Microglia-associated neuroinflammation is a potential therapeutic target for ischemic stroke

TRIM45 causes neuronal damage by aggravating microglia-mediated neuroinflammation upon cerebral ischemia and reperfusion injury

Excessive and unresolved neuroinflammation is a key component of the pathological cascade in brain injuries such as ischemic stroke. Tripartite motif-containing 45 (TRIM45) is a ubiquitin E3 ligase involved in various critical biological processes. However, the role of TRIM45 in cerebral ischemia remains unknown. Here, we found that the TRIM45 protein was highly expressed in the peri-infarct areas of mice subjected to cerebral ischemia and reperfusion injury induced by middle cerebral artery occlusion. This study systemically evaluated the putative role of TRIM45 in the regulation of neuroinflammation during ischemic injury and the potential underlying mechanisms. We found that TRIM45 knockdown significantly decreased proinflammatory cytokine and chemokine production in primary cultured microglia challenged with oxygen-glucose deprivation and reoxygenation (OGD/R) treatment. Mechanistically, we demonstrated that TRIM45 constitutively interacted with TAB2 and consequently facilitated the Lys-63-linked polyubiquitination of TAB2, leading to the formation of the TAB1-TAK1-TAB2 complex and activation of TAK1, which was ultimately followed by activation of the nuclear factor-kappa B (NF-κB) signaling pathway. In an in vitro coculture Transwell system, downregulation of TRIM45 expression also inhibited the OGD/R-induced activation of microglia and alleviated neuronal apoptosis. More importantly, microglia-specific knockdown of TRIM45 in mice significantly reduced the infarct size, mitigated neurological deficit scores, and improved cognitive function after ischemic stroke. Taken together, our study reveals that the TRIM45-TAB2 axis is a crucial checkpoint that controls NF-κB signaling in microglia during cerebral ischemia and reperfusion injury. Therefore, targeting TRIM45 may be an attractive therapeutic strategy.

Functional tissue-engineered microtissue formed by self-aggregation of cells for peripheral nerve regeneration

Background

Peripheral nerve injury (PNI) is one of the essential causes of physical disability with a high incidence rate. The traditional tissue engineering strategy, Top-Down strategy, has some limitations. A new tissue-engineered strategy, Bottom-Up strategy (tissue-engineered microtissue strategy), has emerged and made significant research progress in recent years. However, to the best of our knowledge, microtissues are rarely used in neural tissue engineering; thus, we intended to use microtissues to repair PNI.

Methods

We used a low-adhesion cell culture plate to construct adipose-derived mesenchymal stem cells (ASCs) into microtissues in vitro, explored the physicochemical properties and microtissues components, compared the expression of cytokines related to nerve regeneration between microtissues and the same amount of two-dimension (2D)-cultured cells, co-cultured directly microtissues with dorsal root ganglion (DRG) or Schwann cells (SCs) to observe the interaction between them using immunocytochemistry, quantitative reverse transcription polymerase chain reaction (qRT-PCR), enzyme-linked immunosorbent assay (ELISA). We used grafts constructed by microtissues and polycaprolactone (PCL) nerve conduit to repair sciatic nerve defects in rats.

Results

The present study results indicated that compared with the same number of 2D-cultured cells, microtissue could secrete more nerve regeneration related cytokines to promote SCs proliferation and axons growth. Moreover, in the direct co-culture system of microtissue and DRG or SCs, axons of DRG grown in the direction of microtissue, and there seems to be a cytoplasmic exchange between SCs and ASCs around microtissue. Furthermore, microtissues could repair sciatic nerve defects in rat models more effectively than traditional 2D-cultured ASCs.

Conclusion

Tissue-engineered microtissue is an effective strategy for stem cell culture and therapy in nerve tissue engineering.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02676-0.

Allicin, an Antioxidant and Neuroprotective Agent, Ameliorates Cognitive Impairment

Allicin (diallylthiosulfinate) is a defense molecule produced by cellular contents of garlic (Allium sativum L.). On tissue damage, the non-proteinogenic amino acid alliin (S-allylcysteine sulfoxide) is converted to allicin in an enzyme-mediated process catalysed by alliinase. Allicin is hydrophobic in nature, can efficiently cross the cellular membranes and behaves as a reactive sulfur species (RSS) inside the cells. It is physiologically active molecule with the ability to oxidise the thiol groups of glutathione and between cysteine residues in proteins. Allicin has shown anticancer, antimicrobial, antioxidant properties and also serves as an efficient therapeutic agent against cardiovascular diseases. In this context, the present review describes allicin as an antioxidant, and neuroprotective molecule that can ameliorate the cognitive abilities in case of neurodegenerative and neuropsychological disorders. As an antioxidant, allicin fights the reactive oxygen species (ROS) by downregulation of NOX (NADPH oxidizing) enzymes, it can directly interact to reduce the cellular levels of different types of ROS produced by a variety of peroxidases. Most of the neuroprotective actions of allicin are mediated via redox-dependent pathways. Allicin inhibits neuroinflammation by suppressing the ROS production, inhibition of TLR4/MyD88/NF-κB, P38 and JNK pathways. As an inhibitor of cholinesterase and (AChE) and butyrylcholinesterase (BuChE) it can be applied to manage the Alzheimer's disease, helps to maintain the balance of neurotransmitters in case of autism spectrum disorder (ASD) and attention deficit hyperactive syndrome (ADHD). In case of acute traumatic spinal cord injury (SCI) allicin protects neuron damage by regulating inflammation, apoptosis and promoting the expression levels of Nrf2 (nuclear factor erythroid 2-related factor 2). Metal induced neurodegeneration can also be attenuated and cognitive abilities of patients suffering from neurological diseases can be ameliorates by allicin administration.

Neuroprotective effect of herniarin following transient focal cerebral ischemia in rats

Ischemic stroke is a devastating central nervous disease. Despite extensive research in to this area, few innovative neuroprotective treatments have been presented. 7-methoxycoumarin, also known as herniarin, is a common natural coumarin in several plant species. This project examined the effects of the herniarin in rats subjected to the middle cerebral artery occlusion (MCAO). Herniarin at doses of 10 and 20 mg/kg was administered through intraperitoneal injection for 7 days before MCAO induction. Rats were subjected to a 30 min MCAO and a subsequent 24 h' reperfusion. 24 h after the termination of MCAO, neurologic outcome, volume of brain infarction, level of interleukin-1β (IL-1β) and tumor necrosis factor alpha (TNF-α), as inflammatory markers, and oxidative stress markers including levels of total thiol, malondialdehyde (MDA), and superoxide dismutase (SOD) activity were estimated. Herniarin administration decreased the MCAO-induced infarct volume and neurological deficits. Moreover, pretreatment with herniarin significantly decreased the levels of MDA while simultaneously increasing the level of total thiol and SOD activity in the brain tissues of MCAO rats. Moreover, herniarin pretreatment decreased the levels of IL-1β and TNF-α in the brain tissues of MCAO rats. These results suggest that herniarin presents beneficial effects against ischemic stroke, partly through the inhibition of oxidative stress and inflammation.

Baicalein ameliorates ischemic brain damage through suppressing proinflammatory microglia polarization via inhibiting the TLR4/NF-κB and STAT1 pathway

Microglial polarization mediated neuroinflammation plays an important role in the pathological process of stroke. The aim of this study is to determine whether baicalein indirectly ameliorates neuronal injury through modulating microglial polarization after stroke and if so, then by what mechanism. The effects of baicalein on microglial polarization were revealed through the middle cerebral artery occlusion mouse model (MCAO, n = 6), the lipopolysaccharide (LPS) + interferon-γ (IFN-γ) and oxygen-glucose deprivation (OGD) induced neuroinflammatory microglia model (BV2, n = 3), respectively. Mice were treated with baicalein (100 mg/kg, i.g.) after reperfusion, and followed by daily administrations for 3 days. Results showed that the infarct volumes at 3 d in vehicle and baicalein-treated MCAO mice were 91.18 ± 4.02% and 55.36 ± 4.10%. Baicalein improved sensorimotor functions (p < 0.01) after MCAO. Real-time PCR revealed that baicalein decreased proinflammatory markers expression (p < 0.05), while elevated the anti-inflammatory markers (p < 0.05) in vivo and in vitro. Both western blot and immunofluorescent staining further confirmed that baicalein reduced proinflammatory marker CD16 levels (p < 0.01) and enhanced anti-inflammatory marker CD206 or Arg-1 levels (p < 0.05). Notably, baicalein suppressed the release of proinflammatory cytokines (p < 0.05) and nitric oxide (NO, p < 0.001). Mechanistically, baicalein prevented increases in TLR4 protein levels (p < 0.001), the phosphorylation of IKBα and p65 (p < 0.01), and the nuclear translocation of NF-κB p65 (p < 0.05). The NF-κB inhibitor, BAY 11-7085, enhanced the inhibitory effect of baicalein on the proinflammatory microglial polarization. Baicalein also inhibited the phosphorylation of signal transducer and activator of transcription 1 (STAT1, p < 0.001). A microglia-neuron co-culture system revealed that baicalein driven neuroprotection against OGD induced neuronal damage through modulating microglial polarization (p < 0.05). Baicalein indirectly ameliorates neuronal injury after stroke by polarizing microglia toward the anti-inflammatory phenotype via inhibition of the TLR4/NF-κB pathway and down-regulation of phosphorylated STAT1, suggesting that baicalein might serve a potential therapy for stroke.

PDCD4 Simultaneously Promotes Microglia Activation via PDCD4-MAPK-NF-κB Positive Loop and Facilitates Neuron Apoptosis During Neuroinflammation

Neuroinflammation and neuron injury are common features of the central nervous system (CNS) diseases. It is of great significance to identify their shared key regulatory molecules and thus explore the potential therapeutic targets. Programmed cell death factor 4 (PDCD4), an apoptosis-related molecule, extensively participates in tumorigenesis and inflammatory diseases, but its expression and biological function during CNS neuroinflammation remain unclear. In the present study, utilizing the lipopolysaccharide (LPS)-induced neuroinflammation model in mice, we reported an elevated expression of PDCD4 both in injured neurons and activated microglia of the inflamed brain. A similar change in PDCD4 expression was observed in vitro in the microglial activation model. Silencing PDCD4 by shRNA significantly inhibited the phosphorylation of MAPKs (p38, ERK, and JNK), prevented the phosphorylation and nuclear translocation of NF-κB p65, and thus attenuated the LPS-induced microglial inflammatory activation. Interestingly, LPS also required the MAPK/NF-κB signaling activation to boost PDCD4 expression in microglia, indicating the presence of a positive loop. Moreover, a persistent elevation of PDCD4 expression was detected in the H₂O₂-induced neuronal oxidative damage model. Knocking down PDCD4 significantly inhibited the expression of pro-apoptotic proteins BAX and Cleaved-PARP, suggesting the proapoptotic activity of PDCD4 in neurons. Taken together, our data indicated that PDCD4 may serve as a hub regulatory molecule that simultaneously promotes the microglial inflammatory activation and the oxidative stress-induced neuronal apoptosis within CNS. The microglial PDCD4-MAPK-NF-κB positive feedback loop may act as pivotal signaling for neuroinflammation which subsequently exaggerates neuronal injury, and thus may become a potential therapeutic target for neuroinflammatory diseases.

MLIF Modulates Microglia Polarization in Ischemic Stroke by Targeting eEF1A1

Monocyte locomotion inhibitory factor (MLIF) is a heat-stable pentapeptide from Entamoeba histolytica. Our previous study found that MLIF protects against ischemic stroke in rats and mice and exerts a neuroprotection effect in human neuroblastoma SH-SY5Y cells. Microglia/macrophage polarization has been proven to be vital in the pathology of ischemic stroke. Nevertheless, whether MLIF is able to modulate microglia/macrophage polarization remains unclear. We performed middle cerebral artery occlusion (MCAO) on C57BL/6J male mice and induced cultured BV2 microglia by oxygen-glucose deprivation (OGD), respectively. Immunfluorescence was utilized to detect the M1/2 markers, such as CD206 and CD16/32. qPCR and ELISA were used to detect the signature gene change of M1/2. The MAPK and NF-κB pathway associated proteins were measured by Western blot. To identify the protein target of MLIF, a pull-down assay was performed. We found that MLIF promoted microglia transferring from a “sick” M1 phenotype to a “healthy” M2 phenotype in vivo or in vitro. Furthermore, we proved that eukaryotic elongation factor 1A1 (eEF1A1) was involved in the modulation of microglia/macrophage polarization. Knocking down eEF1A1 by siRNA exhibited the M1 promotion effect and M2 inhibition effect. Taken together, our results demonstrated MLIF modulated microglia/macrophage polarization by targeting eEF1A1 in ischemic stroke.

Research progress of stem cell therapy for ischemic stroke

Ischemic stroke is a serious cerebrovascular disease with high morbidity, disability and mortality. There is no doubt that the disease has a severe impact on the physical and mental health and quality of life of patients, as well as impose a heavy burden on families and societies. Unfortunately, there has been a lack of effective treatment. This overview reviews the pathophysiology of stem cell therapy in Ischemic stroke, and discuss its effects on neurogenesis, the latest clinical trials, and advances in tracking and monitoring of endogenous and exogenous stem cells.

Microglia as the Critical Regulators of Neuroprotection and Functional Recovery in Cerebral Ischemia

Microglial activation is considered as the critical pathogenic event in diverse central nervous system disorders including cerebral ischemia. Proinflammatory responses of activated microglia have been well reported in the ischemic brain and neuroinflammatory responses of activated microglia have been believed to be the potential therapeutic strategy. However, despite having proinflammatory roles, microglia can have significant anti-inflammatory roles and they are associated with the production of growth factors which are responsible for neuroprotection and recovery after ischemic injury. Microglia can directly promote neuroprotection by preventing ischemic infarct expansion and promoting functional outcomes. Indirectly, microglia are involved in promoting anti-inflammatory responses, neurogenesis, and angiogenesis in the ischemic brain which are crucial pathophysiological events for ischemic recovery. In fact, anti-inflammatory cytokines and growth factors produced by microglia can promote neuroprotection and attenuate neurobehavioral deficits. In addition, microglia regulate phagocytosis, axonal regeneration, blood-brain barrier protection, white matter integrity, and synaptic remodeling, which are essential for ischemic recovery. Microglia can also regulate crosstalk with neurons and other cell types to promote neuroprotection and ischemic recovery. This review mainly focuses on the roles of microglia in neuroprotection and recovery following ischemic injury. Furthermore, this review also sheds the light on the therapeutic potential of microglia in stroke patients.

Fyn Kinase Activity and Its Role in Neurodegenerative Disease Pathology: a Potential Universal Target?

Fyn is a non-receptor tyrosine kinase belonging to the Src family of kinases (SFKs) which has been implicated in several integral functions throughout the central nervous system (CNS), including myelination and synaptic transmission. More recently, Fyn dysfunction has been associated with pathological processes observed in neurodegenerative diseases, such as multiple sclerosis (MS), Alzheimer's disease (AD) and Parkinson's disease (PD). Neurodegenerative diseases are amongst the leading cause of death and disability worldwide and, due to the ageing population, prevalence is predicted to rise in the coming years. Symptoms across neurodegenerative diseases are both debilitating and degenerative in nature and, concerningly, there are currently no disease-modifying therapies to prevent their progression. As such, it is important to identify potential new therapeutic targets. This review will outline the role of Fyn in normal/homeostatic processes, as well as degenerative/pathological mechanisms associated with neurodegenerative diseases, such as demyelination, pathological protein aggregation, neuroinflammation and cognitive dysfunction.

The Slow-Releasing and Mitochondria-Targeted Hydrogen Sulfide (H2S) Delivery Molecule AP39 Induces Brain Tolerance to Ischemia

Ischemic stroke is the third leading cause of death in the world, which accounts for almost 12% of the total deaths worldwide. Despite decades of research, the available and effective pharmacotherapy is limited. Some evidence underlines the beneficial properties of hydrogen sulfide (H₂S) donors, such as NaSH, in an animal model of brain ischemia and in in vitro research; however, these data are ambiguous. This study was undertaken to verify the neuroprotective activity of AP39, a slow-releasing mitochondria-targeted H₂S delivery molecule. We administered AP39 for 7 days prior to ischemia onset, and the potential to induce brain tolerance to ischemia was verified. To do this, we used the rat model of 90-min middle cerebral artery occlusion (MCAO) and used LC-MS/MS, RT-PCR, Luminex^TM assays, Western blot and immunofluorescent double-staining to determine the absolute H₂S levels, inflammatory markers, neurotrophic factor signaling pathways and apoptosis marker in the ipsilateral frontal cortex, hippocampus and in the dorsal striatum 24 h after ischemia onset. AP39 (50 nmol/kg) reduced the infarct volume, neurological deficit and reduced the microglia marker (Iba1) expression. AP39 also exerted prominent anti-inflammatory activity in reducing the release of Il-1β, Il-6 and TNFα in brain areas particularly affected by ischemia. Furthermore, AP39 enhanced the pro-survival pathways of neurotrophic factors BDNF-TrkB and NGF-TrkA and reduced the proapoptotic proNGF-p75^NTR-sortilin pathway activity. These changes corresponded with reduced levels of cleaved caspase 3. Altogether, AP39 treatment induced adaptative changes within the brain and, by that, developed brain tolerance to ischemia.

Involvement of Microglia in the Pathophysiology of Intracranial Aneurysms and Vascular Malformations-A Short Overview

Aneurysms and vascular malformations of the brain represent an important source of intracranial hemorrhage and subsequent mortality and morbidity. We are only beginning to discern the involvement of microglia, the resident immune cell of the central nervous system, in these pathologies and their outcomes. Recent evidence suggests that activated proinflammatory microglia are implicated in the expansion of brain injury following subarachnoid hemorrhage (SAH) in both the acute and chronic phases, being also a main actor in vasospasm, considerably the most severe complication of SAH. On the other hand, anti-inflammatory microglia may be involved in the resolution of cerebral injury and hemorrhage. These immune cells have also been observed in high numbers in brain arteriovenous malformations (bAVM) and cerebral cavernomas (CCM), although their roles in these lesions are currently incompletely ascertained. The following review aims to shed a light on the most significant findings related to microglia and their roles in intracranial aneurysms and vascular malformations, as well as possibly establish the course for future research.

Upregulation of Neuronal Cylindromatosis Expression is Essential for Electroacupuncture-Mediated Alleviation of Neuroinflammatory Injury by Regulating Microglial Polarization in Rats Subjected to Focal Cerebral Ischemia/Reperfusion

Background

Activated microglia are polarized into the M1 or M2 phenotype. We previously reported that electroacupuncture (EA) effectively prevented nuclear factor-κB (NF-κB) nuclear translocation and improved neuronal C-X-C motif 3 chemokine ligand 1 (CX3CL1) expression, repressing microglial activation by upregulating neuronal cylindromatosis (CYLD) expression in the periischemic cortex. However, the potential mechanisms are unclear. Therefore, we explored whether EA improved CYLD protein expression to regulate microglial polarization-mediated neuroinflammation and the potential mechanisms in an ischemic stroke model.

Methods

A middle cerebral artery occlusion/reperfusion (MCAO/R) model was established in male Sprague-Dawley (SD) rats. The rats were treated with EA at the Baihui, Hegu and Taichong acupoints once daily beginning 2 h after focal cerebral ischemia. CYLD gene interference was used to investigate the role of CYLD in microglial polarization. We used neurobehavioral evaluations and TTC staining to examine the neuroprotective effect of EA via CYLD upregulation. Immunofluorescence and RT-qPCR were used to measure NLRP3 activation, M1/M2 microglial activation, pro-/anti-inflammatory gene mRNA expression and crosstalk (CX3CL1/CX3CR1 axis) between neurons and microglia. Western blotting was used to assess the underlying molecular mechanism.

Results

CYLD inhibited M1 microglial activation and improved M2 microglial activation after 72 h of reperfusion. CYLD overexpression decreased the NLRP3 mRNA level. CYLD suppressed microglial overactivation by inhibiting NLRP3 activation. CYLD gene silencing partially weakened EA improvement of neurological function deficits and reduction of infarct volumes after 72 h reperfusion. In addition, EA inhibited M1-like phenotypic microglial activation and promoted M2-like phenotypic microglia through upregulating CYLD expression. Finally, EA-mediated modulation of the CX3CL1/CX3CR1 axis and NLRP3 inflammasome was reversed by CYLD gene silencing in the periischemic cortex.

Conclusion

EA-induced upregulation of neuronal CYLD expression plays anti-inflammatory and neuroprotective roles and regulates the interaction between neurons and microglia, thereby suppressing M1 and improving M2 microglial activation in the periischemic cortex.

Targeting integrated stress response regulates microglial M1/M2 polarization and attenuates neuroinflammation following surgical brain injury in rat

Integrated stress response (ISR) contributes to various neuropathological processes and acting as a therapy target in CNS injuries. However, the fundamental role of ISR in regulating microglial polarization remains largely unknown. Currently no proper pharmacological approaches to reverse microglia-driven neuroinflammation in surgical brain injury (SBI) have been reported. Here we found that inhibition of the crucial ISR effector, activating transcription factor 4 (ATF4), using the RNA interference suppressed the lipopolysaccharide (LPS)-stimulated microglial M1 polarization in vitro. Interestingly, counteracting ISR with a small-molecule ISR inhibitor (ISRIB) resulted in a significant microglial M1 towards M2 phenotype switching after LPS treatment. The potential underlying mechanisms may related to downregulate the intracellular NADPH oxidase 4 (NOX4) expression under the neuroinflammatory microenvironment. Notably, ISRIB ameliorated the infiltration of microglia and improved the neurobehavioral outcomes in the SBI rat model. Overall, our findings suggest that targeting ISR exerts a novel anti-inflammatory effect on microglia via regulating M1/M2 phenotype and may represent a potential therapeutic target to overcome neuroinflammation following SBI.

Tripartite-motif protein 21 knockdown extenuates LPS-triggered neurotoxicity by inhibiting microglial M1 polarization via suppressing NF-κB-mediated NLRP3 inflammasome activation

Tripartite motif-containing 21 (TRIM21) has been confirmed to mediate the production of inflammatory mediators via NF-κB signaling. However, the function of TRIM21 in microglia-mediated neuroinflammation remains unclear. This study aimed to explore the effect of TRIM21 on LPS-activated BV2 microglia and its underlying mechanism. BV2 cells exposed to lipopolysaccharide (LPS) were used to simulated neuroinflammation in vitro. Loss-of-function and gain-of-function of TRIM21 in BV2 cells were used to assess the effect of TRIM21 on LPS-induced neuroinflammation. BV2 microglia and HT22 cells co-culture system were used to investigate whether TRIM21 regulated neuronal inflammation-mediated neuronal death. TRIM21 knockdown triggered the polarization of BV2 cells from M1 to M2 phenotype. Knockdown of TRIM21 reduced the secretion of TNF-α, IL-6, and IL-1β, while increased the content of IL-4 in LPS-treated cells. Knockdown of TRIM21 inhibited the expression of p65 and the binding activity of NF-κB-DNA. Additionally, TRIM21 siRNA eliminated the increase in NLRP3 and cleaved caspase-1 proteins expression and caspase-1 activity induced by LPS. TRIM21 knockdown could resist cytotoxicity induced by activated microglia, including increasing the viability of co-cultured HT22 cells and reducing the emancipation of LDH. Moreover, the increased apoptosis and caspase-3 activity of HT22 neurons induced by activated BV2 cells were blocked by TRIM21 siRNA. Blocking of NF-κB abolished the effect of TRIM21 in promoting the expression of M1 phenotype marker genes. Similarly, the blockade of NF-κB pathway eliminated the promotion of TRIM21 on neurotoxicity induced by neuroinflammation. TRIM21 knockdown suppressed the M1 phenotype polarization of microglia and neuroinflammation-mediated neuronal damage via NF-κB/NLRP3 inflammasome pathway, which suggested that TRIM21 might be a potential therapeutic target for the therapy of central nervous system diseases.

Neuroinflammation in Post-Ischemic Neurodegeneration of the Brain: Friend, Foe, or Both?

One of the leading causes of neurological mortality, disability, and dementia worldwide is cerebral ischemia. Among the many pathological phenomena, the immune system plays an important role in the development of post-ischemic degeneration of the brain, leading to the development of neuroinflammatory changes in the brain. After cerebral ischemia, the developing neuroinflammation causes additional damage to the brain cells, but on the other hand it also plays a beneficial role in repair activities. Inflammatory mediators are sources of signals that stimulate cells in the brain and promote penetration, e.g., T lymphocytes, monocytes, platelets, macrophages, leukocytes, and neutrophils from systemic circulation to the brain ischemic area, and this phenomenon contributes to further irreversible ischemic brain damage. In this review, we focus on the issues related to the neuroinflammation that occurs in the brain tissue after ischemia, with particular emphasis on ischemic stroke and its potential treatment strategies.

Neuroprotective Effects of Salicin in a Gerbil Model of Transient Forebrain Ischemia by Attenuating Oxidative Stress and Activating PI3K/Akt/GSK3β Pathway

Salicin is a major natural compound of willow bark and displays diverse beneficial biological properties, such as antioxidant activity. However, little information available for the neuroprotective potential of salicin against ischemic brain injury has been reported. Thus, this study was performed to investigate the neuroprotective potential of salicin against ischemia and reperfusion (IR) injury and its mechanisms in the hippocampus using a gerbil model of 5-min transient ischemia (TI) in the forebrain, in which a massive loss (death) of pyramidal neurons cells occurred in the subfield Cornu Ammonis 1 (CA1) among the hippocampal subregions (CA1-3) at 5 days after TI. To examine neuroprotection by salicin, gerbils were pretreated with salicin alone or together with LY294002, which is a phosphatidylinositol 3-kinase (PI3K) inhibitor, once daily for 3 days before TI. Treatment with 20 mg/kg of salicin significantly protected CA1 pyramidal neurons against the ischemic injury. Treatment with 20 mg/kg of salicin significantly reduced the TI-induced increase in superoxide anion generation and lipid peroxidation in the CA1 pyramidal neurons after TI. The treatment also reinstated the TI-induced decrease in superoxide dismutases (SOD1 and SOD2), catalase, and glutathione peroxidase in the CA1 pyramidal cells after TI. Moreover, salicin treatment significantly elevated the levels of phosphorylation of Akt and glycogen synthase kinase-3β (GSK3β), which is a major downstream target of PI3K, in the ischemic CA1. Notably, the neuroprotective effect of salicin was abolished by LY294002. Taken together, these findings clearly indicate that salicin protects against ischemic brain injury by attenuating oxidative stress and activating the PI3K/Akt/GSK3β pathway.

Prospects of Therapeutic Target and Directions for Ischemic Stroke

Stroke is a serious, adverse neurological event and the third leading cause of death and disability worldwide. Most strokes are caused by a block in cerebral blood flow, resulting in neurological deficits through the death of brain tissue. Recombinant tissue plasminogen activator (rt-PA) is currently the only immediate treatment medication for stroke. The goal of rt-PA administration is to reduce the thrombus and/or embolism via thrombolysis; however, the administration of rt-PA must occur within a very short therapeutic timeframe (3 h to 6 h) after symptom onset. Components of the pathological mechanisms involved in ischemic stroke can be used as potential biomarkers in current treatment. However, none are currently under investigation in clinical trials; thus, further studies investigating biomarkers are needed. After ischemic stroke, microglial cells can be activated and release inflammatory cytokines. These cytokines lead to severe neurotoxicity via the overactivation of microglia in prolonged and lasting insults such as stroke. Thus, the balanced regulation of microglial activation may be necessary for therapy. Stem cell therapy is a promising clinical treatment strategy for ischemic stroke. Stem cells can increase the functional recovery of damaged tissue after post-ischemic stroke through various mechanisms including the secretion of neurotrophic factors, immunomodulation, the stimulation of endogenous neurogenesis, and neovascularization. To investigate the use of stem cell therapy for neurological diseases in preclinical studies, however, it is important to develop imaging technologies that are able to evaluate disease progression and to “chase” (i.e., track or monitor) transplanted stem cells in recipients. Imaging technology development is rapidly advancing, and more sensitive techniques, such as the invasive and non-invasive multimodal techniques, are under development. Here, we summarize the potential risk factors and biomarker treatment strategies, stem cell-based therapy and emerging multimodal imaging techniques in the context of stroke. This current review provides a conceptual framework for considering the therapeutic targets and directions for the treatment of brain dysfunctions, with a particular focus on ischemic stroke.

Minocycline promotes functional recovery in ischemic stroke by modulating microglia polarization through STAT1/STAT6 pathways

BACKGROUND

Increasing evidence suggests that microglia experience two distinct phenotypes after acute ischemic stroke (AIS): a deleterious M1 phenotype and a neuroprotective M2 phenotype. Promoting the phenotype shift of M1 microglia to M2 microglia is thought to improve functional recovery after AIS. Minocycline, a tetracycline antibiotic, can improve functional recovery after cerebral ischemia in pre-clinical and clinical research. However, the role and mechanisms of minocycline in microglia polarization is unclear.

METHODS

Using the transient middle cerebral artery occlusion - reperfusion (MCAO/R) model, we treated mice with saline or different minocycline concentration (10, 25, or 50 mg/kg, i.p., daily for 2 wk) at 24 h after reperfusion. Neurobehavioral evaluation, rotarod test, and corner turning test were carried out on day 14 after reperfusion. Then, neuronal injury, reactive gliosis, and microglia polarization were performed on day 7 following MCAO/R. Finally, we treated primary microglial cultures with LPS (Lipopolysaccharide; 100 ng/mL) plus IFN-γ (20 ng/mL) 24 h to induce M1 phenotype and observed the effects of minocycline on the M1/M2-related mRNAs and the STAT1/STAT6 pathway.

RESULTS

We found that a 14-day treatment with minocycline increased the survival rate and promoted functional outcomes evaluated with neurobehavioral evaluation, rotarod test, and corner turning test. Meanwhile, minocycline reduced the brain infarct volume, alleviated neuronal injury, and suppressed reactive gliosis on day 7 following MCAO/R. Moreover, we observed an additive effect of minocycline on microglia polarization to the M1 and M2 phenotypes in vivo and in vitro. In the primary microglia, we further found that minocycline prevented neurons from OGD/R-induced cell death in neuron-microglia co-cultures via regulating M1/M2 microglia polarization through the STAT1/STAT6 pathway.

CONCLUSION

Minocycline promoted microglial M2 polarization and inhibited M1 polarization, leading to neuronal survival and neurological functional recovery. The findings deepen our understanding of the mechanisms underlying minocycline-mediated neuroprotection in AIS.

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

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