Astrocytic Toll-like receptor 3 is associated with ischemic preconditioning-induced protection against brain ischemia in rodents

Toll-Like Receptor mRNA Levels in Schizophrenia: Association With Complement Factors and Cingulate Gyrus Cortical Thinning

BACKGROUND AND HYPOTHESES

Previous studies revealed innate immune system activation in people with schizophrenia (SZ), potentially mediated by endogenous pathogen recognition receptors, notably Toll-like receptors (TLR). TLRs are activated by pathogenic molecules like bacterial lipopolysaccharides (TLR1 and TLR4), viral RNA (TLR3), or both (TLR8). Furthermore, the complement system, another key component of innate immunity, has previously been linked to SZ.

STUDY DESIGN

Peripheral mRNA levels of TLR1, TLR3, TLR4, and TLR8 were compared between SZ and healthy controls (HC). We investigated their relationship with immune activation through complement expression and cortical thickness of the cingulate gyrus, a region susceptible to immunological hits. TLR mRNA levels and peripheral complement receptor mRNA were extracted from 86 SZ and 77 HC white blood cells; structural MRI scans were conducted on a subset.

STUDY RESULTS

We found significantly higher TLR4 and TLR8 mRNA levels and lower TLR3 mRNA levels in SZ compared to HC. TLRs and complemental factors were significantly associated in SZ and HC, with the strongest deviations of TLR mRNA levels in the SZ subgroup having elevated complement expression. Cortical thickness of the cingulate gyrus was inversely associated with TLR8 mRNA levels in SZ, and with TLR4 and TLR8 levels in HC.

CONCLUSIONS

The study underscores the role of innate immune activation in schizophrenia, indicating a coordinated immune response of TLRs and the complement system. Our results suggest there could be more bacterial influence (based on TLR 4 levels) as opposed to viral influence (based on TLR3 levels) in schizophrenia. Specific TLRs were associated with brain cortical thickness reductions of limbic brain structures.

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

Background

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

Materials and methods

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

Results

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

Conclusion

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

Toll-like receptor 4 (TLR4): new insight immune and aging

TLR4, a transmembrane receptor, plays a central role in the innate immune response. TLR4 not only engages with exogenous ligands at the cellular membrane's surface but also interacts with intracellular ligands, initiating intricate intracellular signaling cascades. Through MyD88, an adaptor protein, TLR4 activates transcription factors NF-κB and AP-1, thereby facilitating the upregulation of pro-inflammatory cytokines. Another adapter protein linked to TLR4, known as TRIF, autonomously propagates signaling pathways, resulting in heightened interferon expression. Recently, TLR4 has garnered attention as a significant factor in the regulation of symptoms in aging-related disorders. The persistent inflammatory response triggered by TLR4 contributes to the onset and exacerbation of these disorders. In addition, alterations in TLR4 expression levels play a pivotal role in modifying the manifestations of age-related diseases. In this review, we aim to consolidate the impact of TLR4 on cellular senescence and aging-related ailments, highlighting the potential of TLR4 as a novel therapeutic target that extends beyond immune responses.

Nonpharmacological modulation of cortical spreading depolarization

AIMS

Cortical spreading depolarization (CSD) is a wave of pathologic neuronal dysfunction that spreads through cerebral gray matter, causing neurologic disturbance in migraine and promoting lesion development in acute brain injury. Pharmacologic interventions have been found to be effective in migraine with aura, but their efficacy in acutely injured brains may be limited. This necessitates the assessment of possible adjunctive treatments, such as nonpharmacologic methods. This review aims to summarize currently available nonpharmacological techniques for modulating CSDs, present their mechanisms of action, and provide insight and future directions for CSD treatment.

MAIN METHODS

A systematic literature review was performed, generating 22 articles across 3 decades. Relevant data is broken down according to method of treatment.

KEY FINDINGS

Both pharmacologic and nonpharmacologic interventions can mitigate the pathological impact of CSDs via shared molecular mechanisms, including modulating K⁺/Ca²⁺/Na⁺/Cl^- ion channels and NMDA, GABA_A, serotonin, and CGRP ligand-based receptors and decreasing microglial activation. Preclinical evidence suggests that nonpharmacologic interventions, including neuromodulation, physical exercise, therapeutic hypothermia, and lifestyle changes can also target unique mechanisms, such as increasing adrenergic tone and myelination and modulating membrane fluidity, which may lend broader modulatory effects. Collectively, these mechanisms increase the electrical initiation threshold, increase CSD latency, slow CSD velocity, and decrease CSD amplitude and duration.

SIGNIFICANCE

Given the harmful consequences of CSDs, limitations of current pharmacological interventions to inhibit CSDs in acutely injured brains, and translational potentials of nonpharmacologic interventions to modulate CSDs, further assessment of nonpharmacologic modalities and their mechanisms to mitigate CSD-related neurologic dysfunction is warranted.

Early activation of Toll-like receptor-3 reduces the pathological progression of Alzheimer's disease in APP/PS1 mouse

BACKGROUND

Toll-like receptor 3 (TLR3) plays an important role in the immune/inflammatory response in the nervous system and is a main pathological feature of Alzheimer's disease (AD). This study investigates the role of early activation of TLR3 in the pathophysiological process of AD.

METHODS

In the experiment, the agonist of TLR3, Poly(I:C), was intraperitoneally injected into the APP/PS1 mouse model of AD and wild-type control mice starting from the age of 4 to 9 months. At the age of 14 months, behavioral tests were conducted. Western blot and immunohistochemistry staining were used to evaluate the level of amyloid β-protein (Aβ), the activation of inflammatory cells, and neuron loss. In addition, the levels of inflammatory cytokines were measured using a quantitative polymerase chain reaction.

RESULTS

The results demonstrated that the early activation of TLR3 attenuated neuronal loss and neurobehavioral dysfunction. Moreover, the early activation of TLR3 reduced Aβ deposition, inhibited the activation of microglia and astrocytes, and decreased the transcription of pro-inflammatory factors in the hippocampus.

CONCLUSIONS

The results indicated that the activation of TLR3 by Poly (I:C) in the early stage of development of AD in a mouse model attenuated neuron loss and improved neurobehavioral functions. The underlying mechanisms could be attributed to its role in Aβ clearance, the inhibition of glial cells, and the regulation of neuroinflammation in the hippocampus.

Neuroprotective effects and mechanisms of ischemic/hypoxic preconditioning on neurological diseases

As the organ with the highest demand for oxygen, the brain has a poor tolerance to ischemia and hypoxia. Despite severe ischemia/hypoxia induces the occurrence and development of various central nervous system (CNS) diseases, sublethal insult may induce strong protection against subsequent fatal injuries by improving tolerance. Searching for potential measures to improve brain ischemic/hypoxic is of great significance for treatment of ischemia/hypoxia related CNS diseases. Ischemic/hypoxic preconditioning (I/HPC) refers to the approach to give the body a short period of mild ischemic/hypoxic stimulus which can significantly improve the body's tolerance to subsequent more severe ischemia/hypoxia event. It has been extensively studied and been considered as an effective therapeutic strategy in CNS diseases. Its protective mechanisms involved multiple processes, such as activation of hypoxia signaling pathways, anti-inflammation, antioxidant stress, and autophagy induction, etc. As a strategy to induce endogenous neuroprotection, I/HPC has attracted extensive attention and become one of the research frontiers and hotspots in the field of neurotherapy. In this review, we discuss the basic and clinical research progress of I/HPC on CNS diseases, and summarize its mechanisms. Furthermore, we highlight the limitations and challenges of their translation from basic research to clinical application.

Traumatic Brain Injury: Ultrastructural Features in Neuronal Ferroptosis, Glial Cell Activation and Polarization, and Blood-Brain Barrier Breakdown

The secondary injury process after traumatic brain injury (TBI) results in motor dysfunction, cognitive and emotional impairment, and poor outcomes. These injury cascades include excitotoxic injury, mitochondrial dysfunction, oxidative stress, ion imbalance, inflammation, and increased vascular permeability. Electron microscopy is an irreplaceable tool to understand the complex pathogenesis of TBI as the secondary injury is usually accompanied by a series of pathologic changes at the ultra-micro level of the brain cells. These changes include the ultrastructural changes in different parts of the neurons (cell body, axon, and synapses), glial cells, and blood–brain barrier, etc. In view of the current difficulties in the treatment of TBI, identifying the changes in subcellular structures can help us better understand the complex pathologic cascade reactions after TBI and improve clinical diagnosis and treatment. The purpose of this review is to summarize and discuss the ultrastructural changes related to neurons (e.g., condensed mitochondrial membrane in ferroptosis), glial cells, and blood–brain barrier in the existing reports of TBI, to deepen the in-depth study of TBI pathomechanism, hoping to provide a future research direction of pathogenesis and treatment, with the ultimate aim of improving the prognosis of patients with TBI.

Resolvin D1 Attenuates Innate Immune Reactions in Experimental Subarachnoid Hemorrhage Rat Model

Excessive inflammation is a major cause contributing to early brain injury (EBI) and is associated with negative or catastrophic outcomes of subarachnoid hemorrhage (SAH). Resolvin D1 (RvD1) exerts strong anti-inflammatory and pro-resolving effects on either acute or chronic inflammation of various origin. Henceforth, we hypothesized that RvD1 potentially attenuates excessive inflammation in EBI following SAH. Therefore, we generated a filament perforation SAH model and administered 3 different doses (0.3, 0.6, and 1.2 nmol) of RvD1 after experimental SAH. Neurological scores, brain edema, and blood-brain barrier integrity were evaluated; besides, neutrophil infiltration, neuronal deaths, and microglial pro-inflammatory polarization were observed using histopathology or immunofluorescence staining, western blots, and qPCR. After confirming the effectiveness of RvD1 in SAH, we administered the FPR2-specific antagonist Trp-Arg-Trp-Trp-Trp-Trp-NH2 (WRW4) 30 min before SAH establishment to observe whether this compound could abolish the anti-inflammatory effect of RvD1. Altogether, our results showed that RvD1 exerted a strong anti-inflammatory effect and markedly reduced neutrophil infiltration and microglial pro-inflammatory activation, leading to remarkable improvements in neurological function and brain tissue restoration. After addition of WRW4, the anti-inflammatory effects of RvD1 were abolished. These results indicated that RvD1 could exert a good anti-inflammatory effect and alleviate EBI, which suggested that RvD1 might be a novel therapeutic alternative for SAH-induced injury.

Nuclear heme oxygenase-1 improved the hypoxia-mediated dysfunction of blood-spinal cord barrier via the miR-181c-5p/SOX5 signaling pathway

Our previous study demonstrated that adenovirus-delivered GFP nuclear heme oxygenase-1 (nuclear HO-1, NHO-1) fragments lacking 23 amino acids at the C-terminus (Ad-GFP-HO-1C[INCREMENT]23) showed the potential therapeutic effects mediated by its improvement of the blood-spinal cord barrier (BSCB) integrity. However, the NHO-1-mediated molecular mechanism in regulating the BSCB function remains unclear. The BSCB model in vitro was established via a coculture of primary rat brain microvascular endothelial cells (RBMECs) and spinal cord astrocytes on transwell system. NHO-1 markedly reduced the disruption of the BSCB integrity induced by hypoxia. And NHO-1 significantly attenuated the expression of miR-181c-5p, but increased the expression level of SOX5 protein. miR-181c-5p was shown as an essential miRNA for increasing the BSCB permeability under hypoxia condition. Furthermore, we identified that miR-181c-5p could regulate the expression of SOX5 through binding to the 3'-UTR of its mRNA. And the decreased BSCB permeability and upregulation of tight junction (TJ) protein expression induced by NHO-1 could be partly reversed by the inhibition of SOX5 or miR-181c-5p (+). The present study results provide a better understanding of the molecular mechanisms induced by NHO-1 in improving the BSCB integrity, which is associated with the regulation of miR-181c-5p/SOX5/TJ signaling pathway.

Review Cerebral Ischemic Tolerance and Preconditioning: Methods, Mechanisms, Clinical Applications, and Challenges

Stroke is one of the leading causes of morbidity and mortality worldwide, and it is increasing in prevalence. The limited therapeutic window and potential severe side effects prevent the widespread clinical application of the venous injection of thrombolytic tissue plasminogen activator and thrombectomy, which are regarded as the only approved treatments for acute ischemic stroke. Triggered by various types of mild stressors or stimuli, ischemic preconditioning (IPreC) induces adaptive endogenous tolerance to ischemia/reperfusion (I/R) injury by activating a multitude cascade of biomolecules, for example, proteins, enzymes, receptors, transcription factors, and others, which eventually lead to transcriptional regulation and epigenetic and genomic reprogramming. During the past 30 years, IPreC has been widely studied to confirm its neuroprotection against subsequent I/R injury, mainly including local ischemic preconditioning (LIPreC), remote ischemic preconditioning (RIPreC), and cross preconditioning. Although LIPreC has a strong neuroprotective effect, the clinical application of IPreC for subsequent cerebral ischemia is difficult. There are two main reasons for the above result: Cerebral ischemia is unpredictable, and LIPreC is also capable of inducing unexpected injury with only minor differences to durations or intensity. RIPreC and pharmacological preconditioning, an easy-to-use and non-invasive therapy, can be performed in a variety of clinical settings and appear to be more suitable for the clinical management of ischemic stroke. Hoping to advance our understanding of IPreC, this review mainly focuses on recent advances in IPreC in stroke management, its challenges, and the potential study directions.

Molecular Basis of Sex Difference in Neuroprotection induced by Hypoxia Preconditioning in Zebrafish

Hypoxia, the major cause of ischemic injury, leads to debilitating disease in infants via birth asphyxia and cerebral palsy, whereas in adults via heart attack and stroke. A widespread, natural protective phenomenon termed 'hypoxic preconditioning' (PH) occurs when prior exposures to hypoxia eventually result in robust hypoxia resistance. Accordingly, we have developed and optimized a novel model of hypoxic preconditioning in adult zebrafish to mimic the tolerance of mini stroke(s) in human, which appears to protect against the severe damage inflicted by a major stroke event. Here, we observed a remarkable difference in the progression pattern of neuroprotection between preconditioning hypoxia followed by acute hypoxia (PH) group, and acute hypoxia (AH) only group, with noticeable sex difference when compared with normoxia behaviour upon recovery. Since gender difference has been reported in stroke risk factors and disease history, it was pertinent to investigate whether any such sex difference also exists in PH's protective mechanism against acute ischemic stroke. In order to elucidate the neural molecular mechanisms behind sex difference in neuroprotection induced by PH, a high throughput proteomics approach utilizing iTRAQ was performed, followed by protein enrichment analysis using ingenuity pathway analysis (IPA) tool. Out of thousands of significantly altered proteins in zebrafish brain, the ones having critical role either in neuroglial proliferation/differentiation or neurotrophic functions were validated by analyzing their expression levels in preconditioned (PH), acute hypoxia (AH), and normoxia groups. The data indicate that female zebrafish brains are more protected against the severity of AH when exposed to the hypoxic preconditioning. The study also sheds light on the involvement of many signalling pathways underlying sex difference in preconditioning-induced neuroprotective mechanism, which can be further validated for the therapeutic approach.

Berberine Ameliorates Subarachnoid Hemorrhage Injury via Induction of Sirtuin 1 and Inhibiting HMGB1/Nf-κB Pathway

Excessive cerebral inflammation plays a key role in early brain injury (EBI) after subarachnoid hemorrhage (SAH). Berberine, an isoquinoline alkaloid isolated from Chinese herb Coptis chinensis, possesses anti-inflammatory, and neuroprotective effects. Here we evaluated the beneficial effects of berberine against SAH-induced inflammatory response and the subsequent brain injury. Our data showed that berberine treatment significantly inhibited microglia activation and proinflammatory cytokines release. Concomitant with suppressed cerebral inflammation, berberine mitigated the subsequent brain injury as demonstrated by improved neurological behavior, reduced brain edema, and decreased neural apoptosis. Moreover, berberine significantly inhibited high mobile group box 1 (HMGB1)/nuclear factor-κB (Nf-κB)-dependent pathway and enhanced sirtuin 1 (SIRT1) expression after SAH. Treatment with ex527, a selective SIRT1 inhibitor, reversed berberine-induced SIRT1 activation and inhibitory effects on HMGB1/Nf-κB activation. In addition, ex527 pretreatment abated the anti-inflammatory and neuroprotective effects of berberine on SAH. Taken together, these findings suggest that berberine provides beneficial effects against SAH-triggered cerebral inflammation by inhibiting HMGB1/Nf-κB pathway, which may be modulated by SIRT1 activation.

Aneurysmal Subarachnoid Hemorrhage: an Overview of Inflammation-Induced Cellular Changes

Aneurysmal subarachnoid hemorrhage (SAH) is a devastating disease that leads to poor neurological outcomes and is characterized by both vascular and neural pathologies. Recent evidence demonstrates that inflammation mediates many of the vascular and neural changes observed after SAH. Although most studies focus on inflammatory mediators such as cytokines, the ultimate effectors of inflammation in SAH are parenchymal brain and peripheral immune cells. As such, the present review will summarize our current understanding of the cellular changes of both CNS parenchymal and peripheral immune cells after SAH.

Toll-like receptor 3 dynamics in female C57BL/6J mice: Regulation of alcohol intake

Although there are sex differences in the effects of alcohol on immune responses, it is unclear if sex differences in immune response can influence drinking behavior. Activation of toll-like receptor 3 (TLR3) by polyinosinic:polycytidylic acid (poly(I:C)) produced a rapid proinflammatory response in males that increased alcohol intake over time (Warden et al., 2019). Poly(I:C) produced a delayed and prolonged innate immune response in females. We hypothesized that the timecourse of innate immune activation could regulate drinking behavior in females. Therefore, we chose to test the effect of two time points in the innate immune activation timecourse on every-other-day two-bottle-choice drinking: (1) peak activation; (2) descending limb of activation. Poly(I:C) reduced ethanol consumption when alcohol access occurred during peak activation. Poly(I:C) did not change ethanol consumption when alcohol access occurred on the descending limb of activation. Decreased levels of MyD88-dependent pathway correlated with decreased alcohol intake and increased levels of TRIF-dependent pathway correlated with increased alcohol intake in females. To validate the effects of poly(I:C) were mediated through MyD88, we tested female mice lacking Myd88. Poly(I:C) did not change alcohol intake in Myd88 knockouts, indicating that poly(I:C)-induced changes in alcohol intake are dependent on MyD88 in females. We next determined if the innate immune timecourse also regulated drinking behavior in males. Poly(I:C) reduced ethanol consumption in males when alcohol was presented at peak activation. Therefore, the timecourse of innate immune activation regulates drinking behavior and sex-specific dynamics of innate immune response must be considered when designing therapeutics to treat excessive drinking.

Toll-like receptor 3 activation increases voluntary alcohol intake in C57BL/6J male mice

Many genes differentially expressed in brain tissue from human alcoholics and animals that have consumed large amounts of alcohol are components of the innate immune toll-like receptor (TLR) pathway. TLRs initiate inflammatory responses via two branches: (1) MyD88-dependent or (2) TRIF-dependent. All TLRs signal through MyD88 except TLR3. Prior work demonstrated a direct role for MyD88-dependent signaling in regulation of alcohol consumption. However, the role of TLR3 as a potential regulator of excessive alcohol drinking has not previously been investigated. To test the possibility TLR3 activation regulates alcohol consumption, we injected mice with the TLR3 agonist polyinosinic:polycytidylic acid (poly(I:C)) and tested alcohol consumption in an every-other-day two-bottle choice test. Poly(I:C) produced a persistent increase in alcohol intake that developed over several days. Repeated poly(I:C) and ethanol exposure altered innate immune transcript abundance; increased levels of TRIF-dependent pathway components correlated with increased alcohol consumption. Administration of poly(I:C) before exposure to alcohol did not alter alcohol intake, suggesting that poly(I:C) and ethanol must be present together to change drinking behavior. To determine which branch of TLR signaling mediates poly(I:C)-induced changes in drinking behavior, we tested either mice lacking MyD88 or mice administered a TLR3/dsRNA complex inhibitor. MyD88 null mutants showed poly(I:C)-induced increases in alcohol intake. In contrast, mice pretreated with a TLR3/dsRNA complex inhibitor reduced their alcohol intake, suggesting poly(I:C)-induced escalations in alcohol intake are, at least partially, dependent on TLR3. Together, these results strongly suggest that TLR3-dependent signaling drives excessive alcohol drinking behavior.

Effects of hypoxic preconditioning on memory evaluated using the T-maze behavior test

Perioperative brain ischemia and stroke are leading causes of morbidity and mortality. Brief hypoxic preconditioning is known to have protective effects against hypoxic-ischemic insult in the brain. Current studies on the neuroprotective effects of ischemic preconditioning are based on histologic findings and biomarker changes. However, studies regarding effects on memory are rare. To precondition zebrafish to hypoxia, they were exposed to a dissolved oxygen (DO) concentration of 1.0 ± 0.5 mg/L in water for 30 s. The hypoxic zebrafish were then exposed to 1.0 ± 0.5 mg/L DO until the third stage of hypoxia, for 10 min ± 30 s. Zebrafish were assessed for memory retention after the hypoxic event. Learning and memory were tested using the T-maze, which evaluates memory based on whether or not zebrafish moves to the correct target compartment. In the hypoxic preconditioning group, infarct size was reduced compared with the hypoxic-only treated zebrafish group; memory was maintained to a degree similar to that in the hypoxia-untreated group. The hypoxic-only group showed significant memory impairments. In this study, we used a hypoxic zebrafish model and assessed the effects of ischemic preconditioning not only on histological damages but also on brain function, especially memory. This study demonstrated that a brief hypoxic event has protective effects in hypoxic brain damage and helped maintain memory in zebrafish. In addition, our findings suggest that the zebrafish model is useful in rapidly assessing the effects of ischemic preconditioning on memory.

Innate Immune Signaling and Its Role in Metabolic and Cardiovascular Diseases

The innate immune system is an evolutionarily conserved system that senses and defends against infection and irritation. Innate immune signaling is a complex cascade that quickly recognizes infectious threats through multiple germline-encoded cell surface or cytoplasmic receptors and transmits signals for the deployment of proper countermeasures through adaptors, kinases, and transcription factors, resulting in the production of cytokines. As the first response of the innate immune system to pathogenic signals, inflammatory responses must be rapid and specific to establish a physical barrier against the spread of infection and must subsequently be terminated once the pathogens have been cleared. Long-lasting and low-grade chronic inflammation is a distinguishing feature of type 2 diabetes and cardiovascular diseases, which are currently major public health problems. Cardiometabolic stress-induced inflammatory responses activate innate immune signaling, which directly contributes to the development of cardiometabolic diseases. Additionally, although the innate immune elements are highly conserved in higher-order jawed vertebrates, lower-grade jawless vertebrates lack several transcription factors and inflammatory cytokine genes downstream of the Toll-like receptors (TLRs) and retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) pathways, suggesting that innate immune signaling components may additionally function in an immune-independent way. Notably, recent studies from our group and others have revealed that innate immune signaling can function as a vital regulator of cardiometabolic homeostasis independent of its immune function. Therefore, further investigation of innate immune signaling in cardiometabolic systems may facilitate the discovery of new strategies to manage the initiation and progression of cardiometabolic disorders, leading to better treatments for these diseases. In this review, we summarize the current progress in innate immune signaling studies and the regulatory function of innate immunity in cardiometabolic diseases. Notably, we highlight the immune-independent effects of innate immune signaling components on the development of cardiometabolic disorders.

Melatonin receptor activation provides cerebral protection after traumatic brain injury by mitigating oxidative stress and inflammation via the Nrf2 signaling pathway

Traumatic brain injury (TBI) is a principal cause of death and disability worldwide. Melatonin, a hormone made by the pineal gland, is known to have anti-inflammatory and antioxidant properties. In this study, using a weight-drop model of TBI, we investigated the protective effects of ramelteon, a melatonin MT1/MT2 receptor agonist, and its underlying mechanisms of action. Administration of ramelteon (10 mg/kg) daily at 10:00 a.m. alleviated TBI-induced early brain damage on day 3 and long-term neurobehavioral deficits on day 28 in C57BL/6 mice. Ramelteon also increased the protein levels of interleukin (IL)-10, IL-4, superoxide dismutase (SOD), glutathione, and glutathione peroxidase and reduced the protein levels of IL-1β, tumor necrosis factor, and malondialdehyde in brain tissue and serum on days 1, 3, and 7 post-TBI. Similarly, ramelteon attenuated microglial and astrocyte activation in the perilesional cortex on day 3. Furthermore, ramelteon decreased Keap 1 expression, promoted nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear accumulation, and increased levels of downstream proteins, including SOD-1, heme oxygenase-1, and NQO1 on day 3 post-TBI. However, in Nrf2 knockout mice with TBI, ramelteon did not decrease the lesion volume, neuronal degeneration, or myelin loss on day 3; nor did it mitigate depression-like behavior or most motor behavior deficits on day 28. Thus, timed ramelteon treatment appears to prevent inflammation and oxidative stress via the Nrf2-antioxidant response element pathway and might represent a potential chronotherapeutic strategy for treating TBI.

Potential Medications or Compounds Acting on Toll-like Receptors in Cerebral Ischemia

Background:

Toll-like receptors play an integral role in the process of inflammatory response after ischemic in-jury. The therapeutic potential acting on TLRs is worth of evaluations. The aim of this review was to introduce readers some potential medications or compounds which could alleviate the ischemic damage via TLRs.

Methods:

Research articles online on TLRs were reviewed. Categorizations were listed according to the follows, methods acting on TLRs directly, modulations of MyD88 or TRIF signaling pathway, and the ischemic tolerance induced by the pre-conditioning or postconditioning with TLR ligands or minor cerebral ischemia via acting on TLRs.

Results:

There are only a few studies concerning on direct effects. Anti-TLR4 or anti-TLR2 therapies may serve as promis-ing strategies in acute events. Approaches targeting on inhibiting NF-κB signaling pathway and enhancing interferon regu-latory factor dependent signaling have attracted great interests. Not only drugs but compounds extracted from traditional Chinese medicine have been used to identify their neuroprotective effects against cerebral ischemia. In addition, many re-searchers have reported the positive therapeutic effects of preconditioning with agonists of TLR2, 3, 4, 7 and 9. Several trails have also explored the potential of postconditioning, which provide a new idea in ischemic treatments. Considering all the evidence above, many drugs and new compounds may have great potential to reduce ischemic insults.

Conclusion:

This review will focus on promising therapies which exerting neuroprotective effects against ischemic injury by acting on TLRs.

Cerebroprotection by salvianolic acid B after experimental subarachnoid hemorrhage occurs via Nrf2- and SIRT1-dependent pathways

Salvianolic acid B (SalB), a natural polyphenolic compound extracted from the herb of Salvia miltiorrhiza, possesses antioxidant and neuroprotective properties and has been shown to be beneficial for diseases that affect vasculature and cognitive function. Here we investigated the protective effects of SalB against subarachnoid hemorrhage (SAH)-induced oxidative damage, and the involvement of underlying molecular mechanisms. In a rat model of SAH, SalB inhibited SAH-induced oxidative damage. The reduction in oxidative damage was associated with suppressed reactive oxygen species generation; decreased lipid peroxidation; and increased glutathione peroxidase, glutathione, and superoxide dismutase activities. Concomitant with the suppressed oxidative stress, SalB significantly reduced neurologic impairment, brain edema, and neural cell apoptosis after SAH. Moreover, SalB dramatically induced nuclear factor-erythroid 2-related factor 2 (Nrf2) nuclear translocation and increased expression of heme oxygenase-1 and NADPH: quinine oxidoreductase-1. In a mouse model of SAH, Nrf2 knockout significantly reversed the antioxidant effects of SalB against SAH. Additionally, SalB activated sirtuin 1 (SIRT1) expression, whereas SIRT1-specific inhibitor sirtinol pretreatment significantly suppressed SalB-induced SIRT1 activation and Nrf2 expression. Sirtinol pretreatment also reversed the antioxidant and neuroprotective effects of SalB. In primary cultured cortical neurons, SalB suppressed oxidative damage, alleviated neuronal degeneration, and improved cell viability. These beneficial effects were associated with activation of the SIRT1 and Nrf2 signaling pathway and were reversed by sirtinol treatment. Taken together, these in vivo and in vitro findings suggest that SalB provides protection against SAH-triggered oxidative damage by upregulating the Nrf2 antioxidant signaling pathway, which may be modulated by SIRT1 activation.

Hippo/YAP signaling pathway mitigates blood-brain barrier disruption after cerebral ischemia/reperfusion injury

Ischemia/reperfusion (I/R) injuries commonly lead to breakdown of the blood-brain barrier (BBB). Restoration of the BBB can relieve neurologic damage caused by I/R injuries. The Hippo/YAP signaling pathway mediates cell proliferation, regulated cell death, and differentiation in various organisms and has been shown to participate in the restoration of the heart after I/R. In this study, we investigated whether the Hippo/YAP pathway plays a role in I/R injury in brain, especially in regard to I/R-induced BBB breakdown. The results of our study indicate that I/R injury led to an overall decrease in activity of the core proteins, YAP and TAZ, over a 24-h period. The most dramatic change was observed 1.5 h after reperfusion. In rats that underwent 1.5 h of reperfusion, intraperitoneal injection of YAP agonist dexamethasone activated YAP and TAZ and led to improved neurologic function, smaller brain infarct sizes, increased levels of tight junction proteins, decreased BBB permeability, decreased cerebral edema, and less apoptosis. Our results suggest that YAP exerts neuroprotective effects on the damaged brain that are likely related to restoration of the BBB.

miR-132-3p boosts caveolae-mediated transcellular transport in glioma endothelial cells by targeting PTEN/PI3K/PKB/Src/Cav-1 signaling pathway

Blood-brain tumor barrier (BTB) impedes the transportation of antitumor therapeutic drugs into brain tumors. Its mechanism is still unknown, but learning how to improve the BTB permeability is critical for drug intervention. Recently, microRNAs (miRNAs) have appeared as regulation factors of numerous biologic processes and therapeutic targets of diverse diseases. In this study, we have identified that miR-132-3p is an essential miRNA by increasing the transcellular transport through the BTB. We found that miR-132-3p expression was significantly up-regulated in glioma endothelial cells (GECs). Furthermore we showed that miR132-3p⁺ greatly induced the endocytosis of cholera toxin subunit B and FITC-bovine serum albumin and up-regulated the expression of p-PKB, p-Src and Tyr14 phosphorylation of caveolin-1 (p-Cav-1), while phosphatase and tensin homolog deleted on chromosome 10 (PTEN) expression was markedly down-regulated in GECs. Our results identify PTEN as a direct and functional downstream target of miR-132-3p, which is involved in the regulation of p-PKB, p-Src, and p-Cav-1. The inhibitors for PI3K and Src significantly reversed the increase of p-Cav-1 induced by miR-132-3p. Moreover, overexpression of PTEN greatly reduced the endocytosis of cholera toxin subunit B and the up-regulation of p-Cav-1 induced by agomiR132-3p, suggesting that miR132-3p⁺ increases the endothelial permeability by inhibition of PTEN expression. In addition, miR132-3p⁺ significantly increased the delivery of doxorubicin across the BTB in vitro and contributed to the accumulation of doxorubicin within the brain tumor tissue. Our results show that miR-132-3p contributes to the increased permeability of BTB by targeting PTEN/PI3K/PKB/Src/Cav-1, thereby revealing a novel drug target for the treatment of brain gliomas.-Gu, Y., Cai, R., Zhang, C., Xue, Y., Pan, Y., Wang, J., Zhang, Z. miR-132-3p boosts caveolae-mediated transcellular transport in glioma endothelial cells by targeting PTEN/PI3K/PKB/Src/Cav-1 signaling pathway.

Carbon monoxide-releasing molecule-3 protects against ischemic stroke by suppressing neuroinflammation and alleviating blood-brain barrier disruption

Background

At low levels, carbon monoxide (CO) has been shown to have beneficial effects on multiple organs and tissues through its potential anti-inflammatory, anti-apoptotic, and anti-proliferative properties. However, the effect of CO-releasing molecule (CORM)-3, a water-soluble CORM, on ischemic stroke and its mechanism of action are still unclear.

Methods

We investigated the role of CORM-3 in the mouse model of transient middle cerebral artery occlusion (tMCAO). CORM-3 or saline was administered to mice by retro-orbital injection at the time of reperfusion after 1-h tMCAO or at 1 h after sham surgery. We assessed infarct volume and brain water content at 24 and 72 h after ischemia, blood-brain barrier permeability at 6 and 72 h after ischemia, and neurologic deficits on days 1, 3, 7, and 14.

Results

Among mice that underwent tMCAO, those that received CORM-3 had significantly smaller infarct volume and greater expression of neuronal nuclear antigen (NeuN) and microtubule-associated protein 2 than did saline-treated mice. CORM-3-treated mice had significantly fewer activated microglia in the peri-infarction zone than did control mice and exhibited downregulated expression of ionized calcium-binding adapter molecule (Iba)-1, tumor necrosis factor-α, and interleukin 1β. CORM-3-treated mice had significantly lower brain water content and enhanced neurologic outcomes on days 3, 7, and 14 post-tMCAO. Lastly, CORM-3 treatment reduced Evans blue leakage; increased expression of platelet-derived growth factor receptor-β, tight junction protein ZO-1, and matrix protein laminin; and decreased protein level of matrix metalloproteinase-9.

Conclusion

CORM-3 treatment at the time of reperfusion reduces ischemia-reperfusion-induced brain injury by suppressing neuroinflammation and alleviating blood-brain barrier disruption. Our data suggest that CORM-3 may provide an effective therapy for ischemic stroke.

Correction to: Neuroimmune Response in Ischemic Preconditioning

Ischemic preconditioning (IPC) is a robust neuroprotective phenomenon in which a brief period of cerebral ischemia confers transient tolerance to subsequent ischemic challenge. Research on IPC has implicated cellular, molecular, and systemic elements of the immune response in this phenomenon. Potent molecular mediators of IPC include innate immune signaling pathways such as Toll-like receptors and type 1 interferons. Brain ischemia results in release of pro- and anti-inflammatory cytokines and chemokines that orchestrate the neuroinflammatory response, resolution of inflammation, and transition to neurological recovery and regeneration. Cellular mediators of IPC include microglia, the resident central nervous system immune cells, astrocytes, and neurons. All of these cell types engage in cross-talk with each other using a multitude of signaling pathways that modulate activation/suppression of each of the other cell types in response to ischemia. As the postischemic neuroimmune response evolves over time there is a shift in function toward provision of trophic support and neuroprotection. Peripheral immune cells infiltrate the central nervous system en masse after stroke and are largely detrimental, with a few subtypes having beneficial, protective effects, though the role of these immune cells in IPC is largely unknown. The role of neural progenitor cells in IPC-mediated neuroprotection is another active area of investigation as is the role of microglial proliferation in this setting. A mechanistic understanding of these molecular and cellular mediators of IPC may not only facilitate more effective direct application of IPC to specific clinical scenarios, but also, more broadly, reveal novel targets for therapeutic intervention in stroke.

Toll-like receptor 3 modulates the behavioral effects of cocaine in mice

BACKGROUND

The nucleus accumbens in the midbrain dopamine limbic system plays a key role in cocaine addiction. Toll-like receptors (TLRs) are important pattern-recognition receptors (PPRs) in the innate immune system that are also involved in drug dependence; however, the detailed mechanism is largely unknown.

METHODS

The present study was designed to investigate the potential role of TLR3 in cocaine addiction. Cocaine-induced conditioned place preference (CPP), locomotor activity, and self-administration were used to determine the effects of TLR3 in the rewarding properties of cocaine. Lentivirus-mediated re-expression of Tlr3 (LV-TLR3) was applied to determine if restoration of TLR3 expression in the NAc is sufficient to restore the cocaine effect in TLR3^-/- mice. The protein levels of phospho-NF-κB p65, IKKβ, and p-IκBα both in the cytoplasm and nucleus of cocaine-induced CPP mice were detected by Western blot.

RESULTS

We showed that both TLR3 deficiency and intra-NAc injection of TLR3 inhibitors significantly attenuated cocaine-induced CPP, locomotor activity, and self-administration in mice. Importantly, the TLR3^-/- mice that received intra-NAc injection of LV-TLR3 displayed significant increases in cocaine-induced CPP and locomotor activity. Finally, we found that TLR3 inhibitor reverted cocaine-induced upregulation of phospho-NF-κB p65, IKKβ, and p-IκBα.

CONCLUSIONS

Taken together, our results describe that TLR3 modulates cocaine-induced behaviors and provide further evidence supporting a role for central pro-inflammatory immune signaling in drug reward. We propose that TLR3 blockade could be a novel approach to treat cocaine addiction.

Effects of TLR3 and TLR9 Signaling Pathway on Brain Protection in Rats Undergoing Sevoflurane Pretreatment during Cardiopulmonary Bypass

OBJECTIVE

To investigate the effects of TLR3 and TLR9 signaling pathway on brain injury during CPB in rats pretreated with sevoflurane and its possible molecular mechanism.

METHODS

SD rats were randomly assigned to sham group, CPB group, and Sev group. Brain tissue was obtained at before CPB (T0), at CPB for 30 minutes (T1), 1 hour after CPB (T3), and 3 hours after CPB (T5). ELISA was used to measure S100-β and IL-6. Western blot was utilized to determine TLR3 and TLR9 expression. TUNEL was applied to detect neuronal apoptosis.

RESULTS

Compared with CPB group, at T1, at termination after 1 hour of CPB (T2), T3, 2 hours after CPB (T4) and T5, S100-β and IL-6 decreased in Sev group. Compared with CPB group, IFN-β were increased in Sev group, except T0. Compared with CPB group, TLR3 expression increased, and TLR9 and NF-κB decreased in Sev group. The apoptotic neurons were less in Sev group than in CPB group (P < 0.05).

CONCLUSION

Sevoflurane intervention can activate TLR3 and TLR9 signaling pathway, upregulate TLR3 expression and downstream TRIF expression, decrease TLR9 expression, and downregulate downstream NF-κB expression in CPB rat models, thereby mitigating brain injury induced by inflammatory response during CPB.

Pharmacologic activation of cholinergic alpha7 nicotinic receptors mitigates depressive-like behavior in a mouse model of chronic stress

Background

It has been shown that chronic stress-induced depression is associated with exaggerated inflammatory response in the brain. Alpha7 nicotinic acetylcholine receptors (α7nAChRs) regulate the cholinergic anti-inflammatory pathway, but the role of cholinergic signaling and α7nAChR in chronic stress has not yet been examined.

Methods

In this study, we used a well-documented model of depression in which mice were exposed to 6 h of restraint stress for 21 consecutive days. Components of cholinergic signaling and TLR4 signaling were analyzed in the hippocampus. The main targets of neuroinflammation and neuronal damage were also evaluated after a series of tests for depression-like behavior.

Results

Chronic restraint stress (CRS) induced alterations in components of central cholinergic signaling in hippocampus, including increases in choline acetyltransferase protein expression and decreases in nuclear STAT3 signaling. CRS also increased TLR4 signaling activity, interleukin-1β, and tumor necrosis factor-α expression, microglial activation, and neuronal morphologic changes. Cholinergic stimulation with the α7nAChR agonist DMXBA significantly alleviated CRS-induced depressive-like behavior, neuroinflammation, and neuronal damage, but these effects were abolished by the selective α7nAChR antagonist α-bungarotoxin. Furthermore, activation of α7nAChRs restored the central cholinergic signaling function, inhibited TLR4-mediated inflammatory signaling and microglial activity, and increased the number of regulatory T cells in the hippocampus.

Conclusions

These findings provide evidence that α7nAChR activation mitigates CRS-induced neuroinflammation and cell death, suggesting that α7nAChRs could be a new therapeutic target for the prevention and treatment of depression.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-1007-2) contains supplementary material, which is available to authorized users.

Inhibition of tPA-induced hemorrhagic transformation involves adenosine A2b receptor activation after cerebral ischemia

Tissue plasminogen activator (tPA) is administered after ischemic stroke to dissolve intravascular clots, but its use can lead to hemorrhagic transformation (HT). Therapeutic strategies to reduce hemorrhagic complications of tPA might be of benefit for stroke patients. Adenosine A2b receptor (A2bR) plays pivotal roles in regulating vascular protection in peripheral organs. This study explored whether A2bR agonist BAY 60-6583 reduces hemorrhage risk after tPA usage. Using a rat transient middle cerebral artery occlusion model, we showed that mRNA and protein expression of A2bR increased to a greater extent after ischemia-reperfusion than did expression of the other three adenosine receptors (A1, A2a, and A3). tPA administration reduced A2bR expression in ischemic brain microvessels. Post-treatment with BAY 60-6583 (1mg/kg) at the start of reperfusion reduced lesion volume in the absence or presence of tPA (10mg/kg) and attenuated brain swelling, blood-brain barrier disruption, and tPA-exacerbated HT at 24h. Additionally, BAY 60-6583 mitigated sensorimotor deficits in the presence of tPA. BAY 60-6583 inhibited tPA-enhanced matrix metalloprotease-9 activation, probably through elevation of tissue inhibitor of matrix metalloproteinases-1 expression, and thereby reduced degradation of tight junction proteins. These effects would likely protect cerebrovascular integrity. A2bR agonists as an adjuvant to tPA could be a promising strategy for decreasing the risk of HT during treatment for ischemic stroke.

Rifampicin inhibits rotenone-induced microglial inflammation via enhancement of autophagy

Mitochondrial and autophagic dysfunction, as well as neuroinflammation, are associated with the pathophysiology of Parkinson's disease (PD). Rotenone, an inhibitor of mitochondrial complex I, has been associated as an environmental neurotoxin related to PD. Our previous studies reported that rifampicin inhibited microglia activation and production of proinflammatory mediators induced by rotenone, but the precise mechanism has not been completely elucidated. BV2 cells were pretreated for 2h with rifampicin followed by 0.1μM rotenone, alone or in combination with chloroquine. Here, we demonstrate that rifampicin pretreatment alleviated rotenone induced release of IL-1β and IL-6, and its effects were suppressed when autophagy was inhibited by chloroquine. Moreover, preconditioning with 50μM rifampicin significantly increased viability of SH-SY5Y cells cocultured with rotenone-treated BV2 cells in the transwell coculture system. Chloroquine partially abolished the neuroprotective effects of rifampicin pretreatment. Rifampicin pretreatment significantly reversed rotenone-induced mitochondrial membrane potential reduction and reactive oxygen species accumulation. We suggest that the mechanism for rifampicin-mediated anti-inflammatory and antioxidant effects is the enhancement of autophagy. Indeed, the ratio of LC3-II/LC3-I in rifampicin-pretreated BV2 cells was significantly higher than that in cells without pretreatment. Fluorescence and electron microscopy analyses indicate an increase of lysosomes colocalized with mitochondria in cells pretreated with rifampicin, which confirms that the damaged mitochondria were cleared through autophagy (mitophagy). Taken together, the data provide further evidence that rifampicin exerts neuroprotection against rotenone-induced microglia inflammation, partially through the autophagy pathway. Modulation of autophagy by rifampicin is a novel therapeutic strategy for PD.

Stem cells and heart disease - Brake or accelerator?

After two decades of intensive research and attempts of clinical translation, stem cell based therapies for cardiac diseases are not getting closer to clinical success. This review tries to unravel the obstacles and focuses on underlying mechanisms as the target for regenerative therapies. At present, the principal outcome in clinical therapy does not reflect experimental evidence. It seems that the scientific obstacle is a lack of integration of knowledge from tissue repair and disease mechanisms. Recent insights from clinical trials delineate mechanisms of stem cell dysfunction and gene defects in repair mechanisms as cause of atherosclerosis and heart disease. These findings require a redirection of current practice of stem cell therapy and a reset using more detailed analysis of stem cell function interfering with disease mechanisms. To accelerate scientific development the authors suggest intensifying unified computational data analysis and shared data knowledge by using open-access data platforms.

Sex differences in stroke across the lifespan: The role of T lymphocytes

Stroke is a sexually dimorphic disease. Ischemic sensitivity changes throughout the lifespan and outcomes depend largely on variables like age, sex, hormonal status, inflammation, and other existing risk factors. Immune responses after stroke play a central role in how these factors interact. Although the post-stroke immune response has been extensively studied, the contribution of lymphocytes to stroke is still not well understood. T cells participate in both innate and adaptive immune responses at both acute and chronic stages of stroke. T cell responses also change at different ages and are modulated by hormones and sex chromosome complement. T cells have also been implicated in the development of hypertension, one of the most important risk factors for vascular disease. In this review, we highlight recent literature on the lymphocytic responses to stroke in the context of age and sex, with a focus on T cell response and the interaction with important stroke risk factors.

Astrocyte-mediated inflammation in cortical spreading depression

Background Cortical spreading depression (CSD) related diseases such as migraine, cerebrovascular diseases, and epilepsy have been associated with reactive astrocytosis, yet the mechanisms of these tissue changes remain unclear. CSD-induced inflammatory response has been proposed to play a role in some neurological disorders and thus may also contribute to reactive astrocytosis. Methods Using ex vivo brain slices and in vitro astrocytic cultures, we aimed to characterize CSD related changes in astrocytes and markers of inflammation by immunocyto- and immunohistochemistry. CSD was induced by application of KCl (3 mol/l) on neocortical tissues. The application of KCl was repeated weekly over the course of four weeks. Results CSD induced an increase in the mean number and volume of astrocytes in rat brain tissue when compared to controls, whereas no changes in neuronal numbers and volumes were seen. These cell-type specific changes, suggestive of reactive astrocytosis, were paralleled by an increased expression of protein markers indicative of astrocytes and neuroinflammation in ex vivo brain slices of animals undergoing CSD when compared to sham-treated controls. Cultured astrocytes showed an increased expression of the immune modulatory enzyme indoleamine 2,3-dioxygenase and an elevated expression of the pro-inflammatory markers, IL-6, IL-1β, and TNFα in addition to increased levels of toll like receptors (TLR3 and TLR4) and astrocytic markers after induction of CSD. Conclusion These findings indicate that CSD related reactive astrocytosis is linked to an upregulation of inflammatory markers. Targeting inflammation with already approved and available immunomodulatory treatments may thus represent a strategy to combat or ameliorate CSD-related disease.

Preconditioning in neuroprotection: From hypoxia to ischemia

Sublethal hypoxic or ischemic events can improve the tolerance of tissues, organs, and even organisms from subsequent lethal injury caused by hypoxia or ischemia. This phenomenon has been termed hypoxic or ischemic preconditioning (HPC or IPC) and is well established in the heart and the brain. This review aims to discuss HPC and IPC with respect to their historical development and advancements in our understanding of the neurochemical basis for their neuroprotective role. Through decades of collaborative research and studies of HPC and IPC in other organ systems, our understanding of HPC and IPC-induced neuroprotection has expanded to include: early- (phosphorylation targets, transporter regulation, interfering RNA) and late- (regulation of genes like EPO, VEGF, and iNOS) phase changes, regulators of programmed cell death, members of metabolic pathways, receptor modulators, and many other novel targets. The rapid acceleration in our understanding of HPC and IPC will help facilitate transition into the clinical setting.

(-)-Epicatechin, a Natural Flavonoid Compound, Protects Astrocytes Against Hemoglobin Toxicity via Nrf2 and AP-1 Signaling Pathways

(-)-Epicatechin is a brain-permeable, natural product found at high concentrations in green tea and cocoa. Our previous research has shown that (-)-epicatechin treatment reduces hemorrhagic stroke injury via nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway in vivo. However, the mechanism of action of this compound in modulation of oxidant stress and in protection against hemoglobin-induced astrocyte injury is unclear. Therefore, we explored the cellular and molecular mechanisms that underlie these protective effects in vitro. Mouse primary astrocytes isolated from wild-type mice and Nrf2 knockout (KO) mice were preconditioned with hemoglobin to simulate intracerebral hemorrhage (ICH) in vitro. Effects of (-)-epicatechin were measured by Western blotting, immunostaining, MTT assay, and reactive oxidant stress (ROS) assay. (-)-Epicatechin increased Nrf2 nuclear accumulation and cytoplasmic levels of superoxide dismutase 1 (SOD1) in wild-type astrocytes but did not increase SOD1 expression in Nrf2 knockout (KO) astrocytes. Furthermore, (-)-epicatechin treatment did not alter heme oxygenase 1 (HO1) expression in wild-type astrocytes after hemoglobin exposure, but it did decrease HO1 expression in similarly treated Nrf2 KO astrocytes. In both wild-type and Nrf2 KO astrocytes, (-)-epicatechin suppressed phosphorylated JNK and nuclear expression of JNK, c-jun, and c-fos, indicating that inhibition of activator protein-1 (AP-1) activity by (-)-epicatechin is Nrf2-independent. These novel findings indicate that (-)-epicatechin protects astrocytes against hemoglobin toxicity through upregulation of Nrf2 and inhibition of AP-1 activity. These cellular and molecular effects may partially explain the cerebroprotection as we previously observed for (-)-epicatechin in animal models of ICH.

An inhibitory alternative splice isoform of Toll-like receptor 3 is induced by type I interferons in human astrocyte cell lines

Toll-like receptor 3 (TLR3) recognizes viral double-stranded RNA. It stimulates pro-inflammatory cytokine and interferon production. Here we reported the expression of a novel isoform of TLR3 in human astrocyte cell lines whose message is generated by alternative splicing. The isoform represents the N-terminus of the protein. It lacks many of the leucine-rich repeat domains, the transmembrane domain, and the intracellular Toll/interleukin-1 receptor domain of TLR3. Type I interferons (interferon-α and interferon-β) induced the expression of this isoform. Exogenous overexpression of this isoform inhibited interferon regulatory factor 3, signal transducers and activators of transcription 1, and Inhibitor of kappa B α signaling following stimulation. This isoform of TLR3 also inhibited the production of chemokine interferon-γ-inducible protein 10. Our study clearly demonstrated that the expression of this isoform of TLR3 was a negative regulator of signaling pathways and that it was inducible by type I interferons. We also found that this isoform could modulate inflammation in the brain. [BMB Reports 2015; 48(12): 696-701]

Neuroimmune Response in Ischemic Preconditioning

Ischemic preconditioning (IPC) is a robust neuroprotective phenomenon in which a brief period of cerebral ischemia confers transient tolerance to subsequent ischemic challenge. Research on IPC has implicated cellular, molecular, and systemic elements of the immune response in this phenomenon. Potent molecular mediators of IPC include innate immune signaling pathways such as Toll-like receptors and type 1 interferons. Brain ischemia results in release of pro- and anti-inflammatory cytokines and chemokines that orchestrate the neuroinflammtory response, resolution of inflammation, and transition to neurological recovery and regeneration. Cellular mediators of IPC include microglia, the resident central nervous system immune cells, astrocytes, and neurons. All of these cell types engage in cross-talk with each other using a multitude of signaling pathways that modulate activation/suppression of each of the other cell types in response to ischemia. As the postischemic neuroimmune response evolves over time there is a shift in function toward provision of trophic support and neuroprotection. Peripheral immune cells infiltrate the central nervous system en masse after stroke and are largely detrimental, with a few subtypes having beneficial, protective effects, though the role of these immune cells in IPC is largely unknown. The role of neural progenitor cells in IPC-mediated neuroprotection is another active area of investigation as is the role of microglial proliferation in this setting. A mechanistic understanding of these molecular and cellular mediators of IPC may not only facilitate more effective direct application of IPC to specific clinical scenarios, but also, more broadly, reveal novel targets for therapeutic intervention in stroke.

Toll-like Receptors in the Vascular System: Sensing the Dangers Within

Toll-like receptors (TLRs) are components of the innate immune system that respond to exogenous infectious ligands (pathogen-associated molecular patterns, PAMPs) and endogenous molecules that are released during host tissue injury/death (damage-associated molecular patterns, DAMPs). Interaction of TLRs with their ligands leads to activation of downstream signaling pathways that induce an immune response by producing inflammatory cytokines, type I interferons (IFN), and other inflammatory mediators. TLR activation affects vascular function and remodeling, and these molecular events prime antigen-specific adaptive immune responses. Despite the presence of TLRs in vascular cells, the exact mechanisms whereby TLR signaling affects the function of vascular tissues are largely unknown. Cardiovascular diseases are considered chronic inflammatory conditions, and accumulating data show that TLRs and the innate immune system play a determinant role in the initiation and development of cardiovascular diseases. This evidence unfolds a possibility that targeting TLRs and the innate immune system may be a novel therapeutic goal for these conditions. TLR inhibitors and agonists are already in clinical trials for inflammatory conditions such as asthma, cancer, and autoimmune diseases, but their study in the context of cardiovascular diseases is in its infancy. In this article, we review the current knowledge of TLR signaling in the cardiovascular system with an emphasis on atherosclerosis, hypertension, and cerebrovascular injury. Furthermore, we address the therapeutic potential of TLR as pharmacological targets in cardiovascular disease and consider intriguing research questions for future study.

TLR3 ligand Poly IC Attenuates Reactive Astrogliosis and Improves Recovery of Rats after Focal Cerebral Ischemia

AIMS

Brain ischemia activates astrocytes in a process known as astrogliosis. Although this process has beneficial effects, excessive astrogliosis can impair neuronal recovery. Polyinosinic-polycytidylic acid (Poly IC) has shown neuroprotection against cerebral ischemia-reperfusion injury, but whether it regulates reactive astrogliosis and glial scar formation is not clear.

METHODS

We exposed cultured astrocytes to oxygen-glucose deprivation/reoxygenation (OGD/R) and used a rat middle cerebral artery occlusion (MCAO)/reperfusion model to investigate the effects of Poly IC. Astrocyte proliferation and proliferation-related molecules were evaluated by immunostaining and Western blotting. Neurological deficit scores, infarct volumes and neuroplasticity were evaluated in rats after transient MCAO.

RESULTS

In vitro, Poly IC inhibited astrocyte proliferation, upregulated Toll-like receptor 3 (TLR3) expression, upregulated interferon-β, and downregulated interleukin-6 production. These changes were blocked by a neutralizing antibody against TLR3, suggesting that Poly IC function is TLR3-dependent. Moreover, in the MCAO model, Poly IC attenuated reactive astrogliosis, reduced brain infarction volume, and improved neurological function. In addition, Poly IC prevented MCAO-induced reductions in soma size, dendrite length, and number of dendritic bifurcations in cortical neurons of the infarct penumbra.

CONCLUSIONS

By ameliorating astrogliosis-related damage, Poly IC is a potential therapeutic agent for attenuating neuronal damage and promoting recovery after brain ischemia.

l-Lactate mediates neuroprotection against ischaemia by increasing TREK1 channel expression in rat hippocampal astrocytes in vitro

Brain ischaemia is a highly debilitating condition where shortage of oxygen and glucose leads to profuse cell death. Lactate is a neuroprotective metabolite whose concentrations increase up to 15-30 mmol/L during ischaemia and TREK1 is a neuroprotective potassium channel which is upregulated during ischaemia. The aim of this study was to investigate the effect of l-lactate on TREK1 expression and to evaluate the role of l-lactate-TREK1 interaction in conferring neuroprotection in ischaemia-prone hippocampus. We show that 15-30 mmol/L l-lactate increases functional TREK1 protein expression by 1.5-3-fold in hippocampal astrocytes using immunostaining and electrophysiology. Studies with transcription blocker actinomycin-D and quantitative PCR indicate that the increase in TREK1 expression is due to enhanced TREK1 mRNA transcription. We further report that l-lactate-mediated increase in TREK1 expression is via protein kinase A (PKA)-dependent pathway. This is the first report of an ischaemic metabolite affecting functional expression of an ion channel. Our studies in an in vitro model of ischaemia using oxygen glucose deprivation show that 30 mmol/L l-lactate fails to reduce cell death in rat hippocampal slices treated with TREK1 blockers, PKA inhibitors and gliotoxin. The above effects were specific to l-lactate as pyruvate failed to increase TREK1 expression and reduce cell death. l-Lactate-induced TREK1 upregulation is a novel finding of physiological significance as TREK1 channels contribute to neuroprotection by enhancing potassium buffering and glutamate clearance capacity of astrocytes. We propose that l-lactate promotes neuronal survival in hippocampus by increasing TREK1 channel expression via PKA pathway in astrocytes during ischaemia. Insufficient blood supply to the brain leads to cerebral ischaemia and increase in extracellular lactate concentrations. We incubated hippocampal astrocytes in lactate and observed increase in TREK1 channel expression via protein kinase A (PKA). Inhibition of TREK1, PKA and metabolic impairment of astrocytes prevented lactate from reducing cell death in ischaemic hippocampus. This pathway serves as an alternate mechanism of neuroprotection. Cover image for this issue: doi: 10.1111/jnc.13326.

Hind limb perconditioning renoprotection by modulation of inflammatory cytokines after renal ischemia/reperfusion

Purpose Renal ischemia/reperfusion (I/R) injury is a common clinical problem associated with significant mortality and morbidity. One newly described strategy to reduce this damage is remote perconditioning (RPEC), in which short-time ischemia of a limb during renal ischemia reduces the I/R-induced kidney injury. This study aimed to assess whether RPEC confer protection through changes in pro-inflammatory mediators. Methods Rats were subjected to right nephrectomy and randomized into: sham (no intervention), I/R (subjected to 45-min left renal ischemia) and RPEC group (subjected to four cycles of 5-min I/R of the femoral artery administered during renal ischemia). After 24-h, blood, urine, and kidney samples were collected. Biochemical indicators of renal dysfunction were measured in the cases of Neutrophil gelatinase-associated lipocalin (NGAL), and N-acetyl-B-diglucosaminidase (NAG) activity. Inflammatory cytokines [interleukin (IL)-6 and tumor necrosis factor-alpha, TNF-α] expression in the renal tissues as well as Periodic acid-Schiff stained histological sections were evaluated. Results I/R resulted in renal dysfunction, as evidenced by higher renal NGAL expression and urinary NAG activities. This was accompanied by increased TNF-α and IL-6 expressions as well as histological changes in this group. However, RPEC improved renal histology and function compared with the I/R group. Furthermore, the RPEC group showed decreases in TNF-α and IL-6 expression. Conclusions These results suggest that RPEC reduces the dysfunction and injury associated with I/R of the kidney. This technique reduced the pro-inflammatory cytokine in the kidney. RPEC could be a promising strategy against I/R-induced acute kidney injury partly by down-regulation of inflammatory mediators.

Activation of microglial Toll-like receptor 3 promotes neuronal survival against cerebral ischemia

Emerging experimental evidence suggests that activation of Toll-like receptor 3 (TLR3) by its agonist polyinosinic polycytidylic acid (poly-ICLC) protects neurons against cerebral ischemia, but the underlying mechanisms remain largely unknown. In the brain, TLR3 is mostly expressed in glial cells. Therefore, we assess the hypothesis that TLR3 activation in microglia is required for neuroprotection against ischemia. After transient focal cerebral ischemia, microglia/macrophages (MMs) demonstrate a significant reduction in TLR3 and its downstream cytokine interleukin 6 (IL-6). Subsequently, activation of TLR3 by poly-ICLC restored TLR3 expression and decreased infarction. To further investigate these mechanisms, we turned to a primary cell culture system. Consistent with the in vivo findings, oxygen-glucose deprivation (OGD) significantly reduced TLR3 and IL-6 mRNA expression in microglia, but poly-ICLC significantly rescued TLR3 and IL-6 expression. Importantly, conditioned media from OGD-treated microglia increased neuronal death after OGD. In contrast, the conditioned media from microglia treated with poly-ICLC after OGD significantly protected against OGD-induced neuron death. Taken together, our findings provide proof-of-concept that activation of TLR3 in microglia may promote neuron survival after ischemia. We assessed the hypothesis that Toll-like receptor 3 (TLR3) activation in microglia is required for neuroprotection against ischemia. After transient focal cerebral ischemia, microglia/macrophage demonstrates a reduction in TLR3 and Interleukin 6 (IL-6). Also, oxygen-glucose deprivation (OGD) reduces TLR3 and IL-6 expression in microglia, but polyinosinic polycytidylic acid (poly-ICLC) rescues TLR3 and IL-6. Importantly, conditioned media from microglia treated with poly-ICLC protects against OGD-induced neuron death. We propose that activation of TLR3 in microglia may promote neuron survival after ischemia.

Functional polarization of neuroglia: Implications in neuroinflammation and neurological disorders

Recent neuroscience research has established the adult brain as a dynamic organ having a unique ability to undergo changes with time. Neuroglia, especially microglia and astrocytes, provide dynamicity to the brain. Activation of these glial cells is a major component of the neuroinflammatory responses underlying brain injury and neurodegeneration. Glial cells execute functional reaction programs in response to diverse microenvironmental signals manifested by neuropathological conditions. Activated microglia exist along a continuum of two functional states of polarization namely M1-type (classical/proinflammatory activation) and M2-type (alternative/anti-inflammatory activation) as in macrophages. The balance between classically and alternatively activated microglial phenotypes influences disease progression in the CNS. The classically activated state of microglia drives the neuroinflammatory response and mediates the detrimental effects on neurons, whereas in their alternative activation state, which is apparently a beneficial activation state, the microglia play a crucial role in tissue maintenance and repair. Likewise, in response to immune or inflammatory microenvironments astrocytes also adopt neurotoxic or neuroprotective phenotypes. Reactive astrocytes exhibit two distinctive functional phenotypes defined by pro- or anti-inflammatory gene expression profile. In this review, we have thoroughly covered recent advances in the understanding of the functional polarization of brain and peripheral glia and its implications in neuroinflammation and neurological disorders. The identifiable phenotypes adopted by neuroglia in response to specific insult or injury can be exploited as promising diagnostic markers of neuroinflammatory diseases. Furthermore, harnessing the beneficial effects of the polarized glia could undoubtedly pave the way for the formulation of novel glia-based therapeutic strategies for diverse neurological disorders.

Rational modulation of the innate immune system for neuroprotection in ischemic stroke

The innate immune system plays a dualistic role in the evolution of ischemic brain damage and has also been implicated in ischemic tolerance produced by different conditioning stimuli. Early after ischemia, perivascular astrocytes release cytokines and activate metalloproteases (MMPs) that contribute to blood–brain barrier (BBB) disruption and vasogenic oedema; whereas at later stages, they provide extracellular glutamate uptake, BBB regeneration and neurotrophic factors release. Similarly, early activation of microglia contributes to ischemic brain injury via the production of inflammatory cytokines, including tumor necrosis factor (TNF) and interleukin (IL)-1, reactive oxygen and nitrogen species and proteases. Nevertheless, microglia also contributes to the resolution of inflammation, by releasing IL-10 and tumor growth factor (TGF)-β, and to the late reparative processes by phagocytic activity and growth factors production. Indeed, after ischemia, microglia/macrophages differentiate toward several phenotypes: the M1 pro-inflammatory phenotype is classically activated via toll-like receptors or interferon-γ, whereas M2 phenotypes are alternatively activated by regulatory mediators, such as ILs 4, 10, 13, or TGF-β. Thus, immune cells exert a dualistic role on the evolution of ischemic brain damage, since the classic phenotypes promote injury, whereas alternatively activated M2 macrophages or N2 neutrophils prompt tissue remodeling and repair. Moreover, a subdued activation of the immune system has been involved in ischemic tolerance, since different preconditioning stimuli act via modulation of inflammatory mediators, including toll-like receptors and cytokine signaling pathways. This further underscores that the immuno-modulatory approach for the treatment of ischemic stroke should be aimed at blocking the detrimental effects, while promoting the beneficial responses of the immune reaction.

Ischemia preconditioning protects astrocytes from ischemic injury through 14-3-3γ

Stroke is a leading cause of death and disability, and new strategies are required to reduce neuronal injury and improve prognosis. Ischemia preconditioning (IPC) is an intrinsic phenomenon that protects cells from subsequent ischemic injury and might provide promising mechanisms for clinical treatment. In this study, primary astrocytes exhibited significantly less cell death than control when exposed to different durations of IPC (15, 30, 60, or 120 min). A 15-min duration was the most effective IPC to protect astrocytes from 8-hr-ischemia injury. The protective mechanisms of IPC involve the upregulation of protective proteins, including 14-3-3γ, and attenuation of malondialdehyde (MDA) content and ATP depletion. 14-3-3γ is an antiapoptotic intracellular protein that was significantly upregulated for up to 84 hr after IPC. In addition, IPC promoted activation of the c-Jun N-terminal kinase (JNK), extracellular signal-related kinase (ERK)-1/2, p38, and protein kinase B (Akt) signaling pathways. When JNK was specifically inhibited with SP600125, the upregulation of 14-3-3γ induced by IPC was almost completely abolished; however, there was no effect on ATP or MDA levels. This suggests that, even though both energy preservation and 14-3-3γ up-regulation were turned on by IPC, they were controlled by different pathways. The ERK1/2, p38, and Akt signaling pathways were not involved in the 14-3-3γ upregulation and energy preservation. These results indicate that IPC could protect astrocytes from ischemia injury by inducing 14-3-3γ and by alleviating energy depletion through different pathways, suggesting multiple protection of IPC and providing new insights into potential stroke therapies.

The ebb and flow of traumatic brain injury research

The purpose of this chapter is to summarize some key topics discussed in this volume and describe trends suggesting the direction of future traumatic brain injury (TBI) research. Interest in, and funding for, TBI has ebbed and flowed with the public awareness of injury risk from combat, sports, or everyday life. Advances in acute resuscitation, emergency response systems, and early management have had a major impact on survival after TBI, while recent research has emphasized underlying genetic substrates and the molecular mechanisms of brain injury, repair, and neuroplasticity. This in turn impacts not only on primary and secondary neuroprotection strategies for minimizing injury, but also on the other critical remaining challenge, that of identification and validation of optimal strategies for physical and cognitive TBI rehabilitation. New information also highlights long-term degenerative conditions associated with earlier TBI and mediated by a signature cascade of abnormal molecular processes. Thus, TBI has emerged as a recognized significant public health risk with both immediate and lifelong repercussions. The linkage of a TBI to late-life neurodegenerative diseases, the observation of persistent pathologic processes including neuroinflammation and accumulation of tau protein, as well as individual differences in the genetic predisposition for brain repair and plasticity should lead to meaningful translational research with a significant impact on the efficacy and cost-efficiency of acute and chronic treatment for TBI survivors.

Immunomodulatory Effect of Toll-Like Receptor-3 Ligand Poly I:C on Cortical Spreading Depression

The release of inflammatory mediators following cortical spreading depression (CSD) is suggested to play a role in pathophysiology of CSD-related neurological disorders. Toll-like receptors (TLR) are master regulators of innate immune function and involved in the activation of inflammatory responses in the brain. TLR3 agonist poly I:C exerts anti-inflammatory effect and prevents cell injury in the brain. The aim of the present study was to examine the effect of systemic administration of poly I:C on the release of cytokines (TNF-α, IFN-γ, IL-4, TGF-β1, and GM-CSF) in the brain and spleen, splenic lymphocyte proliferation, expression of GAD65, GABAAα, GABAAβ as well as Hsp70, and production of dark neurons after induction of repetitive CSD in juvenile rats. Poly I:C significantly attenuated CSD-induced production of TNF-α and IFN-γ in the brain as well as TNF-α and IL-4 in the spleen. Poly I:C did not affect enhancement of splenic lymphocyte proliferation after CSD. Administration of poly I:C increased expression of GABAAα, GABAAβ as well as Hsp70 and decreased expression of GAD65 in the entorhinal cortex compared to CSD-treated tissues. In addition, poly I:C significantly prevented production of CSD-induced dark neurons. The data indicate neuroprotective and anti-inflammatory effects of TLR3 activation on CSD-induced neuroinflammation. Targeting TLR3 may provide a novel strategy for developing new treatments for CSD-related neurological disorders.

Toll-like receptor 3 activation drives the inflammatory response in oxygen-induced retinopathy in rats

AIMS

Ischaemia is one of the most important causes of blindness. The purpose of this study was to investigate the potential role and mechanisms by which toll-like receptor 3 (TLR3) influences the progression of the inflammatory response in a rat model of oxygen-induced retinopathy (OIR).

METHODS

OIR rat models were successfully established and received single intravitreal injections of polyinosine-polycytidylic acid (poly (I:C)) and anti-TLR3 antibody, respectively, on postnatal day 17 (P17). Pathological retinal neovascularisation was evaluated by haematoxylin and eosin staining and immunohistochemistry with Isolectin B4 FITC (fluorescein isothyocyanate). Retinal expressions of TLR3 and nuclear factor kappa B (NF-κB) were measured using real-time PCR, immunohistochemistry and western blot. Furthermore, interleukin-6 (IL-6) and tumour necrosis factor α (TNFα) expression levels were assessed with real-time PCR and ELISA.

RESULTS

Both gene and protein expression levels of TLR3 and NF-κB were significantly elevated in the retinas of OIR rats compared to the controls. Increased IL-6 and TNFα expression levels were also observed in the retinas of OIR rats. Furthermore, TLR3 signalling pathway components, including NF-κB and IL-6/TNFα, were markedly upregulated upon stimulation with poly(I:C). In addition, the pre-treatment of TLR3 neutralising antibody in OIR models significantly decreased TLR3 and NF-κB expressions, as well as related inflammatory factors IL-6/TNFα expression.

CONCLUSIONS

Our results suggest that upregulation of the TLR3 signalling pathway is involved in the pro-inflammatory response in OIR rat retinas.