Noggin improves ischemic brain tissue repair and promotes alternative activation of microglia in mice

Bone morphogenetic protein 4 derived from the cerebrospinal fluid in patients with postherpetic neuralgia induces allodynia via the crosstalk between microglia and astrocyte

INTRODUCTION

During postherpetic neuralgia (PHN), the cerebral spinal fluid (CSF) possesses the capability to trigger glial activation and inflammation, yet the specific changes in its composition remain unclear. Recent findings from our research indicate elevations of central bone morphogenetic protein 4 (BMP4) during neuropathic pain (NP), serving as an independent modulator of glial cells. Herein, the aim of the present study is to test the CSF-BMP4 expressions and its role in the glial modulation in the process of PHN.

METHODS

CSF samples were collected from both PHN patients and non-painful individuals (Control) to assess BMP4 and its antagonist Noggin levels. Besides, intrathecal administration of both CSF types was conducted in normal rats to evaluate the impact on pain behavior, glial activity, and inflammation.; Additionally, both Noggin and STAT3 antagonist-Stattic were employed to treat the PHN-CSF or exogenous BMP4 challenged cultured astrocytes to explore downstream signals. Finally, microglial depletion was performed prior to the PHN-CSF intervention so as to elucidate the microglia-astrocyte crosstalk.

RESULTS

BMP4 levels were significantly higher in PHN-CSF compared to Control-CSF (P < 0.001), with a positive correlation with pain duration (P < 0.05, r = 0.502). Comparing with the Control-CSF producing moderate paw withdrawal threshold (PWT) decline and microglial activation, PHN-CSF further exacerbated allodynia and triggered both microglial and astrocytic activation (P < 0.05). Moreover, PHN-CSF rather than Control-CSF evoked microglial proliferation and pro-inflammatory transformation, reinforced iron storage, and activated astrocytes possibly through both SMAD159 and STAT3 signaling, which were all mitigated by the Noggin application (P < 0.05). Next, both Noggin and Stattic effectively attenuated BMP4-induced GFAP and IL-6 upregulation, as well as SMAD159 and STAT3 phosphorylation in the cultured astrocytes (P < 0.05). Finally, microglial depletion diminished PHN-CSF induced astrogliosis, inflammation and endogenous BMP4 expression (P < 0.05).

CONCLUSION

Our study highlights the role of CSF-BMP4 elevation in glial activation and allodynia during PHN, suggesting a potential therapeutic avenue for future exploration.

β-elemene promotes microglial M2-like polarization against ischemic stroke via AKT/mTOR signaling axis-mediated autophagy

BACKGROUND

Resident microglia- and peripheric macrophage-mediated neuroinflammation plays a predominant role in the occurrence and development of ischemic stroke. Microglia undergo polarization to M1/M2-like phenotype under stress stimulation, which mediates intracellular inflammatory response. β-elemene is a natural sesquiterpene and possesses potent anti-inflammatory activity. This study aimed to investigate the anti-inflammatory efficacy and mechanism of β-elemene in ischemic stroke from the perspective of balancing microglia M1/M2-like polarization.

METHODS

The middle cerebral artery occlusion (MCAO) model and photothrombotic stroke model were established to explore the regulation effect of β-elemene on the cerebral ischemic injury. The LPS and IFN-γ stimulated BV-2 cells were used to demonstrate the anti-inflammatory effects and potential mechanism of β-elemene regulating M1/M2-like polarization in vitro.

RESULTS

In C57BL/6 J mice subjected to MCAO model and photothrombotic stroke model, β-elemene attenuated neurological deficit, reduced the infarction volume and neuroinflammation, thus improving ischemic stroke injury. β-elemene promoted the phenotype transformation of microglia from M1-like to M2-like, which prevented neurons from oxygen and glucose deprivation/reoxygenation (OGD/R) injury by inhibiting inflammatory factor release, thereby reducing neuronal apoptosis. Mechanically, β-elemene prevented the activation of TLR4/NF-κΒ and MAPK signaling pathway and increased AKT/mTOR mediated-autophagy, thereby promoting M2-like polarization of microglia.

CONCLUSIONS

These results indicated that β-elemene improved cerebral ischemic injury and promoted the transformation of microglia phenotype from M1-like to M2-like, at least in part, through AKT/mTOR-mediated autophagy. This study demonstrated that β-elemene might serve as a promising drug for alleviating ischemic stroke injury.

Delayed Chronic Acidic Postconditioning Improves Poststroke Motor Functional Recovery and Brain Tissue Repair by Activating Proton-Sensing TDAG8

Acidic postconditioning by transient CO2 inhalation applied within minutes after reperfusion has neuroprotective effects in the acute phase of stroke. However, the effects of delayed chronic acidic postconditioning (DCAPC) initiated during the subacute phase of stroke or other acute brain injuries are unknown. Mice received daily DCAPC by inhaling 5%/10%/20% CO2 for various durations (three cycles of 10- or 20-min CO2 inhalation/10-min break) at days 3-7, 7-21, or 3-21 after photothrombotic stroke. Grid-walk, cylinder, and gait tests were used to assess motor function. DCAPC with all CO2 concentrations significantly promoted motor functional recovery, even when DCAPC was delayed for 3-7 days. DCAPC enhanced the puncta density of GAP-43 (a marker of axon growth and regeneration) and synaptophysin (a marker of synaptogenesis) and reduced the amoeboid microglia number, glial scar thickness and mRNA expression of CD16 and CD32 (markers of proinflammatory M1 microglia) compared with those of the stroke group. Cerebral blood flow (CBF) increased in response to DCAPC. Furthermore, the mRNA expression of TDAG8 (a proton-activated G-protein-coupled receptor) was increased during the subacute phase of stroke, while DCAPC effects were blocked by systemic knockout of TDAG8, except for those on CBF. DCAPC reproduced the benefits by re-expressing TDAG8 in the peri-infarct cortex of TDAG8-/- mice infected with HBAAV2/9-CMV-TDAG8-3flag-ZsGreen. Taken together, we first showed that DCAPC promoted functional recovery and brain tissue repair after stroke with a wide therapeutic time window of at least 7 days after stroke. Brain-derived TDAG8 is a direct target of DCAPC that induces neuroreparative effects.

Atorvastatin Promotes Pro/anti-inflammatory Phenotypic Transformation of Microglia via Wnt/β-catenin Pathway in Hypoxic-Ischemic Neonatal Rats

Inflammatory reaction plays a key role in the pathogenesis of hypoxic-ischemic encephalopathy (HIE) in neonates. Microglia are resident innate immune cells in the central nervous system and are profoundly involved in neuroinflammation. Studies have revealed that atorvastatin exerts a neuroprotective effect by regulating neuroinflammation in adult animal models of brain stroke and traumatic brain injury, but its role regarding damage to the developing brain remains unclear. This study aimed to clarify the effect and mechanism of atorvastatin on the regulation of microglia function in neonatal hypoxic-ischemic brain damage (HIBD). The oxygen glucose deprivation (OGD) of microglia and neonatal rat HIBD model was established. Atorvastatin, recombinant sclerostin protein (SOST), and XAV939 (degradation of β-catenin) were administered to OGD microglia and HIBD rats. The pathological changes of brain tissue, cerebral infarction volume, learning and memory ability of rats, pro-inflammatory (CD16+/Iba1+) and anti-inflammatory (CD206+/Iba1+) microglia markers, inflammation-related indicators (Inos, Tnfα, Il6, Arg1, Tgfb, and Mrc1), and Wnt/β-catenin signaling molecules were examined. Atorvastatin reduced OGD-induced pro-inflammatory microglia and pro-inflammatory factors, while increasing anti-inflammatory microglia and anti-inflammatory factors. In vivo, atorvastatin attenuated hypoxia-ischemia (HI)-induced neuroinflammation and brain damage. Mechanistically, atorvastatin decreased SOST expression and activated the Wnt/β-catenin signaling pathway, and the administration of recombinant SOST protein or XAV939 inhibited Wnt/β-catenin signaling and attenuated the anti-inflammatory effect of atorvastatin. Atorvastatin promotes the pro/anti-inflammatory phenotypic transformation of microglia via the Wnt/β-catenin pathway in HI neonatal rats. Atorvastatin may be developed as a potent agent for the treatment of HIE in neonates.

Mechanism of Efferocytosis in Determining Ischaemic Stroke Resolution-Diving into Microglia/Macrophage Functions and Therapeutic Modality

After ischaemic cerebral vascular injury, efferocytosis-a process known as the efficient clearance of apoptotic cells (ACs) by various phagocytes in both physiological and pathological states-is crucial for maintaining central nervous system (CNS) homeostasis and regaining prognosis. The mechanisms of efferocytosis in ischaemic stroke and its influence on preventing inflammation progression from secondary injury were still not fully understood, despite the fact that the fundamental process of efferocytosis has been described in a series of phases, including AC recognition, phagocyte engulfment, and subsequent degradation. The genetic reprogramming of macrophages and brain-resident microglia after an ischaemic stroke has been equated by some researchers to that of the peripheral blood and brain. Based on previous studies, some molecules, such as signal transducer and activator of transcription 6 (STAT6), peroxisome proliferator-activated receptor γ (PPARG), CD300A, and sigma non-opioid intracellular receptor 1 (SIGMAR1), were discovered to be largely associated with aspects of apoptotic cell elimination and accompanying neuroinflammation, such as inflammatory cytokine release, phenotype transformation, and suppressing of antigen presentation. Exacerbated stroke outcomes are brought on by defective efferocytosis and improper modulation of pertinent signalling pathways in blood-borne macrophages and brain microglia, which also results in subsequent tissue inflammatory damage. This review focuses on recent researches which contain a number of recently discovered mechanisms, such as studies on the relationship between benign efferocytosis and the regulation of inflammation in ischaemic stroke, the roles of some risk factors in disease progression, and current immune approaches that aim to promote efferocytosis to treat some autoimmune diseases. Understanding these pathways provides insight into novel pathophysiological processes and fresh characteristics, which can be used to build cerebral ischaemia targeting techniques.

Melatonin: a promising neuroprotective agent for cerebral ischemia-reperfusion injury

Cerebral ischemia-reperfusion (CIR) injury is initiated by the generation of reactive oxygen species (ROS), which leads to the oxidation of cellular proteins, DNA, and lipids as an initial event. The reperfusion process impairs critical cascades that support cell survival, including mitochondrial biogenesis and antioxidant enzyme activity. Failure to activate prosurvival signals may result in increased neuronal cell death and exacerbation of CIR damage. Melatonin, a hormone produced naturally in the body, has high concentrations in both the cerebrospinal fluid and the brain. However, melatonin production declines significantly with age, which may contribute to the development of age-related neurological disorders due to reduced levels. By activating various signaling pathways, melatonin can affect multiple aspects of human health due to its diverse range of activities. Therefore, understanding the underlying intracellular and molecular mechanisms is crucial before investigating the neuroprotective effects of melatonin in cerebral ischemia-reperfusion injury.

Decoding the molecular crosstalk between grafted stem cells and the stroke-injured brain

Stem cell therapy shows promise for multiple disorders; however, the molecular crosstalk between grafted cells and host tissue is largely unknown. Here, we take a step toward addressing this question. Using translating ribosome affinity purification (TRAP) with sequencing tools, we simultaneously decode the transcriptomes of graft and host for human neural stem cells (hNSCs) transplanted into the stroke-injured rat brain. Employing pathway analysis tools, we investigate the interactions between the two transcriptomes to predict molecular pathways linking host and graft genes; as proof of concept, we predict host-secreted factors that signal to the graft and the downstream molecular cascades they trigger in the graft. We identify a potential host-graft crosstalk pathway where BMP6 from the stroke-injured brain induces graft secretion of noggin, a known brain repair factor. Decoding the molecular interplay between graft and host is a critical step toward deciphering the molecular mechanisms of stem cell action.

Noggin-mediated effects on metabolite profiles of microglia and oligodendrocytes after ischemic insult

Recent studies show that shifts in energy metabolism in activated microglia are linked to their functions and immune responses in the ischemic brain. We previously reported that an antagonist of the bone morphogenetic protein, noggin, enhanced myelination in the ischemic brain during the chronic phase, and conditioned media (CM) from activated BV2 microglia treated with noggin after ischemia/reperfusion (I/R) increased the expression of myelin basic protein (MBP) in oligodendrocytes (MO3.13). To determine whether noggin induced changes in cell metabolism, metabolite profiles in BV2 and MO3.13 cells were analyzed by untargeted metabolomics using ¹H nuclear magnetic resonance spectroscopy. Compared to vehicle-treated BV2 cells, noggin treatment (100 ng/mL for 3 h after I/R) suppressed the I/R-induced increase in intracellular glucose and lactate levels but increased extracellular levels of glucose and several amino acids. When MO3.13 cells were exposed to noggin CM from BV2 cells, most of the vehicle CM-induced changes in the levels of metabolites such as choline, formate, and intermediates of oxidative phosphorylation were reversed, while the glycerol level was markedly increased. An increase in glycerol level was also observed in the noggin-treated ischemic brain and was further supported by the expression of glycerol-3-phosphate dehydrogenase 1 (required for glycerol synthesis) in the cytoplasm of MBP-positive oligodendrocytes in the ischemic brains treated with noggin. These results suggest that noggin-induced changes in the metabolism of microglia provide a favorable environment for myelin synthesis in oligodendrocytes during the recovery phase after ischemic stroke.

Infiltrating circulating monocytes provide an important source of BMP4 at the early stage of spinal cord injury

Bone morphogenetic protein (BMP)4 plays a critical role in regulating neuronal and glial activity in the course of spinal cord injury (SCI). The underlying cause and cellular source of BMP4 accumulation at the injured spinal cord remain unclear. Here, we observed that plasma BMP4 levels are statistically higher in SCI patients than in healthy donors. When comparing rats in the sham group (T9 laminectomy without SCI) with rats in the SCI group, we found a persistent decline in BBB scores, together with necrosis and mononuclear cell accumulation at the contusion site. Moreover, during 2 weeks after SCI both plasma and cerebrospinal fluid levels of BMP4 displayed notable elevation, and a positive correlation. Importantly, percentages of circulating BMP4-positive (BMP4+) monocytes and infiltrating MDMs were higher in the SCI group than in the sham group. Finally, in the SCI+clodronate liposome group, depletion of monocytes effectively attenuated the accumulation of both BMP4+ MDMs and BMP4 in the injured spinal cord. Our results indicated that, following SCI, infiltrating MDMs provide an important source of BMP4 in the injured spinal cord and, therefore, might serve as a potential therapeutic target.

The Role of Bone Morphogenetic Protein 4 in Microglial Polarization in the Process of Neuropathic Pain

Background

Neuropathic pain (NP) is known to be highly correlated with microglial polarization, of which the regulatory mechanism remains to be elucidated. Here, the aim of this study is to further investigate the relationship between bone morphogenetic protein 4 (BMP4) and microglial polarization in the process of NP.

Methods

Firstly, normal adult rats received intrathecal BMP4 administration to assess BMP4ʹs effect on microglial polarization. Secondly, a BMP4 antagonist – Noggin – was applied to a rat NP model achieved by L5 spinal nerve ligation (SNL) to investigate whether antagonizing BMP4 signaling could alleviate allodynia by reversing the imbalance of the M1/M2 polarization ratio. In both experiments, Von-Frey filaments were used to test the changes in the paw withdrawal threshold (PWT), and Western blotting, immuno-fluorescence, PCR and flow cytometry were further performed to investigate microglial activity and the expression patterns of M1 and M2 markers, respectively.

Results

Firstly, BMP4 administration induced a significant PWT decrease and microglial activation in normal rats; Western blotting, PCR and flow cytometry further revealed that M1 markers including CD16, MHCII, and TNF-α showed a marked elevation after BMP4 application; while M2 markers, such as Arg-1, CD204 and IL-4, peaked at an early stage (P1 or P4) and then fell to the Sham level on P7, leading to a persistent imbalance of the M1/M2 ratio throughout the 1st week. Secondly, Noggin treatment significantly relieved allodynia and microglial activation in SNL rats. Moreover, Noggin persistently downregulated the M1 marker levels and simultaneously induced a late-stage elevation of M2 markers expressions, thereby reversing the imbalance of the M1/M2 polarization ratio.

Conclusion

Our results indicate that BMP4 has the ability to induce microglial polarization. Antagonizing BMP4 signaling can relieve pain behavior via mitigating microglial activation and reversing the imbalance of the M1/M2 polarization ratio in the process of NP.

Identification of Regulatory Factors and Prognostic Markers in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive degeneration of motor neurons, leading to muscle atrophy, paralysis and even death. Immune disorder, redox imbalance, autophagy disorder, and iron homeostasis disorder have been shown to play critical roles in the pathogenesis of ALS. However, the exact pathogenic genes and the underlying mechanism of ALS remain unclear. The purpose of this study was to screen for pathogenic regulatory genes and prognostic markers in ALS using bioinformatics methods. We used Gene Ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, gene set enrichment analysis (GSEA), and expression regulation network analysis to investigate the function of differentially expressed genes in the nerve tissue, lymphoid tissue, and whole blood of patients with ALS. Our results showed that the up-regulated genes were mainly involved in immune regulation and inflammation, and the down-regulated genes were mainly involved in energy metabolism and redox processes. Eleven up-regulated transcription factors (CEBPB, CEBPD, STAT5A, STAT6, RUNX1, REL, SMAD3, GABPB2, FOXO1, PAX6, and FOXJ1) and one down-regulated transcription factor (NOG) in the nerve tissue of patients with ALS likely play important regulatory roles in the pathogenesis of ALS. Based on construction and evaluation of the ALS biomarker screening model, cluster analysis of the identified characteristic genes, univariate Cox proportional hazards regression analysis, and the random survival forest algorithm, we found that MAEA, TPST1, IFNGR2, and ALAS2 may be prognostic markers regarding the survival of ALS patients. High expression of MAEA, TPST1, and IFNGR2 and low expression of ALAS2 in ALS patients may be closely related to short survival of ALS patients. Taken together, our results indicate that immune disorders, inflammation, energy metabolism, and redox imbalance may be the important pathogenic factors of ALS. CEBPB, CEBPD, STAT5A, STAT6, RUNX1, REL, SMAD3, GABPB2, FOXO1, PAX6, FOXJ1, and NOG may be important regulatory factors linked to the pathogenesis of ALS. MAEA, TPST1, IFNGR2, and ALAS2 are potential important ALS prognostic markers. Our findings provide evidence on the pathogenesis of ALS, potential targets for the development of new drugs for ALS, and important markers for predicting ALS prognosis.

Acute Response and Neuroprotective Role of Myo/Nog Cells Assessed in a Rat Model of Focal Brain Injury

Focal brain injury in the form of a needlestick (NS) results in cell death and induces a self-protective response flanking the lesion. Myo/Nog cells are identified by their expression of bone morphogenetic protein inhibitor Noggin, brain-specific angiogenesis inhibitor 1 (BAI1) and the skeletal muscle specific transcription factor MyoD. Myo/Nog cells limit cell death in two forms of retinopathy. In this study, we examined the acute response of Myo/Nog cells to a NS lesion that extended from the rat posterior parietal cortex to the hippocampus. Myo/Nog cells were identified with antibodies to Noggin and BAI1. These cells were the primary source of both molecules in the uninjured and injured brain. One day after the NS, the normally small population of Myo/Nog cells expanded approximately eightfold within a 1 mm area surrounding the lesion. Myo/Nog cells were reduced by approximately 50% along the lesion with an injection of the BAI1 monoclonal antibody and complement. The number of dying cells, identified by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL), was unchanged at this early time point in response to the decrease in Myo/Nog cells. However, increasing the number of Myo/Nog cells within the lesion by injecting BAI1-positive (+) cells isolated from the brains of other animals, significantly reduced cell death and increased the number of NeuN+ neurons compared to brains injected with phosphate buffered saline or exogenous BAI1-negative cells. These findings demonstrate that Myo/Nog cells rapidly react to injury within the brain and increasing their number within the lesion is neuroprotective.

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.

New Insights Into the Roles of Microglial Regulation in Brain Plasticity-Dependent Stroke Recovery

Stroke remains the leading cause of long-term disability worldwide with significant long-term sequelae. However, there is no highly effective treatment to enhance post-stroke recovery despite extensive efforts in exploring rehabilitative therapies. Neurorehabilitation is recognized as the cornerstone of functional restoration therapy in stroke, where treatments are focused on neuroplastic regulation to reverse neural structural disruption and improve neurofunctional networks. Post-stroke neuroplasticity changes begin within hours of symptom onset and reaches a plateau by 3 to 4 weeks within the global brain in animal studies. It plays a determining role in spontaneous stroke recovery. Microglia are immediately activated following cerebral ischemia, which has been found both proximal to the primary ischemic injury and at the remote brain regions which have functional connections to the primary injury area. Microglia exhibit different activation profiles based on the microenvironment and adaptively switch their phenotypes in a spatiotemporal manner in response to brain injuries. Microglial activation coincides with neuroplasticity after stroke, which provides the fundamental base for the microglia-mediated inflammatory responses involved in the entire neural network rewiring and brain repair. Microglial activation exerts important effects on spontaneous recovery after stroke, including structural and functional reestablishment of neurovascular networks, neurogenesis, axonal remodeling, and blood vessel regeneration. In this review, we focus on the crosstalk between microglial activation and endogenous neuroplasticity, with a special focus on the plastic alterations in the whole brain network and their implications for structural and functional restoration after stroke. We then summarize recent advances in the impacts of microglial phenotype polarization on brain plasticity, trying to discuss the potential efficacy of microglia-based extrinsic restorative interventions in promoting post-stroke recovery.

Substrate stiffness modulates bone marrow-derived macrophage polarization through NF-κB signaling pathway

The stiffness of the extracellular matrix (ECM) plays an important role in regulating the cellular programming. However, the mechanical characteristics of ECM affecting cell differentiation are still under investigated. Herein, we aimed to study the effect of ECM substrate stiffness on macrophage polarization. We prepared polyacrylamide hydrogels with different substrate stiffness, respectively. After the hydrogels were confirmed to have a good biocompatibility, the bone marrow-derived macrophages (BMMs) from mice were incubated on the hydrogels. With simulated by the low substrate stiffness, BMMs displayed an enhanced expression of CD86 on the cell surface and production of reactive oxygen species (ROS) in cells, and secreted more IL-1β and TNF-α in the supernatant. On the contrary, stressed by the medium stiffness, BMMs expressed more CD206, produced less ROS, and secreted more IL-4 and TGF-β. In vivo study by delivered the hydrogels subcutaneously in mice, more CD68+CD86+ cells around the hydrogels with the low substrate stiffness were observed while more CD68+CD206+ cells near by the middle stiffness hydrogels. In addition, the expressions of NIK, phosphorylated p65 (pi-p65) and phosphorylated IκB (pi-IκB) were significantly increased after stimulation with low stiffness in BMMs. Taken together, these findings demonstrated that substrate stiffness could affect macrophages polarization. Low substrate stiffness promoted BMMs to shift to classically activated macrophages (M1) and the middle one to alternatively activated macrophages (M2), through modulating ROS-initiated NF-κB pathway. Therefore, we anticipated ECM-based substrate stiffness with immune modulation would be under consideration in the clinical applications if necessary.

Enhanced repair processes and iron uptake by ischemic preconditioning in the brain during the recovery phase after ischemic stroke

Ischemic preconditioning (IP) reduces brain damage after subsequent ischemic strokes by activating endogenous protective mechanisms in rodents. Transient ischemic attack (TIA) induces tolerance in the human brain after ischemic strokes; defining mechanisms of IP effects may provide therapeutic targets to improve recovery of patients with ischemic strokes. Iron transported across the blood-brain barrier (BBB) is required for brain functions, including myelination, and its levels should be finely regulated to avoid harmful effects. This study aimed to determine whether IP enhances repair processes by modulating iron metabolism during the post-stroke chronic phase. Male mice were divided into sham and IP groups, and IP was induced 24 h before a transient focal ischemic stroke. Sensorimotor recovery was observed over 8 weeks after the stroke, and brain volumes and levels of proteins related to repair processes and iron metabolism in the ischemic brains were examined 8 weeks after the stroke. There was significantly less ischemic brain atrophy in the IP group than in the sham group, with no differences in sensorimotor recovery between the groups. Levels of tight junction proteins of BBB, neurites outgrowth markers, and myelin sheath proteins and markers for mature oligodendrocytes were significantly increased in the IP group. Iron import proteins, transferrin receptor 1 and DMT1, were also increased in the IP group. These results indicate that IP increases brain repair processes and iron uptake during the chronic phase after an ischemic stroke, and provide new insights to understand the molecular mechanisms of TIA effects on post-stroke recovery.

Treadmill exercise mitigates neuroinflammation and increases BDNF via activation of SIRT1 signaling in a mouse model of T2DM

Although previous studies showed that exercise can improve cognitive dysfunction in type 2 diabetes (T2DM), the underlying mechanism remains unclear. Sirtuin 1 (SIRT1) has been shown to play a role in regulating inflammatory responses in the brain and increasing BDNF expression. This study investigated the effects of treadmill exercise on the hippocampal inflammatory response and BDNF expression in a T2DM mice model. We also tested whether these effects are SIRT1-dependent. In this study, C57BL/ 6 mice were used to construct T2DM model by a high-fat diet and STZ injection. We found that treadmill exercise for 8 weeks can significantly improve the cognitive dysfunction, alleviate activation of proinflammatory microglia M1 (Iba1 labeling) in the hippocampus of T2DM mice, and reduce the levels of proinflammatory factors IL-1β, IL-6, TNF-α, increase the expression levels of anti-inflammatory factors IL-10, TGF-β1, and promote the release of BDNF. We also found that exercise activate the signaling pathway of SIRT1/ NF-κB and SIRT1/ PGC-1α/ FNDC5/ BDNF. After the application of nicotinamide (NAM, SIRT1 inhibitor), the positive effects of exercise were remarkably suppressed. Our results showed that long-term moderate intensity treadmill exercise can alleviate inflammatory response in the hippocampus and increase BDNF expression in T2DM mice by activating SIRT1.

Communications Between Peripheral and the Brain-Resident Immune System in Neuronal Regeneration After Stroke

Cerebral ischemia may cause irreversible neural network damage and result in functional deficits. Targeting neuronal repair after stroke potentiates the formation of new connections, which can be translated into a better functional outcome. Innate and adaptive immune responses in the brain and the periphery triggered by ischemic damage participate in regulating neural repair after a stroke. Immune cells in the blood circulation and gut lymphatic tissues that have been shaped by immune components including gut microbiota and metabolites can infiltrate the ischemic brain and, once there, influence neuronal regeneration either directly or by modulating the properties of brain-resident immune cells. Immune-related signalings and metabolites from the gut microbiota can also directly alter the phenotypes of resident immune cells to promote neuronal regeneration. In this review, we discuss several potential mechanisms through which peripheral and brain-resident immune components can cooperate to promote first the resolution of neuroinflammation and subsequently to improved neural regeneration and a better functional recovery. We propose that new insights into discovery of regulators targeting pro-regenerative process in this complex neuro-immune network may lead to novel strategies for neuronal regeneration.

LncRNA SNHG4 Attenuates Inflammatory Responses by Sponging miR-449c-5p and Up-Regulating STAT6 in Microglial During Cerebral Ischemia-Reperfusion Injury

Background

Inflammatory response mediated by microglia plays a key role in cerebral ischemia-reperfusion injury. This study intends to probe the role of lncRNA SNHG4 in regulating the inflammatory response of the microglia during cerebral ischemia reperfusion.

Materials and Methods

Blood samples and cerebrospinal fluid samples were collected from acute cerebral infarction (ACI) patients and healthy controls. The middle cerebral artery occlusion (MCAO) models were constructed with rats. LPS induction and oxygen-glucose deprivation methods were respectively applied to simulate the activation of microglia in vitro. qRT-PCR was employed to determine the expressions of SNHG4, miR-449c-5p and related inflammatory factors in vivo and in vitro. The inflammatory responses of the microglia subject to the varied expressions of SNHG4 and miR-449c-5p were detected. Luciferase assays were conducted to verify the crosstalk involving SNHG4, miR-449c-5p and STAT6.

Results

Compared with the control group, the expression of SNHG4 derived from the samples of ACI patients and the microglia of MCAO group were remarkably down-regulated, but the expression of miR-449c-5p was dramatically up-regulated. Overexpression of SNHG4 and knock-down of miR-449c-5p could inhibit the expression of pro-inflammatory cytokine in the microglia and promote the expression of anti-inflammatory factors. Meanwhile, the phospho-STAT6 was up-regulated, whereas the knock-down of SNHG4 and over-expression of miR-449c-5p in microglia had the opposite effects. Luciferase assay confirmed that SNHG4 could target miR-449c-5p, while miR-449c-5p could target STAT6.

Conclusion

SNHG4 can regulate STAT6 and repress inflammation by adsorbing miR-449c-5p in microglia during cerebral ischemia-reperfusion injury.

Uncovering the Potential Differentially Expressed miRNAs and mRNAs in Ischemic Stroke Based on Integrated Analysis in the Gene Expression Omnibus Database

INTRODUCTION

Ischemic stroke is the third leading cause of death. There is no known treatment or cure for the disease. Moreover, the pathological mechanism of ischemic stroke remains unclear.

OBJECTIVE

We aimed to identify potential microRNAs (miRNAs) and mRNAs, contributing to understanding the pathology of ischemic stroke.

METHODS

First, the data of miRNA and mRNA were downloaded for differential expression analysis. Then, the regulatory network between miRNA and mRNAs was constructed. Third, top 100 differentially expressed mRNAs were used to construct a protein-protein interaction network followed by the function annotation of mRNAs. In addition, in vitro experiment was used to validate the expression of mRNAs. Last, receiver operating characteristic diagnostic analysis of differentially methylated genes was performed.

RESULTS

Totally, up to 26 differentially expressed miRNAs and 1,345 differentially expressed mRNAs were identified. Several regulatory interaction pairs between miRNA and mRNAs were identified, such as hsa-miR-206-HMGCR/PICALM, hsa-miR-4491-TMEM97, hsa-miR-3622b-5p/hsa-miR-548k-KLF12, and hsa-miR-302a-3p/hsa-miR-3145-3p-CTSS. MAPK signaling pathway (involved DUSP1) and the Notch signaling pathway (involved NUMB and CREBBP) were identified. The expression validation of KLF12, ARG1, ITGAM, SIRT4, SERPINH1, and DUSP1 was consistent with the bioinformatics analysis. Interestingly, hsa-miR-206, hsa-miR-4491, hsa-miR-3622b-5p, hsa-miR-548k, hsa-miR-302a-3p, hsa-miR-3145-3p, KLF12, and ID3 had the potential diagnostic value of ischemic stroke.

CONCLUSIONS

The identified differentially expressed miRNAs and mRNAs may be associated with the development of ischemic stroke.

Transcriptome Analyses in BV2 Microglial Cells Following Treatment With Amino-Terminal Fragments of Apolipoprotein E

Despite the fact that harboring the apolipoprotein E4 (APOE4) allele represents the single greatest risk factor for late-onset Alzheimer’s disease (AD), the exact mechanism by which ApoE4 contributes to disease progression remains unknown. Recently, we demonstrated that a 151 amino-terminal fragment of ApoE4 (nApoE4_1–151) localizes within the nucleus of microglia in the human AD brain and traffics to the nucleus causing toxicity in BV2 microglia cells. In the present study, we examined in detail what genes may be affected following treatment by nApoE4_1–151. Transcriptome analyses in BV2 microglial cells following sublethal treatment with nApoE4_1–151 revealed the upregulation of almost 4,000 genes, with 20 of these genes upregulated 182- to 715-fold compared to untreated control cells. The majority of these 20 genes play a role in the immune response and polarization toward microglial M1 activation. As a control, an identical nApoE3_1–151 fragment that differed by a single amino acid at position 112 (Cys→Arg) was tested and produced a similar albeit lower level of upregulation of an identical set of genes. In this manner, enriched pathways upregulated by nApoE3_1–151 and nApoE4_1–151 following exogenous treatment included Toll receptor signaling, chemokine/cytokine signaling and apoptosis signaling. There were unique genes differentially expressed by at least two-fold for either fragment. For nApoE3_1–151, these included 16 times as many genes, many of which are involved in physiological functions within microglia. For nApoE4_1–151, on the other hand the number genes uniquely upregulated was significantly lower, with many of the top upregulated genes having unknown functions. Taken together, our results suggest that while nApoE3_1–151 may serve a more physiological role in microglia, nApoE4_1–151 may activate genes that contribute to disease inflammation associated with AD. These data support the hypothesis that the link between harboring the APOE4 allele and dementia risk could be enhanced inflammation through activation of microglia.

Microglia and Their Promising Role in Ischemic Brain Injuries: An Update

Ischemic brain injuries are common diseases with high morbidity, disability, and mortality rates, which have significant impacts on human health and life. Microglia are resident cells of the central nervous system (CNS). The inflammatory responses mediated by microglia play an important role in the occurrence and development of ischemic brain injuries. This article summarizes the activation, polarization, depletion, and repopulation of microglia after ischemic brain injuries, proposing new treatment strategies for such injuries through the modulation of microglial function.

Post-Ischaemic Immunological Response in the Brain: Targeting Microglia in Ischaemic Stroke Therapy

Microglia, the major endogenous immune cells of the central nervous system, mediate critical degenerative and regenerative responses in ischaemic stroke. Microglia become "activated", proliferating, and undergoing changes in morphology, gene and protein expression over days and weeks post-ischaemia, with deleterious and beneficial effects. Pro-inflammatory microglia (commonly referred to as M1) exacerbate secondary neuronal injury through the release of reactive oxygen species, cytokines and proteases. In contrast, microglia may facilitate neuronal recovery via tissue and vascular remodelling, through the secretion of anti-inflammatory cytokines and growth factors (a profile often termed M2). This M1/M2 nomenclature does not fully account for the microglial heterogeneity in the ischaemic brain, with some simultaneous expression of both M1 and M2 markers at the single-cell level. Understanding and regulating microglial activation status, reducing detrimental and promoting repair behaviours, present the potential for therapeutic intervention, and open a longer window of opportunity than offered by acute neuroprotective strategies. Pharmacological modulation of microglial activation status to promote anti-inflammatory gene expression can increase neurogenesis and improve functional recovery post-stroke, based on promising preclinical data. Cell-based therapies, using preconditioned microglia, are of interest as a method of therapeutic modulation of the post-ischaemic inflammatory response. Currently, there are no clinically-approved pharmacological options targeting post-ischaemic inflammation. A major developmental challenge for clinical translation will be the selective suppression of the deleterious effects of microglial activity after stroke whilst retaining (or enhancing) the neurovascular repair and remodelling responses of microglia.

The Cannabinoid WIN 55,212-2 Reduces Delayed Neurologic Sequelae After Carbon Monoxide Poisoning by Promoting Microglial M2 Polarization Through ST2 Signaling

Delayed neurologic sequelae (DNS) are among the most serious complications of carbon monoxide (CO) poisoning caused partly by elevated neuroinflammation. WIN 55,212-2, a non-selective agonist of cannabinoid receptors, has been demonstrated to have anti-inflammatory properties in various brain disorders. The anti-inflammatory action of WIN 55,212-2 is potentially associated with driving microglial M2 polarization. ST2 signaling is important in regulating inflammatory responses and microglial polarization. Therefore, we aimed to investigate the neuroprotective effect of WIN 55,212-2 on DNS after CO poisoning and elucidate its relationship with ST2-mediated microglial M2 polarization. The behavioral tests showed that treatment with WIN 55,212-2 significantly ameliorates the cognitive impairment induced by CO poisoning. This behavioral improvement was accompanied by reduced neuron loss, decreased production of pro-inflammatory cytokines, and a limited number of microglia in the hippocampus. Moreover, WIN 55,212-2 elevated the protein expression of IL-33 (the ligand of ST2) and ST2, increased the ratio of CD206-positive (M2 phenotype) and ST2-positive microglia, and augmented production of M2 microglia-associated cytokines in the hippocampus of CO-exposed rats. Furthermore, we observed that the WIN 55,212-2-mediated increases in ST2 protein expression, CD206-positive and ST2-positive microglia, and microglia-associated cytokines were blocked by the cannabinoid receptor 2 (CB2R) antagonist AM630 but not by the cannabinoid receptor 1 (CB1R) antagonist AM251. In contrast, the WIN 55,212-2-induced upregulation of the IL-33 protein expression was inhibited by AM251 but not by AM630. Altogether, these findings reveal cannabinoid receptors as promising therapeutic agents for CO poisoning and identify ST2 signaling-related microglial M2 polarization as a new mechanism of cannabinoid-induced neuroprotection.

Silencing of Long Noncoding RNA Nespas Aggravates Microglial Cell Death and Neuroinflammation in Ischemic Stroke

Background and Purpose- Ischemic stroke is one of the leading causes of morbidity and mortality worldwide and a major cause of long-term disability. Recently, long noncoding RNAs have been revealed, which are tightly associated with several human diseases. However, the functions of long noncoding RNAs in ischemic stroke still remain largely unknown. In the current study, for the first time, we investigated the role of long noncoding RNA Nespas in ischemic stroke. Methods- We used in vivo models of middle cerebral artery occlusion and in vitro models of oxygen-glucose deprivation to illustrate the effect of long noncoding RNA Nespas on ischemic stroke. Results- We found expression of Nespas was significantly increased in ischemic cerebral tissues and oxygen-glucose deprivation-treated BV2 cells in a time-dependent manner. Silencing of Nespas aggravated middle cerebral artery occlusion operation-induced IR injury and cell death. In addition, proinflammatory cytokine production and NF-κB (nuclear factor-κB) signaling activation were inhibited by Nespas overexpression. TAK1 (transforming growth factor-β-activated kinase 1) was found to directly interact with Nespas, and TAK1 activation was significantly suppressed by Nespas. At last, we found Nespas-inhibited TRIM8 (tripartite motif 8)-induced K63-linked polyubiquitination of TAK1. Conclusions- We showed that Nespas played anti-inflammatory and antiapoptotic roles in cultured microglial cells after oxygen-glucose deprivation stimulation and in mice after ischemic stroke by inhibiting TRIM8-related K63-linked polyubiquitination of TAK1.

Activation of microglia synergistically enhances neurodegeneration caused by MPP+ in human SH-SY5Y cells

While MPP⁺ may not directly activate microglia, the initial neuronal damage inflicted by the toxin may trigger microglia, possibly leading to synergistic pro-apoptotic interaction between neuro-inflammation and toxin-induced neurotoxicity, which may further aggravate neurodegeneration. However, what molecular targets are synergistically up or downregulated during this interaction is not well understood. Here, we addressed this by co-culturing fully differentiated human SH-SY5Y cells treated with parkinsonian toxin 1-Methyl-4-phenylpyridinium (MPP⁺), with endotoxin-activated microglial cell line EOC 20 to determine how this interaction affects pro-apoptotic (p38, JNK, and bax:bcl2 ratios) and pro-survival (NF-κB, MEK1) signaling at both mRNA and protein levels. Concurrent MPP⁺ and endotoxin-treatment aggravated a decrease in SH-SY5Y cell viability and caused strong synergistic increases in the bax:bcl2 ratio, but also NF-κB and JNK signaling. These effects were attenuated by microglia inhibitor minocycline. Altogether, these data provide further molecular insights into the important role or even conditional requirement of microglia activation in the progressive neurodegenerative nature of PD.

Non-invasive Vagus Nerve Stimulation Protects Against Cerebral Ischemia/Reperfusion Injury and Promotes Microglial M2 Polarization Via Interleukin-17A Inhibition

Microglia play an essential role during cerebral an ischemia/reperfusion (I/R)-related inflammatory process. Because the M2 phenotype of microglia exhibits anti-inflammation activity, it has become a promising target for anti-inflammatory therapy. Vagus nerve stimulation (VNS) reportedly has neuroprotective effects against cerebral I/R injuries via its anti-inflammatory action. The aim of this study was to investigate the ability of non-invasive VNS (nVNS) to alleviate cerebral I/R in mice by promoting microglial M2 polarization. Neurological scoring and cerebral infarct volume assessments were performed 72 h after a middle cerebral artery occlusion (MCAO)-induced stroke. M2 phenotype microglia were identified by immunohistochemistry staining using Arg-1 and Iba-1 antibodies. The protein expressions of Arg-1, IL-17A, IL-10, Bax, and Bcl-2 were detected by Western blot. Apoptotic cells were detected using TUNEL staining. According to our results, nVNS decreased infarct volume, improved neurological outcomes, reduced apoptotic neurons (TUNEL⁺NeuN⁺ cells), and promoted microglial M2 polarization as indicated by elevated Arg-1 protein expression and increased Arg-1⁺ cells after MCAO. Moreover, nVNS attenuated the increased levels of IL-17A protein expression after MCAO. To test the possible involvement of IL-17A in nVNS-induced neuroprotection and microglial M2 polarization, 1-μg recombinant IL-17A (rIL-17A) was intranasally administered once daily for three consecutive days after reperfusion. We found that the intranasal administration of rIL-17A nullified the nVNS-induced promotion of microglial M2 polarization. Furthermore, rIL-17A administration abolished the neuroprotective effect of nVNS. In conclusion, our study identifies microglial M2 polarization as an important mechanism underlying the nVNS-mediated neuroprotection against cerebral I/R. This effect of nVNS could be attributed to the inhibition of IL-17A expression.

Pivotal role of innate myeloid cells in cerebral post-ischemic sterile inflammation

Inflammatory responses play a multifaceted role in regulating both disability and recovery after ischemic brain injury. In the acute phase of ischemic stroke, resident microglia elicit rapid inflammatory responses by the ischemic milieu. After disruption of the blood-brain barrier, peripheral-derived neutrophils and mononuclear phagocytes infiltrate into the ischemic brain. These infiltrating myeloid cells are activated by the endogenous alarming molecules released from dying brain cells. Inflammation after ischemic stroke thus typically consists of sterile inflammation triggered by innate immunity, which exacerbates the pathologies of ischemic stroke and worsens neurological prognosis. Infiltrating immune cells sustain the post-ischemic inflammation for several days; after this period, however, these cells take on a repairing function, phagocytosing inflammatory mediators and cellular debris. This time-specific polarization of immune cells in the ischemic brain is a potential novel therapeutic target. In this review, we summarize the current understanding of the phase-dependent role of innate myeloid cells in ischemic stroke and discuss the cellular and molecular mechanisms of their inflammatory or repairing polarization from a therapeutic perspective.

Antagonizing bone morphogenetic protein 4 attenuates disease progression in a rat model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult-onset, fatal neurodegenerative syndrome characterized by the systemic loss of motor neurons with prominent astrocytosis and microgliosis in the spinal cord and brain. Astrocytes play an essential role in maintaining extracellular microenvironments that surround motor neurons, and are activated by various insults. Growing evidence points to a non-cell autonomous neurotoxicity caused by chronic and sustained astrocytic activation in patients with neurodegenerative diseases, including ALS. However, the mechanisms that underlie the harmful effects of astrocytosis in patients with ALS remain unresolved. We focused on bone morphogenetic proteins as a major soluble factor that promotes astrocytogenesis and its activation in the adult spinal cord. In a transgenic rat model with ALS-linked mutant Cu/Zn superoxide dismutase gene, BMP4 was progressively up-regulated in reactive astrocytes of the spinal ventral horns, whereas the BMP-antagonist noggin was decreased in association with neuronal degeneration. Continuous intrathecal noggin supplementation after disease onset significantly ameliorated motor dysfunction symptoms, neurogenic muscle atrophy, and extended survival of symptomatic ALS model rats, despite lack of deterrence against neuronal death itself. The exogenous noggin inhibited astrocytic hypertrophy, astrocytogenesis, and neuroinflammation by inactivating both Smad1/5/8 and p38 mitogen-activated protein kinase pathways. Moreover, intrathecal infusion of a Bmp4-targeted antisense oligonucleotides and provided selective Bmp4 knockdown in vivo, which suppressed astrocyte and microglia activation, reproducing the aforementioned results by noggin treatment. Collectively, we clarified the involvement of BMP4 in the processes of excessive gliosis that exacerbate the disease progression of the ALS model rats. Our study demonstrated that BMP4, with its downstream signaling, might be a novel therapeutic target for disease-modifying therapies in ALS.

Treatment targets for M2 microglia polarization in ischemic stroke

As the first line of defense in the nervous system, resident microglia are the predominant immune cells in the brain. In diseases of the central nervous system such as stroke, Alzheimer's disease, and Parkinson's disease, they often cause inflammation or phagocytosis; however, some studies have found that despite the current controversy over M1, M2 polarization could be beneficial. Ischemic stroke is the third most common cause of death in humans. Patients who survive an ischemic stroke might experience a clear decline in their quality of life, owing to conditions such as hemiplegic paralysis and aphasia. After stroke, the activated microglia become a double-edged sword, with distinct phenotypic changes to the deleterious M1 and neuroprotective M2 types. Therefore, methods for promoting the differentiation of microglia into the M2 polarized form to alleviate harmful reactions after stroke have become a topic of interest in recent years. Subsequently, the discovery of new drugs related to M2 polarization has enabled the realization of targeted therapies. In the present review, we discussed the neuroprotective effects of microglia M2 polarization and the potential mechanisms and drugs by which microglia can be transformed into the M2 polarized type after stroke.

Loss of neuronal CD200 contributed to microglial activation after acute cerebral ischemia in mice

CD200 has been proved to play a role in immuno-inflammatory reaction. However, little information is available on CD200 in the acute stage of cerebral ischemia. We investigated the association between neuronal death and expression of CD200, and explored the relationship between CD200 and microglia in cerebral ischemic mice. Firstly, localization of CD200 expression in the normal brain tissue was detected by immunofluorescent assay. Then, focal cerebral ischemia was induced in mice by permanent middle cerebral artery occlusion (pMCAO) and then cortical tissues were collected at 6, 12, 24 and 48 h after surgery. Changes of CD200 and neuron-specific enolase (NSE) after pMCAO were assessed by western blotting. Meanwhile flow cytometry analysis was implemented to analyze the death of cortical cells. Results of these two parts were analyzed by Pearson correlation analysis. To further study, intracerebroventricular (ICV) injection of recombinant CD200 (rCD200) protein was carried out immediately after pMCAO. Iba-1 was measured by western blotting to evaluate activation of microglia, and inflammatory cytokines including IL-1β, TNF-α and IL-10 were tested by enzyme-linked immuno sorbent assay (ELISA). The results showed that CD200 was expressed in neurons and was not observed on mircroglia in cortex of normal mice. Expression of CD200 was decreased within 48 h after pMCAO, with a concomitant decrease of NSE expression. The rate of neuronal cell death was approximately around 30% and statistical analysis revealed a negative correlation between level of CD200 and the rate of neuronal death. Compared with control, exogenous rCD200 reduced expressions of Iba-1, IL-1β, TNF-α and IL-10. Taking together, our results demonstrated that loss of CD200 was caused by neuronal death and was one of contributing factors in microglial activation after cerebral ischemia. ICV injection of rCD200 protein could suppress activation of microglia in vivo.

Bone Morphogenetic Protein-Based Therapeutic Approaches

Bone morphogenetic proteins (BMPs) constitute the largest subdivision of the transforming growth factor (TGF)-β family of ligands and exert most of their effects through the canonical effectors Smad1, 5, and 8. Appropriate regulation of BMP signaling is critical for the development and homeostasis of numerous human organ systems. Aberrations in BMP pathways or their regulation are increasingly associated with diverse human pathologies, and there is an urgent and growing need to develop effective approaches to modulate BMP signaling in the clinic. In this review, we provide a wide perspective on diseases and/or conditions associated with dysregulated BMP signal transduction, outline the current strategies available to modulate BMP pathways, highlight emerging second-generation technologies, and postulate prospective avenues for future investigation.

Temporal Gene Expression Profiles after Focal Cerebral Ischemia in Mice

A cascade of pathological processes is triggered in the lesion area after ischemic stroke. Unfortunately, our understanding of these complicated molecular events is incomplete. In this investigation, we sought to better understand the detailed molecular and inflammatory events occurring after ischemic stroke. RNA-seq technology was used to identify whole gene expression profiles at days (D1, D3, D7, D14, D21) after focal cerebral ischemia in mice. Enrichment analyses based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) terms for the differentially expressed genes (DEGs) were then analyzed. Inflammation-related genes that were significantly expressed after stroke were selected for analysis and the temporal expression patterns of pro-inflammatory and anti-inflammatory genes were reported. These data illustrated that the number of DEGs increased accumulatively after cerebral ischemia. In summary, there were 1967 DEGs at D1, 2280 DEGs at D3, 2631 DEGs at D7, 5516 DEGs at D14 and 7093 DEGs at D21. The significantly enriched GO terms also increased. 58 GO terms and 18 KEGG pathways were significantly enriched at all inspected time points. We identified 87 DEGs which were functionally related to inflammatory responses. The expression levels of pro-inflammation related genes CD16, CD32, CD86, CD11b, Tumour necrosis factor α (TNF-α), Interleukin 1β (IL-1β) increased over time and peaked at D14. Anti-inflammation related genes Arginase 1 (Arg1) and Chitinase-like 3 (Ym1) peaked at D1 while IL-10, Transforming growth factor β (TGF-β) and CD206, which were induced at 1 day after cerebral ischemia, peaked by 7 to 14 days. These gene profile changes were potentially linked to microglia/macrophage phenotype changes and could play a role in astroglial activation. This study supplies new insights and detailed information on the molecular events and pathological mechanisms that occur after experimental ischemic stroke.

Iron released from reactive microglia by noggin improves myelin repair in the ischemic brain

We previously reported that the bone morphogenetic protein (BMP) antagonist, noggin, improved the repair process with an increase in the reactive microglia/macrophage population in the ischemic brain. Since BMP plays a role in intracellular iron homeostasis via the hepcidin/ferroportin axis, and iron is required for myelination, this study was aimed to determine whether noggin affected iron status and remyelination in the brain following ischemic stroke. We further examined the effect of blocking the BMP/hepcidin pathway on reactive microglia (BV2) and myelination of oligodendroglial cells (MO3.13) to define the link between microglial iron status and myelin formation. Following the noggin infusion into the ischemic brain of mice, the induction of hepcidin and ferritin protein levels decreased, and the number of myelinated axons and myelin thickness increased at 8 weeks after ischemic stroke. Noggin repressed the increase in hepcidin and ferritin levels in BV2 exposed to lipopolysaccharide (LPS) and oxygen/glucose deprivation and reperfusion (OGD/R). When MO3.13 were exposed to the conditioned media from noggin-treated BV2 (noggin CM) during reperfusion, OGD/R-induced MO3.13 cell death was reduced. Under normal conditions, noggin CM induced myelin production with an increase in ferritin levels in MO3.13, which was reversed by the iron chelator, deferoxamine. These results indicated that noggin altered the iron status in reactive microglia from the iron-storing to the iron-releasing phenotype, which contributed to myelin synthesis by providing iron. We suggest that the BMP/hepcidin pathway can be a target for the regulation of the iron status in microglia to enhance remyelination in the ischemic brain.

Homocysteine exaggerates microglia activation and neuroinflammation through microglia localized STAT3 overactivation following ischemic stroke

Background

Elevated plasma homocysteine (Hcy) levels have been indicated as a strong and modifiable risk factor of ischemic stroke; the previous studies have shown that exposure to Hcy activates cultured microglia. However, whether neurotoxicity of Hcy involves microglia activation following brain ischemia and the underlying mechanisms remains incompletely understood.

Methods

The cerebral damage was evaluated by staining with 2,3,5-triphenyltetrazolium chloride, hematoxylin-eosin, and Fluoro Jade B. The activation state of microglia was assessed via immunoreaction using the microglial markers Iba1 and OX-42. Then, the inflammatory factors such as tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), and phosphorylated signal transducer and activator of transcription 3 (pSTAT3) were examined by Western blot analysis and fluorescence immunohistochemistry.

Results

Elevated Hcy level augmented brain damage and neural cell toxicity in the brain cortex and the dentate gyrus region of the hippocampus after cerebral ischemia/reperfusion. Meanwhile, Hcy activated microglia and induced the expression of the inflammatory factors such as TNF-α and IL-6. Moreover, Hcy caused an increase in pSTAT3 expression which occurs in microglial cells. AG490, a JAK2-STAT3 inhibitor, effectively inhibited the phosphorylation of STAT3, microglial cell activation and the secretion of IL-6, TNF-α raised by Hcy treatment.

Conclusions

STAT3 signaling pathway located in microglia plays a critical role in mediating Hcy-induced activation of microglia and neuroinflammation in rat MCAO model. This suggests the feasibility of targeting the JAK2/STAT3 pathway as an effective therapeutic strategy to alleviate the progression of Hcy-associated ischemia stroke.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-0963-x) contains supplementary material, which is available to authorized users.

Regulation of microglial activation in stroke

When ischemic stroke occurs, oxygen and energy depletion triggers a cascade of events, including inflammatory responses, glutamate excitotoxicity, oxidative stress, and apoptosis that result in a profound brain injury. The inflammatory response contributes to secondary neuronal damage, which exerts a substantial impact on both acute ischemic injury and the chronic recovery of the brain function. Microglia are the resident immune cells in the brain that constantly monitor brain microenvironment under normal conditions. Once ischemia occurs, microglia are activated to produce both detrimental and neuroprotective mediators, and the balance of the two counteracting mediators determines the fate of injured neurons. The activation of microglia is defined as either classic (M1) or alternative (M2): M1 microglia secrete pro-inflammatory cytokines (TNFα, IL-23, IL-1β, IL-12, etc) and exacerbate neuronal injury, whereas the M2 phenotype promotes anti-inflammatory responses that are reparative. It has important translational value to regulate M1/M2 microglial activation to minimize the detrimental effects and/or maximize the protective role. Here, we discuss various regulators of microglia/macrophage activation and the interaction between microglia and neurons in the context of ischemic stroke.

Cerebral Vascular Disease and Neurovascular Injury in Ischemic Stroke

The consequences of cerebrovascular disease are among the leading health issues worldwide. Large and small cerebral vessel disease can trigger stroke and contribute to the vascular component of other forms of neurological dysfunction and degeneration. Both forms of vascular disease are driven by diverse risk factors, with hypertension as the leading contributor. Despite the importance of neurovascular disease and subsequent injury after ischemic events, fundamental knowledge in these areas lag behind our current understanding of neuroprotection and vascular biology in general. The goal of this review is to address select key structural and functional changes in the vasculature that promote hypoperfusion and ischemia, while also affecting the extent of injury and effectiveness of therapy. In addition, as damage to the blood-brain barrier is one of the major consequences of ischemia, we discuss cellular and molecular mechanisms underlying ischemia-induced changes in blood-brain barrier integrity and function, including alterations in endothelial cells and the contribution of pericytes, immune cells, and matrix metalloproteinases. Identification of cell types, pathways, and molecules that control vascular changes before and after ischemia may result in novel approaches to slow the progression of cerebrovascular disease and lessen both the frequency and impact of ischemic events.

Role of Myo/Nog Cells in Neuroprotection: Evidence from the Light Damaged Retina

PURPOSE

To identify Myo/Nog cells in the adult retina and test their role in protecting retinal photoreceptors from light damage.

METHODS

Light damage was induced by exposing albino rats raised in dim cyclic light to 1000 lux light for 24 hours. In one group of rats, Myo/Nog cells were purified from rat brain tissue by magnetic cell sorting following binding of the G8 monoclonal antibody (mAb). These cells were injected into the vitreous humour of the eye within 2 hours following bright light exposure. Retinal function was assessed using full-field, flash electroretinogram (ERG) before and after treatment. The numbers of Myo/Nog cells, apoptotic photoreceptors, and the expression of glial fibrillary acidic protein (GFAP) in Muller cells were assessed by immunohistochemistry.

RESULTS

Myo/Nog cells were present in the undamaged retina in low numbers. Light induced damage increased their numbers, particularly in the choroid, ganglion cell layer and outer plexiform layer. Intravitreal injection of G8-positive (G8+) cells harvested from brain mitigated all the effects of light damage examined, i.e. loss of retinal function (ERG), death of photoreceptors and the stress-induced expression of GFAP in Muller cells. Some of the transplanted G8+ cells were integrated into the retina from the vitreous.

CONCLUSIONS

Myo/Nog cells are a subpopulation of cells that are present in the adult retina. They increase in number in response to light induced stress. Intravitreal injection of Myo/Nog cells was protective to the retina, in part, by reducing retinal stress as measured by the Muller cell response. These results suggest that Myo/Nog cells, or the factors they produce, are neuroprotective and may be therapeutic in neurodegenerative retinal diseases.

Pharmacological approaches to intervention in hypomyelinating and demyelinating white matter pathology

White matter disease afflicts both developing and mature central nervous systems. Both cell intrinsic and extrinsic dysregulation result in profound changes in cell survival, axonal metabolism and functional performance. Experimental models of developmental white matter (WM) injury and demyelination have not only delineated mechanisms of signaling and inflammation, but have also paved the way for the discovery of pharmacological approaches to intervention. These reagents have been shown to enhance protection of the mature oligodendrocyte cell, accelerate progenitor cell recruitment and/or differentiation, or attenuate pathological stimuli arising from the inflammatory response to injury. Here we highlight reports of studies in the CNS in which compounds, namely peptides, hormones, and small molecule agonists/antagonists, have been used in experimental animal models of demyelination and neonatal brain injury that affect aspects of excitotoxicity, oligodendrocyte development and survival, and progenitor cell function, and which have been demonstrated to attenuate damage and improve WM protection in experimental models of injury. The molecular targets of these agents include growth factor and neurotransmitter receptors, morphogens and their signaling components, nuclear receptors, as well as the processes of iron transport and actin binding. By surveying the current evidence in non-immune targets of both the immature and mature WM, we aim to better understand pharmacological approaches modulating endogenous oligodendroglia that show potential for success in the contexts of developmental and adult WM pathology. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

Delayed Treatment with Green Tea Polyphenol EGCG Promotes Neurogenesis After Ischemic Stroke in Adult Mice

(-)-Epigallocatechin-3‑gallate (EGCG), the predominant constituent of green tea, has been demonstrated to be neuroprotective against acute ischemic stroke. However, the long-term actions of EGCG on neurogenesis and functional recovery after ischemic stroke have not been identified. In this study, C57BL/6 mice underwent middle cerebral artery occlusion (60 min) followed by reperfusion for 28 days. Neural progenitor cells (NPCs) were isolated from ipsilateral subventricular zone (SVZ) at 14 days post-ischemia (dpi). The effects of EGCG on the proliferation and differentiation of NPCs were examined in vivo and in vitro. Behavioral assessments were made 3 days before MCAO and at 28 dpi. SVZ NPCs were stimulated with lipopolysaccharide (LPS) in vitro to mimic the inflammatory response after ischemic stroke. We found that 14 days treatment with EGCG significantly increased the proliferation of SVZ NPCs and the migration of SVZ neuroblasts, as well as functional recovery, perhaps through M2 phenotype induction in microglia. LPS stimulation promoted the neuronal differentiation in cultured NPCs from the ischemic SVZ. EGCG treatment (20 or 40 μM) further significantly increased the neuronal differentiation of LPS-stimulated SVZ NPCs. After screening for multiple signaling pathways, the AKT signaling pathway was found to be involved in EGCG-mediated proliferation and neuronal differentiation of NPCs in vitro. Taken together, our results reveal a previously uncharacterized role of EGCG in the augment of proliferation and neuronal differentiation of SVZ NPCs and subsequent spontaneous recovery after ischemic stroke. Thus, the beneficial effects of EGCG on neurogenesis and stroke recovery should be considered in developing therapeutic approaches.

Smad signal pathway regulates angiogenesis via endothelial cell in an adipose-derived stromal cell/endothelial cell co-culture, 3D gel model

Co-implantation of adipose-derived stromal cells (ASCs) and endothelial cells (ECs) can markedly expedite the formation of functional microvascular beds and provides possible methods for cell-based revascularization therapies to treat various diseases. Furthermore, we investigated the role of TGFβ/Smad signaling pathway for angiogenesis in a three-dimensional (3D) collagen gel model established in vitro with co-culture between ASCs and ECs. We found that angiogenesis was attenuated in the co-culture gels after inhibition of ALK5/Smad2/3 with SB431542. Genes coding for VEGF-A, VEGF-B, VE-ca, FGF-1, PDGF, BMP-4, and BMP-7 were significantly reduced in both mono-cultured and co-cultured ECs. Furthermore, the decrease in co-cultured ECs was prominent relative to mono-cultured ECs. Taken together, these findings suggest that in the co-culture between ASCs and ECs, TGFβ/Smad signal pathway regulates angiogenesis via ECs; moreover, the findings that the co-cultured ECs were regulated more significantly than mono-cultured ECs suggest that suppression of Smad signal pathway may regulate the paracrine secretion of ASCs to further modulate angiogenesis of ECs.

Gene expression profiling in stroke: relevance of blood-brain interaction

Biomarker profiling is utilized to identify diagnostic and prognostic candidates for stroke. Clinical and preclinical biomarker data suggest altered circulating immune responses may illuminate the mechanisms of stroke recovery. However, the relationship between peripheral blood biomarker profile(s) and brain profiles following stroke remains elusive. Data show that neutrophil lymphocyte ratio (NLR) predicts stroke outcome. Neutrophils release Arginase 1 (ARG1) resulting in T lymphocyte suppression in peripheral blood. Interestingly, the cellular response to stroke may have implications for known biomarker profiles. Conversely, preclinical evidence suggests that upregulation of ARG1 in microglia is a marker of M2 macrophages and may influence neuroprotection. Comparing clinical and preclinical studies creates opportunities to explore the molecular mechanisms of blood and brain biomarker interactions in stroke.

Microglia in the TBI brain: The good, the bad, and the dysregulated

As the major cellular component of the innate immune system in the central nervous system (CNS) and the first line of defense whenever injury or disease occurs, microglia play a critical role in neuroinflammation following a traumatic brain injury (TBI). In the injured brain microglia can produce neuroprotective factors, clear cellular debris and orchestrate neurorestorative processes that are beneficial for neurological recovery after TBI. However, microglia can also become dysregulated and can produce high levels of pro-inflammatory and cytotoxic mediators that hinder CNS repair and contribute to neuronal dysfunction and cell death. The dual role of microglial activation in promoting beneficial and detrimental effects on neurons may be accounted for by their polarization state and functional responses after injury. In this review article we discuss emerging research on microglial activation phenotypes in the context of acute brain injury, and the potential role of microglia in phenotype-specific neurorestorative processes such as neurogenesis, angiogenesis, oligodendrogenesis and regeneration. We also describe some of the known molecular mechanisms that regulate phenotype switching, and highlight new therapeutic approaches that alter microglial activation state balance to enhance long-term functional recovery after TBI. An improved understanding of the regulatory mechanisms that control microglial phenotypic shifts may advance our knowledge of post-injury recovery and repair, and provide opportunities for the development of novel therapeutic strategies for TBI.

Hyperbaric oxygen preconditioning attenuates neuroinflammation after intracerebral hemorrhage in rats by regulating microglia characteristics

Intracerebral Hemorrhage (ICH) results in a detrimental neurologic disorder with complicated secondary brain injury. Hyperbaric oxygen preconditioning (HBOP) may be a safe and effective therapeutic method for ICH victims. Our previous studies have demonstrated that HBOP induces neuroprotection in cerebral ischemia and traumatic brain injury. This study aimed to investigate whether HBOP could alleviate neuroinflammation by regulating changes in microglia characteristics in a rat model of ICH. ICH was induced by autologous arterial blood injection, and animals were sacrificed at 12, 24, and 72 h post injury. We measured motor function and brain water content to evaluate the extent of inflammation. Fluoro-Jade C and TNF-α staining was used to characterize neuronal degeneration and neuroinflammatory cytokines, and immunofluorescence staining was performed for CD11b to show activated microglia and Iba-1 to show microglia. Our results indicate that motor dysfunction and brain water content are alleviated by HBOP, and Fluoro-Jade C staining demonstrates that neuron degeneration decreased in the HBOP group. The growth of Iba-1-positive microglia decreased in the HBOP group. Moreover, TNF-α was dynamically reduced in the HBOP group compared with the ICH group. CD11b-Iba-1 double staining demonstrated that the ratio of CD11b and Iba-1 was significantly decreased in the HBOP group. Overall, the data demonstrated that HBOP could significantly alleviate the ICH-induced neuroinflammation by regulating microglia characteristics changing. The phenomenon may propel the progress of the relation between microglia and HBOP and represent a novel target for ICH treatment.

The Bone Morphogenetic Proteins and Their Antagonists

The bone morphogenetic proteins (BMPs) and the growth and differentiation factors comprise a single family of some 20 homologous, dimeric cytokines which share the cystine-knot domain typical of the TGF-β superfamily. They control the differentiation and activity of a range of cell types, including many outside bone and cartilage. They serve as developmental morphogens, but are also important in chronic pathologies, including tissue fibrosis and cancer. One mechanism for enabling tight spatiotemporal control of their activities is through a number of antagonist proteins, including Noggin, Follistatin, Chordin, Twisted gastrulation (TSG), and the seven members of the Cerberus and Dan family. These antagonists are secreted proteins that bind selectively to particular BMPs with high affinity, thereby blocking receptor engagement and signaling. Most of these antagonists also possess a TGF-β cystine-knot domain. Here, we discuss current knowledge and understanding of the structures and activities of the BMPs and their antagonists, with a particular focus on the latter proteins. Recent advances in structural biology of BMP antagonists have begun the process of elucidating the molecular basis of their activity, displaying a surprising variety between the modes of action of these closely related proteins. We also discuss the interactions of the antagonists with the glycosaminoglycan heparan sulfate, which is found ubiquitously on cell surfaces and in the extracellular matrix.

Alternatively activated microglia and macrophages in the central nervous system

Macrophages are important players in the fight against viral, bacterial, fungal and parasitic infections. From a resting state they may undertake two activation pathways, the classical known as M1, or the alternative known as M2. M1 markers are mostly mediators of pro-inflammatory responses whereas M2 markers emerge for resolution and cleanup. Microglia exerts in the central nervous system (CNS) a function similar to that of macrophages in the periphery. Microglia activation and proliferation occurs in almost any single pathology affecting the CNS. Often microglia activation has been considered detrimental and drugs able to stop microglia activation were considered for the treatment of a variety of diseases. Cumulative evidence shows that microglia may undergo the alternative activation pathway, express M2-type markers and contribute to neuroprotection. This review focuses on details about the role of M2 microglia and in the approaches available for its identification. Approaches to drive the M2 phenotype and data on its potential in CNS diseases are also reviewed.

Gene profile of soluble growth factors involved in angiogenesis, in an adipose-derived stromal cell/endothelial cell co-culture, 3D gel model

OBJECTIVES

The aim of this study was to investigate gene expressions of growth factors for angiogenesis, in a three-dimensional (3D) gel populated with adipose-derived stromal cells (ASCs) and endothelial cells (ECs) in co-culture.

MATERIALS AND METHODS

The 3D gel, mixed with green fluorescent protein (GFP)-positive ASCs and DsRed-Express-positive ECs, 1:1 ratio, was established in vitro. The phenomenon of angiogenesis was observed using confocal microscopy. To detect gene expressions for growth factor proteins in both ASCs and ECs, transwell co-culture was used, and cell lysate samples were collected at 1, 3, 5 and 7 days. Semi-quantitative polymerase chain reaction (PCR) was conducted to quantify mRNA expressions of the growth factors.

RESULTS

Angiogenesis was first observed in the gels by 7 days post-implantation. Over this time in ECs, genes coding for VEGFA/B, IGF-1, HIF-1α, FGF-1/-2 and BMP-5/-7 significantly increased. Meanwhile in ASCs, genes coding for VEGFA/B, IGF-1, HIF-1α, FGF-1/-2 and BMP-6 also were significantly enhanced. In particular, increased amounts of IGF-1 and HIF-1α in both ECs and ASCs were prominent relative to other factors.

CONCLUSIONS

Contact co-culture with ASCs and ECs at 1:1 ratio, in the 3D gel promoted angiogenesis; non-contact co-culture further confirmed gene expressions for growth factors, VEGFA/B, IGF-1, HIF-1α and FGF-1/-2 in both ASCs and ECs; BMP-5/-7 in ECs and BMP-6 in ASCs were also confirmed. This establishment of growth factor expression seemed to be responsible for enhancement of angiogenesis. This indicates that these factors could be utilized as targets for engineered angiogenesis.