DJ-1 Regulates Microglial Polarization Through P62-Mediated TRAF6/IRF5 Signaling in Cerebral Ischemia-Reperfusion

Crosstalk Among Glial Cells in the Blood-Brain Barrier Injury After Ischemic Stroke

Blood-brain barrier (BBB) is comprised of brain microvascular endothelial cells (ECs), astrocytes, perivascular microglia, pericytes, neuronal processes, and the basal lamina. As a complex and dynamic interface between the blood and the central nervous system (CNS), BBB is responsible for transporting nutrients essential for the normal metabolism of brain cells and hinders many toxic compounds entering into the CNS. The loss of BBB integrity following stroke induces tissue damage, inflammation, edema, and neural dysfunction. Thus, BBB disruption is an important pathophysiological process of acute ischemic stroke. Understanding the mechanism underlying BBB disruption can uncover more promising biological targets for developing treatments for ischemic stroke. Ischemic stroke-induced activation of microglia and astrocytes leads to increased production of inflammatory mediators, containing chemokines, cytokines, matrix metalloproteinases (MMPs), etc., which are important factors in the pathological process of BBB breakdown. In this review, we discussed the current knowledges about the vital and dual roles of astrocytes and microglia on the BBB breakdown during ischemic stroke. Specifically, we provided an updated overview of phenotypic transformation of microglia and astrocytes, as well as uncovered the crosstalk among astrocyte, microglia, and oligodendrocyte in the BBB disruption following ischemic stroke.

CD147 Sparks Atherosclerosis by Driving M1 Phenotype and Impairing Efferocytosis

BACKGROUND

Atherosclerosis is a globally prevalent chronic inflammatory disease with high morbidity and mortality. The development of atherosclerotic lesions is determined by macrophages. This study aimed to investigate the specific role of myeloid-derived CD147 (cluster of differentiation 147) in atherosclerosis and its translational significance.

METHODS AND RESULTS

We generated mice with a myeloid-specific knockout of CD147 and mice with restricted CD147 overexpression, both in an apoE-deficient (ApoE-/-) background. Here, the myeloid-specific deletion of CD147 ameliorated atherosclerosis and inflammation. Consistent with our in vivo data, macrophages isolated from myeloid-specific CD147 knockout mice exhibited a phenotype shift from proinflammatory to anti-inflammatory macrophage polarization in response to lipopolysaccharide/IFN (interferon)-γ. These macrophages demonstrated a weakened proinflammatory macrophage phenotype, characterized by reduced production of NO and reactive nitrogen species derived from iNOS (inducible NO synthase). Mechanistically, the TRAF6 (tumor necrosis factor receptor-associated factor 6)-IKK (inhibitor of κB kinase)-IRF5 (IFN regulatory factor 5) signaling pathway was essential for the effect of CD147 on proinflammatory responses. Consistent with the reduced size of the necrotic core, myeloid-specific CD147 deficiency diminished the susceptibility of iNOS-mediated late apoptosis, accompanied by enhanced efferocytotic capacity mediated by increased secretion of GAS6 (growth arrest-specific 6) in proinflammatory macrophages. These findings were consistent in a mouse model with myeloid-restricted overexpression of CD147. Furthermore, we developed a new atherosclerosis model in ApoE-/- mice with humanized CD147 transgenic expression and demonstrated that the administration of an anti-human CD147 antibody effectively suppressed atherosclerosis by targeting inflammation and efferocytosis.

CONCLUSIONS

Myeloid CD147 plays a crucial role in the growth of plaques by promoting inflammation in a TRAF6-IKK-IRF5-dependent manner and inhibiting efferocytosis by suppressing GAS6 during proinflammatory conditions. Consequently, the use of anti-human CD147 antibodies presents a complementary therapeutic approach to the existing lipid-lowering strategies for treating atherosclerotic diseases.

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

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

Park7 protects retinal ganglion cells and promotes functional preservation after optic nerve crush via regulation of the Nrf2 signaling pathway

PURPOSE

We aim to investigate the effect of Park7 on mice RGC survival and function following optic nerve crush (ONC), and to explore its potential mechanism.

METHODS

Wild-type male C57BL/6J mice were subjected to optic nerve crush. Six weeks before ONC, mice received rAAV-shRNA (Park7)-EGFP or rAAV-EGFP intravitreally. Western blotting was used to detect Park7 levels. RGC survival was measured using immunofluorescence. Retinal cell apoptosis was detected using terminal deoxynucleotidyl transferase nick-end-labelling. An electroretinogram (ERG) and the optomotor response (OMR) were used to assess RGC function. Kelch-like ECH-associated protein 1 (Keap1), nuclear factor erythroid 2-related factor (Nrf2), and heme oxygenase 1 (HO-1) levels were assessed using western blotting.

RESULTS

ONC injury increased the relative expression of Park7 significantly and decreased RGC survival, the amplitude of the photopic negative response (PhNR), and OMR. Intravitreal injection of rAAV-shRNA(Park7)-EGFP downregulated Park7 expression and was clearly demonstrated by the green fluorescence protein in many retinal layers. Moreover, Park7 downregulation aggravated the decrease in RGC survival and amplitude of PhNR as well as the visual acuity after ONC. However, inhibition of Park7 significantly increased Keap1 levels, decreased the total and nuclear Nrf2 levels, and reduced HO-1 levels.

CONCLUSIONS

Park7 downregulation enhanced RGC injury and decreased retinal electrophysiological response and OMR after ONC in mice via the Keap1-Nrf2-HO-1 signaling pathway. Park7 may have neuroprotective effects and could represent a novel way to treat optic neuropathy.

DJ-1 inhibits ferroptosis in cerebral ischemia-reperfusion via ATF4/HSPA5 pathway

DJ-1 has been confirmed to have neuroprotective effects. Ferroptosis is an iron-dependent programmed cell death mode associated with ischemic stroke. The ATF4/HSPA5 pathway has been shown to play an important role in the regulation of ferroptosis. To explore the role and possible mechanism of DJ-1 in regulating ferroptosis in cerebral ischemia-reperfusion injury. In this study, Middle cerebral artery occlusion/reperfusion (MCAO/R) was used to simulate cerebral ischemia-reperfusion injury in vivo. Detected ferroptosis-related indicators and observed mitochondrial morphology in brain tissue using transmission electron microscopy. ATF4 was subsequently interfered to observe the effect of DJ-1 on ferroptosis. The results suggest that after interfering with DJ-1, the iron content and malondialdehyde (MDA) content of ferroptosis-related indicators increased, the GSH content decreased, and the mitochondrial structure was severely damaged. We then found that DJ-1 attenuated ferroptosis following ATF4 reduction. In this study, we found that the neuroprotective effect of DJ-1 is related to the inhibition of ferroptosis, and its molecular mechanism is closely related to the ATF4/HSPA5 pathway, which may play a key role in inhibiting brain ischemia-reperfusion (I/R) ferroptosis.

Long-term iTBS Improves Neural Functional Recovery by Reducing the Inflammatory Response and Inhibiting Neuronal Apoptosis Via miR-34c-5p/p53/Bax Signaling Pathway in Cerebral Ischemic Rats

To investigate intermittent theta-burst stimulation (iTBS) effect on ischemic stroke and the underlying mechanism of neurorehabilitation, we developed an ischemia/reperfusion (I/R) injury model in Sprague-Dawley (SD) rats using the middle cerebral artery occlusion/reperfusion (MCAO/r) method. Next, using different behavioral studies, we compared the improvement of the whole organism with and without iTBS administration for 28 days. We further explored the morphological and molecular biological alterations associated with neuronal apoptosis and neuroinflammation by TTC staining, HE staining, Nissl staining, immunofluorescence staining, ELISA, small RNA sequencing, RT-PCR, and western blot assays. The results showed that iTBS significantly protected against neurological deficits and neurological damage induced by cerebral I/R injury. iTBS also significantly decreased brain infarct volume and increased the number of surviving neurons after 28 days. Additionally, it was observed that iTBS decreased synaptic loss, suppressed activation of astrocytes and M1-polarized microglia, and simultaneously promoted M2-polarized microglial activation. Furthermore, iTBS intervention inhibited neuronal apoptosis and exerted a positive impact on the neuronal microenvironment by reducing neuroinflammation in cerebral I/R injured rats. To further investigate the iTBS mechanism, this study was conducted using small RNA transcriptome sequencing of various groups of peri-infarcted tissues. Bioinformatics analysis and RT-PCR discovered the possible involvement of miR-34c-5p in the mechanism of action. The target genes prediction and detection of dual-luciferase reporter genes confirmed that miR-34c-5p could inhibit neuronal apoptosis in cerebral I/R injured rats by regulating the p53/Bax signaling pathway. We also confirmed by RT-PCR and western blotting that miR-34c-5p inhibited Bax expression. In conclusion, our study supports that iTBS is vital in inhibiting neuronal apoptosis in cerebral I/R injured rats by mediating the miR-34c-5p involvement in regulating the p53/Bax signaling pathway.

Loureirin B protects against cerebral ischemia/reperfusion injury through modulating M1/M2 microglial polarization via STAT6 / NF-kappaB signaling pathway

The latest research indicates that modulating microglial polarization from M1 to M2 phenotype may be a coping therapy for ischemic stroke. The present study thereby evaluated the effects of loureirin B (LB), a monomer compound extracted from Sanguis Draconis flavones (SDF), on cerebral ischemic injury and the potential mechanisms. The middle cerebral artery occlusion (MCAO) model was established in male Sprague-Dawley rats to induce cerebral ischemia/reperfusion (I/R) injury in vivo, and BV2 cells were exposed to oxygen-glucose deprivation and reintroduction (OGD/R) to mimic cerebral I/R injury in vitro. The results showed that LB significantly reduced infarct volume, neurological deficits and neurobehavioral deficits, apparently improved histopathological changes and neuronal loss in cortex and hippocampus of MCAO/R rats, markedly decreased the proportion of M1 microglia cells and the level of pro-inflammatory cytokines, and increased the proportion of M2 microglia and the level of anti-inflammatory cytokines both in vivo and in vitro. In addition, LB evidently improved the p-STAT6 expression and reduced the NF-κB (p-p65) expression after cerebral I/R injury in vivo and in vitro. IL-4 (a STAT6 agonist) exhibited a similar impact to that of LB, while AS1517499 (a STAT6 inhibitor) significantly reversed the effect of LB on BV-2 cells after OGD/R. These findings point to the protection of LB against cerebral I/R injury by modulating M1/M2 polarization of microglia via the STAT6/NF-κB signaling pathway, hence LB may be a viable treatment option for ischemic stroke.

DJ-1 Protein Inhibits Apoptosis in Cerebral Ischemia by Regulating the Notch1 and Nuclear Factor Erythroid2-Related Factor 2 Signaling Pathways

DJ-1 plays a neuroprotective role in cerebral ischemia- reperfusion (I/R) injury and participates in the apoptosis of brain nerve cells, but the underlying mechanism is unclear. We explored the molecular pathways underlying this role using in vivo and in vitro approaches. Middle cerebral artery occlusion- reperfusion (MCAO/R) rat models and oxygen- glucose deprivation- reoxygenation (OGD/R) HAPI cell cultures were used to simulate cerebral ischemia-reperfusion injury. The interaction between DJ-1 and Notch1 was enhanced after MCAO/R in rats. After treatment of rats with DJ-1 siRNA, the expression of Notch1 and Nrf2 was down-regulated, and apoptosis was promoted. In contrast, the DJ-1 based peptide ND-13 upregulated the expression of Notch1 and Nrf2, and prevented apoptosis. In vitro, the Notch1 signaling pathway inhibitor DAPT reversed the neuroprotective effect of ND-13 and promoted apoptosis, weakened the interaction between DJ-1 and Notch1, and decreased the expression of proteins in the Notch1 and Nrf2 pathways. Thus, we found that DJ-1 inhibits apoptosis by regulating the Notch1 signaling pathway and Nrf2 expression in cerebral I/R injury. These results imply that DJ-1 is a potential therapeutic target for cerebral I/R injury.

DJ-1 Alleviates Neuroinflammation and the Related Blood-Spinal Cord Barrier Destruction by Suppressing NLRP3 Inflammasome Activation via SOCS1/Rac1/ROS Pathway in a Rat Model of Traumatic Spinal Cord Injury

DJ-1 has been shown to play essential roles in neuronal protection and anti-inflammation in nervous system diseases. This study aimed to explore how DJ-1 regulates neuroinflammation after traumatic spinal cord injury (t-SCI). The rat model of spinal cord injury was established by the clamping method. The Basso, Beattie, Bresnahan (BBB) score and the inclined plane test (IPT) were used to evaluate neurological function. Western blot was then applied to test the levels of DJ-1, NLRP3, SOCS1, and related proinflammatory factors (cleaved caspase 1, IL-1β and IL-18); ROS level was also examined. The distribution of DJ-1 was assessed by immunofluorescence staining (IF). BSCB integrity was assessed by the level of MMP-9 and tight junction proteins (Claudin-5, Occludin and ZO-1). We found that DJ-1 became significantly elevated after t-SCI and was mainly located in neurons. Knockdown of DJ-1 with specific siRNA aggravated NLRP3 inflammasome-related neuroinflammation and strengthened the disruption of BSCB integrity. However, the upregulation of DJ-1 by Sodium benzoate (SB) reversed these effects and improved neurological function. Furthermore, SOCS1-siRNA attenuated the neuroprotective effects of DJ-1 and increased the ROS, Rac1 and NLRP3. In conclusion, DJ-1 may alleviate neuroinflammation and the related BSCB destruction after t-SCI by suppressing NLRP3 inflammasome activation by SOCS1/Rac1/ROS pathways. DJ-1 shows potential as a feasible target for mediating neuroinflammation after t-SCI.

Long Non-coding RNA ANRIL Downregulation Alleviates Neuroinflammation in an Ischemia Stroke Model via Modulation of the miR-671-5p/NF-κB Pathway

The aim of this study was to investigate the role and underlying mechanism of the long non-coding RNA ANRIL (antisense noncoding RNA in the INK4 locus, ANRIL) in ischemia stroke (IS) injury. Downregulation of ANRIL by right intracerebroventricular injected si-ANRIL in middle cerebral artery occlusion-reperfusion (MCAO/R) C57/BL6 mice and by transferring si-ANRIL in oxygen glucose deprivation/reperfusion (OGD/R) HT22 cells. The results showed that ANRIL levels increased in IS model, downregulation of ANRIL reduced infract area, neurological deficit scores and injured cells, and prolong fall latency time in MCAO/R mice, improved cell viability and reduced cell cytotoxicity in OGD/R cells. Fluorescence in Situ Hybridization detected that there were both ANRIL and miR-671-5p in neurons; miranda v3.3a and dual luciferase reporter assay demonstrated that miR-671-5p was one of direct target of ANRIL; and our previously published research demonstrated that NF-κB was one of direct target of miR-671-5p. Downregulation of ANRIL alleviated neuroinflammation and reduced p-NF-κB, NF-κB, pro-inflammatory cytokines (IL-1β, IL-6, TNF-a), and iNOS, which diminished by miR-671-5p antagomir both in in vivo and in vitro IS models. Downregulation of ANRIL alleviated disruption of blood brain barrier, and protected against tight junction (ZO-1, occludin and claudin 5) disorder in MCAO/R mice. This work clarified that downregulation of ANRIL reduced neuroinflammation by negatively regulating miR-671-5p to inhibit NF-κB in IS models, which provided a theoretical foundation for the protective effect of downregulating ANRIL for IS patients.

A Primeval Mechanism of Tolerance to Desiccation Based on Glycolic Acid Saves Neurons in Mammals from Ischemia by Reducing Intracellular Calcium-Mediated Excitotoxicity

Stroke is the second leading cause of death and disability worldwide. Current treatments, such as pharmacological thrombolysis or mechanical thrombectomy, reopen occluded arteries but do not protect against ischemia-induced damage that occurs before reperfusion or neuronal damage induced by ischemia/reperfusion. It has been shown that disrupting the conversion of glyoxal to glycolic acid (GA) results in a decreased tolerance to anhydrobiosis in Caenorhabditis elegans dauer larva and that GA itself can rescue this phenotype. During the process of desiccation/rehydration, a metabolic stop/start similar to the one observed during ischemia/reperfusion occurs. In this study, the protective effect of GA is tested in different ischemia models, i.e., in commonly used stroke models in mice and swine. The results show that GA, given during reperfusion, strongly protects against ischemic damage and improves functional outcome. Evidence that GA exerts its effect by counteracting the glutamate-dependent increase in intracellular calcium during excitotoxicity is provided. These results suggest that GA treatment has the potential to reduce mortality and disability in stroke patients.

Dexmedetomidine exerts cerebral protective effects against cerebral ischemic injury by promoting the polarization of M2 microglia via the Nrf2/HO-1/NLRP3 pathway

INTRODUCTION

Cerebral ischemic injury is associated with long-term disability. Dexmedetomidine (Dex) can exert neuroprotective effects on cerebral ischemic/reperfusion injury. The present study explored the mechanism of Dex in cerebral ischemic injury.

MATERIALS AND METHODS

To this end, the permanent middle cerebral artery occlusion (p-MCAO) mouse model was established and treated with Dex or/and Nrf2 inhibitor ML385. Subsequently, microglia were subjected to oxygen-glucose deprivation (OGD) in sugar-free environment and thereafter treated with Dex, Nrf2 inhibitor, and NLRP3 lentiviral overexpression vector, respectively.

RESULTS

Dex alleviated the neurobehavioral deficit of p-MCAO mice, reduced brain water content, relieved pathological changes, and reduced cerebral infarction size. Dex promoted the polarization of microglia from M1 to M2, thus ameliorating oxidative stress and inflammatory responses. Our results showed that Dex promoted M2-polarization of microglia in vivo and in vitro by promoting HO-1 expression via Nrf2 nuclear import. Moreover, the Nrf2/HO-1 axis inhibited the activation of NLRP2 inflammasome and NLRP3 overexpression reversed the effect of Dex.

CONCLUSION

In conclusion, Dex promoted M2-polarization of microglia and attenuated oxidative stress and inflammation, and thus protected against cerebral ischemic injury by activating the Nrf2/HO-1 pathway and inhibiting NLRP3 inflammasome.

Ginkgo biloba leaf extract (EGb-761) elicits neuroprotection against cerebral ischemia/reperfusion injury by enhancement of autophagy flux in neurons in the penumbra

Objective(s):

Ginkgo biloba leaf extract (EGb-761) injection has been widely used as adjuvant therapy for cerebral stroke in China. However, its underlying pharmacological mechanism is not completely understood. The present study aimed to investigate whether the therapeutic effects of EGb-761 are exerted by modulating autophagy flux.

Materials and Methods:

Ischemic cerebral stroke was prepared in male Sprague-Dawley rats by middle cerebral artery occlusion (MCAO) followed by reperfusion. The MCAO/reperfusion rats were then treated with EGb-761 injection once daily for 7 days. Thereafter, the brain tissues in the ischemic penumbra were obtained to detect the key proteins in the autophagic/lysosomal pathway with Beclin1, LC3, (SQSTM1)/p62, ubiquitin, LAMP-1, cathepsin B, and cathepsin D antibodies by western blot and immunofluorescence. Meanwhile, the infarct volume, neurological deficits, and neuronal apoptosis were assessed to evaluate the therapeutic outcomes.

Results:

The results illustrated that EGb-761 treatment was not only able to promote the autophagic activities of Beclin1 and LC3-II in neurons, but also could enhance the autophagic clearance, as indicated by reinforced lysosomal activities of LAMP-1, cathepsin B, and cathepsin D, as well as alleviating autophagic accumulation of ubiquitin and insoluble p62 in the MCAO+EGb-761 group, compared with those in the MCAO+saline group. Meanwhile, cerebral ischemia-induced neurological deficits, infarct volume, and neuronal apoptosis were significantly attenuated by 7 days of EGb-761 therapy.

Conclusion:

Our data suggest that EGb-761 injection can elicit a neuroprotective efficacy against MCAO/reperfusion injury, and this neuroprotection may be exerted by enhancement of autophagy flux in neurons in the ischemic penumbra.

The Pathogenesis of Parkinson's Disease: A Complex Interplay Between Astrocytes, Microglia, and T Lymphocytes?

Parkinson's disease (PD), the second most common neurodegenerative disease, is characterised by the motor symptoms of bradykinesia, rigidity and resting tremor and non-motor symptoms of sleep disturbances, constipation, and depression. Pathological hallmarks include neuroinflammation, degeneration of dopaminergic neurons in the substantia nigra pars compacta, and accumulation of misfolded α-synuclein proteins as intra-cytoplasmic Lewy bodies and neurites. Microglia and astrocytes are essential to maintaining homeostasis within the central nervous system (CNS), including providing protection through the process of gliosis. However, dysregulation of glial cells results in disruption of homeostasis leading to a chronic pro-inflammatory, deleterious environment, implicated in numerous CNS diseases. Recent evidence has demonstrated a role for peripheral immune cells, in particular T lymphocytes in the pathogenesis of PD. These cells infiltrate the CNS, and accumulate in the substantia nigra, where they secrete pro-inflammatory cytokines, stimulate surrounding immune cells, and induce dopaminergic neuronal cell death. Indeed, a greater understanding of the integrated network of communication that exists between glial cells and peripheral immune cells may increase our understanding of disease pathogenesis and hence provide novel therapeutic approaches.