LPS preconditioning redirects TLR signaling following stroke: TRIF-IRF3 plays a seminal role in mediating tolerance to ischemic injury

Repetitive acute intermittent hypoxia does not promote generalized inflammatory gene expression in the rat CNS

Modest protocols of repetitive acute intermittent hypoxia (rAIH) enhance motor function in patients with chronic incomplete spinal injury. Since chronic intermittent hypoxia (CIH) elicits neuroinflammation, there is potential for rAIH to have similar effects. Thus, we tested the hypothesis that rAIH has minimal impact on microglial inflammatory gene expression, but up-regulates key neurotrophic factor expression in a CNS region-specific manner. Using real time PCR, we evaluated mRNA levels of inflammatory and neurotrophic factors in immunomagnetically-isolated microglia from rat frontal cortex, brainstem and upper and lower cervical spinal cord following rAIH (ten, 5-min episodes, thrice weekly, 4 weeks). In agreement with our hypothesis, rAIH had no significant impact on microglial inflammatory gene expression in any region studied. On the other hand, neurotrophic factor expression was altered in a gene- and region-specific pattern. These results have important implications for the safety of rAIH as a potential therapy to enhance neuroplasticity and motor function in patients with spinal injury or other neurologic disorders.

Cerebral Ischemic Preconditioning: the Road So Far…

Cerebral preconditioning constitutes the brain's adaptation to lethal ischemia when first exposed to mild doses of a subtoxic stressor. The phenomenon of preconditioning has been largely studied in the heart, and data from in vivo and in vitro models from past 2-3 decades have provided sufficient evidence that similar machinery exists in the brain as well. Since preconditioning results in a transient protective phenotype labeled as ischemic tolerance, it can open many doors in the medical warfare against stroke, a debilitating cerebrovascular disorder that kills or cripples thousands of people worldwide every year. Preconditioning can be induced by a variety of stimuli from hypoxia to pharmacological anesthetics, and each, in turn, induces tolerance by activating a multitude of proteins, enzymes, receptors, transcription factors, and other biomolecules eventually leading to genomic reprogramming. The intracellular signaling pathways and molecular cascades behind preconditioning are extensively being investigated, and several first-rate papers have come out in the last few years centered on the topic of cerebral ischemic tolerance. However, translating the experimental knowledge into the clinical scaffold still evades practicality and faces several challenges. Of the various preconditioning strategies, remote ischemic preconditioning and pharmacological preconditioning appears to be more clinically relevant for the management of ischemic stroke. In this review, we discuss current developments in the field of cerebral preconditioning and then examine the potential of various preconditioning agents to confer neuroprotection in the brain.

The macrophage mediates the renoprotective effects of endotoxin preconditioning

Preconditioning is a preventative approach, whereby minimized insults generate protection against subsequent larger exposures to the same or even different insults. In immune cells, endotoxin preconditioning downregulates the inflammatory response and yet, preserves the ability to contain infections. However, the protective mechanisms of preconditioning at the tissue level in organs such as the kidney remain poorly understood. Here, we show that endotoxin preconditioning confers renal epithelial protection in various models of sepsis in vivo. We also tested the hypothesis that this protection results from direct interactions between the preconditioning dose of endotoxin and the renal tubules. This hypothesis is on the basis of our previous findings that endotoxin toxicity to nonpreconditioned renal tubules was direct and independent of immune cells. Notably, we found that tubular protection after preconditioning has an absolute requirement for CD14-expressing myeloid cells and particularly, macrophages. Additionally, an intact macrophage CD14-TRIF signaling pathway was essential for tubular protection. The preconditioned state was characterized by increased macrophage number and trafficking within the kidney as well as clustering of macrophages around S1 proximal tubules. These macrophages exhibited increased M2 polarization and upregulation of redox and iron-handling molecules. In renal tubules, preconditioning prevented peroxisomal damage and abolished oxidative stress and injury to S2 and S3 tubules. In summary, these data suggest that macrophages are essential mediators of endotoxin preconditioning and required for renal tissue protection. Preconditioning is, therefore, an attractive model to investigate novel protective pathways for the prevention and treatment of sepsis.

Lipopolysaccharide pretreatment inhibits LPS-induced human umbilical cord mesenchymal stem cell apoptosis via upregulating the expression of cellular FLICE-inhibitory protein

Mesenchymal stem cell (MSC)-based regenerative therapy is currently regarded as a novel approach with which to repair damaged tissues. However, the efficiency of MSC transplantation is limited due to the low survival rate of engrafted MSCs. Lipopolysaccharide (LPS) production is increased in numerous diseases and serves an essential function in the regulation of apoptosis in a variety of cell types. Previous studies have indicated that low-dose LPS pretreatment contributes to cytoprotection. In the current study, LPS was demonstrated to induce apoptosis in human umbilical cord mesenchymal stem cells (hUCMSCs) via the activation of caspase, in a dose-dependent manner. Low-dose LPS pretreatment may protect hUCMSCs against apoptosis induced by high-dose LPS, by upregulating the expression of cellular FADD-like IL-1β-converting enzyme-inhibitory protein (c-FLIP). The results of the present study indicate that pretreatment with an appropriate concentration of LPS may alleviate high-dose LPS-induced apoptosis.

Role of adaptor protein MyD88 in TLR-mediated preconditioning and neuroprotection after acute excitotoxicity

Excitotoxic cell death is a crucial mechanism through which neurodegeneration occurs in numerous pathologies of the central nervous system (CNS), such as Alzheimer's disease, stroke and spinal cord injury. Toll-like receptors (TLRs) are strongly expressed on microglial cells and are key regulators of the innate immune response to neuronal damage. However, it is still unclear whether their stimulation is protective or harmful in excitotoxic contexts. In this study, we demonstrate that systemic administration of lipopolysaccharide (LPS) or Pam3CSK4 24h prior to an intrastriatal injection of kainic acid (KA) significantly protected cortical neurons in the acute phase of injury. Protection could not be detected with the TLR3 ligand poly-IC. Histological analyses revealed that microglia of LPS and Pam3CSK4 pre-conditioned group were primed to react to injury and exhibited a stronger expression of Tnf and Tlr2 mRNA. We also found that mice deficient for MyD88, a critical adaptor protein for most TLR, were more vulnerable than WT mice to KA-induced excitotoxicity at early (12h and 24h) and late (10days) time points. Finally, bone-marrow chimeric mice revealed that MyD88 signaling in CNS resident cells, but not in cells of hematopoietic origin, mediates the protective effect. This study unravels the potential of TLR2 and TLR4 agonists to induce a protective state of preconditioning against KA-mediated excitotoxicity and further highlights the beneficial role of cerebral MyD88 signaling in this context.

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.

Function and mechanism of toll-like receptors in cerebral ischemic tolerance: from preconditioning to treatment

Increasing evidence suggests that toll-like receptors (TLRs) play an important role in cerebral ischemia-reperfusion injury. The endogenous ligands released from ischemic neurons activate the TLR signaling pathway, resulting in the production of a large number of inflammatory cytokines, thereby causing secondary inflammation damage following cerebral ischemia. However, the preconditioning for minor cerebral ischemia or the preconditioning with TLR ligands can reduce cerebral ischemic injury by regulating the TLR signaling pathway following ischemia in brain tissue (mainly, the inhibition of the TLR4/NF-κB signaling pathway and the enhancement of the interferon regulatory factor-dependent signaling), resulting in TLR ischemic tolerance. Additionally, recent studies found that postconditioning with TLR ligands after cerebral ischemia can also reduce ischemic damage through the regulation of the TLR signaling pathway, showing a significant therapeutic effect against cerebral ischemia. These studies suggest that the ischemic tolerance mediated by TLRs can serve as an important target for the prevention and treatment of cerebral ischemia. On the basis of describing the function and mechanism of TLRs in mediating cerebral ischemic damage, this review focuses on the mechanisms of cerebral ischemic tolerance induced by the preconditioning and postconditioning of TLRs and discusses the clinical application of TLRs for ischemic tolerance.

Anti-inflammatory effects of Gualou Guizhi decoction in transient focal cerebral ischemic brains. [Corrected]

The aim of the present study was to explore the neuroprotective effects of Gualou Guizhi decoction (GLGZD) in a rat model of middle cerebral artery occlusion (MCAO). Sprague-Dawley rats were divided into three groups: Sham (no MCAO), MCAO (MCAO with no GLGZD treatment) and GLGZD (MCAO with GLGZD treatment). Rats in the MCAO and GLGZD groups were subjected to permanent occlusion of the left middle cerebral artery. Neurological function and infarct volume were measured. Microglial activation and inflammatory cell accumulation were measured using immunohistochemistry. mRNA and protein expression of inflammatory mediators were examined using reverse transcription-quantitative polymerase chain reaction and an enzyme-linked immunosorbent assay. The expression of proteins associated with the nuclear factor κ-B (NF-κB) inflammation signaling pathway was analyzed using western blotting. The results of the present study suggested that infarct size was significantly reduced and neurological behavior function was improved in rats with MCAO treated with GLGZD compared with rats in the MCAO group. Amoeboid microglial expansion and inflammatory cell migration were observed in the infarcted areas of rats in the GLGZD group and were not identified in those of the MCAO group. Target mRNA and protein levels, and inflammatory cell infiltration were significantly reduced in the GLGZD group compared with the MCAO model group. Notably, GLGZD treatment induced neuroprotective effects, reducing inflammation and inhibiting NF-κB signaling compared with the MCAO group. Therefore, GLGZD may exhibit anti-inflammatory effects against ischemia-reperfusion brain injury and may be a therapeutic target for ischemic stroke.

The interferon regulatory factors as novel potential targets in the treatment of cardiovascular diseases

The family of interferon regulatory factors (IRFs) consists of nine members (IRF1-IRF9) in mammals. They act as transcription factors for the interferons and thus exert essential regulatory functions in the immune system and in oncogenesis. Recent clinical and experimental studies have identified critically important roles of the IRFs in cardiovascular diseases, arising from their participation in divergent and overlapping molecular programmes beyond the immune response. Here we review the current knowledge of the regulatory effects and mechanisms of IRFs on the immune system. The role of IRFs and their potential molecular mechanisms as novel stress sensors and mediators of cardiovascular diseases are highlighted.

Mice lacking α1,3-fucosyltransferase 9 exhibit modulation of in vivo immune responses against pathogens

Carbohydrate structures, including Lewis X (Le^x), which is not synthesized in mutant mice that lack α1,3‐fucosyltransferase 9 (Fut9^−/−), are involved in cell–cell recognition and inflammation. However, immunological alteration in Fut9^−/− mice has not been studied. Thus, the inflammatory response of Fut9^−/− mice was examined using the highly neurovirulent mouse hepatitis virus (MHV) JHMV srr7 strain. Pathological study revealed that inflammation induced in the brains of Fut9^−/− mice after infection was more extensive compared with that of wild‐type mice, although viral titers obtained from the brains of mutant mice were lower than those of wild‐type mice. Furthermore, the reduction in cell numbers in the spleens of wild‐type mice after infection was not observed in the infected Fut9^−/− mice. Although there were no clear differences in the levels of cytokines examined in the brains between Fut9^−/− and wild‐type mice except for interferon‐β (IFN‐β) expression, some of those in the spleens, including interferon‐γ (IFN‐γ), interleukin‐6 (IL‐6), and monocyte chemoattractant protein‐1 (MCP‐1), showed higher levels in Fut9^−/− than in wild‐type mice. Furthermore, Fut9^−/− mice were refractory to the in vivo inoculation of endotoxin (LPS) compared with wild‐type mice. These results indicate that Le^x structures are involved in host responses against viral or bacterial challenges.

CpG preconditioning regulates miRNA expression that modulates genomic reprogramming associated with neuroprotection against ischemic injury

Cytosine-phosphate-guanine (CpG) preconditioning reprograms the genomic response to stroke to protect the brain against ischemic injury. The mechanisms underlying genomic reprogramming are incompletely understood. MicroRNAs (miRNAs) regulate gene expression; however, their role in modulating gene responses produced by CpG preconditioning is unknown. We evaluated brain miRNA expression in response to CpG preconditioning before and after stroke using microarray. Importantly, we have data from previous gene microarrays under the same conditions, which allowed integration of miRNA and gene expression data to specifically identify regulated miRNA gene targets. CpG preconditioning did not significantly alter miRNA expression before stroke, indicating that miRNA regulation is not critical for the initiation of preconditioning-induced neuroprotection. However, after stroke, differentially regulated miRNAs between CpG- and saline-treated animals associated with the upregulation of several neuroprotective genes, implicating these miRNAs in genomic reprogramming that increases neuroprotection. Statistical analysis revealed that the miRNA targets were enriched in the gene population regulated in the setting of stroke, implying that miRNAs likely orchestrate this gene expression. These data suggest that miRNAs regulate endogenous responses to stroke and that manipulation of these miRNAs may have the potential to acutely activate novel neuroprotective processes that reduce damage.

Evidence for ProTα-TLR4/MD-2 binding: molecular dynamics and gravimetric assay studies

OBJECTIVE

During preconditioning, lipopolysaccharide (LPS) selectively activates TLR4/MD-2/Toll/IL-1 receptor-domain-containing adaptor inducing IFN-β (TRIF) pathway instead of pro-inflammatory myeloid differentiation protein-88 (MyD88)/MyD88-adaptor-like protein (MAL) pathway. Extracellular prothymosin alpha (ProTα) is also known to selectively activate the TLR4/MD2/TRIF-IRF3 pathway in certain diseased conditions. In the current study, biophysical evidence for ProTα/TLR4/MD-2 complex formation and its interaction dynamics have been studied.

RESEARCH DESIGN AND METHODS

Gravimetric assay was used to investigate ProTα/TLR4/MD-2 complex formation while molecular dynamics (MD) simulation was used to study its interaction dynamics.

RESULTS

Through electrostatic interaction, full-length ProTα (F-ProTα) C-terminal peptide (aa 91 - 111) superficially interacts with similar TLR4/MD-2 (KD = 273.36 nm vs 16.07 μg/ml [LPS]) conformation with LPS at an overlapping three-dimensional space while F-ProTα is hinged to the TLR4 scaffold by one-amino acid shift-Mosoian domain (aa-51 - 90). Comparatively, F-ProTα better stabilizes MD-2 metastable states transition and mediates higher TLR4/MD-2 interaction than LPS.

CONCLUSIONS

ProTα via its C-terminal peptide (aa 91 - 111) exhibits in vitro biophysical contact with TLR4/MD-2 complex conformation recognized by LPS at overlapping LPS-binding positions.

Innate immune programing by endotoxin and its pathological consequences

Monocytes and macrophages play pivotal roles in inflammation and homeostasis. Recent studies suggest that dynamic programing of macrophages and monocytes may give rise to distinct "memory" states. Lipopolysaccharide (LPS), a classical pattern recognition molecule, dynamically programs innate immune responses. Emerging studies have revealed complex dynamics of cellular responses to LPS, with high doses causing acute, resolving inflammation, while lower doses are associated with low-grade and chronic non-resolving inflammation. These phenomena hint at dynamic complexities of intra-cellular signaling circuits downstream of the Toll-like receptor 4 (TLR4). In this review, we examine pathological effects of varying LPS doses with respect to the dynamics of innate immune responses and key molecular regulatory circuits responsible for these effects.

Kinetic characteristics of euflammation: the induction of controlled inflammation without overt sickness behavior

We found recently that controlled progressive challenge with subthreshold levels of E. coli can confer progressively stronger resistance to future reinfection-induced sickness behavior to the host. We have termed this type of inflammation "euflammation". In this study, we further characterized the kinetic changes in the behavior, immunological, and neuroendocrine aspects of euflammation. Results show euflammatory animals only display transient and subtle sickness behaviors of anorexia, adipsia, and anhedonia upon a later infectious challenge which would have caused much more severe and longer lasting sickness behavior if given without prior euflammatory challenges. Similarly, infectious challenge-induced corticosterone secretion was greatly ameliorated in euflammatory animals. At the site of E.coli priming injections, which we termed euflammation induction locus (EIL), innate immune cells displayed a partial endotoxin tolerant phenotype with reduced expression of innate activation markers and muted inflammatory cytokine expression upon ex vivo LPS stimulation, whereas innate immune cells outside EIL displayed largely opposite characteristics. Bacterial clearance function, however, was enhanced both inside and outside EIL. Finally, sickness induction by an infectious challenge placed outside the EIL was also abrogated. These results suggest euflammation could be used as an efficient method to "train" the innate immune system to resist the consequences of future infectious/inflammatory challenges.

A Molecular Approach to Epilepsy Management: from Current Therapeutic Methods to Preconditioning Efforts

Epilepsy is the most common and chronic neurological disorder characterized by recurrent unprovoked seizures. The key aim in treating patients with epilepsy is the suppression of seizures. An understanding of focal changes that are involved in epileptogenesis may therefore provide novel approaches for optimal treatment of the seizure. Although the actual pathogenesis of epilepsy is still uncertain, recently growing lines of evidence declare that microglia and astrocyte activation, oxidative stress and reactive oxygen species (ROS) production, mitochondria dysfunction, and damage of blood-brain barrier (BBB) are involved in its pathogenesis. Impaired GABAergic function in the brain is probably the most accepted hypothesis regarding the pathogenesis of epilepsy. Clinical neuroimaging of patients and experimental modeling have demonstrated that seizures may induce neuronal apoptosis. Apoptosis signaling pathways are involved in the pathogenesis of several types of epilepsy such as temporal lobe epilepsy (TLE). The quality of life of patients is seriously affected by treatment-related problems and also by unpredictability of epileptic seizures. Moreover, the available antiepileptic drugs (AED) are not significantly effective to prevent epileptogenesis. Thus, novel therapies that are proficient to control seizure in people who are suffering from epilepsy are needed. The preconditioning method promises to serve as an alternative therapeutic approach because this strategy has demonstrated the capability to curtail epileptogenesis. For this reason, understanding of molecular mechanisms underlying brain tolerance induced by preconditioning is crucial to delineate new neuroprotective ways against seizure damage and epileptogenesis. In this review, we summarize the work to date on the pathogenesis of epilepsy and discuss recent therapeutic strategies in the treatment of epilepsy. We will highlight that novel therapy targeting such as preconditioning process holds great promise. In addition, we will also highlight the role of gene reprogramming and mitochondrial biogenesis in the preconditioning-mediated neuroprotective events.

A Genomic Profile of the Immune Response to Stroke With Implications for Stroke Recovery

Objectives:

The objectives of this study were to determine the change in gene expression between two time points following stroke and to identify biomarkers of stroke recovery through gene expression profiling and pathway analysis.

Methods:

Peripheral blood was collected from 34 ischemic stroke patients (confirmed by magnetic resonance imaging) ≥18 years of age, within 24 hr of symptom onset and 24–48 hr later, and from healthy controls. The Modified Rankin Scale (MRS) was used to determine 30-day recovery. Total RNA was extracted from whole blood in Paxgene RNA tubes, amplified, and hybridized to Illumina HumanRef-8v2 bead chips. Gene expression was compared in a univariate manner between stroke patients at both time points and good versus bad outcome using t-test in GeneSpring. Inflation of Type 1 error was corrected by false discovery rate (FDR), and Ingenuity Systems Pathway analysis (IPA) was performed. A secondary validation cohort was recruited from a local hospital.

Results:

Three genes were significantly downregulated over time ( LY96, IL8, and SDPR; FDR corrected p < .05). This finding was confirmed in a validation cohort of stroke patients ( n = 8). IPA revealed cytotoxic T-lymphocyte antigen 4 (CTLA4) signaling was the most significant pathway present in the peripheral whole blood of stroke patients 24–48 hr after onset. When controlling for age and National Institutes of Health Stroke Scale score, high baseline expression of TLR2 and TLR4 significantly predicted worse scores on the MRS.

Conclusion:

CTLA4 signaling is a novel pathway for the study of stroke-induced immune suppression. Markers of immune dysfunction early after stroke may prove useful for identifying patients with increased risk of poor recovery.

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

Background

Cerebral ischemic preconditioning (IPC) protects brain against ischemic injury. Activation of Toll-like receptor 3 (TLR3) signaling can induce neuroprotective mediators, but whether astrocytic TLR3 signaling is involved in IPC-induced ischemic tolerance is not known.

Methods

IPC was modeled in mice with three brief episodes of bilateral carotid occlusion. In vitro, IPC was modeled in astrocytes by 1-h oxygen-glucose deprivation (OGD). Injury and components of the TLR3 signaling pathway were measured after a subsequent protracted ischemic event. A neutralizing antibody against TLR3 was used to evaluate the role of TLR3 signaling in ischemic tolerance.

Results

IPC in vivo reduced brain damage from permanent middle cerebral artery occlusion in mice and increased expression of TLR3 in cortical astrocytes. IPC also reduced damage in isolated astrocytes after 12-h OGD. In astrocytes, IPC or 12-h OGD alone increased TLR3 expression, and 12-h OGD alone increased expression of phosphorylated NFκB (pNFκB). However, IPC or 12-h OGD alone did not alter the expression of Toll/interleukin receptor domain-containing adaptor-inducing IFNβ (TRIF) or phosphorylated interferon regulatory factor 3 (pIRF3). Exposure to IPC before OGD increased TRIF and pIRF3 expression but decreased pNFκB expression. Analysis of cytokines showed that 12-h OGD alone increased IFNβ and IL-6 secretion; 12-h OGD preceded by IPC further increased IFNβ secretion but decreased IL-6 secretion. Preconditioning with TLR3 ligand Poly I:C increased pIRF3 expression and protected astrocytes against ischemic injury; however, cells treated with a neutralizing antibody against TLR3 lacked the IPC- and Poly I:C-induced ischemic protection and augmentation of IFNβ.

Conclusions

The results suggest that IPC-induced ischemic tolerance is mediated by astrocytic TLR3 signaling. This reprogramming of TLR3 signaling by IPC in astrocytes may play an important role in suppression of the post-ischemic inflammatory response and thereby protect against ischemic damage. The mechanism may be via activation of the TLR3/TRIF/IRF3 signaling pathway.

Synergistic white matter protection with acute-on-chronic endotoxin and subsequent asphyxia in preterm fetal sheep

Background

Perinatal asphyxia and exposure to intrauterine infection are associated with impaired neurodevelopment in preterm infants. Acute exposure to non-injurious infection and/or inflammation can either protect or sensitize the brain to subsequent hypoxia-ischemia. However, the effects of subacute infection and/or inflammation are unclear. In this study we tested the hypothesis that acute-on-chronic exposure to lipopolysaccharide (LPS) would exacerbate white matter injury after subsequent asphyxia in preterm fetal sheep.

Methods

Fetal sheep at 0.7 gestational age received a continuous LPS infusion at 100 ng/kg for 24 hours, then 250 ng/kg/24 hours for 96 hours, plus 1 μg boluses of LPS at 48, 72, and 96 hours or the same volume of saline. Four hours after the last bolus, complete umbilical cord occlusion or sham occlusion was induced for 15 minutes. Sheep were sacrificed 10 days after the start of infusions.

Results

LPS exposure was associated with induction of microglia and astrocytes and loss of total and immature and mature oligodendrocytes (n = 9) compared to sham controls (n = 9). Umbilical cord occlusion with saline infusions was associated with induction of microglia, astrogliosis, and loss of immature and mature oligodendrocytes (n = 9). LPS exposure before asphyxia (n = 8) was associated with significantly reduced microglial activation and astrogliosis and improved numbers of immature and mature oligodendrocytes compared to either LPS exposure or asphyxia alone.

Conclusions

Contrary to our initial hypothesis, the combination of acute-on-chronic LPS with subsequent asphyxia reduced neuroinflammation and white matter injury compared with either intervention alone.

Polyinosinic-polycytidylic acid has therapeutic effects against cerebral ischemia/reperfusion injury through the downregulation of TLR4 signaling via TLR3

Recent reports have shown that preconditioning with the TLR3 ligand polyinosinic-polycytidylic acid (poly(I:C)) protects against cerebral ischemia/reperfusion (I/R) injury. However, it is unclear whether poly(I:C) treatment after cerebral I/R injury is also effective. We used mouse/rat middle cerebral artery occlusion and cell oxygen-glucose deprivation models to evaluate the therapeutic effects and mechanisms of poly(I:C) treatment. Poly(I:C) was i.p. injected 3 h after ischemia (treatment group). Cerebral infarct volumes and brain edemas were significantly reduced, and neurologic scores were significantly increased. TNF-α and IL-1β levels were markedly decreased, whereas IFN-β levels were greatly increased, in the ischemic brain tissues, cerebral spinal fluid, and serum. Injuries to hippocampal neurons and mitochondria were greatly reduced. The numbers of TUNEL-positive and Fluoro-Jade B(+) cells also decreased significantly in the ischemic brain tissues. Poly(I:C) treatment increased the levels of Hsp27, Hsp70, and Bcl2 and decreased the level of Bax in the ischemic brain tissues. Moreover, poly(I:C) treatment attenuated the levels of TNF-α and IL-1β in serum and cerebral spinal fluid of mice stimulated by LPS. However, the protective effects of poly(I:C) against cerebral ischemia were abolished in TLR3(-/-) and TLR4(-/-)mice. Poly(I:C) downregulated TLR4 signaling via TLR3. Poly(I:C) treatment exhibited obvious protective effects 14 d after ischemia and was also effective in the rat permanent middle cerebral artery occlusion model. The results suggest that poly(I:C) exerts therapeutic effects against cerebral I/R injury through the downregulation of TLR4 signaling via TLR3. Poly(I:C) is a promising new drug candidate for the treatment of cerebral infarcts.

Preconditioning as a potential strategy for the prevention of Parkinson's disease

Parkinson's disease (PD) is a chronic neurodegenerative movement disorder characterized by the progressive and massive loss of dopaminergic neurons by neuronal apoptosis in the substantia nigra pars compacta and depletion of dopamine in the striatum, which lead to pathological and clinical abnormalities. A numerous of cellular processes including oxidative stress, mitochondrial dysfunction, and accumulation of α-synuclein aggregates are considered to contribute to the pathogenesis of Parkinson's disease. A further understanding of the cellular and molecular mechanisms involved in the pathophysiology of PD is crucial for developing effective diagnostic, preventative, and therapeutic strategies to cure this devastating disorder. Preconditioning (PC) is assumed as a natural adaptive process whereby a subthreshold stimulus can promote protection against a subsequent lethal stimulus in the brain as well as in other tissues that affords robust brain tolerance facing neurodegenerative insults. Multiple lines of evidence have demonstrated that preconditioning as a possible neuroprotective technique may reduce the neural deficits associated with neurodegenerative diseases such as PD. Throughout the last few decades, a lot of efforts have been made to discover the molecular determinants involved in preconditioning-induced protective responses; although, the accurate mechanisms underlying this "tolerance" phenomenon are not fully understood in PD. In this review, we will summarize pathophysiology and current therapeutic approaches in PD and discuss about preconditioning in PD as a potential neuroprotective strategy. Also the role of gene reprogramming and mitochondrial biogenesis involved in the preconditioning-mediated neuroprotective events will be highlighted. Preconditioning may represent a promising therapeutic weapon to combat neurodegeneration.

Curcumin attenuates acute inflammatory injury by inhibiting the TLR4/MyD88/NF-κB signaling pathway in experimental traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) initiates a neuroinflammatory cascade that contributes to substantial neuronal damage and behavioral impairment, and Toll-like receptor 4 (TLR4) is an important mediator of thiscascade. In the current study, we tested the hypothesis that curcumin, a phytochemical compound with potent anti-inflammatory properties that is extracted from the rhizome Curcuma longa, alleviates acute inflammatory injury mediated by TLR4 following TBI.

METHODS

Neurological function, brain water content and cytokine levels were tested in TLR4⁻/⁻ mice subjected to weight-drop contusion injury. Wild-type (WT) mice were injected intraperitoneally with different concentrations of curcumin or vehicle 15 minutes after TBI. At 24 hours post-injury, the activation of microglia/macrophages and TLR4 was detected by immunohistochemistry; neuronal apoptosis was measured by FJB and TUNEL staining; cytokines were assayed by ELISA; and TLR4, MyD88 and NF-κB levels were measured by Western blotting. In vitro, a co-culture system comprised of microglia and neurons was treated with curcumin following lipopolysaccharide (LPS) stimulation. TLR4 expression and morphological activation in microglia and morphological damage to neurons were detected by immunohistochemistry 24 hours post-stimulation.

RESULTS

The protein expression of TLR4 in pericontusional tissue reached a maximum at 24 hours post-TBI. Compared with WT mice, TLR4⁻/⁻ mice showed attenuated functional impairment, brain edema and cytokine release post-TBI. In addition to improvement in the above aspects, 100 mg/kg curcumin treatment post-TBI significantly reduced the number of TLR4-positive microglia/macrophages as well as inflammatory mediator release and neuronal apoptosis in WT mice. Furthermore, Western blot analysis indicated that the levels of TLR4 and its known downstream effectors (MyD88, and NF-κB) were also decreased after curcumin treatment. Similar outcomes were observed in the microglia and neuron co-culture following treatment with curcumin after LPS stimulation. LPS increased TLR4 immunoreactivity and morphological activation in microglia and increased neuronal apoptosis, whereas curcumin normalized this upregulation. The increased protein levels of TLR4, MyD88 and NF-κB in microglia were attenuated by curcumin treatment.

CONCLUSIONS

Our results suggest that post-injury, curcumin administration may improve patient outcome by reducing acute activation of microglia/macrophages and neuronal apoptosis through a mechanism involving the TLR4/MyD88/NF-κB signaling pathway in microglia/macrophages in TBI.

Comparison of the innate immune responses of porcine monocyte-derived dendritic cells and splenic dendritic cells stimulated with LPS

Dendritic cell (DC) subsets form a remarkable cellular network that regulate innate and adaptive immune responses. Although pigs are the most approximate model to humans, little is known about the regulation of monocyte-derived DCs (moDCs) and splenic DCs (SDCs) in the initiation of immune responses under inflammatory conditions. We investigated the activation and maturation of porcine moDC and SDC subpopulations following LPS stimulation. Porcine monocytes that would differentiate into moDCs were isolated. SDCs were isolated directly from the porcine spleen. Following LPS stimulation, phagocytosis activity, TLR4/MyD88-dependent gene expression, co-stimulatory molecule, and pro-inflammatory cytokine (TNF-α, IL-1β) and chemokine (IL-8) expressions were increased in both cell subsets. Furthermore, moDCs showed higher levels of gene and protein expression compared with SDCs. Interestingly, moDCs were found to be more responsive via the TLR4/TRAF-dependent signalling pathway of activation. Only SDCs expressed higher level of IL-12p40 gene and protein, whereas, IFN-γ gene and protein expression were likely to be unchanged after LPS stimulation in both cell subtypes. These data demonstrate that porcine moDCs display a greater ability to initiate innate immune responses, and could be used as a model to investigate immune responses against Ags.

Immune mechanisms in cerebral ischemic tolerance

Stressor-induced tolerance is a central mechanism in the response of bacteria, plants, and animals to potentially harmful environmental challenges. This response is characterized by immediate changes in cellular metabolism and by the delayed transcriptional activation or inhibition of genetic programs that are not generally stressor specific (cross-tolerance). These programs are aimed at countering the deleterious effects of the stressor. While induction of this response (preconditioning) can be established at the cellular level, activation of systemic networks is essential for the protection to occur throughout the organs of the body. This is best signified by the phenomenon of remote ischemic preconditioning, whereby application of ischemic stress to one tissue or organ induces ischemic tolerance (IT) in remote organs through humoral, cellular and neural signaling. The immune system is an essential component in cerebral IT acting simultaneously both as mediator and target. This dichotomy is based on the fact that activation of inflammatory pathways is necessary to establish IT and that IT can be, in part, attributed to a subdued immune activation after index ischemia. Here we describe the components of the immune system required for induction of IT and review the mechanisms by which a reprogrammed immune response contributes to the neuroprotection observed after preconditioning. Learning how local and systemic immune factors participate in endogenous neuroprotection could lead to the development of new stroke therapies.

The Delay Phenomenon: A Compilation of Knowledge across Specialties

Objective The purpose of this article is to review and integrate the available literature in different fields to gain a better understanding of the basic physiology and optimize vascular delay as a reconstructive surgery technique. Methods A broad search of the literature was performed using the Medline database. Two queries were performed using "vascular delay," a search expected to yield perspectives from the field of plastic and reconstructive surgery, and "ischemic preconditioning," (IPC) which was expected to yield research on the same topic in other fields. Results The combined searches yielded a total of 1824 abstracts. The "vascular delay" query yielded 76 articles from 1984 to 2011. The "ischemic preconditioning" query yielded 6534 articles, ranging from 1980 to 2012. The abstracts were screened for those from other specialties in addition to reconstructive surgery, analyzed potential or current uses of vascular delay in practice, or provided developments in understanding the pathophysiology of vascular delay. 70 articles were identified that met inclusion criteria and were applicable to vascular delay or ischemic preconditioning. Conclusion An understanding of IPC's implementation and mechanisms in other fields has beneficial implications for the field of reconstructive surgery in the context of the delay phenomenon. Despite an incomplete model of IPC's pathways, the anti-oxidative, anti-apoptotic and anti-inflammatory benefits of IPC are well recognized. The activation of angiogenic genes through IPC could allow for complex flap design, even in poorly vascularized regions. IPC's promotion of angiogenesis and reduction of endothelial dysfunction remain most applicable to reconstructive surgery in reducing graft-related complications and flap failure.

Lrg participates in lipopolysaccharide preconditioning-induced brain ischemia injury via TLR4 signaling pathway

Lipopolysaccharide (LPS) preconditioning is a powerful neuroprotective phenomenon by which an injurious stimulus renders the brain resistant to a subsequent damaging ischemic insult. The LPS response gene (Lrg) is a recently identified gene in human dental pulp cells treated with LPS. However, the role and mechanism of Lrg in brain ischemia injury have not yet been demonstrated. Here, we sought to determine whether Lrg participates in LPS preconditioning-induced brain ischemia injury. The Lrg protein accumulates in brain tissue after middle cerebral artery occlusion (MCAO). Furthermore, knockdown of Lrg by small interfering RNA (siRNA) significantly increased the infarct size of brain injury. In addition, we investigated the mechanism of Lrg in brain ischemia injury. Lrg-siRNA could regulate inflammatory cytokine expression. Moreover, interleukin-1 receptor-associated kinase 1 (IRAK-1) and nuclear factor Kappa B (NF-κB) p65 protein levels were significantly increased by Lrg-siRNA in mice after MCAO. Conversely, interferon regulatory factor 3 (IRF3) protein level was decreased by Lrg-siRNA. Taken together, these results suggest that Lrg regulates the expression of inflammatory cytokines in LPS preconditioning-induced brain ischemia injury via the toll-like receptor 4 (TLR4) signaling pathway. Lrg may therefore serve as a novel therapeutic target for brain ischemia injury.

Mechanism of focal cerebral ischemic tolerance in rats with ischemic preconditioning involves MyD88- and TRIF-dependent pathways

The aim of this study was to explore the involvement of Toll-like receptor 4 (TLR4) and the downstream myeloid differentiation factor 88 (MyD88)-dependent and -independent pathways in the mechanisms of cerebral ischemic tolerance. Using an improved middle cerebral artery occlusion method, we constructed a preconditioned ischemic brain model in rats. Sham and ischemia-reperfusion groups were also established. The expression levels of proteins in the MyD88/nuclear factor-κB (NF-κB) pathway (MyD88-dependent) were compared with those in the Toll/interleukin-1 receptor-domain-containing adaptor-inducing interferon-β (TRIF)/interferon regulatory factor-3 (IRF-3) pathway (MyD88-independent) by western blot analysis. NF-κB and IRF-3 protein expression levels within cells were determined by immunofluorescence staining of frozen tissue sections. Western blot analysis showed a downregulation of MyD88 protein expression in the brain tissue of ischemic preconditioned rats; however, NF-κB, TRIF and IRF-3 protein expression levels were upregulated. Immunofluorescence staining showed that NF-κB protein was mainly located in the cytoplasm in ischemic preconditioned rats and IRF-3 was predominantly located in the nucleus. The results indicate that changes in the two TLR4 downstream pathways are the main mechanisms involved in the development of brain ischemic tolerance with ischemic pretreatment.

Signaling mechanism for Aspergillus fumigatus tolerance in corneal fibroblasts induced by LPS pretreatment

TLRs, particularly TLR2 and TLR4, play primary roles in inflammatory responses triggered by Aspergillus fumigatus and lead to the activation of signaling pathways that initiate host defense responses. We previously demonstrated that LPS, a ligand of TLR4, can induce tolerance of A. fumigatus hyphae in telomerase-immortalized human stroma fibroblasts (THSFs). In the present study we investigated the role of TLR4, TLR2 and their downstream signaling pathways in this activity. The THSFs were pretreated with low-dose LPS and then exposed to A. fumigatus hyphae. It was demonstrated that enhanced expression of TLR4, but not of TLR2, was associated with LPS pretreatment. Inhibition of TLR4 with monoclonal Ab prevented reduction of pro-inflammatory cytokine secretion in LPS-pretreated THSFs. Pretreatment of THSFs with low-dose LPS caused an impaired response of the MyD88-dependent classical and MAPK signaling pathway upon subsequent A. fumigatus challenge, while expression of signaling molecules in the MyD88-independent Toll-IL-1 receptor domain-containing adaptor inducing IFN-β pathway was increased in THSFs pretreated with LPS. These results indicated that TLR4 mediates attenuated cytokine production induced by LPS pretreatment, and regulation of MyD88-dependent and MyD88-independent pathways may contribute to the development of A. fumigatus hyphae tolerance in LPS-pretreated THSFs.

Effect of TRIF on permeability and apoptosis in bovine microvascular endothelial cells exposed to lipopolysaccharide

Bovine respiratory disease complex (BRDC) can be caused by several Gram negative bacteria. Lung endothelial cells may be damaged by the release of lipopolysaccharide (LPS) from these organisms. Toll-like receptor (TLR-4) signaling pathways include the myeloid differentiation primary response gene 88 (MyD88) and the Toll/interleukin (IL)-1 receptor (TIR) domain-containing adapter-inducing interferon-β (TRIF) pathways. The aim of this study was to determine which of these pathways is responsible for permeability changes, apoptosis and cytokine production in bovine lung microvascular cells exposed to LPS. Bovine lung endothelial cells were treated with a peptide to inhibit MyD88 signaling or small interfering RNA (siRNA) to inhibit TRIF signaling. Effects were measured using trans-well endothelial electrical resistance to determine cell monolayer permeability, annexin staining to estimate apoptosis and real-time PCR to measure levels of expression of IL-1β and tumor necrosis factor (TNF)-α mRNA. Inhibition of TRIF signaling reduced permeability changes and apoptosis in endothelial cells exposed to LPS. In contrast, MyD88 inhibition reduced expression of IL-1β and TNF-α mRNA in LPS treated cells, but had no effect on permeability. It was concluded that TRIF signaling in LPS-stimulated lung endothelial cells results in permeability changes and apoptosis.

TLR2 and TLR4 in the brain injury caused by cerebral ischemia and reperfusion

Brain injury caused by cerebral ischemia/reperfusion is a complicated pathophysiological course, in which inflammation is thought to play an important role. Toll-like receptors are a type of transmembrane proteins, which can recognize either exogenous pathogen-associated molecular patterns or endogenous stress or damage-associated molecular patterns in the innate immune system and initiate inflammatory responses. Among Toll-like receptors, TLR2 and TLR4 are found to be more important than others in the pathological progression of cerebral injury due to ischemia and reperfusion. This review will focus on the biological characteristics and functions of TLR2 and TLR4 and their downstream signal pathways.

Microglia and ischemic stroke: a double-edged sword

Inflammatory processes have a fundamental role in the pathophysiology of stroke. A key initial event is the rapid activation of resident immune cells, primarily microglia. This cell population is an important target for new therapeutic approaches to limit stroke damage. Activation of microglia is normally held in check by strictly controlled mechanisms involving neuronal-glial communication. Ischemic stroke is a powerful stimulus that disables the endogenous inhibitory signaling and triggers microglial activation. Once activated, microglia exhibit a spectrum of phenotypes, release both pro- and anti-inflammatory mediators, and function to either exacerbate ischemic injury or help repair depending on different molecular signals the microglial receptors receive. Various ligands and receptors have been identified for microglial activation. Experimental tools to detect these inflammatory signals are being increasingly developed in an effort to define the functional roles of microglia. Fine-tuning immunomodulatory interventions based on the heterogeneous profiles of microglia are urgently needed for ischemic stroke.

IRAK4 kinase activity is not required for induction of endotoxin tolerance but contributes to TLR2-mediated tolerance

Prior exposure to LPS induces "endotoxin tolerance" that reprograms TLR4 responses to subsequent LPS challenge by altering expression of inflammatory mediators. Endotoxin tolerance is thought to limit the excessive cytokine storm and prevent tissue damage during sepsis but renders the host immunocompromised and susceptible to secondary infections. Tolerance initiated via one TLR can affect cellular responses to challenge via the same TLR ("homotolerance") or through different TLRs ("heterotolerance"). IRAK4, an essential component of the MyD88-dependent pathway, functions as a kinase and an adapter, activating subsets of divergent signaling pathways. In this study, we addressed mechanistically the role of IRAK4 kinase activity in TLR4- and TLR2-induced tolerance using macrophages from WT versus IRAK4(KDKI) mice. Whereas IRAK4 kinase deficiency decreased LPS signaling, it did not prevent endotoxin tolerance, as endotoxin pretreatment of WT and IRAK4(KDKI) macrophages inhibited LPS-induced MAPK phosphorylation, degradation of IκB-α and recruitment of p65 to the TNF-α promoter, expression of proinflammatory cytokines, and increased levels of A20 and IRAK-M. Pretreatment of WT macrophages with Pam3Cys, a TLR2-TLR1 agonist, ablated p-p38 and p-JNK in response to challenge with Pam3Cys and LPS, whereas IRAK4(KDKI) macrophages exhibited attenuated TLR2-elicited homo- and heterotolerance at the level of MAPK activation. Thus, IRAK4 kinase activity is not required for the induction of endotoxin tolerance but contributes significantly to TLR2-elicited homo- and heterotolerance.

Toll-like receptor 4 signaling in intracerebral hemorrhage-induced inflammation and injury

Intracerebral hemorrhage (ICH) is a common type of fatal stroke, accounting for about 15% to 20% of all strokes. Hemorrhagic strokes are associated with high mortality and morbidity, and increasing evidence shows that innate immune responses and inflammatory injury play a critical role in ICH-induced neurological deficits. However, the signaling pathways involved in ICH-induced inflammatory responses remain elusive. Toll-like receptor 4 (TLR4) belongs to a large family of pattern recognition receptors that play a key role in innate immunity and inflammatory responses. In this review, we summarize recent findings concerning the involvement of TLR4 signaling in ICH-induced inflammation and brain injury. We discuss the key mechanisms associated with TLR4 signaling in ICH and explore the potential for therapeutic intervention by targeting TLR4 signaling.

Exercise Therapy Downregulates the Overexpression of TLR4, TLR2, MyD88 and NF-κB after Cerebral Ischemia in Rats

Toll-like receptor 2 (TLR2) and Toll-like receptor 4 (TLR4) are considered to mediate the inflammatory reaction of cerebral ischemia injury, and exercise can inhibit the activity of the Toll-like receptor signaling pathway in the peripheral blood of humans. Although physical exercise has been demonstrated to be neuroprotective in both clinical and laboratory settings, the underlying mechanism remains unclear. To clarify this critical issue, this study investigated the effects of treadmill training on the recovery of neurological function and the expression of TLR2 and TLR4 and their main downstream targets, nuclear factor-kappaB (NF-κB) and myeloid differentiation factor 88 (MyD88), in the ischemic rat brain after middle cerebral artery occlusion-reperfusion (MCAo/R). Rats were divided into seven groups: sham control without MCAo/R and five, nine and 16 days post-ischemic exercise or non-exercise. The neurological function and infarct volume were measured, and reverse transcription polymerase chain reaction (RT-PCR) and Western blotting were used to detect the expression of TLR2, TLR4, NF-κB and MyD88 in ischemic brain tissue. The results indicated that treadmill training promoted functional recovery and reduced the overexpression of TLR2, TLR4, NF-κB and MyD88 in rat brain tissue after ischemia, a finding that may have implications for understanding the mechanism of exercise therapy after brain ischemia and indicating new therapeutic strategies for the pharmacological modulation of TLR signaling.

Mitochondrial biogenesis contributes to ischemic neuroprotection afforded by LPS pre-conditioning

Although alterations in mitochondrial dynamics are associated with cellular responses to injury, the functional role of these dynamic changes in ischemic neurons is underexplored. One of these dynamic responses to injury includes mitochondrial biogenesis. Various sublethal pre-conditioning stimuli that induce an ischemic-tolerant state [e.g., lipopolysaccharide (LPS)] may also induce mitochondrial biogenesis. Using neuron-enriched cultures, we found that sublethal LPS pre-conditioning induced both ischemic tolerance and markers of mitochondrial biogenesis with overlapping dose-response temporal kinetics. Sublethal LPS transiently increased the expression of critical components of the mitochondrial transcriptional machinery, including nuclear respiratory factor 1 (NRF1) and mitochondrial transcription factor A (TFAM), as well as mtDNA copy number, mitochondrial protein levels, and markers of functional mitochondria, such as increased cellular ATP content, citrate synthase activity, and maximal respiration capacity. Importantly, knockdown of TFAM abrogated both the induction of mitochondrial biogenesis and the neuroprotective pre-conditioning effects of LPS. Several signaling pathways coordinated these events. AMPK inhibition suppressed NRF1 and TFAM expression by LPS, whereas PI3K/Akt signaling was necessary for the nuclear translocation of NRF1 and subsequent induction of TFAM. This is the first demonstration that LPS pre-conditioning initiates multiple signaling pathways leading to mitochondrial biogenesis in neurons and that these dynamic changes contribute to ischemic tolerance.

Microbial cell components induced tolerance to flagellin-stimulated inflammation through Toll-like receptor pathways in intestinal epithelial cells

In the intestine, bacterial components activate innate responses that protect the host. We hypothesize that bacterial components reduce Interleukin-8 (IL-8) production in intestinal epithelial cells stimulated by flagellin via the Toll-like receptor (TLR) signaling pathway. Caco-2 cells were pretreated with various doses of lipopolysaccharide (LPS), lipoteichoic acid (LTA), or low-dose flagellin (LDFL) for 24h. Cells were then treated with flagellin (FL) 500 ng/ml (HDFL) for another 48 h. IL-8 production was measured in the cell culture medium by ELISA. Eighty-four genes in the TLR pathway were evaluated by RT Profiler PCR Array. Pathway Studio 8.0 software was used for altered pathway analysis. HDFL induced IL-8 production by 19-fold (p<0.01). Pretreatment with LDFL at 20, 10 or 1 ng/ml reduced HDFL-induced IL-8 production by 61%, 52% and 40%, respectively (p<0.05). LPS at 50 μg/ml decreased HDFL-induced IL-8 production by 38% (p<0.05). HDFL up-regulated CXCL10, IL1B, IL-8, IRAK2, NF-κB1 and I-κB (all p<0.05). Pathway Studio analysis showed that HDFL induced cell processes including inflammation, cell death and apoptosis. Pretreatment with LDFL at 10 ng/ml down-regulated FADD, FOS, MAP4K4, MyD88, TLR2, TLR3 and TNFERSF1A compared to HDFL (all p<0.05). These down-regulated genes are integral for numerous cell functions including inflammatory response, cell death, apoptosis and infection. These results demonstrate that LPS and LDFL provoke tolerance to HDFL-induced IL-8 production. This tolerance effect was accompanied by a complex interaction of multiple genes related to inflammatory as well as other responses in the TLR pathway rather than a single gene alteration.

Innate immune regulation by toll-like receptors in the brain

The innate immune system plays an important role in cerebral health and disease. In recent years the role of innate immune regulation by toll-like receptors in the brain has been highlighted. In this paper the expression of toll-like receptors and endogenous toll-like receptor ligands in the brain and their role in cerebral ischemia will be discussed. Further, the ability of systemic toll-like receptor ligands to induce cerebral inflammation will be reviewed. Finally, the capacity of toll-like receptors to both increase (sensitization) and decrease (preconditioning/tolerance) the vulnerability of the brain to damage will be disclosed. Studies investigating the role of toll-like receptors in the developing brain will be emphasized.

Modeling dynamic regulatory processes in stroke

The ability to examine the behavior of biological systems in silico has the potential to greatly accelerate the pace of discovery in diseases, such as stroke, where in vivo analysis is time intensive and costly. In this paper we describe an approach for in silico examination of responses of the blood transcriptome to neuroprotective agents and subsequent stroke through the development of dynamic models of the regulatory processes observed in the experimental gene expression data. First, we identified functional gene clusters from these data. Next, we derived ordinary differential equations (ODEs) from the data relating these functional clusters to each other in terms of their regulatory influence on one another. Dynamic models were developed by coupling these ODEs into a model that simulates the expression of regulated functional clusters. By changing the magnitude of gene expression in the initial input state it was possible to assess the behavior of the networks through time under varying conditions since the dynamic model only requires an initial starting state, and does not require measurement of regulatory influences at each time point in order to make accurate predictions. We discuss the implications of our models on neuroprotection in stroke, explore the limitations of the approach, and report that an optimized dynamic model can provide accurate predictions of overall system behavior under several different neuroprotective paradigms.

Computational modeling aims to use mathematical and algorithmic principles to link components of biological systems to predict system behavior. In the past such models have described a small set of carefully studied molecular interactions (proteins in signal transduction pathways) or larger abstract components (cell types or functional processes in the immune system). In this study we use data from global transcriptional analysis of the processes of neuroprotection in a mouse model of stroke to generate functional modules, groups of genes that coherently act to accomplish functions. We then derive equations relating the expression of these modules to one another, treating these individual equations as a closed system, and demonstrate that the model can be used to simulate the gene expression of the system over time. Our work is novel in describing the use of global transcriptomic data to develop dynamic models of expression in an animal model. We believe that the models developed will aid in understanding the complex dynamics of neuroprotection and provide ways to predict outcomes in terms of neuroprotection or injury. This approach will be broadly applicable to other problems and provides an approach to building dynamic models from the bottom up.

Mice lacking the β2 adrenergic receptor have a unique genetic profile before and after focal brain ischaemia

The role of the β2AR (β2 adrenergic receptor) after stroke is unclear as pharmacological manipulations of the β2AR have produced contradictory results. We previously showed that mice deficient in the β2AR (β2KO) had smaller infarcts compared with WT (wild-type) mice (FVB) after MCAO (middle cerebral artery occlusion), a model of stroke. To elucidate mechanisms of this neuroprotection, we evaluated changes in gene expression using microarrays comparing differences before and after MCAO, and differences between genotypes. Genes associated with inflammation and cell deaths were enriched after MCAO in both genotypes, and we identified several genes not previously shown to increase following ischaemia (Ccl9, Gem and Prg4). In addition to networks that were similar between genotypes, one network with a central core of GPCR (G-protein-coupled receptor) and including biological functions such as carbohydrate metabolism, small molecule biochemistry and inflammation was identified in FVB mice but not in β2KO mice. Analysis of differences between genotypes revealed 11 genes differentially expressed by genotype both before and after ischaemia. We demonstrate greater Glo1 protein levels and lower Pmaip/Noxa mRNA levels in β2KO mice in both sham and MCAO conditions. As both genes are implicated in NF-κB (nuclear factor κB) signalling, we measured p65 activity and TNFα (tumour necrosis factor α) levels 24 h after MCAO. MCAO-induced p65 activation and post-ischaemic TNFα production were both greater in FVB compared with β2KO mice. These results suggest that loss of β2AR signalling results in a neuroprotective phenotype in part due to decreased NF-κB signalling, decreased inflammation and decreased apoptotic signalling in the brain.

Toll-like receptor 7 preconditioning induces robust neuroprotection against stroke by a novel type I interferon-mediated mechanism

BACKGROUND AND PURPOSE

Systemic administration of Toll-like receptor (TLR) 4 and TLR9 agonists before cerebral ischemia have been shown to reduce ischemic injury by reprogramming the response of the brain to stroke. Our goal was to explore the mechanism of TLR-induced neuroprotection by determining whether a TLR7 agonist also protects against stroke injury.

METHODS

C57Bl/6, TNF(-/-), interferon (IFN) regulatory factor 7(-/-), or type I IFN receptor (IFNAR)(-/-) mice were subcutaneously administered the TLR7 agonist Gardiquimod (GDQ) 72 hours before middle cerebral artery occlusion. Infarct volume and functional outcome were determined after reperfusion. Plasma cytokine responses and induction of mRNA for IFN-related genes in the brain were measured. IFNAR(-/-) mice also were treated with the TLR4 agonist (lipopolysaccharide) or the TLR9 agonist before middle cerebral artery occlusion and infarct volumes measured.

RESULTS

The results show that GDQ reduces infarct volume as well as functional deficits in mice. GDQ pretreatment provided robust neuroprotection in TNF(-/-) mice, indicating that TNF was not essential. GDQ induced a significant increase in plasma IFNα levels and both IRF7(-/-) and IFNAR(-/-) mice failed to be protected, implicating a role for IFN signaling in TLR7-mediated protection.

CONCLUSIONS

Our studies provide the first evidence that TLR7 preconditioning can mediate neuroprotection against ischemic injury. Moreover, we show that the mechanism of protection is unique from other TLR preconditioning ligands in that it is independent of TNF and dependent on IFNAR.

Antioxidant-induced stress

Antioxidants are among the most popular health-protecting products, sold worldwide without prescription. Indeed, there are many reports showing the benefits of antioxidants but only a few questioning the possible harmful effects of these "drugs". The normal balance between antioxidants and free radicals in the body is offset when either of these forces prevails. The available evidence on the harmful effects of antioxidants is analyzed in this review. In summary, a hypothesis is presented that "antioxidant-induced stress" results when antioxidants overwhelm the body's free radicals.