Temporal and Spatial Dynamics of Inflammasome Activation After Ischemic Stroke

Inflammasome Proteins Are Reliable Biomarkers of the Inflammatory Response in Aneurysmal Subarachnoid Hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is caused by abnormal blood vessel dilation and subsequent rupture, resulting in blood pooling in the subarachnoid space. This neurological insult results in the activation of the inflammasome, a multiprotein complex that processes pro-inflammatory interleukin (IL)-1 cytokines leading to morbidity and mortality. Moreover, increases in inflammasome proteins are associated with clinical deterioration in many neurological diseases. Limited studies have investigated inflammasome protein expression following aSAH. Reliable markers of the inflammatory response associated with aSAH may allow for earlier detection of patients at risk for complications and aid in the identification of novel pharmacologic targets. Here, we investigated whether inflammasome signaling proteins may serve as potential biomarkers of the inflammatory response in aSAH. Serum and cerebrospinal fluid (CSF) from fifteen aSAH subjects and healthy age-matched controls and hydrocephalus (CSF) no-aneurysm controls were evaluated for levels of inflammasome signaling proteins and downstream pro-inflammatory cytokines. Protein measurements were carried out using Simple Plex and Single-Molecule Array (Simoa) technology. The area under the curve (AUC) was calculated using receiver operating characteristics (ROCs) to obtain information on biomarker reliability, specificity, sensitivity, cut-off points, and likelihood ratio. In addition, a Spearman r correlation matrix was performed to determine the correlation between inflammasome protein levels and clinical outcome measures. aSAH subjects demonstrated elevated caspase-1, apoptosis-associated speck-like protein with a caspase recruiting domain (ASC), IL-18 and IL-1β levels in serum, and CSF when compared to controls. Each of these proteins was found to be a promising biomarker of inflammation in aSAH in the CSF. In addition, ASC, caspase-1, and IL-1β were found to be promising biomarkers of inflammation in aSAH in serum. Furthermore, we found that elevated levels of inflammasome proteins in serum are useful to predict worse functional outcomes following aSAH. Thus, the determination of inflammasome protein levels in CSF and serum in aSAH may be utilized as reliable biomarkers of inflammation in aSAH and used clinically to monitor patient outcomes.

HMGB1/TLR4 axis promotes pyroptosis after ICH by activating the NLRP3 inflammasome

BACKGROUND

We previously reported that the HMGB1/TLR4 axis promoted inflammation during the acute phase of intracerebral hemorrhage. Given that this phase is known to involve neuronal pyroptosis and neuroinflammation, here we explore whether HMGB1/TLR signaling activate inflammasome and pyroptosis after intracerebral hemorrhage.

METHODS

Autologous blood was injected into Sprague-Dawley rats to induce intracerebral hemorrhage. Neurological deficits were assessed using a modified neurological severity score. These expression and localization of NLRP1 and NLRP3 inflammasomes, as well as the levels of pyroptosis and pyroptosis-associated proteins were assessed using Western blot or immunocytochemistry. These experiments were repeated in animals that received treatment with short interfering RNAs against NLRP1 or NLRP3, with HMGB1 inhibitor ethyl pyruvate or TLR4 inhibitor TAK-242.

RESULTS

Intracerebral hemorrhage upregulated NLRP1 and NLRP3 in the ipsilateral striatum and increased the proportions of these cells that were pyroptosis-positive. Additionally, the levels of caspase protein family (e.g., pro-caspase-1 and caspase-1), apoptosis-associated speck-like protein (ASC), pro-interleukin-1β (IL-1β), and IL-1β were also elevated. These effects on pyroptosis and associated neurological deficit, were partially reversed by knockdown of NLRP1 or NLRP3, or by inhibition of HMGB1 or TLR4. Inhibition of HMGB1 or TLR4 resulted in the downregulation NLRP3 but not NLRP1.

CONCLUSIONS

The HMGB1/TLR4 signaling may activate the NLRP3 inflammasome during the acute phase of intracerebral hemorrhage, resulting in the inflammatory process known as pyroptosis. These insights suggest potential therapeutic targets for the mitigation tissue injury and associated neurological deficits following hemorrhagic stroke.

The cerebroprotection and prospects of FNDC5/irisin in stroke

Stroke, the leading cause of disability and cognitive impairment, is also the second leading cause of death worldwide. The drugs with multi-targeted brain cytoprotective effects are increasingly being advocated for the treatment of stroke. Irisin, a newly discovered myokine produced by cleavage of fibronectin type III domain 5, has been shown to regulate glucose metabolism, mitochondrial energy, and fat browning. A large amount of evidence indicated that irisin could exert anti-inflammatory, anti-apoptotic, and antioxidant properties in a variety of diseases such as myocardial infarction, inflammatory bowel disease, lung injury, and kidney or liver disease. Studies have found that irisin is widely distributed in multiple brain regions and also plays an important regulatory role in the central nervous system. The most common cause of a stroke is a sudden blockage of an artery (ischemic stroke), and in some circumstances, a blood vessel rupture can also result in a stroke (hemorrhagic stroke). After a stroke, complicated pathophysiological processes lead to serious brain injury and neurological dysfunction. According to recent investigations, irisin may protect elements of the neurovascular unit by acting on multiple pathological processes in stroke. This review aims to outline the currently recognized effects of irisin on stroke and propose possible directions for future research.

STAT4-Mediated Klotho Up-Regulation Contributes to the Brain Ischemic Tolerance by Cerebral Ischemic Preconditioning via Inhibiting Neuronal Pyroptosis

Our previous study has proved that the Klotho up-regulation participated in cerebral ischemic preconditioning (CIP)-induced brain ischemic tolerance. However, the exact neuroprotective mechanism of Klotho in CIP remains unclear. We explored the hypothesis that STAT4-mediated Klotho up-regulation contributes to the CIP-induced brain ischemic tolerance via inhibiting neuronal pyroptosis. Firstly, the expressions of pyroptosis-associated proteins (i.e., NLRP3, GSDMD, pro-caspase-1, and cleaved caspase-1) in hippocampal CA1 region were determined during the process of brain ischemic tolerance. We found the expression of pyroptosis-associated proteins was significantly up-regulated in the ischemic insult (II) group, and showed no significant changes in the CIP group. The expression level of each pyroptosis-associated proteins was lower in the CIP + II group than that in the II group. Inhibition of Klotho expression increased the expression of pyroptosis-associated proteins in the CIP + II group and blocked the CIP-induced brain ischemic tolerance. Injection of Klotho protein decreased the expression of pyroptosis-associated proteins in the II group, and protected neurons from ischemic injury. Secondly, the transcription factor STAT4 of Klotho was identified by bioinformatic analysis. Double luciferase reporter gene assay and chromatin immunoprecipitation assay showed STAT4 can bind to the site between nt - 881 and - 868 on the Klotho promoter region and positively regulates Klotho expression. Moreover, we found CIP significantly enhanced the expression of STAT4. Knockdown STAT4 suppressed Klotho up-regulation after CIP and blocked the CIP-induced brain ischemic tolerance. Collectively, it can be concluded that STAT4-mediated the up-regulation of Klotho contributed to the brain ischemic tolerance induced by CIP via inhibiting pyroptosis.

NLRP3 inflammasome activation after ischemic stroke

Cerebral ischemia is a pathological condition resulting from the cessation or reduction of blood supply to the cerebral arteries. Neurological deficits that are clinically relevant can arise as a result of brain damage. The etiology of stroke is multifaceted and intricate, with the inflammatory response being a crucial component that warrants significant attention. Following a cerebrovascular accident, the levels of interleukin-1 beta and interleukin-18 within the central nervous system escalate due to the activation of the nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 inflammasome. The inflammation is aggravated by the subsequent occurrence of pyroptosis. The mechanisms that activate the NLRP3 inflammasome pyroptosis signaling pathway axis are described in this article. In addition, we go over how pyroptosis interacts with other processes for regulated cell death. In addition, specific NLRP3 inflammasome pathway inhibitors are identified, which offer new approaches to preventing ischemic brain injury.

cRel and Wnt5a/Frizzled 5 Receptor-Mediated Inflammatory Regulation Reveal Novel Neuroprotectin D1 Targets for Neuroprotection

Wnt5a triggers inflammatory responses and damage via NFkB/p65 in retinal pigment epithelial (RPE) cells undergoing uncompensated oxidative stress (UOS) and in experimental ischemic stroke. We found that Wnt5a-Clathrin-mediated uptake leads to NFkB/p65 activation and that Wnt5a is secreted in an exosome-independent fashion. We uncovered that docosahexaenoic acid (DHA) and its derivative, Neuroprotectin D1 (NPD1), upregulate c-Rel expression that, as a result, blunts Wnt5a abundance by competing with NFkB/p65 on the Wnt5a promoter A. Wnt5a increases in ischemic stroke penumbra and blood, while DHA reduces Wnt5a abundance with concomitant neuroprotection. Peptide inhibitor of Wnt5a binding, Box5, is also neuroprotective. DHA-decreased Wnt5a expression is concurrent with a drop in NFkB-driven inflammatory cytokine expression, revealing mechanisms after stroke, as in RPE cells exposed to UOS. Limiting the Wnt5a activity via Box5 reduces stroke size, suggesting neuroprotection pertinent to onset and progression of retinal degenerations and stroke consequences. NPD1 disrupts Wnt5a feedback loop at two sites: (1) decreasing FZD5, thus Wnt5a internalization, and (2) by enhancing cREL activity, which competes with p65/NFkB downstream endocytosis. As a result, Wnt5a expression is reduced, and so is its inflammatory signaling in RPE cells and neurons in ischemic stroke.

CY-09 Alleviates the Depression-like Behaviors via Inhibiting NLRP3 Inflammasome-Mediated Neuroinflammation in Lipopolysaccharide-Induced Mice

Depression is a serious mental illness, mainly characterized as large mood swings and sleep, diet, and cognitive function disorders. NLPR3, one of the inflammasomes that can be activated by a variety of stimuli to promote the maturation and secretion of pro-inflammatory cytokines, has been considered to be involved in the pathophysiology of depression. In this study, the putative role of CY-09, a selective and direct inhibitor of NLRP3, was evaluated in the lipopolysaccharide (LPS)-induced mice. The results of the study indicated that CY-09 significantly decreased the levels of NLRP3 in the hippocampus of LPS-induced mice. In addition, CY-09 increased the sucrose preference and shortened the immobility time in LPS-induced mice, suggesting the antidepressant-like effects of inhibiting NLRP3 inflammasome. Biochemical analysis showed that LPS significantly activated the NLRP3/ASC/cytokine signaling pathway and caused microglial activation, while CY-09 prevented the changes. Moreover, CY-09 increased the brain-derived neurotrophic factor (BDNF) only in microglia but not in the whole hippocampus. Meanwhile, CY-09 did not promote neurogenesis in the hippocampus of LPS mice. In conclusion, the results of the study showed that the antidepressant-like effects of NLRP3 inhibitor CY-09 were mediated by alleviating neuroinflammation in microglia and independent of the neurotrophic function in the hippocampus.

Pivotal regulatory roles of traditional Chinese medicine in ischemic stroke via inhibition of NLRP3 inflammasome

ETHNOPHARMACOLOGICAL RELEVANCE

Many studies have demonstrated the powerful neuroprotection abilities of multiple traditional Chinese medicines (TCMs) against NLRP3 inflammasome-mediated ischemic cerebral injury. These TCMs may be in the form of TCM prescriptions, Chinese herbal medicines and their extracts, and TCM monomers.

AIM OF THE STUDY

This review aimed to analyze and summarize the existing knowledge on the assembly and activation of the NLRP3 inflammasome and its role in the pathogenesis of ischemic stroke (IS). We also summarized the mechanism of action of the various TCMs on the NLRP3 inflammasome, which may provide new insights for the management of IS.

MATERIALS AND METHODS

We reviewed recently published articles by setting the keywords "NLRP3 inflammasome" and "traditional Chinese medicines" along with "ischemic stroke"; "NLRP3 inflammasome" and "ischemic stroke" along with "natural products" and so on in Pubmed and GeenMedical.

RESULTS

According to recent studies, 16 TCM prescriptions (officially authorized products and clinically effective TCM prescriptions), 7 Chinese herbal extracts, and 29 TCM monomers show protective effects against IS through anti-inflammatory, anti-oxidative stress, anti-apoptotic, and anti-mitochondrial autophagy effects.

CONCLUSIONS

In this review, we analyzed studies on the involvement of NLRP3 in IS therapy. Further, we comprehensively and systematically summarized the current knowledge to provide a reference for the further application of TCMs in the treatment of IS.

NLRP3 Inflammasome Activation: A Therapeutic Target for Cerebral Ischemia–Reperfusion Injury

Millions of patients are suffering from ischemic stroke, it is urgent to figure out the pathogenesis of cerebral ischemia–reperfusion (I/R) injury in order to find an effective cure. After I/R injury, pro-inflammatory cytokines especially interleukin-1β (IL-1β) upregulates in ischemic brain cells, such as microglia and neuron. To ameliorate the inflammation after cerebral I/R injury, nucleotide-binding oligomerization domain (NOD), leucine-rich repeat (LRR), and pyrin domain-containing protein 3 (NLRP3) inflammasome is well-investigated. NLRP3 inflammasomes are complicated protein complexes that are activated by endogenous and exogenous danger signals to participate in the inflammatory response. The assembly and activation of the NLRP3 inflammasome lead to the caspase-1-dependent release of pro-inflammatory cytokines, such as interleukin (IL)-1β and IL-18. Furthermore, pyroptosis is a pro-inflammatory cell death that occurs in a dependent manner on NLRP3 inflammasomes after cerebral I/R injury. In this review, we summarized the assembly and activation of NLRP3 inflammasome; moreover, we also concluded the pivotal role of NLRP3 inflammasome and inhibitors, targeting the NLRP3 inflammasome in cerebral I/R injury.

The neuroprotective mechanism of lithium after ischaemic stroke

Stroke causes degeneration and death of neurones leading to the loss of motor function and frequent occurrence of cognitive impairment and depression. Lithium (Li⁺), the archetypal mood stabiliser, is neuroprotective in animal models of stroke, albeit underlying mechanisms remain unknown. We discover that Li⁺ inhibits activation of nucleotide-binding oligomerisation domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasomes in the middle cerebral artery occlusion (MCAO) stroke model in mice. This action of Li⁺ is mediated by two signalling pathways of AKT/GSK3β/β-catenin and AKT/FoxO3a/β-catenin which converge in suppressing the production of reactive oxygen species (ROS). Using immunocytochemstry, MRI imaging, and cell sorting with subsequent mRNA and protein quantification, we demonstrate that Li⁺ decreases the infarct volume, improves motor function, and alleviates associated cognitive and depressive impairments. In conclusion, this study reveals molecular mechanisms of Li⁺ neuroprotection during brain ischaemia, thus providing the theoretical background to extend clinical applications of Li⁺ for treatment of ischemic stroke.

Wedelolactone Attenuates N-methyl-N-nitrosourea-Induced Retinal Neurodegeneration through Suppression of the AIM2/CASP11 Pathway

N-methyl-N-nitrosourea (NMU) is widely used to model oxidative stress and inflammation mediated retinal neurodegeneration. Wedelolactone (WD) is known to have antioxidant, anti-inflammatory, and neuroprotective roles. This study tested the therapeutic potential of WD in NMU-induced retinal neurodegeneration and investigated the underlying mechanisms in mice. NMU (40 mg/kg) was injected intraperitoneally into C57BL/6J mice with/without an intravitreal injection of WD (1 μL/eye, 200 μM). Seven days later, retinal function and structure were evaluated by electroretinography (ERG) and Spectral Domain Optical Coherence Tomography (SD-OCT). The expression of inflammasome components (Aim2, Caspase 1/11, and Il1b/Il18) in the total retina lysate was evaluated by RT-qPCR. In vitro, 661W photoreceptor cells were transfected with synthetic double-strand DNA (Poly(dA:dT)) with/without WD pre-incubation. The aim2-related inflammasome expression was evaluated by RT-qPCR and immunocytochemistry. The production of IL18 was measured by ELISA. NMU treatment significantly impaired A- and B-wave response (ERG) and reduced neuroretina thickness (OCT). This was significantly attenuated upon intravitreal injection of WD. The expression of Aim2, ACasp1, and Casp11 was increased in the retina from NMU-treated mice, and this was prevented by WD treatment. Transfection of Poly(dA:dT) upregulated Aim2, Casp11, and Il18 expression in 661W cells. WD prevented their upregulation and reduced IL18 production. Aim2 inflammasome activation is critically involved in NMU-induced retinal neurodegeneration and WD can protect the retina particularly through the suppression of this inflammasome-linked pathway.