Pathogenesis of acute stroke and the role of inflammasomes

The Role of Inflammatory Response in Stroke Associated Programmed Cell Death

Stroke represents devastating pathology which is associated with a high morbidity and mortality. Initial damage caused directly by the onset of stroke, primary injury, may be eclipsed by secondary injury which may have a much more devastating effect on the brain. Primary injury is predominantly associated with necrotic cell death due to fatal insufficiency of oxygen and glucose. Secondary injury may on the contrary, lead apoptotic cell death due to structural damage which is not compatible with cellular functions or which may even represent the danger of malign transformation. The immune system is responsible for surveillance, defense and healing processes and the immune system plays a major role in triggering programmed cell death. Severe pathologies, such as stroke, are often associated with deregulation of the immune system, resulting in aggravation of secondary brain injury. The goal of this article is to overview the current knowledge about the role of immune system in the pathophysiology of stroke with respect to programmed neuronal cell death as well as to discuss current therapeutic strategies targeting inflammation after stroke.

P2X7 Receptor-Associated Programmed Cell Death in the Pathophysiology of Hemorrhagic Stroke

Hemorrhagic stroke is a life-threatening disease characterized by a sudden rupture of cerebral blood vessels, and cell death is widely believed to occur after exposure to blood metabolites or subsequently damaged cells. Recently, programmed cell death, such as apoptosis, autophagy, necroptosis, pyroptosis, and ferroptosis, has been demonstrated to play crucial roles in the pathophysiology of stroke. However, the detailed mechanisms of these novel kinds of cell death are still unclear. The P2X7 receptor, previously known for its cytotoxic activity, is an ATP-gated, nonselective cation channel that belongs to the family of ionotropic P2X receptors. Evolving evidence indicates that the P2X7 receptor plays a pivotal role in central nervous system pathology; genetic deletion and pharmacological blockade of the P2X7 receptor provide neuroprotection in various neurological disorders, including intracerebral hemorrhage and subarachnoid hemorrhage. The P2X7 receptor may regulate programmed cell death via (I) exocytosis of secretory lysosomes, (II) exocytosis of autophagosomes or autophagolysosomes during formation of the initial autophagic isolation membrane or omegasome, and (III) direct release of cytosolic IL-1β secondary to regulated cell death by pyroptosis or necroptosis. In this review, we present an overview of P2X7 receptor- associated programmed cell death for further understanding of hemorrhagic stroke pathophysiology, as well as potential therapeutic targets for its treatment.

Pioglitazone ameliorates retinal ischemia/reperfusion injury via suppressing NLRP3 inflammasome activities

AIM

To explore the role of Pioglitazone (Pio) on a mouse model of retinal ischemia/reperfusion (I/R) injury and to elucidate the potential mechanism.

METHODS

Retinal ischemia was induced in mice by increasing the intraocular pressure, and Pio was administered 4h though periocular injection before I/R. The number of cells in the ganglion cell layer (GCL) was counted 7d after retinal I/R injury. Glial fibrillary acidic protein (GFAP), nuclear factor-kappa B (NF-κB), p38, phosphorylated-p38, PPAR-γ, interleukin-1β (IL-1β), Toll-like receptor 4 (TLR4), NLRP3, cleaved caspase-1, caspase-1 were determined by real-time polymerase chain reaction and Western blotting.

RESULTS

Pio promoted the survival of retinal cells in GCL following retinal I/R injury (P<0.05). Besides, retinal I/R injury stimulated the expression of GFAP and TLR4, which were partially reversed by Pio treatment (P<0.05). Retinal I/R injury-upregulated expression of NLRP3, cleaved caspase-1, IL-1β was attenuated after Pio treatment (P<0.05). Moreover, I/R injury induced activation of NF-κB and p38 were inhibited by Pio treatment (P<0.05).

CONCLUSION

Pio promotes retinal ganglion cells survival by suppressing I/R-induced activation of TLR4/NLRP3 inflammasomes via inhibiting NF-κB and p38 phosphorylation.

Suppression of NLRP3 attenuates hemorrhagic transformation after delayed rtPA treatment in thromboembolic stroke rats: Involvement of neutrophil recruitment

BACKGROUND

Inflammation and neutrophils play pivotal roles in hemorrhagic transformation (HT) after recombinant tissue plasminogen activator (rtPA) treatment in stroke; however, the contribution of Nod-like receptor protein 3 (NLRP3), a key component of the innate immune system, is not yet known. This study aimed to explore the role of NLRP3 in the delayed rtPA-induced HT and its association with the neutrophil recruitment.

METHODS

Rats were subjected to thromboembolic focal cerebral ischemia and delayed rtPA treatment at 4 h after ischemia to mimic HT. NLRP3 short hairpin RNAs (shRNA) were administered 72 h before ischemia. Additionally, rabbit anti-rat neutrophil serum (inducing neutropenia) was administered before cerebral ischemia. The infarct volume, edema volume, neurological deficit, hemorrhages, blood-brain barrier (BBB) integrity and brain neutrophil recruitment were evaluated at 24 h after cerebral ischemia.

RESULTS

Our results demonstrated that delayed rtPA treatment at 4 h after ischemia promoted the expression of NLRP3 in neurons, microglia and endothelial cells, degradation of BBB components, and HT. NLRP3 knockdown significantly attenuated NLRP3 expression, BBB disruption, and HT. It also improved neurological functions and reduced neutrophil recruitment. Rabbit anti-rat neutrophil serum, like NLRP3 shRNA, reduced hemorrhage score and hemorrhage volumes after rtPA treatment. Furthermore, the anti-rat neutrophil serum combined with NLRP3 shRNA didn't further increase the protective effect on HT compared to rabbit anti-rat neutrophil serum used alone.

CONCLUSIONS

Together, our data suggest that NLRP3 inhibition can reduce neutrophil recruitment, which may contribute to the inhibitory effect on HT.

Low-level light emitting diode (LED) therapy suppresses inflammasome-mediated brain damage in experimental ischemic stroke

Use of photostimulation including low-level light emitting diode (LED) therapy has broadened greatly in recent years because it is compact, portable, and easy to use. Here, the effects of photostimulation by LED (610 nm) therapy on ischemic brain damage was investigated in mice in which treatment started after a stroke in a clinically relevant setting. The mice underwent LED therapy (20 min) twice a day for 3 days, commencing at 4 hours post-ischemia. LED therapy group generated a significantly smaller infarct size and improvements in neurological function based on neurologic test score. LED therapy profoundly reduced neuroinflammatory responses including neutrophil infiltration and microglia activation in the ischemic cortex. LED therapy also decreased cell death and attenuated the NLRP3 inflammasome, in accordance with down-regulation of pro-inflammatory cytokines IL-1β and IL-18 in the ischemic brain. Moreover, the mice with post-ischemic LED therapy showed suppressed TLR-2 levels, MAPK signaling and NF-kB activation. These findings suggest that by suppressing the inflammasome, LED therapy can attenuate neuroinflammatory responses and tissue damage following ischemic stroke. Therapeutic interventions targeting the inflammasome via photostimulation with LED may be a novel approach to ameliorate brain injury following ischemic stroke. Effect of post-ischemic low-level light emitting diode therapy (LED-T) on infarct reduction was mediated by inflammasome suppression.

Inflammasomes in neurological diseases: emerging pathogenic and therapeutic concepts

Inflammasome activation in the central nervous system occurs in both health and disease. Inflammasomes are cytosolic protein complexes that sense specific infectious or host stimuli and initiate inflammatory responses through caspase activation. Assembly of inflammasomes results in caspase-1-mediated proteolytic cleavage and release of the pro-inflammatory cytokines, interleukin-1β and interleukin-18, with initiation of pyroptosis, an inflammatory programmed cell death. Recent developments in the inflammasome field have uncovered novel molecular mechanisms that contribute to a broad range of neurological disorders including those associated with specific mutations in inflammasome genes as well as diseases modulated by inflammasome activation. This update focuses on recent developments in the field of inflammasome biology highlighting different inflammasome activators and pathways discovered in the nervous system. We also discuss targeted therapies that regulate inflammasomes and improve neurological outcomes.

Disrupted Ionic Homeostasis in Ischemic Stroke and New Therapeutic Targets

BACKGROUND

Stroke is a leading cause of long-term disability. All neuroprotectants targeting excitotoxicity have failed to become stroke medications. In order to explore and identify new therapeutic targets for stroke, we here reviewed present studies of ionic transporters and channels that are involved in ischemic brain damage.

METHOD

We surveyed recent literature from animal experiments and clinical reports in the databases of PubMed and Elsevier ScienceDirect to analyze ionic mechanisms underlying ischemic cell damage and suggest promising ideas for stroke therapy.

RESULTS

Dysfunction of ionic transporters and disrupted ionic homeostasis are most early changes that underlie ischemic brain injury, thus receiving sustained attention in translational stroke research. The Na⁺/K⁺-ATPase, Na⁺/Ca²⁺ Exchanger, ionotropic glutamate receptor, acid-sensing ion channels (ASICs), sulfonylurea receptor isoform 1 (SUR1)-regulated NC_Ca-ATP channels, and transient receptor potential (TRP) channels are critically involved in ischemia-induced cellular degenerating processes such as cytotoxic edema, excitotoxicity, necrosis, apoptosis, and autophagic cell death. Some ionic transporters/channels also act as signalosomes to regulate cell death signaling. For acute stroke treatment, glutamate-mediated excitotoxicity must be interfered within 2 hours after stroke. The SUR1-regulated NC_Ca-ATP channels, Na⁺/K⁺-ATPase, ASICs, and TRP channels have a much longer therapeutic window, providing new therapeutic targets for developing feasible pharmacological treatments toward acute ischemic stroke.

CONCLUSION

The next generation of stroke therapy can apply a polypharmacology strategy for which drugs are designed to target multiple ion transporters/channels or their interaction with neurotoxic signaling pathways. But a successful translation of neuroprotectants relies on in-depth analyses of cell death mechanisms and suitable animal models resembling human stroke.

Nrf2 inhibits NLRP3 inflammasome activation through regulating Trx1/TXNIP complex in cerebral ischemia reperfusion injury

The nod-like receptor protein 3 (NLRP3) inflammasome has a critical role in inflammation damage in ischemic injury, and the activation of the inflammasome is closely related to the interaction with thioredoxin interacting protein (TXNIP), which dissociates from the thioredoxin1 (Trx1)/TXNIP complex under oxidative stress. However, the negative regulator of NLRP3 inflammasome activation has not been fully investigated. Nuclear factor erythroid 2-related factor 2 (Nrf2) takes on a critical part in the antioxidant stress system, that controls the driven genes of antioxidant response element (ARE). Activate Nrf2 could inhibit the activation of NLRP3 inflammasome in acute liver injury and severe lupus nephritis. We aimed to explore the protective effect of Nrf2 in inhibiting the NLPR3 inflammasome formulation through the Trx1/TXNIP complex in cerebral ischemia reperfusion (cerebral I/R) injury. Middle cerebral artery occlusion/reperfusion (MCAO/R) model was used to imitate ischemic insult. Nrf2 was activated by tert-butylhydroquinone (tBHQ) intraperitoneally (i.p.) injection (16.7mg/kg), Nrf2,Trx1 and NLRP3 siRNAs were infused into the left paracele (12μl per rat), protein and mRNA levels were assessed by Western blot, qRT-PCR. ELISA was used for IL-1β and IL-18 activity measurements. After upregulating Nrf2, the expression of TXNIP in cytoplasm, NLRP3 inflammasome, and downstream factors caspase-1, IL-18, and IL-1β were significantly reduced, and Nrf2 knockdown yielded the opposite results. Trx1 knockdown produced the same effect of Nrf2 inhibition and the protective effect of Nrf2 was mostly abolished. Our results suggested that Nrf2 acted as a protective regulator against NLRP3 inflammasome activation by regulating the Trx1/TXNIP complex, which could possibly represent an innovative insight into the treatment of ischemia and reperfusion injury.

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.

Chronic glucocorticoid exposure activates BK-NLRP1 signal involving in hippocampal neuron damage

BACKGROUND

Neuroinflammation mediated by NLRP1 (nucleotide-binding oligomerization domain (NOD)-like receptor protein 1) inflammasome plays an important role in many neurological diseases such as Parkinson's disease (PD) and Alzheimer's disease (AD). Our previous studies showed that chronic glucocorticoid (GC) exposure increased brain inflammation via NLRP1 inflammasome and induce neurodegeneration. However, little is known about the mechanism of chronic GC exposure on NLRP1 inflammasome activation in hippocampal neurons.

METHODS

Hippocampal neurons damage was assessed by LDH kit and Hoechst 33258 staining. The expression of microtubule-associated protein 2 (MAP2), inflammasome complex protein (NLRP1, ASC and caspase-1), inflammatory cytokines (IL-1β), and large-conductance Ca²⁺ and voltage-activated K⁺ channel (BK channels) protein was detected by Western blot. The inflammatory cytokines (IL-1β and IL-18) were examined by ELISA kit. The mRNA levels of NLRP1, IL-1β, and BK were detected by real-time PCR. BK channel currents were recorded by whole-cell patch-clamp technology. Measurement of [K⁺]_i was performed by ion-selective electrode (ISE) technology.

RESULTS

Chronic dexamethasone (DEX) treatment significantly increased LDH release and neuronal apoptosis and decreased expression of MAP2. The mechanistic studies revealed that chronic DEX exposure significantly increased the expression of NLRP1, ASC, caspase-1, IL-1β, L-18, and BK protein and NLRP1, IL-1β and BK mRNA levels in hippocampal neurons. Further studies showed that DEX exposure results in the increase of BK channel currents, with the subsequent K⁺ efflux and a low concentration of intracellular K⁺, which involved in activation of NLRP1 inflammasome. Moreover, these effects of chronic DEX exposure could be blocked by specific BK channel inhibitor iberiotoxin (IbTx).

CONCLUSION

Our findings suggest that chronic GC exposure may increase neuroinflammation via activation of BK-NLRP1 signal pathway and promote hippocampal neurons damage, which may be involved in the development and progression of AD.

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.

Positive effects of intermittent fasting in ischemic stroke

Intermittent fasting (IF) is a dietary protocol where energy restriction is induced by alternate periods of ad libitum feeding and fasting. Prophylactic intermittent fasting has been shown to extend lifespan and attenuate the progress and severity of age-related diseases such as cardiovascular (e.g. stroke and myocardial infarction), neurodegenerative (e.g. Alzheimer's disease and Parkinson's disease) and cancerous diseases in animal models. Stroke is the second leading cause of death, and lifestyle risk factors such as obesity and physical inactivity have been associated with elevated risks of stroke in humans. Recent studies have shown that prophylactic IF may mitigate tissue damage and neurological deficit following ischemic stroke by a mechanism(s) involving suppression of excitotoxicity, oxidative stress, inflammation and cell death pathways in animal stroke models. This review summarizes data supporting the potential hormesis mechanisms of prophylactic IF in animal models, and with a focus on findings from animal studies of prophylactic IF in stroke in our laboratory.

The NLRC4 inflammasome: The pieces of the puzzle are falling into place

Inflammasomes are intracellular multiprotein platforms for the activation of inflammatory caspases. As components of the innate immune system, they play an important role in the fight against microbes. However, aberrant inflammasome activation has been implicated in auto-inflammatory syndromes. This review focuses on the NLRC4 inflammasome. This is perhaps not the most extensively studied, yet its mechanism of activation is by far the best understood. The NLRC4 inflammasome is activated by several proteins originating from intracellular bacteria, which are first sensed by receptors of the NAIP family. Activated NAIP binds NLRC4, which further recruits dormant NLRC4 molecules in a prion-like oligomerization event. NLRC4 enables a strong amplification of the signal, providing a fast and robust host response. The review also discusses peculiar NLRC4 inflammasome functions in promoting eicosanoid biosynthesis, actin reorganization, and its roles in autoinflammatory syndromes and sterile inflammation. Finally, the first inflammasome-independent engagement of NLRC4 in suppressing melanoma tumor growth is presented. The emerging roles of NLRC4 in various normal and pathological processes demonstrate that there is still plenty to be learned about the NLRC4 mechanism of activation and downstream functions.

Postischemic Inflammation in Acute Stroke

Cerebral ischemia is caused by arterial occlusion due to a thrombus or an embolus. Such occlusion induces multiple and concomitant pathophysiological processes that involve bioenergetic failure, acidosis, loss of cell homeostasis, excitotoxicity, and disruption of the blood-brain barrier. All of these mechanisms contribute to neuronal death, mainly via apoptosis or necrosis. The immune system is involved in this process in the early phases after brain injury, which contributes to potential enlargement of the infarct size and involves the penumbra area. Whereas inflammation and the immune system both exert deleterious effects, they also contribute to brain protection by stimulating a preconditioning status and to the concomitant repair of the injured parenchyma. This review describes the main phases of the inflammatory process occurring after arterial cerebral occlusion, with an emphasis on the role of single mediators.

The Emerging Role of Thioredoxin-Interacting Protein in Myocardial Ischemia/Reperfusion Injury

Myocardial ischemia/reperfusion injury represents a major threat to human health and contributes to adverse cardiovascular outcomes worldwide. Despite the identification of numerous molecular mechanisms, understanding of the complex pathophysiology of this clinical syndrome remains incomplete. Thioredoxin-interacting protein (Txnip) has been of great interest in the past decade since it has been reported to be a critical regulator in human diseases with several important cellular functions. Thioredoxin-interacting protein binds to and inhibits thioredoxin, a redox protein that neutralizes reactive oxygen species (ROS), and through its interaction with thioredoxin, Txnip sensitizes cardiomyocytes to ROS-induced apoptosis. Interestingly, evidence from recent studies also suggests that some of the effects of Txnip may be unrelated to changes in thioredoxin activity. These pleiotropic effects of Txnip are mediated by interactions with other signaling molecules, such as nod-like receptor pyrin domain-containing 3 inflammasome and glucose transporter 1. Indeed, Txnip has been implicated in the regulation of inflammatory response and glucose homeostasis during myocardial ischemia/reperfusion injury. This review attempts to make the case that in addition to interacting with thioredoxin, Txnip contributes to some of the pathological consequences of myocardial ischemia and infarction through endogenous signals in multiple molecular mechanisms.

Increased Risk of Stroke in Patients With Nonarteritic Anterior Ischemic Optic Neuropathy: A Nationwide Retrospective Cohort Study

PURPOSE

To investigate the incidence and prevalence of nonarteritic anterior ischemic optic neuropathy (NAION), and to extrapolate the risk of cerebrovascular events following NAION.

DESIGN

Retrospective cohort study.

METHODS

We identified NAION patients first, and then looked for the diagnosis of stroke after the diagnosis of NAION.

SETTING

The study group was composed of patients diagnosed with NAION seeking ambulatory care from 2000 to 2011. The control group was extracted from a database by randomly selecting 2 patients for every NAION patient, matched by age and sex.

MAIN OUTCOME MEASURES

Cox proportional hazards regression analysis was performed to calculate adjusted hazard ratio (aHR) of stroke for the 2 groups. Subgroup analysis of subjects with or without comorbidities was also investigated.

RESULTS

Four hundred and fourteen patients were included in the study group and 789 in the control group. The mean follow-up period was 5.9 years. The incidence of NAION was 3.72/100 000 person-years in Taiwan, and the prevalence of NAION was 48.18/100 000 persons. The study group was more likely to have ischemic stroke (aHR = 2.03, P = .003), but not hemorrhagic stroke (aHR = 1.24, P = .696), than the control group. Among the subgroup with comorbidities, the risk of ischemic stroke among the subjects with NAION was 3.35 times higher than those without NAION (95% confidence interval: 1.67, 6.70).

CONCLUSIONS

Patients with NAION have an increased risk of ischemic stroke. Physicians should refer all patients with NAION for systemic survey of vasculopathy and control of modifiable risk factors to prevent irreversible neurological sequelae.

Ruscogenin Attenuates Cerebral Ischemia-Induced Blood-Brain Barrier Dysfunction by Suppressing TXNIP/NLRP3 Inflammasome Activation and the MAPK Pathway

Ruscogenin, an important steroid sapogenin derived from Ophiopogon japonicus, has been shown to inhibit cerebral ischemic injury. However, its potential molecular action on blood-brain barrier (BBB) dysfunction after stroke remains unclear. This study aimed to investigate the effects of ruscogenin on BBB dysfunction and the underlying mechanisms in middle cerebral artery occlusion/reperfusion (MCAO/R)-injured mice and oxygen–glucose deprivation/reoxygenation (OGD/R)-injured mouse brain microvascular endothelial cells (bEnd.3). The results demonstrated that administration of ruscogenin (10 mg/kg) decreased the brain infarction and edema, improved neurological deficits, increased cerebral brain flow (CBF), ameliorated histopathological damage, reduced evans blue (EB) leakage and upregulated the expression of tight junctions (TJs) in MCAO/R-injured mice. Meanwhile, ruscogenin (0.1–10 µM) treatment increased cell viability and trans-endothelial electrical resistance (TEER) value, decreased sodium fluorescein leakage, and modulated the TJs expression in OGD/R-induced bEnd.3 cells. Moreover, ruscogenin also inhibited the expression of interleukin-1β (IL-1β) and caspase-1, and markedly suppressed the expression of Nucleotide-binding domain (NOD)-like receptor family, pyrin domain containing 3 (NLRP3) and thiredoxin-interactive protein (TXNIP) in vivo and in vitro. Furthermore, ruscogenin decreased reactive oxygen species (ROS) generation and inhibited the mitogen-activated protein kinase (MAPK) pathway in OGD/R-induced bEnd.3 cells. Our findings provide some new insights into its potential application for the prevention and treatment of ischemic stroke.

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.

MicroRNA-155 Regulates ROS Production, NO Generation, Apoptosis and Multiple Functions of Human Brain Microvessel Endothelial Cells Under Physiological and Pathological Conditions

The microRNA-155 (miR155) regulates various functions of cells. Dysfunction or injury of endothelial cells (ECs) plays an important role in the pathogenesis of various vascular diseases. In this study, we investigated the role and potential mechanisms of miR155 in human brain microvessel endothelial cells (HBMECs) under physiological and pathological conditions. We detected the effects of miR155 silencing on ROS production, NO generation, apoptosis and functions of HBMECs at basal and in response to oxidized low density lipoprotein (ox-LDL). Western blot and q-PCR were used for analyzing the gene expression of epidermal growth factor receptor (EGFR)/extracellular regulated protein kinases (ERK)/p38 mitogen-activated protein kinase (p38 MAPK), phosphatidylinositol-3-kinase (PI3K) and serine/threonine kinase(Akt), activated caspase-3, and intercellular adhesion molecule-1 (ICAM-1). Results showed that under both basal and challenge situations: (1) Silencing of miR155 decreased apoptosis and reactive oxygen species (ROS) production of HBMECs, whereas, promoted nitric oxide (NO) generation. (2) Silencing of miR155 increased the proliferation, migration, and tube formation ability of HBMECs, while decreased cell adhesion ability. (3) Gene expression analyses showed that EGFR/ERK/p38 MAPK and PI3K/Akt were increased and that activated caspase-3 and ICAM-1 mRNA were decreased after knockdown of miR155. In conclusion, knockdown of miR155 could modulate ROS production, NO generation, apoptosis and function of HBMECs via regulating diverse gene expression, such as caspase-3, ICAM-1 and EGFR/ERK/p38 MAPK and PI3K/Akt pathways.

A Polymorphism Within the 3'UTR of NLRP3 is Associated with Susceptibility for Ischemic Stroke in Chinese Population

Stroke was regarded as a severe disorder with high morbidity and high mortality worldwide, ischemic stroke (IS) accounts for 85 to 90 % of new increased stroke cases. Partial mechanisms were elucidated by genetic factors including genomic instability such as single nucleotide polymorphism (SNP). Previous reports demonstrated that inflammation was involved in IS, NLRP3 [nucleotide-binding domain (NOD)-like receptor protein 3], acting as a specific inflammatory gene, however, its function and influence on IS was not well clarified. In this study, a case-control study including 1102 IS patients and 1610 healthy controls was conducted to investigate the association between IS susceptibility with a SNP (rs10754558) in 3'UTR of NLRP3. Logistic regression analysis showed that the heterozygote and the homozygote GG confer a significantly increased risk of CRC after controlling for other covariates (adjusted OR = 1.52, 95 % C.I. 1.19-1.97, P = 0.002; adjusted OR = 2.22, 95 % C.I. 2.18-3.67, P < 0.001, respectively). Carriage of G allele was associated with a greatly increased risk of developing the disease (OR = 1.69, 95 % C.I. 1.31-1.83, P < 0.001). Stratification analysis found that hypertension had interaction with rs10754558 to modulate IS risk. Further in vitro assay revealed that rs10754558 can affect mRNA level of NLRP3, suggesting its possible functional significance. Our data suggested that genetic polymorphisms in NLRP3 may influence IS risk in Chinese population. Replication of our studies in other populations and further functional studies are required for complete comprehension of the roles of NLRP3 polymorphisms in IS risk.

Protective effect of n-butyl alcohol extracts from Rhizoma Pinelliae Pedatisectae against cerebral ischemia-reperfusion injury in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Rhizoma Pinelliae Pedatisectae (RPP) has been commonly used in traditional Chinese medicine (TCM) for treatment of various neurological related diseases. However, the mechanisms have not been fully clarified yet. The present study was designed to investigate the therapeutic effect of RPP against cerebral ischemic/reperfusion (I/R) injury in rats models, and more importantly, to explore the underlying mechanism.

MATERIALS AND METHODS

Cerebral ischemia and reperfusion was established through the classic middle cerebral artery occlusion (MCAO) for 2h, followed by 24h reperfusion. Rats were orally given different doses of n-butyl alcohol extracts (NBES) of RPP or saline for one week before induction of ischemia. Neurological defect scoring, cerebral infarct volume, oxidative stress markers, inflammatory reaction and nerve cell apoptosis were then estimated.

RESULTS

It showed that NBES could alleviate in a dose-dependent manner neurological deficit and reduce the infarct volume in vivo. The protective effects of NBES were associated with increased Superoxide dismutase (SOD) activity and decreased malonaldehyde (MDA), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) levels. In addition, ischemia-induced neuron apoptosis was inhibited by NBES pretreatment, and western blot showed NBES upregulated expressions of B-cell leukemia-2 (Bcl-2) and downregulated Bcl-2-associated X (Bax) expression.

CONCLUSION

NBES prevent cerebral I/R injury by alleviating neuronal oxidative injury, inflammatory reaction and neuron apoptosis. The research for the traditional use of RPP provided certain theoretical basis.

Interleukin-18 gene promoter 607A polymorphism, but not 137C polymorphism, is a protective factor for ischemic stroke in the Chinese population: A meta-analysis

Some epidemiological studies have evaluated the association between interleukin (IL)-18 promoter polymorphisms and the risk of ischemic stroke (IS), but the results were inconsistent. The present meta-analysis was therefore performed to investigate the relationship between IL-18 promoter 137G/C and 607C/A polymorphisms and the risk of IS in the Chinese population. Related studies from PubMed, Embase, Web of Science, CBMdisc and CNKI databases up to November 1, 2014 were systematically searched, also the reference lists of identified articles were manually searched. Information was extracted to calculate for the allelic, genotypic, dominant and recessive models using the pooled odds ratios (ORs) along with 95% confidence intervals (CIs). Evidence of significant association between 607C/A polymorphism and risk of IS was found in four genetic models based on the overall population. However, no significant association between 137G/C polymorphism and risk of IS was found in four genetic models. In summary, the present study suggests that IL-18 gene promoter 607A polymorphism is a protective factor for IS in the Chinese population, while 137C polymorphism has weaker or no protective properties. Still, a larger number of studies with large scale and sufficient original information are required to further confirm our findings.

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We performed a meta-analysis to investigate the relationship between IL-18 gene promoter polymorphisms and ischemic stroke.

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IL-18 gene promoter 607C/A polymorphism is a protective factor for ischemic stroke in the Chinese population.

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This is the first meta-analysis studying such association in Chinese ischemic stroke patients.

Phytochemicals in Ischemic Stroke

Stroke is the second foremost cause of mortality worldwide and a major cause of long-term disability. Due to changes in lifestyle and an aging population, the incidence of stroke continues to increase and stroke mortality predicted to exceed 12 % by the year 2030. However, the development of pharmacological treatments for stroke has failed to progress much in over 20 years since the introduction of the thrombolytic drug, recombinant tissue plasminogen activator. These alarming circumstances caused many research groups to search for alternative treatments in the form of neuroprotectants. Here, we consider the potential use of phytochemicals in the treatment of stroke. Their historical use in traditional medicine and their excellent safety profile make phytochemicals attractive for the development of therapeutics in human diseases. Emerging findings suggest that some phytochemicals have the ability to target multiple pathophysiological processes involved in stroke including oxidative stress, inflammation and apoptotic cell death. Furthermore, epidemiological studies suggest that the consumption of plant sources rich in phytochemicals may reduce stroke risk, and so reinforce the possibility of developing preventative or neuroprotectant therapies for stroke. In this review, we describe results of preclinical studies that demonstrate beneficial effects of phytochemicals in experimental models relevant to stroke pathogenesis, and we consider their possible mechanisms of action.

Functions and mechanisms of microglia/macrophages in neuroinflammation and neurogenesis after stroke

Microglia/macrophages are the major immune cells involved in the defence against brain damage. Their morphology and functional changes are correlated with the release of danger signals induced by stroke. These cells are normally responsible for clearing away dead neural cells and restoring neuronal functions. However, when excessively activated by the damage-associated molecular patterns following stroke, they can produce a large number of proinflammatory cytokines that can disrupt neural cells and the blood-brain barrier and influence neurogenesis. These effects indicate the important roles of microglia/macrophages in the pathophysiological processes of stroke. However, the modifiable and adaptable nature of microglia/macrophages may also be beneficial for brain repair and not just result in damage. These distinct roles may be attributed to the different microglia/macrophage phenotypes because the M1 population is mainly destructive, while the M2 population is neuroprotective. Additionally, different gene expression signature changes in microglia/macrophages have been found in diverse inflammatory milieus. These biofunctional features enable dual roles for microglia/macrophages in brain damage and repair. Currently, it is thought that the proper inflammatory milieu may provide a suitable microenvironment for neurogenesis; however, detailed mechanisms underlying the inflammatory responses that initiate or inhibit neurogenesis remain unknown. This review summarizes recent progress concerning the mechanisms involved in brain damage, repair and regeneration related to microglia/macrophage activation and phenotype transition after stroke. We also argue that future translational studies should be targeting multiple key regulating molecules to improve brain repair, which should be accompanied by the concept of a "therapeutic time window" for sequential therapies.

Association of interleukin 18-607A/C and -137C/G polymorphisms with oxidative stress in renal transplant recipients

Objectives IL-18 mediates various inflammatory and oxidative responses including renal injury, fibrosis, and graft rejection. It has been reported that the promoter -607 and -137 polymorphisms of IL-18 influence the level of IL-18. This prospective observational study investigated the association between oxidative stress with IL-18-607 and -137 polymorphisms in renal transplant recipients. Patients and methods This study included 75 renal transplant recipients (28 female, 47 male) from living-related donors. Blood samples were collected immediately before and after transplantation at day 7 and month 1. Serum IL-18, creatinine, cystatin C, CRP, and oxidative stress markers (TOS, TAC) were measured. The Oxidative Stress Index (OSI) was calculated. Polymorphisms of the promoter region of the IL-18 gene, IL18-607A/C, and -137C/G were determined by analysis of a "real-time PCR/Melting curve". Results Serum creatinine, cystatin C, CRP, IL-18, TOS, and OSI levels significantly decreased after transplantation. Post-transplant levels of serum TAC and estimated GFR demonstrated consistent significant increases. Serum IL-18 levels were significantly higher in patients with IL-18-137 GG and IL-18-607 CC genotypes before transplantation. Conclusion Our results indicate that the IL-18-137 GG and -607 CC genotypes contribute to higher IL-18 levels; however, the influence of these polymorphisms on oxidative stress has not been observed.

Key Immune Events of the Pathomechanisms of Early Cardioembolic Stroke: Multi-Database Mining and Systems Biology Approach

While inflammation has generally been regarded as a negative factor in stroke recovery, this viewpoint has recently been challenged by demonstrating that inflammation is a necessary and sufficient factor for regeneration in the zebrafish brain injury model. This close relationship with inflammation suggests that a re-examination of the immune system’s role in strokes is necessary. We used a systems biology approach to investigate the role of immune-related functions via their interactions with other molecular functions in early cardioembolic stroke. Based on protein interaction models and on microarray data from the blood of stroke subjects and healthy controls, networks were constructed to delineate molecular interactions at four early stages (pre-stroke, 3 h, 5 h and 24 h after stroke onset) of cardioembolic stroke. A comparative analysis of functional networks identified interactions of immune-related functions with other molecular functions, including growth factors, neuro/hormone and housekeeping functions. These provide a potential pathomechanism for early stroke pathophysiology. In addition, several potential targets of miRNA and methylation regulations were derived based on basal level changes observed in the core networks and literature. The results provide a more comprehensive understanding of stroke progression mechanisms from an immune perspective and shed light on acute stroke treatments.

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

CNS ischemia results in locally confined and rapid tissue damage accompanied by a loss of neurons and their circuits. Early and time-delayed inflammatory responses are critical variables determining the extent of neural disintegration and regeneration. Inflammasomes are vital effectors in innate immunity. Their activation in brain-intrinsic immune cells contributes to ischemia-related brain damage. The steroids 17β-estradiol (E2) and progesterone (P) are neuroprotective and anti-inflammatory. Using a transient focal rat ischemic model, we evaluated the time response of different inflammasomes in the peri-infarct zone from the early to late phases after poststroke ischemia. We show that the different inflammasome complexes reveal a specific time-oriented sequential expression pattern with a maximum at approximately 24 h after the infarct. Within the limits of antibody availability, immunofluorescence labeling demonstrated that microglia and neurons are major sources of the locally activated inflammasomes NOD-like receptor protein-3 (NLRP3) and associated speck-like protein (ASC), respectively. E2 and P given for 24 h immediately after ischemia onset reduced hypoxia-induced mRNA expression of the inflammasomes NLRC4, AIM2 and ASC, and decreased the protein levels of ASC and NLRP3. In addition, mRNA protein levels of the cytokines interleukin-1β (IL1β), IL18 and TNFα were reduced by the steroids. The findings provide for the first time a detailed flow chart of hypoxia-driven inflammasome regulation in the peri-infarct cerebral cortex. Further, we demonstrate that E2 and P alleviate the expression of certain inflammasome components, sometimes in a hormone-specific way. Besides directly regulating other cellular neuroprotective pathways, the control of inflammasomes by these steroids might contribute to its neuroprotective potency.

Acid-sensing ion channel 1a contributes to the effect of extracellular acidosis on NLRP1 inflammasome activation in cortical neurons

Background

Acid-sensing ion channels (ASICs) are cation channels which were activated by extracellular acidosis and involved in various physiological and pathological processes in the nervous system. Inflammasome is a key component of the innate immune response in host against harmful and irritable stimuli. As the first discovered molecular platform, NLRP1 (nucleotide-binding oligomerization domain (NOD)-like receptor protein 1) inflammasome is expressed in neurons and implicated in many nervous system diseases such as brain injury, nociception and epilepsy. However, little is known about the effect of ASICs on NLRP1 inflammasome activation under acidosis.

Methods

The expression of inflammasome complex protein (NLRP1, ASC (apoptosis-associated speck-like protein containing a caspase-activating recruitment domain) and caspase-1), inflammatory cytokines (IL-1β and IL-18), and apoptosis-related protein (Bax, Bcl-2, and activated caspase-3) was detected by Western blot. Large-conductance Ca²⁺ and voltage-activated K⁺ (BK) channel currents were recorded by whole-cell patch-clamp technology. Measurement of [K⁺]_i was performed by fluorescent ion imaging system. Co-expression of ASICs and BK channels was determined by dual immunofluorescence. Cell viability was assessed by MTT and LDH kit.

Results

ASICs and BK channels were co-expressed in primary cultured cortical neurons. Extracellular acidosis increased the expression of NLRP1, ASC, caspase-1, IL-1β, and IL-18. Further mechanistic studies revealed that acidosis-induced ASIC1a activation results in the increase of BK channel currents, with the subsequent K⁺ efflux and a low concentration of intracellular K⁺, which activated NLRP1 inflammasome. Furthermore, these effects of acidosis could be blocked by specific ASIC1a inhibitor PcTX1 and BK channel inhibitor IbTX. The data also demonstrated neutralization of NLRP1-protected cortical neurons against injury induced by extracellular acidosis.

Conclusions

Our data showed that NLRP1 inflammasome could be activated by extracellular acidosis though ASIC-BK channel K⁺ signal pathway and was involved in extracellular acidosis-induced cortical neuronal injury.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0465-7) contains supplementary material, which is available to authorized users.

Endogenous recovery after brain damage: molecular mechanisms that balance neuronal life/death fate

Neuronal survival depends on multiple factors that comprise a well-fueled energy metabolism, trophic input, clearance of toxic substances, appropriate redox environment, integrity of blood-brain barrier, suppression of programmed cell death pathways and cell cycle arrest. Disturbances of brain homeostasis lead to acute or chronic alterations that might ultimately cause neuronal death with consequent impairment of neurological function. Although we understand most of these processes well when they occur independently from one another, we still lack a clear grasp of the concerted cellular and molecular mechanisms activated upon neuronal damage that intervene in protecting damaged neurons from death. In this review, we summarize a handful of endogenously activated mechanisms that balance molecular cues so as to determine whether neurons recover from injury or die. We center our discussion on mechanisms that have been identified to participate in stroke, although we consider different scenarios of chronic neurodegeneration as well. We discuss two central processes that are involved in endogenous repair and that, when not regulated, could lead to tissue damage, namely, trophic support and neuroinflammation. We emphasize the need to construct integrated models of neuronal degeneration and survival that, in the end, converge in neuronal fate after injury. Under neurodegenerative conditions, endogenously activated mechanisms balance out molecular cues that determine whether neurons contend toxicity or die. Many processes involved in endogenous repair may as well lead to tissue damage depending on the strength of stimuli. Signaling mediated by trophic factors and neuroinflammation are examples of these processes as they regulate different mechanisms that mediate neuronal demise including necrosis, apoptosis, necroptosis, pyroptosis and autophagy. In this review, we discuss recent findings on balanced regulation and their involvement in neuronal death.

RIG-I contributes to the innate immune response after cerebral ischemia

Background

Focal cerebral ischemia induces an inflammatory response that when exacerbated contributes to deleterious outcomes. The molecular basis regarding the regulation of the innate immune response after focal cerebral ischemia remains poorly understood.

Methods

In this study we examined the expression of retinoic acid-inducible gene (RIG)-like receptor-I (RIG-I) and its involvement in regulating inflammation after ischemia in the brain of rats subjected to middle cerebral artery occlusion (MCAO). In addition, we studied the regulation of RIG-I after oxygen glucose deprivation (OGD) in astrocytes in culture.

Results

In this study we show that in the hippocampus of rats, RIG-I and IFN-α are elevated after MCAO. Consistent with these results was an increased in RIG-I and IFN-α after OGD in astrocytes in culture. These data are consistent with immunohistochemical analysis of hippocampal sections, indicating that in GFAP-positive cells there was an increase in RIG-I after MCAO. In addition, in this study we have identified n-propyl gallate as an inhibitor of IFN-α signaling in astrocytes.

Conclusion

Our findings suggest a role for RIG-I in contributing to the innate immune response after focal cerebral ischemia.

Inflammasomes are neuroprotective targets for sex steroids

Neuroinflammation in the central nervous system is triggered by toxic stimuli or degenerative events, orchestrates the interplay of brain-intrinsic immune cells and neighboring neural cells, and sequentially allows leukocyte extravasation from the periphery into the brain parenchyma. During the inflammatory cascade, immune-competent cells become activated and secrete a plethora of cytokines and chemokines which form a local inflammatory signaling network important for warding off harmful stimuli to the host but are likewise necessary to preserve damaged brain tissue. Inflammatory responses are initiated by extra- and intra-cellular pathogen and danger-associated receptors. These signals are processed by multi-protein complexes termed inflammasomes which trigger the production of biologically active interleukins-1 and 18 after the cleavage of caspase-1. Estrogens and progesterone are neuroprotective and anti-inflammatory in diverse disease models of the brain in particular under acute inflammatory conditions such as stroke and traumatic brain injury. Both steroids are able to attenuate pro-inflammatory cytokine activity. Recent literature and our own studies provide convincing evidence that the anti-inflammatory potency of these steroids result from a complex interaction with the inflammasome activation and their up-stream regulatory network of miRNAs in brain-intrinsic innate immune cells. This article examines steroid-inflammasome interactions in the brain during brain injury and illuminates the importance of regulation initial upstream events during neuroinflammation. This article is part of a Special Issue entitled 'Steroid Perspectives'.

HMGB1 promotes the activation of NLRP3 and caspase-8 inflammasomes via NF-κB pathway in acute glaucoma

Background

Acute glaucoma is a significantly sight-threatening cause of irreversible blindness in the world characterized by a sudden and substantial intraocular pressure (IOP) increase and subsequent retinal ganglion cell (RGC) death. This study aims to explore the role of high-mobility group box 1 (HMGB1) in an acute glaucoma mouse model.

Methods

An acute glaucoma model was induced by a rapid and substantial increase IOP to 70 mmHg for 60 min via anterior chamber punctured and affused with Balance Salt Solution in C57BL/6 mice. Retinal tissue ischemic damage and loss of RGCs were assessed at 6, 24, 48, 72 h after high IOP treatment, and at 48 h, group with or without recombinant high-mobility group box 1 (rHMGB1), the HMGB1 inhibitor, glycyrrhizic acid (GA), and by HE and immunofluorescent staining. The nuclear factor κB (NF-κB) inhibitor, JSH-23, and caspase-8 inhibitor, Z-IETD-fmk, were injected into vitreous. Reverse transcription and semi-quantitative reverse transcription polymerase chain reaction (RT-PCR), western blotting, and immunoprecipitation were performed to evaluate the expression level of nucleotide-binding domain, leucine-rich repeat containing protein 3 (NLRP3), phosphor-NF-κB p65, caspase-8, caspase-1, apoptosis-associated speck-like protein containing a CARD (ASC), and interleukin-1β (IL-1β).

Results

HMGB1 was increased in ischemic retinal tissue during acute glaucoma as early as 6 h after rapid IOP elevation. Exogenous HMGB1 exacerbated retinal ischemic damage, RGC loss, and inhibition of endogenous HMGB1 significantly reduced the severity of disease. HMGB1 significantly induced the elevation of canonical NLRP3, ASC, caspase-1, and non-canonical capase-8-ASC inflammasome and promoted the processing of IL-1β. Furthermore, the effect of HMGB1 on NLRP3 inflammasome activation and IL-1β production was dependent on NF-κB pathway. Thus, HMGB1/caspase-8 pathway promoted the processing of IL-1β via NF-κB pathway.

Conclusion

The findings of this study identified a novel signaling pathway in which HMGB1, in response to acutely elevated intraocular pressure, activated the canonical NLRP3 and non-canonical caspase-8 inflammasomes and production of IL-1β during acute glaucoma development. These results provide new insights to the understanding of the innate response that contributes to pathogenesis of acute glaucoma.

The Zinc Ion Chelating Agent TPEN Attenuates Neuronal Death/apoptosis Caused by Hypoxia/ischemia Via Mediating the Pathophysiological Cascade Including Excitotoxicity, Oxidative Stress, and Inflammation

AIMS

We aim to determine the significant effect of TPEN, a Zn(2+) chelator, in mediating the pathophysiological cascade in neuron death/apoptosis induced by hypoxia/ischemia.

METHODS

We conducted both in vivo and in vitro experiments in this study. PC12 cells were used to establish hypoxia/ischemia model by applying oxygen-glucose deprivation (OGD). SHR-SP rats were used to establish an acute ischemic model by electrocoagulating middle cerebral artery occlusion. The effect of TPEN on neuron death/apoptosis was evaluated. In addition, the relative biomarks of excitotoxicity, oxidative stress, and inflammation reactions in hypoxia/ischemia PC12 cell model as well as in SHR-SP rat hypoxia/ischemia model were also assessed.

RESULTS

TPEN significantly attenuates the neurological deficit, reduced the cerebral infarction area and the ratio of apoptotic neurons, and increased the expression of GluR2 in the rat hypoxia/ischemia brain. TPEN also increased blood SOD activity, decreased blood NOS activity and blood MDA and IL-6 contents in rats under hypoxia/ischemia. In addition, TPEN significantly inhibited the death and apoptosis of cells and attenuated the alteration of GluR2 and NR2 expression caused by OGD or OGD plus high Zn(2+) treatments.

CONCLUSIONS

Zn(2+) is involved in neural cell apoptosis and/or death caused by hypoxia/ischemia via mediating excitotoxicity, oxidative stress, and inflammation.

Umbelliferone ameliorates cerebral ischemia-reperfusion injury via upregulating the PPAR gamma expression and suppressing TXNIP/NLRP3 inflammasome

Umbelliferone (UMB), a natural antioxidant belonging to coumarin derivatives, is able to cross the blood-brain barrier and protect neuronal cells from death. Here we aimed to investigate the effects of UMB in a rat model of focal cerebral ischemia induced by middle cerebral artery occlusion/reperfusion (MCAO/R). Pretreatment with UMB (15 and 30 mg/kg) for 7 consecutive days ameliorated the neurological outcomes, infarct volume and brain edema in brains of MCAO rats. Our results provided evidence that UMB significantly protected neuronal cells against cerebral ischemia reperfusion-induced injury. Furthermore, UMB treatment could inhibited the level of oxidative stress and the production of inflammatory cytokines in brain tissues of MCAO rats. In addition, UMB significantly upregulated the expression of peroxisome proliferator-activated receptor-γ (PPAR-γ), which exhibited neuroprotective effects in neurodegenerative disease. UMB treatment also suppressed NLRP3 inflammasome activation via reducing expression of Thiredoxin-interactive protein (TXNIP). These results suggest that UMB may have beneficial effects for neuroprotection against focal cerebral ischemic partly through the inhibition of TXNIP/NLRP3 inflammasome and activation of PPAR-γ.

Phenotype-dependent alteration of pathways and networks reveals a pure synergistic mechanism for compounds treating mouse cerebral ischemia

AIM

Our previous studies have showed that ursodeoxycholic acid (UA) and jasminoidin (JA) effectively reduce cerebral infarct volume in mice. In this study we explored the pure synergistic mechanism of these compounds in treatment of mouse cerebral ischemia, which was defined as synergistic actions specific for phenotype variations after excluding interference from ineffective compounds.

METHODS

Mice with focal cerebral ischemia were treated with UA, JA or a combination JA and UA (JU). Concha margaritifera (CM) was taken as ineffective compound. Cerebral infarct volume of the mice was determined, and the hippocampi were taken for microarray analysis. Particular signaling pathways and biological functions were enriched based on differentially expressed genes, and corresponding networks were constructed through Ingenuity Pathway Analysis.

RESULTS

In phenotype analysis, UA, JA, and JU significantly reduced the ischemic infarct volume with JU being superior to UA or JA alone, while CM was ineffective. As a result, 4 pathways enriched in CM were excluded. Core pathways in the phenotype-positive groups (UA or JA) were involved in neuronal homeostasis and neuropathology. JU-contributing pathways included all UA-contributing and the majority (71.7%) of JA-contributing pathways, and 10 new core pathways whose effects included inflammatory immunity, apoptosis and nervous system development. The functions of JU group included all functions of JA group, the majority (93.1%) of UA-contributing functions, and 3 new core functions, which focused on physiological system development and function.

CONCLUSION

The pure synergism between UA and JA underlies 10 new core pathways and 3 new core functions, which are involved in inflammation, immune responses, apoptosis and nervous system development.

Role of inflammasome activation in the pathophysiology of vascular diseases of the neurovascular unit

SIGNIFICANCE

Inflammation is the standard double-edged defense mechanism that aims at protecting the human physiological homeostasis from devastating threats. Both acute and chronic inflammation have been implicated in the occurrence and progression of vascular diseases. Interference with components of the immune system to improve patient outcome after ischemic injury has been uniformly unsuccessful. There is a need for a deeper understanding of the innate immune response to injury in order to modulate, rather than to block inflammation and improve the outcome for vascular diseases.

RECENT ADVANCES

Nucleotide-binding oligomerization domain-like receptors or NOD-like receptor proteins (NLRPs) can be activated by sterile and microbial inflammation. NLR family plays a major role in activating the inflammasome.

CRITICAL ISSUES

The aim of this work is to review recent findings that provided insights into key inflammatory mechanisms and define the place of the inflammasome, a multi-protein complex involved in instigating inflammation in neurovascular diseases, including retinopathy, neurodegenerative diseases, and stroke.

FUTURE DIRECTIONS

The significant contribution of NLRP-inflammasome activation to vascular disease of the neurovascular unit in the brain and retina suggests that therapeutic strategies focused on specific targeting of inflammasome components could significantly improve the outcomes of these diseases.

MicroRNA-223 regulates inflammation and brain injury via feedback to NLRP3 inflammasome after intracerebral hemorrhage

NLRP3 inflammasome, the multimeric protein complexes involved in the processing of IL-1β through Caspase-1 cleavage, facilitates the inflammatory response. The control and activation of NLRP3 after intracerebral hemorrhage have not been fully studied. In the current study, we explore the specific microRNA which could regulate the NLRP3 inflammasome and inflammation after intracerebral hemorrhage. We detected the inverse relationship between the expression of miR-223 and NLRP3. We found that NLRP3 mRNA contains conserved miR-223 binding sites in its 3' UTR, and miR-223 could directly regulate NLRP3 expression through these 3' UTR sites. Our results indicate that miR-223 could downregulate NLRP3 to inhibit inflammation through caspase-1 and IL-1β, reduce brain edema and improve neurological functions. Together, miR-223 may be a vital regulator of NLRP3 inflammasome activation. The results suggest that miR-223 represents a novel target reducing the inflammatory response, and offers a new therapeutical strategy following ICH.

Inhibition of the NLRP3 inflammasome provides neuroprotection in rats following amygdala kindling-induced status epilepticus

Background

NLRP3 inflammasome is proposed to regulate inflammation in several neurological diseases, but its role in epilepsy remains largely unknown. This study aimed to investigate the role of the NLRP3 inflammasome in neuroinflammation, spontaneous recurrent seizures (SRS) and hippocampal neuronal loss in rat brain following amygdala kindling-induced status epilepticus (SE).

Methods

We detected the protein levels of IL-1β and NLRP3 inflammasome components by Western blot in the hippocampus of shams and SE rats at different time points following SE. To further examine whether the activation of the NLRP3 inflammasome contributes to SE-associated neuronal damage, we employed a nonviral strategy to knock down NLRP3 and caspase-1 expression in brain before undergoing SE. Proinflammatory cytokine levels and hippocampal neuronal loss were evaluated at 12 hours and at 6 weeks following SE respectively in these NLRP3 and caspase-1 deficient rats. Meanwhile, SRS occurrence was evaluated through a 4-week video recording started 2 weeks after SE in these NLRP3 and caspase-1 deficient rats.

Results

IL-1β levels and NLRP3 inflammasome components levels dramatically increased at 3 hours after SE, and reached a maximum at 12 hours after SE compared with the control group. Knock down of NLRP3 or caspase-1 decreased the levels of IL-1β and IL-18 at 12 hours after SE, which was accompanied by a significant suppression in the development and severity of SRS during the chronic epileptic phase. Meanwhile, knock down of NLRP3 or caspase-1 led to a remarkable reduction of hippocampal neuronal loss in the CA1 and CA3 area of the hippocampus at 6 weeks after SE.

Conclusions

Our study provides the first evidence that the NLRP3 inflammasome was significantly up-regulated following SE. More importantly, we show that inhibition of the NLRP3 inflammasome provides neuroprotection in rats following SE. These findings suggest that NLRP3 may represent a potential target for the treatment of epileptogenesis

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-014-0212-5) contains supplementary material, which is available to authorized users.

Molecular regulation of cell fate in cerebral ischemia: role of the inflammasome and connected pathways

Analogous to Toll-like receptors, NOD-like receptors represent a class of pattern recognition receptors, which are cytosolic and constitute part of different inflammasomes. These large protein complexes are activated not only by different pathogens, but also by sterile inflammation or by specific metabolic conditions. Mutations can cause hereditary autoinflammatory systemic diseases, and inflammasome activation has been linked to many multifactorial diseases, such as diabetes or cardiovascular diseases. Increasing data also support an important role in different central nervous diseases such as stroke. Thus, the current knowledge of the functional role of this intracellular 'master switch' of inflammation is discussed with a focus on its role in ischemic stroke, neurodegeneration, and also with regard to the recent data which argues for a relevant role in other organs or biologic systems which influence stroke incidence or prognosis.

Emerging roles of the γ-secretase-notch axis in inflammation

γ-Secretase is a distinct proteolytic complex required for the activation of many transmembrane proteins. The cleavage of substrates by γ-secretase plays diverse biological roles in producing essential products for the organism. More than 90 transmembrane proteins have been reported to be substrates of γ-secretase. Two of the most widely known and studied of these substrates are the amyloid precursor protein (APP) and the Notch receptor, which are precursors for the generation of amyloid-β (Aβ) and the Notch intracellular domain (NICD), respectively. The wide spectrum of γ-secretase substrates has made analyses of the pathology of γ-secretase-related diseases and underlying mechanisms challenging. Inflammation is an important aspect of disease pathology that requires an in-depth analysis. γ-Secretase may contribute to disease development or progression by directly increasing and regulating production of pro-inflammatory cytokines. This review summarizes recent evidence for a role of γ-secretase in inflammatory diseases, and discusses the potential use of γ-secretase inhibitors as an effective future treatment option.