C3a receptor antagonist attenuates brain injury after intracerebral hemorrhage

Targeting complement C3a receptor resolves mitochondrial hyperfusion and subretinal microglial activation in progranulin-deficient frontotemporal dementia

Mutations in progranulin ( GRN ) cause frontotemporal dementia ( GRN -FTD) due to deficiency of the pleiotropic protein progranulin. GRN -FTD exhibits diverse pathologies including lysosome dysfunction, lipofuscinosis, microgliosis, and neuroinflammation. Yet, how progranulin loss causes disease remains unresolved. Here, we report that non-invasive retinal imaging of GRN -FTD patients revealed deficits in photoreceptors and the retinal pigment epithelium (RPE) that correlate with cognitive decline. Likewise, Grn -/- mice exhibit early RPE dysfunction, microglial activation, and subsequent photoreceptor loss. Super-resolution live imaging and transcriptomic analyses identified RPE mitochondria as an early driver of retinal dysfunction. Loss of mitochondrial fission protein 1 (MTFP1) in Grn -/- RPE causes mitochondrial hyperfusion and bioenergetic defects, leading to NF-kB-mediated activation of complement C3a-C3a receptor signaling, which drives further mitochondrial hyperfusion and retinal inflammation. C3aR antagonism restores RPE mitochondrial integrity and limits subretinal microglial activation. Our study identifies a previously unrecognized mechanism by which progranulin modulates mitochondrial integrity and complement-mediated neuroinflammation.

Revisiting the role of the complement system in intracerebral hemorrhage and therapeutic prospects

Intracerebral hemorrhage (ICH) is a stroke subtype characterized by non-traumatic rupture of blood vessels in the brain, resulting in blood pooling in the brain parenchyma. Despite its lower incidence than ischemic stroke, ICH remains a significant contributor to stroke-related mortality, and most survivors experience poor outcomes that significantly impact their quality of life. ICH has been accompanied by various complex pathological damage, including mechanical damage of brain tissue, hematoma mass effect, and then leads to inflammatory response, thrombin activation, erythrocyte lysis, excitatory amino acid toxicity, complement activation, and other pathological changes. Accumulating evidence has demonstrated that activation of complement cascade occurs in the early stage of brain injury, and the excessive complement activation after ICH will affect the occurrence of secondary brain injury (SBI) through multiple complex pathological processes, aggravating brain edema, and pathological brain injury. Therefore, the review summarized the pathological mechanisms of brain injury after ICH, specifically the complement role in ICH, and its related pathological mechanisms, to comprehensively understand the specific mechanism of different complements at different stages after ICH. Furthermore, we systematically reviewed the current state of complement-targeted therapies for ICH, providing a reference and basis for future clinical transformation of complement-targeted therapy for ICH.

Factors ameliorate pro-inflammatory microglia polarization through inhibition of reactive astrocytes induced by 2-chloroethanol

Our previous studies have demonstrated that the crosstalk between astrocytes and microglia may trigger and amplify the neuroinflammatory response and, in turn, cause brain edema in 1,2-dichloroethane (1,2-DCE)-intoxicated mice. Moreover, findings from our in vitro studies showed that astrocytes are more sensitive to 2-chloroethanol (2-CE), an intermediate metabolite of 1,2-DCE, than microglia, and 2-CE-induced reactive astrocytes (RAs) can promote microglia polarization through releasing the pro-inflammatory mediators. Therefore, it is essential to explore therapeutic agents that may ameliorate microglia polarization through inhibition of 2-CE-induced RAs, which remains unclear till now. Results of this study revealed that exposure to 2-CE could induce RAs with pro-inflammatory effects, and fluorocitrate (FC), GIBH-130 (GI) and diacerein (Dia) pretreatment could all abolish the pro-inflammatory effects of 2-CE-induced RAs. FC and GI pretreatment might suppress 2-CE-induced RAs through inhibition of p38 mitogen-activated protein kinase (p38 MAPK)/activator protein-1 (AP-1) and nuclear factor-kappaB (NF-κB) signaling pathways, but Dia pretreatment might only inhibit p38 MAPK/NF-κB signaling pathway. FC, GI, and Dia pretreatment could all suppress the pro-inflammatory microglia polarization through inhibition of 2-CE-induced RAs. Meanwhile, GI and Dia pretreatment could also restored the anti-inflammatory microglia polarization via inhibition of 2-CE-induced RAs. However, FC pretreatment could not affect the anti-inflammatory polarization of microglia through inhibition of 2-CE-induced RAs. Taken together, findings from the present study demonstrated that FC, GI, and Dia might be the potential candidates with different characteristic for therapeutic use in 1,2-DCE poisoning.

Brain edema formation and therapy after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) accounts for about 10% of all strokes in the United States of America causing a high degree of disability and mortality. There is initial (primary) brain injury due to the mechanical disruption caused by the hematoma. There is then secondary injury, triggered by the initial injury but also the release of various clot-derived factors (e.g., thrombin and hemoglobin). ICH alters brain fluid homeostasis. Apart from the initial hematoma mass, ICH causes blood-brain barrier disruption and parenchymal cell swelling, which result in brain edema and intracranial hypertension affecting patient prognosis. Reducing brain edema is a critical part of post-ICH care. However, there are limited effective treatment methods for reducing perihematomal cerebral edema and intracranial pressure in ICH. This review discusses the mechanisms underlying perihematomal brain edema formation, the effects of sex and age, as well as how edema is resolved. It examines progress in pharmacotherapy, particularly focusing on drugs which have been or are currently being investigated in clinical trials.

The Critical Role of Erythrolysis and Microglia/Macrophages in Clot Resolution After Intracerebral Hemorrhage: A Review of the Mechanisms and Potential Therapeutic Targets

Intracerebral hemorrhage (ICH) is a common cerebrovascular disorder with high morbidity and mortality. Secondary brain injury after ICH, which is initiated by multiple hemolytic products during erythrolysis, has been identified as a critical factor accounting for the poor prognosis of ICH patients. Clot resolution and hematoma clearance occur immediately after ICH via erythrolysis and erythrophagocytosis. During this process, erythrolysis after ICH results in the release of hemoglobin and products of degradation along with rapid morphological changes in red blood cells (RBCs). Phagocytosis of deformed erythrocytes and products of degradation by microglia/macrophages accelerates hematoma clearance, which turns out to be neuroprotective. Thus, a better understanding of the mechanism of erythrolysis and the role of microglia/macrophages after ICH is urgently needed. In this review, the current research progresses on the underlying mechanism of erythrolysis and erythrophagocytosis, as well as several useful tools for the quantification of erythrolysis-induced brain injury, are summarized, providing potential intervention targets and possible treatment strategies for ICH patients.

Complement C3a Receptor (C3aR) Mediates Vascular Dysfunction, Hippocampal Pathology, and Cognitive Impairment in a Mouse Model of VCID

Vascular contributions to cognitive impairment and dementia (VCID) secondary to chronic mild-moderate cerebral ischemia underlie a significant percentage of cases of dementia. We previously reported that either genetic deficiency of the complement C3a receptor (C3aR) or its pharmacological inhibition protects against cerebral ischemia in rodents, while others have implicated C3aR in the pathogenesis seen in rodent transgenic models of Alzheimer's disease. In the present study, we evaluated the role of complement C3a-C3aR signaling in the onset and progression of VCID. We utilized the bilateral common carotid artery stenosis (BCAS) model to induce VCID in male C57BL/6 wild-type and C3aR-knockout (C3aR-/-) mice. Cerebral blood flow (CBF) changes, hippocampal atrophy (HA), white matter degeneration (WMD), and ventricular size were assessed at 4 months post-BCAS using laser speckle contrast analysis (LSCI) and magnetic resonance imaging (MRI). Cognitive function was evaluated using the Morris water maze (MWM), and novel object recognition (NOR), immunostaining, and western blot were performed to assess the effect of genetic C3aR deletion on post-VCID outcomes. BCAS resulted in decreased CBF and increased HA, WMD, and neurovascular inflammation in WT (C57BL/6) compared to C3aR-/- (C3aR-KO) mice. Moreover, C3aR-/- mice exhibited improved cognitive function on NOR and MWM relative to WT controls. We conclude that over-activation of the C3a/C3aR axis exacerbates neurovascular inflammation leading to poor VCID outcomes which are mitigated by C3aR deletion. Future studies are warranted to dissect the role of cell-specific C3aR in VCID.

Molecular, Pathological, Clinical, and Therapeutic Aspects of Perihematomal Edema in Different Stages of Intracerebral Hemorrhage

Acute intracerebral hemorrhage (ICH) is a devastating type of stroke worldwide. Neuronal destruction involved in the brain damage process caused by ICH includes a primary injury formed by the mass effect of the hematoma and a secondary injury induced by the degradation products of a blood clot. Additionally, factors in the coagulation cascade and complement activation process also contribute to secondary brain injury by promoting the disruption of the blood-brain barrier and neuronal cell degeneration by enhancing the inflammatory response, oxidative stress, etc. Although treatment options for direct damage are limited, various strategies have been proposed to treat secondary injury post-ICH. Perihematomal edema (PHE) is a potential surrogate marker for secondary injury and may contribute to poor outcomes after ICH. Therefore, it is essential to investigate the underlying pathological mechanism, evolution, and potential therapeutic strategies to treat PHE. Here, we review the pathophysiology and imaging characteristics of PHE at different stages after acute ICH. As illustrated in preclinical and clinical studies, we discussed the merits and limitations of varying PHE quantification protocols, including absolute PHE volume, relative PHE volume, and extension distance calculated with images and other techniques. Importantly, this review summarizes the factors that affect PHE by focusing on traditional variables, the cerebral venous drainage system, and the brain lymphatic drainage system. Finally, to facilitate translational research, we analyze why the relationship between PHE and the functional outcome of ICH is currently controversial. We also emphasize promising therapeutic approaches that modulate multiple targets to alleviate PHE and promote neurologic recovery after acute ICH.

Curcumin attenuates intracerebral hemorrhage-induced neuronal apoptosis and neuroinflammation by suppressing the JAK1/STAT1 pathway

To date, there is no effective treatment strategy for Intracerebral hemorrhage (ICH). Curcumin, a major active ingredient of curcuma longa L, possesses a potential anti-inflammatory activity in many types of disease. In the current study, the mechanism underlying curcumin attenuates ICH-induced neuronal apoptosis and neuroinflammation was explored. Herein, we studied curcumin decreased brain edema and improved neurological function by using brain edema measurement, assessment of neurological-deficient score, immunofluorescence, and western blotting analyses after ICH. The results showed that curcumin improved ICH-induced neuronal apoptosis and neuroinflammation. Functionally, the polarization of microglia was assessed by immunofluorescence and western blotting analyses after ICH in the absence or presence of curcumin. The results suggested that the M1-type microglia were activated after ICH, while the effect was blocked by curcumin treatment, suggesting that curcumin alleviates the neuroinflammation and apoptosis of neurons by suppressing the M1-type polarization of microglia. Mechanically, M1 polarization of microglia was regulated by JAK1/STAT1 and the activation of JAK1/STAT1 was blocked by curcumin. Meanwhile, the protective function of curcumin can be blocked by RO8191, an activator of JAK1. Taken together our study suggests that curcumin improved the ICH-induced brain injury through alleviating M1 polarization of microglia/macrophage and neuroinflammation via suppressing JAK1/STAT1 pathway.

Complement C3 activation in the ICU: Disease and therapy as Bonnie and Clyde

Patients in the intensive care unit (ICU) often straddle the divide between life and death. Understanding the complex underlying pathomechanisms relevant to such situations may help intensivists select broadly acting treatment options that can improve the outcome for these patients. As one of the most important defense mechanisms of the innate immune system, the complement system plays a crucial role in a diverse spectrum of diseases that can necessitate ICU admission. Among others, myocardial infarction, acute lung injury/acute respiratory distress syndrome (ARDS), organ failure, and sepsis are characterized by an inadequate complement response, which can potentially be addressed via promising intervention options. Often, ICU monitoring and existing treatment options rely on massive intervention strategies to maintain the function of vital organs, and these approaches can further contribute to an unbalanced complement response. Artificial surfaces of extracorporeal organ support devices, transfusion of blood products, and the application of anticoagulants can all trigger or amplify undesired complement activation. It is, therefore, worth pursuing the evaluation of complement inhibition strategies in the setting of ICU treatment. Recently, clinical studies in COVID-19-related ARDS have shown promising effects of central inhibition at the level of C3 and paved the way for prospective investigation of this approach. In this review, we highlight the fundamental and often neglected role of complement in the ICU, with a special focus on targeted complement inhibition. We will also consider complement substitution therapies to temporarily counteract a disease/treatment-related complement consumption.

Inflammation and the Link to Vascular Brain Health: Timing Is Brain

Inflammation and its myriad pathways are now recognized to play both causal and consequential roles in vascular brain health. From acting as a trigger for vascular brain injury, as evidenced by the coronavirus disease 2019 (COVID-19) pandemic, to steadily increasing the risk for chronic cerebrovascular disease, distinct inflammatory cascades play differential roles in varying states of cerebrovascular injury. New evidence is regularly emerging that characterizes the role of specific inflammatory pathways in these varying states including those at risk for stroke and chronic cerebrovascular injury as well as during the acute, subacute, and repair phases of stroke. Here, we aim to highlight recent basic science and clinical evidence for many distinct inflammatory cascades active in these varying states of cerebrovascular injury. The role of cerebrovascular infections, spotlighted by the severe acute respiratory syndrome coronavirus 2 pandemic, and its association with increased stroke risk is also reviewed. Rather than converging on a shared mechanism, these emerging studies implicate varied and distinct inflammatory processes in vascular brain injury and repair. Recognition of the phasic nature of inflammatory cascades on varying states of cerebrovascular disease is likely essential to the development and implementation of an anti-inflammatory strategy in the prevention, treatment, and repair of vascular brain injury. Although advances in revascularization have taught us that time is brain, targeting inflammation for the treatment of cerebrovascular disease will undoubtedly show us that timing is brain.

C3/C3aR inhibition alleviates GMH-IVH-induced hydrocephalus by preventing microglia-astrocyte interactions in neonatal rats

Activation of microglia and astrocytes following germinal matrix hemorrhage and intraventricular hemorrhage (GMH-IVH) plays a detrimental role in posthemorrhagic hydrocephalus (PHH). It is still unclear whether or how an interaction occurs between microglia and astrocytes in PHH. Here, we investigated the role of the C3/C3aR pathway in microglia and astrocyte interactions and whether C3/C3aR-targeted inhibition could alleviate PHH following GMH-IVH. A total of 152 Sprague-Dawley rats at postnatal day seven (P7) were enrolled in the study, and collagenase VII was used to induce GMH-IVH. Minocycline (45 mg/kg) was administered to inhibit microglial activation. Complement C3a peptide and C3aR antagonist (SB 290157, 10 mg/kg) were used to regulate the C3/C3aR pathway. As a result, the data demonstrated that periventricular C3aR⁺/Iba-1⁺ microglia and C3⁺/GFAP⁺ astrocytes were significantly increased in GMH-IVH pups at 28 days after surgery. Intranasal C3a peptide upregulated C3aR expression in microglia. Inhibition of microglia by minocycline decreased both C3⁺/GFAP⁺ astrocytes and the colocalization volume of Iba-1 and GFAP. In addition, intraperitoneally injected C3aRA alleviated the periventricular colocalization volume of microglia and astrocytes. Compared with vehicle-treated pups, the protein level of IL-1β, IL-6 and TNF-α in cerebral spinal fluid and brain tissue at 28 days following GMH-IVH were reduced in C3aRA-treated pups. Moreover, hydrocephalus was alleviated, and long-term cognitive ability were improved in the C3aRA-treated group. Our data presented simultaneous periventricular astrogliosis and microgliosis of pups following GMH-IVH and proved their potential interaction through the C3/C3aR pathway, indicating C3aRA as a potential pharmacological treatment of PHH in neonates.

Expression of a Crry/p65 is reduced in acute lung injury induced by extracellular histones

Acute lung injury (ALI) occurs in patients with severe sepsis and has a mortality rate of 40%–60%. Severe sepsis promotes the release of histones from dying cells, which can induce platelet aggregation, activate coagulation and cause endothelial cell (EC) death. We previously reported that the expression of membrane complement receptor type 1‐related gene Y (Crry)/p65, which plays a principal role in defence against abnormal activation of complement in the blood, is reduced in response to peritoneal mesothelial cell injury, and we hence hypothesized that a similar mechanism occurs in pulmonary ECs. In this study, we examined the role of Crry/p65 in histone‐mediated ALI using an experimental animal model. In ALI model mice, exposure to extracellular histones induces lung injury and results in a decrease in Crry/p65 expression. The levels of lactic acid dehydrogenase (LDH), a marker of cell damage, were significantly increased in the serum of ALI model compared with vehicle mice. The significant inverse correlation between the expression of Crry/p65 and LDH levels in plasma revealed an association between Crry/p65 expression and cell damage. The levels of complement component 3a (C3a) were also significantly increased in the serum of the ALI model compared with vehicle mice. Notably, a C3a receptor antagonist ameliorated lung injury induced by histones. We hypothesize that extracellular histones induce complement activation via down‐regulation of Crry/p65 and that C3a might serve as a therapeutic target for the treatment of ALI.

Identification of Candidate Blood mRNA Biomarkers in Intracerebral Hemorrhage Using Integrated Microarray and Weighted Gene Co-expression Network Analysis

Purpose

Intracerebral hemorrhage (ICH) is a serious public health hazard due to its high morbidity, disability, and mortality. Currently, the exact molecular mechanisms of ICH are unknown. We tried to identify the ICH-related candidate blood messenger RNA (mRNA) biomarkers by microarray analysis and weighted gene co-expression network analysis (WGCNA).

Materials and Methods

We collected the blood samples from patients with ICH (n = 4) and from vascular risk factor (VRF) controls (n = 4) and analyzed the mRNA expression profiles by competitive endogenous RNA (ceRNA) microarray. Differentially expressed genes (DEGs) were identified and then a weighted gene co-expression network was constructed. Modules with clinical significance were distinguished. Then, we downloaded two Gene Expression Omnibus (GEO) datasets (GSE24265 and GSE125512). Candidate mRNAs were identified by taking the intersection of the DEGs in our microarray, the interesting genes in the key module, and the DEGs in GSE24265. Functional analysis involving Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) and construction of a protein–protein interaction (PPI) network were conducted.

Results

A total of 340 DEGs in our microarray were identified between the ICH group and the control group. Among the eight gene modules established by WGCNA, the yellow module containing 191 genes was the most strongly associated with ICH. Four candidate mRNAs (C3AR1, PAWR, ARNTL2, and LDLRAD4) were identified. In the early stage of ICH (within 24 h), C3AR1, PAWR, and ARNTL2 were highly expressed in the perihematomal tissue, but with low expressions in peripheral blood; in the late stage (72 h after the first blood draw), an obvious upward trend of C3AR1 and PAWR in peripheral blood was seen. Functional analysis showed that candidate mRNAs were concerned with multiple pathways, such as the Wnt signaling pathway and calcium signaling pathway. They might affect the process of ICH through neuroinflammation, cell apoptosis, and pyroptosis.

Conclusion

We identified four candidate blood mRNAs (C3AR1, PAWR, ARNTL2, and LDLRAD4) related to ICH. They showed different expression patterns in peripheral blood and perihematomal tissues and changed with time. They might play important roles in ICH through neuroinflammation, cell apoptosis, and pyroptosis and might shed new light to novel biomarkers or therapeutic targets in ICH.

When the Blood Hits Your Brain: The Neurotoxicity of Extravasated Blood

Hemorrhage in the central nervous system (CNS), including intracerebral hemorrhage (ICH), intraventricular hemorrhage (IVH), and aneurysmal subarachnoid hemorrhage (aSAH), remains highly morbid. Trials of medical management for these conditions over recent decades have been largely unsuccessful in improving outcome and reducing mortality. Beyond its role in creating mass effect, the presence of extravasated blood in patients with CNS hemorrhage is generally overlooked. Since trials of surgical intervention to remove CNS hemorrhage have been generally unsuccessful, the potent neurotoxicity of blood is generally viewed as a basic scientific curiosity rather than a clinically meaningful factor. In this review, we evaluate the direct role of blood as a neurotoxin and its subsequent clinical relevance. We first describe the molecular mechanisms of blood neurotoxicity. We then evaluate the clinical literature that directly relates to the evacuation of CNS hemorrhage. We posit that the efficacy of clot removal is a critical factor in outcome following surgical intervention. Future interventions for CNS hemorrhage should be guided by the principle that blood is exquisitely toxic to the brain.

The role of complement in brain injury following intracerebral hemorrhage: A review

Intracerebral hemorrhage (ICH) is a significant cause of death and disability and current treatment is limited to supportive measures to reduce brain edema and secondary hematoma expansion. Current evidence suggests that the complement cascade is activated early after hemorrhage and contributes to brain edema/injury in multiple ways. The aim of this review is to summarize the most recent literature about the role of the complement cascade after ICH. Primary literature demonstrating complement mediated brain edema and neurologic injury through the membrane attack complex (MAC) as well as C3a and C5a are reviewed. Further, attenuation of brain edema and improved functional outcomes are demonstrated after inhibition of specific components of the complement cascade. Conversely, complement also plays a significant role in neurologic recovery after ICH and in other neurologic disorders. We conclude that the role of complement after ICH is complex. Understanding the role of complement after ICH is essential and may elucidate possible interventions to reduce brain edema and injury.

Toxoplasma Infection Induces Sustained Up-Regulation of Complement Factor B and C5a Receptor in the Mouse Brain via Microglial Activation: Implication for the Alternative Complement Pathway Activation and Anaphylatoxin Signaling in Cerebral Toxoplasmosis

Toxoplasma gondii is a neurotropic protozoan parasite, which is linked to neurological manifestations in immunocompromised individuals as well as severe neurodevelopmental sequelae in congenital toxoplasmosis. While the complement system is the first line of host defense that plays a significant role in the prevention of parasite dissemination, Toxoplasma artfully evades complement-mediated clearance via recruiting complement regulatory proteins to their surface. On the other hand, the details of Toxoplasma and the complement system interaction in the brain parenchyma remain elusive. In this study, infection-induced changes in the mRNA levels of complement components were analyzed by quantitative PCR using a murine Toxoplasma infection model in vivo and primary glial cells in vitro. In addition to the core components C3 and C1q, anaphylatoxin C3a and C5a receptors (C3aR and C5aR1), as well as alternative complement pathway components properdin (CFP) and factor B (CFB), were significantly upregulated 2 weeks after inoculation. Two months post-infection, CFB, C3, C3aR, and C5aR1 expression remained higher than in controls, while CFP upregulation was transient. Furthermore, Toxoplasma infection induced significant increase in CFP, CFB, C3, and C5aR1 in mixed glial culture, which was abrogated when microglial activation was inhibited by pre-treatment with minocycline. This study sheds new light on the roles for the complement system in the brain parenchyma during Toxoplasma infection, which may lead to the development of novel therapeutic approaches to Toxoplasma infection-induced neurological disorders.

The good, the bad, and the opportunities of the complement system in neurodegenerative disease

The complement cascade is a critical effector mechanism of the innate immune system that contributes to the rapid clearance of pathogens and dead or dying cells, as well as contributing to the extent and limit of the inflammatory immune response. In addition, some of the early components of this cascade have been clearly shown to play a beneficial role in synapse elimination during the development of the nervous system, although excessive complement-mediated synaptic pruning in the adult or injured brain may be detrimental in multiple neurogenerative disorders. While many of these later studies have been in mouse models, observations consistent with this notion have been reported in human postmortem examination of brain tissue. Increasing awareness of distinct roles of C1q, the initial recognition component of the classical complement pathway, that are independent of the rest of the complement cascade, as well as the relationship with other signaling pathways of inflammation (in the periphery as well as the central nervous system), highlights the need for a thorough understanding of these molecular entities and pathways to facilitate successful therapeutic design, including target identification, disease stage for treatment, and delivery in specific neurologic disorders. Here, we review the evidence for both beneficial and detrimental effects of complement components and activation products in multiple neurodegenerative disorders. Evidence for requisite co-factors for the diverse consequences are reviewed, as well as the recent studies that support the possibility of successful pharmacological approaches to suppress excessive and detrimental complement-mediated chronic inflammation, while preserving beneficial effects of complement components, to slow the progression of neurodegenerative disease.

Precision Medicine in Neurology: The Inspirational Paradigm of Complement Therapeutics

Precision medicine has emerged as a central element of healthcare science. Complement, a component of innate immunity known for centuries, has been implicated in the pathophysiology of numerous incurable neurological diseases, emerging as a potential therapeutic target and predictive biomarker. In parallel, the innovative application of the first complement inhibitor in clinical practice as an approved treatment of myasthenia gravis (MG) and neuromyelitis optica spectrum disorders (NMOSD) related with specific antibodies raised hope for the implementation of personalized therapies in detrimental neurological diseases. A thorough literature search was conducted through May 2020 at MEDLINE, EMBASE, Cochrane Library and ClinicalTrials.gov databases based on medical terms (MeSH)" complement system proteins" and "neurologic disease". Complement's role in pathophysiology, monitoring of disease activity and therapy has been investigated in MG, multiple sclerosis, NMOSD, spinal muscular atrophy, amyotrophic lateral sclerosis, Parkinson, Alzheimer, Huntington disease, Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, stroke, and epilepsy. Given the complexity of complement diagnostics and therapeutics, this state-of-the-art review aims to provide a brief description of the complement system for the neurologist, an overview of novel complement inhibitors and updates of complement studies in a wide range of neurological disorders.

Neuroinflammation Mediated by NLRP3 Inflammasome After Intracerebral Hemorrhage and Potential Therapeutic Targets

Intracerebral hemorrhage (ICH) is the most fatal subtype of stroke; there is still a lack of effective treatment. Microglia are a major component of the innate immune system, and they respond to acute brain injury by activating and forming classic M1-like (pro-inflammatory) or alternative M2-like (anti-inflammatory) phenotype. The existence of the polarization indicates that the role of microglia in disease's progression and recovery after ICH is still unclear, perhaps involving microglial secretion of anti-inflammatory or pro-inflammatory cytokines and chemokines. The NOD-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome is considered to be the main participant in neuroinflammation. Recent evidence has shown that NLRP3 inflammasome can be activated after ICH, resulting in inflammatory cascade reactions and aggravating brain injury. Furthermore, previous studies have reported that NLRP3 inflammasome is mainly present in microglia, so we speculate that its activation may be strongly associated with microglial polarization. Many scholars have investigated the role of brain injury caused by NLRP3 inflammasome after ICH, but the precise operating mechanisms remain uncertain. This review summarized the activation mechanism of NLRP3 inflammasome after ICH and the possible mechanism of NLRP3 inflammasome promoting neuroinflammation and aggravating nerve injury and discussed the relevant potential therapeutic targets.

Complement C3a induces axonal hypomyelination in the periventricular white matter through activation of WNT/β-catenin signal pathway in septic neonatal rats experimentally induced by lipopolysaccharide

Neuroinflammation is thought to play a pivotal role in the pathogenesis of periventricular white matter (PWM) damage (PWMD) induced by neonatal sepsis. Because the complement cascade is implicated in inflammatory response, this study was carried out to determine whether C3a is involved in PWMD, and, if so, whether it would induce axonal hypomyelination. Furthermore, we explored if C3a would act through its C3a receptor (C3aR) and thence inhibit maturation of oligodendrocyte precursor cells (OPCs) via the WNT/β-catenin signal pathway. Sprague Dawley (SD) rats aged 1 day were intraperitoneally injected with lipopolysaccharide (LPS) (1 mg/kg). C3a was upregulated in activated microglia and astrocytes in the PWM up to 7 days after LPS injection. Concomitantly, enhanced C3aR expression was observed in NG2⁺ oligodendrocytes (OLs). Myelin proteins including CNPase, PLP, MBP and MAG were significantly reduced in the PWM of 28-day septic rats. The number of PLP⁺ and MBP⁺ cells was markedly decreased. By electron microscopy, myelin sheath thickness was thinner and the average g-ratios were higher. This was coupled with an increase in number of NG2⁺ cells and decreased number of CC1⁺ cells. Olig1, Olig2 and SOX10 protein expression was significantly reduced in the PWM after LPS injection. Very strikingly, C3aRa administration for the first 7 days could reverse the above-mentioned pathological alterations in the PWM of septic rats. When incubated with C3a, expression of MBP, CNPase, PLP, MAG, Olig1, Olig2, SOX10 and CC1 in primary cultured OPCs was significantly downregulated as opposed to increased NG2. Moreover, WNT/β-catenin signaling pathway was found to be implicated in inhibition of OPCs maturation and differentiation induced by C3a in vitro. As a corollary, it is speculated that C3a in the PWM of septic rats is closely associated with the disorder of OPCs differentiation and maturation through WNT/β-catenin signaling pathway, which would contribute ultimately to axonal hypomyelination.

Bone marrow mesenchymal stem cells transplantation alleviates brain injury after intracerebral hemorrhage in mice through the Hippo signaling pathway

Intracerebral hemorrhage (ICH) is a common acute nervous system disease with high mortality and severe disability. Mesenchymal stem cells (MSCs) have been reported to promote neurogenesis and to alleviate side effects in areas of brain injury areas. The Hippo pathway regulates diverse cellular processes, including cell survival, proliferation, differentiation, and organ size. Here, we found that transplantation of bone marrow MSCs (BM-MSCs) into the brains of mice could alleviate ICH-mediated injury and protect astrocytes from apoptosis by regulating mammalian sterile 20-like kinase (MST)1 and Yes-associated protein (YAP). Knocking down of MST1 by si-RNA triggered YAP nuclear translocation. We further demonstrated that astrocytes undergo astroglial-mesenchymal phenotype switching and become capable of proliferating after BM-MSC transplantation via the Hippo signaling pathway. Together, our identification of the Hippo pathway in mediating the beneficial effects of BM-MSCs may provide a novel therapeutic target in the treatment and management of ICH.

C3a receptor antagonist therapy is protective with or without thrombolysis in murine thromboembolic stroke

BACKGROUND AND PURPOSE

Intravenous thrombolysis (IVT) after stroke enhances C3a generation, which may abrogate the benefits of reperfusion. The C3aR antagonist SB290157 is neuroprotective following transient but not permanent middle cerebral artery occlusion (MCAo). SB290157 remains untested in thromboembolic (TE) models, which better approximate human stroke and also facilitate testing in combination with IVT. We hypothesized SB290157 would confer neuroprotection in TE stroke with and without "late" IVT.

EXPERIMENTAL APPROACH

We used two different models of TE stroke to examine the efficacy of SB290157 alone and in combination with late IVT. We evaluated the benefit of SB290157 in attenuating post-ischaemic behavioural deficits, infarction, brain oedema and haemorrhage.

KEY RESULTS

Plasma C3a was elevated 6 hr after TE stroke alongside increased cerebrovascular C3aR expression, which was sustained to 4 weeks. Increased C3aR expression also was visualized in human ischaemic brain. In a photothrombotic (PT) stroke model, which exhibits rapid spontaneous reperfusion, SB290157 given at 1 hr post-PT significantly improved neurofunction and reduced infarction at 48 hr. In an embolic (eMCAo) model, SB290157 administered at 2 hr improved histological and functional outcomes. Conversely, late IVT administered 4.5 hr post-eMCAo was ineffective likely due to increased haemorrhage and brain oedema. However, SB290157 administered prior to late IVT ameliorated haemorrhage and oedema and improved outcomes.

CONCLUSIONS AND IMPLICATIONS

We conclude that SB290157 is safe and effective with and without late IVT following TE stroke. Therefore, C3a receptor antagonist therapy represents a promising candidate for clinical translation in stroke, particularly as an adjuvant to IVT.

Surgically-induced brain injury: where are we now?

Neurosurgical procedures cause inevitable brain damage from the multitude of surgical manipulations utilized. Incisions, retraction, thermal damage from electrocautery, and intraoperative hemorrhage cause immediate and long-term brain injuries that are directly linked to neurosurgical operations, and these types of injuries, collectively, have been termed surgical brain injury (SBI). For the past decade, a model developed to study the underlying brain pathologies resulting from SBI has provided insight on cellular mechanisms and potential therapeutic targets. This model, as seen in a rat, mouse, and rabbit, mimics a neurosurgical operation and causes commonly encountered post-operative complications such as brain edema, neuroinflammation, and hemorrhage. In this review, we elaborate on SBI and its clinical impact, the SBI animal models and their clinical relevance, the importance of applying therapeutics before neurosurgical procedures (i.e., preconditioning), and the new direction of applying venom-derived proteins to attenuate SBI.

Coupling Between Interleukin-1R1 and Necrosome Complex Involves in Hemin-Induced Neuronal Necroptosis After Intracranial Hemorrhage

Background and Purpose- Accumulated evidence suggests that hemin-a breakdown product of hemoglobin-plays a pivotal role in the inflammatory injuries that result after hemorrhagic stroke through the Toll Like Receptor 2-Toll Like Receptor 4 signal pathway. However, the mechanism of how hemin triggers neuronal necroptosis directly after intracranial hemorrhage (ICH) is still an area of active research. As animal model and preclinical studies have shown, the recombinant interleukin-1 receptor antagonist (IL-1RA) improves clinical outcomes after stroke. As such, we have chosen to investigate the mechanism of how IL-1RA exerts protective effect in hemin-induced neuronal necroptosis after ICH. Methods- Our ICH model was induced by hemin injection in C57BL/6 mice and IL-1R1^-/- mice. In addition, we used primary cultured neurons to assess hemin-induced cell death. Co-immunoprecipitation, immunoblot, immunofluorescent staining, neurological deficit scores, and brain water content were used to study the mechanisms of IL-1R1 modulation in neuronal necroptosis both in vitro and in vivo. Results- Free hemin could mediate neuronal necroptosis directly by assembling necrosome complex and then to trigger cell death. This phenomenon was driven by IL-1R1 as IL-1R1 can form a complex with necrosome. After treatment with IL-1RA, both the expression and translocation of the necrosome decreased while disruption of the interaction between IL-1R1 and RIP1/RIP3 (receptor interacting protein 1/3) increased neuron survival. In addition, the IL-1R1-deficient mice demonstrated lower levels of necrosome components, including RIP1, RIP3, and MLKL (mixed lineage kinase domain-like protein), compared with control groups after hemin treatment. In addition, the neurological deficit scores, brain water content, and inflammatory response were all also reduced in the IL-1R1-deficient mice. Conclusions- Functional inhibition of the interaction between IL-1R1 and the necrosome complex improves neuron survival and promotes the recovery of neurological function in experimental ICH. Targeting IL-1R1/RIP1/RIP3 assembly could be a promising therapeutic strategy for patients with ICH.

Therapeutic Modulation of the Complement Cascade in Stroke

Stroke is a leading cause of death and disability worldwide and an increasing number of ischemic stroke patients are undergoing pharmacological and mechanical reperfusion. Both human and experimental models of reperfused ischemic stroke have implicated the complement cascade in secondary tissue injury. Most data point to the lectin and alternative pathways as key to activation, and C3a and C5a binding of their receptors as critical effectors of injury. During periods of thrombolysis use to treat stroke, acute experimental complement cascade blockade has been found to rescue tissue and improves functional outcome. Blockade of the complement cascade during the period of tissue reorganization, repair, and recovery is by contrast not helpful and in fact is likely to be deleterious with emerging data suggesting downstream upregulation of the cascade might even facilitate recovery. Successful clinical translation will require the right clinical setting and pharmacologic strategies that are capable of targeting the key effectors early while not inhibiting delayed repair. Early reports in a variety of disease states suggest that such pharmacologic strategies appear to have a favorable risk profile and offer substantial hope for patients.

C3a Receptor Inhibition Protects Brain Endothelial Cells Against Oxygen-glucose Deprivation/Reperfusion

The complement cascade is a central component of innate immunity which plays a critical role in brain inflammation. Complement C3a receptor (C3aR) is a key mediator of post-ischemic cerebral injury, and pharmacological antagonism of the C3a receptor is neuroprotective in stroke. Cerebral ischemia injures brain endothelial cells, causing blood brain barrier (BBB) disruption which further exacerbates ischemic neuronal injury. In this study, we used an in vitro model of ischemia (oxygen glucose deprivation; OGD) to investigate the protective effect of a C3aR antagonist (C3aRA, SB290157) on brain endothelial cells (bEnd.3). Following 24 hours of reperfusion, OGD-induced cell death was assessed by TUNEL and Caspase-3 staining. Western blot and immunocytochemistry were utilized to demonstrate that OGD upregulates inflammatory, oxidative stress and antioxidant markers (ICAM-1, Cox-2, Nox-2 and MnSOD) in endothelial cells and that C3aRA treatment significantly attenuate these markers. We also found that C3aRA administration restored the expression level of the tight junction protein occludin in endothelial cells following OGD. Interestingly, OGD/reperfusion injury increased the phosphorylation of ERK1/2 and C3aR inhibition significantly reduced the activation of ERK suggesting that endothelial C3aR may act via ERK signaling. Furthermore, exogenous C3a administration stimulates these same inflammatory mechanisms both with and without OGD, and C3aRA suppresses these C3a-mediated responses, supporting an antagonist role for C3aRA. Based on these results, we conclude that C3aRA administration attenuates inflammation, oxidative stress, ERK activation, and protects brain endothelial cells following experimental brain ischemia.

Significance of Complement System in Ischemic Stroke: A Comprehensive Review

The complement system is an essential part of innate immunity, typically conferring protection via eliminating pathogens and accumulating debris. However, the defensive function of the complement system can exacerbate immune, inflammatory, and degenerative responses in various pathological conditions. Cumulative evidence indicates that the complement system plays a critical role in the pathogenesis of ischemic brain injury, as the depletion of certain complement components or the inhibition of complement activation could reduce ischemic brain injury. Although multiple candidates modulating or inhibiting complement activation show massive potential for the treatment of ischemic stroke, the clinical availability of complement inhibitors remains limited. The complement system is also involved in neural plasticity and neurogenesis during cerebral ischemia. Thus, unexpected side effects could be induced if the systemic complement system is inhibited. In this review, we highlighted the recent concepts and discoveries of the roles of different kinds of complement components, such as C3a, C5a, and their receptors, in both normal brain physiology and the pathophysiology of brain ischemia. In addition, we comprehensively reviewed the current development of complement-targeted therapy for ischemic stroke and discussed the challenges of bringing these therapies into the clinic. The design of future experiments was also discussed to better characterize the role of complement in both tissue injury and recovery after cerebral ischemia. More studies are needed to elucidate the molecular and cellular mechanisms of how complement components exert their functions in different stages of ischemic stroke to optimize the intervention of targeting the complement system.

Astrocyte activation and reactive gliosis-A new target in stroke?

Stroke is an acute insult to the central nervous system (CNS) that triggers a sequence of responses in the acute, subacute as well as later stages, with prominent involvement of astrocytes. Astrocyte activation and reactive gliosis in the acute stage of stroke limit the tissue damage and contribute to the restoration of homeostasis. Astrocytes also control many aspects of neural plasticity that is the basis for functional recovery. Here, we discuss the concept of intermediate filaments (nanofilaments) and the complement system as two handles on the astrocyte responses to injury that both present attractive opportunities for novel treatment strategies modulating astrocyte functions and reactive gliosis.

Blood-brain barrier (BBB) and the complement landscape

The brain is an immune privileged organ, uniquely placed in the body. Two systems involved in maintaining brain homeostasis and in protecting the brain are the blood-brain barrier (BBB) and the complement system. The BBB is present in the vasculature of the brain and is the dynamic interface between brain and body that regulates what enters and leaves the brain, thereby maintaining the brain microenvironment optimal for brain function. The complement system is ubiquitous, being present systemically and in the brain, both membrane bound and in circulation. It is an important arm of the body's defense that helps maintain homeostasis by eliminating debris and damaged cells, participating in destroying pathogens, promoting inflammation and conveying 'danger signals'. Recent studies reveal that the complement system plays an important role in normal brain development. However, when the complement system is overwhelmed, complement activation could contribute to loss of BBB integrity resulting in brain pathology. Studies support an association between complement proteins and BBB dysfunction, with the mechanisms being slowly unraveled. This review will provide an overview of both these systems, how they intersect and interact with each other.

New concepts on the therapeutic control of complement anaphylatoxin receptors

The complement system is a pivotal driver of innate immunity, coordinating the host response to protect against pathogens. At the heart of the complement response lie the active fragments, C3a and C5a, acting through their specific receptors, C3aR, C5aR1, and C5aR2, to direct the cellular response to inflammation. Their potent function however, places them at risk of damaging the host, with aberrant C3a and C5a signaling activity linked to a wide range of disorders of inflammatory, autoimmune, and neurodegenerative etiologies. As such, the therapeutic control of these receptors represents an attractive drug target, though, the realization of this clinical potential remains limited. With the success of eculizumab, and the progression of a number of novel C5a-C5aR1 targeted drugs to phase II and III clinical trials, there is great promise for complement therapeutics in future clinical practice. In contrast, the toolbox of drugs available to modulate C3aR and C5aR2 signaling remains limited, however, the emergence of new selective ligands and molecular tools, and an increased understanding of the function of these receptors in disease, has highlighted their unique potential for clinical applications. This review provides an update on the growing arsenal of drugs now available to target C5, and C5a and C3a receptor signaling, and discusses their utility in both clinical and pre-clinical development.

Regulatory T cells ameliorate intracerebral hemorrhage-induced inflammatory injury by modulating microglia/macrophage polarization through the IL-10/GSK3β/PTEN axis

Inflammation mediated by the peripheral infiltration of inflammatory cells plays an important role in intracerebral hemorrhage (ICH) induced secondary injury. Previous studies have indicated that regulatory T lymphocytes (Tregs) might reduce ICH-induced inflammation, but the precise mechanisms that contribute to ICH-induced inflammatory injury remain unclear. Our results show that the number of Tregs in the brain increases after ICH. Inducing Tregs deletion using a CD25 antibody or Foxp3^DTR-mice increased neurological deficient scores (NDS), the level of inflammatory factors, hematoma volumes, and neuronal degeneration. Meanwhile, boosting Tregs using a CD28 super-agonist antibody reduced the inflammatory injury. Furthermore, Tregs depletion shifted microglia/macrophage polarization toward the M1 phenotype while boosting Tregs shifted this transition toward the M2 phenotype. In vitro, a transwell co-culture model of microglia and Tregs indicated that Tregs changed the polarization of microglia, decreased the expression of MHC-II, IL-6, and TNF-α and increased CD206 expression. IL-10 originating from Tregs mediated the microglia polarization by increasing the expression of Glycogen Synthase Kinase 3 beta (GSK3β), which phosphorylates and inactivates Phosphatase and Tensin homologue (PTEN) in microglia, TGF-β did not participate in this conversion. Thus, Tregs ameliorated ICH-induced inflammatory injury by modulating microglia/macrophage polarization toward the M2 phenotype through the IL-10/GSK3β/PTEN axis.

NLRP3 is Required for Complement-Mediated Caspase-1 and IL-1beta Activation in ICH

Complement-mediated inflammation plays a vital role in intracerebral hemorrhage (ICH), implicating pro-inflammatory factor interleukin-1beta (IL-1β) secretion. Brain samples and contralateral hemiencephalon were all collected and detected by Western blot. NLRP3 expression was located by dual immunofluorescence staining at 1, 3, and 5 days post-ICH. Brain water content was examined post-ICH. The neural deficit scores were evaluated by observers blindly. ILs were detected by ELISA. SiRNAs targeting NLRP3 (siNLRP3), siASC, and siControl were injected to inhibit NLRP3 function. To test the complement activation via Nod-like receptor (NLR) family pyrin domain-containing 3 (NLRP3), normal rabbit complement (NRC) was injected with lipopolysaccharide (LPS) to facilitate the complement function. As a result, complement 3a (C3a) and complement 5a (C5a) were upregulated during the ICH-induced neuroinflammation, and ablation of C3 attenuates ICH-induced IL-1β release. Though the LPS rescues the neuroinflammation in the ICH model, C3 deficiency attenuates the LPS-induced inflammatory effect. The NLRP3 inflammasome was activated after ICH and was located in the microglial cell of the mouse brain, which exhibits a time-dependent manner. However, the number of NLRP3/Iba-1 dual-labeled cells in the C3^-/- group is less than that in the WT group in each time course, respectively. IL-1β and IL-18 released in perihematoma tissue, caspase-1-p20, brain water content, and behavioral outcomes were attenuated in the siNLRP3 and siASC groups than in the siControl and ICH groups. We also found that 5% of complement supplement enhances ICH-induced IL-1β release, while NLRP3 and ASC inhibition attenuates it. In conclusion, complement-induced ICH neuroinflammation depended on NLRP3 activation, which facilities LPS- and ICH-induced neuroinflammation, and NLRP3 is required for ICH-induced inflammation.

Stages of the Inflammatory Response in Pathology and Tissue Repair after Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is a major health concern, with high rates of mortality and morbidity and no highly effective clinical interventions. Basic research in animal models of ICH has provided insight into its complex pathology, in particular revealing the role of inflammation in driving neuronal death and neurologic deficits after hemorrhage. The response to ICH occurs in four distinct phases: (1) initial tissue damage and local activation of inflammatory factors, (2) inflammation-driven breakdown of the blood-brain barrier, (3) recruitment of circulating inflammatory cells and subsequent secondary immunopathology, and (4) engagement of tissue repair responses that promote tissue repair and restoration of neurologic function. The development of CNS inflammation occurs over many days after initial hemorrhage and thus may represent an ideal target for treatment of the disease, but further research is required to identify the mechanisms that promote engagement of inflammatory versus anti-inflammatory pathways. In this review, the authors examine how experimental models of ICH have uncovered critical mediators of pathology in each of the four stages of the inflammatory response, and focus on the role of the immune system in these processes.

Therapeutic targeting of complement to modify disease course and improve outcomes in neurological conditions

The recognition that complement proteins are abundantly present and can have pathological roles in neurological conditions offers broad scope for therapeutic intervention. Accordingly, an increasing number of experimental investigations have explored the potential of harnessing the unique activation pathways, proteases, receptors, complexes, and natural inhibitors of complement, to mitigate pathology in acute neurotrauma and chronic neurodegenerative diseases. Here, we review mechanisms of complement activation in the central nervous system (CNS), and explore the effects of complement inhibition in cerebral ischemic-reperfusion injury, traumatic brain injury, spinal cord injury, Alzheimer's disease, amyotrophic lateral sclerosis, Parkinson's disease and Huntington's disease. We consider the challenges and opportunities arising from these studies. As complement therapies approach clinical translation, we provide perspectives on how promising complement-targeted therapeutics could become part of novel and effective future treatment options to improve outcomes in the initiation and progression stages of these debilitating CNS disorders.

Complement in the Homeostatic and Ischemic Brain

The complement system is a component of the immune system involved in both recognition and response to pathogens, and it is implicated in an increasing number of homeostatic and disease processes. It is well documented that reperfusion of ischemic tissue results in complement activation and an inflammatory response that causes post-reperfusion injury. This occurs following cerebral ischemia and reperfusion and triggers secondary damage that extends beyond the initial infarcted area, an outcome that has rationalized the use of complement inhibitors as candidate therapeutics after stroke. In the central nervous system, however, recent studies have revealed that complement also has essential roles in synaptic pruning, neurogenesis, and neuronal migration. In the context of recovery after stroke, these apparent divergent functions of complement may account for findings that the protective effect of complement inhibition in the acute phase after stroke is not always maintained in the subacute and chronic phases. The development of effective stroke therapies based on modulation of the complement system will require a detailed understanding of complement-dependent processes in both early neurodegenerative events and delayed neuro-reparatory processes. Here, we review the role of complement in normal brain physiology, the events initiating complement activation after cerebral ischemia-reperfusion injury, and the contribution of complement to both injury and recovery. We also discuss how the design of future experiments may better characterize the dual role of complement in recovery after ischemic stroke.

Carboxypeptidase B2 deficiency reveals opposite effects of complement C3a and C5a in a murine polymicrobial sepsis model

BACKGROUND AND OBJECTIVES

Carboxypeptidase B2 (CPB2) is a basic carboxypeptidase with fibrin and complement C3a and C5a as physiological substrates. We hypothesized that in polymicrobial sepsis, CPB2-deficient mice would have sustained C5a activity, leading to disease exacerbation.

METHODS

Polymicrobial sepsis was induced by cecal ligation and puncture (CLP).

RESULTS

Contrary to our hypothesis, Cpb2(-/-) mice had significantly improved survival, with reduced lung edema, less liver and kidney damage, and less disseminated intravascular coagulation. Hepatic pro-CPB2 was induced by CLP, leading to increased pro-CPB2 levels. Thrombomodulin present on mesothelium supported thrombin activation of pro-CPB2. Both wild-type and Cpb2(-/-) animals treated with a C5a receptor antagonist had improved survival, demonstrating that C5a was detrimental in this model. Treatment with a fibrinolysis inhibitor, tranexamic acid, caused a decrease in survival in both genotypes; however, the Cpb2(-/-) animals retained their survival advantage. Administration of a C3a receptor antagonist exacerbated the disease in both wild-type and Cpb2(-/-) mice and eliminated the survival advantage of Cpb2(-/-) mice. C5a receptor is expressed in both peritoneal macrophages and neutrophils; in contrast, C3a receptor expression is restricted to peritoneal macrophages, and C3a induced signaling in macrophages but not neutrophils.

CONCLUSIONS

While C5a exacerbates the peritonitis, resulting in a deleterious generalized inflammatory state, C3a activation of peritoneal macrophages may limit the initial infection following CLP, thereby playing a diametrically opposing protective role in this polymicrobial sepsis model.

Impaired adult hippocampal neurogenesis and cognitive ability in a mouse model of intrastriatal hemorrhage

Thrombin released by hematoma is an important mediator of the secondary injury of intracerebral hemorrhage (ICH), however, the effect of thrombin on adult neurogenesis and cognitive ability remains elusive. In this study, intrastriatal injection of 0.05 U thrombin didn't affect the neurogenesis at the subgranular zone (SGZ), which was distal to the injection site. 0.1 U thrombin increased the 5-bromo-2-deoxyuridine(+) (BrdU(+), S-phase proliferating cells)/doublecortin(+) (DCX(+), immature neurons) double labelled neurons, but decreased BrdU(+)/NeuN(+) double labelled mature neurons. Higher doses of thrombin (1 U, 2 U, and 5 U) significantly decreased the BrdU(+)/DCX(+) and BrdU(+)/NeuN(+) double labelled cells. After 1 U thrombin injection, cell apoptosis was found at the dentate gyrus of hippocampus at 3-24 h, but not 5 d post-injury. Thrombin infusion (1 U) induced spatial memory deficits in Morris water maze test; whereas, hirudin, the thrombin antagonist, significantly reversed both neurogenesis loss and spatial learning and memory impairment. In conclusion, at least at short term (5 days) after striatum ICH, the effect of high dose of thrombin on neurogenesis of SGZ, and the spatial learning and memory ability, is detrimental.

Toll-like receptor 4 antagonist attenuates intracerebral hemorrhage-induced brain injury

BACKGROUND AND PURPOSE

Accumulating evidence indicates that inflammatory responses cause secondary injury after intracerebral hemorrhage (ICH). We recently demonstrated the involvement of toll-like receptor 4 (TLR4) signaling in these processes. The purpose of the current study was to investigate the protective effect and mechanism of TAK-242 (Ethyl (6R)-6-[N-(2-chloro-4-fluorophenyl) sulfamoyl] cyclohex-1-ene-1 -carboxylate, Takeda), a TLR4 antagonist, in an ICH mouse model.

METHODS

TAK-242 was intraperitoneally injected 6 hours after ICH once daily for 5 successive days. We assessed neurological deficit scores; changes in brain water content; and levels of inflammatory factors, DNA damage, and neuronal degeneration in perihematomal region 1, 3, and 5 days after ICH. Peripheral inflammatory cell infiltration was determined using flow cytometry; and the expression of TLR4 downstream signaling molecules was assessed by Western blot.

RESULTS

TAK-242 significantly reduced brain water content, neurological deficit scores, and levels of inflammatory factors. The levels of DNA damage and neuronal degeneration were also significantly decreased, as was peripheral inflammatory cell infiltration. The expression of TLR4 downstream signaling molecules, including myeloid differentiation primary response gene 88, toll/IR-1(TIR)-domain-containing adaptor protein inducing interferon-beta IκBα, nuclear factor-κBp65, and phosphorylated nuclear factor-κBp65, was significantly downregulated.

CONCLUSIONS

The results suggest that TLR4 antagonist reduced inflammatory injury and neurological deficits in a mouse model of ICH. The mechanism may involve decreased expression of signaling molecules downstream of TLR4.

International Union of Basic and Clinical Pharmacology. [corrected]. LXXXVII. Complement peptide C5a, C4a, and C3a receptors

The activation of the complement cascade, a cornerstone of the innate immune response, produces a number of small (74-77 amino acid) fragments, originally termed anaphylatoxins, that are potent chemoattractants and secretagogues that act on a wide variety of cell types. These fragments, C5a, C4a, and C3a, participate at all levels of the immune response and are also involved in other processes such as neural development and organ regeneration. Their primary function, however, is in inflammation, so they are important targets for the development of antiinflammatory therapies. Only three receptors for complement peptides have been found, but there are no satisfactory antagonists as yet, despite intensive investigation. In humans, there is a single receptor for C3a (C3a receptor), no known receptor for C4a, and two receptors for C5a (C5a₁ receptor and C5a₂ receptor). The most recently characterized receptor, the C5a₂ receptor (previously known as C5L2 or GPR77), has been regarded as a passive binding protein, but signaling activities are now ascribed to it, so we propose that it be formally identified as a receptor and be given a name to reflect this. Here, we describe the complex biology of the complement peptides, introduce a new suggested nomenclature, and review our current knowledge of receptor pharmacology.

Autoantibody-mediated complement C3a receptor activation contributes to the pathogenesis of preeclampsia

Preeclampsia (PE) is a prevalent life-threatening hypertensive disorder of pregnancy associated with increased complement activation. However, the causative factors and pathogenic role of increased complement activation in PE are largely unidentified. Here we report that a circulating maternal autoantibody, the angiotensin II type 1 receptor agonistic autoantibody, which emerged recently as a potential pathogenic contributor to PE, stimulates deposition of complement C3 in placentas and kidneys of pregnant mice via angiotensin II type 1 receptor activation. Next, we provide in vivo evidence that selectively interfering with C3a signaling by a complement C3a receptor-specific antagonist significantly reduces hypertension from 167±7 to 143±5 mm Hg and proteinuria from 223.5±7.5 to 78.8±14.0 μg of albumin per milligram creatinine (both P<0.05) in angiotensin II type 1 receptor agonistic autoantibody-injected pregnant mice. In addition, we demonstrated that complement C3a receptor antagonist significantly inhibited autoantibody-induced circulating soluble fms-like tyrosine kinase 1, a known antiangiogenic protein associated with PE, and reduced small placental size with impaired angiogenesis and intrauterine growth restriction. Similarly, in humans, we demonstrate that C3 deposition is significantly elevated in the placentas of preeclamptic patients compared with normotensive controls. Lastly, we show that complement C3a receptor activation is a key mechanism underlying autoantibody-induced soluble fms-like tyrosine kinase 1 secretion and decreased angiogenesis in cultured human villous explants. Overall, we provide mouse and human evidence that angiotensin II type 1 receptor agonistic autoantibody-mediated activation contributes to elevated C3 and that complement C3a receptor signaling is a key mechanism underlying the pathogenesis of the disease. These studies are the first to link angiotensin II type 1 receptor agonistic autoantibody with complement activation and to provide important new opportunities for therapeutic intervention in PE.

Complement inhibition promotes endogenous neurogenesis and sustained anti-inflammatory neuroprotection following reperfused stroke

Background and Purpose

The restoration of blood-flow following cerebral ischemia incites a series of deleterious cascades that exacerbate neuronal injury. Pharmacologic inhibition of the C3a-receptor ameliorates cerebral injury by attenuating post-ischemic inflammation. Recent reports also implicate C3a in the modulation of tissue repair, suggesting that complement may influence both injury and recovery at later post-ischemic time-points.

Methods

To evaluate the effect of C3a-receptor antagonism on post-ischemic neurogenesis and neurological outcome in the subacute period of stroke, transient focal cerebral ischemia was induced in adult male C57BL/6 mice treated with multiple regimens of a C3a receptor antagonist (C3aRA).

Results

Low-dose C3aRA administration during the acute phase of stroke promotes neuroblast proliferation in the subventricular zone at 7 days. Additionally, the C3a receptor is expressed on T-lymphocytes within the ischemic territory at 7 days, and this cellular infiltrate is abrogated by C3aRA administration. Finally, C3aRA treatment confers robust histologic and functional neuroprotection at this delayed time-point.

Conclusions

Targeted complement inhibition through low-dose antagonism of the C3a receptor promotes post-ischemic neuroblast proliferation in the SVZ. Furthermore, C3aRA administration suppresses T-lymphocyte infiltration and improves delayed functional and histologic outcome following reperfused stroke. Post-ischemic complement activation may be pharmacologically manipulated to yield an effective therapy for stroke.

Depletion of GR-1-Positive Cells Is Associated with Reduced Neutrophil Inflammation and Astrocyte Reactivity after Experimental Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is the stroke subtype with the highest mortality and morbidity with 25% of patients dying within the first 48 h and a high incidence of poor outcomes. Because of high early mortality rates, an understanding of acute brain injury mechanisms is essential. In this study, we have investigated the putative role of acute inflammation in brain injury after experimental ICH. We depleted GR-1(+) cells in mice by intraperitoneal administration of anti-GR-1 antibody or normal rat serum (control). We then induced ICH by infusion of autologous whole blood into the striatum and compared functional outcome and brain injury markers between the two groups. We found that administration of anti-GR-1 antibody led to a profound decrease in circulating GR-1(+) cells (1.5 ± 0.34% vs. 50.3 ± 8.3% of CD45(+) cells, p ≤ 0.01) and that brain neutrophils decreased by approximately 50% (p ≤ 0.05). We observed a reduction in astrocyte immunoreactivity in the GR-1(+) cell-depleted group (p ≤ 0.05). Conversely, we did not find attenuation of brain edema or differences in behavioral deficits between the two groups. In summary, our results are promising and suggest that larger studies or different neutrophil manipulations may produce greater attenuation of injury after ICH.

The Molecular Mechanisms that Promote Edema After Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is a devastating type of stroke with no effective therapies. Clinical advances in ICH treatment are limited by an incomplete understanding of the molecular mechanisms responsible for secondary injury and poor outcome. Increasing evidence suggests that cerebral edema is a major contributor to secondary injury and poor outcome in ICH. ICH activates specific signaling pathways that promote edema and damage neuronal tissue. By increasing our understanding of these pathways, we may be able to target them pharmaceutically to reduce edema in ICH patients. In this review, we focus on three major signaling pathways that promote edema after ICH: (1) the coagulation cascade and thrombin, (2) the inflammatory response and matrix metalloproteinases, and (3) the complement cascade and hemoglobin toxicity. We will describe the experimental evidence that confirms these pathways promote edema in ICH, discuss potential targets for new therapies, and comment on important directions for future research.

Complement and the alternative pathway play an important role in LPS/D-GalN-induced fulminant hepatic failure

Fulminant hepatic failure (FHF) is a clinically severe type of liver injury with an extremely high mortality rate. Although the pathological mechanisms of FHF are not well understood, evidence suggests that the complement system is involved in the pathogenesis of a variety of liver disorders. In the present study, to investigate the role of complement in FHF, we examined groups of mice following intraperitoneal injection of LPS/D-GalN: wild-type C57BL/6 mice, wild-type mice treated with a C3aR antagonist, C5aR monoclonal antibody (C5aRmAb) or CR2-Factor H (CR2-fH, an inhibitor of the alternative pathway), and C3 deficient mice (C3^−/− mice). The animals were euthanized and samples analyzed at specific times after LPS/D-GalN injection. The results show that intraperitoneal administration of LPS/D-GalN activated the complement pathway, as evidenced by the hepatic deposition of C3 and C5b-9 and elevated serum levels of the complement activation product C3a, the level of which was associated with the severity of the liver damage. C3a receptor (C3aR) and C5a receptor (C5aR) expression was also upregulated. Compared with wild-type mice, C3^−/− mice survived significantly longer and displayed reduced liver inflammation and attenuated pathological damage following LPS/D-GalN injection. Similar levels of protection were seen in mice treated with C3aR antagonist,C5aRmAb or CR2-fH. These data indicate an important role for the C3a and C5a generated by the alternative pathway in LPS/D-GalN-induced FHF. The data further suggest that complement inhibition may be an effective strategy for the adjunctive treatment of fulminant hepatic failure.

Anti-adrenergic medications and edema development after intracerebral hemorrhage

BACKGROUND

Use of antihypertensive medications is common after intracerebral hemorrhage (ICH). Medications that block adrenergic activation (e.g., beta-blockers and the alpha(2)-agonist, clonidine) may reduce the inflammatory response and therefore have secondary benefit after ICH.

METHODS

The patients with acute ICH enrolled in the placebo arm of the CHANT trial were included. Univariate and multivariate analyses were undertaken for factors associated with blood pressure medication use, edema at 72 h, and clinical outcome at 90 days.

RESULTS

Of the 303 patients, 87.8% received some antihypertensive treatment during the first 72 h of hospitalization. Edema volume on neuroimaging at 72 h was independently associated with clinical outcome. Use of anti-adrenergic medications was associated with less edema after controlling for hemorrhage volume and blood pressure.

CONCLUSIONS

Antihypertensive medications that antagonize the sympathetic nervous system may reduce perihematomal edema after ICH.

The Neuroprotective Effect of Genetic Mannose-binding Lectin Deficiency is not Sustained in the Sub-acute Phase of Stroke

INTRODUCTION

The complement cascade is a critical mediator of the inflammatory response following cerebral ischemia. Recent work has demonstrated that genetic-deficiency of Mannose-binding lectin(MBL) ameliorates reperfusion injury and improves outcome in the acute phase of stroke. The present study sought to further delineate the pathogenic role of MBL in stroke and to examine whether the neuroprotection associated with MBL-deficiency is sustained beyond the acute phase. We hypothesized that genetic MBL deficiency would suppress complement activation and ameliorate reperfusion injury in the acute phase, but that persistent inhibition of complement into the sub-acute phase would serve to abrogate this neuroprotective effect.

METHODS

The time-course and localization of post-ischemic cerebral MBL and C3 deposition were characterized using both Western-blot and immunohistochemistry. MBL-a/c null(MBL-KO) mice subjected to transient middle cerebral artery occlusion(MCAO) were then employed to investigate the histologic injury and functional outcome associated with genetic MBL deletion at both 24 hours and 7 days.

RESULTS

MBL-a/c rapidly deposit on ischemic endothelium and trigger downstream complement activation in the acute phase. Genetic deficiency of MBL abrogates C3 cleavage as well as the sub-acute accumulation of mononuclear cells in the ischemic region. Although MBL-KO mice demonstrate significantly improved outcome at 24 hours, the neuroprotective effect associated with genetic MBL deletion is not sustained.

CONCLUSIONS

Development of a successful anti-complement neuroprotective strategy will require carefully-tailored inhibition coupled with a greater understanding of the functional effects of complement activation during later phases of stroke recovery.

Minocycline attenuates photoreceptor degeneration in a mouse model of subretinal hemorrhage microglial: inhibition as a potential therapeutic strategy

Hemorrhage under the neural retina (subretinal hemorrhage) can occur in the context of age-related macular degeneration and induce subsequent photoreceptor cell death and permanent vision loss. Current treatments with the objective of removing or displacing the hemorrhage are invasive and of mixed efficacy. We created a mouse model of subretinal hemorrhage to characterize the inflammatory responses and photoreceptor degeneration that occur in the acute aftermath of hemorrhage. It was observed that microglial infiltration into the outer retina commences as early as 6 hours after hemorrhage. Inflammatory cells progressively accumulate in the outer nuclear layer concurrently with photoreceptor degeneration and apoptosis. Administration of minocycline, an inhibitor of microglial activation, decreased microglial expression of chemotactic cytokines in vitro and reduced microglial infiltration and photoreceptor cell loss after subretinal hemorrhage in vivo. Inflammatory responses and photoreceptor atrophy occurred after subretinal hemorrhage, however, the degree of response and atrophy were similar between C3-deficient and C3-sufficient mice, indicating a limited role for complement-mediated processes. Our data indicate a role for inflammatory responses in driving photoreceptor cell loss in subretinal hemorrhage, and it is proposed that microglial inhibition may be beneficial in the treatment of subretinal hemorrhage.