in blood seeping into the brain parenchyma and causing varying degrees of neurological impairment, including intracerebral hemorrhage (ICH) and subarachnoid hemorrhage (SAH). Current treatment methods mainly include hematoma evacuation surgery and conservative treatment. However, these methods have limited efficacy in enhancing neurological function and prognosis. The current challenge in treating HS lies in inhibiting the occurrence and progression of secondary brain damage after bleeding, which is a key factor affecting the prognosis of HS patients. Studies have shown that medical gas therapy is gaining more attention and has demonstrated various levels of neuroprotective effects on central nervous system disorders, such as hyperbaric oxygen, hydrogen sulfide, nitric oxide, carbon monoxide, and other inhalable gas molecules. These medical gas molecules primarily improve brain tissue damage and neurological dysfunction by regulating inflammation, oxidative stress, apoptosis, and other processes. However, many of these medical gasses also possess neurotoxic properties. Therefore, the use of medical gases in HS deserves further exploration and research. In this review, we will elucidate the therapeutic effects and study the advances in medical gas molecules in HS.

CD22 exacerbates brain injury in subarachnoid hemorrhage by inhibiting microglial phagocytic function

INTRODUCTION

Subarachnoid hemorrhage (SAH) is a neurological emergency with a high mortality rate. The phagocytic and homeostatic functions of microglial cells play a crucial role after SAH. This study aims to investigate the mechanism of CD22-mediated abnormal microglial phagocytosis in brain injury caused by SAH.

MATERIALS AND METHODS

BV2 microglial cells were exposed to 10 µM oxyhemoglobin for 24 hours to establish an in vitro SAH model. After CD22 knockdown, cell viability was assessed using the cell counting kit-8. The microglial phagocytic function was evaluated using pHrodo Red E.coli BioParticles and fluorescence microscopy. The expression levels of Kruppel-like factor 4 (KLF4), miR-150-3p, and CD22 were analyzed by real-time quantitative reverse transcription polymerase chain reaction and Western blot analysis. The binding relationship of KLF4 to the miR-150-3p promoter and the binding relationship of miR-150-3p to the CD22 3'UTR sequence were analyzed. Overexpression of KLF4 and inhibition of miR-150-3p in SAH cells were conducted to validate the mechanism.

RESULTS

SAH inhibited the microglial phagocytic function. CD22 was overexpressed in the SAH cell model. CD22 inhibition increased the microglial phagocytic function. miR-150-3p targeted and inhibited CD22 expression. Overexpression of miR-150-3p resulted in downregulation of CD22 and increased phagocytic function in microglial cells. KLF4 bound to the miR-150-3p promoter and promoted miR-150-3p expression. Overexpression of KLF4 reversed the inhibitory effect of miR-150-3p inhibition on phagocytic function in SAH cell model.

CONCLUSION

KLF4 enhances the microglial phagocytic function in SAH by promoting miR-150-3p and inhibiting CD22.

Severity of Repetitive Mild Traumatic Brain Injury Depends on Microglial Heme Oxygenase-1 and Carbon Monoxide

Traumatic brain injury is one of the most common cerebral incidences worldwide. Repetitive mild traumatic brain injuries occurring, for example, in athletes or victims of abuse, can cause chronic neurodegeneration due to neuroinflammation, in which the crosstalk between reactive astrocytes and activated microglia is crucial for modulating neuronal damage. The inducible enzyme heme oxygenase-1 and its product carbon monoxide are known to be ascribed neuroprotective and anti-inflammatory properties. We caused repetitive mild traumatic brain injuries in wild-type mice compared to mice without microglial heme oxygenase-1 expression. Additionally, mice were treated daily with either air or carbon monoxide exogenously. In wild-type mice, we observed enhanced microglia activation and astrogliosis as well as vasodilation after repetitive trauma. In heme oxygenase-1 knockout mice, we observed enhanced activation of microglia and astrocytes at baseline pretrauma with a lack of an adequate inflammatory response to repetitive injury. However, the knockout led to enhanced NF-κB and IFNγ expression in the post-trauma period. Carbon monoxide exerted neuroprotection, as suggested by reduced wake-up times in mice and by beneficially altering inflammation post-traumatic brain injury. This study further underlines the crucial role of the heme oxygenase-1/carbon monoxide system in the modulation of neuronal damage and the associated neuroinflammatory response after repetitive traumatic brain injury.

Promoted coagulant activity and disrupted blood-brain barrier depending on phosphatidylserine externalization of red blood cells exposed to ZnO nanoparticles

Zinc oxide nanoparticles (ZnO-NPs) are nanomaterials mainly produced and used worldwide. They translocate to circulatory systems from various exposure routes. While blood and endothelial cells are persistently exposed to circulating ZnO-NPs, the potential risks posed by ZnO-NPs to the cardiovascular system are largely unknown. Our study identified the potential risk of thrombosis and disturbance of the blood-brain barrier (BBB) by coagulant activity on red blood cells (RBCs) caused by ZnO-NPs. ZnO-NPs promoted the externalization of phosphatidylserine and the generation of microvesicles through an imbalance of intracellular mechanisms regulating procoagulant activity in human RBCs. The coagulation cascade leading to thrombin generation was promoted in ZnO-NPs-treated human RBCs. Combined with human RBCs, ZnO-NPs caused coagulant activity on isolated rat RBCs and rat venous thrombosis models. We identified the erythrophagocytosis of RBCs into brain endothelial cells via increased PS exposure induced by ZnO-NPs. Excessive erythrophagocytosis contributes to disrupting the BBB function of endothelial cells. ZnO-NPs increased the procoagulant activity of RBCs, causing venous thrombosis. Excessive erythrophagocytosis through ZnO-NPs-treated RBCs resulted in the dysfunction of BBB. Our study will help elucidate the potential risk ZnO-NPs exert on the cardiovascular system.

Advancing stroke recovery: unlocking the potential of cellular dynamics in stroke recovery

Stroke stands as a predominant cause of mortality and morbidity worldwide, and there is a pressing need for effective therapies to improve outcomes and enhance the quality of life for stroke survivors. In this line, effective efferocytosis, the clearance of apoptotic cells, plays a crucial role in neuroprotection and immunoregulation. This process involves specialized phagocytes known as "professional phagocytes" and consists of four steps: "Find-Me," "Eat-Me," engulfment/digestion, and anti-inflammatory responses. Impaired efferocytosis can lead to secondary necrosis and inflammation, resulting in adverse outcomes following brain pathologies. Enhancing efferocytosis presents a potential avenue for improving post-stroke recovery. Several therapeutic targets have been identified, including osteopontin, cysteinyl leukotriene 2 receptor, the µ opioid receptor antagonist β-funaltrexamine, and PPARγ and RXR agonists. Ferroptosis, defined as iron-dependent cell death, is now emerging as a novel target to attenuate post-stroke tissue damage and neuronal loss. Additionally, several biomarkers, most importantly CD163, may serve as potential biomarkers and therapeutic targets for acute ischemic stroke, aiding in stroke diagnosis and prognosis. Non-pharmacological approaches involve physical rehabilitation, hypoxia, and hypothermia. Mitochondrial dysfunction is now recognized as a major contributor to the poor outcomes of brain stroke, and medications targeting mitochondria may exhibit beneficial effects. These strategies aim to polarize efferocytes toward an anti-inflammatory phenotype, limit the ingestion of distressed but viable neurons, and stimulate efferocytosis in the late phase of stroke to enhance post-stroke recovery. These findings highlight promising directions for future research and development of effective stroke recovery therapies.

Diffuse microglial responses and persistent EEG changes correlate with poor neurological outcome in a model of subarachnoid hemorrhage

The mechanism by which subarachnoid hemorrhage (SAH) leads to chronic neurologic deficits is unclear. One possibility is that blood activates microglia to drive inflammation that leads to synaptic loss and impaired brain function. Using the endovascular perforation model of SAH in rats, we investigated short-term effects on microglia together with long-term effects on EEG and neurologic function for up to 3 months. Within the first week, microglia were increased both at the site of injury and diffusely across the cortex (2.5-fold increase in SAH compared to controls, p = 0.012). Concomitantly, EEGs from SAH animals showed focal increases in slow wave activity and diffuse reduction in fast activity. When expressed as a fast-slow spectral ratio, there were significant interactions between group and time (p < 0.001) with less ipsilateral recovery over time. EEG changes were most pronounced during the first week and correlated with neurobehavioral impairment. In vitro, the blood product hemin was sufficient to increase microglia phagocytosis nearly six-fold (p = 0.032). Immunomodulatory treatment with fingolimod after SAH reduced microglia, improved neurological function, and increased survival. These findings, which parallel many of the EEG changes seen in patients, suggest that targeting neuroinflammation could reduce long-term neurologic dysfunction following SAH.

Incidence and Factors in Delayed Neurological Deficits after Subarachnoid Hemorrhage in Mice

Background

Delayed cerebral ischemia (DCI) is one of the most feared complications in aneurysmal subarachnoid hemorrhage (SAH). Animal models are crucial to studying the disease mechanisms and potential treatments. DCI in rodents was thought to not exist; herein we examine literature and our experience with DCI in rodents.

Methods

Daily behavioral performance was assessed every day from day 1 to up to 7 days post-SAH on mice from 5 different studies that used the endovascular perforation model. Performance was graded using an 8-test sensorimotor neuroscore previously described. The daily neuroscore was then used to identify the incidence and timing of delayed neurological deficits, a clinical surrogate for DCI. A total number of 298 mice (134 males, 164 females) were subjected to SAH. Fifty-one mice had histological staining done to identify infarct volume.

Results

The overall incidence of DND was 33.9%; 27.6% in males and 39.0% in females, but this difference was not statistically significant. The overall incidence of delayed death was 21.1%, and there was no significant difference for delayed mortality in females versus male mice. There is a non-statistically significant trend towards increased infarct volume in mice suffering DND.

Conclusions

Mice with endovascular puncture induced SAH develop DND at rates comparable to human patients. Future work needs to correlate the DND seen with decreased regional cerebral blood flow, another hallmark of DCI, but in spite of this need, researchers may use the murine models to test therapies for DCI after SAH.

Neuroprotection via Carbon Monoxide Depends on the Circadian Regulation of CD36-Mediated Microglial Erythrophagocytosis in Hemorrhagic Stroke

The molecular basis for circadian dependency in stroke due to subarachnoid hemorrhagic stroke (SAH) remains unclear. We reasoned that microglial erythrophagocytosis, crucial for SAH response, follows a circadian pattern involving carbon monoxide (CO) and CD36 surface expression. The microglial BV-2 cell line and primary microglia (PMG) under a clocked medium change were exposed to blood ± CO (250 ppm, 1 h) in vitro. Circadian dependency and the involvement of CD36 were analyzed in PMG isolated from control mice and CD36-/- mice and by RNA interference targeting Per-2. In vivo investigations, including phagocytosis, vasospasm, microglia activation and spatial memory, were conducted in an SAH model using control and CD36-/- mice at different zeitgeber times (ZT). In vitro, the surface expression of CD36 and its dependency on CO and phagocytosis occurred with changed circadian gene expression. CD36-/- PMG exhibited altered circadian gene expression, phagocytosis and impaired responsiveness to CO. In vivo, control mice with SAH demonstrated circadian dependency in microglia activation, erythrophagocytosis and CO-mediated protection at ZT2, in contrast to CD36-/- mice. Our study indicates that circadian rhythmicity modulates microglial activation and subsequent CD36-dependent phagocytosis. CO altered circadian-dependent neuroprotection and CD36 induction, determining the functional outcome in a hemorrhagic stroke model. This study emphasizes how circadian rhythmicity influences neuronal damage after neurovascular events.

Circadian dependency of microglial heme oxygenase-1 expression and inflammation determine neuronal injury in hemorrhagic stroke

BACKGROUND

The heme oxygenase-1 (HO-1) enzyme pathway is of crucial importance in the removal of toxic blood components and regulation of neuroinflammation following hemorrhagic stroke. Although a circadian pattern dependency in the incidence and severity of hemorrhagic stroke exists, it is unknown whether the activity of the HO-1 system in the context of hemorrhagic injury also exhibits circadian dependency. We hypothesized that the circadian regulation of microglial HO-1 would determine the extent of neuroinflammation and neuronal injury in a murine model of subarachnoid hemorrhage (SAH).

METHODS

In vitro expression patterns of HO-1 and circadian rhythm genes were analyzed in the microglial BV-2 cell line and primary microglia (PMG) using Western blot and qPCR. PMG isolated from Hmox1fl/fl and LyzM-Cre-Hmox1fl/fl mice were used to evaluate the role of microglial HO-1. We further investigated the in vivo relevance in a murine subarachnoid hemorrhage (SAH) model using Hmox1fl/fl and LyzM-Cre-Hmox1fl/fl mice with myeloid cell HO-1 deficiency, inducing SAH at different zeitgeber (ZT) times and analyzing the expression of HO-1 and the circadian control gene Period-2 (Per-2), respectively. Furthermore, we measured the inflammatory cytokine Monocyte Chemoattractant Protein-1 (MCP-1) in the cerebrospinal fluid of SAH patients in correlation with clinical outcome.

RESULTS

HO-1 baseline expression and response to CO with blood exposure depended on ZT. In vitro expression of circadian control genes was de-synchronized in LyzM-Cre-Hmox1fl/fl PMG and did not respond to exogenous CO exposure. We found that circadian rhythm plays a crucial role in brain damage after SAH. At ZT2, we observed less phagocytic function, more vasospasm and increased microglial activation. CO reduced mortality at ZT12 in HO-1 deficient mice and reduced the difference between ZT2 and ZT12 in the inflammatory response. Induction of MCP-1 in the CSF from SAH patients was time-dependent and correlated with the expression of circadian control genes, SAH severity, functional impairment and delirium.

CONCLUSIONS

Our data point towards a crucial role for the HO-1 enzyme system and circadian control in neuronal injury after a hemorrhagic stroke.

Regulators of phagocytosis as pharmacologic targets for stroke treatment

Stroke, including ischemic and hemorrhagic stroke, causes massive cell death in the brain, which is followed by secondary inflammatory injury initiated by disease-associated molecular patterns released from dead cells. Phagocytosis, a cellular process of engulfment and digestion of dead cells, promotes the resolution of inflammation and repair following stroke. However, professional or non-professional phagocytes also phagocytose stressed but viable cells in the brain or excessively phagocytose myelin sheaths or prune synapses, consequently exacerbating brain injury and impairing repair following stroke. Phagocytosis includes the smell, eating and digestion phases. Notably, efficient phagocytosis critically depends on phagocyte capacity to take up dead cells continually due to the limited number of phagocytes vs. dead cells after injury. Moreover, phenotypic polarization of phagocytes occurring after phagocytosis is also essential to the proresolving and prorepair properties of phagocytosis. Much has been learned about the molecular signals and regulatory mechanisms governing the sense and recognition of dead cells by phagocytes during the smell and eating phase following stroke. However, some key areas remain extremely understudied, including the mechanisms involved in digestion regulation, continual phagocytosis and phagocytosis-induced phenotypic switching following stroke. Here, we summarize new discoveries related to the molecular mechanisms and multifaceted effects of phagocytosis on brain injury and repair following stroke and highlight the knowledge gaps in poststroke phagocytosis. We suggest that advancing the understanding of poststroke phagocytosis will help identify more biological targets for stroke treatment.

Brucella induces heme oxygenase-1 expression to promote its infection

Brucellosis is a zoonotic and contagious infectious disease caused by Brucella spp, which causes substantial economic losses to animal husbandry and leads to severe public health problems. Brucella have evolved multiple strategies to escape host immunity and survive within host cells. Elucidating the immune evasion strategies during Brucella infection will facilitate the control of brucellosis. The host enzyme, heme oxygenase-1 (HO-1), is a multifunctional protein that functions during inflammatory diseases and microbial infections. However, how HO-1 functions during Brucella infection is rarely studied. In this study, we evaluated the role of HO-1 during Brucella infection. We found that Brucella infection induced HO-1 expression in macrophages. We further showed that HO-1 was regulated by PI3K, AMPK kinase, and nuclear erythroid-related factor 2 (Nrf2) in macrophages. Interestingly, knocking out HO-1 or inhibiting the activity of HO-1 significantly decreased Brucella intracellular growth. Inducing the expression of HO-1 by treatment with CoPP promoted Brucella intracellular growth. Mechanistic analyses indicated that the effect of HO-1 was not meditated by HO-1 metabolites, but by decreasing the production of reactive oxygen species (ROS), TNF-α, and IL-1β. Moreover, Brucella induced HO-1 expression in bone marrow-derived macrophages (BMDMs) and mice. When the expression of HO-1 was knocked down in BMDMs, the intracellular survival of Brucella was reduced. Furthermore, the induction of HO-1 by CoPP significantly increased bacterial loads in vivo. Thus, we demonstrated that Brucella induced HO-1 expression to promote its survival and growth in vitro and in vivo. This study also identified HO-1 as a novel innate immune evasion factor during Brucella infection.

Phagocytic microglia and macrophages in brain injury and repair

AIMS

Phagocytosis is the cellular digestion of extracellular particles, such as pathogens and dying cells, and is a key element in the evolution of central nervous system (CNS) disorders. Microglia and macrophages are the professional phagocytes of the CNS. By clearing toxic cellular debris and reshaping the extracellular matrix, microglia/macrophages help pilot the brain repair and functional recovery process. However, CNS resident and invading immune cells can also magnify tissue damage by igniting runaway inflammation and phagocytosing stressed-but viable-neurons.

DISCUSSION

Microglia/macrophages help mediate intercellular communication and react quickly to the "find-me" signals expressed by dead/dying neurons. The activated microglia/macrophages then migrate to the injury site to initiate the phagocytic process upon encountering "eat-me" signals on the surfaces of endangered cells. Thus, healthy cells attempt to avoid inappropriate engulfment by expressing "do not-eat-me" signals. Microglia/macrophages also have the capacity to phagocytose immune cells that invade the injured brain (e.g., neutrophils) and to regulate their pro-inflammatory properties. During brain recovery, microglia/macrophages engulf myelin debris, initiate synaptogenesis and neurogenesis, and sculpt a favorable extracellular matrix to support network rewiring, among other favorable roles. Here, we review the multilayered nature of phagocytotic microglia/macrophages, including the molecular and cellular mechanisms that govern microglia/macrophage-induced phagocytosis in acute brain injury, and discuss strategies that tap into the therapeutic potential of this engulfment process.

CONCLUSION

Identification of biological targets that can temper neuroinflammation after brain injury without hindering the essential phagocytic functions of microglia/macrophages will expedite better medical management of the stroke recovery stage.

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.

Therapeutic potential of carbon monoxide in hypertension-induced vascular smooth muscle cell damage revisited: from physiology and pharmacology

As a chronic and progressive disorder, hypertension remains to be a serious public health problem around the world. Among the different types of hypertension, pulmonary arterial hypertension (PAH) is a devastating disease associated with pulmonary arteriole remodeling, right ventricular failure and death. The contemporary management of systemic hypertension and PAH has substantially grown since more therapeutic targets and/or agents have been developed. Evolving treatment strategies targeting the vascular remodeling lead to improving outcomes in patients with hypertension, nevertheless, significant advancement opportunities for developing better antihypertensive drugs remain. Carbon monoxide (CO), an active endogenous gasotransmitter along with hydrogen sulfide (H₂S) and nitric oxide (NO), is primarily generated by heme oxygenase (HO). Cumulative evidence suggests that CO is considered as an important signaling molecule under both physiological and pathological conditions. Studies have shown that CO confers a number of biological and pharmacological properties, especially its involvement in the pathological process and treatment of hypertension-related vascular remodeling. This review will critically outline the roles of CO in hypertension-associated vascular remodeling and discuss the underlying mechanisms for the protective effects of CO against hypertension and vascular remodeling. In addition, we will propose the challenges and perspectives of CO in hypertensive vascular remodeling. It is expected that a comprehensive understanding of CO in the vasculature might be essential to translate CO to be a novel pharmacological agent for hypertension-induced vascular remodeling.

Erythrophagocytosis by Microglia/Macrophage in Intracerebral Hemorrhage: From Mechanisms to Translation

Intracerebral hemorrhage (ICH) is a devastating condition characterized by hematoma related mass effect. Microglia/macrophage (M φ) are rapidly recruited in order to remove the red blood cells through erythrophagocytosis. Efficient erythrophagocytosis can detoxify hemolytic products and facilitate neurological recovery after ICH. The underlying mechanisms include modulation of inflammatory response and oxidative stress, among others. It is a dynamic process mediated by a cascade of signal transduction, including “find-me” signals, “eat-me” signals and a set of phagocytotic receptors-ligand pairs that may be exploited as therapeutic targets. This review summarizes mechanistic signaling pathways of erythrophagocytosis and highlights the potential of harnessing M φ-mediated phagocytosis for ICH treatment.

Carbon Monoxide in Pancreatic Islet Transplantation: A New Therapeutic Alternative to Patients With Severe Type 1 Diabetes Mellitus

Pancreatic islet transplantation is a minimally invasive procedure to replace β-cells in a subset of patients with autoimmune type 1 diabetic mellitus, who are extremely sensitive to insulin and lack counter-regulatory measures, and thereby increasing their risk of neuroglycopenia and hypoglycemia unawareness. Thus, pancreatic islet transplantation restores normoglycemia and insulin independence, and prevents long-term surgical complications associated with whole-organ pancreas transplantation. Nonetheless, relative inefficiency of islet isolation and storage process as well as progressive loss of islet function after transplantation due to unvoidable islet inflammation and apoptosis, hinder a successful islet transplantation. Carbon monoxide (CO), a gas which was once feared for its toxicity and death at high concentrations, has recently emerged as a medical gas that seems to overcome the challenges in islet transplantation. This minireview discusses recent findings about CO in preclinical pancreatic islet transplantation and the underlying molecular mechanisms that ensure islet protection during isolation, islet culture, transplantation and post-transplant periods in type 1 diabetic transplant recipients. In addition, the review also discusses clinical translation of these promising experimental findings that serve to lay the foundation for CO in islet transplantation to replace the role of insulin therapy, and thus acting as a cure for type 1 diabetes mellitus and preventing long-term diabetic complications.

Role of perivascular and meningeal macrophages in outcome following experimental subarachnoid hemorrhage

The distribution and clearance of erythrocytes after subarachnoid hemorrhage (SAH) is poorly understood. We aimed to characterize the distribution of erythrocytes after SAH and the cells involved in their clearance. To visualize erythrocyte distribution, we injected fluorescently-labelled erythrocytes into the prechiasmatic cistern of mice. 10 minutes after injection, we found labelled erythrocytes in the subarachnoid space and ventricular system, and also in the perivascular spaces surrounding large penetrating arterioles. 2 and 5 days after SAH, fluorescence was confined within leptomeningeal and perivascular cells. We identified the perivascular cells as perivascular macrophages based on their morphology, location, Iba-1 immunoreactivity and preferential uptake of FITC-dextran. We subsequently depleted meningeal and perivascular macrophages 2 days before or 3 hours after SAH with clodronate liposomes. At day 5 after SAH, we found increased blood deposition in mice treated prior to SAH, but not those treated after. Treatment post-SAH improved neurological scoring, reduced neuronal cell death and perivascular inflammation, whereas pre-treatment only reduced perivascular inflammation. Our data indicate that after SAH, erythrocytes are distributed throughout the subarachnoid space extending into the perivascular spaces of parenchymal arterioles. Furthermore, meningeal and perivascular macrophages are involved in erythrocyte uptake and play an important role in outcome after SAH.

Involvement of Microglia in the Pathophysiology of Intracranial Aneurysms and Vascular Malformations-A Short Overview

Aneurysms and vascular malformations of the brain represent an important source of intracranial hemorrhage and subsequent mortality and morbidity. We are only beginning to discern the involvement of microglia, the resident immune cell of the central nervous system, in these pathologies and their outcomes. Recent evidence suggests that activated proinflammatory microglia are implicated in the expansion of brain injury following subarachnoid hemorrhage (SAH) in both the acute and chronic phases, being also a main actor in vasospasm, considerably the most severe complication of SAH. On the other hand, anti-inflammatory microglia may be involved in the resolution of cerebral injury and hemorrhage. These immune cells have also been observed in high numbers in brain arteriovenous malformations (bAVM) and cerebral cavernomas (CCM), although their roles in these lesions are currently incompletely ascertained. The following review aims to shed a light on the most significant findings related to microglia and their roles in intracranial aneurysms and vascular malformations, as well as possibly establish the course for future research.

Soluble Receptors Affecting Stroke Outcomes: Potential Biomarkers and Therapeutic Tools

Soluble receptors are widely understood to be freestanding moieties formed via cleavage from their membrane-bound counterparts. They have unique structures, are found among various receptor families, and have intriguing mechanisms of generation and release. Soluble receptors’ ability to exhibit pleiotropic action by receptor modulation or by exhibiting a dual role in cytoprotection and neuroinflammation is concentration dependent and has continually mystified researchers. Here, we have compiled findings from preclinical and clinical studies to provide insights into the role of soluble/decoy receptors, focusing on the soluble cluster of differentiation 36, the soluble cluster of differentiation 163, and soluble lipoprotein-related protein 1 (sCD36, sCD163, and sLRP1, respectively) and the functions they could likely serve in the management of stroke, as they would notably regulate the bioavailability of the hemoglobin and heme after red blood cell lysis. The key roles that these soluble receptors play in inflammation, oxidative stress, and the related pharmacotherapeutic potential in improving stroke outcomes are described. The precise pleiotropic physiological functions of soluble receptors remain unclear, and further scientific investigation/validation is required to establish their respective role in diagnosis and therapy.