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

JR14a: A novel antagonist of C3aR attenuates neuroinflammation in cerebral ischemia-reperfusion injury

Cerebral ischemia-reperfusion injury (CIRI), a prevalent stroke-related complication, can lead to severe brain damage. Inflammation is a crucial factor in CIRI pathogenesis, and the complement component 3a receptor (C3aR) could be a key mediator in the post-CIRI inflammatory cascade. In this study, the role of C3aR in CIRI was investigated utilizing a middle cerebral artery occlusion (MCAO) model in C3aR knockout (KO) mice. Magnetic resonance imaging (MRI) and neurofunctional assessments revealed that C3aR KO mice exhibited significantly diminished cerebral infarction and improved neurological impairments. Consequently, the focus shifted to searching for a small molecule antagonist of C3aR. JR14a, a new potent thiophene antagonist of C3aR, was injected intraperitoneally into mice 1-h post-MCAO model implementation. The mass spectrometry (MS) results indicated the ability of JR14a to penetrate the blood-brain barrier. Subsequent TTC staining and neurofunctional assessments revealed the efficacy of JR14a in reducing cerebral infarct volume and neurological impairment following MCAO. In addition, immunofluorescence (IF) and immunohistochemistry (IHC) demonstrated attenuated microglial activation, neutrophil infiltration, and blood-brain barrier disruption by JR14a in the MCAO model. Furthermore, enzyme-linked immunosorbent assay (ELISA) and Western blotting supported the role of JR14a in downregulating the expression levels of C3aR, tumor necrosis factor-alpha (TNF-α), and interleukin-6 (IL-6), as well as the phosphorylation of p65. In conclusion, the findings suggested that C3aR could be a potential therapeutic target for CIRI, and JR14a emerged as a promising treatment candidate.

CD36 deletion prevents white matter injury by modulating microglia polarization through the Traf5-MAPK signal pathway

BACKGROUND

White matter injury (WMI) represents a significant etiological factor contributing to neurological impairment subsequent to Traumatic Brain Injury (TBI). CD36 receptors are recognized as pivotal participants in the pathogenesis of neurological disorders, including stroke and spinal cord injury. Furthermore, dynamic fluctuations in the phenotypic polarization of microglial cells have been intimately associated with the regenerative processes within the injured tissue following TBI. Nevertheless, there is a paucity of research addressing the impact of CD36 receptors on WMI and microglial polarization. This investigation aims to elucidate the functional role and mechanistic underpinnings of CD36 in modulating microglial polarization and WMI following TBI.

METHODS

TBI models were induced in murine subjects via controlled cortical impact (CCI). The spatiotemporal patterns of CD36 expression were examined through quantitative polymerase chain reaction (qPCR), Western blot analysis, and immunofluorescence staining. The extent of white matter injury was assessed via transmission electron microscopy, Luxol Fast Blue (LFB) staining, and immunofluorescence staining. Transcriptome sequencing was employed to dissect the molecular mechanisms underlying CD36 down-regulation and its influence on white matter damage. Microglial polarization status was ascertained using qPCR, Western blot analysis, and immunofluorescence staining. In vitro, a Transwell co-culture system was employed to investigate the impact of CD36-dependent microglial polarization on oligodendrocytes subjected to oxygen-glucose deprivation (OGD).

RESULTS

Western blot and qPCR analyses revealed that CD36 expression reached its zenith at 7 days post-TBI and remained sustained at this level thereafter. Immunofluorescence staining exhibited robust CD36 expression in astrocytes and microglia following TBI. Genetic deletion of CD36 ameliorated TBI-induced white matter injury, as evidenced by a reduced SMI-32/MBP ratio and G-ratio. Transcriptome sequencing unveiled differentially expressed genes enriched in processes linked to microglial activation, regulation of neuroinflammation, and the TNF signaling pathway. Additionally, bioinformatics analysis pinpointed the Traf5-p38 axis as a critical signaling pathway. In vivo and in vitro experiments indicated that inhibition of the CD36-Traf5-MAPK axis curtailed microglial polarization toward the pro-inflammatory phenotype. In a Transwell co-culture system, BV2 cells treated with LPS + IFN-γ exacerbated the damage of post-OGD oligodendrocytes, which could be rectified through CD36 knockdown in BV2 cells.

CONCLUSIONS

This study illuminates that the suppression of CD36 mitigates WMI by constraining microglial polarization towards the pro-inflammatory phenotype through the down-regulation of the Traf5-MAPK signaling pathway. Our findings present a potential therapeutic strategy for averting neuroinflammatory responses and ensuing WMI damage resulting from TBI.

Atorvastatin Promotes Pro/anti-inflammatory Phenotypic Transformation of Microglia via Wnt/β-catenin Pathway in Hypoxic-Ischemic Neonatal Rats

Inflammatory reaction plays a key role in the pathogenesis of hypoxic-ischemic encephalopathy (HIE) in neonates. Microglia are resident innate immune cells in the central nervous system and are profoundly involved in neuroinflammation. Studies have revealed that atorvastatin exerts a neuroprotective effect by regulating neuroinflammation in adult animal models of brain stroke and traumatic brain injury, but its role regarding damage to the developing brain remains unclear. This study aimed to clarify the effect and mechanism of atorvastatin on the regulation of microglia function in neonatal hypoxic-ischemic brain damage (HIBD). The oxygen glucose deprivation (OGD) of microglia and neonatal rat HIBD model was established. Atorvastatin, recombinant sclerostin protein (SOST), and XAV939 (degradation of β-catenin) were administered to OGD microglia and HIBD rats. The pathological changes of brain tissue, cerebral infarction volume, learning and memory ability of rats, pro-inflammatory (CD16+/Iba1+) and anti-inflammatory (CD206+/Iba1+) microglia markers, inflammation-related indicators (Inos, Tnfα, Il6, Arg1, Tgfb, and Mrc1), and Wnt/β-catenin signaling molecules were examined. Atorvastatin reduced OGD-induced pro-inflammatory microglia and pro-inflammatory factors, while increasing anti-inflammatory microglia and anti-inflammatory factors. In vivo, atorvastatin attenuated hypoxia-ischemia (HI)-induced neuroinflammation and brain damage. Mechanistically, atorvastatin decreased SOST expression and activated the Wnt/β-catenin signaling pathway, and the administration of recombinant SOST protein or XAV939 inhibited Wnt/β-catenin signaling and attenuated the anti-inflammatory effect of atorvastatin. Atorvastatin promotes the pro/anti-inflammatory phenotypic transformation of microglia via the Wnt/β-catenin pathway in HI neonatal rats. Atorvastatin may be developed as a potent agent for the treatment of HIE in neonates.

The Impact of VEGF-C-Induced Dural Lymphatic Vessel Growth on Ischemic Stroke Pathology

Timely relief of edema and clearance of waste products, as well as promotion of anti-inflammatory immune responses, reduce ischemic stroke pathology, and attenuate harmful long-term effects post-stroke. The discovery of an extensive and functional lymphatic vessel system in the outermost meningeal layer, dura mater, has opened up new possibilities to facilitate post-stroke recovery by inducing dural lymphatic vessel (dLV) growth via a single injection of a vector encoding vascular endothelial growth factor C (VEGF-C). In the present study, we aimed to improve post-stroke outcomes by inducing dLV growth in mice. We injected mice with a single intracerebroventricular dose of adeno-associated viral particles encoding VEGF-C before subjecting them to transient middle cerebral artery occlusion (tMCAo). Behavioral testing, Gadolinium (Gd) contrast agent-enhanced magnetic resonance imaging (MRI), and immunohistochemical analysis were performed to define the impact of VEGF-C on the post-stroke outcome. VEGF-C improved stroke-induced behavioral deficits, such as gait disturbances and neurological deficits, ameliorated post-stroke inflammation, and enhanced an alternative glial immune response. Importantly, VEGF-C treatment increased the drainage of brain interstitial fluid (ISF) and cerebrospinal fluid (CSF), as shown by Gd-enhanced MRI. These outcomes were closely associated with an increase in the growth of dLVs around the region where we observed increased vefgc mRNA expression within the brain, including the olfactory bulb, cortex, and cerebellum. Strikingly, VEGF-C-treated ischemic mice exhibited a faster and stronger Gd-signal accumulation in ischemic core area and an enhanced fluid outflow via the cribriform plate. In conclusion, the VEGF-C-induced dLV growth improved the overall outcome post-stroke, indicating that VEGF-C has potential to be included in the treatment strategies of post-ischemic stroke. However, to maximize the therapeutic potential of VEGF-C treatment, further studies on the impact of an enhanced dural lymphatic system at clinically relevant time points are essential.

Polyphyllin I alleviates neuroinflammation after cerebral ischemia-reperfusion injury via facilitating autophagy-mediated M2 microglial polarization

Microglial activation and polarization play a central role in poststroke inflammation and neuronal damage. Modulating microglial polarization from pro-inflammatory to anti-inflammatory phenotype is a promising therapeutic strategy for the treatment of cerebral ischemia. Polyphyllin I (PPI), a steroidal saponin, shows multiple bioactivities in various diseases, but the potential function of PPI in cerebral ischemia is not elucidated yet. In our study, the influence of PPI on cerebral ischemia-reperfusion injury was evaluated. Mouse middle cerebral artery occlusion (MCAO) model and oxygen-glucose deprivation and reoxygenation (OGD/R) model were constructed to mimic cerebral ischemia-reperfusion injury in vivo and in vitro. TTC staining, TUNEL staining, RT-qPCR, ELISA, flow cytometry, western blot, immunofluorescence, hanging wire test, rotarod test and foot-fault test, open-field test and Morris water maze test were performed in our study. We found that PPI alleviated cerebral ischemia-reperfusion injury and neuroinflammation, and improved functional recovery of mice after MCAO. PPI modulated microglial polarization towards anti-inflammatory M2 phenotype in MCAO mice in vivo and post OGD/R in vitro. Besides, PPI promoted autophagy via suppressing Akt/mTOR signaling in microglia, while inhibition of autophagy abrogated the effect of PPI on M2 microglial polarization after OGD/R. Furthermore, PPI facilitated autophagy-mediated ROS clearance to inhibit NLRP3 inflammasome activation in microglia, and NLRP3 inflammasome reactivation by nigericin abolished the effect of PPI on M2 microglia polarization. In conclusion, PPI alleviated post-stroke neuroinflammation and tissue damage via increasing autophagy-mediated M2 microglial polarization. Our data suggested that PPI had potential for ischemic stroke treatment.

Advancing stroke therapy: the potential of MOF-based nanozymes in biomedical applications

In this study, we explored the growing use of metal-organic framework (MOF)-based Nanozymes in biomedical research, with a specific emphasis on their applications in stroke therapy. We have discussed the complex nature of stroke pathophysiology, highlighting the crucial role of reactive oxygen species (ROS), and acknowledging the limitations of natural enzymes in addressing these challenges. We have also discussed the role of nanozymes, particularly those based on MOFs, their structural similarities to natural enzymes, and their potential to improve reactivity in various biomedical applications. The categorization of MOF nanozymes based on enzyme-mimicking activities is discussed, and their applications in stroke therapy are explored. We have reported the potential of MOF in treating stroke by regulating ROS levels, alleviation inflammation, and reducing neuron apoptosis. Additionally, we have addressed the challenges in developing efficient antioxidant nanozyme systems for stroke treatment. The review concludes with the promise of addressing these challenges and highlights the promising future of MOF nanozymes in diverse medical applications, particularly in the field of stroke treatment.

Pannexin1 Channel-Mediated Inflammation in Acute Ischemic Stroke

Emerging evidence suggests that inflammation mediated by the pannexin1 channel contributes significantly to acute ischemic stroke. It is believed that the pannexin1 channel is key in initiating central system inflammation during the early stages of acute ischemic stroke. Moreover, the pannexin1 channel is involved in the inflammatory cascade to maintain the inflammation levels. Specifically, the interaction of pannexin1 channels with ATP-sensitive P2X7 purinoceptors or promotion of potassium efflux mediates the activation of the NLRP3 inflammasome, triggering the release of pro-inflammatory factors such as IL-1 and IL-18, exacerbating and sustaining inflammation of brain. Also, increased release of ATP induced by cerebrovascular injury activates pannexin1 in vascular endothelial cells. This signal directs peripheral leukocytes to migrate into ischemic brain tissue, leading to an expansion of the inflammatory zone. Intervention strategies targeting pannexin1 channels may greatly alleviate inflammation after acute ischemic stroke to improve this patient population's clinical outcomes. In this review, we sought to summarize relevant studies on inflammation mediated by the pannexin1 channel in acute ischemic stroke and discussed the possibility of using brain organoid-on-a-chip technology to screen miRNAs that exclusively target the pannexin1 channel to provide new therapeutic measures for targeted regulation of pannexin1 channel to reduce inflammation in acute ischemic stroke.

The immunomodulatory mechanism of acupuncture treatment for ischemic stroke: research progress, prospects, and future direction

Ischemic stroke (IS) is one of the leading causes of death and disability. Complicated mechanisms are involved in the pathogenesis of IS. Immunomodulatory mechanisms are crucial to IS. Acupuncture is a traditional non-drug treatment that has been extensively used to treat IS. The exploration of neuroimmune modulation will broaden the understanding of the mechanisms underlying acupuncture treatment. This review summarizes the immune response of immune cells, immune cytokines, and immune organs after an IS. The immunomodulatory mechanisms of acupuncture treatment on the central nervous system and peripheral immunity, as well as the factors that influence the effects of acupuncture treatment, were summarized. We suggest prospects and future directions for research on immunomodulatory mechanisms of acupuncture treatment for IS based on current progress, and we hope that these will provide inspiration for researchers. Additionally, acupuncture has shown favorable outcomes in the treatment of immune-based nervous system diseases, generating new directions for research on possible targets and treatments for immune-based nervous system diseases.

Sulfated Polysaccharide-Based Nanocarrier Drives Microenvironment-Mediated Cerebral Neurovascular Remodeling for Ischemic Stroke Treatment

Stroke is a leading cause of global mortality and severe disability. However, current strategies used for treating ischemic stroke lack specific targeting capabilities, exhibit poor immune escape ability, and have limited drug release control. Herein, we developed an ROS-responsive nanocarrier for targeted delivery of the neuroprotective agent rapamycin (RAPA) to mitigate ischemic brain damage. The nanocarrier consisted of a sulfated chitosan (SCS) polymer core modified with a ROS-responsive boronic ester enveloped by a red blood cell membrane shell incorporating a stroke homing peptide. When encountering high levels of intracellular ROS in ischemic brain tissues, the release of SCS combined with RAPA from nanoparticle disintegration facilitates effective microglia polarization and, in turn, maintains blood-brain barrier integrity, reduces cerebral infarction, and promotes cerebral neurovascular remodeling in a mouse stroke model involving transient middle cerebral artery occlusion (tMCAO). This work offers a promising strategy to treat ischemic stroke therapy.

Neutrophil Membrane-Camouflaged Polyprodrug Nanomedicine for Inflammation Suppression in Ischemic Stroke Therapy

Neuroinflammation has emerged as a major concern in ischemic stroke therapy because it exacebates neurological dysfunction and suppresses neurological recovery after ischemia/reperfusion. Fingolimod hydrochloride (FTY720) is an FDA-approved anti-inflammatory drug which exhibits potential neuroprotective effects in ischemic brain parenchyma. However, delivering a sufficient amount of FTY720 through the blood-brain barrier into brain lesions without inducing severe cardiovascular side effects remains challenging. Here, a neutrophil membrane-camouflaged polyprodrug nanomedicine that can migrate into ischemic brain tissues and in situ release FTY720 in response to elevated levels of reactive oxygen species. This nanomedicine delivers 15.2-fold more FTY720 into the ischemic brain and significantly reduces the risk of cardiotoxicity and infection compared with intravenously administered free drug. In addition, single-cell RNA-sequencing analysis identifies that the nanomedicine attenuates poststroke inflammation by reprogramming microglia toward anti-inflammatory phenotypes, which is realized via modulating Cebpb-regulated activation of NLRP3 inflammasomes and secretion of CXCL2 chemokine. This study offers new insights into the design and fabrication of polyprodrug nanomedicines for effective suppression of inflammation in ischemic stroke therapy.

Rhoa/ROCK, mTOR and Secretome-Based Treatments for Ischemic Stroke: New Perspectives

Ischemic stroke triggers a complex cascade of cellular and molecular events leading to neuronal damage and tissue injury. This review explores the potential therapeutic avenues targeting cellular signaling pathways implicated in stroke pathophysiology. Specifically, it focuses on the articles that highlight the roles of RhoA/ROCK and mTOR signaling pathways in ischemic brain injury and their therapeutic implications. The RhoA/ROCK pathway modulates various cellular processes, including cytoskeletal dynamics and inflammation, while mTOR signaling regulates cell growth, proliferation, and autophagy. Preclinical studies have demonstrated the neuroprotective effects of targeting these pathways in stroke models, offering insights into potential treatment strategies. However, challenges such as off-target effects and the need for tissue-specific targeting remain. Furthermore, emerging evidence suggests the therapeutic potential of MSC secretome in stroke treatment, highlighting the importance of exploring alternative approaches. Future research directions include elucidating the precise mechanisms of action, optimizing treatment protocols, and translating preclinical findings into clinical practice for improved stroke outcomes.

Postoperative cognitive dysfunction: Review of pathophysiology, diagnostics and preventive strategies

Postoperative cognitive impairment is a common disorder after major surgery. Advances in medicine and treatment have resulted in an increasingly ageing population undergoing major surgical procedures. Since age is the most important risk factor for postoperative cognitive decline, it is not surprising that impairment of cognitive functions after surgery was recorded in almost a third of elderly patients. Postoperative cognitive dysfunction is part of the spectrum of postoperative cognitive impairment and researchers often confuse it with postoperative delirium and delayed neurocognitive recovery. This is the cause of great differences in the results of research that is focused on the incidence and possible prevention of postoperative cognitive dysfunction. In this review, we focused on current recommendations for a uniform nomenclature of postoperative cognitive impairment and diagnosis of postoperative cognitive dysfunction, the presumed pathophysiology of postoperative cognitive dysfunction and recommendations for its treatment and possible prevention strategies.

Dihydroergotamine protects against ischemic stroke by modulating microglial/macrophage polarization and inhibiting inflammation in mice

OBJECTIVES

The search for drugs that can protect the brain tissue and reduce nerve damage in acute ischemic stroke has emerged as a research hotspot. We investigated the potential protective effects and mechanisms of action of dihydroergotamine against ischemic stroke.

METHODS

C57BL/6 mice were subjected to middle cerebral artery occlusion (MCAO), and dihydroergotamine at a dose of 10 mg/kg/day was intraperitoneally injected for 14 days. Adhesive removal and beam walking tests were conducted 1, 3, 5, 7, 10, and 14 days after MCAO surgery. Thereafter, the mechanism by which dihydroergotamine regulates microglia/macrophage polarization and inflammation and imparts ischemic stroke protection was studied using enzyme-linked immunosorbent assay, immunofluorescence staining, and western blotting.

RESULTS

From the perspective of a drug repurposing strategy, dihydroergotamine was found to inhibit oxygen-glucose deprivation damage to neurons, significantly improve cell survival rate, and likely exert a protective effect on ischemic brain injury. Dihydroergotamine significantly improved neural function scores and survival rates and reduced brain injury severity in mice. Furthermore, dihydroergotamine manifests its protective effect on ischemic brain injury by reducing the expression of TNF-α and IL-1β in mouse ischemic brain tissue, inhibiting the polarization of microglia/macrophage toward the M1 phenotype and promoting polarization toward the M2 phenotype.

CONCLUSION

This study is the first to demonstrate the protective effect of dihydroergotamine, a first-line treatment for migraine, against ischemic nerve injury in vitro and in vivo.

AZD1390, an ataxia telangiectasia mutated inhibitor, attenuates microglia-mediated neuroinflammation and ischemic brain injury

AIMS

Excessive neuroinflammation mediated mainly by microglia plays a crucial role in ischemic stroke. AZD1390, an ataxia telangiectasia mutated (ATM) specific inhibitor, has been shown to promote radio-sensitization and survival in central nervous system malignancies, while the role of AZD1390 in ischemic stroke remains unknown.

METHODS

Real-time PCR, western blot, immunofluorescence staining, flow cytometry and enzyme-linked immunosorbent assays were used to assess the activation of microglia and the release of inflammatory cytokines. Behavioral tests were performed to measure neurological deficits. 2,3,5-Triphenyltetrazolium chloride staining was conducted to assess the infarct volume. The activation of NF-κB signaling pathway was explored through immunofluorescence staining, western blot, co-immunoprecipitation and proximity ligation assay.

RESULTS

The level of pro-inflammation cytokines and activation of NF-κB signaling pathway was suppressed by AZD1390 in vitro and in vivo. The behavior deficits and infarct size were partially restored with AZD1390 treatment in experimental stroke. AZD1390 restrict ubiquitylation and sumoylation of the essential regulatory subunit of NF-κB (NEMO) in an ATM-dependent and ATM-independent way respectively, which reduced the activation of the NF-κB pathway.

CONCLUSION

AZD1390 suppressed NF-κB signaling pathway to alleviate ischemic brain injury in experimental stroke, and attenuated microglia activation and neuroinflammation, which indicated that AZD1390 might be an attractive agent for the treatment of ischemic stroke.

TXNIP/NLRP3 aggravates global cerebral ischemia-reperfusion injury-induced cognitive decline in mice

Global cerebral ischemia/reperfusion (GCI/R) injury poses a risk for cognitive decline, with neuroinflammation considered pivotal in this process. This study aimed to unravel the molecular mechanisms underlying GCI/R injury and propose a potential therapeutic strategy for associated cognitive deficits. Utilizing bioinformatics analysis of a public microarray profile (GSE30655 and GSE80681) in cerebral ischemic mice, it was observed that neuroinflammation emerged as a significant gene ontology item, with an increase in the expression of thioredoxin-interacting protein (TXNIP) and NLRP3 genes. Experimental models involving bilateral occlusion of the common carotid arteries in mice revealed that GCI/R induced cognitive impairment, along with a time-dependent increase in TXNIP and NLRP3 levels. Notably, TXNIP knockdown alleviated cognitive dysfunction in mice. Furthermore, the introduction of adeno-associated virus injection with TXNIP knockdown reduced the number of activated microglia, apoptosis neurons, and levels of oxidative stress and inflammatory cytokines in the hippocampus. Collectively, these findings underscore the significance of TXNIP/NLRP3 in the hippocampus in exacerbating cognitive decline due to GCI/R injury, suggesting that TXNIP knockdown holds promise as a therapeutic strategy.

Neuroinflammation of Microglial Regulation in Alzheimer's Disease: Therapeutic Approaches

Alzheimer's disease (AD) is a complex degenerative disease of the central nervous system that is clinically characterized by a progressive decline in memory and cognitive function. The pathogenesis of AD is intricate and not yet fully understood. Neuroinflammation, particularly microglial activation-mediated neuroinflammation, is believed to play a crucial role in increasing the risk, triggering the onset, and hastening the progression of AD. Modulating microglial activation and regulating microglial energy metabolic disorder are seen as promising strategies to intervene in AD. The application of anti-inflammatory drugs and the targeting of microglia for the prevention and treatment of AD has emerged as a new area of research interest. This article provides a comprehensive review of the role of neuroinflammation of microglial regulation in the development of AD, exploring the connection between microglial energy metabolic disorder, neuroinflammation, and AD development. Additionally, the advancements in anti-inflammatory and microglia-regulating therapies for AD are discussed.

S100A9 aggravates early brain injury after subarachnoid hemorrhage via inducing neuroinflammation and inflammasome activation

Subarachnoid hemorrhage (SAH) is a stroke subtype with high mortality, and its severity is closely related to the short-term prognosis of SAH patients. S100 calcium-binding protein A9 (S100A9) has been shown to be associated with some neurological diseases. In this study, the concentration of S100A9 in clinical cerebrospinal fluid samples was detected by enzyme-linked immunosorbent assay (ELISA), and the relationship between S100A9 and the prognosis of patients was explored. In addition, WT mice and S100A9 knockout mice were used to establish an in vivo SAH model. Neurological scores, brain water content, and histopathological staining were performed after a specified time. A co-culture model of BV2 and HT22 cells was treated with heme chloride to establish an in vitro SAH model. Our study confirmed that the expression of S100A9 protein in the CSF of SAH patients is increased, and it is related to the short-term prognosis of SAH patients. S100A9 protein is highly expressed in microglia in the central nervous system. S100A9 gene knockout significantly improved neurological function scores and reduced neuronal apoptosis. S100A9 protein can activate TLR4 receptor, promote nuclear transcription of NF-κB, increase the activation of inflammatory body, and ultimately aggravate nerve injury.

A One-Stone-Two-Birds Strategy of Targeting Microbubbles with "Dual" Anti-Inflammatory and Blood-Brain Barrier "Switch" Function for Ischemic Stroke Treatment

Inflammation is considered to be the main target of the development of new stroke therapies. There are three key issues in the treatment of stroke inflammation: the first one is how to overcome the blood-brain barrier (BBB) to achieve drug delivery, the second one is how to select drugs to treat stroke inflammation, and the third one is how to achieve targeted drug delivery. In this study, we constructed hydrocortisone-phosphatidylserine microbubbles and combined them with ultrasound (US)-targeted microbubble destruction technology to successfully open the BBB to achieve targeted drug delivery. Phosphatidylserine on the microbubbles was used for its "eat me" effect to increase the targeting of the microvesicles. In addition, we found that hydrocortisone can accelerate the closure of the BBB, achieving efficient drug delivery while reducing the entry of peripheral toxins into the brain. In the treatment of stroke inflammation, it was found that hydrocortisone itself has anti-inflammatory effects and can also change the polarization of microglia from the harmful pro-inflammatory M1 phenotype to the beneficial anti-inflammatory M2 phenotype, thus achieving dual anti-inflammatory effects and enhancing the anti-inflammatory effects in ischemic areas after stroke, well reducing the cerebellar infarction volume by inhibiting the inflammatory response after cerebral ischemia. A confocal microendoscope was used to directly observe the polarization of microglial cells in living animal models for dynamic microscopic visualization detection showing the advantage of being closer to clinical work. Taken together, this study constructed a multifunctional targeted US contrast agent with the function of "one-stone-two-birds", which can not only "on-off" the BBB but also have "two" anti-inflammatory functions, providing a new strategy of integrated anti-inflammatory targeted delivery and imaging monitoring for ischemic stroke treatment.

Interleukin-4 from curcumin-activated OECs emerges as a central modulator for increasing M2 polarization of microglia/macrophage in OEC anti-inflammatory activity for functional repair of spinal cord injury

Microglia/macrophages are major contributors to neuroinflammation in the central nervous system (CNS) injury and exhibit either pro- or anti-inflammatory phenotypes in response to specific microenvironmental signals. Our latest in vivo and in vitro studies demonstrated that curcumin-treated olfactory ensheathing cells (aOECs) can effectively enhance neural survival and axonal outgrowth, and transplantation of aOECs improves the neurological outcome after spinal cord injury (SCI). The therapeutic effect is largely attributed to aOEC anti-inflammatory activity through the modulation of microglial polarization from the M1 to M2 phenotype. However, very little is known about what viable molecules from aOECs are actively responsible for the switch of M1 to M2 microglial phenotypes and the underlying mechanisms of microglial polarization. Herein, we show that Interleukin-4 (IL-4) plays a leading role in triggering the M1 to M2 microglial phenotype, appreciably decreasing the levels of M1 markers IL‑1β, IL‑6, tumour necrosis factor-alpha (TNF-α) and inducible nitric oxide synthase (iNOS) and elevating the levels of M2 markers Arg-1, TGF-β, IL-10, and CD206. Strikingly, blockade of IL-4 signaling by siRNA and a neutralizing antibody in aOEC medium reverses the transition of M1 to M2, and the activated microglia stimulated with the aOEC medium lacking IL-4 significantly decreases neuronal survival and neurite outgrowth. In addition, transplantation of aOECs improved the neurological function deficits after SCI in rats. More importantly, the crosstalk between JAK1/STAT1/3/6-targeted downstream signals and NF-κB/SOCS1/3 signaling predominantly orchestrates IL-4-modulated microglial polarization event. These results provide new insights into the molecular mechanisms of aOECs driving the M1-to-M2 shift of microglia and shed light on new therapies for SCI through the modulation of microglial polarization.

Erianin promotes endogenous neurogenesis in traumatic brain injury rats

The objective of this study was to explore the positive influence and potential mechanism of Erianin on the recovery of brain cells following a traumatic brain injury (TBI). TBI rat models were prepared and treated with Erianin injection via tail vein. The assessment included evaluating the rats' levels of oxidative stress, inflammation, neuronal damage, mitochondrial damage, neuronal regeneration, transformation of pro-inflammatory microglial cells, activation status of the ERK signal pathway, and the functionality of their learning and memory. After administering Erianin, there was a suppression of oxidative stress, inflammation, nerve cell damage, and mitochondrial damage in the TBI rats. Additionally, there was an increase in neuronal regeneration in the cortex and hippocampus, inhibition of pro-inflammatory microglial cell transformation in the cortex, improvement in learning and memory function in TBI rats, and simultaneous inhibition of the activation of the ERK1/c-Jun signal pathway. The findings suggest that Erianin has the potential to reduce oxidative stress and inflammatory reaction in rats with TBI, safeguard nerve cells against apoptosis, stimulate the growth of new neural cells, ultimately enhancing the cognitive abilities and memory function of the rats. The inhibition of the ERK signaling pathway could be closely associated with these effects.

Eriocalyxin B alleviated ischemic cerebral injury by limiting microglia-mediated excessive neuroinflammation in mice

Excessive neuroinflammation mediated by microglia has a detrimental effect on the progression of ischemic stroke. Eriocalyxin B (EriB) was found with a neuroprotective effect in mice with Parkinson's disease via the suppression of microglial overactivation. This study aimed to investigate the roles of EriB in permanent middle cerebral artery occlusion (pMCAO) mice. The pMCAO was induced in the internal carotid artery of the mice by the intraluminal filament method, and EriB (10 mg/kg) was administered immediately after surgery by intraperitoneal injection. The behavior score, 2,3,5-triphenyltetrazole chloride staining, Nissl staining, TUNEL, immunohistochemistry, immunofluorescence, PCR, ELISA, and immunoblotting revealed that EriB administration reduced brain infarct and neuron death and ameliorated neuroinflammation and microglia overactivation in pMCAO mice, manifested by alterations of TUNEL-positive cell numbers, ionized calcium binding adaptor molecule 1 (Iba-1)-positive cell numbers, and expression of tumor necrosis factor-α, interleukin 6, IL-1β, inducible nitric oxide synthase, and arginase 1. In addition, EriB suppressed ischemia-induced activation of nuclear factor kappa B (NF-κB) signaling in the brain penumbra, suggesting the involvement of NF-κB in EriB function. In conclusion, EriB exerted anti-inflammatory effects in ischemia stroke by regulating the NF-κB signaling pathway, and this may provide insights into the neuroprotective effect of EriB in the treatment of ischemic stroke.

Electroacupuncture attenuates middle cerebral artery occlusion-induced learning and memory impairment by regulating microglial polarization in hippocampus

BACKGROUND

As a traditional medical therapy, electroacupuncture (EA) has been demonstrated to have beneficial effects on ischemic stroke-induced cognitive impairment. However, the underlying mechanism is largely unclear.

METHODS

Adult rats received occlusion of the middle cerebral artery and reperfusion (MCAO/R) to establish the ischemic stroke model. Morris water maze test was performed following EA stimulation at the GV20, PC6, and KI1 acupoints in rats to test the learning and memory ability. Western blot, immunofluorescent staining, and enzyme-linked immunosorbent assay were conducted to assess the cellular and molecular mechanisms.

RESULTS

EA stimulation attenuated neurological deficits. In the Morris water maze test, EA treatment ameliorated the MCAO/R-induced learning and memory impairment. Moreover, we observed that MCAO/R induced microglial activation and polarization in the ischemic hippocampus, whereas, EA treatment dampened microglial activation and inhibited M1 microglial polarization but enhanced M2 microglial polarization. EA treatment inhibited the increased expression of proinflammatory cytokines and enhanced the increased expression of anti-inflammatory cytokines. Finally, we found that EA treatment dampened microglial p38 mitogen-activated protein kinase (MAPK) phosphorylation.

CONCLUSION

Collectively, our data suggested that EA treatment ameliorated cognitive impairment induced by MCAO/R and the underlying mechanism may be p38-mediated microglia polarization and neuroinflammation.

The Role of Microglia in Brain Metastases: Mechanisms and Strategies

Brain metastases and related complications are one of the major fatal factors in cancer. Patients with breast cancer, lung cancer, and melanoma are at a high risk of developing brain metastases. However, the mechanisms underlying the brain metastatic cascade remain poorly understood. Microglia, one of the major resident macrophages in the brain parenchyma, are involved in multiple processes associated with brain metastasis, including inflammation, angiogenesis, and immune modulation. They also closely interact with metastatic cancer cells, astrocytes, and other immune cells. Current therapeutic approaches against metastatic brain cancers, including small-molecule drugs, antibody-coupled drugs (ADCs), and immune-checkpoint inhibitors (ICIs), have compromised efficacy owing to the impermeability of the blood-brain barrier (BBB) and complex brain microenvironment. Targeting microglia is one of the strategies for treating metastatic brain cancer. In this review, we summarize the multifaceted roles of microglia in brain metastases and highlight them as potential targets for future therapeutic interventions.

Absence in CX3CR1 receptor signaling promotes post-ischemic stroke cognitive function recovery through suppressed microglial pyroptosis in mice

BACKGROUND

Post-stroke cognitive impairment (PSCI) is a major source of morbidity and mortality after stroke, but the pathological mechanisms remain unclear. Previous studies have demonstrated that the CX3CR1 receptor plays a crucial role in maintaining an early protective microenvironment after stroke, but whether it persistently influences cognitive dysfunction in the chronic phase requires further investigation.

METHODS

Mouse was used to establish a middle cerebral artery occlusion (MCAO)/reperfusion model to study PSCI. Cognitive function was assessed by the Morris water maze (MWM) and the novel object recognition test. Neurogenesis was assessed by immunofluorescence staining with Nestin+ /Ki67+ and DCX+ /BrdU+ double-positive cells. The cerebral damage was monitored by [18 F]-DPA-714 positron emission tomography, Nissel, and TTC staining. The pyroptosis was histologically, biochemically, and electron microscopically examined.

RESULTS

Upon MCAO, at 28 to 35 days, CX3CR1 knockout (CX3CR1-/- ) mice had better cognitive behavioral performance both in MWM and novel object recognition test than their CX3CR1+/- counterparts. Upon MCAO, at 7 days, CX3CR1-/- mice increased the numbers of Nestin+ /Ki67+ and DCX+ /BrdU+ cells, and meanwhile it decreased the protein expression of GSDMD, NLRP3 inflammasome subunit, caspase-1, mature IL-1β/IL-18, and p-P65 in the hippocampus as compared with CX3CR1+/- mice. In addition, CX3CR1-/- mice could reverse infarct volume in the hippocampus region post-stroke.

CONCLUSION

Our study demonstrated that CX3CR1 gene deletion was beneficial to PSCI recovery. The mechanism might lie in inhibited pyroptosis and enhanced neurogenesis. CX3CR1 receptor may serve as a therapeutic target for improving the PSCI.

Hypoxic postconditioning drives protective microglial responses and ameliorates white matter injury after ischemic stroke

BACKGROUND

Ischemic stroke (IS) is a cerebrovascular disease with high incidence and mortality. White matter repair plays an important role in the long-term recovery of neurological function after cerebral ischemia. Neuroprotective microglial responses can promote white matter repair and protect ischemic brain tissue.

AIMS

The aim of this study was to investigate whether hypoxic postconditioning (HPC) can promote white matter repair after IS, and the role and mechanism of microglial polarization in white matter repair after HPC treatment.

MATERIALS & METHODS

Adult male C57/BL6 mice were randomly divided into three groups: Sham group (Sham), MCAO group (MCAO), and hypoxic postconditioning group (HPC). HPC group were subjected to 45 min of transient middle cerebral artery occlusion (MCAO) immediately followed by 40 min of HPC.

RESULTS

The results showed that HPC reduced the proinflammatory level of immune cells. Furthermore, HPC promoted the transformation of microglia to anti-inflammatory phenotype on the third day after the procedure. HPC promoted the proliferation of oligodendrocyte progenitors and increased the expression of myelination-related proteins on the 14th day. On the 28th day, HPC increased the expression of mature oligodendrocytes, which enhanced myelination. At the same time, the motor neurological function of mice was restored.

DISCUSSION

During the acute phase of cerebral ischemia, the function of proinflammatory immune cells was enhanced, long-term white matter damage was aggravated, and motor sensory function was decreased.

CONCLUSION

HPC promotes protective microglial responses and white matter repair after MCAO, which may be related to the proliferation and differentiation of oligodendrocytes.

Hypoxic Preconditioning Attenuates Neuroinflammation via Inhibiting NF-κB/NLRP3 Axis Mediated by p-MLKL after Transient Global Cerebral Ischemia

Hypoxic preconditioning (HPC) has been reported to alleviate neuronal damage and microglial activation in hippocampal CA1 after transient global cerebral ischemia (tGCI). However, the molecular mechanism is unclear. Recent studies identified that nuclear factor-kappa-B (NF-κB)/oligomerization domain-like receptors protein (NLRP) 3 inflammasome pathway is mainly involved in the activation of microglia and that phosphorylated (p)-mixed lineage kinase domain-like (MLKL) is related to the regulation of NF-κB/NLRP3 axis. Hence, in this study, we set out to investigate whether HPC attenuates neuronal damage and microglial activation through inhibiting NF-κB/NLRP3 axis mediated by p-MLKL after tGCI in CA1 of male rats. We found that HPC decreased NLRP3 inflammasome in microglia and inhibited M1 polarization of microglia in CA1 after tGCI. Mechanistically, HPC inhibited the activation of NF-κB signaling pathway and reduced the mRNA and protein levels of NLRP3 inflammasome after tGCI. Additionally, the knockdown of p-MLKL by short hairpin RNA (shRNA) administration inhibited the activation of the NF-κB signaling pathway and reduced the formation of NLRP3 inflammasome, thus attenuating M1 polarization of microglia and decreasing the release of interleukin 1 beta (IL-1β) and necrosis factor alpha (TNF-α) in CA1 post ischemia. We consider that p-MLKL in microglia may be derived from necroptotic neurons after tGCI. In conclusion, the new finding in this study is that HPC-induced neuroprotection against tGCI through inhibiting NF-κB/NLRP3 pathway mediated by p-MLKL.

ULK1 confers neuroprotection by regulating microglial/macrophages activation after ischemic stroke

Microglial activation and autophagy play a critical role in the progression of ischemic stroke and contribute to the regulation of neuroinflammation. Unc-51-like kinase 1 (ULK1) is the primary autophagy kinase involved in autophagosome formation. However, the impact of ULK1 on neuroprotection and microglial activation after ischemic stroke remains unclear. In this study, we established a photothrombotic stroke model, and administered SBI-0206965 (SBI), an ULK1 inhibitor, and LYN-1604 hydrochloride (LYN), an ULK1 agonist, to modulate ULK1 activity in vivo. We assessed sensorimotor deficits, neuronal apoptosis, and microglial/macrophage activation to evaluate the neurofunctional outcome. Immunofluorescence results revealed ULK1 was primarily localized in the microglia of the infarct area following ischemia. Upregulating ULK1 through LYN treatment significantly reduced infarct volume, improved motor function, promoted the increase of anti-inflammatory microglia. In conclusion, ULK1 facilitated neuronal repair and promoted the formation of anti-inflammatory microglia pathway after ischemic injury.

New Insights into Roles of IL-7R Gene as a Therapeutic Target Following Intracerebral Hemorrhage

Background

Spontaneous intracerebral hemorrhage (ICH) is a subtype of stroke leading to high rates of morbidity and mortality in adults. Recent studies showed that immune and inflammatory responses might play essential roles in secondary brain injury. The purpose of this article was to provide a reference for further therapeutic strategies for ICH patients.

Methods

GSE206971 and GSE216607 datasets from the gene expression omnibus (GEO) database were used to screen the highly immune-related differentally expressed genes (IRDEGs). We used the CIBERSORT algorithm to assess the level of immune signatures infiltration and got the possible function of IRDEGs which was analyzed through Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. Protein-protein interaction (PPI) networks and six hub genes were identified in the Cytoscape plug-in. GSVA algorithm was performed to evaluate the potential pathways of six hub genes in ICH samples. The expression level of IL-7R chosen from six hub genes was further validated by Western blotting. The cell models of ICH were established for the research of IL-7/IL-7R signaling way.

Results

A total of six hub genes (ITGAX, ITGAM, CCR2, CD28, SELL, and IL-7R) were identified. IL-7R was highly expressed in the mice ICH group, as shown by immunoblotting. Next, we constructed ICH cell models in RAW264.7 cells and BV2 cells. After treatment with IL-7, iNOS expression (M1 marker) was greatly inhibited while Arg-1(M2 marker) was enhanced, and it might function via the JAK3/STAT5 signaling pathway.

Conclusion

The hypothesis is proposed that the IL-7/IL-7R signaling pathway might regulate the inflammatory process following ICH by regulating microglia polarization. Our study is limited and requires more in-depth experimental confirmation.

Single-Cell Transcriptomic Sequencing Reveals Tissue Architecture and Deciphers Pathological Reprogramming During Retinal Ischemia in Macaca fascicularis

Purpose

Acute retinal arterial ischemia diseases (ARAIDs) are ocular emergencies that require immediate intervention within a restricted therapeutic window to prevent blindness. However, the underlying molecular mechanisms contributing to the pathogenesis of ARAIDs remain enigmatic. Herein, we present the single-cell RNA sequencing (scRNA-seq) alterations during ischemia in the primate retina as a preliminary endeavor in understanding the molecular complexities of ARAIDs.

Methods

An ophthalmic artery occlusion model was established through ophthalmic artery ligation in two Macaca fascicularis. scRNA-seq and bioinformatics analyses were used to detect retinal changes during ischemia, which are further validated by immunofluorescence analysis. Western blot and flow cytometry assays were performed to measure the microglia polarization status.

Results

The findings of this study reveal notable changes in the retina under acute ischemic conditions. Particularly, retinal ischemia compromised mitochondrial functions of rod photoreceptors, partly leading to the rapid loss of healthy rods. Furthermore, we observed a noteworthy transcriptional alteration in the activation of microglia induced by ischemia. The targeted correction of the proinflammatory cytokine CXCL8 effectively suppresses microglia M1 polarization in retinal ischemia, ultimately reducing the proinflammatory transformation in vitro. In addition, retina ischemia induced the apoptotic inclination of endothelial cells and the heightened interaction with microglia, which signifies the influence of microglia in disrupting the retinal-blood barrier.

Conclusions

Our research has successfully identified and described the pathologic alterations occurring in several cell types during a short period of ischemia. These observations provide valuable insights for ameliorating retinal damage and promoting the restoration of vision.

Potential biomaterials and experimental animal models for inventing new drug delivery approaches in the neurodegenerative disorder: Multiple sclerosis

The tight junction of endothelial cells in the central nervous system (CNS) has an ideal characteristic, acting as a biological barrier that can securely regulate the movement of molecules in the brain. Tightly closed astrocyte cell junctions on blood capillaries are the blood-brain barrier (BBB). This biological barrier prohibits the entry of polar drugs, cells, and ions, which protect the brain from harmful toxins. However, delivering any therapeutic agent to the brain in neurodegenerative disorders (i.e., schizophrenia, multiple sclerosis, etc.) is extremely difficult. Active immune responses such as microglia, astrocytes, and lymphocytes cross the BBB and attack the nerve cells, which causes the demyelination of neurons. Therefore, there is a hindrance in transmitting electrical signals properly, resulting in blindness, paralysis, and neuropsychiatric problems. The main objective of this article is to shed light on the performance of biomaterials, which will help researchers to create nanocarriers that can cross the blood-brain barrier and achieve a therapeutic concentration of drugs in the CNS of patients with multiple sclerosis (MS). The present review focuses on the importance of biomaterials with diagnostic and therapeutic efficacy that can help enhance multiple sclerosis therapeutic potential. Currently, the development of MS in animal models is limited by immune responses, which prevent MS induction in healthy animals. Therefore, this article also showcases animal models currently used for treating MS. A future advance in developing a novel effective strategy for treating MS is now a potential area of research.

Jasminoidin reduces ischemic stroke injury by regulating microglia polarization via PASK-EEF1A1 axis

Jasminoidin (JAS) can alleviate ischemic stroke (IS) injury, but its molecular mechanism remains undefined. The polarization of microglia affects IS process. This research is powered to probe whether the molecular mechanism of JAS for IS treatment is coupled with microglia polarization. IS modeling in mice was accomplished by middle cerebral artery occlusion (MCAO) and model mice were injected with 25 and 50 mg/mL JAS, followed by determination of infarct volume, brain water content, and histological changes in mouse brains. The microglia modeling was performed by 1-h oxygen-glucose deprivation and 24-h reoxygenation. Oxygen-glucose deprivation/reoxygenation (OGD/R)-induced microglia were treated with JAS and transfected with Per-Arnt-Sim kinase (PASK)-overexpressing plasmid, subsequent to which cell viability and lactate dehydrogenase (LDH) level were determined. The mRNA or protein expressions of examined genes in microglia and brain tissues were detected by quantitative real-time polymerase chain reaction or western blot. MCAO-induced massive infarction, edema, and injury in mouse brain tissues, upregulated interleukin-1 beta (IL-1β), FcγRIIB (CD32), tumor necrosis factor alpha (TNF-α), PASK, p-eukaryotic elongation factor 1A1 (EEF1A1), and p-EEF1A1/EEF1A1 levels, but downregulated mannose receptor 1 (CD206), arginase-1 (Arg-1) and interleukin-10 (IL-10), and EEF1A1 expressions, which was reversed by JAS. OGD/R treatment decreased microglial viability as well as expressions of CD206, Arg-1, IL-10, and EEF1A1, yet increased cytotoxicity and levels of IL-1β, CD32, TNF-α, PASK, p-EEF1A1, and p-EEF1A1/EEF1A1, which was reversed by JAS. PASK overexpression reversed the effects of JAS on microglia. JAS reduces IS injury by regulating microglia polarization via PASK-EEF1A1 axis.

Low-dose ionizing radiation promotes motor recovery and brain rewiring by resolving inflammatory response after brain injury and stroke

Traumatic brain injury (TBI) and stroke share a common pathophysiology that worsens over time due to secondary tissue injury caused by sustained inflammatory response. However, studies on pharmacological interventions targeting the complex secondary injury cascade have failed to show efficacy. Here, we demonstrated that low-dose ionizing radiation (LDIR) reduced lesion size and reversed motor deficits after TBI and photothrombotic stroke. Magnetic resonance imaging demonstrated significant reduction of infarct volume in LDIR-treated mice after stroke. Systems-level transcriptomic analysis showed that genes upregulated in LDIR-treated stoke mice were enriched in pathways associated with inflammatory and immune response involving microglia. LDIR induced upregulation of anti-inflammatory- and phagocytosis-related genes, and downregulation of key pro-inflammatory cytokine production. These findings were validated by live-cell assays, in which microglia exhibited higher chemotactic and phagocytic capacities after LDIR. We observed substantial microglial clustering at the injury site, glial scar clearance and reversal of motor deficits after stroke. Cortical microglia/macrophages depletion completely abolished the beneficial effect of LDIR on motor function recovery in stroke mice. LDIR promoted axonal projections (brain rewiring) in motor cortex and recovery of brain activity detected by electroencephalography recordings months after stroke. LDIR treatment delayed by 8 h post-injury still maintained full therapeutic effects on motor recovery, indicating that LDIR is a promising therapeutic strategy for TBI and stroke.

Modulating the polarization phenotype of microglia - A valuable strategy for central nervous system diseases

Central nervous system (CNS) diseases have become one of the leading causes of death in the global population. The pathogenesis of CNS diseases is complicated, so it is important to find the patterns of the disease to improve the treatment strategy. Microglia are considered to be a double-edged sword, playing both harmful and beneficial roles in CNS diseases. Therefore, it is crucial to understand the progression of the disease and the changes in the polar phenotype of microglia to provide guidance in the treatment of CNS diseases. Microglia activation may evolve into different phenotypes: M1 and M2 types. We focused on the roles that M1 and M2 microglia play in regulating intercellular dialogues, pathological reactions and specific diseases in CNS diseases. Importantly, we summarized the strategies used to modulate the polarization phenotype of microglia, including traditional pharmacological modulation, biological therapies, and physical strategies. This review will contribute to the development of potential strategies to modulate microglia polarization phenotypes and provide new alternative therapies for CNS diseases.

Extracellular vesicles from hiPSC-NSCs can prevent peripheral inflammation-induced cognitive dysfunction with inflammasome inhibition and improved neurogenesis in the hippocampus

Extracellular vesicles (EVs) released by human induced pluripotent stem cell-derived neural stem cells (hiPSC-NSCs) are enriched with miRNAs and proteins capable of mediating robust antiinflammatory activity. The lack of tumorigenic and immunogenic properties and ability to permeate the entire brain to incorporate into microglia following intranasal (IN) administrations makes them an attractive biologic for curtailing chronic neuroinflammation in neurodegenerative disorders. We tested the hypothesis that IN administrations of hiPSC-NSC-EVs can alleviate chronic neuroinflammation and cognitive impairments induced by the peripheral lipopolysaccharide (LPS) challenge. Adult male, C57BL/6J mice received intraperitoneal injections of LPS (0.75 mg/kg) for seven consecutive days. Then, the mice received either vehicle (VEH) or hiPSC-NSC-EVs (~ 10 × 109 EVs/administration, thrice over 6 days). A month later, mice in all groups were investigated for cognitive function with behavioral tests and euthanized for histological and biochemical studies. Mice receiving VEH after LPS displayed deficits in associative recognition memory, temporal pattern processing, and pattern separation. Such impairments were associated with an increased incidence of activated microglia presenting NOD-, LRR-, and pyrin domain containing 3 (NLRP3) inflammasomes, elevated levels of NLRP3 inflammasome mediators and end products, and decreased neurogenesis in the hippocampus. In contrast, the various cognitive measures in mice receiving hiPSC-NSC-EVs after LPS were closer to naive mice. Significantly, these mice displayed diminished microglial activation, NLRP3 inflammasomes, proinflammatory cytokines, and a level of neurogenesis matching age-matched naïve controls. Thus, IN administrations of hiPSC-NSC-EVs are an efficacious approach to reducing chronic neuroinflammation-induced cognitive impairments.

Acute ischemia induces spatially and transcriptionally distinct microglial subclusters

BACKGROUND

Damage in the ischemic core and penumbra after stroke affects patient prognosis. Microglia immediately respond to ischemic insult and initiate immune inflammation, playing an important role in the cellular injury after stroke. However, the microglial heterogeneity and the mechanisms involved remain unclear.

METHODS

We first performed single-cell RNA-sequencing (scRNA-seq) and spatial transcriptomics (ST) on middle cerebral artery occlusion (MCAO) mice from three time points to determine stroke-associated microglial subclusters and their spatial distributions. Furthermore, the expression of microglial subcluster-specific marker genes and the localization of different microglial subclusters were verified on MCAO mice through RNAscope and immunofluorescence. Gene set variation analysis (GSVA) was performed to reveal functional characteristics of microglia sub-clusters. Additionally, ingenuity pathway analysis (IPA) was used to explore upstream regulators of microglial subclusters, which was confirmed by immunofluorescence, RT-qPCR, shRNA-mediated knockdown, and targeted metabolomics. Finally, the infarct size, neurological deficits, and neuronal apoptosis were evaluated in MCAO mice after manipulation of specific microglial subcluster.

RESULTS

We discovered stroke-associated microglial subclusters in the brains of MCAO mice. We also identified novel marker genes of these microglial subclusters and defined these cells as ischemic core-associated (ICAM) and ischemic penumbra-associated (IPAM) microglia, according to their spatial distribution. ICAM, induced by damage-associated molecular patterns, are probably fueled by glycolysis, and exhibit increased pro-inflammatory cytokines and chemokines production. BACH1 is a key transcription factor driving ICAM generation. In contrast, glucocorticoids, which are enriched in the penumbra, likely trigger IPAM formation, which are presumably powered by the citrate cycle and oxidative phosphorylation and are characterized by moderate pro-inflammatory responses, inflammation-alleviating metabolic features, and myelinotrophic properties.

CONCLUSIONS

ICAM could induce excessive neuroinflammation, aggravating brain injury, whereas IPAM probably exhibit neuroprotective features, which could be essential for the homeostasis and survival of cells in the penumbra. Our findings provide a biological basis for targeting specific microglial subclusters as a potential therapeutic strategy for ischemic stroke.

Metabolic reprogramming regulates microglial polarization and its role in cerebral ischemia reperfusion

The brain is quite sensitive to changes in energy supply because of its high energetic demand. Even small changes in energy metabolism may be the basis of impaired brain function, leading to the occurrence and development of cerebral ischemia/reperfusion (I/R) injury. Abundant evidence supports that metabolic defects of brain energy during the post-reperfusion period, especially low glucose oxidative metabolism and elevated glycolysis levels, which play a crucial role in cerebral I/R pathophysiology. Whereas research on brain energy metabolism dysfunction under the background of cerebral I/R mainly focuses on neurons, the research on the complexity of microglia energy metabolism in cerebral I/R is just emerging. As resident immune cells of the central nervous system, microglia activate rapidly and then transform into an M1 or M2 phenotype to correspond to changes in brain homeostasis during cerebral I/R injury. M1 microglia release proinflammatory factors to promote neuroinflammation, while M2 microglia play a neuroprotective role by secreting anti-inflammatory factors. The abnormal brain microenvironment promotes the metabolic reprogramming of microglia, which further affects the polarization state of microglia and disrupts the dynamic equilibrium of M1/M2, resulting in the aggravation of cerebral I/R injury. Increasing evidence suggests that metabolic reprogramming is a key driver of microglial inflammation. For example, M1 microglia preferentially produce energy through glycolysis, while M2 microglia provide energy primarily through oxidative phosphorylation. In this review, we highlight the emerging significance of regulating microglial energy metabolism in cerebral I/R injury.

The role of microglial activation on ischemic stroke: Modulation by fibroblast growth factors

Stroke is one of the devastating clinical conditions that causes death and permanent disability. Its occurrence causes the reduction of oxygen and glucose supply, resulting in events such as inflammatory response, oxidative stress, and apoptosis in the brain. Microglia are brain-resident immune cells in the central nervous system (CNS) that exert diverse roles and respond to pathological process after an ischemic insult. The discovery of fibroblast growth factors (FGFs) in mammals, resulted to the findings that they can treat experimental models of stroke in animals effectively. FGFs function as homeostatic factors that control cells and hormones involved in metabolism, and they also regulate the secretion of proinflammatory (M1) and anti-inflammatory (M2) cytokines after stroke. In this review, we outline current evidence of microglia activation in experimental models of stroke focusing on its ability to exacerbate damage or repair tissue. Also, our review sheds light on the pharmacological actions of FGFs on multiple targets to regulate microglial modulation and highlighted their theoretical molecular mechanisms to provide possible therapeutic targets, as well as their limitations for the treatment of stroke. DATA AVAILABILITY: Not applicable.

Nanomaterial-Based Drug Delivery Systems for Ischemic Stroke

Ischemic stroke is a leading cause of death and disability in the world. At present, reperfusion therapy and neuroprotective therapy, as guidelines for identifying effective and adjuvant treatment methods, are limited by treatment time windows, drug bioavailability, and side effects. Nanomaterial-based drug delivery systems have the characteristics of extending half-life, increasing bioavailability, targeting drug delivery, controllable drug release, and low toxicity, thus being used in the treatment of ischemic stroke to increase the therapeutic effects of drugs. Therefore, this review provides a comprehensive overview of nanomaterial-based drug delivery systems from nanocarriers, targeting ligands and stimulus factors of drug release, aiming to find the best combination of nanomaterial-based drug delivery systems for ischemic stroke. Finally, future research areas on nanomaterial-based drug delivery systems in ischemic stroke and the implications of the current knowledge for the development of novel treatment for ischemic stroke were identified.

Regulated necrosis pathways: a potential target for ischemic stroke

Globally, ischemic stroke causes millions of deaths per year. The outcomes of ischemic stroke are largely determined by the amount of ischemia-related and reperfusion-related neuronal death in the infarct region. In the infarct region, cell injuries follow either the regulated pathway involving precise signaling cascades, such as apoptosis and autophagy, or the nonregulated pathway, which is uncontrolled by any molecularly defined effector mechanisms such as necrosis. However, numerous studies have recently found that a certain type of necrosis can be regulated and potentially modified by drugs and is nonapoptotic; this type of necrosis is referred to as regulated necrosis. Depending on the signaling pathway, various elements of regulated necrosis contribute to the development of ischemic stroke, such as necroptosis, pyroptosis, ferroptosis, pathanatos, mitochondrial permeability transition pore-mediated necrosis and oncosis. In this review, we aim to summarize the underlying molecular mechanisms of regulated necrosis in ischemic stroke and explore the crosstalk and interplay among the diverse types of regulated necrosis. We believe that targeting these regulated necrosis pathways both pharmacologically and genetically in ischemia-induced neuronal death and protection could be an efficient strategy to increase neuronal survival and regeneration in ischemic stroke.

Electroacupuncture Alleviates Neuroinflammation by Regulating Microglia Polarization via STAT6/PPARγ in Ischemic Stroke Rats

Previous study showed that electroacupuncture (EA) produced a protective effect on cerebral ischemia-reperfusion injury (CIRI) in rats and may correlate with the anti-inflammatory effects of microglia. This study aimed to investigate further whether EA could modulate neuroinflammation by targeting the Signal Transducer and Activator of Transcription 6 (STAT6) and Peroxisome Proliferator-Activated Receptor γ (PPARγ) pathway, the key regulator of microglia. Middle cerebral artery occlusion (MCAO) rats were used, and 6 h after reperfusion, EA interventions were performed in Chize (LU 5), Hegu (LI 4), Sanyinjiao (SP 6), and Zusanli (ST 36) on the affected side of the rats, the group that received EA + STAT6 phosphorylation inhibitor AS1517499 was used as a parallel control. The degree of neurological impairment, infarct volume, microglia polarization, inflammation levels and activity of STAT6/PPARγ pathway were then assessed by neurological deficit score, triphenyl tetrazolium chloride (TTC) staining, immunofluorescence, western blotting (WB), quantitative real-time PCR (qPCR) and Enzyme linked immunosorbent assay (ELISA). The data showed that EA significantly alleviated nerve injury, reduced infarct volume, enhanced the expression and activity of STAT6/PPARγ pathway, inhibited NF-κB activity, increased M2 microglia numbers and anti-inflammatory factor release, and inhibited microglia M1-type polarization and pro-inflammatory factor expression. In contrast, inhibition of STAT6 phosphorylation exacerbated neural damage, inhibited STAT6/PPARγ pathway activity, promoted microglia M1-type polarization and exacerbated neuroinflammation, resulting in an attenuated positive effect of EA intervention. Therefore, we concluded that EA intervention could attenuate microglia-associated neuroinflammation by enhancing the expression and activity of STAT6/PPARγ pathway, thereby reducing CIRI in MCAO rats.

Electro-nape-acupuncture regulates the differentiation of microglia through PD-1/PD-L1 reducing secondary brain injury in acute phase intracerebral hemorrhage rats

INTRODUCTION

This study aimed to investigate the effect of electro-nape-acupuncture (ENA) on the differentiation of microglia and the secondary brain injury in rats with acute-phase intracerebral hemorrhage (ICH) through the programmed cell death protein-1/ligand-1 (PD-1/PD-L1) pathway.

METHODS

A total of 27 male Sprague-Dawley rats were randomly divided into three groups: sham group, ICH group, and ENA group. The autologous blood infusion intracerebral hemorrhage model was used to study the effects of ENA by administering electroacupuncture at GB20 (Fengchi) and Jiaji (EX-B2) acupoints on 24 h after the modeling, once per day for 3 days. The neurological function damage, hematoma lesion, and inflammatory cell infiltration were measured by the beam walking test and hematoxylin-eosin staining. The expression of PD-1, PD-L1, CD86, CD206, and related cytokines around the hematoma was measured by western blot, quantitative reverse transcription polymerase chain reaction, and immunofluorescence.

RESULTS

The ICH group had significant neurological deficits (p < .001), hematoma lesions, and inflammatory cell infiltration. The levels of CD86 protein, inflammatory factors tumor necrosis factors (TNF)-α, interleukin (IL)-1β, and IL-6 were increased (p < .001), while CD206 protein was reduced (p < .01), and the number of CD86+ /CD11b+ cells was also increased (p < .001) compared to the sham group. However, after ENA intervention, there was a significant reduction in neurological function damage (p < .05), infiltration of inflammatory cells, and the expression levels of CD86+ /CD11b+ cells (p < .05), resulting in the increased expression of PD-1 protein and differentiation of M2 phenotype significantly (p < .001).

CONCLUSION

The study concludes that ENA could reduce neurological function damage, inhibit the expression of pro-inflammatory cytokines, and improve the infiltration of inflammatory cells to improve secondary brain injury in acute-phase intracerebral hemorrhage rats. These effects could be related to the increased expression of PD-1 around the lesion, promoting the differentiation of microglia from M1 to M2 phenotype.

Scientific Landscape of Oxidative Stress in Stroke: From a Bibliometric Analysis to an in-Depth Review

Stroke is an acute cerebrovascular disease resulting from either obstruction or rupture of a blood vessel in the brain. Oxidative stress (OS), referred to a status where cellular oxidative capacities overwhelm antioxidative defenses, is involved in the pathophysiology of stroke. The bibliometric analysis and in-depth review aim to depict the research trend of OS in stroke. Relevant scientific publications were acquired from the Web of Science Core Collection database. Scientific landscape of OS in stroke was illustrated by general quantitative trend, impactful journals, and co-authorship of various academic units (i.e., countries/regions, organizations, and authors). Furthermore, theme analysis predicting the hot research issues and frontiers was performed. 15,826 documents regarding OS in stroke were obtained over a time span of more than 20 years from 1992 to 2021. The overall tendency of publication counts was continuously on the rise. Bibliometric analysis indicated China and the United States were predominant in this study field, as reflected by their high publication counts and intensive collaboration with other countries. Current key research areas of OS in stroke may lie in the investigation of neuroinflammation, and interaction among multiple cell death mechanisms including apoptosis, autophagy, and ferroptosis to search for effective treatments. Moreover, another hot topic could be the association between air pollution and stroke, and its underlying mechanisms. As the exploration of OS in stroke is speculated to be a continuous hot spot in the future, this article may be helpful for researchers to conduct future studies with the understanding of influential academic forces and research highlights.

The Role and Therapeutic Implications of Inflammation in the Pathogenesis of Brain Arteriovenous Malformations

Brain arteriovenous malformations (bAVMs) are focal vascular lesions composed of abnormal vascular channels without an intervening capillary network. As a result, high-pressure arterial blood shunts directly into the venous outflow system. These high-flow, low-resistance shunts are composed of dilated, tortuous, and fragile vessels, which are prone to rupture. BAVMs are a leading cause of hemorrhagic stroke in children and young adults. Current treatments for bAVMs are limited to surgery, embolization, and radiosurgery, although even these options are not viable for ~20% of AVM patients due to excessive risk. Critically, inflammation has been suggested to contribute to lesion progression. Here we summarize the current literature discussing the role of the immune system in bAVM pathogenesis and lesion progression, as well as the potential for targeting inflammation to prevent bAVM rupture and intracranial hemorrhage. We conclude by proposing that a dysfunctional endothelium, which harbors the somatic mutations that have been shown to give rise to sporadic bAVMs, may drive disease development and progression by altering the immune status of the brain.

Role of Crosstalk between Glial Cells and Immune Cells in Blood-Brain Barrier Damage and Protection after Acute Ischemic Stroke

Blood-brain barrier (BBB) damage is the main pathological basis for acute ischemic stroke (AIS)-induced cerebral vasogenic edema and hemorrhagic transformation (HT). Glial cells, including microglia, astrocytes, and oligodendrocyte precursor cells (OPCs)/oligodendrocytes (OLs) play critical roles in BBB damage and protection. Recent evidence indicates that immune cells also have an important role in BBB damage, vasogenic edema and HT. Therefore, regulating the crosstalk between glial cells and immune cells would hold the promise to alleviate AIS-induced BBB damage. In this review, we first introduce the roles of glia cells, pericytes, and crosstalk between glial cells in the damage and protection of BBB after AIS, emphasizing the polarization, inflammatory response and crosstalk between microglia, astrocytes, and other glia cells. We then describe the role of glial cell-derived exosomes in the damage and protection of BBB after AIS. Next, we specifically discuss the crosstalk between glial cells and immune cells after AIS. Finally, we propose that glial cells could be a potential target for alleviating BBB damage after AIS and we discuss some molecular targets and potential strategies to alleviate BBB damage by regulating glial cells after AIS.

Trends in NLRP3 inflammasome research in ischemic stroke from 2011 to 2022: A bibliometric analysis

BACKGROUND

Ischemic stroke is a leading cause of permanent disability and death globally. The nucleotide-biding oligomaerization domain (NOD)-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome is a multi-protein complex that plays a role in ischemic stroke. Recently, research on the role of NLRP3 in ischemic stroke has developed rapidly worldwide. However, there is no bibliometric analysis of NLRP3 in ischemic stroke to date.

AIM

Through bibliometric analysis, the aim of this study was to assess the current state of research on NLRP3 in the field of ischemic stroke research worldwide over the past 12 years and to identify important results, major research areas, and emerging trends.

METHODS

Publications related to NLRP3 in ischemic stroke from January 1, 2011 to December 31, 2022 were obtained from the Web of Science Core Collection (WoSCC). We used HistCite, VOSviewer, CiteSpace, and Bibliometrix for bibliometric analysis and visualization. The Total Global Citation Score (TGCS) was employed to assess the impact of publications.

RESULTS

We found that research of NLRP3 in ischemic stroke developed rapidly starting in 2011. 601 relevant studies have been published in 245 journals over the past 12 years. Journal of Neuroinflammation and International Immunopharmacology were the most productive journals and Journal of Neuroinflammation was the most cited journal. Additionally, Stroke and Journal of Cerebral Blood Flow & Metabolism were the most co-cited journal. The most productive country was China (records = 430) and the most productive university was the Zhejiang University (records = 24). Arumugam TV (TGCS = 949) was the most cited author in this field. NLRP3 inflammasome activation, nf-κb, oxidative stress, and inflammation were the knowledge bases for the research in this field.

CONCLUSION

This study is a scientometric study utilizing quantitative and qualitative methods to comprehensively review the publications on NLRP3 in ischemic stroke. This information provides a reference for scholars to further study NLRP3 in ischemic stroke.

USP25 Inhibits Neuroinflammatory Responses After Cerebral Ischemic Stroke by Deubiquitinating TAB2

Cerebral ischemic stroke is a leading cause of morbidity and mortality globally. However, the mechanisms underlying ischemic stroke injury remain poorly understood. Here, it is found that deficiency of the ubiquitin-specific protease USP25 significantly aggravate ischemic stroke injury in mice. USP25 has no impact on neuronal death under hypoxic conditions, but reduced ischemic stroke-induced neuronal loss and neurological deficits by inhibiting microglia-mediated neuroinflammation. Mechanistically, USP25 restricts the activation of NF-κB and MAPK signaling by regulating TAB2. As a deubiquitinating enzyme, USP25 removeds K63-specific polyubiquitin chains from TAB2. AAV9-mediated TAB2 knockdown ameliorates ischemic stroke injury and abolishes the effect of USP25 deletion. In both mouse and human brains, USP25 is markedly upregulated in microglia in the ischemic penumbra, implying a clinical relevance of USP25 in ischemic stroke. Collectively, USP25 is identified as a critical inhibitor of ischemic stroke injury and this data suggest USP25 may serve as a therapeutic target for ischemic stroke.

Nissl Granules, Axonal Regeneration, and Regenerative Therapeutics: A Comprehensive Review

Nissl granules, traditionally recognized for their pivotal role in protein synthesis within neuronal cell bodies, are emerging as intriguing components with far-reaching implications in the realm of regenerative therapeutics. This abstract encapsulates the essence of a comprehensive review, exploring the nexus between Nissl granules, axonal regeneration, and their transformative applications in regenerative medicine. The molecular intricacies of Nissl granules form the foundation of this exploration, unraveling their dynamic role in orchestrating cellular responses, particularly in the context of axonal regeneration. As we delve into the interplay between Nissl granules and regenerative processes, this review highlights the diverse mechanisms through which these granules contribute to neuronal repair and recovery. Beyond their conventional association with neurobiology, recent advancements underscore the translational potential of Nissl granules as therapeutic agents. Insights into their involvement in enhancing axonal regeneration prompt a reconsideration of these granules as key players in the broader field of regenerative medicine. The abstract encapsulates evidence suggesting that modulating Nissl granule-related pathways holds promise for augmenting tissue regeneration, extending their applicability beyond the confines of the nervous system. This review aims to serve as a valuable resource for medical professionals, researchers, and clinicians seeking to comprehend the multifaceted role of Nissl granules in regenerative therapeutics. By illuminating the intricate connections between Nissl granules, axonal regeneration, and therapeutic applications, this work aspires to catalyze further research and innovation, ultimately contributing to the evolution of regenerative strategies that harness the innate reparative capacities within cellular constituents.

Degradation of NLRP3 by p62-dependent-autophagy improves cognitive function in Alzheimer's disease by maintaining the phagocytic function of microglia

BACKGROUND

Activation of the NLRP3 inflammasome promotes microglia to secrete inflammatory cytokines and induce pyroptosis, leading to impaired phagocytic and clearance functions of microglia in Alzheimer's disease (AD). This study found that the autophagy-associated protein p62 interacts with NLRP3, which is the rate-limiting protein of the NLRP3 inflammasome. Thus, we aimed to prove that the degradation of NLRP3 occurs through the autophagy-lysosome pathway (ALP) and also demonstrate its effects on the function of microglia and pathological changes in AD.

METHODS

The 5XFAD/NLRP3-KO mouse model was established to study the effect of NLRP3 reduction on AD. Behavioral experiments were conducted to assess the cognitive function of the mice. In addition, immunohistochemistry was used to evaluate the deposition of Aβ plaques and morphological changes in microglia. BV2 cells treated with lipopolysaccharide (LPS) followed by Aβ1-42 oligomers were used as in vitro AD inflammation models and transfected with lentivirus to regulate the expression of the target protein. The pro-inflammatory status and function of BV2 cells were detected by flow cytometry and immunofluorescence (IF). Co-immunoprecipitation, mass spectrometry, IF, Western blot (WB), quantitative real-time PCR, and RNA-seq analysis were used to elucidate the mechanisms of molecular regulation.

RESULTS

Cognitive function was improved in the 5XFAD/NLRP3-KO mouse model by reducing the pro-inflammatory response of microglia and maintaining the phagocytic and clearance function of microglia to the deposited Aβ plaque. The pro-inflammatory function and pyroptosis of microglia were regulated by NLRP3 expression. Ubiquitinated NLRP3 can be recognized by p62 and degraded by ALP, slowing down the proinflammatory function and pyroptosis of microglia. The expression of autophagy pathway-related proteins such as LC3B/A, p62 was increased in the AD model in vitro.

CONCLUSIONS

P62 recognizes and binds to ubiquitin-modified NLRP3. It plays a vital role in regulating the inflammatory response by participating in ALP-associated NLRP3 protein degradation, which improves cognitive function in AD by reducing the pro-inflammatory status and pyroptosis of microglia, thus maintaining its phagocytic function.

Ipsilesional Hippocampal GABA Is Elevated and Correlates With Cognitive Impairment and Maladaptive Neurogenesis After Cortical Stroke in Mice

BACKGROUND

Cognitive dysfunction is a frequent stroke sequela, but its pathogenesis and treatment remain unresolved. Involvement of aberrant hippocampal neurogenesis and maladaptive circuitry remodeling has been proposed, but their mechanisms are unknown. Our aim was to evaluate potential underlying molecular/cellular events implicated.

METHODS

Stroke was induced by permanent occlusion of the middle cerebral artery occlusion in 2-month-old C57BL/6 male mice. Hippocampal metabolites/neurotransmitters were analyzed longitudinally by in vivo magnetic resonance spectroscopy. Cognitive function was evaluated with the contextual fear conditioning test. Microglia, astrocytes, neuroblasts, interneurons, γ-aminobutyric acid (GABA), and c-fos were analyzed by immunofluorescence.

RESULTS

Approximately 50% of mice exhibited progressive post-middle cerebral artery occlusion cognitive impairment. Notably, immature hippocampal neurons in the impaired group displayed more severe aberrant phenotypes than those from the nonimpaired group. Using magnetic resonance spectroscopy, significant bilateral changes in hippocampal metabolites, such as myo-inositol or N-acetylaspartic acid, were found that correlated, respectively, with numbers of glia and immature neuroblasts in the ischemic group. Importantly, some metabolites were specifically altered in the ipsilateral hippocampus suggesting its involvement in aberrant hippocampal neurogenesis and remodeling processes. Specifically, middle cerebral artery occlusion animals with higher hippocampal GABA levels displayed worse cognitive outcome. Implication of GABA in this setting was supported by the amelioration of ischemia-induced memory deficits and aberrant hippocampal neurogenesis after blocking pharmacologically GABAergic neurotransmission, an intervention which was ineffective when neurogenesis was inhibited. These data suggest that GABA exerts its detrimental effect, at least partly, by affecting morphology and integration of newborn neurons into the hippocampal circuits.

CONCLUSIONS

Hippocampal GABAergic neurotransmission could be considered a novel diagnostic and therapeutic target for poststroke cognitive impairment.

Inhibition of neutrophil extracellular trap formation ameliorates neuroinflammation and neuronal apoptosis via STING-dependent IRE1α/ASK1/JNK signaling pathway in mice with traumatic brain injury

BACKGROUND

Neuroinflammation is one of the most important pathogeneses in secondary brain injury after traumatic brain injury (TBI). Neutrophil extracellular traps (NETs) forming neutrophils were found throughout the brain tissue of TBI patients and elevated plasma NET biomarkers correlated with worse outcomes. However, the biological function and underlying mechanisms of NETs in TBI-induced neural damage are not yet fully understood. Here, we used Cl-amidine, a selective inhibitor of NETs to investigate the role of NETs in neural damage after TBI.

METHODS

Controlled cortical impact model was performed to establish TBI. Cl-amidine, 2'3'-cGAMP (an activator of stimulating Interferon genes (STING)), C-176 (a selective STING inhibitor), and Kira6 [a selectively phosphorylated inositol-requiring enzyme-1 alpha [IRE1α] inhibitor] were administrated to explore the mechanism by which NETs promote neuroinflammation and neuronal apoptosis after TBI. Peptidyl arginine deiminase 4 (PAD4), an essential enzyme for neutrophil extracellular trap formation, is overexpressed with adenoviruses in the cortex of mice 1 day before TBI. The short-term neurobehavior tests, magnetic resonance imaging (MRI), laser speckle contrast imaging (LSCI), Evans blue extravasation assay, Fluoro-Jade C (FJC), TUNEL, immunofluorescence, enzyme-linked immunosorbent assay (ELISA), western blotting, and quantitative-PCR were performed in this study.

RESULTS

Neutrophils form NETs presenting in the circulation and brain at 3 days after TBI. NETs inhibitor Cl-amidine treatment improved short-term neurological functions, reduced cerebral lesion volume, reduced brain edema, and restored cerebral blood flow (CBF) after TBI. In addition, Cl-amidine exerted neuroprotective effects by attenuating BBB disruption, inhibiting immune cell infiltration, and alleviating neuronal death after TBI. Moreover, Cl-amidine treatment inhibited microglia/macrophage pro-inflammatory polarization and promoted anti-inflammatory polarization at 3 days after TBI. Mechanistically, STING ligand 2'3'-cGAMP abolished the neuroprotection of Cl-amidine via IRE1α/ASK1/JNK signaling pathway after TBI. Importantly, overexpression of PAD4 promotes neuroinflammation and neuronal death via the IRE1α/ASK1/JNK signaling pathway after TBI. However, STING inhibitor C-176 or IRE1α inhibitor Kira6 effectively abolished the neurodestructive effects of PAD4 overexpression after TBI.

CONCLUSION

Altogether, we are the first to demonstrate that NETs inhibition with Cl-amidine ameliorated neuroinflammation, neuronal apoptosis, and neurological deficits via STING-dependent IRE1α/ASK1/JNK signaling pathway after TBI. Thus, Cl-amidine treatment may provide a promising therapeutic approach for the early management of TBI.