Expression of tumor necrosis factor alpha in nerve fibers and oligodendrocytes after transient focal ischemia in mice

MyD88 Inhibition Attenuates Cerebral Ischemia-reperfusion Injury by Regulating the Inflammatory Response and Reducing Blood-brain Barrier Damage

Myeloid differentiation primary response gene 88 (MyD88), a downstream molecule directly linked to Toll-like receptor (TLRs) and IL1 receptor, has been implicated in ischemia-reperfusion injury across various organs. However, its role in cerebral ischemia-reperfusion injury (CIRI) remains unclear. Five transient middle cerebral artery occlusion (tMCAO) microarray datasets were obtained from the Gene Expression Omnibus (GEO) database. We screened these datasets for differentially expressed genes (DEGs) using the GSE35338 and GSE58720 datasets and performed weighted gene co-expression network analysis (WGCNA) using the GSE30655, GSE28731, and GSE32529 datasets to identify the core module related to tMCAO. A protein-protein interaction (PPI) network was constructed using the intersecting DEGs and genes in the core module. Finally, we identified Myd88 was the core gene. In addition, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Set Enrichment Analysis (GSEA) validated that TNFα, IL17, and MyD88 signaling pathways were significantly enriched in tMCAO. Subsequently, we investigated the mechanistic role of MyD88 in the tMCAO model using male C57BL/6 mice. MyD88 expression increased significantly 24 h after reperfusion. After intraperitoneal administration of TJ-M2010-5, a MyD88-specific inhibitor, during reperfusion, the infarction volumes in the mice were ameliorated. TJ-M2010-5 inhibits the activation of microglia and astrocytes. Moreover, it attenuates the upregulation of inflammatory cytokines TNFα, IL17, and MMP9 while preserving the expression level of ZO1 after tMCAO, thereby safeguarding against blood-brain barrier (BBB) disruption. Finally, our findings suggest that MyD88 regulates the IRAK4/IRF5 signaling pathway associated with microglial activation. MyD88 participates in CIRI by regulating the inflammatory response and BBB damage following tMCAO.

An Animal Trial on the Optimal Time and Intensity of Exercise after Stroke

INTRODUCTION

Although exercise is a safe, cost-effective, and therapeutic poststroke therapy, the proper time window and dosage of exercise are still unknown. We aim to determine the optimal combination of time window and intensity of exercise by assessing infarct volume, neurological recovery, and underlying mechanisms in middle cerebral artery occlusion rats.

METHODS

The study contains two parts: the time-window and the dosage experiments. The time-window experiment assessed the effects of moderate-intensity exercise that was initiated at 24, 48, 72, 96 h and the control. In the dosage experiment, moderate and another two intensity exercise groups (low, high) were assessed. Forced wheel running was the exercise technique used. Infarct volume and neurological function (modified neurological severity scores [mNSS]) were measured. Inflammatory cytokines, cell death, and proliferation were further detected in the ischemic penumbra.

RESULTS

The time window part revealed that neither infarct volume nor mNSS was reduced in the exercise group initiated at 24 h. The other three groups with exercise initiated after 24 h had reduced infarct volume and reduced mNSS but those outcomes do not differ from each other. In the dosage part, the low- and moderate-intensity groups with exercise initiated at 48 h were both better than the high-intensity group in terms of infarct volume and mNSS at 14 d; however, there was no statistical difference between these low and moderate groups. Exercise initiated at 24 h or high-intensity promoted proinflammatory cytokines and cell death.

CONCLUSIONS

Exercise at 24 h is harmful. Low- and moderate-intensity exercise initiated at 48 h poststroke appears to be the optimal combination for maximal functional recovery.

Minocycline Ameliorates Depressive-Like Behavior and Demyelination Induced by Transient Global Cerebral Ischemia by Inhibiting Microglial Activation

Global cerebral ischemia (GCI) commonly occurs in the elderly. Subcortical white matter lesions and oligodendrocyte (OLG) loss caused by cerebral ischemia have been implicated in the development of post-ischemic depression and cognitive impairment. OLGs are necessary for axonal myelination; the disrupted differentiation of OLG progenitor cells (OPCs) is associated with impaired remyelination. Evidence has indicated that increased levels of inflammatory cytokines released from activated microglia induce depression-like behaviors by affecting neurotransmitter pathways, but the mechanisms remain elusive. We explored the potential mechanisms that link microglia activation with GCI-induced depression and cognitive dysfunction by studying effects of minocycline on white matter damage, cytokine levels, and the monoaminergic neurotransmitters. An acute GCI animal model was generated through bilateral common carotid artery occlusion to induce ischemic inflammation and subcortical white matter damage. Minocycline, an inhibitor of microglia activation, was intraperitoneally administrated immediately after surgery and continued daily for additional six days. Minocycline shortened the immobile duration in tail suspension test and forced swimming test, while no improvement was found in Morris water maze test. The plasma levels of IL-1β, IL-6, TNF-α, HMGB1, and netrin-1 were significantly reduced with the treatment of minocycline. Minocycline treatment substantially reversed demyelination in corpus callosum and hippocampus, alleviated hippocampal microglia activation, and promoted OPCs maturation, while no effect was found on hippocampal neurodegeneration. Besides, the content of dopamine (DA) in the hippocampus was upregulated by minocycline treatment after GCI. Collectively, our data demonstrated that minocycline exerts an anti-depressant effect by inhibiting microglia activation, promoting OPCs maturation and remyelination. Increased DA in hippocampus may also play a role in ameliorating depressive behavior with minocycline treatment.

Neuroprotective effects of neurotropin in a mouse model of hypoxic-ischemic brain injury

PURPOSE

Ischemic-hypoxic insult leads to detrimental effects on multiple organs. The brain is especially vulnerable, and it is hard to regenerate once damaged. Currently, therapeutic options are very limited. Previous studies have reported neuroprotective effects of neurotropin, a non-protein extract derived from the inflamed skin of rabbits inoculated with vaccinia virus, using a murine model of peripheral nerve injury and cultured cell lines. However, whether neurotropin might have protective effects against brain injuries remains unclear. We, therefore, investigated the neuroprotective effect of neurotropin and possible underlying mechanisms, using a mouse model of hypoxic-ischemic brain injury.

METHODS

Hypoxic-ischemic brain injury was induced via a combination of the left common carotid artery occlusion and exposure to hypoxic environment (8% oxygen) in adult male C57BL/6 mice. Immediately following induction of hypoxia-ischemia, mice received either saline or 2.4 units of neurotropin. The survival rate, neurological function, infarct volume, and expression of inflammatory cytokines were evaluated.

RESULTS

Compared to the control group, the neurotropin group exhibited a significantly higher survival rate (100% vs. 62.5%, p < 0.05) and lower neurological deficit scores (1; 0-2 vs. 3; 0-5, median; range, p < 0.05) after the hypoxic-ischemic insult. The administration of neurotropin also reduced infarct volume (18.3 ± 5.1% vs. 38.3 ± 7.2%, p < 0.05) and mRNA expression of pro-inflammatory cytokines.

CONCLUSIONS

The post-treatment with neurotropin improved survival and neurological outcomes after hypoxic-ischemic insult. Our results indicate that neurotropin has neuroprotective effects against hypoxic-ischemic brain injury by suppressing pro-inflammatory cytokines.

Targeted intracerebral delivery of the anti-inflammatory cytokine IL13 promotes alternative activation of both microglia and macrophages after stroke

Background

Subtle adjustment of the activation status of CNS resident microglia and peripheral macrophages, to promote their neuroprotective and neuroregenerative functions, may facilitate research towards curing neurodegenerative disorders. In the present study, we investigated whether targeted intracerebral delivery of the anti-inflammatory cytokine interleukin (IL)13, by means of transplanting IL13-expressing mesenchymal stem cells (IL13-MSCs), can promote a phenotypic switch in both microglia and macrophages during the pro-inflammatory phase in a mouse model of ischemic stroke.

Methods

We used the CX₃CR1^eGFP/+ CCR2^RFP/+ transgenic mouse model to separately recognize brain-resident microglia from infiltrated macrophages. Quantitative immunohistochemical analyses were applied to characterize polarization phenotypes of both cell types.

Results

Distinct behaviors of both cell populations were noted dependent on the anatomical site of the lesion. Immunohistochemistry revealed that mice grafted with IL13-MSCs, in contrast to non-grafted and MSC-grafted control mice, were able to drive recruited microglia and macrophages into an alternative activation state, as visualized by a significant increase of Arg-1 and a noticeable decrease of MHC-II expression at day 14 after ischemic stroke. Interestingly, both Arg-1 and MHC-II were expressed more abundantly in macrophages than in microglia, further confirming the distinct behavior of both cell populations.

Conclusions

The current data highlight the importance of controlled and localized delivery of the anti-inflammatory cytokine IL13 for modulation of both microglia and macrophage responses after ischemic stroke, thereby providing pre-clinical rationale for the application of L13-MSCs in future investigations of neurodegenerative disorders.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1212-7) contains supplementary material, which is available to authorized users.

Neurogenesis and inflammation after ischemic stroke: what is known and where we go from here

This review covers the pathogenesis of ischemic stroke and future directions regarding therapeutic options after injury. Ischemic stroke is a devastating disease process affecting millions of people worldwide every year. The mechanisms underlying the pathophysiology of stroke are not fully understood but there is increasing evidence demonstrating the contribution of inflammation to the drastic changes after cerebral ischemia. This inflammation not only immediately affects the infarcted tissue but also causes long-term damage in the ischemic penumbra. Furthermore, the interaction between inflammation and subsequent neurogenesis is not well understood but the close relationship between these two processes has garnered significant interest in the last decade or so. Current approved therapy for stroke involving pharmacological thrombolysis is limited in its efficacy and new treatment strategies need to be investigated. Research aimed at new therapies is largely about transplantation of neural stem cells and using endogenous progenitor cells to promote brain repair. By understanding the interaction between inflammation and neurogenesis, new potential therapies could be developed to further establish brain repair mechanisms.

Dynamics of major histocompatibility complex class II-positive cells in the postischemic brain--influence of levodopa treatment

Background

Cerebral ischemia activates both the innate and the adaptive immune response, the latter being activated within days after the stroke onset and triggered by the recognition of foreign antigens.

Methods

In this study we have investigated the phenotype of antigen presenting cells and the levels of associated major histocompatibility complex class II (MHC II) molecules in the postischemic brain after transient occlusion of the middle cerebral artery (tMCAO) followed by levodopa/benserazide treatment. Male Sprague Dawley rats were subjected to tMCAO for 105 minutes and received levodopa (20 mg/kg)/benserazide (15 mg/kg) for 5 days starting on day 2 after tMCAO. Thereafter, immune cells were isolated from the ischemic and contralateral hemisphere and analyzed by flow cytometry. Complementarily, the spatiotemporal profile of MHC II-positive (MHC II⁺) cells was studied in the ischemic brain during the first 30 days after tMCAO; protein levels of MHC II and the levels of inflammation associated cytokines were determined in the ischemic hemisphere.

Results

We found that microglia/macrophages represent the main MHC II expressing cell in the postischemic brain one week after tMCAO. No differences in absolute cell numbers were found between levodopa/benserazide and vehicle-treated animals. In contrast, MHC II protein levels were significant downregulated in the ischemic infarct core by levodopa/benserazide treatment. This reduction was accompanied by reduced levels of IFN-γ, TNF-α and IL-4 in the ischemic hemisphere. In the contralateral hemisphere, we exclusively detected MHC II⁺ cells in the corpus callosum. Interestingly, the number of cells was increased by treatment with levodopa/benserazide independent from the infarct size 14 days after tMCAO.

Conclusions

Results suggest that dopamine signaling is involved in the adaptive immune response after stroke and involves microglia/macrophages.

Inflammatory cytokines in experimental and human stroke

Inflammation is a hallmark of stroke pathology. The cytokines, tumor necrosis factor (TNF), interleukin (IL)-1, and IL-6, modulate tissue injury in experimental stroke and are therefore potential targets in future stroke therapy. The effect of these cytokines on infarct evolution depends on their availability in the ischemic penumbra in the early phase after stroke onset, corresponding to the therapeutic window (<4.5 hours), which is similar in human and experimental stroke. This review summarizes a large body of literature on the spatiotemporal and cellular production of TNF, IL-1, and IL-6, focusing on the early phase in experimental and human stroke. We also review studies of cytokines in blood and cerebrospinal fluid in stroke. Tumor necrosis factor and IL-1 are upregulated early in peri-infarct microglia. Newer literature suggests that IL-6 is produced by microglia, in addition to neurons. Tumor necrosis factor- and IL-1-producing macrophages infiltrate the infarct and peri-infarct with a delay. This information is discussed in the context of suggestions that neuronal sensitivity to ischemia may be modulated by cytokines. The fact that TNF and IL-1, and suppossedly also IL-6, are produced by microglia within the therapeutic window place these cells centrally in potential future stroke therapy.

Does inflammation after stroke affect the developing brain differently than adult brain?

The immature brain is prone to hypoxic-ischemic encephalopathy and stroke. The incidence of arterial stroke in newborns is similar to that in the elderly. However, the pathogenesis of ischemic brain injury is profoundly affected by age at the time of the insult. Necrosis is a dominant type of neuronal cell death in adult brain, whereas widespread neuronal apoptosis is unique for the early postnatal synaptogenesis period. The inflammatory response, in conjunction with excitotoxic and oxidative responses, is the major contributor to ischemic injury in both the immature and adult brain, but there are several areas where these responses diverge. We discuss the contribution of various inflammatory mechanisms to injury and repair after cerebral ischemia in the context of CNS immaturity. In particular, we discuss the role of lower expression of selectins, a more limited leukocyte transmigration, undeveloped complement pathways, a more rapid microglial activation, differences in cytokine and chemokine interplay, and a different threshold to oxidative stress in the immature brain. We also discuss differences in activation of intracellular pathways, especially nuclear factor kappaB and mitogen-activated protein kinases. Finally, we discuss emerging data on both the supportive and adverse roles of inflammation in plasticity and repair after stroke.

Role of PACAP in ischemic neural death

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that was first isolated from an ovine hypothalamus in 1989. Since its discovery, more than 2,000 papers have reported on the tissue and cellular distribution and functional significance of PACAP. A number of papers have reported that PACAP but not the vasoactive intestinal peptide suppressed neuronal cell death or decreased infarct volume after global and focal ischemia in rodents, even if PACAP was administered several hours after ischemia induction. In addition, recent studies using PACAP gene-deficient mice demonstrated that endogenous PACAP also contributes greatly to neuroprotection similarly to exogenously administered PACAP. The studies suggest that neuroprotection by PACAP might extend the therapeutic time window for treatment of ischemia-related conditions, such as stroke. This review summarizes the effects of PACAP on ischemic neuronal cell death, and the mechanism clarified in vivo ischemic studies. In addition, the prospective mechanism of PACAP on ischemic neuroprotection from in vitro neuronal and neuronal-like cell cultures with injured stress model is reviewed. Finally, the development of PACAP and/or receptor agonists for human therapy is discussed.

Decreased peripheral nerve damage after ischemia-reperfusion injury in mice lacking TNF-alpha

We sought to explore the role of tumor necrosis factor-alpha (TNF-alpha) in the pathogenesis of peripheral nerve ischemia-reperfusion (IR) injury. We established an ischemia-reperfusion model in wild type (WT) and TNF-alpha knockout (KO) mice. Electrophysiology, behavioral score and morphological indices (edema and ischemic fiber degeneration [IFD]) were examined to determine the influence of TNF-alpha on peripheral nerve structure and function following ischemia followed by reperfusion. TNF-alpha and nuclear factor-kappa B (NF-kappaB) expression were evaluated using immunohistochemistry. TNF-alpha KO mice, compared to WT had, in sciatic nerve, marked improvement in nerve pathology. This is a region subject to moderate ischemia-reperfusion injury. There was also a significant improvement in electrophysiological and some behavioral indices. TNF-alpha and NF-kappaB expression were abundant in sciatic-tibial nerves of WT mice subjected to IR, but there was less, or complete lack of, expression in ischemic nerve of TNF-alpha KO mice. We conclude that TNF-alpha plays an essential role in the pathogenesis of peripheral nerve ischemia-reperfusion injury, possibly partly through the activation of NF-kappaB.

Inflammation in adult and neonatal stroke

This chapter will discuss the current knowledge of the contribution of systemic and local inflammation in acute and sub-chronic stages of experimental stroke in both the adult and neonate. It will review the role of specific cell types and interactions among blood cells, endothelium, glia, microglia, the extracellular matrix and neurons - cumulatively called "neurovascular unit" - in stroke induction and evolution. Intracellular inflammatory signaling pathways such as nuclear factor kappa beta and mitogen-activated protein kinases, and mediators produced by inflammatory cells such as cytokines, chemokines, reactive oxygen species and arachidonic acid metabolites, as well as the modifying role of age on these mechanisms, will be reviewed as well as the potential for therapy in stroke and hypoxic-ischemic injury.

Expression of tumor necrosis factor alpha and neuronal apoptosis in the developing rat brain after neonatal stroke

Increased expression of tumor necrosis factor alpha (TNFalpha) has been shown in adult stroke models. However, its expression and relationship with neuronal apoptosis in neonatal rats with transient middle cerebral artery occlusion (MCAO) have not been clearly elucidated. We studied the expression and distribution of TNFalpha and neuronal apoptosis in a postnatal Day 10 rat MCAO model using reverse transcriptase-polymerase chain reaction (RT-PCR), Western blot, immunohistochemistry, fluorescence double-labeling, and terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) analyses. We found TNFalpha mRNA expression increased at 2h and was maintained at high levels until 24h after reperfusion. TNFalpha protein expression was significantly increased from 4 to 8h (p < 0.01) lasting through 24h (p < 0.05) after reperfusion compared to the sham controls. TNFalpha immunoreactive cells were colocalized to neurons in both the core and the penumbra areas of the ischemic cortex. However, apoptotic cells were mainly distributed in the penumbra area and colocalized to neurons as well as to TNFalpha immunoreactive cells in the ischemic cortex. Our findings suggest that TNFalpha expression increases after neonatal stroke and is associated with neuronal apoptosis after transient focal cerebral ischemia.

Pharmacological brain cooling with indomethacin in acute hemorrhagic stroke: antiinflammatory cytokines and antioxidative effects

We evaluated the effects of a novel pharmacological brain cooling (PBC) method with indomethacin (IND), a nonselective cyclooxygenase inhibitor, without the use of cooling blankets in patients with hemorrhagic stroke. Forty-six patients with hemorrhagic stroke (subarachnoid hemorrhage; n = 35, intracerebral hemorrhage; n = 11) were enrolled in this study. Brain temperature was measured directly with a temperature sensor. Patients were cooled by administering transrectal IND (100 mg) and a modified nasopharyngeal cooling method (positive selective brain cooling) initially. Brain temperature was controlled with IND 6 mg/kg/day for 14 days. Cerebrospinal fluid concentrations of interleukin-1beta (CSF IL-1beta) and serum bilirubin levels were measured at 1, 2, 4, and 7 days. The incidence of complicating symptomatic vasospasm after subarachnoid hemorrhage was lower than in non-PBC patients. CSF IL-1beta and serum bilirubin levels were suppressed in treated patients. IND has several beneficial effects on damaged brain tissues (anticytokine, free radical scavenger, antiprostaglandin effects, etc.) and prevents initial and secondary brain damage. PBC treatment for hemorrhagic stroke in patients appears to yield favorable results by acting as an antiinflammatory cytokine and reducing oxidative stress.

ADAMTS-1 and -4 are up-regulated following transient middle cerebral artery occlusion in the rat and their expression is modulated by TNF in cultured astrocytes

ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) enzymes are a recently described group of metalloproteinases. The substrates degraded by ADAMTS-1, -4 and -5 suggest that they play a role in turnover of extracellular matrix in the central nervous system (CNS). ADAMTS-1 is also known to exhibit anti-angiogenic activity. Their main endogenous inhibitor is tissue inhibitor of metalloproteinases (TIMP)-3. The present study was designed to investigate ADAMTS-1, -4 and -5 and TIMP-3 expression after experimental cerebral ischaemia and to examine whether cytokines known to be up-regulated in stroke could alter their expression by astrocytes in vitro. Focal cerebral ischaemia was induced by transient middle cerebral artery occlusion in the rat using the filament method. Our results demonstrate a significant increase in expression of ADAMTS-1 and -4 in the occluded hemisphere but no significant change in TIMP-3. This was accompanied by an increase in mRNA levels for interleukin (IL)-1beta, IL-1 receptor antagonist (IL-1ra) and tumour necrosis factor (TNF). ADAMTS-4 mRNA and protein were up-regulated by TNF in primary human astrocyte cultures. The increased ADAMTS-1 and -4 in experimental stroke, together with no change in TIMP-3, may promote ECM breakdown after stroke, enabling infiltration of inflammatory cells and contributing to brain injury. In vitro studies suggest that the in vivo modulation of ADAMTS-1 and -4 may be controlled in part by TNF.

Angiotensin II type 1 receptors in cerebral ischaemia-reperfusion: initiation of inflammation

Cerebral ischaemia-reperfusion injury is associated with an inflammatory response, with contributions from leucocytes and microglia. Formation of free radicals and nitric oxide contributes to the development of cerebral infarction and of the neurological deficit that follows transient focal ischaemia. The circulating and cerebral renin-angiotensin systems contribute, via stimulation of the angiotensin II (Ang II) types 1 (AT1) and 2 receptors, to the initiation or progression of inflammatory processes, and blockade of AT1-receptors prevents irreversible tissue injury and improves outcome from stroke in animal experiments. Such cerebral protection can be achieved even when treatment is initiated hours after established reperfusion. Blockade of AT1-receptors also reduces the incidence of stroke and cardiovascular mortality associated with stroke in patients; however, the mechanisms underlying the prevention of stroke by AT1-receptor blockade in patients remain to be elucidated. In this review we summarize the existing experimental and clinical data demonstrating that the renin-angiotensin system contributes to the inflammation and subsequent irreversible injury after cerebral ischaemia-reperfusion. We conclude that AT1-receptor blockade reduces cerebral ischaemia-reperfusion injury in part by attenuating inflammatory processes.

Controlled normothermia during ischemia is important for the induction of neuronal cell death after global ischemia in mouse

A stable model of neuronal damage after ischemia is needed in mice to enable progression of transgenic strategies. We performed transient global ischemia induced by common carotid artery occlusions with and without maintaining normal rectal temperature (Trec) in order to determine the importance of body temperature control during ischemia. We measured brain temperature (Tb) during ischemia/reperfusion. Mice with normothermia (Trec within +/- 1 degrees C) had increased mortality and neuronal cell death in the CA1 region of hippocampus, which did not occur in hypothermic animals. If the Trec was kept within +/- 1 degrees C, the Tb decreased during ischemia. After reperfusion, Tb in the normothermia group developed hyperthermia, which reached > 40 degrees C and was > 2 degrees C higher than Trec. We suggest that tightly controlled normothermia and prevention of hypothermia (Trec) during ischemia are important factors in the development of a stable neuronal damage model in mice.