Microglial-specific depletion of TAK1 is neuroprotective in the acute phase after ischemic stroke

Microglial Inflammatory Mechanisms in Stroke: The Jury Is Still Out

Microglia represent the main immune cell population in the CNS with unique homeostatic roles and contribution to broad neurological conditions. Stroke is associated with marked changes in microglial phenotypes and induction of inflammatory responses, which emerge as key modulators of brain injury, neurological outcome and regeneration. However, due to the limited availability of functional studies with selective targeting of microglia and microglia-related inflammatory pathways in stroke, the vast majority of observations remain correlative and controversial. Because extensive review articles discussing the role of inflammatory mechanisms in different forms of acute brain injury are available, here we focus on some specific pathways that appear to be important for stroke pathophysiology with assumed contribution by microglia. While the growing toolkit for microglia manipulation increasingly allows targeting inflammatory pathways in a cell-specific manner, reconsideration of some effects devoted to microglia may also be required. This may particularly concern the interpretation of inflammatory mechanisms that emerge in response to stroke as a form of sterile injury and change markedly in chronic inflammation and common stroke comorbidities.

Activation of Inflammasomes and Relevant Modulators for the Treatment of Microglia-mediated Neuroinflammation in Ischemic Stroke

As the brain's resident immune patrol, microglia mediate endogenous immune responses to central nervous system injury in ischemic stroke, thereby eliciting either neuroprotective or neurotoxic effects. The association of microglia-mediated neuroinflammation with the progression of ischemic stroke is evident through diverse signaling pathways, notably involving inflammasomes. Within microglia, inflammasomes play a pivotal role in promoting the maturation of interleukin-1β (IL-1β) and interleukin-18 (IL-18), facilitating pyroptosis, and triggering immune infiltration, ultimately leading to neuronal cell dysfunction. Addressing the persistent and widespread inflammation holds promise as a breakthrough in enhancing the treatment of ischemic stroke.

Primary microglia cell cultures in translational research: Strengths and limitations

Microglia are the resident macrophages in the central nervous system, accounting for 10-15% of the cell mass in the brain. Next to their physiological role in development, monitoring neuronal function and the maintenance of homeostasis, microglia are crucial in the brain's immune defense. Brain injury and chronic neurological disorders are associated with neuroinflammation, in which microglia activation is a central element. Microglia acquire a wide spectrum of activation states in the diseased or injured brain, some of which are neurotoxic. The investigation of microglia (patho)physiology and therapeutic interventions targeting neuroinflammation is a substantial challenge. In addition to in vivo approaches, the application of in vitro model systems has gained significant ground and is essential to complement in vivo work. Primary microglia cultures have proved to be a useful tool. Microglia cultures have offered the opportunity to explore the mechanistic, molecular elements of microglia activation, the microglia secretome, and the efficacy of therapeutic treatments against neuroinflammation. As all model systems, primary microglia cultures have distinct strengths and limitations to be weighed when experiments are designed and when data are interpreted. Here, we set out to provide a succinct overview of the advantages and pitfalls of the use of microglia cultures, which instructs the refinement and further development of this technique to remain useful in the toolbox of microglia researchers. Since there is no conclusive therapy to combat neurotoxicity linked to neuroinflammation in acute brain injury or neurodegenerative disorders, these research tools remain essential to explore therapeutic opportunities.

Microglia-neuron-vascular interactions in ischemia

Cerebral ischemia is a devastating condition that results in impaired blood flow in the brain leading to acute brain injury. As the most common form of stroke, occlusion of cerebral arteries leads to a characteristic sequence of pathophysiological changes in the brain tissue. The mechanisms involved, and comorbidities that determine outcome after an ischemic event appear to be highly heterogeneous. On their own, the processes leading to neuronal injury in the absence of sufficient blood supply to meet the metabolic demand of the cells are complex and manifest at different temporal and spatial scales. While the contribution of non-neuronal cells to stroke pathophysiology is increasingly recognized, recent data show that microglia, the main immune cells of the central nervous system parenchyma, play previously unrecognized roles in basic physiological processes beyond their inflammatory functions, which markedly change during ischemic conditions. In this review, we aim to discuss some of the known microglia-neuron-vascular interactions assumed to contribute to the acute and delayed pathologies after cerebral ischemia. Because the mechanisms of neuronal injury have been extensively discussed in several excellent previous reviews, here we focus on some recently explored pathways that may directly or indirectly shape neuronal injury through microglia-related actions. These discoveries suggest that modulating gliovascular processes in different forms of stroke and other neurological disorders might have presently unexplored therapeutic potential in combination with neuroprotective and flow restoration strategies.

AIM2 inflammasome: A potential therapeutic target in ischemic stroke

Ischemic stroke (IS) is a significant global public health issue with a high incidence, disability, and mortality rate. A robust inflammatory cascade with complex and wide-ranging mechanisms occurs following ischemic brain injury. Inflammasomes are multiprotein complexes in the cytoplasm that modulate the inflammatory response by releasing pro-inflammatory cytokines and inducing cellular pyroptosis. Among these inflammasomes, the Absent in Melanoma 2 (AIM2) inflammasome shows the ability to detect a wide range of pathogen DNAs, thereby triggering an inflammatory response. Recent studies have indicated that the aberrant expression of AIM2 inflammasome in various cells is closely associated with the pathological processes of ischemic brain injury. This paper summarizes the expression and regulatory role of AIM2 in CNS and peripheral immune cells and discusses current therapeutic approaches targeting AIM2 inflammasome. These findings aim to serve as a reference for future research in this field.

Research progress on mechanisms of ischemic stroke: Regulatory pathways involving Microglia

Microglia, as the intrinsic immune cells in the brain, are activated following ischemic stroke. Activated microglia participate in the pathological processes after stroke through polarization, autophagy, phagocytosis, pyroptosis, ferroptosis, apoptosis, and necrosis, thereby influencing the injury and repair following stroke. It has been established that polarized M1 and M2 microglia exhibit pro-inflammatory and anti-inflammatory effects, respectively. Autophagy and phagocytosis in microglia following ischemia are dynamic processes, where moderate levels promote cell survival, while excessive responses may exacerbate neurofunctional deficits following stroke. Additionally, pyroptosis and ferroptosis in microglia after ischemic stroke contribute to the release of harmful cytokines, further aggravating the damage to brain tissue due to ischemia. This article discusses the different functional states of microglia in ischemic stroke research, highlighting current research trends and gaps, and provides insights and guidance for further study of ischemic stroke.

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.

Receptor-interacting protein kinase 2 (RIPK2) profoundly contributes to post-stroke neuroinflammation and behavioral deficits with microglia as unique perpetrators

BACKGROUND

Receptor-interacting protein kinase 2 (RIPK2) is a serine/threonine kinase whose activity propagates inflammatory signaling through its association with pattern recognition receptors (PRRs) and subsequent TAK1, NF-κB, and MAPK pathway activation. After stroke, dead and dying cells release a host of damage-associated molecular patterns (DAMPs) that activate PRRs and initiate a robust inflammatory response. We hypothesize that RIPK2 plays a damaging role in the progression of stroke injury by enhancing the neuroinflammatory response to stroke and that global genetic deletion or microglia-specific conditional deletion of Ripk2 will be protective following ischemic stroke.

METHODS

Adult (3-6 months) male mice were subjected to 45 min of transient middle cerebral artery occlusion (tMCAO) followed by 24 h, 48 h, or 28 days of reperfusion. Aged male and female mice (18-24 months) were subjected to permanent ischemic stroke and sacrificed 48 h later. Infarct volumes were calculated using TTC staining (24-48 h) or Cresyl violet staining (28d). Sensorimotor tests (weight grip, vertical grid, and open field) were performed at indicated timepoints. Blood-brain barrier (BBB) damage, tight junction proteins, matrix metalloproteinase-9 (MMP-9), and neuroinflammatory markers were assessed via immunoblotting, ELISA, immunohistochemistry, and RT-qPCR. Differential gene expression profiles were generated through bulk RNA sequencing and nanoString®.

RESULTS

Global genetic deletion of Ripk2 resulted in decreased infarct sizes and reduced neuroinflammatory markers 24 h after stroke compared to wild-type controls. Ripk2 global deletion also improved both acute and long-term behavioral outcomes with powerful effects on reducing infarct volume and mortality at 28d post-stroke. Conditional deletion of microglial Ripk2 (mKO) partially recapitulated our results in global Ripk2 deficient mice, showing reductive effects on infarct volume and improved behavioral outcomes within 48 h of injury. Finally, bulk transcriptomic profiling and nanoString data demonstrated that Ripk2 deficiency in microglia decreases genes associated with MAPK and NF-κB signaling, dampening the neuroinflammatory response after stroke injury by reducing immune cell activation and peripheral immune cell invasion.

CONCLUSIONS

These results reveal a hitherto unknown role for RIPK2 in the pathogenesis of ischemic stroke injury, with microglia playing a distinct role. This study identifies RIPK2 as a potent propagator of neuroinflammatory signaling, highlighting its potential as a therapeutic target for post-stroke intervention.

Mitochondrial dysfunctions induce PANoptosis and ferroptosis in cerebral ischemia/reperfusion injury: from pathology to therapeutic potential

Ischemic stroke (IS) accounts for more than 80% of the total stroke, which represents the leading cause of mortality and disability worldwide. Cerebral ischemia/reperfusion injury (CI/RI) is a cascade of pathophysiological events following the restoration of blood flow and reoxygenation, which not only directly damages brain tissue, but also enhances a series of pathological signaling cascades, contributing to inflammation, further aggravate the damage of brain tissue. Paradoxically, there are still no effective methods to prevent CI/RI, since the detailed underlying mechanisms remain vague. Mitochondrial dysfunctions, which are characterized by mitochondrial oxidative stress, Ca²⁺ overload, iron dyshomeostasis, mitochondrial DNA (mtDNA) defects and mitochondrial quality control (MQC) disruption, are closely relevant to the pathological process of CI/RI. There is increasing evidence that mitochondrial dysfunctions play vital roles in the regulation of programmed cell deaths (PCDs) such as ferroptosis and PANoptosis, a newly proposed conception of cell deaths characterized by a unique form of innate immune inflammatory cell death that regulated by multifaceted PANoptosome complexes. In the present review, we highlight the mechanisms underlying mitochondrial dysfunctions and how this key event contributes to inflammatory response as well as cell death modes during CI/RI. Neuroprotective agents targeting mitochondrial dysfunctions may serve as a promising treatment strategy to alleviate serious secondary brain injuries. A comprehensive insight into mitochondrial dysfunctions-mediated PCDs can help provide more effective strategies to guide therapies of CI/RI in IS.

Dual-specificity phosphatase 26-dificient neurons are susceptible to oxygen-glucose deprivation/reoxygenation-evoked apoptosis and proinflammatory response by affecting the TAK1-medaited JNK/P38 MAPK pathway

Dual-specificity phosphatase 26 (DUSP26) is linked to a broad range of human disorders as it affects numerous signaling cascades. However, the involvement of DUSP26 in ischemic stroke has not been explored. Here, we investigated DUSP26 as a key mediator of oxygen-glucose deprivation/reoxygenation (OGD/R)-associated neuronal injury, an in vitro model for investigating ischemic stroke. A decline in DUSP26 occurred in neurons suffering from OGD/R. A deficiency in DUSP26 rendered neurons more susceptible to OGD/R by aggravating neuronal apoptosis and inflammation, while the overexpression of DUSP26 blocked OGD/R-evoked neuronal apoptosis and inflammation. Mechanistically, enhanced phosphorylation of transforming growth factor-β-activated kinase 1 (TAK1), c-Jun N-terminal kinase (JNK) and P38 mitogen-activated protein kinase (MAPK) was evidenced in DUSP26-deficient neurons suffering from OGD/R, whereas the opposite effects were observed in DUSP26-overexpressed neurons. Moreover, the inhibition of TAK1 abolished the DUSP26-deficiency-elicited activation of JNK and P38 MAPK and exhibited anti-OGD/R injury effects in DUSP26-deficiency neurons. Results from these experiments show that DUSP26 is essential for neurons in defending against OGD/R insult, while neuroprotection is achieved by restraining the TAK1-mediated JNK/P38 MAPK pathway. Therefore, DUSP26 may serve as a therapeutic target for the management of ischemic stroke.

Aberrantly activated TAK1 links neuroinflammation and neuronal loss in Alzheimer's disease mouse models

Neuroinflammation is causally associated with Alzheimer's disease (AD) pathology. Reactive glia cells secrete various neurotoxic factors that impair neuronal homeostasis eventually leading to neuronal loss. Although the glial activation mechanism in AD has been relatively well studied, how it perturbs intraneuronal signaling, which ultimately leads to neuronal cell death, remains poorly understood. Here, we report that compound stimulation with the neurotoxic factors TNF and glutamate aberrantly activates neuronal TAK1 (also known as MAP3K7), which promotes the pathogenesis of AD in mouse models. Glutamate-induced Ca2+ influx shifts TNF signaling to hyper-activate TAK1 enzymatic activity through Ca2+/calmodulin-dependent protein kinase II, which leads to necroptotic cellular damage. Genetic ablation and pharmacological inhibition of TAK1 ameliorated AD-associated neuronal loss and cognitive impairment in the AD model mice. Our findings provide a molecular mechanism linking cytokines, Ca2+ signaling and neuronal necroptosis in AD.

TGF-β Activated Kinase 1 (TAK1) Is Activated in Microglia After Experimental Epilepsy and Contributes to Epileptogenesis

Increasing evidence suggests that inflammation promotes epileptogenesis. TAK1 is a central enzyme in the upstream pathway of NF-κB and is known to play a central role in promoting neuroinflammation in neurodegenerative diseases. Here, we investigated the cellular role of TAK1 in experimental epilepsy. C57Bl6 and transgenic mice with inducible and microglia-specific deletion of Tak1 (Cx3cr1^CreER:Tak1^fl/fl) were subjected to the unilateral intracortical kainate mouse model of temporal lobe epilepsy (TLE). Immunohistochemical staining was performed to quantify different cell populations. The epileptic activity was monitored by continuous telemetric electroencephalogram (EEG) recordings over a period of 4 weeks. The results show that TAK1 was activated predominantly in microglia at an early stage of kainate-induced epileptogenesis. Tak1 deletion in microglia resulted in reduced hippocampal reactive microgliosis and a significant decrease in chronic epileptic activity. Overall, our data suggest that TAK1-dependent microglial activation contributes to the pathogenesis of chronic epilepsy.

TAK1 inhibition increases proliferation and differentiation of chick retinal cells

The factors necessary for the differentiation of cell types within the retina are incompletely understood. The transforming growth factor beta (TGF-β) superfamily, including TGF-β1 and 2, the bone morphogenetic proteins, and the activins have all been implicated in differentiation; however, the mechanisms by which these factors affect differentiation are only partially understood. The studies herein focus on a potential role for transforming growth factor β-activated kinase 1 (TAK1), a hub kinase that lies at the intersection of multiple signaling pathways, in the differentiation of cell types within the chick retina. Previous studies have focused predominantly on the role this kinase plays in the inflammation process and axonal growth. TAK1 is downstream of multiple signaling pathways that are critical to development of the central nervous system, including transforming growth factor β (TGFβ), bone morphogenetic proteins (BMPs), and activins. The present study indicates that activated TAK1 is found throughout the developing retina; however, it is localized at higher levels in dividing and differentiating cells. Further, ex ovo retinal studies using TAK1 inhibitor 5Z-7-oxozeaenol increased both progenitor and differentiating cell populations, accompanied by a substantial increase in proliferation and a smaller increase in cell death. These results indicate a unique role for TAK1 in differentiating and proliferating retinal cells.

Lysosomal-associated transmembrane protein 5 deficiency exacerbates cerebral ischemia/reperfusion injury

Lysosomal-associated transmembrane protein 5 (LAPTM5) has been demonstrated to be involved in regulating immunity, inflammation, cell death, and autophagy in the pathophysiological processes of many diseases. However, the function of LAPTM5 in cerebral ischemia-reperfusion (I/R) injury has not yet been reported. In this study, we found that LAPTM5 expression was dramatically decreased during cerebral I/R injury both in vivo and in vitro. LAPTM5 knockout (KO) mice were compared with a control, and they showed a larger infarct size and more serious neurological dysfunction after transient middle cerebral artery occlusion (tMCAO) treatment. In addition, inflammatory response and apoptosis were exacerbated in these processes. Furthermore, gain- and loss-of-function investigations in an in vitro model revealed that neuronal inflammation and apoptosis were aggravated by LAPTM5 knockdown but mitigated by its overexpression. Mechanistically, combined RNA sequencing and experimental verification showed that the apoptosis signal-regulating kinase 1 (ASK1)-c-Jun N-terminal kinase (JNK)/p38 pathway was mainly involved in the detrimental effects of LAPTM5 deficiency following I/R injury. Specifically, LAPTM5 directly interacts with ASK1, leading to decreased ASK1 N-terminal dimerization and the subsequent reduced activation of downstream JNK/p38 signaling. In conclusion, LAPTM5 was demonstrated to be a novel modulator in the pathophysiology of brain I/R injury, and targeting LAPTM5 may be feasible as a stroke treatment.

Conditional knockout of ASK1 in microglia/macrophages attenuates epileptic seizures and long-term neurobehavioural comorbidities by modulating the inflammatory responses of microglia/macrophages

Background

Apoptosis signal-regulating kinase 1 (ASK1) not only causes neuronal programmed cell death via the mitochondrial pathway but also is an essential component of the signalling cascade during microglial activation. We hypothesize that ASK1 selective deletion modulates inflammatory responses in microglia/macrophages(Mi/Mϕ) and attenuates seizure severity and long-term cognitive impairments in an epileptic mouse model.

Methods

Mi/Mϕ-specific ASK1 conditional knockout (ASK1 cKO) mice were obtained for experiments by mating ASK1^flox/flox mice with CX3CR1^creER mice with tamoxifen induction. Epileptic seizures were induced by intrahippocampal injection of kainic acid (KA). ASK1 expression and distribution were detected by western blotting and immunofluorescence staining. Seizures were monitored for 24 h per day with video recordings. Cognition, social and stress related activities were assessed with the Y maze test and the three-chamber social novelty preference test. The heterogeneous Mi/Mϕ status and inflammatory profiles were assessed with immunofluorescence staining and real-time polymerase chain reaction (q-PCR). Immunofluorescence staining was used to detect the proportion of Mi/Mϕ in contact with apoptotic neurons, as well as neuronal damage.

Results

ASK1 was highly expressed in Mi/Mϕ during the acute phase of epilepsy. Conditional knockout of ASK1 in Mi/Mϕ markedly reduced the frequency of seizures in the acute phase and the frequency of spontaneous recurrent seizures (SRSs) in the chronic phase. In addition, ASK1 conditional knockout mice displayed long-term neurobehavioral improvements during the Y maze test and the three-chamber social novelty preference test. ASK1 selective knockout mitigated neuroinflammation, as evidenced by lower levels of Iba1⁺/CD16⁺ proinflammatory Mi/Mϕ. Conditional knockout of ASK1 increased Mi/Mϕ proportion in contact with apoptotic neurons. Neuronal loss was partially restored by ASK1 selective knockout.

Conclusion

Conditional knockout of ASK1 in Mi/Mϕ reduced seizure severity, neurobehavioral impairments, and histological damage, at least via inhibiting proinflammatory microglia/macrophages responses. ASK1 in microglia/macrophages is a potential therapeutic target for inflammatory responses in epilepsy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02560-5.

Erythropoietin Enhances Post-ischemic Migration and Phagocytosis and Alleviates the Activation of Inflammasomes in Human Microglial Cells

Recombinant human erythropoietin (rhEPO) has been shown to exert anti-apoptotic and anti-inflammatory effects after cerebral ischemia. Inflammatory cytokines interleukin-1β and -18 (IL-1β and IL-18) are crucial mediators of apoptosis and are maturated by multiprotein complexes termed inflammasomes. Microglia are the first responders to post-ischemic brain damage and are a main source of inflammasomes. However, the impact of rhEPO on microglial activation and the subsequent induction of inflammasomes after ischemia remains elusive. To address this, we subjected human microglial clone 3 (HMC-3) cells to various durations of oxygen-glucose-deprivation/reperfusion (OGD/R) to assess the impact of rhEPO on cell viability, metabolic activity, oxidative stress, phagocytosis, migration, as well as on the regulation and activation of the NLRP1, NLRP3, NLRC4, and AIM2 inflammasomes. Administration of rhEPO mitigated OGD/R-induced oxidative stress and cell death. Additionally, it enhanced metabolic activity, migration and phagocytosis of HMC-3. Moreover, rhEPO attenuated post-ischemic activation and regulation of the NLRP1, NLRP3, NLRC4, and AIM2 inflammasomes as well as their downstream effectors CASPASE1 and IL-1β. Pharmacological inhibition of NLRP3 via MCC950 had no effect on the activation of CASPASE1 and maturation of IL-1β after OGD/R, but increased protein levels of NLRP1, NLRC4, and AIM2, suggesting compensatory activities among inflammasomes. We provide evidence that EPO-conveyed anti-inflammatory actions might be mediated via the regulation of the inflammasomes.

The Assessment of Endovascular Therapies in Ischemic Stroke: Management, Problems and Future Approaches

Ischemic stroke accounts for over 80% of all strokes and is one of the leading causes of mortality and permanent disability worldwide. Intravenous administration of recombinant tissue plasminogen activator (rt-PA) is an approved treatment strategy for acute ischemic stroke of large arteries within 4.5 h of onset, and mechanical thrombectomy can be used for large arteries occlusion up to 24 h after onset. Improving diagnostic work up for acute treatment, reducing onset-to-needle time and urgent radiological access angiographic CT images (angioCT) and Magnetic Resonance Imaging (MRI) are real problems for many healthcare systems, which limits the number of patients with good prognosis in real world compared to the results of randomized controlled trials. The applied endovascular procedures demonstrated high efficacy, but some cellular mechanisms, following reperfusion, are still unknown. Changes in the morphology and function of mitochondria associated with reperfusion and ischemia-reperfusion neuronal death are still understudied research fields. Moreover, future research is needed to elucidate the relationship between continuously refined imaging techniques and the variable structure or physical properties of the clot along with vascular permeability and the pleiotropism of ischemic reperfusion lesions in the penumbra, in order to define targeted preventive procedures promoting long-term health benefits.

Neuroprotective effects of alisol A 24-acetate on cerebral ischaemia-reperfusion injury are mediated by regulating the PI3K/AKT pathway

BACKGROUND

Neuroinflammation and apoptosis are involved in the pathogenesis of ischaemic stroke. Alisol A 24-acetate (24A) exerts a strong inhibitory effect on inflammation and cell apoptosis. The neuroprotective effect of 24A on global cerebral ischaemia/reperfusion (GCI/R) injury remains unclear.

METHODS

GCI/R mice were used to investigate the neuroprotective effect of 24A. Modified neurological deficit scores, Morris water maze and object recognition tests were used to evaluate behaviours. Metabolism in brain regions was detected using magnetic resonance spectroscopy (MRS), and changes in microglia, astrocytes and neurons were detected. Inflammation and apoptosis were measured.

RESULTS

The results showed that 24A suppressed neurological deficits scores and improved GCI/R induced cognitive dysfunction. It was also observed that 24A could alleviate neuroinflammation, which manifested as 24A inhibited microglia and astrocytes proliferation, downregulated the expression of interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and inducible nitric oxide synthase (iNOS) in the GCI/R mice brain. The apoptosis of neurons reduced, and dendritic spines of hippocampal neurons increased in the presence of 24A. In addition, 24A could up-regulate the expression of phosphorylated phosphoinositide 3-kinases (p-PI3K) and phosphorylated protein kinase B (p-AKT) in GCI/R mice brain, and all the morphological, neurological, and biochemical changes of 24A treatment were abolished by the application of PI3K/AKT pathway inhibitor LY294002.

CONCLUSIONS

Taken together, our study indicated that 24A alleviated GCI/R injury by inhibiting neuroinflammation and apoptosis through the regulation of the PI3K/AKT pathway.

Small-molecule modulators of TRMT2A decrease PolyQ aggregation and PolyQ-induced cell death

Polyglutamine (polyQ) diseases are characterized by an expansion of cytosine-adenine-guanine (CAG) trinucleotide repeats encoding for an uninterrupted prolonged polyQ tract. We previously identified TRMT2A as a strong modifier of polyQ-induced toxicity in an unbiased large-scale screen in Drosophila melanogaster. This work aimed at identifying and validating pharmacological TRMT2A inhibitors as treatment opportunities for polyQ diseases in humans. Computer-aided drug discovery was implemented to identify human TRMT2A inhibitors. Additionally, the crystal structure of one protein domain, the RNA recognition motif (RRM), was determined, and Biacore experiments with the RRM were performed. The identified molecules were validated for their potency to reduce polyQ aggregation and polyQ-induced cell death in human HEK293T cells and patient derived fibroblasts. Our work provides a first step towards pharmacological inhibition of this enzyme and indicates TRMT2A as a viable drug target for polyQ diseases.

Do pyroptosis, apoptosis, and necroptosis (PANoptosis) exist in cerebral ischemia? Evidence from cell and rodent studies

Some scholars have recently developed the concept of PANoptosis in the study of infectious diseases where pyroptosis, apoptosis and necroptosis act in consort in a multimeric protein complex, PANoptosome. This allows all the components of PANoptosis to be regulated simultaneously. PANoptosis provides a new way to study the regulation of cell death, in that different types of cell death may be regulated at the same time. To test whether PANoptosis exists in diseases other than infectious diseases, we chose cerebral ischemia/reperfusion injury as the research model, collected articles researching cerebral ischemia/reperfusion from three major databases, obtained the original research data from these articles by bibliometrics, data mining and other methods, then integrated and analyzed these data. We selected papers that investigated at least two of the components of PANoptosis to check its occurrence in ischemia/reperfusion. In the cell model simulating ischemic brain injury, pyroptosis, apoptosis and necroptosis occur together and this phenomenon exists widely in different passage cell lines or primary neurons. Pyroptosis, apoptosis and necroptosis also occurred in rat and mouse models of ischemia/reperfusion injury. This confirms that PANoptosis is observed in ischemic brain injury and indicates that PANoptosis can be a target in the regulation of various central nervous system diseases.

TBC1Domain Family Member 25 deficiency aggravates cerebral ischemia-reperfusion injury via TAK1-JNK/p38 pathway

TBC1Domain Family Member 25 (TBC1D25) is a protein that contains a TBC/RAB-GTPase activating protein (GAP) domain, which was shown to participate in autophagy in previous studies. However, the role of TBC1D25 in cerebral ischemia-reperfusion (I/R) injury remains unknown. In this study, we found that the mRNA and protein expression levels of TBC1D25 decreased in mouse brain after I/R injury and primary cortical neurons treated with oxygen and glucose deprivation/reoxygenation (OGD/R). Then TBC1D25 knockout (KO) mice were applied to demonstrate that TBC1D25 ablation aggravated cerebral I/R-induced neuronal loss and infarct size. In addition, neuronal apoptosis and inflammation were significantly potentiated in the TBC1D25-KO group. In in vitro OGD/R model, TBC1D25 knockdown can attenuate neuronal cell viability and aggravate the process of inflammation and apoptosis. Conversely, over-expression of TBC1D25 in primary neurons ameliorated the aforementioned processes. Mechanistically, RNA-sequencing (RNA-seq) analysis revealed mitogen-activated protein kinase (MAPK) signaling pathway was the most significant pathway that contributed to TBC1D25-mediated brain I/R injury process. Through experimental verification, TBC1D25 deficiency increased the phosphorylation of the transforming growth factor-β-activated kinase 1 (TAK1)-c-Jun N-terminal kinase (JNK)/p38 axis in neurons during the brain I/R injury. Furthermore, we found that TAK1 blockade abrogated the apoptosis and inflammatory response produced by TBC1D25 knockdown in vitro. In conclusion, this study is the first to demonstrate the functional significance of TBC1D25 in the pathophysiology of brain I/R injury, and the protective mechanism of TBC1D25 is dependent on the TAK1-JNK/p38 pathway.

Erythropoietin Abrogates Post-Ischemic Activation of the NLRP3, NLRC4, and AIM2 Inflammasomes in Microglia/Macrophages in a TAK1-Dependent Manner

Inflammasomes are known to contribute to brain damage after acute ischemic stroke (AIS). TAK1 is predominantly expressed in microglial cells and can regulate the NLRP3 inflammasome, but its impact on other inflammasomes including NLRC4 and AIM2 after AIS remains elusive. EPO has been shown to reduce NLRP3 protein levels in different disease models. Whether EPO-mediated neuroprotection after AIS is conveyed via an EPO/TAK1/inflammasome axis in microglia remains to be clarified. Subjecting mice deficient for TAK1 in microglia/macrophages (Mi/MΦ) to AIS revealed a significant reduction in infarct sizes and neurological impairments compared to the corresponding controls. Post-ischemic increased activation of TAK1, NLRP3, NLRC4, and AIM2 inflammasomes including their associated downstream cascades were markedly reduced upon deletion of Mi/MΦ TAK1. EPO administration improved clinical outcomes and dampened stroke-induced activation of TAK1 and inflammasome cascades, which was not evident after the deletion of Mi/MΦ TAK1. Pharmacological inhibition of NLRP3 in microglial BV-2 cells did not influence post-OGD IL-1β levels, but increased NLRC4 and AIM2 protein levels, suggesting compensatory activities among inflammasomes. Overall, we provide evidence that Mi/MΦ TAK1 regulates the expression and activation of the NLRP3, NLRC4, AIM2 inflammasomes. Furthermore, EPO mitigated stroke-induced activation of TAK1 and inflammasomes, indicating that EPO conveyed neuroprotection might be mediated via an EPO/TAK1/inflammasome axis.

Microglial TLR4-induced TAK1 phosphorylation and NLRP3 activation mediates neuroinflammation and contributes to chronic morphine-induced antinociceptive tolerance

BACKGROUND AND PURPOSE

The aim of this work was to investigate the role and signal transduction of toll-like receptor 4 (TLR4), TGF-β-activated kinase 1 (TAK1) and nod-like receptor protein 3 (NLRP3) in microglial in the development of morphine-induced antinociceptive tolerance.

METHODS

TLR4 and NLRP3 knockout mice and 5Z-7-oxozeaeno (a selective inhibitor against TAK1 activity) were used to observe their effect on the development of morphine tolerance. Intrathecal injections of morphine (0.75 mg/kg once daily for 7 days) were used to establish anti-nociceptive tolerance, which was measured by the tail-flick test. Spinal TLR4, TAK1, and NLRP3 expression levels and phosphorylation of TAK1 were evaluated by Western blotting and immunofluorescence.

RESULTS

Repeated treatment with morphine increased total expression of spinal TLR4, TAK1, and NLRP3 and phosphorylation of TAK1 in wild-type mice. TLR4 knockout attenuated morphine-induced tolerance and inhibited the chronic morphine-induced increase in NLRP3 and phosphorylation of TAK1. Compared with controls, mice that received 5Z-7-oxozeaenol showed decreased development of morphine tolerance and inhibition on repeated morphine-induced increase of NLRP3 but not TLR4. NLRP3 knockout mice showed resistance to morphine-induced analgesic tolerance with no effect on chronic morphine-induced expression of TLR4 and TAK1. TLR4, TAK1, and NLRP3 were collectively co-localized together and with the microglia marker Iba1.

CONCLUSIONS

Microglial TLR4 regulates TAK1 expression and phosphorylation and results in NLRP3 activation contributes to the development of morphine tolerance through regulating neuroinflammation. Targeting TLR4-TAK1-NLRP3 signaling to regulate neuro-inflammation will be alternative therapeutics and strategies for chronic morphine-induced antinociceptive tolerance.

Receptors, Channel Proteins, and Enzymes Involved in Microglia-mediated Neuroinflammation and Treatments by Targeting Microglia in Ischemic Stroke

Stroke is the largest contributor to global neurological disability-adjusted life-years, posing a huge economic and social burden to the world. Though pharmacological recanalization with recombinant tissue plasminogen activator and mechanical thrombectomy have greatly improved the prognosis of patients with ischemic stroke, clinically, there is still no effective treatment for the secondary injury caused by cerebral ischemia. In recent years, more and more evidences show that neuroinflammation plays a pivotal role in the pathogenesis and progression of ischemic cerebral injury. Microglia are brain resident innate immune cells and act the role peripheral macrophages. They play critical roles in mediating neuroinflammation after ischemic stroke. Microglia-mediated neuroinflammation is not an isolated process and has complex relationships with other pathophysiological processes as oxidative/nitrative stress, excitotoxicity, necrosis, apoptosis, pyroptosis, autophagy, and adaptive immune response. Upon activation, microglia differentially express various receptors, channel proteins, and enzymes involved in promoting or inhibiting the inflammatory processes, making them the targets of intervention for ischemic stroke. To inhibit microglia-related neuroinflammation and promote neurological recovery after ischemic stroke, numerous biochemical agents, cellular therapies, and physical methods have been demonstrated to have therapeutic potentials. Though accumulating experimental evidences have demonstrated that targeting microglia is a promising approach in the treatment of ischemic stroke, the clinical progress is slow. Till now, no clinical study could provide convincing evidence that any biochemical or physical therapies could exert neuroprotective effect by specifically targeting microglia following ischemic stroke.

TMEM59 protects against cerebral ischemic stroke by suppressing pyroptosis and microglial activation

Ischemic stroke is a common disease worldwide with high mortality and disability rates. Nevertheless, pathogenesis of ischemic stroke is still vague, and finding novel therapeutic target is urgently necessary. TMEM59 (also known as dendritic cell-derived factor 1, DCF1), a type I transmembrane protein, contains a minimal 19-amino-acid peptide in its intracellular domain, and has been involved in neurological pathology. However, its biological impacts on ischemic stroke are still unknown. In this study, we provided new evidence that TMEM59 expression was significantly down-regulated upon ischemia/reperfusion (I/R). The effect of stroke insult on TMEM59 expression change was only detected in microglial cells by in vitro studies. We observed that TMEM59 knockout markedly accelerated cerebral I/R in mice induced by middle cerebral artery occlusion (MCAO), as evidenced by the elevated infarction volume, neurological deficit scores, brain water contents and neuronal death, further contributing to the abnormal behaviors for mice. We then found that microglial activation reflected by the enhanced expression of Iba-1 was dramatically potentiated by TMEM59 knockout in MCAO-treated mice. Pyroptosis was highly triggered in mice with cerebral I/R, while being further aggravated in mice with TMEM59 deletion, as proved by the considerably increased expression of NLRP3, ASC, cleaved Caspase-1, GSDMD-N, mature-IL-1β and mature-IL-18. Additionally, TMEM59 knockout mice exhibited accelerated activation of NF-κB signaling pathway compared with the wild type group of mice after MCAO operation, indicating the anabatic neuroinflammation. The effects of TMEM59 suppression on ischemic stroke were confirmed in microglial cells with exposure to oxygen-glucose deprivation/reoxygenation (OGD/R). In contrast, the in vitro studies verified that improving TMEM59 expression effectively hindered pyroptosis and inflammation in microglial cells upon OGD/R treatment. Taken together, these findings illustrated protective effects of TMEM59 against ischemic stroke through restraining pyroptosis and inflammatory response.

A panel of two miRNAs correlated to systolic blood pressure is a good diagnostic indicator for stroke

BACKGROUND

We aimed to develop a diagnostic indicator of stroke based on serum miRNAs correlated to systolic blood pressure.

METHODS

Using miRNA expression profiles in GSE117604 from the Gene Expression Omnibus (GEO), we utilized the WGCNA to identify hub miRNAs correlated to systolic blood pressure (SBP). Differential analysis was applied to highlight hub differentially expressed miRNAs (DE-miRNAs), whereby we built a miRNA-based diagnostic indicator for stroke using bootstrap ranking Least Absolute Shrinkage and Selection Operator (LASSO) regression with 10-fold cross-validation. The classification value of the indicator was validated with receiver operating characteristic (ROC) analysis in both the training set and test set, as well as quantitative real-time PCR (qRT-PCR) for the feature miRNAs. Further, target genes of hub miRNAs and hub DE-miRNAs were retrieved for functional enrichment.

RESULTS

A total of 447 hub miRNAs in the blue modules were significantly correlated with systolic blood pressure (r = 0.32, false discovery rate = 10-6). Target genes predicted with the hub miRNAs were mostly implicated in the Kyoto Encyclopedia of Genes and Genomes (KEGG) terms including mitogen-activated protein kinase (MAPK) pathway, senescence, and TGF-β signaling pathway. The diagnostic indicator with miR-4420 and miR-6793-5p showed remarkable performance in the training set (area under curve [AUC]= 0.953), as well as in the test set (AUC = 0.894). Results of qRT-PCR validated the diagnostic value of the two miRNAs embedded in the proposed indicator.

CONCLUSIONS

We developed a panel of two miRNAs, which is a good diagnostic indicator for stroke. These results require further investigation.