Microglia as target for anti-inflammatory approaches to prevent secondary brain injury after subarachnoid hemorrhage (SAH)

A Novel Mechanism Linking Melatonin, Ferroptosis and Microglia Polarization via the Circodz3/HuR Axis in Subarachnoid Hemorrhage

A subarachnoid hemorrhage (SAH) is life-threatening bleeding into the subarachnoid space that causes brain damage. Growing evidence has suggested that melatonin provides neuroprotection following SAH. Exploring the mechanisms underlying melatonin-mediated neuroprotection contributes to its clinical application in SAH. The plasma and cerebrospinal fluid (CSF) were collected from SAH patients, and SAH mice were established via pre-chiasmatic injection. Circodz3 expression, levels of IL-1β and TNF-α, brain water content, neurological and beam-waling scores were determined. Ferroptosis was evaluated by analyzing levels of iron, lipid ROS, MDA, and GSH. The colocalization of circodz3 and Iba-1 was analyzed by immunofluorescence staining. Interaction of circodz3 and HuR was determined with RNA pull-down and RNA immunoprecipitation assays. Herein, we found that circodz3 was highly abundant in SAH patients and mice. Colocalization of circodz3 and Iba-1 in the left hemisphere of SAH mice suggested the implication of circodz3 in regulating microglia activation following SAH. Melatonin alleviated brain edema, neurological impairment, and microglia activation and inhibited circodz3 expression in SAH mice. Moreover, melatonin inhibited M1 polarization, oxidative stress and ferroptosis and restrained circodz3 expression in primary microglia following SAH. These effects were abrogated by circodz3 overexpression. Circodz3 knockdown inhibited ferroptosis and M1 polarization of BV2 microglia after SAH. Circodz3 interacted with HuR to facilitate β-Trcp1-mediated ubiquitination and degradation, thus restraining the expression of SLC7A11 and GPX4. Collectively, melatonin exerted neuroprotection following SAH via inhibiting ferroptosis and M1 polarization through the circodz3/HuR axis. Our study suggests potential application of melatonin in the treatment of SAH.

Diffuse microglial responses and persistent EEG changes correlate with poor neurological outcome in a model of subarachnoid hemorrhage

The mechanism by which subarachnoid hemorrhage (SAH) leads to chronic neurologic deficits is unclear. One possibility is that blood activates microglia to drive inflammation that leads to synaptic loss and impaired brain function. Using the endovascular perforation model of SAH in rats, we investigated short-term effects on microglia together with long-term effects on EEG and neurologic function for up to 3 months. Within the first week, microglia were increased both at the site of injury and diffusely across the cortex (2.5-fold increase in SAH compared to controls, p = 0.012). Concomitantly, EEGs from SAH animals showed focal increases in slow wave activity and diffuse reduction in fast activity. When expressed as a fast-slow spectral ratio, there were significant interactions between group and time (p < 0.001) with less ipsilateral recovery over time. EEG changes were most pronounced during the first week and correlated with neurobehavioral impairment. In vitro, the blood product hemin was sufficient to increase microglia phagocytosis nearly six-fold (p = 0.032). Immunomodulatory treatment with fingolimod after SAH reduced microglia, improved neurological function, and increased survival. These findings, which parallel many of the EEG changes seen in patients, suggest that targeting neuroinflammation could reduce long-term neurologic dysfunction following SAH.

Single-Cell Transcriptomics Revealed White Matter Repair Following Subarachnoid Hemorrhage

Existing research indicates the potential for white matter injury repair during the subacute phase following subarachnoid hemorrhage (SAH). However, elucidating the role of brain cell subpopulations in the acute and subacute phases of SAH pathogenesis remains challenging due to the cellular heterogeneity of the central nervous system. In this study, single-cell RNA sequencing was conducted on SAH model mice to delineate distinct cell populations. Gene Set Enrichment Analysis was performed to identify involved pathways, and cellular interactions were explored using the CellChat package in R software. Validation of the findings involved a comprehensive approach, including magnetic resonance imaging, immunofluorescence double staining, and Western blot analyses. This study identified ten major brain clusters with cell type-specific gene expression patterns. Notably, we observed infiltration and clonal expansion of reparative microglia in white matter-enriched regions during the subacute stage after SAH. Additionally, microglia-associated pleiotrophin (PTN) was identified as having a role in mediating the regulation of oligodendrocyte precursor cells (OPCs) in SAH model mice, implicating the activation of the mTOR signaling pathway. These findings emphasize the vital role of microglia-OPC interactions might occur via the PTN pathway, potentially contributing to white matter repair during the subacute phase after SAH. Our analysis revealed precise transcriptional changes in the acute and subacute phases after SAH, offering insights into the mechanism of SAH and for the development of drugs that target-specific cell subtypes.

Role of microglia after subarachnoid hemorrhage

Subarachnoid hemorrhage is a devastating sequela of aneurysm rupture. Because it disproportionately affects younger patients, the population impact of hemorrhagic stroke from subarachnoid hemorrhage is substantial. Secondary brain injury is a significant contributor to morbidity after subarachnoid hemorrhage. Initial hemorrhage causes intracranial pressure elevations, disrupted cerebral perfusion pressure, global ischemia, and systemic dysfunction. These initial events are followed by two characterized timespans of secondary brain injury: the early brain injury period and the delayed cerebral ischemia period. The identification of varying microglial phenotypes across phases of secondary brain injury paired with the functions of microglia during each phase provides a basis for microglia serving a critical role in both promoting and attenuating subarachnoid hemorrhage-induced morbidity. The duality of microglial effects on outcomes following SAH is highlighted by the pleiotropic features of these cells. Here, we provide an overview of the key role of microglia in subarachnoid hemorrhage-induced secondary brain injury as both cytotoxic and restorative effectors. We first describe the ontogeny of microglial populations that respond to subarachnoid hemorrhage. We then correlate the phenotypic development of secondary brain injury after subarachnoid hemorrhage to microglial functions, synthesizing experimental data in this area.

Low-dose IL-2 treatment confers anti-inflammatory effect against subarachnoid hemorrhage in mice

Objective

Subarachnoid hemorrhage (SAH) was a stroke with high occurrence and mortality. At the early stage, SAH patients have severe cerebral injury which is contributed by inflammation. In this study, we aimed to explore the anti-inflammation effect of low-dose IL-2 in SAH mice.

Methods

The 12-week-old C57BL/6J male mice were conducted with SAH surgery (Internal carotid artery puncture method). Different dose of IL-2 was injected intraperitoneally for 1 h, 1 day, and 2 days after SAH. Single-cell suspension and flow cytometry were used for the test of regulatory T (Treg) cells. Immunofluorescence staining was used to investigate the phenotypic polarization of microglia and inflammation response around neurons. Enzyme-Linked Immuno-sorbent Assay (ELISA) was applied to detect the level of pro-inflammatory factors.

Results

Low-dose IL-2 could enrich the Treg cells and drive the microglia polarizing to M2. The level of pro-inflammatory factors, IL-1α, IL-6, and TNF-α decreased in the low-dose IL-2 group. The inflammation response around neurons was attenuated. Low-dose IL-2 could increase the number of Treg cells, which could exert a neuroprotective effect against inflammation after SAH.

Conclusion

Low-dose IL-2 had the potential to be an effective clinical method to inhibit inflammation after SAH.

The ins and outs of microglial cells in brain health and disease

Microglia are the brain's resident macrophages that play pivotal roles in immune surveillance and maintaining homeostasis of the Central Nervous System (CNS). Microglia are functionally implicated in various cerebrovascular diseases, including stroke, aneurysm, and tumorigenesis as they regulate neuroinflammatory responses and tissue repair processes. Here, we review the manifold functions of microglia in the brain under physiological and pathological conditions, primarily focusing on the implication of microglia in glioma propagation and progression. We further review the current status of therapies targeting microglial cells, including their re-education, depletion, and re-population approaches as therapeutic options to improve patient outcomes for various neurological and neuroinflammatory disorders, including cancer.

Mesenchymal Stem Cell-Derived Extracellular Vesicles Alleviate Brain Damage Following Subarachnoid Hemorrhage via the Interaction of miR-140-5p and HDAC7

Subarachnoid hemorrhage (SAH) triggers severe neuroinflammation and cognitive impairment, where microglial M1 polarization exacerbates the injury and M2 polarization mitigates damage. Mesenchymal stem cell-derived extracellular vesicles (MSC-EVs), carrying microRNA (miR)-140-5p, offer therapeutic promise by targeting the cAMP/PKA/CREB pathway and modulating microglial responses, demonstrating a novel approach for addressing SAH-induced brain injury. This research explored the role of miR-140-5p delivered by MSC-EVs in mitigating brain damage following SAH. Serum from SAH patients and healthy individuals was analyzed for miR-140-5p and cAMP levels. The association between miR-140-5p levels, brain injury severity, and patient survival was examined, along with the target relationship between miR-140-5p and histone deacetylases 7 (HDAC7). MSC-EVs were characterized for their ability to cross the blood-brain barrier and modulate the HDAC7/AKAP12/cAMP/PKA/CREB axis, reducing M1 polarization and inflammation. The therapeutic effect of MSC-EV-miR-140-5p was demonstrated in an SAH mouse model, showing reduced neuronal apoptosis and improved neurological function. This study highlights the potential of MSC-EV-miR-140-5p in mitigating SAH-induced neuroinflammation and brain injury, providing a foundation for developing MSC-EV-based treatments for SAH.

Inhibiting RIPK1-driven neuroinflammation and neuronal apoptosis mitigates brain injury following experimental subarachnoid hemorrhage

RIPK1, a receptor-interacting serine/threonine protein kinase, plays a crucial role in maintaining cellular and tissue homeostasis by integrating inflammatory responses and cell death signaling pathways including apoptosis and necroptosis, which have been implicated in diverse physiological and pathological processes. Suppression of RIPK1 activation is a promising strategy for restraining the pathological progression of many human diseases. Neuroinflammation and neuronal apoptosis are two pivotal factors in the pathogenesis of brain injury following subarachnoid hemorrhage (SAH). In this study, we established in vivo and in vitro models of SAH to investigate the activation of RIPK1 kinase in both microglia and neurons. We observed the correlation between RIPK1 kinase activity and microglia-mediated inflammation as well as neuronal apoptosis. We then investigated whether inhibition of RIPK1 could alleviate neuroinflammation and neuronal apoptosis following SAH, thereby reducing brain edema and ameliorating neurobehavioral deficits. Additionally, the underlying mechanisms were also explored. Our research findings revealed the activation of RIPK1 kinase in both microglia and neurons following SAH, as marked by the phosphorylation of RIPK1 at serine 166. The upregulation of p-RIPK1(S166) resulted in a significant augmentation of inflammatory cytokines and chemokines, including TNF-α, IL-6, IL-1α, CCL2, and CCL5, as well as neuronal apoptosis. The activation of RIPK1 in microglia and neurons following SAH could be effectively suppressed by administration of Nec-1 s, a specific inhibitor of RIPK1. Consequently, inhibition of RIPK1 resulted in a downregulation of inflammatory cytokines and chemokines and attenuation of neuronal apoptosis after SAH in vitro. Furthermore, the administration of Nec-1 s effectively mitigated neuroinflammation, neuronal apoptosis, brain edema, and neurobehavioral deficits in mice following SAH. Our findings suggest that inhibiting RIPK1 kinase represents a promising therapeutic strategy for mitigating brain injury after SAH by attenuating RIPK1-driven neuroinflammation and neuronal apoptosis.

Research hotspots and frontiers of preconditioning in cerebral ischemia: A bibliometric analysis

Background

Preconditioning is a promising strategy against ischemic brain injury, and numerous studies in vitro and in vivo have demonstrated its neuroprotective effects. However, at present there is no bibliometric analysis of preconditioning in cerebral ischemia. Therefore, a comprehensive overview of the current status, hot spots, and emerging trends in this research field is necessary.

Materials and methods

Studies on preconditioning in cerebral ischemia from January 1999-December 2022 were retrieved from the Web of Science Core Collection (WOSCC) database. CiteSpace was used for data mining and visual analysis.

Results

A total of 1738 papers on preconditioning in cerebral ischemia were included in the study. The annual publications showed an upwards and then downwards trend but currently remain high in terms of annual publications. The US was the leading country, followed by China, the most active country in recent years. Capital Medical University published the largest number of articles. Perez-Pinzon, Miguel A contributed the most publications, while KITAGAWA K was the most cited author. The focus of the study covered three areas: (1) relevant diseases and experimental models, (2) types of preconditioning and stimuli, and (3) mechanisms of ischemic tolerance. Remote ischemic preconditioning, preconditioning of mesenchymal stem cells (MSCs), and inflammation are the frontiers of research in this field.

Conclusion

Our study provides a visual and scientific overview of research on preconditioning in cerebral ischemia, providing valuable information and new directions for researchers.

Panax quinquefolium saponins attenuates microglia activation following acute cerebral ischemia-reperfusion injury via Nrf2/miR-103-3p/TANK pathway

Ischemic stroke is one of the leading causes of death and disability among adults worldwide. Intravenous thrombolysis is the only approved pharmacological treatment for acute ischemic stroke. However, reperfusion by thrombolysis will lead to the rapid activation of microglia cells which induces interferon-inflammatory response in the ischemic brain tissues. Panax quinquefolium saponins (PQS) has been proven to be effective in acute ischemic stroke, but there is no unified understanding about its specific mechanism. Here, we will report for the first time that PQS can significantly inhibit the activation of microglia cells in cerebral of MCAO rats via activation of Nrf2/miR-103-3p/TANK axis. Our results showed that PQS can directly bind to Nrf2 protein and inhibit its ubiquitination, which result in the indirectly enhancing the expression of TANK protein via transcriptional regulation on miR-103-3p, and finally to suppress the nuclear factor kappa-B dominated rapid activation of microglial cells induced by oxygen-glucose deprivation/reoxygenation  vitro and cerebral ischemia-reperfusion injury in vivo. In conclusion, our study not only revealed the new mechanism of PQS in protecting against the inflammatory activation of microglia cells caused by cerebral ischemia-reperfusion injury, but also suggested that Nrf2 is a potential target for development of new drugs of ischemic stroke. More importantly, our study also reminded that miR-103-3p might be used as a prognostic biomarker for patients with ischemic stroke.

Consistency of mouse models with human intracerebral hemorrhage: core targets and non-coding RNA regulatory axis

Intracerebral hemorrhage (ICH) has a high mortality and disability rate. Numerous basic studies on pathogenesis and therapeutics have been performed in mice. However, the consistency of the experimental mouse model and the human ICH patient remains unclear. This has slowed progress in translational medicine. Furthermore, effective therapeutic targets and reliable regulatory networks for ICH are needed. Therefore, we determined the differentially expressed (DE) messenger RNAs (mRNAs), microRNAs (miRNAs) and circular RNAs (circRNAs) before and after murine ICH and analyzed their regulatory relationships. Subsequently, data on mRNAs from human peripheral blood after ICH were obtained from the Gene Expression Omnibus database. The DE mRNAs after human ICH were compared with those of the mouse. Finally, we obtained seven genes with translational medicine research value and verified them in mice. Then the regulatory network of these genes was analyzed in humans. Similarly, species homologies of these regulatory pathways were identified. In conclusion, we found that the mouse ICH model mimics the human disease mainly in terms of chemokines and inflammatory factors. This has important implications for future research into the mechanisms of ICH injury and repair.

Transfer of cGAMP from neuron to microglia activates microglial type I interferon responses after subarachnoid hemorrhage

Primary subarachnoid hemorrhage (SAH) is a type of acute stroke, accounting for approximately 10% of cases, with high disability and mortality rate. Early brain injury (EBI) is a critical factor in determining SAH mortality; however, there are no effective treatment interventions for EBI. Based on our results, the transmission of cyclic GMP-AMP (cGAMP) from neurons to microglia is a key molecular event that triggers type I interferon response, amplifies neuroinflammation, and leads to neuronal apoptosis. Abnormal intracytoplasmic mitochondrial DNA (mtDNA) is the initiating factor of the cGAS-cGAMP-STING signaling axis. Overall, the cGAS-cGAMP-STING signaling axis is closely associated with neuroinflammation after subarachnoid hemorrhage. Targeting cGAS triggered by cytoplasmic mtDNA may be useful for comprehensive clinical treatment of patients after SAH. Further studies targeting cGAS-specific antagonists for treating SAH are warranted. Video Abstract.

Repurposing of pexidartinib for microglia depletion and renewal

Pexidartinib (PLX3397) is a small molecule receptor tyrosine kinase inhibitor of colony stimulating factor 1 receptor (CSF1R) with moderate selectivity over other members of the platelet derived growth factor receptor family. It is approved for treatment of tenosynovial giant cell tumors (TGCT). CSF1R is highly expressed by microglia, which are macrophages of the central nervous system (CNS) that defend the CNS against injury and pathogens and contribute to synapse development and plasticity. Challenged by pathogens, apoptotic cells, debris, or inflammatory molecules they adopt a responsive state to propagate the inflammation and eventually return to a homeostatic state. The phenotypic switch may fail, and disease-associated microglia contribute to the pathophysiology in neurodegenerative or neuropsychiatric diseases or long-lasting detrimental brain inflammation after brain, spinal cord or nerve injury or ischemia/hemorrhage. Microglia also contribute to the growth permissive tumor microenvironment of glioblastoma (GBM). In rodents, continuous treatment for 1-2 weeks via pexidartinib food pellets leads to a depletion of microglia and subsequent repopulation from the remaining fraction, which is aided by peripheral monocytes that search empty niches for engraftment. The putative therapeutic benefit of such microglia depletion or forced renewal has been assessed in almost any rodent model of CNS disease or injury or GBM with heterogeneous outcomes, but a tendency of partial beneficial effects. So far, microglia monitoring e.g. via positron emission imaging is not standard of care for patients receiving Pexidartinib (e.g. for TGCT), so that the depletion and repopulation efficiency in humans is still largely unknown. Considering the virtuous functions of microglia, continuous depletion is likely no therapeutic option but short-lasting transient partial depletion to stimulate microglia renewal or replace microglia in genetic disease in combination with e.g. stem cell transplantation or as part of a multimodal concept in treatment of glioblastoma appears feasible. The present review provides an overview of the preclinical evidence pro and contra microglia depletion as a therapeutic approach.

Takinib inhibits microglial M1 polarization and oxidative damage after subarachnoid hemorrhage by targeting TAK1-dependent NLRP3 inflammasome signaling pathway

Transforming growth factor-β-activated kinase 1 (TAK1) positively regulates oxidative stress and inflammation in different diseases. Takinib, a novel and specific TAK1 inhibitor, has beneficial effects in a variety of disorders. However, the effects of takinib on early brain injury (EBI) after subarachnoid hemorrhage (SAH) and the underlying molecular mechanisms remain unknown. Our study showed that takinib administration significantly inhibited phosphorylated TAK1 expression after SAH. In addition, takinib suppressed M1 microglial polarization and promoted M2 microglial polarization. Furthermore, blockade of TAK1 by takinib reduced neuroinflammation, oxidative damage, brain edema, and neuronal apoptosis, and improved neurological behavior after SAH. Mechanistically, we revealed that TAK1 inhibition by takinib mitigated reactive oxygen species (ROS) production and ROS-mediated nod-like receptor pyrin domain-containing protein 3 (NLRP3) inflammasome activation. In contrast, NLRP3 activation by nigericin abated the neuroprotective effects of takinib against EBI after SAH. In general, our study demonstrated that takinib could protect against EBI by targeting TAK1-ROS-NLRP3 inflammasome signaling. Inhibition of TAK1 might be a promising option in the management of SAH.

Sirtuins as Potential Targets for Neuroprotection: Mechanisms of Early Brain Injury Induced by Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a prevalent cerebrovascular disease with significant global mortality and morbidity rates. Despite advancements in pharmacological and surgical approaches, the quality of life for SAH survivors has not shown substantial improvement. Traditionally, vasospasm has been considered a primary contributor to death and disability following SAH, but anti-vasospastic therapies have not demonstrated significant benefits for SAH patients' prognosis. Emerging studies suggest that early brain injury (EBI) may play a crucial role in influencing SAH prognosis. Sirtuins (SIRTs), a group of NAD + -dependent deacylases comprising seven mammalian family members (SIRT1 to SIRT7), have been found to be involved in neural tissue development, plasticity, and aging. They also exhibit vital functions in various central nervous system (CNS) processes, including cognition, pain perception, mood, behavior, sleep, and circadian rhythms. Extensive research has uncovered the multifaceted roles of SIRTs in CNS disorders, offering insights into potential markers for pathological processes and promising therapeutic targets (such as SIRT1 activators and SIRT2 inhibitors). In this article, we provide an overview of recent research progress on the application of SIRTs in subarachnoid hemorrhage and explore their underlying mechanisms of action.

Low-dose LPS alleviates early brain injury after SAH by modulating microglial M1/M2 polarization via USP19/FOXO1/IL-10/IL-10R1 signaling

BACKGROUND

Low-dose lipopolysaccharide (LPS) protects against early brain injury (EBI) after subarachnoid hemorrhage (SAH). However, the mechanism underlying the neuroprotective roles of low-dose LPS remain largely undefined.

METHODS

A SAH mice model was established and the pathological changes of brain were evaluated by wet-dry weight method, HE and Nissl staining, and blood-brain barrier (BBB) permeability assay. Cell apoptosis and inflammation were monitored by TUNEL, flow cytometry and ELISA assays. qRT-PCR, immunofluorescence and Western blot were used to detect the expression of microglial polarization-related or oxidative stress-associated markers. Bioinformatics analysis, luciferase and ChIP assays were employed to detect the direct association between FOXO1 and IL-10 promoter. The ubiquitination of FOXO1 in the in vitro SAH model was detected by co-IP.

RESULTS

Low-dose LPS alleviated SAH-induced neurological dysfunction, brain edema, BBB disruption, damage in the hippocampus, neuronal apoptosis and inflammation via modulating microglial M1/M2 polarization by IL-10/IL-10R1 signaling. Mechanistic studies showed that FOXO1 acted as a transcriptional activator of IL-10. USP19 mediated the deubiquitination of FOXO1 to activate IL-10/IL-10R1 signaling, thereby regulating microglial M1/M2 polarization. Functional experiments revealed that low-dose LPS upregulated USP19 to modulate microglial M1/M2 polarization via FOXO1/IL-10/IL-10R1 signaling in SAH mice.

CONCLUSION

Low-dose LPS protected against EBI after SAH by modulating microglial M1/M2 polarization via USP19/FOXO1/IL-10/IL-10R1 signaling.

Dental Pulp Stem Cell-Derived Conditioned Medium Alleviates Subarachnoid Hemorrhage-Induced Microcirculation Impairment by Promoting M2 Microglia Polarization and Reducing Astrocyte Swelling

Aneurysmal subarachnoid hemorrhage (SAH) can cause severe neurological deficits and high mortality. Early brain edema following SAH contributes to the initiation of microcirculation impairment and may further lead to delayed ischemic neurologic deficit (DIND). This study aimed to investigate whether dental pulp stem cell conditioned medium (DPSC-CM) ameliorates SAH-induced microcirculation impairment and the underlying mechanisms. SAH was induced via intrathecal injection of fresh autologous blood in Wistar male adult rat. DPSC-CM or DPSC-CM + insulin growth factor-1 (IGF-1) antibody was randomly administered by intrathecal route 5 min after SAH induction. To evaluate the underlying mechanisms of DPSC-CM in the treatment of SAH, primary rat astrocyte and microglia co-cultures were challenged with hemolysate or SAH-patient CSF in the presence or absence of DPSC-CM. The results showed that in vivo, DPSC-CM treatment decreased the brain water content, improved microcirculation impairment and enhanced functional recovery at 24 h post-SAH. DPSC-CM treatment also alleviated the expressions of water channel protein aquaporin-4 (AQP4) and pro-inflammatory cytokines, and enhanced the expressions of anti-inflammatory factors in the cortical region. However, all the beneficial effects of DPSC-CM were abrogated after treatment with IGF-1 neutralizing antibody. The in vitro results further showed that DPSC-CM treatment reduced hemolysate/SAH-patient CSF-induced astrocyte swelling and promoted M2 microglia polarization, partially through IGF-1/AKT signaling. The data suggested that DPSC-CM significantly reduced brain edema and rescued microcirculation impairment with concomitant anti-inflammatory benefits after SAH, and may potentially be developed into a novel therapeutic strategy for SAH.

Resolution of Cerebral Inflammation Following Subarachnoid Hemorrhage

BACKGROUND

Aneurismal subarachnoid hemorrhage (SAH) is a type of hemorrhagic stroke that, despite improvement through therapeutic interventions, remains a devastating cerebrovascular disorder that has a high mortality rate and causes long-term disability. Cerebral inflammation after SAH is promoted through microglial accumulation and phagocytosis. Furthermore, proinflammatory cytokine release and neuronal cell death play key roles in the development of brain injury. The termination of these inflammation processes and restoration of tissue homeostasis are of utmost importance regarding the possible chronicity of cerebral inflammation and the improvement of the clinical outcome for affected patients post SAH. Thus, we evaluated the inflammatory resolution phase post SAH and considered indications for potential tertiary brain damage in cases of incomplete resolution.

METHODS

Subarachnoid hemorrhage was induced through endovascular filament perforation in mice. Animals were killed 1, 7 and 14 days and 1, 2 and 3 months after SAH. Brain cryosections were immunolabeled for ionized calcium-binding adaptor molecule-1 to detect microglia/macrophages. Neuronal nuclei and terminal deoxyuridine triphosphate-nick end labeling staining was used to visualize secondary cell death of neurons. The gene expression of various proinflammatory mediators in brain samples was analyzed by quantitative polymerase chain reaction.

RESULTS

We observed restored tissue homeostasis due to decreased microglial/macrophage accumulation and neuronal cell death 1 month after insult. However, the messenger RNA expression levels of  interleukin 6  and  tumor necrosis factor α were still elevated at 1 and 2 months post SAH, respectively. The gene expression of interleukin 1β reached its maximum on day 1, whereas at later time points, no significant differences between the groups were detected.

CONCLUSIONS

By the herein presented molecular and histological data we provide an important indication for an incomplete resolution of inflammation within the brain parenchyma after SAH. Inflammatory resolution and the return to tissue homeostasis represent an important contribution to the disease's pathology influencing the impact on brain damage and outcome after SAH. Therefore, we consider a novel complementary or even superior therapeutic approach that should be carefully rethought in the management of cerebral inflammation after SAH. An acceleration of the resolution phase at the cellular and molecular levels could be a potential aim in this context.

Cortical Spreading Depolarization and Delayed Cerebral Ischemia; Rethinking Secondary Neurological Injury in Subarachnoid Hemorrhage

Poor outcomes in Subarachnoid Hemorrhage (SAH) are in part due to a unique form of secondary neurological injury known as Delayed Cerebral Ischemia (DCI). DCI is characterized by new neurological insults that continue to occur beyond 72 h after the onset of the hemorrhage. Historically, it was thought to be a consequence of hypoperfusion in the setting of vasospasm. However, DCI was found to occur even in the absence of radiographic evidence of vasospasm. More recent evidence indicates that catastrophic ionic disruptions known as Cortical Spreading Depolarizations (CSD) may be the culprits of DCI. CSDs occur in otherwise healthy brain tissue even without demonstrable vasospasm. Furthermore, CSDs often trigger a complex interplay of neuroinflammation, microthrombi formation, and vasoconstriction. CSDs may therefore represent measurable and modifiable prognostic factors in the prevention and treatment of DCI. Although Ketamine and Nimodipine have shown promise in the treatment and prevention of CSDs in SAH, further research is needed to determine the therapeutic potential of these as well as other agents.

Resistance to Degradation of Silk Fibroin Hydrogels Exposed to Neuroinflammatory Environments

Central nervous system (CNS) diseases represent an extreme burden with significant social and economic costs. A common link in most brain pathologies is the appearance of inflammatory components that can jeopardize the stability of the implanted biomaterials and the effectiveness of therapies. Different silk fibroin scaffolds have been used in applications related to CNS disorders. Although some studies have analyzed the degradability of silk fibroin in non-cerebral tissues (almost exclusively upon non-inflammatory conditions), the stability of silk hydrogel scaffolds in the inflammatory nervous system has not been studied in depth. In this study, the stability of silk fibroin hydrogels exposed to different neuroinflammatory contexts has been explored using an in vitro microglial cell culture and two in vivo pathological models of cerebral stroke and Alzheimer's disease. This biomaterial was relatively stable and did not show signs of extensive degradation across time after implantation and during two weeks of in vivo analysis. This finding contrasted with the rapid degradation observed under the same in vivo conditions for other natural materials such as collagen. Our results support the suitability of silk fibroin hydrogels for intracerebral applications and highlight the potentiality of this vehicle for the release of molecules and cells for acute and chronic treatments in cerebral pathologies.

The Critical Role of Sirt1 in Subarachnoid Hemorrhages: Mechanism and Therapeutic Considerations

The subarachnoid hemorrhage (SAH) is an important cause of death and long-term disability worldwide. As a nicotinamide adenine dinucleotide-dependent deacetylase, silent information regulator 1 (Sirt1) is a multipotent molecule involved in many pathophysiological processes. A growing number of studies have demonstrated that Sirt1 activation may exert positive effects on SAHs by regulating inflammation, oxidative stress, apoptosis, autophagy, and ferroptosis. Thus, Sirt1 agonists may serve as potential therapeutic drugs for SAHs. In this review, we summarized the current state of our knowledge on the relationship between Sirt1 and SAHs and provided an updated overview of the downstream molecules of Sirt1 in SAHs.

Spatio-Temporal Characterization of Brain Inflammation in a Non-human Primate Stroke Model Mimicking Endovascular Thrombectomy

Reperfusion therapies in acute ischemic stroke have demonstrated their efficacy in promoting clinical recovery. However, ischemia/reperfusion injury and related inflammation remain a major challenge in patient clinical management. We evaluated the spatio-temporal evolution of inflammation using sequential clinical [11C]PK11195 PET-MRI in a non-human primate (NHP) stroke model mimicking endovascular thrombectomy (EVT) with a neuroprotective cyclosporine A (CsA) treatment. The NHP underwent a 110-min transient endovascular middle cerebral artery occlusion. We acquired [11C]PK11195 dynamic PET-MR imaging at baseline, 7 and 30 days after intervention. Individual voxel-wise analysis was performed thanks to a baseline scan database. We quantified [11C]PK11195 in anatomical regions and in lesioned areas defined on per-occlusion MR diffusion-weighted imaging and perfusion [15O2]H2OPET imaging. [11C]PK11195 parametric maps showed a clear uptake overlapping the lesion core at D7, which further increased at D30. Voxel-wise analysis identified individuals with significant inflammation at D30, with voxels located within the most severe diffusion reduction area during occlusion, mainly in the putamen. The quantitative analysis revealed that thalamic inflammation lasted until D30 and was significantly reduced in the CsA-treated group compared to the placebo. In conclusion, we showed that chronic inflammation matched ADC decrease at occlusion time, a region exposed to an initial burst of damage-associated molecular patterns, in an NHP stroke model mimicking EVT. We described secondary thalamic inflammation and the protective effect of CsA in this region. We propose that major ADC drop in the putamen during occlusion may identify individuals who could benefit from early personalized treatment targeting inflammation.

LDC7559 inhibits microglial activation and GSDMD-dependent pyroptosis after subarachnoid hemorrhage

Mounting evidence indicates that inhibition of microglial activation and neuronal pyroptosis plays important roles in brain function recovery after subarachnoid hemorrhage (SAH). LDC7559 is a newly discovered gasdermin D (GSDMD) inhibitor. Previous studies have demonstrated that LDC7559 could inhibit microglial proliferation and pyroptosis. However, the beneficial effects of LDC7559 on SAH remain obscure. Based on this background, we investigated the potential role and the mechanism of LDC7559 on SAH-induced brain damage both in vivo and in vitro. The findings revealed that microglial activation and neuronal pyroptosis were evidently increased after SAH, which could be markedly suppressed by LDC7559 both in vivo and in vitro. Meanwhile, LDC7559 treatment reduced neuronal apoptosis and improved behavior function. Mechanistically, LDC7559 decreased the levels of GSDMD and cleaved GSDMD after SAH. In contrast, nod-like receptor pyrin domain-containing 3 (NLRP3) inflammasome activation by nigericin increased GSDMD-mediated pyroptosis and abated the beneficial effects of LDC7559 on SAH-induced brain damage. However, LDC7559 treatment did not significantly affect the expression of NLRP3 after SAH. Taken together, LDC7559 might suppress neuronal pyroptosis and microglial activation after SAH by inhibiting GSDMD, thereby promoting brain functional recovery.

Pathological changes in the brain after peripheral burns

Brain injuries are common complications in patients with thermal burns and are associated with unpleasant outcomes. In clinical settings, it was once believed that brain injuries were not major pathological processes after burn, at least in part due to the unavailability of specific clinical manifestations. Burn-related brain injuries have been studied for more than a century, but the underlying pathophysiology has not been completely clarified. This article reviews the pathological changes in the brain following peripheral burns at the anatomical, histological, cytological, molecular and cognitive levels. Therapeutic indications based on brain injury as well as future directions for research have been summarized and proposed.

Mild hypothermia alleviates early brain injury after subarachnoid hemorrhage via suppressing pyroptosis through AMPK/NLRP3 inflammasome pathway in rats

As a subtype of stroke, subarachnoid hemorrhage (SAH) has a notoriously high rate of disability and mortality owing to the lack of effective intervention. Early brain injury (EBI) is the main factor responsible for the dismal prognosis of SAH patients. The current study intends to explore the molecular mechanism underlying the effect of MH on EBI after SAH from a novel perspective of pyroptosis, a highly specific inflammatory programmed cell death, in the SAH rat model. Sprague-Dawley (SD) rats were divided into different groups in accordance with various treatments. In the treatment group, the rats underwent mild hypothermia for 4 h after modeling; in the inhibitor group, Compound C (an inhibitor of AMPK) was administered intravenous injections (i.v.) 30 min before modeling. Neurological score, neuronal death, brain water content, inflammatory reaction, and expression levels of pyroptosis-related proteins were evaluated in the rats. Our results indicate that the MH therapy significantly increased the neurological score and assuaged brain edema, neuronal injury, and inflammatory reaction induced by SAH. Meanwhile, MH therapy upregulated the level of AMPK phosphorylation whereas downregulated the protein expressions of NLRP3, ASC, cleaved caspase-1, GSDMD, IL-1β, and IL-18. The reversed effect of MH therapy by Compound C concretely indicated that MH therapy inhibited pyroptosis through an AMPK-dependent pathway. Our study also found that MH therapy potently curbed the increasing trend of brain temperature (BT), rectal temperature (RT), and ICP after SAH. Taken together, our data indicate that the neuroprotective effects of MH therapy were manifested by inhibiting pyroptosis via the AMPK/NLRP3 inflammasome pathway, which may serve as a promising therapy for the intervention of SAH.

CNS-peripheral immune interactions in hemorrhagic stroke

Stroke is a sudden and rapidly progressing ischemic or hemorrhagic cerebrovascular disease. When stroke damages the brain, the immune system becomes hyperactive, leading to systemic inflammatory response and immunomodulatory disorders, which could significantly impact brain damage, recovery, and prognosis of stroke. Emerging researches suggest that ischemic stroke-induced spleen contraction could activate a peripheral immune response, which may further aggravate brain injury. This review focuses on hemorrhagic strokes including intracerebral hemorrhage (ICH) and subarachnoid hemorrhage (SAH) and discusses the central nervous system-peripheral immune interactions after hemorrhagic stroke induction. First, inflammatory progression after ICH and SAH is investigated. As a part of this review, we summarize the various kinds of inflammatory cell infiltration to aggravate brain injury after blood-brain barrier interruption induced by hemorrhagic stroke. Then, we explore hemorrhagic stroke-induced systemic inflammatory response syndrome (SIRS) and discuss the interactions of CNS and peripheral inflammatory response. In addition, potential targets related to inflammatory response for ICH and SAH are discussed in this review, which may lead to novel therapeutic strategies for hemorrhagic stroke.

MicroRNA-140-5p shuttled by microglia-derived extracellular vesicles attenuates subarachnoid hemorrhage-induced microglia activation and inflammatory response via MMD downregulation

BACKGROUND

It is documented that microglia-secreted extracellular vesicles (microglia-EVs) exert neuroprotection which is important following subarachnoid hemorrhage (SAH). Herein, we focused on the mechanism of microglia-EVs harboring microRNA-140-5p (miR-140-5p) in SAH development.

METHODS

After the successful establishment of SAH rats, neurological function was evaluated, and behaviors were observed. Serum inflammatory factors (IL-1β and TNF-α) were quantified by ELISA, followed by the detection of microglial polarization by immunofluorescence. The relationship between miR-140-5p and monocyte to macrophage differentiation-associated (MMD) was evaluated using luciferase assay. Following the extraction of microglia and microglia-EVs, the transferring of miR-140-5p by microglia-EVs was assessed by co-culture experiments. SAH rats were treated with the EVs sourced from microglia overexpressing miR-140-5p (microglia-EVs-miR-140-5p) or EVs sourced from miR-140-5p-deficient microglia (microglia-EVs-miR-140-5p inhibitor) for in vivo effect assessment.

RESULTS

Microglia-EVs inhibited microglia activation and secretion of TNF-α and IL-1β by delivering miR-140-5p. Microglia-EVs could transmit miR-140-5p into microglia. Furthermore, microglia-EVs-miR-140-5p reduced the expression of its target MMD, resulting in blocked inflammatory response and activation of microglia in SAH rats by disrupting the PI3K/AKT and Erk1/2 signaling.

CONCLUSION

In summary, microglia-EVs transmitted miR-140-5p into microglia to downregulate MMD and finally contributed to neuroprotection in SAH rats.

PHLDA1 modulates microglial response and NLRP3 inflammasome signaling following experimental subarachnoid hemorrhage

Balancing microglia M1/M2 polarization is an effective therapeutic strategy for neuroinflammation after subarachnoid hemorrhage (SAH). Pleckstrin homology-like domain family A member 1 (PHLDA1) has been demonstrated to play a crucial role in immune response. However, the function roles of PHLDA1 in neuroinflammation and microglial polarization after SAH remain unclear. In this study, SAH mouse models were assigned to treat with scramble or PHLDA1 small interfering RNAs (siRNAs). We observed that PHLDA1 was significantly increased and mainly distributed in microglia after SAH. Concomitant with PHLDA1 activation, nod-like receptor pyrin domain-containing protein 3 (NLRP3) inflammasome expression in microglia was also evidently enhanced after SAH. In addition, PHLDA1 siRNA treatment significantly reduced microglia-mediated neuroinflammation by inhibiting M1 microglia and promoting M2 microglia polarization. Meanwhile, PHLDA1 deficiency reduced neuronal apoptosis and improved neurological outcomes after SAH. Further investigation revealed that PHLDA1 blockade suppressed the NLRP3 inflammasome signaling after SAH. In contrast, NLRP3 inflammasome activator nigericin abated the beneficial effects of PHLDA1 deficiency against SAH by promoting microglial polarization to M1 phenotype. In all, we proposed that PHLDA1 blockade might ameliorate SAH-induced brain injury by balancing microglia M1/M2 polarization via suppression of NLRP3 inflammasome signaling. Targeting PHLDA1 might be a feasible strategy for treating SAH.

Deletion of Bak1 alleviates microglial necroptosis and neuroinflammation after experimental subarachnoid hemorrhage

Microglial necroptosis exacerbates neurodegenerative diseases, central nervous system (CNS) injury, and demonstrates a proinflammatory process, but its contribution to subarachnoid hemorrhage (SAH) is poorly characterized. BCL-2 homologous antagonist-killer protein (Bak1), a critical regulatory molecule of endogenous apoptosis, can be involved in the pathologic process of necroptosis by regulating mitochondrial permeability. In this study, we revealed microglia undergo necroptosis after SAH in vivo and vitro. Western blot revealed that Bak1 was elevated at 24 h after SAH. Knocked down of Bak1 by adeno-associated virus attenuates microglial necroptosis, alleviates neuroinflammation, and improves neurologic function after SAH in mice. Furthermore, oxyhemoglobin (10 μM) induced necroptosis in BV2 microglia, increasing Bak1 expression and mediating proinflammatory phenotype transformation, exacerbating oxidative stress and neuroinflammation. Abrogating BV2 Bak1 could reduce necroptosis by down-regulating the expression of phosphorylated pseudokinase mixed lineage kinase domain-like protein (p-MLKL), then down-regulating proinflammatory phenotype gene expression. RNA-Seq showed that disrupting BV2 Bak1 down-regulates multiple immune and inflammatory pathways and ameliorates cell injury by elevating thrombospondin 1 (THBS1) expression. In summary, we identified a critical regulatory role for Bak1 in microglial necroptosis and neuroinflammation after SAH. Bak1 is expected to be a potential target for the treatment strategy of SAH.

Comprehensive analysis of immune cell infiltration and role of MSR1 expression in aneurysmal subarachnoid haemorrhage

Aneurysmal subarachnoid haemorrhage (aSAH), resulting from the rupture of intracranial aneurysms, can yield high mortality and disability. This study aimed to explore the immune infiltration of aneurysmal tissues and investigate a novel mechanism underlying aSAH. We downloaded datasets containing expression profiles of aneurysmal and normal arterial tissues from the online database. Then a comprehensive bioinformatic strategy was conducted to select the biomarkers of aneurysmal tissues. Two calculation algorithms were performed to identify the unique immune characteristics between aneurysmal tissues and normal arteries. Double immunofluorescence staining was used to investigate the role of pathway-related proteins in the inflammatory process after aSAH. Six microarray datasets were integrated, and another RNA-sequencing dataset was used as the validation dataset. Functional enrichment analysis of the differentially expressed genes indicated that immune-related processes were closely related to the progression of aSAH. We then performed immune microenvironment infiltration analysis, and the results suggested macrophages were abnormally enriched in aneurysmal tissues. Core gene MSR1 was filtered through a comprehensive bioinformatic strategy. Our analysis suggested that MSR1 might be associated with macrophage activation and migration. Our study elucidated the impact of macrophage and MSR1 on aSAH progression. These findings were helpful in gaining insight into the immune heterogeneity of aneurysmal tissues and normal arteries, and in identifying patients who might benefit from immunotherapy.

FDA-Approved Kinase Inhibitors in Preclinical and Clinical Trials for Neurological Disorders

Cancers and neurological disorders are two major types of diseases. We previously developed a new concept termed "Aberrant Cell Cycle Diseases" (ACCD), revealing that these two diseases share a common mechanism of aberrant cell cycle re-entry. The aberrant cell cycle re-entry is manifested as kinase/oncogene activation and tumor suppressor inactivation, which are hallmarks of both tumor growth in cancers and neuronal death in neurological disorders. Therefore, some cancer therapies (e.g., kinase inhibition, tumor suppressor elevation) can be leveraged for neurological treatments. The United States Food and Drug Administration (US FDA) has so far approved 74 kinase inhibitors, with numerous other kinase inhibitors in clinical trials, mostly for the treatment of cancers. In contrast, there are dire unmet needs of FDA-approved drugs for neurological treatments, such as Alzheimer's disease (AD), intracerebral hemorrhage (ICH), ischemic stroke (IS), traumatic brain injury (TBI), and others. In this review, we list these 74 FDA-approved kinase-targeted drugs and identify those that have been reported in preclinical and/or clinical trials for neurological disorders, with a purpose of discussing the feasibility and applicability of leveraging these cancer drugs (FDA-approved kinase inhibitors) for neurological treatments.

Pterostilbene Attenuates Subarachnoid Hemorrhage-Induced Brain Injury through the SIRT1-Dependent Nrf2 Signaling Pathway

Neuroinflammatory injury, oxidative insults, and neuronal apoptosis are major causes of poor outcomes after subarachnoid hemorrhage (SAH). Pterostilbene (PTE), an analog of resveratrol, has been verified as a potent sirtuin 1 (SIRT1) activator. However, the beneficial actions of PTE on SAH-induced brain injury and whether PTE regulates SIRT1 signaling after SAH remain unknown. We first evaluated the dose-response influence of PTE on early brain impairment after SAH. In addition, EX527 was administered to suppress SIRT1 signaling. The results revealed that PTE significantly attenuated microglia activation, oxidative insults, neuronal damage, and early neurological deterioration. Mechanistically, PTE effectively enhanced SIRT1 expression and promoted nuclear factor-erythroid 2-related factor 2 (Nrf2) accumulation in nuclei. Furthermore, EX527 pretreatment distinctly repressed PTE-induced SIRT1 and Nrf2 activation and deteriorated these beneficial outcomes. In all, our study provides the evidence that PTE protects against SAH insults by activating SIRT1-dependent Nrf2 signaling pathway. PTE might be a therapeutic alternative for SAH.

Microglia dynamics in aging-related neurobehavioral and neuroinflammatory diseases

Microglia represent the first line of immune feedback in the brain. Beyond immune surveillance, they are essential for maintaining brain homeostasis. Recent research has revealed the microglial cells' spatiotemporal heterogeneity based on their local and time-based functions in brain trauma or disease when homeostasis is disrupted. Distinct "microglial signatures" have been recorded in physiological states and brain injuries, with discrete or sometimes overlapping pro- and anti-inflammatory functions. Microglia are involved in the neurological repair processes, such as neurovascular unit restoration and synaptic plasticity, and manage the extent of the damage due to their phenotype switching. The versatility of cellular phenotypes beyond the classical M1/M2 classification, as well as the double-edge actions of microglia in neurodegeneration, indicate the need for further exploration of microglial cell dynamics and their contribution to neurodegenerative processes. This review discusses the homeostatic functions of different microglial subsets focusing on neuropathological conditions. Also, we address the feasibility of targeting microglia as a therapeutic strategy in neurodegenerative diseases.

TLR4-Pathway-Associated Biomarkers in Subarachnoid Hemorrhage (SAH): Potential Targets for Future Anti-Inflammatory Therapies

Subarachnoid hemorrhage is associated with severe neurological deficits for survivors. Among survivors of the initial bleeding, secondary brain injury leads to additional brain damage. Apart from cerebral vasospasm, secondary brain injury mainly results from cerebral inflammation taking place in the brain parenchyma after bleeding. The brain’s innate immune system is activated, which leads to disturbances in brain homeostasis, cleavage of inflammatory cytokines and, subsequently, neuronal cell death. The toll-like receptor (TLR)4 signaling pathway has been found to play an essential role in the pathophysiology of acute brain injuries such as subarachnoid hemorrhage (SAH). TLR4 is expressed on the cell surface of microglia, which are key players in the cellular immune responses of the brain. The participants in the signaling pathway, such as TLR4-pathway-like ligands, the receptor itself, and inflammatory cytokines, can act as biomarkers, serving as clues regarding the inflammatory status after SAH. Moreover, protein complexes such as the NLRP3 inflammasome or receptors such as TREM1 frame the TLR4 pathway and are indicative of inflammation. In this review, we focus on the activity of the TLR4 pathway and its contributors, which can act as biomarkers of neuroinflammation or even offer potential new treatment targets for secondary neuronal cell death after SAH.

Identification of the key immune-related genes in aneurysmal subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a major cause of death and morbidity worldwide, often due to rupture of intracranial aneurysms (IAs). Immune infiltration and inflammatory activation play key roles in the process of aneurysmal SAH (aSAH). This study aimed to elaborate the immune infiltration and identify related biomarkers both in blood and tissue samples from patients with aSAH. Expression data of aSAH and healthy control samples were obtained from gene expression omnibus (GEO) database. Overall, a blood sample dataset GSE36791 and a tissue sample dataset GSE122897 were included. Differentially expressed genes (DEGs) between aSAH and healthy samples were explored. We applied GO biological and Gene Set Enrichment Analyses (GSEA) processes to access the functional enrichment. Then feature elimination algorithms based on random forest were used to screen and verify the biomarkers of aSAH. We performed three computational algorithms including Cell type Identification by Estimating Relative Subsets of RNA Transcripts (CIBERSORT), Microenvironment Cell Populations-counter (MCPcounter), and xcell to evaluate the immune cell infiltration landscape to identify the unique infiltration characteristics associated with rupturing. We found 2,220 DEGs (856 upregulated and 1,364 downregulated) in the original dataset. Functional analysis revealed most of these genes are enriched in immunological process, especially related with neutrophil response. Similar signaling pathway enrichment patterns were observed in tissue sample dataset and ClueGo. Analysis of immune microenvironment infiltration suggested neutrophils were abnormally upregulated in aSAH compared with those in the control group. Key gene SRPK1 was then filtered based on feature elimination algorithms, and transcription factor (TF) ZNF281 is assumed to participate in immunomodulation by regulating expression of SRPK1. Several immunomodulators such as CXCR1 and CXCR2 also appear to be involved in the progression of aSAH. In the present study, we performed a comprehensive stratification and quantification of the immune infiltration status of aSAH. By exploring the potential mechanism for aSAH based on several computational algorithms, key genes including SRPK1 and ZNF281 were filtered. This study may be of benefit to patients who are at high risk of suffering aSAH which allows for early diagnosis and potential therapy.

Microglia and Post-Subarachnoid Hemorrhage Vasospasm: Review of Emerging Mechanisms and Treatment Modalities

Vasospasm is a potentially severe complication of subarachnoid hemorrhage. It can be attributed to neuroinflammation and the robust recruitment of microglia. Emerging evidence has linked this sustained inflammation to the development of delayed cerebral ischemia following subarachnoid hemorrhage. In this focused review, we provide an overview of the historical understanding of vasospasm. We then delve into the role of neuroinflammation and the activation of microglia. These activated microglia releases a host of inflammatory cytokines contributing to an influx of peripheral macrophages. This thereby opens a new and innovative treatment strategy to prevent vasospasm. Pre-clinical work has been promising, and the transition to clinical trials is warranted. Finally, some of the key mechanistic targets are outlined with emphasis on translation. This review will serve as a catalyst for researchers and clinicians alike in the quest to improve treatment options for vasospasm.

TRPM2 mediates CaMKⅡ-Beclin-1 signaling in early cortical injury after induced subarachnoid hemorrhage in mice

BACKGROUND

Though early brain injury (EBI) is the primary cause of poor outcomes among patients with subarachnoid hemorrhage (SAH), its exact molecular mechanisms remain unclear. Improved the understanding of how transient receptor potential melastatin-related 2 (TRPM2) is involved in SAH-induced EBI will help develop novel interventions.

METHODS

Wild type (WT) male C57BL/6J mice were subjected to SAH for 12 h, 24 h or 48 h, after which neurological scores and pathological changes in the hippocampus (CA3, DG, and CA1) and temporal base cortex were observed. Expressions of TRPM2, Ca²⁺/calmodulin (CaM)-dependent protein kinase Ⅱ (CaMKⅡ), and Beclin-1 in hippocampus (CA3, DG, and CA1) and temporal base cortex were compared across post-SAH timepoints. TRPM2-deficient (TRPM2^-/-) male C57BL/6 J mice and a CaMKⅡ inhibitor (KN-93) were used to analyze the effects oTRPM2 on the CaMKⅡ-Beclin-1 signaling post SAH.

RESULTS

Neurological and temporal base cortex deterioration were more severe with increased time post-SAH induction, whereas hippocampal damage was not observed. Post-SAH, TRPM2-CaMKⅡ-Beclin-1 cascade was activated in the temporal base cortex, but not the hippocampus. Using TRPM2^-/- mice and KN-93 administration, SAH-induced EBI was improved, and CaMKⅡ and Beclin-1 expressions in the temporal base cortex were significantly decreased compared with WT mice. TRPM2^-/- mice also showed better neurological improvement compared with KN-93 treated mice.

CONCLUSION

TRPM2 mediates CaMKⅡ-Beclin-1 signaling that aggravates SAH-induced EBI in the temporal base cortex. TRPM2 may be an alternative therapy target in EBI after SAH.

DATA AVAILABILITY

The datasets generated and/or analysed during the current study are available from the corresponding author.

S100A8 regulates autophagy-dependent ferroptosis in microglia after experimental subarachnoid hemorrhage

Targeting microglial activation has been shown to ameliorate early brain injury (EBI) after subarachnoid hemorrhage (SAH). Ferroptosis is a new form of programmed cell death after SAH, but these molecular features were not recognized as evidence of microglial function so far. In this study, we constructed microglial S100A8-specific knockdown and established the SAH model in vivo and in vitro. Multi-technology strategies, including high throughput sequencing, adeno-associated virus gene gene-editing and several molecular biotechnologies to validate the effects of S100A8 on microglial autophagy and ferroptosis after SAH. Our results revealed that the expression of S100A8 was significantly increased in brain tissue after SAH. Targeted microglial S100A8 inhibition improved neural function and neuronal apoptosis in mice after SAH. Further mechanism exploration found that favourable effects of S100A8 depletion in EBI may be through the inhibition of microglia autophagy-dependent ferroptosis. In conclusion, S100A8 may be a potential intervention target for microglial ferroptosis in EBI after SAH.

Microglial TLR4 is Critical for Neuronal Injury and Cognitive Dysfunction in Subarachnoid Hemorrhage

Background

Toll-like receptor 4 (TLR4) activation causes excessive production of proinflammatory mediators and an increased expression of costimulatory molecules that leads to neuroinflammation after subarachnoid hemorrhage (SAH). Although TLR4-mediated inflammatory pathways have long been studied in neuroinflammation, the specific glia implicated in initiation and propagation of neuroinflammation in SAH have not been well elucidated. In this study, we investigated the involvement of glial TLR4 including microglia and astrocytes in brain damage and poor neurological outcome.

Methods

In this study, global TLR4 knockout, cell-specific TLR4 knockout, and floxxed control male and female mice were used. The mice were injected with 60 μl autologous blood near the mesencephalon to induce SAH; animals were euthanized on postoperative day 7 for immunohistochemistry of glia and apoptotic cells. Microglial morphology was evaluated by using immunofluorescence density quantification to determine correlations between morphology and neuroinflammation. Microglial depletion was accomplished with the intracerebroventricular administration of clodronate liposomes. Cognitive function was assessed with Barnes maze.

Results

On postoperative day 7 after SAH induction, neuronal apoptosis was markedly reduced in the clodronate liposome group compared with phosphate-buffered saline control liposomes, and cognitive performance in the clodronate group was improved, as well. Differences in microglial activation, assessed by morphometric analysis, and neuronal apoptosis were significantly greater in wildtype knockouts compared with cell-specific and global TLR4 knockouts. The mice lacking TLR4 on astrocytes and neurons showed no differences compared with wildtype mice on any end points.

Conclusions

Our data suggest that microglial depletion with the intracerebroventricular administration of clodronate can improve the cognitive function in an SAH mouse model, and TLR4 is critical for microglial activation and neuronal injury. Only microglial TLR4 is necessary for brain damage and poor cognitive outcome rather than astrocyte or neuronal TLR4. Thus, microglial TLR4 could be a potent therapeutic target to treat SAH-associated neuronal injury and protect against cognitive dysfunction.

The Putative Role of Astaxanthin in Neuroinflammation Modulation: Mechanisms and Therapeutic Potential

Neuroinflammation is a protective mechanism against insults from exogenous pathogens and endogenous cellular debris and is essential for reestablishing homeostasis in the brain. However, excessive prolonged neuroinflammation inevitably leads to lesions and disease. The use of natural compounds targeting pathways involved in neuroinflammation remains a promising strategy for treating different neurological and neurodegenerative diseases. Astaxanthin, a natural xanthophyll carotenoid, is a well known antioxidant. Mounting evidence has revealed that astaxanthin is neuroprotective and has therapeutic potential by inhibiting neuroinflammation, however, its functional roles and underlying mechanisms in modulating neuroinflammation have not been systematically summarized. Hence, this review summarizes recent progress in this field and provides an update on the medical value of astaxanthin. Astaxanthin modulates neuroinflammation by alleviating oxidative stress, reducing the production of neuroinflammatory factors, inhibiting peripheral inflammation and maintaining the integrity of the blood-brain barrier. Mechanistically, astaxanthin scavenges radicals, triggers the Nrf2-induced activation of the antioxidant system, and suppresses the activation of the NF-κB and mitogen-activated protein kinase pathways. With its good biosafety and high bioavailability, astaxanthin has strong potential for modulating neuroinflammation, although some outstanding issues still require further investigation.

Alantolactone reduced neuron injury via activating PI3K/Akt signaling pathway after subarachnoid hemorrhage in rats

Subarachnoid hemorrhage (SAH) is a common disease with high morbidity and mortality, which can cause pathological, physiological, and biological reactions. SAH causes a series of responses such as neuronal and cerebral cortex damage, which in turn leads to inflammation and apoptosis. Traditional Chinese medicine has a strong anti-inflammatory effect, such as Alantolactone (ATL). However, studies on ATL therapy for SAH have not been reported. We observed the neurological scores, brain water content, Evans blue (EB) extravasation, neuroinflammation, and apoptosis via performing an enzyme-linked immunosorbent assay (ELISA), western blotting, immunofluorescence staining, and other methods after SAH. In this study, we found that ATL treatment attenuated the neurologic deficits, inhibited neuronal apoptosis and inflammatory reaction, promoted polarization of microglia toward the M2 phenotype, and activated the PI3K/Akt signaling pathway. ATL can reduce the neurons and cerebral cortex damage of SAH rats through activating PI3K/Akt signaling pathway.

Cycloastragenol Confers Cerebral Protection after Subarachnoid Hemorrhage by Suppressing Oxidative Insults and Neuroinflammation via the SIRT1 Signaling Pathway

Subarachnoid hemorrhage (SAH) is an acute cerebral vascular disease featured by oxidative insults and neuroinflammation. Cycloastragenol (CAG), the major active component of Astragalus radix, has a wide range of biological functions. However, the potential beneficial effects and the underlying molecular mechanisms of CAG on SAH remain obscure. In the current study, the cerebroprotective effects and mechanism of CAG on SAH were evaluated both in vivo and in vitro. Our results indicated that CAG significantly suppressed SAH-triggered oxidative insults, inflammatory mediators production, microglia activation, and the neutrophil infiltration in the brain. In addition, CAG improved neurological function and ameliorated neuronal apoptosis and degeneration after SAH. In vitro results also revealed the therapeutic effects of CAG on neurons and microglia co-culture system. Mechanistically, CAG treatment upregulated sirtuin 1 (SIRT1) expression, inhibited the levels of FoxO1, nuclear factor-kappa B, and p53 acetylation, and suppressed the subsequent oxidative, inflammatory, and apoptotic pathways. In contrast, inhibiting SIRT1 by pretreatment with Ex527 abrogated the protective actions of CAG both in vivo and in vitro models of SAH. Collectively, our findings indicated that CAG could be a promising and effective drug candidate for SAH.

Melatonin as a Potential Neuroprotectant: Mechanisms in Subarachnoid Hemorrhage-Induced Early Brain Injury

Subarachnoid hemorrhage (SAH) is a common cerebrovascular disease with high mortality and disability rates. Despite progressive advances in drugs and surgical techniques, neurological dysfunction in surviving SAH patients have not improved significantly. Traditionally, vasospasm has been considered the main cause of death and disability following SAH, but anti-vasospasm therapy has not benefited clinical prognosis. Many studies have proposed that early brain injury (EBI) may be the primary factor influencing the prognosis of SAH. Melatonin is an indole hormone and is the main hormone secreted by the pineal gland, with low daytime secretion levels and high nighttime secretion levels. Melatonin produces a wide range of biological effects through the neuroimmune endocrine network, and participates in various physiological activities in the central nervous system, reproductive system, immune system, and digestive system. Numerous studies have reported that melatonin has extensive physiological and pharmacological effects such as anti-oxidative stress, anti-inflammation, maintaining circadian rhythm, and regulating cellular and humoral immunity. In recent years, more and more studies have been conducted to explore the molecular mechanism underlying melatonin-induced neuroprotection. The studies suggest beneficial effects in the recovery of intracerebral hemorrhage, cerebral ischemia-reperfusion injury, spinal cord injury, Alzheimer’s disease, Parkinson’s disease and meningitis through anti-inflammatory, antioxidant and anti-apoptotic mechanisms. This review summarizes the recent studies on the application and mechanism of melatonin in SAH.

Wild Bitter Melon Extract Abrogates Hypoxia-Induced Cell Death via the Regulation of Ferroptosis, ER Stress, and Apoptosis in Microglial BV2 Cells

Microglial cells are well-known phagocytic cells that are resistant to the central nervous system (CNS) and play an important role in the maintenance of CNS homeostasis. Activated microglial cells induce neuroinflammation under hypoxia and typically cause neuronal damage in CNS diseases. In this study, we propose that wild bitter melon extract (WBM) has a protective effect on hypoxia-induced cell death via regulation of ferroptosis, ER stress, and apoptosis. The results demonstrated that hypoxia caused microglial BV-2 the accumulation of lipid ROS, ferroptosis, ER stress, and apoptosis. In this study, we investigated the pharmacological effects of WBM on BV-2 cells following hypoxia-induced cell death. The results indicated that WBM reversed hypoxia-downregulated antiferroptotic molecules Gpx4 and SLC7A11, as well as upregulated the ER stress markers CHOP and Bip. Moreover, WBM alleviated hypoxia-induced apoptosis via the regulation of cleaved-caspase 3, Bax, and Bcl-2. Our results suggest that WBM may be a good candidate for preventing CNS disorders in the future.

Targeting iNOS Alleviates Early Brain Injury After Experimental Subarachnoid Hemorrhage via Promoting Ferroptosis of M1 Microglia and Reducing Neuroinflammation

Numerous studies have demonstrated the role of neuroinflammation in mediating acute pathophysiological events of early brain injury after subarachnoid hemorrhage (SAH). However, it is not clear how to target this inflammatory cascade after SAH. M1 activation of microglia is an important pathological mechanism driving neuroinflammation in SAH, which is considered aggressive, leading to cytotoxicity and robust inflammation related to the release of proinflammatory cytokines and chemokines after SAH. Thus, reducing the number of M1 microglia represents a potential target for therapies to improve outcomes after SAH. Previous studies have found that inducible nitric oxide synthase (iNOS/NO•) plays an essential role in promoting the survival of M1 microglia by blocking ferroptosis. Ferroptosis is a new type of iron-dependent cellular procedural death associated with pathological cell death related to mammalian degenerative diseases, cerebral hemorrhage, and traumatic brain injury. Here, we investigated the effect of L-NIL, an inhibitor of iNOS, on M1 microglia, neuroinflammation, neuronal cell death, brain edema, and neurological function in an experimental SAH model in vivo and in vitro. We found that L-NIL reduced the number of M1 microglia and alleviated neuroinflammation following SAH. Notably, treatment with L-NIL relieves brain edema and neuronal injury and improves outcomes of neurological function after SAH in rats. Mechanistically, we found that L-NIL inhibited the expression of iNOS and promoted ferroptosis of M1 microglia by increasing the expression of ferroptosis-related proteins and lipid peroxidation in an in vitro model of SAH, which was reversed by a ferroptosis inhibitor, liproxstatin-1. In addition, inhibiting iNOS had no significant effect on ferroptosis of neurons after oxyhemoglobin stimulation in vitro. Thus, our research demonstrated that inhibition of iNOS might represent a potential therapeutic strategy to improve outcomes after SAH by promoting ferroptosis of M1 microglia and reducing neuroinflammation.

Innate immune stimulation by monophosphoryl lipid A prevents chronic social defeat stress-induced anxiety-like behaviors in mice

Background

Innate immune pre-stimulation can prevent the development of depression-like behaviors in chronically stressed mice; however, whether the same stimulation prevents the development of anxiety-like behaviors in animals remains unclear. We addressed this issue using monophosphoryl lipid A (MPL), a derivative of lipopolysaccharide (LPS) that lacks undesirable properties of LPS but still keeps immune-enhancing activities.

Methods

The experimental mice were pre-injected intraperitoneally with MPL before stress exposure. Depression was induced through chronic social defeat stress (CSDS). Behavioral tests were conducted to identify anxiety-like behaviors. Real-time polymerase chain reaction (PCR) and biochemical assays were employed to examine the gene and protein expression levels of pro-inflammatory markers.

Results

A single MPL injection at the dose of 400 and 800 μg/kg 1 day before stress exposure prevented CSDS-induced anxiety-like behaviors, and a single MPL injection (400 μg/kg) five but not 10 days before stress exposure produced similar effect. The preventive effect of MPL on anxiety-like behaviors was also observed in CSDS mice who received a second MPL injection 10 days after the first MPL injection or a 4 × MPL injection 10 days before stress exposure. MPL pre-injection also prevented the production of pro-inflammatory cytokines in the hippocampus and medial prefrontal cortex in CSDS mice, and inhibiting the central immune response by minocycline pretreatment abrogated the preventive effect of MPL on CSDS-induced anxiety-like behaviors and pro-inflammatory cytokine productions in the brain.

Conclusions

Pre-stimulation of the innate immune system by MPL can prevent chronic stress-induced anxiety-like behaviors and neuroinflammatory responses in the brain in mice.

Luteolin Confers Cerebroprotection after Subarachnoid Hemorrhage by Suppression of NLPR3 Inflammasome Activation through Nrf2-Dependent Pathway

Luteolin (LUT) possesses multiple biologic functions and has beneficial effects for cardiovascular and cerebral vascular diseases. Here, we investigated the protective effects of LUT against subarachnoid hemorrhage (SAH) and the involvement of underlying molecular mechanisms. In a rat model of SAH, LUT significantly inhibited SAH-induced neuroinflammation as evidenced by reduced microglia activation, decreased neutrophil infiltration, and suppressed proinflammatory cytokine release. In addition, LUT markedly ameliorated SAH-induced oxidative damage and restored the endogenous antioxidant systems. Concomitant with the suppressed oxidative stress and neuroinflammation, LUT significantly improved neurologic function and reduced neuronal cell death after SAH. Mechanistically, LUT treatment significantly enhanced the expression of nuclear factor-erythroid 2-related factor 2 (Nrf2), while it downregulated nod-like receptor pyrin domain-containing 3 (NLRP3) inflammasome activation. Inhibition of Nrf2 by ML385 dramatically abrogated LUT-induced Nrf2 activation and NLRP3 suppression and reversed the beneficial effects of LUT against SAH. In neurons and microglia coculture system, LUT also mitigated oxidative stress, inflammatory response, and neuronal degeneration. These beneficial effects were associated with activation of the Nrf2 and inhibitory effects on NLRP3 inflammasome and were reversed by ML385 treatment. Taken together, this present study reveals that LUT confers protection against SAH by inhibiting NLRP3 inflammasome signaling pathway, which may be modulated by Nrf2 activation.

α7-Acetylcholine Receptor Signaling Reduces Neuroinflammation After Subarachnoid Hemorrhage in Mice

Aneurysmal subarachnoid hemorrhage (aSAH) causes a robust inflammatory response which leads worse brain injury and poor outcomes. We investigated if stimulation of nicotinic acetylcholine α7 receptors (α7-AChR) (receptors shown to have anti-inflammatory effects) would reduce inflammation and improve outcomes. To investigate the level of peripheral inflammation after aSAH, inflammatory markers were measured in plasma samples collected in a cohort of aSAH patients. To study the effect of α7-AChR stimulation, SAH was induced in adult mice which were then treated with a α7-AChR agonist, galantamine, or vehicle. A battery of motor and cognitive tests were performed 24 h after subarachnoid hemorrhage. Mice were euthanized and tissue collected for analysis of markers of inflammation or activation of α7-AChR-mediated transduction cascades. A separate cohort of mice was allowed to survive for 28 days to assess long-term neurological deficits and histological outcome. Microglia cell culture subjected to hemoglobin toxicity was used to assess the effects of α7-AChR agonism. Analysis of eighty-two patient plasma samples confirmed enhanced systemic inflammation after aSAH. α7-AChR agonism reduced neuroinflammation at 24 h after SAH in male and female mice, which was associated with improved outcomes. This coincided with JAK2/STAT3 and IRAK-M activity modulations and a robust improvement in neurological/cognitive status that was effectively reversed by interfering with various components of these signaling pathways. Pharmacologic inhibition partially reversed the α7-AChR agonist's benefits, supporting α7-AChR as a target of the agonist's therapeutic effect. The cell culture experiment showed that α7-AChR agonism is directly beneficial to microglia. Our results demonstrate that activation of α7-AChR represents an attractive target for treatment of SAH. Our findings suggest that α7-AChR agonists, and specifically galantamine, might provide therapeutic benefit to aSAH patients.

Toll-Like Receptor Signaling Pathways: Novel Therapeutic Targets for Cerebrovascular Disorders

Toll-like receptors (TLRs), a class of pattern recognition proteins, play an integral role in the modulation of systemic inflammatory responses. Cerebrovascular diseases (CVDs) are a group of pathological conditions that temporarily or permanently affect the brain tissue mostly via the decrease of oxygen and glucose supply. TLRs have a critical role in the activation of inflammatory cascades following hypoxic-ischemic events and subsequently contribute to neuroprotective or detrimental effects of CVD-induced neuroinflammation. The TLR signaling pathway and downstream cascades trigger immune responses via the production and release of various inflammatory mediators. The present review describes the modulatory role of the TLR signaling pathway in the inflammatory responses developed following various CVDs and discusses the potential benefits of the modulation of different TLRs in the improvement of functional outcomes after brain ischemia.