Poststroke Inflammasome Expression and Regulation in the Peri-Infarct Area by Gonadal Steroids after Transient Focal Ischemia in the Rat Brain

Furosine, a Maillard Reaction Product, Triggers Necroptosis in Hepatocytes by Regulating the RIPK1/RIPK3/MLKL Pathway

As one of the typical Maillard reaction products, furosine has been widely reported in a variety of heat-processed food. Though furosine was shown to be toxic on organs, its toxicity mechanism is still unclear. The present study aimed to investigate the toxicity mechanism of furosine in liver tissue. An intragastric gavage mice model (42-day administration, 0.1/0.25/0.5 g/kg of furosine per day) and a mice primary hepatocyte model were employed to investigate the toxicity mechanism of furosine on mice liver tissue. A metabonomics analysis of mice liver, serum, and red blood cells (RBC) was performed. The special metabolic mediator of furosine, lysophosphatidylcholine 18:0 (LPC (18:0)) was identified. Then, the effect of the upstream gene phospholipase A2 gamma (PLA2-3) on LPC (18:0), as well as the effect of furosine (100 mg/L) on the receptor-interacting serine/threonine-protein kinase (RIPK)1/RIPK3/mixed lineage kinase domain-like protein (MLKL) pathway and inflammatory factors, was determined in liver tissue and primary hepatocytes. PLA2-3 was found to regulate the level of LPC (18:0) and activate the expression of RIPK1, RIPK3, P-MLKL, and of the inflammatory factors including tumor necrosis factor α (TNF-α) and interleukin (IL-1β), both in liver tissue and in primary hepatocytes. Upon treatment with furosine, the upstream sensor PLA2-3 activated the RIPK1/RIPK3/MLKL necroptosis pathway and caused inflammation by regulating the expression of LPC (18:0), which further caused liver damage.

NLRP3 inflammasome in ischemic stroke: As possible therapeutic target

Inflammation is a devastating pathophysiological process during stroke, a devastating disease that is the second most common cause of death worldwide. Activation of the NOD-like receptor protein (NLRP3)-infammasome has been proposed to mediate inflammatory responses during ischemic stroke. Briefly, NLRP3 inflammasome activates caspase-1, which cleaves both pro-IL-1 and pro-IL-18 into their active pro-inflammatory cytokines that are released into the extracellular environment. Several NLRP3 inflammasome inhibitors have been promoted, including small molecules, type I interferon, micro RNAs, nitric oxide, and nuclear factor erythroid-2 related factor 2 (Nrf2), some of which are potentially efficacious clinically. This review will describe the structure and cellular signaling pathways of the NLRP3 inflammasome during ischemic stroke, and current evidence for NLRP3 inflammasome inhibitors.

Hypoxia Induces Astrocyte-Derived Lipocalin-2 in Ischemic Stroke

Ischemic stroke causes rapid hypoxic damage to the core neural tissue which is followed by graded chronological tissue degeneration in the peri-infarct zone. The latter process is mainly triggered by neuroinflammation, activation of inflammasomes, proinflammatory cytokines, and pyroptosis. Besides microglia, astrocytes play an important role in the fine-tuning of the inflammatory network in the brain. Lipocalin-2 (LCN2) is involved in the control of innate immune responses, regulation of excess iron, and reactive oxygen production. In this study, we analyzed LCN2 expression in hypoxic rat brain tissue after ischemic stroke and in astrocyte cell cultures receiving standardized hypoxic treatment. Whereas no LCN2-positive cells were seen in sham animals, the number of LCN2-positive cells (mainly astrocytes) was significantly increased after stroke. In vitro studies with hypoxic cultured astroglia revealed that LCN2 expression is significantly increased after only 2 h, then further increased, followed by a stepwise decline. The expression pattern of several proinflammatory cytokines mainly followed that profile in wild type (WT) but not in cultured LCN2-deficient astrocytes. Our data revealed that astrocytes are an important source of LCN2 in the peri-infarct region under hypoxic conditions. However, we must also stress that brain-intrinsic LCN2 after the initial hypoxia period might come from other sources such as invaded immune cells and peripheral organs via blood circulation. In any case, secreted LCN2 might have an influence on peripheral organ functions and the innate immune system during brain hypoxia.

The regulatory role of Toll-like receptors after ischemic stroke: neurosteroids as TLR modulators with the focus on TLR2/4

Ischemic stroke is the most common cerebrovascular disease and considered as a worldwide leading cause of death. After cerebral ischemia, different pathophysiological processes including neuroinflammation, invasion and aggregation of inflammatory cells and up-regulation of cytokines occur simultaneously. In this respect, Toll-like receptors (TLRs) are the first identified important mediators for the activation of the innate immune system and are widely expressed in glial cells and neurons following brain trauma. TLRs are also able to interact with endogenous and exogenous molecules released during ischemia and can increase tissue damage. Particularly, TLR2 and TLR4 activate different downstream inflammatory signaling pathways. In addition, TLR signaling can alternatively play a role for endogenous neuroprotection. In this review, the gene and protein structures, common genetic polymorphisms of TLR2 and TLR4, TLR-related molecular pathways and their putative role after ischemic stroke are delineated. Furthermore, the relationship between neurosteroids and TLRs as neuroprotective mechanism is highlighted in the context of brain ischemia.

[A role of inflammasomes in the pathogenesis of neurological and mental diseases]

Inflammasomes are macromolecular complexes that contain many copies of receptors recognizing molecular patterns of pathogenic agents (PAMP) and damage-associated structures (DAMP), and also include molecules of adapter protein ASC and procaspase-1. Activation of inflammasomes leads to the formation of active caspase-1 that, in turn, provides the maturation of pro-IL-1β and pro-IL-18 to IL-1β and IL-18. The latter cytokines play an important role in control of neuroinlfammation in the central nervous system contributing to the pathogenesis of a series of neurological, neurodegenerative and mental disorders. The review discusses the involvement of NLRP3 inflammasome and other their types in the development of the traumatic brain injury, ischemic and hemorrhagic stroke, brain tumors, CNS infections, Alzheimer's and Parkinson's diseases, epilepsy, amyotrophic lateral sclerosis, depressiver, and consequences of alcohol abuse. The elucidation of molecular mechanisms and signaling pathways controlled by inflammasomes will allow the development of new therapeutic measures for diseases, in which neuroinflammation plays a leading pathogenetic role.

NLRP3 inflammasome contributes to neurovascular unit damage in stroke

Recently, a wealth of information has emerged connecting the activation of the NLRP3 (NOD-like receptor family pyrin domain-containing 3) inflammasome to stroke pathogenesis, although the exact influence of the NLRP3 inflammasome on stroke is still in the stage of preliminary study and is awaiting further confirmation. In this paper, we will review the structure, assembly and activation of the NLRP3 inflammasome and its expression in the neurovascular units and will speculate on its possible roles in neurovascular injury post-stroke. Evidence on this topic suggests that targeting NLRP3-mediated inflammation at multiple levels may provide a new therapeutic strategy to prevent the deterioration of neurovascular units after stroke. However, many aspects of the biological link between the NLRP3 inflammasome and stroke remain ill-defined or even completely unknown. As fresh insights come to light regarding the NLRP3 inflammasome, the opportunities to develop new therapeutic strategies for stroke patients are expected to improve accordingly.

The role of inflammasome complex in ischemia-reperfusion injury

Ischemia-reperfusion injury refers to a temporary interruption of blood flow in a tissue. Restoration of blood flow initiates the inflammation in tissue causing ischemic damage through the activation of a multiprotein complex termed inflammasome. The complex contains a receptor, mainly a member of nucleotide oligomerization domain-like receptors, that receives danger signals. The receptor is oligomerized as a response to danger signals and then the apoptosis-associated speck-like protein containing a caspase recruitment domain and procaspase protein are added to the oligomerized receptors to form the inflammasome complex. In the next step, the isolated procaspase is converted into an active caspase molecule that initiates the inflammation through the release of interleukin-1β and interleukin-18. The inflammasome has an important role in the pathogenesis of ischemia-reperfusion injury in different tissues. Here, we summarized the role of inflammasome in the pathogenesis of ischemia-reperfusion of brain, liver, kidney, and heart. Moreover, we highlighted the expression of inflammasome components, the mechanisms involved in activation of the complex, and its inhibition as an optimistic therapeutic technique in ischemia-reperfusion injuries.

Evidence and perspective for the role of the NLRP3 inflammasome signaling pathway in ischemic stroke and its therapeutic potential (Review)

Ischemic stroke is one of the main causes of death and disablement globally. The NLR family pyrin domain containing 3 (NLRP3) inflammasome is established as a sensor of detecting cellular damage and modulating inflammatory responses to injury during the progress of ischemic stroke. Inhibiting or blocking the NLRP3 inflammasome at different stages, including expression, assembly, and secretion, may have great promise to improve the neurological deficits during ischemic stroke. The current review provides a comprehensive summary of the current understanding in the literature of the molecular structure, expression, and assembly of the NLRP3 inflammasome, and highlights its potential as a novel therapeutic target for ischemic stroke.

Impact of steroid hormones E2 and P on the NLRP3/ASC/Casp1 axis in primary mouse astroglia and BV-2 cells after in vitro hypoxia

Clinical and animal model studies have demonstrated the neuroprotective and anti-inflammatory effects of 17beta-estradiol (E2) and progesterone (P) in different disease models of the central nervous system (CNS) including ischemic stroke. Inflammasomes are involved in the interleukin-1 beta (IL1beta) maturation, in particular, NLRP3, the adaptor protein apoptosis-associated speck-like protein containing a CARD (ASC) and the active caspase-1 (Casp1) form. Recently, we showed that administration of E2 or P selectively regulated these components after experimental ischemic stroke in rats. Therefore, we investigated the impact of E2 and P on the NLRP3/ASC/Casp1 axis in the murine microglia-like cell line BV-2 cells and primary astrocytes after short-term in vitro hypoxia. The inflammatory cytokine IL1beta but not IL18 was increased after short-term hypoxia in astroglia and BV-2 cells. The same applied to NLPR3 and ASC. Casp1 activity was also elevated in astroglia and BV-2 cells after hypoxia. The administration of E2 or P selectively dampened IL1beta, ASC and NLRP3 expression mainly in BV-2 cells. Both steroid hormones failed to reduce Casp1 activity after hypoxia. We conclude that E2- and P-mediated anti-inflammatory mechanisms occur upstream of Casp1 through the regulation of NLRP3 and its adaptor ASC.

The psychoneuroimmunology of pregnancy

Pregnancy is associated with a number of significant changes in maternal physiology. Perhaps one of the more notable changes is the significant alteration in immune function that occurs during pregnancy. This change in immune function is necessary to support a successful pregnancy, but also creates a unique period of life during which a female is susceptible to disease and, as we'll speculate here, may also contribute to mental health disorders associated with pregnancy and the postpartum period. Here, we review the known changes in peripheral immune function that occur during pregnancy and the postpartum period, while highlighting the impact of hormones during these times on immune function, brain or neural function, as well as behavior. We also discuss the known and possible impact of pregnancy-induced immune changes on neural function during this time and briefly discuss how these changes might be a risk factor for perinatal anxiety or mood disorders.

Development of a novel progesterone analog in the treatment of traumatic brain injury

Although systemic progesterone (PROG) treatment has been shown to be neuroprotective by many laboratories and in multiple animal models of brain injury including traumatic brain injury (TBI), PROG's poor aqueous solubility limits its potential for use as a therapeutic agent. The problem of solubility presents challenges for an acute intervention for neural injury, when getting a neuroprotectant to the brain quickly is crucial. Native PROG (nPROG) is hydrophobic and does not readily dissolve in an aqueous-based medium, so this makes it harder to give under emergency field conditions. An agent with properties similar to those of PROG but easier to store, transport, formulate, and administer early in emergency trauma situations could lead to better and more consistent clinical outcomes following TBI. At the same time, the engineering of a new molecule designed to treat a complex systemic injury must anticipate a range of translational issues including solubility and bioavailability. Here we describe the development of EIDD-1723, a novel, highly stable PROG analog with >10⁴-fold higher aqueous solubility than that of nPROG. We think that, with further testing, EIDD-1723 could become an attractive candidate use as a field-ready treatment for TBI patients. This article is part of the Special Issue entitled "Novel Treatments for Traumatic Brain Injury".

Combined effects of rat Schwann cells and 17β-estradiol in a spinal cord injury model

Spinal cord injury (SCI) is a devastating traumatic event which burdens the affected individuals and the health system. Schwann cell (SC) transplantation is a promising repair strategy after SCI. However, a large number of SCs do not survive following transplantation. Previous studies demonstrated that 17β-estradiol (E2) protects different cell types and reduces tissue damage in SCI experimental animal model. In the current study, we evaluated the protective potential of E2 on SCs in vitro and investigated whether the combination of hormonal and SC therapeutic strategy has a better effect on the outcome after SCI. Primary SC cultures were incubated with E2 for 72 h. In a subsequent experiment, thoracic contusion SCI was induced in male rats followed by sustained administration of E2 or vehicle. Eight days after SCI, DiI-labeled SCs were transplanted into the injury epicenter in vehicle and E2-treated animals. The combinatory regimen decreased neurological and behavioral deficits and protected neurons and oligodendrocytes in comparison to vehicle rats. Moreover, E2 and SC significantly decreased the number of Iba-1+ (microglia) and GFAP⁺ cells (astrocyte) in the SCI group. In addition, we found a significant reduction of mitochondrial fission-markers (Fis1) and an increase of fusion-markers (Mfn1 and Mfn2) in the injured spinal cord after E2 and SC treatment. These data demonstrated that E2 protects SCs against hypoxia-induced SCI and improves the survival of transplanted SCs.

Is Targeting the Inflammasome a Way Forward for Neuroscience Drug Discovery?

Neuroinflammation is becoming increasingly recognized as a critical factor in the pathology of both acute and chronic neurological conditions. Inflammasomes such as the one formed by NACHT, LRR, and PYD domains containing protein 3 (NLRP3) are key regulators of inflammation due to their ability to induce the processing and secretion of interleukin 1β (IL-1β). IL-1β has previously been identified as a potential therapeutic target in a variety of conditions due to its ability to promote neuronal damage under conditions of injury. Thus, inflammasome inhibition has the potential to curtail inflammatory signaling, which could prove beneficial in certain diseases. In this review, we discuss the evidence for inflammasome contributions to the pathology of neurodegenerative conditions such as Alzheimer's disease and Parkinson's disease, epilepsy, and acute degeneration following brain trauma or stroke. In addition, we review the current landscape of drug development targeting the NLRP3 inflammasome.

17β-Estradiol Regulates Microglia Activation and Polarization in the Hippocampus Following Global Cerebral Ischemia

17β-Estradiol (E2) is a well-known neuroprotective hormone, but its role in regulation of neuroinflammation is less understood. Recently, our lab demonstrated that E2 could regulate the NLRP3 (NOD-like receptor protein 3) inflammasome pathway in the hippocampus following global cerebral ischemia (GCI). Here, we examined the ability of E2 to regulate activation and polarization of microglia phenotype in the hippocampus after global cerebral ischemia (GCI). Our in vivo study in young adult ovariectomized rats showed that exogenous low-dose E2 profoundly suppressed microglia activation and quantitatively shifted microglia from their "activated," amoeboid morphology to a "resting," ramified morphology after GCI. Further studies using M1 "proinflammatory" and M2 "anti-inflammatory" phenotype markers showed that E2 robustly suppressed the "proinflammatory" M1 phenotype, while enhancing the "anti-inflammatory" M2 microglia phenotype in the hippocampus after GCI. These effects of E2 may be mediated directly upon microglia, as E2 suppressed the M1 while enhancing the M2 microglia phenotype in LPS- (lipopolysaccharide-) activated BV2 microglia cells in vitro. E2 also correspondingly suppressed proinflammatory while enhancing anti-inflammatory cytokine gene expression in the LPS-treated BV2 microglia cells. Finally, E2 treatment abolished the LPS-induced neurotoxic effects of BV2 microglia cells upon hippocampal HT-22 neurons. Collectively, our study findings suggest a novel E2-mediated neuroprotective effect via regulation of microglia activation and promotion of the M2 "anti-inflammatory" phenotype in the brain.

Expression profile of pattern recognition receptors in skeletal muscle of SOD1(G93A) amyotrophic lateral sclerosis (ALS) mice and sporadic ALS patients

AIMS

Amyotrophic lateral sclerosis (ALS) is characterized by degeneration of motoneurons and progressive muscle wasting. Inflammatory processes, mediated by non-neuronal cells, such as glial cells, are known to contribute to disease progression. Inflammasomes consist of pattern recognition receptors (PRRs), apoptosis-associated speck-like protein (ASC) and caspase 1 and are essential for interleukin (IL) processing and a rapid immune response after tissue damage. Recently, we described inflammasome activation in the spinal cord of ALS patients and in SOD1^(G93A) ALS mice. Since pathological changes in the skeletal muscle are early events in ALS, we hypothesized that PRRs might be abnormally expressed in muscle fibre degeneration.

METHODS

Western blot analysis, real-time PCR and immunohistochemistry were performed with muscle tissue from presymptomatic and early-symptomatic male SOD1^(G93A) mice and with muscle biopsies of control and sporadic ALS (sALS) patients. Analysed PRRs include nucleotide-binding oligomerization domain-like (NOD-like) receptor protein 1 (NLRP1), NLR protein 3 (NLRP3), NLR family CARD domain-containing 4 (NLRC4) and absent in melanoma 2. Additionally, expression levels of ASC, caspase 1, interleukin 1 beta (IL1β) and interleukin 18 (IL18) were evaluated.

RESULTS

Expression of PRRs and ASC was detected in murine and human tissue. The PRR NLRC4, caspase 1 and IL1β were significantly elevated in denervated muscle of SOD1^(G93A) mice and sALS patients. Furthermore, levels of caspase 1 and IL1β were already increased in presymptomatic animals.

CONCLUSION

Our findings suggest that increased inflammasome activation may be involved in skeletal muscle pathology in ALS. Furthermore, elevated levels of NLRC4, caspase 1 and IL1β reflect early changes in the skeletal muscle and may contribute to the denervation process.

Diverse roles of mitochondria in ischemic stroke

Stroke is the leading cause of adult disability and mortality in most developing and developed countries. The current best practices for patients with acute ischemic stroke include intravenous tissue plasminogen activator and endovascular thrombectomy for large-vessel occlusion to improve clinical outcomes. However, only a limited portion of patients receive thrombolytic therapy or endovascular treatment because the therapeutic time window after ischemic stroke is narrow. To address the current shortage of stroke management approaches, it is critical to identify new potential therapeutic targets. The mitochondrion is an often overlooked target for the clinical treatment of stroke. Early studies of mitochondria focused on their bioenergetic role; however, these organelles are now known to be important in a wide range of cellular functions and signaling events. This review aims to summarize the current knowledge on the mitochondrial molecular mechanisms underlying cerebral ischemia and involved in reactive oxygen species generation and scavenging, electron transport chain dysfunction, apoptosis, mitochondrial dynamics and biogenesis, and inflammation. A better understanding of the roles of mitochondria in ischemia-related neuronal death and protection may provide a rationale for the development of innovative therapeutic regimens for ischemic stroke and other stroke syndromes.

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Review of current treatment of ischemic stroke indicates deficiency in the contemporary methods.

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Discuss the mitochondrial ROS-related signaling that affect neuronal fate after ischemic stroke.

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Mechanisms of mitochondrial dynamics and mitophagy could be pivotal for ischemic stroke.

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Inhibiting mitochondrion-induced inflammatory response is a potential treatment for ischemic stroke.

A brain in flame; do inflammasomes and pyroptosis influence stroke pathology?

Stroke is one of the leading causes of death and disability worldwide. Inflammation plays a key role across the time course of stroke, from onset to the post-injury reparative phase days to months later. Several regulatory molecules are implicated in inflammation, but the most established inflammatory mediator of acute brain injury is the cytokine interleukin-1. Interleukin-1 is regulated by large, macromolecular complexes called inflammasomes, which play a central role in cytokine release and cell death. In this review we highlight recent advances in inflammasome research and propose key roles for inflammasome components in the progression of stroke damage.

NLRP3-dependent synaptic plasticity deficit in an Alzheimer's disease amyloidosis model in vivo

Pro-inflammatory mechanisms have recently emerged as an important component of early Alzheimer's disease (AD) pathogenesis. A particularly attractive therapeutic strategy is to selectively prevent the disruptive effects of activation of the innate immune system in the brain at an early transitional stage by reducing the production or directly neutralizing pro-inflammatory cytokines, in particular IL-1β and TNF-α. Here we tested their in vivo effects on synaptic plasticity deficits, which provide sensitive and robust measures of synaptic failure, in a rat model of AD amyloidosis. Using electrophysiological techniques we longitudinally studied the effects of the NLRP3 inflammasome inhibitor Mcc950, the IL-1 receptor antagonist (anakinra) and an anti-TNF-α agent (etanercept) in awake freely moving transgenic rats overexpressing AD associated β-amyloid precursor protein at a pre-plaque stage of amyloidosis. Repeated treatment with Mcc950 reversibly abrogated the inhibition of long-term potentiation. The IL-1 receptor antagonist and etanercept also had a similar beneficial effect on the deficit in synaptic plasticity. Our findings support the clinical development of Mcc950 and clinically available IL-1- and TNF-α-neutralizing agents in early AD.

Brain inflammasomes in stroke and depressive disorders: Regulation by oestrogen

Neuroinflammation is a devastating pathophysiological process that results in brain damage and neuronal death. Pathogens, cell fragments and cellular dysfunction trigger inflammatory responses. Irrespective of the cause, inflammasomes are key intracellular multiprotein signalling platforms that sense neuropathological conditions. The activation of inflammasomes leads to the auto-proteolytic cleavage of caspase-1, resulting in the proteolysis of the pro-inflammatory cytokines interleukin (IL)1β and IL18 into their bioactive forms. It also initiates pyroptosis, a type of cell death. The two cytokines contribute to the pathogenesis in acute and chronic brain diseases and also play a central role in human aging and psychiatric disorders. Sex steroids, in particular oestrogens, are well-described neuroprotective agents in the central nervous system. Oestrogens improve the functional outcome after ischaemia and traumatic brain injury, reduce neuronal death in Parkinson's and Alzheimer's disease, as well as in amyotrophic lateral sclerosis, attenuate glutamate excitotoxicity and the formation of radical oxygen species, and lessen the spread of oedema after damage. Moreover, oestrogens alleviate menopause-related depressive symptoms and have a positive influence on depressive disorders probably by influencing growth factor production and serotonergic brain circuits. Recent evidence also suggests that inflammasome signalling affects anxiety- and depressive-like behaviour and that oestrogen ameliorates depression-like behaviour through the suppression of inflammasomes. In the present review, we highlight the most recent findings demonstrating that oestrogens selectively suppress the activation of the neuroinflammatory cascade in the brain in acute and chronic brain disease models. Furthermore, we aim to describe putative regulatory signalling pathways involved in the control of inflammasomes. Finally, we consider that psychiatric disorders such as depression also contain an inflammatory component that could be modulated by oestrogen.

Inflammasomes in CNS Diseases

Neuroinflammation is a common pathological feature in almost all neurological diseases and is a response triggered as a consequence of the chronic activation of the innate immune response in the CNS against a variety of stimuli, including infection, traumatic brain injury, toxic metabolites, aggregated proteins, or autoimmunity. Crucial mediators of this neurinflammatory process are the intracellular protein complexes known as inflammasomes which can be triggered by pathogens as well as pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). However, chronic inflammasome activation can eventually result in cellular death and tissue damage, leading to the release of DAMPs that can reactivate the inflammasome, thereby propagating a vicious cycle of inflammation. The primary cells involved in CNS inflammasome activation are the immunocompetent microglia and the infiltrating macrophages into the CNS. However, astrocytes and neurons also express inflammasomes, and the understanding of how they are engaged in the pathogenesis of a variety of neurological diseases is crucial to develop effective therapeutic approaches for CNS pathologies that are propagated by chronic inflammasome activation. This chapter covers the activation mechanisms of relevant inflammasomes in the brain and summarizes their roles in the pathogenesis and progression of different neurological conditions.

An examination of changes in maternal neuroimmune function during pregnancy and the postpartum period

There is strong evidence that the immune system changes dramatically during pregnancy in order to prevent the developing fetus from being "attacked" by the maternal immune system. Due to these alterations in peripheral immune function, many women that suffer from autoimmune disorders actually find significant relief from their symptoms throughout pregnancy; however, these changes can also leave the mother more susceptible to infections that would otherwise be mitigated by the inflammatory response (Robinson and Klein, 2012). Only one other study has looked at changes in microglial number and morphology during pregnancy and the postpartum period (Haim et al., 2016), but no one has yet examined the neuroimmune response following an immune challenge during this time. Therefore, in this study, we investigated the impact of an immune challenge during various time-points throughout pregnancy and the postpartum period on the expression of immune molecules in the brain of the mother and fetus. Our results indicate that similar to the peripheral immune suppression measured during pregnancy, we also see significant suppression of the immune response in the maternal brain, particularly during late gestation. In contrast to the peripheral immune system, immune modulation in the maternal brain extends moderately into the postpartum period. Additionally, we found that the fetal immune response in the brain and placenta is also suppressed just before parturition, suggesting that cytokine production in the fetus and placenta are mirroring the peripheral cytokine response of the mother.

Stress primes microglial polarization after global ischemia: Therapeutic potential of progesterone

Despite the fact that stress is associated with increased risk of stroke and worsened outcome, most preclinical studies have ignored this comorbid factor, especially in the context of testing neuroprotective treatments. Preclinical research suggests that stress primes microglia, resulting in an enhanced reactivity to a subsequent insult and potentially increasing vulnerability to stroke. Ischemia-induced activated microglia can be polarized into a harmful phenotype, M1, which produces pro-inflammatory cytokines, or a protective phenotype, M2, which releases anti-inflammatory cytokines and neurotrophic factors. Selective modulation of microglial polarization by inhibiting M1 or stimulating M2 may be a potential therapeutic strategy for treating cerebral ischemia. Our laboratory and others have shown progesterone to be neuroprotective against ischemic stroke in rodents, but it is not known whether it will be as effective under a comorbid condition of chronic stress. Here we evaluated the neuroprotective effect of progesterone on the inflammatory response in the hippocampus after exposure to stress followed by global ischemia. We focused on the effects of microglial M1/M2 polarization and pro- and anti-inflammatory mediators in stressed ischemic animals. Male Sprague-Dawley rats were exposed to 8 consecutive days of social defeat stress and then subjected to global ischemia or sham surgery. The rats received intraperitoneal injections of progesterone (8mg/kg) or vehicle at 2h post-ischemia followed by subcutaneous injections at 6h and once every 24h post-injury for 7days. The animals were killed at 7 and 14days post-ischemia, and brains were removed and processed to assess outcome measures using histological, immunohistochemical and molecular biology techniques. Pre-ischemic stress (1) exacerbated neuronal loss and neurodegeneration as well as microglial activation in the selectively vulnerable CA1 hippocampal region, (2) dysregulated microglial polarization, leading to upregulation of both M1 and M2 phenotype markers, (3) increased pro-inflammatory cytokine expression, and (4) reduced anti-inflammatory cytokine and neurotrophic factor expression in the ischemic hippocampus. Treatment with progesterone significantly attenuated stress-induced microglia priming by modulating polarized microglia and the inflammatory environment in the hippocampus, the area most vulnerable to ischemic injury. Our findings can be taken to suggest that progesterone holds potential as a candidate for clinical testing in ischemic stroke where high stress may be a contributing factor.

Cordycepin confers neuroprotection in mice models of intracerebral hemorrhage via suppressing NLRP3 inflammasome activation

Neuroinflammation has been recognized as a major contributor to brain injury caused by intracerebral hemorrhage (ICH). Nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome acts as an important mediator of inflammatory response in various inflammation-related diseases including hemorrhagic insults. Cordycepin has recently been shown to possess anti-inflammatory effect; however, its role and the possible underlying mechanisms in ICH remain unclear. This study was designed to investigate the neuroprotective effect of cordycepin in mice models of ICH and to elucidate the underlying molecular mechanisms. ICH was induced in male ICR mice by injecting autologous blood infusion stereotactically. Cordycepin was then given intraperitoneally (i.p.) at 30 min after ICH induction. The results demonstrated that NLRP3 inflammasome was activated and exacerbated the inflammatory progression after ICH. Cordycepin treatment significantly alleviated neurological deficits, brain edema, and perihematomal tissue damage following ICH. These changes were accompanied by downregulated NLRP3 inflammasome components expression and a reduction of production and release of inflammasome substrates interleukin-1beta (IL-1β) and interleukin-18 (IL-18). Furthermore, cordycepin ameliorated neuronal death in the perihematomal regions, accompanied by a large reduction in the expression of high-mobility group protein B 1 (HMGB1) post-ICH. In conclusion, this study provides in vivo evidence that cordycepin confers neuroprotective effect in the models of ICH, possibly through the suppression of NLRP3 inflammasome activation.

Lysophosphatidylcholine activates caspase-1 in microglia via a novel pathway involving two inflammasomes

Inflammasomes regulate microglial caspase-1 activation and subsequent neuroinflammatory processes in brain pathology. In the present study, we have identified inflammasomes causing caspase-1 activation following stimulation of microglia with lysophosphatidylcholine (LPC), a proinflammatory lipid generated under pathological conditions in the brain. LPC-induced caspase-1 activation in microglia was found to depend on LPS prestimulation, inflammasome NLRP3 and adaptor molecule ASC. Furthermore, knockdown of inflammasome NLRC4 inhibited LPC-stimulated caspase-1 activity in microglia, suggesting the requirement of two inflammasomes for optimal caspase-1 activity.

Neurodegeneration and NLRP3 inflammasome expression in the anterior thalamus of SOD1(G93A) ALS mice

Nowadays, amyotrophic lateral sclerosis (ALS) is considered as a multisystem disorder, characterized by a primary degeneration of motor neurons as well as neuropathological changes in non-motor regions. Neurodegeneration in subcortical areas, such as the thalamus, are believed to contribute to cognitive and behavioral abnormalities in ALS patients. In the present study, we investigated neurodegenerative changes including neuronal loss and glia pathology in the anterodorsal thalamic nucleus (AD) of SOD1(G93A) mice, a widely used animal model for ALS. We detected massive dendrite swelling and neuronal loss in SOD1(G93A) animals, which was accompanied by a mild gliosis. Furthermore, misfolded SOD1 protein and autophagy markers were accumulating in the AD. Since innate immunity and activation inflammasomes seem to play a crucial role in ALS, we examined protein expression of Nod-like receptor protein 3 (NLRP3), apoptosis-associated speck-like protein containing a caspase-1 recruitment domain (ASC) and the cytokine interleukin 1 beta (IL1β) in AD glial cells and neurons. NLRP3 and ASC were significantly up-regulated in the AD of SOD1(G93A) mice. Finally, co-localization studies revealed expression of NLRP3, ASC and IL1β in neurons. Our study yielded two main findings: (i) neurodegenerative changes already occur at an early symptomatic stage in the AD and (ii) increased inflammasome expression may contribute to neuronal cell death. In conclusion, neurodegeneration in the anterior thalamus may critically account for cognitive changes in ALS pathology.

NLRP3 Inflammasome in Neurological Diseases, from Functions to Therapies

Neuroinflammation has been identified as a causative factor of multiple neurological diseases. The nucleotide-binding oligomerization domain-, leucine-rich repeat- and pyrin domain-containing 3 (NLRP3) inflammasome, a subcellular multiprotein complex that is abundantly expressed in the central nervous system (CNS), can sense and be activated by a wide range of exogenous and endogenous stimuli such as microbes, aggregated and misfolded proteins, and adenosine triphosphate, which results in activation of caspase-1. Activated caspase-1 subsequently leads to the processing of interleukin-1β (IL-1β) and interleukin-18 (IL-18) pro-inflammatory cytokines and mediates rapid cell death. IL-1β and IL-18 drive inflammatory responses through diverse downstream signaling pathways, leading to neuronal damage. Thus, the NLRP3 inflammasome is considered a key contributor to the development of neuroinflammation. In this review article, we briefly discuss the structure and activation the NLRP3 inflammasome and address the involvement of the NLRP3 inflammasome in several neurological disorders, such as brain infection, acute brain injury and neurodegenerative diseases. In addition, we review a series of promising therapeutic approaches that target the NLRP3 inflammasome signaling including anti-IL-1 therapy, small molecule NLRP3 inhibitors and other compounds, however, these approaches are still experimental in neurological diseases. At present, it is plausible to generate cell-specific conditional NLRP3 knockout (KO) mice via the Cre system to investigate the role of the NLRP3 inflammasome, which may be instrumental in the development of novel pharmacologic investigations for neuroinflammation-associated diseases.

Estrogen Attenuates Local Inflammasome Expression and Activation after Spinal Cord Injury

17-estradiol (E2) is a neuroprotective hormone with a high anti-inflammatory potential in different neurological disorders. The inflammatory response initiated by spinal cord injury (SCI) involves the processing of interleukin-1beta (IL-1b) and IL-18 mediated by caspase-1 which is under the control of an intracellular multiprotein complex called inflammasome. We recently described in a SCI model that between 24 and 72 h post-injury, most of inflammasome components including IL-18, IL-1b, NLRP3, ASC, and caspase-1 are upregulated. In this study, we investigated the influence of E2 treatment after spinal cord contusion on inflammasome regulation. After contusion of T9 spinal segment, 12-week-old male Wistar rats were treated subcutaneously with E2 immediately after injury and every 12 h for the next 3 days. Behavioral scores were significantly improved in E2-treated animals compared to vehicle-treated groups. Functional improvement in E2-treated animals was paralleled by the attenuated expression of certain inflammasome components such as ASC, NLRP1b, and NLRP3 together with IL1b, IL-18, and caspase-1. On the histopathological level, microgliosis and oligodendrocyte injury was ameliorated. These findings support and extend the knowledge of the E2-mediated neuroprotective function during SCI. The control of the inflammasome machinery by E2 might be a missing piece of the puzzle to understand the anti-inflammatory potency of E2.

Administration of 17β-Estradiol Improves Motoneuron Survival and Down-regulates Inflammasome Activation in Male SOD1(G93A) ALS Mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease manifested by the progressive loss of upper and lower motoneurons. The pathomechanism of ALS is complex and not yet fully understood. Neuroinflammation is believed to significantly contribute to disease progression. Inflammasome activation was recently shown in the spinal cord of human sporadic ALS patients and in the SOD1(G93A) mouse model for ALS. In the present study, we investigated the neuroprotective and anti-inflammatory effects of 17β-estradiol (E2) treatment in pre-symptomatic and symptomatic male SOD1(G93A) mice. Symptomatic mice with E2 substitution exhibited improved motor performance correlating with an increased survival of motoneurons in the lumbar spinal cord. Expression of NLRP3 inflammasome proteins and levels of activated caspase 1 and mature interleukin 1 beta were significantly reduced in SOD1(G93A) mice supplemented with E2.

Gonadal steroids block the calpain-1-dependent intrinsic pathway of apoptosis in an experimental rat stroke model

OBJECTIVES

Apoptosis plays an important role in the progression of the ischemic penumbra after reperfusion. Estrogen and progesterone have neuroprotective effects against ischemic brain damage, however the exact mechanisms of neuroprotection and signaling pathways is not completely understood. In this study, we investigated the possible regulatory effects of a combined steroid treatment on extrinsic and intrinsic apoptotic signaling pathways after cerebral ischemia.

METHODS

Adult male Wistar rats were subjected to transient middle cerebral artery occlusion (tMCAO) using an intraluminal filament technique for 1 h followed by 23 h reperfusion. Estrogen and progesterone were immediately injected after tMCAO subcutaneously. Sensorimotor functional tests and the infarct volume were evaluated 24 h after ischemia. Protein expression of calpain-1 and Fas receptor (FasR), key members of intrinsic and extrinsic apoptosis, were determined in the penumbra region of the ischemic brain using western blot analysis, immunohistochemistry, and TUNEL staining.

RESULTS

Neurological deficits and infarct volume were significantly reduced following hormone therapy. Calpain-1 up-regulation and caspase-3 activation were apparent 24 h after ischemia in the peri-infarct area of the cerebral cortex. Steroid hormone treatment reduced infarct pathology and attenuated the induction of both proteases. FasR protein levels were not affected by ischemia and hormone application.

CONCLUSION

We conclude that a combined steroid treatment inhibits ischemia-induced neuronal apoptosis through the regulation of intrinsic pathways.

NLRP3 Inflammasome Activation in the Brain after Global Cerebral Ischemia and Regulation by 17β-Estradiol

17β-Estradiol (E2) is a well-known neuroprotective factor in the brain. Recently, our lab demonstrated that the neuroprotective and cognitive effects of E2 require mediation by the estrogen receptor (ER) coregulator protein and proline-, glutamic acid-, and leucine-rich protein 1 (PELP1). In the current study, we examined whether E2, acting via PELP1, can exert anti-inflammatory effects in the ovariectomized rat and mouse hippocampus to regulate NLRP3 inflammasome activation after global cerebral ischemia (GCI). Activation of the NLRP3 inflammasome pathway and expression of its downstream products, cleaved caspase-1 and IL-1β, were robustly increased in the hippocampus after GCI, with peak levels observed at 6-7 days. Expression of P2X7 receptor, an upstream regulator of NLRP3, was also increased after GCI. E2 markedly inhibited NLRP3 inflammasome pathway activation, caspase-1, and proinflammatory cytokine production, as well as P2X7 receptor expression after GCI (at both the mRNA and protein level). Intriguingly, the ability of E2 to exert these anti-inflammatory effects was lost in PELP1 forebrain-specific knockout mice, indicating a key role for PELP1 in E2 anti-inflammatory signaling. Collectively, our study demonstrates that NLRP3 inflammasome activation and proinflammatory cytokine production are markedly increased in the hippocampus after GCI, and that E2 signaling via PELP1 can profoundly inhibit these proinflammatory effects.

Recent Advances of the NLRP3 Inflammasome in Central Nervous System Disorders

Inflammasomes are multiprotein complexes that trigger the activation of caspases-1 and subsequently the maturation of proinflammatory cytokines interleukin-1β and interleukin-18. These cytokines play a critical role in mediating inflammation and innate immunity response. Among various inflammasome complexes, the NLRP3 inflammasome is the best characterized, which has been demonstrated as a crucial role in various diseases. Here, we review recently described mechanisms that are involved in the activation and regulation of NLRP3 inflammasome. In addition, we summarize the recent researches on the role of NLRP3 inflammasome in central nervous system (CNS) diseases, including traumatic brain injury, ischemic stroke and hemorrhagic stroke, brain tumor, neurodegenerative diseases, and other CNS diseases. In conclusion, the NLRP3 inflammasome may be a promising therapeutic target for these CNS diseases.

Progesterone improves long-term functional and histological outcomes after permanent stroke in older rats

Previous studies have shown progesterone to be beneficial in animal models of central nervous system injury, but less is known about its longer-term sustained effects on recovery of function following stroke. We evaluated progesterone's effects on a panel of behavioral tests up to 8 weeks after permanent middle cerebral artery occlusion (pMCAO). Male Sprague-Dawley rats 12m.o. were subjected to pMCAO and, beginning 3h post-pMCAO, given intraperitoneal injections of progesterone (8mg/kg) or vehicle, followed by subcutaneous injections at 8h and then every 24h for 7 days, with tapering of the last 2 treatments. The rats were then tested on functional recovery at 3, 6 and 8 weeks post-stroke. We observed that progesterone-treated animals showed attenuation of infarct volume and improved functional outcomes at 8 weeks after stroke on grip strength, sensory neglect, motor coordination and spatial navigation tests. Progesterone treatments significantly improved motor deficits in the affected limb on a number of gait parameters. Glial fibrillary acidic protein expression was increased in the vehicle group and considerably lowered in the progesterone group at 8 weeks post-stroke. With repeated post-stroke testing, sensory neglect and some aspects of spatial learning performance showed spontaneous recovery, but on gait and grip-strength measres progesterone given only in the acute stage of stroke (first 7 days) showed sustained beneficial effects on all other measures of functional recovery up to 8 weeks post-stroke.