The Relationship of Astrocytes and Microglia with Different Stages of Ischemic Stroke

Buyang Huanwu decoction promotes gray and white matter remyelination by inhibiting Notch signaling activation in the astrocyte and microglia after ischemic stroke

ETHNOPHARMACOLOGICAL RELEVANCE

Ischemic stroke causes damages to both gray and white matter, resulting in long-term motor impairments. Myelin repair is a promising strategy for poststroke motor rehabilitation. Buyang Huanwu Decoction (BHD) is a classical traditional Chinese medicine formula for managing the sequelae of ischemic stroke. Whether BHD benefits gray and white matter remyelination following stroke remains to be elucidated.

AIM OF THE STUDY

The present study aimed to investigate the effects of BHD on the gray and white matter remyelination following ischemic stroke and further explore the underlying mechanisms by combining magnetic resonance imaging (MRI) and histological experiments.

MATERIALS AND METHODS

The ischemic stroke model was established in male Sprague-Dawley rats by permanently occluding the middle cerebral artery (MCAO). BHD (16.6 g/kg and 8.3 g/kg) was intragastrically administered to rats for 30 days. The motor function was assessed by an automated Digi gait system. The structural integrity of the motor cortex and external capsule was monitored by MRI, including T2 mapping and diffusion tensor imaging (DTI). The remyelination was examined by Olig2/Ki67, 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase)/Ki67 double immunofluorescence staining and Luxol fast blue (LFB) staining. Subsequently, the Notch signaling activation in astrocytes and microglia was assessed by double immunofluorescence staining with JAG1/Notch1/Notch intracellular domain (NICD) and glial fibrillary acidic protein (GFAP)/ionized calcium binding adaptor molecule 1 (Iba1).

RESULTS

BHD treatments remarkably improved motor function of the MCAO rats by reducing steps, swing time and ataxia coefficient of the left forelimb. The MRI examinations found that BHD treatments significantly reduced infarct volume and preserved the motor cortex and external capsule integrity, as reflected by decreased T2 values, RD, and increased FA. Notably, the gait parameters of the left forelimb were correlated to the MRI index obtained from the perilesional motor cortex and external capsule to varying degrees. Furthermore, BHD treatments enhanced gray and matter remyelination by elevating the numbers of Olig2+/Ki67+, CNPase+/Ki67+ cells, and the integrated optical density of LFB. Finally, BHD effectively inhibited the activation of Notch signaling in the astrocytes and microglia of the corresponding gray and white matter, as evidenced by decreased numbers of cells co-expressing JAG1/Notch1/NICD and GFAP/Iba1.

CONCLUSION

This study demonstrated that BHD treatment could promote poststroke motor recovery by preserving the structural integrity of the gray and white matter and facilitating their remyelination. Notably, the pro-remyelination effects of BHD treatment might be attributed to suppressed activation of Notch signaling within the reactive astrocytes and microglia.

Myeloid-derived suppressor cells in metabolic and cardiovascular disorders

Dysregulation of immune homeostasis can precipitate chronic inflammation, thus significantly contributing to the onset and progression of metabolic and cardiovascular diseases. Myeloid-derived suppressor cells (MDSCs) constitute a heterogeneous population of immature myeloid cells that are mobilized in response to biological stressors such as tissue damage and inflammation. Although MDSCs have been extensively characterized in the contexts of cancer and infectious diseases, emerging evidence highlights their pivotal roles in the pathophysiology of metabolic and cardiovascular disorders. We discuss growing evidence for the involvement of MDSCs in the progression of metabolic and cardiovascular diseases, with the aim of deepening our understanding of MDSCs in cardiometabolic physiology and identifying the necessary steps for the development of innovative MDSC-targeted therapeutic strategies.

The pathogenesis of depression: Roles of connexin 43-based gap junctions and inflammation

BACKGROUND

Depression is a leading chronic mental illness worldwide, characterized by anhedonia and pessimism. Connexin is a kind of widely distributed protein in the body. Connexin 43 (Cx43) plays an important role in the pathogenesis of depression. Growing evidence has indicated that inflammation is closely associated with neuropsychiatric diseases such as depression. Inflammation occurs in patients with mood disorders, and symptomatic relief after multiple treatments is often accompanied by proinflammatory restoration. In this study, we sought to determine the upstream and downstream relationship of Cx43 abnormalities and peripheral inflammation in inducing depression.

METHODS AND RESULTS

Gap27, as a Cx43 mimetic peptide, specifically blocks Cx43 gap junction channels in the brain. The mice were treated with injection of Gap27 into the prefrontal cortex (PFC), conditional knockout of Cx43 in the PFC, and lipopolysaccharide (LPS) intraperitoneal injection. Our results revealed that the treatments gave rise to the depressive-like behavior occurrence in mice, including reducing the sucrose preference and spontaneous activities, and increasing immobility time in the forced swimming test. Functional blockade of Cx43 induced abnormal expression of peripheral inflammatory cytokines including interleukin (IL)-1β, IL-6, tumor necrosis factor-α, IL-2, IL-10, and IL-18. Furthermore, depression associated with peripheral inflammation derived from LPS intraperitoneal injection significantly reduced the Cx43 expression and the diffusion distance of gap junction channel permeability dye in the PFC.

CONCLUSION

These results showed that blockade of Cx43 in the PFC and peripheral inflammation are complicatedly intertwined, and reinforcing each other during the induction of depression.

miRNA in blood-brain barrier repair: role of extracellular vesicles in stroke recovery

Ischemic stroke is a leading cause of mortality and long-term disability globally. One of its aspects is the breakdown of the blood-brain barrier (BBB). The disruption of BBB's integrity during stroke exacerbates neurological damage and hampers therapeutic intervention. Recent advances in regenerative medicine suggest that mesenchymal stem cells (MSCs) derived extracellular vesicles (EVs) show promise for restoring BBB integrity. This review explores the potential of MSC-derived EVs in mediating neuroprotective and reparative effects on the BBB after ischemic stroke. We highlight the molecular cargo of MSC-derived EVs, including miRNAs, and their role in enhancing angiogenesis, promoting the BBB and neural repair, and mitigating apoptosis. Furthermore, we discuss the challenges associated with the clinical translation of MSC-derived EV therapies and the possibilities of further enhancing EVs' innate protective qualities. Our findings underscore the need for further research to optimize the therapeutic potential of EVs and establish their efficacy and safety in clinical settings.

Circulating miR-574-5p shows diagnostic and prognostic significance and regulates oxygen-glucose deprivation (OGD)-induced inflammatory activation of microglia by targeting ATP2B2

BACKGROUND

Early screening is critical for the prevention of ischemic stroke. miR-574-5p was considered a promising biomarker for ischemic stroke but lacks direct confirmation. This study evaluated miR-574-5p in discriminating ischemic stroke and predicting the severity and prognosis of patients, aiming to provide novel insights into the clinical prevention of ischemic stroke.

METHODS

The clinical significance of miR-574-5p was evaluated in 103 ischemic stroke patients with 87 healthy individuals as control. The potential of serum miR-574-5p in the diagnosis and prognosis of ischemic stroke was assessed by ROC and logistic regression analyses. In vitro, oxygen-glucose deprivation (OGD)-induced microglia was established. The regulation of inflammation, oxidative stress, and proliferation of microglia by miR-574-5p were assessed by cell transfection. The downstream targets of miR-574-5p were predicted from public databases, and the targeting relationship was evaluated by luciferase reporter assay.

RESULTS

Reducing serum miR-574-5p was observed in ischemic stroke patients relative to healthy individuals, which discriminated ischemic stroke patients. Serum miR-574-5p was negatively correlated with the NIHSS score of ischemic stroke patients and was identified as a risk factor for patients' adverse prognosis. In OGD-induced microglia, overexpressing miR-574-5p could alleviate OGD-induced inflammation and oxidative stress and promote cell growth. Among predicted targets, ATP2B2 was upregulated in ischemic stroke and showed a negative correlation with miR-574-5p. miR-574-5p negatively regulated ATP2B2 in OGD-induced microglia, and the overexpression of ATP2B2 reversed the protective effect of miR-574-5p.

CONCLUSION

miR-574-5p acted as a biomarker for ischemic stroke and mediated neuroinflammation via targeting ATP2B2.

Association of systemic inflammatory response index and stroke: a cross-sectional study of NHANES, 2005-2018

Background

Many inflammatory markers like systemic immune-inflammatory index (SII), neutrophil-lymphocyte ratio (NLR), and platelet-lymphocyte ratio (PLR) are associated with stroke. However, studies on the relationship between stroke and systemic inflammatory response index (SIRI) are scarce. This study was aimed at evaluating the potential association of SIRI with stroke.

Methods

Our cross-sectional study included adults with sufficient SIRI and stroke data from the 2005-2018 National Health and Nutrition Examination Survey (NHANES). We used multivariable logistic regression, interaction tests, smoothed curve fitting, and subgroup analysis for assessing the independent relationship between SIRI and stroke.

Results

Of 36,176 participants in this study, 1,414 (3.9%) had experienced a stroke. In a fully adjusted model, the systemic inflammatory response index displayed a significant and positive correlation with stroke (odds ratio [OR] = 1.09, 95% confidence interval [CI] = 1.04-1.15, p = 0.0006). Meanwhile, the odds of stroke increased by 39% in the 4th quartile, relative to the 1st quartile (OR = 1.39, 95% CI = 1.17-1.65, p = 0.0002). Additional interaction tests and subgroup analysis revealed that age, sex, race, education, marriage, BMI (body mass index), smoking, diabetes mellitus, hypertension, and coronary heart disease (CHD) were not positively correlated (p interaction >0.05). Moreover, we also found a nonlinear correlation between SIRI and stroke, with an inflection point of 2.17.

Conclusion

Our results indicate that SIRI is significantly and positively related to stroke; however, its role in stroke needs to be further confirmed by large-scale prospective studies.

Pulmonary consequences of experimentally induced stroke: differences between global and focal cerebral ischemia

Introduction

Cerebral ischemia leads to multiple organ dysfunctions, with the lungs among the most severely affected. Although adverse pulmonary consequences contribute significantly to reduced life expectancy after stroke, the impact of global or focal cerebral ischemia on respiratory mechanical parameters remains poorly understood.

Methods

Rats were randomly assigned to undergo surgery to induce permanent global cerebral ischemia (2VO) or focal cerebral ischemia (MCAO), or to receive a sham operation (SHAM). Three days later, end-expiratory lung volume, airway and respiratory tissue mechanics were measured at positive end-expiratory pressure (PEEP) levels of 0, 3 and 6 cmH2O. Bronchial responsiveness to methacholine, lung cytokine levels, wet-to-dry ratio, blood gas parameters and cerebral stroke markers were also evaluated.

Results

Global and focal cerebral ischemia had no significant effect on end-expiratory lung volume, bronchial responsiveness, and arterial blood gas levels. No change in respiratory mechanics and inflammatory response was evident after 2VO. Conversely, MCAO decreased airway resistance at PEEP 0, deteriorated respiratory tissue damping and elastance at all PEEP levels, and elevated Hct and Hgb. MCAO also caused lung edema and augmented IL-1β and TNF-α in the lung tissue without affecting IL-6 and IL-8 levels.

Discussion

Our findings suggest that global cerebral ischemia has no major pulmonary consequences. However, deteriorations in the respiratory tissue mechanics develop after permanent focal ischemia due to pulmonary edema formation, hemoconcentration and cytokine production. This respiratory mechanical defect can compromise lung distension at all PEEP levels, which warrants consideration in optimizing mechanical ventilation.

Neuroprotective effects of phenylacetylglycine via β2AR on cerebral ischemia/reperfusion injury in rats

Phenylacetylglycine (PAGly) is a small molecule derived from phenylalanine in the gut via glycine degradation and conjugation. It has been associated with both the progression of atherosclerosis and protective effects on the myocardium. This study evaluated the function and the underlying mechanisms of PAGly in a rat cerebral ischemia/reperfusion (I/R) injury model. The results indicated that PAGly markedly alleviated cerebral infarct volume (P = 0.0024) and improved the neurobehavioral outcomes (P = 0.0149) after I/R injury. PAGly is structurally analogous to catecholamines and binds to β2-adrenergic receptors (β2AR) on microglia without altering the expression of these receptors (P = 0.9137), but instead inhibiting their activity. It was also observed that when β2AR was engaged in microglia, PAGly suppressed the release of TNF-α (P = 0.0018), IL-1β (P = 0.0310), and IL-6 (P = 0.0017), thereby reducing neuronal apoptosis (P = 0.000003). Furthermore, the protective effect of PAGly diminished after the administration of β2AR-specific agonist fenoterol (P = 0.0055). These data indicate that PAGly mitigates cerebral I/R injury by inhibiting microglial inflammation via β2AR, highlighting its potential as a therapeutic agent. These findings position PAGly as a promising candidate for therapeutic intervention in cerebrovascular injuries, warranting further exploration in clinical settings.

Translatome analysis in acute ischemic stroke: Astrocytes and microglia exhibit differences in poststroke alternative splicing of expressed transcripts

Astrocytes and microglia undergo dynamic and complex morphological and functional changes following ischemic stroke, which are instrumental in both inflammatory responses and neural repair. While gene expression alterations poststroke have been extensively studied, investigations into posttranscriptional regulatory mechanisms, specifically alternative splicing (AS), remain limited. Utilizing previously reported Ribo-Tag-seq data, this study analyzed AS alterations in poststroke astrocytes and microglia from young adult male and female mice. Our findings reveal that in astrocytes, compared to the sham group, 109 differential alternative splicing (DAS) events were observed at 4 h poststroke, which increased to 320 at day 3. In microglia, these numbers were 316 and 266, respectively. Interestingly, the disparity between DAS genes and differentially expressed genes is substantial, with fewer than 10 genes shared at both poststroke time points in astrocytes and microglia. Gene ontology enrichment analysis revealed the involvement of these DAS genes in diverse functions, encompassing immune response (Adam8, Ccr1), metabolism (Acsl6, Pcyt2, Myo5a), and developmental cell growth (App), among others. Selective DAS events were further validated by semiquantitative RT-PCR. Overall, this study comprehensively describes the AS alterations in astrocytes and microglia during the hyperacute and acute phases of ischemic stroke and underscores the significance of certain hub DAS events in neuroinflammatory processes.

Astrocyte modulation in cerebral ischemia-reperfusion injury: A promising therapeutic strategy

Cerebral ischemia-reperfusion injury (CIRI) poses significant challenges for drug development due to its complex pathogenesis. Astrocyte involvement in CIRI pathogenesis has led to the development of novel astrocyte-targeting drug strategies. To comprehensively review the current literature, we conducted a thorough analysis from January 2012 to December 2023, identifying 82 drugs aimed at preventing and treating CIRI. These drugs target astrocytes to exert potential benefits in CIRI, and their primary actions include modulation of relevant signaling pathways to inhibit neuroinflammation and oxidative stress, reduce cerebral edema, restore blood-brain barrier integrity, suppress excitotoxicity, and regulate autophagy. Notably, active components from traditional Chinese medicines (TCM) such as Salvia miltiorrhiza, Ginkgo, and Ginseng exhibit these important pharmacological properties and show promise in the treatment of CIRI. This review highlights the potential of astrocyte-targeted drugs to ameliorate CIRI and categorizes them based on their mechanisms of action, underscoring their therapeutic potential in targeting astrocytes.

Acorus tatarinowii oils exert protective effects on microglia-mediated inflammatory injury via restoring gut microbiota composition in experimental stroke rats

Growing evidence has demonstrated that gut microbiota could be developed as a therapeutic target due to its contribution to microglia activation in the pathological process of ischemic stroke. Acorus tatarinowii oils (AT oils), which is considered as the active fraction of a traditional Chinese herbal medicine Acorus tatarinowii, exerts various bioactivities and prebiotic effects. However, it remains unclear that the effect of AT oils on inflammatory response after ischemic stroke and whether its underlying mechanism is associated to gut microbiota and the intestinal barrier. In the current study, we aim to investigate the anti-microglial neuroinflammation mechanism of AT oils in a middle cerebral artery occlusion model of ischemic stroke. The compositions of AT oils were identified by GC-MS. Our results demonstrated that AT oils could effectively relieve cerebral infarction, inhibit neuronal apoptosis, degrade the release of pro-inflammatory factors (TNF-α, IL-17, IL-6 and IFN-γ), and mediate the polarization of microglia. Moreover, AT oils restored the composition and the balance of gut microbiota in stroke rats, and reduced abundance of opportunistic genera including Verrucomicrobia, Akkermansia and Tenericutes, as well as increased beneficial bacteria abundance such as Tenericutes and Prevotella_copri. To investigate the role of gut microbiota on AT oils against ischemic stroke, we conducted the fecal microbiota transplantation (FMT) experiments with gut microbiota consumption, which suggested that the depletion of gut microbiota took away the protective effect of AT oils, confirming the importance of gut microbiota in the protective effect of AT oils on ischemic stroke. FMT experiments have demonstrated that AT oils preserved the gut permeability and blood-brain barrier, as well as mediated the microglial phenotype under the intervention of gut microbiota. In summary, AT oils could efficaciously moderate neuronal damage and intervene microglial phenotype by reversing gut microbiota disorder in ischemic stroke rats.

Role of microglia in stroke

Microglia play key roles in the post-ischemic inflammatory response and damaged tissue removal reacting rapidly to the disturbances caused by ischemia and working to restore the lost homeostasis. However, the modified environment, encompassing ionic imbalances, disruption of crucial neuron-microglia interactions, spreading depolarization, and generation of danger signals from necrotic neurons, induce morphological and phenotypic shifts in microglia. This leads them to adopt a proinflammatory profile and heighten their phagocytic activity. From day three post-ischemia, macrophages infiltrate the necrotic core while microglia amass at the periphery. Further, inflammation prompts a metabolic shift favoring glycolysis, the pentose-phosphate shunt, and lipid synthesis. These shifts, combined with phagocytic lipid intake, drive lipid droplet biogenesis, fuel anabolism, and enable microglia proliferation. Proliferating microglia release trophic factors contributing to protection and repair. However, some microglia accumulate lipids persistently and transform into dysfunctional and potentially harmful foam cells. Studies also showed microglia that either display impaired apoptotic cell clearance, or eliminate synapses, viable neurons, or endothelial cells. Yet, it will be essential to elucidate the viability of engulfed cells, the features of the local environment, the extent of tissue damage, and the temporal sequence. Ischemia provides a rich variety of region- and injury-dependent stimuli for microglia, evolving with time and generating distinct microglia phenotypes including those exhibiting proinflammatory or dysfunctional traits and others showing pro-repair features. Accurate profiling of microglia phenotypes, alongside with a more precise understanding of the associated post-ischemic tissue conditions, is a necessary step to serve as the potential foundation for focused interventions in human stroke.

CSF1R blockade slows progression of cerebral hemorrhage by reducing microglial proliferation and increasing infiltration of CD8 + CD122+ T cells into the brain

Microglia play a pivotal role in the neuroinflammatory response after brain injury, and their proliferation is dependent on colony-stimulating factors. In the present study, we investigated the effect of inhibiting microglia proliferation on neurological damage post intracerebral hemorrhage (ICH) in a mouse model, an aspect that has never been studied before. Using a colony-stimulating factor-1 receptor antagonist (GW2580), we observed that inhibition of microglia proliferation significantly ameliorated neurobehavioral deficits, attenuated cerebral edema, and reduced hematoma volume after ICH. This intervention was associated with a decrease in pro-inflammatory factors in microglia and an increased infiltration of peripheral regulatory CD8 + CD122+ T cells into the injured brain tissue. The CXCR3/CXCL10 axis is the mechanism of brain homing of regulatory CD8 + CD122+ T cells, and the high expression of IL-10 is the hallmark of their synergistic anti-inflammatory effect with microglia. And activated astrocytes around the insult site are a prominent source of CXCL10. Thus, inhibition of microglial proliferation offers a new perspective for clinical translation. The cross-talk between multiple cells involved in the regulation of the inflammatory response highlights the comprehensive nature of neuroimmunomodulation.

Evaluating CXCL12 for Effects on Reactive Gene Expression in Primary Astrocytes

Upon injury to the CNS, astrocytes undergo morphological and functional changes commonly referred to as astrocyte reactivity. Notably, these reactive processes include altered expression of factors that control immune processes and neuronal survival, as well as increased expression of the CXCL12 receptor, CXCR7/ACKR3. We now asked whether these events are related in that the astrocytic CXCL12 system modulates immune responses and/or neuronal survival. Short-term exposure of astrocytes cultured from the postnatal rat cortex to CXCL12 prominently increased the expression of serpine1/PAI1 on the mRNA level, but showed either no or only minor effects on the expression of additional reactive genes, selected from previous array studies. CXCL12-induced increases in PAI1 protein levels were only detectable in the additional presence of chemokines/cytokines, suggesting that translation of serpine1 mRNA depends on the cooperation of various factors. As expected, expression of most of the selected genes increased after acute or chronic activation of astrocytes with either LPS or a combination of IL-1β and TNFα. CXCL12 partially attenuated expression of some of the LPS and IL-1β/TNFα-induced genes under acute conditions, in particular those encoding CXCL9, CXCL10, CXCL11, and CCL5. Taken together, these findings argue for the involvement of the astrocyte CXCL12 system in the control of the immune response of the injured CNS, where it may control distinct steps.

Histone deacetylase inhibition by suberoylanilide hydroxamic acid during reperfusion promotes multifaceted brain and vascular protection in spontaneously hypertensive rats with transient ischaemic stroke

Hypertension is the most prevalent modifiable risk factor for stroke and is associated with worse functional outcomes. Pharmacological inhibition of histone deacetylases by suberoylanilide hydroxamic acid (SAHA) modulates gene expression and has emerged as a promising therapeutic approach to reduce ischaemic brain injury. Here, we have tested the therapeutic potential of SAHA administered during reperfusion in adult male spontaneously hypertensive (SHR) rats subjected to transient middle cerebral artery occlusion (tMCAO; 90 min occlusion/24 h reperfusion). Animals received a single dose of SAHA (50 mg/kg) or vehicle i.p. at 1, 4, or 6 h after reperfusion onset. The time-course of brain histone H3 acetylation was studied. After tMCAO, drug brain penetrance and beneficial effects on behavioural outcomes, infarct volume, oedema, angiogenesis, blood-brain barrier integrity, cerebral artery oxidative stress and remodelling, and brain and vascular inflammation were evaluated. SAHA increased brain histone H3 acetylation from 1 to 6 h after injection, reaching the ischaemic brain administered during reperfusion. Treatment given at 4 h after reperfusion onset improved neurological score, reduced infarct volume and oedema, attenuated microglial activation, prevented exacerbated MCA angiogenic sprouting and blood-brain barrier breakdown, normalised MCA oxidative stress and remodelling, and modulated brain and cerebrovascular cytokine expression. Overall, we demonstrate that SAHA administered during early reperfusion exerts robust brain and vascular protection after tMCAO in hypertensive rats. These findings are aligned with previous research in ischaemic normotensive mice and help pave the way to optimise the design of clinical trials assessing the effectiveness and safety of SAHA in ischaemic stroke.