NLRP3 inflammasome contributes to neurovascular unit damage in stroke

Systematic review of melatonin in cerebral ischemia-reperfusion injury: critical role and therapeutic opportunities

Cerebral ischemia-reperfusion (I/R) injury is the predominant causes for the poor prognosis of ischemic stroke patients after reperfusion therapy. Currently, potent therapeutic interventions for cerebral I/R injury are still very limited. Melatonin, an endogenous hormone, was found to be valid in preventing I/R injury in a variety of organs. However, a systematic review covering all neuroprotective effects of melatonin in cerebral I/R injury has not been reported yet. Thus, we perform a comprehensive overview of the influence of melatonin on cerebral I/R injury by collecting all available literature exploring the latent effect of melatonin on cerebral I/R injury as well as ischemic stroke. In this systematic review, we outline the extensive scientific studies and summarize the beneficial functions of melatonin, including reducing infarct volume, decreasing brain edema, improving neurological functions and attenuating blood-brain barrier breakdown, as well as its key protective mechanisms on almost every aspect of cerebral I/R injury, including inhibiting oxidative stress, neuroinflammation, apoptosis, excessive autophagy, glutamate excitotoxicity and mitochondrial dysfunction. Subsequently, we also review the predictive and therapeutic implications of melatonin on ischemic stroke reported in clinical studies. We hope that our systematic review can provide the most comprehensive introduction of current advancements on melatonin in cerebral I/R injury and new insights into personalized diagnosis and treatment of ischemic stroke.

Serum amyloid A-dependent inflammasome activation and acute injury in a mouse model of experimental stroke

Serum amyloid A (SAA) proteins increase dramatically in the blood following inflammation. Recently, SAAs are increased in humans following stroke and in ischemic animal models. However, the impact of SAAs on whether this signal is critical in the ischemic brain remains unknown. Therefore, we investigated the role of SAA and SAA signaling in the ischemic brain. Wildtype and SAA deficient mice were exposed to middle cerebral artery occlusion and reperfusion, examined for the impact of infarct volumes, behavioral changes, inflammatory markers, TUNEL staining, and BBB changes. The underlying mechanisms were investigated using SAA deficient mice, transgenic mice and viral vectors. SAA levels were significantly increase following MCAo and mice deficient in SAAs showed reduced infarct volumes and improved behavioral outcomes. SAA deficient mice showed a reduction in TUNEL staining, inflammation and decreased glial activation. Mice lacking acute phase SAAs demonstrated a reduction in expression of the NLRP3 inflammasome and SAA/NLRP3 KO mice showed improvement. Restoration of SAA expression via SAA tg mice or adenoviral expression reestablished the detrimental effects of SAA. A reduction in BBB permeability was seen in the SAA KO mice and anti-SAA antibody treatment reduced the effects on ischemic injury. SAA signaling plays a critical role in regulating NLRP3-induced inflammation and glial activation in the ischemic brain. Blocking this signal will be a promising approach for treating ischemic stroke.

Gut-brain axis: Mechanisms and potential therapeutic strategies for ischemic stroke through immune functions

After an ischemic stroke (IS) occurs, immune cells begin traveling to the brain and immune system from the gut and gastrointestinal tract, where most of them typically reside. Because the majority of the body's macrophages and more than 70% of the total immune cell pool are typically found within the gut and gastrointestinal tract, inflammation and immune responses in the brain and immune organs require the mobilization of a large number of immune cells. The bidirectional communication pathway between the brain and gut is often referred to as the gut-brain axis. IS usually leads to intestinal motility disorders, dysbiosis of intestinal microbiota, and a leaky gut, which are often associated with poor prognosis in patients with IS. In recent years, several studies have suggested that intestinal inflammation and immune responses play key roles in the development of IS, and thus may become potential therapeutic targets that can drive new therapeutic strategies. However, research on gut inflammation and immune responses after stroke remains in its infancy. A better understanding of gut inflammation and immune responses after stroke may be important for developing effective therapies. This review discusses the immune-related mechanisms of the gut-brain axis after IS and compiles potential therapeutic targets to provide new ideas and strategies for the future effective treatment of IS.

The NLR family pyrin domain containing 3 inflammasome in the mechanism of electroacupuncture: Current status and future perspectives

Electroacupuncture, which is the most widely used alternative medicine treatment, has been gradually recognized for its effectiveness; however, its mechanism of action is not fully understood. The NLR family pyrin domain containing 3 (NLRP3) inflammasome is a thoroughly studied inflammasome that is closely associated with Alzheimer’s disease, spinal cord injury, and other diseases and plays an important role in the diagnosis and treatment of human immune system diseases. In recent years, some scholars have found that the NLRP3 inflammasome is a part of the mechanism of action of electroacupuncture, which has attracted further attention. In the current review, using “electroacupuncture” and “NLRP3 inflammasome” as keywords and based on the existing randomized controlled trials or clinical trials, we summarize the mechanisms of electroacupuncture targeting NLRP3 inflammasome in the treatment of different diseases and discuss how to optimize the electroacupuncture protocol to obtain thorough mechanisms of NLRP3 inflammasome in electroacupuncture and improve the level of evidence.

Molecular Mechanisms of Inflammasome in Ischemic Stroke Pathogenesis

Ischemic stroke (also called cerebral ischemia) is one of the leading causes of death and severe disability worldwide. NLR inflammasomes play a crucial role in sensing cell damage in response to a harmful stimuli and modulating the inflammatory response, promoting the release of pro-inflammatory cytokines such as IL-18 and IL-1β following ischemic injury. Therefore, a neuroprotective effect is achieved by inhibiting the expression, assembly, and secretion of inflammasomes, thus limiting the extent of brain detriment and neurological sequelae. This review aims to illustrate the molecular characteristics, expression levels, and assembly of NLRP3 (nucleotide-binding oligomerization domain-like receptor [NLR] family pyrin-domain-containing 3) inflammasome, the most studied in the literature, in order to discover promising therapeutic implications. In addition, we provide some information regarding the contribution of NLRP1, NLRP2, and NLRC4 inflammasomes to ischemic stroke pathogenesis, highlighting potential therapeutic strategies that require further study.

Inhibition of PRMT5 Attenuates Cerebral Ischemia/Reperfusion-Induced Infammation and Pyroptosis Through Suppression of NF-κB/NLRP3 Axis

Protein methylation is a prevalent post-translational modification after cerebral ischemia. Protein arginine methyltransferase 5 (PRMT5) is a type of methyltransferase enzyme that can catalyse the formation of methylated residues on histones and non-histone proteins. Accumulating evidence suggested that PRMT5 might play a carcinogenic role in various cancers. However, the role of PRMT5 in cerebral ischaemia/reperfusion (I/R) injury remains unclear. In this project, middle cerebral artery occlusion/reperfusion (MCAO/R) model in mice and oxygen-glucose deprivation/ reoxygenation (OGD/R) model in human neuroblastoma SH-SY5Y cells were utilized to mimic disease state of cerebral I/R. We found that expression of inflammatory-related factors [Interleukin (IL)-1β and IL-6)] and pyroptotic-related factor [N-term cleaved Gasdermin-D (GSDMD-N)] were up-regulated in both MCAO/R mice and OGD/R SH-SY5Y cells. In addition, both in vivo and in vitro, PRMT5 was aberrantly upregulated during cerebral I/R. However, these alterations induced by I/R were blocked by PRMT5 inhibitor LLY-283, and enhanced by overexpression of PRMT5. Furthermore, rescue experiment proved that PRMT5 plays a pro-inflammatory and pro-pyroptotic role by activating nuclear factor kappa B (NF-κB)/nucleotide-binding oligomerization domainlike receptor pyrin domain containing 3 (NLRP3) axis. Finally, we observed that treatment of LLY-283 alleviated neurological deficits and reduced infarct volume in the MCAO/R mice. Taken together, PRMT5 may be a potential therapeutic target for cerebral I/R injury.

KDM2B overexpression prevents myocardial ischemia‑reperfusion injury in rats through regulating inflammatory response via the TLR4/NF‑κB p65 axis

Histone modifier lysine-specific demethylase 2B (KDM2B) has been previously reported to activate the inflammatory response by transcription initiation of the IL-6 gene. However, the effects of KDM2B on the inflammatory response during myocardial ischemia-reperfusion (I/R) injury and corresponding mechanisms remain poorly understood. The present study aimed to investigate the role and mechanism of KDM2B in myocardial I/R injury. Therefore, a myocardial I/R injury model was established in rats through coronary artery ligation. Adeno-associated virus-encoding KDM2B and small interfering RNA-KDM2B were designed to determine the effects of KDM2B on myocardial I/R injury using H&E staining and a TUNEL assay in the myocardial tissues. Reverse transcription-quantitative PCR and western blotting were performed to detect the mRNA and protein expression levels of KDM2B, toll-like receptor 4 (TLR4), NF-κB p65 and NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3). ELISA was used to detect the levels of TNF-α, IL-6 and IL-1β in the peripheral blood samples. Pathological analysis demonstrated that the cells in the model group were disordered, with a large area of necrosis and neutrophil infiltration. Knocking down KDM2B expression significantly upregulated the mRNA and protein expression levels of TLR4, NLRP3, NF-κB p65 and the ratio of phosphorylated (p)-p65 to p65. KDM2B knockdown also significantly increased the levels of IL-1β, IL-6 and TNF-α in the peripheral blood, which aggravated myocardial injury and promoted the apoptosis of myocardial cells. However, overexpression of KDM2B downregulated the mRNA and protein expression levels of TLR4, NLRP3, NF-κB P65, the ratio of p-p65 to p65 whilst reducing the levels of IL-1β, IL-6 and TNF-α in the peripheral blood, which markedly improved myocardial injury and significantly inhibited the apoptosis of cells in myocardial tissue. In conclusion, the results indicated that overexpression of KDM2B may prevent myocardial I/R injury in rats by reducing the inflammatory response through regulation of the TLR4/NF-κB p65 axis.

Immunoproteasome modulates NLRP3 inflammasome-mediated neuroinflammation under cerebral ischaemia and reperfusion conditions

Compelling evidence showed that both nucleotide‐binding oligomerization domain‐like receptor family, pyrin domain‐containing protein 3 (NLRP3) inflammasomes and the immunoproteasome participate in neuroinflammatory responses in cerebral ischaemia injury. Moreover, inhibition of either NLRP3 inflammasomes or the immunoproteasome attenuates both neuroinflammation and neurological deterioration during ischaemic stroke. However, the underlying mechanism between the immunoproteasome and NLRP3 inflammasomes under ischaemic stroke conditions remains to be established. In this study, using both in vitro and in vivo ischaemic models, we demonstrated that the immunoproteasome inhibition reduced the expressions of NLRP3 inflammasome‐associated proteins, including NLRP3, apoptosis‐associated speck‐like protein (ASC), caspase‐1 and mature cytokines (interleukin [IL]‐1β and IL‐18). It also downregulated the levels of nuclear factor (NF)‐κB and pyroptotic‐ and apoptotic‐related proteins, and improved cell viability. In addition, inhibition of NF‐κB by the small molecule inhibitor Bay‐11‐7082 led to lower levels of NLRP3 inflammasomes and cleaved caspase‐1 proteins in BV2 cells after oxygen‐glucose deprivation and reoxygenation. Together, these findings suggest that the immunoproteasome may be responsible for inducing the expression and activation of NLRP3 inflammasomes via the NF‐κB pathway. Therapeutic interventions that target activation of the immunoproteasome/NF‐κB/NLRP3 inflammasome pathway may provide novel prospects for the future treatment of ischaemic stroke.

Gonadal Hormones E2 and P Mitigate Cerebral Ischemia-Induced Upregulation of the AIM2 and NLRC4 Inflammasomes in Rats

Acute ischemic stroke (AIS) is a devastating neurological condition with a lack of neuroprotective therapeutic options, despite the reperfusion modalities thrombolysis and thrombectomy. Post-ischemic brain damage is aggravated by an excessive inflammatory cascade involving the activation and regulation of the pro-inflammatory cytokines IL-1β and IL-18 by inflammasomes. However, the role of AIM2 and NLRC4 inflammasomes and the influence of the neuroprotective steroids 17β-estradiol (E2) and progesterone (P) on their regulation after ischemic stroke have not yet been conclusively elucidated. To address the latter, we subjected a total of 65 rats to 1 h of transient Middle Cerebral Artery occlusion (tMCAO) followed by a reperfusion period of 72 h. Moreover, we evaluated the expression and regulation of AIM2 and NLRC4 in glial single-cell cultures (astroglia and microglia) after oxygen–glucose deprivation (OGD). The administration of E2 and P decreased both infarct sizes and neurological impairments after cerebral ischemia in rats. We detected a time-dependent elevation of gene and protein levels (Western Blot/immunohistochemistry) of the AIM2 and NLRC4 inflammasomes in the post-ischemic brains. E2 or P selectively mitigated the stroke-induced increase of AIM2 and NLRC4. While both inflammasomes seemed to be exclusively abundant in neurons under physiological and ischemic conditions in vivo, single-cell cultures of cortical astrocytes and microglia equally expressed both inflammasomes. In line with the in vivo data, E and P selectively reduced AIM2 and NLRC4 in primary cortical astrocytes and microglial cells after OGD. In conclusion, the post-ischemic elevation of AIM2 and NLRC4 and their down-regulation by E2 and P may shed more light on the anti-inflammatory effects of both gonadal hormones after stroke.

Meisoindigo Protects Against Focal Cerebral Ischemia-Reperfusion Injury by Inhibiting NLRP3 Inflammasome Activation and Regulating Microglia/Macrophage Polarization via TLR4/NF-κB Signaling Pathway

Ischemic stroke is a devastating disease with long-term disability. However, the pathogenesis is unclear and treatments are limited. Meisoindigo, a second-generation derivative of indirubin, has general water solubility and is well-tolerated. Previous studies have shown that meisoindigo reduces inflammation by inhibiting leukocyte chemotaxis and migration. In the present study, we investigated the hypothesis that meisoindigo was also protective against ischemic stroke, then evaluated its underlying mechanisms. In vivo, adult male C57BL/6J wild-type mice were used to produce a middle cerebral artery occlusion (MCAO) stroke model. On day three after reperfusion, obvious improvement in neurological scores, infarct volume reduction and cerebral edema amelioration were observed in meisoindigo treatment. Moreover, immunofluorescence staining and western-blot showed that the expression of NLRP3 inflammasome and its associated proteins in neurons and microglia was inhibited by meisoindigo. The effects of Meisoindigo on NLRP3 inflammasome inactivation and increased the M2 phenotype of microglia/macrophage through shifting from a M1 phenotype, which was possibly mediated by inhibition of TLR4/NF-κB. Furthermore, we verified the inhibitory effect of meisoindigo on TLR4/NF-κB signaling pathway, and found that meisoindigo treatment could significantly suppressed the expression of TLR4/NF-κB pathway-associated proteins in a dose-dependent manner, meanwhile, which resulted in downregulation of HMGB1 and IL-1β. Next, we established an in vitro oxygen glucose deprivation/Reperfusion (OGD/R) model in HT-22 and BV2 cells to simulate ischemic conditions. Cytotoxicity assay showed that meisoindigo substantially improved relative cell vitality and in HT-22 and BV2 cells following OGD/R in vitro. After suffering OGD/R, the TLR4/NF-κB pathway was activated, the expression of NLRP3 inflammasome-associated proteins and M1 microglia/macrophage were increased, but meisoindigo could inhibit above changes in both HT-22 and BV2 cells. Additionally, though lipopolysaccharide stimulated the activation of TLR4 signaling in OGD/R models, meisoindigo co-treatment markedly reversed the upregulation of TLR4 and following activation of NLRP3 inflammasome and polarization of M1 microglia/macrophages mediated by TLR4. Overall, we demonstrate for the first time that meisoindigo post-treatment alleviates brain damage induced by ischemic stroke in vivo and in vitro experiments through blocking activation of the NLRP3 inflammasome and regulating the polarization of microglia/macrophages via inhibition of the TLR4/NF-κB signaling pathway.

Bioinformatics Analysis of Gene Expression Profiles of Sex Differences in Ischemic Stroke

Ischemic stroke (IS) is a complex disease with sex differences in epidemiology, presentations, and outcomes. However, the sex-specific mechanism underlying IS remains unclear. The purpose of this study was to identify key genes contributing to biological differences between sexes. First, we downloaded the gene expression data of GSE22255 from Gene Expression Omnibus (GEO). Differentially expressed genes (DEGs) were identified using R software and related packages. Second, DEGs were separately analyzed by Gene Ontology enrichment and pathways analyses. Third, protein-protein interaction (PPI) network was constructed to further investigate the interactions of DEGs. A total of 123 DEGs were identified between sexes, including 8 upregulated and 115 downregulated genes. In the PPI network, ten key genes were identified, including IL1α, IL1β, IL6, IL8, CXCL1, CXCL2, CXCL20, CCL4, ICAM1, and PTGS2. Functional enrichment analysis revealed that these genes were mainly enriched in biological processes of immune response and apoptotic process, also in pathways of TNF and NOD-like receptor signaling. In conclusion, the above ten genes may have a protective effect on IS females through their direct or indirect involvement in biological processes of immune response and apoptotic process, as well as in TNF and NOD-like receptor signaling pathways. The results of this study may help to gain new insights into the sex-specific mechanisms underlying IS females and may suggest potential therapeutic targets for disease treatment.